-------
6
4
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~ 0-2
"§- 0-1
ZJ
- 4
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— f)
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h-
1
0-8
0-6
0-4
0-3
0^2
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x
(a)
—
—
— x x
— *
x^x
_ XX*
— X
— x
1 1 1 1 1 111
- (c)
—
__
vy y
~~ V 'V*^\> v V
V
X ^ X
—
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- (b)
—
—
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_ X
- v
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ir
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(d)
X
—
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E x x
- ^x
_ XX
—
-
1 1 1 1 1 1 1
20 40 60 80 100 120 140 0 20 40 60 80 100 120 140
SCA at Vmax and 15% ash content (n^/iT^s'1)
FIGURE 3. ARBITRARY SELECTIONS OF POINTS FROM
FIG. 1 SHOWING FALSE CORRELATIONS
192
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Intuitively, most scientists would probably agree that an assembly of
five well-spaced points on a graph should suffice to show up a monotonic
relation between two variables, although many would prefer to have more
than five points to fix such a relation with satisfying precision.
Suppose, however, that there is, in fact, no monotonic relation to be
found between the two variables; what chance is there of meeting a
disposition of the points that leads the observer to conclude (falsely)
that the relation does exist?
To answer this question it was supposed that the five efficiencies
would be dependent on unspecified variables (not coal sulphur) with levels
outside the control of the experimentalist (in precipitation work particle
size is one such variable, but the occurrence of uncontrolled variables
is common in applied scientific work). These variables would be
responsible for such diversity as was observed in the percentage efficiencies,
within a range that all would agree reasonable but otherwise unnecessary
to specify (say 80.0 - 99.8%, possibly in one hundred equal 0.2% steps).
With these imposed (but realistic) conditions, one might as well create
the "measured" efficiencies by a random selection process, such as tables
of random numbers or picking them out of a hat.
Thus in the simulated experiment a hand calculator was used to select
at random the five efficiencies from within a range covering 100 equal steps,
and each efficiency was coupled as it was generated to the next sulphur
content in order on a repeating list of the five of them compiled beforehand.
This procedure was repeated until 96 sets of five points had been assembled,
yielding 96 separate graphs. A panel of thirteen post-graduate scientists,
active and skilled in experimental research, were then asked to select
independently which of the 96 graphs revealed in their judgement a monotonic
relation. As might be expected most of the graphs displayed such a wide
scatter of the five points that no monotonic relation could be seen by anyone,
but seme graphs gave more than a hint of a straight line or gentle curve
through the points, and a few left the observers in no doubt. Since the
scientists' assessments were a matter of personal judgement based on individual
experience, unanimity was the exception, but average results of adequate
precision were readily obtained. The exercise yielded the following main
conclusions :
1. the probability that a monotonic relation in a chosen direction occurred
by chance was estimated to be 1 in 11, this estimate being based only on
instances where the observer was certain of a relation;
2. if instances were included where the observer suspected but was unsure
of a relation, then the probability that a monotonic relation in a
chosen direction occurred by chance became 1 in 4.
Paraphrasing the findings of this desktop study, we may say that, in
a given 5-point experiment of the kind envisaged, the chance that a competent
scientist hopeful of a rising monotonic relation will be happy to see this
when there is none at all is 1 in 4; and the chance that an open-minded
scientist will be quite sure of it is 1 in 11.
193
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Obviously, when two variables are not cause and effect, something
more searching than a 5-point experiment is required to avoid a disturbingly
high chance of reporting the opposite of the truth. Indeed to show
convincingly that coal sulphur and flyash collection efficiency are unrelated
when this is the fact requires much more evidence than to demonstrate they
are related when that is the case. This is not the only pitfall for the
unwary experimentalist, as the following contrasting example shows.
6. CORRELATIONS TO ORDER FROM GENUINE RESULTS
Figure 4 illustrates a plot of total coal sulphur against the size of
precipitator required to achieve the same typical flyash emission. The
size has been normalized to 15% ash for each coal in order to eliminate
one uncontrolled variable. Each of the four points on the graph is fully
experimental, having been obtained from separate combustion and precipitation
trials on the technical-scale plant at the authors' laboratory. The
results are quite comparable, being obtained at the same temperature and
at maximum voltage in every case. Each point is an average based on a
number of efficiency tests, and it may be assumed that no additional amount
of replication could alter the obvious relation to any significant degree.
Although there are only four points (albeit precise ones), the reader may
take it that, had any further trials been carried out between the extremes
of coal sulphur shown, the additional points would only have confirmed the
relation that is there.
Thus, with the reliability of the information in Figure 4 taken for
granted, it is indisputable that it shows a quadrupling of the required size
of precipitator on passing from 5.6% coal sulphur down to 0.6%; and this
behaviour would undoubtedly be reproduced on another occasion if attempted.
The authors stress at this point, however, that the results are totally
unable to support the popular view that low coal sulphur causes poor flyash
precipitation. The reason is important,yet subtle.
The extreme points of Figure 4 (top left and bottom right) originate
from two unrelated coals, but the two intermediate points are from separate
blends of these two coals. Thus the four coals burnt were related. It is
our practical experience that a blend of two coals produces a composite
(or mixed) flyash with precipitating properties intermediate between those
for the two flyashes separately and pro rata on the proportions of each in
the blend. Clearly, the pulverized fragments of each coal burn separately
and the flyash particles from each coal solidify too quickly for collisions
to merge them into hybrids of different identity. Since precipitation is
the sum total of at least as many individual acts of migration as there are
flyash particles to collect, the collection efficiency is pro rata on the
composition of the coal blend. A graph, therefore, of precipitation
properties (observed under comparable conditions) against composition of
coal blend is bound to show a smooth monotonic progression between the extremes.
Furthermore, any property of the coals or of their flyashes that is also
pro rata on the blend will likewise be associated with precipitation properties
in the same monotonic fashion.
194
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5
• — •
75
o
<->
-^
-*-'
c
0>
-t— •
0
C_3
^
.c
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LO
75
"o
7
6
5
4
3
2
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0-7
0-6
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\
\
\
_ x \
^k
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^»_^ fc
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_ \
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-—
-
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10 20 30 40 50 60 70
SCA at Vmax and 15% ash content (morn's"1)
FIGURE 4. PLOT OF TOTAL COAL SULPHUR AGAINST
PRECIPITATOR SIZE AT 120 °C SHOWING FALSE CORRELATION
DUE TO BLENDING OF TWO COALS
195
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In this category is the sulphur content of the coal blend, and thus
Figure 4 shows an inevitable relationship that depends solely on the
relative positions of the extreme points of the graph. It is merely a
matter of selection of coals in the first place to produce any desired
direction of the line displayed in Figure 4 vertical, horizontal, or
diagonal with any direction and slope (hence the heading for this section
of the paper). Figure 4 is thus quite valueless to show a causal general
correlation of coal sulphur with flyash precipitation and it is possible
that some published work (including the Ramsdell data and the recent English
work) has rather restricted validity because it may be dependent, largely
or wholly, on results from coal blends. Certainly, in view of the expense
and complex logistics of dust-collection tests in electric utilities, the
use of coal blends is a most attractive and economic experimental plan to
adopt. It is, however, illusory in the coal sulphur context, as the
above example demonstrates.
7. WHY THERE IS NO OVERRIDING EFFECT OF COAL SULPHUR ON FLYASH COLLECTION
There are several reasons why an overriding effect of coal sulphur on
flyash collection is not to be expected. The chief reasons requiring
comment are (a) the unique surface chemistry of flyash, (b) the existence
of alternative sources of surface conduction for flyash, and (c) the masking
effect of other variables. In discussing these features it will be seen
that some limitations of hot-side precipitation emerge.
The surface chemistry of flyash has recently received considerable
clarification through work at the authors' laboratory (Collin (1974)9).
Most of Collin1s work has been carried out on flyash from coals with below
1% sulphur. No exception has yet been found to the rule that the surface
of fresh flyash consists essentially of a multimolecular but extremely thin
film of aqueous sulphuric acid. Beneath this invisible fil-i is found a
layer of calcium sulphate (or exceptionally aluminum sulphate) which separates
the acid film from a thin sublayer of calcium hydroxide (or exceptionally
alumina). Beneath the sublayer is the glassy aluminosilicate core of the
flyash bead. Storage of fresh flyash in air or at elevated temperature
promptly removes the outermost acid layer by neutralization and volatilization,
and thus the surface properties of the flyash are radically changed. For
this reason recovery of accumulated flyash from precipitator hoppers for further
collection tests or for later analysis is an unreliable procedure yielding
doubtful results. Furthermore, water washing of flyash removes all three
layers, exposing the underlying glassy surface, which has quite different
electrical properties from those of the fresh product. Hence flyash from
lagoons or otherwise washed material is valueless for assessing electrostatic
collection if relevance to electric utility application is required.
The meaning of this surface structure of fresh flyash to its
electrostatic precipitation is that even low-sulphur coals have a good
chance of producing flyash with ample surface electrical conduction at
so-called cold-side precipitation temperatures (approximately 110 - 250°C) .
196
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Thus, the question whether the particles will receive an adequate sulphuric
acid film does not rely in practice on the amount of coal sulphur available,
but is more a matter of how long the dispersed flyash has to scavenge
sulphur trioxide from a supply in the flue gas that is continually replenished
catalytically before the precipitator is reached. That the flyash normally
takes up sulphur trioxide rapidly from a sufficient supply is demonstrated
by the fact that the flyash is recovered with an acid film present, in spite
of a reactive coating of lime (or alumina) and an elevated temperature.
If the sulphur trioxide supply were poor or were not being scavenged
quickly by the flyash, its surface would not carry any free acid because
this would be converted to calcium or aluminium, sulphates as soon as it
reached the surface.
If, on occasion, at cold-side temperatures, the sulphuric acid film
is spread too thinly to be continuous (perhaps as a consequence of poor
catalysis or unusually high flyash area), the flyash still need not display
excessive resistivity since water absorption by the sublayers (lime/calcium
sulphate or alumina/aluminium sulphate) can ensure a complete surface
conduction path. At hot-side temperatures (approximately 300 - 450 C)
neither sulphuric acid nor water appears on the flyash surface, and conduction
must depend on the normal thermal diminution of the resistivity of the glassy
core of the flyash particles to acceptable levels. While this so-called
volume conduction can be relied upon in many cases at hot-side temperatures,
it is dependent on there being no electrically-obstructive coating on the
flyash surface. This possibility seems to have been ignored by proponents
of hot-side precipitation, since the obstructive film may be provided in the
relevant temperature interval by the normal lime (or alumina) coatings on
the particles. Instances of back ionization and associated poor precipitation
of flyash at hot-side temperatures may find their explanation in such
insulating coatings, and this could apply irrespective of the level of
sulphur in the coal.
There are numerous variables that influence the precipitation efficiency
of flyash at constant temperature and at fixed specific collecting area,
including applied voltage, particle size, carrier gas velocity, particle
re-entrainment and gas distribution. None of these variables would appear
to have any connection with coal sulphur level, and hence if important enough
they could mask a presumed effect of coal sulphur. Consider, therefore,
the effect on collection efficiency of particle size (expressed as mass median
diameter with a mixture of sizes as in flyash). The theoretical effect of
particle size is established and enjoys reasonable practical verification
(Paulson et al (1976)10). With voltage, specific collecting area, and
temperature all fixed, the observed migration velocity is directly proportional
to the particle size, ignoring mechanical collection efficiency for
simplicity. This means, for example, that if a given mean size of particle
is associated with a collection efficiency of 90% at a typical operating
condition, then doubling the size elevates the efficiency to 99% and tripling
the size raises it to 99.9%.
197
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Since it is practical experience (Paulson et al (1976) ) to encounter
flyashes from different coals that cover nearly a threefold range of
mean particle sizes, any specific effect of coal sulphur has to be discerned
against an efficiency variation that may range from 90% to over 99% for
size reasons alone. In these circumstances it is not realistic to expect
to see an overriding effect of coal sulphur on precipitation efficiency
of any plausible magnitude. The introduction of the other variables into
the argument only serves to strengthen this conclusion.
Bearing in mind that precipitation experts have long recognized the
considerable effects on collection efficiency of the several variables
listed above, it may well be asked why an overriding influence of coal
sulphur has found such wide and prolonged acceptance at cold-side
precipitator temperatures. The answer to this question appears to be
that low coal sulphur has been considered to render the flyash critically
more resistive, so much so that the resulting back ionization is reckoned
to neutralize the electrostatic precipitation process itself, thus overriding
all other variables. This particular sequence of events now appears to be
more of a fear than a fact for the following reasons:
a) there is normally enough sulphur in low-sulphur coal to produce a
conducting film of sulphuric acid on flyash at cold-side
precipitator temperatures; and discontinuities in the film can
be bridged by water interaction with the sublayers of lime or
alumina that are present;
b) the effect of applied electric field in reducing the resistivity
of highly insulating flyash layers at all practical precipitator
temperatures allays losses of collection efficiency that would
occur;
c) if back, ionization does take place, it is unlikely to neutralize
all collecting areas completely and simultaneously, provided the
phasing and intensity of plate rapping are properly selected.
8. CONCLUSION
1. This paper addressed itself to the question: does sulphur in coal
dominate flyash collection in electrostatic precipitators? To this
we answer: in theory coal sulphur should rot be dominant at any
typical temperature, and. in practice the weight of the evidence
confirms it is not.
2. The combined influence of well-established variables produces such
large variations in flyash collection efficiency among different
coals that any plausible effect of coal sulphur could not be dominating
and at most is probably minor.
198
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3. Some coal sulphur is probably vital to efficient precipitation
at cold-side temperatures, but sufficient is present in low-sulphur
coals to furnish the flyash particles with a conducting film of
sulphuric acid, and this alone is normally adequate to prevent
resistive impediments to precipitation.
4. When poor flyash collection occurs in hot-side precipitation it
is attributable to electrical obstruction by the normal lime or
alumina coatings on flyash particles. This situation has no
potential for being avoided through the intervention of coal sulphur,
as in the case in cold-side precipitation.
5. Experimental tests of whether coal sulphur influences flyash
precipitation may give false results either by chance or if coal
blends are relied upon.
199
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REFERENCES
1. Ramsdell, R.G. Practical Design Parameters for Hot and Cold
Electrostatic Precipitators. Combustion. 45 : 40-43, October 1973.
2. Barrett, A.A. Electrostatic Precipitators - Guidance for Designers
and Purchasers. Filtration and Separation. 67-73, Jan/Feb. 1971.
3. Goard, P.R.C.,and E.G. Potter. Resistivity in Electrostatic
Precipitation - a Re-appraisal. In:Proc. Symp. on "The Changing
Technology of Electrostatic Precipitation", Adelaide, South Australia,
Nov. 8, 1974. Inst. Fuel (Australian Membership), 1974.
4. White, H.J. Industrial Electrostatic Precipitation. Reading, MA,
Addison-Wesley Publishing Co. Inc., 1963, p.297.
5. Potter, E.G. Electrostatic Precipitation Technology : A Different
Viewpoint, JAPCA. 28 : 40-46, January 1978.
6. Paulson, C.A.J., E.G. Potter, and K. Ramus. Pilot-Scale Electrostatic
Precipitator Tests on Copper Converter Flue Gas. In-.Proc. Internat.
Clean Air Conf., Brisbane, Australia, May 15-19, 1978.
Ann. Arbor, Mich., Ann Arbor Science Publishers Inc., 1978, p.499
7. Sochaczewski, Z.W. The Relevance of New and Stricter Standards for
Particulate Emission and Plant Modifications Necessary to Meet Them.
CSIRO Conference on Electrostatic Precipitation, Leura, New South Wales,
Australia, August 23-24, 1978.
8. Paulson, C.A.J. In: discussion at Symposium on "The Changing Technology
of Electrostatic Precipitation", Adelaide, South South Australia, November 8,
1974; separate discussion booklet published by Inst. Fuel (Australian
Membership), see pp. 47-48 and diagrams 20-22.
9. Collin, P.J. Some Aspects of the Chemistry of Flyash Surfaces. In :
Proc. Symp. on "The Changing Technology of Electrostatic Precipitation",
Adelaide, South Australia, November 8, 1974. Inst. Fuel (Australian
Membership), 1974.
10. Paulson, C.A.J., R.B. Kahane, and E.G. Potter. Electrostatic
Precipitation of Flyash from a Range of Australian Coals. 1976
Conference of the Institute of Fuel (Australian Membership), November 3-5,
1976, Sydney, Australia.
200
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APPENDIX 1
A MODIFIED COAL SULPHUR PARAMETER
Assume all particles of a selected flyash are solid spheres of uniform
size, equal to the mass median diameter D.
3
The weight of each particle is irD p/6 when p is the density of flyash
(assumed constant) .
Therefore the number of particles per unit weight of the flyash is
6/rrD3p.
2
Since the surface area of each particle is irD the total area per
unit weight of flyash is SffD^/TD^p , i.e. K/D where K is a constant.
If the weight fraction of ash in the coal is A then the area of the
flyash per unit weight of coal is KA/D.
If the weight fraction of sulphur in the coal is S then coal sulphur
per unit surface area of flyash is SD/KA.
Under circumstances where the available sulphur in coal must be shared
equally by all the flyash area, it is preferable to seek a relation between
precipitator performance and the parameter SD/A.
201
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ANALYSIS OF THERMAL DECOMPOSITION PRODUCTS
OF FLUE GAS CONDITIONING AGENTS
by
Ralph B. Spafford
H. Kenneth Dillon
Edward B. Dismukes
Southern Research Institute
Birmingham, Alabama 35205
and
Leslie E. Sparks
Industrial Environmental Research Laboratory
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
ABSTRACT
The reactions of two proprietary flue gas conditioning agents used in high
temperature applications have been investigated in the laboratory under condi-
tions simulating those in the flue gas train of a coal-burning power plant.
The two agents investigated were Apollo Chemical Corporation's Coaltrol LPA-40
and LPA-445. LPA-40 was found to be primarily an aqueous ammonium sulfate
solution and LPA-445 an aqueous solution of diammonium hydrogen phosphate.
The two predominant types of reactions observed in the study were thermal
decomposition and recombination reactions. The primary thermal degradation
products of LPA-40 at 650 °C were ammonia and sulfur trioxide. At 160 and
90 °C the decomposition fragments recombined into ammonium sulfate salts.
Extensive decomposition of LPA-445 into ammonia and phosphate species was
observed at 650 °C, with recombination into ammonium phosphate salts occurring
at lower temperatures.
INTRODUCTION
Most of the older electrostatic precipitators used in coal-burning power
plants operate at temperatures around 150 °C (300 °F). The recent widespread
use of low-sulfur coals in electric power production in order to comply with
sulfur dioxide emission regulations has led to difficulty in achieving
202
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efficient collection of fly ash in these precipitators. This difficulty is
primarily attributable to an increase in the electrical resistivity of the ash,
which limits the useful voltage and current that can be maintained in a precip-
itator.
A common approach that has been taken to improve the collection efficien-
cies of these precipitators is the injection of chemical additives into the
gas stream before it enters the precipitator in order to modify the electrical
resistivity of fly ash or to obtain some other beneficial effects on precipita-
tor performance. While chemical conditioning agents have substantially
improved precipitator efficiencies in many instances, however, it is conceiv-
able that the injection of chemicals into flue gas may result in the release
to the environment of undesirable compounds consisting of the agents, their
thermal decomposition products, or their reaction products with components of
the flue gas.
We have recently completed a laboratory investigation of the chemical
reactions of several flue gas conditioning agents under conditions simulating
those in the flue gas train of a coal-burning electric power plant. The pri-
mary purposes of the study were to characterize the chemical species resulting
from the addition of conditioning agents to the flue gas of a coal-fired power
plant and to identify hazardous chemical species originating from the agents
that can potentially undergo stack discharge to the environment.
This paper presents the results of our investigations of two proprietary
conditioning formulations marketed by the Apollo Chemical Corporation, Coaltrol
LPA-40 and Coaltrol LPA-445. The work was funded under EPA Contract 68-02-2200
and was monitored by Dr. Leslie E. Sparks of the Industrial Environmental
Research Laboratory at Research Triangle Park, North Carolina.
DESCRIPTION OF THE LABORATORY APPARATUS
For the investigation of the reactions of flue gas conditioning agents, a
laboratory bench-scale facility was constructed to simulate the flue gas train
in a full-scale coal-burning power plant. The basic flue gas mixture consisted
by volume of approximately 76% nitrogen, 12% carbon dioxide, 8% water vapor,
and 4% oxygen. This synthetic flue gas was prepared by mixing charcoal-
filtered compressed air with nitrogen and carbon dioxide from regulated, com-
pressed gas cylinders and then electrically heating the mixture to a tempera-
ture of approximately 650 °C. Water vapor was added to the hot gas mixture by
the flash evaporation of metered, gravity-fed liquid water in the heated gas
stream. Trace amounts of gaseous sulfur dioxide, nitric oxide, and nitrogen
dioxide could be added individually or in various combinations to the hot gas
mixture. Typical concentrations of these oxides in the gas stream were, on
the volume basis, approximately 600 ppm sulfur dioxide, 1000 ppm nitric oxide,
and 100 ppm nitrogen dioxide. The total volume flow rate of the gas mixture
was usually maintained at approximately 35 1/min (expressed for 25 °C).
We had originally planned to suspend fly ash in the gas stream to simulate
the particulate produced from the combustion of coal. However, the anticipa-
tion of technical difficulties associated with resuspending fly ash in the flue
gas stream and with interpreting the results of reaction studies in a hetero-
geneous system led to abandoning the inclusion of fly ash in the system.
203
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The synthetic flue gas mixture was introduced into a series of heated
cylinders of quartz, Pyrex, or stainless steel that represented various parts
of the flue gas train of a coal-fired power plant extending from a point
upstream from the economizer to the outlet of the stack. The principal compo-
nents of the laboratory train are schematically illustrated in Fig. 1 and are
itemized and described briefly below:
• A heated quartz cylinder maintaining a portion of the gas stream
at 650 °C, a representative gas temperature in the duct upstream
from the economizer.
« A Pyrex heat exchanger representing the economizer.
• A heated Pyrex cylinder maintaining a portion of the gas stream
at about 370 °C, a representative gas temperature in the duct
between the economizer and the air preheater.
• A Pyrex heat exchanger representing the air preheater.
• A heated Pyrex cylinder maintaining a portion of the gas stream
at about 160 °C, representing the temperature in the duct
between the air preheater and the electrostatic precipitator.
• A small wire-and-pipe electrostatic precipitator (ESP) main-
tained at a temperature of about 160 °C.
• A Pyrex heat exchanger simulating cooling near the stack exit.
• A heated Pyrex cylinder maintaining a portion of the gas stream
at about 90 °C, a conceivable temperature of the gas stream near
the top of the stack.
The dimensions of the cylinders were chosen to provide gas residence
times of 2 sec within each cylinder except in the heat exchangers and the ESP.
The gas residence time within each of the heat exchangers was a fraction of a
second. The gas residence time within the ESP was about 7 sec. Each cylinder
enclosing a constant temperature zone was provided with an injection port near
its inlet and a sampling port near its outlet.
The ESP was activated in some of the earlier experiments with nonproprie-
tary conditioning agents, but it was not activated in any of the experiments
reported in this paper.
CHEMICAL ANALYSIS "OF LPA-40 AND LPA-445
Samples of Coaltrol LPA-40 and Coaltrol LPA-445 for use in this investiga
tion were supplied by Apollo Chemical Corporation. Both of these formulations
were chemically analyzed so that possible thermal decomposition products of
the agents could be postulated. The flue gas stream would be sampled and
analyzed for the appropriate chemical species.
204
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HEAT
EXCHANGER
r~\\
HEAT
EXCHANGER
(AIR
PREHEATER)
370 °C
ZONE
S02 NC>2 NO
IN IN
N2 N2
HEAT
EXCHANGER
(ECONOMIZER)
650
ZONE
ELECTRIC
HEATER
Figure 1. Schematic diagram of flue gas train.
205
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The sample of LPA-40 supplied by Apollo was a light brown solution with a
density of 1.27 g/ml and a pH of 3.9. The qualitative identification of the
primary components of the formulation was performed by infrared spectroscopy
and ion chromatography.l The solid material resulting from the evaporation
of the solvent from the formulation possessed an infrared spectrum that was
identical to that of ammonium sulfate, (NHi»)2SOi,. Analysis of the formula-
tion by ion chromatography revealed that sulfate ion was the only anion that
was present in significant amounts.
The LPA-40 formulation was quantitatively analyzed for ammonium ion by
the indophenol method2 and by acid-base titration with sodium hydroxide solu-
tion. The sulfate concentration was determined by titration with barium per-
chlorate solution using Thorin as an indicator.3 The results of these
analyses showed that the LPA-40 formulation consisted of about 40% w/w
ammonium sulfate in water.
The brown coloration of our sample of LPA-40 was believed to be due to
the presence of ferric ion in the formulation. The LPA-40 solution was
analyzed by atomic absorption spectroscopy and was found to contain approxi-
mately 0.2% w/w iron. The nature of the iron compound in the formulation was
not characterized; but the compound is speculated to be ferric hydroxide, pres-
ent in the formulation as an impurity in the ammonium sulfate used to prepare
the agent.
The sample of LPA-445 was a clear, colorless liquid with a distinct
ammoniacal odor. Its density was 1.14 g/ml and its pH approximately 8.2.
Mass spectrometrie analysis of the solid residue remaining after evaporation
of the formulation to dryness indicated that the solid residue was an ammonium
phosphate salt.
LPA-445 was identified as an aqueous solution of diammonium hydrogen phos-
phate, (NHit) zHPOit, and the concentration of the solution was determined by
analyzing the formulation for ammonium ion by the indophenol method and for
orthophosphate ion by ion chromatography and by the vanadomolybdophosphoric
acid colorimetric method.1* The LPA-445 formulation was found to consist of a
solution of approximately 24% w/w diammonium hydrogen phosphate in water.
Analysis of the formulation by ion chromatography also revealed the presence
of trace amounts of sulfate ion (approximately 7.30 ymol/g or 0.08% w/w).
Two separate samples of LPA-445 were used during the investigation of
this conditioning agent. Each of the samples was analyzed individually, and
the two samples were found to be identical within the experimental limits of
error of the chemical methods used in the analyses.
POSTULATED REACTION MECHANISMS
The predominant reaction types expected in the study of both LPA-40 and
LPA-445 were thermal decomposition reactions at high temperatures and recombi-
nation of the degradation fragments at lower temperatures. At 650 °C the
probable decomposition of ammonium sulfate, the major component of LPA-40, was
expected to proceed via the following equation:
(NHit)2SOil(s) —> 2NH3(g) + H20(g) + S03(g) (1)
206
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The occurrence of this reaction is consistent with the thermodynamic data of
Kelley et al.5 and Scott and Cattell.6 In addition, based on the findings of
Halstead,7 nitrogen, nitrogen oxides, and sulfur dioxide were expected as
relatively minor products from the thermal decomposition of ammonium sulfate.
The recombination of the major thermal decomposition products was expected to
proceed by the stepwise reversal of equation 1 with decreasing temperature:
S03(g) + H20(g) ~> H2SOi,(g) (2)
NH3(g) + H2S(Mg) — * NH^HSCKd or g) (3)
NH3(g) -f mUHSCMl or g) — > (NHj,)2SOl((s) (4)
We initially expected the major component of LPA-455, diammonium hydrogen
phosphate, to dissociate at 650 °C into gaseous ammonia and phosphoric acid.
The resultant phosphoric acid was then expected to decompose completely into
phosphorus pentoxide (P20s) and water or to polymerize into condensed phosphate
species (linear polyphosphates such as pyrophosphate, cyclic metaphosphates,
or "infinite chain" metaphosphates) .
The thermal decomposition of diammonium hydrogen phosphate was studied by
Erdey, Gal, and Liptay8 by means of thermal gravimetry and differential thermal
analysis. This study indicated that diammonium hydrogen phosphate thermally
decomposes in a stepwise fashion with several decomposition processes proceed-
ing sequentially as the temperature is raised. These processes are:
NH3(g) (5)
) (6)
2NH«lH2POif(l) -i— (NH^)2H2P207(s) + H20(g) (7)
n(NHO2H2P207(s) ^°-°-^> 2 (NH4P03)n(s) + nH20(g) (8)
2(NHlfP03)n(s) SOOzSOO^ 2nNH3(g) + nP205(g) + nH20(g) (9)
Thus, on the basis of this study, at 650 °C diammonium hydrogen phosphate was
expected to thermally decompose into ammonia, phosphorus pentoxide (which
would be analyzed as orthophosphate ion in gas samples removed at 650 °C) , and
water. As the flue gas stream was cooled from 650 to 90 °C the reaction
sequence given in equations 5 through 9 was expected to be reversed. Thus,
near the exit of the gas train, the probable recombination products were
expected to be diammonium hydrogen phosphate and ammonium dihydrogen phosphate.
The decomposition reactions of both LPA-40 and LPA-445 discussed above
were expected to be identical whether or not reactive sulfur and nitrogen
oxides were present in the flue gas. However, significant amounts of the
ammonia formed during the thermal decomposition of injected LPA-40 and LPA-445
were expected to possibly be destroyed in the 650 °C zone in the presence of
added nitrogen oxides in the gas stream due to the reaction of ammonia with
nitrogen oxides.
207
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No unusual or highly toxic decomposition or reaction products of measur-
able concentration were expected to be formed in the gas stream when LPA-40 or
LPA-445 were injected. The only highly toxic compound that we could envision
possibly being formed in the gas stream was phosphine (PH3) from the highly
unlikely reduction of some phosphorus-containing species during the injection
of LPA-445.
INJECTION OF LPA-40 AND LPA-445 INTO THE FLUE GAS
Both of the formulations were introduced into the flue gas stream as aero-
sols. Dilute, filtered aqueous solutions of LPA-40 and LPA-445 were nebulized
at a rate of 0.2 ml/min with a Retec X70/N nebulizer assembly (Burton Division,
Cavitron Corporation, Van Nuys, California). The nebulizer was activated with
dry nitrogen gas, and the aerosol resulting from the nebulization process was
introduced into the 650 °C constant temperature zone through a quartz tube
that extended from the outlet of the nebulizer to the center of the flue gas
stream. Since Apollo's LPA series of additives are normally used for high tem-
perature application (gas stream temperatures of 590 to 900 °C), both LPA-40
and LPA-445 were injected into the hottest constant temperature zone in our
laboratory flue gas train, the 650 °C zone. The rate of injection of LPA-40
was chosen so that the concentration of ammonium sulfate in the flue gas at
650 °C did not exceed the upper limit specified by Apollo, 41 yg/1.9'10 The
measured concentrations of ammonium sulfate injected into the flue gas stream
over the course of the study ranged from 9 to 41 yg/1 at 650 °C. No informa-
tion was found on the concentration of diammonium hydrogen phosphate in the
flue gas recommended by Apollo. The rate of injection of LPA-445 was thus
somewhat arbitrary and ranged from approximately 14 to 67 yg/1 at 650 °C
during the first half of the study of LPA-445. During the second half of the
study, however, the nebulizer began malfunctioning, and the injection rates
ranged from only 4 to 26 yg/1.
The average injection rates of ammonium sulfate and diammonium hydrogen
phosphate were determined by chemically analyzing the solutions in the nebu-
lizer before and after a series of experiments. The solutions of LPA-40 were
analyzed for ammonium ion and sulfate ion, and the LPA-445 solutions were
analyzed for ammonium ion and phosphate ion. The injection rates were calcu-
lated from the differences in the amounts of ammonium ion and sulfate or phos-
phate ion in the nebulizer before and after the nebulization period. These
analyses indicated that in many experiments with LPA-40 as much as 25% more
ammonium ion was injected into the gas stream than was sulfate (based on the
ratio of equivalents lost from the nebulizer). In the experiments with
LPA-445, a 25% excess of ammonium ion relative to phosphate ion (again on an
equivalent basis) was apparently nebulized into the gas stream when the nebu-
lizer was functioning properly. During the later experiments, when the
nebulizer was not functioning properly, the average excess of ammonia over
phosphate averaged 90%. The apparent origin of the excess ammonia during the
nebulization of LPA-40 was the decomposition of a residue of ammonium sulfate
that collected in the quartz tube of the nebulizer at high injection rates.
The excess ammonia, apparently injected during the nebulization of LPA-445,
can be partially explained by the appreciable vapor pressure of ammonia that
is present over solutions of diammonium hydrogen phosphate, even at room
temperature, and by the decomposition of solid ammonium dihydrogen phosphate
208
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that collected in the quartz tube of the nebulizer. However, these cannot
completely accout for the large excess of injected ammonia during the period
of malfunctioning of the nebulizer, and no satisfactory explanation could be
found.
SAMPLING AND ANALYTICAL METHODS
During the investigations of LPA-40 and LPA-445, the flue gas was sampled
and analyzed for a variety of substances. In both studies the gas stream was
analyzed for background sulfur dioxide, sulfur trioxide, nitric oxide, and
nitrogen dioxide. In the investigation of LPA-40, the gas stream was specifi-
cally analyzed for ammonia, ammonium ion, sulfate ion, sulfite ion, nitrate
ion, nitrite ion, and iron. In the investigation of LPA-445, the gas stream
was specifically analyzed for ammonia, ammonium ion, orthophosphate ion, con-
densed phosphate species (pyrophosphates, metaphosphates, etc.), and phosphine.
The selection of these compounds for analysis was based on the anticipated
thermal decomposition reactions of the conditioning agents and the expected
chemical reactions of the agents or their degradation products with various
components of the flue gas stream.
Sulfur trioxide was determined by sampling the flue gas through a con-
trolled condensation coil11'12 and by subsequently measuring the collected
sulfate by the barium perchlorate-Thorin titration method or by ion chromatog-
raphy. Sulfur dioxide was collected downstream from the coil in a bubbler
containing 3% hydrogen peroxide, and the resulting sulfate was determined by
titration of the bubbler solution with 0.1 N sodium hydroxide to the bromphenol
blue endpoint or by analyzing the solution for sulfate by ion chromatography.
In the absence of added nitrogen oxides to the gas stream, nitrogen diox-
ide was determined by the Greiss-Saltzman procedure;13 nitric oxide was first
oxidized to nitrogen dioxide on firebrick impregnated with chromium trioxide
and then analyzed by the Greiss-Saltzman method. In the presence of added
nitrogen oxides, the phenoldisulfonic acid method11* was used to determine the
sum of nitric oxide and nitrogen dioxide concentrations (as nitrate ion), and
the Greiss-Saltzman method was used to determine the nitrogen dioxide concen-
tration. The concentration of nitric oxide was determined by difference.
In the investigation of LPA-40, ammonia was absorbed from the flue gas in
bubblers containing 0.1 N sulfuric acid; the resulting ammonium ion was then
determined by the indophenol colorimetric procedure. Particulate material
from the flue gas was collected ahead of the bubblers on heated quartz wool
plugs at 650 °C and on heated Teflon filters at 160 and 90 °C. Exposed fil-
ters and plugs were usually washed with distilled, deionized water. The
washes were analyzed for ammonium ion by the indophenol method and for sulfate,
sulfite, nitrate, and nitrite by ion chromatography. In some experiments,
exposed filters were washed with tetrachloromercurate solution, and sulfite
was determined by the West-Gaeke method.15 In other experiments, iron was
determined by atomic absorption spectroscopy in either water washes or hot
hydrochloric acid washes of the quartz wool plugs.
209
-------
In the investigation of LPA-445, the gas stream was usually sampled
through a particulate filter (either a quartz wool plug at 650 or 370 °C or a
fine porosity Teflon disc at 160 or 90 °C) and then through a bubbler of 0.1 N
sulfuric acid. The material collected on a filter or in the bubbler was
analyzed for ammonium ion, orthophosphate ion, and condensed phosphate species.
In a few experiments the gas stream was sampled into a bubbler of sodium
bicarbonate-sodium carbonate buffer solution, and the solution was subsequently
analyzed by ion chromatography. Ammonium ion was determined by the indophenol
method. Orthophosphate and condensed phosphate ions were determined colori-
metrically, either by the vanadomolybdophosphoric acid method or by the stan-
nous chloride method.16 In both methods, orthophosphate ion was determined
directly, whereas condensed phosphate ions were first hydrolyzed by boiling
in a dilute acid solution and then determined colorimetrically as ortho-
phosphate ion.
In one set of experiments with LPA-445 the gas stream was sampled through
a bubbler containing silver diethyldithiocarbamate reagent and analyzed colori-
metrically for phosphine.17
VARIATION OF EXPERIMENTAL PARAMETERS
The experimental parameters that were varied in these investigations
included the composition of the flue gas into which LPA-40 and LPA-445 were
added and the temperature of removal of gas samples to be analyzed. The speci-
fic combinations of experimental conditions that were employed are shown in
Table 1. In the investigation of each agent, the first series of experiments
was conducted with a simplified flue gas mixture containing no added oxides of
sulfur or nitrogen. In the later series of experiments, the reactive oxides
of sulfur and nitrogen were added.
Table 1. EXPERIMENTAL CONDITIONS USED IN THE
INVESTIGATIONS OF LPA-40 AND LPA-445
Injection
Gas composition temperature, °C Sampling temperature, °C
No added SOX or NOx 650 650, 370 (LPA-445 only),
160, and 90
600 ppm S02 added 650 650 (LPA-445 only)
600 ppm S02, 650 650, 160, and 90 (LPA-40);
1000 ppm NO, and 160 and 90 (LPA-445)
100 ppm N02 added
As previously discussed, both LPA-40 and LPA-445 were added to the gas
stream at 650 °C in all of the experiments. In the investigation of LPA-40,
the flue gas was usually removed near the outlet of the 650 °C zone into a
sampling manifold. In some experiments the sampling manifold was maintained
as hot as possible (approximately 500 °C) in order to study the thermal
210
-------
degradation of the conditioning agent, and in other experiments the flue gas
was allowed to cool rapidly to 160 or 90 °C in the sampling train in order to
study the recombination reactions of the decomposed conditioning agent. The
purpose of this sampling procedure was to minimize the wall losses that would
have occurred in the flue gas train if the gas stream had been sampled at the
outlets of the 160 and 90 °C constant temperature zones. In the investigation
of LPA-445, the sampling manifold was not used due to gas flow metering prob-
lems encountered in the use of the manifold in the investigation of LPA-40.
Rather, the flue gas was sampled directly from the outlet of the 650 °C zone
in the thermal decomposition studies and from the outlets of the 370, 160, or
90 °C zones in the recombination studies.
EXPERIMENTAL RESULTS OF THE INVESTIGATION OF LPA-40
Thermal Decomposition Studies
Typical results of the thermal decomposition studies of LPA-40 are given
in Table 2. The primary thermal degradation products of LPA-40, at 650 °C in
flue gas containing no added sulfur or nitrogen oxides, were sulfur trioxide,
sulfur dioxide, and ammonia. The sulfur oxides recovered were approximately
90% sulfur trioxide and 10% sulfur dioxide. Microgram quantities of a solid
iron compound were also found, but the iron compound was not further character-
ized. Nitrogen or nitrogen oxides should also have been produced along with
sulfur dioxide from the oxidation of ammonia by sulfur trioxide. Because of
the large background levels of nitrogen in the flue gas, however, measurement
of the trace amounts of nitrogen produced by this reaction was not possible.
Nitrogen oxides were found at levels no higher than the background concentra-
tions of approximately 10 ppb.
In one set of experiments, instead of injecting LPA-40, an aqueous solu-
tion of ordinary ammonium sulfate was injected into flue gas containing no
added sulfur or nitrons a oxides. The primary thermal degradation products of
ammonium sulfate found were the same as those of LPA-40 at 650 °C—ammonia,
sulfur trioxide, and sulfur dioxide. The sulfur oxides recovered consisted of
about 95% sulfur trioxide and 5% sulfur dioxide. There was no indication that
the relative amount of sulfur dioxide changed significantly as the result of
the absence of the iron compound found in LPA-40.
The primary thermal decomposition products of LPA-40 in flue gas contain-
ing added sulfur and nitrogen oxides were sulfur trioxide and ammonia, the
same principal degradation products that were found in the absence of reactive
gases in the flue gas stream. Because of the large background concentrations
of sulfur dioxide that were added to the gas stream in these experiments, how-
ever, the small amounts of sulfur dioxide produced during the thermal degrada-
tion of LPA-40 that were observed in the absence of reactive gases could not
be detected.
Recombination Studies
No Oxides of Sulfur or Nitrogen Added to Flue Gas. The averaged results
of the recombination studies of LPA-40 in the absence of added reactive oxides
in the flue gas are given in Table 3. When the gas stream was sampled at
211
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Table 2. DETERMINATION OF THERMAL DECOMPOSITION PRODUCTS
OF LPA-40 AT 650 °C
Concentration, meq/1 x 10.000*
Observed Injected
Total
Gas composition SO3 S02 SOX NH3 SOiT2 NHi,+
Without added S02 or NOX 4.97 0.56 5.53 4.44 6.11 6.lit
Without added S02 or NO^ 5.54 0.22 5.76 5.01 7.81 7.53
With 600 ppm S02 and 3.43 - - 3.21 7.85 7.85t
1100 ppm NOX added
* Expressed for 25 °C. To convert the concentrations to parts
per million (gas by volume) multiply the SOs and S02 concentra-
tions by 1.22 and the NH3 and NHi/4" concentrations by 2.44.
t Not determined independently. Based on S0ij~2 lost from the
nebulizer.
t An ammonium sulfate solution was injected instead of LPA-40 in
this experiment.
160 °C, the primary product found on the particle filters appeared to be ammo-
nium bisulfate, NHijHSOi,. Evidence of lesser amounts of ammonium sulfate was
also found by analysis of the filters, but the predominance of the bisulfate
salt was indicated by the low ratios of ammonium ion concentration to the
anion concentration. These ratios are listed in Table 4. Expressed in equiva-
lents, the average ratio was 0.59. This corresponded to mole fractions of 0.83
for ammonium bisulfate and 0.17 for ammonium sulfate in the filter catch. An
average of about 4% of the total sulfur species recovered was sulfur trioxide
(or sulfuric acid vapor), and about 4% was recovered as sulfur dioxide.
Ammonia was the only nitrogen compound found at significant concentrations.
Nitrogen oxides were not above the background levels.
When the gas stream was sampled at 90 °C, the primary recombination pro-
duct found appeared to be ammonium sulfate. The average ratio of ammonium ion
concentration to anion concentration expressed in terms of equivalents was
0.89. This corresponded to mole fractions of 0.76 for ammonium sulfate and
0.24 for ammonium bisulfate in the filter catch. Sulfur trioxide (or sulfuric
acid vapor) was found to be present at concentrations representing 0.5 to 0.8%
of the sulfur compounds, while sulfur dioxide represented from 4 to 6%. Since
no sulfuric acid should exist as vapor at 90 °C, the sulfuric acid found must
have occurred as fine particles of condensed liquid that slipped through the
filter. As above, ammonia was the only nitrogen compound found in significant
concentrations.
When ordinary ammonium sulfate was injected into the flue gas instead of
LPA-40, the predominant recombination product found at 160 °C was apparently
ammonium bisulfate; at 90 °C the main product appeared to be ammonium sulfate,
212
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Cable 3. RESULTS OF THE RECOMBINATION STUDIES OF LPA-40 AND AMMONIUM SULFATE
IN FLUE GAS CONTAINING NO ADDED OXIDES OF SULFUR OR NITROGEN
Agent
injected
LPA-40
Sampling
temp.,
°C
Concentration, meq/1 x 10,000*
Observed (averaged values)
HSOi," Total
sulfur
or
160 7.31 0.29 0.31
90 14.80 0.11 0.73
species injected
7.91
15.64
13.81
19-08
Recovery ,
57
82
160 5.29
90 5.35
0.06 0.14
0.06 0.14
5.49
5.55
7.45
7.45
74
74
LPA-40
(NHi»)2SOi,
160
90
160
90
4.28
13.07
5.89
5.52
3.06
4.53
Total
nitrogen NHi,
species injected
10.17
18.59
13.63
19.30
8.01
8.01
75
96
* Expressed for 25 °C. To convert the concentrations to parts per
million on a hypothetical volume basis, multiply the concentrations
of the sulfur species by 1.22 and the concentrations of NHit and
NH3 by 2.44.
Table 4. ANALYSIS OF THE RECOMBINATION PRODUCTS OF LPA--40 AND AMMONIUM
SULFATE IN FLUE GAS CONTAINING NO ADDED OXIDES OF SULFUR OR NITROGEN
Agent
injected
LPA-40
Sampling
temp.,
°C
160
90
[HSOiTl or [SOiTz]
found on filter
0.59
0.89
Mole
fraction
0.83
0.24
Mole
fraction
(NHlt)2SOi)
0.17
0.76
160
90
0.58
0.85
0.84
0.30
0.16
0.70
213
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as during the injection of LPA-40. The predominance of one sulfate salt over
the other was indicated by the ratios of ammonium ion concentrations to the
sulfate and bisulfate concentrations (Table 4). At 160 °C the average ratio
expressed in terms of equivalents was 0.58, which corresponds to mole frac-
tions of 0.84 for ammonium bisulfate and 0.16 for ammonium sulfate. At 90 °C
the average was 0.85, which corresponds to mole fractions of 0.70 for ammonium
sulfate and 0.30 for ammonium bisulfate.
Sulfur and Nitrogen Oxides Added to Flue Gas. The averaged results of
the recombination studies of LPA-40 in flue gas containing added oxides of
sulfur and nitrogen are given in Table 5. The predominant recombination pro-
ducts found at 160 and 90 °C were ammonium sulfate salts. However, uncertain-
ties in the data did not permit a definite conclusion to be drawn about the
distribution of the recombination products between ammonium sulfate and ammo-
nium bisulfate. The data obtained in these experiments were based on only a
few determinations, had a large scatter, and gave poor mass balances. At
160 °C the ratio of ammonium ion concentration to anion concentration (each
expressed in meq/1) was found to range from 0.85 in one experiment (which
would indicate a predominance of ammonium sulfate) to 0.21 in another (which
could indicate the occurrence of ammonium bisulfate in an excess of sulfuric
acid). At 90 °C the ratio ranged from 0.51 to 0.06. With the exception of
one value of 0.41, which corresponds to mole fractions of 0.98 for ammonium
bisulfate and 0.02 for ammonium sulfate, these low ratios indicate an excess
of sulfuric acid over any ammonium salt present. Any sulfate salt initially
formed would have been converted to the bisulfate salt by the excess acid.
Table 5. RESULTS OF THE RECOMBINATION STUDIES OF LPA-40 IN
FLUE GAS CONTAINING ADDED OXIDES OF SULFUR AND NITROGEN
Concentration, meq/1 x 10,000*
Sampling Observed (averaged values)
temp., HSOrt" Total sulfur SOi,"2 Recovery,
^C or SOi,"2 S03 species injectedt %
160 2.08 0.41 2.49 5.12 49
90 6.80 0.37 7.17 9.62 75
Total nitrogen
NHs species injectedt
160
90
2.02
1.93
0.22
0.23
2.24
2.16
5.12 44
9.62 22
* Expressed for 25 °C. To convert the concentrations to parts
per million on a hypothetical volume basis, multiply the con-
centrations of the sulfur species by 1.22 and the concentra-
tions of NHn+ and NH3 by 2.44.
t Based on S0i|~2 lost from nebulizer.
214
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The only chemical species found at significant levels in any of the
experiments with added sulfur and nitrogen oxides in the gas stream were ammo-
nium and sulfate ions, sulfur trioxide, and ammonia. Only negligible amounts
of nitrite, nitrate, and sulfite ions could be detected in any of the filter
washes analyzed by ion chromatography. And because of the high background
levels of nitric oxide, nitrogen dioxide, and sulfur dioxide, the small quan-
tities of these oxides that could possibly be formed in these experiments
could not be determined.
In most of the experiments with added nitrogen oxides present in the gas
mixture, the concentrations of ammonia and ammonium ion recovered from the gas
stream were significantly less than the injected concentrations of ammonium
ion into the flue gas. This observation is consistent with the finding
obtained in earlier studies with ammonia during these investigations that
extensive reaction occurs between nitrogen oxides and ammonia in the flue gas
train at 650 °C.
EXPERIMENTAL RESULTS OF THE INVESTIGATION OF LPA-445
Injection of LPA-445 into Flue Gas Containing No Added Oxides of Sulfur or
Nitrogen
The experimental results of the study of LPA-445 in flue gas containing
no added oxides of sulfur or nitrogen are given in Tables 6 and 7. Table 6
compares the total amounts of ammonium and phosphate ions that were collected
with the amounts injected. Table 7 gives the quantities of ammonium, ortho-
phosphate, and condensed phosphate ions found on the particulate filters and
in the bubbler solutions.
Thermal Decomposition Studies. The thermal degradation products of
LPA-445 found at 650 °C on the filters and in the bubblers in flue gas contain-
ing no added sulfur or nitrogen oxides were ammonium ion, orthophosphate ion,
and condensed phosphate ions. Table 6 shows that, on the average, 88% of the
injected ammonium ion was recovered at 650 °C whereas only 52% of the injected
phosphate ion was recovered. This difference in recoveries strongly suggests
that when LPA-445 was injected into the gas stream at 650 °C diammonium hydro-
gen phosphate decomposed extensively into gaseous ammonia and particulate
phosphate species. The low recovery of the phosphate species can be attrib-
uted chiefly to wall losses of phosphate particles due to either impingement
and adsorption or to settling out of the particles.
From Table 7 it can be seen that about 90% of the recovered ammonium ions
was collected in the bubbler, a result also indicating that extensive decompo-
sition of the diammonium phosphate to ammonia gas occurred. For phosphate
ions, roughly 50% was found either on the filter or in the bubbler. This
result suggests that extensive volatilization of phosphate, perhaps to phos-
phorus pentoxide, also occurred. On the other hand, the presence of a signif-
icant fraction of the phosphate on the filter suggests that part of the phos-
phate remained as particulate. The mole ratio of ammonium ion to total
phosphate on the filter was approximately 0.9. This ratio suggests that the
filter may have collected an ammonium phosphate solid with a mole ratio of
ammonium ion to phosphate of 1:1. The thermal stabilities of ammonium
215
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Table 6. RECOVERY OF DECOMPOSITION AND RECOMBINATION PRODUCTS OF LPA-445
IN FLUE GAS CONTAINING NO ADDED OXIDES OF SULFUR OR NITROGEN
Concentration, pmol/1*
Recovery, %
Total
Sampling
temp . ,
°C
650
370
160
90
Injectedt
NH4+
1.666
2.838
1.949
2.271
Total
POiT3
0.660
1.363
0.706
0.879
Observed
NH4+
1.462
2.173
1.131
0.921
Total
PO.T3
0.344
0.772
0.111
0.119
88 52
77 57
58 16
41 14
* Expressed for 25 °C. To convert to parts per million
on a hypothetical volume basis, multiply by 24.4.
t Based on NHit and P0i»~3 lost from nebulizer.
Table 7. DISTRIBUTION OF DECOMPOSITION AND RECOMBINATION PRODUCTS OF LPA-445
IN FLUE GAS CONTAINING NO ADDED OXIDES OF SULFUR OR NITROGEN
Concentration, ymol/1*
Sampling
temp. ,
°C
650
370
160
90
Collected on
NHtt+
0.124
0.267
0.102
0.127
Ortho-
P04-3
0.123
0.393
0.068
0.087
filter
Condensed
P04-3
0.041
0.148
0.029
0.013
Collected in
NHi,"1"
1.338
1.906
1.028
0.794
Ortho-
POiT3
0.156
0.188
0.002
0.004
bubbler
Condensed
POi+~3
0.025
0.042
0.011
0.016
* Expressed for 25 °C. To convert to parts per million on a hypo-
thetical volume basis, multiply by 24.4.
216
-------
orthophosphates, however, make the existence of an ammonium phosphate solid
appear improbable at 650 °C. Perhaps gaseous compounds were merely adsorbed
on the quartz wool in a ratio suggesting a stoichiometric compound.
The decomposition studies at 650 °C also led to the following observa-
tions :
• Approximately 25% of the original orthophosphate was converted
to condensed phosphate (see Table 7).
• Negligible quantities of ammonia were oxidized to nitrogen
oxides. The total concentration of nitrogen oxides was about 1%
of the concentration of ammonium ion collected on the filter and
in the bubbler.
Recombination Studies. At 370, 160, and 90 °C, ammonium ion, ortho-
phosphate ion, condensed phosphate ion, and traces of nitrogen oxides were
found in the gas stream. These were the same species found in the flue gas
sampled at 650 °C. As shown in Table 6, the recovery of ammonium ion was
greater than the recovery of total phosphate ion at each of the three collec-
tion temperatures. The recovery of ammonium ion averaged 77, 58, and 41%,
respectively, at 370, 160, and 90 °C. The recovery of total phosphate species
averaged 57, 16, and 14% at the same temperatures. The greater recovery of
ammonium ion relative to phosphate ion at all collection temperatures (see
Table 6) seems to indicate, as discussed previously, that the collected ammo-
nium ion originated from a gaseous species (ammonia) in the flue gas stream
and that the collected phosphate ions originated from particulate phosphate
species. However, the data in Table 6 also show a general decrease in the
recoveries of both ammonium ion and phosphate ion, as the physical location of
the sampling point was further removed from the conditioning agent injection
po'int. The decreasing recoveries of phosphate ions can be attributed to wall
losses of particulate phosphate species, but wall losses alone would be inade-
quate to explain decreasing recoveries of gaseous ammonia. Rather, the trend
of decreasing recoveries of ammonium ion indicates that recombination of
ammonia with particulate phosphate species occurred in the gas stream at the
lower temperatures. The decreasing recoveries of ammonium ion at the lower
temperatures can thus be partially attributed to wall losses of particulate
ammonium phosphate salts.
On the average nearly 90% of the ammonium ion collected at each tempera-
ture was found in the bubbler solution. This indicates that the source of the
ammonium ion collected in the bubbler was gaseous ammonia. This ammonia gas
presumably originated from two separate sources: (1) the original decomposi-
tion of diammonium hydrogen phosphate, or (2) the injection of excess ammonia
from the nebulizer.
At 370 °C, approximately 70% of the total collected phosphate was found
on the particle filter. This percentage increased to approximately 85% at 160
and 90 °C. These results indicate that as the temperature was lowered the
extent of recombination of the original decomposition products into solid ammo-
nium phosphate salts increased significantly. At all of the sampling tempera-
tures, approximately 75% of the phosphate ions collected on the particle
filters were orthophosphate ions.
217
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The mole ratios of ammonium ion to orthophosphate ion and ammonium ion to
total phosphate ion collected on the Teflon filters were approximately the
same at both 90 and 160 °C, 1.0:1.0 and 1.0:1.5, respectively. This indicated
that the same recombination product was present at both temperatures. Thermo-
dynamically, ammonium dihydrogen phosphate appeared to be the most probable
recombination product at both 90 and 160 °C. However, based on the amounts of
phosphate ion found at 90 and 160 °C and the equilibrium dissociation pres-
sures of monoammonium and diammonium phosphate at these temperatures, the only
species that would be expected to be found on the particulate filter at either
of these temperatures would be monoammonium phosphate at 90 °C — i.e.,
The assertion that the only stable ammonium phosphate species at either
160 or 90 °C should be monoammonium dihydrogen phosphate at 90 °C is explained
as follows. The weight of phosphate ion collected on the particulate filter
at 90 °C corresponded to an average gas stream concentration of 3.0 ppm of
phosphate as a hypothetical vapor. At 160 °C the weight collected corresponded
to an average of 4.0 ppm of phosphate. The dissociation pressures of diammo-
nium hydrogen phosphate at 90 and 160 °C are 4.57 and 257 mmHg, respectively.18
These dissociation pressures correspond to 6,000 and 340,000 ppm of NHs at 90
and 160 °C, respectively. Thus, the amounts of phosphate collected at 90 and
160 °C were totally insufficient to produce the ammonia concentrations that
would be in equilibrium with diammonium hydrogen phosphate.
The dissociation pressure of monoammonium dihydrogen phosphate is
0.05 mmHg (66 ppm) at 125 °C.19 The value is not known at 90 °C, but it is
probably low enough to be consistent with the occurrence of the monoammonium
salt at 90 °C. The dissociation pressure at 160 °C is also unknown, but it is
certainly too high to be consistent with the occurrence of the monoammonium
salt at 160 °C. But since the experimental data indicate that the same recom-
bination product was present at both 90 and 160 °C, perhaps the monoammonium
phosphate salt was stabilized at 160 °C by some process such as adsorption on
the particulate filter.
Injection of LPA-445 into Flue Gas Containing Added Oxides of Sulfur and
Nitrogen
The experimental results of the study of LPA-445 in flue gas containing
only added sulfur dioxide or both sulfur dioxide and nitrogen oxides are given
in Tables 8 and 9. These tables are analogous to Tables 6 and 7. Table 8 com-
pares the total amounts of ammonium and phosphate ions that were collected with
the amounts injected. Table 9 shows the quantities of ammonium, orthophos-
phate, and condensed phosphate ions found on the filters and in the bubblers.
Thermal Decomposition Studies. When approximately 600 ppm of sulfur
dioxide was added to the flue gas, ammonium ion, orthophosphate ion, and con-
densed phosphate ion were again collected on filters and in bubblers at
650 °C. Table 8 shows that, on the average, approximately 63% of the injected
ammonium ion and 55% of the injected phosphate ion were recovered at 650 °C,
the remainder of the injected ions presumably being lost on the walls of the
650 °C reaction zone and sampling port. Table 9 shows that about 86% of the
ammonium ions was collected in the bubbler, whereas 75% of the total phosphate
ions was found on the filter and 25% in the bubbler. These results indicate
218
-------
Table 8. RECOVERY OF DECOMPOSITION AND RECOMBINATION PRODUCTS OF LPA-445
IN FLUE GAS CONTAINING ADDED OXIDES OF SULFUR AND NITROGEN
Concentration, ymol/1*
Recovery, %
Total
NHi*+ i"v~3
Sampling
temp. ,
°C
650
160
160
90
(S02
(S02
(S02
(S02
only)
only)
and NOX)
and NOx)
Injectedt
NHit"1"
0.
0.
1.
1.
625
893
096
231
Total
POiT3
0
0
0
0
,231
.133
.230
.392
Observed
NH,,"1"
0.
0.
0.
0.
397
297
140
078
Total
POiT3
0.
0.
0.
0.
127
020
017
025
63 55
34 15
13 8
7 6
* Expressed for 25 °C. To convert to parts per million on a
hypothetical volume basis, multiply by 24.4.
t Based on NHit+ and P0n~3 lost from nebulizer.
Table 9. DISTRIBUTION OF DECOMPOSITION AND RECOMBINATION PRODUCTS OF LPA-445
IN FLUE GAS CONTAINING ADDED OXIDES OF SULFUR AND NITROGEN
Concentration, ymol/1*
650
160
160
90
Sampling
temp . ,
°C
(S02 only)
(S02 only)
(SO 2 and NOX)
(S02 and NOX)
Collected on
NIU+
0.057
0.153
0.032
0.027
Ortho-
PO^T3
0.065
0.011
0.010
0.018
filter
Condensed
PO^"3
0.030
0.003
-
0.001
Collected in
NH^"1"
" 0.340
0.143
0.108
0.051
Ortho-
POiT3
0.028
0.002
0.004
0.004
bubbler
Condensed
POiT3
0.004
0.004
0.004
0.002
* Expressed for 25 °C. To convert to parts per million on a hypothetical
volume basis, multiply by 24.4.
219
-------
that at 650 °C the diammonium hydrogen phosphate in LPA-445 decomposed pri-
marily into gaseous ammonia and particulate phosphate species, with some vola-
tilization of phosphate, probably to phosphorus pentoxide, also occurring.
Although these results were qualitatively very similar to the results
obtained in the absence of added reactive gases, there were, however, some
quantitative differences. Much larger recoveries of ammonium ion were found
in the absence of reactive gases (approximately 88%) than in the presence of
added sulfur dioxide, and a larger fraction of the phosphate species was found
in the bubblers (approximately 50%). These results indicate that more exten-
sive thermal decomposition of diammonium hydrogen phosphate and more extensive
volatilization of phosphate ion occurred in the absence of reactive gases than
with sulfur dioxide added to the gas stream. No satisfactory explanation for
this observation, however, can be offered.
Recombination Studies. With both sulfur oxides and nitrogen oxides
added to the flue gas stream, the same general trends in the recovery and dis-
tribution of ammonium ion and phosphate species at 160 and 90 °C (Tables 8 and
9) were observed as those trends observed in the absence of added reactive
gases to the flue gas stream. These results indicate that gaseous ammonia and
particulate phosphate species in the flue gas stream recombined into ammonium
phosphate salts at 160 and 90 °C, with the extent of recombination increasing
as the temperature was lowered. From the thermodynamic considerations dis-
cussed earlier, the most probable recombination product at 160 and 90 °C is
monoammonium dihydrogen phosphate,
From the ion chromatographic analyses of the filter washes, sulfate ion
and nitrate ion were found to be present at concentrations comparable to or
greater than the concentrations of orthophosphate. Thus, in the presence of
added oxides of sulfur and nitrogen, there appears to be a competition for the
available ammonia in the gas stream during recombination reactions at 160 and
90 °C among orthophosphate, sulfate, and nitrate ions. The background level
of sulfur trioxide in the gas stream was the source of the sulfate species in
these experiments. The background concentration of sulfur trioxide was mea-
sured and found to average approximately 2 ppm (0.1 ymol/1, expressed for
25 °C) with an average concentration of 600 ppm sulfur dioxide in the gas
stream. The concentration of nitrate ion in the gas stream, on the other hand,
was expected to be on the trace level. The source of the nitrate ion is
assumed to be the oxidation of ammonia by the nitrogen oxides added to the gas
stream. However, as was pointed out earlier, the average input concentration
of phosphate ion into the gas stream at 650 °C in these experiments was so
small (0.25 pinol/l, only two-and-a-half times greater than the average sulfur
trioxide background level) and the apparent wall losses were so great that
there is little significance to the observed competition between the phosphate
ion and the sulfate and nitrate ions for the available ammonia in the gas
stream. In the presence of a large excess of phosphate ion relative to sulfate
and nitrate ions, the competition might be negligible.
Reaction of Ammonia with Nitrogen Oxides. Table 8 shows that when
nitrogen oxides were present in the gas stream during the injection of LPA-445,
the ammonia recoveries at 160 and 90 °C were significantly less than those in
the absence of added nitrogen oxides. The average recovery of ammonium ion
was 34% at 160 °C with sulfur dioxide as the only reactive oxide added to the
220
-------
gas stream. With both sulfur dioxide and nitrogen oxides added to the gas
stream, the recovery of ammonium ion averaged only 13%, less than one-half the
recovery found at 160 °C witn no nitrogen oxides present. This observation is
consistent with the gas stream reaction of nitrogen oxides with ammonia at
650 °C observed during the investigations of ammonia and ammonium sulfate.
Phosphine Determination
No measurable concentrations of phosphine could be found in flue gas sam-
ples taken from the outlet of the electrostatic precipitator (160 °C) or the
outlet of the 90 °C zone in the absence of added reactive gases or in flue
gas samples from the 650 °C reaction zone during the injection of LPA-445 into
flue gas containing added oxides of sulfur and nitrogen.
CONCLUSIONS
Coaltrol LPA-40
Apollo Chemical Corporation's Coaltrol LPA-40 was found to consist of an
aqueous solution of ammonium sulfate. The formulation was injected into a
simulated flue gas at 650 °C, and the gas stream was sampled downstream from
the point of injection at flue gas temperatures of 650, 160, and 90 °C. The
high injection temperature was selected because of Apollo's practice of inject-
ing LPA-40 ahead of the economizer in a full-scale power plant.
At 650 °C, ammonium sulfate decomposed primarily into its constitutent
compounds: ammonia, sulfur trioxide, and water. Upon cooling of the flue gas
to 160 or 90 °C, recombination of the molecular fragments occurred. Ammonium
bisulfate appeared to be the principal recombination product at 160 °C, and
ammonium sulfate seemed to be predominant at 90 °C.
The implications of these results with respect to stack emissions are
that some ammonia may be present in the stack emissions, and ammonium salts
may also be present if these solids are not effectively removed in the electro-
static precipitator. Ammonia stack emissions appear to be less likely when
the flue gas contains large concentrations of nitrogen oxides due to the appar-
ent chemical reaction of ammonia with nitrogen oxides at high flue gas tempera-
tures .
Coaltrol LPA-445
Coaltrol LPA-445 was found to consist of an aqueous solution of diammo-
nium hydrogen phosphate. The formulation was injected at 650i °C, inasmuch as
Apollo recommends high temperature injection to produce thermal decomposition
of the ammonium phosphate.
Decomposition of diammonium hydrogen phosphate to ammonia and unidenti-
fied phosphate species appeared to occur at 650 °C. Recombination of the high
temperature fragmentation products was observed at 160 to 90 °C. The most
logical explanation for the mechanism of recombination was that ammonia and
phosphate species recombined principally as ammonium dihydrogen phosphate
221
-------
(with the mole ratio of ammonium ion to phosphate ion being 1:1 rather than
2:1 as at the beginning). A considerable excess of ammonia vapor remained in
the gas stream after the solid phosphate was removed by filtration.
It thus appears that some ammonia will be emitted from the stack of a
power plant when LPA-445 is used for conditioning, although the amount emitted
may be decreased when large concentrations of nitrogen oxides are present in
the flue gas. If not removed by electrostatic precipitation, ammonium
dihydrogen phosphate particles will also be emitted.
REFERENCES
1. Small, H., T. S. Stevens, and W. C. Bauman. Novel Ion Exchange Chromato-
graphic Method Using Conductimetric Detection. Anal. Chem., 47:1801-1809,
1975.
2. Harwood, J. E., and A. L. Kuhn. A Colorimetric Method for Ammonia in
Natural Waters. Water Res., 4:805-811, 1970.
3. Fritz, J. S., and S. S. Yamamura. Rapid Microtitration of Sulfate. Anal.
Chem., 27:1461-1464, 1955. ~~
4. Kitson, R. E., and M. G. Mellon. Colorimetric Determination of Phosphorus
as Molybdivanodophosphoric Acid. Ind. Eng. Chem., 16:379-383, 1944.
5. Kelley, K. K., C. H. Shomate, F. E. Young, B. F. Naylor, A. E. Salo, and
E. H. Huffman. Thermodynamic Properties of Ammonium and Potassium Alums
and Related Substances with Reference to Extraction of Alumina from Clay
and Alunite. Technical Paper 688. U. S. Bureau of Mines, Washington,
D. C., 1946. pp 66-69.
6. Scott, W. D., and F. C. R. Cattell. Vapor Pressure of Ammonium Sulfates.
Atmos. Environ., 13:307-317, 1979-
7. Halstead, W. D. Thermal Decomposition of Ammonium Sulphate. J. Appl.
Chem., 20:129-132, 1970.
8. Erdey, L., S. Gal, and G. Liptay. Thermoanalytical Properties of Analyti-
cal-Grade Reagents—Ammonium Salts. Talanta, 11:913-940, 1964.
9. Bennett, R. P., and M. J. O'Connor. Method of Conditioning Flue Gas to
Electrostatic Precipitator. U. S. Patent 4 043 768, August 23, 1977.
Assigned to Apollo Chemical Corporation, Whippany, New Jersey.
10. Bennett, R. P., M. J. O'Connor, A. E. Kober, and I. Kukin. Method of
Conditioning Flue Gas to Electrostatic Precipitator. U. S. Patent
4 042 348, August 16, 1977. Assigned to Apollo Chemical Corporation,
Whippany, New Jersey.
11. Goks^yr, H., and K. Ross. The Determination of Sulfur Trioxide in Flue
Gases. J. Inst. Fuel, 35:177-179, 1962.
222
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12. Maddalone, R. L. Guidelines for Combustion Source Sulfuric Acid Emission
Measurements. TRW Document No. 28055-6005-RU-OO. TRW Defense and Space
Systems Group, Redondo Beach, California, 1977. 14 pp.
13. Recommended Method of Analysis for Nitrogen Dioxide Content of the Atmo-
sphere (Greiss-Saltzman Reaction). In: Methods of Air Sampling and
Analysis^ M. Katz, Ed. American Public Health Association, Washington,
D. C., 1977. pp 527-534.
14. Tentative Method of Analysis for Total Nitrogen Oxides as Nitrate
(Phenoldisulfonic Acid Method). In: Methods of Air Sampling and Analy-
sis, M. Katz, Ed. American Public Health Association, Washington, D. C.,
TT77. pp 534-538.
15. West, P. W., and G. C. Gaeke. Fixation of Sulfur Dioxide as Sulfito-
mercurate III and Subsequent Colorimetric Determination. Anal. Chem.,
28:1816-1818, 1956. ~~
16. Phosphate/Stannous Chloride Method. In: Standard Methods for the Exam-
ination of Water and Wastewater, 14th ed. , M. C. Rand, A. E~] Greenberg,
and M. J. Taras, Eds. American Public Health Association, Washington,
D. C., 1975- pp 479-480.
17. Dechant, R., G. Sanders, and R. Graul. Determination of Phosphine in Air.
Am. Ind. Hyg. Assoc. J., 27:57-79, 1966.
18. Passille, A. Dissociation of Ammonium Phosphates. Comptes rendus, 199:
356-358, 1934.
19. Warren, T. E. Dissociation Pressures of Ammonium Orthophosphates.
J. Am. Chem. Soc., 49:1904-1908, 1927.
223
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BIOTOXICITY OF FLY ASH PARTICULATE
By:
Alan R. Kolber and Thomas J. Wolff
Research Triangle Institute
and
J. Abbott and L. Sparks
Industrial Environmental Research Laboratory (E.P.A.)
Research Triangle Park, N.C. 27709
Abstract
Fly ash samples were collected as part of field tests of electro-
static precipitators on boilers fired with coal of varying sulfur
content, and from hopper and stack plumes. The filter samples were
obtained by isokinetically sampling flue gas. Collection temperatures
ranged from ambient to 350°C. A known weakly mutagenic fly ash was
supplied by Battelle (Columbus).
The mutagenic potential of fifteen fly ash samples from five coal-
fired power plants was evaluated. Mutagenicity was assessed utilizing
the Salmonella/Mammalian microsome assay, employing bacterial strains
TA1535, TA100, TA1537, TA1538, and TA98. Fourteen samples were negative
for mutagenicity; although some of these materials exhibited varying
cytotoxicity to Chinese Hamster Ovary cells as measured by a number of
parameters. One previously tested fly ash (Battelle Columbus Labora-
tories) generated a positive mutagenic response. The effect of solvent
extraction on the apparent mutagenicity of the Battelle Fly Ash was
investigated. The effect of sampling temperature, extraction procedure,
and particulate size on the determination of apparent mutagenicity is
discussed.
224
-------
BIOTOXICITY OF FLY ASH PARTICULATE
INTRODUCTION
Western nations and Japan, faced with the eventual shortage of
commonly used fossil fuels, must now develop technologies to exploit
more abundant less-efficient alternative fuel sources. A greater world
population density resulting from increased net population growth in
this century must now be considered when planning new energy programs,
because of the possible attendant human health risk resulting from
pollutant streams generated by new energy producing industries, and from
production industries planning to utilize low-efficiency, low grade
fuels.
The enormous number of xenobiotic (synthetic, non-biological) sub-
stances being presented to the environment each year has inumdated the
capacity for assessing their insult to human health and to the environ-
ment. Until very recently, classical toxicological methodology was
nearly completely restricted to studies with whole animals. Table 1
illustrates the large investment in time and cost required to test the
toxicity of single substances using whole-animal protocols. The end-
points measured here were carcinogenicity, and general toxicity determin-
ed by acute (death-producing) protocols, and are compared to the much
smaller investment required to determine the same endpoints using recent-
ly-developed in vitro bioassay techniques.
Toxicity from substances present in synthetic fuels production
effluents and other industrial pollutants is not restricted to cancer
risk; there is a possibility of organ-specific toxicity as well (lung,
nervous system, liver, reproductive organs, etc.). In this respect,
teratological effects and disorders of development must also be consid-
ered. Although this report will be concerned only with the mutagenic/
carcinogenic and general cytotoxic potential of energy production byprod-
ucts and effluents, other attendent health risk possibilities must not
be forgotten; especially in the case of the neonate or infant, where
developing organ-systems are often more susceptible to the effects of
environmental agents than the adult (Press, 1978) .
225
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DESCRIPTION OF TEST SAMPLES AND BIOASSAY
Sampling Procedure
The fly ash samples used in this study were collected during exten-
sive field tests of electrostatic precipitators (ESP), collecting fly
ash from combustion of coal. The samples were collected at five different
plants by two different EPA contractors (Southern Research Institute and
Air Pollution Technology, Inc.)- Brief information on the different
plants is given in Table 2.
Except for plants 1 and 5, where only hopper samples were obtained,
filter samples were obtained by isokinetic sampling of the flue gas.
The filter was maintained at the flue gas temperature, which was essential-
ly the same as the ESP operating temperature. At the end of the sampling
period the filters were cooled and placed in sealed containers, which
were shipped to EPA's Industrial Environmental Research Laboratories/
Research Triangle Park, and given to Research Triangle Institute. The
samples from plants 3 and 4 were stored at EPA's Industrial Environmental
Research Laboratories/Research Triangle Park for some time prior to Ames
testing. The plant samples were tested shortly after they were received
from the field.
Inorganic flue gas conditioning agents were used at plants 2,3, and
4 to improve the performance of the ESP's at these plants. Sulfur
trioxide (S0_), was used at plants 2 and 3 while a proprietary agent was
used at plant 4. This agent is believed to be an ammonium phosphate
salt. Particulate samples were obtained for these 3 plants, both with
and without flue gas conditioning. In all cases, samples at the outlet
or the ESP were obtained. Both inlet and outlet samples were obtained
at Plant 2.
Extraction Procedure
Two extraction procedures were employed with the E.P.A. particulate
fly ash samples. Samples A1Q01 were added directly to dimethylsulfoxide
(spec, grade) and exposed to sonic disruption. A1010 through A1014 fly
ash particulates were extracted using 20 ml cyclohexane-methanol
(50% by volume) and sonication. The solvent extract was then
226
-------
evaporated to dryness under nitrogen and the solute transferred to
dimethylsulfoxide.
Four solvents were employed to extract the Battelle samples: horse
serum, water, cyclohexane-methanol, and methylene chloride. Horse serum
was selected for its chemical and physiological similarity to lung
alveolar fluid; the serum protein forms soluble complexes with some
2
carcinogenic heavy metals (Chrisp, et al.) . Water was used by Battelle.
Cyclohexane-methanol, a nonpolar nonmutagenie solvent, was utilized for
extraction of polar organics while methylene chloride was employed for
extraction of nonpolar organics. Both horse serum and deionized water
were incubated with ash for 48 hrs at 37°C prior to bioassay. The
cyclohexane-methanol and methylene chloride extracts were separated from
the particulate by filtration and the solute evaporated to dryness under
nitrogen and suspended in dimethylsulfoxide. EPA fly ash particulates
remained in suspension in vehicle, while the Battelle sample was filtered
prior to bioassay.
Ames/Salmonella Mutagenesis Bioassay
The Ames/Salmonella bioassay provides a rapid, sensitive screening
procedure for determining the mutagenic potential of a given chemical
substance or complex mixture in a genetically well-defined system (Ames,
1979)3. The specific Salmonella strains employed (TA98, TA100, TA1538,
TA1535, TA1537>! allow determination of the class of mutagen (base substi-
3
tution, frame shift etc.) being evaluated (Ames, 1979) . The Salmonella
strains utilized carry mutations in the histidine genes; such that the
normally prototrophic bacteria now requires histidine in the growth
medium due to their inability to synthesize histidine, de novo. When a
substance interacts with the DNA at or very near the site of the original
point mutation, the reading frame may be corrected by the second muta-
tion, reverting the bacterium to protorophy - or enabling the bacterium
to once again grow in minimal medium void of histidine supplement. This
is termed a reverse mutational event. Different mutational events (base
pair substitution and frameshift mutations) are detected by the bacterial
strains employed: TA98, TA1538, and TA1537 detect frame-shift mutations
227
-------
while TA100 and TA1535 are utilized to detect base-pair substitutions
(non-sense, or mis-sense mutations).
As many as 10 -10 bacteria can be plated on a 100 mm diameter
culture dish in minimal medium. The fraction of revertant bacteria
which have acquired mutations in the histidine gene can be scored by
couting the number of colonies (arising from individual revertants)
growing on minimal medium void of histidine.
Many substances are metabolically transformed in mammalian tissue
to mutagenic/carcinogenic intermediates; these substances would exhibit
no mutagenicity in the Ames assay without prior metabolic activation.
Therefore, microsomal preparations (with increased enzyme activity) from
Aroclor-induced rat livers, which metabolize procarcinogens to their
proximate carcinogens, are incorporated into the bioassay (Ames, et.al.,
4
1975) . Thus, the resultant assay can detect different classes of
mutagens/carcinogens (requiring, or not requiring metabolic activation),
as well as different mutational events (frame-shift, substitutions,
etc).
Mammalian Cell Cytotoxicy Assays
Mammalian cells grown in tissue culture might serve as a substitute
for the whole animal as a screening tool for assessing the cellular
toxicity of xenobiotics to mammals. In this assay, a stable tissue-
culture cell line with well known growth characteristics and biochemistry
would serve as the test system. The putative toxins would challenge the
cells by addition to the growth medium when the cells are growing as a
monolayer, attached to a plastic substrate (plastic culture dish). The
cell type chosen for this study is the Chinese Hamster Ovary (CHO) cell
line introduced in 1967 as a parent diploid cell for the production of
mutant cells (Kao and Puck, 1967) . The cell line is available from the
American Type Culture Association, and although no longer diploid,
posesses a constant chromosome number (ploidy), is fairly resistant to
infections, is relatively easy to maintain in culture on defined medium,
and divides rather rapidly (12-14 hr doubling-time) for a mammalian
cell. The CHO cells grow in a uniform population and the levels of
various key metabolites involved in their metabolism can readily be
228
-------
measured. The CHO cell exhibits consistent growth kinetics when cultured
under standard conditions of pCO~ and pCL, temperature and humidity, and
when provided with a standard nutrient culture medium containing serum,
salts and essential amino acids. When exposed to a known cytotoxin (we
have chosen Cadmium; Ozawa, et al., 1976) the growth and metabolism of
the CHO cell is affected (Winiger et al., 1978)7.
Inhibition of cell growth is determined in this study by two assay
methods. In the first, cells are explanted onto a growth substrate by
seeding 10 cells into a 35 mm diameter plastic culture dish, allowing
24 hrs. for cell attachment, and incubating with the compound to be
studied for 24 hrs. The medium is then replaced with fresh medium, and
the dishes incubated for about one week, with cell counts of control and
treated cultures performed at 24 hr. intervals. A control growth curve,
exhibiting the lag, logarithmic, and stationary phases of growth is
depicted in Figure 1. The effect of Cadmium is also shown.
The second method quantitates the ability of a single CHO cell to
give rise to a viable colony (or clone) of cells. This cloning efficiency
assay is performed by seeding a small number of cells (200-1000) in a 60
mm culture dish, allowing 24 hrs. for attachment, adding test substance,
incubating for 24 hrs., replacing medium, and incubating about 10 days,
or until colonies of cells grow large enough to count. These two cell-
growth studies provide an overall screening assay to quantitate general
cytotoxicity, where the parameters measured are the ability of cells to
grow and divide as members of a large population, and the ability of a
single cell to survive the toxic insult, and give rise to progeny.
MATERIALS AND METHODS
Ames Mutagenesis Bioassay
Chemicals. NADPH (tetrasodium salt, Type 1) and known positive
mutagens (highest purity available) were obtained from Sigma Chemical
Company. Dimethylsulfoxide (spectrophotometric grade) and sucrose were
®
obtained from the Fisher Chemical Company. Agar (Difco Bacto-Agar ) was
obtained from Difco Laboratories.
229
-------
Bacterial Strains. Tests were conducted with Salmonella typhimurium
strains TA100, TA1535, (utilized to detect base-pair substitution mutagens),
and strains TA1537, TA1538 and TA98 (employed for detection of frameshift
mutagens). All histidine auxotrophic strains were obtained directly from
Bruce Ames (Biochemistry Department, University of California, Berkeley).
CHO Cytotoxicity
Tissue culture medium was obtained from KC Biologicals (Lanexa, Kansas)
and from Grand Island Biologicals (N.Y.). Cells were obtained from the
American Type Culture Association. Disposable tissue culture dishes, flasks
and pipettes were obtained from Corning Corp. All water used in preparing
medium was triple distilled after passing through ion-exchange resins.
Standard Protocols
Ames Mutagenesis Assay. The procedures for handling the strains and
4
preparing media components were those of Ames et al., 1975) , with the
following exceptions: (a) Craig-Dawley male rat livers were used as the
source for metabolic activation (S-9) {activation potentials were very
similar to Sprague-Dawley male rats (data not shown)], (b) NADPH was added
directly to the plate (per plate, 0.10 ml containing 0.32 mg NADPH), (c) use
of a 2.5 ml agar overlay rather than a 2.0 ml overlay; (d) S-9 microsomal
preparation was diluted in 0.25 M sucrose at a concentration of 30 mg protein/ml
and added at protein concentrations of 3.0mg/ plate for initial testing; (e)
bacterial strains are centrifuged and concentrated in normal saline at 10
cell/ml. The S-9 microsomal preparation was obtained from rats injected
with Aroclor 1254. Protein was measured by the method of Lowry et al. ,
(1951)8.
All test components were added at 100 yl per plate. All dose levels
were performed in triplicate and duplicate experiments were performed on
separate days if sample was available.
230
-------
For quality assurance, the test is divided into five parts:
Toxicity Testing. Plate Incorporation Method. 200-300 cells per petri
dish are plated on histidine containing medium (histidine positive). Toxicity
tests were done with and without induced S-9. Test compound was added at
0.1 ml/plate in all tests. The viability ratio was calculated as the ratio
of surviving colonies with sample to colonies without sample. The schematic
of the test procedure is illustrated in Figure 2.
Mutagenesis Testing, Plate Incorporation Method. With S-9—To a tube
containing 2.5 ml of agar void of histiding (histidine negative) was added
0.1 ml of S-9 microsomal preparation, 0.1 ml of NADPH, 0.1 ml of a solution
of test material or positive control compound in dimethylsulfoxide, and 0.1
ml of bacterial suspension. Without S-9—Prepared as above, 0.1 ml of test
material or positive control, 0.1 ml of bacterial suspension and 0.1 ml of
sucrose and deionized water.
Sterility Testing, Plate Incorporation Method. Sterility tests are
conducted with histidine-positive overlay plates, using the amounts of
components employed in the tests. Components tested were: sample, positive
controls, solvent, water, 0.25M sucrose solution, saline, microsomal prepar-
ation (S-9), and NADPH solution.
Negative Control, Plate Incorporation Method. Solvent control was
taken through the bioassay, and tested for toxicity, mutagenicity and
effect on the metabolic activation S-9 microsome system.
Positive Mutagen Control Testing, Plate Incorporation Method. Using
histidine-negative overlay, 10 cells were plated in each dish. Known
mutagens were tested to assure that the strains were active and the microsomal
preparation was activating promutagens to the desired levels. If known
positive controls do not show proper mutagenic activity, the test components
(cultures and/or microsomes) are rejected. Control compounds currently in
use are:
231
-------
Strain Without S-9 With S-9
TA 1535 Sodium azide 2-Anthramine
200, 20, 2 Mg/plate 100, 10, 1 pg/plate
TA 1537 Quinacrine HC1 2-Anthramine
250, 25, 2.5 pg/plate 100, 10, 1 pg/plate
TA 1538 2-Nitrofluorene 2-Anthramine
TA 98 100, 10, 1 (Jg/plate 100, 10, 1 \Jg/plate
TA 100 Sodium azide 2-Anthramine
200, 20, 2 Mg/Plate 100, 10, 1 [Jig/plate
Mutagenesis Data. No test is considered positive unless all four
sections of the assay are performed, and the spontaneous reversion rate
determined. The experiment is discarded if the spontaneous background
exceeds normally observed values, if positive controls are not accept-
able, or if the sterility test indicates contamination. Mutagenic
ratios of 3 or greater, determined on the linear portion of the dose-
response curve are considered positive.
Cytotoxicity Testing: Growth Kinetics
Chinese Hamster Ovary cells were obtained from the American Type
Culture Association, explanted in Ham's F12 tissue culture medium supple-
mented with 10% fetal calf serum. The cells are explanted and grown to
confluence, the monolayer dispersed, cells diluted with medium containing
10% DMSO and frozen at -80°C in 1 ml aliquots for storage, and are
subsequently thawed and cultured for experiments. No antibiotics were
used in the following experimental protocol. Cells were seeded at 10
cells/35 mm culture dish in 2 ml medium, and incubated at 37°C in a 5%
C09 atmosphere. Three dishes were used for each time point of 6 points
measured (24 hours apart) after 24 hours incubation with a sample added
in not more than 25 Ml DMSO vehicle. After incubation with sample, the
232
-------
medium is discarded and replaced with 2 |Jl fresh medium. The cell
monolayer is dispersed with 0.05% trypsin and the cells counted using a
Fisher automated cell counter.
Cloning efficiency. Chinese Hamster Ovary cells, obtained from
the source described above, and cultured as described above, are explanted
in 60 mm dishes at 200 and 1,000 cells per dish in 5 ml F12 medium with
10% calf serum and no antibiotics. The cells are incubated for 24 hours
to attach, the test substance added in 10 and 25 pi DMSO, incubated 24
hours, the medium replaced with fresh medium, and the cells incubated
until visible colonies arise (about 6-10 days). At this time, the
medium was removed, the colonies washed with methanol, stained with
methylene blue, and counted with an automatic colony counter. Control
colony formation was done with 25 pi DMSO added to the medium.
Quality Control and Assurance Procedures: Ames Mutagenesis Bioassay
Sample Receipt and Dilution Procedures. Extracted samples are
immediately stored at 4°C. Dilution with spectral grade DMSO (N~
bubbled) is done under an operating fume hood (yellow lights are used to
avoid photodeactivation).
Salmonella Strain and S-9 Activation Validations. Quality control
and assurance procedures were undertaken to insure proper functioning of
bacterial strains and microsomal preparations. In general, our quality
assurance and control requirements are in agreement with those suggested
by DeSerres and Shelby (1979)9.
RESULTS
Ames Mutagenesis Bioassay Results
Table 2 illustrates the fly ash particulate results from the Ames/
Salmonella assay. Results were negative for mutagenicity under all
conditions tested. Toxicity to the bacterial strains was apparent for
several samples, as shown in Table 2.
The Battelle Laboratory fly ash data is given in Table 3. Battelle
Laboratories found a water-extract of this sample to be weakly mutagenic
for TA98; a mutagenic ratio of 3.5 was obtained. This response required
S-9 activation. We determined a mutagenic ratio of 3.4 for TA98 requiring
S-9 activation, but only the methylene chloride extract was active.
233
-------
Toxicity determinations are as follows: Both the cyclohexane/methanol
and methylene chloride extracts were toxic for bacterial strains TA98
and TA100 (without S-9 addition). Water and dialized horse serum ex-
tracts were nontoxic to both strains with and without S-9 addition.
Table 3 illustrates that while toxicity decreased with metabolic activa-
tion, mutagenic activity increased.
Chinese Hamster Ovary Cell Cytotoxicity Results
Fourteen fly ash samples were tested for toxicity by the growth
inhibition and clonal toxicity methods using 50 and 125 |Jg samples.
The method was validated using CdCl_ at various concentrations from
8
10 M. The validation results are shown in Figure 1. At concentra-
tions as low as 10" M, CdCl inhibits growth of CHO cells, and as the Cd
concentration is increased, the effect becomes more pronounced. Figure
3 illustrates the effect of 50 and 125 |Jg of fly ash particulate added
to the cells in 10 and 25 (JL DMSO as described above. A marginal affect
was noted. Sample A1008, a hopper sample from a high sulfur Eastern
coal-fired power plant, exhibited medium toxicity measured by the growth
kinetic method. This sample was also toxic to the Salmonella (Table 2).
None of the remaining 13 samples exhibited really significant toxicity
at the concentrations tested, agreeing with the mutagenicity findings.
DISCUSSION
Several investigations of the mutagenicity of fly ash have been
reported. Natush and Torakins (1978) predicted that temperatures near
100° are critical for adsorption of polynuclear aromatics onto fly ash
particulate. Fisher et al., (1979) have shown that heating coal fly
ash to 350°C, eliminates mutagenicity, consistent with the hypothesis
that the bulk of the mutagenicity originates from organic constitutents
which volatilize at 350°C. Natusch et al.., (1979) and Fisher et £l. ,
(1979) have reported the mutagenicity of fly ash to be greatest in the
finest (submicron sized) particles, which have the greatest surface area
per unit mass. These submicron particles have the longest atmospheric
residence time, are the most efficiently deposited in the lung, and are
2
the least efficiently removed. Chrisp et al., (1978) Fisher et al.,
(1979) also reported the E.S.P. collected particulates (whether size
234
-------
classified or not) were not mutagenic, while stack-collected respirable
particulates were mutagenic. It was presumed by these authors that
failure to control mutagens was due to E.S.P. collection temperatures
in excess of 100°, resulting in volatilization of organic mutagens which
were thus not collected by the E.S.P.
Failure to detect mutagenicity in the 14 fly ash samples tested in
this study may have been due to inefficient extraction procedures. Weak
mutagenicity detected for the Battelle sample may be a result of the
very low organic content (<0.1%) of most fly ash samples. Failure to
remove the inorganic matrix permits readsorption of organics onto the
particulate during solvent evaporation, inhibiting mutagenic potential.
Concerning possible control technology, it is suggested that volatilized
mutagenic organics may condense onto cooled inorganic particulate down-
wind of a stack where ambient temperatures are realized.
235
-------
References
1. Press, M.F., Lead Encephalopathy in Neonate Long Evans Rat: Morpho-
logic Studies. J. Neuropath. Exp. Neurol. 36: 169-193, 1977.
2. Crisp, C.E., G.L. Fisher, J.E. Lammert. Mutagenicity of Filtrates
from Respirable Coal Fly Ash. Science Vol. 199 January 6, 1978
pp 73-75.
3. Ames, B. N., Identifying Environmental Chemicals Causing Mutations
and Cancer. Science, 204: 587-593, 1979.
4. Ames, B.N., J. McCann, and E. Yamasaki. Methods for Detecting Car-
cinogens and Mutagens with the Salmonella Mammalian Microsome
Mutagenicity Test. Mutat. Res., 31: 347-364, 1975.
5. Kao, F. and T. Puck. Genetics of Somatic Mannalian Cells. IX.
Properties of Chinese Hamster Cell Mutants with Respect to the
Requirements for Proline. Genetics, 55: 513-524, 1967.
6. Ozawa, K., A. Sato, and H. Okada, Differential Susceptibility of
L Cells in the Experimental and Stationary Phases to Cadmium
Chloride. Japan J. Phannacol. 26: 347-351, 1976.
7. Winiger, H., F. Kukik, and W. Rois, In Vitro Clonal Cylotoxicity
Assay Using Chinese Hamster Ovary Cells (CHO-K1) for Testing
Environmental Chemicals. In Vitro 14: Abstract no. 193, 1978.
8. Lowry, O.K., N.J. Rosebrough, A.L. Farr, and R.J. Randall, Protein
Measurement with the Folin Phenal Reagent. L. Biol. Chem. 193:
265-275 (1951).
9- DeSerres, F., and M. Shelby. The Salmonella Mutagenicity Assay:
Recommendations. Science, 203: 563-565, 1979.
10. Natusch, D.F.S., and B.A. Tomkins, Polynuclear Aromatic Hydro-
carbons, Carcinogenesis 3, P.W. Jones and A.I. Freudenthal, eds.,
Raven Press, pp 145-153 (1978).
11. Fisher, G.L., C.E. Crisp, O.G. Raabe. Physical Factors Effecting
the Mutagenicity of Fly Ash from a Coal-Fired Power Plant. Science,
Vol. 204, May 25, 1979, pp 879-881.
12. Natusch, D.F.S., J.R. Wallace, C.A. Evans, Jr., Science 183, 202
(1974).
236
-------
72 96
TIME (HOURS)
168
Figure 1. The Effect of Cadmium on the Growth of Chinese Hamster
Ovary Cells.
BHK1 Chinese Hamster Ovary cells (10s cells/plate) were explanted
in 35 mm diameter dishes in 2 ml F12 (Harris) culture medium, incubated
24 hr at 37°C with 5% C02. Cadmium was added in 25 pi DMSO at a final
concentration of 10~8 M (A), 10~7 M (A), 10 6M (0). Control cells
were grown in the presence of 25 pi DMSO ( © , Q)- After 24 hrs., the
medium was discarded, replaced with 2 ml fresh medium, and the cells of
3 plates counted at 24 hour intervals, as described in the text.
237
-------
INDUCED
ACTIVATION
FRACTION
SAMPLE
IN
VEHICLE
BACTERIA
'77777777117777771
Figure 2. Scheme of Ames/Salmonella Test Procedure.
238
-------
10
24
72
TIME (HOURS)
Figure 3. The Effect of Selected Fly Ash Particulate Samples
on the Growth of Chinese Hamster Ovary Cells.
Fly ash particulate in 25 yl DMSO (from Plant A.A1008; 300 yg Q ;
150 yg H ) was biotested as described in the text and in the legend to
Figure 1. Control cells were grown in 30 yl DMSO ( •), and with no
added DMSO ( Q )•
239
-------
Table 1. RELATIVE EFFICIENCY OF IN VIVO AND IN VITRO
BIOTESTING FOR ENVIRONMENTAL BIOTOXICITY
Per Substance
Time Required
(Yrs.)
Cost (Dollars)
NCI Whole Animal Carcinogenesis
NCTR Whole Animal Toxicity
Level 1 Biotest (in Vitro Biotesting)
3.5
1.2
0.01 - 0.2
2.5 X 105
1.5X 105
6X 103
240
-------
ro
Table 2. SUMMARY OF BIOTESTING RESULTS OF FLY ASH
SAMPLES FROM COAL-FIRED POWER PLANTS
LABORATORY EXTRACTION PLANT COLLECTION TYPE OK COAL REMARKS AMES /SALMONELLA (Strain) CHINESE HAMSTER OVARY CELLS
CODE NUMBER PROCEDURE NUMBER TEMPERATURE UTILIZED IN COMBUSTION MUTACENICITY
AOOJ
A1002
A1U03
A1004
A1005
A 1006
A1007
A1009
A1008
A1010
A1011
A1C13
A1012
AlOli
*Extrac
A:
B:
A 3
A 3
A 3
A 3
A 3
A 3
A 3
A 3
A I*
B 5
B 2
B 2
8 1
8 1
tlon Procedure
Addition of Dimethyls
The particulace mater
dimettiylsulfoxlde.
115'C
115"C
115"C
115'C
115'C
150"C
1508C
STACK SAMPLE NONMUTACENIC
NONMUTACENIC
NONMUTACENIC
f NONMUTAGENIC
, NONMUTACENIC
Hoppi-r Sample NONMUTACENIC
Hopper Sample NONMUTAGENIC
hopper samp le
hot side E.S.P.
high unburne
176eC
176eC
176'C
1 carbon hopper samp le
NONMUTACENIC
No conditioning NONMUTAGENIC
hopper aample
j NONMUTACENIC
ulfoxide to partlculate with subsequent sonic disruption for 2 minutes.
ials are extracted from filters using cyclohexane methanoi (502 by volume)
TOXICITY
NONTOXIC
TOXIC (37,98)
TOXIC (37,98)
NONTOXIC
NONTOXIC
NONTOXIC
TOXIC (37,98)
TOXIC ALL
STRAINS
TOXIC (37)
TOXIC (98)
TOXIC (98)
NONTOXIC
NONTQX I C
NONTOXIC
KINETICS
NONTOXIC
NONTOXIC
NONTOXIC
NONTOXIC
NONTUX1C
TOXIC (I-)
NONTQXIC
NONTOXIC
TOXIC (H)
NONTOXIC
NONTOXIC
NONTOXIC
NONTOXIC
NONTOXIC
CLONAL EFF.
NONTOXIC
NONTOXIC
TOXIC (M)
TOXIC (M)
TOXIC (M)
TOXIC (L)
NONTOXIC
NONTOXIC
NONTOXIC
_
-------
Table 3. MUTAGENTCITY OF FLY ASH FROM BATTELLE LABORATORY
1N3
MutigiriK Kilio
Solwnt Vihicli
Cyclohnane Mtthanol DMSO
60S by volume
Mithylint Chloridi DMSO
Diioniiad H;0 H20
37°,48hrt
Horn Strum dulued Hunt
37°, 48 hri Serum
Ponlivt Control DMSO
Solvint Control
Dou
5000
1000
SOO
250
100
5000
1000
500
250
100
5000
1000
500
250
100
5000
1000
500
250
100
TA
-MA
.65
.79
.93
.96
.99
.68
.85
.95
.88
.96
1.03
1.13
1.02
1.01
1.00
.88
.95
.97
1.08
1.03
11.98
1.00
100
1-MA
1.09
1.01
1.01
.95
.90
1.06
1.12
1.01
1.05
.87
1.17
1.19
1.07
.98
.98
.90
.98
.93
1.02
.98
17.05
1.00
TA98
-MA
1.17
1.45
.78
.88
.97
.71
1.06
.89
.82
1.10
1.35
1.68
1.60
1.27
1.19
.86
.88
.67
.83
.84
59.19
1.00
+MA
1.70
1.08
.90
1.34
.94
3.41-*-
1.22
1.09
.95
1.39
1.83
1.59
1.63
1.07
1.60
1.38
1.00
1.27
1.19
1.28
53.25
1.00
TA
-MA
.16
.66
.88
.91
1.22
.22
.75
.73
.90
1.02
.95
.89
.84
.99
.76
.94
.95
.86
.86
.77
1.00
Vubility FUlio
100
•HHA
1.15
1.17
1.08
1.09
.99
1.15
.92
1.01
1.00
.90
1.11
1.13
.93
.96
1.04
.99
1.08
1.08
1.10
.90
1.00
TA96
-MA
.54
.69
.78
.67
.96
.06
.13
.52
.58
.86
1.12
1.30
1.29
1.10
.89
.95
1.02
.98
1.07
.86
1.00
+MA
1.20
1.12
1.09
1.16
.97
1.21
1.23
1.35
.30
.14
.15
.14
.14
.04
.06
.99
1.01
1.05
1.10
1.00
1.00
-------
FABRIC FILTERS VERSUS ELECTROSTATIC PRECIPITATORS
By
Edward W. Stenby, Robert W. Scheck,
Stephen D. Severson and Fay A. Horney
of
Steams-Roger Engineering Corporation
and
Donald P. Teixeira
of
Electric Power Research Institute
Presented at the Second Symposium on the Transfer and Utilization of
Particulate Control Technology. Sponsored by the U. S. Environmental
Protection Agency and the Denver Research Institute. July 23-27, 1979;
Denver, Colorado.
ABSTRACT
Control of particulate emissions from pulverized coal fired steam generators
is becoming a significant factor in the siting and public acceptability of
large coal burning power plants. The particulate emission limit established
by the EPA for new coal fired boilers is 0.03 lb/106 Btu (13 ng/J).
Possibly more restrictive than this is the State of New Mexico's particulate
regulation which calls for no more than 0.05 lb/106 Btu (22 ng/J) total, and
no more than 0.02 lb/106 Btu (9 ng/J) less than 2 microns in diameter. This
paper will evaluate the effect of these stringent limitations on the technical
feasibility and economics of dry particulate removal. Electrostatic
precipitators have been the dominant particulate collection device in the
electric utility industry for many years because of their low capital and
operating cost. However, increasingly stringent emission standards have led
to substantially higher costs for precipitators. These costs have increased
sufficiently for fabric filtration to become a competitive alternative in
achieving cost effective control. This paper will compare the economics and
performance of fabric filtration with respect to conventional electrostatic
precipitators. The paper will also address the preliminary evaluation
procedures that should be followed in order to select the appropriate device
for new or existing coal-fired boilers.
243
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FABRIC FILTERS VERSUS ELECTROSTATIC PRECIPITATORS
INTRODUCTION
The particulate emission limit initially set by the EPA under
provisions of the Clean Air Act of 1970 for large, new coal fired
boilers was 0.1 lb/106 Btu (43 ng/J). Under the Clean Air Act of
1977, EPA promulgated on June 11, 1979, (Federal Register, Vol. 44,
Page 33581) a New Source Performance Standard for particulates of 0.03
lb/106 Btu (13 ng/J). Possibly more restrictive (because of the
limit on fine particulate) than this are the State of New Mexico's
limits for new plants of 0.05 lb/106 Btu (22 ng/J) for total
particulates and 0.02 lb/106 Btu (9 ng/J for particulates less than
2 microns in diameter. These more stringent particulate emission
limitations will have a definite impact on the economics of power
production for new coal fired boilers.
Electrostatic precipitators have been the dominate particulate
collection device in the electric utility industry for many years,
because of their relatively low capital and operating costs. However,
increasingly stringent emission standards have led to substantially
higher costs for precipitators. These costs have increased
sufficiently for fabric filters to become a competitive alternative in
achieving cost effective control. This paper presents comparative
data on the economics and performance of fabric filters and
conventional electrostatic precipitators. The data presented are
based on investigations sponsored by the Electric Power Research
Institute.1
SUMMARY OF EPRI STUDY
The economic findings from the EPRI study are presented in
Figure 1. These are 1978 levelized costs of all capital and operating
expenses evaluated for the plant's 35-year life. For particulate
collection at the 0.03 lb/106 Btu emission limit, these costs may
represent 3 to 5 percent of the total cost of power production.
The levelized costs are made up of capital investment costs and
operating and maintenance costs, combined by application of
appropriate economic factors (plant life, finance charges, etc.) to
establish present worth and equivalent revenue requirements. The
levelized costs (or revenue requirements) allow the direct comparison
of the various cases as shown in Figure 1. The significant components
of levelized cost are shown graphically in Figure 2 and tabulated
below in Table 1.
"Capital Charges" are based on a fixed charge rate of 16% per year
applied to the capital investment. This category includes
depreciation, minimum acceptable return on investment, income tax on
return, property taxes and insurance. It is the most significant of
the factors considered, averaging about 60% to 80% of the total cost.
The fixed charge rate varies considerably with the tax situation of
244
-------
the utility, the basic cost of money and the life of the facility. A
municipal or REA utility may use figures as low as 11 or 12% per year,
whereas a private utility may use 18% per year or more. A lower fixed
charge rate narrows the cost difference between the precipitators and
the fabric filter, but not sufficiently to change the general
conclusions.
"T-R Power" refers to the power consumed by the transformer-
rectifier sets of the electrostatic precipitator (ESP). The amount
includes both energy and demand charges. Power consumption for T-R
Sets averages about 10% of the levelized cost. The "Bags" catagory
covers maintenance material, labor, overhead and bag replacements both
scheduled and unscheduled. For a 2 year replacement schedule, the
"Bags" category represents about 17% of the total cost.
The "Fan Power" category represents cost for incremental induced
draft fan power associated with the collector and associated
ductwork. The reverse air fans are also included in the category for
the fabric filter. For ESP's a total pressure drop of 3 inches W.C.
represented about 4% of total cost. For fabric filters a 7 inch W.C.
drop represented about 15% of the total cost.
Finally, the "Miscelleneous" category contains all other operating
and maintenance costs plus power for the hopper heater, purge air
blowers, ash system blowers and other necessary equipment.
TABLE 1
COMPONENTS OF COLLECTOR COST*
Levelized Cost, mills/kwh
Coal
Source
Wyoming
N. Dakota
Lignite
Alabama
Eastern
High Sulfur
Collector
Type**
HS-ESP
ECS-ESP
FF-20/2
FF-20/4
FF-40/2
ACS-ESP
FF-20/2
HS-ESP
ACS-ESP
ECS-ESP
FF-20/2
ACS-ESP
FF-20/2
Capital
Charges
1.52
1.43
0.75
0.75
0.88
1.12
0.90
1.15
13
27
0.78
1.10
0.82
TR Power
or Bag Repl
0.23
0.18
0.23
0.12
0.24
0.26
0.29
0.18
0.16
0.17
0.24
0.35
0.36
Fan
Power
0.08
0.05
0.16
0.16
0.15
0.09
0.23
0.08
0.07
0.07'
0.18
0.10
0.25
Misc TOTAL
0.26
0.25
0.12
0.12
0.13
0.23
0.15
0.20
0.28
0.23
0.13
0.32
0.16
2.09
1.91
1.26
1.15
1.40
1.70
1.57
61
64
74
33
1.87
1.49
**
At NSPS emission level of 0.03 lb/106 Btu.
See Figure 2 for explanation of collector type designation,
245
-------
As shown in Figure 1 the cost of participate collection by
electrostatic precipitation increases significantly as emission limits
become more restrictive. For example, decreasing the outlet
particulate emission from 0.1 lb/106 Btu to 0.03 lb/106 Btu,
increases the cost to own and operate a precipitator by about 30%.
This percentage varies somewhat depending on the type of coal and
properties of the fly ash. Costs for the fabric filter do not change
over the range of emission limitations considered, since the high
efficiency of a fabric filter would enable compliance with limitations
from 0.01 to 0.1 lb/106 Btu. For the new federal limit of 0.03
lb/106 Btu, the economics favors the fabric filter over the
precipitator for all of the coals investigated. In general, it was
found that the economic comparison of precipitators and fabric filters
was dependent on the particulate emission limitation, the ash content
and heating value of the coal, the electrical properties of the fly
ash, the bag replacement schedule of the fabric filter, and site
specific aspects.
Each collector's ability to collect fine particulate matter was
also studied. For the four coals considered, it was predicted that if
the New Mexico limit on total emissions of 0.05 lb/10° Btu were met,
then the limit on emissions of particles less than two microns in size
also would be met. For equal outlet loadings, the fabric filter
collects submicron particulate more effectively than the precipitator,
and so produces correspondingly lower opacities than the
precipitator. Opacity is of more concern for precipitators whereas a
fabric filter normally will produce a clear plume. Computer models
indicate that an opacity of 5 percent (essentially a clear stack) can
be obtained with a design limit of 0.014 lb/10° Btu. Based on the
limited experience to date, fabric filters will have a significant
economic advantage in almost all cases if the design is based on
obtaining a clear plume.
It should be noted that, although fabric filters have some clear
advantages over precipitators, experience with these devices on large
coal fired power plants and with high sulfur coal is minimal. The
largest fabric filter installation to date is at the Monticello
Station of Texas Utilities (equivalent to 500 MW unit). As further
experience is gained with fabric filters, valuable information on
reliability and cost will allow more accurate comparisons of the two
particulate collectors.
CASE STUDIES
Four coals were selected for a hypothetical 500 Megawatt (MW)
pulverized coal fired boiler as shown in Table 2. The collectors
considered appropriate for each of these coals are also shown in
Table 2. The estimated collection areas required to produce various
emission levels are shown in Figure 3.
246
-------
TABLE 2
SUITABILITY OF COLLECTOR SYSTEMS
Type of Coal Suitable Collectors
Hot Side Precipitator
Wyoming Sub-bituminous, European Cold Side Precipitator
Hanna, Wyo. Region (0.5656S) Fabric Filter
North Dakota Lignite American Cold Side Precipitator
High Sodium Ash (0.68JJS) Fabric Filter
Hot Side Precipitator
Alabama Bituminous American Cold Side Precipitator
Warrior River Area of European Cold Side Precipitator
Alabama (1.9%S) Fabric Filter
Eastern Bituminous American Cold Side Precipitator
Ohio Region (4.3%S) Fabric Filter
Selection of the specific collection area (usually referred to as
SCA, expressed in terms of square feet of collecting plate area per
1,000 actual cubic feet of gas per minute) is probably the most
difficult and controversial procedure. The method used in the EPRI
study for establishing the SCA was based on a modified form of the
Deutsch Equation:
n = 1 - exp -
°r SCA »
where n = particulate removal efficiency
w = precipitation rate, fpm
k = dimensionless parameter, used to
modify the original Deutsch equation.
The value for k can vary from 0.4 to 0.6. The EPRI study used a
value of 0.5. The value for w depends on the characteristics of the
fly ash, primarily resistivity and mineral composition. Empirical
data from existing installations were used in assigning the
appropriate values in each case. The collecting plate areas shown in
Figure 3 for precipitators are for specific coals from the
geographical regions and can vary considerably with small changes in
coal analysis. The curves shown in Figure 3 should not be construed
to apply to all coals in general. Cloth area for the fabric filter
changes only with gas volume to be filtered. The gross air to cloth
ratio was selected at 1.81 acfm/ft2 (1.93 net) for all cases over
the range of emission limits considered.
247
-------
CAPITAL COSTS
Installed costs, presented in Figure 4 for the range of outlet
emission levels, are based on 20 different designs and estimates
prepared for the study. Included in the estimates are materials and
labor for installation of the collectors, hoppers, support steel,
ducts, nozzles, dampers, fans, expansion joints, ash-handling
equipment, insulation, and other miscellaneous items. Added to these
are differential and indirect field costs, engineering and fee at 3
percent, and contingency and miscellaneous costs at 10 percent.1
Note that the capital investment for precipitators increases as
the outlet emission is reduced. Since fabric filters operate at high
particulate removal efficiencies with relatively constant outlet
loading, the capital cost is essentially constant for the range of
emission limits. The fabric filter capital cost is different for each
of the four coals, since the cloth area depends on the gas volume.
Options such as air-heater temperature control and preheat, for
controlling the inlet flue gas temperature were not included. Some
plants such as peaking or cycling units, incorporate these elements to
minimize excursions through the acid dew point and to prevent
corrosion to metal components or damage to the filter bags.
Detailed estimates were made for three plant sizes (or gas flow
rates) and for three different precipitator collection areas. For
example, the hot side precipitator was evaluated for 250, 500, and
1000 MW at SCA's 200, 400, and 800 ft2/103 acfm. The fabric
filter was estimated for these plant sizes at air-to-cloth ratios of
1.6, 2.0, and 3.0 acfm/ft2.
Graphical representations of how capital costs were found to vary
with plant size, collection area, and number of compartments (for
fabric filters) are shown in Figures 5, 6, and 7. The discontinuity
in cost versus gas flow for precipitators is due to layout
considerations. For smaller boilers space for the precipitator is not
a problem. For the larger boilers, longer (deeper) precipitators must
be turned sideways (parallel or chevron arrangement) to fit in the 300
feet space allowed between the boiler house and the chimney. Thus,
ducting is more extensive. Generalized relations were developed for
expressing the costs as functions of design parameters, such as
collection area and gas flow rate. The relations listed below allow
the extrapolation of costs for collector systems of different plant
size and gas flow rates.
For electrostatic precipitators (ESP):
CIESP = CI'ESP x ( TT ) x
248
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For fabric filters (FF):
M
Where CI = capital investment; F = inlet gas flow, acfm; SCA = ESP
specific collecting area, ft2/ 1000 acfm; A/C = gross air-to-cloth
ratio of the fabric filter, acfm/ft2; M = number of compartments; f
= flow exponent; s = SCA exponent; a = air-to-cloth exponent; m =
module exponent; and primed variables are those of the base case.
Cost-scale exponents for the four types of collectors for the base
case conditions were determined from the various estimates. These are
given in Table 3.
TABLE 3
EXPONENTS FOR ESTIMATING
CAPITAL COST
Collector f s a m
Hot-Side ESP 0.97 0.58 N.A. N.A.
Cold-Side ESP (Am.) 0.93 0.60 N.A. N.A.
Cold-Side ESP (Eur.) 0.89 0.74 N.A. N.A.
Fabric Filter 0.72 N.A. -0.52 0.24
The base costs and design parameters are listed below in Table 4.
TABLE 4
BASE CASE PARAMETERS AND COST
A/C or Gas Flow No. of Capital Investment
Collector System SCA JIO6 acfm) Modules ($106, 1977)
Hot-Side ESP 400 2.64 N.A. 23.9
Cold-Side ESP (Am.) 350 1.97 N.A. 14.8
Cold-Side ESP (Eur.) 550 1.97 N.A. 20.7
Fabric Filter 1.81 1.97 16 14.6
249
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OPERATION AND MAINTENANCE COSTS
Operation and maintenance costs were estimated for collectors and
ash-removal systems based on information obtained from existing
installations. As shown in Table 5, operation of the collector was
assumed to be constant at $20,000 per year for all collectors and
$60,000 per year for ash handling.
TABLE 5
COST AND UNIT FACTORS FOR
OPERATION AND MAINTENANCE
FOR THE 500 MW BASE CASE SYSTEMS
COLLECTOR EQUIPMENT
Maintenance
Collector Operation ($/yr/106ft2)
System ($/yr) Material Labor
ASH REMOVAL EQUIPMENT
Maintenance
Operation ($/yr/106ft2)
($/yr) Material Labor
Hot-Side
ESP
20,000
Cold-Side 20,000
ESP (Am.)
Cold-Side 20,000
ESP (Eur.)
Fabric
Filter
20,000
25,000
25,000
15,000
*280,000
25,000 60,000 30,000 30,000
25,000 60,000 10,000 10,000
15,000 60,000 10,000 10,000
35,000 60,000 **8,000 **8,000
*This figure, estimated for two year bag replacement cycles, is
approximately halved for four year bag replacement cycles.
**These figures increase to $15,000 per year per 106ft2 for
the 40 comparment system.
Maintenance figures were based on cost per 10^ ft2 of
collection area per year. For fabric filters, maintenance costs were
derived from costs due to scheduled and unscheduled bag replacements
and additional maintenance. Bags were estimated at 90 ft2 per bag
and $40 per bag. Labor was based on $14 per hour for unscheduled
replacements and $4 per hour for scheduled replacement. Unscheduled
bag replacements were estimated to be 5 percent of total inventory per
year, with labor based on one hour per bag replacement. Other
250
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maintenance was assumed to require 350 hours per year, with the cost
of materials at the same rate as the cost of labor. These costs are
summarized in Table 6.
TABLE 6
DETAILS OF BASE CASE
FABRIC FILTER COLLECTOR MAINTENANCE COSTS
Maintenance Costs ($/yr/106ft2)
Type of Maintenance
Scheduled bag replacement*
Unscheduled bag replacement
Additional Maintenance
Materials
Labor
Total
250,000
25,000
5,000
20,000
10,000
5,000
270,000
35,000
10,000
Total
280,000
35,000 315,000
*Costs presented are for a two-year bag replacement cycle. If a
four-year bag replacement cycle is assumed, costs decrease
approximately 50%.
Power requirements were determined for each case. These include
induced-draft and reverse-air fans, transformer-rectifier sets, hopper
heaters, accessories (rappers, valves, compartment dampers, and ash
removal equipment. Power requirement factors are shown in Table 7.
TABLE 7
BASE CASE POWER REQUIREMENTS
Connected Power
Collector
Hot Side ESP
Cold Side ESP
Cold Side ESP
Fabric Filter
Collection
Area
(lQ6ft2)
1.056
(Am.) 0.691
(Eur.) 1.086
1.091
Reverse
Air-Fans
(kW)
0
0
0
780
Hopper
Heaters
(kW per
hopper)
0
10
10
15
Accessories
(kW per
10W)
300
300
300
200
Ash
Removal
System
(kW)
500
500
500
500
251
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The power requirements for the transformer-rectifier sets were
determined separately for each case from estimates of the current and
voltage needed for each precipitator. A factor of 0.60 was used in
the conversion of alternating to direct current. It was assumed that
power connected to the sets would be double the maximum demand for
power. For further details on the factors used to develop the
estimated power requirements, see the detailed EPRI report.!
Annual operation and maintenance costs are presented in Figure 8.
The trends are similar to the capital cost, but the fabric filters
incur higher costs than the precipitators. Operating and maintenance
costs were included for both the collectors and the ash removal
equipment. The major operating cost was the consumption of electrical
power. As expected, the frequency of bag replacement had a
substantial effect on the maintenance costs for the fabric filters.
LEVELIZED COSTS
To compare the collectors, capital investment, operation and
maintenance costs, and power requirements were combined and levelized
over the 35-year life of the plant. For the economic analysis, the
following factors were used:
Minimum acceptable return (MAR): 11%
Fixed charge rate (MAR, depreciation,
insurance, and income on MAR): 16%
Interest during construction: 8.5%
Base year (Time zero): 1977
Escalation (fuel, operation and
for materials and labor): 7%
Plant Capacity Factor: 0.70
The levelized costs for a 500 MW system, shown previously in
Figure 1, represent the added or differential cost of power, in mills
per kilowatt-hour, for particulate collection.
FINE PARTICLE EMISSIONS AND OPACITY
The outlet emission of particulates less than two microns in size
were estimated by applying inlet size distributions of fly ash to
fractional efficiencies for each particular case. Typical fractional
efficiencies, shown in Figure 9, were tailored for collectors of
different size through the use of a modified Deutsch relation.2 By
dividing both the inlet distribution and the fractional efficiency
into particle size increments, an outlet size distribution was
252
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calculated for each case. This calculation is essentially a
prediction of emissions less than two microns in aerodynamic
diameter—the amount limited to 0.02 lb/10^ Btu by New Mexico. For
all cases, it was found that when emissions total less than 0.05
lb/106 Btu (the New Mexico limit for total particulate) the State's
limit on sub-2-micron emissions was also met.
The observed opacity of a plume emitted from a power plant stack
depends on a great number of variables, including the angle of the
sun, wind direction, atmospheric conditions, and the qualifications of
the observer. The measurement of opacity by an in-stack instrument
reduces the variables to: grain loading; size distribution, shape,
density, refractive index, and reflectance of the particle; stack
diameter; and NOX concentration.3 Mathematical correlations based
on these variables may be used to predict opacity, but the two most
important parameters are grain loading and particle size
distribution. Outlet particle size distributions were developed for
each collector based on typical fractional efficiencies, rather than
actual size measurements. The calculated opacities for precipitators
were judged, on the basis of past experience, to be somewhat high.
Upon investigation, it was found that the prediction of high opacity
resulted from larger than expected concentration of fine particles.
The high percentage of fines was a direct result of applying
fractional efficiencies that were adjusted for each precipitator using
the modified Deutsch relation. Based on considerable experience with
existing installations, it was found that precipitators designed for
the limit of 0.1 lb/10° Btu and meeting corresponding guarantees
produced opacities of less than 20 percent. Combining this with the
trends in the calculated opacities yielded Figure 10. The average
curve shown in Figure 10 corresponds closely to good design emission
limits—that is, precipitators designed for these limits will yield,
during operation, approximately the opacities shown. For a design
limit of 0.03 lb/10° Btu, opacities from 5 to 15 percent would be
expected.
EQUIPMENT SELECTION PROCEDURE
The source of coal and the fly ash produced from burning that coal
will have a major impact on the selection of particulate removal
equipment. Within recent years, trends have developed that make the
sizing of precipitators and fabric filters for continuous high
performance more difficult. The four coals selected for the detailed
EPRI study was an attempt to cover the major variation of coal and ash
characteristics in the United States. But with new mines opening,
both east and west, there are coals that are both better and worse for
precipitators and fabric filters.
The Appalachian region production of high, medium, and low sulfur
coals will make the decision extremely difficult between precipitators
and fabric filters. Variation in precipitability of all coals from
this region are well known. In general, precipitability is not
253
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strongly related to sulfur content as would normally be expected.
Washing of the higher sulfur coals to remove sulfur (mainly as iron
pyrite) will probably reduce the precipitability more than would be
indicated by the percent of sulfur removed. The low precipitability
of the low sulfur coals from this region is well known. Hot side
precipitators have been used with varying success, depending mainly on
the sodium content in the ash. Fabric filters need to be proven on
the higher sulfur coals, but they should be considered on most medium
and low sulfur Appalachian coals.
The East Central coal region (Illinois, Indiana, Iowa, Missouri,
etc.) is a medium to high sulfur coal region, with very little low
sulfur coal. These coals produce an ash that, in general, has a high
precipitability, leading to reduced precipitator size and cost.
Because of this fact, this region will probably see a higher
percentage of precipitator installations than any other region in the
United States.
The Northern Great Plains region (comprising North Dakota, South
Dakota, Eastern Montana, and the Powder River Basin of Wyoming)
contains a variety of coals, for which fly ash precipitability ranges
from the highest to the lowest of any in the country. The high
sodium, high moisture, and medium-low sufur North Dakota lignites are
very easy to precipitate. The low sodium, low sulfur, and the medium
moisture coals in the Powder River Basin may present major problems to
precipitators because of the high restivity and high concentration of
fine particulate. Fabric filters may have high pressure drop problems
when handling the same Powder River Basin coal. However, additional
experience is needed to accurately characterize the impact of these
coals.
The low sulfur, low sodium coals in the Rocky Mountain region are
difficult to precipitate, but the high sodium, low sulfur coals in
this region will precipitate quite well. Existing fabric filters are
performing very well with medium to low gas-side pressure drops and
fabric filters will probably see extensive application on Rocky
Mountain coals.
In order to determine what the appropriate device is for a
specific application, the following plan might be considered:
1. Establish the coal to be burned over the life of the plant,
if at all possible.
2. Define particulate characteristics (concentration, particle
size, resistivity, etc.)
3. Determine efficiency required to meet all applicable
regulations.
4. Size precipitator, selecting the appropriate SCA for
guarantee performance, including redundancy for deterioration
and other contingencies.
254
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5. Size fabric filter in a similar manner.
6. Establish economics (capital cost, operating cost,
maintenance cost, present worth or levelized annual costs).
7. Select the appropriate device (considering technical
feasibility as outlined in Table 1, as well as bottom-line
economics as developed in steps 1 through 6).
In developing comparative capital costs for the precipitator
versus the fabric filter, it is extremely important to define all the
components of the particulate removal system. Each device must be
evaluated on a complete and comparable basis. In addition to the
basic device itself, the additional costs that should be developed are
for inlet and outlet ductwork, structural supports, duct insulation,
dampers, expansion joints, turning vanes, foundations, ash handling
equipment (up to a common transfer point), electrical power supply,
hopper heaters, hopper ash level detectors, differential I.D. fan
costs, fabric filter preheat and purge system if appropriate and
erection costs. In the case of a hot side precipitator, the cost
impact of air heater location and longer combustion air duct runs
should be considered.
Careful attention must be paid to development of comparative
operating and maintenance costs. Estimates of electrical power demand
must be developed for the I.D. fan, transformer-rectifier sets,
reverse air fans, hopper heaters, ash removal system and accessories,
such as rappers, damper operators, purge and preheat systems, etc.
The determination of precipitator transformer-rectifier (T-R) set
power consumption can be a difficult number to establish. T-R set
power consumption for high efficiency large SCA precipitators can be a
significant value, almost exceeding the power difference in flue gas
pressure drop between a precipitator and a fabric filter. Fabric
filter bag life is another difficult area. Although the EPRI study
used 2 year or 4 year bag lives, it is apparent from the fabric filter
operating experience to date that bag lives of 3 to 4 years are
common. In other words, the 2 year bag life may be too conservative.
Comprehensive and accurate maintenance data are difficult to
obtain. The best sources for these data are the users; however, only
a few utilities have kept accurate maintenance records. Typically,
annual maintenance costs have been estimated as a small percentage
(from 2 to 5%) of the original installed cost of the equipment.
DESIGN FOR RELIABILITY
The fact that no system can be expected to produce optimal results
100 percent of the time must be addressed in the design of a
particulate collection system. For precipitators, clogged ash hoppers
and broken wires are the biggest detriments to optimal performance.
255
-------
For the fabric filter, the main difficulty is the premature failure of
bags. As previously pointed out, operating experience with fabric
filters has been much less than with precipitators, particularly for
large coal-fired units and applications with high sulfur coal. Fabric
filters now in operation on large low sulfur coal burning units will
help to determine additional factors affecting reliability and
operability.
For precipitators, since on-stream maintenance is not considered
practical, additional bus sections are desireable to enable
satisfactory performance until disabled sections can be repaired.
Generally, utilities schedule a seven to ten day outage each year for
minor maintenance. Major outages are scheduled every two or three
years and can last 30 to 40 days. Since activity during unscheduled
outages is very intense, only very high priority items are likely to
receive attention. Thus, a well-designed precipitator should operate
reliably at or above the efficiency corresponding to the emission
limit for periods of a least one year without internal maintenance.
Degradation of precipitator performance can be minimized by
increased electrical sectionalization. In recent installations,
precipitators having as many as 100 independent electrical sections
(bus sections) are not uncommon. In order to minimize the effect of
an ash valve failure or plugged hopper, the trend is toward locating a
hopper under each bus section. The reliability of a bus section
depends on the design of the precipitator (e.g., rigid vs.
weighted-wire electrode design), the ash-handling system, the
abrasiveness of the dust, the degree of sparking encountered, and the
temperature. Failure of weighted wire electrodes are usually
concentrated in the inlet field where higher dust loadings cause more
sparking and more abrasion. The use of the rigid electrodes has
increased significantly because of this characteristic of the weighted
wire electrode. Ash system failures can occur when a clinker of
semi-fused fly ash falls into a hopper. The net result is that even a
well designed precipitator may have 5 to 25 percent of the bus
sections out of service by the end of a year. The loss in efficiency
must be offset by additional collection area beyond the plate area
added for performance efficiency contingencies. Commonly, this extra
area is expressed in terms of extra fields. For instance, a
precipitator that could meet guarantees with four fields may have a
fifth field installed to account for normal deterioration and
contingency. Occassionally, optimal contingencies are incorporated
into the design, such as the addition of a sixth empty field. The
plates and wires are installed in the sixth field only if performance
proves to be unacceptable.
The reliability of a fabric filter system in meeting performance
requirements is dependent mainly on the frequency of bag breakage, the
time taken to isolate the broken bags, the leakage of bypass dampers,
and sometimes the air-to-cloth ratio. Conservative design and proper
256
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operation can generally minimize the frequency of broken bags. Also,
periodic replacement of all bags in a compartment will reduce the
average age of the bags and the frequency of breakage. Minimizing
excursions below the acid dew point also tends to extend bag life.
The time to isolate a broken bag can be drastically reduced if
detectors are placed on the outlet of each compartment. These
detectors indicate the opacity of the gas stream at the individual
compartment outlet, therby allowing the operators to quickly isolate
the faulty compartment for repair. Leaks through bypass dampers also
affect performance. The design used in the EPRI study incorporated
two louvered dampers in series with a purge of clean reverse air to
block uncleaned flue gas. High air-to-cloth ratios experienced during
cleaning or maintenance can reduce performance. However, fabric
filter efficiency generally is high enough that requirements can be
met even during these periods. The air-to-cloth ratio influences
reliability more strongly than performance because it affects bag life.
In contrast to a precipitator, dampers on the compartments of a
fabric filter pose a possible restriction to the flow of gas from the
boiler. As a result, controls must be designed so that it is
essentially impossible for all compartment valves to close at once.
As a back-up measure, the fabric filter bypass damper should be set to
open automatically at high furnace pressure.
CONCLUSION
Stricter particulate emission standards have increased the costs
for electrostatic precipitation, so that fabric filters have become
cost competitive. Fabric filters remove submicron particles more
thoroughly than do precipitators. However, there is much less
operating experience with fabric filters than precipitators,
particularly on large coal-fired units or applications with high
sulfur coal. In general, the relative economic feasibility of well
designed fabric filters and precipitators is dependent on the emission
limitation, the ash and heating content of the coal, the properties of
the ash, the bag replacement schedule for fabric filter, and site
specific constraints. As a result of these considerations, the
utility industry is comparing these two particulate collectors very
carefully to determine the optimum choice.
REFERENCES
1. R.W. Scheck, S. D. Severson, et. al., "Economics of Fabric Filters
Versus Precipitators," EPRI FP-775, June 1978.
2. S. Matts and P.Q. Ohnfeldt, "Efficient Gas Cleaning with S.F.
Electrostatic Precipitators," SF Review, 1964.
3. D. S. Ensor, R. W. Scheck, et. al., "Fabric Filter Fractional
Efficiency," EPRI FP-297, November 1976.
4. S. D. Severson, R. W. Scheck, et. al., "Economics of Fabric
Filters Versus Precipitators," presented at the 86th National
Meeting of the AICHE, Houston, Texas (April, 1979).
257
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WYOMING
COAL
-EUROPEAN COLD-SIDE ESP
HOT-SIDE'ESP
AMERICAN COLD-
SIDE ESP
LEVELIZED
COSTS,
MILLS/kWH
NORTH DAKOTA
LIGNITE
NO. OF COMP.: A & B = 20, C = 40~\
BAG LIFE, YRS.: A&C = 2, B = 4 J
FABRIC FILTER
EASTERN
HIGH SULFUR
COAL
AMERICAN COLD-SIDE ESP
i i i i I
HOT-SIDE ESP
PARTICULATE EMISSION LIMIT, LB/10 BTU
FIGURE 1
LEVELIZED COSTS FOR 500 MW COLLECTORS (1978)
LEVELI
MILLS/K
2.0 —
1.5-
1.0 —
0.5-
?E[
Wl-
)
< HS
ESP
MISC
FAN
TR
PWR
ECS
ESP
MISC
FAN
TR
PWR
CAP
CHAF
FF
MISC
FAN
BAGS
TAL
?GES
FF
20/4
MISC
FAN
BAGS
FF
40/2
MISC
FAN
BAGS
ACS
ESP
MISC
FAN
TR
PWR
CAP
CHA
FF
20/2
MISC
FAN
BAGS
TAL
1GES
HS
ESP
MISC
FAN
PWR,
ACS
ESP
MISC
FAN-
TR
PWR
CAP
CHA
ECS
ESP
MISC
FAN
TR
TAL
1GES
FF
MISC
FAN
BAGS
ACS
ESP
MISC
FAN
PWR
CAP
CHA
FF
MISC
FAN
BAGS
TAL
iGES
\ WYOMING / NORTH DAKOTA \ ALABAMA / EASTERN HIGH
LIGNITE SULFUR
FIGURE 2
COMPONENTS OF COLLECTOR COST
AT THE 0.03 IB/106 BTU EMISSION LEVEL
KEY
fcfP
ECS EUROPEAN STYLE ESP
FF FABRIC FILTER
20/2 20 COMPARTMENTS, 2 YEAR BAG LIFE
258
-------
•1500
SPECIFIC
COLLECTION
AREA (SCA)
FT2/103 ACFM
EASTERN HIGH SULFUR/COLD-SIDE
NORTH DAKOTA
LIGNITE/COLD'-SIDE
0.01 0.02 0.03 0.05 0.10
\ PARTICULATE EMISSION LIMIT, LB/106 BTU -
FIGURE 3
COLLECTING AREA REQUIREMENTS
FOR ELECTROSTATIC PREC1PITATORS
0.15
ESTIMATED CAPITAL 20
INVESTMENT, $/kW
PARTICULATE EMISSION LIMIT, LB/10 ° BTU •
FIGURE 4
CAPITAL INVESTMENT FOR 500 MW COLLECTORS (1978)
259
-------
01
O
150 200 300 500 700
SCA
FIGURE 5
1000
1.5 2.0
A/C
ESTIMATED CAPITAL INVESTMENT FOR COLLECTORS
0.5 1.0
SCA RATIO TO BASE
2.0 0.5 1.0 2.0
GAS FLOW RATIO TO BASE
FIGURE 6
COST CORRECTION FACTORS FOR ELECTROSTATIC PRECIPITATORS
COST CORRECTION FACTORS ARE APPLIED TO THE CAPITAL INVESTMENT (CD OF THE BASE
CASE ESP SYSTEMS TO ARRIVE AT THE Cl FOR THE CASE WITH A DIFFERENT DESIGN PARA-
METER. FOR EXAMPLE, DOUBLING BOTH SCA AND GAS VOLUME ON A HOT SIDE ESP YIELDS
A COST CORRECTION FACTOR OF 1.57 x 1.96 = 3.08. THIS FACTOR IS APPLIED TO THE Cl OF
THE BASE CASE HOT SIDE ESP SYSTEM ($23.9 X 10B| TO ARRIVE AT THE Cl OF THE NEW SYS-
TEM- DUAL LINES ON GRAPHS ON RIGHT RESULT FROM ORIENTATION CHANGES.
-------
ro
CTl
OPERATION AND 100
MAINTENANCE,
$103/YR
(A, B & 0 SEE FIG. 1)
100
"****r.
EUROPEAN X*"
01 n cine ccp/
COLD-SIDE ESP
0.01
\
*»ir,
0.5
0.5 1.0 " 2.0
NO. OF COMPARTMENTS RATIO TO BASE
FIGURE 7
COST CORRECTION FACTORS FOR FABRIC FILTER
COST CORRECTION FACTORS ARE APPLIED TO THE CAPITAL INVESTMENT (Cl| OF THE BASE
CASE FABRIC FILTER SYSTEM TO ARRIVE AT THE Cl FOR CASES WITH DIFFERENT DESIGN
PARAMETERS. EXAMPLE: DOUBLING AlFi TO CLOTH RATIO, GAS FLOW AND NUMBER OF
COMPARTMENTS WILL YIELD A COST CORRECTION FACTOR OF 0.70 x 1.65 - 1.36. THIS
FACTOR IS APPLIED TO THE Cl OF THE BASE CASE FF SYSTEM ($14.59 x 106> TO ARRIVE AT
THE Cl OF THE NEW SYSTEM.
0.02 0.03 0.05 0.1 0.01
PARTICULATE EMISSION LIMIT,
FIGURE 8
OPERATION AND MAINTENANCE COSTS
FOR 500 MW COLLECTORS (1978)
0.02 0.03 0.05
BTU
-------
PENETRATION
(100-EFF)% 10
TYPICAL EUROPEAN
COLD-SIDE ESP
EFFICIENCY
01 0.2 0.5 1
\
2 5 10 20 0.1 0.2 0.5 1 2
ACTUAL PARTICLE DIAMETER, MICRONS
FIGURE 9
5 10 20
TYPICAL FRACTIONAL EFFICIENCIES FOR EXISTING COLLECTORS
PERCENT OPACITY
APPROXIMATE AVERAGED
1 lb/10" BTU=
0.31 gr/acf (AVERAGE)
EPA AND NM LIMIT
CLEAR PLUME
.005
.02 .03 .05 0.1 0.2 0.3
PARTICULATE EMISSION LIMIT, LB/tO6 BTU
FIGURE 10
PREDICTED OPACITY VS. DESIGN EMISSION LIMIT
FOR PRECIPITATORS
262
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DESIGN AND CONSTRUCTION OF BAGHOUSES
FOR SHAWNEE STEAM PLANT
J. A. Hudson, Head Mechanical Engineer
Fossil Fuel and Air Pollution Equipment
Division of Engineering Design
Tennessee Valley Authority
Knoxville, Tennessee
L. A. Thaxton, Vice President Agency Sales
Envirotech Corporation
Pittsburgh, Pennsylvania
H. D. Ferguson, Jr., Mechanical Engineer
Fossil Fuel and Air Pollution Equipment
Division of Engineering Design
Tennessee Valley Authority
Rnoxville, Tennessee
Neil Clay, Mechanical Engineer
Envirotech Corporation
Lebanon, Pennsylvania
ABSTRACT
This paper is a sequel to "Precipitators? Scrubbers? or Baghouses? for
Shawnee" given at the first EPA symposium in 1978, which explained the basic
reasons and philosophy for TVA's selection of baghouses for Shawnee.
In this Dresentation, the authors deal with the basic considerations of the
specifications, detail design, and construction of the baghouse system for the
10-unit Shawnee Steam Plant. Special attention is given to a unique preheating
and reheating system for each baghouse prior to boiler startup or for cycling
operation, criteria for varying number of compartments online against flow
(ACFM) to minimize dewpoint consideration, criteria of air-to-cloth ratio as
well as filter material and coating, selection of materials, and construction
of a unique raft foundation system—all within a total construction period of
42 months.
263
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DESIGN AND CONSTRUCTION OF BAGHOUSES
FOR SHAWNEE STEAM PLANT
INTRODUCTION AND GENERAL BACKGROUND
The Shawnee Steam Plant is located on the south bank of the Ohio
River about 13 miles downstream from the mouth of the Tennessee River at
Paducah, Kentucky. Construction of the ten 175-MW units was authorized
in January 1951. Unit No. 1 was placed in commercial operation 27 months
later in April 1953 and the last unit, No. 10, went into operation in
October 1956, providing a total plant generating capacity of 1,750,000 kW
at the total cost of $216,500,000 or $124 per kW.
(Based on today's costs for fossil plants, that
sounds like a fairy tale, doesn't it!??)
The plant was first equipped with mechanical dust collectors primarily
for induced-draft fan protection. Then in 1968, shortly after issuance of
a Federal Executive Order in 1966, mandating increased pollution control
TVA initiated a retrofit program for design and construction of electro-
static precipitators in order to comply with this order. This program of
retrofitting ten units with 90 percent efficient electrostatic precipitators
was completed in 1973 at a cost of $9,161,000. At that time, the flue gas
was exiting into the ten stacks as seen here in this aerial photograph. (Show
slide 1.) Then in 1974, in an effort to improve the ambient air quality and
reduce local ground level concentrations of SO-, a program of building two
large 800-foot-high stacks was begun. These stacks were located 187 feet
to the rear of the old stacks with long runs of ductwork connecting into
a common breeching each one serving five units, as can be seen here in the
photograph.
Since there was room for argument regarding our tall stack approach for
control of SO-, we also left room in the ductwork between the old stacks and
new breeching for additional pollution abatement equipment if we lost our
argument. In April of 1976, the Supreme Court ruled against tall stack
control of S0?, so we now had a chance to fill up this space of some 187 feet
with something.
If we recap the chronology of air pollution project work at Shawnee,
it shows up something like the illustration on slide 2.
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Chronology of Air Pollution Projects
Program Cost
1st Retrofit - Ten electrostatic precipitators
at 90 percent efficiency - 1968-1973 $ 9,161,000
2nd Retrofit - Two 800-foot stacks, ductwork
and breeching - 1974-1977 25,600,000
3rd and (Final)(?) Retrofit - Ten structural
baghouses and all auxiliaries - 1978-1981 80,000,000
Total $114,761,000
Total Plant Cost $216,500,000
or
53 percent
Last year at this symposium, I presented a paper explaining the
philosophy and economic advantages of why TVA chose a baghouse and low-
sulfur coal in lieu of scrubbers as the solution. Today, we will try to
explain the basic design criteria we have used in this baghouse installation.
TYPE OF CONTRACT AND SCOPE OF WORK
In considering the workload of our design and construction forces,
it was decided that the Shawnee project should be done on a turnkey basis.
Within this concept we would write specifications and take bids on the
complete job of engineering, furnishing, and erection of equipment for the
project. And so it was that on March 14, 1978, TVA awarded a contract to
Buell Division of Envirotech Corporation in the amount of $53,218,000 for
engineering, furnishing, and erecting ten baghouses and all auxiliaries as
listed in the scope of work shown on slide 3.
Specification Outline
1. Structural Baghouse Fly Ash Collectors
2. Ductwork, Distribution Devices, Expansion Joints, and Louver Dampers
3. Insulation and Lagging
4. Fly Ash Handling Systems and Ash Sluice Water Piping
5. Washdown Pad Sump Pumps, Valves, Pipe, Hangers, Sewerage, and Freeze
Protection
6. Induced-Draft Fans
7. Elevator and Hoists
8. Control Houses
9. Instruments and Control
10. Electrical Work
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11. Structural Steel Supports and Miscellaneous Steel Access Platforms
and Stairs
12. Concrete Foundations
13. Washdown Pads, Drains, and Sumps
14. Site Improvement, Parking Facilities, and Access Roads
15. Painting
16. Fire Protection
The next five slides (show slides 4, 5, 6, 7, and 8 of plans and
elevations, pointing out various features) show the basic equipment layout
and relationship to existing equipment. Significant man-hours have gone into
the scheduling, design, procurement, and construction of the project to date.
Last year little actual work had progressed at the project site; this year
construction is well underway and the first unit is scheduled for tie-in in
late fall. As can be seen from the slides there just is not ample room to
spread out; equipment, laydown area, and workmen all are confined to the
same general area. Scheduling the activities has been a difficult task.
SCHEDULE
The overall schedule, we believe, is very ambitious, and calls for
completion of all ten units 42 months after award of contract. However,
the industry did respond in a favorable manner; no one claimed the time
was too short. Some of the major milestones for the schedule are shown
on the bar chart here in slide 9.
Schedule
Program Schedule
TVA start specification June 29, 1977
Purchasing issue invitation to bid September 22, 1977
Bid opening December 13, 1977
Award of contract March 14, 1978
Start construction April 24, 1978
Construction and Tie-in Schedule
Unit Start Tie-in Complete Tie-in
5 November 1, 1979 December 1, 1979
6 January 15, 1980 February 15, 1980
4 March 15, 1980 April 15, 1980
3 June 1, 1980 July 1, 1980
7 August 15, 1980 September 15, 1980
8 October 15, 1980 November 15, 1980
9 January 1, 1981 February 1, 1981
10 March 15, 1981 April 15, 1981
2 May 15, 1981 June 15, 1981
1 August 1, 1981 September 1, 1981
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The contract provides for a bonus-penalty for early or late completion
of the project. Since it is impossible as well as impractical to identify
a precise cutoff date, we identified a 30-day dead band on each side of the
complete construction date before bonus-penalty would be applied. On the
31st day, the bonus-penalty would accrue and continue until a maximum value
of $500,000 was reached. The Contractor has recognized the potential for
the bonus and from the very start has proceeded with the organization,
design, schedule, and construction to capitalize on receiving the maximum
bonus. All schedules and actions to date indicate they will complete the
tie-in of the final unit early and earn a bonus.
SPECIFICATION REQUIREMENTS
In the spring of 1977 very few baghouses had been installed in utility
plants and it certainly behooved us to take advantage of standing experience
at that time. Therefore, in writing the specifications we had four
objectives. They were:
1. Build on industry experience in adapting baghouses to utility
boilers.
2. Specify a very conservative design (low differential pressure and
air-to-cloth ratio [A/C]).
3. Stretch the industry's practice regarding bag life guarantees.
4. Incorporate and redefine TVA's broad precipitator experience into
their first baghouse.
In short it was our intent to obtain equipment that would perform to
the best available technology while providing ease of maintenance and at a
competitive cost.
One major area of concern was the selection of the method of cleaning.
Early in the project, we selected reverse air cleaning as the only type of
cleaning method acceptable. This was not an accident or casual selection.
As best could be determined, from the industry itself, it was the only
method that had proven itself in utility operation. More experience had
been collected on this cleaning method than any other and we felt that
the Shawnee units should be given every opportunity to become a model design,
not an experiment.
In slide 10 we see a summary of some detailed design criteria. (Show
slide 10.)
Design Criteria
1. Coal - Either separately or blended eastern or western low-sulfur
coal. Sulfur 0.33 percent. Moisture 30.2 percent. Ash 7.44 percent
Heating value 8075 Btu/pound.
2. ACFM - Test block 650,000 with normal operation 585,000.
3. A/C - All compartments online at test block 2:1 (this will be
explored later in the paper in great detail).
4. Bag - 11-7/8-inch diameter by 34-foot-7-3/4-inch 14-ounce fiberglass
bag coated with teflon B finish, 9 percent by weight.
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5. Cor-Ten for casing, hoppers, ductwork, and all gas contact surfaces.
6. Stainless steel bag hardware and poppet valve shafts and seals.
7. Dry fly ash handling system to pond and then wetted.
8. Fans, dampers, expansion joints, control houses, and related
equipment necessary for the operation of the baghouse.
9- Each baghouse has ten compartments with 324 bags per compartment.
Bags are arranged on 14-inch centers with 2-bag reach providing a
grid of 12 by 27 (three walkways).
Well-designed equipment must be capable of being easily maintained. It
was our intention, particularly since this was our first baghouse, to pay
special attention to the ease of maintenance and especially to replacement
of bags. I am well aware of the arguments regarding 2-bag versus 3-bag
reach, but am not prepared to argue all the details and merits of one versus
the other. We all know that Murphy's Law says "If something can go wrong it
will." We could paraphrase that and say "If it is hard to maintain it won't
be" or not often enough. Conversely, if you make it easy to fix or replace,
chances are a lot better care will be taken of that particular feature. Pure
and simple, this was the reason behind °ur decision to use a 2-bag reach in
the design of the Shawnee baghouse. We believe that with ten units,
100 compartments, and 33,000 bags to watch after that anything to make
maintenance or replacement easier is money well spent. One might ask "How
much extra real estate or space does your 2-bag reach design take over the
3-bag reach?" The next slide indicates the difference in space. (Show
slide 11.) There is only a 7 percent differential in the plan area and this
only occurs in one direction. In our view this is "small potatoes" compared
with the overall space required and of very little significance in extra
money spent for 2-bag versus 3-bag reach. As a result of this, our 2-bag
reach decision was really an easy one.
AIR-TO-CLOTH RATIO CRITERIA
As most of you know who have tried to size dust collectors, obtaining
a consistent story of how much cloth area is in a bag is not an easy task.
To keep all bidders on an equal footing, we were very specific on how to
determine active cloth area. The calculating of active cloth area is no
art; it is just important that all bidders understand and calculate the
active cloth area in the same manner. As a guide, I have included how we
calculated active cloth area. (Show slide 12.) On the left you will see
a typical bag configuration and just to the right of it is a flat cloth layout
of the same bag. Our approach was to use the overall cloth area and deduct
the top cuff, vertical seam, anticollapse ring seams, and bottom cuff seam
areas. The overall cloth area is 107.71 square feet and with the deductions
this reduces to 102.47 square feet. On the extreme right-hand side of the
slide is a summary of the cloth area per bag, per compartment, and per
collector. There is only 5.24 square feet differential area per bag, but
this equates to 16,977 square feet per collector. Significant advantages
or disadvantages could be given to a potential bidder if all bidders were
not calculating cloth area in the same manner. This is by no means the only
approach, and I do not intend to pretend other approaches are not acceptable.
It is our method and we believe indicates a conservative approach.
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As a followup to calculating cloth area, we think the definition and
calculation of air-to-cloth ratios is equally important. (Show slide 13.)
AIR-TO-CLQTH RATIO
BASED ON ACTIVE CLOTH AREA (102.47 SQUARE FEET/BAG)
All compartments
online (10)
One compartment
down for
cleaning (9)
One compartment
down for cleaning
and one down for
maintenance (8)
Test Block
(Excluding
Reverse Air)
650,000 ACFM
1.96
2.18
Test Block
(Including
Reverse Air)
708,000 ACFM
2.37
Normal
Operation
(Excluding
Reverse Air)
585,000 ACFM
1.76
1.96
Normal
Operation
(Including
Reverse Air)
643,000 ACFM
2.15
2.45
2.67
2.20
2.42
*Reverse air is not on when ten compartments are filtering.
As can be seen in the slide, it is easy to get confused when talking
A/C ratios, and it is important to know the basis when you talk A/C ratios.
You can see that while a 2 to 1 ratio is referred to, it is more or less
nominal and the real operating condition which the baghouse uses is a more
conservative 1.76 to 1.
The arrows indicate the normal conditions of service that the baghouse
will see. The air-to-cloth ratio changes from 1.76 to 2.15 (for cleaning)
to 2.42 (for cleaning and maintenance). We feel this is consistent with our
conservative approach of providing low maintenance by designing for longevity
of bag life due to low differential pressure. The additional capital cost for
a larger dust collector is easily written off when compared to the subsequent
capitol and maintenance cost of high-pressure drop and more frequent bag
maintenance. The increase in incremental capitol cost for lower air-to-cloth
ratios is relatively insignificant compared to the cost of replacement power.
Our philosophy of conservative air-to-cloth ratio and resultant low-
pressure drop paid off in a suprising bonus. The successful bidder offered
a 3-year bag life guarantee rather than the 2-year as specified. This extra
year of guarantee we feel is the type response that the pollution abatement
equipment suppliers must extend to the utility industry. Last year I
challenged the industry itself that "its success depends upon the industry's
response to new applications of an old technology." We at TVA were glad to
see that not only Envirotech but the industry took steps in a responsive
direction. The extra year of bag life guarantee equates directly to savings
in loss of power generation. Shawnee is a base load station and as such must
run relatively loaded all the time. The utilization rate for Shawnee is the
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highest in the system and runs around 90 percent. Anything that can be
done to reduce maintenance will result in savings over the long haul and help
hold the cost of electricity as low as possible.
GUARANTEES
The next slide highlights a few of the performance and guarantee data that
was required by the specifications and offered by Envirotech. (Show slide 14.)
Performance and Guarantee Data
Maximum allowable outlet
grain loading (grain/ACF)
Maximum allowable pressure drop
(inches of water)
Fabric filter bag life (years)
Specification
Requirement
0.005
6-3/4
Envirotech
Offered
0.005
5-7/8
As can be seen, Envirotech offered the same outlet grain loading while
improving on pressure drop and bag life guarantees as defined in the invitation.
I said earlier that one of our objectives was to stretch the industry's
practice regarding bag life guarantees. We did not expect that a Contractor
would go us one better by offering 1 extra year bag life than we specified
and 7/8-inch less pressure drop. Needless to say we were pleased with this
response, particularly since it was in the two most difficult and important
areas of the specification requirements. These guarantees offered by the
contractor represent hundreds of thousands of dollars if not attained and we
know they were not taken lightly by the contractor.
Again we feel that this type of response on the part of the industry is a
necessary step for baghouse supplier's to take in order to participate in
particulate control for utility applications.
DESIGN SCHEMATIC
The fabric filter baghouse system, as furnished by the contractor,
receives a total of 6,500,000 ACFM of flue gases from twenty air preheaters
(two for each boiler) at 325° F, processes this volume of flue gases through
ten fabric filters and exits at 0.005 grain/ACF. Each of the ten fabric
filters serve one pulverized coal-fired reheat unit of radiant type, natural
circulation. Each fabric filter will be placed downstream of an existing
deenergized precipitator. The fabric filters, as furnished by the contractor,
are capable of being operated immediately upon startup of each boiler, without
adversely affecting operation of the baghouse through the employment of a
uniquely designed warm air preheat system.
Immediately upon leaving the two deenergized precipitators, the flue
gases travel through air preheater pressure equalizing louver-type dampers.
These dampers are interlocked with the boiler logic and they also act to
balance the load on the boiler. The damper blades are of airfoil design,
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stiffened as necessary, have no external ribs, and have built-in provisions
to accommodate the thermal expansion between the blades and the damper frame
proper.
At the inlet area of each of the ten fabric filters are six poppet-type
bypass dampers. (Show slide 15.) The filter bypass poppet valves (three of
which are shown) are activated automatically due to overpressure, excessive
temperature, and low temperature; and manually for the maintenance of an
entire unit. With the bypass dampers in the bypass mode or position, the
differential pressure across the system is not allowed to vary by more
than 2 inches from normal, with fabric filter online, in order to prevent
boiler unbalances associated with significant changes in flue gas pressures.
During normal filtering mode all six bypass poppet valves are closed.
As the flue gases leave the bypass area, they begin their travel to
the fabric filter through the inlet manifold fabricated of 1/4-inch-thick
Cor-Ten A steel plate. It should be noted that all ducts are designed to
support a 1-foot depth of 75 pounds per cubic foot of fly ash. Quick-opening
access and inspection doors, as well as appropriate turning vanes, are provided
throughout the ductwork system.
(Show slide 16.) To enter each of the ten fabric filter compartments, the
flue gases must pass through inlet poppet dampers of a metal-to-metal positive
seal design. There are twenty of these dampers for each fabric filter, and
they normally remain in the open position, except when a compartment is down
for maintenance or inspection and bypass, in which case the inlet poppet dampers
(two per compartment) are closed for complete isolation of flue gases. When a
boiler is operating on reduced load, there will be a lower flue gas volume and
a lower gas temperature. During these periods (especially when a boiler is
in a cycling mode) baghouse compartments can be isolated to reduce the total
cloth area (that is, to keep the A/C ratio close to 2:1) and exposed steel
surfaces to the flue gas. This will accomplish two key objectives: (1) It
will reduce loading and unloading of the filter cloth and should extend over
all bag life and (2) it will reduce the heat sink (large amount of metal surfaces
in contact with gas) that would decrease even further the gas temperature and
help to maintain temperature above the dewpoint. If all ten compartments are
offline for any reason, all twenty inlet poppet dampers would be placed in the
closed position. The dampers are heavy duty air-cylinder driven, and are
designed such that the normal flow of the flue gas aids in establishing a seal.
In addition to the twenty poppet-type inlet dampers, there are twenty similar
design outlet and reverse air dampers. (Show slide 17.) The outlet and reverse
air dampers are continuously used in the continual process of sequentially
operating and cleaning the fabric filter compartments. When a compartment is
down for maintenance all inlet, outlet, and reverse air poppet dampers providing
flue gas to that compartment are in tight closed, sealed position. (Show
slide 18.)
A purge air system is also incorporated in the fabric filter design
to assist in the rapid cooling down of any compartment which is brought offline
for maintenance, while the adjacent compartments remain online. To accomplish
this task, the contractor has included one vaneaxial fan per fabric filter.
The exact design of the ductwork and fabric filter equipment distribution
devices were identified and incorporated as a result of an extensive model
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study of the total system conducted by the contractor. The contractor con-
structed a 1/4-inch 3-dimensional scale model of the fabric filters and of
that portion of ductwork that was necessary to perform tests to minimize fly ash
fallout and provide uniform flue gas and temperature distribution through the
fabric filters and associated ductwork. (Show slides 19, 20, and 21.)
These photographs of the model show turning vanes and gas distribution
devices that were added to aid in the reduction of pressure losses. Good
gasflow distribution in some places was only obtainable through the use of
gas distribution devices. An example of this is obtaining even gasflow across
the grid sheet. (Show slide 22.) The flue gas entering the individual hoppers
from the two inlets passes across a baffle or deflector plate, which has the
effect of equally distributing the flue gases to all bags within the individual
compartments. The hopper flow deflector will aid in the evening of particulate
concentrations across all the cloth in the compartment and this should result
in reducing localized bag failure. Without this deflector plate the flue gas
tended to turn immediately upwards through the tube sheet and not flow across
to the far side as indicated in this slide.
It may be the opinion of some that good gasflow distribution is necessary
only for precipitators. This was basically our "gut feel" at the start but
since this was our first baghouse we felt we would go ahead and model test—"it
couldn't hurt anything." Now we are glad we did. Based on the improvements in
gasflow, reduction of pressure drop, and all we learned from this model test, we
would have to say "it is just as important and beneficial to model test a bag-
house as it is a precipitator."
In order to provide delivery power for the flue gases from the air preheater
through the base of the two 800-foot stacks, two induced-draft fans per fabric
filter are provided. Each of the induced-draft fans are double inlet, double
width units. The two fans per boiler will normally be started and run together.
The test block requirements for each induced-draft fan is 354,000 ACFM at 325° F,
with a fan static pressure of 31.5 inches wg at the inlet, and 0 inch wg static
pressure at the outlet of the fan. The blades of the induced-draft fans are
of the airfoil type. The fans have direct connected 2000-hp motors, operate at
900 rpm, and have inlet louver dampers for isolation. The fans also have
conical variable inlet vanes for inlet volume control and to provide pressure
balancing for the fabric filter and boiler operation.
(Show slide 23.) The most unique feature of the entire baghouse installa-
tion is the reverse air cleaning and prewarming system.
The induced-draft fans are the principal mode of fabric filter reverse
air cleaning with the reverse air fans being provided for backup cleaning
during periods of excessive pressure drop or other unusual conditions. As
such, the induced-draft fans can be subjected to variations in pressure of up
to +1 inch wg every 5 minutes and having a duration of some 30 seconds. The
induced-draft fans, dampers, actuators, and controls have been selected for this
duty. There is a total of ten reverse air fans (one for each fabric filter).
The compartment warming system utilizes the reverse air system to preheat
offstream compartments or an entire baghouse with cleaned, heated flue gas from
the outlet breeching.
Referring to the slide and as noted before there are five baghouses
connected to each breeching and stack. Thus, there is always a constant source
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of clean, heated flue gas to be used for reverse air cleaning or prewarming a
compartment or baghouse. Here is how it works: The pressure in the stack
breeching is approximately 0 to +1 inch tLO and the pressure at the inlet to
the baghouse is approximately -20 inches HO. To initiate cleaning, all that
is required is to open the appropriate damper, bypassing the reverse air
fan, and clean hot gas will flow to the desired compartment. As long as an
induced-draft fan is running, it may never be necessary to use the reverse
air fan. The reverse air fans will be used if pressure upset conditions should
occur or to preheat offstream compartments when the induced-draft fans are out
of service (an example would be on cold startup). To ensure that the bags are
not subjected to violent pressure changes during cleaning or warming, a
modulating reverse air damper will control and maintain a constant flow, thus
providing a constant A/C ratio when cleaning. We believe the real advantage of
this system is the ability to prewarm any baghouse prior to its receiving gas
from the boiler. We can avoid shocking a cold baghouse with 325° F dust-laden
gas without a costly steam or other type preheating system.
QUALITY ASSURANCE PROGRAM FOR BAGS
The quality control program which the contractor established in cooperation
with the bag vendor for the manufacture of the TVA filter bags is necessary to
ensure the bags are manufactured to the customer specifications. (Show
slide 24.)
Fabric Filter Quality Assurance Program
1. Bag hardware: Inspected at 10 percent random sample minimum, includes
weld strength tests on anticollapse rings.
2. Fabric: In-house fiberglass rolls are inspected 100 percent for roll
numbers, lot numbers, and test certifications.
3. Thread: Tested for strength, plies, and compliance to specifications.
4. Equipment: Machines are inspected for proper operation and function,
including layout table marks.
5. Fabrication: Workmanship is checked at all work stations: layout,
seaming, ringing, cuffing, packaging. Cloth condition is inspected
at each work station.
The program provides the bag vendor with the ability to trace all raw
materials used during manufacture back to the original supplier, and due to
various inspections and certifications also ensures that these raw materials
meet the specifications as required by TVA.
The quality assurance program provides methods of inspection whereby all
hardware and fabric items are checked for proper sizing, as well as material
type specifications. The program stipulates work in process quality control
checks be made at the different manufacturing stations for cutting, seaming,
cuffing, and ringing. (Show slide 25.)
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Filter Cloth Test Certifications
Test Method
Weight ASTM D 1910
Thickness ASTM D 1777
Count* ASTM D 1910
Permeability ASTM D 737 '
Tensile strength" ASTM 1682, Method IR-T
Mullen burst ASTM D 231
Mit flex
Organic content ASTM D 578
Water repellancy ASTM D 2721
Yarn weight ASTM D 578
Yarn twist* ASTM D 578
Microscopic exam*
*Warp and fill
After manufacture, each individual bag is then checked for size and any
defects before being individually packaged.
The contractor as well as the bag vendor believes in quality; the quality
assurance program is the tool used to enable them to purchase the raw materials
and produce some 35,000 quality filter bags.
This quality control program, coupled with the conservative air-to-cloth
ratio and low pressure drop and the specification requirement of 14-ounce-per-
square-yard cloth, was the main consideration in the contractor's decision
to offer a 3-year bag life guarantee.
INSTRUMENTATION AND CONTROLS
The Shawnee baghouse has been equipped with a full complement of alarms,
annunicators, monitors, and strip chart recorders in order that the control
room operator can monitor and operate the baghouses. Dual monitoring controls
are provided in the unit control room and baghouse control room. Depending
on the type of maintenance and/or operation, the appropriate control panels can
be selected to perform the activity.
Display boards, mimic panels, lights, and status indicators add much
needed useful information to the operators. The approach for design has been
to make available to the main control room operator controls of the level
and type necessary for the operation of the baghouse in conjunction with the
boiler. At a glance the control room operator can determine the mode of
cleaning operation, baghouse pressure differential, inlet and outlet flue
gas temperatures, reverse air temperature, status of compartments (whether
filtering, cleaning, or maintenance) system draft, various system failures,
or other key operational inputs. Envirotech and TVA have worked closely to
identify and provide the instrumentation, controls, and boiler interlocks
necessary for the operation of the boiler, turbine generator, and baghouse
as an integrated system.
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CONSTRUCTION
There were two schemes considered for constructing the ten baghouses. One
was to start at one end and work towards the other end in progression. However,
after completing the schedule for this scheme it was decided we should try to
find a way to complete the job in a shorter time frame. As a result we struck
upon the scheme now being used of starting at the center on units 5 by 6
simultaneously and working out towards each end at the same time. This scheme
permitted the use of two cranes simultaneously and more efficient scheduling
and use of manpower. (Show slide 26.)
One of the most unusual construction features of this project is the
foundation. Because of the high water table and soil characteristics, it
was necessary to design and build a raft or bathtub type foundation which
would float. The floor of this bathtub foundation for all ten units is
100 feet wide, 825 feet long, and 3 feet thick. The walls are 13-1/2 feet
high and 1-1/2 feet thick around the entire perimeter. A grid work of steel
support columns is erected inside this bathtub to support decking, over which
is poured a washdown slab as a roof over the bathtub at grade level. (Show
slide 27.) The baghouses are then erected above this grade level roof over
the bathtub foundation starting in the center and working outwards to both
ends simultaneously. At the present, construction is proceeding ahead of
schedule and from all indication it appears the contractor will be ready for
an earlier tie-in than called for in the schedule. (Show slides 28, 29, 30,
31, 32, 33, and 34.)
SUMMARY
When we announced our decision to install ten baghouses at Shawnee
two years ago, we were certainly aware of the pioneering nature of the magnitude
of this decision. I shall never forget the question put to me by Ed Stenby
of Stearns Rogers when he asked incredulously "Al, you are putting in ten
baghouses? You're not going to put in one and try it out"? I have explained
before that we did not have the luxury of that option, sensible as it is. We
had to commit all ten units to particulate control, but believe me that
question had its impact on our thinking. If we made a mistake, it would
happen ten times in whatever area of design we were in!I
As a result our goal has been to design a conservative baghouse system.
There has been no attempt at any stage of design to cut corners or economize
at the expense of quality. TVA and the contractor, Envirotech, have recognized
the importance of conservatism and quality in design from the beginning of
this project. The spirit of cooperation could not be better, and the turnkey
concept has proven to be a satisfactory one.
Late this year at Shawnee No. 5, TVA will start up the first baghouse
ever in its system to be followed at approximately 2-month intervals by
nine more. We do not expect that this startup will be trouble-free—nothing
ever is. However, because of conservatism in design, special attention paid
to all details and desire to do a good job on the part of the contractor, we
believe after initial shakedown that the Shawnee plant will be living testimony
to the fact that baghouses can be a viable alternative to successfully collect
particulates in large, multiunit central electric generating stations.
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CHRONOLOGY OF_AIR POLLUTION PROJECTS
UNITS 1-10
SHAWNEE STEAM PLANT
PROGRAM
1ST RETROFIT - 10 ELECTROSTATIC PRECIPITATORS AT 90-5
EFFICIENCY - 1968-1973
COST
$ 9,161,000
2ND RETROFIT - TWO 800-FOOT STACKS, DUCTOWRK, AND
BREECHING - 1974-1977
25,600,000
01
3RD AND (FINAL)(?) RETROFIT - 10 STRUCTURAL BAGHOUSES
AND ALL AUXILIARIES - 1978-1981
TOTAL
TOTAL PLANT COST
80,000,000
$114,761,000 --53% TOTAL PLANT COST
$216,500,000
SLIDE NO. 2
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STRUCTURAL BAGHOUSE
SHAWNEE STEAM PLANT
SPECIFICATION OUTLINE
1. STRUCTURAL BAGHOUSE FLY ASH COLLECTORS
2. DUCTWORK, DISTRIBUTION DEVICES, EXPANSION JOINTS, AND LOUVER DAMPERS
3. INSULATION AND LAGGING
4. FLY ASH HANDLING SYSTEMS AND ASH SLUICE WATER PIPING
5. WASHDOWN PAD SUMP PUMPS, VALVES, PIPE, HANGERS, SEWERAGE, AND FREEZE PROTECTION
6. INDUCED-DRAFT FANS
7. ELEVATOR AND HOISTS
8. CONTROL HOUSES
9. INSTRUMENTS AND CONTROL
10. ELECTRICAL WORK
11. STRUCTURAL STEEL SUPPORTS AND MISCELLANEOUS STEEL ACCESS PLATFORMS AND STAIRS
12. CONCRETE FOUNDATIONS
13. WASHDOWN PADS, DRAINS, AND SUMPS
14. SITE IMPROVEMENT, PARKING FACILITIES, AND ACCESS ROADS
15. PAINTING
16. FIRE PROTECTION
SLIDE NO. 3
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ELEVATOR UNITS
3$8 ONLY
/T\
BYPASS POPPET
REMOVAL MONORAILS
BAG HOIST AND
MONORAIL
BAGHOUSE
PLAN VIEW
SLIDE NO. 4
-------
ro
--J
REVERSE AIR DUCT
TRUNK DUCT
REVERSE AIR
BOOSTER FAN
0 D DID D DID D DiD D D
D"D""D ! 0 D D ! D D 0 : D D D
BAGHOUSE
WEST WALL ELEVATION
SLIDE NO. 5
-------
oo
o
MANUALLY OPERATED
BUTTERFLY DAMPER
REVERSE AIR DAMPER
OUTLET POPPET
REMOVAL MONORAIL
PENTHOUSE
REVERSE AIR DUCT
POPPET DAMPERS IN
CLEANING MODE
POPPET DAMPERS IN
FILTERING MODE
QUICK OPENING
COMPARTMENT
ACCESS DOOR
HOPPER
BAGHOUSE
SECTIONAL VIEW
SLIDE NO. 6
-------
- ELEVATOR
PO
CO
V
/ \
INLE
T DUCT
V
/ \
-SUMP UNITS
3(8 ONLY
T.O.G. EL. 4IS'-l'/j
ra^El-. 407'-l'/s
ELEVATOR LANDING
T.O.G. EL. 375'-!^*
ELEVATOR LANDING
-NOMINAL GRADE
EL. 345'-0*
SLIDE NO._Z
BAGHOUSE
SOUTH V/ALL ELEVATION
-------
PENTHOU3E
ro
c»
ro
I.S. ROOF EL. 415 - 0
T. 0. G. EL. 407 -
HOPPER ENCLOSURE
REVERSE AIR DUCT
T.O.G. EL. 375'-l'j
rNOMINAL GRADE
\ EL. 345'-0"
1.0. FANS-
SLIDE NO. 8
BAGHOUSE
NORTH WALL ELEVATION
-------
ro
oo
oo
SCHEDULE
SHAWNEE STEAM PLANT "UNITS I-10
STRUCTURAL BAGHOUSE FLY ASH COLLECTORS
TVA - ENVIROTECH
PROGRAM SCHEDULE
TVA START SPECIFICATION
PURCHASING ISSUE INVITATION TO BID
BID OPENING
AWARD OF CONTRACT
START CONSTRUCTION
CONSTRUCTION AND TIE-IN SCHEDULE
UNIT START TIE-IN
5 NOVEMBER 1, 1979
6 JANUARY 15,1980
4 MARCH 15, 1980
3 JUNE 1, 1980
7 AUGUST 15, I960
8 OCTOBER 15,1980
9 JANUARY 1, 1981
10 MARCH 15,1981
2 MAY 15, 1981
1 AUGUST 1, 1981
cc
SS I BO ASC ST CT
JUNE £9, 1977
SEPTEMBER 22,1977
DECEMBER 13,1977
MARCH 14, 1978
APRIL 24,1978
COMPLETE TIE-IN CC
SC ST CT
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JULY 1, 1980 1 V\ W\ VV\\\\V\'v\ \V\\\B1
NOVR MH^PV is, iw> I\\\\\\\\\\\\\\\\^\\\M
FEBRUARY !. 1981 !\\\\\\ \V\V\\\ V\ \\V\\IH
APRIL (5.1981 i\\\\\\\\V\'\lv\\'\\\\\\»
JUKJF 15 1981 ( V\ \ K \-T\' \ \ \ \ \ \ \~\ \ S \"V \ N R^
SEPTEMBER ! 1981 1 \ \ v^Ws \\\'\'\VVV'\vvv\^p
II 2-3 41 234 1234 1234 1234
1 1077. 1 IQ70 . 1 I07n_ . 1 ino^ ... .no, 1
LEGEND
E3 - CONSTRUCTION A - AWARD
a -TIE-IN SC - START CONSTRUCTION
SS - START SPECIFICATION CC - COMPLETE CONSTRUCTION
I - ISSUE INVITATION ST - START TIE-IN
BO. -- BID OPENING CT - COMPLETE TIE-IN
SLIDE NO. 9
-------
STRUCTURAL BAGHOUSE FLY ASH COLLECTORS
UNITS 1-10
SHAVINEE STEAM PLANT
DESIGN CRITERIA
1. COAL - EITHER SEPARATELY OR BLENDED EASTERN OR WESTERN LOW-SULFUR COAL. SULFUR .33 PERCENT.
MOISTURE 30.2 PERCENT. ASH 7.44 PERCENT. HEATING VALUE 8075 BTU/POUND.
2. ACFM - TEST BLOCK 650,000 WITH NORMAL OPERATION 585,000.
3. A/C - ALL COMPARTMENTS ONLINE AT TEST BLOCK 2.0 (THIS WILL BE EXPLORED LATER IN THE PAPER
IN GREAT DETAIL).
4. BAG - 11-7/8" DIAMETER BY 34'-7-3/4" FIBERGLASS BAG COATED WITH TEFLON B FINISH; 9% BY WEIGHT.
^ 5. CORTEN CASING, HOPPERS, DUCTWORK, AND ALL GAS CONTACT SURFACES.
oo
"^ 6. STAINLESS STEEL BAG HARDWARE AND POPPET VALVE SHAFTS AND SEALS.
7. DRY FLY ASH HANDLING SYSTEM TO POND AND THEN WETTED.
8. FANS, DAMPERS, EXPANSION JOINTS, CONTROL HOUSES, AND RELATED EQUIPMENT NECESSARY FOR THE
OPERATION OF THE BAGHOUSE.
9. EACH BAGHOUSE HAS 10 COMPARTMENTS WITH 324 BAGS PER COMPARTMENT. BAGS ARE ARRANGED ON 14-INCH
CENTERS WITH TWO BAG REACH PROVIDING A GRID OF 12 BY 27 (3 WALKWAYS).
SLIDE NO. 10
-------
STRUCTURAL BAGHOUSE FLY-ASH COLLECTORS
SHAWfCE STEAM PLANT UNITS I-10
TWO VS. THREE SAG REACH
GRID ARRANGEMENT
STRUCTURAL BAGHOUSE FLY-ASH COLLECTORS
SHAWNEE STEAM PLANT UNITS HO
TWO VS. THREE BAG REACH
BAGHOUSE ARRANGEMENT
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2 BAG
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3 BAG
REACH
2
REACW
3 BAG
REACH
RATO OF PLAN AREA OF 3 BAG VS 2 BAG REACH = -f?H- =
2.06?.
7630
SLIDE NO. 11
-------
<£BAG
VERTICAL SEAM
V/^
1 CUFF BAND
GROSS OVERALL LENGTH
3"'-7}"
ANTICOLLAPSE
RING SPACING
7SPACES "7V7V^,^ \
, , Kl
"^KT—J" VERTICAL SEAM
""l^
7V y 7-7-7 y~7" / •^7r~7'Nj /
ACTIVE CLOTH
AREA DETERMINATION
i.
?
3.
4.
5
LOCATION
OVERALL CLOTH AREA
TOP CUFF SEAM AREA
VERTICAL SEAM AREA
ANTICOLLAPSE RING SEAM AREA
30TTOM CUFF SEAM AREA
TOTAL ACTIVE CLOTH AREA/BAG
SQFT
107.71
-.51
-1.80
-1.91
-1.02
102.47
CLOTH AREA SUMMARY
CLOTH AREA
PER BAG
PER COMPARTMENT
(!2< BAGS)
PER COLLECTOR
BAG SIZE (SQ.FT.)
107.71
31,898
308,930
102.17
33,200
332,003
A CLOTH AREA
(SQ. FT.)
5.24
I698
16,977
FLAT..CLOTH LAYOJJJ_
FABRIC FILTER
ACTIVE CLOTH AREA
STRUCTURAL BAGHOUSE
SHAWNEE STEAM PLANT
UNITS i-IO
SLIDE NO. 12
-------
AIR TO CLOTH RATIO
BASED ON ACTIVE CLOTH AREA~(TQ2T4T SQUARE FEET/BAG)
STRUCTURAL BAGHOUSE - UNITS 1-10
TEST BLOCK
(EXCLUDING
REVERSE AIR)
650,000 ACFM
SHAWNEE STEAM PLANT
TEST BLOCK
(INCLUDING
REVERSE AIR)
708,000 ACFM
NORMAL OPERATION
(EXCLUDING
REVERSE AIR)
585,000 ACFM
NORMAL OPERATION
(INCLUDING
REVERSE AIR)
643.000 ACFM
co
ALL COMPARTMENTS
ON LINE (10) 1.96
ONE COMPARTMENT
DOWN FOR CLEANING (9) 2.18
ONE COMPARTMENT DOWN
FOR CLEANING AND ONE
DOWN FOR MAINTENANCE (8) 2.45
2.37
2.67
1.76
2.20
2.15
^2.42
*REVERSE AIR IS NOT ON WHEN 10 COMPARTMENTS ARE FILTERING.
SLIDE NO. 13
-------
00
00
STRUCTURAL 3AGKOUSE FLY ASH COLLECTOR
SHAWNEE STEAM PLANT UNITS 1-10
PERFORMANCE AND GUARANTEE DATA
TVA AND ENVIROTECH
SPECIFICATION ENVIROTECH
REQUIREMENT OFFERED
MAXIMUM ALLOWABLE OUTLET
GRAIN LOADING (GRAIN/ACF) .005 .005
MAXIMUM ALLOWABLE PRESSURE DROP
(INCHES OF WATER) 6-3/4 5-7/8
FABRIC FILTER BAG LIFE (YEARS) 2 3
SLIDE NO. 14
-------
no
CO
INLET DUCT
FROM BOILER
OUTLET MANiFOLD
TO I D FANS
INLET MANIFOLD
i*. 3 L, s
SLIDE NO. 15
-------
FILTER BAGS
TUBE SHEET
ro
OUTLET MANIFOLD
TO I.D. FANS
INLET IWANfFOLD
FROM BOILER
SLIDE NO. 16
-------
REVERSE AIR MANIFOLD
FROM CLEAN AIR TRUNK DUCT
ro
OUTLET MANIFOLD
TO I D FANS
INLET MANIFOLD
FROM BOILER
SLIDE NO. 17
-------
PURGE DUCT
TO PURGE FAN
ACCESS DOORS Typ
ro
MD
ro
OUTLET MANIFOLD
TO I D FANS
INLET MANIFOLD
FROM BOILER
SLIDE NO. 18
-------
OO
SLIDE NO. 22
-------
UNIT 1-5
SYMMETRICAL
ABOUT-
REVERSE AIR/COMPARTMENT WARMING
FLOW
TVA SHAWf^EE STEAM PLANT
mns 1-10
BAGHOUSE FLOW
SLIDE NO. 23
-------
FABRIC FILTER QUALITY ASSURANCE PROGRAM
I, BAG HARDWARE: INSPECTED AT 10% RANDOM SAMPLE,
MINIMUM, INCLUDES WELD STRENGTH TESTS ON ANTI-
COLLAPSE RINGS,
II. FABRIC: IN-HOUSE FIBERGLASS ROLLS ARE INSPECTED
100% FOR ROLL NUMBERS, LOT NUMBERS, AND TEST
CERTIFICATIONS,
III, THREAD: TESTED FOR STRENGTH, PLIES AND COMPLIANCE
TO SPECIFICATIONS,
IV, EQUIPMENT: MACHINES ARE INSPECTED FOR PROPER
OPERATION AND FUNCTION, INCLUDING LAYOUT TABLE MARKS,
V, FABRICATION: WORKMANSHIP IS CHECKED AT ALL WORK
STATIONS; LAYOUT, SEAMING, RINGING, CUFFING, PACKAGING,
CLOTH CONDITION IS INSPECTED AT EACH WORK STATION,
295
NO. 24
-------
FILTER CLOTH TEST CERTIFICATIONS
TEST METHOD
WEIGHT ASTM D1910
THICKNESS ASTM D1777
COUNT * ASTM D1910
PERMEABILITY ASTM D737
TENSILE STRENGTH * ASTM 1682 - METHOD IR-T
MULLEN BURST ASTM D231
MIT FLEX
ORGANIC CONTENT ASTM D578
WATER REPELLANCY ASTM D2721
YARN WEIGHT ASTM D578
YARN TWIST * ASTM D578
MICROSCOPIC EXAM *
* WARP AND FILL
296
SLIDE No. 25
-------
OPERATING CHARACTERISTICS OF A FABRIC FILTER ON A
PEAKING/CYCLING BOILER WITHOUT AUXILIARY
PREHEAT OR REHEAT
By:
Walter Smit - Engineer, Power Production Department
United Power Association
Elk River, Minnesota 55330
Kirk Spitzer - Product Manager, Fabric Filter Systems
Research-Cottrell, Utility Division
Somerville, New Jersey 08876
A fabric filter system has been on-line for one year on a
coal-fired boiler that is primarily a peaking unit within the power
schedule. For the first six months, Eastern Kentucky coal with
2.5 percent sulfur was the fuel source for 30 percent of the time,
with low-sulfur Montana coal constituting the remaining fuel during
the operation period.
Bag life has been excellent with no bag failures reported to
date, and pressure drops have been low. There has never been an
auxiliary heat source to preheat the fabric filter for start-up,
nor to reheat the fabric filter when operating at reduced load
with associated low back-end temperatures.
Conclusions are that the filter cake formed does' protect the
bags from blinding at low load conditions, and a special acid-
resistant finish applied to the glass fibers protects the bags when
high-sulfur coal is burned at low temperatures. Overall, this
installation provides an excellent data base for cycling service
and high-sulfur coal usage with a fabric filter.
297
-------
OPERATING CHARACTERISTICS OF A FABRIC FILTER ON A PEAKING/CYCLING
BOILER WITHOUT AUXILIARY PREHEAT OR REHEAT
THE HISTORY OF ELK RIVER POWER PLANT
In 1951, United Power Association began coal-fired electrical
generation utilizing two stoker-fired units at the Elk River
Station. In 1959, Unit 3 went on-line with a generating capacity
of 25 MW. In 1964, this unit was one of the first turbine generators
in the country to have steam supplied from a nuclear reactor. The
nuclear program proved quite successful but was discontinued in
1968 and the reactor was dismantled in 1971 due to the lack of
economics for such a small unit.
All three units have the capability to burn coal, oil, or
natural gas. From mid-1975, the plant operated on oil or natural
gas in order to meet State and Federal particulate emission limita-
tions. With the impact of rising oil costs in the mid-1970's,
the decision was made in 1976 to switch the plant back to coal-burning
operation. In order to do this, it was necessary to satisfy the
particulate emission limits of the state of Minnesota. After care-
ful evaluation, a fabric filter was selected to be the control
device. Since the station is not a base load plant, it is not
feasible to secure long-term coal commitments. The stoker-fired
units have test-burned refuse, wood chips, sawdust, and tire chips
in combination with coal. Therefore, fuel variations can be quite
broad, and the fabric filter's inherent ability to meet rigid air
pollution standards on a wide variety of fuels was the determining
factor.
In January, 1977, under a specification prepared by Black &
Veatch consulting engineers of Kansas City, Missouri, a contract
was awarded to Research-Cottrell to supply, fabricate, and erect
the baghouse. Research-Cottrell's portion of the contract was
completed in November, 1977, and the resultant general construction
work was completed in May, '1978. On June 2, 1978, the baghouse
facility began operation with the Elk River units burning coal.
GENERAL DESIGN APPROACH
Prior to 1978, the boilers dispersed flue gases into the
atmosphere through three separate stacks; however, a decision was
made to cap the three stacks with a by-pass damper in each stack
and run flue work across the top of the power plant to the rear
of the plant where the baghouse would be installed. Black & Veatch
engineers analyzed the alternatives and determined that a sub-
stantial savings could be gained by installing one baghouse for
the entire plant rather than three smaller units. This system has
indeed been effective and has not caused any particular boiler
problems. The fabric filter was installed and two half-capacity
booster fans purchased to accommodate the additional pressure drop
298
-------
that would be created by the baghouse. A new metal stack was
erected at the rear of the plant to disperse the clean flue gases
into the atmosphere.
The primary fuel source of the plant is low-sulfur, Montana
coal from Colstrip, Montana. However, a 20,000 ton stockpile of
low-sulfur, Kentucky coal will be used as necessary when mine
service or rail deliveries do not meet the requirements. Also,
the plant is derated by approximately 10 MW when burning Montana
coal. Kentucky coal will be burned when the extra generation
needed justifies the premium cost of this coal. Approximately
10,000 tons of Montana coal are retained as inactive reserve.
A listing of the fuels which have been burned to date and
the fuel characteristics are as follows:
1. Montana Coal
Sulfur - 0.90 percent
Moisture - 25.36 percent
Ash - 9.17 percent
Heating value - 8,447 BTU/lb.
2. Eastern Kentucky Coal
Sulfur - 1 to 3 percent
Moisture - 10 percent
Ash - 10 percent
Heating value - 12,500 BTU/lb.
3. Rubber Tire Chips
A test burn of five percent and ten percent tire chips
in combination with coal was conducted in June, 1979.
A complete report will be made available from United
Power Association or the Minnesota Pollution Control
Agency. Preliminary results indicate no problems in
burning tire chips in combination with coal in a stoker-
fired unit. The AP across the baghouse increased
slightly when burning tire chips, which indicates extra
fly ash, or more likely, extra carbon particles from the
tires. The test analysis of the ash will define any
changes in carbon content or size distribution.
It was decided that reverse air cleaning with fiberglass bags
would be utilized. The gas-to-cloth ratios, as presented in Table
1, might seem aggressive if this were a base-load plant. It is
important to point out that the design volumes are at full load,
and since the baghouse operates on a wide range of boiler loads,
it was not required to be overly conservative in the design approach,
299
-------
In reality, the average gas-to-cloth ratios in the gross and net
mode are substantially less than the design numbers as presented.
The construction technique employed for the eight compartment
unit is a modified modular method to increase work in the fabrica-
ting shop and decrease field labor hours. This system approach
proved very economical and even allowed Research-Cottrell to do a
portion of the final field assembly at grade when the support
steel construction was behind schedule. The added benefit of this
approach on this size unit is the additional quality control that
is gained by greater shop fabrication.
The fiberglass bags were supplied by Globe-Albany Filtration
and are their Q78 design. A breakdown of the bag characteristics
are as follows:
Type: Fiberglass with acid-resistant finish.
Specification: Weight - 14 oz./yd.2
Permeability - 35-50
Count - 44 x 24
Weave -3x1 twill
Size - 8" diameter x 264" long
Components supplied with each bag:
Research-Cottrell snap ring to facilitate installation/
replacement.
Banded top with disposable cap.
Four anti-collapse rings.
Advantages: Resistant to acid attack.
Encapsulated fibers.
Superior lubricity for flexing ability.
The precoating of the bags was accomplished by bringing all
three units to full power with the by-pass dampers open and the
flue gases dispersed directly into the atmosphere. The baghouse
damper was opened and one module of the baghouse was then slowly
placed on-line. As each module was coated with fly ash, another
module inlet damper was opened. After all modules were coated,
the by-pass dampers were closed and the flue gases entered the
baghouse.
Subsequent plant operation has required that the pulverized
coal unit be started on oil and then switched to coal. Initially,
the by-pass dampers were opened when operating on oil; however,
this created an emission of black smoke. Therefore, it is necessary
to utilize the baghouse 100 percent of the time. In this case,
300
-------
the ail smoke passes through the filter bags, which have been
cleaned subsequent to the previous shut-down. There has been no
indication of blinding of the bags.
EXPERIENCE TO DATE
Baghouse operation has been extremely satisfactory and reliable
to date. Bag failures have been non-existant. The on-line reli-
ability has been excellent with no unscheduled outages of the boiler
load due to problems with the fabric filter. Since the plant is
subject to frequent cycling and peaking demand loads, the number
of cold starts in the past 13 months has been extensive. Pressure
drop across the unit has been within the design parameters; Figure
1 indicates the drop across the cloth at various boiler loads.
When operating at full design load, the gas volumes have even
exceeded the original design volume and the baghouse is in the
constant cleaning mode. The pressure drop on the flange-to-flange
unit in no case exceeds 8". A Dynatrol opacity monitor is installed
in the stack for a continuous readout. The opacity since start-
up has been essentially zero. During warm weather it is extremely
difficult to ascertain whether the plant is even on the line. In
colder weather there is a slight vapor plume but it dissipates
quite readily and has no visible trail. This has turned out to be
an advantage that we didn't anticipate and affords good community
relations between United Power Association and the local popula-
tion.
Baghouse performance tests were conducted on July 25, 1978,
and the results are shown in Table 2. Since these tests were
conducted very close to the start-up of the unit, and during the
weeks preceeding the tests the unit had not been on-line, we would
expect better results today with a more adequate filter cake on the
bag surface.
During the test, problems were encountered which resulted in
increased air volume across the baghouse. We could only attribute
this to leakage around the module doors, and subsequent discovery
of corrosion on the inside of the door seals proved this to be
correct. We feel the problem has now been corrected. There were
also minor problems with the seals on the poppet damper operators
located on top of the baghouse. This has also been corrected and
is not recurring.
Located just inside the boiler housing adjacent to the baghouse
site is a dryer for the compressed air supply. This proved quite
reliable during the very cold winter months and no freezing problems
of compressed air were experienced in the pneumatic operators
supplied. The piping to the pneumatic operators is not insulated.
301
-------
Subsequent tests have also indicated incomplete combustion of
the stoker-fired units and a rather high carbon carryover to the
baghouse. To date this has not caused any noticeable problems
either due to high pressure drop across the fabric or fires in the
baghouse hoppers. The ash is pulled every eight hours during full
load operation. A breakdown of the ash analysis from the stoker
and pulverized coal units is shown in Table 3 for your review.
FABRIC CONSIDERATIONS AND FABRIC TESTING PROGRAM
Experience with fabric collectors on both industrial and
utility coal-fired units had not been conclusive as to the need
for auxiliary preheat. The specification and fuel variations
contained sulfur as low as 0.3 percent and as high as 2.0 percent.
Figure 2 depicts a preheat system utilizing steam coils and
the reverse air fan system to raise the temperature from ambient
to at least 250°-30Q°F. The cost per year, based upon a 30% load
factor, would be $11,880 pet year for 200 cold starts.
More costly would be a separate reheat system to raise the
temperature at low load conditions from 190°-220°F. to 250°-300°F.
This system as shown in the figure could cost $27,878 per year.
Therefore, the operating cost for both the preheat and reheat
would be $.83/KW. These figures reflect only the cost 'for the
necessary steam consumption, and do not include additional main-
tenance or capital costs.
The ability to operate the system without any auxiliary heat
source offers a substantial savings to us, and simplifies the
operation of the unit.
Research-Cottrell, upon addressing the fuel specification,
proposed and recommended the acid-resistant finish as developed
by Burlington Industries.
Tables 4 and 5 reflect the merits of this finish, as well as
the justification of utilizing 14 oz. fabrics instead of 9 or 10
oz. The following steps explain the tests for the acid cycle:
A. Heat age fabric for specified time at 500°F.
B. Soak fabric in 5.0% Sulfuric Acid at 175°F. for 5 minutes,
C. Place samples (dripping wet) in oven at 450°F. for 5
minutes.
D. Repeat "B" and "C" for a total of 4 cycles.
E. Heat for one hour at 500°F. in oven.
302
-------
The results to date are extremely encouraging. Figure 1
depicts the severity of the operation when partially burning 2
percent sulfur Eastern Kentucky coal. Particularly note that the
system operates at a temperature as low as 190°F. to 220°F. for
sustained periods of time.
Since the bags have the potential for requiring high mainten-
ance, we were concerned about bag life and the ability to operate
the baghouse on such cycling/peaking service. The plant averages
about four (4) cold starts a week for two (2) months in the summer
and four (4) months in the winter. Therefore, in a year's time the
bags have been through the dew point at least 200 times. Upon
the recommendation of Research-Cottrell, the hopper heaters were
left on during all shutdowns. After two or three months of opera-
tion, United Power Association approached Research-Cottrell and
questioned the necessity for continuous operation of the hopper
heaters. Inasmuch as the bag testing program is ongoing, we
agreed to observe the results monthly for undue degradation.
Since October 1978, the heaters have been left on only during
low load conditions and shut down after the plant is taken off the
line and baghouse flyash pulled. No detrimental effects have been
observed to date. The load of the hopper heaters is 112 KW.
For the bag testing program, every few months a bag is re-
moved and sent to a testing laboratory. The major areas to
review are as follows:
Mullen burst
The pressure necessary to rupture a secured fabric
specimen - #/in.2.
Permeability
The ability of gas to pass through the fabric, expressed
in cubic feet of gas per minute per square foot of fabric
with an 0.5" H20 pressure differential.
Count
The number of warp yarns and filling yarns per inch.
Tensile strength
The ability of yarns or fabric to resist breaking by
direct tension. Ultimate breaking strength is expressed
in pounds per inch. (Increase in fabric weight means
increased strength due to greater bulk density which can
be expected to yield longer service life.)
303
-------
Loss of ignition (L.O.I.)
Heat cleaning the fabric to remove the finish, starches,
collected particles, etc., and comparing initial weight
to final weight.
MIT (fold flex endurance test)
Using a Tinius Olsen Folding Endurance Tester, interpal
abrasion is tested by folding a sample through 270°, 180
times per minute. The samples are 5 inches long and 1/2"
wide with a four-pound weight attached to one end. Tests
are performed at room temperature.
A summary of the test report is shown in Table 6.
There has been no significant decrease in the mullen burst
strength. It is important to note that the permeability after
12 months is unchanged. This verifies that the interstices of
the weave have not blinded due to condensation or acid attack.
The tensile strength degradation levels out as expected. (See
Figure 4)
Loss of ignition measurements indicate that the finish is
stable. Since the acid-resistant finish is applied at a minimum
of 4% by weight of the greige goods, the results clearly indicate
its stability.
Probably the most important measurement is flex-to-failure
tests that indicate individual fiber breakdown and fiber-to-fiber
abrasion.
Figures 5 and 6 present curves which clearly show that the
flex cycles have leveled out after one year of service, and bag
life should exceed the two (2) years as predicted by Research-
Cottrell and Globe-Albany.
SUMMARY
After one year of operation, the fabric collector has met and
exceeded design expectations for the Elk River Station. The
ability to bring the boiler on-line, operate at the low load, and
shut down completely on a random schedule is a necessity of this
plant within our power grid. The baghouse's response and reli-
ability for this type of service has been proven, and certainly
gives us confidence to consider the fabric filter for future
requirements. The acid-resistant bags have alleviated our greatest
fear—could the fabric withstand such vigorous service? For fuel
variations with less than 2% sulfur content,, we can speak with con-
fidence that a fabric filter can be applied without the need or
costly maintenance of a preheat system or a reheat system.
304
-------
Table 1.
BOILER AND FABRIC FILTER DESIGN DATA
Unit # Steam Rating
1 135,000 Ib./hr.
2 135,000 lb./hr.
3 235,000 lb./hr.
Boiler Data
Type
Stoker
Stoker
Pulverized Coal
Manufacturer
Springfield
Springfield
Riley
Fabric Filter Design Data
Flue gas volume 255,800 acfm @ 330°F
Inlet dust loading 1.0 to 1.5 grains/ACF
Gas-to-cloth ratio 2.15:1 Gross
2.45:1 Net
Number of bags per compartment 324
Number of compartments 8
Cloth area per compartment 14,904 sq.ft. (actual)
Bag size 8" diameter x 22' long
305
-------
Table 2. PERFORMANCE TEST RESULTS, JULY 25, 1978, BAGHOUSE EMISSION
RATE AND EFFICIENCY
Inlet
Test
Test
Test
1
2
3
Temperature
in OF
330
Flow Rate
in ACFM
262,027
Particulate
Concentration
in grains/ACF
0.9833
Particulate
Emissions
in #/MM 3TU
4.125
Test 1
Test 2*
Test 3
Temp.
in OF.
300
293
290
Outlet
Particulate Particulate
Flow Rate Concentration Emissions Percent
in ACFM in grains/ACF in #/MM BTU Efficiency
274,019
265,038
268,457
0.0039
0.0094
0.0038
0.017
0.040
0.017
99.59
99.03
99.56
*The probe wash contained numerous particles larger in size than one
would expect downstream of a baghouse. Probable cause — particles
collected from the surface of the sampling port or were reintrained
from the duct walls.
306
-------
Table 3. MONTANA COAL - UPA/ELK RIVER STATION
Ash Analysis of February 16, 1979
(at air heater settling hoppers)
1. Unit 2, Stoker-fired
Sample 1 11 Average
Sulfur, % 0.95 0.88 1.02 0.95
Carbon, % 57.33 45.33 50.24 50.97
2. Unit 3, Pulverized coal-fired
Sample
Sulfur, %
Carbon, %
0.49
0.47
0.52
Average
0.49
307
-------
Table 4. COMPARISON OF 9 OZ. VERSUS 14 OZ. GLASS FABRICS
Tensile Strength
Original
MIT Flex
Original
MIT Flex-Acid Cycle
Original
4 hours @ 500°F
Mullen Burst
Yarn
9 oz. 14 oz.
Acid Resistant Finish Acid Resistant Finish
E^LEE Filling Warp Filling
668 x 360
30,598 x 18,846
30,598 x 18,846
10,428 x 3,072
625
37-1/10 x 75-1/3
325 x 185
20,310 x 5,890
20,310 x 5,890
8,012 x 2,456
500
150% x
308
-------
Table 5,
Test
Tensile
Original
7 days
21 days
FINISHES TESTED AT VARIOUS TEMPERATURE LEVELS
YARNS ONLY)
325QF
Acid Teflon B
Resistant @ 10%
360
331
331
267
281
263
4250F
(FILLING
500°F
Acid
Resistant
360
292
223
Teflon B Acid Teflon B
@ 10% Resistant @ 10%
267
253
161
360
267
201
267
121
109
MIT Flex
Original
7 days
21 days
18,846
10,600
10,600
9,826
7,200
3,200
18,846
6,000
7,600
9,826
3,700
1,300
18,846
6,546
4,346
9,826
625
114
MIT Flex
Acid Cycle
Original
4 hours
7 days
21 days
18,846
5,500
7,700
4,600
9,826
6
9
9
18,846
5,600
6,200
1,200
9,826
1
1
2
18,846
3,072
2,243
1,114
9,826
1
1
1
309
-------
Table 6.
UPA TEST REPORT
Weight
Top*
Center*
Bottom*
New
13.5 + .7
Sept., 1978
20.3
21.6
19.7
Jan., 1979 May, 1979
16.9
18.6
18.1
19.6
18.8
21.2
Permeability
Top
Center
Bottom
40-55
46.0
42.0
44.5
50.75
60.25
62.25
51.0
55.0
56.5
Strength
.. (Warp/Fill)
Top
Center
Bottom
668/360
558/283
562/272
581/281
433/235
432/213
423/240
480/195
465/205
455/213
Mullen Burst
Top
Center
Bottom
540-600
525
538
518
645
620
605
520
520
580
M.I.T.
(Warp/Fill)
Top
Center
Bottom
30,598/18,846
4500/1700
2502/1106
3517/880
2779/898
3593/1099
3161/1367
3543/996
PH
Top/Bottom
7 -
4.3
LOI
Top
Center
Bottom
4% minimum
3.7
4.0
3.8
4.5
4.8
4.7
4.8
4.6
4.6
*As reviewed
310
-------
"I
H-
1
01
A P ACROSS CLOTH COMPARING LOW SULFUR WESTERN
COAL TO HIGH SULFUR EASTERN KENTUCKY COAL -
DATA OBTAINED FROM R-C BAGHOUSE INSTALLATION
AT UNITED POWER ASSOCIATION, ELK RIVER,
MINNESOTA.
(D
Ul
(A
5".
a
h
o
•a
fa
O
l-t
O
Ul
M
rr
tr
IT)
P)
H
H-
O
cr
0
H-
I-"
n>
n
O
PI
a
Ul
a
4J
O
O
Ul
o
o
0.
<3
3" .
2" •
1"
Temperature Range
300° to 310°F
Temperature Range
190° to, 290°F
t _ t f A P across
cloth - Eastern Kentucky Coal
with sulfur > 2%.
A P across
cloth - Western Fuel, operating
temperature = 295 to 320 F.
25
50
75
100
125
150
175
200
—I—
225
250
Volume
1,000 acfm
Note:
Data points reflect the average
A P of eight compartments operating
at a specific time.
-------
PRE MEAT FLOW DIAGRAM
ouitcr MANIFOLD
ro
f^. —,—-
IZIlt
f-
,J
t
1
1
1
t
1
no
/
/
t
t
i
INLt
MANlKUtU
7*7=V^
I
!
!
t
S5^
inrjor]
FiiTi.. Fifty
/
/
t
i
|i C7 i TT^^r
*- I'tlClieAf tlOPPtll DAMI*tH V-l'nE HEAT MANIFOLD
W I \V W
*-lQ i.o FAN
Figure 2. Preheat systam.
-------
REHEAT FLOW DIAGRAM
CO
CO
-4
« Eoooiee
A
f
f
I
4
A
I
Figure 3. Reheat system.
-------
o
H
S-l
Hi
eu
en
TI
3
o
3.
700.
600
500
400
300
200
100
(Warp Yarns)
(Filling Yarns)
CD
Z
3
a
a)
-o >
o O
O Z
o
0)
a
>•
a
Figure 4. Tensile strength.
Months
314
-------
30,000
20,000--
o
>1
u
10,000 •-
a
0)
w
O
o
>
o
Months
a:
Cu
01
S
Figure 5. M.I.T. flex-to-failure results (warp yarns).
315
-------
18,000
15,000
-------
OBJECTIVES AND STATUS
OF
FABRIC FILTER PERFORMANCE STUDY
By:
Kenneth L. Ladd, Jr.
Richard Chambers
Sherry Kunka
Southwestern Public Service Company
Box 1261
Amarillo, Texas 79170
Dale Harmon
Industrial Environmental Research Laboratory
Environmental Protection Agency
Research Triangle Park, North Carolina 27711
ABSTRACT
In October 1977, Southwestern Public Service Company executed a con-
tract with the U. S. Environmental Protection Agency that called for a
study to assess the performance of a fabric filter system installed on a
large utility boiler that utilizes low sulfur Western coal. The project
is now into its second year and the objectives of this paper are to de-
scribe the scope and intent of the study, as well as to report progress to
date. In addition, some of the difficulties that we have encountered are
discussed. Although some of these problems have resulted in procedural
changes, the intent of the study has not been altered.
This paper describes work being done in specific areas that both the
EPA and Southwestern are connected with. These include fabric assessment,
data collection, selection and installation of instrumentation, and overall
fabric filter system performance. Results of the first performance test
are also reviewed and the installation of a pilot baghouse is discussed.
This study is being performed under EPA Contract 68-02-2659-
317
-------
OBJECTIVES AND STATUS
OF
FABRIC FILTER PERFORMANCE STUDY
I. INTRODUCTION
Southwestern Public Service Company is an electric utility headquartered
in Amarillo, Texas. The Company has a generating capacity of 2,921,000 kW
and supplies customers in a service area that stretches from the southwest cor-
ner of Kansas through the Oklahoma Panhandle, Texas Panhandle, South Plains of
Texas, and the Pecos Valley region of Eastern New Mexico.
Southwestern Public Service Company is unique as a utility because it
does all architectural and engineering design of its power plants. Through-
out the planning, engineering, and construction of a generating facility,
the structural, electrical, mechanical, and control engineering groups of the
Plant Design Department interact to design efficient power plants. The de-
sign and construction of all Southwestern's transmission and distribution
facilities is also the responsibility of in-house engineers.
Background
Harrington Station, Southwestern Public Service Company's (Southwestern)
first coal-fired plant, went into operation in July 1976, with one 350 MW unit
on line. Plans for the conversion to coal as a primary boiler fuel were begun
in 1970 when Southwestern's management realized that future natural gas sup-
plies could be affected by increasing prices, limited availability, and im-
pending regulations. The search for alternative fuel focused on low sulfur
Western coal. By 1971 the decision to convert to coal as a fuel base had been
made and construction of Harrington Station began in 1974.
Harrington Station is located approximately 3.1 km (5 miles) northeast of
Amarillo, Texas. A second 350 MW unit went on line in 1978, and Unit 3 is
scheduled for completion in 1980.
The basic problem in designing Harrington's second coal-fired unit was
the selection of a particulate emission control system which would satisfy
the Environmental Protection Agency's (EPA) New Source Performance Standards
(NSPS). Southwestern studied the existing alternatives for controlling coal-
fired boiler emissions which would not require scrubbing for particulate removal.
After comparing all parameters (design, operating, maintenance, costs) South-
western wrote a set of specifications and then negotiated a contract for a
fabric filter system (FFS) to be supplied by Wheelabrator-Frye, Inc. (WFI).
Objective of Study
Only a small amount of information on the performance of fabric filters
at other utility installations was available when Southwestern was making its
318
-------
evaluation; therefore, when the EPA indicated its need for utility input on a
comprehensive study of FFS, Southwestern agreed to participate, hoping other
utilities might some day utilize the data to be collected. When the 2-year
study has been completed, the following objectives will have been met:
1. full characterization of the fabric filter system applied at Har-
rington Station, Unit 2;
2. assessment of the technical and economic feasibility of the system;
3. determination of the system's optimum operating condition.
Following the testing phase of the program, operation and maintenance
data will continue to be recorded until 1982 to determine the long-term re-
liability of the system. Special tests will be conducted through the use of
an on-site pilot baghouse.
II. FIRST YEAR EXPERIENCE
Installation of Support System
Prior to start-up of the FFS it was necessary to install certain support
systems for the collection of reliable data. The following systems were
installed.
1. Instrumentation. Instrumentatdon was located so that the best pos-
sible monitoring of the gases entering and leaving the east and west baghouses
could be used to evaluate the performance of these baghouses. Continuous moni-
tors were placed on the stack so that trends could be established by composite
sampling of flue gas conditions coming from both baghouses. It is to be under-
stood that the location of the continuous monitoring devices is far from ideal,
because of the short runs of flue gas duct prior to turns and transitions. The
monitoring devices were located so that the best samples could be obtained
without impeding access to the monitoring equipment.
Specifications for monitoring equipment needed to meet the study's re-
quirements were submitted to bidders in October 1977. A review and evaluation
of bids was completed in November 1977 and Lear Siegler and IKOR were the two
major.vendors selected. The following equipment was purchased:
5 Lear Siegler SM800, S02/N0 Monitors, ,
5 Lear Siegler CM50, Oxygen Analyzer Control Monitors,
1 Lear Siegler Opacity Monitor,
4 IKOR Continuous Particulate Monitors,
2 Ellison Instruments Annubar,
20 Leeds & Northrup Recorders.
In addition, miscellaneous support equipment, thermocouples, and flow
transmitters were purchased and a software program was developed.
Delivery of the equipment began in February 1978 and continued through
April. Mounting, piping, and wiring of the instruments took place in May and
319
-------
June; during July and August 1978, the Lear Siegler monitors were checked out,
started up, and calibrated.
By September 1978 the Lear Siegler equipment was functional and most of
the initial installation problems had been resolved. The equipment (with the
exception of the IKOR particulate monitors) seems to be performing in an ac-
ceptable manner. With proper maintenance the Lear Siegler equipment is expec-
ted to continue to perform with a reasonable degree of reliability and accuracy.
Calibration factors for the IKOR particulate monitors continue to be erratic.
At this time it appears the IKOR particulate instruments may not produce any
meaningful, quantitative data, although they will be left in place for the
purpose of locating bag failures.
A record of each problem is maintained at the plant which indicates the
date and time it occurred, how it was resolved, and when an instrument went
back into service. Strip charts are also filed at the plant after they have
been changed.
2. Datalogging System. One of the objectives of the FFS is to corre-
late manual sampling results with operating data to define the performance of
the FFS; therefore, the parameters listed below are being continuously moni-
tored at five points in the flue gas stream: S02, NOX, 02> particulate, flue
gas flow, temperature, and duct pressure. Additional operating parameters
being measured or calculated on a continuous basis are pressure drop across
the system, power consumption, load on the unit, fuel flow, cleaning mode and
cleaning frequency. This data will not be as specialized as the manual sam-
pling information; its purpose is to represent everyday operation of the FFS.
The FFS programs are executed under the sublevel processor of the Unit 2
computer. The plant computer is a Westinghouse Model W2500, 16 bit, real time
computer with a one million word disc, and 64 k words of core. All contact
and analog inputs from the five sampling stations are recorded by the computer,
which also has access to other performance parameters concerning the plant.
3. EPA Trailer. In order to accommodate the extra equipment and per-
sonnel required for special testing, it was felt a mobile laboratory facility
should be made available for use during the testing phase of the project. The
EPA had a 9.1 m (30-foot) trailer available for the project work and upon
completion of the necessary paper work the trailer was delivered to Harring-
ton Station on May 12, 1978.
After necessary repairs had been made, the mobile lab was parked under-
neath the FFS, north of the control room. This position offers natural pro-
tection from the elements and is also easily accessible from the different
sample locations. The trailer will remain at this location for the duration
of the project.
4. Manual Stack Sampling Equipment and Sampling Sites. A part of the
study is to perform manual sampling of the flue gas materials entering and
leaving the east and west baghouses as well as the composite of the gases
leaving the stack.
320
-------
To accomplish this manual flue gas sampling, ports were designed and in-
stalled in the inlet and outlet of each baghouse. These four sampling points
do not meet the ideal characteristics of static flow for sampling in a duct.
The sampling platform which is on the stack does meet the criteria of stable
flow and also has provided the most consistent results.
As indicated in this paper, efforts to confirm the actual volume of gas
flow through the baghouses, by performing pitot tube traverses on the inlet
to the baghouse, have indicated a wide distribution of flow patterns within the
inlet ducts and these flow patterns vary with changes of load on the unit. It
was important to make the best possible effort to determine inlet and outlet
loadings of the different flue gas constituents. Also, because of the special
sampling problems of both the inlet and outlet ducts, particular consideration
has been given to design and re-design of equipment used to sample these ducts.
Southwestern1s staff at its System Lab designed and built its own manual stack
sampling equipment; for example, the probes for sampling the duct are designed
for vertical sampling instead of horizontal. Because of the velocities in the
duct these probes are designed to prevent whipping and bending.
One effort to prevent breakage of the sampling tube was to utilize an In-
conel liner instead of glass. Problems with the probe heater and condensation
within the Inconel liners indicated this was a bad decision. The old probe
heaters are being replaced with ones of greater dependability and capacity.
Results of the manual stack sampling are included in III A(l).
j^tart-up Experience
Before a start-up plan was formulated for Harrington Station baghouse,
Southwestern felt it was important to seek the advice of start-up personnel
at other utilities which have baghouses in operation. Individuals known to
have experience in the start-up of these systems were consulted. Addition-
ally, a literature survey x^as made and the recommendations of various manu-
facturers were studied and discussed with WFI and EPA representatives.
The following procedures were felt to be necessary to minimize difficul-
ties during start-up:
1. orient operators;
2. check out equipment;
3. avoid dew point and acid point conditions;
4. preheat compartments;
5. condition and precoat the fabric;
6. start up with natural gas through the boiler;
7. change from natural gas to coal with flue gas going through the
baghouse as quickly as possible;
8. designate specific sequence for compartments to be brought on
line;
9. add compartments as load increases;
321
-------
10. monitor required operating parameters during start-up and the
first cleaning sequence, such as inlet and outlet temperatures,
pressure drop, and opacity.
Because Harrington Station Unit 2 was capable of start-up on natural
gas, the FFS was bypassed for several weeks before it was started. With all
compartments isolated from the flue gas, all hopper heaters were energized
for 2 or 3 days prior to start-up in order to help preheat the compartments.
During the start-up, boiler load was maintained at 200 MW with coal as
the primary fuel; only the igniter natural gas was in service. Compartments
1 and 3 were initially brought into service and the first bypass damper on
the west side was closed. Compartments 16 and 18 (east) were then brought
into service and the first bypass damper on the east side was closed. The
elapsed time between the first compartment being brought into service and
the last bypass damper closed was 3 hours and 50 minutes. The effect of
the FFS on opacity can be seen in Figure 1, which shows a significant de-
crease in opacity after the last bypass damper on each side was closed. At
this point the baghouse was completely in service with the fabric being
conditioned.
Approximately 3 weeks after the FFS was initially started, Southwestern
was able to operate Harrington Station Unit 2 at full load with only coal in
service. The unit has operated at loads consistently above 200 MW and during
the peak periods it has handled 350 MW. Figure 2 shows a history of the time
spent at various loads.
Very high APs were observed shortly after start-up; the AP climbed
quickly to 23 cm (9 inches) w.g. at full load. During subsequent months
the full load AP steadily increased until it was in the 25-30 cm (10-12 inches)
w.g. range. Judging from past performance it appears that the AP tends to
level off a month or so after start-up. In the next few weeks, Southwestern
will know what kind of AP will be present following rebagging of the baghouse
(see discussion under B - Fabric Assessment).
Figure 3 is the plot of AP versus air-to-cloth ratio representative of
the performance of both the east and west baghouses until February 1979,
when plugging began in the west baghouse.
Testing
1. Air Flow Tests. The only comprehensive testing to be performed on
the FFS during the first year of operation was an air flow test which was
conducted by Southwestern personnel in October 1978. The primary reason for
measuring the air flow was to see if the high AP across the baghouse was due
to over-design air flow.
During the preliminary testing a large volume of turbulence was encoun-
tered on the inlet, causing the test results to disagree with the air flow
measurements from stoichiometric combustion calculation. This discrepancy
between calculated and measured values prompted a velocity traverse of the
322
-------
START-UP OPACITY RECORD
Figure 1.
323
-------
5000 -
2^00 -
2OOO -
HOURS
ON
LIME
1500-
IOOO-
500-
2855 HK.
35.66%
60UTHWESTERM PUBLIC 5EEVICE Co.
HARRINGTON - UMIT 2
7.91%
1222 HR.
15.37 %
1090
2175 HK
27.36%
251-275 27^-300 501-525 >325
LOAC? CMWH")
LOAD vs. TOTAL TIME
As OF 7-4-79
Figure 2.
324
-------
60UTHWESTERW PU5LIC SEKVICf. Co.
2
IO.O1
8.0 H
AP
in. H20
Cm
6.0-
4.0H
2.0-
s .97695
- .95443
.0 2.0 3.0 4.0
AP vs.Vc
OCT. '78 - MAY '79
Figure 3-
325
-------
stack. The stack was selected because it met criteria specified in EPA Refer-
ence Method 2 ("eight stack diameters downstream from the disturbance"). The
October air flow tests are summarized in Table 1.
2. Corrosion Testing. Southwestern, in its effort to assess the corro-
siveness of the flue gases passing through the FFS at Harrington Station, placed
low carbon steel coupons in the baghouse structure. Each of the 28 compartments
had a coupon just inside the entrance door on the clean air side 2.1 m (7 feet)
from the floor. Inlet and outlet ducts also had a coupon each. All coupons
were insulated from any baghouse structural metal.
The coupons were thoroughly cleaned and weighed before installation. They
were cleaned and weighed when removed in order to determine weight loss, if any.
During the first year of operation, every other coupon was removed after 120
days for corrosion analyses. The remaining coupons were removed after one
year's exposure (including those in the inlet and outlet ducts).
Analyses performed in Southwestern's System Lab revealed only a minor de-
gree of corrosion after one year's exposure. The average corrosion rate was
0.006 mpy. Test results are still preliminary but Southwestern feels corrosion
will not be a serious problem in this particular emission control installation.
3. The First Fabric Assessment Program. One of the goals of the FFS is
to evaluate the performance of different types of fabric filters. This phase
of the study was begun in June 1978, when 34 Acid Flex and 34 Tri-Treat bags
from Fabric Filters were installed in compartment 22. In addition, the fol-
lowing bags were placed in compartment 7 in September 1978:
1 Nomex All-Spun
2 Nomex Combination
5 Crissoflex Style 446
4 Crissoflex Style 449
These bags were supplied to Southwestern by bag manufacturers for evalu-
ation purposes.
The test bags will remain in the compartments for the duration of the
study and periodically some will be removed for testing.
In addition to installation of small groups of test bags within a compart-
ment to evaluate their endurance to the atmosphere and environment, a cleaning
cycle, and potential chemical attack, it was decided that three full compart-
ments should be fitted with test fabrics for evaluation. This decision fol-
lowed after it was determined that there would be a requirement to replace the
bags in the baghouse. The decision as to which bags should be used for replace-
ment would be a matter of evaluation of a number of fabrics.
In January 1979, compartment 21 was filled with W. W. Criswell 0.28 kg (10
ounce) Style 442 Teflon-coated material; compartment 23 was filled with Fabric
Filters' 0.38 kg (13.5 ounce) Style 502, Tri-Treat coated fabric. As the evalu-
ation proceeded it was determined that a change in the shaker mechanism to clean
326
-------
TABLE 1.
AIR FLOW TEST RESULTS
Stack Flue Gas Flow Rate
0 Press. Avg, AP Velocity
02 C02 H20 C Mol. wt. em % cm H20 m/a mz m*/h jn3/h w3/h
Traverse % % % (°P ) Ib/lb mole (in. HK) (in. H'2Q), (ft/sec) (ag.ft) (ACFM*) (ACFM»*) (ACFH***)
SPS
16fl 67.23 2,852 238,0 31,6 2,750,960 2,746.882 2,679.198
w Tube 4.8 14 9.5 (335) 29.05 (26.47) (1,123) (77,99) (339,8) (1,618,212) (1.615,813) (1.575,999)
IN5
WI'I
pjcoc 168 67-23 2.274 237.0 31.6 2,768,232 - 2,696,020
Tube 4.8 14 9.5 (335) 29.05 (26.47) (0.895) (77.79) (339.8) (1,628.372) - (1,5.85,894)
* Corrected to Baghouse inlet conditions 65.18 cm (25.66 inches) Hg ami 174° C (345° F) and 4.55?.:Qk.
** Stoichiometric calculation.
*** Measured at Stack Conditions
-------
the bags, increasing the frequency 50 percent, resulted in noticeable improvement
in fabric performance.
Another compartment of test fabrics was installed in March 1979 (compartment
20) utilizing an experimental all-filament Teflon-coated material. It was hoped
that this type of fabric would have good efficiency and clean readily.
A third part of the fabric filter assessment program for selection of re-
placement fabric and investigation of cleaning mechanism was to review a mobile
baghouse study which had been performed at Harrington Station in 1978, Over and
above a number of difficulties which had to be overcome in operating this mobile
unit, and maintaining general operating procedures, the study provided some inter-
esting information. The general conclusion which could be made from the data col-
lected indicated that Teflon-coated fabrics had a superior performance to the
silicone-graphite coated fabrics in the pilot test compartment. Another inter-
esting note resulting from the first mobile unit operation was that bags operating
in the test compartment in the reverse air mode could not be successfully cleaned.
A second mobile baghouse study was initiated in the spring of 1979 to assist
with the evaluation and selection of alternate fabrics to replace those in the bag-
house which were experiencing accelerated failures. The following types of fabric
were evaluated:
1. Fabric Filters 504-1 Acid Flex.
2. W. W. Criswell 445-04.
3. Menardi-Southern 601-Tuflex Teflon B.
4. Menardi-Southern 601-Tuflex with rings.
5. Fabric Filter 0.38 kg (10 ounce) All-Filament Teflon.
Although the final evaluation report from this second mobile baghouse testing
is not complete, preliminary results indicate that fabric 1 has a better overall
performance, with fabric 5 producing the least desirable results, and all of the
other fabrics tested would be rated in a close middle group.
It is understood that the performance of the first mobile unit study and the
second mobile unit study should be evaluated in the light of operating conditions
and procedures under which the testing was performed. The results of these unit
studies were used by the Company to assess fabric requirements.
A full-scale compartmental fabric testing program was initiated in an effort
to determine overall performance of both durability in the baghouse environment
and efficiency of particulate removal. Details of this fabric assessment are
covered in III B - Fabric Assessment.
III. SECOND YEAR EXPERIENCE
A. Special Testing
A major objective of the Southwestern/EPA contract is to characterize gaseous
and particulate emissions from the FFS. To do this a series of special tests was
328
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scheduled for the second year of the system's operation. Even though it was
Southwestern's intent to accomplish the objectives of the tasks set forth in the
contract, several problems were experienced during the operation of the baghouse
which kept it from being classified as a typical or standard type of air quality
control device.
These problems centered around the control of the cleaning cycle, control
of the deflation pressure during the cleaning cycle, proper tension on the bags
when they were initially installed, a higher than normal bag failure rate, and
some indications that Harrington Station's fly ash had some unique characteris-
tics which made predicting proper design difficult, if not impossible. Programs
were developed to investigate these problem areas and attempt to come up with
solutions.
During the period of investigation, limited testing of flue gas in and out
of the baghouse was performed because the original intent of the research pro-
gram (to investigate performance of the baghouse) was to characterize a typi-
cal operating system; therefore, many of the flue gas test plans and monitoring
of gases in and out of the fabric filter have been delayed until a more typical
type of operation can occur. It is felt at this time that since the rebagging
of the baghouse and adjustment of cleaning cycle (finalized in July 1979) typi-
cal operation should begin in late September or early October.
With this in mind the description below indicates the performance tests
accomplished by Southwestern and GCA to provide useful information.
The time and expense for performing these tests should have value to those
installations experiencing the same difficulties. A review of the measures
taken by Southwestern to correct the situation might be of benefit and assistance.
1. Southwestern's Performance Test. In December 1978 Southwestern per-
formed the first series of tests to measure mass emissions of particulate, sul-
fur dioxides, and oxides of nitrogen. It was originally planned to sample simul-
taneously at five locations; however, procurement problems with equipment pro-
hibited completion of the outlet sampling trains, and Southwestern"s personnel's
first-time effort in flue gas sampling of so many points at the same time, proved
an adverse factor in sampling at all five locations. For particulate and S02
samples it was believed the test would result in better quality data if only
three stations (both inlets and the stack) were sampled. The sampling procedure
for oxides of nitrogen required less manpower and equipment than sampling for SC>2
and particulate; therefore, sampling for NOX was performed at all five locations
(two inlet, two outlet, one stack).
A crew of test personnel from Southwestern's power plants was assembled at
Harrington Station for the first week-long series of tests. Approximately 26
stack sampling team members participated in the test program. By taking samples
at three locations, rather than five, experienced personnel were able to work
with the less experienced ones. As a result, personnel at all the sampling loca-
tions will have some degree of experience during future tests.
The final analyses of Southwestern's particulate, sulfur dioxide, and oxides
329
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of nitrogen samples are presented in Table 2.
The results of the inlet testing compare favorably with the theoretical in-
let grain loading (the theoretical inlet grain loading is estimated and based
upon generation of 80 percent fly ash). The percent fly ash has never been ac-
curately determined but has been estimated to be between 70 percent and 80
percent.
Because of the use of an unheated probe and Inconel liner, additional de-
posits on the filter media gave indication of the suspected high stack grain
loading. As previously mentioned, these conditions have been recognized and
correction is being applied. The stack concentrations should be accurately de-
termined during the next set of tests. The results of the NOx testing tend to
be very consistent across the baghouse. Results of the sulfur dioxide tests
on the stack compare favorably with the stoichiometric calculation for sulfur
dioxide. The reason for the erratic inlet results has been determined and will
be corrected before the second round of special testing.
2. First GCA Special Test. More specialized tests were conducted by GCA
Corporation under subcontract with Southwestern in February 1979. The gas
stream was sampled at five locations (two inlet, two outlet, and one stack)
for particulate, Cy-Cjy organic compounds, Ci-Cg organic compounds, C02, 02j
CO, S02, 203, NOX, and particulate particle size distribution. Baghouse hop-
per ash samples were also collected.
Only preliminary results from the GCA special test are available at this
time. These preliminary results are reviewed in Table 3. At a later time,
when the complete report is received from GCA, the results can be better
addressed. Examination of the information in Table 3 indicates that even
under the best operating conditions at the time of the test, performance of
the baghouse looks favorable, but it cannot consistently fulfill the new EPA
proposed 13 ng/J (0.03 lb/106 Btu) particulate standard. Further examination
and study will be necessary to evaluate the differences and inconsistencies
in the S02 testing Method 6 and 803 Method 8. It is apparent at this time
from the monitoring instruments and the flue gas test that the fabric filter
has no effect on increasing or reducing NOX flue gas stream.
3. j?lans for Future Special Testing. The second series of special tests
to be performed by Southwestern and GCA was initially scheduled for May 1979.
Due to the decision to rebag the FFS (this decision is discussed under Selec-
tion of Replacement Bags), special testing has been tentatively rescheduled
for October 1979. The experience gained in the first series of tests is
expected to enable stack sampling personnel to conduct tests at all five
sample locations as originally specified in the EPA contract.
B. Fabric Assessment
In September 1978 the Harrington Station baghouse began to experience a
higher than normal failure of bags. Examination of the problem indicated that
two items needed immediate attention: (1) the control of the deflation pressure
during the cleaning cycle which, it was believed, contributed to the high
330
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Table 2.
Southwestern Public Service Company
Flue Gas Tests December 1978
RESULTS OF PARTICULATE TESTING
Run
(Number
* 1
* 2
** 3
East Inlet
g/m3
(gr/Scf)
5.22
(2.28)
4.67
(2.04)
3.82
(1.67)
West Inlet
g/m3
(gr/scf)
6.27
(2.74)
5.86
(2.26)
3.73
(1.63)
Theoretical
Inlet + Stack ***
g/m3
(gr/scf)
5.47
(2.39)
5.13
(2.24)
5.93
(2.59)
g/m3
(gr/scf)
0.121
(0.053)
0.115
(0.050)
0.075
(0.033)
ng/J
(lb/106 Btu)
45.2
(0.106)
41.7
(0.097
26.3
(0.061)
* sootblowing continuously
** not sootblowing
*** the concentrations of particulate obtained from the stack are biased high be-
cause of a reaction that took place in the unheated Inconel probe liner.
+ assumes 80 percent fly ash, no consideration for sootblowing
RESULTS OF NOX TESTING
East Inlet
Method 7
Run ng/J
Number (lb/106 Btu)
East Outlet West Inlet West Outlet Stack
Method 7 Method 7 Method 7 Method 7
ng/J ng/J ng/J ng/J
(lb/106 Btu) (lb/106 Btu) (lb/106 Btu) (lb/106 Btu)
1
2
3
290
(0.68)
310
(0.71)
290
(0.67)
280
(0.64)
290
(0.68)
310
(0.71)
260
(0.61)
250
(0.59)
270
(0.62)
270
(0.62)
270
(0.62)
270
(0.62)
270
(0.63)
280
(0.66)
280
(0.64)
(more)
331
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Table 2.
(continued)
Southwestern Public Service Company
Flue Gas Tests December 1978
RESULTS OF S02 TESTING
Run
Number
1
2
3
East Inlet*
Method 6
ng/J
(lb/106 Btu)
230
(0.53)
250
(0.59)
270
(0.62)
West Inlet*
Method 6
ng/J
(lb/106 Btu)
150
(0.36)
140
(0.32)
86
(0.20)
Stoichio-
metric **
ng/J
(lb/106 Btu)
330
(0.76)
360
(0.84)
380
(0.88)
Stack
Method 6
ng/J
(lb/106 Btu)
310
(0.73)
340
(0.78)
360
(0.84)
These concentrations are suspected of being low because of the high
negative pressure pulling the absorbing solutions forward, with the
absorbed S02 not analyzed.
Assumes all sulfur is converted to S02.
332
-------
RESULTS
Run
Number
1
2
3
4
5
6
Table 3
G C A
OF PARTICULATE TESTING EPA METHOD
East
Inlet
g/m3
(gr/scf)
2.36
(1.03)
2.27
(0.99
3.07
(1.34)
5.06
(2.21)
3.50
(1.53)
3.11
(1,36)
West
Inlet
g/m3
(gr/scf)
3.60
(1.57)
3.85
(1.68)
2.75
(1.20)
3.11
(1-36)
2.34
(1.02)
5.40
(2.36)
East
Outlet
g/m3
(f-r/scf)
0.025
(0.011)
OJ016
(0.007)
0.009
(0.004)
0.009
(0.004)
0.002
(0.001)
0.011
(0.005)
5
West
Outlet
g/m3
(gr/scf)
0.044
(0.019)
0.011
(0.005)
0.018
(0.008)
0.016
(0.007)
0.005
(0.002)
0.096
(0.042)
Stack
g/m3
(gr/scf)
ft
*
0.021
(0.009)
0.018
(0.008)
0.027
(0.012)
0.009
(0.004)
0.039
(0.017)
Stack
ng/J
(lb/106Btu)
ft
ft
7.7
( 0.018)
6.9
(0.016)
10.3
(0.024)
3.0
(0.007)
14.6
(0.034)
RESULTS
Run
Number
2
4
6
OF S02 TESTING EPA METHOD
6
East Inlet West Inlet
ng/J ng/J
(lb/106 Btu) (lb/106Btu)
*
*
420
(0.98)
470
(1-10)
350
(0.82)
400
(0.94)
290
(0.68)
East Outlet
ng/J
(lb/106 Btu)
390
(0.91)
340
(0.80)
260
(0.61)
West Outlet
ng/J
(lb/106Btu)
410
(0.95)
*
A
280
(0.64)
Stack
ng/J
(lb/106Btu)
ft
ft
ft
ft
320
(0.74)
* No data this run.
(more)
333
-------
Table 3.
(continued)
RESULTS
Run
Number
2
4
6
OF NOX TESTING
East Inlet
ng/J
(lb/106Btu)
ft
*
240
(0.55)
270
(0.63)
G
EPA METHOD 7
West Inlet
ng/J
(lb/106Btu)
260
(0.60)**
220
(0.52)
210
(0.48)
C A
East Outlet
ng/J
(lb/106Btu)
ft
ft
220
(0.50)
230
(0.53)
West Outlet
ng/J
(lb/106Btu)
300
(0.69)
230
(0.53)
240
(0.55)
Stack
ng/J
(lb/106Btu)
ft
ft
220
(0.51)
200
(0.47)
RESULTS
Run
Number
2
4
6
OF SO 3 TESTING
East Inlet
ppm
0.27
2.07
2.56
EPA METHOD 8
West Inlet
ppm
0.99
0.60
1.81
East Outlet
ppm
0.79
0.67
1.96
West Outlet
ppm
0.72
0.82
1.67
Stack
ppm
1.10
ft
1.86
* No data this run
** Average based on three runs only
334
-------
pressure drop; and (2) tension on the bag.
By October 1978 a program was begun to redesign the deflation pressure
control system and bags had to be re-tensioned.
By January 1979 Southwestern was becoming concerned at the accelerated
rate of bag failures. These failures were of two types; small pinhole type
failures near the bottom cuff, and a few failures described as "blowouts"
where a whole section of the bag would burst and fray "like a flag whipping
in the wind."
To develop an estimation of the bag failure rate to be expected during
the summer the total number of failures found during outages was plotted
versus service time (see Figure 4) and a simple polynomial curve performed.
At this point two approaches were taken to obtain an estimate of total bag
failures expected in six months of service. The first approach was to simply
extrapolate the curve fit polynomial for 6 additional months of service
(see Point II on Figure 4). This approach predicted = 3200 failures. The
second approach was to assume bag failure rate would remain constant at the
present level (after 9 months of service). The curve fit equation was
differentiated and the slope evaluated at 9 months' service. Point I
(see Figure 4) was calculated to be - 2200 failures, using this slope. Based
on this information Southwestern accelerated a second fabric selection pro-
gram to obtain replacement bags and have them ordered and installed by
July 1979. Figure 4 indicates the extrapolated curve of bag failures which
caused Southwestern's major concern.
The first bag assessment program initiated by Southwestern was used as
a guideline to develop the second fabric assessment program. During the
first assessment program bags had been removed periodically from compartments
and laboratory tested (by a consultant). These tests corroborated Southwes-
tern' s concern about an accelerated bag failure rate which would create a
problem during the 1979 summer peak.
After the decision was made to rebag the entire baghouse with new fab-
rics as quickly as possible, additional fabrics were obtained and installed
in certain compartments for short-term testing. As mentioned previously,
the EPA's mobile baghouse unit was rushed to the site and used to make an
accelerated evaluation of available fabrics. Southwestern was restrained
by the availability or delivery of new bags; therefore, selection was
limited. Types of materials used to rebag the baghouse can be noted in
Figure 5 (shown by compartments).
One of the interesting developments of the second EPA mobile baghouse
study was that by adjusting the cleaning cycle and increasing the frequency
of shake, a greater positive effect was noted (more positive than the dif-
ferences between the fabric treatments tested). As a result of this South-
western began to review, again, the theoretical modeling work of Dr. Richard
Dennis.l
As a result of these two things, the decision was made to increase the
335
-------
Total
Bag
Failures
4000.
3000
2000 -
1000 _
5 10
MONTHS OF OPERATION
Extrapolated Estimate of Bag Failure, April 1979.
15
Figure 4.
336
-------
WEST BAGHOUSE
7 1 Nomex
All-Spun;
2Nomex Comb.
5Crisoflex
446;4Criso-
flex449
Menardi-
Southern
Teflon
Test Bags
8
(Warp In)
11
13
10
12
14
EAST BAGHOUSE
15
Vc*
17
**
19 Original
bags equipped
with special
shaker
mechanism
21 Criswell
442 Teflon
B Test Bags
23 Fabric
Filters 502
Tri-Treat
Test Bags
25
Criswell 449
Teflon B
Test Bags
27
**
16
J-.JU
S\ S\
18
**
Fabric 20
Filters
All-filament
Teflon
34 Acid 22
Flex; 34
Tri-Treat
Balance:
Original
Bags
24
Globe-
Albany
Nomex
26
**
28
**
* Criswell 442 Teflon B, 0.30 kg (10.5 oz.) (rebagging complete).
** Criswell 449 Tri-Treat; 0.40 kg (14 oz) (rebagging complete).
*** Balance of Compartment 7: Criswell 442 Teflon B, 0.30 kg (10.5 oz.)
Fabric Installation, July 1979.
Figure 5.
337
-------
frequency of the shake in compartments 21 and 23. The adjustment in fre-
quency of shake was accomplished simply by changing the size of the shaker's
drive mechanism pulley. Data collected on these two compartments, as a re-
sult of increased shake frequency, exhibited lower pressure drop by as much
as 8.9 cm (3.5 in. w.g.) compared to other compartments at full flow on the
baghouse.
At the time of preparation of this paper the increase in frequency of
shake has not resulted in any bag failures. One problem has developed, how-
ever, on those compartments with a high frequency shake and that is the pil-
low blocks holding the shaker mechanism have begun to fail. An engineering
redesign of these pillow blocks has already been initiated and installation
of the reinforced and strengthened pillow blocks will begin soon.
Another item which should be noted about fabric assessment is that in
November 1978 three Nomex bags were installed to determine if this material
could survive the environment of Harrington Station conditions; i.e., low
sulfur fuel and low moisture and acid dew point. After eight months of
operation, examination of the Nomex bags indicates that they are still in
fine condition, though slightly discolored (turning a shade of tan). Based
on this experience, Southwestern has worked with the supplier and ordered
and installed one compartment of treated Nomex as an additional study in
the program of fabric assessment.
In addition, manometer taps were located across the outlet damper on
each of the compartments to record the flow trends as well as the AP of
each test compartment to be measured and monitored. Bags will be removed
at a given interval and sent to an independent laboratory for testing. Ac-
curate records will be maintained on bag failure rates so that at the end
of the 2-year study both performance and bag life data on these fabrics will
have been obtained. Certain special fabrics will also be tested in a full-
scale pilot unit.
The decision to rebag the entire baghouse before July 1979 resulted in
the need for developing a second start-up procedure for the baghouse and to
recondition the newly installed bags. Summer peak loading conditions were
becoming apparent during the period of rebagging (mid-June 1979) and the
availability of bags, on short notice, required that half the baghouse be
rebagged at a time.
To remain within the emission limitations required by the regulatory
agency, the load on Harrington Station Unit 2 was reduced to 150 MW while
one side of the baghouse was being rebagged. Because the west baghouse
exhibited a higher pressure drop problem, it was rebagged first.
The start-up procedure was amended in the belief that the best way to
condition a fabric is not at design air flow but at a lower flow. It was
felt that lower air flows would allow a more porous, permanent matrix to
establish itself over the pores in the fabric than would be possible at the
very high flows Harrington Station's baghouse was designed for (air-to-cloth
ratio = 3:4).
338
-------
Start-up on the new fabric was accomplished by simply putting the re-
bagged unit on line at 150 MW and holding the load until the baghouse had
gone through the cleaning cycle several times. Cleaning at a AP of 12.7 cm
(5 in.) w.g. required in excess of 36 hours to accomplish. The load was then
increased by 50 MW a day until full load (350 MW) operation was achieved.
The west baghouse was rebagged June 16, 1979 and the east on June 20,
1979. At the present time the AP is between 15.2 cm (6.0 in.) and 17.8 cm
(7.0 in.) w.g. at full flow.
IV. SPECIAL CONSIDERATIONS
A. Air Flow
One of the most difficult assessment problems encountered on Unit 2 FSS
is the measurement of gas flow through an individual compartment. As a. re-
sult, operating data on the amount of gas passing through the bags is limited
thereby prohibiting an analysis of potential bag life. As was mentioned
earlier, in an effort to resolve this problem test compartments 19-24 were
instrumented with manometer taps across the outlet damper. During the recent
rebagging outage, four additional manometer taps were placed in the west bag-
house (compartments 5, 6, 7, and 8) across the outlet damper. When the east
baghouse was brought off the line for rebagging, three additional manometer
taps were installed in compartments 25, 26, and 27. These were located ex-
actly like those in the west baghouse.
The purpose of this instrumentation is to get an indication of the flow
rate through the outlet damper. Complicating the problem is the fact that
so far AP readings across the outlet have been in a very low range; i.e.,
1.3 to 2.5 cm (0.5 to 1.0 in.) w.g.; however, it is felt that by continuously
collecting the manometer readings a relative idea of flow through the test
compartments can be ascertained and correlated to filter performance.
B. Pilot Baghouse
The EPA contract included a provision to exercise an option for a pilot
baghouse. The EPA has elected to exercise this option and Southwestern has
agreed to operate and maintain a pilot unit at Harrington Station. The ob-
jectives of this option are (1) to operate the slipstream unit under the same
operating parameters as the full-scale unit, and (2) to determine if perfor-
mance of the slipstream can be scaled and still represent the large operation.
Additionally, optimization of the operating techniques will be determined on
the pilot baghouse and applied to the full-scale unit. Future activities will
include air-to-cloth ratio studies. These study areas have a high priority at
EPA's research facility. Air-to-cloth ranges, in general, will be from 0.5:1
up to 3:1.
Another activity for the test facility will be to investigate the physi-
cal dynamics of fabric filtering for the purpose of determining GCA's mathe-
matical models for the performance and operation of fabric filtering. Later
other studies may examine baghouse operation at dew point, high temperature
339
-------
flue gas operation, and fabric cleaning techniques. Consideration may also
be given to the effect of chemical injection and moisture injection.
The pilot unit is presently being installed at Harrington Station and
start-up is tentatively scheduled for the first of August 1979. The facil-
ity is a WFI Model 366, Series 11.5RS DUSTUBE Dust Collector. It has two
compartments and initially will be fitted with 12 Criswell Style 442 Teflon
fabric filters. The bags will be 29.2 cm (11.5 in.) diameter by 930 cm
(366 in.) long, complete with caps, clamps, and hardware necessary for
installation. Cloth area per compartment will be 51 m2 (549 sq ft ).
V. CONCLUSIONS
One of the most apparent things found over the last year of operating
experience is that there is a great deal yet to be learned about the design,
selection, installation, and operation of fabric filters on large coal-fired
facilities. In addition to the most common specification of air-to-cloth
ratio and type of cleaning mechanism, information should be collected on
physical and chemical ash properties. Pilot studies are needed on the re-
lease of fly ash cake from the fabric, and investigations should be initiated
in the area of re-entrainment of fly ash back into the gas stream.
The concept that fabric filtration is an easy application and can be
simply applied to any size boiler, with any type of inlet load, with any
type of coal and ash products simply by scaling the units to meet the air
flow requirements, is not correct according to Southwestern's experience.
Southwestern feels that fabric filtration is a developing technology
and in time many of these design and operating problems will be resolved.
Fabric filtration will be a demonstrated alternative for particulate con-
trol but until that time there is not justification for using fabric fil-
tration as a control technology for all coal-fired facilities. Those in
the industry and suppliers of such equipment may wish to select filtra-
tion as an alternative, but the exercise of this option should be with
caution.
During the next couple of years Southwestern will continue its pro-
grams to characterize filters at Harrington Station, arid will continue
programs in the assessment and cleaning of fabrics. As this information
is documented, it can be shared with industry, with vendors, and with regu-
latory groups.
340
-------
References
"Filtration Model for Coal Fly Ash with Glass Fabrics," by Richard Dennis
R. W. Cass, D. W. Cooper, R. R. Hall, Vladimir Hatnpl, H. A. Klemm, J. E.
Langley, and R. W. Stern, GCA Corporation, EPA-600/7-77-084 (NTIS No. PB
276 489), August 1977.
341
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START-UP AND INITIAL OPERATIONAL EXPERIENCE
ON A 400,000 ACFM BAGHOUSE
ON CITY OF COLORADO SPRINGS' MARTIN DRAKE UNIT NO.
By:
Ronald L, Ostop
Department of Public Utilities
Colorado Springs, Colorado 80947
John M. Urich, Jr.
Buell Emission Control Division
Lebonan, Pennsylvania 17042
ABSTRACT
A fabric filter baghouse was installed on an 85 MW unit at the City
of Colorado Springs' Martin Drake Power Plant, This baghouse retrofit
was placed on line in September 1978. During the initial operation,
some minor design and operational problems arose. Minor modifications
were made to the baghouse system which eliminated these problems. The
baghouse is experiencing a relatively low operating pressure drop and
continues to maintain zero visible emissions.
34?
-------
START-UP AND INITIAL OPERATIONAL EXPERIENCE
ON A JtOO,000 ACFM BAGHOUSE
ON CITY OF COLORADO SPRINGS' MARTIN DRAKE UNIT NO.
INTRODUCTION
As a result of dwindling natural gas supplies as a source of fuel for
electric generating plants, each successive boiler installation after the late
1950's was designed to burn western, low-sulfur coal. With this switch from a
relatively clean fuel (natural gas) to coal, and with frequent changes in
environmental regulations, the installation of air pollution control equipment
was a necessity.
The Colorado Springs Department of Public Utilities' experience with air
pollution control equipment is associated with installation of a first gener-
ation, cold-side precipitator with a retrofitted, sulfuric acid gas conditioner;
a second generation, retrofitted, oversized, cold-side electrostatic precipi-
tator with a sulfur dioxide gas conditioner; and a hot-side electrostatic pre-
cipitator. Each successive installation incorporated the latest technological
changes dealing with the problem of collecting high resistivity fly ash at a
high altitude and with semi-arid conditions. But, due to changing regulatory
requirements, these units are marginal performers.
Forecasted energy growth demands and replacement of retired generating
units make it a necessity to install additional generating units. Because
the City of Colorado Springs is located in a valley with the Rocky Mountains
in the background, visible emissions are accentuated; therefore, the par-
ticulate control equipment for these new units must not only meet air pollu-
tion regulatory requirements, but must also result in nearly zero visible
em i s s i on s.
As a result of an extensive study to review the status and long-term per-
formance of the "state-of-the-art" of particulate control technology, a deci-
sion was made to purchase and install a fabric filter baghouse collection
system for the new 200 MW, Ray D. Nixon Unit No. 1, which will go on line in
the last quarter of 1979.
Shortly after this decision was made, the Department of Public Utilities
was sited for a violation of Colorado's opacity regulation on its existing
Martin Drake Unit No. 6. Martin Drake Unit No. 6 was equipped with a cold-side
precipitator of 1968 vintage with a sulfuric acid gas conditioner retrofitted
in 1972. Because of the passage of more stringent air pollution control
requirements and the advancement of the "state-of-the-art" in particulate
control for western, low-sulfur coal-fired power plants since 1968, the
decision was made to retrofit Martin Drake Unit No. 6 with a fabric filter
baghouse similar in design to that of Ray D. Nixon Unit No. 1.
343
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In March 1977, the Department of Public Utilities entered into a coopera-
tive contractural agreement with Buell Emission Control Division, Envirotech
Corporation, to perform a research and development product optimization program
to evaluate the design and various materials and operational parameters on a
full-scale, fabric filter baghouse for Martin Drake Unit No. 6. Martin Drake
Unit No. 6 is an 85 megawatt, pulverized-coal utility boiler with a flue gas
volume of ^00,000 ACFM at full load.
The purpose of the research and development program is to develop a cost
effective method of design and operation of a fabric filter collection system
for pulverized-coal utility boilers not only to reduce particulate emissions
to achieve a clear stack, but also to find an alternative to wet scrubbing
techniques for the reduction of sulfur dioxide by injecting calcium and sodium
compounds into the baghouse system. The overall goal is to advance the "state-
of-the-art" of fabric filtration for particulate and gaseous control. The
four major objectives to approach this goal are to: (l) investigate and eval-
uate the theoretical collection mechanisms of fabric filtration; (2) perform
optimization tests on fabric filter systems; (3) investigate the effectiveness
and impacts of sulfur dioxide control in a fabric filter baghouse by first in-
jecting sodium compounds and then injecting calcium and sodium compounds in a
two-stage spray drying process; and (4) develop a performance prediction model
to simulate the fabric filtration process. It is felt that, in order to obtain
maximum benefit from the data to be obtained, the research and development
testing should be done on a full-scale basis. However, since there is a need
to test the most extreme operating conditions which may irreversibly damage
the full-scale unit, a pilot unit will be run in parallel. This pilot unit
will allow for gathering information under the most extreme operating conditions
without compromising the integrity of the entire system to function as an air
pollution control device.
Although the primary objective of this baghouse installation is to conduct
research and development experimentation on fabric filtration systems, the
remainder of this paper will address only the start-up and initial operation of
the particulate collection system.
DESCRIPTION OF THE FABRIC FILTER SYSTEM
Under the scope of responsibilities of this research and development
project, Buell furnished the full-size fabric filter equipment; provided tech-
pical erection supervision, start-up supervision and initial operation advisory
services; and conducted performance testing and research and development program
activities. The City of Colorado Springs' responsibilities were to furnish the
foundations, ash handling system, induced draft fan, hopper enclosures, piping
and wiring, insulation, and auxiliary equipment; erect the fabric filter system;
and operate the unit during testing.
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Figure 1 briefly describes the fabric filter installation. Bascially,
the baghouse was designed to handle 400,000 ACFM of flue gas at 315F with a
particulate inlet grain loading of 5-55 GR/ACF. The Department of Public
Utilities required a design ai r-to'-cloth ratio of 2.0:1 with one compartment
out for cleaning and one compartment out of service for maintenance. The
Utilities also specified the cleaning method to be reverse-air only, thus
requiring anti-col lapse rings in the bags. Buell responded by providing a
twelve-compartment baghouse with 198 bags per compartment for a total of
2376 bags. The bags in each compartment are arranged so as to provide a
three-bag reach with two walkways on the compartment floor and two in the
upper part of the compartment for easy access to the bags. Each bag is
thirty feet, six inches (30'6") in length and twelve inches (12") in dia-
meter with an effective cloth area of 91 ft, per bag. This cloth area does
not include the cuffs at the top and bottom of the seven anti-col lapse rings.
The reverse-air system was designed to provide up to 36,000 ACFM of flow
at a pressure drop of two inches (2") water gauge. A redundant reverse-air
fan was provided as a backup. The reverse-air flow Is controlled by an inlet
louvered damper.
The nominal average pressure drop across the bags, as estimated by Buell,
was determined to be four inches (4") of water gauge, The maximum pressure
drop across the flange-to-flange baghouse was estimated to be six inches (6n)
of water gauge. The guaranteed maximum pressure drop across the system, in-
cluding the breeching to and from the baghouse, is eight inches (8r) of water
gauge. Because Unit No, 6 is a pressurized-boiler unit, an induced draft fan
was installed only to act as a booster fan for the additional pressure drop
resulting from the baghouse operation. This Induced draft fan was designed to
provide 400,000 ACFM of flow, at 315F, at a pressure drop of eight inches (8n)
of water gauge. The induced draft fan is controlled by an inlet louvered
damper.
Each compartment can be individually isolated for inspection or mainten-
ance purposes while the unit is still on line. Each compartment has its own
hopper, inlet poppet valve, outlet poppet valve, reinflation poppet valve, and
reverse-air poppet valve, To isolate a compartment, all valves can be com-
pletely closed by removing the selected compartment from the automatic operating
mode. This electrically isolates the valve actuators from the automatic clean-
ing cycle and closes all poppet valves. A key interlock system is incorporated
into the system so that manual valve blocks must be put into position, which
physically prohibits any poppet valve from opening before a key is made avail-
able to unlock the compartment doors. The two upper doors and two lower doors
are then opened to cool down a compartment before entering,
All inlet, outlet, reverse^air, and reinflation poppet valves and the by
pass damper are pneumatically operated. Each individual poppet valve can be
operated manually at the main control cabinet in the boiler, turbine^generator
control room or at local control stations in the baghouse itself. For any com-
partment to be manually operated, the master compartment control switch must be
put into the manual mode. This will allow operations at either the local
345
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control station or the main control panel. In normal operation, all master
compartment control switches will be placed in the automatic mode. This
places the operation of all compartment poppet valves under the control of
a solid-state programmable, microprocessor control system. The primary pur-
pose of this control system is to initiate and sequence each compartment
through a cleaning cycle, which is initiated through a flange-to-flange
pressure drop signal. This preset pressure drop is 4.5 inches of water gauge.
Therefore, when the pressure drop across the baghouse reaches 4.5 inches of
water gauge, a cleaning cycle is triggered. Each compartment is reversed-air
cleaned for about 20 seconds at a flow rate of 22,000 ACFM (A/C equals 1.22:1)
in sequence from compartment No. 1 through compartment No. 12. The entire
cycle takes approximately fifty-five minutes. The microprocessor will also
trigger a trip-to-bypass if it receives a preset flange-to-flange pressure drop
which has been determined to be too high to maintain the integrity of the
baghouse system. Other safety features include trip-to-bypass functions which
will protect against high or low operating temperatures. The baghouse controls
are also interconnected with the boiler permissive system to provide for safety
under emergency boiler trip conditions.
START-UP OF THE FABRIC FILTER BAGHOUSE SYSTEM
The start-up fuel for Martin Drake Unit No. 6 is natural gas. Because
natural gas is free of particulate and sulfur, and because there is a bypass
on the baghouse system, the decision was made not to pre-coat the fiberglass
bags before initial operation.
The flue gas was allowed to go through the bypass until a stable boiler
operation was established with the flue gas temperature well above the moisture
dew point. Once this stable operating condition was achieved, this warm dry
flue gas was allowed to pass through the compartments by opening certain com-
partment inlet and outlet poppet valves arid closing of the bypass dampers. As
the flue gas flow rate was increased, more compartments were put on line to
maintain a maximum air-to-cloth ratio of 2.0:1. Once all compartments were
put on line, natural gas firing was allowed until the entire baghouse was fully
expanded and allowed to grow to its fullest extent.
On September 15, 1978, one coal mill was put into operation and the first
fly ash laden flue gas entered the baghouse. At that moment, the opacity
surged to approximately 60%. The opacity rapidly decreased so that after
approximately ten minutes, the opacity was down to 20% and after thirty minutes,
the opacity was 10%. After the first twenty-four hours of operation, there
were practically zero visible emissions being emitted from the stack. The
pressure drop during the initial operating stages across the flange-to-flange
was undetectable.
The first cleaning cycle was triggered approximately twenty-four hours
after start-up. A momentary opacity excursion was detected up to apnroxiirately
40% when the first compartment came on line after completing its reverse-air
cleaning. When the succeeding compartments went through this initial cleaning
346
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cycle, momentary opacity excursions also resulted, but declining in intensity
with compartment No. 2 at approximately 10% to compartment No. 12 at \%. Sub-
sequent cleaning cycles show momentary opacity excursions of 10% after the first
week of operation, 5% after the second week of operation, 2% after the third
week of operation, and zero visible emissions after the first month. It should
be noted that these momentary excursions only occurred during that part of the
cleaning cycle when the first two compartments were put back into service after
reverse-air cleaning. At all other times during its operation, there were zero
visible emissions being emitted from the stack.
There was no detectable pressure drop for the first few days of operation.
After three days, the flange-to-flange pressure drop was approximately 1.0 inch
of water gauge following a cleaning cycle. This pressure drop following a
cleaning cycle is presently 3-0 inches of water gauge. The time period from the
end of one cleaning cycle to the beginning of another is approximately two
hours. This is at full load operation with all twelve compartments in service.
INITIAL OPERATIONAL PROBLEMS
The major operational difficulty with the baghouse was associated with the
pneumatic system that operates all the poppet valves. The original system in-
cluded a 10 CFM dryer and the piping served as the compressed air reservoir.
This proved to be too small and too restrictive for the proper operation of the
baghouse. Also, last winter Colorado Springs experienced its coldest season in
decades. As a result, there were many icing problems encountered which in-
hibited proper operation of the baghouse, especially during the cleaning cycle.
To remedy these situations, the air drying system was enlarged to 100 CFM with
added air receiver to maintain a constant pressure of 82 PSI. Also, filters,
lubricators and regulators were installed at every one of the 49 actuators to
insure that clean, lubricated air at a constant pressure would be provided.
Since the installation of this additional equipment, the problems with the
pneumatic system have ceased to occur.
OPERATIONAL COSTS
Since the baghouse has only been on line ten months, it is difficult to
arrive at any annual operational and maintenance costs that will be indicative
of this system. Since start-up, there have been only two bag failures. This
is about 0.084% of the total bags installed. The first bag failure was caused
by a sharp object that cut the bag fibers. This most likely occurred during
an inspection of the baghouse during the annual boiler outage. The second
failure resulted from fly ash escaping from the first bag leak and impinging
on a nearby bag and causing another leak.
The average operating cost seen to date is approximately 0.03 mills/KWH.
CONCLUSION
In conclusion, the Martin Drake Unit No. 6 fabric filter baghouse is a
very successful particulate control system. There are no visible emissions
detectable during any phase of normal operation. Actual test results indicate
347
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collection efficiency in the range of 99.89% to 99-95?, but the emission rates
were constant at about 0.0013 GR/ACF and 0.00^6 pounds per million Btu. The
cause for the different efficiencies is due to the variations in the inlet
grain loadings during the different tests ranging from 1.2 GR/ACF to
2.6 GR/ACF.
Finally, the pressure drop across the baghouse is averaging about 3-75
inches of water gauge. The baghouse will initiate a cleaning cycle at A.5
inches of water gauge and clean down to 3.0 inches of water gauge. The time
*rom the end of one clearing cycle to the beginning of the next cleaning cycle
is approximately two hours.
As a result, the City of Colorado Springs' Department of Public Utilities
feels it has a highly efficient fabric filter system operating at a relatively
low pressure drop.
348
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ENVIROTECH
BUELL:
FABRIC FILTERS
Fly Ash Application
At City of Colorado Springs
Buell structural baghouse (or an 85
megawatt pulverlzed-coal-flred power
boiler at the City of Colorado Springs
Martin Drake Power Plant. Operational
September 1978.
Buell Project Scope
Research and development program.
Complete process and system design engineering
responsibility.
Material supply includes all material from inlet
flange of baghouse to outlet flange of baghouse
with all related operational instruments and
controls.
(Reproduced with permission.)
Design Criteria
Gas volume 400,000 ACFM
Normal gas temp 315°F
Max. allow, temp 550°F
Min. allow temp 250°F
Coalfired,lb/hr 93,400
Coal Analysis
Moisture 13.4%
Ash 15.6%
Sulfur 0.3%
Volatile matter 29.5%
Fixed carbon 40.9%
BTUperlb 9,300
Performance
Inlet Gr/ACF 1.84
Outlet Gr/ACF . . . 0.002(99.89%)
Equipment Specifications
Overall dimensions 174' x38' x84' high
No. of compartments (ea. with hopper) 12
Hoppers, outlet manifold 1/4" A-36 steel
Casing, inlet manifold 3/16" A-36 steel
Bag cleaning method reverse air
Bag material glass fiber with Teflon coating
Bag diameter 12" nominal
Bag length 30'-6"
Air-to-cloth ratios: Gross 1.85:1
Net 2.01:1
Total no. of bags 2,376 (198/compartment)
Electronic controls solid state design
Copyright © 1979 by Envirotech Corporation
349
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REFERENCES
Ronald L. Ostop and Larry A. Thaxton, "Optimization of Material, Design and
Operational Parameters Associated with a Full-Scale 400,000 ACFM Fabric
Filter Baghouse on the City of Colorado Springs' Martin Drake Generating
Unit No. 6," presented before the 40th Annaul Meeting of the American Power
Conference, April 26, 1978, sponsored by the Illinois Institute of Technology.
Chicago, 1978.
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DESIGN, OPERATION, AND PERFORMANCE TESTING OF
CAMEO WO. 1 UNIT FABRIC FILTER
By:
H. G. "Bill" Brines
Public Service Company of Colorado
Denver, Colorado, 80201
ABSTRACT
A Carborundum fabric filter was retrofitted to the Cameo No. 1
unit in 1978. Cameo Station, owned and operated by Public Service
Company of Colorado, is near Grand Junction, Colorado, and No. 1
unit (22 MW) was first placed in service in 1958. The purchase
contract for the fabric filter was written on July 2, 1976, but
due to problems in obtaining an 'emission permit from the State of
Colorado, actual construction did not begin until February, 1978.
The fabric filter, designed with 1.92 gross air to cloth ratio and
reverse air, was placed in service December 18, 1978. This paper
covers the design aspects, construction features, startup
procedures, and acceptance testing.
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DESIGN, OPERATION, AND PERFORMANCE TESTING OF
CAMEO NO. 1 UNIT FABRIC FILTER
INTRODUCTION
Public Service Company of Colorado's (PSCC) Cameo Station is located lU
miles east of Grand Junction on the Colorado River. The No. 1 unit (22 MW)
was placed in service in 1958, and the No. 2 unit (UU MW") was placed in
service in 1963. The No. 1 unit consists of a Babcock & Wilcox integral
boiler, front fired, with 215,000-pounds-per-hour capacity. Steam conditions
are 890 psig and 910° F. The design flue gas flow is 110,500 acfm at 310° F.
The unit was originally designed for either coal or natural gas firing, and
the only air pollution control device was a mechanical dust collector.
In April 1970, the No. 1 unit was committed to gas firing only as a
pollution control measure. Coal was to be used as the fuel only if a system
electrical emergency existed and natural gas was not available. As gas
supplies dwindled and the unit was required to fire coal more and more fre-
quently, it became apparent that either the unit would have to be retired or
a particulate control device would have to be installed to clean the boiler
flue gas.
Coal contracts for Cameo Station were in a state of flux in 197^ and
1975; and, therefore, the long-term coal supply was unknown. The selection
and engineering design of an electrostatic precipitator under this condition
would be very difficult. Also, economic evaluations indicated the cost of a
fabric filter to be nearly equal to the cost of an electrostatic precipitator.
Field trips to Colorado-Ute's Nucla Station in Nucla, Colorado, and to
Pennsylvania Power & Light's Sunbury Station convinced PSCC's operating and
engineering personnel that fabric filters were a viable pollution control
technology, especially when burning low-sulfur western coals. The performance
of each fabric filter installation visited indicated that a clear-stack status
was possible with fabric filter technology.
DESIGN
In mid-1975, a specification for a fabric filter was prepared and was
issued in November 1975- The basic design criteria for the fabric filter as
specified is included in the following table:
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Table 1. FABRIC FILTER SPECIFICATION
Gas Volume/Baghouse - acfxn 170,000
Temperature - °F. 290
Approximate Inlet Loading - gr/acf 0 - H (2-79 calculated)
Outlet Loading - gr/scfd 0.007
AP across Baghouse (2 Compartments Out) (Max.) 7-0
Bag Spacing (Between Bags) 2"
Abrasion Protection Thimbles Above & Below
Tube Sheet
Rings per Bag 5
Bag Reach (to Center of Farthest Bag) 36"
Air/Cloth Gross ) Without Reverse 2.0/1
Air/Cloth Wet Two Compartments Out; Air 2.3/1
The fabric filter cleaning was specified to be by reverse air only. The
above design criteria were to be met while burning coal from three suppliers:
Energy Fuels Corporation, P & M Coal Company, and Cambridge Mining
Corporation. The origin of the coal, therefore, would be either Routt County
or Mesa County, Colorado. The specification did not give analyses from the
various coal suppliers but specified minimum and maximum values. The proxi-
mate analyses were shown in the specification as follows:
Table 2. COAL ANALYSES
Minimum (%) Maximum (%}
a. Moisture k 17
b. Ash U 18
c. Volatile matter 31 36
d. Fixed carbon ^3 51
The ultimate analyses of the above coals were also given as:
a. Hydrogen U 6
b. Carbon 58 68
c. Nitrogen 1 2
d. Oxygen 9 21
e. Sulfur 0.3 0.7
f. Ash U 18
The heating value (as received) was 9»200 Btu minimum; 12,000 Btu maximum.
The specification also listed ash composition and again was on a minimum-
maximum basis.
A new coal supplier has been added since the specification was issued.
The Bear Coal Company is now supplying more than 80 percent of the coal for
Cameo Station. This coal falls within the minimum and maximum values as
listed in the specification.
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A particle-size distribution test was performed, on Cameo No. 1 at the
inlet to the mechanical collector for the specification. The results are
listed in the table below.
Table 3. PARTICLE SIZE DISTRIBUTION
Particle Size
(microns)
l.U
2.35
>K7
7.6
10.5
17.2
20.9
23.3
Percent (%} by Weight Finer Than
Particle Size Shown
3.88
9-06
22.01
33.37
Hli. 62
65.3U
73-80
77-39
FABRIC FILTER SELECTION
The specification was issued to seven bidders. The evaluation of the
five proposals received was based not only on the bid documents but also on
the total evaluated cost, including the estimated annual operating and
maintenance expense. Carborundum was the successful bidder and a purchase ,
contract was issued to them July 2, 1976 to design, supply and erect the
fabric filter on Cameo No. 1 Unit.
The table below lists the actual design parameters of the fabric filter
as supplied by Carborundum:
Table \. FABRIC FILTER DESIGN PARAMETERS
Gas vblume/Baghouse - acfm
Temperature - °F.
Approximate Inlet Loading - gr/acf
Outlet Loading - gr/scfd
&P Across Baghouse (2 Compartments Out)
Compartments - Number
Bags per Compartment
Bag Material
Bag Dimensions
Bag Spacing (Between Bags)
Abrasion Protection
Rings per Bag
Bag Reach (to Center of Farthest Bag)
Tension (pounds)
Air/Cloth Gross ^ Without
Air/Cloth Net One Compartment Out r Reverse
Air/Cloth Net Two Compartments OutJ Air
Fabric Filter Size
Length
Height
width 354
170,000
290
2.79 calculated
0.007
6.2"
8
2UO
Teflon Coated Fiberglass
8" x 22'6"
2"
Thimbles Above & Below
Tube Sheet
5
36"
1*0-60
1.92/1
2.20/1
2.57/1
69'
33'
8"
It"
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A schematic of the general arrangement of the Cameo No. 1 fabric filter
is shown in Figure 1.
The filter "bags as supplied by Carborundum have the following
specification:
Table 5. FILTER BAGS
Manufacturer Carborundum
Fabric Fiberglass
Treatment 10$ DuPont Teflon B
Weave Twill
Count 5U x 30
Yarn
Warp 150 - 1/2
Fill 150 - 2/2
Weight 9-1/2 oz/sq. yd
Permeability 65 - 80 cfm/sq ft
Textured Surface Inside
The fabric filter as supplied by Carborundum has two reverse air fans.
The reverse air fans have a gas-flow capability of 22,000 acfm with a static-
pressure capability of 12 inches of water. The unit is provided with two
bypass poppet-type dampers. All dampers (including inlet, reverse air,
6utlet, and bypass valves) are installed with electric-motor-driven
operators. The control system located at the base of the fabric filter is an
electro-mechanical relay-type control system with complete controls for each
compartment. The cleaning cycle can be initiated by (a) time of day,
(b) total pressure drop across the fabric filter, (c) lapsed time from last
cleaning cycle, and (d) manually. One compartment has an observation port
installed at the lower and upper walkway levels. Although this port helped
to determine the bag movement when the reverse air fan was taken out of
service, PSCC would not install observation ports on other fabric filters.
The fabric filter was not insulated between compartments nor between the
compartments and the inlet and outlet ductwork.
The I.D. fan was tested and found to be sufficient in both flow and
static pressure characteristics; therefore, no fan modifications were
required.
The Company encountered problems when attempting to obtain a permit to
construct. Therefore, the engineering and procurement of the fabric filter
were put on "hold" October lU, 1976. Following eleven (ll) months of
negotiations, a permit to construct was obtained September l6, 1977- On this
same day, Carborundum was authorized to resume engineering on the project.
In February 1978, the engineering was completed and construction of the fabric
filter commenced with the pouring of the foundations. Carborundum moved on
site and started construction in July 1978, and the fabric filter was com-
pleted and placed in operation December 18, 1978.
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CO
en
CTl
MECHANICAL COLLECTOR
(GUTTED)
FIGURE 1
-------
The condenser cooling water for Cameo Station comes from the Grand Canal.
The canal is taken out of service in March and October for maintenance and
inspection. During the canal outage the plant condenser cooling water- is
provided by a spray pond. During the October 1978 outage the Ho. 1 unit was
taken out of service for 27 days to make the required inlet and outlet duct
connections. Blanking plates were installed in the inlet and outlet duct
and the No. 1 unit returned to service on the bypass. The unit was then
taken, off the line for five days to remove the blanking plates prior to the
December 18 start-up date.
The start-up procedure used to place the fabric filter in service was
accomplished as follows: The No. 1 unit was started up on natural gas and
raised to full load capabilities with the bypass poppet valves in the open
position. After attaining an air-heater-outlet temperature of 270° F. , the
bypass poppet valves were closed, and, while still operating on natural gas,
the fabric filter was heated to within 10° of the boiler outlet temperature.
After attaining the desired fabric-filter temperature throughout, which took
approximately six hours, coal was added to the boiler through one of the coal
mills. This mill was then fully loaded, and the natural gas equivalent to
that mill was removed from the boiler. The second mill was then placed in
operation, and the natural gas was completely removed from the boiler. The
differential pressure from the dust loading took approximately 12 hours to
increase to the desired four inches of water pressure. At this time, the
reverse-air fan was started, and the first cleaning cycle was initiated.
After being cleaned the first time, the fabric filter indicated a differential
pressure of approximately one inch. The differential pressure was again
allowed to build up before the next cleaning cycle was initiated, and this
procedure continued, cleaning only as the differential pressure built to
U-l/2 inches of water.
At the end of each cleaning cycle, it was noted that a visible plume
appeared at the stack. It was apparent that the bags were being "overcleaned"
to the extent that dust was penetrating through the fabric. As a result of
this penetration, the decision was made to try cleaning without the reverse-
air fan. All cleaning since the first week of operation has been without the
reverse-air fan in operation. The cleaning cycle presently is based on the
H.5 inches differential, during which a cleaning cycle is initiated, and each
compartment is sequenced through its cleaning cycle. At the end of the
cleaning cycle, the differential pressure is 1-1/2 to 2 inches of water. This
is allowed to build over a period of eight to 10 hours back to U-l/2 inches,
of water, when another cleaning cycle is initiated. The reverse-air fans,
therefore, have not been used since the first week of operation.
The initial two weeks of operation with the fabric filter were followed
by a routine two-month annual outage of the No. 1 unit. During this outage,
a thorough examination of the fabric filter indicated minor leaks through the
retaining clamps that hold the bags on the thimbles. These were tightened as
needed and the compartments vacuum cleaned. After the unit was put back in
service March ^-, 1979, the operating personnel removed one compartment from
service during each graveyard shift to allow for an inspection during the day
shift. The major problem encountered was loose clamps around the cuff of the
bag where it attaches to the thimble. As leaks were found, the clamps were
tightened; and the compartment was vacuumed in order to make the next visual
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inspection easier. The removal of one compartment each night continued for
two months. How, however, this inspection cycle has been increased to once a
month.
Each compartment has two lower access doors and two upper access doors.
Air leakage at the door seals was noted by rust indications on the inside of
the door facings. An ultrasonic leak detector was used to determine exactly
where the leaks were, and hinge adjustments were made until these leaks were
eliminated. Wo other noticeable maintenance problems or leaks have been
encountered in the four months since the return to service.
PERFORMANCE CRITERIA AND ACCEPTANCE TESTING
The guaranteed performance stipulated in the specification states that
the fabric filter shall remove the particulate emission from the Company's
steam generator to a maximum of seven-thousandths grain per standard cubic
foot (0.007 gr/scf) of flue gas measured at the fabric filter outlet on a dry
basis under the following simultaneous conditions: (a) handling actual gas
volumes over the entire range of the steam generator operation, (b) burning
coal with a maximum of 18 percent ash, (c) handling ash in the ash hoppers,
(.d) isolating any one compartment of the baghouse in a cleaning cycle,
(e) isolating any other compartment for maintenance, and (f) blowing soot in
the boiler or air heater.
The conformance test (EPA Method 5) was used to determine the actual
acceptance of the fabric filter. This test was conducted within 180 days
after completion of the fabric filter. Conformance testing was done, but,
since one test was more than 0.007 gr/scf, the conformance testing was
repeated. Carborundum was asked to optimize the operation of the fabric
filter and to check for any bypass leakage or other problems that might cause
nonconformance. Welding beads were found on the bypass poppet valve, and
minor leakage was occurring. An unwelded seam separating the inlet from the
outlet duct also was found and repaired. The second set of conformance tests
was completed June 5 and 6. The average outlet grain loading of these tests
was 0.0053 gr/scfd. The fabric filter has now been accepted by PSCC as
having met the performance criteria of the purchase contract.
An Environmental Data Corporation performance monitor is installed in
the stack on Cameo No. 1 unit. This instrument which monitors opacity, NOX,
SOX, and percent excess oxygen, was transferred to Cameo from PSCC's Comanc'he
Station near Pueblo. The opacity presently is reading 2 to k percent. Only
the opacity monitor is required by regulation; however, PSCC and EPRI
presently are engineering a dry alkali injection system. The Company will
conduct a series of tests to evaluate the capability of nahcolite, trona,
and/or sodium bicarbonate in this system as a sulfur dioxide removal
mechanism. The tests are to be conducted the latter part of this year.
Public Service Company of Colorado is to date very pleased with the
operation of the Carborundum fabric filter on the Cameo No. 1 unit. The unit
has been operating with a clear stack since the fabric filter went into
operation. Because of this, PSCC has installed a fabric filter at its
Arapahoe Station in Denver and is engineering such filters at two other coal-
fired stations.
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EXPERIENCE AT COOR3 WITH FABRIC FILTERS
FIRING PULVERIZED WESTERN GOAL
By:
Galen L, Pearson
Aciolph COOPS Company
Golden, Colorado 80l[.01
JIBSTRAGT
Coors has been using a fabric filter unit since December,
1976, to control emissions from the Boiler No. ii pulverized coal
fired unit, rated at 250,000 Ibs./hr. steam.
Pressure drop, bag life, etc,, on this shake-deflate 8 module
filter is presented. Data from emission tests is reviewed and
discussed.
The low pressure pulse-jet type fabric filter being installed
on the new Boiler No. 5 is discussed briefly. This 12 module
unit is designed for 320,000 ACFM and an air to cloth ratio of
5.5 to 1.
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EXPERIENCE AT COORS WITH FABRIC FILTERS -
FIRING PULVERIZED WESTERN COAL
INTRODUCTION
Based on energy availability and on cost projections, Coors
made the decision in 197^ to install coal firing capability on
the Boiler No. h. unit which was under construction at that time.
Electrostatic precipitators, scrubbers, and fabric filters were
evaluated carefully for emission control devices. The fabric
filter approach was ultimately selected because it was felt that
it would do the best on a continuous basis of removing particu-
late and achieving a low opacity stack. The fabric filter unit
selected went into service in December, 1976, and has been opera-
ting successfully for the last 2 1/2 years.
EQUIPMENT DESCRIPTION
Boiler No. i|.
The 2pO,000 Ib./hr. steam generator is a tangentially fired
pulverized Combustion Engineering, Inc. VU-lj.0 unit. Pulverization
of the coal is accomplished by two Raymond RB-573 bowl mills. At
the rear of the boiler, flue gas is cooled to approximately 3^4-0 F
by a fin tube boiler feedwater economizer. 'There is no combustion
air preheater in the normal sense on this unit.
The basic arrangement of the baghouse, boiler, baghouse by-
pass, I.D. fan, etc., is illustrated by the schematic of Figure 1.
Fabric Filter
The fabric filter or baghouse on the Boiler No. Lj. unit is a
VJheelabrator-Frye, Inc. shake-deflate cleaning type unit and
operates at a typical flue gas volume of 170,000 ACFM at 3i|0° F
when the boiler is at rated load. The baghouse has 8 compartments
with ISO bags per compartment for a total of l,ijlj.O bags. The bags
are 8 inches in diameter and 22 feet long and do not have rings.
(The total filter area is 66,2l<-0 square feet.) The fabric
description is as follows:
360
-------
FIGURE 1
BAGHOUSE -
BOILER
SCHEMATIC
REVERSE
AIR FAN
180 BAGS PER
COMPARTMENT
1440 BAGS TOTAL
66,240 SQ. FT.
FILTER AREA
TO STACK
CONTROLLER
BOILER NO. 4
250,000 LB/HR STEAM
PULVERIZED
TANGENTIALLY
FIRED
ECONOMIZER
-------
Material Woven Glass
Finish Silicon Graphite
Weave 3x1 KMT
Thread Count 66 x 30
Permeability (new) h$ - 65
Weight 10.5 oz./sq. yd.
Initially, one compartment of W. H. Criswell's Teflon B
finished bags and one compartment of Cris~0-Flex finished bags
were installed. These were removed after a few months of opera-
tion when it was discovered that the inservice permeability was
much lower than with the silicon graphite finished bags.
Each compartment has a 36" diameter manually operated butter-
fly valve at the inlet, a \\2" diameter cylinder operated poppet
valve at the outlet, and a 20" diameter cylinder operated butter-
fly valve for reverse air. The single reverse air fan has a paral-
lel blade damper (20" x 21}.") with an automatic controller on it
set to accomplish a reverse AP across the bags of at least 0.5
inches W.G. but not more than 1.0 inches W.G. during the reverse
air mode of the cleaning cycle. The automatic controller was not
added to the damper until July, 1977.
Bags are located on 9" centers with a three bag reach from
the one foot wide internal walkways. The access door to the bot-
tom elevation is 21}." x 60" and the access door to the up-oer eleva-
tion is 20" x ij.8".
The wall between compartments is insulated as well as all
external areas of compartments, hoppers, and ducts. Bach bottom
hopper has a series of plate type thermostat controlled heaters
1.5.6 KW per hopper).
The cleaning cycle used on this unit is shown graphicall:/ by
Figure 2. The baghouse is cleaned only as necessary when the AP
rises to the designated setpoint for cleaning. When a clean mode
is initiated, all eight compartments are cleaned one at a time in
the sequence of 1, 2, 3, h., 5, 6, 7, and 8. It takes 3 minutes
per compartment, or 2lj. minutes total, to get through all eight
compartments.
PRESSURE DROP CHARACTERISTIC
The pressure drop across the baghouse has been found to be
dependent upon the boiler steaming rate, type of coal being burned,
quality of boiler operation, and quality of baghouse operation.
In general, experience has shown that the typical operating pres-
sure drop for this unit is as illustrated bj the shaded area of
Figure 3. Roughly one inch of this total baghouse pressure drop
can probably be attributed to inlet valve, outlet valve, and duct
362
-------
Figure 2
BAG CLEAN CYCLE SEQUENCE
BOILER NO. 4 BAG HOUSE
(8 MODULES TOTAL CLEAN TIME = 24 MIN.)
cr:
< )
11]
ex:
<— ) O
OUTLET CLOSE (5 SEC)
SETTLE (10 SEC)
LiJ
, §
LU
0 C) 0
1 1
n <£O ^VN^
REVERSE AIR HOLD (15 SEC) |
(2 SEC) ^X"
SETTLE (20 SEC) I
<_j
SHAKE (10 SEC)
LU
SETTLE (65 SEC) 1
(9 SFH
j
BAG REINFLATION (10 SEC) i
CD
(6 SEC)
PAUSE TO NEXT MODULE (30 SEC) &
c
C_)
fe
C_J
i
O
1
<_)
LL
CX
^^^^
i 1
363
-------
FIGURE 3 BOILER NO. 4 BAGHOUSE
CHARACTERISTIC
00 .
01 }
o
:n
cr
CQ
o_
<]
7
6
3
z
0
OPERATION ABOVE THIS LINE IS GENERALLY
THE RESULT OF INADEQUATE CLEANING
OPERATION BELOW THIS LINE (ALTHOUGH POSSIBLE)
GENERALLY INCREASES EMISSIONS AND CAN DECREASE
BAG LIFE THROUGH EXCESSIVE CLEANING
1 r
000
BOILER STEAM OUTPUT
(\B/HR)
-------
losses at the rated boiler load condition. Operation below the
lower line of Figure 3, although possible, generally causes in-
creased emissions and can- possibly decrease bag life through
excessive cleaning. Operation above the upper line in Figure 3
is not very desirable from a power consumption standpoint. In
addition, if the filter cake is built up fairly heavy, a condi-
tion develops where bag cleaning can not be accomplished adequately
without reducing boiler load.
Several different types of western coal have been used to
fire Boiler !To. i|. Four of these coals and their basic properties
are listed in Figure [;. In general, the low BTU, high moisture
coals tend to increase baghouse pressure drop. Also, the higher
the ash content in the coal, the higher the baghouse pressure
drop. VJhen the high BTTJ, low ash coals (like Coal C) are burned,
there is considerable time when the baghouse is not in a clean
mode of operation.
BAG REPLACEMENT INFORMATION
The recorded data on the number of bags replaced per month
for each compartment is illustrated in Figure 5 £or the time period
from February, 19?8, through June, 1979. Unfortunately, no data
was recorded by operating personnel concerning the bags replaced
due to failure prior to February, 1978. Personnel involved in
replacing bags during the llj. month period from December 1, 1976,
through January, 1978, estimate from memory that somewhere in the
range of 200 to 300 bags x^ere replaced during this period due to
failure for one cause or another.
Originally, compartment #6 had Gris-0-Flex bags and compart-
ment -ffl had Teflon B finish bags, both manufactured by W. W.
Griswell. Due to pressure drop considerations, these bags were
replaced with Silicon G-raphite finish bags in July, 1977, and
longer J support hooks were installed in these two compartments.
These longer J hooks developed a top of bag total horizontal
throw of 3.2inches during shake instead of the original 1.9^i
shake throw which is still used on compartments #1, ;,-2, #3,
~5, and ;f8. The bags installed in compartments -j',-6 and -^7
July, 1977, were too long and were cuffed over. It is suspected
that this cuff slipped, eliminating bag tension. The loss of
tension, combined with longer than necessary bag shaking during
certain tests, probably caused the high bag failure rate in May
and June of 197&.
New bags of the proper length for the longer J hooks were
installed in compartments ri-'6 and ;/7 in August, 1978. To develop
comparative data between long and short J hooks, the bags in the
adjacent (mirror image) compartments ;^2 and ^3 were replaced at
the same time. Since _August, ;1978, there have been no bag fail-
ures in compartments £6, ir7> Jr2, or ;~3.
365
-------
FIGURE 4
VARIOUS WESTERN COALS WHICH HAVE BEEN USED
Heating Value (BTU per LB)
Moisture Content (%)
Sulfur Content (%)
Ash Content (%)
I
Ash (Lb Per Million BTU)
& P Baghouse (inches W.G.)
(at 250,000 Ib/hr steam)
COAL A
8,600
26
.5
9
10.5
9.0
COAL B
10,700
9
.9
11
10.3
7.3
COAL C
12,500
7
.5
7
5.6
5.3
COAL D
11,100
8
.5
10
9.0
6.0
366
-------
Figure 5
CO
cr>
BAG FAILURE RATE PER mm - SINCE FEB. 1978
BOILER NO, *J BAGHOUSE - START UP DATE DEC, L 1976
COMP, //I
COMP, #2
COMP, #3
CQ'IP, m
COMP, #>
COMP, #6
CQH3 #7
COMPOS
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MOTES: 1) NO BAG FAILURE RECORDS WERE KEPT PRIOR TO FEB., 1978
2) LONGER J HOOKS WERE INSTALJfD IN COMPS, #6 AND #7 IN JULY 1977, THESE COMPARTMENTS
STILL HAVE THE LONG J HOOKS,
-------
The original bags in compartments .v'h. and 7-8 were replaced in
March, 1979, after approximately 26 months of service. The bags
in compartment ;/^ were replaced on April 30, 1979, after approxi-
mately 27 months in service.
In summary, it is felt that a major portion of the bag fail-
ures were caused over a period of time by a combination of high
flue gas flow rates, excessive bag shaking at times, and improper
operation of the reverse air fan control damper.
.•Jith these items corrected and proper operation in the
future, it is felt that it is reasonable to expect between 2 and
3 years of bag life and possibly more.
EMISSION TESTS
Emission tests measuring the amount of particulate in the
stack gas were conducted June 7, 8, and 9 of 1977, and the results
are presented in Figures 6 and 7. One set of test data (Figure 6)
was obtained by the Coors Spectro-Chemical Laboratory (Ref. 1)
using EPA Reference Method No. 5. The second set of test data
(Figure 7) was gathered on the same days at about the same time
by York Research Corporation (Ref. 2) under an EPA contract using
a modified form of EPA Reference Method No. 17.
The results tend to vary somewhat between tests 7!, ,r2, and
-,r3 in both data tables. However, the composite average of the
three tests compare closely between the Coors Sprectro-Chemical
Laboratory data and the EPA-York Research data if only the
G-rains/SCFD, G-rains/ACP, and LB./MR. data is compared. It appears
that an unrealistically high BTU input number x/as used in calcu-
lating the Ib./million BTU ratio in the EPA-York Research Corpora-
tion Report (Ref. 2).
It is of importance to note, however, that all data points
were less than the Federal and Colorado limit of 0.1 Ib./million
BTU.
During these tests the air to cloth ratio was 2.7 when all
eight compartments were on line and 3.1 when one compartment was
in a clean mode. Baghouse pressure drop outlet plenum to inlet
plenum was 9 inches V/.G., typically at the 3.1 air to cloth ratio.
Coal A, defined earlier, was used during these tests.
A continuous opacity monitor has been installed in the stack
flue gas stream (Lear Siegler RM-kl). Opacity ranges between 2>
and 5/3 but it is less than J>% most of the time. Generally speak-
ing, there is no visible plume from the stack on this unit and we
are pleased that the fabric filter has performed very well.
368
-------
FIGURE 6
EMISSION TESTS - BOILER NO. 4
DATA BY COORS SPECTRO-CHEMICAL LABORATORY
(Using EPA Reference Method No. 5)
Participate
Emissions
Grains/SCFD
Grains/ACF
LB/HR
IB/Million BTU
Test #1
6/7/77
0.03465
0.01654
25.00
0.0714
Test #2
6/8/77
0.01883
0.00902
14.02
0.0401
Test #3 •
6/9/77
0.01085
0.00521
7.90
0.0226
Average
3 Tests
!
0.02144
i
0.01025
15.64
0.0447
NOTE: 40 Sample points of 3 minute duration each were taken for each
test.
FIGURE 7
EMISSION TESTS - BOILER NO. 4
DATA BY EPA AND YORK RESEARCH CORPORATION
(Using the total of in-stack + out of stack by a modified EPA Reference
Method No. 17)
Particulate
Emissions
Grains/SCFD
Grains/ACF
!
LB/HR
LB/Million BTU
Test #1
6/7/77
0.01931
0.00918
14.21
0.0336
Test #2
6/8/77
0.01774
0.00852
13.21
0.0316
Test #3
6/9/77
0.02470
0.01178
20.60
0.0428
Average
3 Tests
0.0206
0.00983
16.01
0.0360
NOTE: 32 Sample points of 4 minute duration each were taken for each
test.
369
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FUTURE PLANS - BOILER HO. 5
A new pulverized coal fired boiler with a generating capacity
of 11-50,000 Ib./hr. is currently under construction and scheduled
for start-up in November or December of 1979. Careful considera-
tion was given to the alternatives of purchasing a reverse air
unit, purchasing a shake-deflate unit, designing and building a
reverse air unit, and purchasing a low pressure pulse-jet type
unit. The low pressure pulse-jet type unit offered by CSA Carter-
Day of Minneapolis, Minnesota was selected based on considerations
of overall lower initial capital cost and system simplicity and
reliability.
The 12 modules for this fabric filter system have been
delivered and field installation is progressing on schedule.
Figure 8 lists the significant information concerning this
fabric filter system and Boiler No. 5.
REFERENCES
1. Coors Spectro-Chemical Laboratory Report ITo. 91353.
Compliance Tests Report for Adolph Coors Company Power
Plant, Boiler No. Lj.~. Coors Spectro-Chemical Laboratory,
P.O. Box 500, Golden, Colorado 80li01. July 7, 1977.
2. Emission Tests at Adolph Coors- Company No. Ij. Coal-Fired
Steam Generator. Report No. 77-SPP-17. Prepared by York
Research Corporation for U.S. Ifoviromaental Protection
Agency under" Contract No. 68-02-lliOl. Task No. 33. "KIC No,
7-8/J.79-33. July 26, 1977.
370
-------
FIGURE 8
BOILER NO. 5 BAGHOUSE UNIT - UNDER CONSTRUCTION
A. Baghouse Information
Manufacture: CEA-Carter Day
Model No.: 376RF10 (High Temperature)
Number of Modules: 12 circular configuration
Number of Bags: 376 per module
4512 bags total
Design Flue Gas Flow: 320,000 ACFM at boiler M.C.R.
Total Filter Area: 57,600 Sq. Ft. (4800 Sq. Ft. per module)
Air to Cloth Ratio: 5.5 (with 12 modules)
6.0 (with 11 modules)
Bag Size: Oval pattern 15.3 inch perimeter by 10 feet long
Bag Material: 22 ounce felted "Daytex" (a Carter-Day felted media)
Cleaning Method: Periodic on-line reverse air pulses from a storage tank
charged at 7.5 PSI6. Each module has its own self-
contained compressor-blower to charge this tank.
System Dampers: Any module can be isolated for maintenance while the
boiler and other modules are in service. All modules
can be bypassed via two 60 inch diameter poppet bypass
valves during start-up or boiler oil firing.
Anticipated Pressure Drop: 3 to 6 inches W.G.
Scheduled Start-Up: November or December, 1979
B. Boiler Information
Manufacture: Combustion Engineering
Type: Model VU-40 tangentially pulverized coal fired with three coal
levels being fed by three Raymond RB-613 pulverizers. Unit will
be operated balanced draft at a minus 1/2 inch W.G.
Economizer: Unit has a boiler feedwater economizer which will lower the
flue gas temperature to less than 360°F.
Steam Rating: 450,000 Ib/hr at 825 PSIG and 850°F
Back Up Fuel: No. 2 fuel oil
Steam Use: Steam produced from this and other units at the plant is or
will be used for process heat requirements, electrical power
generation, and numerous steam turbine mechanical drives.
371
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FABRIC FILTER EXPERIENCE AT WAYNESBORO
BY:
W. R. Marcotte
E.I. du Pont de Nemours & Company, Inc.
Waynesboro, Virginia 22980
ABSTRACT
The paper describes a reverse flow fabric filter installed to
i^aridle the flue gases from four pulverized coal and oil fired boilers.
The unit contains many unique design features which assist with full
time operation. Start up was by procedures designed to minimize gas
condensation and other undesirable occurrences.
The unit has been on the line for 18 months. Operation has been
good with pressure drop varying between 3" and 6" and cleaning frequency
varying between 12 hours and continuous. Some few bags have been damaged
due to sulfuric acid condensation resulting from maloperation and water
leaks. Several operating incidents will be discussed. #6 fuel oil is
sometimes burned with the coal.
372
-------
When the Clean Air Act Admendents were passed in 1970, all Waynesboro
boilers were fired with coal. Since No. 6 fuel oil was plentiful and
reasonably priced, investment monies necessary to equip Waynesboro to burn
oil were authorized. The compliance plan accepted by the State was to be
100% oil fired by the end of 1974. In 1973 the Federal Energy Allocation
Act restricted the use of oil as a power generation fuel. A review of the
situation considering the quadrupled price of oil and our dependence on it
for chemical feed stocks caused us to evaluate available technology to per-
mit burning coal and still meet the Virginia State Implementation Plan of
0.18# particulate/MM BTU input for our plant. Electrostatic precipitators
were ruled out due to:
• Modular design not being available.
• Unacceptable roof loading requiring a cold end location.
• The low sulphur content in the coal we use.
The baghouse route was selected and while basic concept designs and
project strategy were being developed we evaluated the two alternates -
pulse jet and reverse air cleaning. The reverse air cleaning type was
selected and authorization to proceed obtained. Rowan Perkins has pre-
sented a paper on the considerations used in selecting our baghouse.
The full size Waynesboro installation is shown as a single filter in
Slide ^//l manifolded to handle gases supplied by four boilers. Each boiler
has a bypass directly to the stack. Under normal operation the individual
boiler induced draft fans pull the gases from each boiler and discharge them
to the baghouse inlet breeching. The booster fans maintain the 2" suction
at the filter inlet and overcome the resistance of the filter, discharging
gases to the stack breeching. Although we were reluctant to try rapid by-
passing of a boiler unnecessarily, circumstances have caused such bypasses
and the system has worked very successfully - several times. There were no
disturbances of individual boiler controls.
Slide #2 is a "before" picture of the Waynesboro Powerhouse. The left
hand stack is handling the coal burning boilers. The baghouse is under con-
struction on the right. Neil Zittere was the Design Project Engineer and
deserves a great deal of credit for the nice looking and nice operating
unit. Slide #3 is a picture of the completed installation in operation.
The same stack is still operating but you can see nothing. This unit was
started up September 30, 1977.
The elimination of the smoke is a result of a program which took 3
years to Define, Construct and Start up this baghouse and its auxiliaries.
SPECIFICATIONS
The filter is 50' wide, 100' long and 70' high. The system was de-
signed to handle 340,000 acfm of flue gas to clean the fly ash remaining
in the flue gas after individual high efficiency mechanical collectors
373
-------
Specifications are as follows:
2
• air to cloth ratio is 2:1 cfm/ft of filter surface with 2 modules out
of service.
i operating temperature is normally 340 QF with 415°F max.
9 16 modules with 256 bags per module for a total of 4096 bags.
* bags are 8" diameter by 22" long with 5 anit-collapse rings.
f 9.5 oz fiberglass material with a Teflon® B filter fabric finish
(Slide #4)
• filter to operate under suction.
The flue gas to be cleaned comes from 4 water tube pulverized coal
fired boilers with a total capacity around 600M/hr of steam. The coal
we are burning is approximately 15% ash. At rated load this is 66 tons
per day. At present steam loads, the new baghouse collects 7 tons/day
while the remainder is split between furnace ash and that removed by our
mechanical separators.
At Waynesboro we added extra instrumentation to find out more about
fabric filter operation. Normal installations have manometers for measuring
pressure drop across each module. We have added a pitot tube fixed in the
outlet of each module to indicate relative flow. (Slide #5) We wanted to
check the assumptions made on module performance as a result of differential
pressure only. Already we have seen some indications that previous
assumptions are not 100% valid. However, the individual single pitot
measurement is not as accurate as desired. Further study will provide
better means to analyze fabric filter performance. We are also equipped
to test outlet dust loading of each module. All modules are equipped with
sight ports to inspect for ash from loose or damaged bags and to observe
bag cleaning. (Slide #6)
START-UP SEQUENCE
Having selected the type of baghouse with extreme care and evaluation,
we recognized that our goal consisted of 3 major items.
* A good smooth start up.
• Continuous operation firing coal, oil or a combination.
• Low maintenance and long bag life.
We spent considerable time in the development of a start up pro-
cedure under the guidance of Rowan Perkins , Niel Zittere and both
vendors, Western Precipitation (Baghouse) and Minardi Southern (bags) .
Preliminary check out of individual pieces of equipment and systems took
about 2 weeks. (See Appendix 1 for problems.)
374
-------
START-UP WEEK
The first day was a final meeting within Du Pont among Operations,
Engineering Design and Power specialist group. This included a step by
step review of our start up sequence and final modifications to adjust
for the actual operating configuration of the Powerhouse, physical
verification of actual conditions throughout the system and final adjust-
ments of controls.
The second day finished the verification of baghouse conditions and
included a meeting with the baghouse and bag vendors to review their con-
cerns. One of them was the looseness of the bags which indicated a need
to retension the bags in the entire unit. All items were corrected and
by the end of the 3rd day we were ready to commit to start up on the 4th
day and ready to work long hours.
START-UP
Our philosophy was that this would be the only start-up as the baghouse
was scheduled to be on line continuously. Subsequent operations were to
consist of cutting modules in and out of service for maintenance. Our
start-up procedure was very detailed and is contained in Appendix 2.
Briefly, we assumed four boilers would be operating through their by-
passes with a total steam load of 300,000 Ibs/hr equivalent to flue gas
flow of 170,000 acfm (actual feet per minute). While this requires only 8
modules we planned to use 12.
We selected modules 6 and 8 to remain down. The selection was dictated
as 2 and 4 were unbagged and we wanted to minimize outside wall exposure.
We did not precoat the bags, but in order to minimize flue gas conden-
sation on the bags; the baghouse and breeching temperatures were brought up
using gases from one operating boiler through the 2 empty (unbagged) modules
number 2 and 4. All other modules were closed off.
Modules with bags were then brought on line using flue gas at normal
temperatures and with fly ash having normal characteristics. Boiler loads
and baghouse parameters were used as criteria for selecting the number of
modules required as each additional boiler was put into the system. We
continue to use these parameters.
Start-up was smoothly accomplished (with no long hours) during the
week of 9/26/77, three months ahead of schedule and yielded a savings of
$120M by burning 100% coal instead of 80% during 4Q77. Performance was
and is extremely satisfactory with no plume. Optical instrumentation
monitoring the stack reads 2% when the baghouse is used as designed.
OPERATIONS
• This was the smoothest start-up Western Precipitation had witnessed
due to advance preparations which included:
375
-------
- one year studying start-up and operation of other installations
2 man months writing start-up and operating procedures involving
a total of 6 people at various times.
Construction follow-up by operating supervisors and engineers
with documentation of tests and checks.
i We eliminated changes in the booster fan loading due to reverse-air
cycling by taking the reverse air suction off after the booster fan
discharge. Now the cleaning cycle does not disturb booster fans or
boilers and controls operate satisfactorily.
• Mechanically we have had by-pass damper problems associated with
both design and construction. Lack of rigidity in design and some
welding not done during fabrication.
• We have proven the booster fan control concept. Boilers can be by-
passed without upsetting the boilers. This is a first in control
design. No changes were made in boiler controls.
* A performance test was run 8/29/78. The delay was required to
correct the leakage between the thimbles and the tube sheet at the
entrance to bags. Slide #7 and #8 show the sealing compound used
to accomplish sealing. The average emission was 0.0036 gr/A ft ,
which is 0.011 #/MM BTU and well below the State required 0.18#/MM
BTU and less than .01 grains per actual ft3 air, our contractor
guarantee.
f Normal AP is maintained between 3" and 6" across the baghouse or 2"
to 3" across the bags themselves. Reverse-air cleaning is varied to
accomplish this and varies from once every 12 hours to continuous,
depending on boiler loads and ash content.
• Bags have been successful and operate well with an estimated average
life of 5 plus years. One module is equipped with bags of woven
Teflon® fibers as a test for Company fabrics.
• Tests also indicate that there is the same relative particulate size
distribution on inlet and outlet. (Electrostatic units do not filter
the smaller particles.)
• We are selling fly ash from the baghouse for light-weight concrete
products.
t We had an increase of /A P across the baghouse to 6" which required
putting the 13th module in operation. Our plan is to individually
clean the bags in each module that has been on line. Cleaning will
be done by removing modules from service but leaving the bags in
place while they are air blown from top to bottom.
376
-------
• The filter is automatically bypassed if inlet gas temperature exceeds
450°F, or if inlet suction drops below 0.5 in. An automatic atmospheric
damper prevents implosion of the filter house in case of sudden bypass.
• Individual boilers are bypassed if furnace draft remains above 0.1"
for 10 seconds.
MAINTENANCE
There have been a total of 35 bags replaced since January 1, 1978.
Twenty-nine (29) of the defective bags have been in either Module No.
10 or No. 12. These modules were included in the initial start-up but
were removed from service after one or two weeks of service in an attempt
to raise the gas temperature on the baghouse. They were left closed and
it appears that there was flue gas leaking into these modules that set
up an acid condition, loss of bag material strength due to acid attack.
Procedure for removing modules has since been changed to having doors open
on idle modules, thereby maintaining a slight in-flow of air through
dampers so as to prevent leakage of flue gas into the idle units. There
have been two bags replaced in No. 1 Module which has the "Teflon" bags
and these bags appeared to have been installed improperly. One bag has
been replaced in No. 16 Module which was caused by a bent thimble that
may have torn the bag on initial installation. Recently, three bags had
to be replaced in Module No. 9 due to small holes. We feel this must have
been unnoted installation damage as no other causes are apparent.
Module entry has been a question in some minds with the reverse air
type baghouse. The modules are removed from service by closing the inlet
and outlet dampers. Installing a fan in the valve access door located on
top of the module and opening the lower access door provides a purging flow
of air. Heat flow from adjacent modules is reduced by insulation between
modules. After a few hours of module cooling with purge fan in operation,
bag replacement can be accomplished by the mechanic in cool air. Dust
masks are worn because there is some dust on the clean side.
Safety is maintained by following these safety steps:
• Isolating the module, locking it out, obtaining an air analysis
inside the module.
• Defective bags must be located and then dust cleaned from floor
to prevent entrainment when returned to service.
• Bag replacement requires 3 mechanics: one top, one bottom and a
standby exterior to the module.
Our major maintenance efforts have been associated with the fly ash
removal system including the bag filter connected to the ash removal
system. Most of the problems are the results of the ash being damp and
causing line and equipment pluggage. These problems seem to have been
greatly reduced due to enclosing the equipment on top of ash silo and
insulating the electrically traced module hopper discharge valves.
377
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This brings us up-to-date. We are continuing to learn the fine points
of operating and maintaining our $6MM vacuum cleaner and anticipate finding
out more of its capabilities as time goes on.
GENERAL EXPERIENCES
1. Tests were run of mixed coal and #6 fuel oil firing in early 1977
using a reverse-air type pilot baghouse. Using flue gas from coal and
#6 oil at a 50-50 ratio, tests indicated that the pressure drop build
up while filtering and regain after cleaning was better than straight
coal firing. No adverse effects were noted even at low gas gemperatures.
We have passed the flue gas from our large boilers at various ratios of
coal and both #2 and #6 flue gas oil firing up to 50-50 ratio through
the baghouse without seeing any detrimental effect on filtering pressure
drop or regain after cleaning. No bag failures or "smearing" have re-
sulted.
2. There is still some water leakage in and around the valve boxes. We
have located a sealing material which expands to fill a void and plan
to evaluate its ability to seal the leaking joints.
This baghouse is now an integral piece of operating equipment that
will stay efficient. We have 3 other RA fabric filters in the Company which
are giving comparably good performance.
378
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APPENDIX 1
CHECK OUT - PROBLEMS
This phase was continuous through out the construction and even then
we found problems at the end. The main problems were:
• The isolation of individual cells to assure good filtering, bag
cleaning during continuous operation, and satisfactory isolation
for maintenance. This involved checking of actual clearance be-
tween each valve disk and its elastomeric seat over the entire
mating surface. In-place grinding and minute final adjustments
took days.
i Bag installation and tension, 38#/bag, to assure support that
permits normal ballooning and collapsing during operation, Since
the bags had been installed several months previous to start up,
retensioning was required throughout the unit.
• Control sequencing - including the coordination of all the automatic
valves from the panel board used in reverse-air cleaning as well as
the controls for the booster fans.
i Ash removal system was designed to handle hot, dry, free-flowing ash
and did not operate well initially. Line and separation gate pluggage
was severe until we corrected deficiencies such as leaking gates and
insufficient insulation. Initial startup residue had to be cleaned
off hopper slope sheets. Knife edge gates were used finally.
• Internal leakage - This last problem was solved 9 months after start-
up. It involved the loss of the seal where the lower bag thimble goes
through the tube sheet. With our assistance the vendor sealed the
leak between thimble and tube sheet with a hardening liquid called
Pelmor®. This is a liquid suspension of Vitron® elastomeric material.
Registered trademark Pelmor Laboratories
379
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APPENDIX 2
BAGHOUSE START-UP DETAILS
POWERHOUSE OPERATING CONDITIONS
« Boilers 2, 3 and 4 - 200,000 stm/hr total.
• Boiler 1 - 100,000 Ib stm/hr.
START-UP PROCEDURES
1. Check Modules 1, 3, 5, 6, 9, 19, 11, 12, 13, 14, 15 and to to assure
that the inlet and outlet isolation dampers are closed. Flapper
valve box should be open to the outlet, closed to reverse-flow duct.
Inlet and outlet dampers to Modules 6 and 8 are to be locked shut.
No booster fan on standby.
2. Inlet and outlet isolation dampers of Modules 2 and 4 should be wide
open. Flapper valve in the module valve box should be open to the
outlet and closed to the reverse-flow duct.
3. Open inlet and outlet isolation dampers of south and middle (Nos. 3
and 2) booster fans. Close inlet control dampers on the control panel.
(They will be automatically closed when the fans are down, put will
open rapidly when the fan starts.)
4. Set the No. 1 bypass damper to the location (open) to give the desired
start-up condition.
5. Set atmospheric vacuum relief valve open.
6. Start the south (No. 3) booster fan. With the baghouse suction con-
trol (fan inlet damper control) on manual and closed, start the fan.
Adjust vacuum relief valve and fan inlet damper to obtain 2" suction
at the baghouse inlet.
7. Place No. 1 Boiler on manual control. Assure personnel are out of #4
Boiler while damper is switched.
8. Gradually close the No. 1 Boiler bypass manually (highest temperature)
(Gas will flow through Modules 2 and 4, which have no bags, to permit
full warm-up of the inlet and outlet breeching.) Gradually close
vacuum relief valve to maintain 2" suction. Open booster fan inlet
damper as necessary.
380
-------
9. Carefully observe No. 1 furnace suction and baghouse inlet suction
as the bypass transfer is gradually completed. Adjust baghouse
suction control (booster fan inlet dampers) and vacuum relief valve
to maintain -2".
10. Close vacuum relief valve if not already closed.
11. When fan inlet control damper is maintaining 2" suction at the bag-
house inlet, place suction control on automatic. Observe its
operation to assure even control. Adjust control sensitivity as
necessary. By this time the bypass damper on No- 1 should be closed.
12. Carefully observe the warm-up and expansion of the breeching and
Modules 2 and 4. Reference indicators have been installed at many
points. Particular attention should be paid to the compression of
expansion joints. Note the temperature rise at the baghouse outlet
using the boiler control board temperature recorder.
13. When (1) the booster fan controls are operating properly to maintain
2" suction at the baghouse inlet, (2) the proper furnace suction is
maintained in the No. 1 Boiler, and (3) the baghouse outlet temperature
has leveled off (should be 10-25°F belox
-------
b. Reactivate the baghouse by following Steps 8 and 9.
After approval by W. R. Denney (Powerhouse Supervisor)
c. Trip the bypass to place the gases to the stack to determine
all responses. Be careful to observe all furnace fluctuations
in No. 1 Boiler and be prepared to kill the fires if necessary.
Relighting and retrials can be made to determine responses and
best procedures.
d. Close bypass gradually without closing vacuum breaker to check
booster fan pick up.
When satisfied that the booster fan and all controls operate
satisfactorily, proceed to to add more boilers to the baghouse.
19. Open the inlet and outlet dampers to Module 9 and 10- This may
cause a change in baghouse differential (l\ P) , so be sure the
suction control damper is holding proper suction. (Check the
flow indicators. Modules 3, 5 and 7 will probably be less flow
than Modules 9 and 10. If there is more than a 2:1 difference
in flow, open the inlet and outlet isolation valve to Module 11.)
20. Observe the warm-up of the additional modules. Observe both the
expansion clearances and the temperature increase.
21. Gradually close the bypass damper of Boiler No. 3 while watching
the baghouse suction (maintain -2") and the furnace suction. (If
long delay, reverse Step 19.)
22. When the bypass damper is closed, observe the temperature rise of
the baghouse outlet. (It should have dropped when the new modules
were added but should return to normal, 10-20°F lower than the inlet
temperature.) Continue to observe the flow indicators to Modules 3,
5, 7, 9 and 10. They should tend to equalize.
23. Be sure the inlet control damper and automatic/manual control station
on the middle (No. 2) booster fan are closed. (The inlet and outlet
isolation slide gates were opened in Step 3).
24. Start the No. 2 booster fan, observing the effect on the suction of
the No. 3 fan. Inlet dampers may close somewhat to maintain 2"
suction in the baghouse inlet.
25. Gradually open the inlet control damper on the No. 2 fan. The auto-
matic control on the No. 3 fan should gradually close to maintain
suction at 2".
382
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26. When the control positions for both fans are the same, place No. 2
fan on automatic and observe automatic control of the baghouse
suction.
27. By this time the differential of the operating modules may have in-
creased to the point where cleaning is desirable, say 1-2". If not,
continue to Step 27.
a. If so, add another module (11 or 12) per Step 19.
b. Adjust the timers and controls to clean Modules 3, 5, 7, 9, 10
and 11 for settling periods of 40 sec. and one cleaning period
of 40 sec. Do not clean modules with lower A P.
c. Start one reverse-flow fan. (The inlet should be throttled to
use a minimum flow and pressure. Several trials may be necessary.
The pressure and flow should be no more than necessary to effect
the desired cleaning.)
d. Operate the fly ash removal system on hoppers of cleaned modules.
Check ash suction to be sure all are emptied.
Conduct step * only on request of W. R. Denney (Powerhouse
Supervisor).
* At this time, various other items can be tried - switching between
fans (removing the No. 2 booster fan from service and cutting it
back in) and both gradual and sudden bypass damper operation. With
both fans in operation, proceed.
28. Open the inlet and outlet dampers of the next two modules (11 and
12, or 12 and 13). Closely observe the baghouse suction controls
to assure maintenance of the 2" baghouse suction.
29- Gradually close the bypass damper of boiler No. 2, Check bypass
damper operation.
30. When the bypass damper is closed, observe the baghouse outlet
temperature. (It should have dropped when the new modules were
added but should return to normal 10-20°F lower than the inlet
temperature.)
Continue to add modules
31. Open the inlet and outlet dampers to the next two modules (12 and
13 or 13 and 14). Observe that the controls to the fans maintain
the 2" suction.
383
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32. Gradually close the bypass damper of No. 1 Boiler. Observe the
baghouse suction controls. Check bypass damper operation and travel.
33. When the bypass damper is closed, observe the baghouse outlet
temperature. (It will have dropped when the additional modules
were opened but should level out 10-20°F below the inlet temperature.)
34. Open the inlet and outlet dampers to the remaining modules (14 through
16). Observe the suction controls.
After baghouse is operating successfully with all boilers:
35. Shut down #4 Boiler.
36. Observe the baghouse outlet temperature. It should level out 10-20°F
lower than the inlet.
37. Set the cleaning for all modules at one cycle with 40 sec. settle
and 40 sec. clean. Operate single cycle at 40 sec. to maintain
P between 3" and 4".
38. Operate fly ash hopper cleaning system. Check for proper pulling
of all hopper.
384
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REFERENCES
"Case for Fabric Filters or Boilers" by R. P. Perkins. Presented at
Massachusetts-APCP, Philadelphia 1976.
2
"Consideration in the Start-Up of Baghouse in Coal Fired Boilers" by
R. P. Perkins, presented at Second Annual Filter Fabric Alternatives
Conference, Denver 1977.
385
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L_
f. 0. FANS
99
»y PASS
23*5
"SLIDE 1" WAYNESBORO BAG FILTER SCHEMATIC
"SLIDE 2" WAYNESBORO POWER COMPLEX BEFORE
386
-------
"SLIDE 3" WAYNESBORO POWER COMPLEX AFTER
FIBERGLASS WITH TEFLON ^COATING
"SLIDE 4" BAG MATERIAL SAMPLE
387
-------
MODULE PITOT TUBES
"SLIDE 5" ADDITIONAL INSTRUMENTATION
I
"SLIDE 6" MODULE SIGHTGLASS
388
-------
"SLIDE 7" SEALING WITH PELMOR®
"SLIDE 8" SEALING WITH PELMOR®
389
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A NEW TECHNIQUE FOR DRY REMOVAL OF
By
C.C. Shale and G.W- Stewart
United States Department of Energy
Morgantown Energy Technology Center
Morgantown, West Virginia 26505
August 1979
390
-------
ABSTRACT
Experimental studies are reported on a technique for SO flue gas control
X
using a dry limestone sorbent and humidification control of the flue gas.
Kinetic studies of this "modified dry" limestone process (MDLP) show reaction
rates equivalent to high temperature fluid bed processes. SO removal
X
efficiency is shown to increase as the water saturation temperature of the
"conditioned" gas increases. At a saturation temperature of 150 F one can
obtain >90% SO removal from a flue gas stream containing 1600 ppm S09.
X £-
Results of economic analysis based on both a moving bed and a counterflow
design are presented.
391
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A NEW TECHNIQUE FOR DRY REMOVAL OF SO
INTRODUCTION
Lime/limestone scrubbing is presently considered the best available control
technology (BACT) for flue gas desulfurization, but most wet methods have
characteristic problems of high cost and low reliability. Dry alkali injection
has "been proposed as a potentially viable alternative to wet scrubbing for flue
gas desulfurization (FGD). The concept of dry alkali injection is simple and
involves two basic operations: 1) injection of reactant, and 2) removal of
solid reaction products. The reactant may be injected as a dry powder, a
solution of a soluble alkali, or possibly as a slurry of a relatively insoluble
alkaline earth compound. If introduced as a solution or slurry, the liquid
evaporates almost immediately and leaves a suspension of finely-divided solids
in the gas phase, which is very similar to that created by the dry injection
technique. Subsequent reaction of the suspended solid particles with sulfur
dioxide produces solid sulfite and sulfate particles that are admixed with
fly ash and unreacted alkali. Removal of these dry solids is effected by a
filter (moving-bed/baghouse) or an electrostatic precipitator.
Independent studies (Dickerman et al., 1978) have demonstrated that dry
sodium compounds, such as soda ash, trona, or nahcolite, are the preferred
reactant(s) for this mode of FGD because of their high chemical reactivity.
Results of tests using lignite as a fuel show that sodium salts can absorb
approximately 80 percent of the sulfur dioxide from a gas wherein the solids
have a short resident time (~3 sec.). Product solids are then removed in an
electrostatic precipitator. If these solids are removed in a bag filter,
however, additional contact time between the gas and solids is provided and
can result in higher removal efficiencies. The combination of the two processes
(dry injection and filtration) has been used to provide up to 99 percent removal
2
for S0? (Dustin, 1977) . Use of powdered lime/limestone in this mode of treat-
ment normally results in ineffective removal of SO , i.e.,<50 percent (Bechtel
3
Corp., 1976).
By-products from reaction with sodium salts consist of sulfur-bearing
particles that are water soluble and can result in contamination of ground
392
-------
water unless special precautions are taken. One way to avoid water contamination
is to treat the sulfur-bearing sodium particles with a lime/limestone slurry.
This converts the soluble sulfur compounds to relatively insoluble calcium
sulfate (gypsum), thus producing a solution of sodium salts which is available
for recycle. This combined treatment increases process costs. Further develop-
ment of this dry method for FGD, however, could possibly result in a decrease
in overall processing costs and may improve equipment reliability when compared
to existing BACT.
Studies conducted at the Morgantown Energy Technology Center (METC)
indicate that a new approach, using water vapor to "condition" the flue gas,
may be effective in removing S0_ from a cooled gas stream. The patented technique
4 o
(Shale and Cross, 1976) involves adding water vapor to hot flue gas (300 F) to
increase the saturation temperature of the gas above a critical minimum and
then cooling the mixture to a predetermined temperature near the adjusted dew
point. Under the conditions studied, it has been shown that greater than 90
percent of the SO. can be removed using small pellets (up to 1/2-inch) of
crushed limestone in a dry bed. The process is called the modified dry lime-
stone process, or MDLP. Through direct use of limestone, a dry, relatively
inert sulfur product (gypsum) can be produced without the need for secondary
processing of soluble salt solutions. This process has the potential of
providing several economic benefits.
EXPERIMENTAL PROCEDURES
Both laboratory scale and bulk evaluation studies have been conducted on
MDLP. The laboratory studies were performed using a Mettler DTA-TGA instrument
in which kinetic parameters were obtained by observing the change in weight
of limestone as a function of time. The apparatus and experimental procedures
have been described in an earlier publication (Nesbitt et.al, 1978). The
gas stream consisted of 2.5-7.0 percent SO-, 2.0 percent 02> and the balance
nitrogen. Limestone pellets ranged in weight from 590 mg. to 810 mg. The
393
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porosity and surface area of the pellets were monitored and held constant
such that observed changes were the result of a chemical interaction, not
changes in physical properties. The stream humidity was determined by a wet
bulb thermometer and held at the saturation level. Chemical analyses of the
solid product was performed by IR, SEM, X-ray flourescence, and ESCA. All
analyses were consistent in that 1) calcium sulfate was the major product, and
2) reaction occurred on the pellet surface.
Bulk absorption studies were performed on limestone beds 1-inch diameter
x 9- inch deep and 1/2-inch diameter x 4-inch deep, using 1/16 x 1/2-inch
pellets. Gas flow rates were controlled between 1 and 3 scfh and were monitored
by a gas flowmeter. The pressure drop across the beds varied between two inches
of water at the beginning and up to eight inches of water at the end of
individual tests. Pressure loss increased because of water deposition on the
limestone and the physical particle enlargement resulting from chemical reac-
tion. For all studies the gas mixture was 14 percent CO., 4 percent 0 , 0.15
to 0.3 percent SCL and the balance N_. Analysis of the S0_ removal was deter-
mined by commercial gas detector tubes. The tubes were sensitive to water,
and the reliability was ±25 percent of the indicated value. Any SO- level
below 1 ppm was below the detection limit of the detector.
The bulk investigative tests for this system were conducted in equipment
depicted in Figure 1. Simulated flue gas containing up to 3000 ppm sulfur
dioxide flowed at a controlled rate through a heater, a heated saturator, and
a fixed bed of selectively-sized limestone and was exhausted into a hood. In
the experimental program, the gas flow rate, temperature, moisture content,
and sulfur dioxide concentration were controlled as process variables. Two
limestones and two dolomites of variable particle (lump) size were tested in
beds of different diameters and depths to allow for a range in space velocity.
After having established steady state thermal conditions using a selected
flow rate of dry gas through the system, a controlled flow rate of water was
394
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added continually to the saturator to establish a controlled level of moisture
in the "conditioned" gas for each absorption test. Heat added to the saturator
insured complete evaporation of all water. The dry gas was heated to 280°F and
passed through the saturator prior to entry into the bed of crushed stone. The
gas cooled during saturation and flowed through the limestone bed at a temper-
ature of 150 to 160°F and a space velocity of 500 vol/vol/hr.
RESULTS AND DISCUSSION
Thermogravimetric studies on single limestone pellets indicate that S02
removal efficiencies would be a maximum for a saturated stream temperature
of 110-120°F. This can be correlated to the sorption of S0_ in H20 as a
function of temperature. The sorption of SO- in H-0 has been shown to decrease
rapidly as the temperature increases. In addition, thermogravimetric studies
show no observable weight. gain in the temperature range of interest unless
water is present. Therefore, it is fortuitus that the optimum conditions for
MDLP coincide with actual gas stream conditions.
A representative weight gain curve for water and S09 absorption is shown
in Figure 2. Kinetic parameters were obtained using the initial rate method.
For this study the following stoichiometric equation was assumed for the
rate controlling step:
a A (gas) + s S (solid)^-a A (gas) + s S (solid) (1)
rr rr pp pp
where a and s are the stoichiometric coefficients for gases and solids, and
r and p represent reactant and product. It was assumed that both diffusional
and mass transfer resistance were negligible such that the initial reaction
rate can be represented as:
R = a k C Cn (2)
o r s s a
o o
where R is the initial molar rate of reaction of the gas per unit surface
o
area of the solid, k is the rate constant per unit area, C is the initial
s So
395
-------
molar concentration of the solid, C is the molar concentration of the gas
3
o
and n is the reaction order with respect to the gas.
- It can be shown that the initial reaction rate can be calculated from
the weight gain curve by using the following equation (Westmoreland, 1977)
(ar/sr) (dw/dt)o (3)
R°= ^
+ (a' /a )M 1
r p r ' pJ
where (dw/dt) is the initial slope, m is the initial mass of the solid
reactant, a is the specific surface area of the solid and M and M are
o p r
molecular weights of the solid product and reactant.
The reaction rate, as determined by equation (3), is used to determine
the order of reaction with respect to the concentration of the reactant gas
and the reaction rate constant as specified in equation (2). The reaction
was found to be first order in S02 concentration and to obey the classical
Arrhenius relationship
k = A exp (-E /RT) (4)
S 3.
where A is the Arrhenius factor, E is the activation energy, R is the gas
3.
law constant and T is the absolute temperature. Thus, by plotting In k
S
versus 1/T it is possible to determine both A and E .
3
The calculated intrinsic rate of reaction (R ) and the initial rate of
o
change (dw/dt) are given in Table I. From these data the intrinsic rate
constant can be calculated using the initial limestone concentration
-2 3
(2.7 x 10 moles/cm ) and the water concentration at the gas stream
temperature. The intrinsic rate constants evaluated by equation (2) with
n = 1 were found to obey the classical Arrhenius relationship under the
observed conditions where mass transfer resistance was negligible.
396
-------
To obtain the reaction order with respect to the concentration of
sulfur dioxide, experiments were performed in which the SO concentrat
was varied from 2.5 to 7%. A plot of the initial rate of weight gain of SO
concentration at different temperatures is shown in Figure 3 . The linear
dependence indicates that the reaction is first order in SO- concentration.
A mechanism consistant with the experimental kinetic parameters is
as follows:
S02 + H20(ad) •+ IH2S03] j H* •* HS03~ •* 2E* + S03=
HS03~- + -%02 j HS04"
CaC03 + HS04~ £ CaS04 + BC03~
EC03~ + H* •* H20 + C02
This mechanism involves an acid-base reaction in which sulfur dioxide
is dissolved in an adsorbed water layer. The pH conditions in the stream
_ _ -j
favors the formation of HSO and are unfavorable for SO } (Schroeder, 1966) ,
8 —
(Roberts, 1979) . Therefore, HSO,. is considered the dominate species. It is
proposed that the HSO is oxidized to HSO, by dissolved oxygen present in the
adsorbed water. This reaction has been shown to be governed by a free radical
mechanism and thus occurs rapidly in solution (Schroeder, 1966) . Small
impurities of iron and/or copper present in the limestone have also been shown
9
to catalyze this oxidation (Rand, 1965) . The calcium carbonate subsequently
reacts with HSO, to form calciun sulfate and bicarbonate ion. The bicarbonate
4
ion reacts with a proton to form C0~ and water. This mechanism predicts first
order kinetics which has been verified experimentally. The product proposed
by this mechanism is CaSO, which has been verified experimentally by IR and
ESCA analysis.
For practical considerations it is interesting to compare the kinetic
parameters obtained for the modified dry limestone process with the kinetic
397
-------
parameters obtained in the reaction of calcined limestone with S09
10
(Borgwardt, 1970) . As seen in Table II, the activation energies and
rate constants are very similar for the two processes. This similarity is
fortuitious since the processes occur at greatly different temperatures and
the Arrhenius plots are not continuous. However, since the calcined lime-
stone process is economically viable with other techniques, it seems reasonable
that MDLP may also be economically viable with other FGD processes.
Bulk studies were performed using conditions similar to those used for
the thermogravimetric studies. The effect of saturation temperature on S07
removal efficiency is shown in Figure 4. At a space velocity of 500 v/v/hr,
an S0_ concentration of 1600 ppm, a gas temperature of 150 F, and a saturation
temperature of 100 F the S09 removal efficiency is ~90% for approximately
30 min. and then drops off rapidly with an increase in exposure time. These
conditions simulate a stack gas from a conventional coal-fired combustion
source burning a 2% sulfur coal and having an exit gas temperature of 150 F.
At the higher removal efficiencies the uncertainty in data is considered to
be ±5%. As the saturation temperature increases from 100 F to 150 F the
maximum removal efficiency is maintained for longer periods of time. Note
on curve 2 that after ~2.5 hours, the moisture content of the gas was increased
from a level corresponding to a saturation temperature of 110 F to that of
120 F. The subsequent increase in SCL removal efficiency is consistent with
the overall variation of removal efficiency with moisture content. At a sat-
uration temperature of 150 F a removal efficiency of ^90% was maintained for
at least 3.5 hours using a bed of Greer limestone. Tests with other lime-
11 12
stones and dolomites show a similar high level of induced chemical activity
upon additions of water vapor to the simulated gas stream. The effects of
moisture on increasing the S0~ removal efficiency have also been observed by
13
workers at Battelle (Rosenberg, 1979)
Experiments at higher space velocities (4,000 v/v/hr) have shown that
SCL removal efficiencies of >90% can be achieved when the gas is at complete
398
-------
saturation, that is, the water vapor saturation temperature is no more than
30 F below the actual gas temperature as it flows through the fixed bed. For
these studies the SO. concentration in the test gas was 1400 ppm.
Examination of the limestone at the completion of each test showed that
the pellets were covered with a relatively thick, soft shell of reaction
products. After partial drying of the pellets the product layer could be
removed by mild agitation leaving the harder unreacted core of limestone.
Analysis of the initial limestone reaction product and the unreacted core
are given in Table III. From these results it is apparent that the shell is
composed of calcium sulfate plus some unreacted calcium carbonate. Earlier
4
reports (Shale and Cross, 1976) estimated that ~90% of the limestone was
utilized in the reaction. However, a more recent reevaluation of the original
data suggest that the actual utilization of the limestone is somewhat lower.
14
A preliminary analysis by the Cost Evaluation Group (1971) of the
U.S. Bureau of Mines, using only the data obtained from the bulk studies,
indicated that capital and operating costs for MDLP could be as much as
40 percent less than corresponding costs for removal of SCL by lime/limestone
wet scrubbing systems when a cross-flow moving-bed concept is utilized for
the dry absorber. The conceptual design used for this study is shown in
Figure 5. A more recent cost analysis has been conducted by TRW (Rao, 1978)
which is based on both the bulk studies and the thermogravimetric studies.
This latter study, however, uses a concept based upon a counterflow moving-
bed which characteristically consumes an excess of energy in pressure loss
through the absorber. This study shows capital and operating costs for MDLP
in excess of those for lime/limestone scrubbing. The use of dry sorbents and
fabric filtration in FGD systems has been evaluated in a report by TRW for EPA
(Lutz et. al, 1979) . The capital cost for a dry solvent system utilizing
nahcolite was found to be approximately 40% of that for a lime/limestone
scrubber system while the operating costs were estimated to be approximately
equal. Adaptations of MDLP to a dry injection technique might offer similarly
induced capital costs.
399
-------
CONCLUSIONS
Kinetic studies indicate that limestone is an effective sorbent for SO
in moisture laden flue gas streams. Rate data indicate that the reaction
process is first order in SO concentration and is reaction rate limited. The
prodjucts from this reaction are gaseous C09 and solid calcium sulfate. The
rate of SO,, removed by MDLP is comparable to the higher temperature fluid
bed processes and unlike the low temperature lime/limestone scrubbers, MDLP
produces a solid waste product. It is also evident from the experimental
studies that the duration of enhanced removal efficiency increases as the water
saturation temperature of the "conditioned" gas approaches the actual gas
temperature of 150 F. At substantially complete saturation, removal
efficiencies of~90% are achieved over an extended period of time.
Whereas the saturation temperature of combustion gas from coal is about
95 to 100 F (depending on the age of the coal), combustion gas from oil firing
is saturated at about 110°F, while the product from gas firing is saturated at
about 130 F. The high moisture content of combustion gases from a natural gas-
fired source would appear to make this gas ideally suited to cleanup of sulfur
dioxide by dry limestone, without modification, as indicated by the data
given previously in Figure 4. The saturation temperature of gases from oil-
and coal-fired sources, however, is below the established critical minimum
(120 F), so the dew point of these gases must be adjusted to a higher level
for effective application of this sorption technique. Through addition of
adequate moisture and through adequate control of temperature, as specified for
MDLP, a properly "conditioned" gas can in principle be produced from any fuel,
thus yielding the maximum removal efficiency for sulfur dioxide.
Preliminary economic evaluations have been made on the modified dry lime-
stone process. Early evaluations made before the kinetic data were available and
using a moving bed design were quite favorable. However, a later evaluation
which included the kinetic data and a counter flow design indicated a negative
energy incentive. Favorable capital and operating costs have been found for
nahcolite by dry injection techniques. The possible use of a dry injection/MDLP
4QQ
-------
technique might offer similar advantages and thus needs to be evaluated.
Since each assessment is extremely dependent on the engineering design used,
a detailed systems analysis must be performed before any final conclusions
as to possible economic advantages or disadvantages can be made.
Additional experimentation is needed to assess the efficiency of a limestone
bed on particulate removal and as a combined NO /SO removal device. Numerous
X X
studies have been reported in which calcium salts and sulfite/bisulfite ions
were responsible for the catalytic decomposition of nitric oxides . Evidence
for combined NO /SO removal would greatly enhance the interest in MBLP.
A
401
-------
REFERENCES
1. Dickerman, J.C. et al. Evaluation of Dry Alkali for FGD Systems. Prepared
for Pacific Power and Light Company and Public Service Company of Colorado by
Radian Corporation, Austin, TX. March 1978.
2. Dustin, D. F. Report of Coyote Pilot Plant Test Program. Test Report, Canoga
Park, CA, Rockwell International, Atomics International Div. November 1977.
3. Bechtel Corporation. Evaluation of Dry Al*kalis for Removing Sulfur Dioxide
from Boiler Flue Gases. Electric Power Research Institute, Palo Alto, CA,
EPRI FP-207. October 1976. Pages 18 and 19.
4. Shale, C.C., and W.G. Cross. Modified Dry Limestone Process for Control of
Sulfur Dioxide Emissions. U.S. Pat. 3,976,747. August 24, 1976.
5. Nesbitt, F.L. Kinetic Study of Flue Gas Desulfurization by Limestone. Thesis,
Graduate School, West Virginia University, Morgantown, WV. 1978.
6. Westmoreland, P.R. et_ _al_. Comparative Kinetics of High-Temperature Reaction
Between H S and Selected Metal Oxides. Environ. Sci. Technol. 11:488 (1977).
7. Schroeder, L.C. Sulfur Dioxide. New York, Permagon Press, Inc., 1966. p. 63.
8. Roberts, D.L. Sulfur Dioxide Transport Through Aqueous Solutions. Ph.D Thesis,
California Institute of Technology, Pasadena, CA. January 1979- p. 165.
9. Rand, M.C. Principles of Applied Water Chemistry. In: Proc. Rudolfs Res. Conf.
4th, Rutgers State Univ., 1965. p. 380.
10. Borgwardt, R.H. Kinetics of the Reaction of SO with Calcined Limestone.
Environ. Sci. Technol. 4:59 (1970).
11. (a) Greer Limestone Ca., Morgantown, WV. (b) Limestone No. 1359, Grove Limestone
Co., Stephens City, VA.
12. (a) Dolomite No. 1341. Environmental Protection Agency, Department of Health,
Education and Welfare, Cincinnati, OH 45227.
(b) Charles Pfizer and Co., Inc., Minerals, Pigments, and Metals Division, Gib-
sonburg, OH.
13. Rosenberg, H.S. Chemical Process Development Section, Battelle Columbus
Laboratories, Columbus, OH. Personal communication.
14. Process Evaluation Group. Modified Dry Limestone Process for Removal of SO.
from Powerplant Flue Gases, An Economic Evaluation. Report No. 71-26, U.S.
Department of the Interior, Bureau of Mines. February 1971.
402
-------
15. Rao, A. K. Modified Dry Limestone Process Engineering Assessment, Morgantown
Energy Technology Center, Department of Energy. Prepared by TRW Energy Systems
Planning Division, Morgantown, WV. September 1978.
16. Lutz, S.J. et_ a^. Evaluation of Dry Sorbents and Fabric Filtration for FGD.
EPA-600/7-79-005, Prepared by TRW, Inc., Durham, NC for Industrial Environmental
Research Lab. Research Triangle Park, NC, Jan. 1979.
17. For example, see English Patent No. 1,134,881. November 27, 1968.
TABLE 1
KINETIC PARAMETERS FOR THE ABSORPTION
OF H20+S02 ON LIMESTONE
E =13.0 kcal/mole
3.
Temp ( c) (dw/dt)Q R (mole/mg min) kg (cm /mole min)
35 .140 2.4xlO~9 113
38 .181 2.8xlO~9 133
43 .309 3.8xlO~9 212
403
-------
TABLE II
COMPAIRSON OF CALCINED LIMESTONE WITH MDLP
MDLP Calcined*
E 13+1 kcal/mole 8-18 kcal/molet
a
R 3 x 10 ° g-mole/g sec 2 x 10 g-mole/g sec
A 4.1 x 10^ g-mole/g sec 2.07 x 10^ g-mole/g sec
AS -7.86 cal/mole deg
AH 16.2 kcal/mole
* For calcined data Rwas 1 x 10~8 g-mole/cm3 S02 at 870°C,
O _Q
whereas MDLP was 1 x 10 g-mole/cm3 S02 at 38°C.
Activation energies vary as to the type of limestone.
TABLE III
ANALYSIS OF VIRGINIA LIMESTONE FRACTIONS
Sample
No.
1
2
3
Description
Original limestone
Surface material
removed
Recovered limestone
CaC03
97.5
5.6
97.5
Composition,
CaS04-l/2 H20
0.0
90.0
0.0
wt . -pet .
SiO Other
2.5 0.0
2.5 1.9
2.5 0.0
404
-------
o
en
V
GAS
SAMPLE
GAS
HEATER
FLOWMETER
GAS
SAMPLE
WATER
RESERVOIR
HOOD
LIMESTONE
REACTOR
GAS
SATURATOR
HEATER
FIGURE 1 - Flowsheet for Modified Dry Limestone Process
-------
O
Ol
8
6
0
1 I I 1
I I
o
o
o
o
o
o
S0
I I
0 20 40 60 80 100
TIME (MIN.)
FIGURE 2 - MEASURED WEIGHT CHANGES DURING THE REACTION OF H20 AND H20 + S02
WITH LIMESTONE AT 100°F AND 5% S02
(PELLET WEIGHT = 749.8 MG.)
-------
o
'o
o
ce
T = 42°C
1
= 38°C
r
Cso *
2 3
~R ,moles.
J2 cm"
FIGURE 3 - ANALYSIS OF REACTION ORDER AS A FUNCTION OF SO 7 CONCENTRATION
407
-------
O
CO
C
0)
O
0>
a
O
z
UJ
O
uu
u_
UJ
O
s
LU
cc
CM
O
CO
100
90
80
70
60
50
40
30
20
10
SOz concentration, 1,600 ppm
Crushed Greer Limestone, 1/16" x 1/4
Space velocity, 500 v/v/hr
Gas temperature, 150° F
« Saturated 100° F
A Saturated (a) 110° F, (b) 120° F
O Saturated 150° F
34567
TIME, hours
8
FIGURE 4 - EFFECT OF MOISTURE ON S02 REMOVAL BY CRUSHED LIMESTONE
-------
(0
• ;"':::-
: ;!:i::; ;;:T;
CONVEYOR, LIMESTONE RECYCLE //
LIMESTONE BIN V3i£/
CRUSHED LIMESTONE '
1/1 6"x 1/2"
STACK
150° F
WATER SPRAY
LIMESTONE MOVING BED
CROSS-FLOW ABSORBER
100.0% (Dry Basis)
plus RESIDUAL FLY ASH
CaSO4
(Disposal)
FIGURE 5 - CONCEPTUAL APPLICATION FOR THE MODIFIED DRY LIMESTONE PROCESS
-------
SPRAY DRYER/BAGHOUSE SYSTEM
FOR PARTICULATE & SULFUR DIOXIDE CONTROL,
EFFECTS OF DEW POINT, COAL AND
PLANT OPERATING CONDITIONS
By:
William R. Lane
Bechtel Power Corp.
P.O. Box 3965
San Francisco, CA 94119
ABSTRACT
This paper discusses the use of a combination spray dryer
and baghouse or spray dryer and electrostatic precipitator for
particulate and sulfur dioxide control. Reactant compounds
are injected into the spray dryer in a solution or slurry.
The dry reaction products and coal fly ash are removed in a
downstream baghouse or precipitator.
Several factors influence the system performance including
coal moisture and sulfur content, plant altitude, dew point
temperature approach and boiler design. A TI-59 computer pro-
gram was developed to perform combustion calculations and to
calculate dew point, spray dryer operating temperature drop
and chemical spray rates. Operating limits of coal sulfur con-
tent and sulfur dioxide removal were determined. Graphs are
presented which can be used to study a wide variety of appli-
cation conditions.
It is concluded that applicability of the spray dryer/bag-
house concept is limited by flue gas temperature, startup con-
ditions and required sulfur removal. Boiler design changes or
extending the averaging period for sulfur dioxide removal could
alleviate the limitations.
410
-------
SPRAY DRYER/BAGHOUSE SYSTEM
FOR PARTICULATE & SULFUR DIOXIDE CONTROL,
EFFECT OF DEW POINT, COAL AND
PLANT OPERATING CONDITIONS
INTRODUCTION ,
Interest has increased rapidly in the concept of a combina-
tion spray dryer/baghouse or spray dryer/electrostatic precipi-
tator for removal of sulfur dioxide and particulate from coal
burning plants. Several such systems are now on order and one
will soon be in operation. The objective of this paper is to
provide information regarding the limits of applicability of
this system. The limit is determined by system temperature
drop and the need to stay above the flue gas adiabatic satura-
tion temperature.
The limits are summarized by the graphs which can be used
to study a wide range of conditions.
SPRAY DRYER SYSTEM DESCRIPTION
The spray dryer for sulfur dioxide removal is located up-
stream of a fabric filter or electrostatic precipitator. The
flue gas passes through the dryer vessel and chemical solution
or slurry is sprayed into the dryer. The absorbent reacts with
sulfur dioxide while in the liquid solution or slurry.
The liquid droplets dry before leaving the vessel and the dry
reaction products and fly ash are removed from the flue gas by
the downstream baghouse or precipitator. Some sulfur removal
also occurs in the dry phase if a baghouse is used. Spray
dryer systems presently on order will use sodium carbonate or
calcium oxide (calcium hydroxide after mixing with water) as
the' absorbent.
The spray dryer system reduces the flue gas temperature
to a level near the adiabatic saturation level (near the moist-
ure dew point for typical spray dryer conditions). The system
must be operated above the saturation temperature to assure
that the droplets dry before reaching the vessel walls or enter-
ing the downstream particulate collector.
411
-------
Creation of a fine spray is achieved by several methods
being offered by various system suppliers. These include high
speed rotary atomizers, steam atomizers and high pressure noz-
zles .
A key to efficient utilization of chemical is to spray
enough liquid into the system to bring the flue gas close to
the saturation temperature. This increases the droplet drying
time which increases chemical utilization (reduces chemical
consumption) because the reaction is more efficient in the wet
phase. Utilization is defined as the percent of the absorbent
reacting with sulfur dioxide. Thus, higher utilization rates
are desirable.
Sodium carbonate solutions must be limited to concentra-
tions under 30% due to solubility limits. A calcium hydroxide
slurry is also limited to approximately 30%*(based on calcium
oxide) due to heat generation when slaked with water and by
grit removal requirements. Thus the amount of absorbent which
can be sprayed into the system is limited because of the con-
centration limits and the need to stay above saturation tempe-
rature. This limits the amount of sulfur dioxide which can be
removed from the flue gas. Thus there is a coal sulfur content
limit for a given required percent sulfur dioxide removal.
The coal sulfur limit is dependent on many factors in-
cluding coal hydrogen and moisture content, boiler excess air,
plant altitude, duct pressure and boiler exit gas temperature.
An objective of this paper is to show the relative importance
of each of these variables and to establish sulfur limits. To
do this, a computer program was developed and curves were
drawn for typical lignite, sub-bituminous and bituminous coals.
THE COMPUTER PROGRAMS
The computer programs were developed for the Texas Instru-
ments TI-59 calculator/computer with magnetic card recording
capability. The programs fit onto three magnetic cards (each
approximately 0.6" by 2.7"). Two computer programs were devel-
oped. The first is a combustion calculation program to deter-
mine gas flow rates and flue gas analysis. The second program
uses the output of the first for spray dryer calculations.
The 418 step combustion program input and ouput consists
of:
Input:
1. Fuel analysis
2. Percent excess air
3. Barometric pressure
4. Duct pressure
*Concentrations of about 40% have been piloted by recycling unused
absorbent and fly ash.
-------
5. Boiler heat input rate
6. Gas temperature
Output:
1. Gas flow rate, weight
2. Gas flow rate, volume
3. Gas molecular weight and density
4. Flue gas analysis
The 547 step spray dryer program input and output consists
of:
Input:
1. Gas flow rate
2. Sulfur dioxide flow rate
3. Flue gas analysis
4. Plant altitude
5. Duct pressure
6. Required sulfur dioxide removal, %
7. Percent weight absorbent in solution or slurry
8. Absorbent molecular weight
9. Absorbent percent utilization
10. Flue gas temperature
Output:
1. Absorbent flow rate
2 . Water flow rate
3. Final flue gas temperature
4. Flue gas specific heat
5. Flue gas moisture dew point
6. Temperature margin above dew point
7. Flue gas molecular weight
8. Flue gas moisture content
9. Flue gas vapor pressure.
The method of spray dryer calculations is as follows.
Moisture due point temperature is approximated by:
Dew point (°F) = e(In P + 14.562 )/3 .3
where P = (29.92*- altitude in feet/1000) x(% vol. moisture/100)
This formula is sufficiently accurate over the range of
conditions of interest here. Dew point temperature is very
close to the adiabatic saturation temperature for typical
spray dryer conditions.
Flue gas specific heat is calculated for each gas consti-
tuent and an overall specific heat is calculated based on the
percentage of each gas constitutent in the flue gas. 2The form
of the specific heat equations is: Cp = a + b T - CT - d/T
* +0.0735 x ("WG duct pressure)
413
-------
where coefficients a, b, c and d are given for each gas consti-
tuent in several references including "Manual for Process Engi-
neering Calculations" by Clarke and Davidson.
The heat given up by the flue gas to evaporate the spray
water consists of the energy to raise the water and absorbent
to dew point, latent heat of evaporation and the heat to raise
the evaporated liquid and absorbent to the final temperature.
The latet heat of evaporation is calculated by a linear equa-
tion approximation based on steam table data over the range of
interest.
The forgoing was combined to estimate flue gas final tem-
perature and moisture dew point.
PERFORMANCE GRAPHS
Figures 1 through 7 show flue gas data and spray dryer
performance limits for three classes of coal: lignite, sub-
bituminous and bituminous. Typical coal analyses used for
this study are as follows:
Lignite Sub-Bitum. Bitum.
Carbon 37.48 53.56 72.0
Hydrogen 3.36 3.80 4.40
Nitrogen 0.64 1.08 1.40
Oxygen 8.90 10.40 3.60
Water 40.00 20.15 8.00
Sulfur 0.86 0.84 2.00
Ash 8.76 10.17 8.60
Btu/lb 6,500 9,400 12,800
As sulfur content was varied for study, other constituents were
adjusted proportionally. The above analyses were selected as
typical for each coal class.
The attached figures were developed for the above coals.
Figure 1 shows the effect of moisture content, duct pressure,
plant altitude and percent excess air on flue gas moisture dew
point. Figure 1 is for conditions prior to spray dryer opera-
tion. Figure 2 shows flue gas temperature drop with spraying
of a 30% sodium carbonate solution or a 20% calcium hydroxide
slurry. Calcium hydroxide concentration is expressed as per-
cent calcium oxide. Data are shown for a range of sub-bitumi-
nous coal sulfur contents, percent sulfur dioxide removals and
chemical utilization rates. Figure 3 shows coal sulfur limits
for a sodium carbonate solution spray dryer. This figure is
for a 30% solution. Usually the solution would be more diluted
to obtain temperatures near the dew point. A concentration of
30% is shown to indicate the limit of tolerable coal sulfur
content. Figures 4, 5 and 6 show sulfur limits for calcium
hydroxide slurry dryers. These figures are arranged different-
ly from Figure 3 because three different slurry concentrations
are shown. '
414
-------
Figures 3 through 6 are for a dryer exit temperature 40°F
(4-4 C) above the flue gas moisture dew point. Some believe
that much closer approaches can be used without substantial
risk of baghouse or precipitator fouling. An example will be
presented to show the effect of decreasing the margin above
dew point.
WHAT THE FIGURES SHOW
Figures 1 through 7 include a large number of curves.
This is necessary because the number of variables is large.
Curves are drawn for two absorbents, three flue gas inlet
temperatures and three classes of coal. Among the information
shown are:
1. Flue gas moisture content upstream of the spray dryer
varies from 7-17% for the three coals selected. This signi-
ficantly affects the flue gas moisture dew point (Figure 1).
Lignites would have a higher moisture dew point and thus lower
spray dryer sulfur removal capability. Fortunately, lignite
often has less sulfur than bituminous coal. Bituminous coal
often has the highest sulfur content but a lower moisture con-
tent. Thus more heat would be available above the moisture
dew point and more absorbent could be added.
2. Significant differences in sulfur removal capability for
the three classes of coal are shown on Figures 3 through 6.
Percent chemical utilization is a key factor. For a given
chemical concentration, increased absorbent flow will require
increased water flow. Dew point approach limits the amount of
chemical and water that can be sprayed into the system. A
higher percent utilization will result in an ability to handle
higher coal sulfur contents.
It is not the purpose of this paper to establish absorbent
utilization percentages. These are determined by the system
suppliers and vary with operating conditions and system design.
Values of 70 to 95% are typical. Recycle of fly ash and unused
reactant can improve utilization.
3. Duct pressure (spray dryer inlet pressure) influences dew
point slightly whereas plant altitude and boiler excess air
have a significant effect (Figure 1). Lower duct pressure,
higher plant altitutde and increased excess air are beneficial
to spray dryer system capability because of larger available
temperature drop.
4. The curves can be used in conjunction with each other.
For example, Figure 3 shows data for sub-bituminous coal for a
plant at sea level and operation of the spray dryer at an exit
temperature 40°F above dew point. For 90% sulfur dioxide re-
moval, if 90% absorbent utilization is assumed with 250°F flue
gas, the figure indicates that 2.9% coal sulfur content is the
maximum that can be used.
415
-------
What is the limit if the design is for 20°F above dew point
rather than 40 F? Figure 2 shows a 20°F drop in temperature
can handle about 0.7% sulfur. This, added to 2.9%, would give
a capability to handle 3.6% sulfur coal. What if the plant is
at 6,000 ft altitude rather than at sea level? Figure 1 indi-
cates that the dew point would be reduced by about 8 F. Figure
2 indicates a capability to handle 0.3% more sulfur or 3.9%
total.
The above are approximations however, the more accurate
computer program gives a sulfur limit within 0.1% of the above.
It should be noted that flue gas temperature drops for lignite
and bituminous coals would not be exactly the same as those
shown on Figure 2 because of flue gas composition differences.
5. Figures 3 through 6 indicate maximum tolerable sulfur con-
tents for a variety of conditions. For example if 80% utiliza-
tion of a 20% calcium oxide slurry is achieved for a case re-
quiring 90% sulfur dioxide removal from 300 F flue gas; lignite
could have up to 3.1% sulfur (Figure 4), sub-bituminous up to
4.4% sulfur (Figure 5) and bituminous coal in excess of 6% sul-
fur (Figure 6). It should be noted that there has not been
pilot plant demonstation with high sulfur coal.*
6. Figure 7 shows the effect on maximum sulfur content with
closer approach to dew point for lignite and sub-bituminous
coals. Closer approach would also increase absorbent percent
utilization and thus further increase maximum tolerable sulfur
content. The absorbent percent utilizations shown are illus-
trative and are not meant to imply that they would occur.
7. The figures are not affected by any additional sulfur di-
oxide removal in a downstream baghouse. The baghouse would
increase absorbent percent utilization. The higher utilization
would be used on the figures to determine the maximum tolerable
sulfur content.
BOILER INFLUENCE ON SYSTEM CAPABILITY
Figures 3 through 6 indicate a limited sulfur dioxide re-
moval capability when flue gas is at a low temperature (200 F
for example). The lower temperature limits the amount of water
and absorbent which can be sprayed into the system. Operating
limits are more likely to occur during each boiler startup or
during low load operation because of probable lower flue gas
temperature during these conditions.
Methods of alleviating this problem include the following:
1. Reducing the amount of boiler economizer surface. This
would increase the spray dryer inlet temperature but would de-
crease boiler efficiency. This cost penalty could be severe
because it would apply at high loads as well as at low loads.
*There have been some tests where flue gas was spiked with SC>2 •
416
-------
2. Install steam coil heaters to increase primary air and/or
secondary air temperature. The steam heaters would only be
used when operating at low loads.
3. Install steam coil heaters upstream of the spray dryer.
Potential for heater fouling should be evaluated.
4- Bypass some of the flue gas around the air preheaters.
This may not be acceptable for some installations because the
air preheater cold end temperature must be maintained above
the minimum recommended level to prevent corrosion. Also, the
primary air temperature could be too low to dry the coal in
the pulverizers.
5. Operate the spray dryer closer to dew point and reheat
the dryer discharge to protect the baghouse or precipitator.
6. Each of the above would increase the plant heat rate (coal
consumption). As an alternate to the above, sulfur dioxide
removal philosophy could be altered. Lower spray rates and
sulfur dioxide removal during startup may be allowable. Appli-
cable laws should be considered for each case. The new federal
emission limit allows thirty day averaging of sulfur dioxide
emissions. Local regulations should also be considered. If
higher emissions during startups can be averaged with lower
emissions during the remainder of the averaging period, boiler
desing changes or a plant heat rate penalty may not be required.
OTHER COMMENTS
Again, it is not in the scope of this paper to establish
what absorbent utilization can be expected. This is a key in
determining sulfur limit capability. Much pilot plant testing
has been done and much more is going to be done by several sup-
pliers.
The spray dryer will have an influence on the baghouse or
precipitator. Gas volume and temperature will decrease, moist-
ure content will increase, inlet grain loading will increase,
particle size distribution and ash electrical resistivity will
change. Thus far, system suppliers report no detrimental ef-
fect on pilot baghouse operation. The effect on precipitator
operation may be beneficial in some cases and detrimental in
others. Further pilot testing is warranted and will be con-
ducted this year.
At this time, the future of this method of sulfur dioxide
control looks promising. It is hoped that operational experi-
ence with the first units will justify the high level of opti-
mism prevalent at this time.
417
-------
c
"o
03
Q
o
150
130
90
/~
-------
* 4
I
•+-*
I'
5 2
100% Utilization 75% Utilization
^^^^^^^^s^^^^^^^ .^^^^^^^""^^^^^^^^
% S02 Removal % S02 Removal
70 80 90 70 80 90
-Sodium Carbonate, 30% Solution -Sub-Bituminous Coal-
Based on Coal Analysis and Conditions
Shown in this Paper
20
40
60
80 100 120 140
Temperature Drop (°F)
100% Utilization
160
180
200
75% Utilization
% SOo Removal
70 80 90 70
.30-
Calcium Oxide, 20% Slurry - Sub-Bituminous Coal
i I I l
Based on Coal Analysis and Conditions
Shown in this Paper
80 100 120
Temperature Drop (°F)
200
Figure 2. Spray dryer temperature drop related to coal sulfur content for sodium carbonate and
calcium oxide absorbents. 419
-------
200°F Gas 250°F Gas
100! J
1 2 34 5
Coal % Sulfur Limit'1'
200° F Gas
250° F Gas 300° F Gas
.90 70 % S02 90 80^70 90 80—
' ' 'I Remova.l / '
r
Sub-Bitu,
V
ninous Coal
70
0 12 3 4 5 6
Coal % Sulfur Limit'1)
200°F Gas
,908070"
250°F Gas
Removal
l 90^80
I/
Bituminous Coal
234
Coal % Sulfur Limit*1)
Removal
NOTES
(1) To stay 40° F (4.4°C) above moisture dew point
(2) Based on sea level ambient pressure —16" WG duct
pressure and 35% excess air
(3) Sodium carbonate solution is 30% concentration
(4) Based on coal analysis shown in this paper
Figure 3. Coal sulfur content limit related to sodium carbonate utilization for three types of coal.
-------
20% Slurry 30% Slurry
100
90
80
70
O
E
'_o
3
ro
60
50
40
30
90 70 90 70
'% S02i
Remova
Lignite
200°F (93°C) Flue Gas
234
Coal % Sulfur Limit'1)
10% Slurry 20% Slurry 30% Slurry
90 70
90 70
90 80 70
S0
2
Removal
Lignite
250°F (121°C)'Flue Gas
234
Coal % Sulfur Limit (1)
10% Slurry
90 70
20% Slurry
90 80 70
SO2
Removal
30%
Slurry
3Q00F(149°C) Flue Gas'
90
80
70
234
Coal % Sulfur Limit*1)
Notes
(1) To stay 40°F (4.4°C) above moisture dew point.
(2) Based on sea level ambient pressure, —16" WG duct
pressure and 35% excess air.
(31 Based on coal analysis shown in this paper
Figure 4. Coal sulfur content limit for lignite using calcium oxide absorbent for three flue gas
temperatures.
-------
100-
90
I 80
==
5
70
CD
;g
'x
O
60
O
50
ro 40
30
10% Slurry 20% Slurry 30% Slurry
1 70 90 70 90 80 70 % SOo
III
lemoval
Sub-Bituminous
200°F (93°C) Flue Gas
234
Coal % Sulfur Limit'11
6 0
10% Slurry
1)0 ~7Q
20% Slurry
S02
70
Sub-Bitummous
250°F (121°C) Flue Gas
234
Coal % Sulfur Limit'1
6 0
10% Slurry
90 80'70 % SO?
Removal
/
//I /
Sub-Bituminous
300°F (149°C) Flue Gas
234
Coal % Sulfur Limit'1'
lo
/70
30
i]
7-70
Notes
(1) To stay 40°F (4.4°C) above moisture dew point
(2) Based on seal level ambient pressure, —16" WG duct
pressure and 35% excess air
(3) Based on coal analysis shown in this paper
Figure 5. Coal sulfur content limit for sub-bituminous coal using calcium oxide absorbent for three
flue gas temperatures.
-------
100
90
c 80
o
70
0)
;o
'x
Q 60
E
50
40
30
10% Slurry
90 70
>S02
/Removal
20% Slurry
90 80 70
J_L
30% Slurry
90 80 70
> ..
.Removal
/
Bituminous
200°F (3SFC) Flue
234
Coal % Sulfur Limit (1)
Gas
10% Slurry
90~80700/c
S02_
Removal
. / /I /
Bituminous
25q°F (121°C) Flue Gas
20% Slurry
90 80
1234
Coal % Sulfur Limit*1)
70
70
6 0
10% Slurry
_90 80 70 % S02
Removal
Bituminous /
300°F (149°C> Flue Gas
Coal % Sulfur Limit'1'
90
80
70
NOTES
(1) To stay 40°F (4.4°C) above moisture dew point
(2) Based on sea level ambient pressure — 16" WG duct
pressure and 35% excess air
(3) Based on coal analysis shown in this paper
Figure 6. Coal sulfur content limit for bituminous coal using calcium oxide absorbent for three
flue gas temperatures.
-------
30% CaO Slurry
& 85% Utilization
20% CaO Slurry
& 70% Utilization
1 2
Coal % Sulfur Limit.
Figure 7. Coal sulfur content limit related to dew point approach for 250° flue gas and 90% SO?
removal.
424
-------
SELECTION, PREPARATION AND DISPOSAL
OF SODIUM COMPOUNDS
FOR DRY SOV SCRUBBERS
By:
Dale A. Furlong
Buell Emission Control Division
Envirotech Corporation
Lebanon, PA 17042
Ronald L. Ostop
Department of Public Utilities
City of Colorado Springs
Colorado Springs, CO 80903
Dennis C. Drehmel
Industrial Environmental Research Laboratory
United States Environmental Protection Agency
Research Triangle Park, NC 27711
ABSTRACT
A program has been initiated to assess an S02 removal method wherein
dry powdered sodium compounds are injected into the gas stream ahead of the
baghouse filter. The compounds are collected on the surface of the filter
bags for reaction with the gaseous S02- Initial program efforts include a
survey of suitable and available sodium compounds, methods of preparing
the compounds for injection, and an investigation of environmentally
acceptable methods of disposal.
425
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SELECTION, PREPARATION AND DISPOSAL
OF SODIUM COMPOUNDS
FOR DRY SOx SCRUBBERS
INTRODUCTION
The increasing use of high-performance fabric filters for removing
fly ash from coal^-fired boilers instigated the investigation of dry alkalis
for removing SO2 from flue gas. The possibilities of such a process were
suggested by the aluminum industry's success with a dry additive fabric
filter collector system for the control of gaseous and particulate fluorides
in the aluminum potline effluent. Subsequently there have been a number of
investigations of ways to remove SO2 with solid sorbents.
The sorbents have been various limestones or dolomites, quicklime,
hydrated lime, manganese dioxide, sodium bicarbonate, sodium carbonate, and
potassium permanganate. Investigations have confirmed that only sodium car-
bonate and sodium bicarbonate have shown good capability for reducing SO2-
Figure 1 schematically presents the key features of a system that would
inject sodium compounds into the flue gas after the preheaters.
Considerable economic incentive exists for developing a dry sodium
SO2 scrubbing system in view of current costs of wet SO2 scrubbing systems.
Using data from a recent study by Genco, et al (1975)1 (with escalation to
1979) indicates an installed capital cost of about $6 per kilowatt for the
dry sodium crushing, grinding and injection system compared to current costs
of at least $70 per kilowatt for a wet scrubbing system. The baghouse cost
was not included in the dry sodium system since all current wet scrubbing
systems also require a comparable, separate fly ash collection device.
Escalated operating costs for the dry S02 scrubber (again without baghouse)
are 1.5 mills/KWH compared to an estimated, and escalated, 2.2 mills/KWH
for a wet limestone scrubbing system.
To assure utility acceptance of a dry SOX removal system by injecting
dry sorbents upstream of a baghouse filter, it is essential to identify a
near-term and long-term supply of sorbents. Previous testing has shown
the apparent superiority of sodium bicarbonate in the form of nahcolite
for reaction with SOX/NOX in the dry form. Other candidate sorbents were
evaluated as alternates considering the current availability of nahcolite.
To prepare the sodium compounds for use in the dry SOX removal systems,
they must be reduced to fine powders for injection and to increase the
426
-------
SODIUM
CARBONATE
COAL
COMMINUTE [GRIND]
SODIUM + SODIUM + FLYASH
SULFATE NITRATE
FIGURE 1
"DRY SCRUBBING" WITH SODIUM SALTS
-------
surface area for improved chemical resistivity. Currently, tests are under
way to evaluate mechnical grinding and thermal comminution.
Several methods of disposal for the spent sodium compounds from dry SO2
removal systems are being considered, including clay isolation land fill and
insolubilization by chemical methods and by sintering.
POTENTIAL SOURCES OF SODIUM COMPOUNDS
Nahcolite
Nahcolite ore is a naturally occurring mineral containing 70 to 90%
sodium bicarbonate. it is found almost exclusively associated with oil
shale. Vast resources of oil shale and associated nahcolite exist in the
Eocene Green River formation in the Piceance Creek basin of northwest
Colorado. According to the United States Bureau of Mines, this area is
conservatively estimated to contain 32 billion short tons of nahcolite.
In 1976, the Bureau launched a multi-year oil shale research and testing
program to identify and resolve environmental problems associated with the
development and mining of the deep deposits of oil shale and associated
saline materials. A ten-foot diameter pilot mine shaft was completed in
1978 at the Bureau's research facilities in Horse Draw, Rio Blanco County,
Colorado.
Vast resources of the sodium minerals, nahcolite (NaHCOs) and dawsonite
(NaAl(OH)2CO3)i exist in the rich oil shale of the Green River Formation.
The significant quantities of the sodium minerals are restricted to the lower
portion of a geologic unit called the Parachute Creek Member. The nahcolite-
bearing oil shale reaches a maximum thickness of about 1130 feet at the chemi-
cal depositional center for the nahcolite, dawsonite, and the associated halite
(NaCl). The top of the sodium mineral-bearing section ranges in depth from
approximately 1400 to 2000 feet below the ground surface. Nahcolite occurs
in four distinctive forms:
1. Brown microcrystalline beds
2. White coarse-grained beds
3. Laterally continuous units of fine-grained crystals disseminated
in oil shale
4. Disseminated rionbedded crystalline aggregates
In coreholes analyzed by the United States Geological Survey, the nahcolite
resource ranges from a low of 174 million short tons to a maximum value of 489
million short tons per square mile. About 257 square miles are underlain by
nahcolite-bearing oil shale with thicknesses in excess of 100 feet. According
to the United States Bureau of Mines, this area is conservatively estimated to
contain 32 billion short tons of nahcolite.
428
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Trona
Trona contains about 50% sodium carbonates. Major trona deposits are
in the Green River formation in southwestern Wyoming. The total reserves
in this area are estimated at 85 billion short tons. The Green River trona
is currently a major source of ore for commercial production of soda ash.
Unfortunately, tax considerations (depletion allowances) do not favor the
use of small quantities of trona as a raw ore.
The Owens Lake in California is a source of sodium compounds available
for immediate use. The relatively small current production could be readily
expanded. Depletion allowance taxes are not a problem. However, the limited
quantity of sodium available means that the source is only of interim interest
assuming widespread acceptance of dry SC>2 removal.
The evaporite deposit at Owens Lake is a complex mixture of sodium
carbonate, sodium bicarbonate, sodium sulfate and sodium chloride including
double salts, hydrates and saturated brine, all resulting from the dessication
of a large saline lake that existed until about 60 years ago.
In 1917 the City of Los Angeles completed construction of an aqueduct
which draws water from the Owens River. The Owens River was the principal
source of water feeding the then 100-square-mile lake. Its diversion allowed
the lake level to decline due to evaporation. As a consequence, its dissolved
salts became concentrated until they began to precipitate onto the lake bed.
When the lake finally reached a new state of equilibrium, it had shrunk to
less than 40 percent of its original size, forming a solid deposit of mixed
salts wet with interstitial brine.
The Owens Lake evaporite deposit covers an area of approximately 35
square miles at the lower end of the Owens Valley in Inyo County, California.
The nearest town is Lone Pine which lies about 10 miles north. The elevation
of the surface of the lake is about 3500 feet above sea level. The lofty
Sierra Nevada range (including Mt. Whitney) rises abruptly to the West while
the eastern side of the valley is formed by the lower and more arid Inyo
Mountains. Precipitation averages only 4 to 5 inches per year and the net
evaporation rate is about 66 inches.
The area is served by a branch line of the Southern Pacific Railroad
which passes along the western edge of the lake, providing a direct rail
linkage with the harbors of Los Angeles and Long Beach, a distance of roughly
240 miles. Also the U.S. Highway 395 between Los Angeles and Reno passes
immediately alongside the lake.
The raw ore from Owens Lake, upgraded only by mining methods, appears
attractive for use as a sorbent in the SOp removal system. However, it also
appears attractive to upgrade the raw ore to relatively pure sodium bicarbonate.
It has been estimated that 92% pure sodium bicarbonate could be produced at
the Owens Lake for approximately $50 per ton compared to estimates of $17
per ton for the raw ore. This appears quite attractive assuming improved
performance and lower handling and shipping costs.
429
-------
Supply Prospect
Primarily because the oil shale program is still in its exploratory phase,
immediate supply of nahcolite in quantity at reasonable cost is questionable.
Assuming that full-scale dry SOx/NOx removal systems were successfully demon-
strated both technically and economically, commitments from utilities on
nahcolite consumption still would be needed to start the commerical mining
of nahcolite.
To resolve sodium compound supply problems for immediate implementation
of dry SOx/NOx removal systems, it is possible to use crude trona and/or high
purity sodium bicarbonate upgraded from the crude dry lake ore. Production
of 1.5 million short tons per year of sodium bicarbonate for 35 years is a
possibility from Owens Lake.
Potential Demands
The estimated 32 billion tons of nahcolite could be used to desulfur
610 billion tons of 0.7% sulfur coal assuming the requirement of 7.5 pounds
of nahcolite per pound of sulfur removed. This indicates the adequacy of
the nahcolite resource since the entire reserve of western bituminous and
sub-bituminous coal is estimated at 430 billion tons.
DISPOSAL OF SPENT SORBENTS
Land Fill
Possibly the simplest method for disposal of spent sorbents is the land
filling technique. In this technique a combined trench and area land fill
method is used. The basic building block for the land fill is the isolation
cell concept, such as has been used for sanitary fill. The spent product
for one working day is transported to the site, emplaced, and compacted,
The day's production constitutes the basic volume for one cell. This com-
pacted cell is completely covered with a layer of claylike material, which
in turn is also compacted at the end of each working day. Therefore, the
soluble spent sorbent is encapsulated in an essentially impermeable shell
of silty clay or similar material. It is important that the landfill be
constructed on a base of material that has low permeability so that leaching
is minimized.
Chemical Fixation
The Envirotech Chemical Sludge Fixation Process is based on the patents,
research, and commercial operations of the Chemfix Process. This process
involves the reaction of two or more chemical additives with the waste material
to form a chemically and mechanically stable solid. This inorganic chemical
system has proven stability when in contact with all of the usual environ-
mental elements of change: soil, water, air, sunlight and micro-organisms.
The quantity of chemicals added to the waste usually does not increase the
final volume of the solidified material by more than 10 percent; in most
cases, the increase is less than 5 percent.
430
-------
The particular choice, ratio, and quantities of chemicals used for any
given waste treatment application depend upon three factors:
1. The waste
2. The speed of reaction require
3. The end use of the solidified material
Since the reaction process involves a gelatin stage followed by a hardening
period, gelationtime is an important factor in designing the chemical para-
meters of the system. Desired gelation time may depend, for example, on
whether the material is to be pumped for some distance after mixing and
on the method of disposal. End use of the solidified waste is important
because the end product can be either hard of quite soft and can be made to
have varying textures. If it is to be in contact with a high water table,
or even be under water, the nature of the contacting water will also determine
chemical design.
The system, as it is normally used, reacts with all polyvalent metal
ions producing stable, insoluble, inorganic compounds. It is also reactive
with acids, certain nonmetallic ions, and some organic compounds. Nonreactive
materials are physically entrapped in the matrix structure resulting from the
reaction process. Because of this variety of entrapment and reaction possi-
bilities, each system must be custom designed for the particular chemical
problem presented by the waste material to be processed.
Sintering
Laboratory experiments have also demonstrated that spent sorbent can be
insolubilized by mixing it with, fly ash and/or bottom ash, forming an agglomerate,
and sintering at about 1800°F. The sintered material may be disposed of by
known landfill techniques or used as an aggregate for road beds, concrete, etc.
REFERENCES
1. Genco, Rosenberg, Anastas, Rosar and Dulin, "The Use of Nahcolite Ore
and Bag Filters for Sulfur Dioxide Emission Control", APCA Journal,
Vol. 25 No. 12, December 1975, p. 1244
METRIC CONVERSION TABLE
1 inch = 2.54 centimeters
1 foot = 0.3048 meters
1 mile = 1.6093 kilometers
1 square mile = 2.590 square kilometers
1 ton/square mile = 2.855 kilograms/square meter
1 short ton = 907.2 kilograms
1 dollar/ton = 0.1103 cents/kilogram
431
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HIGH VELOCITY FABRIC FILTRATION FOR CONTROL OF COAL-FIRED BOILERS
By
John C. Mycock
Enviro-Systems & Research, Inc.
Roanoke, Virginia
Rodney A. Gibson
Joyce M. Foster
Environmental Testing Services, Inc.
Roanoke, Virginia
ABSTRACT
As a follow-up to a pilot plant study, a full scale investigation of
applying high velocity fabric filtration to coal-fired boiler fly ash control
was conducted. Two filter systems were separately applied to two 60,000
Ib./hr. coal-fired boilers. Performance evaluations conducted over the.
course of a year included total mass removal efficiency and fractional effi-
ciencies. One filtration system employed Teflon felt as the filter medium
while the second system employed Gore-Tex, a PTFE laminate on PTFE woven
backing. During the course of the year, a limited number of glass, felt;and
woven glass bags were introduced into the house containing Gore-Tex.
As a separate option, the second system was outfitted entirely with woven
glass bags. Preliminary results indicate acceptable performance at an air-to-
cloth ratio of 6 to 1. Future plans call for utilizing one of the baghouse
systems for S02 removal.
INTRODUCTION
For the past six years Enviro-Systems & Research, Inc. has been involved
in an EPA project to determine the techno-economic feasibility of applying
high velocity fabric filtration to control the fly ash emissions of an indus-
trial coal-fired stoker boilerJ
432
-------
The program started on a small scale in 1973 and financial participation
was divided equally among EPA, Kerr Finishing Division of FabricsAmerica and
Enviro-Systems & Research, Inc. The Kerr plant, located in Concord, North
Carolina, served as the host site for the program while Enviro-Systems &
Research designed, fabricated and installed the pilot baghouse (Figure 1).
The pilot program provided a short-term screening of a number of filter media
and the data gathered along with preliminary economic analysis indicated that
long-term bag life and performance studies were warranted.2 EPA at this point
decided to award a contract for the full scale demonstration unit for this
approach to fly ash control. The demonstration contract was awarded Fabrics-
America, with Enviro-Systems & Research as the major subcontractor responsible
for the design, fabrication, installation and operation of the full scale
fabric filter system (Figure 2).
The purpose of the demonstration program is the testing of a full scale
fabric filter system installed on an industrial coal-fired stoker boiler and
data generated by the program include general operating parameters, media
changes and life data and particle size removal efficiencies as a function of
on-stream time.
Contract options called for the long term testing of other promising filter
media and to evaluate the fabric filter system as a vehicle for the removal of
sulfur dioxide
KERR - THE HOST SITE
The Kerr Finishing Division of FabricsAmerica is a textile dye and finish-
ing plant located in the textile belt of central North Carolina.
Kerr's normal production schedule is three shifts per day, five days per
week with 450-500 employees. Plant capabilities include processes to bleach,
mercerize, dye, nap, finish and sanforize both cotton and synthetic fabrics,
as well as cutting and preparing corduroy.
Two Babcock & Wilcox steam boilers are in operation at the Kerr facilities.
Each has a design capacity of sixty thousand pounds of steam per hour and both
are equipped with spreader stokers. Each boiler has a two-hour peaking
capacity of seventy thousand pounds per hour. The design efficiency of these
units is 82 percent. Based on the above parameters, the heat input for these
units is 73.2 million BTU/hour each. Both boilers are equipped with fans for
supplying draft and unit number two, the unit tapped for the pilot plant
stream, has overfire steam injection for better combustion control. In Jan-
uary, 1973, emission tests were conducted on these boilers. The particulate
emission rates were found to be approximately 130 pounds/hour versus an
allowable rate of about 25 pounds/hour. Gas volumes were determined to be
about 35,000 ACFM at a temperature of about 355°. Thus the grain loading
measured was about 0.4 grains per ACFM. Orsat analysis indicated 9.5%, C02,
10% 03, 0% CO and 80.5% N2- Coal analysis indicated the sulfur content to be
about 0.6%.3
433
-------
Figure 1
Kerr Pilot Plant
434
-------
Figure 2
EPA DEMONSTRATION OF THE ENVIRO-SYSTEMS FABRIC FILTER SYSTEM
AT KERR FINISHING DIV FAERICSAMERICA,CONCORD,NORTH CAROLINA
-------
HARDWARE DESCRIPTION
Each boiler is serviced by its own fabric filter system. The heart of
each system is the baghouse which is identical in terms of basic hardware.
Each baghouse is designed to contain a total of 7,440 square feet of cloth.
The house is subdivided into eighteen (18) cells, each cell containing thirty-
six (36) bags giving a total house capacity of 648 bags. The bags are 8' - 8"
long and 5" in diameter, giving 11.5 square feet of cloth per bag. The bags
are hung from the tube sheet, locked in place by two snap rings which are sewn
into the bags. The bags are secured to a metal grid at the bottom. A metal
cage is set inside the bags to prevent collapse. The baghouses are constructed
of 10 gauge mild steel while the hoppers are of 3/16" mild steel plate con-
struction. Both house and hopper are insulated with two (2) inches of fiber
board covered with a mild steel skin (Figure 3).
BAGHOUSE OPERATION
The system is brought on line by closing the boiler stack damper and
opening the system inlet damper. An auxiliary heater can be employed to pre-
heat the house prior to start-up and it can also be used to purge the house
prior to shutdown. The vortex damper is employed to maintain a predetermined
pressure at the boiler stack, independent of pressure drop fluctuations
through the baghouse system (Figure 4). The operation of the baghouse is as
follows: The dirty gases enter one end of the house, pass through the tapered
duct.into a classifier, then through the bags. The classifier forces the
dirty gases to change direction abruptly, forcing the heavier particles
directly into the hopper. Dirty gases enter the classifier through a central
tapered duct to feed the same quantity of gas into each cell.
The gases are now forced through the fabric, the particulate is deposited
on the outside of the bag while the clean gas passes through the center of
the bag and into a center exit plenum via an open damper above the tube sheet.
The bags are cleaned one cell at a time by closing the cell damper and at the
same time introducing clean gas in the reverse direction. The in-rush of
cleaning gas expands the bag with a shock causing the "cake" to crack and the
particulate falls off the bag into the hopper.
Now that the shock has broken off the outer crust, the flow of clean gas
continues pushing and pulling the dust particles away from the fabric in an
operation called "drag". This phase of the cleaning has proven significant
in minimizing the re-entrainment of fine particles during the cleaning cycle
(Figure 5).
The entire operation is monitored and controlled by a console located in
the control house. The control panel (Figure 6) is arranged in three sections,
with test instrumentation located in the center and baghouse controls at left
and right.
436
-------
General Arrangement 5D-IO
"Not For Construction Purposes
CO
Pyramid Hopper
Figure 3
SD General Arrangement with Pyramid Hoppers
-------
TO ATMOSPHERE.
(EXHAUST)
CO
CO
PiSCHAK&E. VALVES
Figure 4
EXHAUST
fSHuT OFF)
Fabric Filter Schematic
-------
STEP 2
THE FABRIC FILT
Otrty
the Ctaealfler at one
wOWWwIWO Hi 10 IfMI ftOf^JDMW.
mvvran cMf*c*
TMs quick change In
lifa^illiiii jkj Until **MU«M*« lh_a '
OTWHvff v* ROW fwffwVn tnw
Step 1
Baghouse Pictorial Shov;ing Gas Flow
The g«M« now p**t Ihrouflh th«
fibrtc. depoiltlng Hi* remaining
p*rticul*t* on the oul«t turfict ol
th» bag*. Thl* dvpotll I* periodi-
cally rcmovad from th« laoric
aurfac* by th« unlqu* SHOCK-
DRAG Cleaning Sytl»m. deilgn-
ed to prolong bag life by mini-
mizing dltlortton of the fiber*.
Step 2
Baghouse Pictorial Showing Gas Flow
FEP 3
STEP 4
SHOCK
A* *oHd matter collect* on the
outtkte of the filter bag, a cake or
cruet to formed which begin* to
rtMrfct the flow of ga*. When the
. pressure drop aero** the fabric
rtache* a predetermined level, a
damper I* actuated which teolate*
Hie cell from the main gat stream
and rimuftaneoutly Introduce*
cleaning ga* flowing In the re-
v*r»e direction. The biruah of
cleaning ga* rapidly clittend* the
finer bags, cracking the dust cake
and permitting the large agglo-
merated piece* to fall into the
hopper.
DRAG
Now lhat the SHOCK ha* broken
off In* outer crutl, lite flow of
clean ga* continue*, pushing and
pulling (he du*t particle* away
from the fabric In an operation
called DRAG. The*e finer parti-
cle* are forced from the bag and
propelled Into the hopper The
Envlro-Clean SO I* unique In that
It provide* both SHOCK and
DRAG In Independently control-
lable amount*. The Drag cleaning
pha*e ha* proven significant In
minimizing re-*ntralnment of the
fine particulate during the clean-
Ing cycle.
Step 3 Step 4
Baghouse Pictorial Showing Gas Flow - Shock Baghouse Pictorial Showing Gas Flow - Drag
Figure
439
-------
Figure 6
Control Panel
440
-------
Since the 1976 start-up, several modifications have been made to the system,
both to solve unanswered questions as well as to create optimum operating con-
ditions. In order to obtain more effective cleaning of the bags, two differ-
ent measures were undertaken. On Baghouse No. 2, the original flapper dampers
at the top of each cell were replaced by poppet valves. Six months operation
indicates that the dampers now seal better and have increased cleaning pres-
sure. In Baghouse No. 1, a pulse-jet system was added to the existing reverse-
flush cleaning systems. The combination cleaning system (shock-drag with
pulse assist) has proven extremely effective and indications are that the
system can clean down even under the most severe conditions.
One other major modification was made to System No. 1. In 1978, a multi-
cyclone was installed after the pre-heater but prior to the baghouse system
inlet damper. Particle size data, obtained both before and after installation,
show some reduction, after installation, in the concentration of larger
particles.
FILTER MEDIA
The fabrics screened in the original pilot program were: Teflon Felt Style
2663 (21-29 oz./yd.2), a tetrafluoroethylene fluorocarbon; Gore-Tex (4-5 oz./
yd.2), a microporous Polytetrafluoroethylene (PTFE) membrane on a woven PTFE
fabric backing; Dralon-T felt (12-15 oz./yd.2), an Acrylonitrile homopolymer;
and Nomex felt, a high temperature resistant nylon fiber (polyamide). Of these
media, Teflon felt and Gore-Tex PTFE laminate proved the most promising and
were selected as the first to be employed in the demonstration project.
Baghouse No. 1 was outfitted entirely with Teflon felt and in the ensuing
twenty-four (24) months of operation has yielded an average replacement rate
of 5% per year with no recorded failures during the first year. During this
time the house was on-stream five or six days per week with the only signifi-
cant maintenance being industrial vacuuming of the bags which occurred twice
during the first year's operation.
Baghouse No. 2 was started up in 1976 with a complete complement of Gore-
Tex bags. One cell (36 bags) was replaced with Huyck glass felt bags in March
of 1977 while another cell was outfitted with Globe Albany 22% oz. woven glass
bags in May of 1977. Neither of these last cells has shown failure to date.
Gore-Tex, which had shown a 10% replacement rate after the first year's
operation, was completly replaced with 22.5 oz. woven glass bags during the
summer of 1978. It is felt that a large number of the Gore-Tex failures can
be attributed to manual cleaning and movement of the bags.
Nomex felt and a 15 oz. woven glass bag were also tested in Baghouse No. 2
during 1978. Both were found to be lacking in endurance.
441
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DATA
A profile of the flue gas at the inlet of each baghouse is shown in Table
1.
Characterization of the outlet particle size distribution shows that each
of the media tested thus far (Teflon felt, Globe Albany 22.5 oz./yd/ woven
glass and Gore-Tex), emits essentially the same range of particle sizes (Table
2 and Figure 7). All comparisons are made at a 6/1 A/C ratio which has been
the predominant level of operation at Kerr.
All media tested performed well within the emission boundries set for the
Kerr boilers by the State of North Carolina, with the woven glass showing the
lowest outlet emissions and Teflon felt the highest (Figure 8).
ECONOMICS
The economics of applying the three media tested to the Kerr boilers were
evaluated and compared with those of an electrostatic precipitator.
Installed costs were developed for a fabric filter collector sized to
handle 70,000 ACFM at 350° F at air-to-cloth ratios of 3, 6 and 9 to 1.
Table 3 shows the influence that the cost of the bags exerts on total installed
costs.
Figure 9 shows a comparison of the installed costs for the three bag
materials versus the installed costs for an ESP handling the same volume of
flue gas but at efficiencies of 95% and 99%. The ESP costs were developed by
summing flange-to-flange costs (supplied by an ESP manufacturer) and 70% of
the purchase price for erection costs. (This same 70% was used in developing
fabric filter erection costs.)
Operating costs were developed for the fabric filters with two, four and
six year bag lives and compared with those of the electrostatic precipitator.
Fabric filter operating costs were based on actual pressure drops observed at
the 6 to 1 air-to-cloth ratio. Precipitator pressure drops were assumed to
be 0.5" W.G. Electrical rates are actuals obtained from Kerr. These costs
presented in Figure 10 illustrate the importance of achieving longer bag life.
Annualized costs were calculated using the straight line method of depre-
ciation, 6 2/3% per year over 15 years. Other costs called capital charges,
which include interest, taxes and insurance, are assumed equal to the amount
of depreciation or 6 2/3% of the initial installed costs. Therefore, depre-
ciation plus these other annual charges amount to 13 1/3% of the installed
costs. As illustrated in Figure 11, the baghouse employing any of the fabric
systems is favorable once a four-year bag life is achieved.
Development of annualized costs employed the formulae published by
Edminsten and Bunyard.H)
442
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Table 1
Inlet Gas Stream Profile
Inlet to Teflon
Felt House
Inlet to Gore-Tex
(1977), Then Woven
Glass (1978) House
Flue Gas Composition
CO? (%)
CO (%}
02 (X)
H20 (%}
Temperature (° F)
Gas Volume (ACFM)
Grain Loading (Grains/dscf)
Inlet Flow Rate (Ft./Sec.)
Inlet Opacity (%}
4.5
0
15.2
5.1
322
37,700
0.5356
76.7
4.4
0
14.6
3.1
317
35,300
0.4272
61.1
40
443
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Table 2
Outlet Characterization by Andersen Irrpactor
(Particle Sizing)
G/C Ratio 6/1
Teflon Felt
Stage
1
2
3
.P> ^
"5
6
7
8
Back-Up
Filter
Diameterf
Microns
>11.40
8.00
4.93
3.47
2.2.6
1.04
.63
.46
<.46
Total
Loading-
Grains/
dscf
.01503
. 00348
.00326
.00271
.00266
. 00230
.00174
.00101
.00174
.03393
Cumulative^
7,
55.70
45.45
35.84
27.85
20.01
13.23
8.10
5.13
-
Woven Glass
Diameter,
Microns
>10.89
7.64
4.70
3.31
2.15
.99
.59
.43
<.43
Total
Loading,
Grains/
dscf
.00319
. 00062
.00057
. 00041
.00043
.00044
.00035
.00036
. 00027
.00664
Cumulative
51.96
42.62
34.04
27.86
21.39
14.76
9.49
4.07
-
Diameter ,
Microns
>10.43
7.32
4.51
3.17
2.06
.95
.57
.41
Total
Gore-Tex*
Loading,
Grains
dscf
.00304
.00102
.00116
.00063
.00075
.00085
.00069
. 00035
.00056
.00905
Cumulative
70
66.41
55.14
42.32
35.36
27.07
17.68
10.06
6.19
-
"Wan Effective Cut Diameter
rfean Loading Per Stage
~Vfean Cumulative 70 Less Than Size Indicated
Probe and Nozzle Washes Were Collected
-------
co
Pi
o
^
o
•H
(1)
J-J
•H
4-1
a
cu
w
10
8.0
6.0
4.0
2.0
1.0
.8
.6
O Teflon Felt
!•
& Woven Glass, 22.5 oz/yd"
Gore-Tex
2 5 10 20 40 60 80 90
Cumulative % Le,ss Than Size Stated
Figure 7
Outlet Particle Size Distribution for Each of
Three Filter Media
(G/C Ratio 6/1)
445
-------
30 -
20
•I-l
M
CO
•P
CU
§ 10
0
State of North CarolinaLimt 25Lb./Hr_J_
4->
i-l
(^
M-J
I
CJ
§
o
G/C Ratio 6/1
Figure 8
Performance of Three Filter Media in Controlling
Emissions from a Coal-Fired Boiler"~
probe and nozzle washes were collected.
446
-------
Table 3
Bag Cost as a Percentage of Installed Cost
Filter Media
Installed Cost
Bag Cost
Bag Cost as % of
Installed Cost
Teflon Felt
A/C: 3/1
6/1
9/1
$285,080
153,700
120,570
$114,480
57,240
38,160
40.2%
37.2
31.6
Woven Glass
A/C: 3/1
6/1
9/1
210,884
116,602
95,838
40,284
20,142
13,428
19.1
17.3
14.0
Gore-Tex
A/C: 3/1
6/1
9/1
267,800
145,060
114,810
97,200
48,600
32,400
36.3
33.5
28.2
447
-------
400 _
300
co
I-l
a
on
o
i-i
X
CO
-u
en
13
4-1
CO
200
100
50
O Teflon Felt
A Globe Albany Woven Glass
D Gore-Tex/Gore-Tex
• ESP (At 2 Efficiencies)
2/1
4/1
6/1
G/C Ratio
3/1
10/1
Figure 9
Comparison of installed Costs for Three Filter
Media and Electrostatic Precipitators
448
-------
60 r
50
§ 40
i—i
r-j
a
CO
O
30
a
<§•
20
10
o Teflon Felt
A Globe Albany
Woven Glass
n Gore-Tex/Gore-Tex
—- ESP (At 2 Efficiencies)
6A
24 6
Filter *fedia Life, Years
Figure 10
Comparison of Operating Costs for Three Filter Media
and Electrostatic Precioitators
449
-------
90 r
w
cd
r-4
rH
a
ro
o
X
1-1
8
•U
4-1
U3
to
80
70
60
50
40
30
99%
O Teflon Felt
^ Globe Albany
Woven Glass
Q Gore-Tex/Gore-Tex
ESP (At 2 Efficiencies)
G/C Ratio 6/1
95%
246
Filter Media Life, Years
Figure 11
Comparison of Annualized Cost of Control for Three
Filter Media and Electrostatic Precipitatdrs'
450
-------
CONCLUSIONS
During the first two years of the full-scale demonstration project, three
filter media (Teflon Felt Style 2663, Woven Glass 22.5 Oz./Yd.2 and Gore-Tex
PTFE Laminate) were evaluated for performance and economy in controlling the
fly ash emissions from a stoker boiler. The media all performed well within
the particulate emission limits set by the State of North Carolina and each of
the media tested emits essentially the same range of particle sizes.
Teflon felt has been operating for better than twenty-four (24) months
and appears the most likely candidate to achieve a four-year (and possibly
more) bag life.
All of the media studied appear favorable in terms of annualized costs
when compared with an electrostatic precipitator at 99% efficiency, once a
two-year bag life is achieved.
In January of 1979 a fire of major proportions destroyed the operating
facilities at Kerr. The boilers and baghouses, although unharmed, have not
operated since. Present plans call for the relocation of the baghouses to a
recently acquired Kerr facility in Travelers Rest, South Carolina.
It is anticipated that the test program will start again in the fall of
1979 at its new location.
451
-------
REFERENCES
^cKenna, 0. D., "Applying Fabric Filtration to Coal-Fired Industrial Boilers:
A Preliminary Pilot Scale Investigation". EPA 650/2-74-058, July, 1974.
2McKenna, J. D., Mycock, J. C. and Lipscomb, W. 0., "Applying Fabric Filtration
to Coal-Fired Industrial Boilers: A Pilot Scale Investigation". NTIS PB-245-
186, August, 1975.
3McKenna, J. D. and Brandt, K. D., "Demonstration of a High Velocity Fabric
Filtration System Used to Control Fly Ash Emissions". Presented at the Third
Symposium of Fabric Filters for Particle Collection, Tucson, Arizona,
December 5-6, 1977.
4Edminsten, N. G. and Bunyard, F. L., "A Systematic Procedure for Determining
the Cost of Controlling Particulate Emissions from Industrial Sources".
Journal of the Air Pollution Control Association, V20, N7, p. 446 (1970).
ACKNOWLEDGEMENTS
This program was sponsored by the Federal Environmental Protection Agency
with participation by Kerr Industries and Enviro-Systems & Research, Inc.
452
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EPA MOBILE FABRIC FILTER - PILOT INVESTIGATION OF
HARRINGTON STATION PRESSURE DROP DIFFICULTIES
by
W.O. Lipscomb, S.P. Schliesser, and S. Malani
Acurex Corporation
Research Triangle Park, North Carolina
ABSTRACT
This report describes the Environmental Protection Agency mobile fabric
filtration performance evaluation at Harrington Station, Amarillo, Texas. The
primary objective was to evaluate several bag candidates for new and retrofit
application for the full-scale baghouse systems. A secondary objective was to
evaluate operating and cleaning parameters. The purpose was to assess alter-
nate means for reducing high pressure drop levels currently being experienced
at Harrington Station. The mobile facility was operated in a representative
manner with the full-scale baghouse for candidate bag evaluation. Appropriate
changes in cleaning parameters showed reduction in pressure drop levels, as
did alternate bag types. Results from electrostatic measurements indicated
that significant charging levels exist. Performance results from the mobile
baghouse are discussed and related to the full-scale system.
INTRODUCTION AND OBJECTIVE
This pilot-scale fabric filter is one of three conventional particulate
emission control devices mobilized by the Particulate Technology Branch,
Utilities and Industrial Power Division, Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency (PATB/UIPD/IERL/EPA), Research
Triangle Park, North Carolina. The objective is to evaluate and compare the
performance characteristics of a pilot-scale baghouse, electrostatic precipitator
(ESP), and scrubber on industrial particulate emission sources. The purpose
is to provide characteristic information and insight for appropriate selection
of particulate control devices, in light of operation, performance, and cost
considerations.
The Harrington Station Unit No. 2 fabric filter system, belonging to
Southwestern Public Service Company (SPS Co.), was of interest to IERL/EPA
prior to its startup in June 1978. Among other evaluations, IERL had directed
a performance evaluation to be conducted with its mobile baghouse system on
Unit No. 1 during the spring of 1977.* One of the bag/cleaning cases studied
during this evaluation was representative of the Unit No. 2 baghouse system.
Data from this representative case were integrated into the baghouse perfor-
mance model by GCA Corporation.2 The model predicted that operating pressure
drop levels would be significantly higher than the design levels. As pre-
dicted, the operating pressure drop level currently being experienced is
significantly higher than the design level. In light of these circumstances,
SPS Co. and IERL have cooperatively entered into an investigation to be
453
-------
conducted with the EPA mobile baghouse to assess pressure drop remedies.
Acurex performed and conducted this investigation by evaluating several bag
candidates and other pertinent pressure drop parameters.
This report summarizes the results of the second EPA mobile baghouse
performance evaluation at Harrington Station during the spring of 1979- The
mobile baghouse treated a slipstream from Unit No. 1 educted upstream from the
pollution control system. The conditions of the slipstream and the pilot
baghouse were representative of the Unit No. 2 flue stream and baghouse sys-
tem, respectively. Boiler and pilot baghouse operating data were collected on
a regular basis. Particulate concentration and size distribution measurements
were conducted on the influent and effluent streams. Several glass fiber bag
types were methodically evaluated, with emphasis on pressure drop performance
and characterization. Performance levels and trends are included in this
report, along with analytical discussions on operating and particulate data,
coal type, and means of data reduction and interpretation.
CONCLUSIONS
• Acid-Flex fabric had the best operating performance characteristics
of the candidate bags evaluated.
• The Teflon B fabrics and the silicone-graphite fabric had comparable
performance characteristics.
• Increasing shake frequency resulted in dramatic improvements in
cleandown for all fabric types.
• Increasing deflation pressure resulted in significant improvement in
cleandown for all fabrics.
• Silicone-graphite bags had slightly higher emission levels than the
other bag types.
• Cage voltage measurements indicated that sufficient electrostatic
levels are present to have a potential effect on cleandown and
porosity.
• The Wyoming/New Mexico coal blend appeared to generate a dust cake
with slightly better cleandown characteristics.
DESCRIPTION OF FACILITIES
Test Site
Harrington Station is owned and operated by Southwestern Public Service
Company. It consists of two 350 MWe pulverized coal (PC)-fired boilers. The
identical boilers were completed from 1976 to 1978 and represent current
design and operating methodology. Emissions are controlled by a series com-
bination ESP/marble-bed wet scrubber on Unit No. 1, and by a baghouse with
454
-------
silicone-graphite coated glass bags on Unit No. 2. A third unit, now under
construction, will employ a baghouse. Bag selection for Unit 3 has not been
finalized.
Harrington Station generally burns a low sulfur coal from Gillette,
Wyoming. Due to limited availability of Wyoming coal, a New Mexico type was
fired to supplement coal reserves. Site characterization data for the
Harrington Station boiler, flue gas and coals are presented in Tables 1 and 2.
Full-Scale Baghouse
The emissions from Unit No. 2 are controlled by a fabric filter, consis-
ting of two houses designated East and West, each with 14 compartments.
Detailed design and operating specifications are given in Table 3.3 In
March 1979, after 6 to 8 months of on-stream time, the operating pressure drop
ranged from 9 to 11 inches W.C. at full load and SPS Co. projected additional
bag life to be a maximum of 6 months.
Pilot Baghouse
The EPA mobile baghouse consists of a single compartment containing three
14.1 cm (5 9/16 in.) diameter by 1.83 m (6 ft.) long bags. Designed for the
purpose of determining the effects of dust properties, fabric media, cleaning
parameters and other operating parameters on fabric filter performance, the
system has the following capabilities:
• Filtration at cloth velocities as high as 6 m/min with a pres-
sure differential up to 50 cm of water and at gas temperatures
up to 260°C.
• Adaptability of mobile system to cleaning by mechanical shake,
pulse jet, or low pressure reverse flow with cleaning param-
eters varying over a wide range.
• Continuous 24-hour operation with use of automatic instruments
and controls.
The mobile fabric filter is housed in a 2.4 m by 12 m tandem-axle
trailer. A more complete description of the EPA mobile baghouse is
presented in Reference 4.
PROGRAM METHODOLOGY
Installation
The mobile baghouse was located adjacent to and then slipstreamed
from Unit 1. The slipstream probe was installed in the ductwork down-
stream of the air preheater and upstream of the pollution control de-
vices. The slipstream was withdrawn and isothermally transported to the
pilot unit at velocities somewhat less than plant conditions. A return
line from the pilot baghouse back to the site inlet duct was employed due
455
-------
TABLE 1. HARRINGTON STATION
COAL ANALYSIS* SUMMARY
Slack Thunder Mine
Campbell County, Wyoming
Moisture
Ash
Volatile
Fixed Carbon
MJ/kg
Sulfur Content
Typical
28.4
4.8
31.9
35.0
100%
20.0
0.33
Rant
24.2 -
3.3 -
27.4 -
31.0 -
13.3 -
0.09 -
je_
34.4
5.7
38.0
40.0
21.3
0.51
*all analyses as received
McKinley Mine
Gallup, New Mexico
Range
14.0 - 15.5
11.5 - 13.5
23.2 - 24.8
.33 - .40
TABLE 2. BOILER AND FLUE GAS CHARACTERISTICS7
Boiler Type
Generation Capacity
Coal Type
Flue Gas Flow Rate
Gas Velocity
Temperature
Particulate Loading
C02
H20
Pulverized Coal (PC)
350 MW
Low Sulfur Low Ash Wyoming
Low Sulfur High Ash New Mexico/
Wyoming Blend
34000 acm/min
24 - 30 m/sec (78.7 - 98.4 ft/sec)
125 - 185°C (257 - 365°F)
2.4 - 3.4 gm/DNCM (1.05 - 1.5 gn/OSCF)
12.3%
5.0%
77.0%
5.7%
456
-------
TABLE 3. DESIGN AND OPERATING SPECIFICATIONS
FOR HARRINGTON UNIT NO. 2, SAGHOUSE 3'8
Desian
Metric
Gas temperature
Gas Flow Rate
A/C Ratio
Sag type
Compartments
Sags/Compartments
Sag Design
Bag Dimensions
Number of Sags
Total Cloth Area
Cleaning Mode
156°C
4.67 x 10 aonn
1 m/sec
Sill cone/Graphite
coated glass fiber
28
204
Caps with Eye Bolts
0.29 x 9.3-m
5712
4.78 x 104m2
Deflate/Shake
313°F
1.65 x 105 acfm
3.27 ft/sec
11.5" x 30.5'
5,14 x 105 ft2
Cleaning Parameters
Acceleration
Amp!itude
Frequency
Duration
Reverse Air £P W. C.
1.56 g (15.3 m/sec2)
3.8 cm
3.2 cps/sec
23 sec
0 - 0.5 in.
1.56 g (50.2 ft/sec2)
1.5 in.
0 - 1.27 cm
Operating
Bag Pressure Drop
Gas Temperature
Gas Flow Rate
A/C Ratio
15 - 28 on.
127 - 188°C
2.8 - 4.0 x 10 acmn
0.9 - 1.2 m/sec
5-11 in.
250 - 370°F
1.0 - 1.4 x 10s acfm
3.0 - 4.0 ft/sec
457
-------
to high negative static pressure in the plant duct and limited blower capacity in
the pilot baghouse. The slipstream was heated arid insulated while the
return line was insulated only. Inspection of the ducting after testing
indicated marginal dropout of particulate, due to either gravitational or
centrifugal forces.
Operation
The pilot baghouse was operated and tested continuously in weekly
increments of 4 to 5 days. Normal baghouse startup and operating pro-
cedures were employed and included a preheat procedure to avoid the acid
dew point. Candidate bags were installed in a methodical manner and were
conditioned for 24 hours prior to any performance testing. Bag test
periods ranged from 1 to 8 days, depending on performance and interest
levels.
Candidate Bags
The candidate bags for this program included the following:
* W-W, Criswell silicone-graphite coated fiber glass, style
445-04 (same bag installed in Harrington Unit 2 baghouse).
• W.W. Criswell Teflon B coated fiber glass, style 442-570C2.
• Menardi-Southern Teflon B coated fiber glass, style MS-601.
• Fabric Filter Acid-Flex fiber glass, style 504-1.
• Fabric Filter all filament fiber glass, style 50G-ITC.
• Fabric Filter Goretex laminate fiber glass.
• Menardi-Southern Teflon B coated fiber glass, reverse-air bags
with spreader rings.
Due to performance and/or interest level, the last three bags were not
tested for a sufficient length of time to generate meaningful data and
are not included in further discussions. A summary of bag specifications
for the other four candidate bags is given in Table 4.
Test. Conditions .
The mobile baghouse was operated at relatively constant temperature
and air/cloth levels. Cleaning conditions for each bag type were initi-
ally set to be consistent with cleaning conditions for the full-scale
unit. Discretionary modifications of pertinent cleaning parameters were
made to assess alternate means of pressure drop reduction other than and
in relation to bag type. Further clarification of bag cleaning rationale
will be discussed later. A summary of the operating conditions, cleaning
parameters and cleaning modes is presented in Table 5.
458
-------
TADLE 4. COMPARISON OF BAG SPECIFICATIONS
Fabric
Weight
Oi./yd2
Weave
Thread Count
4=.
c_n
10 Permeability
cfm/ft'e.S in. H20
Finish
Warp Yarn
Fill Yarn
Fabric Filter
Acid Flex
Style 504-1
woven glass
9.8
3x1 twill (left hand)
54x30
45-60
4.0 - 4.5%
mill ti -component
proprietary finish
graphite/si) Icone/teflon/x
base ^ teflon B coating
75 1/0
50 1/0 text., 9 .
150 1/0 ' * P'y
W. W. Crlswell
Teflon B
Style 442-57IIC2
woven glass
10.5
3x1 twill (right hand)
54x30
60-80
Teflon B
10Z by wt.
150 1/2
150 1/4 all textured
W. W. Crlswell
Silicone/Graphite
Style 445-04
woven glass
11.0
3x1 twill (right hand)
65x33
45-65
silicone 1 graphite
1% by wt. total
150 1/2
37/S textured
Menardl -Southern
Teflon B
Style MS-601
woven glass
9.5
3x1 twill
54x30
75
Teflon B
10% by wt.
150 1/2
150 1/4 all textured
(turned inside)
-------
TABLE 5. SUMMARY OF OPERATING CONDITIONS FOR PILOT 3AGHOUSE
Flue Gas Flow Rate
Temperature
Bag Terminal Pressure Drop
Air/Cloth Ratio
2.3 - 2.5 aon/min (80 - 90 acfm)
130 - 190°C (266 - 374°F)
15, 20, 25, cm W. C. (6, 8, 10, in. W. C.
0.95 - 1.07 m/min (3.1 - 3.5 ft/min)
CLEANING CHARACTERISTICS
Shake Parameters
Amplitude
Frequency
First Delay
Shake Duration
Final Delay
Acceleration
Bag Tension
Deflation Parameter
Reverse AP
0.95 cm (.375 in.)"
3.2 and 6.4 cycles per second
30 seconds
10 seconds
60 seconds
0.39 g (3.8 m/sec2} at 3.2 cps
1.56g (15.2m/sec2) at 5.4 cps
13.5 kg (30 IDS)
1.2, 12 cm (0.5, 5.0 in.)
CLEANING MOOES SYMBOL
aLow Deflation - Low Shake Frequency (LO-LSF) A
bHigh Deflation - Low Shake Frequency (HO-LSF) B
Low Deflation - High Shake Frequency (LO-HSF) C
High Deflation - High Shake Frequency (HD-HSF) 0
a. Low Deflation : 1.2 cm reverse air pressure drop (corresponds to reverse
flow air-to-cloth ratio of approximately 1.7
b. High Deflation : 12 cm reverse air pressure drop (corrssoonds to reverse
flow 3 to 4 times that for low 'deflation " '!
460
-------
Two coal types were fired in Unit No. 1 during the evaluation period
with a two- to threefold difference in ash content between the coal
types. Previous experience with the high-ash New Mexico coal showed
higher concentration and bag pressure drop on the full-scale baghouse.
Despite the known performance sensitivity to coal type, accountability of
coal type usage was indefinite during segments of this study.
Data Acquisition
The following pilot baghouse data were recorded continuously through-
out the program:
• Pressure drop across the bags
• Gas flow rate pressure drop across a Stairmand disc
Other pilot baghouse data were manually recorded semihourly:
• Temperature profile across the system
• Static pressure profile across the sytem
• Slipstream interface temperature
• Cleaning cycle data (APR> APT, flow AP, shakes/cycle, etc.)
Pertinent boiler operating data were recorded hourly in the control
room, and copies of the logs were made available for the test period.
Coal samples were taken 3 times a day, and results of coal analyses were
also made available.
Flue gas composition and velocity data were taken at least once per
shift for methodology-assurance and particulate sampling preparation.
Particulate Measurements
Total mass and impactor measurements at the inlet and outlet loca-
tions were conducted at isokinetic conditions. Brink and Andersen impact-
ors measured the inlet and outlet size distributions, respectively. All
filters and substrates were made of Reeve Angel 934 AH material because
of low sulfur dioxide (802) absorptivity. All substrates were precondi-
tioned for 6 hours. Samples were obtained with extractive probes fitted
with interchangeable nozzles at average velocity locations. Sampling
trains similar to that described in Method 5 of the FEDERAL REGISTER were
used.
Data Reduction
Several analytical tools were employed in the reduction and analysis
of bag pressure drop, particulate concentration and size distribution
461
-------
data. The large number of tests taken over a variety of conditions for
the program duration required a substantial analytical effort.
A computer program was used to calculate impactor stage cut-points
and dust loadings. Fractional penetrations were calculated using a
program that performs the following:5
• Log-normal transformation of inlet and outlet cumulative size
distributi ons
• Linear, quadratic, and spline fits to the transformed data
• Analytical differentiation of the fitted curve
• Calculation of fractional penetrations from differential inlet
and outlet size distributions
Operating performance was evaluated primarily with respect to fabric/
cake drag and cleandown levels. Fabric/cake drag, known as specific cake
resistance coefficient (K2), was estimated by a methodical approach.
Cleandown levels were determined by records of residual drag. The funda-
mentals of baghouse performance modeling were utilized to eliminate
fluctuations in particulate concentration and filtration velocity.
Since it was impractical to measure cake mass for all the candidate
bags, values of Kg were determined on the basis of dust concentration
instead. Values of estimated K2 were calculated by the following rela-
tionship:
K =
V2Ct
where:
TT
c =
Terminal Drag
Residual Drag
Filtration velocity
Dust concentration
t = Filtration time
N/m2
N/m2
m/min
g/m3
min
Prior to averaging K2 values, they were arranged in chronological order
and the transient values (corresponding to bag conditioning) were elimin-
ated. Since the pressure drop-time profiles showed a linear relation-
ship, the mean pressure drop is the average of residual and terminal
values. This approach provided a fundamental basis for comparing bag
types and cleaning conditions.
462
-------
RESULTS AND DISCUSSION
This program was directed to assess alternate means for reducing
high pressure drop levels that were being experienced at Harrington
Station. Factors contributing to high pressure drop levels were bag type,
cleaning parameters, and air-to-cloth ratio. Available means of reduc-
tion were appropriate selection of bag type and cleaning conditions.
Optimization of these means is recommended, since their synergistic
effects can be substantial.
SUMMARY OF OPERATING PERFORMANCE
A summary-level accounting for this evaluation is presented and
displayed in Table 6 and Figure 1, respectively. The residual bag pres-
sure drop values in Table 6 and the curves for average pressure drop vs.
filtration time allow a ranking of candidate bags and an assessment of
cleaning conditions. The results from the analytical and graphic treat-
ment clearly show the Acid-Flex bags to exhibit the lowest pressure drop
performance. The Acid-Flex bags achieved both the lowest residual pres-
sure drop and lowest specific cake resistance coefficient values con-
sistently for all cleaning conditions. The other three bag types per-
formed to a lesser degree with essentially comparable operating charac-
teristics.
Results from bag cleaning characterization show that higher cleaning
energy also reduces operating pressure drop levels. Enhancement of
deflation and/or shake cleaning levels consistently achieved lower resi-
dual and mean pressure drops. Increasing shake frequency is a more
effective and available means for pressure drop reduction.
Estimated K2 Results
Specific cake resistance is the effective porosity indicator re-
lating fabric cake drag to operating conditions. By the straightforward
approach discussed earlier, a realistic porosity or drag indicator can be
derived directly from the operating data. The estimated K2 values rep-
resent the effective fabric/cake porosity.
Compilation of estimated K2 values is presented in Table 6 for each
bag and cleaning mode. The first column of estimated K2 values repre-
sents the test conditions, while the values in the second column are for
standard conditions as defined in the GCA performance model. These
results consistently demonstrate that the effective porosity of the dust
cake on the Acid-Flex bags was significantly lower than that for the
other candidate bags.
463
-------
TABLE 6. PILOT 3AGHOUSE RESIDUAL PRESSURE DROPS AND
SPECIFIC CAKE RESISTANCE CO-EFFTCIENTS
Bag Type
Acid Flex
Minardi Southern
Teflon 3
Cri swell Teflon 3
Cri swell Graph i ta/Si 1 icone
APT
CM
15
20
25
IS
20
25
15
20
25
15
20
25
AP, CM
Cleaning Mode
Af
3.9
9.7
10.2
10.7
12.9
-
12.7
14.0
-
11.4
14.0
-
3f
4.3
5.1
5.5
7.6
3.5
3.4
3.9
cf
3.6
4.1
-
9.7
-
-
-
10. Z\ -
-
*5.5 | -
*6.S
•7.1
-
-
0 +
-
-
-
5.1
6.1
-
-
-
-
-
-
KZ
l*-Wn
Actual
1603C
Im/min
10.4
20.4
15.7
13.0
11. S
5ta.
ie v*»
25 u
O.olm/mini
5.2
12.2
9.4
7.3
7.0
Wyoming : iNew Mexico Coal 1:1 Blend
All others Wyoming Coal
t
See Table 5 for key.
464
-------
Q-
o
ce
Q
25 -
O
20
BAG TYPE
O FABRIC FILTER ACID-FLEX
A MENARDI SOUTHERN TEFLON B
D H*CRISWELL GRAPHITE-SILICONE
O CRISWELL TEFLON B
O FULL SCALE BAGHOUSE,
CRtSWELL GRAPHITE-SILICONE BAG
• *DENOTES USE OF NEW MEXICOIWYOMING COAL III
ALL OTHERS, WYOMING COAL
CC
Q-
O
X
15
10
KEY
SHAKE MODE
LD-LSF
HD-LSF
LD-HSF
HD-HSF
I
25
50 75 100
FILTRATION CYCLE TIME, MINUTES
125
Figure 1.
25
Q_
O
ce
20
Baghouse operating pressure drop versus
filtration cycle time.
O
BAG TYPE
O FABRIC FILTER ACID-FLEX
A MENARDI SOUTHERN TEFLON B
Q • CRISWELL GRAPHITE-SILICONE
O CRISWELL TEFLON B
<> FULL SCALE BAGHOUSE,
CRISWELL GRAPHITE-SILICONE BAG
• 'DENOTES USE OF NEW MEXICOIWYOMING COAL in
ALL OTHERS, WYOMING COAL
i-
<
a.
o
O
I
IS
15
10
SHAKE MODE
HD-LSF
_L
25
50 75 100
FILTRATION CYCLE TIME, MINUTES
125
Figure 2. Comparison of performance characteristics
of candidate bags.
465
-------
Effect of Cleaning Conditions
The factors which ultimately define the degree of cleandown are
those which determine the type and degree of cleaning energy delivered to
the bags for dislodgement of the dust cake. The fabric must be flexed in
some manner and to a degree sufficient to break the dust cake. This
flexure overcomes the adhesive forces between particles within the dust
cake and/or those between the particles and the fabric.
Discussions with representatives of the utility and baghouse vendor
led to the conclusion that the shake cleaning cycle in the pilot
baghouse could not duplicate that in the full-scale house. This con-
clusion was based on differences in amplitude and harmonic shaker motion
and bag size (e.g., aspect ratio). Consequently, the cleaning parameters
were varied with respect to deflation pressure, shake frequency, and
shake duration to determine if any one of the bag candidates would perform
in a superior.fashion over the range of cleaning modes. Cleaning was
initiated at the terminal levels of 15, 20, and 25 cm W.C.
The difference in the cleandown characteristics for the four fabrics
is shown in Table 6. In mode A, when cleaning was initiated at a termi-
nal pressure drop, AP™, of 15 cm W.C., the resulting residual pressure
drop, AP , is lowest for the Acid-Flex fabric. This differential becomes
even more significant as the AP™ increases. At a AP™ of 25 cm W.C., the
Acid-Flex still had a lower APD than the other three fabrics at a AP™ of
-.I- K J
i5 cm.
The greatest differential in APR levels was realized between low and
high shake frequency (modes A and C). The Acid-Flex responded to a
higher degree, 140-150 percent improved cleandown, than did the silicone/
graphite bag, 100-115 percent, while the Teflon B fabric showed minimal
improvement in the range of only 10 percent.
Significant improvement in cleandown was also realized when going
from low to high deflation pressure (modes A and B). However, this would
not be a practical change in the Harrington cleaning cycle since experi-
ence has already shown that operation at design deflation pressure of 1.3
cm (0.5 in W.C.) causes the bags to pancake and prevents dust cake re-
moval during the shake cycle. However, it does focus interest on a
combination reverse air/shake cleaning cycle with ring bags.
The curves displayed in Figures 2 and 3, which are the average pilot
baghouse AP vs. filtration time for modes A and B, again show Acid-Flex
to be the most attractive fabric, with the other three fabrics exhibiting
essentially comparable levels of performance. These curves reflect the
effect of the K2 values for each bag type since they determine the filtra-
tion time required to reach a predetermined AP™.
466
-------
25 _
O
Q.
O
g 20
UJ
BAG TYPE
O FABRIC FILTER ACID-FLEX
A MENARDI SOUTHERN TEFLON B
D B*CRISWELL GRAPHITE-SI LICONE
O CRISWELL TEFLON B
O FULL SCALE BAGHOUSE,
CRISWELL GRAPHITE-SILICONE
JAG
*DENOTES USE OF NEW MEXICO:KYOMING COAL 1:1
ALL OTHERS, WYOMING COAL
2 15
o
UJ
a
x
10
KEY
A
SHAKE MODE
LD-LSF
J_
_L
25
50 75 100
FILTRATION CYCLE TIME, MINUTES
125
Figure 3. Comparison of performance characteristics
of candidate bags.
25
BAG TYPE
O FABRIC FILTER ACID-FLEX
Li
QT20
O
a:
Q
UJ
o:
15
10
SHAKE MODE
LD-LSF
HD-LSF
LD-HSF
_L
_L
0 25 50 75 100
FILTRATION CYCLE TIME, MINUTES
Figure 4. Comparison of acid-flex performance for
cleaning modes A, B & C.
467
125
-------
The curves displayed in Figure 4 demonstrate the improvement in
Acid-Flex bag performance as the degree of cleaning energy is increased.
The curves for modes A and C depict the improved operating levels ob-
tained with the high shake frequency, while curves A and B depict
improvement related to the higher deflation pressure drop across the
bags.
The normal 10 sec. shake duration was extended to 30 sec. within
several cleaning modes and for several bag types. Results indicated no
appreciable improvements in cleandown; thus, use of an extended shake
duration was discontinued.
Selection of the optimum cleaning mode must be based not only on
performance characteristics, but also on the degree of physical wear due
to fabric flexing with each cleaning cycle. Economics dictate achieving
a minimum bag life before attempting to improve operating pressure drop
levels and the resultant annual operating costs.
Effect of Coal Type
Two coal types were fired at Harrington Station during this study.
The 50:50 blend of Wyoming and New Mexico coals was fired for the first 2
test weeks and corresponded to 2 of 3 weeks testing for the silicone/
graphite bags.
A comparison of the performance characteristics for the silicone/
graphite (S/G) bags in Figures 4 and 1 would appear to indicate dif-
ferences related to coal type. In Figure 4, the S/G bags are closely
grouped with the two Teflon B bags for cleaning mode A. _;,dse data were
generated when only Wyoming coal was being fired. The same curves for
cleaning mode B in Figure 1 find the S/G bags demonstrating an appre-
ciably higher level of performance. The S/G curve in Figure 1, however,
was generated during Wyoming/New Mexico blend firing while the other
curves of Figure 1 relate to Wyoming coal only. It would appear from
this single case that the Wyoming/New Mexico coal blend resulted in
better performance levels for the S/G bags than those observed for Wyoming
coal only. This observation illustrates the sensitivity and specificity
of the fabric/cake interface, evidenced in this and other studies on
fabric/cake characterization.
Collection Performance Measurements
The control device characteristic of practical importance is that of
overall collection performance. This performance can be described and
measured by the emissions which penetrate the device and pass into the
atmosphere. Collection performance and fractional efficiency are a
function of inlet particle size distribution, as well as other variables.
468
-------
Cumulative and differential inlet particle size distribution curves
are shown in Figures 5 and 6, respectively, for Amarillo and three other
utility PC boilers. As illustrated, the size distribution at Harrington
Station falls in the same general range as the other sites.
Since fabric filters with glass bags typically deliver efficiencies
in the range of 99.8 percent or higher, only a moderate effort was made
to document collection performance for the four bag types. A summary of
the inlet and outlet loadings, efficiency, and emission levels in ng/J
are presented in Table 7. All four bag types performed at a level which
yields emissions an order of magnitude less than the New Source Performance
Standard (NSPS) of 13 ng/J (0.03 Ib/MBtu). Figure 7 shows fractional penetra-
tion for the Acid-Flex and Criswell Teflon B bags.
Electrostatic Effects
It has been speculated that electrostatic effects may be a contri-
buting factor to the bag cleaning problems at Harrington Station. A
cursory attempt was made to measure the electrostatic voltage levels
present on the silicone/graphite bags in the pilot baghouse. The metho-
dology was the same as that employed by Bob Donovan, Research Triangle
Institute, on the Harrington baghouse.6
A cage voltage measurement was made by attaching a Type 430 stain-
less steel screen (0.0075-inch wire, 24 mesh) cage to the bottom of the
middle bag in the pilot baghouse. The cage was attached to the bag by
sewing it to the bag cuff at the cage top, middle, and bottom points in
such a way that no penetration of the filtering surface of the bag was
required. The cage was 25.4 cm high and was constructed such that the
diameter was only slightly larger than that of the bag. A Teflon-shielded
cable from the cage was passed through the adjacent glass window jamb and
coupled to an electrometer immediately adjacent to the baghouse compartment.
The profile of cage voltage measurements over two typical cleaning/
filtration cycles is shown in Figure 8. A detailed analysis or hypo-
thesis of the resultant, effect on bag pressure drop is beyond the scope
of this report. However, it appears that sufficient charge levels were
shown to exist to be a potential contributing factor to pressure drop
problems and to indicate the need for further definition, clarification
and evaluations.
RECOMMENDATIONS
Reduction of operating pressure drop at Harrington Station:
• Evaluate higher shake frequencies and monitor bag at quarterly
intervals via diagnostic tests (i.e., Muller Burst Strength,
Tensile Strength, MIT Flex Fold tester, etc.).
469
-------
90 _
70
t-
§ 50
30
1 10
u
Ol
0.01
0.1
O AMARILLO, TEXAS 7-4
O PAGE, ARIZONA 9-6
O COLSTRIP, MONTANA 20-°
£1 MICHIGAN STATE UNIVERSITY 9-0
GEOMETRIC
U50 STANDARD
MICRONS DEVIATION
fi. 2
10
PARTICIPATE DIAMETER/ MICRONS
Figure 5. Boiler effluent cumulative particle size
distributions at four power plants.
10*
-z.
a
o
-I
o
10
10
O PAGE, ARIZONA
COLSTRIP, MONTANA
MICHIGAN STATE UNIVERSITY
I
0.1 1 10
PARTICIPATE DIAMETER/ MICRONS
100
Figure 6. Comparison of boiler effluent fractional
size distribution at four power plants.
470
-------
TABLE 7. SUMMARY OF PARTICIPATE CONCENTRATION MEASUREMENTS
Bag Type
**Criswell Graph He-Si Itcone
Fabric Filter
Acid Flex
Menardi Southern
Teflon B
Criswell Teflon B
Average Inlet
Loading
gin/DNCM
3.2
2.4
2.4
2.4
Average Outlet
Loading
(jm/ONCM
0.0038
0.0018
0,0007
0,0006
Efficiency
Percent
99.88
99.92
99.97
99.575
*Einiss1on
Level
ng/J
0.71
0.34
0.13
0.11
* 'Current NSPS 13 ng/J
k* 1:1 blend of Wyoming and New Mexico coals. All others Wyoming coal.
-------
1.0 ,_
0.1
0.01
0.1
A FABRIC FILTER ACID-FLEX
O CRI SWELL TEFLON B
1 10
PARTICIPATE DIAMETERi MICRONS
Figure 7. Fractional penetration characteristics
for two bag types.
472
-------
ELECTROSTATIC
CAGE VOLTAGE, KV
0315
25 30 35 40 45
FILTRATION TIME, MINUTES
BAG AP,CM
15
12
9
6
3
0
0315 20
25 30 35 40 45
FILTRATION TIME, MINUTES
50 55
Figure 8. Electrostatic cage voltage profile for two typical cleaning cycles.
-------
• Evaluate performance characteristics of Acid-Flex or an equi-
valent fabric.
• Evaluate performance characteristics of higher deflation pres-
sures with ring bags.
Suggested future studies:
• Extend characterization of electrostatics at Harrington and
other coal-fired boiler/baghouse sites.
® Develop improved hardware and methodology for experimental
pilot-scale determination of specific cake resistance coef-
ficients (1(2) -
REFERENCES
1. Lipscomb, W.O. Environmental Protection Agency Fabric Filter Program -
A Comparison Study of Utility Boilers Firing Eastern and Western
Coal. In: Symposium on the Transfer and Utilization of Particulate
Control Technology: Volume 2. Fabric Filters and Current Trends in
Control Equipment, Venditti, F.P., J.A. Armstrong, and M. Durham
(eels,)- Research Triangle Park, N.C., U.S. Environmental Protection
Agency, February 1979. Publication No. EPA-600/7-79-044b. p. 53-74.
2. Dennis, R., and H. A. Klemm. Fabric Filter Model Format Change:
Volume 1. Detailed Technical Report. GCA Corporation, GCA/Technology
Division. Bedford, Massachusetts. Publication No. GCA-TR-78-51-G(l).
January 1979. I69p.
3. Faulkner, G., and K.L. Ladd. Startup, Operation and Performance
Testing of Fabric Filter System - Harrington Station, Unit No. 2.
In: Symposium on the Transfer and Utilization of Particulate Control
Technology: Volume 2. Fabric Filters and Current Trends in Control
Equipment, Venditti, F.P., J.A. Armstrong, and M. Durham (eds.).
Research Triangle Park, N.C., U.S. Environmental Protection Agency,
February 1979. Publication No. EPA-600/7-79-044b. p. 219-232.
4. Hall, R.R. Mobile Fabric Filter System: Design Report. GCA Cor-
poration, GCA/Technology Division. Bedford, Massachusetts. October
1974. 73p. NTIS No. PB246-287/7BA.
5. Lawless, P.A. Analysis of Cascade Impactor Data for Calculating
Particle Penetration. U.S. Environmental Protection Agency, Indus-
trial Environmental Research Laboratory. Research Triangle Park,
N.C. Publication No. EPA-600/7-78-189. September 1978. 39p.
474
-------
6. Donovan, R.P. Passive Electrostatic Effects in Flyash Fabric
Filtration. Presented at the Second Symposium on the Transfer and
Utilization of Particulate Control Technology. Hosted by the
U.S. Environmental Protection Agency, Research Triangle Park, N.C.,
and the Denver Research Institute, University of Denver. Denver,
Colorado, July 25, 1979.
7. Emission Test Results: Harrington No. 1. C-E Power Systems, Combustion
Engineering, Inc. Windsor, Connecticut. June 1977. 24p.
8. Chambers, R. Personal Communication. Southwestern Public Service
Company, Harrington Station. Amarillo, Texas. March 6, 1979.
ACKNOWLEDGEMENTS
The authors wish to express their appreciation to Southwestern
Public Service Company personnel for their assistance and cordial coopera-
tion, and to Dale Harmon and Jim Turner, EPA, Technical Project Officers.
475
-------
PASSIVE ELECTROSTATIC EFFECTS IN FABRIC FILTRATION
by
R.P. Donovan
Research Triangle Institute
Research Triangle Park, N.C. 27709
and
J.H. Turner and J.H. Abbott
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
ABSTRACT
Electrical charge transport accompanies the flow of dust and flyash
through particulate control equipment. In a fabric filter these charges can
accumulate on the fabric and other electrically isolated regions. The magni-
tude of the charge buildup depends upon the electrical properties of both the
dust and the fabric and especially the relative humidity of the gas stream.
This paper presents laboratory measurements of fabric charge accumulation in
both pulse jet and shaker-cleaned baghouses. Brief field measurements show
similar charging patterns. No effect on baghouse performance can yet be
unambiguously attributed to these charges.
476
-------
PASSIVE ELECTROSTATIC EFFECTS IN FLYASH FABRIC FILTRATION
That electrical charges exist on flyash and other aerosol particles is
well known.1 Such charges arise: 1) because of charge exchange between
neutral materials in contact and their subsequent separation, or 2) because of
ion capture by the particles and the resultant Boltzmann charge equilibrium.
Particle deposition or collection is necessarily accompanied by charge deposi-
tion and collection; and particle flow is to some degree a charge flow, as
evident by the pipe charging effects brought about by particle flow through that
pipe.2
It is these charging effects that make up the passive electrostatic effects
to be discussed in this paper. These effects are passive because no overt
charging action is required to create the charges; the charges are an inherent
property of virtually all flowing dust systems. The questions to be considered
include:
1. What is the magnitude of these passive charges in a baghouse and on
what does the magnitude of these charges depend?
2. What influence, if any, do these charges have upon baghouse perfor-
mance?
BACKGROUND
Measurements of voltage buildup on the support cages of a pulse jet fabric
filter have previously been reported.3'4 This measurement, shown schematically
in Figure 1, consists simply of connecting an electrometer to the support cage
of a bag and recording current or voltage during operation.
For voltage measurements the electrical resistance of the fabric determines
the "load" resistance across which the electrostatic voltage is measured.
Physically, this load resistance is the electrical resistance of the fabric
separating the cage collar from the venturi shoulder. When the resistive
coupling to electrical ground dominates the cage voltage, the magnitude of the
cage voltage is directly proportional to the fabric resistance. For conductive
fabrics an insulating sleeve must be added between the fabric and the venturi
in order to support a significant cage voltage.
For current measurements the electrical resistance between the cage and
the collar should exceed the input resistance of the electrometer by several
orders of magnitude. Again, for electrically conducting fabrics, an insulating
sleeve is necessary in'order to make a meaningful measurement.
Previous publications summarized the initial observations of such measure-
ments3 and noted a correlation between high cage voltage and dust penetration
through the bag.4 This correlation has been explored further using different
fabrics as described in the first part of this paper. A second measuring
configuration, appropriate for inside-out filtration, was subsequently developed
and used to make measurements on both a field installation and a laboratory
shaker baghouse. These experiments are also described in this paper.
477
-------
LABORATORY PULSE JET EXPERIMENTS
As an extension to the measurements reported in Reference 4, a fresh set
of fabrics was obtained through the courtesy of E. de Garbolewski of W.L. Gore
Associates. Table 1 lists these fabrics, their Run Identifiers, and some
properties. The set of four different fabric types was prepared so that each
differed from another only in its electrical properties or in the addition of
a specific compositional change—the Gore Tex* layer. The number contained in
the Run Identifier gives the sequence in which the runs were carried out.
When all cages of the nine bag array are tied together electrically, a
typical composite cage voltage appears as sketched in Figure 2. Three quanti-
ties are defined in Figure 2: 1) V is the value of cage voltage immediately
prior to the reverse pulse cleaning spike; 2) AV is the height of the voltage
spike induced by the cleaning pulse; and 3) T is the time required for the
cage voltage to recover to 1/e of its value prior to cleaning.
V and AV correlate with dust penetration through the fabric as shown in
Figure 3. Each datum point in Figure 3 represents the average of two sequential
measurements of dust penetration, both values being determined by a 20 minute
sampling of the outlet. The cage voltage for each datum is the arithmetic
average of 20 measurements. The standard deviation of the cage voltage is
about 5% of the mean when, as is true here, all cages are tied together
electrically.
Cage voltage and dust penetration both correlate with relative humidity.
Because of this dependence, relative humidity was used as an independent control
of cage voltage over a limited range.
With fixed inlet dust loading and constant air-to-cloth ratio, the buildup
of bag pressure drop between cleaning pulses was lower at 70% relative humidity
than at either 50% or 30% relative humidity. The absolute pressure drop was
also lower at the high relative humidities. No dependence of these pressure
drops upon cage voltage was apparent.
The relationship between flyash penetration and relative humidity is
emphasized by replotting the V data of Figure 3 in Figure 4. The shaded
regions represent the data envelope of each fabric. All data in Figure 4
were measured after 6 hours of operation at the desired set point on the
humidity control unit. Operation at each relative humidity was repeated with
sequencing in the opposite directions; for example, 50%-30%-70%-70%-30%-50%.
Sequence effects do exist in that the data collected at a given relative
humidity depend on the relative humidity of the immediately preceding datum
point. For example, the dust penetration measured at 70% relative humidity
depended on whether the preceding test point was at 30% or 70% relative
humidity. This observation implies that the 6 hour equilibrating time
allowed was inadequate and that a major source of error in collecting the data
was failure to reach a steady state at each value of relative humidity.
Even so the trend toward reduced flyash penetration at high relative
humidity is clear for all these fabrics. That relative humidity also correlates
*
Registered Trademark of W.L. Gore £/ Associates, Inc.
478
-------
with cage voltage for a given fabric raises the possibility that the relative
humidity dependence portrayed in Figure 4 originates from electrostatic forces.
Indeed one major reason for including epitropic blends in the fabric test group
was to explore this possibility.
The preliminary observation of these evaluations is to refute this electro-
static force hypothesis as an explanation of the dependence of flyash penetration
upon relative humidity. In Figure 4 flyash penetration through the epitropic
polyester fabric (PJ53) is comparable to that through the standard polyester
(PJ50) in spite of the essentially negligible cage voltage measured during
epitropic polyester operation. While the Gore Tex/polyester fabric differs
from the Gore Tex/epitropic polyester fabric in absolute dust penetration, both
fabrics exhibit the same general relative humidity dependence and it is this
property rather than the absolute values of flyash penetration that is crucial
for the electrostatic hypothesis. If the relative humidity dependence is elec-
trostatic in origin, a conductive fabric should remove the charge and eliminate
the relative humidity dependence. The epitropic blend failed to eliminate the
relative humidity dependence in either of the two samples, although it effectively
eliminated the cage voltage of the straight epitropic fiber blended polyester and
greatly reduced it for the Gore Tex/epitropic polyester fabric.
These experiments still leave room for doubt, however, because of the
composition of the epitropic blended fabrics. The epitropic fibers with which
the epitropic polyester fabrics are blended consist of polyester fibers impreg-
nated with carbon black particles. One technique is to draw a bicomponent
fiber whose outer layer has a lower softening point than its core. When the
outer layer is subsequently softened, carbon black particles can be incorporated
into the surface shell but the fiber retains most of its original dimensions
because of its unaffected core component. The resulting fiber is one with a
highly electrically conductive surface.
In the preparation of epitropic fabrics a small percentage of these epi-
tropic fibers blended with conventional polyester staple fibers (5% is typical,
although 3.5% was the blend percentage in our samples) produces a fabric of
greatly reduced surface resistivity which is useful for eliminating static
charge buildup in textile products.5 The presence of these epitropic fibers
in the test fabrics was to reduce the electrical resistance between the cage
and the venturi shoulder (electrical ground) to 104 to 106 ohms, preventing the
buildup of any significant charges on the cage.
At the fiber level, however, most of the fibers are not coupled to the
cage by a conductive fiber—96.5% of the fibers are still the relatively non-
conductive polyester. The fabric surface seen by the incoming dust could still
be much the same as for the 100% polyester fabric, even though the cage is well
coupled to electrical ground.
Plans are underway to extend these measurements to 100% stainless steel
felt fabrics. Here all fibers should be closely tied to electrical ground and
no charge accumulation should occur initially. As the dust cake builds up, the
electrical properties of the dust will impede charge transfer to the conductive
fabric but this interference requires some minimum operating time before becoming
significant.
479
-------
BAG DUST LOAD
A second independent hypothesis seeking to explain the relationship between
relative humidity and flyash penetration also invokes electrostatic forces. In
this model the role of charges building up on the fabric surface is to intro-
duce an electrostatic force which binds the dust to the fabric and hence
creates a larger dust load on the bag than would exist in the absence of such
electrical forces. Increased dust load on the bag in turn is then postulated
to cause increased dust penetration and higher pressure drop.6'7
To investigate this hypothesis total bag weights following operation at
various relative humidities were measured. The technique was to stop the
filtration cycle immediately after the Row 3 cleaning pulse had fired. The
baghouse was opened gingerly and a large plastic bag slipped over the dusty bag,
including its cage, before demounting. Once the plastic cover was in place so
as to catch dust inadvertently shaken loose during removal, the bag was demounted
and weighed—plastic bag, dusty fabric, and cage together. Each of the nine
bags were weighed one after the other and then remounted at the same location
in the baghouse for the next run.
These admittedly crude weighings uniformly confirmed a dependence of bag
dust load upon relative humidity, the lowest dust loads on the bag occurring at
the highest values of relative humidity.
Table 2 summarizes a recent data set showing this relationship. The run
identifier is PJ54. The bags used in this run were the same polyester bags
removed after completing Run PJ50. Nine months after the last PJ50 run each
used bag was remounted on a cage, weighed, and inserted in the baghouse for
the PJ54 series. Table 2 lists the average weight change in the three bags
making up a row after operating for 6 hours at the indicated relative humidity.
Inlet loading for all these data was 9 g/m3 (4 grains/ft3). Total gas flow
was 7 m3/iain (250 ft3/min), yielding an air-to-cloth ratio of 3 cm/sec (6 fpm).
Table 2 and the curves constructed from the data (Figure 5) show a dust
load dependence in accordance with the qualitative predictions of the electro-
static model—at high relative humidity, less charge exists on the fabric and
also less dust. However this confirmation by no means proves an electrostatic
interaction. Other nonelectrostatic mechanisms could also produce the same
effect. What is shown is that at high relative humidity (> 60%) less dust
ends up on the bag and less dust penetrates the bag. The data do not distin-
guish between the postulated reduced electrostatic binding forces at the bag
surface and some other humidity dependent phenomenon, such as enhanced agglom-
eration and fallout, which reduces the dust that reaches the bag at high
relative humidity even though that quantity fed into the baghouse remains
constant for all test humidities.
480
-------
FIELD MEASUREMENTS
The data reported so far have been collected with a laboratory-sized
pulse jet baghouse filtering redispersed flyash and operating at room tempera-
ture. Because these conditions are sufficiently different from typical boiler
operations, some pause seemed warrented before embarking on a detailed study
in order to confirm that the charge buildups detected in the laboratory also
occurred in operating field installations.
Measurements were therefore carried out at two field sites:
1. A stoker fed boiler at Kerr Finishing Plant, Concord, NC.
2. Harrington No. 2 unit of Southwestern Public Service, Amarillo, TX.
The baghouse installation at Kerr consists of two parallel modules. At the time
of the electrostatic measurements one module operated in a reverse air cleaning
mode with woven fiberglass bags; the second module used 100% teflon felt bags
cleaned by reverse air with a pulse jet assist. Both modules are outside-in
filters and employ steel cages electrically isolated from ground by the fabric.
Cage voltage measurement technique therefore was identical to that used in the
laboratory.
The flyash from the Kerr boiler appears carbon rich and had coated both
fabrics with a black deposit which proved relatively conductive. The electri-
cal resistance between the cage and ground was on the order of 10^ ohms when
measured during the weekend before the Monday startup. Cage voltages at oper-
ating temperature and flue gas flow were less than 0.1 volts for both fabrics,
as the low values of "load" resistance would anticipate. Only one bag from
each module was monitored and each of these had been in service for over a
year. The conclusion was that only negligible charge accumulation on the bags
could be detected; no measurement of charge on the inlet flyash was made.
Harrington Unit No. 2 includes a pulverized coal boiler fired with low
sulfur western coal from Black Thunder Mine in Wyoming. The baghouse is a
Wheelabrator Frye unit, cleaned by reverse-deflate air and shake. The fabric
in service in the compartment monitored for electrostatic effects was silicone-
graphite coated fiberglass. This utility boiler baghouse, as most utility
baghouses, is an inside-out filter and hence has no cage with which to monitor
voltage or current. To gather data comparable to that measured with the cage
electrodes of the outside-in baghouses aim (40 in.) section of stainless steel
screen was wrapped around the bottom of one of the 29.2 cm (11.5 in.) diameter
bags. This bag was adjacent to the compartment door so that an insulated lead
could be easily fed through to an outside electrometer. Electrical resistance
between this outside screen "cage" and ground was about 5xl08 ohms at ambient
temperature and no flue gas flow.
The flyash entering the baghouse on Harrington is negatively charged.
Brief sampling of current and mass yielded an average charge/mass value of
1.7 uC/g, a value perhaps typical of a low efficiency stage of an electrostatic
precipitator.
Immediately upon admission of this charged flue gas to the monitored com-
partment a large negative voltage appeared on the screen cage. This signal
481
-------
settled down to a steady state value of -100 to -300 V during the filtering
cycle, although excursions beyond this range in both directions also occurred.
During the cleaning cycle as gas flow stops, a voltage spike appeared! in
the trace of cage voltage and the sign of the voltage changed—much like the
laboratory observations of pulse jet cleaning except that the transition was
slower. During the reverse air, pause, and shake periods the cage voltage was
small and usually positive. Upon resumption of flue gas flow the large nega-
tive signal reappeared and relaxed to its previous steady state range,
typically -100 to -300 volts.
This type of behavior generally conforms with the prediction of a simple
RC equivalent circuit as sketched in Figure 6. This circuit is identical to
that previously postulated for the pulse jet cage voltage. Flue gas flow is
assumed to produce a square wave voltage source, Vp, that is coupled through ,
an effective R? and C? to the detecting screen cage, V . The cage itself,
CciSG ' -• • ' *
is coupled to ground by an effective RI and Cj. Under sach assumptions V.
responds to a square wave input V as shown in Figure 7. The key qualitative
point being made is that the gas on/gas off voltage spikes and sign changes
observed in both the lab and the field can be explained in terms of simple RC
couplings and a forcing function V^ associated with the gas flow.
sL
The overriding significance of the observations at Harrington is that
charge buildup of magnitude and behavior similar to what has previouslv been
observed in laboratory pulse jet equipment, operating with redispersed flyash
and at room temperature, is observed in the field with full-scale equipment,
reverse air cleaning, and typical flue gas composition and temperature. No
unambigu^"': orfect of electrostatic charges upon baghouse performance has been
uncoverf-1 > > the need to further Investigate the existence of such an effect
is reinf<» fti
LrUWKAi'ORY SHAKER BAGHOUSE EXPERIMENTS
To extend the fabric charge detection measurements to the laboratory shaker
baghouse a modified screen cage was added plus a center-line probe within the
bag as sketched in Figure 8. The external cage is similar to that employed at
Harrington except that it is supported by insulating phenolic hangers rather
than tied to the bag itself.
The center-line probe on the inside of the bag also hangs from a top support.
Gas flows from inside to outside in this unit and enters at the top of the bag so
that the center-line probe is in the entry way of the dusty gas. It detects
charges on the incoming dust and the adjacent dust cake that builds up on the
inside of the bag.
The external cage is outside the bag on the clean air side of thetfabric.
It was sized to allow 1.3 cm (% In.) clearance between the outside of the bag and
the screen. However, the fabric loosens and stretches under pressure so that
in operation the bag usually makes direct contact with the cage, much like'the
support cage of the outside-in flowing pulse jet baghouse.
• • (.
The external cage construction is .analogous to the internal cage of the
pulse jet; the center-line probe is a new feature in the measurement schemes
Figure 9 shows various views of these electrodes with and without the bag in
I'l.K-e Th<= shaker mechanism (not shown) moves the bottom of the 1.5 m bag-, at
i i r^qu^ncy of 4 cycles/sec and a p -ak-to-peaK displacement of 2.5 cm.
-------
Various operating cycles using redispersed flyash originally collected
from the baghouse hopper at Harrington and a custom sewn silicone-graphite
fiberglass bag are now underway with these electrodes in place. Typical
electrode voltage traces are sketched in Figures 10 and 11. Figure 10 shows
an early current and voltage plot measured with the center-line probe. While
not recorded simultaneously, these curves were recorded within 10 minutes of
each other and during the first 10 hours of new bag operation. The baghouse
operation cycle for these data was 5 minutes filtration - 30 seconds pause -
30 seconds shake - 30 seconds pause - 5 minutes filtration and so on. This
rapid cycling mode allows frequent observation of the current and voltage
behavior during the regeneration stage but suppresses dust accumulation below
that normally expected in field operations.
For all shaker data collected so far, the dust inlet loading has been 6.9
g/m3 (3 grains/ft3); total gas flow, 0.91 m3/min (32 cfm) for an air-to-cloth
ratio of 2 cm/sec (4 fpm). These conditions are the standard operating condi-
tions for this EPA shaker baghouse, the same conditions at which the majority
of all previous shaker evaluations and experiments have been carried out.
Preliminary observations from these shaker baghouse electrostatic measure-
ments are:
1. the center-line probe detects larger currents and voltages than the
cage at low relative humidity (<50% R.H.);
2. the center-line probe current tracks with gas flow—when gas flow
stops, the probe current drops to zero;
3. the center-line probe voltage lags the gas flow behaving like a
charging and discharging capacitor with respect to a charged gas flow;
4. an inductive coupling may also exist between a charge sheet on the
inside of the fabric and the probe, causing probe current during the
shake cl^ r. and preventing probe discharge by grounding during the pause
period (other explanations are possible—the probe current may come
from dust reentrained during the shake and the probe voltage may be
controlled by charge on the probe that is isolated from the probe by
the resistivity of the flyash); and
5. the cage currents and voltages exhibit the sign changes during gas
stop and start that would be predicted from the equivalent circuit of
Figure 6 and as illustrated in Figure 7.
The cage voltage and current depicted in Figure 11 generally approximates
that seen at Harrington except that the signs are reversed! Since the dust and
the fabric are identical in the two experiments, the changing charge sign on
the dust and on the cage presumably reflects the different charging properties
of the dust feed lines and the gas induction system. The Harrington ducts are
steel; the laboratory feed lines are rubber.
A second general conclusion of the experiments is that the charge appearing
on the bags is dominated by the charge on the incoming dust rather than any
triboelectric interaction between the dust and the fabric as previously postu-
lated. 3>Lt The crucial triboelectric interactions seem to occur upstream of
the baghouse.
483
-------
The double electrode configuration in the shake baghouse has now been
switched to a longer filtration period, more representative of field operation
(and previous laboratory work). This cycle consists of the following sequence:
18 minute filtration
1
minute
pause
1
minute
pause
2
minute
shake
About 100 hours operation have now been logged under these conditions.
Probe currents decrease with increasing relative humidity, resulting in reduced
probe voltage and cage voltage at high relative humidity. This dependence on
relative humidity is similar to that previously noted in the pulse jet experi-
ments .
STATUS SUMMARY
What has been shown is that electrical charges do accumulate in standard
baghouse operation. The magnitude of these charges depends on the electrical
properties of the dust and the fabric as well as the relative humidity of the
gas stream. No unambiguous influence of these charges upon baghouse performance
has yet been identified and such an influence is deemed necessary before more
detailed modeling of the charging/discharging process. Such a relationship
seems highly likely in view of reported observations of electrostatically
assisted fabric filtration.8 The next phase of this EPA work is to measure and
control inlet dust charge as this variable appears to be the chief source of
passive charges. These experiments will bridge the gap between passive and
active electrostatic effects in fabric filtration.
ACKNOWLEDGMENTS
It is a pleasure to acknowledge the contributions of: E. de Garbolewski,
W.L. Gore Associates, who donated four sets of fabrics for the pulse jet meas-
urements and critiqued the pulse jet experimental plans and results; J. McKenna,
J. Mycock, and R. Gibson, Environmental Testing Services, who hosted the Kerr
field measurements; K. Ladd and R. Chambers, Southwestern Public Service, who
hosted the field measurements at Harrington; and A. Ranade and P. Lawless,
Research Triangle Institute, who participated in and contributed to all phases
of the work.
484
-------
REFERENCES
1. Whitby, K.T. and B.Y.H. Liu. "The Electrical Behavior of Aerosols."
Chap. 3, pp.59-86 in Aerosol Science, edited by C.N. Davies, Academic
Press, New York, 1966.
2. Masuda, H., T. Komatsu, N. Mitsui, and K. linoya. "Electrification of
Gas-Solid Suspensions Flowing in Steel and Insulating-Coated Pipes."
J. of Electrostatics 2, 1976/1977, pp.341-350.
3. Donovan, R.P., R.L. Ogan, and J.H. Turner. "Electrostatic Effects in Pulse-
jet Fabric Filtration of Room Temperature Flyash." Proceedings of the
Engineering Foundation Conference, "Theory, Practice and Process Principles
for Physical Separations," Asilomar, 1977.
4. Donovan, R.P., R.L. Ogan, and J.H. Turner. "The Influence of Electrostati-
cally-Induced Cage Voltage Upon Bag Collection Efficiency during the Pulse-
jet Fabric Filtration of Room Temperature Flyash." pp.289-327 in Proceedings
of the Third Symposium on Fabric Filters for Particle Collection, EPA-600/
7-78-087, NTIS No. PB 284-969, June 1978.
5. Ellis, V.S. "Epitropics—Third Generation Conductive Fibres." Textile
Manufacturer and Knitting World 101, July 1974, pp.19-23.
6. Leith, D., M.W. First, M. Ellenbecker, and D.D. Gibson. "Performance of a
Pulse-jet Filter at High Filtration Velocities." pp.11-25, in Symposium
on the Transfer and Utilization of Particulate Control Technology: Vol. 2
Fabric Filters and Current Trends in Control Equipment, EPA-600/7-79-044b,
NTIS No. PB 295-227, Feb. 1979.
7. Dennis, R., R.W. Cass, and R.R. Hall. "Dust Dislodgement from Woven Fabrics
Versus Filter Performance." J. Air Pollut. Control Assn. 28, Jan. 1978,
pp. 47-52.
8. Lamb, G.E.R., and P.A. Costanza. "Role of Filter Structure and Electro-
statics in Dust Cake Formation." Presentation at the Second Symposium on
the Transfer and Utilization of Particulate Control Technology, Denver, CO.,
July 1979.
Table 1. Pulse Jet Fabrics
Run No.
PJ50
PJ49
PJ53
PJ51
PJ52
Fabric Description
Polyester Felt
Polyester Felt + Gore Tex Layer
Polyester Felt with Epitropic Fibers
Polyester Felt with Epitropic Fibers +
Gore Tex Layer
Teflon Felt
Sample Bag Weight (g)
(1 bag, nominally 1.2 m long,
11.4 cm dia) [4 ft; 4^ inches]
220
190
236
212
415
Nominal Collar
Resistance at
50% R.H. (ohms)
5xl09
AxlO14
5xlOs
2xl012
485
-------
Table 2. Bag Weighing Summary, PJ54
co
— . — „__ , — , — , , _ .... — -. . ... •
Bag Weight Change*
Run R.H. (grams)
No. (%) Row 1 Row 2 Row 3
A 51 79.7 48.7 6.0
B 38 84.3 53.0 8.0
C 64 67.9 38.7 -2.7
D 66 52.0 26.7 -5.3
E 34 89.7 52.3 6.7
F 48 83.3 46.7 1.3
2
Pressure Drops, N/m
(in. of H20)
398
(1.60)
460
(1.85)
323
(1.30)
323
(1.30)
386
(1.55)
398
(1.60)
348
(1.40)
400
(1.61)
311
(1.25)
311
(1.25)
336
(1.35)
361
(1.45)
50
(0.20)
60
(0.24)
12
(0.05)
12
(0.05)
50
(0.20)
37
(0.15)
C0, g/m3
grains/103ft3)
0.46
(201)
0.48
(210)
0.22
(94.7)
0.14
(60.4)
0.55
(239.4)
0.44
(190.4)
E (%)
95.5
95.3
97.7
98.6
94.6
95.7
JU
'Actual bag weight after each run less the
Used Bag + Cage
Row 1
Left 1490
Center 1473
Right 1500
following
+ 60 gram
Row 2
1490
1495
1485
initial wei§
plastic ba£
Row 3
1500
1483
1481
jhts
7 '
•J *
-------
CAGE
BAG
VENTURI
PLENUM FLOOR
VENTUR! SHOULDER
HOSE CLAMP
BANANA JACK
Figure 1. Cage electrical contact, pulse jet baghouse.
Figure 2, Cage voltage during pulse-jet fabric filtration
487
-------
oo
CO
10
0.1
X Vc (VOLTS)
O AVR (VOLTS)
0.1
1 10
CAGE VOLTAGE (V)
100
H 99.99
Figure 3. Correlation of cage voltages with outlet concentration.
-------
-i 0
PJ52°
10J r-
o
o
o
10
cc
o
x PJ50
and
0 PJ53
0.1
PJ49
PJ 51
30
40
50 60
RELATIVE HUMIDITY
TEFLON
POLYESTER AND
0 EPITROPIC POLYESTER
0 GORE TEX/POLYESTER
*( )
GORE TEX/EPITROPIC
POLYESTER
x( ) = hi stress test
75
90
97.5
99.0
99.75 3
99.9
99.97
99.99
70
Figure 4. Dependence of dust outlet concentration upon relative humidity.
489
-------
5 2
6 1
3 4
RUN ORDER
500
400
300 —
_ 100 —
LU
C3
I
o
ca
80
60
40
20
10
O
40 50
RELATIVE HUMIDITY (%)
X X
e> Q
o e
x APF
O APE
60
70
APn
ROW 1
ROW 2
ROW 3
Figure 5. Relative humidity dependence of bag weight changes and pressure
drops.
490
-------
VE<
-O vc
C2
-I- C1
C2
7Vc-2^-
1
Rl
1 = (C^ + C2I
R, + R2
Figure 6. Simple equivalent circuit. Figure 7, Circuit response.
INLET
GAS
TO ELECTROMETER [ / RG-58 CABLE
INSULATORS
BAG
Figure 8. Shaker baghouse electrode
configuration.
491
-------
a. front view.
b. front view, bag in place,
c. bottom view.
Figure 9. Electrodes for r*haker baghouse-
492
-------
ZU.
<0 , ,"* , ,--
"' ''" "•""•-'"'^''•M/Y SHAKE |*"'--"'^>r: '
1 MINUTE' " x ;
i 1 1 i \ ' i '•' — •
UJ —
D0<
Oco
IT I
3£°
Z1^— •
£m
1 2°=
00
TIME
1 MINUTE
-
°
arm
OO
TIME
Figure 10i Centerline probe current and voltage.
§2
2o
I
I
*' -~i- • •** i- '' '&
,Kf >»*»• ^ ' ^*"* ^ir " ^.- »'»*'"*
I !•
j 1 »
Zu.
»•-,, .t,^'v _
I !
, --
1 MINUTE
TIME
3
2
1
0
-1
-2
CD
I
0
I-
UJ
oc
CC
o
UJ
0
<
o
Zu.
1 MINUTE
TIME
Figure 11. Shaker cage current and voltage.
493
-------
A WORKING MODEL FOR COAL FLY ASH FILTRATION
By:
Richard Dennis and Hans A. Klemm
GCA/Technology Division
Bedford, Massachusetts 01730
ABSTRACT
A compact mathematical model Ls described for use by enforcement, design
or user personnel to determine whether a fabric filter system can comply with
particulate emission regulations. All calculations have been incorporated in
the computer program to facilitate model application by control agency and
other concerned groups. Given the correct combustion, design and operating
parameters, the model will predict emission and pressure loss characteristics.
The model user has the option of requesting a summary printout of key
performance data or highly detailed results for research purposes. Several
built in error checks prevent the generation of useless data. The model
considers dust properties and concentration, face velocity, compartmentized
operation and cleaning procedures. The model function depends upon the unique
fabric cleaning and dust penetration properties observed for coal fly ash and
woven glass bags. Examples of model applications are presented including
typical data inputs and outputs.
494
-------
A WORKING MODEL FOR COAL FLY ASH FILTRATION
INTRODUCTION
Fabric filter systems represent an effective and often the only prac-
tical means for controlling fly ash emissions from coal-fired industrial or
utility boilers. In the latter case, the physical size and cost of large
baghouses (often filtering more than 30,000 m3/min at temperature) demands
that the design and operation of the system be undertaken with a priori
assurances that compliance with emission regulations can be attained at an
acceptable energy expenditure.
To avoid risky extrapolation of design parameters for existing but not
necessarily replicate systems to new designs and to reduce dependence on
"engineering judgement" as a basis for designing a new filter system, the
U.S. Environmental Protection Agency has sponsored the development of a
mathematical model for predicting the performance of filter systems (Contract
No. 68-02-1438, Tasks 5, 6, and 7). Detailed results of these studies from
the inception of the fundamental modeling concepts to the recent publication
of a working model for use by agencies responsible for enforcement of
emission regulations have been described in the literature.O~6)
The purpose of this paper is to describe how enforcement personnel can
use the filtration model as a diagnostic tool to determine whether a
proposed or existing filter system design affords a reasonable chance of
successful field performance. The qualification "reasonable" is emphasized
because the model output depends not only upon the proper physical descrip-
tion of the filtration process (which we believe to be essentially correct)
but also upon accurate definition of key variables necessary to the modeling
process.
Model Role
The present model is designed for use with woven fabrics that are
cleaned by (a) collapse and reverse flow, (b) mechanical shaking, or
(c) some combination of the above. Although not restricted to fly ash
filtration, the model is not intended for use with pulse jet cleaned, felt
fabrics. A new model based upon GCA studies^7*8) and recent Harvard
research^9'10) has been proposed by Dennis and Klemm for predicting
performance of pulse jet filters with fly ash and other dusts.O1) Although
the present paper deals mainly with the diagnostic applications of the
model, it should also be noted that the model may be applied equally well by
system designers and equipment users as a predictive device and/or in support
of whatever historical or experience backlog is available.
The model discussed in this paper describes the overall performance of
real field systems in terms of the variables considered to exert a significant
impact on filter performance. Past use of the term "mathematical model"
has often referred to specific mathematical relationships between dust,
fabric and gas properties and filter performance. Although such correlations
495
-------
have in many cases correctly defined certain aspects of the filtration
process, they cannot, taken singly, be used to predict overall filter
system performance.
Modeling Approach and Requirements
The new model takes into account that air flow, pressure loss and dust
penetration through the many compartments and bags of a sequentially cleaned
system will vary from point to point in accordance with the local fabric
dust loadings. Because these flow interrelationships are highly complex it
is only by means of iteration techniques and a computer that the model can
be adapted to the solution of practical problems. Therefore, it was very
important to exercise extreme care in designing the model so that it can
be used by experienced environmental engineers who are not necessarily
specialists in filtration and/or computer technology.
The pollution control engineer wants a relatively uncomplicated
prodedure whereby he can input specific values for the controlling filtration
and process variables into a predictive model and receive as output a summary
of the probable system performance. He is concerned not only with average
and maximum particulate emissions but also with the probable ranges in
fabric pressure loss and predicted cleaning frequency, the latter information
for comparison with design specifications.
PRE-MODELING PROCEDURES
It is emphasized again that the reliability of the filtration model
output is only as good as the quality of the data inputs available for the
modeling process. Additionally, the degree to which the model user under-
stands the operation of the boiler of interest and the rationale for the
design parameters for the existing or proposed fabric filter system will
play an important role in model utilization. Again, it must be stressed
that the model is normally intended to augment the available data base and
not to replace it unless the information quality is suspect.
Before undertaking any modeling operations, a thorough inspection of the
filtration plant should be made, preferably by both enforcement and user
personnel. This procedure will help to identify specific problem areas
that may or have contributed to unsatisfactory performance, e.g., missing or
defective bags, lack of thermal insulation, defective gauges, overflowing
hoppers, leaking gasketing and signs of corrosion. The above defects should
be corrected before comparisons are made with the results of detailed
modeling efforts.
BASIS FOR MODEL DESIGN
Working Equations
The developmental aspects for the filtration model have been discussed
at length in recent publications.1"5 It suffices here to point out that the
model embraces several well recognized filtration principles that have been
496
-------
reviewed extensively by Billings and Wilder.8 A listing of the basic equations
used to estimate individual filtration parameters and/or to establish their
roles within the filtration model is given in Table 1.
Many of these relationships appear in the open literature5'8 such as the
equations used to calculate filter drag, S, or resistance, P, (Equations la,
Ib, and 4); specific resistance coefficient, K2 (Equation 7) and specific
surface parameter, So, (Equation 9). Certain of the equations were developed,
however, in conjunction with recent modeling studies. ^ '1+' ' These include
the expression describing nonlinear drag curves (Equation 2), the effect of
filtration velocity and dust surface properties on K2 (Equations 5 and 6),
the relationship between the degree of cleaning, ac, the method and intensity
of cleaning (Equation 11-12, 14-16); and finally, the general expressions
used to estimate overall filter system drag and penetration (Equations 4 and 20)
New Filtration Concepts
The introduction of three new concepts, however, has made it possible to
estimate the performance of a multicompartment filter system in much more
realistic fashion than previously possible. The first describes dust
separation from woven fabrics as a spalling-off process wherein the application
of cleaning energy causes dust separation to occur at the dust layer-fabric
interface.1'2 The above phenomenon permits the use of Equation 4, Table 1,
for computation of resultant filter system drag. The second concept is based
upon a straightforward description of the fabric cleaning process1>^,^
that relates the amount of dust removed to the method of cleaning and the
prior dust loading on the fabric. Equations 10 through 14, Table 1,
depict the types of calculations carried out within the program to estimate
the fraction of cleaned fabric area, ac, by reverse flow cleaning. If
mechanical shaking is used, Equations 10, 15, and 16 are employed to compute
penetration behavior exhibited by many fabrics woven from multifilament and
bulked yarns. Temporarily or permanently unblocked pores or pinholes
contribute to extensive penetration of the upstream aerosol such that
up- and downstream particle size properties are very similar. Because of this
phenomenon, the model treats filter emissions on a mass basis only
(Equations 17 through 20).
MODEL FIELD APPLICATIONS
In this section, the actual application of the model is described as
intended for use by field engineers to determine whether a proposed or existing
fabric filter system is able to reduce fly ash emissions to required levels.
The following material represents an abridgement of model operating
instructions appearing in a recent EPA report.^
Input Variables
For immediate reference, a listing of the input variables used with the
filtration model is presented in Table 2. Data inputs are grouped in four
497
-------
TABLE 1. SUMMARY OF MATHEMATICAL RELATIONSHIPS USED TO MODEL FABRIC FILTER PERFORMANCE
CC
Squat i on
number Equation
(la} S = P/V = Sr + K:H
- I IT ' - ' ' D " 3
(2) S = SR + K: W + (KR - K;) W*(l-exp
W = '.' - W
(3) W* = (S - S + K;, W )/K - K?
S = P/V =1 > -J2 + — ^ + T~
\4~f c sUl V /
(T) K^ = 1. 8 V'
(6> r 2
CK2)f - "u m3
A = dimens ion less = 1.0
See Figures 1 and 2.
MMD = cm"1
o = dimensionless
T = °C
S S cnT1
°c 0
f , n
V = poise
£ = dimensionless
Cc = dimensionless
-------
TABLE 1. (continued).
Equation
number
(9)
(10)
(11)
(12)
(13)
(14)
Equation
„ _ Jio'-i" Log%\
o ' MMD /
P. - S V C. V It
u' i U i -1
WP K2V ' HR 2
ac - 1.51 x 10~8 Wp2-52
ac = (6.00 x 10~3) (V C tc)°-715
tc = It + t£
Wp = 166.4 (C± V Zt)0-28"
a = (6.00 x 10-3) (V C. Zt)°-715
Comments
Equation (9) computes distribution specific surface parameter, So>
from cascade impactor data for a logarithmic normal mass distribution.
Reverse Flow with Bag Collapse
Intermittent, pressure controlled cleaning. Substitution of W' from
Equation (10) in Equation (11) gives area fraction cleaned, a ,
as function of limiting pressure loss, PL, and previously cited system
parameters. Wp accounts for the fact that the average Wp value over
the cleaning cycle will exceed the initial values.
Intermittent, time controlled cleaning. Equation (12) applies when
total cycle time, tc, is given. Note that t is the sum of time re-
quired to clean all compartments, £t, plus the time between compart-
ment cleaning, t^. Face velocity, V, and inlet concentration, C^,
must be nearly constant for safe use of time control.
Continuously cleaned system. Equation (13), which shows dust loading
on compartment ready for cleaning, applies when Wp ilO times WR.
Equation (14) computes ac for a continuously cleaned system where £t
Terms and units
S = cm"1
a = dimensionless
c
t , It, t,, = min
c f
C = 8/m3
V = m/min
n = number of compartments
is the time to clean all compartments.
Mechanical Shaking
(15) ac = 2.23 x 10~12 (f2 Ag wp2-52 Intermittent, pressure controlled cleaning system. Substitution of ac = dimensionless
Wp from Equation (10) in Equation (15) in conjunction with shaking _ , , . _
parameters f and As determines ac. Wp accounts for the fact that * ~ shaking frequency - Hz
the average W value over the cleaning cycle will exceed the initial A = shaking frequency = cm
values.
(16) ac = 4.9 * 10~3 (f2 AS Ci Vlt)0-715 Continuously cleaned system. Equation (16) computes ac in terms of It = time to clean all
cleaning parameters f and Ag and the dust accumulation over the time compartments = min
required to clean all compartments (C, VSt).
(17) C = [pn + (0 1 - Pn ) e~aW~| C + C Equations (17) through (19) are empirical relationships used to com- Cis Co, CR - g/m3
o L s " s J i R pute outlet concentrations, Co, in terms of incremental increase in rj _ / 2
,.g. = 1 5 x IQ-7 fi2 7(1- 1.03V-J fabric loading (W = W - WR); inlet dust concentration C.; and local ~ g
s [ J face velocity, V. The term CR is a constant, low level outlet con- V = m/min
, Irt, , , v ,M_3 T_u , _ nn, centration that is characteristic of the dust fabric combination. ^ , .
(19) a = 3.6 x 10 V-" +0.094 Pns and a are curve fitting constants for specific systems. PV P"t = dimensionless
I J 3 =m2/g
,„„, _ I ^^ V "• Equation (20) depicts basic iterative structure for defining system I = No. compartments
"t V IJ f j f J "-"-Jf ^ penetration at any time, Pnt as a function of parallel flow through
i=l j=l "I" compartments (each subdivided into "j" individual areas) where ~ areas per
local face velocities and fabric loadings are variable with respect compartment
to time and location. t = time
-------
TABLE 2. SUMMARY LISTING OF INPUT DATA FOR FILTRATION MODEL
Item Symbol Units Card Valid range Default Note
0 Title
1 Number of compartments n
2 Compartment cleaning time At
$ 3 Cleaning cycle time £t
Q 4 Time between cleaning cycles tf
M 5 Limiting pressure drop PL
§ 6 Reverse flow velocity VR
7 Shaking frequency f
8 Shaking amplitude A
o 9 Average face velocity V
H< 10 Gas temperature T
w3 11 Inlet dust concentration C;
fr<
12 measured at temperature of T
13 Specific resistance coefficient KZ
14 measured at temperature of T
15 measured at velocity of V
16 measured at mass median diameter of MMDi
17 measured at geometric standard ogj
u deviation of
H
oj 18 Mass median diameter of inlet dust HMD?
H
O 19 Geometric standard deviation of inlet dust 0£2
20 Discrete particle density of inlet dust p
a 21 Bulk density of inlet dust p
9
h 22 Effective residual drag Sg
S 23 measured at temperature of T
EH 24 Residual fabric loading WR
o 25 Residual drag SR
26 measured at temperature of T
27 Initial slope KR
28 measured at temperature of T
29 Maximum number of cycles modeled nc
30 Accuracy code 0 or
2 w 31 Type of tabular results -
OB:
at M 32 Type of plotted results
^ tj
^ g 33 Fractional area cleaned ac
o en 34 x axis length
S M
to 35 y axis length
*
These values are used when no entry has been made for the
Used only when K2 is to be estimated from size properties
Notes: a. Enter item 4 or 5, but not both.
b. Enter item 6 or 7 and 8, but not both.
c. Enter items 13 through 15 when K2 measurement
d. Enter items 13 through 19 when Kj measurement
-
-
min
min
min
N/tn2
m/min
cps
cm
m/min
°C
g/m3
°C
N-min/g-ra
°C
m/min
ym
_
ym
-
g/cm3
g/cm3
N-min/m3
°C
g/m2
N-min/m3
°C
N-min/g-m
°C
-
1
-
-
-
inches
inches
parameter.
is available.
1
2
2
2
2
2
2
2
2
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
6
6
6
6
6
7
7
must be corrected
1 to 30
O.Sdtem 3/Item 1) s
a
a
0 b
b
b
0.3 to 3.0
>0
25
0.25 to 10 c,d
>0 25
0.6L
2 to 50 d
2 to 4 d
2 to 50 d,e
2 to 4 d,e
e
e
350 f,g
>0 25
50+ f,g
f
>0 25
f
>0 25
h
0 or 1 0
Average i
i
>0 to 1 j
6 k
5
for size properties.
e. Enter items 18 through 21 when Ka is to be estimated from dust size and density parameters.
f. Enter items 22 through 28 for nonlinear drag model.
g. Enter items 22 through 24 for linear drag model.
h. Generally 20 cycles are sufficient.
i. For tabular results specify DETAILED, SUMMARY or AVERAGE; for graphical results specify
PLOT or leave blank.
j. Enter only in special case when ac measurement is available.
k. Card can be left out if default values are sufficient or if no plotted output is desired.
500
-------
FABRIC FILTER MODEL - DATA INPUT FORM
11 OK THE SAME CARD, ENTER OIK OH
blTHE OTHER. BUT HOT BOTH
•-REQUIRED IF Kj IS KKOWI
4 -REOmRED IF I] IS TO BE COMtECTEC
FOB SUE PROPERTIES
• -REouoreo F KJ a TO u ESTMATEO
I- REOUREO FOR HOM-UMEAJ) MUC H09CL
1- REQUIRED FOR LIRCAB MAS HOOEL
UUE Of FCRSM
COWUTIM FORV
1 2
3
4
S
6
T
>
9
«
1
B
13
TITLE
M
a
e
J7
18
19
20
M
77
n
M
a
ji
a
a
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31
S
«l
M
•
EO
61
2
Ea
M
a
a
s?
n
mxj
CLEAMBS TIMES
1234967* 9 KNI C IS 14 O I61J7 18 19M it
2 3 4 5 K 7 ) 9l«|» C 13 H OIfel 17 18 19
22 ,. 23 24 25 26
34 S 67 IS 9 10 I S 13 H Blie J7 18 W
1234 5 l« 7 I 9 W I
35
DCUMAL POMT
ALL OTHER EMTHIES MUST BE RTOHT JUSTIFIED EXCEPT FOB ITEMS 0. 31 AND 52.
Figure 1. Fabric filter model - data input form.
501
-------
categories: Design Data, Operating Data, Dust and Fabric Properties and
Special Program Instructions. Table 2 also shows the correct units for each
data input as well as the Card and Item number for entry on the Data Input
Form, Figure 1. Additionally, the valid ranges; i.e., the range of numerical
values that will allow the program to run, are indicated for key variables.
Table 2 also indicates Default Values which are automatically assigned by
the program when no data inputs are available or when the model user forgets
to make an entry. In the Table 2 footnotes, those conditions defining
specific or mutally exclusive data inputs are summarized. A more detailed
treatment of user instructions is given in the User's Guide.4
Data Input Forms
The specific data inputs to be entered on each of the seven cards are
listed below:
1 - Heading or Title Card
2 - Design Data
3 - Operating Data
4 - Specific Resistance Coefficient/Gas and Dust Properties
5 - Fabric and Dust Properties
6 - Special Program Instructions
7 - Plot (Graph) Dimensions
To facilitate data entry and subsequent card punching, a "FABRIC FILTER
MODEL-DATA INPUT FORM" has been prepared, Figure 1, with the data entry
locations labeled to correspond to their respective code numbers on Table 2.
In those blocks where no decimal point indicator is shown, right justification
of the entry is required. Some items requiring special consideration are dis-
cussed in this section. If more than one compartment is cleaned simultaneously
(Item 1, Card 2) the revised or effective value for number of compartments is
the total compartment number divided by the number undergoing simultaneous
cleaning. Failure to enter a value for compartment cleaning time (Item 2,
Card 2) will result in a DEFAULT entry. However, the program will not
function if the cleaning cycle time (Item 3, Card 2) is omitted. In the
case of back-to-back or continuous cleaning, Items 4 and 5, Card 2, may be
left blank although a "zero" entry avoids confusion. It should also be
noted that the program will function when no value or a zero value is entered
for reverse flow velocity (Item 6, Card 2). The average face velocity
(Item 9, Card 3) as computed from the total volume flow through the
baghouse and the total available filtration area must always be entered at
the actual gas stream temperature (Item 10, Card 3). In the case of K£
estimation, DEFAULT values for temperature and velocity (Items 14 and 15,
Card 4) are automatically entered. Note that if no value for K2 is entered,
the program will not function unless specific size and density parameters
(Item 18 through 21, Card 4) are entered. Except for those cases where data
inputs are available for the terms S-g, W^, S-^, and K^ (Items 22, 24, 25,
27, Card 5) the program will always select the linear modeling approach.
In most cases, it is advisable to select 20 operating cycles (Item 29,
Card 6). With respect to accuracy code, (Item 30, Card 6) "0" and "1"
entries, respectively, define -convergence limits within 1 and 0.3 percent
of the estimated limiting values for the key performance variables. The
502
-------
selection of "DETAILED" for Item 31, Card 7 provides highly specialized
outputs that are only necessary for research applications. Specification
of SUMMARY will furnish information on the changes in overall system effluent
concentration, penetration and fabric pressure loss with time as well as
average, maximum and minimum values for the above performance characteristics
(the AVERAGE output). For many practical situations, selection of AVERAGE
parameters is sufficient to assess compliance potential. Although the
graphing capability is an extra feature, the curves produced when PLOT is
specified may elimiante considerable hand plotting.
Error Messages
In accordance with good programming procedures, an attempt has been made
to anticipate the major causes of computer program malfunctions, most of which
relate to improper data entries. Thus, when the program fails an error mes-
sage(s) will appear on a separate print-out sheet captioned DIAGNOSTIC
MESSAGES. A listing of typical error messages and their probable causes and
means of correction is given in Table 3. Note also that this same print-
out also signifies a "go ahead" by the statement "THERE ARE NO ERRORS IN
THE INPUT DATA."
EXAMPLE OF MODEL APPLICATION
The following example illustrates how the filtration model may be used
by enforcement personnel to help solve a typical field problem. An electric
utility operates two, coal-burning steam-electric plants, the first of
which now uses a pressure-controlled baghouse to maintain particulate
(fly ash) emissions at or below compliance levels. It has been proposed
that a continuously cleaned fabric filter system be installed at the second
plant. Both the utility operator and the local emission enforcement groups
would like to determine whether operation of the new filter system in
accordance with the input data shown in Table 4 will satisfy local emission
requirements while maintaining average system pressure drop levels within
the exhaust capacity range of the induced draft fans. For present purposes,
it is assumed that operation at an efficiency of 99.5 percent (equivalent
to 0.5 percent penetration) and an average pressure drop of, < 1750 N/m2
(7 in. water) indicates acceptable performance. Although a lower operating
pressure loss is usually preferred, limited physical space and a desire to
make use of the existing draft fans has led to the utilities acceptance
of the indicated pressure drop characteristics ( <1750 N/m2).
Design and operating data appearing in Table 4 for the proposed
"second" plant baghouse represent a composite of information received from
both utility personnel and the dust collector manufacturer. It is also
assumed that previous measurements of uncontrolled mass emission rates and
fly ash size distributions at both plants are available as well as estimates
for the terms K2, SE and WR based upon special tests performed at the first
plant. It should be noted that the above terms might have been estimated
from strip chart records from the first plant showing the pressure loss
versus time traces. There is the important constraint, however, that the
time intervals between cleaning be long enough (^2 hours) to develop a uniform
density dust deposit on the fabric surface.
503
-------
TABLE 3. SUMMARY OF DIAGNOSTIC MESSAGES AND THEIR INTERPRETATION
Message
Probable cause/corrective measures
- ILLEGAL REQUEST FOR TYPE OF RESULTS
- THE NUMBER OF COMPARTMENTS MUST HOT EXCEED 30
- THE NUMBER OF COMPARTMENTS TIMES THE COMPARTMENT
CLEANING TIME MUST BE LESS THAN THE CLEANING
CYCLE TIME
- THE COMPARTMENT CLEANING TIME MUST BE LESS THAN
THE TOTAL CYCLE TIME
- TIME INCREMENT TOO SMALL, I.E., < 0.01 MINUTES
- AVERAGE FACE VELOCITY OUT OF RANGE, 0.3 TO 3.0
- A GAS TEMPERATURE HAS NOT BEEN ENTERED
- INVALID FREQUENCY OR AMPLITUDE FOR SHAKER
- INVALID ACCURACY CODE
- BOTH TIMED AND PRESSURE CONTROLLED CLEANING
SPECIFIED - ONLY ONE IS VALID
- PARTICLE SIZE DATA FOR K2 ARE INCOMPLETE
- MASS MEDIAN DIAMETER OF MEASUREMENT OUT OF
RANGE 2 TO 50
- THE PROGRAM HAS BEEN TERMINATED BECAUSE OF
ERRORS IN THE INPUT DATA
- THERE ARE NO ERRORS IN THE INPUT DATA
Incorrecc spelling of DETAILED, SUMMARY, AVERAGE or
PLOT for Items 31 and 32, Card 6.
Too many compartments were entered for Item 1,
Card 2.
Too many compartments, too large a compartment
cleaning time or too small a cleaning cycle time
were specified - Items 1, 2, and 3, Card 2.
Too large a compartment cleaning time, Item 2,
Card 2, or too small a cleaning cycle time, Item 3,
Card 2, were specified.
The time increment calculated by the program is too
small. Too many compartments (Item 1, Card 2) or
too small a cleaning cycle time, Item 3, Card 2,
will cause this problem.
Too large or too small an average face velocity was
entered for Item 9, Card 3.
A value less than or equal to 0°C was entered for
Item 10, Card 3.
A > 0 value entered for either frequency, Item 7,
Card 2 or amplitude, Item 8, Card 2. Both must be
entered or left blank for program to operate.
Only 0 and 1 are valid codes. Make certain the
number is right justified when entered for Item 30,
Card 6.
On Card 2, values for both Items 4 and 5 were
entered. Only one item may be entered per test.
A value for K2, Item 13, Card 4, was entered along
with data to be used in correcting K2 for dust
size properties, Items 16 through 19, Card 4.
However, an omission from Items 16 through 19 has
led to any of the following error messages.
The MMD of the reference dust, Item 16, Card 4, is
out of the valid range.
Since one or more of the above errors has occurred,
program execution is stopped. Correct the error(s)
and rerun the program.
No errors were detected. The simulation will be
performed.
Out of order and missing cards (with the exception of Card 7) will cause many of the above errors to
occur. Check card order before running program.
504
-------
TABLE 4. AVAILABLE INPUT DATA FOR MODELING BAGHOUSE PERFORMANCE
AT ELECTRIC UTILITY, PLANT 2
Inlet dust geometric standard
deviation
Dust specific resistance, K2
Measured @
Measured @
Effective residual drag
Measured @
Residual fabric loading
Existing Plant A
Proposed Plant B
Number of compartments
Cleaning cycle duration
Time to clean one compartment
Cleaning type
Reverse flow volume
Cleaning cycle initiation
Volume flow into baghouse
Total filtration area
Temperature of flue gas
Inlet concentration
Inlet dust mass median diameter
10 ym (Reference)
3.0 (Reference)
10.2 in.W.C.-ft-min/lb
500°F
2 ft/min
0.636 in.W.C.-min/ft
500°F
0.015 lb/ft2
30
30 minutes
A
1 minute
Collapse/reverse air
30,000 acfm
Continuous cleaning
600,000 acfm
200,000 ft2
350°F
5 grains/scf
7 ym
2.5
Note: All English units must be converted to their metric equivalents,
Usually 2 to 3 minutes are allowed for cleaning.
505
-------
The data summarized in Table 4 are sufficient to carry out the predictive
modeling operation. Following transcription of the information from Table 4
into the units and format shown in Figure 2, the data inputs are ready for
punch-carding.
Card 1 contains the title which will appear with the results. Note that
on Card 2 the time between cleaning cycles, Item 4, and the limiting pressure,
Item 5, have been left blank because a continuous cleaning system has been
chosen. The reverse flow velocity, Item 6, Card 2, is calculated from the
total reverse flow rate (30,000 acfm) and the cloth area per compartment
(200,000 ft2/30) as 4.5 ft/min or 1.37 m/min. The average face velocity,
Item 9, Card 3, is computed from the indicated value for the total gas
flow (600,000 acfm) and the total fabric area (200,000 ft2) as 3.0 ft/min
(0.915)m/min). Inlet concentration is reported at ambient temperature,
^25°C, the value entered for Item 12, Card 3.
The data available for K2 are sufficient to allow for correction of the
measured K2 at the first plant to the size properties of the dust at the
second plant. Thus K2, the temperature and face velocity at which it was
measured and the size properties of the two dusts are entered as shown on
Card 4. The model user should note that much of the raw field data may
appear in English units, necessitating their conversion to the metric units
used in the model. See Table 5
Twenty cycles are considered sufficient to complete the simulation and
achieve steady state conditions (see Card 6). Similarly, an accuracy level
of zero is considered acceptable for the first trial. Because the utility
personnel and the enforcement agency are concerned mainly with average emis-
sion rates and average pressure drop, AVERAGE results are requested. Since
no plotting is desired, Item 32, Card 7 has been left blank.
If the results of the simulation had indicated emission levels close to,
but greater than, the allowable level, the simulation could bave been rerun
with an accuracy level of 1. If convergence had not been reached within
20 cycles, a value of 40, for example, might have been entered provided that
the costs for added computer time were acceptable.
In Table 6, the actual computer printout provided for the input data and
instructions of Figure 2 have been arranged in a convenient tabulation showing
each of four separate printout sheets. Printout No. 1 shows the actual sum-
marized input data as entered into the program so that the user can check the
data for errors or omissions. Printout No. 2 instructs the user via the
statement "There are no errors in the input data" that the modeling program
will be executed as requested. Printout No. 3 provides a listing of those
parameters whose values were computed or corrected by the program such as ac
and K2. Again, inspection of these data by the model user allows him to
determine the reasonableness of the indicated values. Finally, the AVERAGE
data shown in Printout No. 4 indicate that both the pressure drop and penetra-
tion expectations for the filter system (< 1750 N/m2 and 0.5 percent) should
be realized. In addition, Printout No. 4 also indicates that 10 cycles rather
than the 20 requested on the data input form, were sufficient to define steady
state operating conditions.
506
-------
a Ion T
bfTHE
TIC SAME CARD, EUTOI CMC OH
OTHW.BUT NOT BOTH
C -REWIRED If Kj IS
4 -ReOUMED IF «z IS TO BE CORRECTED
FOR SIZE H1WERT1ES
C -REWIRED IT KZ IS TO tf ESTIMATED
f-KOWRID rtm WOU-LIHCAR
10
NAME Of PERSON
COMP1.CTIHS FORU
•"•"* TITLE
1 2
EL
3
e
4
C
5
T
6
R
7
/
8
C
9
10
u
i
T
c
/
0
J_
M
/
a
T
*
y
J7
18
/
19
20
P
21
1.
22
4
S
A/
24
7
?5
26
i
2'
T
•»[*
90
t
3<
W
32
<7
S3
L>
34
5
a
£
K
57
38
3$
4C
41
42
43
44
45
4C
47
<£
«i
9C
31
&
S3
S4
S5
56
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^
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6J
5?
T
i
59
a
67
58
S97D
CLEAMIMC TIMtS
2345671 9 10 I B 13 H O «J7 18 19
Figure 2. Fabric filter model - data input form.
507
-------
TABLE 5. ENGLISH/METRIC CONVERSION FACTORS
Quantity
Filter resistance
Filter drag
Velocity
Volume flew
Fabric area
Areal density
Specific resistance coefficient
Dust concentration
Density
To convert from
in. H20
in. H20-min/ft
f t/min
ft3/min
ft2
lb/ft2
in.W.C.-rain-ft/lb
grains/ft3
lb/ft3
To
N/m2
N-min/m
m/min
m /min
m2
g/m2
N-min/g-m
g/m3
g/cm3
Multiply by
249
817
0.305
0.0283
0.093
4882
0.167
2.29
0.0160
508
-------
TABLE 6. SAMPLES OF TABULAR PRINTOUT FOR EXAMPLE OF MODEL APPLICATION
PRINTOUT NO. 1
SUM"A«Y Of INPUT CATA FOR BAGHOUSE ANALYSIS
AN ELECTRIC UTILITY / PLANT 8 BAGHOUSE
HASIC DESIGN DATA
NUVBE« OF" COMPARTMENTS 30
CQwPAHTMt-jT CLEANING TI"E 1,0
(OFF LINE TIVE)
CLEANING CYCLE TI M E JO.n
CONTIGUOUSLY CLEANED SYSTE"
REVERSE FLHrt VELOCITY 1.3725
OPfWATING DATA
AVEPAGE FACE VELOCITY
GAS TEWPERATUPE
INLET DUST CCNCEMTKATIQN
"•EASUREC AT
FABRIC AND OUST PROPEHTItS
SPECIFIC RESISTANCE, KE
MEASURED AT
CORRECTED TO w"D2
EFFECTIVE RESIDUAL DRAG, SE
RESIDUAL LOADING, rtH
0.9150
177.
1 1 ,«5
1 .70
?feO,
O.blOO
10.0
7.0
520.
260.
73.2
DEGREES CENTIGRADE
G/M3
DEGREES CENTIGRADE
DEGREES CENTIGRADE
MICRONS
DICKONS
-STANDARD DEVIATION 3.00
-STANDARD DEVIATION 2.50
DEGREES CENTIGRADE
SPECIAL PROGRAM INSTRUCTIONS
WAX MUMHER OF CYCLES MODELED 20
ACCURACY LEVEL 0
TYPE OF RESULTS REQUESTED AVERAGE /
PRINTOUT NO. 2
DIAGNOSTIC -FSSAGES
ARE NO ERRORS IN THE INPUT DATA
(continued)
509
-------
TABLE 6. (continued)
PRINTOUT NO. 3
CALCULATED VALOfS
I'-LET OUST CONCENTRATION
TED TO OPERATING TEl'PERATORE
7.58
FCHMC "NO DUST CA»F PROPERTIES CORRECTED FriR f, t, s VISCOSITY
SPECIFIC CAKE RESISTANCE, K? 2.i« N-WIN/G-*
EFFECTIVE CRAG, St b J 0 . \ . w ; /g / M j
«NEa CLEANED,
TI»E
" C i INSTANT A'*
0.0
PRINTOUT NO. 4
RESl'LTS OF BAGrinijSE ANALYSIS
tLFCIHIC UTILITY / PLANT B BA&HOUSE
FQR
30.00
CYCLF
PtNETWAlJON=
AVERAGE PRESSURE DROP*
AVERAGE SYSTEU K0rt =
PRESSURE
3. J1E-01
1SS6.78
FOR 30.00 "IMlTtS OPERATION, CYCLE MJWHER <)
AVERAGE PENE TRATION =
AVERAGE PRESSURE DROP=
AVERAGE SYSTEM FLO*=
wftxl«'jw PENETRATION:
VAXIUUW PRESSURE DROP:
u.7u£-0i
FOR
30,00 MINUTES OpERAT !
CYCLE NUMBER 10
svERAGE PENETRATIfJK =
AvERAGF PRESSURE D«CP=
AVERAGE SYSTEM FLOA:
««AXIMUW PENETRATION^
WAXIWU" PRESSURE DWOP=
3.33E-03
O.P607 "/WIN
U.7UE-03
1S74.50 N/M?
510
-------
SUMMARY
The primary purpose of this paper has been to highlight the develop-
mental aspects of the filtration model that have been described in detail in
precursor studies and to show precisely how the model can be used to estimate
the performance of a new filter system while design and operating parameters
are still open to change. The example chosen to illustrate the model
application indicates that a basic understanding of filtration concepts with
concurrent definition of key input parameters enables the model user to
obtain a simple answer as to the probable success of the filter system
design undergoing evaluation.
ACKNOWLEDGMENTS
The authors express their appreciation to Dr. James H. Turner, EPA
Project Officer, for his continued technical support throughout the
programs under which the present filtration model has been developed.
This project has been funded at least in part with Federal funds from
the Environmental Protection Agency under contract number 68-02-1438, Task
Order Nos. 5, 6 and 7, and contract number 68-02-2607, Task Order Nos. 7
and 8. The contents of this publication do not necessarily reflect the
views or policies of the U.S. Environmental Protection Agency, nor does
mention of trade names, commercial products, or organizations imply
endorsement by the U.S. Government.
REFERENCES
1. Dennis, R., et. al. Filtration Model for Coal Fly Ash with Glass
Fabrics. U.S. Environmental Protection Agency, Industrial Environmental
Research Laboratory, Research Triangle Park, North Carolina.
EPA-600/7-77-084. August 1977.
2. Dennis, R., R. W. Cass, and R. R. Hall. Dust Dislodgement From Woven
Fabrics Versus Filter Performance. J Air Pollut Control Assoc.
4_8 No. 1, 47-52, 1978.
3. Dennis, R., and N. F. Surprenant. Particulate Control Highlights: Re-
search on Fabric Filtration Technology. U.S. Environmental Protection
Agency, Industrial Environmental Research Laboratory, Research Triangle
Park, North Carolina. EPA-600/8-78-005d. June 1978.
4. Dennis, R. and H. A. Klemm. Fabric Filter Model Format Change. Vol. I
Detailed Technical Report, Vol. II User's Guide. U.S. Enivronmental Pro-
tection Agency, Industrial Environmental Research Laboratory, Research
Triangle Park, North Carolina. EPA-600/7-79-043a, EPA-600/7-79-043b.
February 1979.
5. Dennis, R. and H. A. Klemm. A Model for Coal Fly Ash Filtration. J Air
Pollut Control Assoc. 49 No. 3,230-234, 1979.
511
-------
6. Dennis, R., H. A. Klemm and W. Battye. Fabric Filter Sensitivity
Analysis. U.S. Enivronmental Protection Agency, Industrial Environmental
Research Laboratory, Research Triangle Park, North Carolina. EPA-600/
7-79-043c. April 1979.
7. Dennis, R., and J. E. Wilder. Fabric Filter Cleaning Studies. U.S. En-
vironmental Protection Agency, Control Systems Laboratory, Research
Triangle Park, North Carolina. EPA-650/2-75-009 (NTIS No. PB-240-372-3G1)
January 1975.
8. Billings, C. E., and J. E. Wilder. Handbook of Fabric Filter Technology,
Volume I, Fabric Filter Systems Study, 1970. U.S. Environmental Protec-
tion Agency, Control Systems Laboratory, Research Triangle Park, North
Carolina. EPA-APTD 0690 (NTIS No. PB-200-648). December 1970.
9. Leith, D. H. , M. W. First and H. Feldman. Performance of a Pulse-Jet
Filter at High Filtration Velocity - II. Filter Cake Redeposition,
J. Air Pollut Control Assoc. 27_ No. 7, 636-640, 1977.
10. Ellenbecker, M. J., and D. Leith. Effect of Dust Cake Redeposition on
Pressure Drop in Pulse-Jet Fabric Filters. Paper Presented at 3rd
International Powder & Bulk Solids Handling & Processing Conference,
Rosemont, 111., May 1978.
11. Dennis, R. and H. A. Klemm. A System Model for Pulse-Jet Filtration.
Publication pending editorial review. 1979-
512
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PARTICULATE REMOVAL AND OPACITY USING A WET VENTURI
SCRUBBER - THE MINNESOTA POWER. AND LIGHT EXPERIENCE
By:
David Nixon
Plant Mechanical Engineer
Minnesota Power & Light Company
Duluth, Minnesota 55802
and
Carlton Johnson
Manager of Process Engineering
Peabody Process Systems, Inc.
Stamford, Connecticut 07907
Minnesota Power and Light is installing a wet venturi
particulate scrubber and a spray tower S02 absorber as
the Air Quality Control System for their 500MW Unit #4,
Clay Boswell Station, Cohasset, Minnesota. The System is
being designed and installed by Peabody Process Systems,
Inc., Stamford, Connecticut.
Prior to start-up the full scale unit, a 1MW pilot plant
was installed and tested to evaluate the performance of
the system. Estensive data was collected for two differ-
ent western coals with regard to venturi particulate re-
moval characteristics and its effect on opacity. Corre-
lations were also developed using pilot plant opacity
data to predict full seale opacity results.
This paper summarizes the test results obtained and
conclusions reached.
513
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PARTICULATE REMOVAL AND_OPACITY USING A WET VENTURI SCRUBBER-
THE MINNESOTA POWER AND LIGHT EXPERIENCE
1. INTRODUCTION
Minnesota Power & Light is currently expanding its power
generating capacity at its Clay-Boswell station, Cohasset,
Minnesota by the addition of Unit #4 with a capacity of 500
MW. The Air Quality Control System this unit was designed
and installed by Peabody Process Systems, Stamford, Conn.,
and consisit of an integral venturi particulate scrubber
and a spray tower S02 absorber... The system is designed
for 99.7% particulate removal and 90% S02 removal based
upon burning a sub-bituminous coal from the "Big Sky" mine
at Colstrip, Montana where the Rosebud and McKay seams vary
In sulfur content from 0.4% to 2.8% with about 10% ash con-
tent .
The initial design of the plant called for a hot-side or
coId-side electrostatic precipitator followed by a spray
tower S02 absorber. However, when Minnesota Power &
Light solicited bids on this basis, the quoted costs ap-
peared to be very high. In addition, Minnesota Power &
Light had some doubts that the precipitator could meet the
stringent performance required for their system. Likewise,
It was also known that the alkali contained in the flyash
could offer economic benefits in S02 remova 1.These
factors led Minnesota Power & Light to explore the concept
of using a wet venturi for particulate removal and
integrating it with the S02 spray tower absorber.
2 • E CONQMI C^^E V ALUAT ION
Three alternate systems were evaluated by Minnesota Power &
Light. They were:
System #1: Hot-side electrostatic precipitator followed by
an S02 absorber. Reheat by means of a 5% hot
flue gas bypass which is treated for particu-
late removal via a small hot-side electrostatic
precipitator.
System #2: CoId-side electrostatic precipitator followed
by an SO2 absorber. Reheat by means of a 5%
flue gas bypass which is treated for particu-
late removal via a small hot-side electrostatic
precipitator.
System #3: Venturi scrubber followed by an S02 absorber.
Reheat by means of a 5% flue gas bypass which
514
-------
is treated for particulate removal via a small
hot-side electrostatic precipitator.
The economic evaluation, based upon actual bids received,
included investment, operating and maintenance costs for
the three systems. Special emphasis was placed on de-
termining the availability of these systems and the risk
factors associated with each.
The total investment for each system, including necessary
sub-systems (e.g. , waste disposal for ash and scrubber
sludge; induced fans; and air preheaters), is tabulated
below in thousands of dollars:
System 1
73,939
20,660
System 2
81 ,091
27,812
System 3
53,279
BASE
INVESTMENT
DIFFERENTIAL
The following table summarizes annual owning and operating
costs in thousands of dollars:
FIXED CHARGES
CAPABILITY CHARGE
REAGENT & UTILITIES
OPERATING & MAINTENANCE
TOTAL ANNUAL CHARGES
DIFFERENTIAL
PRESENT WORTH - 30 YEARS
DIFFERENTIAL
Sy s tern 1
1
2
9
2
1
4
5
3
3
3
,57
,33
,12
0
5
9
,096
,130
,07
9
,000
Sys
13,
1,
3,
51
24,
4,
203,
7
5
7
5
tern 2 System 3
8
6
8
7
30
2
0
5
1
5
3
1
7
6
3
4
9
1
3
6
20
,05
7
,606
,30
7
,083
,05
3
BASE
167
,50
5
25,696
35,509
BASE
The conclusions of the economic analysis are self-evident.
System 3 is a great deal lower in installed cost, but
operating and maintenance costs are only slightly greater
than -the ESP/spray tower systems. The net result is that
515
-------
the integral venturi/spray tower absorber system is the
most economical method of achieving Minnesota Power &
Light's air quality control requirements.
DESCRIPTION OF PILOT PLANT AND TEST OBJECTIVES
In November 1977, Minnesota Power & Light awarded a con-
tract to Peabody Process Systems, Inc., Stamford, Conn, for
the design and installation of an Air Quality Control Sys-
tem (AQCS) based upon using the venturi for particulate re-
moval and a spray tower absorber for SC>2 removal. As
part of its contractual commitment, Peabody offered
guarantees with regard to both particulate and S02 re-
moval. To confirm these guarantees and to further Min-
nesota Power & Light's understanding of the operating
characteristics of the system which they purchased, Peabody
was authorized to design, install and supervise a pilot
plant test program for the evaluation of the system. This
test program covered an 18 month period and involved a cost
of approximately two million dollars. The objectives of
this pilot plant included the following:
1. Confirm the pressure drop in the venturi required to
meet particulate and opacity emission standards.
2. Confirm that the system can remove 90% SO? when burn-
ing coals containing up to 2.8% sulfur.
3. Demonstrate that the system can operate on a closed
loop water balance.
4. Determine the alkali utilization of the flyash.
5. Evaluate alternative alkalis.
6. Define waste solids characteristics such as settling
rates, percent moisture and settled solids, etc.
The pilot plant installed to achieve the above objectives
was installed at the Clay-Boswell station taking the flue
gas from Unit #3. Unit #3 has the same boiler design and
is burning the same coals which are to be burned in Unit
#4. Thus, the results obtained from the pilot plant could
be considered representative of the results to be expected
for Unit #4.
516
-------
Minnesota Power and Light
Pilot Plant Installation
Clay Boswell Station-Unit no. 3
The pilot plant system was identical in concept to proposed
full scale unit with some modifications based on practical
considerations. The lime slakers system was not installed.
An in line electric reheater was used in lieu of the hot
gas bypass system. A thickener and vacuum filter was used
in lieu of a waste solids pond system.
The pilot plant was designed to treat 3200 ACFM of gas.
The flue gas is taken from Unit #3 ahead of an existing
particulate scrubbing system and contacted in the venturi
with slurry for removal of the particulate matter. This
slurry is the same material used for absorbtion of S02.
The gas and slurry leaving the venturi flows to the base of
the spray tower absorber where the gas and slurry separate.
The slurry drains to the recycle tank, the gas flows upward
through the spray tower absorber where it is further con
tacted with recirculated slurry which is pumped through
multiple spray headers to achieve the desired degree of
S02 removal. The clean gas prior to leaving the absorber
flows through a mist eliminator section consisting of an
interface tray and chevron mist eliminator. After leaving
the absorber, the gas is reheated by an in-line electric
heater. The reheated gas then goes through an I.D. fan^and
is reintroduced into the suction of the I.D. fan for Unit
#3. The pilot plant also contains an alkali feed tank from
which alkali is fed to maintain the desired slurry pll , a
supplemental flyash feeding system and a thickener and
vacuum filter for treatment of waste solids. Particular
attention was given to the quality of instrumentation to
insure reliability of the pilot plant operation and test
results. Inlet and outlet S02 concentrations were con-
tinuously monitored by means of S02 analyzers. A nuclear
517
-------
d e n s i t y device was maintaining the slurry c o n c e n t r at i o n.
Automatic pH control and an optical opacity meter were also
provided with the system.
—i
AI.KAU j lr
l-Ll-.b TANM f*3
J >~ •
Ven t ur i
The vcnturi selected for pa rticulate removal is based upon
the radial flow design concept. The design of a venturi
must contend with the problems of abrasion and also solids
build up due to hot gas contacting the slurry used for
parti c. ul ate removal. To avoid solids build up, the venturi
is designed using a "dentist bowl" concept. The upper sec-
tion of the venturi consists of a conical section in which
slurry is introduced tangentially. The quantity of slurry
used is several times greater than the potential evapora-
tive capacity of: the hot flue gas. The excess quantity of
the tangentiable flows of the slurry insures that the con-
ical section is completely wetted. The hot flue gas enters
the venturi through an insulated thimble section which
introduces the gas below the slurry injection point and
this keeps the gas slurry contact point below the wet-dry
line and avoids solid build up.
518
-------
Abrasion can occur in three distinct areas of the venturi.
The first is where the gas makes a 90° turn to flow
through the cylindrical orifice. Abrasion in this area is
avoided by having the gas impinge on a pan filled with
slurry, which absorbs the impact of the gas. This pan is
maintained full by the flow of slurry from the "dentist
bowl" and supplemental slurry added via a bull nozzle.
The slurry overflow from the pan and the gas are then
mixed intimately in the cylindrical orifice around the pan.
It is at this point that particulate removal is achieved.
Abrasion is also a factor at the orifice which cannot be
eliminated. However, the wear surface in the orifice area
is fabricated from disposible angle iron sections which
provided for simplified maintenance.
The gas and. slurry mixtur-e leaving the orifice area has a
high velocity which if allowed to impact on a surface,
could also cause severe abrasion problems. This situation
is avoided by maintaining a sufficient distance between the
orifice area and the wall of the venturi. This allows the
gas to expand and slow down sufficiently to be nonabrasive.
As an added precaution the wall is rubber lined to with-
stand any residual abrasive impact.
Thus of the three intended abrasive cases, two have been
eliminated and the third one minimized by providing a de-
sign for simplified replacement. The radial flow venturi
design is a balance force system since the gas velocity is
equal in the 360° lateral plane circumference of the ori-
fice. The force exerted on the mechanical operator due to
the venturi pressure drop therefore becomes zero. This
balanced design will minimize maintenance problems and is a
519
-------
key design feature in the reliable operation of the
v e n t u r. i .
The design concepts discussed above are those used for the
full scale system as well as the pilot plant test program.
All of the objectives of the test program were achieved.
However, only the results pertinent to particulate removal
and opacity will be discussed in this paper.
4. CHARACTERIZATION OF FLYASH PARTICLE SIZE
The flue gas duct to the pilot plant had a 14" diameter.
The Unit #3 duct from which the flue gas was to be sampled
has a dimension of approximately 10 feet high x 146 feet
wide. From previous testing that the Minnesota Power &
Light performed it was known that some segregation of the
flyash occured in the section of ductwork where the flue
gas was to be sampled. As a result, there was a concern
that the flue gas to the pilot plant would not be re-
presentative with regard to both total grain loading and
particle size distribution. Prior to locating the pilot
plant test port connection in the Unit #3 duct, extensive
work was done to characterize the particulates in the cross
section of the Unit #3 duct. Based upon this data, a test
port was selected with two alternates provided should later
results dictate changing the test port. After the instal-
lation of the pilot plant, repeated particulate a n—
alyses were made of the flue gas flowing to the pilot plant
and simultaneously the flue gas from Unit #3. The com-
parison showed that a proper sampling port had been
selected and the flue gas to the pilot plant was re-
presentative of that obtained from the full scale unit.
For particle size distribution data, EPA method 5 was used.
However, the method was modified by the use of an Anderson
Impactor. This device allows measurement of both total
grain loading and particle size distribution down to 0.3
microns. The standard EPA method 5 was also used as a
check against the modified method. There was good agree-
ment between the two methods.
At the start of the project there was some question as to
how the size distribution varied with total grain loading.
Some theories were expounded that the absolute quantity of
fines would be a constant and that higher grain loadings
• would-be the .result of greater quantities of larger
, particles. The work done in characterizing both Rosebud
• and McKay coals demonstrated that the size distribution re-
mains approximately constant under varying total grain
loadings. When-the absolute quantity of submicron:material
520
-------
was plotted against the total grain loading in the raw flue
gas a linear relationship existed for both Rosebud and
McKay coals. However, the McKay coals had a greater
percentage of submicron material.
Absolute Amount Less Than One Micron
Tolal Inlet Grain Loading
Total Inlet Gram Loading. Gram/SCFD
Total Inlet Grain Loading. Grain/SCFD
5. PART1CULATE REMOVAL
Having characterized the size distribution of the two coals
tested, the effect-of venturi pressure drop was evaluated
withregard to percent particulate removal. For a given
test condition, simultaneous particulate measurements were
made of the inlet and outlet flue gasses. Again the An-
521
-------
derson Impactor was used to that the removal efficiency as
a function of particle size could be determined. Data for
the Rosebud and McKay coals were established for venturi
pressure drops ranging from 6" to 31" w.c.
The percent removal of various particle sizes for different
venturi pressure drop was plotted for both coals. The
curves all follow the s-ame trend for both different pres-
sure drops and different coals. A typical'set of curves is
shown below.
I
Panicle Diameter. Midoris
For particle sizes of L'. 3 microns -or larger, the percent
removed is essentially 100%, regardless of venturi pressure
drop. The percent removed drops off slightly as particle
size decrease.^ from 2.5 microns to 0.8 microns. It is in
the less than 0.8 micron size that the venturi pressure
drop has the greatest significance.
For a given venturi pressure drop, a comparison of the two
coals showed that a greater percentage removal of submicron
particles for MeKay coal was achieved as compared to the
Rosebud coal. This higher removal efficiency partically
offsets the higher quantity of submicron particles 1n the
McKay coal. ,
D,a t a was also plotted showing the. total .outlet gra.in loa-
ding, a.s a.function of venturi pressure drop. The curves
for both coals, are shown. The economics the venturi system
had been based,.upon achieving a 0.03 gr./SCFD .(0.06 Ibs/MM
BTU) u s i n..g a 12 "w.c. pressure drop. The curye,s_ show that
with Rosebud coal the 0.03 gr/SCFD could be achieved with a
6" w.c. drop pressure, whereas the McKay coal required a 8"
w.c. pressure drop. Both curves appear to indicate that re-
gardless of pressure drop, outlet grain loadings
522
-------
significantly less than 0.01 gr./SCFD (0.02 Ibs/MM BTU) is
not achievable.
.10
09
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10 12 14 16 1B 20 22
Pressure Drop, Inches W.C.
Venturi Pressure Drop, Inches W.C.
6. OPACITY
In addition to meeting particulate emission standards
flue gas stack opacity of 20%
performance criteria. It was
burned significantly effected
was also established as a
known that the type of coal
opacity results. Therefore,
Minnesota Power & Light wanted a means of predicting stack
523
-------
opacity as a function of both venturi performance and type
of coal being burned. To achieve this objective, tech-
niques were devised for measuring opacity in the pilot
plant tn'd then extrapolating the data to the full scale
system.
To obtain pilot'plant opacity data a Lear Siegler RM41 op-
acity instrument was used. The opacity instrument was
located down stream of the venturi and absorber system and
thus, reflected total system performance. Initially the
unit was installed with the light beam traversing the dia-
meter of the 12" gas duct. After limited experience with
this ins talla'tion it became apparent that the margin for
error with this small a path length was too great. Con-
sequently, a second installation was made in which the path
length was increased to 6'6". To achieve this path length
the unit was installed between two elbows in which the
larger path was parallel to the gas flow. The installation
is shown below.
Opacity Meter Installation
n Reflector
Path
Length •
Venturi performance was varied to allow various outlet
grain loadings to exist and thus permit measuring opacity
over a range of grain loadings. Data was collected for
both Rosebud and McKay coals. A semi-log plot of percent
opacity vs. grain loading resulted in a straight line.
When comparing opacity data forthe two different coals it
can be seen that the slope of the lines are different.
524
-------
Outlel Grain Loading, Grsin/SCFD
For a grain loading of 0.03 g r ./. SCF, the Rosebud coal would
produce the higher percent opacity. For grain loading of
0.01 gr/SCF or less the McKay coal would produce the..higher
opacityvalue
Opacity as a function of venturi pressure drop was also
correlated for each coal. As night he expected, the curves
which result are consistent with the particulate removal
curves. As the pressure drop increases, the opacity
achieved approaches a limiting value. Consistent with the
other opacity curves, at the expected venturi pressure drop
of 12" w.c. which was required to meet particualate emis-
sion standards Rosehu.
o a I h ;
525
he. lower percent opacity.
-------
e Drop, Inches W.C
Having m. - vired opacity in the pilot plar-", the question
still r e v, •. •• n e d as to how to scale up the * ,^ta for Unit #4
to the sicick tip diameter of 35 feet. A correlation be-
tween particulate grain loadings and opacity has been shown
to be as follows:
1. W=KPlnLl/J_°l. Formula from paper by D.S. Ensor and
_ _,_MN.J. Pilot - U. of Washington APCA
Journal,
Vol. 21, No. 8, August 1971.
W= Total Particulate Mass Concentration in Effluent
K= Specific Particulate Constant
p= Density of Particulate
1= Intensity of Transmitted Light
Io= Intensity of Incident Light
D= Illumination Path Length of Diameter of Plume
I/Io= Light. Transmittance
526
-------
^n the. assumption, that the particulate characteristics in
the. pilot plant are identical to those in the full scale
system the following relations were developed:
log (100-0S) = log (100 Ops
where: ^ - percent opacity measured in the pilot
plant.
0 s = predicted percent Opacity in the Unit #4
stack.
D = pilot plant optical path length.
D s = optical path length in the Unit #4 stack.
Using this relationship , a .04.1% opacity reading in the
pilot plant would be equal to a 20% opacity in the stack.
This opacity relationship when plotted is shown below:
This curve, highlights the significance of stack geometry in
determining the measured opacity. The conclusion that can
be reached is that as stack diameter is increased, the flue
gas particulate loading would have to be significantly d e -
creasedto achieve desired opacity value.
527
-------
At the required design particulate emissions level of 0.03
gr/SCF (0.06 Ibs/MM BTU), the opacity for Rosebud coal
would be 75% as opposed to 64% for McKay coal. The lowest
measured pilot plant opacity reading obtained was 6% for
either coal burned. To achieve this minimum opacity value,
particulate emissions of 0.01 gr/SCF (0.02 Ibs/MM BTU) or
lower were required. When scaled up to Unit # 4 , this 6%
pilot plant opacity value is equivalent to a 28% stack op-
acity. Thus is appears that for Minnesota Power ft Light's
situation, a 20% stack opacity is not achievable.
7. CONCLUSION
The Minnesota Power & Light experience has shown that:
a. A venturi for particulate removal can offer significant
economic savings.
b. The pilot plant data confirmed that the required
particulate emission standards can be met.
c. The pilot plant data indicated that for Clay Boswell
Station Unit #4 particulate emission standards and op-
acity requirements are not consistent. Even when
particulate emission standards are far exceeded, a 20%
stack opacity is not achievable.
528
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"PERFORMANCE OF ENVIROMENTALLY
APPROVED NLA SCRUBBER FOR S02"
By:
J.A. Bacchetti
Pfizer, Inc.
East St. Louis, Illinois 62201
ABSTRACT
This paper describes the commercial development and operation
of the NLA - Lewis scrubber for flue gas. The scrubber was installed
on three coal fired boilers at Pfizer1s chemical plant in East St.
Louis, Illinois. Total operating cost, including depreciation,
is budgeted at $0.90/MM BTU. Further improvements have reduced
this to $0.60. On stream time averaged 94% the first year of full
operation. Both S02 and particulates are within legal limits.
529
-------
INTRODUCTION
The subject of this paper is the technical success of a gas absorption
unit with impingement and condensation particulate collection.
But more importantly it is a success story of our present regulated
technostructure.
This is a young nation. We have a strong spirit of economic progress.
As a result, we have produced a record of major contributions to the health
and welfare of this country and the world. Classical economics has produced
much human progress and well-being.
Yet, as a nation, we have a limited sense of history and future; of
tradition and culture. We depend on classical economic motivations to pro-
vide our direction.
However, classical economics alone cannot provide motivations for controll-
ing the aggregate, long-term or probabalistic side effects of economic progress.
Therefore, we have asked our government to place constraints on the
side effects of this progress.
One major side effect is aggregate air pollution. My car, my stack, by
itself, has no effect on my well being or that of the community. But our
cars - our stacks, together, do1.
This paper is a case study of a chemical plant which installed a stack
gas scrubber for purely classical economic reasons - we wanted to stay in
business - legally. And, we wished to do so at the least expenditure of
resources - both present and future.
Therefore, what will be presented today is primarily development history
and final results, with a limited amount of technical data.
Most of the papers of this conference are research oriented. This paper
is user oriented.
The net result is this: A 140,000 Ib/hr. steam boiler system firing 3.5%
sulfur coal that meets SO2 and particulate standards while burning high sulfur
coal, for a total add'l cost, including depreciation of less than 90C/MM BTU.
530
-------
THE PROBLEM
Pfizer's plant in East St. Louis, 111., produces iron oxide pigments for
end use products such as colorants and magnetic tape. It is the largest plant
in the MPM division. This plant has three coal fired boilers, (see table 1),
with a total rated output of 140,000 Ib/hr. of steam. All three boilers were
designed to burn high sulfur coal (4%) from the local Illinois #6 seam.
TABLE 1
BOILERS
HEAT INPUT
MM BTU/HR
STEAM PRODUCED
M LBS/HR
TYPE
MANUFACTURER
150
50
20
100
30
10
SPREADER
TRAVELING GRATE
TRAVELING GRATE
ERIE CITY
B&W
O'BRIEN
The Illinois high sulfur coal (table 2) is purchased from any of four or
more mines (both strip and underground) within 75 miles of the plant. Both
price and availability are extremely favorable when compared to alternate
fuels.
TABLE 2
COAL TYPE
SULFUR
ASH
HEAT CONTENT
WASHED SIZE
3.5%
10.0%
11,000 BTU/LB.
1 1/4 X 0
However, when burning this fuel the boilers did not meet the allowable
emission standards for either S02 or particulates. (tables 3&4)
TABLE 3
SO2 EMISSIONS
NATURAL
ALLOWED
REMOVAL EFFECIENCY REQUIRED
1408
396
72%
TABLE 4
PARTICULATE EMISSIONS
NATURAL
ALLOWED
REMOVAL EFFECIENCY REQUIRED
145
49
66%
SOLUTIONS
We therefore had three alternates: Switch fuels, stack gas treatment or
do nothing.
531
-------
In a country based on law, we cannot pick and choose those we wish to obey
so that rules out alternate three, unless we cease operation.
The remaining alternates are strictly an economic choice. We chose the
stack gas treatment route as being inherently more economical and, long term,
more reliable than dependence on oil and gas. Yet, we wished to minimize the
commitment of technical resources.
We wish to concentrate our technical resources on iron oxide, not pollu-
tion control. We needed a device that had the following characteristics:
Reliability - Higher than the boilers
Reasonable Cost - Low enough to still be more economical than alternate
fuels.
Enviromentally sound - Not create new problems
Compatible with boiler operation - Should not require more complexity.
There are many types of FGD systems presently in some phase of development
or operation. Due to political and economic considerations, the relative re-
liabilities and costs are difficult to obtain on a comparable basis. However,
the following qualitative evaluation is accepted.
1.) Throw away systems (those that produce a sulfate or sulfite solid
waste) are presently the most satisfactory.
2.) Calcium based systems, such as lime, are inherently simple and use
inexpensive raw materials. However, the plugging characteristic
of lime requires more complex systems and reduces reliability.
3.) Sodium based systems, such as double aklali, seem to be impractical
for large facilities. For smaller facilities, they are in use, but
add the operational and maintainance complexity of a major chemical
plant; also, chemical costs can be quite high.
Of course, all the systems must have sludge separation and disposal systems,
Some of these can be quite massive due to the large quantity of water required
for the scrubber to prevent plugging.
THE SELECTION
We believe the scrubber we are about to describe is a reasonable answer
to many of these difficulties.
It inherently resists plugging
It is simple to operate
It uses very little water, so no water recycle is required
And, of course, it uses an inexpensive reagent - Lime
The simplicity is the most important feature for us at East St. Louis,
111. It can be operated by existing boiler house personnel with very little
additional training. It can be maintained with existing shop personnel with
no additional training. The flow chart is simple.
532
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So, what is this magic device?
Very simple - a kiln.
In 1974, through Mr. Wayne McCoy's membership on the Clean Air Committee
of the Nat'l. Lime Assn., Pfizer at East St. Louis became aware of the develop-
ment of Mr. Clifford Lewis. Mr. Lewis is a consultant to the National Lime
Association and, as such, had developed a stack gas scrubber that,
a.) Used lime/limestone manufacturing technology and
b.) Used lime as the scrubbing reagent. Pfizer, through its membership
in the Nat'l. Lime Association, had access to Mr. Lewis's work and
rights to the ultimate patent as well.
The basic concept of Mr. Lewis's device is similar to most scrubbing
systems. The flue gas is contacted with an aqueous aklaline material to remove
SC>2 by absorption and subsequent precipitation,- particulates are captured by
impingment and condensation agglomeration. In the NLA - Lewis scrubber, (see
figure 1) flue gases pass through a rotating kiln - a cylindrical shell
sloped about 1/8"/ft. to provide gravity flow of the lime slurry scrubbing
liquid. The apparatus contains rings of lifter boxes and great quantities of
loosely hung chain. A circular dam confines a lime slurry pool through which
the lifter boxes pass as the shell rotates. In this way, lime slurry is lifted
and poured over the chains, providing wetted chain surface for contact with the
flue gas. Internal pumping rate in our particular unit is about 5000 GPM. The
loosely hung chain also scours the internal scrubber surfaces to prevent plugging.
FIGURE 1
SCRUBBER CONCEPT
U.S. Patent NOV. 29,1977
4,060,587
We will now review the developmental history of this device at the East
St. Louis plant.
PFIZER'S SCRUBBER
In 1975 Pfizer installed at 87-foot kiln, 11-foot diameter and fitted it
with a modified NLA - Lewis chain system. (figure 2&3) In addition, Pfizer
Incorporated our own design concept of a drying zone contiguous to and down
stream of the wet scrubber section to dewater the waste sludge by contacting
it with the incoming hot flue gases. This offers a dry waste product suitable
for landfill with reduced disposal costs. It was installed as shown to handle
flue gas from the large boiler only. r,"
-------
To Stack
PFIZER SCRUBBER-1975 ORIGINAL
Boiler
^7 Spent Lime, Particulates
FIGURE 3
o
ORIGINAL SCRUBBER CONFIGURATION
30-
SCRUBBING
40'
The gas exit section of the rotating kiln contained eight lifter box cages
and 15 tons of chain. The center drying section had about five tons of chain in
a "garland" arrangement. Except for a few test chains, all scrubber and scrubbed
gas handling equipment was of mild steel.
From the start, tests on this first configuration indicated excellent SO?
removal, but inadequate particulate capture. Particulate emissions were still
twice the allowable limit.
We felt that, with our type of boilers and coal, we should be able to
meet particulate as well as SO2 requirements with this scrubber. Therefore,
we shifted the scrubbing section to the center of the kiln, using heavier
chains, (figure 4) We also eliminated the drier chains, added a de-mister
section and a dropout, or disengaging section.
534
-------
FIGURE 4
SECOND SCRUBBER CONFIGURATION
- 1977
1977
^
f
\Z"
BARE
28"
SC
f~\j -
RU
35
BBING
f , -
[
DROP-
OUT
»• -tr^.
DEMISTER3' ID
Wiih -his design, S02 collection further improved. The particulate
t->;:t i in i was doubled - to about only 20% more than allowable, (see table 5)
TABLE 5
1977 SCRUBBER PERFORMANCE
S02
PART.
NATURAL
960
115
ALLOWED
270
21
ACHIEVED
30
26
We now felt quite sure that, with only minor modifications, the scrubber
would handle the load of all 3 boilers. This would be a substantial break-
through since it eliminated the need for additional scrubbing devices for the
other boilers. This offered significant savings in investment and operating costs.
Therefore, in early 1978, we tied in both small boilers to the scrubber,
added a mist eliminator at the stack, enlarged the ID fan and added 30 tons
more chain upstream of the scrubber section - back to the concept of drying.
So we now have this configuration, (see figure 5 & 6)
FIGURE 5
FINAL CONFIGURATION
To Stack
Boilers
]Irx' Lime Slurry
•^7 Spent Lime, Participates
o
Demister
535
-------
FIGURE 6
FINAL CONFIGURATION
DEMISTER
In August of last year, we achieved the SO and particulate limits on all
3 boilers and, shortly thereafter, obtained the final signed permit from the
State of Illinois Environmental Protection Agency. (see table 6)
FINAL EMI
TABLE 6
S S I 0 N
TESTS
UNABATED
ALLOWABLE
ACTUAL
so2
PARTICULATE
1408
145
396
49
42
37
Here are some operating characteristics of the scrubber.
The lime utilization is excellent (table 7). The water flow is low and
we have operated with dry discharge. Our data and experience with dry discharge
is limited, since our primary concern has been to meet emission limits and
generate steam for pigment manufacturing. Also, recently an improved plant
wide solid waste disposal system provides minimal economic incentive for adding
the complexity of dry discharge.
TABLE 7
SCRUBBER FLOWS
LIME
WATER IN
SLURRY OUT
pH
1000 Ibs/hr.
(90 + % Utilization)
50 GPM
30 GPM
6.0
536
-------
The energy use is quite low (table 8). Our total energy penalty is less
than 3%. Many FGD's require from 3 to as much as 8% of the output.
TABLE 8
ENERGY USE
KILN 100 H.P.
I.D. FAN 400 H.P.
PUMPS 43 H.P.
TOTAL P 15" H2O
Our actual costs are shown in table 9. Though we did invest $1,800,000
we modified the scrubber several times. We would anticipate that this system
could be duplicated for less than $1,000,000. (in 1976 dollars)
TABLE 9
ANNUAL COSTS - BUDGETED FOR 1979
LIME PURCHASE $170,000
WASTE DISPOSAL 120,000
POWER 50,000
DEPRECIATION 150,000 ($1,800,000 Investment)
MAINTENACE 200,000
$690,000
A comparison of costs with other fuels shows that we can still use coal
at lower cost than any other competitive fuel.
Since last fall we have had some other noteable successes. Monthly on
stream time has never been below 90% and has averaged over 94%.
Recently we have experimented with lower cost raw materials and have been
successful. We have found that lime kiln dust can be used as effectively as
quicklime. Lime kiln dust is a by-product from Pfizer lime plants and all
other lime plants. This has further reduced operating costs.
Also, actual maintenance for 1979 is well below what we had anticipated.
These economic improvements have reduced our total operating cost to about
60C/MM BTU - including depreciation'.
Let me review what we have here - a stack gas scrubber that works. It
is simple to operate, has demonstrated on-stream times in excess of 90% its
first year, costs less than $0.60/MM BTU, and perhaps its most unique feature
is, it was developed, designed and commissioned without public funds. This
device was created entirely within the private sector'. Classical economics
wins again.
537
-------
DESIGN GUIDELINES FOR AN OPTIMUM SCRUBBER SYSTEM
by
Madhav B. Ranade and Edward R. Kashdan
Research Triangle Institute
Research Triangle Park, N.C. 27709
and
Dale L. Harmon
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
ABSTRACT
The revised New Source Performance Standards (NSPS) for the utility
industry mandates reduced particulate matter and sulfur dioxide emissions from
new utility boilers. A wet scrubber system can be an advantage in controlling
both of these emissions. Existing wet scrubber systems may meet the new
standards with significant increase in power consumption. A careful design of
the entire scrubber system, based on the-experience gained at the existing
installations, is necessary to ensure cost effectiveness.
The experience with existing wet scrubber systems used on coal-fired
utility boilers is reviewed and their performance is correlated with power
consumptions. Based on a correlation of scrubber pressure drop against outlet
concentration, conventional scrubber-systems would be able to meet the revised
NSPS with a theoretical scrubber pressure drop of 17±2 in. W.G. Overall system
pressure drop, however, could easily run as high as 30 in. W.G. ; Novel scrubber
systems such as the electrostatically augmented scrubber may provide the
necessary collection performance at lower pressure drops.
The performance of the various scrubber components such as mist eliminators
and reheaters is reviewed. Operating problems are also discussed.
538
-------
CONVERSION TABLE
To Convert From
To
Multiply By
Btu/lb
scfm (60°F)
cfm
°F
ft
gal/mcf
gpm
gr/scf
hp
in.
in. W.G-
Ib
psia
1 ton (short)
nm3/hr (0°C)
m /hr
m /hr
°C
m
1/m3
1/min
gm/m
kW
cm
mm Hg
gm
kilopascal
metric ton
2.324
1.61
1.70
<°F-3:
0.305
0.134
3.79
2.29
0.746
2.54
1.87
454
6.895
0.907
539
-------
DESIGN GUIDELINES FOR AN OPTIMUM SCRUBBER SYSTEM
INTRODUCTION
The U.S. Environmental Protection Agency has lowered its New Source
Performance Standard for particulate emissions from coal-fired boilers to
0.03 Ibs of particulate/million Btu.l In the case of power plants which
require a scrubber system to meet S02 emission standards, it is economically
advantageous to also collect the particulate matter with the scrubber system.
But existing utility scrubber systems either would require relatively large
power consumptions to meet the standard, or would be incapable of meeting it at
all. Hence it is desirable to design an optimum wet scrubber system which would
have a high and acceptable collection efficiency at low energy requirements.
The performance data and operating experiences of existing scrubber systems
were summarized in an EPA report by Kashdan and Ranade (1979) . This information
is essential for the design of an optimum wet scrubber system for coal-fired
utility boilers.
The particulate emissions from power plants exhibit tremendous variability
in flyash particle size distribution, composition, and the flue gas composition.
For given emission properties the scrubber components need to be chosen so that
acceptable performance is obtained at the lowest cost. The past operating
experience from the scrubber systems used with power plants will provide guid-
ance in selecting various components of the scrubber system. However, the
technology of the scrubber system components has not advanced far enough to
prevent problems arising after construction. Flexibility of the design to
allow easy replacements of various components is desirable to accomodate devel-
opments in the scrubber technology. Highlights of the review of operating
experiences are presented in the next few pages.
PROCESS DESCRIPTION
For a complete understanding of the problem, the source of pollutant
emissions must be considered as well as the collection device. A brief descrip-
tion of a coal-fired electric generating plant and its effluents follows with
emphasis on aspects relevant to a scrubber system.
Modern coal-fired, electric generating plants consist of boilers, genera-
tors, condensers, coal handling equipment, dust collection and disposal equip-
ment, water handling and treatment facilities, heat recovery systems (such as
economizers and air heaters), and possibly flue gas desulfurization systems.
Boiler types in use include cyclone, pulverized, and stoker units, but
nearly 90 percent are pulverized coal boilers (Sitig, 1977). Pulverized coal
boilers are commonly classified as either wet bottom or dry bottom depending
on whether the slag in the furnace is molten.
See Conversion Table, pg.2.
540
-------
Two condensing cooling systems are used by the electric utility industry:
the once-through system and the recirculatory system. In the once-through
system, all the cooling water is discharged to a heat sink, such as a river or
lake. In recirculating systems, cooling devices, such as cooling towers or
spray ponds, permit the use of recirculated water.
Wet scrubbing systems in coal-fired electric generating plants may be
used to collect particulate matter and/or to scrub 862 from the flue gas. In
any case, a wet scrubbing system increases both the solid and wastewater
disposal problems of the plant.
Combustion of coal in the furnace produces both flyash (airborne) and
bottom ash (settled). Both bottom ash and collected flyash along with sludge
from a throwaway flue gas desulfurization system (where used) are the major
sources of solid waste from coal-fired utilities. These solid wastes, which
are in a slurry form, are usually sluiced to a solid-liquid separator; the
solids settle out and clarified water is returned to the system or discharged.
Ultimate disposal of the wastes may be either in an onsite settling pond or,
after further dewatering and treatment, in a landfill.
CHARACTERIZATION OF EMISSIONS FROM COAL-FIRED UTILITY BOILERS
The successful design of a wet scrubber system on a particular coal-fired
boiler requires careful consideration of the flue gas characteristics of that
boiler.
Physical and Chemical Properties of Flue Gas
In designing a wet scrubber system, the volume of gas handled, inlet and
outlet temperatures, humidity, and S02 concentration are all important consid-
erations. Typical power plant flue gas volumes range from 3000 to 4000 acfm/MW
depending on coal composition, boiler heat rate, gas temperature, 'and amount of
excess air. Because of economies of scale, the utility industry has tended
toward larger and larger power stations implying that scrubber systems must be
capable of handling volumes of gas as large as 4,000,000 acfm.
The temperature of the gas entering the scrubber is determined by the
efficiency of the air heater. Most steam power plants operate in the range of
250-300°F downstream of the air heater. Exit temperatures from the scrubber
vary with sulfur content and range from 150°F for coals with less than 1 percent
sulfur to 180°F for coals containing above 3 percent sulfur (Mcllvaine, 1974).
Because exit temperatures are low, most scrubbing systems incorporate reheat
systems which provide greater plume buoyancy and prevent corrosive condensation.
Flue gas contains from 5 to 15 percent moisture depending on the amount of
volatile matter and on the moisture content of the coal. The concentration of
sulfur dioxide in the flue gas depends on the sulfur content of the coal: for
an average sulfur content of 2.5 percent, there will be approximately 1500 ,.ppm
of SOg in the flue gas (Mcllvaine, 1974). On the average, 1-3 percent of the
S02 will be converted to SOs- Sulfur oxides in the flue gas make for a corrosive
environment; special alloys, coatings, and linings must be used on scrubber
internals.
541
-------
Of particular concern to the designer of a wet scrubber system is the
chlorine content of the coal. The chlorine content of coal (in the form of
sodium and potassium chlorides) may vary from a trace amount to as high as
0.5 percent. During combustion, some of the chlorine is converted to
hydrogen chloride or other volatile chlorides. Most of the hydrogen chloride
will be absorbed in scrubbing liquor, thereby increasing the potential for
chloride stress-corrosion.
Characterization of Flyash
The characteristics of flyash (concentration, size distribution, and
chemical composition) affect both the performance and maintenance of the
scrubber.
Particulate Emission Quantity—The concentration of flyash in utility flue
gas depends primarily on the following variables: (1) amount of ash in the coal,
(2) method of burning the coal, and (3) rate at which coal is burned (Sitig,
1977). Pulverized coal units produce greater quantities of dust than stoker
or cyclone units. Furthermore, for a given furnace type, the flyash emission
quantity will be approximately proportional to the ash content of the coal.
Inlet dust loadings in utility flue gas may vary from 2 to 12 gr/dscf, but 4 or
5 gr/dscf is fairly typical.
In general, the size distribution of the flyash and not the emission quanti-
ty determines the collection efficiency of a particular scrubber. However, the
dust concentration does affect the abrasiveness of the flue gas, and hence, the
potential for eroding a scrubber system. In cases where the inlet dust loading
is very heavy, some scrubbing systems use mechanical collectors before the
scrubber.
Flyash Size Distribution—The particle collection efficiency of a scrubber
is lowest for the fine particles (<3.0 microns, aerodynamic). Hence, the
collection efficiency of a particular scrubber will depend on the amount of fine
particles in the inlet dust.
Figure 1 shows flyash size distributions from four utility boilers. The
fine fraction varies widely, ranging from roughly 4 percent to 45 percent of
the inlet dust loading, and representing about 0.05 gr/dscf to 0.5 gr/dscf.
This variation is accounted for in part by the coal and furnace type. Lignite,
for example, appears to produce a very fine distribution. Because of the lim-
ited amount of data, however, generalizations are difficult to make. Further,
the effect of process variables on the size distribution is not known. Suffice
it to say that if the design of the optimum wet scrubber system is to be based
on impactor measurements of the inlet flyash size distribution, then careful
measurements in sufficient number must be made to accurately determine the fine
particle fraction.
(Figure 1 shows that the flyash size distribution from the stoker unit had
a large fraction of fine particles, contrary to what one would expect from this
method of firing. The distribution was indeed biased toward the smaller sizes
by the scrubbing system sampling duct which acted like a mechanical collector
(Hesketh, 1975). Nevertheless, the sampled flue gas did contain approximately
0.1 gr/dscf below 3.0 microns.)
542
-------
40
20
10
8
93
O
i 2
Q
1.0
0.8
0.6
0.4
0.2
0.1
D
LEGEND
PC: Bituminous (1.3 gr/dscf)
Lee et al. (1975)
PC: Subbituminous (2.0 gr/dscf)
Accort et at. (1974)
Stoker (0.4 gr/dscf)
Hesketh (1975)
Lignite (1.0 gr/dscf)
Fox (1978)
0.05 0.5 1 2 5 10 20 40 60 80 90 95 99
Cumulative % by Weight Less Than Dp
Figure 1. Flyash size distributions from four utility boilers.
543
-------
Chemical Composition of Flyash—Flyash is composed primarily of silicates,
oxides, sulfates, and unburned carbon. For purposes of designing a particulate
scrubber system, the calcium oxide content of the flyash is an important consid-
eration: the calcium oxide will scrub a certain amount of S02 thereby forming
calcium sulfate and increasing scaling potential. In cases where the flyash
was extremely alkaline, the design of a combined particulate-SOp scrubbing
system encorporated the collected flyash as the scrubbing reagent (Grimm
et al., 1978).
SUMMARY OF EXISTING SCRUBBER SYSTEMS IN THE U.S.
Table 1 is a summary of the design and operating parameters of the various
particulate and particulate-S02 scrubber systems in use at coal-fired power
plants across the U.S. Gas-atomized scrubbers, and particularly, Venturis, are
the most widely used scrubber design for particulate removal.
The newer installations generally have better particulate removal capabili-
ties, greater availabilities (defined as the fraction of a year that the scrubber
appeared to be in operable condition), and treat larger volumes of flue gas.
Landfill and ponding are the predominant methods of waste disposal. Few of the
existing scrubber systems are now meeting the New Source Performance Standard
for particulates, 0.03 Ib of particulate/million Btu, or about 0.017 gr/dscf.
As shown in Table 1, the particulate scrubber at the Four Corners Station
(Arizona Public Service) operates with an overall system pressure drop of 28 in.
W.G. and is capable of just meeting the standard.
ESTIMATING POWER REQUIREMENTS
Estimating the power requirements of a particulate wet scrubber is a two-
step process: first a determination of the size distribution of the dust is
made; and second, an estimate is made of the power requirements for the scrubber
which are necessary to meet emission standards. Two approaches, the contact-
power rule and the cut-power rule, have been developed and are discussed below.
Contacting-Power Rule
The contacting-power rule, developed by Semrau (1977), represents a
completely empirical approach to the design of particulate scrubbers. The
fundamental assumption is that, for a given dust, scrubber performance depends
only on the power consumed in gas-liquid contacting, regardless of scrubber size
or geometry.
Power consumed in gas-liquid contacting depends on the manner in which the
energy is introduced. For gas-atomized scrubbers, where the energy comes from
the gas stream, theoretical power consumption is given by
Pr = 0.158 AP, hp/1000 acfm (1)
Lr
where AP = pressure loss across unit in inches W.G.
For preformed spray scrubbers, where the energy comes from the liquid stream,
theoretical power consumption is given by
544
-------
TABLE 1. CONDENSED SUMMARY OF PARTICULATE AMD PARTICULATE-S02 SCRUBBERS IN THE U.S.
PARTICULATE-S02 SCRUBBERS
Utility
Stat.on
Design and Operating Parameters
Start-up date
Reagent
Vendor
Design
Number of equipped boilers
Number of scrubber modules
Installed scrubber capacity, MW
Collector preceding scrubber
Reheat7
Bypass'
Annual cost, mills/kWh
Coal heating value, Btu Ib
Sulfur m coal, pet
Ash in coal, pel.
Calcium oxide in ash, pet
L/C, gal/1000 acf
P partieolate scrubbet, in W.G
P system, m W.G
Inlet dust loading, gr/rlscf
Inlet SC12. PPm
Outlet dust loading, yr/dscf
S02 removal, pet.
Waste disposal
Availability
Reference
Pennsylvania
Power Co.
Bruce Mansfield
No 1, 2
4 76
line
Chemico
Vpnturi
2
12
1650
Yes
No
4.25
11,900
4 7
125
NA
20
20
NA
5-65
2,200-2,600
0.007 0 017
92%ldesign)
Landfill
974
38, 10, 21
Kentucky
Utilities
Green River
Station
9 75
ime
AAF
Ventur
Moving Bed
3
1
180
Mech
Yes
Yes
2.0
10.800
3 /
13.4
NA
39 5
7
NA
2.2
2,200
99%ldesign)
90
Pond
854
21,22
Montana
Power Co.
Colslrip
No 1. 2
9 75
flyash 'lime
CEA
Ventur
Wasti Tray
2
6
720
Yes
No
0.26
8.840
08
9
22
15 lor venturi
18 for spray
17
25.5
27
800
0.018
80
Pond
90*
21, 16, 27
Tennessee
Valley Authority
Shawnee
IDA
[Test lacility)
4 72
lime'limestone
UOP
Moving Bed
1
1
10
Yes
No
lO.SOOIave i
coal type variable
37
8 16
3.5 8.5
2.500 4,000
0.035-0.090
60 99
Pond
31, 2, 39
Tennessee
Valley Authority
Shawnee
10B
(Test facility)
472
lime-limestone
Chemico
Ventori-1
Spray Tower
1
1
10
Yes
No
10,500lave.)
coal type variable
21 for venturi
9 4 far tower
3 16
3.5-8,5
2,500-4,000
0.003 0050
60 99
Pond
31, 2, 39
Arizona Public
Service Co.
Cholla Station
12/73
limestone
R-C
Venturi
Spray Tower
1
2
115
Yes
Yes
2 2
10,400
0,5
13.5
35
10 for ventur
49 far towP'
15
235
20
420
0.016
59
Pond
95
21, 23, 20
Northern
States Power
Sherburne
No 1, 2
3 76
limestone
CE
Venturi
Moving Bed
2
24
1400
Yes
No
04
8,300
08
9
NA
17 lor venturi
10 for bed
11
22
2040
400-800
0.035 0044
50 55
Pond
90
10, 21, 19
Kansas City
Power & Light
La Cygne
No 1
2'7j
hmestone
B&W
Venturi,
Sieve Tray
1
8
870
Yes
No
1 4
9.000 9.700
5 6
20 30
69
12 loi vfnturi
26 5 for tower
7
22
56
4,500
0074
80
Pour!
NA
10, 21, 24
Kansas
Power & Light
Lawrence
No 4
1 77
limestone
CE
Rod Scrubber
Spray Tower
1
2
125
Yes
Yes
NA
10,000
05
9.8
132
20 fur sc'iibbe'
30 for tower
9
24
43
425
004
90
Pond
NA
10,21, IS
Nevada
Power Co.
Reid Gardner
No 1.2.3
3 74
soda asfi
CEA
Venturi
Wash Tray
2
2
330
Mech
Yes
Yes
MA
11.800
00
9 4
18
12 5
15
20
0306
300
0.02
85
Pond
90
20
-------
TABLE 1 (cont.) CONDENSED SUMMARY OF PARTICULATE ARID PARTICULATE-S02 SCRUBBERS IN THE U.S.
PARTICULATE SCRUBBERS
en
-l^
01
Utility
Station
design and Operating Parameters:
Start-up date
Vendor
Design
Number of equipped boilers
Number of scrubber modules
Installed scrubber capacity, MW
Collector preceding scrubber
Reheat'
Bypass?
Annual cost, mills/kWti
Coal heating value, Btu/lh
Sulfur in coal, pet.
Ash in coal, pet.
Calcium oxide in ash, pet. ,
L/G, gal/1,000 acf
^ P paniculate scrubber, in. W.G.
i P system, in. W.G.
Inlet dust loading, gr/dscf
Inlet S02, ppn>
Outlet dust loading, gr/dscf
S02 removal, pet.
Waste disposal
Availability
Reference
Arizona
Public Service
Four Corners
12/71
Chemico
Venturi
3
6
575
Yes
No
NA
9,200
0.75
22
S.3
8.5
18
28
12
650
0.01-0.02
30-40
Mine
100
38, 20
Picific Power
& Light
Dave Johnston
4/72
Chemico
Ventur
1
3
330
No
No
NA
7,430
0.5
12
20
13.3
10
15
4
500
0.04
40
Landfill
NA
20
Valmont
11/71
UOP
TCA
1
2
118
Mech
Yes
Yes
NA
10,800
0.8
9.0
10
50
10-15
NA
0.8
500
0.02(min.)a
40
Landfill
75
20, 29
Public Service
Company of Colorado
Cherokee
11/72-7/74
UOP
TCA
3
9
660
Mech/ESP
Yes
Yes
NA
10,100
0.6
12
4
50
10 15
NA
0.4 - 0.8
500
0.02(min.)a
20
Landfill
70-90
20, 29
Arapahoe
9/73
UOP
TCA
1
1
112
Mech/ESP
Yes
Yes
NA
10,100
0.6
12
4
50
10 15
NA
0.8
500
0.02(min.)a
20
Landfill
40-70
20, 29
Minnesota
Power & Light
Clay Boswell
5/73
Krebs
Preformed Spray
1
1
350
No
No
NA
8,400
0.9
9
11
8
2.5
4
1.25
1,125
0.03
40
Pond
100
20, 36
Syl Laskin
6/71
Krebs
Preformed Spray
2
2
116
No
No
NA
8,400
0.9
9
11
8
2.5
4
2
1,125
0.04-0.046
40
Pond
100
20, 36
Montana-Dakota
Utilities
Lewis and Clark
12/75-
R-C
Venturi
1
1
55
Mech
No
No
NA
6,450
0.5
8.5
NA
11
13
14.5
1
520
0.03
50
Pond
NA
20, 33, 32
aBest performance of scrubber at highest pressure drop (29).
-------
PL = 0,583 APL QL/QG, hp/1000 acfm (2)
where AP = pressure loss in liquid, lb/in2
Q = liquid flow rate, gal/min
Li
Q = gas flow rate, ft3/min
When scrubber overall particle collection efficiency for a constant inlet dust
is measured over a range of power consumptions, it is often found that the
"scrubber performance curve" plots as a straight line on log-log paper, implying
a power relationship given by
where N is the dimensionless number of transfer unit related to efficiency (n)
by N = In (l/(l-n)), and P is given by
P = P + P
T G L
The empirical constants, a and y> depend only on the characteristics of the
particulate, but are little affected by scrubber size or geometry.
The contacting-power rule implies that scrubbers operated at higher power
consumptions will be more 'efficient particulate collectors—provided the increased
energy results in better gas-liquid contact. Figure 2, derived from the above
Table 1, is a log-log plot of operating points, outlet dust loading at a given
power consumption for various power plant scrubber systems. (Theoretical
power consumption was determined by Equations 1 and 2. Plotting outlet dust
loading against power consumption is essentially equivalent to the procedure used
in the contacting-power rule, assuming that flyash size distributions are the
same for various utility boilers.) As shown, the operating points can be
readily fitted to a straight line, implying a power-function relationship be-
tween scrubber overall collection efficiency and power consumption. The
least-squares correlation was Y = 0.068X i"^1 and r2 = 0.86. The good fit is
quite remarkable given the variety of coals, furnaces, process variables, and
inlet particle size distributions among the plants. Based on this correlation,
to achieve the New Source Performance Standard for particulates of about 0.017
gr/dscf, approximately 2.7±0.3 hp/1000 acfm (95 percent confidence limits)
theoretical power consumption, or eqUivalently, 17±2 in. W.G. pressure drop is
required. Although this value is only approximate, it does underscore the fact
that conventional scrubbers require a large power consumption to meet the New
547
-------
0.08
0.07
0.06
0.05
U
C/9
1 0.04
ts
0.03
co
=3
a
0 0.02
KCPL
Cr
MPL C\ O
(SL)KPL\PL NSP
O
MPL
(CB)
ON
MDU"
KCPL - KANSAS CITY POWER AND LIGHT
MPL - MINNESOTA POWER AND LIGHT
SL - SYL LASKIN
CB - CLAY BOSWELL
KPL - KANSAS POWER AND LIGHT
PPL - PACIFIC POWER AND LIGHT
NSP - NORTHERN STATES POWER
MDU - MONTANA-DAKOTA UTILITIES
NPC - NEVADA POWER COMPANY
PSCC - PUBLIC SERVICE COMPANY OF COLORADO
APS - ARIZONA PUBLIC SERVICE
FC - FOUR CORNERS
CH - CHOLLA
PPC - PENNSYLVANIA POWER COMPANY
MPC-MONTANA POWER COMPANY
Y = 0.068X"1'41
(r2 = 0.86)
PSCC. NPC
MPC
O
APS
(CH) Aps
(FC)
PPC
j I
I 2 3 456789 10
THEORETICAL POWER CONSUMPTION, hp/1,000 acfm
Figure 2. Correlation of scrubber outlet dust loading with
theoretical power consumption.
548
-------
Source Performance Standard. Further, this figure represents only the
theoretical power consumption across the particulate scrubber. The actual
system pressure drop will include fan losses, losses across the absorber, mist
eliminator, and ductwork.
Cut-Power Rule
Whereas the contacting power rule provides an empirical approach to the
design of particulate scrubbers, it lacks generality because it is specific to
a particular dust. A more general and theoretical approach was taken by
Calvert (1972, 1977) who related scrubber fractional efficiency to power
consumption.
The cut-power rule uses the quantity called the "cut diameter," the diameter
at which the collection efficiency of the scrubber is 50 percent. Most scrubbers
that collect particles by inertial impaction perform in accordance with the
following equation:
P = exp(-A d B) (3)
where P = particle penetration
A,B = constants
d = aerodynamic particle diameter
Assuming a log-normal distribution, Equation 3 can be integrated, yielding a
plot of overall penetration against the ratio of required cut diameter to mass
median diameter. Hence, by knowing the inlet particle size distribution and
the efficiency needed to meet emission standards, one can determine the required
cut diameter. For example, for a "typical" flyash particle size distribution of
d = 17 ym, a = 4, to achieve 99% collection efficiency would require a cut
diameter of approximately 0.6 ym. To determine which scrubber types can meet
this cut diameter, Calvert developed theoretical impaction models of scrubber
performance (cut diameter) versus power consumption for various scrubber types.
To achieve a cut diameter of 0.6 ym, a venturi scrubber would require a
theoretical pressure drop of 15 in. W.G., which agrees with the figure of
17±2 in. W.G. determined from the empirical correlation above.
Figure 3 is a plot of theoretical venturi scrubber performance curves and
actual performance points for scrubbers operating on coal-fired boilers (based
on published data). The performance of the actual scrubbers suggests that, as
expected, lower cut diameters (higher collection efficiencies) are achieved at
the expense of greater power consumption. Further, the performance of the
venturi scrubbers agrees well with the theoretically predicted performance for
wettable particles. The venturi scrubber performance model is evaluated for
different values of the dimensionless factor f. The value f = 0.50 corresponds
to wettable particles, whereas f = 0.25 corresponds to nonwettable particles
(Calvert, 1977).
The case of the moving-bed scrubber at Cherokee Station deserves special
mention. As shown in Figure 3, independent measurements at similar pressure
drops resulted in radically different values for the cut diameter. In this
549
-------
5.0
4.0
3.0
2.0
E
ST.
UJ
§ '( 0
5 fl.8
o
o 0.6
0.4
o
ec
0.2
I
JL
t.O 2.0 3.0
POWER, hp/1,000 acfm
4.0 5.0 6.07.0
JL
10 15 20 25 30 40
PRESSURE DROP, in. W.G.
__J L_ L I i
10 20 40
PRESSURE DROP, cm. W.G.
60 80 100
VENTURI SCRUBBERS
(f = 0.25, f = 0.50)
TCA [CHEROKEE, 1975,1974]
CHEMICO VENTURi
CEAVENTURI[COLSTRIP]
VENTURI
TCA
TCA [MOHAVE]
[TVA]
200
Figure 3. Theoretical and experimental cut diameters.
-------
regard, Ensor et al., (1975) reported highly variable outlet particle concen-
trations which did not correlate with pressure drop suggesting the presence of
reentrained solids from the mist eliminator. The authors concluded that the
"evidence...weighs against one considering the agreement between predicted and
experimental cut diameters to be anything more than coincidence."
In general, the limitations of the techniques for measuring flyash size
distributions undermine the usefulness of the cut-power approach.
NOVEL SCRUBBERS
Conventional scrubbers collect particles primarily by inertial impaction.
However, the collection efficiency of conventional scrubbers decreases signifi-
cantly for fine particles, resulting in the need for relatively large power
consumptions to remove the fine particles. As has been shown, flyash contains
a substantial fraction of fine particles, with the result that scrubber systems
operating on utility boilers may require overall system pressure drops as high
as 30 in. W.G. This pressure drop represents a large power loss to a utility.
In 1973, EPA initiated a novel device evaluation program. The purpose of
the program was to identify, evaluate, and where necessary, develop devices
which would have better collection efficiencies for fine particles. The results
of this program indicate that the most efficient novel scrubbers are those that
utilize additional collection mechanisms other than just inertial impaction.
The most promising of these novel devices are electrostatically augmented
scrubbers and condensation scrubbers. The former increases particle collection
by increasing the electrostatic attraction between particles and droplets. The
latter increases particle collection by growing particles into a size range
which is easier to collect and, also, by increasing diffusiophoretic forces.
Other novel scrubbers, which either consume large amounts of power or require
the use of waste heat, are deemed inappropriate for use on utility boilers and
are not discussed below.
Condensation Scrubbers—The use of condensing water to improve scrubber
particle collection efficiency is not a new idea, but until EPA sponsored
research on the subject, only small-scale laboratory studies had been done.
Calvert (1973, 1974, 1975, 1977) developed models for particle collection in
condensation scrubbers and attempted to verify those models in bench- and
pilot-scale studies. His studies indicate that collection of fine particles in
a condensation scrubber depends strongly on the inlet dust concentration and the
flue gas enthalpy. In assessing the possible uses of condensation scrubbing,
Calvert (1975) gives an approximate minimum enthalpy of 100 kcal/kg (about 180
Btu/lb) which would be necessary for high efficiency particle removal in a con-
densation scrubber. Flue gas from utility boilers typically contain 5 to 15 per-
cent moisture. Even at 15 percent moisture, the enthalpy would only be about
180 Btu/lb, indicating that condensation scrubbers would have only marginal
application to power plants. Furthermore, the collection efficiency of
condensation scrubbers decreases with increasing dust concentration because
there is less water available to condense on'each particle. Theoretical
calculations by Calvert (1974) have shown, for example, that for a three-plate
551
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condensation scrubber operating at a condensation ratio of 0.1 g vapor condensed/
g dry air, particle collection efficiency for 0.75 ym (aerodynamic) particles
decreased from 100 percent at a concentration of 2xl05 particles/cm3 (about
0.01 gr/scf, assuming a density of 2.0 gm/cm3) to about 60 percent at a
concentration of 107 particles/cm3 (about 0.6 gr/scf). Insofar as utility flue
gas may contain dust loadings as high as 8 gr/scf, condensation scrubbing does
not seem very feasible.
In short, whereas it may be possible to incorporate some condensation
effects in scrubbers operating on utility flue gas, a condensation scrubber
per se would not be recommended.
Electrostatically Augmented Scrubbers—A number of novel devices have
been developed recently which use electrostatic forces to enhance particle
collection. The scrubber types using electrostatic augmentation vary consider-
ably in design, but can be classified according to whether the particles and/or
the water is charged, and whether an external electric field is applied.
Two of the most tested electrostatically augmented scrubbers are the TRW
Charged Droplet Scrubber and the UW Electrostatic Scrubber. The TRW scrubber
uses charged droplets and an externally applied electric field to collect parti-
cles. It has been used successfully on emissions from a coke oven battery.
The UW scrubber charges both the water droplets and the particles (charged to
opposite polarity); a pilot-scale unit has been successfully used on emissions
from a power plant. Both of these devices have shown high efficiencies (over
90 percent) for submicron particles at substantially less power consumption
than would be required for a conventional venturi.
Whereas the performance of these small-scale units has been encouraging,
several points must be taken into consideration before a full-scale unit is
planned for use on a power plant. First, utility flue gas contains a heavy
dust loading, as large as 8 gr/dscf, and even greater. (The UW scrubber,
although showing good collection efficiency of flyash from a power plant, because
of the sampling arrangement, had extremely low inlet dust loadings of 0.5 gr/dscf
or less (Pilat and Raemhild, 1978). Heavy dust loading, for example, would
probably necessitate greater charging in a UW-type scrubber. Secondly, most
utilities handle large volumes of gas compared to the volumes handled by these
small units. The same cost savings may not be realized in a scaled-up version
of these smaller units; the economics would have to be worked out on an
individual basis.
MIST ELIMINATORS
Mist elimination is a requisite for every scrubber system. Mist elimina-
tors remove scrubber-liquid droplets that are entrained in the flue gas and
return the liquid to the scrubber. Poor mist elimination, an all too common
problem, can have serious consequences, including corrosion downstream, an
increase in particle outlet loading, an increase in power requirements for
reheat, and an increase in water consumption.
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In a system study for EPA, Calvert, Yung, and Leung (1975) evaluated the
performance of various mist eliminators. The results of this study that are
relevant to a utility scrubber system are as follows:
•Overall droplet collection efficiency of a mist eliminator depends on
primary collection and reentrainment. Both overall and primary collection
increase with increasing gas velocity,, But at high gas velocities
(nominally, 5 m/sec and over), reentrainment occurs, decreasing the over-
all collection even though primary collection remains high.
•Higher reentrainment velocities (greater mist eliminator capacity) are
obtained with mist eliminators which have good drainage. Thus, horizonal
gas flow mist eliminators have greater capacities than vertical gas flow
types. Similarly, vertical gas flow mist eliminators with 45° baffles had
larger capacities than those with baffles inclined at 30° or 0°.
•Pressure drop across a baffle mist eliminator is reasonably well predicted
by a model based on the drag coefficient for a single plate held at an
angle to the gas flow.
•Solids deposition is greater on inclined baffles than on vertical ones
because of the increase in settling rate of suspended solids. Deposition
rate decreases as the slurry flux on the surface increases.
A review of commercial mist eliminator designs in use in the utility indus-
try revealed the following practices (Ellison, 1978) :
•Vertical gas flow mist eliminators are used almost exclusively. The chev-
ron multipass (continuous vane) construction and the baffle construction
(noncontinuous slats) are common.
•Vane spacing is generally 1.5 to 30 inches except in the second stage of
two-stage designs which generally use 7/8 to 1 inch spacing.
•Plastic is the most common material of construction due to reduced weight,
cost, and corrosion potential.
•Precollection and prewashing stages are commonly used to improve demister
operation.
•Demister wash systems typically operate intermittently using a mixture of
clear scrubber liquid and fresh makeup water.
Horizontal gas flow mist eliminators have only recently been used in this
country, although they are common in Japan and Germany. This type of mist
eliminator has better drainage than vertical flow types, but space requirements
are greater.
REHEATERS
General Considerations
Although reheating of scrubbed flue gas is not required by law, reheaters
are often incorporated into flue gas wet scrubber systems. Usually, little
553
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attention is given to the design of reheaters, yet failure of the reheater can
cause severe operational problems.
There are four major reasons for providing reheat in flue gas wet scrubber
systems:
•avoid downstream condensation
•avoid a visible plume
eenhance plume rise and pollutant dispersion
•protection of the induced-draft fan.
Reheat may also prevent acid rain and stack icing as well as reduce plume
opacity.
There are three types of reheaters commonly used at utilities. These are
in-line reheaters, direct combustion reheaters, and indirect hot air reheaters.
In-line reheaters are heat exchangers placed within the gas stream. Steam or
water is used as the source of heat. Direct combustion reheaters burn either
oil or gas, mixing the combustion gas with the flue gas. Combustion chambers
can be located either in-line or external to the duct. Indirect hot air re-
heaters inject heated ambient air into the flue gas stream. The air is heated
either in an external heat exchanger or in the boiler preheater. Alternatively,
some utilities have chosen not to use any reheat system, operating the stack
under wet conditions.
Experience gained with reheaters has produced some useful caveats. In-line
reheaters are subject to plugging, corrosion, and vibration. Plugging can be
minimized by good mist elimination and by soot blowing done at frequent inter-
vals. Corrosion is a difficult problem since carbon steel, 304SS, 316SS, and
Corten do not appear to be able to withstand combined acid and chloride-
stress corrosion.. More exotic and expensive materials, such as Inconel 6z5 and
Hastealloy G, have been used successfully at Colstrip. Design against vibration
can readily be done by using frequency analysis. Direct combustion reheaters
are best designed with an external combustion chamber, preventing the problems
encountered with in-line reheaters. Both direct combustion reheaters and
indirect hot air reheaters require interlocks to prevent the heated gas from
damaging ductwork when the cold flue gas is not present. At the Dave Johnston
Plant, where reheat is not used, the induced draft fan is periodically washed
with water to prevent solid deposits and an acid-resistant lining is used on
the stack.
SCALING AND OTHER.. OPERATING PROBLEMS
Scaling is the single greatest operational problem in wet scrubbers and
one that is most difficult to control. In scrubbers used for particulate
removal only, the calcium and other alkalis present in the flyash react with
SC>2 causing scale deposits (calcium sulfate) . In lime and limestone systems,
calcium sulfite (from the reaction of absorbed SC>2 and slurry alkali) and
calcium sulfate (from the reaction of dissolved sulfite and oxygen) tend to
precipitate out and form scale. In lime systems, calcium carbonate may also be
precipitated when CC>2 from the flue gas reacts with the lime (pH is high) .
554
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Various techniques for controlling scale include:
> Control of pH — If a limestone system is operated at pH's above 5.8 to
6.0 or if a lime system is operated above 8.0 to 9.0, there is a danger of
sulfite scaling (Leivo, 1978), The pH is controlled by adjusting the
feed stoichiometry. On-line pH sensors have been successful in controlling
the feed in lime systems but not in limestone systems because the pH is
fairly insensitive to the limestone feed rate in the normal pH range.
However in the limestone system, the feed can be controlled by varying the
flue gas flow rate. In particulate control systems, the pH is generally
low, hold time in the retention tank is short, and suspended solids con-
centration is low. All these contribute to the formation of calcium
sulfate scale. Hence, it is desirable to increase the scrubber liquor
pH by addition of supplementary alkali.
•Hold Tank Residence Time — By providing greater residence times in the
scrubber hold tank, the supersaturation of the liquor can be decreased
before recycle to the scrubber. Typical retention times of 5 to 15 minutes
are used.
•Control of Suspended Solids Concentration — Supersaturation can be mini-
mized by maintaining a supply of seed crystals in the scrubber slurry.
Typical concentrations range from Z to 15 percent suspended solids. Solids
are generally controlled by regulating slurry bleed rate.
•Regulating Oxygen Concentration — Since calcium sulfate scaling depends
on the presence of dissolved oxygen, control techniques center on regula-
ting the oxygen concentration. In the forced oxidation method, air is
bubbled into the reaction tanks to encourage sulfate crystal formation.
These crystals have better settling characteristics than sulfite crystals.
In the co-precipitation method, magnesium sulfite is used to depress the
sulfate saturation level. Precipitation of sulfate in the holding tank is
achieved by co-precipitation of'sulfate with sulfite in a mixed crystal.
>Liquid-to-Gas Ratio — High liquid-to-gas ratios reduce scaling potential
since the scrubber outlet is more dilute with respect to absorbed S02-
Unfortunately, increasing the liquid-to-gas ratio also increases operating
costs and sludge disposal.
•Additives — Two additives, Calnox 214DN and Calgon CL-14, when used
together, have been found to effectively reduce sulfate scaling in lime-
stone systems (Federal Power Commission, 1977) .
•Alkali Utilization — Experience at the TVA test facility at Shawnee
indicated that certain mud-type solid deposits, which tended to form
particularly in the mist eliminators, could be reduced by improving alkali
utilization. Above about 85 percent alkali utilization, these solids
could be removed easily with infrequent (once per 8 hours) washings. Con-
trol of calcium sulfate scaling at TVA was effected by varying the operating
parameters listed above (Williams, 1977).
CONCLUSIONS AND RECOMMENDATIONS
Design of the optimum wet scrubber system for use on coal-fired utility
boilers is a two-step process consisting of characterizing the inlet gas stream,
and then choosing the best designs for the various scrubber components based on
operating experiences and research studies.
555
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Characterization of the inlet flue gas stream is essential, but too fre-
quently, neglected. The following properties should be determined.
Flyash Size Distribution — Flyash size distributions vary greatly among
power plants, depending on boiler and coal types. For a particular scrubber,
particle collection efficiency is determined by the inlet size distribution.
Flyash Composition — The chemical composition of the flyash is important.
If the flyash contains substantial quantities of alkalis, calcium and magnesium
oxides, it will scrub some SC>2 from the flue gas leading to scale formation.
Flyash may also contain chlorides which can cause stress corrosion in stainless
steels.
Flue Gas Composition — The concentration of S03 (or I^SO^) should be
determined because of its corrosiveness. Flue gas may also contain hydrogen
chloride which poses another corrosion problem.
Once the inlet gas stream has been characterized, it is necessary to
select the best scrubber components to obtain maximum performance. The choice
of components should be based on past operating experiences and research studies.
Unfortunately, operating experiences do not always present a consistent picture,
making it difficult to formulate hard-and-fast rules. It should also be borne
in mind, that scrubber design technology has not advanced far enough to prevent
problems from arising after construction. Hence the best overall designs are
those that are flexible enough to permit easy replacement of damaged parts.
This study recommends the following for the various scrubber components.
Particulate Scrubber and S02 Absorber — Current practice suggests the
use of simpler designs for both the particulate scrubber and SC-2 absorber.
Hence, of the conventional particulate scrubber types, a gas-atomized scrubber,
such as a venturi or rod scrubber, is recommended. Other types are less effi-
cient or have more operating problems. Also, spray towers are preferable for
use as the S02 absorber.
Based on a correlation of scrubber performance against energy requirements,
a theoretical pressure drop of 17+2 in. W.G. would be necessary to meet the
New Source Performance Standard of 0.03 Ibs particulate/million Btu in a con-
ventional scrubber. When fan losses and pressure drops across the absorber,
ductwork, and mist eliminator are taken into account, total system pressure drop
may run as high as 30 in. W.G. If this energy requirement is considered too
high, a novel particulate scrubber should be chosen. Of the novel scrubbers
tested by EPA to date, the electrostatically augmented scrubbers appear to be
the most suitable for use on coal-fired utility boilers. Pilot units have shown
good collection efficiency for flyash, coke oven battery emissions, and steel
mill electric arc furnace emissions.
Mist Eliminator — Horizontal mist eliminators have greater capacities than
vertical types, but space requirements are also greater. Vertical mist elimina-
tors are best designed with sharp angled baffles to promote good drainage.
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Reheaters — Operating experience with reheaters militates against the use
of in-line reheaters because of combined acid and chloride stress corrosion.
The two other types of commonly used reheaters, direct combustion and indirect
hot air reheaters, are recommended and should be designed with interlocks to
prevent heated gas from damaging ductwork when flue gas is not present. Adequate
mixing is sometimes a problem with these types of reheaters.
Materials of Construction — The most common construction material for
scrubbers is 316 stainless steel. At points of high abrasion, wear plates,
brick linings, or high grade nickel alloys are recommended. The higher grade
alloys are also recommended in areas subject to chloride attack.
The best material for in-line reheaters appears to be the higher grade
alloys—Inconel and Hastelloy have worked well at Colstrip (Montanta Power).
Carbon steel and lower grade stainless steels have worked at some plants but
have failed at others.
Plastic is the best material for mist eliminators because of low cost,
light weight, and reduced corrosion potential.
Waste Disposal — Disposal of collected flyash from a particulate scrubber
is easily controlled, typically it is disposed of along with bottom ash. With
a dual-function particulate-S02 scrubber system, waste disposal is problematic
because of the thixotropic nature of the sludge. Ponding is the most common
and least expensive method of disposal, but creates a large unreclaimable
area. Landfill is a better method of disposal, but the sludge requires greater
dewatering as well as stabilization. In some site-specific cases, it may be
possible to use less common places, such as a dry lake (arid regions) or a
mine.
REFERENCES
1. Accortt, J.L., A.L. Plumley, and J.R. Martin. "Fine Particulate Matter
Removal and S02 Absorption with a Two-State Wet Scrubber," EPA-APT Fine
Particle Scrubber Symposium, San Diego, May 1974.
2. Bechtel Progress Report, "EPA Alkali Scrubbing Test Facility TVA Shawnee
Power Plant," June 1977.
3. Calvert, S., J. Goldshmid, D. Leith, and D. Methta. Scrubber Handbook,
NTIS No. PB 213-016, July 1972.
4. Calvert, S., J. Goldshmid, D. Leith, and N. Jhaveri. Feasibility of Flux
Force/Condensation Scrubbing for Fine Particulate Collection, EPA-650/2-
73-036, NTIS No. PB 227-307, October 1973.
5. Calvert, S., and N. Jhaveri. "Flux-Force Condensation Scrubbing," in
EPA Fine Particle Scrubber Symposium, EPA-650/2-74-112,. NTIS No. PB 239-
335, October 1974. .
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6. Calvert, S. , N. Jhaveri, and T. Huisking. Study of Flux Force Condensation
Scrubbing of Fine Particles, EPA-600/2-75-018, NTIS No. PB 249-297, August
1975.
7. Calvert, S. , S. Yung, and J. Leung. Entrainment Separators for Scrubbers-
Final Report, NTIS No. PB 248-050, August 1975.
8. Calvert, S. "How to Choose a Particulate Scrubber," Chemical Engineering,
Vol. 18, No. 84, August 29, 1977, pp.54-68.
9. Calvert, S. , and S. Gandhi. Fine Particle Collection by a Flux-Force
Condensation Scrubber: Pilot Demonstration, EPA-600/2-77-238, NTIS No.
PB 277-075, December 1977.
10. Devitt, T., R. Gerstle, L. Gibbs, S. Hartman, and N. Klier. Flue Gas
Desulfurization System Capabilities for Coal-Fired Steam Generators.
Volume II Technical'Report,"^PA=600/7-78-032b7"NTIS No. FB 279-417, March
1978.
11. Ellison, W. "Scrubber Demister Technology for Control of Solids Emissions
from SC>2 Absorbers," in Symposium on the Transfer and Utilization of
Particulate Control_Technoiogy, EPA-600/7-79-044c, February 1979.
12. Ensor, D. et al. Evaluation of a Particulate Scrubber on a Coal-Fired
Utility BoTle7,~NTls~No. PB 249-562, November I975~.
13. Federal Power Commission. The Status of Flue Gas Desulfurization Applica-
tions in the United States: A Technological Assessment, July 1977.
14. Fox, Harvey. Personal communication, Research-Cottrell, Bound Brook, New
Jersey, July 1978.
15. Green, K., and J. Martin. "Conversion of the Lawrence No. 4 Flue Gas
Desulfurization System," in Proceedings: Symposium on Flue Gas Desulfuri-
zation - Hollywood, Florida, NTIS No. PB 282-091, November 1977.
16. Grimm, C., J.Z. Abrams, W.W. Leffman, I.A. Raben, and C. LaMantia. "The
Colstrip Flue Gas Cleaning System," Chemical Engineering Progress, Vol.
74, No. 2, February 1978, pp.51-57.
17. Hesketh, H.E. "Pilot Plant S02 and Particulate Removal Study, Report of
Fiscal Year 1974-1975 Operations," Sponsored by Illinois Institute for
Environmental Quality and Southern'Illinois University, Project No. 10.027,
August 1975.
18. Kashdan, E.R. and M.B. Ranade. Design Guidelines for an Optimum Scrubber
System, EPA-600/7-79-018, NTIS No. PB 292-327, January 1979.
19. Kruger, R., and M. Dinville. "Northern States Power Company Sherburne County
Generating Plant Limestone Scrubber Experience," Presented at the Utilities
Representative Conference on Wet Scrubbing, Las Vegas, Nevada, February 1977.
558
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20. LaMantia, C. et_ al. Application of Scrubbing Systems to Low Sulfur/Alkaline
Ash Coals, EPRI FP-595, December 1977.
21. Laseke, B. EPA Utility Flue Gas Desulfurization Survey: December 1977-
January 1978, EPA-600/7-78-051a, NTIS No. PB 279-011, March 1978.
22. Laseke, B. Survey of Flue Gas Desulfurization Systems: Green River Sta-
tion, Kentucky Utilities, EPA-600/7-78-048e, NTIS No. PB 279-543, March 1978.
23. Laseke, B. Survey of Flue Gas Desulfurization Systems: Cholla Station;
Arizona Public Service Company, EPA-600/7-78-048a, NTIS No. PB 281-104,
March 1978.
24. Laseke, B. Survey of Flue Gas Desulfurization Systems: LaCygne Station,
Kansas City Power and Light Company, EPA-600/7-78-048d, NTIS No. PB 281-107,
March 1978.
25. Lee, R.E., H.L. Crist, A.E. Riley, and K.E. MacLeod. "Concentration and
Size of Trace Metal Emissions from a Power Plant, a Steel Plant, and a Cotton
Gin," Environmental Science & Technology, Vol. 9, No. 7, July 1975, pp.643-647,
26. Leivo, C.C. Flue Gas Desulfurization Systems: Design and Operation Con-
siderations, Volume II, Technical Report, EPA-600/7-78-030b, NTIS No. PB 280-
254, March 1978.
27. McCain, J.D. CEA Variable-Throat Venturi Scrubber Evaluation, EPA-600/7-78-
094, NTIS No. PB 285-723, June 1978.
28. Mclllvaine, R.W. The Mclllvaine Scrubber Manual, Volume II, The Mclllvaine
Company, 1974.
29. Pearson, B., Private communication, Public Service Company of Colorado.
30. Pilat, M., and G. Raemhild. "University of Washington Electrostatic
Scrubber Evaluation at Coal-Fired Power Plant," EPA-600/7-78-177b, NTIS No.
PB 292-646, December 1978.
31. Rhudy, R., and H. Head. "Results of EPA Flue Gas Characterization Testing
at the EPA Alkali Wet-Scrubbing Test Facility," Presented at the 2nd EPA
Fine Particles Scrubber Symposium, EPA-600/2-77-193, NTIS No. PB 273-828,
September 1977.
32. Richmond, M. and H. Fox, Private communication, Research-Cottrell, Inc.
33. Sadowsky, D., Private communication, Montana-Dakota Utilities.
34. Semarau, K. "Practical Process Design of Particulate Scrubbers," Chemical
Engineering, Vol. 84, No. 20, September 26, 1977.
35. Sitig, M. Particulates and Fine Dust Removal, Processess and Equipment,
Noyes Data Corporation,,Park Ridge, New Jersey, 1977.
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36. VanTassel, D., Private communication, Minnesota Power and Light.
37. Williams, J.E. "Mist Eliminator Testing at the Shawnee Prototype Lime/
Limestone Test FAcility," 2nd US/USSR Symposium on Particulate Control,
EPA-600/7-78-037, NTIS No. PB 279-628, March 1978.
38. Winkler, P., Private communication, Chemico Air Pollution Control Company.
39. Dallabetta, G., Private communication, Bechtel Corporation.
560
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TESTS ON UW ELECTROSTATIC SCRUBBER FOR
PARTICIPATE AND SULFUR DIOXIDE COLLECTION
by
Michael J. Pllat
Department of Civil Engineering
University of Washington
Seattle, Washington 98~!95
Abstract
The University of Washington Electrostatic Scrubber pilot plant was tested for
participate and sulfur dioxide collection at the unit no. 2 coal-fired boiler
at the Centralia Power Plant. The UW Electrostatic Scrubber involves the use of
electrostatically charged water (or alkaline absorbing liquor) to collect a^r
pollutant particles charged to the polarity opposite from the droplets and to
absorb gaseous a'ir pollutants. The portable UW electrostatic Scrubber pilot
plant (located inside a 40 ft. trailer) is designed for 1,000 acfm gas flow at
the inlet to the scrubber; however, at Centralia inlet flows as high as 1,600
acfm were used. Simultaneous inlet-outlet source tests using the UW Source
Test Cascade Impactors (Mark 10 model at the inlet to the scrubber and Mark 20
model at the outlet} and 'in-stack filters showed the overall particle cc/! lection
efficiency ranged from 99.30 to 99.992 (depending on the scrubber operating
conditions) and the outlet particle concentration ranging from .00013 to .00116
grains/sdcf. Using a sodium carbonate scrubbing liquor, the sulfur dioxide
collection efficiency ranged from 36.2 to 98.8% depending on the operating
parameters such as the liquor to gas flow rate ratio, liquor pH, inlet S00
concentration, etc., and spray voltage. The test results illustrate that^the
addition of electrostatic charging of the aerosol particles and the spray liquor
droplets can enhance the collection efficiency for both particulates and sulfur
dioxide.
561
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Tests on UW Electrostatic Scrubber for Participate
and Sulfur Dioxide Collection
by
Michael J. Pilat
I. INTRODUCTION
A. Objectives of Research Project
The objectives of this on-going research project are to demonstrate
the effectiveness of the UW Electrostatic Scrubber for controlling
emissions of fine particulates and gaseous air pollutants from various
industrial sources. The test data obtained is to be used to improve
scrubber performance and to develop preliminary designs and economic
information of full-scale electrostatic scrubber systems.
B. Review of Previous Work
Penney (1944) patented an electrified liquid spray test precipitator
involving particle charging by corona discharge and droplet charging by
either ion impaction or induction. Penney's system consisted of a spray
scrubber with electrostatically charged water droplets collecting aerosol
particles charged to the opposite polarity. Kraemer and Johnstone (1955)
reported theoretically calculated single droplet (50 micron diameter
droplet charged negatively to 5,000 volts) collection efficiencies of
332,000% for 0.05 micron diameter particles (4 electron unit positive
charges per particle). Pilat, Jaasund, and Sparks (1974) reported on
theoretical calculation results and laboratory tests with an electrostatic
spray scrubber apparatus. Pilat (1975) reported on field testing during
1973-1974 with a 1,000 acfm UW Electrostatic Scrubber (Mark IP model)
funded by the Northwest Pulp and Paper Association. Pilat and Meyer
(1976) reported on the design and testing of a newer 1,000 acfm UW
Electrostatic Scrubber (Mark 2P model) portable pilot plant funded by the
EPA, Pilat, Raemhild, and Harmon (1977) reported on tests of the UW
Electrostatic Scrubber pilot plant (Mark 2P model) on collecting laboratory
generated DOP aerosols and emissions from a coal-fired boiler and an
electric arc steel furnace. Pilat, Raemhild, and Gault (1978) reported
on some of the results of SO^ and particulate collection efficiency tests
performed on the UW Electrostatic Scrubber at the Centralia Coal-Fired
Power Plant. Pilat, Raemhild, and Prem (1978) reported on the tests at
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a steel plant (Bethlehem Steel Co., Seattle). The UW Electrostatic Scrubber
(patent pending) has been licensed to the Pollution Control Systems
Corporation (of Renton and Seattle, Washington) for production and sales.
II. Description of UW Electrostatic Spray Scrubber
The UW Electrostatic Scrubber involves the use of electrostatically
charged water droplets to collect air pollutant particles electrostatically
charged to a polarity opposite from the droplets. A schematic illustration
of the UW Electrostatic Scrubber system is presented in Figure 1.
s&s OUTLET
CORONA
(ARTICLE CHARGING)
CHARGED WATER SPRAYS MIST ELIMINATOR
(COLLECTION OF CHARGED PARTICLES
BY OPPOSITELY CHARGED WATER DROPLETS)
Figure 1, UW Electrostatic Scrubber
The particles are electrostatically charged (negative polarity) in
the corona section. From the corona section the gases and charged
particles flow into a scrubber chamber into which electrostatically
charged water droplets (positive polarity) are sprayed. The gases and
some entrained water droplets flow out of the spray chamber into a mist
eliminator consisting of a positively charged corona section in which
the positively charged water droplets are removed from the gaseous stream.
The general layout of the UW Electrostatic Scrubber pilot plant
CMark 2P model) which was used during the tests at the Centralia Power
Plant is shown in Figure 2, The system (in the direction of gas flow)
includes a gas cooling tower, an iniet test duct with sampling port, a
particle charging corona section (corona #1, not used for these tests),
563
-------
a charged water spray tower (tower #1, not used for these tests), a
a particle charging corona section (corona #2), a charged water spray
tower (tower #2). a positively charged corona section to collect the
positively charged water droplets, an outlet test duct with sampling
port, and a fan.
TUT
\P
OWSS KCTiO**'. Vltw C*
TMKtt mSS HCft-iONTA* ICCTKX
mot TEJT ewer
] S*IUT TOwCH MO X
i
B-P^1
j
E
CORONA MO 1
»**«,
K1ST
twurr TDWEA «1 i
— -^^^^
J
•MY TT*£» w t [
Figure 2, General Layout of Electrostatic Scrubber Pilot Plant
(Model Mark 2P)
The model Mark 2P has a scrubbing liquor recycle system. This system
utilizes an electrically isolated pump, insulated hosing, and a current
limiting spray system for current containment and safety.
III. Experimental Procedure
The particle size distributions were measured simultaneously at the
inlet and outlet of the elctrostatic scrubber using UW Source Test Cascade
Impactors. The inlet test port is located downstream of a spray cooling
tower (as shown in Figure 2) and hence, the measured particle collection
efficiencies are for the electrostatic scrubber portion of the system,
The 27 stage Mark 10 model (sampling at about 0.2 acfm) was used at the
inlet where the particle concentration is higher. The 14 stage Mark 20
model (sampling at about 2.0 acfm) was used at the scrubber outlet where
the particle concentration is typically low. Both the Mark 10 and Mark
20 models utilize reduced absolute gas pressure in the outlet jet stages
in order to provide stage aerodynamic cut diameters (dj-n) down to about
Q.02 microns. bu
564
-------
Thermo Electron Model 40 Fluorescent S02 Analyzer was used to
measure S0~ levels in the gas stream at the inlet and outlet of the pilot
plant. The principle of operation of this monitor is based upon the
measurement of the fluorescence of S02 produced by its absorption of
ultraviolet radiation. The analyzer was connected to a strip chart
recorder so that 5-minute averages of the inlet and outlet S02
concentrations were used to calculate the scrubber's S02 collection
efficiencies.
IV. Results of Particulate Tests
In October 1977, the UW Electrostatic Scrubber pilot plant (Mark 2P
model) was transported to the Centralia Steam-Electric Project (two
655-megawatt pulverized coal-fired boilers) operated by Pacific Power
and Light Company. A sample gas stream was tapped from the outlet of
PP & L no. 2 and transported via ducting to the Electrostatic Scrubber
pilot plant. The UW Electrostatic Scrubber pilot plant system was
modified prior to testing by: (1) the installation of a larger booster
fan at the inlet to the scrubber in order to accomodate the large
negative pressure (around -14 inches water) in the main duct and to allow
a higher gas flow rate through the scrubber pilot plant; and (2) the
connection of a newly constructed liquor recycle system in a 40 ft. trailer
to the spray scrubber tower which enabled operation with either an
open-loop or a closed-loop liquor recycle system.
The results of the particle collection efficiency tests over the
O.Q75 to 15 micron aerodynamic diameter size range are presented in
Figure 3. These efficiency curves are based on log-normal approximations
of the inlet and outlet particle size distributions, and hence the minimum
in the collection efficiency at about 0.5 microns diameter is smoothed out.
The tests were run in an open-loop liquor recycle mode with the water used
as the scrubbing liquor. The outlet particle mass concentration for these
tests ranged from .00065 to .00459 grains/sdcf.
V, Results of Sulfur Dioxide Tests
Sulfur dioxide collection efficiency tests were conducted at the
Centralia Power Plant with an open-loop liquor system using scrubber
liquor of water and of sodium carbonate solution. The measured S0?
collection efficiencies were found to be a function of the liquor/gas
flow rate ratio (L/G), the S02 inlet concentration, the stoichrometric
ratio (moles of alkaline liquor sprayed/moles of inlet S02), and the
liquor spray voltage, Figure 4 shows that the S02 collection efficiency
increases with incoming stoichrometric ratio, witn increasing spray
voltage, and with increasing liquor/gas flow rate ratios.
565
-------
ioa
UW Electrostatic Scrubber
Centralia Power Plant
March-May 1979
Test Series #3-N
Liquor
502 I" * 552 ppm
= 0.87
Test Series #2-N
Liquor
* 0.96 £/akm3
= 545 ppm (average)
TF6FCN Fog Nozzle
Pressure = .79 MPa
.5 1.0
Stoichiometric Ratio
1.5
Figure 4. SCL Collection Efficiency as a Function of Stoichrometrie Ratio
566
-------
8
CJ
•"4
u_
UJ
CJ
UJ
UJ
d
89.0
g| 10.0
0.0
UW Electrostatic Scrubber
Centralia Power Plant
March-May 1979
Units
Overall Efficiency (%)
Overall Penetration (%)
SCA (m2/(sm3/min))
L/G
Test
No.
1
2
3
4
7
8
Symbol
s>
©
A
4-
US
H
Overall
Eff.
98.99
99.55
99.58
99.48
99.79
99.80
Pen.
1.01
0.45
0.42
0.52
0.21
0.20
SCA
.091
.091
.087
.095
.095
.101
L/G
1.14
1.12
1.05 j
1.02
1.13
1.18
6
8
Orl
4 UJ
O
8 £
Q_
8 ~
oog
(X
ce
UJ
UJ
Q-
B4JO 10"1 2 S 10° 2 5 101
PflRHCLE flERODYNRMIC DIRMETER. DSDtMICRONS)
Figure 3. Particle Collection Efficiency versus Particle Size
567
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VI. Conclusions
The test results on the UW Electrostatic Scrubber on the emissions
from the Centralia coal-fired power boiler demonstrates the system's
effectiveness for collecting particulates and sulfur oxides. The outlet
concentrations from the UW Electrostatic Scrubber system were .00065 to
.00459 grains/sdcf particulates and 10 to 510 ppm SC2 depending on the
inlet concentrations, operating parameters, and liquor alkalinity. With
sodium carbonate liquor the S09 collection efficiency ranged from 41.1
to 97.4%. *•
VII. Acknowledgements
This research was supported by the US EPA (IERL) Research Grant
(EPA Grant Nos. R-8-4393 and R-06035). The assistance, advice, and
cooperation of our EPA Project officer, Dale A. Harmon is gratefully
acknowledged. The assistance of University of Washington students and
staff, Terrell Gault (whose MSE thesis research was on the effects of
electrostatics on the sulfur dioxide collection efficiency), Tracey Steig,
and, Gary Raemhild is acknowledged. The cooperation and assistance of
Pacific Power and Light Company personnel including Tom White, Ted
Phillips, Bob Werner, Gary Slanina, Steve Lambert, Don Sakata, Al
Seekamp, John Angelovich, and Pete Steinbrenner is greatly appreciated.
568
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References
1. Kraemer, H. F. and H. F. Johnstone (1955). Collection of Aerosol Particles
in the Presence of Electric fields. Ind. Engr. Chem. 47:2426.
2. Penney, G. W. (1944). Electrified Liquid Spray Dust Precipitator. U.S.
Patent No. 2,357,354.
3. Pilat, M. J., Jaasund, S. A., and L. E. Sparks (1974). Collection of
Aerosol Particles by Electrostatic Droplet Spray Scrubbers, Envir. Sci.
& Tech. 8:340-348.
4. Pilat, M. J. (1975). Collection of Aerosol Particles by Electrostatic
Droplet Spray Scrubbers. APCA Journal. 25:176-178.
5. Pilat, M. J. and D. F. Meyer (1976). University of Washington Electrostatic
Spray Scrubber Evaluation. Final Report on Grant No. R-803278, EPA Report
No. EPA-600/2-76-100 (NTIS No. PB 252653/AS).
6. Pilat, M. J., Raemhild, G. A., and D. L. Harmon (1977). Fine Particle
Control with UW Electrostatic Scrubber. Presented at Second Fine Particle
Scrubber Symposium, May 2-3, 1977, New Orleans.
7. Pilat, M. J., Raemhild, G. A., and D. L. Harmon (1977). Tests of
University of Washington Electrostatic Scrubber at an Electric Arc Steel
Furnace. Presented at Conference on Particle Collection Problems in the
Use of Electrostatic Precipitators in the Metallurgical Industry,
June 1-3, 1977, Denver.
8. Pilat, M. J. and G. A. Raemhild (1978). Control of Particulate Emissions
with UW Electrostatic Spray Scrubber. Presented at EPA Symposium on the
Transfer and Utilization of Particulate Control Technology, July 24-28,
1978, Denver.
9, Pilat, M. J., Raemhild, G. A., and A. Prem (1978). University of Washington
Electrostatic Scrubber Tests at a Steel Plant. EPA Report No. EPA-
600/7-78-177a, September 1978.
10, Ptlat, M. J. and G. A, Raemhild (1978). University of Washington
Electrostatic Scrubber Tests at a Coal-Fired Power Plant. EPA Report
No. EPA-600/7-78/177b, December 1978.
11, Pilat, M, J,, Raemhild, G. A., and T. W. Gault 0978). Tests on UW
Electrostatic Scrubber for Particulate and Sulfur Dioxide Collection.
Presented at Pacific Northwest International Section of Air Pollution
Control Association meeting, November 9-10, 1978, Portland.
569
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EPA MOBILE VENTURI SCRUBBER PERFORMANCE
Environmental Protection Agency Mobile Venturi Scrubber Performance - An
empirical and modeling study of New Source Performance Standard-level venturi
performance on pulverized coal boiler characteristics
By:
S. Malani, S.P. Schliesser, and W.O. Lipscomb
Acurex Corporation
Research Triangle Park, North Carolina
ABSTRACT
This report describes the Environmental Protection Agency's mobile venturi
scrubber performance evaluation conducted at the power plants of Michigan
State University, East Lansing, Michigan, and the City of Ames, Ames, Iowa.
The effects of pulverized coal emission characteristics on venturi scrubber
collectability are reported. Controlled variables were boiler operation, fuel
type, and scrubber pressure drop. Use of a mathematical performance model
provides support and insight into scrubber performance and measurement metho-
dologies. Cost modeling data are shown for different boiler and scrubber
characteristics for performance in the range of current and projected New
Source Performance Standards.
The following highlights emerge from this study of conventional venturi
scrubber performance on coal-fired boilers:
• Conventional venturi scrubber performance is cost-sensitive in
the New Source Performance Standards' range of interest.
• Scrubber operation and performance characteristics are
predictable with complete characterization and an improved
computerized model.
« Scrubber operation, performance and cost levels are strongly
dependent on influent fine particle concentration levels.
• Fuel type and/or boiler design are the primary factors for
generation of fine particle concentration levels.
• Cofiring coal with refuse fuel increases fine particulate
generation, causing dramatic increases in scrubber costs.
570
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INTRODUCTION AND OBJECTIVE
This pilot scale venturi scrubber is one of three conventional particu-
late emission control devices mobilized by the Utilities and Industrial Power
Division, Industrial Environmental Research Laboratory, U.S. Environmental
Protection Agency (UIPD/IERL/EPA), Research Triangle Park, North Carolina.
The objective is to evaluate and compare the performance characteristics of a
scrubber, baghouse and electrostatic precipitator (ESP) on industrial parti-
culate emission sources. The purpose is to provide characteristic information
and insight for appropriate selection of particulate control devices, in light
of operation, performance, and cost considerations.
This report summarizes the results of mobile scrubber tests conducted at
the power plants of Michigan State University, East Lansing, Michigan and City
of Ames, Ames, Iowa over a 4-month period beginning July 1978. The particu-
late emission source at each site was a pulverized coal (PC) boiler; the Ames
utility had refuse cofiring capability. The particulate-laden flue gas was
slipstreamed and sampled at inlet and outlet locations of the scrubber by
total mass measurements and Brink and Andersen cascade impactors. The test
matrix was designed to study the effects of scrubber pressure drop and
liquid-to-gas (L/G) ratio for different boiler/fuel cases. Scrubber perform-
ance and cost modeling generated the following:
• Comparison of empirical overall and fractional collection effi-
ciencies with model predictions
* Comparison of experimental pressure drops with model predictions
• Scrubbing costs for tested boiler/fuel cases in New Source Performance
Standards' (NSPS) range of interest (43 to 13 ng/J)
CONCLUSIONS
The following conclusions result from this study:
• Scrubbing costs become very sensitive to required performance levels;
cost factors can range as much as 100-200 percent across the NSPS
range of 43 to 13 ng/J (0.1 to 0.03 Ib/million Btu).
• Boiler effluent characteristics are strongly dependent on fuel type
and/or boiler design; differences in generated fine particle concen-
trations can impact scrubbing costs as much as 25-300 percent,
dependent on required performance level.
• Cofiring coal with refuse fuel increases fine particle concentration;
economic gains in fuel cost savings are offset by 10-80 percent cost
penalties for scrubbing costs.
• The EPA/Calvert scrubber model was modified to incorporate two
improvements:
571
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1) The log-normal size distribution format was changed to
accommodate a more realistic particle size-histogram
format.
2) The effect of flue gas quenching in the venturi throat was
mathematically defined, affording a more reasonable
description of droplet formation, pressure loss and
particulate collection.
« The model predicts venturi scrubber operation and performance with
fair accuracy and precision; the model's accuracy is better for a
6 cm (2.3 in.) throat than a 3.5 cm (1.4 in.) throat, indicating
appreciable wall effects for throat sizes less than 6 cm.
• For a given set of scrubber conditions, the model tends to: under-
predict overall collection performance; underpredict the collection
of fine particles (less than 2 (Jm); overpredict the collection of
large particles (greater than 4 (Jm) .
• The discrepancy between the model predictions and data can be attri-
buted partly to measurement methodology, since the existing methodology
does not account for differences in aerodynamic characteristics
between the influent (dry) and effluent (wet) particles.
DESCRIPTION OF FACILITIES
Power Plants
Michigan State University (MSU) Power Plant 65. This power plant consists
of three boilers designated as Units I, 2 and 3. The pilot scrubber was
tested on Unit 2 which is a 113,600 kg/hr (250,000 Ib/hr) 30-35 MW boiler.
The boiler fires pulverized Eastern Kentucky Coal (6 to 7 percent moisture,
8 percent ash, 0-75 percent sulfur, 29 million J/kg (12,500 Btu/lb)).
Ames Power Plant. Owned and operated by the city of Ames, this power
plant consists of three boilers designated Units 5, 6 and 7. Scrubber tests
were done on Unit 7 which is a 33 MW PC-fired boiler capable of firing up to
20 percent refuse-derived fuel (RDF). The plant uses a blend of 55 percent
Iowa coal at 3 to 5 percent sulfur and 45 percent Colorado low-sulfur western
coal. The heating value for the coal blend is 24.1 million J/kg (10,400 Btu/lb),
compared to 13.9 million J/kg (6,000 Btu/lb) for the RDF.
Scrubber
The mobile scrubber facility is contained inside a standard freight
trailer (12.2m x 2.4m, or 40 ft. x 8 ft.). It is equipped with three available
venturi throats (3.5, 6.0, and 8.5 cm), a presaturator, a cyclone separator,
and a baffled mist eliminator. Each venturi has a throat length of 30.5 cm
and a radial water dumping nozzle 5.1 cm below the throat entrance. Appropriate
auxiliaries and instrumentation are provided inside the trailer.
572
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PROGRAM METHODOLOGY
Installation
Care was taken to ensure that a representative stream was withdrawn and
delivered to the pilot scrubber. The slipstream was extracted isokinetically
and transported isothermally to the pilot unit through heated ducting at
velocities comparable to plant conditions. Inspection of the ducting after
each test series revealed marginal dropout of particulate, due to either
gravitational or centrifugal forces. At each test site, the slipstream was
educted downstream of the air preheater and upstream of the pollution control
device. For the Ames site, a second ducting was installed downstream of the
full scale ESP.
Operation
The pilot scrubber was operated and tested on a daily start-up/shutdown
basis. Equipment startup and system equilibrium were carried out in the
morning, and performance measurements were conducted in the afternoon. There
were indications of scaling at the wet/dry interface, a condition which
warranted scale removal daily. Each set of inlet and outlet mass and impactor
measurements were conducted concurrently. Sampling periods required 2-3 hour
tests, enabling two sets of tests to be conducted daily. The scrubber liquor
pH was maintained between four and six by adding a lime solution. The filtrate
recycle-to-purge ratio was maintained at approximately 1:1 to restrict sulfate/
sulfite accumulation.
Test Conditions
Table 1 summarizes scrubber test conditions and operating parameters.
Pressure drops were varied from ~25 to 125 cm H^O (~10 to 50 in. I^O). Gas
flowrates ranged from 7 to 16 am3/min. (250 to 560 acfm). The liquid/gas
(L/G) ratio was evaluated at 2 and 4 1/m3 (15 and 30 gal/kcfm).
Data Acquisition
After setting the prescribed test conditions, the important operating
parameters were recorded on a semihourly basis and included:
• Scrubber pressure drop
• Gas flowrate
• Scrubber liquor flowrate
• Gas temperature (before and after scrubber)
• Makeup water flowrate
• Scrubber liquor pH
573
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On-site analyses of performance measurements were conducted to provide
feedback on performance data and data quality.
Particulate Measurements
Total mass and impactor measurements at the inlet and outlet points were
conducted at isokinetic conditions. Brink and Andersen impactors measured the
inlet and outlet size distributions, respectively. Gelman glass fiber sub-
strates were used at MSU, whereas Reeve Angel 934 AH material was preferred at
Ames because of low S02 absorptivity. All substrates were preconditioned for
6 hours. Samples were obtained with extractive probes fitted with inter-
changeable nozzles at average velocity locations. Sampling trains similar to
that described in Method 5 of the Federal Register were used.
Data Reduction
A computer program was used to calculate impactor stage cutpoints, parti-
cle size distributions and overall particulate loading. Fractional penetra-
tions were calculated by a program that performs linear least square, quadra-
tic least square and spline fits to log normal transformed inlet and outlet
cumulative size distribution data.1 This program was supplemented by manual
graphical procedures whenever data showed excessive scatter.
The computer program for the scrubber model was applied to predict and
compare scrubber operation and performance levels.2 The original program was
modified to accept inlet size distribution histograms and account for gas
cooling in the venturi throat, assuming instantaneous quenching. The program's
inlet requirements include seven parameters to define scrubber conditions and
several descriptors for the influent particulate stream. The model then
determines the fractional penetration relationship from the specified conditions
to--
1) relate the influent size distribution for the prediction
of the effluent size distribution, and
2) integrate the influent size distribution to predict the
effluent particulate concentration.
RESULTS AND DISCUSSION
Overall Collection Performance
The control device characteristic of practical importance is that of
overall collection performance. This performance can be described and measured
by the emission level which penetrates the device and passes into the atmosphere.
Emission levels are used by the regulatory agency to stipulate NSPS. The
scope of this report entails venturi scrubber performance and costs in the
range of current and projected NSPS for coal-fired utility boilers. Analyses
were made for NSPS levels of 43 and 13 ng/J, and for an intermediate emission
level of 21.5 ng/J, respectively.
574
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Scrubber performance levels as a function of pressure drop are shown in
Figure 1 for the three fuel types studied. Two performance curves for each
fuel case are included, comparing results from the empirical data and comput-
erized model. The three model curves methodically reflect distinct performance
requirements for the three fuel cases. The fuel-specific performance relation-
ships should be considered realistic since they account for measured differences
in influent size distributions. These performance relationships are presented
over the range of current and projected NSPS.
A correspondence between the model and data curves is observed (Table 2),
although the model results are consistently overpredictive to the data. The
spread between the data curves is more apparent than between the model curves
due to appreciable wall effects in pilot scale Venturis discussed below.
Considering that better data/model correlations have been shown by others,
scrubber performance can be described or bracketed by the paired curves in
Figure 1.
Particle Size Collection Performance
Analysis of particle size collection performance (i.e., fractional efficiency
or fractional penetration) offers support of and insight into overall collection
performance. As technological advances are being made, it is becoming appropriate
to evaluate performance in terms of penetration, rather than collection. In
this text, fractional penetration is used to describe particle size collection
performance.
This study was conducted on three different fly ash species with two
venturi throat sizes. Figures 2 through 6 compare fractional penetration
curves predicted by the model with the data for various pressure drops and L/G
ratios. Most of the data are for the 6 cm throat; the results for the 3.5 cm
throat are noted in Figures 5 and 6. The graphs show a fair comparison between
the model predictions and the empirical data. The following peculiarities are
worth noting:
• The data are skewed with respect to the model with recurring simi-
larity.
• In general the model overpredicts penetration for particles below
2 microns aerodynamic diameter.
• The model generally underpredicts penetration for particles above
4 microns aerodynamic diameter.
• In the middle of the particle size range, model and data curves
intersect, showing better correlation.
• The degree of correlation is higher in the case of the 6.0 cm venturi
as compared to the 3.5 cm venturi.
These discrepancies/peculiarities are somewhat accountable in that there
are several difficulties in measuring scrubber effluent size distribution,
575
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including:
• Concentration of particulate is reduced,
• most of the penetrated material is composed of fine particulate,
• saturation conditions occur with the presence of penetrated and
re-entrained droplets, and
• the particle species measured as the effluent is distinct from the
dry species measured as the influent.
For the first three difficulties listed, procedural improvements can be made
to resolve or minimize the complications. However, the problem of comparing
dry fly ash size concentrations to wet fly ash size concentrations requires
further analysis. Demonstration of the anomalous effects attributable to this
dry/wet phenomenon are shown by the hypothetical diagrams in Figure 7.
Pressure Drop
Figures 8 and 9 compare experimental and predicted pressure drops for the
6 cm venturi. MSU data show excellent correlation, whereas Ames data show the
model slightly overpredicts the pressure drop. However, the model overpredicts
pressure drop by about 100 percent for the 3.5 cm venturi (Table 3). This
reiterates the need to completely account for scrubber geometry, throat size
and wall effects in pilot scale Venturis.
The above predictions for fractional collection efficiency and pressure
drop assume instantaneous quenching of flue gas to outlet1 conditions upon
contact with scrubber water. The predictions by quench-corrected modeling
give higher penetration in small particle range and lower penetration in large
particle range (the difference being less than 10 percent for each particle
size, and about 30 percent less pressure drop for tested scrubber conditions).
Scrubber Influent Characteristics
The fractional collection in a venturi scrubber is a function of particle
diameter, and hence overall penetration is a strong function of inlet particle
size distribution. The average inlet particle size distributions are>plotted
in Figure 10 with fuel type and slipstream location as parameters. The overall
particle concentration for each case is also tabulated.
Particular attention should be drawn to the comparison of these size
curves in the fine particle range. The apparently small divergence of the
three size curves below 2 (Jm corresponds with substantial differences in
outlet loading. The Ames case in which coal plus 20 percent RDF were fired
shows the highest concentration of fine particulate, whereas the MSU case
offers the lowest concentration.
Effluent concentrations with operating pressure, drop for the three fuel
cases are presented in Figure 1. Comparison of .the two extreme cases in fine
particle concentration show that pressure drop requirements can vary from
576
-------
• 25 to 35 cm at the NSPS level of 43 ng/J, and
• 40 to 140 cm at the NSPS level of 13 ng/J
These dramatic differences in pressure drop were generated by the model, and
were supported by the empirical particle size and concentration results. The
cost impact of these results will be discussed later.
Effect of L/G Ratio
At MSU, scrubber tests were conducted for two L/G ratios (2 and 4 1/m3)
to study their effect. Figure 11 presents the data and model predictions.
The model shows that a L/G ratio of 4 1/m3 gives inferior scrubber performance.
The data do not show an equally dramatic difference, but they do show qualitative
agreement. Calvert, et al. have shown that the optimum L/G range is 1-2 1/m3,
which supports these results.5
Scrubber Performance as a Secondary Device
In Ames, the scrubber was also tested as a secondary device slipstreaming
downstream of a full scale ESP. Figure 12 shows data and model predictions.
The results are fairly similar to the case in which the scrubber operates
upstream of the ESP. These results, along with Reference 4, indicate that
particle collection by a venturi scrubber is not affected by an upstream ESP.
Cost Analysis
The cost analysis objective was to obtain an estimate of scrubbing costs
in the NSPS range. The analysis is based on the following factors:
The analysis is based on the following factors:
1. Emission source is 350 MW PC boiler.
2. Flue gas flow rate is 130 acm/min per MW at 177°C.
3. Flue gas is treated in three parallel modular venturi scrubbers.
4. Sludge treatment involves clarification, filtration and land-filling.
Capital, operating and maintenance costs for three scrubber systems
designed to operate at 25.4, 76.2, and 127 cm (10, 30, 50 in.) pressure drop,
respectively, are summarized in Table 4. The capital costs have been annual-
ized, assuming an equipment life of 10 years and an annual discount rate of
8 percent. Annualized capital costs are added to annual 0 & M costs to obtain
scrubbing cost per kW-h energy. Scrubbing costs in mils/kW-h are plotted
against scrubber pressure drop in Figure 13. This figure in conjunction with
Figure 1 gives scrubbing costs as a function of emission level for each fuel
type, as plotted in Figure 14.
Scrubber costs for various emission levels are shown in Figure 14. This
figure shows that for NSPS, 43 ng/J (0.1 Ib/million Btu) scrubbing costs are
577
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between 2.6 to 3.1 mils/kW-h. The costs increase slightly to 3.1 to
4.1 mils/kW-h for emission level 21.5 ng/J (0.05 Ib/million Btu). Between
21.5 and 13 ng/J 0.03 Ib/million Btu) costs increase exponentially, resulting
in a 6.4 to 9.2 mils/kW-h cost estimate for the 13 ng/J NSPS level.
The range of costs associated with the above emission levels reflect the
cost impact of the range of fly ash characteristics encountered in this study.
The cost range for the three levels increases for decreasing levels because of
the exponential nature of the cost/performance relationship. As evidenced by
this cost range, scrubber performance and cost become specific and sensitive
to boiler/fuel types.
From this performance/cost analysis, the following conclusions can be
drawn:
• Venturi scrubbing can be considered a competitive control option for
an emission level range of 21.5 to 43 ng/J for particulate and
gaseous control.
• For the emission range below 21.5 ng/J, venturi scrubbing costs rise
dramatically, indicating scrubbing becomes less cost-attractive in
this range.
® As NSPS levels become stricter, selections of coal/boiler types
become increasingly cost sensitive considerations for venturi scrubbing.
REFERENCES
1. Lawless, Phil A. Analysis of Cascade Impactor Data for Calculating
Particle Penetration. EPA - 600/7-78-189, U. S. Environmental Protection
Agency, Washington, DC, September 1978. 39 p.
2. Yung, S. C. , S. Calvert, and H. F. Barbarika. Venturi Scrubber Performance
Model. EPA - 600/2-77-172, Research Triangle Park, NC, August 1977. 197
P-
3. Ramsey, G. H., L. E. Sparks, and B. E. Daniel. Experimental Study of
Particle Collection by a Venturi Scrubber Downstream from an Electro-
static Precipitator. In: Symposium on the Transfer and Utilization of
Particulate Control Technology: Volume 3. Scrubbers, Advanced Technology,
and HTP Applications. EPA - 600/7-79-044c, U. S. Environmental Protection
Agency, Washington, DC, February 1979. p. 161-177.
4. McCain, Joseph D. CEA Variable - Throat Venturi Scrubber Evaluation.
EPA - 600/7-78-094, U. S. Environmental Protection Agency, Washington,
DC, June 1978. 75 p.
5. Yung, S., H. Barbarika, S. Calvert, and L. Sparks. Venturi Scrubber
Design Model. In: Symposium on the Transfer and Utilization of Particulate
Control Technology: Volume 3. Scrubbers, Advanced Technology, and HTP
Applications. EPA - 600/7-79-044c, U. S. Environmental Protection Agency,
Washington, DC, February 1979. p. 149-159.
578
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Acknowledgements
This program was sponsored by the Utilities and Industrial Power Division,
Industrial Environmental Research Laboratory, U.S. Environmental Protection
Agency (UIPD/IERL/EPA), Research Triangle Park, North Carolina.
The authors express sincere appreciation to the following individuals
for their involvement with and contributions toward this program:
• Dale Harmon, Les Sparks, and James Turner of IERL/EPA, Research
Triangle Park, North Carolina.
• Robert Olexsey of IERL/EPA, Cincinnati, Ohio.
• Joe Kavanaugh of Michigan State University Power Plant, East
Lansing, Michigan.
• Merlin Hove of Ames Power Plant, Ames, Iowa.
• Fred Hall, John Bruck, and Diane Albrinck of PEDCo Environmental,
Inc., Cincinnati, Ohio.
Mailing address: Route 1, Box 423, Morrisville, North Carolina 27560
579
-------
Table 1 SCRUBBER TEST CONDITIONS AND OPERATING PARAMETERS
1.
2.
3.
4.
5.
6.
7.
8.
9-
10.
Parameter
Fuels Tested
Mode
Venturis Tested
L/G Ratio
Pressure Drops
3.5 cm Throat
(L/G = 2 1/m3)
6.0 cm Throat
(L/G = 4 1/m3)
6.0 cm Throat
(L/G = 2 1/m3)
Gas Flow Rate
Acm/m (acfm)
Water Flow Rate
1/m (GPM)
Throat Velocity
m/sec (ft/sec)
Temperature before
venturi (Inlet) °C
Temperature before
Mist - Eliminator
(Outlet) °C
MSU
Coal
As primary device
3.5 and 6 cm
2 and 4 1/m3
(15 to 30 gal/1,000 ft3)
cm of W.C. (in. of W.C.)
101.6, 127
(40, 50)
25.4 to 127
(10 - 50)
20.3 to 76.2
(8 - 30)
8.5 - 10.8
(301 - 380)
15.9 - 30.2
(4.2 - 8.0)
43.8 - 157.2
(144 - 516.0)
131° - 182°
90° - 139°
Ames
Coal only and coal +
20 percent RDF
As primary and
secondary device
6 cm
2 1/m3
(15 gal/1,000 ft3)
cm of W.C. (in. of W.C.)
25.4 to 76.2
(10 - 30)
7.22 - 15.9
(255 - 560)
12.5 - 30.2
(3.3 - 8.0)
42.6 - 93.6
(140 - 307.0)
149° - 168°
103° - 156°
580
-------
C71
CO
Table 2 SCRUBBER PRESSURE DROP AND COST REQUIREMENTS
AT THREE PERFORMANCE LEVELS
Performance
Level
SNO
1.
2.
3.
4.
5.
6
43 nanograms/ joule
Scrubber AP Scrubbing Cost
Parameter cm W.C. mils/kW-h
Ames-RDF-Data
Ames-RDF-Model
Ames -Coal-Data
Ames -Coal-Model
MSU-Coal-Data
MSU-Coai -Model
20.3
35.6
7.62
25.4
5.08
15.?
2.76
3.12
2.52
2.88
2.50
2.64
21 5 nanograms/ joule
k. ibbet AP Scrubbing Cost
cm W.C. .. mils/kW-h
35.0
67.0
20.0
50.0
18.0
37.0
3.1
4.06
2.7
3.48
2.7
3.16
13 nanograms/ joule
Scrubber AP Scrubbing Cost
cm W.C. mils/kW-h
114.3
152.4
53.3
135.0
30.48
109.2
6.7
9.2
3.58
8.16
3.04
6.4
-------
Table 3 COMPARISON OF EXPERIMENTAL AND PREDICTED
PRESSURE DROP (MSU)
3.5 cm Throat
Test ID
Al
A2
A3
A4
A5
Bl
B2
B3
B4
AP - Experimental cm W.C.
101.6
101.6
101.6
101.6
101.6
127.0
127.0
127.0
127.0
AP - Predicted cm W.C.
173
185
185
226
225
253
253
243
249
582
-------
Table 4 SUMMARY OF COSTS
All Costs in December 1979 dollars
SNO
1.
2.
Scrubber
Scrubber
Parameter
pressure drop
and auxiliary
cm W.C.
equip-
Case A
25.4
$
Case B
76.2
$
Case C
127
$
ment capital cost on turnkey
basis. (excluding sludge
treatment plant) 6,738,800 12,355,500 18,579,100
3. Operating and maintenance
costs. (per annum) 2,081,800 3,453,800 5,352,700
4. Capital cost of sludge
disposal system. 6,443,000 6,443,000 6,443,000
5. Operating cost of sludge
disposal system, (per annum) 4,145,000 4,145,000 4,145,000
6. Total capital costs (2 + 4) 13,182,000 18,799,000 25,022,000
7. Total operating and maintenance
costs, (per annum) (3 + 5) 6,227,000 7,599,000 9,497,700
8. Uniform annual equivalent of
capital cost at 8 percent dis-
count and 10 years equipment
life (Ref. 4, page 4-89 and
Table A-8) 1,965,000 2,801,000 3,729,000
9. Uniform annual equivalent of
capital cost. (mils/kW-h) 0.67 0.95 1.27
10. 0 & M costs (mils/kW-h) 2.11 2.58 3.23
11. Scrubbing costs (mils/kW-h)
(9 + 10) 2.88 3.53 4.5
percent of 4 C/kW-h energy
cost 7.2 8.8 11.25
583
-------
1000 i—
MODEL
DATA
MODEL
DATA
MODEL
•— DATA
COAL + 20Z RDF, AMES
COAL, AMFS
COAL, MSU
6.0 cm THROAT
11
10
~JO 75100 115 ISO I7i l°
SCRUBOER PRESSURE DROP, cm W.C.
Figure 1
Comparison of predicted scrubber effluent
particulate concentration with data.
o
o
o
DATA dP 25'4 CI"
P 76.2 on
6.0 cm THROAT ,
L/G = 2 liters/mj
COAL, AMES
_L
4 a 10 1 4 • 10 3 4 • 10*
PARTICLE AERODYNAMIC DIAMETER, MICRONS
Figure 2
Comparison of predicted fractional pene-
trations with data for pulverized coal
at Ames.
-------
10
1O
•
tj
oc
o,£
OOUJ
01°-
2 -
10'
10*
J L.
--- DATA
--- MODEL
.......... DATA
* n o c A
AP 25.4 cm
A0 7, , „„,
AP 76"2 cm
6.0 cm VENTURI .,
= 2 Hters/mJ
COAL + 20% RDF. AMES
J L.
J L
• 10*
MODEL
DATA
MODEL
DATA
6.0 cm VENTURI ,
L/G » 2 Uters/m
COAL, AMES
SECONDARY DEVICE
Lf)
o
o
o
25.4 cm
76.2 cm
10
4 • 10 1 4
PARTICLE AERODYNAMIC DIAMATER, MICRONS
F i g u re 3
Lui,1(jdr-iiOn of predicted fractional pene-
trations with data for pulverized coal
plus 20% RDF at Ames.
no
! 4 * 10" 2 4 (10* 2 4
PARTICLE AERODYNAMIC DIAMETER, MICRONS
Figure 4
comparison of predicted fractional pene-
trations with data for pulverized coal
at Ames, scrubber operating as secondary
device downstream of full scale ESP.
»icr
-------
o
o
o
I
6.0 cm VENTURI m
6.0 cm VENTURI
cm VENTURI '
COAL, HSU
L/G = 2 liters/m
17.8 cm
76.2 cm
127.0 cm
3
6.0 cm VENTURI
3.5 cm VENTURI
2 4 » W 2 4 • 10* 2
PARTICLE AERODYNAMIC DIAMETER, MICRONS
Figjre 5
Comparison of predicted fractional pene-
trations with data for pulverized coal at
Michigan State University.
4 8 10" 2 4 » 10* 2
PARTICLE AERODYNAMIC DIAMETER, MICRONS
Figure 6
Comparison of predicted fractional pene-
trations with data for pulverized coal at
Michigan State University.
-------
r-.
O
o
O
I
-------
00
o
o
o
I
Figure 9
25 SO 75 WO 125 150
EXPERIMENTAL PRESSURE DROP, cm W.C.
5
-^
f
13
o
10
OVERALL INLET LOADINGS
nm/DNCM
PRIMARY DEVICE
COAL + 20t RDF. AMES 8.38
COAL. AMES 6.11
COAL. MSU 4,65
SECONDARY DEVICE
COAL + 20% RDF. AMES 0.46
COAL. AMES 0.318
_L
10
• 10 3 « • 10 »
PARTICLE AERODYNAMIC DIAMETER. MICRONS
* 10
Comparison of predicted and experimental
scrubber pressure drop at Ames.
Figure 10 Average inlet particle size distributions
and overall loadings.
-------
too
•
JO
0 •
CJT—
-rir
DATA
L/G - 4 liters/,
L/G =2 liters/.3
6.0 cm THROAT
COAL, HSU
-is-
75
SCRUBBER PRESSURE DROP, cm M.C.
Figure 11 Effect of L/G ratio on scrubber per-
formance.
too
•
£
g
5 10
l/J
a:
cr>
0
O
O
-MODEL
-DATA
COAL * 201 RDF. AMES
AVERAGE INLET CONCENTRATION
-------
10
10
_L
25
20
-E
3:
15
o
ta
10
Figure 13
50 100 150
SCRUBBER PRESSURE DROP, cm W.C.
Scrubbing cost per kW-h as a function
of pressure drop.
8
t/i
o
CD
*T
h—t
02 4
cc
=>
ct:
DATA
•MODELCOAL AMES
DATA
DATAL
COAL, MSU
13 NG/J 21.5 NG/J
—U J L_
43 NG/J
i I
10 20 30 40 50
NSPS NANOGRAMS/JOULE
25
o
o
o
20
CD
LU
z:
LiJ
15 U_
o
H;
^1_
LU
OL
UJ
Q-
f\
(—
10 o
o
CO
cc
a:
60
Figure 14 Scrubbing cost per kW-h as a function
of NSPS.
-------
THE RESULTS OF A TWO-STAGE SCRUBBER/
CHARGED PARTICULATE SEPARATOR
PILOT PROGRAM
By:
J. R. Martin
K. W. Malki
N. Graves
Combustion Engineering, Inc.
Birmingham, Alabama 35223
ABSTRACT
Until recently, the two-stage wet scrubbing system (a venturi followed by
an S02 absorber) has been successful in meeting the old EPA particulate matter
and S02 emission levels. However, the two-stage scrubber may have limited
application because of the power required to meet the new EPA particulate emis-
sion standards.
With this in mind, Combustion Engineering developed a new wet scrubbing
concept: a two-stage scrubber that incorporates a charged.particulate separator
(wet precipitator).
To demonstrate performance and obtain design data, a test program was con-
ducted at a Midwestern utility.
This paper presents the test results, a conceptual design for a full-size
unit, and an economic evaluation that will show the potential for this unique
system to meet the new EPA requirements.
591
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THE RESULTS OF A TWO-STAGE SCRUBBER/
CHARGED PARTICULATE SEPA.RATOR
PILOT PROGRAM
INTRODUCTION
In the past decade, the EPA standards for emissions from stationary sources
have gradually become more stringent. To meet today's standards, Combustion
Engineering, Inc. developed an improved scrubbing concept, the Two Stage Plus.
The Two Stage Plus, which is a low pressure drop rod scrubber (venturi), follow-
ed by a spray tower absorber and a charged particulate separator, is capable of
meeting the new EPA requirements without restriction on the quality of coal.
Additionally, the Two Stage Plus is economically attractive compared to a
conventional dry collector followed by a wet 862 absorber. Its attractiveness
is demonstrated by its low capital and operating costs over a wide range of
sulfur and ash contents in the coal.
Compared to the dry scrubbing concept, the "Two Stage Plus" is economically
favorable with Western coals (which produce alkaline flyash), even with sulfur
content in the coal as low as 0.7%.
BACKGROUND
Prior to June 1979, the EPA emission standards for power plants were 0.1 lb/
106 Btu for particulate and 1.2 lb/106 Btu for SC^.^1) To meet these standards,
Combustion Engineering offered two concepts for particulate and S02 removal: a
two-stage scrubber system and an electrostatic precipitator followed by an S02
absorber. The two stage system is comprised of a rod scrubber (venturi) followed
by a spray tower absorber with an integral mist eliminator and reheater. The rod
scrubber is designed to remove mostly particulate and a fraction of S02> whereas
the spray tower is designed to remove mostly SOo and a small fraction of partic-
ulate.
For most coals, particulate emission from the two stage scrubbing and the
ESP/S02 absorber has generally been below the EPA requirement. The particulate
emission level achieved was less than 0.08 lb/10" Btu at Northern States Power's
Sherburne County Units 1 and 2 (two-stage system), less than 0.04 Ib/lO^ Btu at
The Kansas Power and Light Company's Lawrence 4 (two-stage system), and less
than 0.04 lb/10^ Btu at Louisville Gas and Electric Company's Cane Run 5 (ESP
followed by an S02 absorber). See Kruger (1977),2 Green and Martin (1977),3
Green et. al. (1978),4 and Van Ness et. al. (1979).5
In June 1979, EPA issued new emission standards. The proposed stand-
ards will limit the emission of particulate matter from steam generators that
fire more than 250 x 10^ Btu/hr (73 megawatts) of fossil fuel. The partic-
ulate emissions are limited to 13 nanograms/joule heat input (0.03 Ib/lO^ Btu)
and must be reduced 99% from uncontrolled emission levels. In the case of S02»
the following three conditions must be satisfied:
592
-------
a) SCL emission must not exceed 520 ng/J (1.2 lb/10 Btu).
b) SO must be reduced 90% from uncontrolled emission levels, unless
c) tbe emission level is 250 ng/J (0.6 lb/10 Btu) or less, in which case a,
sliding scale of removal efficiency applies down to a level of 0.2 lb/10
Btu, at which level and below a 70% minimum removal is required.
Presently, C-E offers several design concepts that have the capability of
achieving the new EPA S0_ and particulate emission requirements. These con-
cepts are:
The Two Stage Wet Scrubbing
This concept can achieve EPA's new particulate requirements; however, it
requires a relatively high pressure drop depending on the flyash characteristics
and, therefore, its effectiveness is limited to certain coals.
ESP/Single Stage Wet Scrubber
With proper design of the ESP, this system can meet the EPA particulate
emission requirements. This system may be costly, depending on the flyash
characteristics, especially if requiring a precipitator SCA of greater than
500 to 600.
Dry Absorber Particulate Collector
This concept can achieve the EPA particulate requirement, but has not
been demonstrated in full size and may not be practical with high sulfur coals.
THE TWO STAGE PLUS CONCEPT
In an effort to meet the EPA emission requirement without restriction on
the quality of coal, C-E has developed a modified two-stage scrubber, Two
Stage Plus. The Two Stage Plus is comprised of a low pressure drop rod scrub-
ber (venturi) followed by a spray tower and a "Charged Particulate Separator"
(CFS) based on the concept of wet precipitation. The offering of this con-
cept is predicated on C-E's long and successful experience with two-stage
scrubbing and wet precipitators. Two-stage scrubbing using the rod design has
demonstrated success in terms of performance and availability. The rod scrub-
ber has been used in AQCS installations totalling over 2000 megawatts of gener-
ating capacity. The two-stage system at i\TSP's Sherburne County Units 1 and 2,
representing 1520 MW, has been in operation for 3% years. Component development
and material evaluation during this period has resulted in design improvements
to the rod scrubber.
The charged particulate separator (GPS) has been designed as a wet
electrostatic precipitator, which was demonstrated on a full size unit in
Bressoux, Belgium over 16 years ago. The wet ESP was installed behind a wet
filter. The wet filter is similar to C-E's rod scrubber except that the flow is
horizontal. The design fuel for this application was as follows:
593
-------
Sulfur 0.85%
Moisture 14.0
Ash 29.0
Volatiles 13.0
Carbon 44.0
Tests conducted in June, 1976 (13 years after start-up) by an independent
Belgium laboratory showed that the particulate collection efficiency of the
wet precipitator was 90%. The design gas volume for the wet precipitator is
100 cubic meters per second (211, 765 ACFM). The water spray system is designed
for two level application. Below the precipitator, water is sprayed against
the gas flow at a rate of 20 cubic meters per hour (80 GPM). Above the precip-
itator the spray was intermittent at the rate of 60 cubic meters per hour (264
GPM). During cleaning, the precipitator voltage level is reduced to avoid heavy
sparking and power arcing.
The shell and ductwork are rubber-coated mild steel and internal parts are
stainless steel. There has been no significant corrosion of the precipitator
during 16 years of operation.
The use of the wet electrostatic precipitator preceded by an S0« absorber
for particulate removal, as opposed to a conventional dry ESP was necessitated
at that time by the stringent Belgium emission requirements. These require-
ments limited particulate and SO,., emission to very low levels. Since then,
however, the European SO,, emission limits have been relaxed precluding the need
for the SO,., absorber. As a result, the S0« absorber/wet ESP became economic-
ally less attractive than a dry ESP for particulate removal only and is no
longer a practical design in Europe.
TWO STAGE PLUS BENEFITS
To demonstrate the benefits of the Two Stage Plus, it will be compared
to several other flue gas desulfurization techniques. These techniques include:
the two-stage scrubber (venturi for particulate collection followed by an SO
absorber), a cold ESP for particulate collection followed by an S0» absorber,
and finally the dry SO absorber followed by a particulate collector.
The charged particulate separator in the Two Stage Plus is much smaller
that a conventional cold ESP because:
1) To meet the EPA limits the CPS requires a low particulate removal effic-
iency compared with the ESP. This is due to precollection in the rod scrub-
ber, which causes the particulate at the CPS inlet to become small compared
with the ESP inlet, 0.10 vs. 7 lb/lQ6 Btu.
2) The gas treated in the CPS is saturated and is relatively cold (130 F) ,
thereby resulting in conditions favorable for particulate collection. The
gas treated in the ESP on the other hand is drier and hotter (300 F). Both
conditions tend to increase the resistivity of the ash reducing the ability
of the ESP to collect ash.
594
-------
3) Because of the lower gas temperature, the volumetric flow through the CPS
is smaller than flow through the ESP.
4) Re-entrainment of the ash deposit is usually a major consideration in
choosing the right gas velocity for an electrostatic precipitator. Since
the charged particulate separator (CPS) operates in a wet environment, the
deposit on the collecting electrodes is wet, and therefore, more difficult
to re-entrain. As a result, it is usually safe to operate the CPS at
gas velocities higher than usually required in a conventional ESP.
Calcium compounds are commonly present in varying concentrations and
degrees of alkalinity in the flyash. If an ESP is used ahead of an 862
absorber, the flyash with its calcium is collected and sent to disposal. If
allowed in the scrubber, these calcium compounds can be very useful in absorb-
ing SC>2' In the Two Stage Plus, all the ash generated by the furnace can be
used in absorbing S02- Thus the addition of supplementary limestone is mini-
mized, resulting in significant operating cost savings.
In a conventional two-stage scrubber, the pressure loss across the venturi,
is usually set at high levels (15-20 in. w.g.) to achieve high particulate re-
moval efficiency. In the Two Stage Plus, where the venturi acts only as a
precollecting device, the pressure loss Is much lower (3-5 in. w.g.). As a
result, the operating cost of the Two Stage Plus will be reduced significantly.
The charged particulate separator has been successfully used in various
applications as a high efficiency mist eliminator. The mechanism for removing
mist in the CPS is similar to that for dust in an electrostatic precipitator.
With its mist removal capability, the CPS precludes the need for a fine mist
eliminator, which is usually required in conventional S02 scrubbers.
The Two Stage Plus collects particulate and SC^ in one system. This is
because the particulate collection stage and the SC^ absorber stage both dis-
charge into a common disposal system. In contrast, systems that require dry
precollectors such as an ESP followed by a wet scrubber require two waste
disposal systems. The single disposal system is simpler than the double
disposal system since it includes fewer components to operate and ruaintain.
Unlike some concepts, such as dry scrubbing, where SC>2 removal is
limited at high sulfur levels, the two stage plus is capable of removing SCU
to any required emission level for any sulfur level in the coal. More impor-
tantly, the additive consumption is only slightly above the theoretical require-
ment. The additive consumption for the dry absorber on the other hand is
significantly higher than the theoretical requirement, especially with high
sulfur conditions.
PILOT PLANT TEST PROGRAM
Pilot Plant Description
To demonstrate the capability of the Two Stage Plus, a pilot plant was
installed at Northern States Power Company, Sherburne County Plant. The purpose
of the pilot program is:
595
-------
1) To demonstrate that a particulate emission level of (13 ng/J) 0.03 lb/10°
Btu can be achieved.
2) To determine a method of maintaining the CPS in a clean state that will not
hinder performance.
3) To develop design criteria for a full-size system.
The 10,000 cfm pilot plant was installed at the 730-MW NSP's Sherburne
County Unit 1. The fuel fired was Sarpy Creek coal. The coal and ash analyses
are shown in Tables 1 and 2. The air quality control system at Unit 1 consists
of 11 (+1 spare) scrubber modules. Each module consists of a rod scrubber
(venturi) and a marble bed, a mist eliminator and a reheater.
TABLE 1 TWO-STAGE PLUS PILOT PLANT
COAL PROXIMATE ANALYSIS
Mean
Moisture 23.9%
Ash 10.3%
Volatile Matter 27.7%
Carbon 37.6%
Sulfur 1.0%
Heating value 8300 Btu/lb.
TABLE 2 TWO-STAGE PLUS PILOT PLANT
FLYASH ANALYSIS
Mean % by wt
P205 OT'5
Si02 35.2
Fe203 6.9
A1203 17.2
Ti02 0.7
CaO 17.4
MgO 4.3
Na20 1.50
K20 0.4
S03 15.3
Undetermined 0.6
Total 100.0
596
-------
The marble bed of one module was converted to a spray tower several years
ago for test purposes. The Two Stage Plus pilot plant was installed on the
module with the spray tower (Figure 1). Flue gas was extracted from the outlet
of the two stage scrubber via a duct, and treated in two horizontal CPS's in
series. To insure that the slip stream was representative of the gas in the
scrubber, the duct extended about 6 ft. into the 18 x 26 ft. scrubber, and
pointed in a direction opposite to the gas flow. Additionally, to prevent
condensation in the CPS, the inlet and outlet ducts were insulated. The amount
of gas treated varied between 4800 to 8000 ACFM. Initially the gas was extract-
ed downstream of the mist eliminator. Later tests were conducted with the gas
extracted from a point ahead of the demister.
Phase 1 tests were conducted on a two field CPS that contained five gas
lanes on eleven-inch centers. The collecting plate height was four feet and
each field has 38 inches of treatment length. The CPS was equipped with a
flat bottom and has a spray system for removing collected particles from the
discharge and collecting electrode surfaces. The location of the seven banks
of spray nozzles is shown in Figure 2.
Each electrical field was served by a separate transformer-rectifier set
with automatic voltage controls. The spray system was operated manually with
the effluent being drained back into the spray tower. Figures 3 and 4 show
equipment layout for the two-field CPS.
Figure 1 NSP Sherco 1
597
-------
SPRAY NOZZLE
Figure 2 Spray nozzle arrangement in CPS pilot
Phd j ? tests were conducted on a five field CPS. The field height,
number of gas lanes, and plate spacing were as described earlier. Treatment
length and total collecting surface were 2.5 times the values used for the two
field unit.
Upon leaving the CPS, the treated gas was exhausted back to the scrubber at
a location downstream of the mist eliminator.
Pilot Plant Results
A total of 35 tests were conducted as part of the test program. These tests
were designed to determine the particulate and S02 removal capability of Two Stage
Plus. Immediately following these tests, several extended tests were conducted to
determine the cleaning requirements of the CP'S and its performance as a function
of time.
Tables 3 and 4 summarize the test results of the program. The data reveals
that the Two Stage scrubber is capable of removing 96% of the particulate leav-
ing the boiler air heater outlet. This was achieved with a rod scrubber pressure
drop of 5 to 6 inches w.g., a total spray liquid-to-gas ratio of 27 gallons/1000
cfm, and an average inlet ^articulate loading of 2.5 gr/DSCF. To be successful
the CPS had to produce an emission level of 0.03 lb/10 Btu or less.
The phase 1 two-field CPS tests were performed in accordance with EPA
method 5 and were each three hours long. Test runs were made at these oper-
ating conditions:
598
-------
CPS
t
'FAN
Figure 3 CPS pilot plant
(1) CPS velocity: 4, 5 & 6.5 FPS
(2) Electrical Current Density: 100% and 50%
(3) With and without On-line washing.
The results of phase 1 are shown in Table 3. During Phase 1 the scrubber
aas extracted after the mist eliminator was varied. The results indicate that
the CPS was capable of achieving the 0.03 lb/106 Btu (0.013 gr/DSCF) at a velo-
city of up to 4.5 ft/sec.
The results of these tests also indicated no difference in performance
with or without washing. Inspection of the CPS upon completion of a three-
hour test run revealed expected wetness of collecting plates and a measurable
quantity of water and dust in the hopper. The majority of tests were there-
fore conducted without use of washing.
During the second phase of the program, the extraction point was relocated
upstream of the mist eliminator, thus resulting in a higher particular loading
due to increased mist (slurry) carryover, and a five - instead of two - field
CPS was used. The results of changing the extraction point reveals that the mist
599
-------
CHARGED
PARTICULATE
SEPARATOR
A A A A
A A A
Figure 4 CPS pilot plant
eliminator is capable of removing about 60% of the solids leaving the spray
tower (0.095 versus 0.035 gr/DSCF).
The phase 2 tests were conducted on a five-field CPS and the results are
listed in Table 3. The data is very consistent and the 0.013 gr/DSCF (0.03
lb/106 Btu) desired emission was achieved at velocities in excess of 6.5 ft/sec,
Detailed results of 20 short-term test with five fields are listed in Table 4.
The emission particulate loadings were plotted as a function of treatment
time in the CPS. The graph is shown in Figure 5. The results show that 2.4
seconds of treatment time is required to meet the desired .013 gr/DSCF.
1.
2.
The following conclusions can be made from the pilot results:
On-line washing made marginal improvement on the CPS performance, when
compared with no washing.
The effect of current density in the five-field CPS using high velo-
cities was marginal in the 50 to 100% range.
600
-------
TABLE 3 TWO STAGE PLUS CHARGED PARTICULATE SEPARATOR TEST RESULTS
CTi
O
Scrubber
Extraction
Location
Downstream B.E.S.
Downstream B.E.S.
Downstream B.E.S.
Upstream B.E.S.
Upstream B.E.S.
Upstream B.E.S.
Upstream B.E.S.
Rod P Treatment Velocity
(in. w.g.) Time (sec) (EPS)
6" 1.7 3.9
6" 1.3 5.4
6" 1.1 6.15
6" 1.1 6.10
6" 3.2 5.5
6" 2.7 6.5
6" 2.7 6.4
# of Current
Fields Density %
Phase I
2 100
2 100
2 100
Phase II
2 100
5 100
5 100
5 100
Wash
On/Off
Off
Off
Off
Off
Off
Off
On
Inlet Interim
(qr/DSCF) (qr/DSCF)
2.5 .03
2.5 .026
2.5 .045
2.5 .093
2.5 .089
2.5 .100
2.5 . 07 9
Outlet
(gr/DSCF)
.007
.012
.012
.027
.008
.009
.009
-------
TABLE 4 ?[LOT TESTS RESULTS FOR TWO STAGE PLUS CHARGED PARTLCULATE SEPARATOR
jummary ofJ5_Fie_ld__Test Results
Velocity
FPS
6.42
6.40
6.50
6.50
6.36
6.27
6.4
6.34
6.13
6.01
6.63
6.62
6.33
6.37
6.38*
5.33
5.37
5.50
5.45
5.32
5.30
5.38*
* Average Values
Dust
Inlet to CPS
.0550
.0972
.0834
.1213
.0908
.1389
.1565
.1048
.1032
.0554
.0610
.1443
.1026
.0686
.0998*
.1036
.0571
.0830
.1117
.2622
.0273
.1075*
Load-GR/DSCF
Outlet from CPS
.0061
.0069
.0088
.0075
.0088
.0064
.0061
.0110
.0100
.0084
.0130
.0104
.0085
.0107
.0088*
.0061
.0075
.0077
.0116
.0067
.0063
.0077*
602
-------
0.03 -
0.02
0.01
I I i
1 2 3
TREATMENT TIME-SECONDS
Figure 5 Pilot tests on GPS performance vs. treatment time
3. The required CPS treatment time to achieve 0.013 gr/DSCF (0.03 lb/106 Btu)
is 2.4 seconds.
4. During the test program S02 levels were measured entering and leaving the
Two Stage Plus. The results show a removal of 75% with an inlet concen-
tration of 700 ppm. This is comparable with two stage scrubbing, indicat-
ing the CPS has no significant effect on S02 removal.
To determine any degradation in performance, a 140-hour test run on the
five-field pilot CPS was conducted. Emission was checked periodically during
the week using EPA method 5. A portable opacity monitor was installed down-
stream of the CPS to yield a continuous surveillance of the operation. Figure 6
is a bar chart indicating test and cleaning cycles for this long-term perform-
ance test. Four tests conducted during this period showed consistent CPS per-
formance. The outlet particulate loading did not exceed 0.01 gr/DSCF. A
minimal amount of washing (six) was required during this period with each cycle
lasting 10 minutes only.
FLUSH PERIODS
5:00 PM 8:00 AM
11:00 AM
4:30 PM
4:30 PM
6:00 AM
TUES
WED
THURS
FRI
SAT
SUN
Figure 6 CPS pilot long-term performance test
603
-------
CONCEPTUAL DESIGN
Design Criteria
The full size unit selected for the conceptual design application is a
500-MW unit. The fuel fired is a Western coal with about 8000 Btu/lb heating
value, and two levels of sulfur, 0.54 and 2.3%. The design requires 70 and
90% S02 removal for respective sulfur levels and an outlet particulate emission
of 0.03 lb/106 Btu (0.013 gr/DSCF).
The rod scrubber/spray tower design selected for this application requires
a liquid-to-gas ratio of 85 gpm/1000 cfm. The pressure drop across the rod
scrubber has been set at 4 in. w.g. The CPS gas treatment time used in this
design assumes 3.13 seconds, which is 30% higher than the pilot value of 2.4
seconds.
An intermittent wash system to operate off or on-line is required to keep
the CPS clean. The wash system frequency of operation will be in the order of
once per day.
The material selection for the Two Stage Plus is based on C-E's experience
with two stage scrubbers, charged particulate separators, and the pilot plant
at Sherburne County. Material evaluation over the years has led to improve-
ments, especially in the high wear components, such as rod scrubbers, piping,
and pumps. In addition, the CPS experience in Belgium provided telling testimony
on the use of Type 316L stainless steel, where it has shown little wear in the
last 15 years. Type 316L ss Is the material for the scrubber shell and elec-
trodes, refractory the material for the rods, fiberglass for the piping, and
rubber lining for the pumps. For C-E experience with 316L ss in flue gas
scrubbers, see Lewis et. al. (1978).°
Description
The conceptual design is shown isometrically in Figure 7. The Two Stage
Plus consists of 5 modules including a spare. The gas flow entering each module
is approximately 450,000 cfm.
In the rod section, the vertical spacing between the rods is automatically
controlled to maintain 4 inches w.g. of pressure drop. The rod scrubber, not
only removes most of the particulate matter from the flue gas, but also a portion
of the S02 in the flue gas. A steam soot blower located in the inlet duct pre-
vents deposit from building on the wet/dry interface. The spray slurry in the
rod scrubber discharges into the reaction tank. Figure 8 shows a flow schematic
of the Two Stage Plus.
From the rod scrubber, the flue gas turns 180 degrees and enters the second
stage consisting of a spray tower. The spray tower is a low pressure drop SOo
absorber. In the spray tower the spray slurry is sprayed counter-current to the
gas. The spent spray tower slurry is also discharged into the reaction tank.
The flue gas then passes through a bulk entrainment separator (BES). The
BES consists of vanes mounted at 45-degree angles on 3-inch parallel spacing.
The BES is maintained in a clean state by intermittent washing with a fixed grid
arrangement.
-------
TWO STAGE
PLUS
Figure 7 Isometric cutaway of Two Stage Plus
605
-------
TO STACK
en
o
CTl
REHEATER::
CHARGED
PARTICIPATE
SEPARATOR
SEPARATOR WASH
0-E
ROD SPRAY
PUMP
REAC
TlOf
M
TANK
O
*
MIXER
«
i
c
— , L
ABSORBER
SPRAY PUMPS
TO POND
ABSORBER BLEED PUMPS
D
MIXER
ADDITIVE STORAGE
TANK
*- MAKE-UP WATER
Figure 8 Two Stage Plus flow schematic
-------
Upon leaving the BBS, the gas enters the charged particulate separator,
where liquid entrainment and particulate matter are further reduced. The GPS
is a vertical compartment containing a grid of electrical cells. These cells
are comprised of 316L stainless steel discharge and collecting electrodes.
To facilitate the particulate removal, the gas is allowed to travel at a reduced
velocity through the GPS. The collector plates will be cleaned periodically
using a fixed grid flush system.
The GPS is divided into two cells powered with a transformer rectifier.
Insulator compartments external to the CPS shell span two opposite sides of
the shell. The discharge electrode wire frames extend below the collecting
plates and are connected to give greater stability to the high voltage system.
Upon leaving the CPS, the gas temperature is increased by 30 F to
eliminate the plume and to bring the gas above its dewpoint.
The auxiliary equipment, which includes the reaction tank, bleed,
additive feed, and makeup water, will not be described in this paper. Instead,
the reader is referred to a paper presented by Martin (1977).6
Economic Evaluation
The capital and operating costs for the full scale Two Stage Plus are shown
in Table 5. Four cases were evaluated for two sulfur levels, 2.3 and 0.54%, with
and without taking credit for the alkalinity in the ash. These specific variables
were selected in order to facilitate comparison with competing concepts.
The capital costs were based on 1981 dollars (present worth) for 35 years.
The installed capital cost includes, the scrubbing system, steel, building,
electrical, controls, etc. The Two Stage Plus installed cost for a 500-MW unit
increases by 10% as the sulfur in the coal increases from 0.54% to 2.3%. This
is primarily due to the increase in pumping capacity. The presence of calcium
in the ash reduces the installed cost slightly primarily due to a reduction in
the additive subsystem.
The operating cost has been evaluated based on a 35 year life, load factor
of 75%, and present worth dollars. Unlike the installation cost the operating
cost is significantly higher for the higher sulfur coal. The cost is further
increased when the alkalinity in the ash is ignored.
The economic data for the Two Stage Plus design is of even more interest
when compared against other FGD concepts. Table 5 also shows a comparison of
the costs for four FGD concepts, 3 wet scrubbing and 1 dry scrubbing. The wet
scrubbers include the Two Stage Plus, the Two Stage, and the ESP/Spray Tower.
The dry scrubbing data is based on information presented by Basin Electric at
the EPA Scrubber Symposium in March 1979. For the high sulfur condition the
stoichiometric lime feed rate was assumed to be 160% based on S02 removal. The
manpower requirement was also adjusted to allow for the dry system.
In evaluating the four concepts, the following assumptions were made:
607
-------
TABLE 5 ECONOMIC EVALUATION WITH CREDIT FOR ALKALINITY IN FLYASH
BASIS: 500 MW UNIT
2.3% SULFUR IN COAL
TWO-STAGE
Cost*/Basis
$
Capital 39.0 X 106/Actual
Additive 24.7 x 106/95,200 tons/yr.
CaC03
cr, Power 51.3 X 106/22,000 KW
o
CO
Reheat 20.0 X 105/71.4 mm BTU/hr
Manpower 32.8 X 106/j° ^
Replacement 26.8 X 106/Actual
TWO-STAGE PLUS
Cost*/Basis
$
43.0 X 105/Actual
24.7 X 105/95,200 tons/yr.
CaC03
39.0 X 106/16,500 KW
20.0 X 106/71.4 mm BTU/hr
34 2 X 106/10 oper"
w.d. A lu /13 maint_
29.8 X 106/Actual
ESP/SPRAY TOWER DRY SCRUBBER/BAG FILTER
Cost*/Basis Cost*/Basis
60.0 X 106/Actual 50.0 X 106/Actual
47.0 X 106/181,000 tons/yr. 196.8 X 106/147,000 tons/hr
CaC03 CaO
44.0 X 106/19,000 KW 21.0 X 106/9,100 KW
20.0 X 106/71.4 rim BTU/hr O/-
•u ? x in6/10 oper- ?fi R x in6/10 °Per-
34'2 X 10 713 maint. 26'8 X 10 78 maint.
29.8 X 106/Actual 18.0 X 106/bag filter, atom-
bearings, etc.
Total
194.6 X 10U
196.7 X 10U
235.0 X 10
312.0 X 10
* Cost is based on 35 year life, 75% load factor, and 1981 worth, with commercial date set at 1981.
-------
TABLE 5 CONT'D ECONOMIC EVALUATION WITH NO CREDIT FOR ALKALINITY IN FLYASH
BASIS: 500 MW UNIT
2.3% SULFUR IN COAL
TWO
Cost*
Capital 40.0 X
Additive 47.0 X
Power 51.3 X
o Reheat 20.0 X
UD
Manpower 32.8 X
Replacement 26.8 X
10
10
10
70
10
10
STAGE
/Basi
$
TWO
STAGE PLUS
ESP/SPRAY TOWER
s Cost/Basis
J
6/Actual
6/18T
CaCO
6/22,
6/71.
6,10
712
,000 tons/yr.
3
000 KW
4 mm BTU/hr
rS.
6/Actual
44.0
47 X
39 X
20.0
34.2
29.8
X 106/Actual
106/181 ,000 tons/yr
CaC03
106/16,800 KW
X 106/71 .4 mm BTU/hr
v ,,,6,10 oper.
1 3 rnaint.
X 106/Actual
60
47
44
20.
34.
29.
DRY
Cost/Basis
X
X
X
0
2
8
10
10
10
X
X
X
5/Actual
6/181,000 tons/yr
CaC03
6/19,000 KW
106/71.4 mm BTU/hr
,~6,10 oper.
13 maint.
106/Actual
50 X
196. f
21.0
O/-
26.8
18.0
SCRUBBER/BAG FILTER
Cost/ Actual
S
106/ Actual
3 X 106/147,000 tons/yr
CaO
X 106/9,100 KW
X Io6/8°rna°in[:
X 106/bag filters, star
bearings, etc.
Total
217.9 X 10U
214.0 X 10C
235.0 X 10°
312.0 X 10
Cost is based on 35 year life, 751 load factor, and 1981 worth, with commercial date set at 1981.
-------
TABLE 5 CONT'I> ECONOMIC EVALUATION WITH CREDIT FOR ALKALINITY IN FLYASH
BASIS: 500 MW UNIT
0.54% SULFUR IN COAL
en
O
Capital
Additive
Power
Reheat
Manpower
Replacement
Total
TWO-STAGE
CostVBasis
34. OX 10/Actual
O/-
45.0 X 106/19,300 KW
20.0 X 10V71 .4 mm BTU/hr
32.8 X 10 /
&,10 oper.
12 maint.
26.8 X 10 /Actual
158.6 X 10
TWO-STAGE PLUS
CostVBasis
$
39.0 X 106/Actual
O/-
32.8 X 106/14,000 KW
20.0 X 106/71.4 mm BTU/hr
34.2 X 106/!°°P?!V
29.8 X 10°/Actual
155.8 X 10
ESP/SPRAY TOWER
CostVBasis
$
54.0 X 106/Actual
8.5 X 10"/42,500 tons/yr.
CaC00
37.8 X 10/16,200 KW
29.8 X 10u/Actual
184.3 X 10
DRY SCRUBBER/BAG FILTER
CostVBasts
50.0 X 10/Actual
5.8 X 10/25,800 tons/yr
CaO
20.0 X TOYS,700 KW
20.OX 10D/71.4 mm BTU/hr O/-
26.8 X
18.0 X 10 /bag filters, atomizers
bearings, etc.
141.9 X 10
Cost is based on 35 years life, 75% load factor, and 1981 worth, with commercial date set at 1981,
-------
TABLE 5 CONT'D ECONOMIC EVALUATION WITH NO CREDIT FOR ALKALINITY IN FLYASH
BASIS: 500 MW UNIT
.54% SULFUR IN COAL
Capital
Additive
Power
Reheat
Manpower
Replacement
Total
TWO-STAGE
Cost*/Basis
fi$
35.0 X 10 /Actual
8.50 X 10D/42,500 tons/yr
CaCO,
45 x 10°/19,300 KW
TWO-STAGE PLUS
CostVgasis
40.0 X 106/Actual
8.5 x 106/42,50Q tons/yr.
CaCO,,
32.8 X 10D/14,OOX) KW
ESP/SPRAY TOMER
CostVBasis
54.0 X 105/Actual
8.5 x 106/42,500 tons/yr
CaCO
3
37.8 X 10°/16,000
y m6/10 °Per-
X 10 712 maint.
26.8 X 10D/Actual
168.T X 10"
34.2 X 106/™ °P?r:
13 ma int.
29.8 X 10°/Actual
T65.3 X 10°
34.2 X 10°/10 oper.
13 maint.
29.8 X 105/Actual
184.3 X TOD
DRY SCRUBBER/BAG FILTER
Cost*/&asis
,- $
50.0 X 10 /Actual
26.8 X ](f/25,&CiO tons/yr.
CaO
20.0 X 10D/8,700 KW
20.0 X 10D/71.4 mm BTU/hr 20.0 X 10b/71.4 mm BTU/hr 20.0 X T0b/71,4 mm BTU/hr O/-
26.8 X
+
8 maint.
18.0 X 10D/bag filters, atomizers,
bearings, etc.
14T.9 x 106
* Cost is based on 35 year Tife, 75% load factor, and'1981 worth, with commercial date at 1981.
-------
1) Limestone stoichiometry for the wet scrubbers of 110% based on the SC^
removal.
2) Credit for calcium in the ash was taken only .for the wet concepts.
3) 75% load factor.
4) 35 year plant .life with 8% escalation and 9% discount rates. Start-up date
set at 1981.
5) Limestone cost as of 1981: $8.7/ton. Lime cost as of 1981: $45/ton.
6) Steam cost set at $2.0/106 Btu in 1981.
7) Power cost set at $-013/kWh (1981).
8) Operator cost/year = $50,000
The cost breakdown shows that additive feed, power and reheat are the
determining factors in evaluating the four concepts. As the sulfur in the coal
increases, the differential in power and reheat costs between the dry and the wet
concepts remains relatively constant, but the additive cost differential becomes
extremely high.
A plot of evaluated cost versus the % sulfur in the coal is shown in Figures
9 and 10. The graph shows that among the wet concepts the Two Stage Plus has
the least evaluated cost. When compared with dry scrubbing the Two Stage Plus is
slightly more costly at the 0.54% sulfur level, but at the 2.3% sulfur level,
the Two Stage Plus is significantly less. The Two Stage Plus appears to be
economical above 0.7% sulfur in the coal if credit for the alkalinity in the
flyash is considered, and above 0.8% if the ash alkalinity is ignored.
CONCLUSION
The Two Stage Plus is technically and economically viable as an SOo and
particulate control system. Its ability to meet the new EPA requirements can
be predicted safely.
In terms of cost, Two Stage Plus is the most economical of the majority
of the wet scrubbing concepts. When compared with the dry system, Two Stage
Plus is economical if the sulfur in the coal exceeds 0.8%. When the coal's ash
has high alkaline quantities, as do many western subituminous and lignite coals,
the breakpoint is even lower, i.e. (0.7% Sulfur).
For Western fuel-fired plants, with highly alkaline flyash that is
difficult to collect in precipitators, Two Stage Plus looks very promising.
ACKNOWLEDGMENT
Special appreciation is given for the assistance provided by Northern
States Power Company's management and plant personnel during the test program.
612
-------
300x 106
35 YEAR
EVALUATED
COST
200x10° -
140 x 10'
6
TWO STAGE PLUS
O ESP/SPRAY TOWER
ED DRY SCRUBBER/BAG HOUSE
TWO STAGE SCRUBBING
1.0
% SULFUR IN COAL
Figure 9 35-year evaluated cost as a function of sulfur in coal
with credit for alkalinity in flyash
613
-------
300x 106
35 YEAR
EVALUATED
COST
200x1P6
140x 10°
A TWO STAGE PLUS
O ESP/SPRAY TOWER
D DRY SCRUBBER/BAG HOUSE
• TWO STAGE SCRUBBING
0,54
1.0
% SULFUR INCOAL
2.0
2.3
Figure 10 35-year evaluated cost as a function of sulfur in coal
with no credit for flyash alkalinity
614
-------
REFERENCES
1. 36 Federal Register, page 24876, December 23, 1971.
2. Kruger, R. J. Experience with Limestone Scrubbing At Sherburne County
Generating Plant, Northern States Power Co., (Presented at EPA Symposium
on Flue Gas Desulfurization, Hollywood, Florida, November 1977).
3. Green, K. and Martin, J. R., Conversion of the Lawrence #4 Flue Gas
Desulfurization Systems. (Presented at EPA Symposium on Flue Gas Desulfur-
ization, Hollywood, Florida, November 1977).
4. Green, K., Conrad, L., Martin, J. R., and Kingston, W. H. Commitment to
Air Quality Control. In: Proceedings of the American Power Conference,
Haigh, B. (ed). Chicago, American Power Conference, 1978. p. 632-645
5. Van Ness, R. P., Kingston, W. H., and Borsare, D, C. Operation of C-E
Flue Gas Desulfurization System for High Sulfur Coal at Louisville Gas
& Electric Company, Cane Run #5. (Presented at American Power Conference,
Chicago, Illinois, April 23-25, 1979).
6. Kettner, D. C., Hickok, W. W., Martin, J. R., and Dutton, R. W. Design of
a Spray Tower Scrubber For Coal Creek Station. (Paper presented at PACHEC
'77 - The Second Pacific Area Chemical Engineering Conference, Denver, Col.,
August 28-31, 1977).
7. Lewis, E. C., Stengel, M. P., and Maurin, P. Gr Performance of Type 316L
Stainless Steel and other Materials in Electric Utility Flue Gas Wet Scrubbers
(Paper presented at APCA, IGCI and NACE Seminar on Corrosion In Air
Pollution Control Equipment, Atlanta, GA, January 17-19, 1978). Combustion
Engineering Publication TIS-5366.
615
-------
AUTHOR INDEX
AUTHOR NAME PAGE
Ariman, T. 111-222
Bacchetti, J. A. 1-529
Bernstein, S. 11-125
Bibbo, P. P. 11-219
Bickelhaupt, R. E. 1-154
Blackwood, T. R. IV-312
Bloomfield, D. P. III-145
Brackbill, E. A. III-472
Brines, H. G. 1-351
Brookman, E. T. IV-274
Brown, J. T. (Jr. ) III-439
Buchanan, W. J. 11-168
Burckle, J. 0. III-484
Bush, J. R. IV-154
Carlsson, B. III-260
Carr, R. C. 1-35, III-270
Chang, C. M. 11-314
Chapman, R. A. 1-1
Chmielewski, R. III-l
Cooper, D. W. III-127
Cowen, S. J. IV-424
Cowherd, C. (Jr.) IV-240
Czuchra, P. A. III-104
Darby, K. 1-15
Daugherty, D. P. IV-182
616
-------
AUTHOR NAME PAGE
Dennis, R. 1-494
Dietz, P. W. III-429
Donovan, R. P. 1-476
Drehmel, D. C. IV-170
Durham, M. D. IV-368
Dybdahl, A. W. IV-443
Ellenbecker, M. J. III-171, III-190
Engelbrecht, H. L. 11-279
Ensor, D.S. 111-39
Ernst, M. IV-30, IV-42
Eschbach, E. J. 11-114
Evans, J. S. IV-252
Fasiska, E. J. IV-486
Faulkner, M. G. IV-508
Fedarko, W. IV-64
Ferrigan, J. J. 1-170
Finney, W. C. 11-391
Furlong, D. A. 1-425
Garrett, N. E. IV-524
Gastler, J. H. IV-291
Gavin, J. H. 111-81
Giles, W. B. IV-387
Gooch, J. P. 1-132
Gooding, C. H. III-404
Grace, D. S. III-289
Guiffre, J. T. 1-80
617
-------
AUTHOR NAME
Hall, F. D. . HI-25
Hardi son, L. C. III-382
Hoenig, S. A. • IV-201
Hudson, J. A. I" 263
linoya, K. III-237
Isodas T. I-H-16
Jaasund, S. A. H-452
Kalinowski, T. W. ,111-363
Kallio, G. A. III-344
Kearns, M. T. 111-61
Kelly, D. S. 1-100
Kinsey, J. S. 111-95
Kolber, A. R. 1-22^
Ladd, K. L. 1-317
Lamb', G. E.R. III-209
Lane, W. R. 1-410
Langan, W. T. 1-117, 11-256
Larson, R. C. I I 1-448
Leonard, G. 11-146
Lipscomb, W. 0. 1-453
Malani, S.' 1-570
Marcotte, W. R. I-.372
Martin, J. R. 1-591
Masuda, S, 11-65, 11-334, 11-483
McCain, J. D. 1V-496
McDonald, J. R. 11-93
618
-------
AUTHOR NAME PAGE
Mitchell, D. A. III-162
Media, 0. C. 11-399
Mosley, R. B. 11-45
Mycock, Jr C. 1-432
Neundorfer, M. 11-189
Nixon, 0. 1-513
Noll, q, G. 11-374
Nunn, M. 11-369
Ondov, J. M. IV-454
Ostop, R. L 1-342
Parker, R. IV-1
Patch, R. W. IV-136
Patterson, R. G. IV-84
Pearson, G, L. 1-359
feders,en} G. Q. III-416
Petersen, H. H. 11-352
Pilat, M. J. 1-561
Pptter, E. C. 1-184
Ranade, M. B, 1-538
Raymond, R. K. 11-173
Rinard, G. 11-31, IV-127
Roehr, J. D. 11-208
Rolschau, D. W. IH-251
Ruth, D. HH27, 11-441
Samuel, E. A. II-l
Schliesser, S, P. 1-56
619
-------
AUTHOR NAME PAGE
Self, S. A. III-309
Severance, R. L. IV-321
Shale, C. C. 1-390
Smit, W. 1-297
Smith, S. B. 11-502
Spafford, R. B. 1-202
Sparks, L, E. 11-417, IV-411
Stenby, E. W. 1-243
Stock, W. E. IV-333
Surati, H. 11-469
Szabo, M. F. III-508
Tendulkar, S. P. IV-338
Tennyson, R. P. Ill-Ill
Tsao, K. C. IV-14
Umberger, J. H, 11-296
VanOsdell, D. W. 11-74
VanValkenburg, E. S. IV-351
Wang, J. C.F. IV-396
Weber, E, IV-98
Wybenga, F. A. 11-242
Yung, S. IV-217
620
-------
TECHNICAL REPORT DATA
(Please read Imiructions on the reverse before completing)
REPORT NO.
EPA-600/9-80-Q39a
2.
IERL-RTP-1061
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Second Symposium on the Transfer and Utilization of
Particulate Control Technology (Denver, July 1979)
Volume I. Control of Emissions from Coal Fired Boilers
5. REPORT DATE
Sept. 1980 issuing date.
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S) ' " '
P.P. Venditti, J.A. Armstrong and Michael Durham
S. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Denver Research Institute
P.O. Box 10127
Denver, Colorado 80210
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
R805725
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Trianplfi Park J NP 77711
13. TYPE OF RE PORT AND PERIOD COVERED
Proceedings: 6/79-6/80
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES
IERL-RTP project officer is Dennis C. Drehmel, MD-61, 919/541-2925.
thru-044d are proceedings of the 1978 symposium.
EPA-600/7-79-044a
16. ABSTRACT
The proceedings document the approximately 120 presentations at the EPA/IERL-RTP-
sponsored symposium, attended by nearly 800 representatives of a wide variety of
companies (including 17 utilities). The keynote speech for the 4-day meeting was by
EPA's Frank Princiotta. The meeting included a plenary session on enforcement.
Attendees were polled to determine interest areas: most (488) were interested in
operation and maintenance, but electrostatic precipitators (ESPs) and fabric filters
were a close second (422 and 418, respectively). Particulate scrubber interest appears
to be waning (288). Major activities of attendees were: users, 158; manufacturers*
184; and R and D, 182. Technical presentations drawing great interest were the
application of ESPs and baghouses to power plants and the development of novel ESPs.
As important alternatives to ESPs, baghouses were shown to have had general success
in controlling coal-fired power plant emissions. When operating properly, baghouses
can limit emissions to^5 mg/cu nm at pressure drops of^2 kPa. Not all baghouse
installations have been completely successful. Both high pressure drop and bag loss
have occurred (at the Harrington Station), but these problems appear to be solved.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Pollution Scrubbers
Dust Flue Gases
Aerosols
Electrostatic Precipitators
Filters
Fabrics
Pollution Control
Stationary Sources
Particulate
Baghouses
13B
11G
07D
131
14G
HE
07A
21B
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. ijr FA
637
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Foim 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
U.S. GOVERNMENT PRINTING OFFICE: 1980--657-165/Ol57
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