United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/042 Dec. 1985
6ER& Project Summary
Application of Oil Agglomeration
For Effluent Control from
Coal Cleaning Plants
E. J. Mezey, T. D. Hayes, Richard Mayer, and David Dunn
This study shows the potential appli-
cability of oil agglomeration for the
control of black water effluents from
coal cleaning plants processing four dif-
ferent coals. Removal and recovery of
the coal from each of the black waters
produced aqueous suspensions of min-
eral matter that settled more rapidly
than the original black water. The sedi-
ment recovered from agglomeration
appears to be less prone to acid genera-
tion during aeration than the total black
water sediment.
The ash and sulfur content of the coal
recovered by agglomeration is less
than that of the cleaned coal. The qual-
ity of the recovered coal can be im-
proved by chemical treatment of the
sediment before agglomeration.
Sodium sulfide appears to be one of the
better agents to use because of the sim-
plicity of the treatment process. Such
pretreatment of the sediment can re-
duce the pyrites by up to 50 percent in
the recovered coal over that without
pretreatment. Even greater reductions
in pyrite and ash are realized after pre-
treatment when the amount of oil used
for agglomeration is reduced from 10 to
about 2 percent and a two-stage air-
float separation is used to recover the
agglomerated coal.
The cost of the oil-agglomeration re-
covery of fine coal from coal prepara-
tion effluent streams would approxi-
mate $18 to $22 per ton* of coal
recovered, assuming an oil price of
$0.90 per gal.*
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report or-
dering information at back).
Introduction
Physical coal cleaning (PCC) proc-
esses have been used worldwide to up-
grade coal quality, usually by elaborate
systems to produce sulfur-free metal-
lurgical coals and more simple systems
to remove ash-forming minerals from
coals used for boiler fuels. Coal cleaning
processes usually treat three size
ranges of coalscoarse {3 x 3/8-in.*),
fine (3/8-in. x 28 mesh), and ultrafine
(28 mesh x 0)in individual circuits
suited to maximize Btu recovery and the
rejection of mineral matter and pyritic
sulfur. Coal contaminated rejects are
found in the waste streams from the
fine and ultrafine coal circuits which,
when combined with other wastewater
discharged from the coal cleaning plant,
make up a major portion of the waste-
water from the process. As a result of
stream pollution control and the desire
of the coal industry to improve fine coal
recovery, recirculation and treatment of
process water is incorporated into mod-
ern coal cleaning plants.
This study was initiated to determine
the applicability of oil agglomeration for
effluent and solid waste control from
physical coal cleaning processes. The
technique has the potential of recover-
ing coal from rejects and producing a
solid waste stream made up of finely
divided mineral matter free of any sig-
nificant coal values. In addition, if the
liberated pyritic sulfur from the coal can
be separated during effluent treatment,
the recovered coal quality might be sig-
nificantly improved. This program also
included a study of achieving greater re-
moval of the liberated pyrite in ultrafine
(*)1 ton = 907.2 kg; 1 gal. = 3.785 t
(*) 1 in. = 2.54 cm.
-------
and fine rejects, than possible under
conventional oil agglomeration.
Background
Water immiscible liquids, usually hy-
drocarbons, have been used to separate
coal from associated mineral matter.
The two phases are separated after ag-
glomeration or coalescence occurs and
produces agglomerates of clean coal
wetted by the oil and an aqueous sus-
pension of the mineral matter nearly
free of combustible material. Hydrocar-
bon fluids such as kerosene and fuel oils
are very effective in separating the min-
eral matter from finely divided coal sus-
pended in an aqueous slurry (thus
reducing ash). The selective agglomera-
tion process is also attractive because,
after wet face mining, wet size reduc-
tion, and conventional coal preparation,
the coal does not have to be dried be-
cause the agglomerated coal can be
readily dewatered mechanically. There-
fore, use of oil for agglomeration pro-
vides energy trade-offs between oil
used to dewater coal and fuel used for
drying coal.
A major limitation of oil agglomera-
tion is separation of the liberated pyrite
from coal. The separation is poor be-
cause the surface properties of pyrites
are similar to those of coal and in some
coals pyritic sulfur is uniformly dissemi-
nated in the coal in the size range of 0.5
to 20 jim. Extensive size reduction to
liberate pyrites prior to oil agglomera-
tion has had only limited success.
To keep the pyrites from accumulat-
ing in the oil phase, their surface prop-
erties must be altered to make them hy-
drophilic so that they will accumulate in
the aqueous phase. The common pyrite
depressant reagents developed for
metallurgical froth flotation separations
were only partially successful in altering
their surface properties and enhancing
pyrite removal. Using Iowa coals, chem-
ically pretreating pulverized coal to oxi-
dize the surface of the pyrite (to render
it hydrophilic) was more effective than
applying pyrite depressants. The most
effective treatment sequence involved
chemical comminution, float and sink
separations at a specific gravity of 1.6,
grinding of the float fraction, and recov-
ery of the fine-size coal by agglomera-
tion.
Earlier EPA-sponsored studies
showed that coal recoveries of 90 per-
cent or more are attainable from fine
coal slurry wastes using oil agglomera-
tion. These high levels of recovery are
attainable from fresh black water sedi-
ments generated during coal cleaning;
aged sediments accumulated in slurry
ponds; and excavated, weathered, and
partially dried slurry pond sediments.
The coal was of good quality and had
lower ash and sulfur content than the
cleaned coal shipped from the mine.
These results, albeit for only one coal
type, suggest that oil agglomeration
may be further developed as a method
to control effluents from coal cleaning
plants. The current program was under-
taken to assess the applicability of the
technique to a wider range of coals and
coal cleaning wastes.
Specific objectives of the work per-
formed in this program were to:
1. Explore pretreatment methods of
making the pyrite particles in black
water hydrophilic.
2. Perform pretreatment and oil ag-
glomeration to determine the
pyrite rejection and coal recovery
from coal cleaning plant black
water.
3. Assess the performance of oil ag-
glomeration as an alternative for
effluent control from coal cleaning
plants and make recommenda-
tions for further study.
Experimental Materials and
Procedures
Sample Acquisition and
Handling
Two sets of samples used in this
study were acquired at the Brecken-
ridge coal cleaning plant near Morgan-
field, Union County, KY (Kentucky No. 9
seam) and the AMAX Delta coal clean-
ing plant in Williamson County, IL (Illi-
nois No. 6 seam). The third sample set,
from McDowell County, WV (Pocahon-
tas No. 3 and 4 seams), was selected
'because of its low sulfur content com-
pared to the two other samples. A
fourth set of samples from Belmont
County, OH (Pittsburgh No. 8 seam), ac-
quired during a previous EPA study,
was used early in the program for per-
forming experiments, until the Ken-
tucky No. 9 sample was supplied.
Test Procedures
The oil agglomeration procedure
used was found to be less subject to
variations in technique than previous
procedures. It incorporated an air-float
separation of the agglomerated coal
from the aqueous suspension of the
mineral matter and a resuspension of
the separated coal in clean water fol-
lowed by a second air-float step. To en-
sure at least 90 percent recovery of a
coal with an ash content lower than for
the shipped clean coal, an unweathered
black water sediment had to be used.
Several modifications of the proce-
dure were studied. For example, the ef-
fect of pH was examined by adding sul-
furic acid or sodium hydroxide. The pH
measured before adding oil was taken
as the pH of the agglomeration. The
sediment was pretreated chemically at
the desired agglomeration slurry con-
centration (usually 10 or 15 percent), be-
fore adding the oil used in the agglom-
eration.
Potential pretreatment techniques
were screened using finely divided
pyrites (minus 100 mesh) prepared by
grinding coarse pyrite specimens se-
lected from the coarse refuse gathered
at the site along with the coal and slurry
samples. The pretreatment screening
tests were designed to determine if the
treated pyrite remained in the water
phase after shaking with oil. Treatment
was either with known pyrite depress-
ing agents, oxidizing agents, or expo-
sure to microwave energy.
To determine the effects of selected
process variations of oil agglomeration
or the effects of chemical pretreatment
of the sediment on the quality of coal
recovered, a point of reference had to
be established for each sediment used
in this study. To do this, the results of
the oil agglomeration of a slurry using a
10 percent oil concentration (based on
the solids weight) following the stand-
ard oil-agglomeration/air-float proce-
dure were considered to be baseline re-
sults with which comparisons could be
made. Coal recovery, one evaluation
criterion, is calculated using:
Percentage _
Coal Recovery
(100 - % Ash)product x (% of Feed)product |
(100 - % Ash)feed
x 100
The product is the recovered coal, while
the feed is the solids content of the sed-
iment; the recovered coal product is
given as the percentage of solids in the
feed slurry.
Another aspect of the study which
needed baseline data was the reduction
of the pyrites on a moisture- and ash-
free basis that occurs during the stand-
ard agglomeration/air-float treatment.
This was necessary to determine the ef-
fect that pretreatment of the sediment
-------
or changes in the agglomeration condi-
tions had on the pyrites remaining in
the recovered coal. The percentage re-
duction in the pyritic sulfur was deter-
mined using:
Percentage
Reduction
in Pyritic =
Sulfur
/% Spyr without _ /% Spyr witrA
V Pretreatment ;coa} \ Treatment /coa,
(% SpYr without Pretreatment)coai .
x 100
To estimate the amount of pyritic sulfur
reduction during the standard agglom-
eration/air-float procedure (i.e., the dif-
ference between the pyritic sulfur in the
sediment and that in the recovered
coal), the same equation was used sub-
stituting the percent Spyr in the sedi-
ment for the untreated coal and the per-
cent Spyr in the recovered coal both on a
moisture- and ash-free basis.
Summary of Results
Each black water sediment sample set
was characterized and tested using oil
agglomeration or pretreatment/oil ag-
glomeration. Results are described
below for each sample set.
Morganfield (KY) Sediments
Table 1 compares the sulfur and ash
values of coal recovered by agglomera-
tion after pretreatment with other sam-
ples of coal received from the Morgan-
field, KY, coal cleaning plant. These data
show that:
1. There is only a modest reduction in
sulfur, but a significant reduction
in ash during the coal cleaning.
2. The coal recovered from black
water by standard agglomeration
is lower in ash than the cleaned
coal shipped from the plant, but no
reduction in pyrite occurs, sug-
gesting that any liberated pyrite
was isolated with the recovered
coal.
3. The coal recovered after pretreat-
ment is significantly lower in ash
and pyritic (and total) sulfur, sug-
gesting that liberated pyritic sulfur
is not recovered with the coal.
Williamson County (IL) Sedi-
ments
Table 2 compares the sulfur and ash
values for the coal recovered by ag-
glomeration, before and after pretreat-
Tabte 1. Analysis of Coal Samples from Morganfield, KY, Coal Cleaning Plant Compared
with Coals Recovered by Agglomeration /Samples Obtained October 24, 1979)
Percent
Run-of-Mine Coal
TVA sampleb
Cleaned Coal
TVA sample
Black Water Sediment
Ash (MF)a
23.1
19.0
n.2
10.3
45.6
Spyr (MAF)a
1.39
1.50
2.88
S,ot (MAP)
3.62°
5.70
6.24
4.24
4.39
Coal Recovered by Agglomeration
No pretreatment
After pretreatment with
sodium sulfide
7.2
5.2
1.40
0.86
3.20
2.60
MF = moisture-free; MAP = moisture/ash-free.
Values from an average of four samples received at TVA Cumberland steam plant.
MF = moisture-free; MAF = moisture/ash-free.
ment, with the other samples of the Illi-
nois No. 6 coal. These data show that:
1. The coal can be cleaned to lower
levels of ash and pyritic sulfur than
can be attained in coal recovered
by standard oil agglomeration of
the black water sediment.
2. Liberated pyritic sulfur is agglom-
erated with the coal recovered
from the black water.
3. The coal recovered after pretreat-
ment has ash and pyritic sulfur val-
ues at least as low as those of the
shipped clean coal.
Reduced oil experiments were also
run to evaluate the effects of concentra-
tion on the quality of agglomerated
coal. These experiments indicated that:
1. The amount of coal recovered per
gram of kerosene was a maximum
of about 19 g coal when only 2 per-
cent kerosene concentration was
used. The recovered coal had the
lowest ash of those recovered by
this technique.
2. As the amount of oil used for ag-
glomeration of sediments treated
with sodium sulfide was de-
creased (i.e., 4.4 percent or less
compared to 10 percent), the
amount of pyrite in the recovered
coal decreased. In the absence of
sodium sulfide treatment the re-
sults are equally dramatic, sug-
gesting that for these sediments
pretreatment may not be neces-
sary to achieve good coal/pyrite
separation.
3. Two air-float separations at the
same kerosene level (3.4 percent)
and pretreatment conditions give
lower ash and pyritic sulfur in the
recovered coal than a single air-
float separation.
McDowell County (WV) Sedi-
ments
The sulfur and ash values for the coal
recovered by agglomeration before and
after treatment are compared with ROM
and clean coal samples from McDowell
-------
County, WV, in Table 3. These data indi-
cate that:
1. The coal can be cleaned to very
low levels of ash and pyritic sulfur.
Coal recovered by standard ag-
glomeration results in similar ash
and sulfur levels.
2. The amount of liberated pyritic sul-
fur in the black water is small and,
during standard agglomeration, is
recovered with the coal.
3. The coal recovered after pretreat-
ment or after two air-float collec-
tions is lower in ash and pyritic sul-
fur than the coal recovered by
standard agglomeration. It ap-
pears to be of a similar quality as
the shipped clean coal.
Reduced oil concentration and soy-
bean oil tests on the West Virginia sedi-
ments produced the following results:
1. Use of 2.8 to 3.4 percent oil con-
centrations reduced the pyritic sul-
fur content in the recovered coal
from that obtained during stand-
ard agglomeration. Soybean oil
appeared to be better than
kerosene.
2. Treatment with sodium sulfide had
little effect on the pyrite level in
the recovered coal; however, after
treatment the ash values were sig-
nificantly lowered from those with-
out pretreatment.
3. The yields of coal per gram of oil
used were greater at the lower oil
concentrations; however, the coal
recoveries were lower than when
higher oil (kerosene) concentra-
tions were used.
4. The coal recovered with the soy-
bean oil did not have any of the
undesirable dusty properties of the
coal recovered using kerosene as
the agglomerating oil.
Belmont County, OH, Sedi-
ments
The effect of pretreatment on the
amount of pyritic sulfur in coal recov-
ered from black water sediments from a
coal cleaning plant in Belmont County,
OH, was studied earlier. When the cur-
rent program began, the only black
water sediment readily available was
the preserved sediment from Ohio. This
material (the result of cleaning Pitts-
burgh No. 8 coal) and the aged and
weathered sediments excavated from
slurry pond sediments had been well
characterized and were well suited not
only to train technicians, but also to es-
tablish the conditions for the testing on
other sediments.
Engineering Analysis of Oil Ag-
glomeration Applied to Black
Water Effluent Control
Two major goals of the engineering
analysis were to present a conceptual
design of a process scheme requiring
relatively low energy inputs, and to per-
form a preliminary economic analysis
on the selected system.
Process Design
A coal agglomeration processing
scheme was developed as shown in Fig-
ure 1. Typical coal preparation opera-
tions generate fine waste coal at rates
exceeding 50 tons/hr (TPH); the waste
coal is usually discharged as a thick-
ened sludge at a consistency of 30 to 36
percent total solids (TS). The coal recov-
ery scheme of Figure 1 is sized for an
input of 50 TPH of coal and mineral mat-
Table 3.
Analysis of Coal Samples from McDowell County, WV, Coal Cleaning Plant Com-
pared with Coals Recovered by Agglomeration
Percent
Ash (MF)a
, MF = moisture-free; MAP = moisture/ash-free.
Data questionable.
ter, received from the coal plant thick-
ener as a 34.5 percent TS slurry. In this
example it is assumed that the coal frac-
tion comprises about 50 percent of the
TS. Coal particles to be recovered will
contain 4 to 6 percent of noncom-
bustible components; however, the in-
herent ash content of the coal particle
matrix is not considered a part of the
mineral fraction in this discussion.
Rather, the mineral fraction referred to
here consists of discrete mineral partic-
ulates, including clays and sediment,
formed in waste coal sludges.
Mass flows throughout the entire coal
cleaning scheme, indicated in the dia-
gram, are based on several assump-
tions:
Suspended solids concentrations of
coal/mineral matter slurries pre-
pared in the influent rapid mix tank
and in the resuspension rapid mix
tanks are prepared as 10 percent TS
solutions.
About 100 ppm of soda ash/sodium
sulfide is added to this influent rapid
mix system for the pH-control/
chemical-pretreatment necessary to
enhance pyrite wetting and to en-
hance alum flocculation and sedi-
mentation in the treatment of turbid
recycle water.
Oil introduced into the system
(0.024 ton per ton solids processed)
is rapidly attached to coal particles
and is conserved through the sys-
tem as a component of the recov-
ered coal float.
Coal recoveries are assumed to be
90 percent in the static flotation
basin and 95 percent in the
dissolved-air flotation (OAF) unit.
About 10 percent of discrete min-
eral matter introduced into the
static flotation basin and the DAF
system is entrained in the coal float.
The moisture of agglomerated coal
skimmed from the static and
dissolved-air flotation basins is 20
percent of the total weight.
About 90 percent of the discrete
mineral and coal paniculate matter
in the recycle stream can be re-
moved with flocculation and sedi-
mentation.
Mineral and alum sludges gener-
ated by the process scheme can be
deposited in existing storage pond
facilities.
Economic Analysis
A detailed breakdown of equipment
and construction costs of the 50 TPH oil-
agglomeration process scheme was de-
-------
veloped. Many of the cost estimates
used were obtained from EPA docu-
ments and chemical engineering litera-
ture; all of the costs include installation
except for pumps and external piping.
All capital costs were adjusted for infla-
tion to July 1980. Total equipment costs
were estimated at $1.1 million, more
than half of which was expended for
sedimentation basins ($319,000) and for
the DAF unit ($255,900). Using the
equipment cost total, the fixed capital
costs for the oil-agglomeration scheme
were calculated using standard cost es-
timating procedures. The total fixed
capital cost was estimated at $3.7 mil-
lion.
Operating and maintenance costs
were also estimated for the 50 TPH coal
agglomeration plant. These costs in-
clude operating labor, equipment repair
and maintenance, chemicals, oil, and
electricity. Electricity costs were based
on detailed electric power estimates for
the process scheme. It is significant that
the highest operating cost of the oil-
agglomeration process scheme is in oil
purchases, amounting to almost $2 mil-
lion (59 percent of the total annual oper-
ating cost).
The results of the economic analysis
are shown in Table 4. The total process-
ing cost of the final oil-coal agglomer-
1.0 TPD
90% Coal Recovery
10% of Minerals Entrained
in Coal
20% Moisture in
Coal/Mineral Float
95% Coal Recovery
1O% of Minerals
Entrained in Coal
20% Moisture in
Coal/Mineral float
Legend:
' = 10% moisture
DAF- dissolved air flotation
GPMW = gal./min water
RT- residence time
TS - total solids
SO TPM .
329 GPMW
(34.5% TSI
Assume
50% Combustible
Particulates
50% Discrete Mineral
Matter
Rapid
Mix
1834 GPMW
1.25 TPM Oil
25.2 TPM Coal
26.6 TPM Mineral
Agglomeration
and Flocculation
Static Flotation
Basin
20-30 minR.T.
25 GPMW
1.25 TPM Oil
Tailings
1809GPM
22.7 TPM Coal
2.7 TPM Mineral
Resuspension
957 GPMW
1.25 TPM Oil
22.9 TPM Coal
3.8 TPM Mineral
DAF
935
GPMW
22 GPMW \21.8 TPM Coal
1.25 TPM Oil \ 0.4 TPM Mineral
'11 GPMW
432 GPM
0.2 TPM Coal
1.1 TPM Mineral
2755 GPMW
Recycle
Water
1455 GPM
0.2 TPM Coal
1.6 TPM Mineral
3.6 TPM Coal
27.3 TPM Mineral
Alum
30 TPD
"Rapid Mix
Followed by
Flocculation
Dewatering
Screen
11.2 GPMW \21.8 TPM Coal ~J -24 TPM
1.25 TPM Oil 0.4 TPM Mineral Oil-Coal-
I J Mineral
I Product
Coal Product
Mineral
Refuse
3.2 TPM Coal
24.6 TPM Mineral
368 GPMW
23% Solids
To
Refuse
Pond
Figure 1. Conceptual flow scheme of a 50 TPH oil-agglomeration waste coal recovery plant.
-------
ated product was calculated at $19.42
per ton. Assuming the agglomerated
coal product has an energy value of
14,000 Btu per Ib*, the per unit energy
cost of product recovery is about $0.69
per 106 Btu ($0.73 per GJ).
As shown in Table 4, the largest sin-
gle cost incurred over the life of the coal
separation system is the oil demand.
About 58 percent of the per ton cost of
coal recovery is traceable to the large
purchases of oil that would be required
for agglomeration. Thus, the economics
of this system are highly sensitive to the
dosages of oil used. Therefore, a reex-
amination of the trade-offs between oil
dosage rates and product recoveries is
(*)1 Btu = 1.055 kJ; 1 Ib = 0.454 kg.
needed to determine the profitability of
the system at various levels of oil ex-
penditures. Such an optimization, how-
ever, may result in reducing coal recov-
ery efficiencies for the sake of
controlling oil costs. A more detailed
study would be needed to determine
the potential for system improvements
to reduce oil demand and to optimize
the operation of existing coal agglomer-
ation systems.
To further illustrate the relative im-
portance of various parameters to the
economics of oil-agglomeration coal re-
covery, a sensitivity analysis on each
factor is presented in Table 5. A 25 per-
cent increase in the cost of oil either
through rising commodity prices or
through increased dosages would in-
Table 4. Summary of Results of the Economic Analysis of a 50 TPH Oil-Agglomeration
Waste Coal Recovery Plant
Cost,
$ (1980)
I. Fixed Capital Investment
II. Total Payments on Loan (inflation adjusted)
III. Lifetime Operating Costs
Labor and overhead
Supplies
Electricity
Chemicals
Oil
Soda Ash/NazS
Alum
Tax
TOTAL OPERATING COST
IV. Lifetime Depreciation Credit (inflation adjusted)
V. Total Coal Recovery Over Lifetime = 3,484,800 tons
$ 3,746,400
4,473,800
13,372,000
964,000
648,000
38,880,000
722,000
1,842,000
7,492,000
$63,920,000
711,100
VI. Cost per Ton Product
(II + III - IV)
(V)
$19.42
crease the per unit coal recovery cost by
more than 14 percent. In contrast, com-
parable increases in the costs of other
chemicals, such as alum and soda ash,
and in energy would result in less than
a 1 percent increase in oil/coal produc-
tion cost.
The second most influential parame-
ter controlling waste coal recovery
costs was operating labor and associ-
ated overhead. A 25 percent increase in
this parameter would likely predispose
an 8.0 percent increase in product cost.
To summarize, this preliminary analy-
sis would indicate several fundamental
observations that generally characterize
oil-agglomeration economics. The first
observation is that the total fixed capital
cost is far outstripped by the lifetime
operating cost (labor + chemicals
+ electricity + oil + tax + supplies, etc)
by a ratio of more than 14:1. This rather
large imbalance in the economics
would suggest a great potential for cost
improvement through further process
research and development to reduce
sensitive operating cost parameters,
such as oil demand and labor require-
ments.
Conclusions
This study shows the potential appli-
cability of oil agglomeration for the con-
trol of black water effluents from coal
cleaning plants processing four differ-
ent coals. Removal and recovery of the
coal from each of the black waters pro-
duced aqueous suspensions of mineral
matter that settled more rapidly than
the original black water. The sediment
recovered from agglomeration appears
to be less prone to acid generation dur-
ing aeration than the total black water
sediment.
Table 5. Sensitivity of the Cost of Oil Agglomeration Coal Recovery to Percentage Changes in Selected Parameters
Parameter
Base Value'a>
% Change in
Parameter
New Cost,
$/ton Coal
% Change
in Cost
Chemicals Cost
Oil
Soda Ash/Na^S
Alum
Capital Cost (Fixed)
$2.59/ton productlbt
$0.048/ton product
$0.12/ton product
$3.75 million
+25
+25
+25
+25
22.21
19.47
19.55
19.69
+ 14.4
+ 0.3
+ 0.7
+ 1.4
Operating Labor
Overhead and Supplies
Energy Cost
Days of Operation/yr
$1.09 million/yr
$0. 19/ton product
300
+25
+25
-25
20.99
19.47
20.59
+8.1
+ 0.3
+ 6.0
<*>Base cost of recovered coal = $19.42/ton.
>" Product" is the resulting oil/coal mixture produced by the process.
-------
The ash and sulfur content of the coal
recovered by agglomeration is less than
that of the cleaned coal. The quality of
the recovered coal can be improved by
chemical treatment of the sediment be-
fore agglomeration. Sodium sulfide ap-
pears to be one of the better agents to
use because of the simplicity of the
treatment process. Such pretreatment
of the sediment can reduce the pyrites
by up to 50 percent in the recovered
coal over that without pretreatment.
Even greater reductions in pyrite and
ash are realized after pretreatment
when the amount of oil used for ag-
glomeration is reduced from 10 to about
2 percent and a two-stage air-float sepa-
ration is used to recover the agglomer-
ated coal.
Findings in this study suggest the fol-
lowing environmental and conservation
advantages of the modified agglomera-
tion process for the separation of the
coal from the mineral matter in black
water effluents:
The recovered coal is easily dewa-
tered despite its fine size.
Chemical treatment of sediments
before agglomeration tends to re-
duce the pyrite content of the recov-
ered coal.
Black water from cleaning low sul-
fur coals that contain fine and uni-
formly dispersed pyrites is less re-
sponsive to pretreatment probably
because the pyrites are not present
as liberated particles.
The quantity of oil used for agglom-
eration affects the amount of pyrites
and ash recovered with coal.
Smaller amounts favor lower
pyrites and ash in the recovered
coal as well as high yields of coal
per unit weight of oil; however, total
recoveries are diminished.
Use of a vegetable oil for agglomer-
ation gives coal yields and recover-
ies equally as good as kerosene
over an oil concentration range of
from 2 to 10 percent. The recovered
coal is less dusty.
Problems inherent in recovering coal
from aged and weathered black water
sediments, and the very high recovery
of coal from fresh black water, led to the
conclusion that a process to control ef-
fluents from a coal cleaning plant
should be designed to treat the dis-
charge at the rate it is generated rather
than to treat the sediments accumu-
lated and weathered in ponds.
Engineering analysis results which
considered unit processes that could be
combined with oil agglomeration effec-
tively and economically to treat black
water discharges are:
Oil agglomeration could be imple-
mented using unit processes and
equipment conventionally em-
ployed by municipal water and
wastewater treatment plants and
by the coal industry.
The cost of the oil-agglomeration
recovery of fine coal from coal
preparation effluent streams would
approximate $18 to $22 per ton of
coal recovered, assuming an oil
price of $0.90 per gal.
Recommendations
Continued development of oil ag-
glomeration could lead to better control
of effluents from coal cleaning plants
and recovery of the energy value they
contain, especially on samples of black
water from processing plants in other
regions and/or seams such as western
coals.
An experimental program could es-
tablish process parameters and equip-
ment needed to minimize the coal con-
tent in the coal cleaning plant effluent.
This could be done on a scale suitable
for developing detailed process flow
sheets and refining preliminary cost es-
timations for add-on or replacement ef-
fluent control systems. The data base
could be increased sufficiently to permit
detailed evaluation as to whether the
technique should be considered on a
pilot plant scale for on-site studies.
Continued studies could also deter-
mine not only the fate of the sediments
resulting from the oil agglomeration
process but also the impact of success-
ful chemical pretreatments on the pyrite
loading of the sediments and their acid-
generation potential.
GOVERNMENT PRINTING OFFICE:1986/646-116/20738
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E. J. Mezey, T. D. Hayes, R. Mayer, and D. Dunn are with Battelle-Columbus
Laboratories, Columbus, OH 43201.
James D. Kilgroe is the EPA Project Officer (see below).
The complete report, entitled "Application of Oil Agglomeration for Effluent
Control from Coal Cleaning Plants," (Order No. PB86-119 567; Cost: $16.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-85/042
OC00329 PS
U S 6NVIR PROTECTION AGENCY
RfSION 5 LIBRARY
230 S DEARBORN STREET
CHICAGO IL 60604
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