UNISEARCH LIMITED
THE UNIVERSITY OF NEW SOUTH WALES
SURVEY OF AUSTRALIAN EXPERIENCE
IN COLLECTING HIGH RESISTIVITY FLY ASH
WITH ELECTROSTATIC PRECIPITATORS
KENNETH J. McLEAN
Prepared for
THE ENVIRONMENTAL PROTECTION AGENCY,
RESEARCH TRIANGLE, NORTH CAROLINA, 27701.
Contract No. 68-02-0245
Wpllongong University College
University of New South Wales
WOLLONGONG, N.S.W. 2500.
SEPTEMBER, 1972
(i)
-------
SURVEY OF AUSTRALIAN EXPERIENCE IN COLLECTING
HIGH RESISTIVITY FLY ASH WITH ELECTROSTATIC
PRECIPITATORS
by
KENNETH 3. McLEAN
Prepared for
The Environmental Protection Agency,
Research Triangle, North Carolina, 27701
Contract No. 68-02-0245
Wollongong University College
University of New South Wales
WOLLONGONG. N.S.W. 2500.
September, 1972.
(i)
-------
CONTENTS
1. METHOD OF COLLECTION AND PRESENTATION
OF INFORMATION
1.1 Electricity Authorities Burning LOUJ Sulphur Coal 1
1.2 Method of Collecting & Evaluating Data 1
1.3 Some Aspects of Electrostatic Precipitator Theory 2
2. COAL AND FLY ASH CHARACTERISTICS
2.1 Introduction 7
2.2 Chemical Characteristics 7
2.3 Physical Characteristics 11
2.4 Resistivity 13
3. PERFORMANCE OF FULL SIZE ELECTROSTATIC 17
PRECIPITATORS
3.1 Introduction 17
3.2 Specification of Existing Installations 17
3.3 Performance 18
3.4 Operating Experience 23
(a) Rapping
(b) Discharge Wires
(c) Electrical Characteristics
(d) Mechanical Collectors
(e) Outages & Maintenance
(f) Influence of Operating Conditions
(g) Pipe Type Precipitators
3.5 Variation of EMU with Sulphur 28
3.6 Hot Side Precipitators 28
(ii)
-------
. DTLOT SCALE PRECIPITATOR TESTC 30
4.1 IntroauL.uj.on 30
4.2 Factors Affecting the Interpretation of Pilot 32
Precipitator Tests
(a) Gas Velocity
(b) Gas & Temperature Distribution
(c) Alignment of Electrodes
(d) Leakage & End Effects
(e) Rapping
(f) Particle Size
(g) Electrical Energization
(h) Coal Variation
4.3 Scaling Factor . 33
4.4 Test Arrangement 34
4.5 Typical Daily Test Routine 34
4.6 Relationship to Full Size Precipitator Performance 35
4.7 General Data from Pilot Tests 40
(a) Flue Gas Temperature
(b) Carbon Content of Fly Ash
(c) Gas Velocity
(d) Migration Velocity Variation with Efficiency
(e) Sulphur
5. FLUE GAS CONDITIONING 44
5.1 Introduction 44
5.2 Conditioning Agents & Methods of Injection 45
(a) Permanent Installations on Full Size
Precipitators
(b) Temporary Installations
5.3 Effects of Conditioning on Fly Ash Electrostatic
Precipitation Properties 47
5.4 Conditioning During Pilot Precipitator Tests 50
5.5 Effect of Conditioning on Fly Ash Properties 51
(iii)
-------
6. THE CSIRO TECHNICAL SCALE COMBUSTION AND 53
ELECTROSTATIC PRECIPITATION FACILITY
6.1 Introduction 53
6.2 Experimental Apparatus 54
6.3 Test Procedure 56
6.4 Limitations 56
6.5 Results 6. Discussion 57
;. LABORATORY TECHNIQUES FOR EXAMINING
ELECTROSTATIC PRECIPITATING PROPERIIES
rf FL' ASH 59
?.l Objective ' 59
7.2 ACIhL. Small Furnace 59
7.3 WUC Test Rig 'j. Analyser 61
7.4 Discussion 64
. SUMMARY OF SALIENT FEATURES
9. ACKNOWLEDGEMENTS 69
10. ^EFE
-------
ABSTRACT
A survey is made of the Australian experience in using
electrostatic precipitators to collect fly ash resulting from the
combustion of the IDUJ sulphur bituminous coal in pulverized fired
boilers. This ash has a very high resistivity and is exceptionally
difficult to collect, requiring in some cases, precipitators uiith
specific collecting areas above 600 ft /kcfm. Typical precipitator
dimensions and operating parameters are included together with a
survey of the main problems and experience obtained in collecting
this fly ash. The performance of the precipitators has been improved
by operating at low temperatures and by conditioning the flue gas
aiith sulphur trioxide and ammonia. The various conditioning injection
systems are described and the effectiveness of the agents on the
different ashes is discussed. Since the sulphur content of the coal
cannot be used to reliably predict the electrostatic precipitating
properties of the fly ash, pilot, technical scale and laboratory
tests are carried out in order to determine the characteristics of
the fly ash. These test procedures are described and evaluated.
The report concludes with a comprehensive list of publications and
reports related to the survey.
-------
CHAPTER 1
METHOD OF COLLECTION AND PRESENTATION
OF INFORMATION
1 .1 Electricity Authorities Burning Low Sulphur Coals
The louj sulphur bituminous coal deposits which are used for the
generation of electrical energy are located along the east coast of the
Australian continent in the states of Neuj South Wales and Queensland.
These reserves are being developed by three separate, government
controlled, electricity authorities. The names of each of these author-
ities and their addresses are given belouj,
Electricity•Commission of
(ECNSW)
I.S.W.
G.P.O. Box 5257,
SYDNEY. N.S.W. 2001
Southern Electric Authority of Queensland
(SEAQ)
G.P.O. Box 403,
BRISBANE. Qld. 4001.
Northern Electric Authority of Queensland
(NEAQ)
P.O. Box 721,
TOWNSVILLE. Qld. 4810.
The ECNSW has gained the most experience in collecting fly ash from
low sulphur bituminous coals by electrostatic precipitators and
consequently this report is centered around the information obtained
from them. The SEAQ and NEAQ are both much smaller electrical
authorities and have had much-less experience. However the coal they
burn is geographically from quite different areas so their test results
and general experiences contribute significantly to the breadth of this
report.
1.2 Method of Collecting and Evaluating Data
In order to collect and evaluate the data available in Australia,
each of the electricity authorities was visited and the information
obtained from the personnel directly involved with electrostatic
precipitators and from official and unofficial records of tests. In the
case of ECNSW, an office was made available and direct access given to
all relevant data.
-------
2.
A large amount of material and data has been made available for
assessment. The problem was,'to select from sometimes conflicting
evidence, that which was relevant to this report. The main guide line
adopted was to make it sufficiently comprehensive so as to elucidate
and yet not too detailed so as to be confusing. The correct balance
betmeen the two depends to some extent on the subjective judgment of
the writer and it is hoped that a reasonable balance has been obtained.
Considerable assistance was obtained by office engineers in
interpreting, evaluating and selecting information to be included. In
order to confirm some of the conclusions, visits were made to the
appropriate power stations and the views obtained from the station staff
directly involved in some of the projects. The. data and opinions
expressed in this report are therefore drawn from many engineers
directly involved with electrostatic precipitators. In the final
analysis however, this information still"has to be interpreted by the
writer and presented in a manner that seems reasonable to him. While
the report is therefore based on the very wide experience of engineers
in Australia it must not be regarded as an expression of the official
view of any one of them nor of the authorities who supplied information.
1.3 Some Aspects of Electrostatic Precipitator Theory
The method of presenting and interpreting the performance of
electrostatic precipitators depends to some extent on the mathematical
and physical models adopted to explain their operation. The approach
used in this report is the traditional one which is extensively
elaborated on by White (1) and more recently by Oglesby and Nichols (2).
However, in order to appreciate the significance of some of the graphs
in this report and the points raised in the discussion, some of the more
important aspects of this model are explained in this section.
One approach, which at least has the advantage of starting with a
theoretical expression, is to use the efficiency equation developed by
Deutsch. As originally derived, this equation refers to the efficiency
of collection of homogeneous particles all of uniform size. It is
given by,
n.i-.'*" • <1>
where, A = plate area
Q = gas flow rate
oo = migration velocity
In this case to is the actual migration velocity for a given particle
size. In an industrial situation, where the particles are seldom
homogeneous, each particle size has its own theoretical migration
velocity. If the penetration for each size is individually summed, the
equation for the overall efficiency becomes,
-------
T
Jo
n- 1 - da ,(2,
F-or any given particle size distribution, the penetration component
of Eq. 2 may be calculated and then a value of to determined so as to
give the same efficiency when substituted in the equation,
_
= 1-e Q .(3)
This is the Deutsch-Anderson equation. It is essentially a semi-
empirical equation in which to has the dimensions of velocity and is
called sometimes "effective drift velocity", "precipitation factor" and
"effective migration velocity"(EMU).
One of the important limitations of Eq. 3 is that for a given set
of electrical conditions in the electrostatic precipitator, to mill
change as the A/Q varies (i.e. as the efficiency changes). This is a
well known phenomenon and is reported on generally in the literature.
Fig. Id shows the variation of the migration velocity with particle
size when field and diffusion charging is considered separately (29).
Since the very fine particles are difficult to collect, their effect on
the effective migration velocity (EMU) in the Deutsch-Anderson equation
is to reduce its value as the efficiency improves. This is illustrated
in Fig. 1.2. If the value of EMU at 95% efficiency is a given value,
then to obtain 99.5$ the value of EMU must be assumed to be half this
value.
Another important factor which can cause considerable variation in
the value of EMU is the temperature. The resistivity of in-situ fly
ash increases for temperatures up to about 300 F and then decreases at
higher temperatures. Since the overall performance of a precipitator
is an inverse function of resistivity, the effective migration velocity
will vary with temperature, and have a minimum value at the temperature
at which the resistivity is approximately a maximum.
The actual value of the effective migration velocity cannot be
theoretically calculated even through Eq. 2. There are additional
factors affecting the overall precipitator performance which are not
taken into account in this theoretically derived equation. This includes
such factors as gas turbulence, particle diffusion, electric wind,
particle charging time and the voltage drop across the deposited
layers (13). Additional factors found in practical precipitators include
-------
100
o
U
O
LU
0. I
Field Chargi ng
E. = \ .5*\
-------
100
o
c
(D
80
o
-------
such things as re-entrainment, gas velocity variation across the precipi-
tator, reverse gas flows, temperature gradients, electrode misalignments
and zone failures. All these result in an overall efficiency different
from the theoretically calculated value. In practice the value of EMU
is strictly an empirical constant. It is calculated from Eq. 3 in uuhich
the efficiency is measured, and the value of A/Q is known.
One method of quantifying the electrostatic precipitating properties
of a given fly ash is to determine its effective migration velocity. Ash
from low sulphur coals has a low value u/hile ash from high sulphur coals
has relatively higher values. Comparisons between different•ashes are
possible on this basis providing due consideration is given to,
(a) efficiency level, and
(b) temperature at which the efficiency
is measured.
There could be some problem in correlating the value of the EMU
calculated for one electrostatic precipitator to that calculated for
another and it is theoretically possible that for a given ash, the EMU
could vary for different makes of precipitators. It seems likely
however, that provided the units are well maintained and adequately
sized, the values will be similar for all full scale units. This may not
be the case for the much smaller pilot scale units. Differences seem to
occur with pilot scale units of different manufacturers 'and between the
pilot scale and full scale units. This will be discussed more fully in
Chapter 4.
-------
CHAPTER 2
COAL AND FLY ASH CHARACTERISTICS
2. 1 Introduction
The low sulphur bituminous coals of Australia are located along the
east coast of the continent in the states of New South Wales and
Queensland. They are mainly of Permian origin and possess inherent
differences in mineral content when compared with the carbonaceous coal
seams of Europe and North America.
In New South Wales, the coal used by the Electricity Commission of
New South Wales in its pulverized fuel-fired power stations comes from
four main sources; the Northern, Hunter Valley, Western and Southern
coal fields. The first two of these are located roughly north of
Sydney and the last two are respectively in the western and southern
directions. Each coal field usually comprises a number of different
seams, some of which have been extensively mined and others have had
only small samples removed for testing. It is not uncommon for a number
of different collieries to be located on the one seam. Coal may be
designated by the seam name or by the colliery at which it is mined;
both nomenclatures are extensively used. Tables 2.1 - 2.2 set out the
main coal fields, seams and collieries from which coal has been burnt in
existing power stations and the resultant fly ash tested for its electro-
static precipitating properties.
The main coal in the southern part of Queensland being fired in
pulverized fuel power stations comes from the West Moreton field, located
25 miles :west of Brisbane. Coal from the Blackwater field, 400 milss
north west of Brisbane has been tested using a pilot scale plant and
be burnt in a future power station.
In the northern part of Queensland the main source of coal for the
NEAQ is from the Bowen field located 120 miles south of Townsville.
2.2 Chemical (10)(11)(14)(22)(26)
Typical chemical properties of the New South Wales and Queensland
low sulphur coals and resulting fly ash are given in Tables 2.1 - 2.3.
-------
TABLE 2.1 - CHEMICAL COMPOSITION OF NSW COAL AND FLY ASH
(Dry Air Basis)
Coal Field
Seam
Colliery
Gt. Northern
Neujuale
Northern
Wallarah
Fassifern
Hunter Valley
Baysiuater
Ravensujorth
Coal Analysis
Cal. Value BTU/lb
Volatile Matter
Fixed Carbon
Moisture
Ash
Sulphur: Total
I Pyritic
Sulphate
^Organic
Ash Analysis
SiO
AI2°3
Fe 0
CaO
MgO
Na 0
2
KJD
2
so3
TiO,
Combustible
11 ,950
30.6
50.7
3.1
15.6
0.36
OoOO
0.00
0.36
55.6
29.6
4.53
2.27
1.35
0.65
2.98
1.00
1.41
-
2.0
12.3
0.29
50.3
28.2
5.0
4.12
1.10
0.29
0.30
0.31
1 .30
8.3
2.0
16.5
0.44
56.1
26.5
3.44
0.61
0.46
0.24
1.04
0.13
1.11
9.6
9,130
23.4
43oO
4.0
30.0
0.36
0.12
0.00
0.24
57.8
28.9
4.71
1.76
1.70
0.50
1.27
1.35
1.10
-
-------
TABLE 2.2 - CHEMICAL COMPOSITION OF N.S.W. COAL AND FLY ASH
Coal Field
Seam
Colliery
Coal Analysis
Cal. Value BTU/lb
Volatile Matter
Fixed Carbon
Moisture
Ash
Sulphur: Total
Pyritic
Sulphate
Organic
Ash Analysis
Si02
AI2°3
Fe2°3
CaO
MgO
Na20
K2°
so3
Ti°2
Combustible
(Dry
Western Main
10,740
26.9
47.7
10.0
15.5
0.69
55.9
31.2
2.45
0.56
0.32
0.06
2.35
0.22
0.92
5.8
Air Basis)
Western
Lithgou
Wallerawang
11 ,480
28.5
49.7
9.0
12.6
0,62
57.5
25.6
1.22
0.82
0.24
0.06
2.89
0.22
1.10
9.7
IMeu/com
11,040
29.1
45.9
7.0
17.9
Oc58
63.1
26.8
0.59
0.51
0.30
0.12
2.52
0.30
0.88
4.6
Southern
Wongaiuilli
Huntley
9,720
22.8
43.3
1.1
32.8
0.42
65.0
25.0
7.24 '
0.33
0.48
0.07
1.01
0.20
0.60
_
-------
TABLE 2.3 - CHEMICAL COMPOSITION OF QUEENSLAND COAL AND FLY ASH
(Dry Air Basis)
Coal Field
Seam
Coal Analysis
Cal. Value BTU/lb
Volatile Matter
Fixed Carbon
Moisture
Ash
Sulphur: Total
Pyritic
Sulphate
Organic
Ash Analysis
sio2
AI2°3
Fe2°3
CaO
MgO
Na20
K2°
S°3
Ti°2
Combustible
Blackwater
Main Lower
12,070
23.0
61.5
4.4
11.1
0.43
0.21
0.02
0.20
46.1
29.6
3.71
2.86
1.5
1.9
1.45
0.49
0.86
9.26
West Moreton*
Bluff
Four Foot
Bergin
10,380
27.1
44.9
7.0
21.0
0.27
0.06
0.00
0.21
54.5
34.1
3.4
2.4
1.5
0.1
0.4
1.0
2.2
3.7
Boiuen
12,400
20.3
61 .0
4.2
14.5
1.3
56.7
26.9
10.5
1.1
0.3
0.2
0.2
0.3
2.4
_
Bowen
Blake
11 ,400
20.0
56.2
1.3
22.5
1.14
Oo58
0.16
0.40
53.1
36.6
1.4
0.8
0.4
0.2
. . 0.3
0.3
2.2
_
Total ash analysis
-------
11.
The values recorded are typical for a test series which may have been
conducted over a period lasting for several months. Uariations
however exist even in the same seam from one colliery to another so the
values may only be taken as representative. The significant features of
the composition of the fly ash when compared with the mean ranges encoun-
tered in the United States are;
(a) silicon oxide content is higher,
(b) iron oxide content is lower, and
(c) calcium oxide is generally lower.
It is also probable that the ratio of acidic components (SiO ) to-
basic components (AI 0 , M 0, CaO) is generally.higher than in.the
fly ash from United States coals.
A very extensive analysis of the trace element content has been made
on a large number of ashes and the results have been recorded elsewhere
(10). Typical trace element content of fly ashes from two different
coal fields is given in Table 2.4. The figures.are given as parts per
million on an air-dried basis.
No obvious correlation has been found between the coal or ash
chemical composition or trace element content, and the electrostatic
precipitating properties of the fly ash.
2.3 Physical Characteristics
I
(a) Sizing: During acceptance tests, the size distribution of the fly
ash entering the inlet of the more modern electrostatic precipi-
tators had a mean particle size from 19.0 to 21.5/tm when measured
on the Bacho sizing instrument. (The mean particle size is the
value below which 50 percent of the fly ash weight falls). For the
older plants, at which most of the pilot scale tests were conducted,
the mean particle size is in the range 7 to 14/>m«
(b) Density; The fly ash density while still warm varied over a fairly
wide range as indicated, in Table 2.5.
Table 2.5 - Bulk Densities of Warm Fly Ash
Seam Authority Av. Density Ib/ft
Lithgow ECIMSW 40.5
Bayswater ECNSW 30.5
Main Lower SEAQ 37.5
Blake NEAQ . 48.0
The density was found from the following measurements,
-------
12.
TABLE 2.4 - TRACE ELEMENT ANALYSIS OF FLY ASH SAMPLES
Seam
Colliery
Element
Ag
B
Ba
Be
Bi
Cd
Co
Cr
Cu
Ga
Ge
In
La
Mn
Mo
Mi
Pb
Sb
Sc
Sn
Sr
Th
Tl
V
W
Y
Zn
Zr
FROM TWO NSW COALS
Great Northern
Netuuale ,
0.2
30
60
1 ;
10
50
1.5
5
10
6
5
1.5
10
60
1
5
9
15
5
10
150
50
10
15
10
9
50
100
Wongawilli
Huntley
0.3
30
100
2
20
100
3
7
15
10
2.5
4
30
500
1.5
15
10
40
8
7
100
100
20
15
20
15
100
250
-------
13.
(i) The weight of fly ash, and
(ii) The distance of the dust level below the top of the
collecting bin immediately it was removed from the
pilot precipitator and after settling had ceased.
From these measurements and a knowledge of the bin's dimensions,
the density of the ash was determined.
In one series of pilot scale tests, it was observed that higher
efficiencies resulted in lower bulk density. This was thought to
be due to the hollow spheroidal form of the small particles which
occur in greater proportion under conditions of high efficiency.
(c) Flow properties; In the normal operating temperature range of
electrostatic precipitators, the fly ash flows freely and no
"holding up" normally takes place. It is generally thought that
this is also true for much lower temperatures. However, some
cases of the ash not flowing freely have been reported and it is
now usual practice for heaters to be fitted to the hoppers.
2.4 Resistivity (19)
The in-situ resistivity of the fly ash at the normal temperatures
encountered in conventional electrostatic precipitators is very high by
world standards. Peak values varying from 10^ to 2 x 10^4 ohm-cm have
been measured using the Kevatron Electrostatic Precipitator Analyser 223.
A typical set of in-situ resistivity values for a wide temperature range
is shown in Fig. 2.1 for fly ash from three different coal fields.
These measurements were made during an extensive pilot plant test
program.
For temperatures below about 300 F, the resistivity is dominated
by the surface conduction over the fly ash particles which in turn is
greatly influenced by the chemical composition of the flue gas
(i.e. H20j 503 etc). At higher temperatures, or in a perfectly dry
atmosphere, the fly ash behaves as a semi-insulator following the
Rash Henrichsen's Law.
p = AeB/T
If the reciprocal of the absolute temperature is plotted against the
resistivity, a straight line is obtained, the slope of which gives B.
Fig. 2.2, shows this plot for fly ashes from two main coal fields.
This indicates that for temperatures in the 700-800°F range, the normal
values for a hot side precipitator, the resistivity of the most difficult
Australian fly ash is reduced to less than 10'"-' ohm-cms.
-------
14.
15
10
14
E
U
I
E
.c
O
in
0)
or
10
13
12
50
Northirn
Hunter Valley
-Western
y 1
\
V
200 250
300
350 400 450 500
Tempe ratu re "F
Fig. 2.I
Variation of In-situ Resistivity with Temperature
-------
15.
Temperature
800 600 400
200 °F
1U '
io13-
{= io12-
£
.c
0
•H 1011-
>
4-
K 1010'
io9 •
io8 .
1
y
/
/.
/
1
/
.
/ t
1 -r
1
i '
I ,
f /
1 *
1
L r
/ /
*
/ /
/ /'
/ .
• /
/
' 1
: i
-/ — — -i
/
/ *
i
i
i
i
.
'
t
i
-
/
/
1
'
2
1000/T °K
— — — — Southern
. Northern
Fig. 2.2
Variation of Moisture Free Resistivity
with Temperature.
-------
16,
. Considerable care needs to be exercised in interpreting resistivity
measurements and especially in comparing the values measured by one
instrument with those measured by another. This caution is particularly
necessary in the case of the in-situ measurements of these very high
resistivity fly ashes. Extensive investigations have been made into the
insignificance of some of the parameters affecting resistivity and it
has been shown that, in addition to the environmental conditions, the
resistivity is dependent on,
(a) compaction,
(b) particle size distribution,
(c) magnitude of the applied electric field,
(d) time of application of the applied field, and
(e) method of measurement.
The resistivity measurements recorded in this report mere made at
an electric field E = 1,5 kV/cm and the current read ujithin 30 seconds
of applying the measuring field.
-------
17.
CHAPTER 3
PERFORMANCE OF FULL SIZE ELECTROSTATIC
PRECIPITATORS
3.1 Introduction
This section discusses the general specifications and performance
levels of existing plate type electrostatic precipitators without flue
gas conditioning, and gives some details of future plant. Some
information which is of interest is either proprietary or confidential
and cannot be reproduced here in any detail, but where possible, this
has been included in the generalized statements and curves.
i
The electrostatic precipitating properties of the different fly
ashes is also included. This is measured in terms of the effective
migration velocity, EMU, and is calculated from the Deutsch-Anderson
equation using the measured efficiency of the precipitators. The value
of' the EMU as determined in this manner still has to be interpreted
carefully as mas pointed out in Section 1.3 by making allowance for
the efficiency level and temperature at which the measurements are
made.
3.2 Electrostatic Precipitator Specifications (3)(5)(18)
The electrostatic precipitator manufacturers who have been
successful in tendering for precipitators in New South Wales and
Queensland are given in Table 3.1. The Table only lists those
manufacturers who have supplied parallel plate type units since 1960,
and includes the number of units together with the total capacity in
MW connected to the particular manufacturer's precipitators. Existing
and future plants have been included.
-------
It.
TABLE 3.1 - ELECTROSTATIC PRECIPITATOR MANUFACTURERS
„ , . 'M P n -4. Total Capacity
Supplier No. or Units MW
IMoyes - Research Cottrell 15 3,078
Suenska Flaktfabriken 9 2,973
Hoiuden - Lurgi 3 . 760
The basic range of dimensions and operating parameters of the
existing and future electrostatic precipitators are given in Table 3.2.
Gas velocities tend to be lower than those commonly used in the United
States, the maximum being approximately 5 ft/sec. Flue gas temperatures
are generally in the range 260 to 280°F, although two large precipi-
tators have been ordered to operate at gas temperature of 240°F. One
of these units is expected to have a flue gas temperature as low as
220°F. By operating at these low temperatures, advantage is taken of
the lower fly ash resistivity.
On the whole the SCA's have risen sharply from 270 in 1960 to
values in the order of 400 - 600 ft //kcfm. The actual value depends on
the type of coal being burnt, the efficiency level required and several
other factors associated with operating conditions and precipitator
design.
There has been no particular trend with regard to the electrical
sectionalization of the precipitators. At least 3 series zones are
used with the maximum number being 6. The plate area connected to a
single transformer-rectifier unit varies from 9,000 to 40,000 ft^. One
manufacturer tends to use smaller plate areas in each zone than do the
others. This same manufacturer is the only one to connect some of the
rectifiers in the half wave mode of operation, claiming that under some
conditions this gives better performance than full wave. All the
electrical supply authorities regard sectionalization as important but
none have formed any firm opinion with regard to the optimum arrangement.
This, together with the use of half wave rectifier connections, is a
matter which is generally left to the manufacturer's discretion.
Current densities are generally lower than that encountered in
collecting ash from high sulphur coals. The values recorded in
Table 3.2 include a significant component of back corona current so
the real current which is contributing to the precipitation of the fly
ash is lower than these figures.
3.3 Performance Levels (3)(5)(18)
The technique used for making efficiency measurements is in accord-
ance with B.S. 893. Preceding the efficiency test, a traverse is made
-------
19.
TABLE 3.2 - RANGE OF ELECTROSTATIC PRECIPITATOR
PARAMETERS
Parameter
Range
Gas and Dust
Flue gas temperature
Gas velocity
Moisture
Inlet dust burden
Carbon in Ash
Particle size 50%
UF
ft/sec.
% \J/\j
gr/ft-5
220
2.5
5
5
0.8
9
280
5.0
.9
11
9.0
28
Electrodes
Collecting plate height
Aspect ratio
SCA
Discharge electrode construction
Discharge electrode shape
ft' 24 - 40
7 .55 - .90
ft /kcfm 260 - 600
Frame and suspension
Wire, spiral wire,
barbed and star.
Electrical
No. series electrical zones
Plate area per zone ft
Rectifier connections
Rectifier voltage rating kV
current rating ma
Normal operating current density
Control: system
method
3 - 6
9,000 - 40,000
F. W. and H. F. W.
60 - 70
230 - 960
8-23
Manual and automatic
Spark rate, voltage
and current limit.
The values given in this table do not necessarily
give the extreme values obtained in practice but
rather indicate the typical range over which these
parameters vary.
-------
20.
uiith pilot tubes to determine the flue gas velocity distribution in the
duct. The sampling probe is then placed in the duct and the flue gas
is extracted isokinetically. The particulate is collected by a
Whatman's seamless thimble located in the probe but external to the
duct. The flue gas sample passes through a condenser to a metering
orifice, gas meter and pump. The condensate is measured at the
completion of each test and is used to calculate the moisture content
of the gas. The metering orifice is used to keep sampling velocities
at their precalculated isokinetic value as determined from the velocity
traverse.
The filter thimbles are carefully removed from the holder and the
dust deposited in the probe brushed out and add.ed to the dust in the
thimble. The thimble is then placed in a drying oven for one and a
half hours and dried at 170°F, after which it is placed in a desicator
for 20 minutes before weighing. The efficiency measurement is made by
concurrently measuring both the input and output flue gas dust burdens.
Where possible, the usual practice is to measure the efficiency of each
separate gas passage and the affective efficiency then calculated.
During each series of tests boiler conditions are held constant and the
significant parameters monitored.
The performance levels of the full size electrostatic precipitators
burning coals from the different seams are shouin in Fig. 3.1 and 3.2.
The electrostatic precipitation performance level does not fall on a
well defined line but tends to lay in a band. This has been determined
from tests on full size and pilot precipitators. The variations within
the band are dependent on a number of factors, one of the most important
being the variation of the chemical composition of the coal. For any
one coal field there are variations from one seam to another, and even
in one seam, differences occur from one mine to another.
Superimposed on these bands are the guaranteed efficiencies of
existing and future precipitators burning coal from these coal fields.
These figures may be regarded as being indicative of the performance
level of each electrostatic precipitator and take into account the mine
from which the coal comes and a number of other factors. At the
acceptance tests, most of the precipitators performed better than the
guaranteed figure and in some cases, significantly exceeded them.
Fly ash from the Wongawilli coal seam is the most difficult to
catch in an electrostatic precipitator. The precipitator efficiency
level given in Fig. 3.1 is a typical value and shows that the EMU is
less than 3 cm/sec. With flue gas conditioning however the precipitator
performs at a satisfactory level.
For some precipitators lower efficiency values have been measured
after the units have been in service for a period of time. This decay
is probably due to dust build up on the electrodes, loss of discharge
electrodes due to breakages, electrical zones being out of service,
incorrect adjustment of the automatic control and a general deterioration
of the mechanical components and alignments. It is not uncommon for the
effective drift velocity to fall to at least 75 percent of its accep-
-------
21.
10
99.9
60.0
50.0
150 200 250 300 350 400 450 500 550
2
Specific Collecting Area ft /kcfm
Fig. 3. I
Electrostatic Precipitation Performance Levels
of Fly-ash from NSW s Coals.
O Specified efficiency and. SCA (Northern)
jjf Typical Performance Level (Southern)
-------
22.
99.9
99. 8
99.7
99.5
99.3
o
S 99.0
o
98.5
LU
cn 98.0
o 97.0
0)
^ 96.0
o 95.0
93.0
90.0
85.0
80.0
70.0
60.0
50.0
X
X
0
0
**>/
X
/
200
250
300
350 400
450
500
550
600
650
Specific collecting area ft /kcfm.
Fig. 3.2
Electrostatic Precipitation Performance Levels
of Fly-ash from Queensland's Coals.
0 Specified Efficiency and Design SCA.(West Moreton)
O Specified Efficiency and Design SCA.(BIackwater)
-------
23,
tance test value. The efficiency of some makes of precipitators seems
to decay more rapidly than others and is influenced by changes in
boiler conditions. It is quite likely that precipitators collecting
high resistivity ash are more sensitive to these factors than precipi-
tators collecting low resistivity ash. No statistical evidence'however,
is available to confirm this.
3.4 Operating Experience (3)(5)
In this section some observations are made concerning the general
experience in collecting high resistivity fly ash.
(a) Rapping;
The magnitude of the force holding the fly ash to the electrodes
is a function of the effective resistivity of the deposited layer and
the corona current density. The corona current densities in precipi-
tators collecting high resistivity fly ash are usually lower than those
for high sulphur coals by a factor of 2 or 3, but the resistivity is
2 to 3 orders of magnitude higher. The net effect of this is that the
adhesive forces holding the fly ash to the plate are very much higher
than for the low sulphur coals and large forces are required to dislodge
the dust from the collecting plate.
The ECIMSW has carried out extensive tests on measuring the
acceleration forces on different collecting plate configurations and
has concluded that a minimum acceleration of 60 g in the transverse
direction (i.e. normal to the plate) is required to dislodge the fly
ash. In practice,transverse accelerations from 100 to 400 g have been
measured at some locations on modern precipitator plates. Some of the
older installations have accelerations well below the 60 g value.
There does appear to be some correlation between poor performance
and the magnitude of the acceleration forces. In one instance, a
modern precipitator's performance tends to deteriorate with time in
service and it is considered that this may be due to the generally
lower acceleration levels associated with this plant. In the case of
one of the older plants, where the acceleration forces are low, it
has been necessary to introduce periodic washing of the collecting
plates with water in order to prevent excessive build up of the dust
layer.
One consequence of the higher acceleration requirements, is that
the rapping forces must be higher than normal. Initially this caused
considerable maintenance problems and in some cases considerable
structural damage has occured. In all the plants however where this
trouble occured, modifications were made to rectify the faults and
reliable performance obtained.
The rapping frequency for the collecting plates varies from one
manufacturer to another. It seems possible to classify the systems
used into three distinct categories,
-------
24,
(i) Continuous rapping at constant frequency for all electrical
zones. Each plate section receives a single rap at regular time
intervals of about two minutes irrespective of the electrical
zone.
(ii) All the plates in the one zone are rapped together, or
consecutively in a short time period, with a frequency that
varies from one-zone to another. The usual practice is to rap
the inlet zone most frequently and the center and outlet zones
less frequently. A typical rapping period for the three zones
would be 15/30/60 minutes.
(iii) A combination of the above two. The plates in orte zone
are all rapped at the one frequency but are phased to give
continuous rapping, i.e.. equal t^.me intervals between the
rapping of each plate section in; the zone. The zone rapping
frequencies are similar to those used in (ii) above. This
system has the advantage of reducing at any given time, the
visual obscuration of the smoke plume during the rapping period'.
It is also likely that this system also reduces the total
emissions.
The optimum rapping frequency and magnitude has to be found by
experiment for each particular plant and fly ash. An important part of
tuning a precipitator is the correct adjustment of the rapping. The
general experience in the ECNSW seems to indicate that less frequent
rapping probably gives better results than a series of frequent raps.
The policy of all the electric authorities concerned in this survey
is to ask for a minimum acceleration of 60 g in their specifications.
Because of the EClMSW's extensive testing programme they are able to
anticipate with good accuracy the magnitudes of acceleration to be
expected for standard collecting plate construction. If there is any
uncertainty, acceptance tests are asked for in order to check the
manufacturer's claims.
(b) Discharge Wires;
One of the principal causes of electrical zone unavailability is
the grounding of the high voltage discharge electrode system due to wire
failure. The effect of this is partly reduced by providing a number of
zones which may be electrically isolated and by providing isolating
dampers in each gas path which enables a faulty zone to be repaired
without shutting down the boiler.
Most European manufacturers provide frames for holding the discharge
wires. These electrodes may comprise a solid rod or twisted square
securely welded top and bottom, or it may be a spiral wire held in
tension. The only United States manufacturer who has modern precipi-
tators installed, uses the single long wire held in tension by a weight.
Both types of support construction have been in service for reasonable
periods of time and it has not been found that one system has any
marked advantage over the other. Electrodes in frames have a good
operating record although in- some of the older plants, the frames have
-------
25.
warped a little. One advantage of this construction is that in the
event of a discharge wire breaking it does not always cause the
electrical zone to be shorted out. Operation can often be maintained
although sometimes at a reduced' voltage. It is likely that better
alignment is possible with the single suspended wire although difficul-
ties have been found with the, movement of the bottom holding frame.
Anti-sway insulators have been installed to remedy this.
The discharge electrodes of the two European manufacturers differ
from the practice of the United States manufacturer. One uses spiral
wires and the other a mixture of barbed and star shaped electrodes.
No information on their relative merits is available for release.
(c) Electrical Characteristics;(21)(23)(24)
Because of the high resistivity of the fly ash, the electrical
characteristics of the Australian installations differ somewhat from
those units collecting ash from high sulphur coals. They are
characterised by,
(i) Low applied voltages,
(ii) Existence of back corona,
(iii) High ineffective currents.
A typical set of voltage-current characteristics is shown in
Fig. 3.3. The initial part of each curve is the normal corona charac-
teristic suppressed to some extent by the voltage drop across the dust
layer. At point 'A1, back corona is established in the layer on the
collecting plate and a positive ions flow back to the discharge
electrode. This component of the current flow does not contribute to
the collection of the particulates but has a deleterious effect. In
some instances, this component may comprise 60 percent of the total
current flowing.
Sparking does not usually occur at the onset of back corona as
may be seen in the figure. It appears that at the ons.et of back
corona, the voltage gradient in the air gap is not sufficient to
propagate a spark. As the back corona increases, the positive charge
in the gap must so modify the field as to cause sparking.
The type of automatic control used varies with the manufacturer.
It may be completely dependent on the spark rate, it may be designed
to operate at the maximum voltage below sparking or it may have
voltage, current and spark rate limits. In the latter case, the current
limit usually determines the operating point. Under some operating
conditions all these methods of control have some limitations. If the
control is based on the spark rate alone, it is possible for a
precipitator to operate at less than its maximum voltage as shown by
point 'B1 in Fig. 3.3. This occurs when the resistivity is particularly
high and the corona d.c. voltage falls off with increased current flow.
However, current limit control may also not give optimum conditions
for all operating modes. If the current limit.is set at 'level 'C1, the
resultant voltage level of the precipitator collecting the lower
resistivity fly ash is not at its optimum value and may be raised with
-------
26.
Q)
O)
ro
o
>
ro
c
o
i_
O
o
7
Lowe r
Res i st i v i ty
7
Hi gh
Res i st i v i ty
Corona Current
Fig. 3.3
Typical Shape of the Corona VoItaqe-Current
Characteristic for the Inlet Zone.
-------
27.
advantage. The current control setting in this c.ase would however, be
satisfactory for the higher resisitivty fly ash.
(d) Mechanical Collectors;
In the older plants where mechanical collectors were used, they
preceded the electrostatic precipitators. As the result of a series of
pilot tests with the inlet before and after the mechanical collectors,
it was concluded that the'precipitating characteristics of the ash
reaching the electrostatic precipitator after the mechanical collector
was altered to such a degree as to materially reduce the overall
efficiency. As a result of this experimental evidence and other
investigations, it was decided to use only electrostatic precipitators.
This policy has been implemented since 1960.
(e) Outages and Maintenance;
An electrostatic precipitator may be put out of operation for any
one of a number of different reasons. Neither the type of fault nor
their frequency indicates that the collecting of high resistivity fly
ash introduces any special maintenance problems.
Table 3.3 gives the outages that occured for .all the modern
precipitators during a 3-month period. The precipitator availability
varied from 85.4 to 99.5 percent of the boiler service hours over this
period.
TABLE 3.3 - PRECIPITATOR OUTAGES
Fault Type No.
Discharge electrode short 6
Rectifier or control circuit 27
Frame or structure failure 6
Dust level in hoppers 1
Collecting electrodes control circuit 9
Rapper failure 19
Miscellaneous (incl. alarms) 15
(f) Influence .pf Operating Conditions;
It has been observed that the performance level of some precipi-
tators is dependent on operating conditions. In one case, the
precipitator does not reach maximum efficiency until it has been in
service for a period of seven to eight days, and its performance falls
off rapidly with any variation in the boiler conditions. These
precipitators can be tuned to give very good performance levels
providing boiler conditions remain stable. On the other hand, other
precipitators appear to be less sensitive to these variations. The
reasons for this have not been resolved.
-------
28.
(g) Pipe Type Precipitators;
Pipe precipitators were installed at four of the earlier pouuer
stations. On the luhole their performance in terms of EMU is well belom
that of the modern plate precipitators. This is probably due to the
difficulty in obtaining sufficiently high accelerations during rapping
because of the rigid clamping of the pipes at the top end, and that they
effectively only haweone series zone. Neuj rapping methods mere designed
by the ECNSW and improved performance qbtained. It is considered that
this type of precipitator is generally unsatisfactory for handling the
large volumes of gas necessary at modern plants and for collecting
high resistivity fly ash. No pipe precipitators have been installed
since 1961.
3-. 5 Variations of EMU with Sulphur Content of Coal
Fig. 3.4 shows the variation of the EMU, as determined from the
full size precipitators, with the sulphur content of the coal. Where
possible the values recorded are calculated from actual measurements
but in some cases design figures are included. No adjustment has been
made for the different SCA's and temperatures at which measurements
are made. There is no obvious correlation between the electrostatic
precipitating properties of the ash and the sulphur content of the
coal. The two most difficult fly ashes to collect, Southern and
Western, do not have the lowest sulphur content. It is quite possible
that this may be a characteristic of all coals with a sulphur content
below one percent.
>. 6 Hot Side Precipitators
Certain manufacturers have offered precipitators designed to
operate ahead of the air heaters so as to take advantage of the higher
temperature to reduce the resistivity of the fly ash. The resultant
increase in EMU is offset to some extent by a number of factors, of
which the increased volume of flue gas the precipitators have to
handle, is one of the most important (29).
, !
Pilot precipitator tests have been conducted for temperatures
from 170 F to 650 F and have shown that the EMU is considerably improved
at both the lower and higher ends of this temperature range. For the
Australian fly ash, it is considered that at this stage of precipitator
design knowledge, more desirable to rely on the lower temperatures to
reduce the resistivity rather than the higher temperatures.
It is considered possible that experience may show hot precipi-
tators to be more uniformly efficient
-------
9
29.
a
6
u
0)
10
"e 4
o
I 3
a
2
0
3
0.2 0.4 0.6 0.8
Per Cent Sulphur in Coal
I .0
I .2
Fig. 3.4
Variation of EMV with Sulphur Content in Coal.
Test f i gures
Des i gn f i gures
I. Northe rn
2. Western
3. Southern
4. West Moreton
5. BIackwate r
6. Bowen
SCA = 280-520
SCA >500
SCA = 275
SCA = 450-530
SCA = 490-520
SCA = 250
T =
T =
T =
T =
"T" —
"T* •••
260-280
240 °F
276°F
260-270
300 °F
300 °F
-------
30,
CHAPTER 4
PILOT SCALE PRECIPITATOR TESTS
4.1 Introduction
Up to the late 1950's, the electrostatic precipitators installed
at the power stations of the ECNSW had been uniformly unsatisfactory in
collecting fly ash from the low sulphur coals. From 1959 the ECNSW
indicated to manufacturers of electrostatic precipitators that it
would be necessary for them to demonstrate the effectiveness of their
equipment by means of pilot plant tests before serious consideration
u/ould be given to its purchase. ' Since then a large number of pilot
scale tests have been carried out by a number of manufacturers
(Research Cottrell, Svenska Flaktfabriken, Howden-Lurgi, Lodge-Cottrell,
Simon Carves, Sturtevants and Western Precipitation). These tests were
initially conducted at one of the older power stations and in some
cases the coal to be tested was imported and burnt under controlled
conditions. Later on, pilot tests were conducted at the larger modern
power stations.
The range of the main parameters of three important pilot precipi-
tators used in tests over the last 12 years is given in Table.4.1. It
is considered important that the electrode sizes and spacing be the
same as in the full scale precipitators and that they should comprise
a number of series electrical zones.
-------
31,
TABLE 4.1 - PILOT PRECIPITATOR PARAMETERS
Precipitator Parameter Range
Collecting area ft 576 - 825
Electrode spacing in 9 - 10.75
Plate height ft 6.5 - 8
Treatment length ft 12 - 25.5
Parallel gas passages 1 - 4
No. of rectifiers 1 - 3
No. of series zones 2 - 3
Rectifier connection H. W..and F. W.
Gas velocity ft/sec /I - 5
-------
32.
o 2 Factors Affecting the Interpretation of Pilot Precipitator Tests
It is considered that any test series with the pilot precipitator.
should include tests at the specific collecting area and temperature at
which it is proposed to operate the future full size precipitator.
Although it is possible to extrapolate the results to some extent it
does introduce additional elements of uncertainty and should be avoided
if possible. Even when these conditions are satisfied there are still
a number of factors which may cause the- performance of the pilot
precipitator to differ from that of the full size units. Some of these
are briefly discussed below.
(a) Gas velocity
Because of the overall dimensions of the pilot precipitator, the
gas flow velocity is usually considerably lower for a given SCA than it
would be in a full size unit for the same SCA. The lower gas velocity
in the pilot plants probably reduces the re-entrainment and scouring
of the dust off the plates and may therefore produce a more optimistic
result.
(b) Gas and Temperature Distribution
Because of the smaller geometrical dimensions in the pilot
precipitator it is easier to obtain better gas and temperature distri-
bution than is often obtained in the full scale units.
(c) Alignment of Electrodes
Any misalignment of the discharge electrodes reduces the maximum
voltage that can be maintained without excessive sparking occuring. In
the pilot plants where the length of the electrodes is less and their
number much smaller than in the full size plants, it is much easier to
obtain optimum operating conditions.
(d) Leakage and End Effects
Any leakage of air into an electrostatic precipitator will have
an adverse effect on its performance as this increases the volume of
gas passing through it.
Because of the high ratio of jointing length to total exterior
area, leakage is more of a problem in pilot precipitators than in the
full scale units. In addition, since the plates are relatively short
the movement of gas around the outside and over the top and bottom can
be disproportionately large in a pilot precipitator. The net result
of these effects is to produce a less favourable performance than that
of the full size plants.
(e) Rapping
Since the collecting plate area of the pilot precipitators is
small, it is relatively easy to provide adequate rapping facilities
and no problems are generally experienced in removing the deposited
fly ash. This can only be achieved in full scale precipitators by
having well cissigned rapping systems carefully tuned to give maximum
performance. Hence it may be assumed that in this respect the perform-
-------
33.
ance of the pilot precipitators is probably more favourable than for the
full size units.
(f) Particle Size
It is possible that the particle size distribution at the plant
at which the pilot precipitator is being tested may differ from that
produced at the future plant. This has occured in N.S.W. At two
of the older power stations, the size distribution of the ash from the
Great Northern coal seam is in the range 7-14/*m whereas at the modern
plants the actual size distribution is -19,0-27.5uma In this case,
the pilot precipitator would be expected to give a more pessimistic
result than the full scale precipitator,,
(g) Electrical Energization
Several different approaches have been adopted for setting the
electrical conditions of the pilot precipitators. These are,
(i) Adjust the voltage to give light sparking.
(ii) Set the voltage to the maximum value that can
be maintained without sparking.
(iii) Adjust the control to give a constant current
density.
The method of voltage control used varies with the manufacturer
and is related to the philosophy each adopts for their control system
in the full size precipitators. The ECNSW has had tests carried out
in all the three modes mentioned above. It has been observed that
when the pilot precipitator is operated in the light sparking mode,
its efficiency is temperature dependent but this is not always the
case when operated in the constant current mode.
It is generally thought that because of the much larger area
connected to one rectifier in the full size precipitators, there is
an increased probability of sparking and other abnormalities,, This
means that the electrical conditions in the pilot precipitators will
generally be more favourable than in the full size precipitators and
so will give a better performance level.
(h) Coal V/ariation
An additional factor which makes correlation with full size
precipitators difficult is the variation in the coal being burnt during
the life of the power station. Variations in the precipitating proper-
ties of ash from the coal in a given seam occur from one colliery to
another and recently it has been observed that changes also occur over
a period of time in coal from the same colliery. This makes it very
difficult to be sure that the sample used in the pilot precipitator
tests is representative of what is going to be used in the full scale
plant.
4.3 Scaling Factor
Altogether there are a number of factors which must be considered
in scaling the results from tests obtained on a pilot precipitator to
-------
34,
that of a full scale unit. If the effect of each parameter is indicated
by a constant factor K, then it is possible to write the simple
equation,
WFS = Upp KT
where KT = K. x K0 x K_. . .K
i i i j n
uipg = EMV of full size precipitator
W = EMV measured by the pilot precipitator
The constants Kn may be either greater or less than one, depending on
which parameter they are associated with. The value of Kj will vary
from one precipitator to another. One manufacturer uses a Ky= 1
while others use values less than 1.
4.4 Test Arrangement (11)(14)(22)(26)
Generally, flue gas take off points for the pilot precipitator
are provided before and after the air heater to enable high temperature
tests to be carried out. The final temperature control of the flue
gas for the unit is obtained by means of a heat exchanger and electric
heaters located in the inlet duct. The pilot precipitator casing is
fitted with heating elements to assist in keeping a constant temperature
through the stages. The actual temperature range varies from one test
location to another but typically ranges from 170 to 600°F0 A disc and
two perforated plates are installed at the inlet to the pilot precipi-
tator in order to provide reasonable gas distribution across the
precipitator.
The dust sizing and burden at the inlet to the pilot plant in all
tests were in reasonable agreement uuthv. that measured in the main duct.
The efficiency of the pilot plant is determined by isokinetically
measuring the input and output duct mass flow loadings by the method
described in Section 3.3. An alternative method which is found to be
satisfactory is to compare the catch with the outlet burden.
4.5 Typical Daily Test Routine (11)(14)(22)(26)
Normally the boilers are kept in service overnight on reduced
output but during the testing period the boiler operates at rated load
-------
35.
with a constant setting for the fuel/air ratio; . Soot blowing is carried
out before testing starts each morning and quite often between tests so
as to maintain metal temperatures within acceptable operating limits.
Before each test, the pilot precipitator is operated at the
desired condition for at least half an hour. When the voltage and current
readings indicate that constant conditions are reached, the test is
started. Three one hour tests are carr.ied out for each set of conditions,
and up to six one hour tests are carried out in a day. The voltage-
current characteristics are measured once for each set of test
conditions immediately after the last test is completed.
The actual test programme usually includes:-
(•a) A series of tests on the main coal covering a wide temperature
range. For these tests the SCA was kept constant.
(b) Tests at the design back end temperature of the new plant with
different values of specific collecting area using the main
test coal.
(c) Test (b) repeated for other coal samples.
The electrical conditions are normally kept constant for each set
of tests, although in any given test program the pilot precipitator is
often operated in both the light sparking and constant current mode.
4.6 Relationship to Full Size Precipitator Performance
The fly ash from the Great Northern, Bayswater, Wongawilli, West
Moreton and the Main Lower Blackwater coal seams have been tested by
both pilot scale precipitators and by adequately designed plate type
full size units so that it is possible to obtain some indication of
how well the pilot p'recipitators model the full scale units.
The fly ash from the Great Northern coal seam has been extensively
tested with pilot electrostatic precipitators manufactured by Research
Cottrell, Lurgi, Svenska Flaktfabriken and Western. The earlier tests
were conducted at the older power stations but since the construction of
modern plants, comparative pilot precipitator tests have been carried
out at these stations. Figs. 4.1 to 4.3 give a summary of these results
and compares the EMU's as calculated from the pilot and full size
precipitator tests. The comparison is made at an SCA of 350 ft /kcfm
and for a temperature range of 260 to 290 F.
Fig. 4.1 records the results of tests on the Great Northern coal
seam. Column C gives the EMU of the same pilot precipitator operating
at two of the older power stations burning Great Northern coal. They
indicate that little variation exists in the value of the EMU as the
result of burning the same coal in two different boilers. Point B is
the value determined from the tests with a second pilot precipitator
at one of these older power stations. After the construction 'of a
modern station, the pilot precipitator, used to measure results in
Column C, was set up at this station in order to check whether its
-------
36.
performance mould agree with the earlier tests. A wide range of results
were obtained but the mean value of the EMU at the reference SCA is
shown by point A in Fig. 4.1. The improved performance over that
obtained in the earlier tests indicated by Column C may in part be
accounted for by,
(a) Difference in mean particle size. At the modern plant this is
in the order of 22^/m where as at, the older stations the size
was closer to 1
(b) The temperatures at modern plants (265-5°F) are lower than those
at the older plants (286°F and 280°F).
On these two points alone, the test results at the modern plant
should give a more optimistic result than given at the other two power
stations.
The EMU's of the full size electrostatic precipitators are
indicated by Column D in Fig. 4.1. These values are calculated from
the acceptance tests of precipitators operating at SCA's from 250 to
530 ft /kcfm; the lower EMV/'s being associated with the higher SCA's.
In order to make a more realistic comparison at the reference SCA, the
EMU's at the lower values of SCA need to be decreased and at the higher
SCA's, they need to be increased. The writer has made an estimate of
what these values should be and is shown by Column E.
Column F gives the EMU range of the nominal performance band of
the Great Northern coal seam.
It is. generally held by the ECIMSW engineers that the pilot tests
for their own coals give much better quantitative information than might
at first be concluded from Figure 4.1. The reason for the wide scatter
of results can be better appreciated when it is realised that the tests
recorded here for the Great Northern seam have been made over a 12 year
period for coals mined at six different locations, fired by 10 different
boilers and tested by 7 different types of electrostatic precipitators.
The Wongawilli fly ash was tested by a pilot precipitator in the
early sixties and these tests indicated that this fly ash was particu-
larly difficult to collect with resulting EMU's of 3-4cm/sec. The
tests on the full scale units at Tallawarra gave results a little lower
than these values. This is shown in Fig. 4.2.
At Swanbank Power Station, Queensland, both pilot and full size
electrostatic precipitator efficiency tests have been made on fly ash
from the Blackwater Main Lower and West Moreton coals and the calculated
values of the EMU's are summarized in Fig. 4.3. The full size precipi-
tator tests were made for SCA's in the range of 450 to 530 ft /kcfm. An
estimate of the EMU for the reference SCA of 350 ft /kcfm is shown for
both types of coal.
-------
37.
u
0)
I/)
E
U
u
o
c
O
(0
L
cn
u
(C
UJ
o
CM
in
o
in
CM
i/i to
t_ ^^
O
+- l/l
(0 4-
+- t/1
— Q)
0. h-
U (D
-------
38,
C
i_ ro
O -Q
jL
ro -
+-
— 5
o
o
(D
> 4
c
O
^ 3
(D
L.
CT,
^ 2
>
^ 1
u
CD
»»-
**-
uj n
I- Q- >+-
Q_ • — ' L_
U • Q)
(DO) Q.
N l-
— Q. —
10 ID
-1- C
— o
1- _ _ E
3 0
U- CL 2
m
_ 1 •! ^—J
w
Southern CoaI Field
Fia. 4.2
Comparison of EMVs for the Southern Coa
Field Fly-ash. SCA = 350 ft2/kcfm.
-------
39.
o
in o
to eo
to CM
i i
in o
to o
CM CM
II II
< h-
o
to
t/1
4-
(/)
Q>
O
4-
(D
O
to
~
i
^^
in
0>
4-
0>
O
C
(D
4-
Q.
(I)
O
U
<
O
to
0)
o
C.
0)
l_
0)
>»-
Q)
l_
O
4-
X)
0)
.L.
^^
0)
;j
•— >
T5
ID
(ft
I
^^
I/)
4-
Q)
U
C
ID
,L_
^^
Q.
0)
U
U
<
o
o
00
CM
O
•sr
CM
n
c
ID
.0
0)
O
C
ID
E
l_
O
(U
a.
(D
E
O
u_
0
in o
CM O
to to
1 1
0 0
to o
CM CM
II II
< H
O
to
^*
•
U)
4- •
0)
4-
1_
O
4-
ID
4-
._
Q.
S-*
U-
0
0
0
to
II
H
*,
O
CM
in
i
o
Q\
^J-
II
^
O
CO
+-*
.
tf>
4-
(/)
0)
4-
•D
Q)
4-
(/)
3
•— j
T3
ID
V)
4-
(/>
Q)
4-
U
O
4-
ID
4-
.»—
O.
„
U
Q)
l_
•
O
in
to
•*-
o
<;
O
*—
U.
0
0
o
to
1
o
0
CM
II
h-
s^
.
T5
C
ID
.0
(D
O
C
to
E
L.
o
>4-
— 1— O-tO t-
o
0)
t_
o.
4-
0
.—
d>
N
.—
to
—
—
3
0)
N
~-
U)
—
—
3
0)
0
C
0
L_
CD
>*-
(U
0)
a.
—
ID
C
—
E
O
D
a
West Moreton
BIackwater
Coal Field
Fig.
4.3
Comparison of EMVs for West Moreton and Blackwater
Coals. Reference SCA = 350ft /kcfm.
-------
40.
The pilot precipitator tests were carried out at a constant
current density and not at light sparking as mas the case with the
ECIMSW. This makes comparison some what more difficult. The tests on
the West Moreton coal is probably representative as the corona voltage-
current characteristics shouj that the precipitator was operating in
the back corona mode. This was not the case for the Blackwater Main
Lower coal and it seems most likely that a better level of performance
could have been obtained by operating in the light sparking mode.
It is the writer's view that the'.pilot precipitator tests, when
operated in the light sparking mode, generally give a slightly more
optimistic result than do the full size precipitators. It is generally
considered in Australia that, providing the same pilot precipitator is
used, the test results may be used to accurately rank the precipitating
properties of the different fly ashes and that a reliable scaling
factor may be found to predict the effective migration velocity in
future full size units.
4.7 General Data from Pilot Tests (11)(14)(22)(26)(3)
One of the secondary benefits gained from these tests is the better
understanding obtained of the effect different parameters have on the
electrostatic precipitation of high resistivity fly ash. Some of these
have already been discussed in other publications and are only briefly
referred to in this report.
(a) Flue Gas Temperature(l4)
A wide range of tests have been made at different gas temperatures
for the same SCA. Because the resistivity is very high it is particu-
larly sensitive to temperature variations as is also the efficiency. A
typical temperature-efficiency relationship is shown in Fig. 4.4. Some
pilot tests have shown no variations in the efficiency with temperature
but it is of interest to note that in these cases the precipitator has
been operated in the constant current density mode.
(b) Carbon Content of Fly Ash
Pilot tests at two power stations indicate that the electrostatic
precipitator performance is not significantly affected by a carbon
content in the range 2 to 10%. Resistivity tests at Wollongong
University College have shown that for carbon content up to 15% the dry-
air resistivity is only reduced by a factor of 2, but for contents much
greater than this, the resistance drops to a very low value. Once there
is sufficient carbon to form a complete path through the dust layer,
then the carbon determines the effective resistivity and not the high
resistivity fly ash particles.
(c) Gas Velocity (3)
It is generally considered that the overall performance of electro-
static precipitators collecting high resistivity fly ash is largely
independent of the gas velocity in the range 2-8 ft/sec.
-------
41.
S
u
99 9
99.8
99.7
99.5
99.0
98.0
97.0
95.0
90.0
80.0
150
Y\
\
\
\
250 350 450
Temperature °F.
550
650
Fig. 4.4
Variation of Pilot Precipitator Efficiency
with Temperature for Two Different Fly-ash
Samples. SCA = 325-363.
Control: light sparking.
-------
42.
(d) Migration Velocity Variation with Efficiency
In all tests with pilot precipitators, the migration velocity
for any given fly ash and temperature decreased in value for higher
SCA's and efficiencies. A typical shape of the curve is shown by the
bands in Figs. 3.1 and 3.2. The explanation for this is given in
Section 1.3 and is due to the increased difficulty in collecting the
finer particle sizes which is necessary in order to obtain the higher
efficiencies.
(e) Sulphur
It has been traditional to expect the pe-rformance of an electro-
static precipitator to be related to the sulphur content of the coal,
the higher is the resistivity of the fly ash and hence the more
difficult it is to collect. ;
It has already been pointed out in the discussion on the full
size units that the sulphur content of these low sulphur coals does
not indicate the order of precipitability. This is confirmed by these
pilot tests. The effective migration velocities of 11 coals from
different seams are shown in Fig. 4.5 plotted against sulphur content.
Most of these measurements are made with the same pilot precipitator
at an SCA of 360 ft2/kcfm at a temperature of 260°F.
In some analyses, the sulphur content was divided into pyritic
and organic but even plots on this basis did not produce a better
correlation.
This tends to confirm the view that the sulphur content probably
gives a general indication of difficulty of precipitation when comparing
a "\% sulphur coal with a !>% coal, but it is not reliable in ranking fly
ashes when its content is below "]%.
-------
43.
0--
u
E
U
o
o
0)
c
o
ro
i_
co
O
O O
Q)
>
U
0)
UJ
0.2
0.4 0.6
Per cent Sulphur
0.8
I .0
I .2
Fig. 4.5
Variation of EMV with Sulphur Content of Coal as
Measured by _ a PI | otPrecipitetor. Temp. = 260 F,
SCA = 360 ft /kcfm.
-------
44.
CHAPTER 5
FLUE GAS CONDITIONING
5.1 Introduction
One ujell knoujn method of improving the performance of an existing
electrostatic precipitator collecting high resistivity fly ash, is to
condition the flue gas. The generally accepted theory is that the
conditioning agent combines with mater to form a higher conductivity
surface over the.' particles thus reducing their effective resistivity.
This then is accompanied by an improved performance of the precipitator.
In the ECNSW, a range of different conditioning agents have been
tested, on both full size and pilot precipitators. In general, sulphur
trioxide conditioning is; the most successful, followed by ammonia. A
number of different gas>conditioning techniques have been tried.
I
The conditioning of flue gas is carried out for two related, but
still distinguishable, purposes. (a) The first is to improve the
efficiency of the precipitators so that their emissions are within the
requirements of the Clean Air Act, This is applicable to the older
plants which are under sized to collect ash from the low sulphur coals.
(b) The modern precipitators all met the requirements of the Act during
the acceptance tests but, as described in Chapter 3, it is possible
under some conditions for the day by day performance to fall below the
required level. Also, in the event of a zone failure, it may be
necessary to close off one gas passage in order to effect repairs.
Under these conditions the overall efficiency level drops. So as to
maintain the required emission level under these contingencies, ammonia
conditioning systems are being installed on many of the modern precipi-'
tators.
-------
45.
The cost of the conditioning is partly offset by the low maintenance
requirement of these precipitators and the possibility of maintaining
full load on the boiler during a gas passage outage.
5.2 Conditioning Agents and Methods of Injection (3)(5)(4)
One of the common methods used overseas to condition uiith S0_ is
to use stabilized SO,. The liquid is vapourized, mixed with hot air and
injected into the gas stream. Unfortunately this .product is not commercially
available in Australia and uiould be uneconomical to import or manufacture
for a permanent conditioning system. It has however been used during the
pilot precipitator test programs. The following gives a brief descrip-
tion of the different conditioning systems used on the full size
electrostatic precipitators.
(a) Permanent Installations on Full Size Precipitators
(i) High Temperature H?SD. Evaporation
The sulphuric acid is pumped into an evaporator where its
temperature is raised to about 1,000 F. At this temperature
the acid decomposes into SO., and H^O. This is then mixed ujith
hot air at 700-1,000°F and injected into the duct ahead of the
economizer through a single pipe with graded injection holes.
The whole injection system has appropriate control valves and
safety devices.
To ensure continuity of injection, the acid injection system
is duplicated where it is installed as the main means of conditioning.
No corrosion problems have been encountered in the electrostatic
precipitator or in the duct work with this method of conditioning.
The injection of the acid on the precipitator side of the
air heater has been tried at one power -station and it worked
well on a pilot precipitator. When it was attempted to
condition the fly ash for the full size precipitator it did not
perform as well. It is considered that this is probably due to
the poor injection system. This will be re-engineered and the
system tried again in the future.
(ii) Anhydrous Ammonia
The anhydrous Ammonia is drawn from a storage tank in the
liquid phase, passed through an evaporator and injected into the
duct between the air heater and precipitator as close to the air
heater as possible. Good distribution in the duct is obtained
by using a number of injection pipes with graded injection holes.
An alternative arrangement, suitable for lower injection
rates, is to draw off the ammonia in the gas phase and inject it
directly into the duct. At one station, the injection system
comprises three -J" open ended pipes each of which projects
different distances into the duct.
The anhydrous ammonia system is very simple, easy to
operate and is free from blockages. In the initial stage of
-------
46,
development, it was found that a solid crust tended to build up
at the outlets of the injection pipes and sometimes at points
along its length. This seems to occur when the injection gas is
switched off and is due to the action of leakage or residue NH^
with the flue gas. The usual practice to eliminate this is to
purge the system with air during the shut down.
Some doubts have been expressed about injecting the ammonia
before the air heater as it is considered that blockages in the
air heater may occur. This is still regarded as unproven and it
is possible that this may not occur with, the low sulphur coals.
(iii) Concentrated Ammonical Liquor (GAL).
This is a by-product of the local steel industry and is very
inexpensive. Tests have been carried out using this as a
conditioning agent and efficiency levels have been obtained
similar, and at one station, better than that obtained with
anhydrous ammonia.
The liquid CAL, after diluting and filtering, is run directly
into large diameter pipes which project into the duct. These have
12 inch stand pipes which face the direction of gas flow (upwards)
and the CAL liquid level is raised to about half this height. The
heat of the flue gas, aided by additional heat from heaters in the
pipe' itself, evaporates the CAL and the resultant gas flows out of
the ends of the stand pipes into the main gas stream.
Some initial difficulty was experienced with CAL at ambient
temperatures below 40°F through line blockages as a result of
ammonia bicarbonate crystallising out of solution.- This may be
eliminated by diluting the ammonia concentration to less than 15
percent. The initial cost of the product is cheap but it does
require more handling than anhydrous ammonia. It is usual practice
for anhydrous ammonia to be used during station start up and a
switch made to CAL once temperature levels are high enough.
(iv) Water Injection.
At one power station, six water sprays each with injection
capacity of 6 gals per minute, are permanently installed on a
100 MW boiler. Normal practice is to use two sprays for loads
above 80 MW in conjunction with the CAL conditioning. The water
injection reduces the emissions a further 7 percent below what is
obtained by using CAL alone.
(b) Temporary Installations.
(i)Sulphur Burner
Elemental sulphur is burned in the presence of dry air and
the resultant gas is passed over a catalyst to give a high
concentration of SOj. The system was tried in the early sixties
and satisfactory conditioning was obtained. It was never used on
a permanent basis because of operating and maintenance problems.
(ii) Water Injection (4).
The first extensive trials using water conditioning were
carried out at Pyrmont. Water was introduced as steam from the
soot-blowers, by spraying water into the combustion chamber and
-------
47.
spraying finely atomized mater into the flue gas stream after the
air heater. It mas. found that maximum efficiency was obtained
when the water rate was 0.5^-1.0 lb/1,000 ft^ gas. If this
quantity of water is injected into the combustion chamber, the
heat energy 'used to evaporate the water would materially reduce
the boiler efficiency. Injection into the gas stream was not
'satisfactory as complete evaporation could not be ensured and
water droplets were carried over-into the precipitator to cause
rapid build up of ash on the electrodes.
Similar tests have been carried out at other power stations
but none have been very successful except as an adjunct to ammonia
conditioning.
5.3 Effect of Conditioning on Fly Ash Electrostatic Precipitation
Properties (3)(4)(5)(20).
The effect of flue gas conditioning on the performance of full
siz-e electrostatic precipitators has been tested on fly ash; resulting
from the combustion of coal from the Northern, Western and .Southern
coal fields at six different power stations. Table 5.1 gives a list of
the conditioning systems permanently installed and grouped to show which
coal is being burnt at the power stations. Fig. 5.1 sets out the
improvement in the value of the EMU for ash from each of the three coal
fields. The top of the unshaded vertical column gives-an estimate of
the normal performance level without conditioning and the shaded area
gives the range of improvement obtained with conditioning. All
measurements were made for the precipitators operating at their normal
SCA's and temperatures. •
In general, the electrostatic precipitating properties of fly ash
from all three coal fields is improved by both acid and ammonia
conditioning. The trend of the data available on full size plants
indicates that acid conditioning is more effective than ammonia, although
it is not always the preferred system.
There are several anomalies which occur at some of the older
plants. At one of the stations burning Northern coal, conditioning with
ammonia is very successful, where as excessive concentrations of acid are
required to obtain the same result. At another station, also burning
Northern coal, acid conditioning is very effective but ammonia has never
worked satisfactorily. In the former case, tests on a pilot precipi-
tator with specially designed conditioning unit showed that the fly
ash could be conditioned adequately with acid. This and other evidence
suggests that the failure to condition with one of the agents is not a
function of the fly ash itself but is associated with the injection
system or the overall operating /conditions of the plant.
!' j.
The fly ash from the Western coal field has been successfully
conditioned u/ith acid and ammonia. In this case, the improvement with
ammonia is only temporary with the performance falling off dramatically
after only several days in service. Pilot scale tests confirm that this
-------
48.
TABLE 5.1 - PERMANENT CONDITIONING INSTALLATIONS
IN ECNSW
Coal Field
Northern
Western
Southern
Permanent Installations
Agent
Ammonia
CAL
Acid
Acid
Ammonia
CAL
Water
No. Power
Station
3 (4)
1
1
1
1
Typical
ppm \i/\i
40 - 55
50 - 80
50 - 60
65 -75
20 - 30
160 - 20
Remarks
Ammonia system is
being installed at
a 4th power station.
Ammonia works but
performance decays
with time. Not as
good as acid.
The injection rate of CAL is expressed as NH-j
equivalent and acid as 503 equivalent.
-------
49,
1 U
9
8
7
u
0)
en
"E 6
u
LU
4
3
2
1
n
AC Id
CAL
NH,
Ac
-
-
id
I
^
N
1
I
CAL
NH,
Ac i d
j
7~]
//
so3
Northe rn
Weste rn
CoaI Field
Southe rn
Figure 5.1 Effect of Flue Gas Conditioning on the
EMV of Full Size Electrostatic Precipitators
-------
50.
ash can be conditioned with ammonia but they also indicate that the
improvement is not as large as with other ashes.
The Southern coal field ash has been successfully conditioned
math ammonia, acid and SO-j. This is of particular importance as this
is an acidic ash and it was once thought that it could only be
conditioned ujith a basic agent.
Where it is possible to use either ammonia or acid conditioning,
power station staff prefer to use ammonia. The main advantages being
that a very simple injection system is required, it is easy to operate,
little maintenance is required, operating costs are low and ammonia is
safer to handle than acid. In a number of applications where only a
moderate improvement is required ammonia conditioning is the natural
choice.
One remarkable feature of the conditioning tests is that
conditioning has not resulted in very high values for the EMU. In no
case does this exceed 8 cm/sec and in the modern precipitators it only
improves the day by day performance to the acceptance test level. In
the older plants, the lack of improvement is not surprising as the main
limitation is probably the unsatisfactory design of the precipitators
themselves. It is more difficult to explain the relatively low EMU in
the well designed units. It seems likely that once the overall
efficiency exceeds 99%, other factors associated with the operation of
the full size precipitators may limit the EMU to about this value,, This
could include such factors as reintrainment, scouring, end leakage and
the number of submicron particles in the size distribution of the fly
ash ,>
The presence of the mechanical col-lectors in the older plants does
not appear to affect the conditioning of the fly ash. It is common
practice to remove the rotors as it is considered that they do not
contribute to the overall performance level of the ash collecting system
for reasons already given in Section 3.4.
5.4 Conditioning During Pilot Precipitator Tests (11)(14).
During many of the pilot precipitator tests, efficiency measure-
ments were made during the injection of several conditioning agents.
The main systems used are given below.
(i) Stabilized SD^.
This comprised a drum of stabilized sulphur trioxide, a
metering rotameter and a length of heated feed pipe to the point
of injection in the inlet pipe of the pilot precipitator. The
liquid sulphur trioxide was gravitated from the drum via the
heated pipe to the inlet duct where vaporization occured.
(ii) Sulphuric Acid.
The equipment comprises an electrically heated evaporator
which vaporises the liquid, and appropriate injection pipes. The
-------
51.
resultant vapor may be injected into the gas stream before the
economiser or after the air heater.
(iii) Ammonia
Ammonia gas obtained from a cylinder of anhydrous ammonia
is injected into the inlet duct, to the pilot precipitator upstream
of the heat exchanger.
Fig. 5.2 shows the effect conditioning has. .on the EMU of ashes
from the different coal fields, as measured by the pilot precipitators.
Most of these measurements mere made in the temperature range 240 -
300°F and SCA's 150 - 360 ft /kcfm. The figures in brackets are the
concentrations in ppm on a v/v basis.
5.5 Effect of Conditioning on Fly Ash Properties.
The flow properties of the fly ash are affected to some extent
by conditioning. In the modern plate precipitators with moderate rates of
acid or ammonia conditioning this is not noticeable in the flow and
handling properties of the ash and no problems are normally encountered.
If excessive acid is used the fly ash becomes sticky and fallout of
relatively large acidic agglomerates occur from the stack. Ammonia
does appear to increase the adhesion of the ash making it more difficult
to remove from the collecting plates of the older plants where the
acceleration levels are very low. In this case it is necessary to
wash the plates down every two weeks. This is not necessary for the
unconditioned ash.
Sulphur trioxide and acid conditioning significantly reduce the
resistivity of the fly ash. Measurements made with the Kevatroa
Electrostatic Precipitator Analyser gives values well below 10 ohm-cms.
The mechanism of conditioning with Sulphur trioxide has been exten-
sively investigated.
The mechanism of ammonia conditioning has not been thoroughly
investigated. It clearly affects the performance of the precipitator
by improving its efficiency and increasing the operating voltage level.
The change in the electrical characteristics is consistent with a
reduction in ash resistivity. In-situ resistivity measurements have
shown a one order of magnitude reduction for Western fly ash, and in
the case of the Hunter Valley fly ash, the resistivity was reduced to
values well below 10 ohm-cms. Other in-situ measurements have not
shown such a large reduction in resistivity due to ammonia
conditioning.
-------
52.
15
14
.
u
S 1 3
E
U
1 2
u
o
o> 10
c
0
._ 9
ro
cr,
- 8
(D
•— 7
u
(U
H-
LU 6
5
4
*T
""I
*
H2
(2
1
S°4
0)
(40)
I
x
1
'V
^
« S KXsXXXXXXXX
X
£
_^
>4
(55)
^
X
x
y
'/
y,
y
i
so3
( 2)
\71 NH-
X(40) X
^ /
Ss
/
/
Hunter Northern Western Southern
Val ey
GoaI Field
Fiq. 5.2
Effect of Flue Gas Conditioning on the EMV
of Pilot FreeiDitators.
-------
53.
CHAPTER 6
•THE CSIRO TECHNICAL SCALE COMBUSTION AND
ELECTROSTATIC PRECIPITATION FACILITY
6*1 Introduction
Although the in-situ pilot electrostatic precipitator tests, as
described in the previous chapter, provide very useful information about
the precipitating properties of fly ash, they do have some limitations.
These tests are expensive, they require a large number of man-hours
and have limited flexibility. In order to overcome some of these
limitations, the Mineral Research Laboratories of the Commonujealth
Scientific and Industrial Research Organization (CSIRO), undertook to
construct a technical scale combustion and electrostatic precipitator
rig which could be set up and operated in their own laboratory.
The basic objective of the project is to model in the laboratory
both the combustion and precipitating conditions that occur in full
size units, so that forewarning of precipitation difficulties can be
given for unfamiliar coals and guidance on plant parameters offered.
In the ideal case, such an arrangement could be expected to predict
exactly how a full scale electrostatic precipitator will perform under.
given conditions. In practice however, it is almost impossible to
reproduce the full scale conditions. The minimum requirement therefore
is that the technical scale unit reproduces the essential features of the
full size units so that it can be expected to at least rank the
coals as far as the precipitating properties of their fly ash is con-
cerned. A possible extension is to find some empirical relationship
between the performance of the technical scale and the full size units.
-------
54.
i.2 Experimental Apparatus (7)(28).
The experimental arrangement is shown in Fig. 6.1. The pulverized
fuel furnace is a down fired U-shaped designed for a nominal heat
release rate of 15,000 BTU/ft hr., equivalent to a bituminous coal feed
rate of about 60 lb/hr., and is built of high temperature refractory
brick with an outer layer of insulating brick. The coal burner is located
in the centre of the combustion chamber roof and the hot gases and fly
ash leave the combustion chamber via a short horizontal duct leading to
a vertical flue.
The gas cooling system comprises water cooled copper coils over
which the hot flue gas passes. The temperature is controlled by the
water flow rate into each of the cooling coils. Only part of the gas
produced in the furnace is passed through the precipitator. The
remainder is by-passed to the stack through a cyclone collector to remove
the ash.
The electrostatic precipitator is one tube of a standard industrial
tube type electrostatic precipitator. It comprises a tubular collecting
electrode 10 inches in diameter and 10 ft. long surrounding a discharge
electrode wire axially suspended and kept taut and vertical by means of
a weight attached to its lower end. Tumbling hammers are used for rapping
both the collecting and discharge electrodes. The gas enters the chamber
at the bottom and flows out of the top. The gas temperature is kept
constant at the desired value by thermostatically controlled electric
heaters.
The precipitator is energized from a transformer rectifier set
with a maximum rating of 60 kU and 60ma. The rectifier is connected
full wave, and full voltage is derived from a voltage doubling circuit.
Manual voltage control is provided by means of a variac type transformer.
The main parameters of the electrostatic precipitator are summarized
in Table 6.1
TABLE 6.1 - MAIN PARAMETER DIMENSIONS OF CSIRD TECHNICAL
SCALE ELECTROSTATIC PRECIPITATOR
10.0
10.0-
26.2
0.1
0.547
102.
260-
3.1
60.
60.
1.1
42.
The performance of the electrostatic precipitator is measured
by sampling the flue gas at the input and output and calculating
the efficiency on the basis of the weights caught in the
sampling thimbles.
Cgllecting plate. Length'.
Diameter
Area
Discharge electrode diam.
Cross section area
Flow rate
SCA
Gas velocity
Rectifier Rating. Voltage
Current
Typical corona current
Corona current density
ft'.
ins.
ft
ins.
ft
cfm
ft /1000 cfm
ft/sec
kU
ma
ma
/I a/ft
-------
Furnaca
Electrostctic prcc!plt:lor
Fig. 6.1
CSIRO Pulverized fuel rig and Electrostatic
Precipitator Facility.
VJl
Ul
-------
56.
6.3 Test Procedure
Before a test series the furnace is preheated with town gas for
16 hours, after which it is operated at a coal feed rate of 60-70 lbs/hr.,
the actual rate being adjustable to give a furnace heat rate similar to
that of the proposed boiler. The combustion air is controlled to give an
excess air rate similar to the likely operating value for the full size
poiuer plant. The combustion air temperature, flow rate, furnace ujall
temperatures, gas temperature and the coal feed.rate are all monitored.
The temperature of the flue gas to the precipitator is adjusted to the
required value by the cooler. Any deposit in the cooler is cleaned out
at the end of each day.
After the coal has been introduced -into the furnace, conditions are
allowed to stabilize. At this stage the corona voltage current charac-
teristics are measured and then the current is set at 1.1 ma, or some
other predetermined value and the tests commenced. It is usual for three
one hour tests to be carried out each day. At the end of each day the
corona voltage current characteristic is again measured and the remaining
ash removed by rapping and hosing down. Ash samples are taken from the
collecting electrode after each test.
6.4 Limitations
While the test rig has a number of significant experimental
advantages over the pilot precipitator, it is acknowledged by the CSIRO
that it has some limitations in simulating full scale combustion and
precipitation. Some of the possible limitations are discussed below but
as will be seen, many of them are not important. i
(a) In the experimental furnace it is possible to simulate the size
distribution of the pulverized coal, the rate of heat release for unit
furnace volume and the amount of excess air used during combustion.
Since the furnace is refractory lined, it might be expected not to
accurately simulate a modern power station boiler furnace which is lined
with relatively cool water tubes. CSIRO know of no essential difference
in the chemical composition of the resulting fly ash from that obtained
from the full size furnace. • ; ,
(b) Because of the aerodynamics of the experimental furnace, up to about
50 percent of the ash is retained in the furnace where as in modern
power station furnaces only 15 to 20 percent is retained. It is also
likely that the larger quartz grains and heavier ion-bearing components
tend to be left behind in the technical scale furnace. Because of this
and the drop out in the ductwork, the particle size entering the electrostatic
precipitator is finer than is usually encountered in industrial units.
The grain loading is also lower, although it is not unreasonably so. In
one. series of tests, inlet dust loadings of 2 to 6 grains/ft at IMTP was
normal.
(c) The test precipitator is a tubular type with a small total
collecting area in which the gas flow is vertical along the length of
-------
57.
the discharge wires. The usual full size precipitators are plate type
in which the gas f.Vows horizontally and at right angles to the discharge
wires.
Although the geometrical arrangement of the electrodes differ from
the full size unit it seeks to model, the diameter of the discharge wire
and its distance from the collecting electrode are similar. Hence it is
not unreasonable to expect the charging and precipitating electric fields
of this precipitator to correspond clos,ely to those of a full size plate
precipitator.
(d) The technicsl scale precipitator Is not sectionalized and this
results in a lower average EMU than if it were sectionalized,
(e) The collecting area of the technical scale prec.ipitator is only
26.2 ft . Becaus'e of this it is generally considered that a precipitator
with such a low plate area will operate at much higher voltages than a
unit with a much larger collecting plate area. This may be true for
precipitators collecting low resistivity dusts but it need not be applicable
for precipitators collecting high resistivity fly ashes since the voltage
level is determined by the onset of back corona and is not dependent on
the normal sparking characteristics. The CSIRO have conducted many of
their tests at a current density of 48/ua/ft . At this current density
the precipitator would normally, operate in the back corona region for
high resistivity ashes and hence at its maximum voltage.
One of the complications experienced by the CSIRO with their
testing is that the voltage current characteristic sometimes changes
throughout the day as the deposited layer on the collecting plate
builds up. Initially the voltage is high but often it reduces during the
test period.
i
This voltage change, together with the good alignment of the
electrodes, probably results in better electrical voltage levels than
in a full scale precipitator and will cause the precipitator, to give
more optimistic results. This is counter balanced to some extent by
(b) and (d) above.
6.5 Results and Discussion (10)(15)(28)
The CSIRO has carried out a very extensive range of tests on a
large number of coal- samples from New South Wales, Queensland and one
of the low sulphur coals f-rom the United States. Many of these test
results are not available for inclusion in this report.
One of the most extensive series of tests which may be reported,
was carried out for the ECNSW. These tests were part of a testing
program aimed at investigating the electrostatic precipitation properties
of fly ash from the Hunter Valley coal field. All together a total of
17 different coal samples were tested with a sulphur content varying
from 0.33 to 0.99 percent and an ash content from 10.2 to 32.8 percent.
A detailed report covering these tests was prepared by the CSIRO and
also reported in the general literature.
-------
58.
It is of considerable importance to know the extent to which this
technical scale testing rig simulates the performance of the full size
units. The CSIRO acknowledges that because of the difficulties in
modelling, it cannot exactly represent a full size unit. However, they
conclude, "it would appear that despite obvious differences between the
experimental rig and full scale power station plant, and notwithstanding
the ash deposition problem in the technical scale furnace, there is no
serious difficulty in predicting from the test rig results the relative
performance of full scale plate type pr'ecipitators on fly ashes from
different coals."(10)
The electrostatic precipitating properties of the different fly
ashes as measured by this rig. have been compared with measurements made
by the in-situ pilot precipitator and in some cases with full size
precipitators. The comparison of the characteristics of three different
NSW fly ashes^may be seen in Table 6.2.
SCA of 260 ft /kcfm. is taken as the basis for the comparison.
A temperature of 250 F and an
The
coals are arranged in their order of difficulty of collection and this
agrees with that predicted by the CSIRO technical scale rig.
It has been traditional to expect the efficiency of collection of
fly ash-to be related to the sulphur content of the coal. Measurements
by/ the CSIRO technical scale rig on coal from NSW, Queensland and one
sample from the United States have not been able to show that any
correlation exists. Coals with sulphur contents as low as .35 percent
have given remarkably good performances(28). This is in agreement with
results obtained from the full size and pilot electrostatic precipitators.
TABLE 6.2 - COMPARISON OF EMU
Temp = 250 F
SCA = 260 ft /kcfm
Coal Field
Effective Migration Velocity
cm/sec
CSIRO Precipitator Precipitator
Northern
Hunter Valley
Southern
8.5
7.9
5.4
8.5
7.5
3.0 - 4.2
7.0 - 8.5
N.A.
2.5 - 3.5
N.A. - not available
-------
59.
CHAPTER 7
LABORATORY TECHNIQUES FOR EXAMINING ELECTROSTATIC
PRECIPITATING PROPERTIES OF FLY ASH
7.1 Objective
One of the objectives of a number of research efforts overseas has been
to devise tests by which the performance of coals and the properties of the
re'sultant fly ash can be predicted from small bore core'samples. In
Australia, an attempt is made to do this by the combined efforts of the
Australian Coal Industry Research Laboratories Ltd. (ACIRL), Ryde, N.S.W.,
Wollongong University College (WUC), and the Electricity Commission of
New South Wales. The burning of the coal sample together mith physical and
microscopic examination of the resultant fly ash is carried out by ACIRL
and the electrical properties of the ash is measured by WUC.
The ECNSW and Bechtel of the United States on behalf of various
clients, have both made use of this facility.
7.2 ACIRL Small Furnace (12)
The apparatus consists of a 'conventional laboratory tube furnace as
shown diagramatically in Fig. 7.1. The central mullite tube 3.8 cm bore
and 100 cm long, is heated by a number of 'Crusilite' hairpin and spiral
elements to'give a maximum temperature of 1,500 C. Pulverised coal is
fed into'j the path of incoming gases of desired composition at the top of
the tube-and fly ash is collected from the bottom of the tube.
The coal feeder consists of a stirred glass hopper leading to a screw
feeder driven by a variable speed motor. Coal is then gravity fed into the
furnace. I
-------
60,
Gas in.
Pu I ver i zed coaI i n
Central combustion tube
Heat i ng rods.
Insulating
brick.
ThermocoupIe
Ash sampling probe
Fig. 7. I
ACIRL Small Laboratory Furnace
-------
61,
Incoming gases are metered through a system of manometers and passed
through a mixing bottle prior to entry at the top of the furnace. In
this fashion both total flow and gas composition is closely regulated.
The furnace is operated at approximately maximum temperature with
oxygen concentrations adjusted to provide the desired gas compositoh for
specific operations. A set of furnace conditions would be:-
Furnace temperature at centre - 1,500 C
Gas compositon - 88$ 0-, 12% N_
Gas Flow (S.T.P.) . - 1800 cc/minute
Coal feed - 0.2 grams/minute
Residence time - 2.4 seconds •
At 1,500°C the furnace power is 5kW. With a feed rate of 0.2 grams/
minute of 12,000 B.T.U.lb coal, the energy from combustion is O.lkW or
2% of the total input.
The original and still main performance of this furnace is to predict
from a number of small samples, usually borecores, the likely performance
of unused and unknown coals in large scale industrial firing. The use
of this furnace to produce the fly ash which may be tested physically,
microscopically and for its electrostatic precipitating properties, is
one of the specialised applications for which it may be used.
7.3 The WUC Test Rig and Analyser (17)(27)
The arrangement of the environmental test chamber is shown in
Fig. 7.2. A synthetic gas mixture is made up of appropriate amounts
of S09, 09, C09 and N9, and passed through a humidifier to the reaction
vessel. This contains the resistivity measuring cell in which the sample
of fly ash is placed and the resistivity measured between two parallel
plates. Typical resistivity temperature curves for varying humidities
are obtained with excellent repeatability.
The output from the environmental chamber may be fed into the
Kevatron Electrostatic Precipitation Analyser 223, details of which are
shown in Fig. 7.3. The fly ash sample is introduced into the gas
stream after the humidifier and then electrostatically collected in the
upper chamber of the Analyser. Although the efficiency of collection
may be measured, at the present stage of development it is being used
to examine the corona voltage-current characteristics in order to
determine the voltage at onset of back corona and spark-over. It is
considered that this measurement gives an indication of the electro-
static precipitating properties of the fly ash. Fig. 7.4 shows an
example of the type of results obtained for an ash which has been
conditioned with ammonia.
-------
c I o w n o t e r s
S0_+00)
X /_
Heater
Control Ie r
r ^
0,
CO
Water bath-M Stirrer-—
Gas wash bottIe
Spec!men and
test elect nodes
•React ion vessel
Fin. 7.2
WUC Test Rig for Measurina Resistivity under Varying
Environmental Conditions.
cr>
-------
63.
(-V)
TENSIOniXG
SPRING
Fig. 7.3
Kevatron Electrostatic Precipitator Analyser 223,
Gas to be examined enters the inlet to the
precipitator chamber where the particles are
removed and corona characteristics measured.
After rapping the deposit falls into the lower
chamber, where after compaction, resistivity
i s measu red.
(2a) = 0.35mm; (2b) = 6.3cm; L = 0.324 m.
-------
64:.
7.4 Discussion
In order to check the effectiveness of the modelling of the ACIRL
furnace as far as the electrical properties of the fly ash is concerned,
a sample of coal urns taken from the hoppers of one of the power stations
and burnt in the AGIRL furnace. At the same time a sample of the fly
ash produced by the pwer station boilers uias removed from the electro-
static precipitator hoppers. The resis.tivity of both these ashes was
then measured in the environmental chamber for similar conditions and
agreement to within a factor of 2 to 3 was obtained. Similar results
ujere obtained with other test samples. Because of variations in the
coal over a 24 hour period, this scatter of results is quite 'normal.
It is sbill an open question ,as to whether the resistivity measured
in this manner is the same as the in-situ value. Fig. 7.5 shows some
in-situ measurements made on the fly ash at Tallawarra. These measure-
ments were made at different times so direct comparison is not possible.
Even allowing for this, the'known variations that occur in the coal and
the well known difficulty in measuring in-situ resistivity, the values
are in good agreement with only a decade difference between them.
• \
It may well be argued that the in-situ resistivity would not be
too different from that measured in this laboratory apparatus. The one
important flue gas component which significantly affects resistivity is
SO,. The percentage of this gas in the case of high sulphur coals
materially affects the resistivity but it seems likely that for coals
with less than i.% 'sulphur, the SO, content is no longer important and
that the resistivity is determined by other factors as well. This view
seems to be supported by evidence in Australia that the sulphur content
of the coal does not give any correlation! with the electrostatic
precipitating properties of the ash 'as measured by either the full size
precipitators, the CSIRO technical scale or the pilot precipitators.
\
It is not considered at\ this stage that sufficient data has been
obtained to relate any of these readings directly to the EMU used in
sizing a full size precipitator. However, it is considered that both
the resistivity and corona measurements may be used to rank the coals
as far as the electrostatic precipitating properties of their ash is
concerned.
-------
65.
3.0
ro
E
c
0)
3
o
to
c
o
l_
o
o
Ammon i a
con d i t i onec
10 15
Corona Voltage KV.
Fig. 7.4
Corona Characteristics of the Kevatron 223
with and without Ammonia Conditioning.
Temperature = I43°C.
-------
66.
10
16
10
15
E
O
E
.c
O
(SI
I/)
Q)
o:
14
160 180 200 220
Temperature 'C.
Fiq. 7.5
In-situ Resistivity Compared with Resistivity
Measured in the Laboratory with Synthetic Flue
Gas.
In-situ 1970.
Laboratory 1971. (Synthetic flue gas)
-------
67.
CHAPTER 8
SUMMARY OF SALIENT FEATURES
In'this chapter an attempt is made to summarize the main features
which characterize the electrostatic precipitation of fly ash from low
sulphur coals. Some of these features highlight hoiu the collection of
this fly ash differs from the collection of ash from the high sulphur
coals.
1. The fly ash has very high in-situ resistivity with maximum values
above 10 ohm-cm occuring in the temperature range 240 to 300 F. At
temperatures above BOO F, the resistivity drops to below 10 ohm-cm.
2. These fly ashes are very difficult to collect with electrostatic
precipitators, in some cases requiring units with SCA's in the order of
600 ft /kcfm if no gas conditioning is used. In order to assist in
the collection, the 'flue gas temperature in the collectors is in the
order of 260 F, and it is proposed in the future to operate one unit at
220 F. The EMV's are very low with values varying from,below 3 cm/sec
up to a maximum of 8 cm/sec.
3. Good rapping is neceslsary if high performance is to be obtained.
Transverse accelerations of 60 g are necessary in order to adequately
remove the deposited layer from the collecting plate.
4. In many instances the electrostatic precipitators operate with some
back corona cu'rrent flowing. Voltage levels-are .down and current densities
are usually lower than is required for collecting ash from high sulphur
coals. The useful corona current density Imay be in the order of 8^ua/ft
and the back eoron.a current may be 2 to 3 ;times this value. Optimum
operating conditions are :often found to be at/a/voltage 'level just
beloiu sparking. ' . V, / .
t t / /
-------
68.
5. It is a characteristic of electrostatic precipitators collecting
high resistivity fly ash that maximum performance can only be obtained
by very careful tuning and maintaining the units in excellent mechanical
and electrical condition.
6. The performance of all the Australian ashes can be improved by
flue gas conditioning. Sulphur trioxide probably gives a better
performance level although good results have been obtained with ammonia.
Because of its simplicity and economy, ammonia is the preferred
conditioning agent. In no case however does the EMU of a full size
precipitator with conditioning exceed 8 cm/sec. The sulphur trioxide is
obtained from sulphuric acid and the ammonia from anhydrous ammonia and
more recently from Concentrated Ammonical Liquor. (CAL.)
7. The sulphur content of the coal cannot be used as a guide to
determine the electrostatic precipitating properties of a fly ash. This
is probably true for coals with a sulphur content of less than 1 percent,
although it need not be so for coals with higher levels.
8. In Australia, good indication of the precipitating properties of
unknown fly ashes has been obtained from pilot precipitator tests, the
CSIRO test rig and the ACIRL-WUC test facility.
9. Pilot Precipitators have been used very successfully to predict
the electrostatic precipitating properties of fly ash with unknown
characteristics. Reasonably consistent results have been obtained, and
after the application of an appropriate scaling factor, these are in
agreement with results obtained from full size electrostatic precipi-
tators.
10. The CSIRO test facility provides a valuable method of quickly and
economically ranking the precipitating properties of an unknown fly ash.
11. By using bore core samples the ACIRL-WUC laboratory scale test
facility provides a very simple and economic method of measuring some
important parameters of fly ash samples which may then be used to assist
in the sizing of electrostatic precipitators.
-------
69.
9, ACKNOWLEDGEMENTS
The author gratefully acknowledges the assistance given to him by
The Electricity Commission of Mem South Wales, Southern Electric
Authority of Queensland, Northern Electric Authority of Queensland,
Commonujealth Scientific and Industrial Research Organization, Australian
Coal Industry Research Laboratories and Wollongong University College.
Each of these organizations have allowed the author to talk to their
personnel and have supplied the information necessary for the completion
of this report.
In-particular, the author is very much in debt to Messrs. D.B. Kirkiuood,
K.S. Watson and N. Lamb of the ECNSW, each of whom have significantly
contributed to the collection and interpretation of the information in
this report. In addition, valuable assistance mas also given by
Mr. L.A. Toigo (SEAQ), Drs. R. A. Durie and E. C. Potter (CSIRO),
Mr. K. M. Sullivan (ACIRL) and Mr. 0. 3. Tas-sicker (WUC).
Although the data and information recorded in this report has been
gathered from many different organizations and as a result of discussions
with many people, its accuracy and the conclusions arrived at are the
sole responsibility of the author.
-------
70.
,10. REFERENCES
1. WHITE, H.D. - 'Industrial Electrostatic Precipitation',
Addison-Wesley, U.S.A., 1963.
2. OGLESBY, S. & NICHOLS, G.B. - 'A Manual of Electrostatic
Precipitator Technology1, prepared under contract CPA 22-69-73
for the EPA, Research Triangle, N.C., 1970.
3. KIRKWOOD, J.B. - 'Electrostatic Precipitators for the Collection
of Fly Ash from Large Pulverized Fuel Fired Boilers', Paper
No. 14, Clean Air Conf.,. Sydney, Feb. 1962.
4. BUSBY, G.H.T. & DARBY, K, - 'Efficiency of Electrostatic
Precipitators', Inst. of Fuel, Vol. 36, 1963.
5. WATSON, K.S. & BLECHER, K. 3. , - 'Further Investigations of
Electrostatic Precipitators for Large Pulverized Fuel Fired
Boilers', Paper No. 10, Clean Air Conf., Sydney, Aug. 1965.
6. WATSON, K.S., FLANAGAN, B.P. & BLECHER, K.3. - 'Pilot Plant
Testing as an Aid to Evaluating Precipitator Performance', Inst.
Elec. Engrs., Colloquium on Electrostatic Precipitators,,'London,
1965.
7. 'Construction and Operation of Pulverized Fuel Test Rig No. I1,
Coal Research Laboratory, Div. of Mineral Chemistry, CSIRO,
Invest. Rept. 65, 1966.
8. TASSICKER, O.D., HERCEG, Z. .& McLEAN, K.3. - 'The Electrical
Resistivity of Fly Ash from Baysujater and Neujvale Coals', WUC
Bulletin No. 11, 1966.
9. TASSICKER, O.3., HERCEG, Z. & McLEAN, K.3. - 'Mechanism of Current
Conduction Through Precipitated Fly Ash', WUC Bulletin No. 10,
1966.
10. DURIE, R.A. - 'Investigation of the Electrostatic Precipitation
of Fly Ashes from Coals to be Supplied to the Liddell Power
Station', Coal Research Laboratory, Div. of Mineral Chemistry,
CSIRO, Part 1, Invest. Rept. 68, 1967; Part 11, Invest. Rept. 72,
1968.
11. 'Liddell Power Station, Investigation of Requirements for
Electrostatic Precipitators', Research Note No. 59, ECNSW,' 1967.
12. MORAN, V.3. - 'Laboratory Techniques for the Examination of the
Combustion Characteristics of Coal', ACIRL, P.R. 67-8, 1967.
13. McLEAN, K.3. - 'Influence of Contaminated Collecting Plates on the
Performance of Electrostatic Precipitators', Trans. I.E. Aus.,
Vol EE4, No. 1, 1968.
14. LAMB, N & O'BRIAN, A. - 'Walleraujang Power Station, Investigation
of Requirements for Electrostatic Precipitators for No. 7 Boiler',
ECNSW, Invest. Rept., 1969.
-------
71.
15. DURIE, R.A., & POTTER,. E.G. - "Factors Influencing the Efficient
Operation of Electrostatic Precipitators for Pulverized Fuel Ash1,
Paper No. 1.7, Clean Air Conf., Sydney, 1969 (Subsequently pub-
lished in Aust. Chem. Proc. and Eng., Vol. 23, No. 9, 1970).
16. TASSICKER, O.J., HERCEG, Z. & McLEAN, K.J. - "The Collection of Dust
by Electrostatic Precipitation1, Paper No. 1.6, Clean Air Conf.,
Sydney, 1969.
17. TASSICKER, O.J., HERCEG, Z. & McLEAN, K.J. - «A New Method and
Apparatus to Assist the Prediction of Electrostatic Precipitator
Performance1, Trans, I.E. Aus. EE5, No. 2, 1969.
18. POTTINGER, 3.F., - 'The Collection of High Resistivity Materials by
Electrostatic Precipitation1, 2nd Int. Clean Air Cong., Washington
D.C., 1970.
19. McLEAN, K.J. - 'Electrical Conduction in High Resistivity Particulate
Solids1, Doctoral dissertation, University of (\leuj South Wales,
Sydney, 1970.
20. BUSBY, H.G.T., WHITEHEAD, C. & DARBY, K. - 'High Efficiency
Precipitator Performance on Modern Power Stations Firing Fuel
Oil and Low Sulphur Coals', 2nd Int. Clean Air Cong., Washington
D.C., 1970.
21. HERCEG, Z. - 'Electrical Characteristics of Contaminated Corona
Systems', Doctoral dissertation, University of New South Wales,
Sydney, 1970.
22. TOIGO, L.A. & HAMILTON, 3.R. - 'Investigations of Electrostatic
Precipitation of Fly Ashes', SEAQ Invest. Rept., 1970.
23. McLEAN, K.3. - 'Some Effects of High Resistivity Fly Ash on
Electrostatic Precipitator Operation1, Electrostatic Precipitator
Symp., EPA, Birmingham, Alabama, 1971.
24. HERCEG, Z. & McLEAN, K.O. - 'Efficiency of Electrostatic
Precipitators and Relationship to Corona Voltage Current Charac-
teristics', 64th Ann. Meeting APCA, Atlantic City, N.3.,
Paper No. 71-178, 1971.
25. TASSICKER, 0.3. - 'The Dielectric Constant of a Dispersoid in
Relation to Electrostatic Precipitator Performance1, Staub-Reinhalt,
Vol. 31, No. 8, 1971.
26. LAMB,.N. & WATERS, M. - 'Collinsville Power Station, Investigation
of Requirements for Electrostatic Precipitators for Nos. 5 & 6
Boilers', NEAQ Invest. Rept., 1971.
-------
72.
27. TASSICKER, 0.3. - 'Experiences with an Electrostatic Precipitator
Analyser in the Evaluation of Difficult Dusts', Paper No. 2.3,
Int. Clean Air Conf., Melbourne, 1972.
28. DURIE, R.A., PAULSON, C.A.3., & POTTER, E.G. - 'Mitigating Fly Ash
Emissions in Australia: The Role of the CSIRO Testing Facility,
Paper No. 2.2, Int. Clean Air Conf., Melbourne, 1972.
29. McLEAN, K.3. - 'The Collection of Particles by Electrostatic Forces',
Int. Clean Air Conf., Paper No. 2.1, Melbourne, 1972.
-------
73,
BlflLIOGRAPHffb'XrA 1- Report No. 2.
SHEET" EPA-R2-73-258
4. Title and Subtitle .
Survey of Australian Experience in Collecting High
Resistivity Fly Ash with Electrostatic Precipitators
7. Auchor(s)
Kenneth J. McLean
9. Performing Organization Name and Address
Uiiisearch Limited
221-227 Anzac Parade
Kensington, New South V/ales 2033
12. 'Sponsoring Organization Name and Address
EPA, Office of Research and Monitoring
NERC-RTP, Control Systems Laboratory
Research Triangle Park, North Carolina 27711
3. Recipient's Accession No.
5- Report Dat®"*" =a***r
September 1972
6.
8. Performing Organization Repc.
No.
10. Project/Task/Work Unit No.
11. Contract/Grant No.
68-02-0245
13. Type of Report & Period
Covered
Final
14.
15. "Supplementary Notes -
16. Abstracts m, , , ., A , ,. . . . ' .
* J^ -------- QJ _ _ _ _ —._._ —_ _ ^ _ _ _^
ators (ESP's) to collect fly ash produced by the combustion of low-sulfur bituminous
coal in pulverized-fired boilers. The ash, with very high resistivity and exception-
ally difficult to collect, in some cases requires ESP's with specific collecting areas
above 600 sq ft/kcfm. It includes typical ESP dimensions and operating parameters,
together with a survey of the main problems and experience obtained in collecting
tMs fly ash. ESP performance has been improved by operating at low temperatures
and by conditioning the flue gas with SOS and NH3. It describes various conditioning
injection systems and discusses the effectiveness of the agents on the different ashes.
1J evaluates procedures used in pilot, technical scale, and laboratory tests that were
carried out to determine the fly ash characteristics, because the sulfur content of
the coal cannot be used reliably to predict ESP properties of fly ash. _•
17. Key Words and Document Analysis. 17q.
Air Pollution
Electrostatic Precipitators
Fly Ash
Combustion
Sulfur
Bituminous Coal
Boilers
Sulfur Trioxide
Ammonia
ITix. .Identifiers/Open-Ended Terms
Air Pollution Control
Stationary Sources
Australia
Descriptors
Tests
Performance
Flue Gases
Treatment
Cleaners
Chemical Analysis
Physical Analysis
17c. COSATI Field/Group
13B
18- Availability Statement
Unlimited
19.. Security Class (This
Report)
UNCLASSIFIED
20. Security Class (This
Page
UNCLASSIFIED
21. No. of Pages
78
22. Price
FORM NTIS-35 (REV. 3-721
USCOMM-DC M952-P72
------- |