CD A u-s- Environmental Protection Agencv Industrial Environmental Research
t W f^ Office of Research and Develonment I ahnratnrv
PDA fiflfl/7 7ft
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Research Triangle Park. North Carolina 27711 MdfCh 1978
MEASUREMENT OF FLY ASH
RESISTIVITY USING SIMULATED
FLUE GAS ENVIRONMENTS
Interagency
Energy-Environment
Research and Development
Program Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
virdnmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer nd a maximum interface in related fields
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. “Special” Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA’s mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control teàhnology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems, and integrated assessments of a wide range of energy-related environ-
mental issues
EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication Approval does not signify that the contents necessarily reflect
the views and policies of the Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-78-035
March 1978
MEASUREMENT OF FLY ASH RESISTIVITY
USING SIMULATED FLUE GAS
ENVIRONMENTS
by
R. E. Bickelhaupt
Southern Research Institute
2000 Ninth Avenue. South
Birmingham, Alabama 35205
Contract No 68-02-2114
Task 4
Program Element No. 1AB012, ROAP 21ADL-027
EPA Project Officer: Leslie E. Sparks
Industrial Environmental Research Laboratory
Office of Energy, Minerals and Industry
Research Triangle Park, N.C. 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, D.C. 20460
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TABLE OF CONTENTS
Page
Figures 1V
Abstract
Acknowledgements Vi
Section
I Summary . 1
II Introduction 3
III Initial Experimental Approach And
Problems Encountered 4
IV Experiments To Develop Apparatus And
Procedure To Utilize Environments
Containing SOS. • S S S ‘ 11
V Development Of A Radial Flow Test Cell
And Procedure . . . . . . . . . . . . . . . 14
VI References 22
iii
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FIGURES
Number Page
1 General apparatus arrangement for resistivity
measurement, initial equipment: chamber and
all plumbing 316 stainless steel 5
2 316 stainless steel environmental
resistivity chamber 7
3 Resistivity test, wiring diagram 8
4 Weightpercentso lub le sulfate 12
5 Combination parallel plate - radial flow
resistivity test cell and electrical
circuit. . . . . . . 15
6 Glass environmental resistivity chamber 17
7 Resistivity vs. time of environmental
e cposure . . 18
8 EffectofSO 3 onresistivity 21
iv
-------
ABSTRACT
This report, describing the apparatus and laboratory pro-
cedures used to determine resistivity for a number of fly ashes
under a variety of test conditions, supports research to develop
a technique for predicting fly ash resistivity from chemical
analyses of coal and coal ash. This effort requires considerable
knowlege regarding the relationship between resistivity and
several coal and ash properties. In particular, the report
relates the experimental problems encountered when attempts were
made to determine the effect of sulfur trioxide on resistivity.
Equipment and procedures were developed to solve this problem.
The report describes the n dified apparatus and technique and
illustrates the type of data acquired.
V
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ACKNOWLEDGEMENTS
This work was financially supported by the Environmental
Protection Agency under Contract No. 68-02—2114. This support
and the time extensions allowed so that unforeseen research
problems could be overcome were greatly appreciated.
Southern Research Institute staff members, Dr. Edward B.
Dismukes, Mr. Walter R. Dickson, and Mr. Sabert Oglesby, Jr.
made important contributions to this work. Conversations with
these gentlemen developed many technical suggestions and offered
encouragement to the investigator.
The special efforts exerted by Mr. Charles A. Reed, Engi-
neering Research Technician, and by the Institut&s machine
shop are gratefully acknowledged.
vi
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SECTION I
SUMMARY
The equipment and technique used to measure the resistivity
of fly ash in the laboratory at the start of this research pro-
gram would be considered conventional and adequate according to
the general literature. However when SO was included in the
simulated flue gas, a number of problems occurred that made the
existing test apparatus and procedures unsuitable.
Retrospectively reviewed, the principal problems encountered
were: a) the presence of uncontrolled amounts of 503 due to the
catalytic oxidiation of SO 2 when using environments containing SO 2
and 02, b) the failure to use an adequate total flow of gas to
maintain a constant concentration of SO 3 during a test, and C)
failure to anticipate the time required to “equilibrate” a rather
small quantity of ash in direct contact with an environment con-
taining sulfuric acid vapor.
To overcome the problem regarding the generation of S03 with-
in the system, all stainless steel equipment, for which it was
technically feasible, was converted to glass, and finally the en-
vironment was changed from a mixture of SO 3 , S Oa , O , H 2 0, CO 2 and
N 2 to a simple mixture of air, water and SO 3 . Changes made to
create a system that produced a constant concentration of SO 3 at
the test site include: a) converting to a glass system to reduce
adsorption by the system, b) increasing the environmental total
flow rate at standard conditions from 1.3 to 5.0 liters/minute,
and C) reducing the number of ash specimens per test from 4 to 1,
and reducing the ash sample area from about 180 to 45 cm 2 .
Several steps were taken to develop a test procedure utilizing
a sufficient and reasonable period of time to observe the effect of
SO 3 (H SO .) on resistivity. It was obvious that the procedure
involving varying test temperature would have to be changed to an
isothermal test. The conventional parallel plate, ASME PTC—28
test cell was converted to a radial flow cell in which only a
surface layer of ash 1 nun thick was under test. The test procedure
was altered to allow overnight exposure of the ash surface to the
environment. The asymptotic approach of the decreasing resistivity
value to some limiting level as a function of ash—environmental ex-
posure time was used to establish a test end point. For many con-
ditions, an exposure lasting nineteen hours was sufficient.
1
-------
The nature of this investigation, a side excursion into the
area of test procedure to be able to accomplish the principal task,
precluded a formal approach to the problem. Many small problems
have not been discussed, and many trial and error experiments were
run. It is difficult therefore to determine whether all changes
in equipment and technique were mandatory. In any event, it was
concluded that one can determine the effect of SO 3 on the re-
sistivity of fly ash in the laboratory if a known, invariant con-
centration of SO 3 (H2SO ) can be maintained at the test site and if
sufficient time is allowed to “equilibrate” the volume of ash under
test with the environment.
Time has not permitted the detailed evaluation of the apparatus
and procedures described herein. The system was considered suitable
for use in continuing the effort regarding the principal research
objective, which was the development of a technique for predicting
the electrical resistivity of fly ash.
2
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SECTION II
INTRODUCT ION
The objective of EPA Contract No. 68—02—2112, Task IV, is to
develop a method for predicting fly ash resistivity as a function
of temperature from the analyses of coal and coal ashes prepared
by simple laboratory ignition. The method must include expres-
sions to reflect the effect of electric field strength, water con-
centration, sulfur trioxide concentration and ash composition on
the resistivity-temperature relationship. To accomplish this, the
resistivity-temperature characteristics for a large number of fly
ashes were investigated using the above test variables.
The research progressed at a satisfactory pace with encourag-
ing interim results until tests were begun to demonstrate the ef-
fect of variations in SO 2 and SO 3 concentrations on ash resistivity
as a function of temperature. The purpose of this report is to
point out the problems encountered in this facet of the work and
to illustrate the equipment and test procedure eventually selected
to complete the program.
3
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SECTION III
INITIAL EXPERIMENTAL APPROACH AND PROBLEMS ENCOUNTERED
Before attempting to deal with the difficulties encountered
in simulating flue gases containing SO , it would be beneficial
to define the apparatus and test proce ure originally designed
for this research. The equipment and technique described below
were used successfully prior to studies in which the environment
included SO, .
Experimental Apparatus
The original experimental arrangement was designed to deter-
mine resistivity for four ash specimens simultaneously using ASME,
PTC-28 test cells’. The test cells were contained in a 316 stain-
less steel chamber that was housed in a high temperature oven.
Simulated flue gas environments were maintained in the test chamber
under a small positive pressure (1 to 2 inches of water). The
electrical circuit allowed the cells to be independently energized
for resistivity measurements.
Figure 1 illustrates the physical arrangement of the apparatus.
Tank gases including commercially prepared and certified 1% SO 2 in
N 2 were metered using precision rotameters to deliver the desired
mixture at a total flow rate of 1.3 liters/minute at standard con-
ditions. Depending on the temperature, this flow rate provided 5 to
10 volume changes per hour for the test chamber. The standard or
baseline simulated environment contained by volume 5% 02, 13% CO 2 ,
9% H 2 0, 500 ppm 502 and the balance N 2 .
The gases leaving the rotameters passed through a stainless
steel manifold into a two liter stainless steel mixing vessel held
at 200°C to preheat the gas. At the exit of this vessel an inlet
was provided for the introduction of SO 3 . The proper amount of SO 3
to be injected was governed by the temperature of the 20% sulfuric
acid bath and the flow rate of the nitrogen used as a carrier.
A temperature of 160°C was maintained for the stainless steel
tubing carrying the gas mixture to the oven. After entering the
oven, the gas was passed through 25 feet of tubing, maintained at
the test temperature, before it entered the resistivity chamber.
Gas exiting the chamber was passed through a bubbler external to
4
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ENVIRONMENTAL
CHAMBER
(SEE FIGURE 2)
LEAD
CONTROLED TEMPERATURE
WATER BATH
GAS OUTLET
SAMPLING PORT
Figure 1. General apparatus arrangement for resistivity measurement
initial equipment: chamber and a/I plumbing 316 stainless steel.
THERMOCOUPLE SELECTOR.
SWITCH. TERMINAL BLOCK,
AND DIGITAL READOUT
TO GAS
HEATING TAPE CYLINDERS
AND INSULATION
FEMALE PHONE JACKS
FOR FOUR TEST
CIRCUITS
PREH EATING
CHAMBER
HEATING TAPE
AND INSULATION
GAS
INLET
25
FOUR TEST
CIRCUITS
KEITHLEY 610C
ELECTROMETER
FLUKE 4088
HV POWER SUPPLY
ROTAMETERS
HIGH VOLTAGE
ACID
RESERVOIR
HEATING
MANTLE
OVEN DOOR
BUBBLER
OVEN
CONTROL
PANEL
TC — THERMOCOUPLE
5
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the oven to provide visual evidence of the maintenance of a small
positive pressure in the chamber.
Experimental Procedure
Ashes were passed through an 80 mesh screen to remove any
foreign material prior to being poured into the cup of the resistiv-
ity cell. While being filled, the cup was tapped to insure that
ash bridging would be minimized. After the cell surface was leveled,
the upper, current-measuring electrode was placed in position, and
the test cell was attached to the proper leads in the chamber, see
Figure 2. The front piece of the chamber was sealed with C clamps
after the four test cells were in position. Clamping together two
finely machined surfaces was suitable for maintaining the small in-
ternal chamber pressure.
Nitrogen, passed through a drying column and the heated plumb-
ing leading to the oven, was maintained in the test chamber over-
night as the specimens were thermally equilibrated at 450—470°C.
Prior to converting the environment to a simulated flue gas, the
resistivity of each test cell was determined. Sequentially each
cell was tested by applying 1000 volts DC (5mm ash layer giving
an E = 2kV/cm) and determining the current one minute after the
application of voltage. Figure 3 shows a schematic of the electri-
cal circuit for the resistivity test.
After the environment was converted to the simulated flue gas,
the current readings were repeated every 10 minutes until the cur-
rent no longer increased with time. This usually took 20 to 40
minutes. At this point the oven was turned off, and current read-
ings were taken periodically as the chamber temperature decreased.
The cells cooled from 460°C to 145°C in about four hours and cool-
ed further to 85°C in an additional two hours.
When it was of interest to determine resistivity as a function
of ash layer field strength, the decreasing temperature was arrested
at 162°C while the necessary measurements were made. Variation in
water concentration was accomplished by changing the temperature of
the water through which the nitrogen was bubbled prior to entering
the 200°C preheating vessel. The nitrogen was valved so that it
could be introduced dry or through the water bubbler. The water
concentration was determined from an exit gas sample at least once
during each resistivity test. Resistivity was calculated as
follows:
6
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TO
KEITH LEY
610 C
ELECTROMETER
FINISHED
SURFACE
GAS
OUTLET
CERAMIC
SUPPORT
THERMOCOUPLE
SWITCHING
DEVICE
AND DIGITAL
READOUT
GAS
INLET
FLUKE 408B
IV POWER SUPPLY
Figure 2 316 stainless steel environmental resistivity chamber.
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PHONE JACKS
F M
I- -1
=1 ‘
—. ,
_._.- /,/
/ /
/1
/
/
—---/ /
Figure 3. Resistivity test, wiring diagram.
-CELL 4
—CELL 3
—CELL 2
—CELL 1
KEITHLEY 610C
ELECTROMETER
OVEN
WALL
GUARD
CENTER
STAINLESS
WITH
STEEL WIRE
CERAMIC SPAGHETti
RG-581U
GUARD
CENTER
:
RG-58/U
(
GUARD
CENTER
GUARD
CENTER
S
•
RG58/U
RG-581U
& . J
J2
RG-581U f -
/
---/
+ 1 RG-58/U
FLUKE 408B HV
POWER SUPPLY
8
-------
= VA (1),
I’L
where: p = resistivity in ohm•cm
V = D.C. volts
I = current in amperes
A = area of measuring electrode in cm 2
L = thickness of ash layer in cm.
Problems Encountered Using SO
It was stated above that the standard or baseline environment
contained “500 ppm of SO 2 and no injected SO 3 . Preliminary ex-
periments had shown a small difference between resistivity data ac-
quired using air—water environments versus the baseline simulated
environment. At the time, it was believed that the small attenua-
tion of resistivity was possibly due to the presence of SO 2 . (Re-
trospectively, the SO 2 would have been deleted from the baseline
environment if it had been realized that an uncontrolled amount of
SO 3 was being introduced by the catalytic oxidation of SO 2 .)
The scope of research required the investigation of the effect
of simulated environments containing 500, 1000, 2000 and 3000 ppm
of SO 2 . When the larger concentrations of SO 2 were incorporated,
it was observed that resistivity values were significantly attenuat-
ed. Although one could not rule out the possibility that SOa af-
fects ash resistivity, it seemed likely that large quantities of
SO 3 were being generated and that the reduction in resistivity was
due to the presence of sulfuric acid. Determination of SO 3 and
SO 2 concentrations in the inlet and outlet gas samples when no SO 3
was being injected verified the presence of SO 3 . Gas analysis pro-
cedure is described in Reference 2.
Several months were spent running ancillary experiments at-
tempting to understand the problem and develop a way in which the
existing equipment and test procedure could be utilized. When SO 2
was included in the environment, SO 3 was catalytically produced.
9
-------
A few ppm were produced even when oxygen was excluded. It was
concluded that some oxygen was present as a trace impurity in
other gases or that air diffused into the test chamber at the im-
perfect seal on the face. Furthermore, the amount of SO 3 catalyti-
cally produced was sensitive to the plumbing temperature and the
temperature of the test chamber. When SO 2 was eliminated and SO 3
was injected, the difference in SO 3 concentration in the inlet and
exhaust gas samples from the test chamber was sensitive to the
chamber temperature. This indicated the chamber was capable of
adsorbing a significant quantity of available SO 3 (H 2 SO..). Since
temperature was one of the test variables and since it was desired
to keep the SO 3 concentration constant during a specific test, the
above observations indicate that the original procedure and equip-
ment were not satisfactory for the evaluation of the effect of SO 3
on resistivity.
10
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SECTION IV
EXPERIMENTS TO DEVELOP APPARATUS AND PROCEDURE
TO UTILIZE ENVIRONMENTS CONTAINING SO,
A series of modifications took place in reaction to the
observed test results. The first modification converted all
plumbing and hardware from stainless steel to glass with the
exceptions of; electrical feedthroughs, test cells, lead wires,
etc. This did not eliminate the formation of SO 3 from the SO 2
and 02 present in the environment; however, the amount of SO 3
adsorbed by the system was decreased. It was then decided to
convert to an environment of air, water vapor and injected SO 3
since no evidence was available to suggest a need for 02, CO 2
and SO 2 to be present.
Under these conditions, the effect of 10 ppm of SO 3 on resis-
tivity was not observed although a significant amount of SO 3 was
removed from the environment as indicated by the measured SO 3 con-
centrations for chamber inlet and outlet gas samples. [ This is in
contrast to the observed reduction of resistivity reported for the
stainless steel system. It has been rationalized that in the case
of the earlier observations either a very great quantity of SO 3
had been generated and/or condensation of acid had taken place.]
At this point the total environmental flow rate under standard con-
ditions was increased from 1.3 liters/minute to 5.0 liters/minute,
and the number of test cells were reduced from four to one. Under
these conditions and with 25 grams of ash present in the single
test cell, an injection rate of ‘l0 ppm SO 3 could be maintained in
both the inlet and outlet gas samples.
However, even overnight exposure to an environment consisting
of air containing 9% water and 10 ppm of SO 3 did not produce a sig-
nificant attenuation of resistivity. The resistivity cell was the
type suggested in ASME PTC-28, previously referenced. The ash is
held in a shallow dish having a porous, stainless steel bottom. The
upper ash surface is exposed to the environment except where the
measuring electrode and guard ring rest. Ash specimens were taken
at various elevations between the exposed surface and the porous
metal base at plan positions exposed to the environment and be-
neath the measuring electrode. The amount of soluble sulfate was
determined 2 for each specimen as a measure of the penetration and
adsorption of sulfuric acid from the environment. The results are
shown in Figure 4 for an ash having a soluble sulfate value of
11
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SAMPLE POSITION:
% SOLUBLE SULFATE: 0.20/0.25 0.80 0.41
SCHEMATIC CROSS-SECTION OF ASME. PTC-28 RESISTIVITY CELL
BLANK 1 2
Figure 4. Weight percent soluble sulfate.
3 4 5 6
0.34 0.25 0.28 0.28
ENVIRONMENT
MEASURING
ELECTRODE
GUARD
RING
A 5 MM
POROUS STAINLESS
STEEL ELECTRODE
12
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0.20 - 0.25% before testing.
These data show that even after 24 hours of exposure at 145°C
to an environment consisting of air, 9% water and 10 ppm of SO 3 ,
a large concentration gradient of adsorbed acid (soluble sulfate)
exists through the ash layer. The data show that in the area di-
rectly exposed to the environment the acid pickup was significant
at the surface and a concentration gradient developed from po—
sition 1 to 3. Between the measuring electrodes there was little
adsorption of acid. Therefore, no appreciable attenuation of re-
sistivity was noted. Obviously even a thin ash layer (1-2mm) be-
tween two parallel, porous electrodes would not be a successful
test geometry under these conditions.
Attempts to utilize vacuum to pull the environment through the
electrodes and ash layer and other schemes to force it through under
pressure failed. Besides the side effects of either compacting or
fluidizing the ash layer, the concentration gradient of acid pick-
up expressed as soluble sulfate could not be eliminated.
The observations described above suggest that in addition to
the ASME resistivity cell, other designs may be unsatisfactory for
examining the effect of SO 3 on resistivity. Nevens et a1 3 recent-
ly evaluated three general types of laboratory resistivity test
cells. Since these cells require the environment to permeate a
porous stainless steel electrode and about 5 mm of ash, these de-
signs are probably undesirable for environments involving SO .
Kanowski and Coughlin 4 were successful in illustrating the ev-
fect of SO 3 on fly ash resistivity using a cell believed to be
similar to that suggested by ASME-PTc-28. Although all apparatus
and procedural details are not available, it would seem that the use
of very high total environmental flow rates and the use of high
concentrations ( 3Oppm) of 503 contributed to this success. This
approach was not attempted in the subject research, because the
facilities limited the low rates available and interest was
restricted to low SO 3 concentrations,
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SECTION V
DEVELOPMENT OF A RADIAL FLOW TEST CELL AND PROCEDURE
Equipment
The observation that the exposed ash surface adsorbed a sig-
nificant amount of sulfuric acid (soluble sulfate), and the as-
suinption that a thin layer of ash at the surface must become es-
sentially “equilibrated” with the environment in a reasonable per-
iod of time lead to the development of a test apparatus and tech-
nique that has provided useful laboratory resistivity data. Ini-
tial experiments showed that surface resistance readily reflected
the effect of sulfuric acid in the environment. The test cell
shown in Figure 5 was constructed to compare simultaneously a con-
ventional test cell with a radial flow test cell using a 1 nun
thick ash layer. With this arrangement, one can alternately mea-
sure resistivity in the conventional parallel plate mode between
electrodes 2 and 3 or in the radial flow mode between electrodes
1 and 2. The cell dimensions selected were based on the work of
Amey and Hamburger 5 regarding optimum geometries for surface and
volume resistance measurements. Resistivity can be calculated for
the radial flow cell from the expression:
= 211 c Vl.56V (2),
R n(r2/r1) I I
where: p — resistivity, ohm’cm
V - volts, applied between electrodes
1 and 2
I - amperes, current flowing between
electrodes 1 and 2
c — 0.1cm, thickness of electrodes
1 and 2
r2 — 1.90cm, radius of I.D. of
electrode I
r 1 — 1.27cm, radius of electrode 2
14
-------
7.6cm
ELECTRODE 1
ELECTRODE 2
ELECTRODE 3
• 5.1 cm OD x 3.8 cm ID x 0.1 cm THICK, SOLID STAINLESS STEEL
• 2.54 cm OD x 0.1 cm THICK, SOLID STAINLESS STEEL
- 7.64 cm OD x 0.1 cm THICK. POROUS STAINLESS STEEL
Figure 5. Combination parallel p/ate - radial flow resistivity
test cell and electrical circuit.
1mm
1
1
3
1
15
-------
Figure 6 shows a radial flow cell in the glass environmental
chamber.
Figure 7 shows the comparative results for the two electrode
geometries expressed as resistivity versus time of environmental
exposure. For this experiment the apparatus shown in Figures 5
and 6 was used, and the ash was thermally equilibrated overnight
in dry air at 145°C. Resistivity was determined, about 1.4 x l0
ohm•cm with either electrode set, and the environment was changed
to include 9% water at time = 0 hours. After 20 minutes, both
electrode sets measured a resistivity of 2 to 3 x 1011 ohmcrn.
This response time is typical. At this temperature, flow rate and
chamber size, the time required to dilute a given environmental
composition to 99% of a different composition was about six minutes.
After the minimum resistivity due to water injection is reached, the
resistivity gradually increases with time of exposure. Even though
the injection of 10 ppm of SO 3 was started at time equal 30 minutes,
the linear flow, parallel plate electrode set showed this increase
in resistivity; i.e., the parallel plate electrode set did not respond
to the presence of SO 3 . However, the resistivity measured with the
radial flow electrode set started to show the effect of SO 3 injection
about 30 to 60 minutes after injection was started. After about two
hours had elapsed, the attenuation of resistivity due to SO 3 injection
was quite apparent and continued at a decreasing rate until a minimum
value was attained about 24 hours after the start of the test. For
this ash and set of conditions, it is assumed that a 24 hour exposure
was required to “equilibrate” the 1 mm thick ash layer between elec-
trodes 1 and 2, Figure 5, with the surrounding environment of air,
water vapor and sulfuric acid vapor.
No effort has been made to formally evaluate the reproducibility
of data using this cell; however, the cursory comparison of many
pairs of tests would indicate the reproducibility is good. Also, no
attempt has been made to evaluate the effect of variations in the
test procedure on the data generated. It has been noted that the in-
let and outlet SO 3 determinations indicate the environment is repro-
ducible and that typically the inlet concentration is slightly great-
er than the outlet concentration for injections of
-------
Figure 6. Glass environmental resistivity chamber.
17
RADIAL FLOW
RESISTIVITY CELL
BASE PLATE
-------
io 14
TIME, hrs
Figure 7. Resistivity vs. time of environmental exposure.
C.)
I
0
I-
>
C#)
C l )
w
i0 1 °
1
2 z
o RADIAL FLOW ELECTRODE SET, 1-2, FIGURE 5
o LINEAR FLOW ELECTRODE SET. 2.3. FIGURE 5
012 4 8 12 16 20 24
18
-------
...load cup of resistivity test cell with ash in the manner
previously mentioned,
...place cup in chamber,
• . .attach lead wires and insert electrodes 1 and 2 by
pressing them into the ash layer using a straight
edge until ash slightly flows on to top of electrodes,
• . . cover chamber base plate with bell jar, start flow of
dry air and turn on oven to desired set point.
•..determine hot, dry resistivity at 2 PM and then divert
dry air flow through controlled temperature water bub-
bler to introduce water vapor,
...determine resistivity at 2:15 and 2:30 PM and start
nitrogen flow to inject desired concentration of SO 3 ,
• . .determine resistivity at 3:30 PM and take inlet and
outlet gas samples for SO 3 determination,
• . .determine resistivity at 4:30 PM,
...determine resistivity at 8:00 AM, take inlet and
outlet gas samples for SO 3 determination and outlet
gas sample for water concentration,
• . .determine resistivity at 9:00 AM, convert environ-
ment to dry air and cool oven,
• . .open oven when cool and take ash sample for soluble
sulfate determination.
...begin new test at 11 AM.
Resistivity is calculated using equation (2) above. Current
is determined one minute after 1200 volts are applied to electrodes
1 and 2 in Figure 5.
The present apparatus has two severe disadvantages: only one
test can be run per day and it is possible that in some cases the
minimum resistivity could occur during the hours when no one is
attending the apparatus or could require environmental exposure
greater than 19 hours. It is hoped that in time these shortcomings
will be overcome. Since the acquisition of quantitative informa-
tion regarding the effect of SO 3 on fly ash resistivity was vital
to this research, the effort has continued by obtaining data of
this type rather than improving or perfecting the test apparatus
and technique.
19
-------
Typical Data
Resistivity was determined at 139, 149 and 173°C using the
isothermal test procedure described immediately above. Sulfur
trioxide concentrations of 0, 5 and 10 ppm were used in an air
environment containing 9 volume percent water. The results are
shown in Figure 8 along with the data (circles) for the same
ash tested using the procedure described at the beginning of
this report. The difference in resistivity shown by circle and
square symbols is a reflection of the variation in test procedure.
The attenuation of resistivity due to the injection of low to
moderate concentrations of sulfur trioxide is dramatic.
The radial flow cell is presently being used to gather ad-
ditional data similar to those shown in Figure 8, to conduct
various miscellaneous experiments to aid in data interpretation,
and to elucidate the mechanism by which the sulfuric acid vapor
participates in the conduction process. While the radial flow
cell and test procedure described have not been extensively eval-
uated and possess certain disadvantages, both the new cell and
test procedure are believed to be worthwhile technical advances.
20
-------
101
2
U
5
I
0
>-
>
I-
U)
w
1011
iOl 0 —
1o 9 —
108 —
iø —
1000/T(°K) —.-3.0
°C —60
°F —141
I I I t I I —
o TEST STARTING AT 460°C. AIR - 9V/o WATER
— 0 ISOTHERMAL TEST, AIR - 9v/o WATER
A ISOTHERMAL TEST. AIR - 9V/o WATER - . 5 PPM SO 3
o ISOTHERMAL TEST. AIR - 9V/o WATER - ‘ 10 PPM SO 3
28 26 2.4 2.2 2.0 1.8 1.6 1.4
84 112 144 182 227 283 352 441
183 233 291 359 441 541 666 826
TEMPERATURE
Figure 8. Effect of SO 3 on resistivity.
0
II
I!
1 o
I
I
I
I
I
0
1.2
560
1041
21
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SECTION VI
REFERENCES
1. ASNE PTC-28, “Determining the Properties of Fine Particulate
Matter, Section 4.05, Method for Determination of Bulk
Electrical Resistivity,” pp. 15—17, 1965.
2. Disniujces, E. B., “Conditioning of Fly Ash with Sulfur Trioxide
and Ammonia,” EPA Report - 600/2-75-015 - TVA Report F75 PRS-5
jointly prepared, August 1975.
3. Nevens, T. D., et al., “A Comparative Evaluation of Cells for
Ash Resistivity Measurement,” presented at the IEEE-ASME Joint
Power Generation Conference, Long Beach, California, September
18—21, 1977.
4. Kanowski, S. and Coughlin, R. W., “Catalytic Conditioning of
Fly Ash Without Addition of SO 3 from External Sources,”
Environmental Science and Technology 11 (1) pp. 67-70, 1977.
5. Amey, W. G., and Hamburger, F., Jr., “A Method for Evaluating
the Surface and Volume Resistance Characteristics of Solid
Dielectric Materials,” A.S.T.M. Proc . 49 pp. 1079—91 (1949).
22
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TECHNICAL REPORT DATA
(Please read Inwucuons on the re erse before comp errng)
1 REPORT NO 2.
EPA-600/7-78-035
3 RECIPIENTS ACCESSIOF*NO.
4 TITLE AND SUBTITLE
Measurement of Fly Ash Resistivity Using Simulated
Flue Gas Environments
5 REPORT DATE
March 1978
5. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
R.E. Bickeihaupt
5. PERFORMING ORGANIZATION REPORT NO.
SORI-EAS77-38
3540-4-F
B PERFORMING ORGANIZATION NAME AND ADDRESS
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
10 PROGRAM ELEMENT NO
1ABO12; ROAP 2]ADL-027
11. CONTRACT/GRANT NO
68-02-2114, Task 4
12 SPONSORING AGENCY NAME AND ADDRESS
EPA Office of Research and Development
.
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 9/76-12/77
14. SPONSORING AGENCY CODE
EPA/600fl3
15.SUPPLEMENTARY NOTES IERL-RTP project officer is Leslie E. Sparks, Mail Drop 61,
919/541-2925.
Ane , nnn
The report, describing the apparatus and laboratory procedures used to determine
resistivity for a number of fly ashes under a variety of test conditions, supports
research to develop a technique for predicting fly ash resistivity from chemical
analyses of coal and coal ash. This effort requires considerable knowledge regarding
the relationship between resistivity and several coal and ash properties. In particu-
lar, the report relates the experimental problems encountered when attempts were
made to determine the effect of sulfur trioxide on resistivity. Equipment and pro-
cedures were developed to solve this problem. The report describes the modified
apparatus and technique and illustrates the type of data acquired.
17. KEY WORDS AND DOCUMENT ANALYSIS
a DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
C COSATI FIeld/Group
Pollution Laboratory Equip-
Fly Ash ment
Electrical Resistivity
Measurement Tests
Flue Gases Forecasting
Simulation Chemical Analysis
Coal Sulfur Trioxide
Pollution Control
Stationary Sources
l3B
2lB
20C
l4B
07D
08G O7B
3 DISTRIBUTION STATEMENT
Unlimited
19 S CuRITY CLAS . ‘‘ ii Report)
Unclassified
21 NO or I’A’E
29
20 SECURITY CLASS
tJnclass ified
22 PRICE
EPA Form 2220-I (9.73)
23
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