FINAL REPORT
ON
SULFUR DIOXIDE SCRUBBERS
STONE & WEBSTER - IONICS PROCESS
CONTRACT NO. CPA 22-69-8O
FOR
DIVISION OF PROCESS CONTROL ENGINEERING
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
U. S. DEPARTMENT OF HEALTH, EDUCATION AND WELFARE
JANUARY 197O
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FINAL REPORT
ON
SULFUR DIOXIDE SCRUBBERS
STONE & WEBSTER/IONICS PROCESS
CONTRACT NO. CPA 22-69-80
FOR
DIVISION OF PROCESS CONTROL ENGINEERING
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
U. S. DEPARTMENT OF HEALTH, EDUCATION AND WELFARE
JANUARY 1970
STONE & WEBSTER ENGINEERING CORPORATION
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STONE 8 WEBSTER ENGINEERING CORPORATION
225 FRANKLIN STREET. BOSTON, MASSACHUSETTS O21O7
NEW YORK
BOSTON
January 30, 1970
ENGINEERING
Mr. Jonathan P. Earhart
New Process Development Unit
Process Control Engineering Division
National Air Pollution Control Administration
5710WoosterPike
Cincinnati, Ohio 45227
Dear Mr. Earhart:
In accordance with the authorization contained in Contract No. 22-69-80, dated
May 1, 1969, we have made a study to determine the most economical scrubber for use in
the removal of sulfur dioxide from flue gas produced by a coal burning power plant.
The scrubber would be specifically designed to operate as part of a system using the
Stone & Webster/Ionics sulfur dioxide recovery process as described in the proprietary
Stone & Webster proposal dated July 22, 1968, previously presented to NAPCA.
The design described in the S&W proposal was based on removing sulfur dioxide from
the flue gases produced in a coal-fired power station rated 1 ,200 Mw and consisting of four
boilers. The flue gas from one boiler amounts to 880,000 actual cfm at 300 F and contains
0.3 mole percent sulfur dioxide. Fly ash loading is 0.05 grains per cu ft. The electrolytic
regeneration system will produce a feed stream to the scrubber system which contains about
4.4 moles of NaOH plus 2.7 moles of Na2SO4 per 100 moles of water.
The equipment provided consisted of a tower with water sprays for cooling the flue gas
and removing some residual fly ash, a sulfur dioxide removal section comprised of two
packed sections of Johnstone wood slat packing, an induced draft blower, scrubbing liquor
circulation pumps, and necessary connecting duct work, piping and instruments.
To determine whether any other type of scrubber is superior to the Johnstone packed
tower, quotations were requested from 23 manufacturers of various types of gas scrubbers.
Of the quotations received, one in each of the following classes of scrubbers was selected for
estimation:
Stone & Webster Ripple Tray tower
Floating ball contactor
Intalox Saddle packed tower
Impingement grid packed tower
Venturi contactor
Cyclonic contactor
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An attempt was made to determine the percentage oxidation of sulfites to sulfate for
each type of scrubber. Values from the literature and quoted values from vendors were used.
No positive conclusions regarding degree of oxidation for each type could be reached.
Investment and operating costs were estimated for each type of scrubber system
studied. The conclusions reached can be summarized as follows:
1. Large single scrubber installations are least expensive to
install and overall least costly to operate.
2. Proprietory equipment such as venturi, cyclonic and floating
ball scrubbers is impractical in the S&W/Ionics process at the
present time. Equipment manufacturers will have to produce
units with much larger throughput to be competitive with
packed towers.
3. The differences in large single scrubbers such as packed and
Ripple Tray towers are not great, although the Johnstone
wood grid packed towers showed some advantages over the
other types.
For further details, we refer you to the following pages of this report.
Yours very truly,
__
E. G. Lowrance
Project Director
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TABLE OF CONTENTS
INTRODUCTION 1
SCOPE OF WORK 1
DESIGN BASIS 2
TYPES OF SCRUBBERS STUDIED 2
VENDORS CONTACTED AND REPLIES 3
DISCUSSION 4
PREQUENCH AND FLY ASH REMOVAL . 4
SULFUR DIOXIDE ABSORPTION 4
Efficiency of Sulfur Dioxide Removal 4
Utilization of Caustic 5
OXIDATION 6
Literature Search 7
Application of Literature Information 10
Estimated Oxidation for Scrubbers Studied 11
MATERIALS OF CONSTRUCTION 11
ECONOMIC COMPARISON OF VARIOUS SCRUBBERS
FOR THE STONE & WEBSTER/IONICS PROCESS 13
INVESTMENT 13
SCRUBBER SYSTEM OPERATING COST 14
SULFUR DIOXIDE SCRUBBER SYSTEM COST EVALUATION 15
APPENDIX A - VAPOR PRESSURE OF SO2 OVER SULFITE SOLUTIONS
APPENDIX B - DERIVATION OF ECONOMIC FACTORS
Table 1 LIST OF VENDORS CONTACTED
Table 2 VENDORS QUOTING ON FLY ASH REMOVAL AND QUENCH EQUIPMENT
Table 3 VENDORS QUOTING ON S02 SCRUBBERS
Table 4 SUMMARY OF VENDORS' QUOTATIONS
Table 5 INVESTMENT COMPARISON
Table6 OPERATING COST COMPARISON
Table 7 COST EVALUATION
FIGURE 1 SCHEMATIC FLOW DIAGRAM
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INTRODUCTION
SCOPE OF WORK
The National Air Pollution Control Administration (NAPCA) of the U. S. Department
of Health, Education and Welfare (HEW) engaged Stone & Webster Engineering Corporation
to make a study to determine the most economical scrubber for the removal of sulfur
dioxide from flue gas produced by a coal burning power plant. The scrubber would be
specifically designed to operate as part of a system, using the Stone & Webster/Ionics sulfur
dioxide recovery process as described in the proprietary Stone & Webster (S&W) Proposal,
dated July 22, 1968, which was presented to NAPCA.
The S&W/Ionics sulfur dioxide recovery process includes a sulfur dioxide scrubber in
which sulfur dioxide is absorbed in a sodium hydroxide solution to form a sodium
sulfite/sodium bisulfite solution which is sent to a neutralization stage.* The economics of
the process are such that a high bisulfite-to-sulfite ratio and a minimum oxidation to sulfate
are desired. The installed and operating costs included in the S&W Proposal of July 22,
1968, were based on using a sulfur dioxide scrubber provided with Johnstone type wood
slat packing as described in the paper by Johnstone & Singh of March 1937,1.E.C., Vol. 29.
Since it seemed probable that an improved means of scrubbing might have been
developed since Johnstone's work of 1937, this study was authorized to accumulate,
organize and report pertinent engineering information on various types of scrubbers which
would be technically feasible for use as a chemical contactor in the S&W/Ionics sulfur
. dioxide removal and recovery process.
The S&W/Ionics Process underwent pilot plant tests during 1967 at the Gannon
Station of Tampa Electric Co. in Tampa, Florida, where the operation as a whole and
critical components were evaluated, using actual flue gas from a boiler fired by pulverized
coal. The pilot unit was sized to process about 200 cfm of flue gas containing approximately
0.25 volume percent sulfur dioxide. The equipment included a flue gas quench which cooled
the gas to about 120 F and removed most of the fly ash and which was followed by an
absorber. Since our primary purpose was to evaluate the electrolytic cell, only a Venturi
type scrubber and later a spray type scrubber were tested. Figure 1 illustrates the flow.
The scope of the study which is described in this report did not allow time or money
for any experimental work. It is anticipated that the results of the study will narrow the
selection of scrubber types to one or two and that some experimental work may be
necessary before the detailed design of a prototype begins.
*The neutralized spent liquor is then regenerated in an electrolytic cell for reclamation of
the caustic for reuse in the process.
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DESIGN BASIS
The design described in the S&W proposal was based on removing sulfur dioxide from
the flue gases produced in a coal-fired power station rated at 1,200 Mw and consisting of
four boilers. The flue gas from each boiler amounts to 880,000 actual cfm at 300 F and
contains 0.3 mole percent sulfur dioxide. Fly ash loading is 0.05 grains per cu ft. The
electrolytic regeneration system will produce a feed stream to the scrubber system which
contains about 4.4 moles of NaOH plus 2.7 moles of Na2 SO4 per 100 moles of water.
The equipment provided consisted of a tower with water sprays for cooling the flue gas
and removing some residual fly ash, a sulfur dioxide removal section comprised of two
packed sections of Johnstone wood slat packing, an induced draft blower, scrubbing liquor
circulation pumps, and necessary connecting duct work, piping and instruments. Because of
the low gas pressure drop in the system, the induced draft fan was placed at the outlet of
the sulfur dioxide scrubber.
TYPES OF SCRUBBERS STUDIED
For the present study of sulfur dioxide scrubbers, the same general arrangement of
equipment has been retained except that the fan is located upstream of the quench and fly
ash removal equipment because of the higher pressure drop associated with most of the
other scrubbers studied. This requires handling a larger volume of gas at 300 F, but avoids
corrosion problems since the flue gas is above its water dew point.
To determine whether any other type of scrubber is superior to the Johnstone packed
tower, quotations were requested from 23 manufacturers of various types of gas scrubbers.
Of the quotations received, one in each of the following classes of scrubbers was selected for
estimation:
Stone & Webster Ripple Tray tower
Floating ball contactor
Intalox Saddle packed tower
Impingement grid packed tower
Venturi contactor
Cyclonic contactor
In some cases, the quench section and the absorption section use the same type of
scrubber, but occasionally a combination was used. In one case, for example, a spray quench
followed by a Stone & Webster Ripple Tray tower was used.
An attempt was made to select equipment which would achieve 90 percent sulfur
dioxide removal. Since no supporting data were supplied by the vendors, at least two actual
contact stages are provided in all cases.
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VENDORS CONTACTED AND REPLIES
Table 1 lists the vendors contacted and indicates those who declined to quote for one
reason or another. Generally, those who declined to quote stated that the gas volume to be
handled was too large for their equipment. Of the 23 companies contacted, nine declined to
quote and one (Research-Cottrell, Inc.) quoted on the fly ash removal stage only. Thus, 13
quotations plus the S&W Ripple Tray design were left for consideration.
Since a 90 percent sulfur dioxide removal was a necessary requirement of this
evaluation, only those vendors offering a minimum of two contact stages were considered as
being acceptable even though no supporting data were supplied by the vendors to
substantiate this selection.
Table 2 shows the type of equipment quoted for the quench/fly ash removal section.
The type of equipment quoted for the sulfur dioxide absorption section is shown in Table 3.
The UOP Air Correction Division declined to quote because they believe that low
liquid velocities and very high retention times are required in producing a liquor high in
bisulfite. This is in opposition to the operating principle of their Turbulent Contact
Absorber (TCA) scrubber.
Most of the vendors offered to test their equipment or to cooperate in test work
preliminary to a design of a prototype unit.
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DISCUSSION
PREQUENCH AND FLY ASH REMOVAL
Flue gas leaving the electrostatic precipitators will normally be at about 300 F and
about 0 psi gage. Fly ash loading is expected to be about 0.05 grains per cu ft. Expected size
distribution of the fly ash is as follows:
Size, Microns Wt %
0-10 45
11-20 23
21-45 20
45 and over 12
An inspection of the proposals received shows that quenching of the flue gas from
300 F to about 130 F can be accomplished. However, only one vendor offered a guarantee
on the extent of cooling.
The extent of fly ash removal is less clear. Claims of the vendors varied from 90 to
99 percent removal of the contained fly ash to no estimate at all. The vendor with the
highest rate offered removal of 99 percent of the fly ash over 1 micron in size. Supporting
data were not submitted by any vendor. We believe some ash will pass through the quench
section and will be captured in the sodium sulfite/sodium bisulfite solution. Thus, filtration
will be required before the solution can be sent to the electrolytic cells. Therefore, some
incremental increase in investment and operating costs will result if fly ash removal in the
quench section is lower than expected. However, due to the indefinite nature of the claims,
this factor was not included in our estimated costs for this study.
SULFUR DIOXIDE ABSORPTION
Efficiency of Sulfur Dioxide Removal
To meet local air pollution standards that are being proposed, it is necessary to reduce
the sulfur dioxide concentration in flue gas to a value equivalent to firing coal with
1 percent sulfur. For a 4 percent sulfur content coal, this would be equivalent to removing
75 percent of the sulfur dioxide produced. Since the S&W/Ionics process recovers sulfur
dioxide as a salable product, we have based our designs on a recovery of 90 percent of the
sulfur dioxide in the flue gas. Based on a sulfur dioxide concentration at the outlet of the
electrostatic precipitators of 0.3 volume percent or 3,000 ppm, this would result in a
reduction to 300 ppm by volume. This high recovery not only adds to the salable sulfur
dioxide but also permits the utility to meet more rigid standards which may be imposed in
the future by local or Federal authorities.
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Calculations based on data developed by Johnstone and Singh22 indicated that about
8 ft of slat packing would be required for this service. Since there is insufficient fresh
caustic solution to wet the packing adequately, recirculation of scrubbing liquor is required.
Thus, we have divided the packing into two stages of 6 ft each, with trap-out trays and
recirculation pumps for each stage. Johnstone and Singh data indicated that, for the wood
slat packing configuration used, the height of a transfer unit was approximately 1.6 ft in this
service. We have provided 7.4 transfer units as compared with 5.0 units which we have
calculated as the required amount.
We do not have a method for comparing the performance of Johnstone wood slat
packing and the other types of contactors offered by the vendors solicited. None of the
vendors supplied information to substantiate the claims for the performance of his
equipment. Most vendors believed that one or, at most, two stages would be adequate. Our
own calculations indicate that two packed sections would be required to obtain 90 percent
removal, with three packed sections needed for 95 percent removal. One contacting stage
would not be adequate because of the high vapor pressure of sulfur dioxide above bi-
sulfite solutions. Most vendors have offered to do test work or to cooperate in test
work to determine the number of contacting stages required. Such test work could be
carried out at vendors' laboratories or in cooperation with a utility. Discussion of a testing
program has been deferred until a prototype unit is under consideration.
Utilization of Caustic
The electrolytic regeneration system will produce a feed to the absorption system
which will contain about 2N or 8 wt % sodium hydroxide (pH of about 14). Since all the
scrubbers being studied require recirculation of absorption liquor in order to provide
adequate liquid loading, this caustic feed will be added to recirculated liquid at the top
stage. The amount of free caustic in the combined liquid to the top stage is a function of the
amount of recirculation to the stage and the amount of sulfur dioxide absorption in the
stage.
The principal reactions that occur in the absorber are as follows:
SO2 + H2O - H2SO3
CO2 +H2O - H2CO3
2 NaOH + H2CO3 *? Na2CO3 + 2 H2O
Na2CO3 +H2CO3 ^ 2NaHCO3
2 NaOH + H2 SO3 - Na2 SO3 + 2 H2 O
Na2 SO3 + H2 SO3 ^ 2 NaHSO3
Na2CO3 +H2SO3 -»• Na2SO3 +CO2t + H2O
NaOH + NaHSO3 ->• Na2 SO3 + H2 O
It is expected that there will be little or no free caustic in the combined feed to the top
section. This stream will contain mostly Na2CO3 and Na2SO3. As the liquid flows down
through the tower, CO2 will be displaced by SO2 and Na2SO3 will be partially converted to
NaHSO3.
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The vapor pressure of sulfur dioxide over neutral sodium sulfite is essentially zero,
while over mixtures of sulfite/bisulfite the vapor pressure is a function of the sodium
bisulfite concentration. Johnstone23 found it convenient to characterize the relative
amounts of sulfite and bisulfite in a solution by using the ratio of S/C or moles of dissolved
SO2 per mole of available sodium ion (S/C = 0.5 for Na2SO3 ; S/C = 1.0 for NaHSO3). The
relationships between the vapor pressure of sulfur dioxide and S/C are discussed in
Appendix A.
The absorption system should have sufficient contact stages to produce a liquor which
contains a high ratio of S/C and should have adequate contacting in each stage to approach
equilibrium between gas and liquid. It is also essential to provide a system in which
entrainment from stage to stage is minimized. A ratio of S/C of 0.9 or higher in the scrubber
product is required to achieve the most economical cell operation. The pH of this solution
leaving the final stage should be about 3.5.
None of the vendors who submitted proposals offered any data that would be useful in
determining the extent of conversion to sodium bisulfite. Actually, not much information
could be expected from the vendors since caustic or sodium carbonate has not been
reported in commercial use to extract sulfur dioxide from flue gas. Recovery of sulfur
dioxide from gases produced by combustion of sulfur is practiced in the paper industry as
part of a magnesium sulfite pulping process, but magnesium hydroxide, rather than sodium
hydroxide, is used as the absorbent. In other sulfite pulping processes, either water or an
alkaline solution is used to absorb sulfur dioxide from the gases. In these cases sulfur
dioxide is present in much higher concentrations than those appearing in a flue gas from a
coal burning power plant.
If vendors could have provided data supporting the claimed sulfur dioxide removal, the
ratio of S/C could be calculated. It is our opinion that none of the claimed figures can be
used in a system where separate recirculation to each contact stage is used.
Since many of the vendors have test facilities, it should be possible to determine the
maximum concentration of bisulfite during the design stage for a prototype unit, but until
this is done we will not be able to evaluate this factor.
OXIDATION
The contract requires that an estimate of the percentage of sulfur dioxide transferred
from gas to liquid which is oxidized shall be made for each scrubber type being considered.
Oxidation is defined as the percentage of net sulfur dioxide absorbed that is converted from
sulfite or bisulfite to sulfate. Oxidation is an important factor in the economics of any
scrubber type being considered, since increased oxidation results in increased electrical
energy requirements. Consequently, a scrubber with excessive oxidation, by virtue of
oxidation alone, could be economically unattractive.
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To predict or estimate oxidation percentages, the relationship between scrubber design
parameters and oxidation must be known. The best but most expensive way to obtain this
information would be to run tests on various scrubber types. However, due to time and
expense, testing was not possible for this study; thus, our inquiries to scrubber
manufacturers requested that they supply us with any data they had on oxidation. We also
made an extensive literature search for such information. None of the vendors was able to
give us any specific information on oxidation, although one, The Norton Company, stated
that oxidation would not exceed 2 percent.
Literature Search
Our literature search had two objectives. The first objective was to search for
information concerning the mechanism of absorption of oxygen into sodium sulfite
solutions and those factors affecting that absorption. The second objective was to relate the
absorption mechanism to the chemical reaction and to see how factors which affect the
reaction also affect the absorption into the liquid. Once this information had been collected,
the task of relating it to absorber types could be done.
Absorption Mechanism and Chemical Reaction. The literature appears to be in
agreement on the mechanisms of absorptions of oxygen into sodium sulfite solutions. It has
been proved that the gas film resistance in this transfer is negligible.4'6 Thus, the oxygen
transfer mechanism can be separated into two individual rate processes:
1. Transfer of gas from gas-liquid interface to the bulk of the
liquid
2. Chemical reaction of O2 with sulfite
However, it has also been shown by Wartman18 that the oxidation of solutions of
normal sulfites is limited by the .rate at which solutions will absorb oxygen. In Wartman's
tests, all carried out at 25 C, 25 cc of distilled water were saturated with pure oxygen and
then 2 cc of 3 molar ammonium sulfite were added, mixed, and allowed to stand for a given
period of time. HC1 was then added to stop further oxidation and the solution was analyzed
for sulfates. The test was repeated for different time intervals varying from 7 sec to 3 min.
Bisulfite solutions were also tested in this manner. All dissolved oxygen was consumed by
normal sulfite within 7 sec, whereas with bisulfites the reaction proceeded much more
slowly. Wartman also measured the amount of oxidation occurring when pure oxygen was
bubbled through a solution of normal sulfite. By increasing the contact surface between gas
and liquid, Wartman found that the rate of oxidation could be greatly increased. It then
follows from this work that the rate-limiting oxygen transfer mechanism becomes the
transfer of gas from gas-liquid interface to the bulk of the liquid.
Qualitatively, there are certain variables which affect the diffusional transfer or rate of
absorption of oxygen.4>6-9 These are:
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1. Area of contact
2. Time of contact
3. Turbulence
4. Concentration gradient (magnitude of driving force)
5. Temperature
Even if there were no chemical reaction in the overall mechanism, the following factors
which would affect chemical reaction also would affect the rate of
absorption:2'3'5'6-8'10'14'17
6. Solute concentration
7. pH
8. Light intensity
9. Catalysis
Our literature search resulted in information showing how the above variables affect
direction and intensity in the oxidation of sodium sulfite to sodium sulfate.
Area of Contact. The literature18 states that oxidation increases as the area of contact
increases. The oxygen transfer mechanism is a function of the transfer of gas from the
gas-liquid interface to the bulk of the liquid and can be expressed as:
rd=kL(A)(Ci-cL) (1)
where
rd = rate of oxygen absorption, grams O2 absorbed/(hr) (liter)
kL = liquid-film mass transfer coefficient, grams O2 transferred/(hr) (sq cm)
(unit concentration difference)
A = transfer area, (sq cm)
(Cj — CL ) = driving force of gas across interface into bulk of liquid, (grams/liter)
We have estimated that 5 percent oxidation would be expected from a Johnstone type
scrubber, and the contract states that this figure should be used as a base case. On this basis,
the effect of gas-liquid contact area on other types of scrubbers can be expressed as follows:
_ ., .. ,_, ., .. J Contact area of new scrubber \
Percent oxidation = (Base case oxidation)!-^—-— ^7— ——r-r— ) (2)
\ Contact area of base case scrubber /
It must be kept in mind, however, that this estimate will be accurate only to the extent
that the base case figure and the determination of the area of contact are exact.
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Time of Contact. The literature made no definitive statements on time of contact.
However, it did imply that as time of contact increased, oxidation increased. Unfortunately,
there was no basis in the literature to show a quantitative relationship between the two.
Turbulence (Agitation). Since absorption is controlled by liquid film resistance, it can
be inferred4'6'9'15 that agitation of the liquid phase enhances the rate of mass transfer and
increases oxidation. However, as in the case of time of contact, there was no basis in the
literature for the development of a quantitative relationship.
Concentration Gradient (Magnitude of Driving Force). Referring to Equation 1 :
rd = kL(A)(Cj-cL)
Cj = concentration of oxygen at the interface, (grams/liter)
CL = concentration of oxygen in the bulk of the liquid, (grams/liter)
The literature4'9'15 defines the term (c; — CL) as the driving force for absorption.
Since oxygen solubility follows Henry's Law very closely and since the gas film coefficient is
negligible, the partial pressure of oxygen at the interface is the same as that in the bulk of
the gas.
PQ = partial pressure of solute in gas phase
HO = Henry's law constant
Also, since the chemical reaction is very rapid, CL =* 0 and the driving force is
approximately equal to the concentration of oxygen at the interface. It can be seen from
the above that by decreasing the oxygen content in the flue gas, oxidation should decrease
proportionately.
It should be emphasized that operators of boiler plants using any process affected by
oxidation should try to maintain excess air at the minimum consistent with good boiler
operation. The exact values of excess air will depend on the type of .coal and the design of
the boiler system.
Temperature. Although published data on the solubility of oxygen in various solvents
indicate that, as temperature increases, solubility of oxygen decreases, Cooper et al6 state
that the oxidation rate of sodium sulfite solutions increases by a factor of 2 when the
temperature is increased from 32 F to 50 F. He also found that in the range of 68-104 F,
the rate increases more slowly with increasing temperature. Our pilot plant data indicate
that as temperature was increased in the range of 100-132 F, oxidation increased, although
we found very little change in oxidation with temperature from 132 F to 140F. A
quantitative explanation for these findings is not available.
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Solute Concentration. The literature is not very clear on this subject. Several
sources10'18 contend that oxidation rate decreases as solute concentration increases. Other
sources6'8'19 indicate that oxidation proceeds at a rate independent of sulfite-ion
concentration over concentration ranges as wide as 0.35-1.0 normal.
pH. One literature source1 ° stated that oxidation apparently increased as acidity of the
solution increased. This position is contested by several sources5'6'8'13 who contend that
oxidation is greatest in a neutral or slightly alkaline solution. We are inclined to accept the
views of the latter since Wartman18 noted that the oxidation of bisulfite, which has a pH of
about 3.5, was slower than for neutral sulfite.
Light Intensity. It has been established that oxidation of sodium sulfite solutions to
sodium sulfate is a chain reaction which is highly light sensitive.2'8'14 However, the
literature fails to provide an insight as to relative increases in oxidation rates due to the
extreme light sensitivity of the reaction. This is not a factor in our process since our
equipment is all metal. However, since light is a factor, laboratory tests done in glass might
have shown higher oxidation than should be expected in a commercial plant.
Catalysis. It has also been shown that oxidation of sodium sulfite solutions is highly
susceptible to both positive and negative catalysis. The heavy, variable-valence metal ions,
such as Fe, Cu, Co, Ni and Mn have a powerful positive catalytic effect.2'3 >5 ;8>14 ]17 There
are inhibitors which tend to reduce activity of these metal catalysts. Organic alcohols,
phenols and potassium cyanide have a very strong negative effect.2'8'10'14 However, if
trace amounts of NOX are present in the gas, oxidation becomes very difficult to inhibit.14
A mechanism1 has been proposed to explain both positive and negative catalysis, but has
not been proved. The literature on catalysis as it affects oxidation yields little information
which is quantitatively applicable.
Application of Literature Information
Of the nine identifiable factors affecting oxidation of sodium sulfite solutions to
sodium sulfate, six are independent of scrubber design parameters. Temperature, solute
concentration, pH, and light intensity will be common to all scrubber types. Concentration
gradient and catalysis (positive) will be a function of boiler operations. Negative catalysis, if
applicable, could be used in any scrubber, regardless of its type. This leaves only the factors
of area of contact, time of contact, and turbulence as variables in the various scrubber
designs.
Time of contact and turbulence, while unique to each scrubber type, were not
determinable from the information provided. Therefore, only area of contact has been used
in this report to estimate oxidation rates for various scrubber types.
As shown in Equation 2. these estimates will be only as accurate as the base case
oxidation percentage and the determinations of area of contact. Even in pilot plant testing,
Johnstone experienced wide ranging oxidation percentages. Because of this, oxidation rates
shown in this report may be very inaccurate. It would seem, then, that testing programs are
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justified to generate good design information on various scrubber types. This cannot be
done within the scope of this report but could be a prerequisite to the final selection of a
scrubber design for application in a commercial plant.
Estimated Oxidation for Scrubbers Studied
The results of pilot plant work and studies of Johnstone's work suggest that oxidation
of sulfite to sulfate over Johnstone wood slat packing will be approximately 5 percent. We
have attempted to make predictions of the percentage of sulfite oxidized in each of the
several types of scrubbers studied. The figures are shown in Table 4. Using the wood slat
packing as a base, with 5 percent oxidation expected, we estimate the other types of
scrubber would produce the following results:
Percent
Type of Scrubber Oxidation
Wood slat packing 5
Intalox Saddle packed tower 10-15
Stone & Webster Ripple Tray 8-10
Glitsch grid impingement packing 3-5
Cyclonic contactor 2-5
Floating ball contactor 2-5
Venturi contactor 10-15
All except the venturi scrubber are based on a contact area relative to wood slat
packing. Since no suitable method was found to determine the surface area of liquid
droplets for the venturi contactor, we have used a value reported for a venturi unit not
quoted (private communication).
The Norton Company 'had stated that oxidation would not exceed 2 percent, whereas
calculations based on surface area indicate 15 percent. Since Norton's value is based on
different operating conditions, it would require testing under our conditions to determine
what the true value would be.
MATERIALS OF CONSTRUCTION
The sulfur dioxide recovery pilot plant in Tampa was constructed of materials that
were available and thought to be suitable from a corrosion standpoint. The quench tower,
the quench water pump casing, impeller shafts and wearing rings were 316 stainless steel.
The scrubber recirculation pumps were also stainless steel. The absorption section was
resin-impregnated fiberglass. Piping was stainless steel or polyvinyl chloride. The blower was
resin-coated carbon steel. After several months of operation, the fiberglass venturi scrubber
was replaced, because of high oxidation rates, with a 3 stage plexiglass tower using plastic
spray nozzles for atomization of the recirculated sulfite solutions. The scrubber
recirculation pumps were replaced with polyethylene pumps at the same time.
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Operation of the pilot plant over a four month period showed that stainless steel was
attacked slightly in the quench system. Thus, a better choice would be a nonmetallic
material or rubber lined steel. As long as there is no carryover from the quench zone, mild
corrosion would not affect the operability of the system. However, carryover would add
metallic products of corrosion and dissolved metal ions from the fly ash to the absorption
circuit and would eventually form metal hydroxides which must be removed from the feed
stream before it enters the electrolytic cells. Because of problems associated with this
possibility, lined equipment is a virtual necessity. The absorption section and internals
should also be constructed of or lined with nonmetallic material. This arrangement would
favor designs using nonmetallic packings assuming that nonmetallic or coated supports and
distributors could be fabricated. Designs with large exposed metal surfaces, such as
multivane cyclonic contactors, would be more difficult to coat and would experience more
erosion from particulate matter and subsequently more corrosion.
We have relocated the blower to the inlet side of the quench tower where hot gas will
be handled and special materials for the blower are not required. This will require a larger
blower, but will eliminate the structure previously required to support the blower and will
make maintenance easier and less expensive.
Piping should also be constructed of or lined with nonmetallic material. Polyvinyl
chloride piping was satisfactory for the pilot plant. Epoxy resin fiberglass should be suitable
for very large piping.
Duct work for the hot gases would be of carbon steel but should be lined or coated
with nonmetallic coating after the quench section.
-------
13
ECONOMIC COMPARISON OF VARIOUS SCRUBBERS
FOR THE STONE & WEBSTER/IONICS PROCESS
INVESTMENT
The cost of a scrubber system based on the work of Johnstone was estimated, to serve
as the base cost of the scrubber system in the S&W/Ionics sulfur dioxide removal and
recovery process. The estimate was made for a four boiler 1,200 Mw station. It included:
1. Duct work required to take hot flue gas from existing
precipitators to quench devices, which would also act as
solids scrubbers
2. Four gas quenchers
3. Four two stage sulfur dioxide scrubbers
4. Fans to provide a pressure boost equal to the overall system
pressure loss
5. Duct work to carry the flue gas from the scrubbers back to
the stack
6. All necessary pumps for quencher and absorption sections to
provide liquid flows as required for each unit
7. Fired reheaters in the quenched, sulfur dioxide cleaned gas to
provide enough reheat to prevent condensation in the stack
8. Construction costs and Contractor's field costs, engineering
burdens, and fees
Investment costs were estimated for each of the other six types of scrubbers for which
manufacturers supplied information. Each estimate considered the same eight cost
categories shown above. In addition to these items, the effect of oxidation on the number of
cells required to process sodium sulfate was estimated and, depending on whether the new
design was more or less prone to oxidation as compared to the Johnstone type, a capital
adjustment was made to the estimate for each type of scrubber.
Where oxidation is shown as a range, the lowest estimated level was used to compute
the investment penalty or credit.
The estimates for the seven types of scrubbers are shown in Table 5. All six of the
scrubber systems have been estimated to cost more than the Johnstone based system
-------
14
originally used by S&W in its proposal to NAPCA. The Johnstone, Glitsch 'grid, Intalox
Saddle and S&W Ripple Tray systems can be scaled up to the point where only one dual
purpose, quench, two stage scrubber tower need be built for each boiler. Since only one
tower is required for each boiler, the cost of duct work for these systems is significantly
smaller than the cost of duct work in the more complex venturi, cyclonic, and floating ball
systems. ;
SCRUBBER SYSTEM OPERATING COST
One of the major operating costs in the scrubber systems is the cost of power for the
flue gas fans which are used to overcome the sulfur dioxide scrubber system pressure drops.
The venturi system, while it has a lower AP in the gas stream than the Johnstone system, uses
the quench and absorption fluids as drivers to boost pressure through the scrubbing device.
In spite of this interesting operational characteristic, the total energy required for fans and
fluid pumps in the venturi system is slightly higher than that required by the Johnstone
unit. All of the other systems studied also have a higher energy cost than the Johnstone
system.
While the oxidation levels in all of the scrubber types studied can only be estimated at
this time, it would appear that the cyclonic (Pulverizing Machinery) and floating ball (Buell)
could well generate lower oxidation levels than the Johnstone type. The Glitsch system
might also offer slight reductions as compared to the Johnstone unit. In addition to the
operating cost associated with pressure drop in the scrubber system, a sum would be needed
to cover the operating cost of an additional (or reduced) number of cells required to cope
with estimated increases (or decreases) in the oxidation level characteristic of each type.
Maintenance costs were assumed to be 2 percent of the installed cost.
A summary of the operating costs is shown in Table 6.
-------
15
SULFUR DIOXIDE SCRUBBER SYSTEM COST EVALUATION
The basis of evaluation for this study was the net present value of the cash flows for
each type of scrubber over a 15 yr period, using a discount factor of 6 percent. The capital
return factor used was 17.50 percent. This includes bonded debt cost, depreciation on a
5 percent straight-line basis, local taxes and insurance, and utility return on equity after
taxes (see Appendix B).
Since the construction period for recovery plants will be short, we have assumed that
the total differential investment will be made in the first year of operation. This assumption
will tend to decrease the effect of capital cost and overemphasize the value of operating cost
savings. The formula used, 10.288 (0.1750 A Investment + A Operating) equals the 15 yr
evaluated cost of the scrubber. The Johnstone unit 15 yr evaluated cost is zero. All of the
other units are considerably more expensive than the Johnstone unit. Based on the estimates
made, it would appear that only the Glitsch grid packed tower would offer any
competition to the Johnstone system proposed by S&W for inclusion in an add-on sulfur
dioxide recovery situation suggested in our proposal to NAPCA.
The evaluated comparative costs of the six types of scrubbers studied are shown in
Table 7.
Until the manufacturers of venturi, cyclonic, and floating ball units can produce very
large single units, the evaluated cost of such units makes their use in the S&W/Ionics process
impractical.
-------
APPENDIX A
VAPOR PRESSURE OF SO2 OVER SULFITE SOLUTIONS
Johnstone22 found that his experimentally determined values for the equilibrium
vapor pressure of sulfur dioxide over solutions of sodium sulfite/sodium bisulfite were well
correlated by an equation of the following form:
p _„ (2S-C)2
so2
(C-S)
where
P = vapor pressure of SO2 (mm. Hg.)
o \j 2
S = total concentration of dissolved SO2 in the form of sulfite and bisulfite
(moles per 100 moles of water)
C = total concentration of "available" Na+, moles per 100 moles of water
M = constant which depends only on temperature
Sodium ions which are in the form of Na2SO4 are not "available" to react with SO2. For a
solution which contains 4.4 moles of NaOH plus 2.7 moles of Na2SO4 per 100 moles of
water, S = 0 and C = 4.4. As sulfur dioxide is added to such a solution, S increases and C
does not change.
Johnstone, Read and Blankmeyer12 give the following relationship between the
constant M, and the absolute temperature in degrees Kelvin:
log,0 M = 4.519- 1987/T
If it is assumed that the scrubbing liquor which is in contact with the flue gas has a
temperature of 130 F, then M = 0.0452. Exhibit 1 is a plot of Pso versus the ratio S/C (for
NaOH, S/C = 0; for Na2SO3, S/C - 0.5; and for NaHS03, S/C = LO). The relative positions
of the lines for C = 4.4 and for C = 8.0 (near saturation) show why the attainment of a ratio
of S/C of 0.9 or higher requires that a relatively dilute solution of NaOH be used.
-------
VAPOR PRESSURE OF SO2 OVER NaHSO3 - ^803 SOLUTIONS
asm
4000
3500
Temperature..= 130 F
C = moles Na+/100 moles H20
S = moles SO2/100 moles H20
m
X
CD
-------
CALCULATED VALUES OF Pg0 USED FOR EXHIBIT 1
so
MC
7.6 x 1CT4
(2S/C- I)2
(1 - S/C)
At 130 F, M = 0.0452
S/C
(AtC=4.4)Pso (ppm)
(AtC=8.0)Pso (ppm)
0.60
0.65
0.70
0.75
0.78
0.80
0.82
0.84
0,86
0.88
0.89
0.90
0.91
0.92
0.93
0.94
26
67
140
262
373
471
595
756
969
1260
1447
1675
1955
2308
2765
3377
48
122
254
476
678
856
1083
1375
1762
2290
2632
3045
3555
—
—
-------
APPENDIX B
DERIVATION OF ECONOMIC FACTORS
1. Annual Capital Return Factors
Bonded Debt, 60% 1 at 6% (3.6%) (I)
Depreciation, 20 yr Straight Line (5.0%) (I)
Local Taxes and Insurance (3.0%) (I)
Utility Return on Investment
40% equity at 7% allowable after tax (2.8%) (I)
Federal Tax (52.2% rate) (3.1%) (I)
Total Return on Annual Basis (17.50%)(I)
2. Annual Cost Differential of Any Process — Johnstone as Base
Annual cost of operation will have two components:
A. Return factor which will be 17.50 percent of differential
investment between Johnstone and other types
B. Operating Cost Component which will be differential
between Johnstone and other types
If it is assumed that the load factor on the recovery plant in later years, i.e., 10 through
15, is equal to the early years, i.e., 1 through 5, the present worth of any alternate is equal
to the discounted sum of (0.1750AI + A Operating) over a 15yr period when the
expression is calculated for the first year. The discount factors when summed equal 10.288.
-------
REFERENCES
STUDY OF SO2 SCRUBBERS
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
1. Aerojet-General Corp.. "Applicability of Aqueous Solutions to the Removal of SO2
from Flue Gases" (Report S-4850-01-2), Contract PH86-68-77
2. Backstrom, H. L. J., "The Chain-Reaction Theory of Negative Catalysis," Journal of
the American Chemical Society, 49, 1460, 1927
3. Barren, C. H., and O'Hern, H. A., "Reaction Kinetics of Sodium Sulfite Oxidation by
the Rapid-Mixing Method," Chemical Engineering Science, 21, 397, 1966
4. Bartholomew, W. H., Karow, E. O., Sfat M. R., and Whilhelm, R. H., "Oxygen Transfer
and Agitation in Submerged Fermentations," Industrial and Engineering Chemistry,
42,1801,1950
5. Betz, W. H., and Betz, L. D., "Oxygen Removal with Na2SO3," Technical Paper
No. 114
6. Cooper. C. M., Fernstrom, G. A., and Miller, S. A., "Performance of Agitated
Gas-Liquid Contactors," Industrial and Engineering Chemistry, 36, 504, 1944
7. Frankenberg, T. T., "Removal of Sulfur from Products of Combustion," API Preprint
No. 53-65, May 12, 1965
8. Fuller, E. C., and Crist, R. H., "The Rate of Oxidation of Sulfite Ions by Oxygen,"
Journal of the American Chemical Society, 63, 1644, 1941
9. Hixson, A. W., and Gaden, E. L., Jr., "Oxygen Transfer in Submerged Fermentation,"
Industrial and Engineering Chemistry, 42, 1792, 1950
10. Johnstone, H. F., and Singh, A. D., "Recovery of Sulfur Dioxide from Waste Gases,"
Industrial and Engineering Chemistry, 32, 1037, 1940
1 1. Johnstone, H. F., and Kleinschmidt, R. V., "The Absorption of Gases in Wet Cyclone
Scrubbers," Transactions of the American Institute of Chemical Engineers, 34, 181,
1938
12. Johnstone, H. F., Read, H. J., and Blankmeyer, H. C., "Recovery of Sulfur Dioxide
from Waste Gases," Industrial and Engineering Chemistry, 30, 101, 1938
13. Mallette. F. S., Problems and Control of Air Pollution, Chapter 15, Reinhold
Publishing Corp., New York, 1955
-------
14. Manvelyan, M. G., Grigoryan, G. O., et al, "Effect of Inhibitors on Oxidation of
Magnesium Sulfite to Sulfate by Atmospheric Oxygen in Presence of Traces of
Nitrogen Oxides," translated from Zhurnal Prikladnoi Khimii, 34, 896, 1961
15. Maxon,W. D., and Johnson, M. J., "Aeration Studies on Propagation of Baker's
Yeast," Industrial and Engineering Chemistry, 45, 2554, 1953
16. Phillips, D. H., and Johnson, M. J., "Oxygen Transfer in Agitated Vessels," Industrial
and Engineering Chemistry, 51, 83, 1959
17. Srivastana, R. D., McMillan, A. F., and Harris, I. J., "The Kinetics of Oxidation of
Sodium Sulphite," Canadian Journal of Chemical Engineering, 46, 181, 1968
18. Wartman, F. S., "Oxidation of Ammonium Sulphite Solution," United States Bureau
of Mines, Progress Reports - R.I. 3339 Metallurgical Division, No. 17, May 1937
19. Yagi, S., and Inoue, H., "The Absorption of Oxygen into Sodium Sulphite Solution,"
Chemical Engineering Science, 17,411, 1962
20. Johnstone, H. F., "Recovery of Sulfur Dioxide from Waste Gases," Industrial and
Engineering Chemistry, 27, 587, 1935
21. Johnstone, H. F., and Keyes, D. B., "Recovery of Sulfur Dioxide from Waste Gases,"
Industrial and Engineering Chemistry, 27, 659, 1935
22. Johnstone, H. F., and Singh, A. D., "Recovery of Sulfur Dioxide from Waste Gases,"
Industrial and Engineering Chemistry, 29, 286, 1937
23. Johnstone, H. F., "Recovery of Sulfur Dioxide from Waste Gases," Industrial and
Engineering Chemistry, 29, 1396, 1937
24. Johnstone, H. F., and Williams, G. C., "Absorption of Gases by Liquid Droplets,"
Industrial and Engineering Chemistry, 31,993, 1939
25. Johnstone, H. F., and Silcox, H. E., "Gas Absorption and Humidification in Cyclone
Spray Towers," Industrial and Engineering Chemistry, 39, 808, 1947
26. Pigford, R. L. and Pyle,C., "Performance Characteristics of Spray Type Absorption
Equipment," Industrial and Engineering Chemistry, 43, 1649, 1951
27. Whitney, R. P., et al, "On the Mechanism of Sulfur Dioxide Absorption in Aqueous
Media," TAPPI, 36, 172, 1953
28. Parkinson, R. V., "The Absorption of Sulfur Dioxide from Gases of Low
Concentration," TAPPI, 39, 522, 1956
29. Pollock, W. A., et al, "Removal of Sulfur Dioxide and Fly Ash from Coal Burning
Power Plant Flue Gases," ASME Preprint, August 5, 1966
-------
30. Katell, S., "Removal of Sulfur Dioxide from Flue Gas," Chemical Engineering Progress,
62,67, 1966
31. Reiss, L. P., "Cocurrent Contacting in Packed Towers," Industrial and Engineering
Chemistry, Process Design and Development, Vol. 6, 486, 1967
32. Kopita, R., and Gleason, T. G., "Wet Scrubbing of Boiler Flue Gas," Chemical
Engineering Progress, 64, 74, 1968
33. Blosser, R. O., and Cooper, H. B. H., "Trends in Atmospheric Participate Matter
Reduction in the Kraft Industry," TAPPI, 51, 73A, 1968
34. Danckwerts, P. V., "Gas Absorption with Instantaneous Reaction," Chemical
Engineering Science, 23, 1045, 1968
-------
Table 1
FLY ASH REMOVAL
LIST OF VENDORS CONTACTED
STUDY OF SO2 SCRUBBERS
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
Pulverizing Machinery Company
(Formerly Aireton Eng. Co.)
Buell Engineering Company, Inc.
Buffalo Forge Company
Burgess-Manning Company
The Ceilcote Company, Inc.
Chemical Construction Corporation
Clermont Engineering Co.
Corning Glass Works
Croll-Reynolds Company, Inc.
Dorr-Oliver
The Ducon Company, Inc.
Fuller Company
Fritz W. Glitsch & Sons, Inc.
Heil Process Equipment Corporation
Maurice A. Knight Co.
Koch Engineering Company, Inc.
National Dust Collector Corporation
Nooter Corporation
Peabody Engineering Corporation
Research-Cottrell, Inc.
U.O.P. Air Correction Division
Claude B. Schneible Co.
Norton Company
(Formerly U. S. Stoneware, Inc.)
Quoted
8-22-69
9-11-69
9-19-69
Reason for Declining to Quote
8-27-69
9-18-69
9-17-69
8-25-69
7-18-69
9-10-69
9-16-69
7-19-69
8-11-69
9-15-69
Equipment too small
Do not have suitable equipment
Will not quote without fee
Do not have equipment this size
Equipment too small
Declined to quote
Do not offer this type of
equipment
Can quote only in connection
with Combustion Engineering
Can offer no information on
flue gas treating
Quote on fly ash removal only
See Note below
Note: The UOP Air Correction Division declined to quote because they believe that low
liquid velocities and very high retention times are required in producing a liquor
high in bisulfite. This is in opposition to the operating principle of their Turbulent
Contact Absorber (TCA) scrubber.
-------
VENDORS QUOTING ON FLY ASH REMOVAL AND QUENCH EQUIPMENT
STUDY OF SO2 SCRUBBERS
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
Type of Fly Ash Removal Section
Manufacturer
Pulverizing Machinery Company
(Formerly Aireton Eng. Co.)
Buell Engineering Company, Inc.
The Ceilcote Company, Inc.
Croll-Reynolds Co., Inc.
Fritz W. Glitsch & Sons, Inc.
Heil Process Equipment Corporation
Maurice A. Knight Co.
Koch Engineering Company, Inc.
Peabody Engineering Corporation
Research-Cottrell, Inc.
Claude B. Schneible Co.
Norton Company
(Formerly U. S. Stoneware, Inc.)
Tray
Venturi
X
X
X
X
X
Impinge-
Cyclone merit
Packed
Bed
Other
X
X
X
X
X
X
X
Q]
CD
NJ
-------
VENDORS QUOTING ON SO2 SCRUBBERS
STUDY OF SO2 SCRUBBERS
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
Manufacturer
Pulverizing Machinery Company
(Formerly Aireton Eng. Co.)
Buell Engineering Company, Inc.
The Ceilcote Company, Inc.
Croll-Reynolds Company, Inc.
Fritz W. Glitsch & Sons, Inc.
Heil Process Equipment Corporation
Maurice A. Knight Co.
Koch Engineering Company, Inc.
Peabody Engineering Corporation
Claude B. Schneible Co.
Norton Company
(Formerly U. S. Stoneware, Inc.)
Type of SO2 Absorption Section
Tray
Venturi Cyclone
Impinge-
ment
Packed
Bed
Other
X
X
X
X
X
X
X
X
Q>
0>
W
-------
SUMMARY OF VENDORS' QUOTATIONS'1'
STUDY OF SO2 SCRUBBERS
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
Table 4
Vendor
Quench Section
Type of Quench
Number of Units in Parallel
Size of Unit
Materials of Construction
Fly Ash Removed, %
Pressure Drop, In. H20
Water Circ. Rate, Gpm
(Total)
S02 Scrubbing Section
Type of Scrubber
Number of Units in Parallel
Total Number o* Units
Size of Unit
Materials of Construction
Total Packed Height, Ft
Stages S02 Removal
SO 2 Removed, %
Pressure Drop, In. H20
Liq. Recirc. Rate, Gpm
Pulverizing
Machinery Co.
Venturi
7
6'-6"diam
xlT
Steel-Coated
Emersite
97 >1
10
725
Cyclonic
7
14
12'-6" diam
x44'
Steel -
Rubber Lined
-
2
95
12
14,700
Buell Eng. Co.
Floating Ball
9
14'-0"diam
x27'
Fiberglass
95
4
1,760
Floating Ball
9
9
.14' diam
x35'
316S.S.
-
2
Not stated
7.5
3,520
The Ceilcote
Co., Inc.
Tellerette
Packing
8
20'x14'
x18'
Reinforced
Plastic
98-99 >5/u +
1
6,800
Tellerette
Packing
8
8
Included in
Quench Sec.
Reinforced
Plastic
-
2
95-97
5
4,000
Croll-Reynolds
Co., Inc.
Venturi
3
10' diam
x40'
Steel with
Amercoat
Most
0
7,500
Venturi
3
6
10' diam
x40'
Fiberglass
Dyne) Liner
-
2
Not stated
0
10,000
The Oucon
Co., Inc.
Venturi
12
9'-2"diam x
13'-6"
316S.S.
99+
10
9,600
Cyclonic
Multivane
12
12
12' diam x
28'-3"
Steel-Epoxy
Lined
-
1
90-92
3
6,000
Fritz W. Glitsch
& Sons, Inc.
Spray
1
38' diam
x20'
Steel -
Rubber Lined
Not stated
-
1,600
Impingement
Grids-410S.S.
1
1
38' diam
x34'
Steel -
Amercoat
16
2
Not stated
7.0
3,400
Heil Process
Equipment Corp.
Water-Jet
8
Not stated
316 S.S.
Most-Over 5/Lt
3
Not stated
Packed
Section
8
8
Not stated
Plastic
Not stated
Not stated
99
Not stated
Not stated
Maurice A. Knight Koch Engineering
Co.
Venturi
6
Not stated
Steel- Lined
95
20
6,600
Packed 2"
Saddles
1
1
Not stated
Steel -
Plastic Lined
Not stated
Not stated
Not stated
4
3.5 Gpm/S.F.
Co., Inc.
Venturi
4
12' diam
x20'
Steel -
Rubber Lined
90
30
6,000
Packed 31/*"
P.P. Rings
2
2
30' diam
x56'
31 6 S.S.& Steel-
Rubber Lined
14
1
Not stated
8
5,000
Peabody Eng.
Corp.
Impingement
Baffle Plate
4
12'x3G'
x25'
31€ S.S.
Not stated
-
3,040
Impingement
Baffle Plate
4
4
Included
Above
316S.S.
-
3
Not stated
11 (Total)
4,080
Research-Cottrell,
Inc.
Flooded Disc
4
8'diam x 13'-9"&
21'diamx33'
Steel - PVC
Lined
98
6
4,400
No Quote
No Quote
No Quote
No Quote
No Quote
No Quote
No Quote
No Quote
No Quote
No Quote
Claude B.
Schneible
Multiwash
Cyclonic
14
10'-9"diam
x26'
304 S.S.
99 >1
-
3,400
Multiwash
Cyclonic
14
14
10'-9"diam
x22'
304 S.S.
-
1
95
6.8 (Total)
3,400
Norton Co.
Packed
3" Intalox
Saddles
1
43' diam
x20'
Steel -
Amercoat
99+
0.5
4,350
Packed
3" Intalox
Saddles
1
1
43' diam
x42'
Steel -
Amercoat
24
2
Not stated
8.5
8,700
S&W Eng. Corp.
Spray
1
37'-6" diam
x20'
Steel -
Amercoat
90+
-
1,600
Ripple Trays
1
1
37'-6" diam
x40'
Steel -
Amercoat
(10 trays)
2
Est.90
18
4,600
S&W Eng. Corp.
Spray
1
37' diam
x20'
Steel -
Amercoat
90+
-
1,600
Johnstone
Slat Packing
1
1
37' diam
x28'
Steel -
Amercoat
10
2
Est.90
4 (Total)
3,400
(Total)
Estimated Oxidation, %
2-5
2-5
(2) 10-15 (2) 3-5 (2) (2)
Notes: (1) Quotations based on equipment required for one boiler for 300 megawatt unit; (U) Not Estimated
(2)
(2)
No Quote
(2)
10-15
8-10
-------
Table 5
INVESTMENT COMPARISON
SO2 SCRUBBERS FOR THE STONE & WEBSTER/IONICS PROCESS
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
Type of Absorber
Johnstons wood slat packing
GIitsci^/id impingement packing
Intalox Saddle packing
Venturi scrubbers
Stone & Webster Ripple Tray
Cyclonic scrubbers
Floating ball
System Cost,1
1,200 Mw
$6,040,000
6,720,000
7,920,000
8,960,000
9,500,000
11,920,000
12,800,000
Differential from
Johnstone Base Cost
0
+$680,000
+1,880,000
+2,920,000
+3,460,000
+5,880,000
+6,760,000
' Cost includes quench, sulfur dioxide scrubber, pumps for two stages, blowers, ducts, piping,
instrumentation, dampers, civil accounts, investment in cells for oxidation differential
from Johnstone base for four 300 Mw boilers.
-------
OPERATING COST COMPARISON
SO2 SCRUBBERS FOR THE STONE & WEBSTER/IONICS PROCESS
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
Scrubber System
Type of Differential Power
Scrubber Cost, $/Year
Johnstone
Glitsch grid
Intalox Saddle
Venturi
Ripple Tray
Cyclonic
Floating ball
_
+$18,800
+42,800
+20,400
+138,800
+212,000
+109,000
Oxidation
Differential Power
Cost, $/Year
-$84,200
+ 100,500
+ 110,500
+126,300
-126,300
-126,300
Maintenance
Differential
$/Year (2%AI)
+$13,600
+37,600
+58,400
+69,200
+117,600
+135,200
Total Operating
Cost Differential,
$/Year
-$41,800
+ 190,900
+ 189,300
+334,300
+203,300
+117,900
Note: The annual operating cost of a Johnstone-based system will be on the order of $2,500,000.
0)
CT
CD
-------
Table 7
COST EVALUATION
SO2 SCRUBBER SYSTEM
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
Comparative
Present Worth,
Johnstone Type
Type of Scrubber as Base
Johnstone wood slat packing Base (Zero)
Glitsch grid impingement packing +$794,000
IntaloxSaddle packing +5,350,000
Venturi scrubbers +7,200,000
Stone & Webster R ipple Tray +9,670,000
Cyclonic scrubbers +12,680,000
Floating ball +13,380,000
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PAGE NOT
AVAILABLE
DIGITALLY
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