United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/016 June 1987
AEPA Project Summary
Water Quality
Characterization of an
Eastern Coal Slurry
C. David Cooper
Current and projected uses of coal
have resulted in several proposals for
coal slurry pipelines in the eastern part
of the United States. While several re-
searchers have reported on the water
quality aspects of western coal slurries,
less work has been done with respect
to eastern coals. An experimental study
was conducted at the University of Cen-
tral Florida from 1982 to 1983 with slur-
ries of 50 percent eastern Kentucky coal
and 50 percent water. Experiments
were conducted with and without the
addition of a corrosion inhibitor.
Twenty-nine water quality parameters
were measured as a function of pump-
ing time in a 12-meter (40-ft) long, 2.54
cm (1 inch) diameter pipeline con-
structed for this study. Also, the
treatability of the 10-day slurry filtrate
was assessed using both lime and alum
addition.
By about the fourth day in the
pipeline, most parameters had reached
equilibrium values. As expected for this
high-ash, medium-sulfur coal, sulfates,
TDS, and conductivity in the slurry fil-
trate started high and increased with
time. Dissolved oxygen quickly
dropped to near zero. Concentrations
of several heavy metals were substan-
tial, but organics were generally very
low, about 5-10 mg/L. Trihalomethane
formation potential was quite low,
never exceeding 35 ppb. Although the
samples were consistent in any one
run, samples from different runs on the
"same'" coal were significantly differ-
ent. Addition of the corrosion inhibitor
increased the concentrations of sul-
fates, TDS, and several other parame-
ters. The characterization of this partic-
ular coal slurry was compared with
those of several western coal slurries
reported in the literature.
This Project Summary was devel-
oped by ERA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
The United States is heavily depend-
ent on coal for electricity generation.
This reliance on coal is projected to in-
crease even more in the future, as oil
and gas decrease in supply and increase
in price. The use of coal is expected to
increase substantially in Florida and
other southeastern and Gulf-coast
states, based on their projected popula-
tion growth and on their previously high
percentage use of oil and gas for power
generation.
In recent years, the coal slurry
pipeline has been promoted as a safe,
reliable, and economical alternative to
railroad transportation of coal. Basi-
cally, coal slurry pipelining is a means
of transporting coal that involves mix-
ing pulverized coal with water and
pumping it in a steel pipeline as shown
schematically in Figure 1. First, the coal
is pulverized to a powder consistency,
then mixed with an equal weight of
water to form a slurry. (A 50 percent
coal slurry is a pumpable fluid that is
somewhat more dense and substan-
tially more viscous than water.) The
slurry is then pumped through a
pipeline, using a number of strategically
placed pumping stations, from the coal
source area to the receiving power
-------
Slurry
Preparation
Export
Figure 1.
Power Plant
Dewatering Plant
Schematic diagram of a full scale coal slurry pipeline system.
Source: A.D. Dorr is. 1981. Used by permission.
plants. At the receiving sites, the slurry
is dewatered and the coal is burned. The
water is treated before re-use or dis-
charge.
One objection to coal slurry pipelines
has been the possible pollution of
waters at the receiving location by con-
taminants leached from the coal while
in the pipeline. Both inorganic and or-
ganic chemicals are solubilized in con-
centrations that depend on the physical
and chemical nature of coal, the water
source, and the time in the pipeline.
Several researchers have studied vari-
ous western coals, but less work has
been done with respect to eastern coal
slurries. Eastern coals typically contain
more sulfur than western coals, and
they typically have lower percentages
of the alkaline metals (Na, K, Ca, Mg) in
their ash. Thus, there could be substan-
tial differences between the slurry water
resulting from eastern coals and that
from western coals.
Purpose and Scope
The primary objective of this work
was to characterize the slurry water re-
sulting from an eastern coal. For charac-
terization, 29 water quality parameters
were measured on slurry filtrate sam-
pled at various pumping times in a
small pipe-loop system built for this
study. The parameters included 11 gen-
eral items (such as pH, dissolved solids,
and sulfates); three organic tests (total
organic carbon, trihalomethane forma-
tion potential, and phenols); and 15
metals. The characteristics observed in
this study were then compared with
those of other coal slurries reported pre-
viously in the literature.
Another major objective was to as-
sess the effects of the addition of a com-
mercial corrosion inhibitor on water
quality. Due to the potential for corro-
sion of the pipeline by coal slurries,
some consideration has been given to
adding a chemical corrosion inhibitor.
The effects of the addition of a nitrite-
based inhibitor on slurry water quality
were investigated in this research.
A third objective was to address the
question of treatability of the slurry
water. Previous researchers have indi-
cated that conventional technology is
adequate to treat coal slurry waste-
waters. Two of the more common treat-
ment processes were used to treat the
10-day slurry water: high pH lime pre-
cipitation and alum coagulation. After
treatment, the wastewaters were ana-
lyzed for the same parameters as above.
In addition, the sludges from the treat-
ment processes were subjected to the
EP toxicity (leaching) test and tested for
eight toxic metals.
Experimental Procedures
The coal used in this study was ob-
tained with the help of personnel at the
Mclntosh Power Plant in Lakeland, Flor-
ida. Coal, shipped by unit train from an
eastern Kentucky mine, was received al
that power plant and processed through
the usual sequence of processing steps.
A portion of the feed stream of pulver-
ized coal to one of the burners was di-
verted into a custom designed barrel
that caught the coal dust, but allowed
the air to exhaust through an attached
filter bag. Approximately two days were
required to obtain a full drum (125 kg),
thus allowing for some "time-
averaging" of the coal sample. About 70
percent of the pulverized coal passed a
200 mesh screen.
All slurries were processed in a pilot-
scale system constructed specifically
for this project. A 50-percent solids
slurry was made by adding tap water
from the University of Central Florida's
potable water system to the pulverized
coal in an open top 210-liter steel drum.
The final volume of slurry was mixed in
about one hour by hand-held steel rods
and a small (12 volt, 15 amp) boat
trolling motor.
The slurry was transferred by hand
into a closed top, nitrogen-inerted, 265-
liter steel tank into which was mounted
a Hazleton submersible slurry pump.
The pump was belt driven with a 1.12
kw motor and had a speed controller.
The pump worked very well; because it
was submersible, seal leaks were not a
problem. A second electric trolling
motor installed in the tank kept the
slurry well mixed during the run. The
slurry was pumped through a 15 meter
long, 2.54 cm diameter schedule 80
steel pipe loop that returned to the bot-
tom of the tank. The pump speed was
adjusted to achieve a slurry velocity of
1.2 to 1.8 m/s in the pipe. The tank was
kept nitrogen-blanketed throughout the
10-day slurry runs. Cooling water
flowed through an external concentric
pipe to maintain the slurry temperature
between 26°C and 32°C for all runs. A
schematic diagram of the experimental
system is presented in Figure 2.
Samples of the slurry were taken sev-
eral times throughout each 10-day run,
more frequently in the first few days.
The sample times were 3 hours,
7 hours, and 1, 2, 4, 7, and 10 days.
Whole slurry samples were immedi-
ately tested for pH, dissolved oxygen,
and redox potential. The remaining
samples were then vacuum filtered
through a 24-cm diameter Whatman
No. 1 filter paper, and then through a
0.45 micron glass filter. Some of the fil-
trate was then acidified and refrigerated
-------
N2
Supply
Slurry Mixer ,->— i
r
Level
Indicator
i
C
;H
a
/nrl
t
«
4*
jj_
r (_r t
i^
IT
,--•
Slurry Pump
- - f i
~i
To Drain
-Slurry Tank From Tap Water
Cooling Pipe
i .
— 1X1 . | — — - (_ |
l/a/ve
; Valve
[ Valve
Sampling Tee
To Drain
Figure 2. Schematic diagram of pilot-scale pipe loop used for coal slurry experiments.
for later metals analysis; the rest of the
filtrate was tested for a variety of water
quality parameters.
All analytical tests were conducted
according to Standard Methods for Ex-
amination of Water and Wastewater,
14th edition (1975), or Methods for the
Analysis of Water and Waste, EPA 6007
4-79-020 (1979). Metals were analyzed
with a DC arc plasma emissions spec-
trophotometer in lieu of an atomic ab-
sorption unit. In all, the tests included 11
general water quality parameters, 3
measures of organic content including
trihalomethane formation potential
(THMFP), and 15 metals. All parameters
were observed on each sample except
for phenols and THMFP due to the
lengthy test procedures for these two.
On the tenth day, large volume sam-
ples were drawn for treatability testing.
A laboratory procedure was used to
simulate conventional treatment proc-
esses that might be anticipated in prac-
tice: coal separation by sedimentation
and decantation, chemical addition, co-
agulation, flocculation, sedimentation,
and filtration. The chemicals added
were either lime or alum. The optimum
dose was defined as that which maxi-
mized turbidity removal on small
aliquots of the untreated decantate. The
remainder of the decantate was then
treated at the optimum dose. The final
treated effluent was analyzed for all the
original parameters (except phenols) to
determine removal efficiencies. Finally,
the sludges produced by the treatments
were later tested according to the EP
toxicity test to assess their potential as a
hazardous waste.
Results and Discussion
The coal used in this research project
came by unit train from eastern Ken-
tucky and can be characterized as a
medium sulfur (1.9%), high ash (16%),
eastern bituminous coal. Some test
data for the coal used in the four exper-
imental runs are presented in Tables 1
and 2. Also, a mineral analysis for the
major components in the ignited ash
showed approximately 50 percent sil-
ica, 25 percent alumina, 17 percent fer-
ric oxide, and about 6 percent basic
metal oxides.
The source water was University of
Central Florida tap water. The water
originated from an underground lime-
stone aquifer and was aerated and chlo-
rinated prior to distribution to the
potable water system. Typical source
water characteristics are shown along
with the slurry filtrate analyses.
Four valid experimental runs were
completed. Runs 2 and 3 without a com-
mercial corrosion inhibitor (nitrite
based) and Runs 4 and 5 with the in-
hibitor. (Run 1 was used for equipment
and procedures shakedown.) The fact
that there were significant variations in
the coal quality was reflected in the re-
sulting slurry qualities. In all runs, simi-
lar trends in the time behavior of the
slurry contaminants were observed.
However, in Run 2 the concentrations of
all pollutants were significantly higher
than in Run 3. A similar situation existed
for Runs 4 and 5. The slurry with the
corrosion inhibitor had significantly
higher concentrations of sulfates, TDS,
conductivity, and alkalinity. Differences
in the other parameters were not so pro-
nounced or may have been masked by
differences in the coal samples.
Results of all the tests are tabulated in
Tables 3 and 4, which present averaged
data of the two runs without the corro-
sion inhibitor and the two with the in-
hibitor. Generally, most parameters
reached equilibrium values in the first
few days of the run. For the runs with-
out inhibitor, the slurry pH dropped im-
mediately on mixing but then rose to
about 6 by the tenth day for all runs. The
initial pH drop was suppressed by the
corrosion inhibitor. Dissolved oxygen
quickly dropped to near zero as it re-
acted with the sulfur and other minerals
in the coal.
As expected for this coal, sulfates
were high and reflected the sulfur con-
tent of the coal. Equilibrium concentra-
tions averaged about 1300 mg/L for the
two runs without corrosion inhibitor,
but surprisingly averaged about 3500
mg/L with the inhibitor. Apparently, the
inhibitor enhanced some ion exchange
process with the coal minerals because
the inhibitor itself did not contain sulfur.
This difference in the sulfates' behavior
is shown graphically in Figure 3. Figure
4 presents the averaged data for pH,
and highlights the differences observed
with and without the corrosion in-
hibitor. Furthermore, for the slurry with
the inhibitor, it was observed that coal-
water separation was more difficult.
The concentrations of dissolved or-
ganics were low for this coal slurry, as
indicated by the tests for total organic
carbon and phenols. TOC was in the
5-10 mg/L range and phenols were
around 1 ppb. Also, for this particular
coal slurry, THMFP was quite low, never
exceeding 35 ppb. As shown in Tables 3
and 4, the concentrations of several
metals increased one to three orders of
magnitude over the levels in the mix
water, the largest percentage gainers
being iron and manganese. Some
heavy metals exhibited little or no in-
crease.
Treatability results are not tabulated
in this Summary. However, it was
shown that both lime and alum addi-
tions were effective in removing certain
contaminants. Lime treatment removed
metals better than alum, but alum re-
moved organics better than lime. It
should be obvious that the treatment
processing sequence specified at a coal
slurry receiving site depends on the
characteristics of the particular coal
slurry and the degree of treatment de-
-------
Table 1. Coal Proximate Analysis (Dry Basis)*
Parameter
%Ash
% Volatiles
% Fixed Carbon
Heating Value (Btu/lb)
% Sulfur
% Passing 200 mesh
Run 2
15.28
32.85
51.87
11,632
2.26
80
Run 3
14.39
36.79
48.82
12,830
1.69
—
Run 4
15.37
36.49
47.63
11,922
1.93
68
Run 5
18.50
35.13
46.37
11,500
1.70
72
Avg.
15.89
35.32
48.67
11,971
1.90
73
Composite as
received, 2
unit trains
(May and
June, 1983)**
14.43
36.10
49.48
12,688
2.13
—
'SOURCE: Mclntosh Power Plant Chem. Lab., Department ofElec. and Water Utilities, Lake-
land, Florida
**SOURCE: Mclntosh Power Plant files
Table 2. Trace Metals Analysis of Coal
ppm in ignited ash, as the element
Component
Hg
Se
Cd
Zn
As
Mn
Cu
Pb
Ni
Cr
Ba
Mg
Ag
Run 2
56
92
3.5
106
156
163
221
122
90
231
585
8,490
4.0
Run 3
47
83
4.3
311
238
541
139
101
136
133
837
15,900
2.0
Run 4
63
72
4.2
228
379
408
154
109
133
150
797
8,190
7.0
Run 5
59
63
4.2
219
421
505
110
104
135
123
720
9,610
2.5
Average
56
78
4.1
216
298
404
156
109
124
159
735
10,550
3.9
sired. However, this and previous stud-
ies reported in the literature, indicate
that conventional treatment with exist-
ing technology should be sufficient.
Conclusions and
Recommendations
Eastern coals typically have higher
sulfur content and less alkaline ash than
western coals. As expected, the slurry
filtrate obtained in this study of an east-
ern coal exhibited higher sulfate con-
centrations and lower pH values than
would be expected from a typical west-
ern coal.
For the particular coal used in this
study, very few organics were leached
into the water. TOC averaged 5-10 mg/L,
phenols averaged about 1 ppb and
THMFP never exceeded 35 ppb. Also,
for this particular coal, very significant
concentrations of iron (100-500 mg/L)
and manganese (5-25 mg/L) leached
into the water. Concentrations of lead,
nickel, and aluminum also increased
significantly, but each remained in the
0.1 to 1 mg/L range. It was shown that
oxygen reacts readily with sulfur and
other minerals in coal slurries, and thus
care should be taken to exclude oxygen
as much as possible when forming,
pumping, or loading coal slurries com-
mercially.
Coal-water interactions require some
time to reach equilibrium. For several
parameters, at least four or five days
must elapse before equilibrium is ap-
proached. A corrosion inhibitor signifi-
cantly increased the concentrations of
sulfates, TDS, conductivity, and alkalin-
ity. In addition, coal-water separation
became more difficult.
Even though the coal samples used in
this study were from the same source
and were obtained in a "time-
averaged" manner, the properties of
the coal samples were apparently differ-
ent enough to result in significant differ-
ences in the slurry filtrate observed in
"replicate" runs. While the time-behav-
ior trends for most parameters were
similar, absolute levels in the filtrate
were different. Thus, it is recommended
that several replications be conducted
to be able to characterize the slurry of
any particular coal with confidence. In
order to reach valid conclusions about
the behavior of eastern coal slurries, at
least 10 more eastern coals should be
studied.
Coal slurry wastewaters likely will re-
quire treatment before reuse or dis-
charge. Studies thus far indicate that
present treatment technology can pro-
vide adequate treatment, but the
specific processing scheme will depend
on the particular coal slurry characteris-
tics and site specific regulations. The
treatment sludges produced in this
study did not fail the EP toxicity test.
-------
4OOO
3000
I
2000
10OO
Runs4 &5(average)
0
Runs2 &3(average)
o
Mix 01234 56 7 8 9 10
Water
Time, days
Figure 3. Effect of corrosion inhibitor (Cl) on sulfates (Runs 2 and 3 without Cl and Runs
4 and 5 with Cl).
-------
7.0
6.0
\
5.0
4.0
3.0 I—t
Mix 0 1 2 3 4 5 6 7 8 9 10
Water
Time, days
Figure 4. Effect of corrosion inhibitor (Cl) on pH (Runs 2 and 3 without Cl and Runs 4
and 5 with Cl).
Table 3. Data Summary Table—Average of Runs 2 and 3
Parameter, Units
Typical
Mix
Water
Average Concentrations in Slurry Filtrate by Time after Start of Run
3-hours
7-hours
1-day
2-days
4-days
7-days
10-day
General
Sulfates, mg/L 2 942 1016 1075 1070 1340 1306 1342
Chlorides, mg/L 19 36 43 58 72 86 108 116
TDS,mg/L 207 1612 1596 1740 1966 2400 2636 2695
Conductivity, mho/cm 366 1483 1468 1590 1713 1974 2120 2452
Dissolved Oxygen, mg/L 7.9 2.5 0.3 0.2 0.15 0.05 0.05 O.C
Redox Potential, mv 526 211 158 62 -32 -84 -152 -196
pH 7.0 4.2 4.8 5.2 5.8 5.9 6.2 6.2
Acidity, mg/L as CaCO3 -96 470 423 480 530 778 878 852
Alkalinity, mg/L as CaCO3 120 12.4 14.3 12.4 22.2 15.2 22.4 13.2
Color, CPU 6 8 7.5 20.5* 94.5* 69* 132* 280*
Turbidity, JTU 5.3 3.8 10.9 18.2* 52.2* 67.2* 65.2* 53.5
Organics
TOC, ppm 6 7.4 5.1 3.6 5.0 6.1 6.2 5.6
THMFP.ppb 60 — — — — — — 23
Phenols, ppb — — 1.0 — 1.0 — 1.2 1.4
-------
Table 3. (continued)
Parameter, Units
Metals (mg/L)
Hg
Se**
Cd
Zn
As**
Mn
Cu
Al
Fe
Pb
Ni
Cr
Ba
Mg
Ag
Typical
Mix
Water
0.076
0.242
0.006
0.071
0.045
0.009
0.016
0.033
1.28
0.029
0.002
0.004
0.015
11.0
0.002
Average Concentrations in
3-hours
0.21
0.20
0.03
1.29
0.35
4.06
0.21
10.7
58.1
0.30
1.02
0.03
0.16
67
0.02
7-hours
0.18
0.22
0.03
0.96
0.38
4.36
0.01
2.89
92.4
0.30
0.76
0.03
0.12
67
0.02
1-day
0.24
0.21
0.02
0.46
0.36
4.98
0.02
0.78
168
0.30
0.30
0.03
0.09
68
0.01
Slurry Filtrate
2-days
0.26
0.23
0.02
0.20
0.50
6.44
0.02
0.30
214
0.28
0.09
0.02
0.12
67
0.02
by Time after Start of Run
4-days
0.40
0.33
0.03
0.17
0.58
10.2
0.03
0.52
313
0.34
0.10
0.03
0.12
74
0.02
7-days
0.42
0.38
0.04
0.17
0.68
10.5
0.02
0.38
344
0.36
0.08
0.03
0.12
76
0.02
10-days
0.45
0.37
0.04
0.15
0.63
10.9
0.03
0.47
358
0.40
0.14
0.04
0.10
78
0.02
NOTE: *=Precipitate formed, data not meaningful.
**=Data suspect—instrument problems, see quality assurance section.
Table 4. Data Summary Table—Average of Runs 4 and 5
Parameter, Units
General
Sulfates, mg/L
Chlorides, mg/L
TDS, mg/L
Conductivity, mho/cm
Dissolved Oxygen, mg/L
Redox Potential, mv
pH
Acidity, mg/L as CaCOj
Alkalinity, mg/L as CaCO3
Color, CPU
Turbidity, JTU
Organics
TOC, ppm
THMFP, ppb
Phenols, ppb
Metals (mg/L)
Hg
Se**
Cd
Zn
As"*
Mn
Cu
Al
Fe
Pb
Ni
Cr
Ba
Mg
Ag
Typical
Mix
Water
2
19
207
366
7.9
526
7.0
-96
120
6
5.3
6
60
—
0.076
0.242
0.006
0.071
0.045
0.009
0.016
0.033
1.28
0.029
0.002
0.004
0.015
11.0
0.002
Average Concentrations in
3-hours
1865
66
4398
4630
0.55
141
6.1
402
258
8
3
2.0
—
—
0.05
0.24
0.007
0.09
0.23
7.55
0.07
0.28
0.52
0.36
0.36
0.79
0.06
775
0.008
7-hours
1920
80
4277
4480
0.35
62
6.6
416
208
9
4
3.8
—
—
0.05
0.23
0.006
0.09
0.24
4.80
0.03
0.29
0.45
0.34
0.08
0.03
0.09
108
0.002
1-day
1955
112
4192
4455
0.10
-118
6.8
323
158
8
32*
12.6
—
—
0.054
0.26
0.007
0.07
0.23
3.11
0.03
0.32
11.3
0.32
0.06
0.03
0.08
104
0.007
Slurry Filtrate by Time after Start of Run
2-days
2860
134
4364
4962
0.05
-102
6.3
568
78
7
50*
5.2
—
—
0.09
0.37
0.07
0.76
0.36
8.80
0.03
0.29
737
0.39
0.72
0.04
0.78
728
0.07
4-days
3425
147
5624
5445
0.05
-744
6.2
920
40
8
774*
7.3
—
7.0
0.74
0.37
0.008
0.75
0.36
77.9
0.02
0.34
259
0.39
0.77
0.03
0.75
758
0.075
7-days
3430
160
5920
5410
0.05
-137
6.2
1010
54
8
94*
7.6
—
7.5
0.75
0.33
0.07
0.76
0.40
74.7
0.07
0.46
270
0.40
0.22
0.03
0.09
762
0.078
10-days
3680
178
5712
5362
0.05
-136
6.3
855
58
6
96*
18.6
8
1.0
0.75
0.37
0.07
0.75
0.38
76.6
0.02
0.45
270
0.42
0.32
0.03
0.03
763
0.076
NOTE:
*=Precipitate formed, data not meaningful.
**=Data suspect—instrument problems, see quality assurance section.
-------
C. D. Cooper, J. D. Dietz, M. J. Flint, and M. R. Todd are with College of
Engineering, University of Central florrda, Orlando, Florida 32816.
Eugene F. Harris is the EPA Project Officer (see below).
The complete report, entitled "Water Quality Characterization of an Eastern
Coal Slurry," (Order No. PB 87-169 9757AS; Cost: $18.95, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES P/>
EPA
PERMIT No G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-87/016
0000329
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