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OAR Box 1828 

Prepped by Ollie Stewart 

Document Number: 

321) IV-B-25 

Docket Number: 

A-83-27 

Printed 11/12/2008 11:12:59 AM Sheet 321 of 325 
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A-83-27 

CORPORATION 

MEMORANDUM 

IV-B-25 

DATE: June 22, 1987 

TO: Walt Stevenson, EPA/OAQPS/ESED 

FROM: David White, Radian Corporation 

SUBJECT: Sulfur Reduction Potential of Advanced Physical Coal 

Cleaning Technologies 

1.0 INTRODUCTION 

The term "physical coal cleaning" (PCC) covers a large number of 

techniques used to separate ash and sulfur from as-mined coal prior to 

1 2 combustion. ' The ability to remove ash and sulfur by PCC depends on 

the washability of the coal (which is a function of the mode of 

physical occurrence of these impurities within the coal), the level of 

coal crushing and grinding used to liberate these materials from the 

coal prior to actual cleaning, and the type of cleaning technology 

used. 

Almost all conventional PCC processes use a separating fluid to 

float the lighter organic material in coal (having a typical specific 

gravity of 1.2-1.3) from the heavier impurities (s.g.=2.0-5.0). The 

lower the specific gravity of the separating fluid, the lower the ash 

and sulfur content of the cleaned coal. With some highly washable 

coals (e.g., some of the high-sulfur coals from Northern Appalachia) 

commercial PCC processes can reduce a coal's SO- emission rate (i.e., 

lb SOp/mi11 ion Btu) by roughly 50 percent. However, for most 

coals, SO- reductions achievable with existing PCC processes are less 

than 30 percent. 

This memo examines the sulfur reduction potential of advanced 

physical coal cleaning (APCC) processes currently under development by 

3 4 the U.S. Department of Energy (DOE) and private industry. ' Of 

Progress Center/3200 E. Chapel Hill Rd./Nelson Hwy./P.O. Box 13000/Research Triangle Park. N.C. 27709/(919)541-9100 
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specific interest are the ability of APCC to 1) decrease SO- emissions 

by 90 percent, and 2) yield very low-sulfur coals with an SO- emission 

rate of less than 1.2 lbs/million Btu. Chemical and biological 

processes for removing sulfur from coal are also under development, 

but are not expected to be of commercial significance within the next 

5-10 years. Because of their limited near-term commercial 

significance, they are not discussed further in this memo. 

The memo is divided into four sections covering 1) the importance 

of modes of sulfur occurrence in coal on sulfur removal during PCC, 2) 

the design of APCC processes, 3) the level of sulfur reduction 

achievable with APCC processes, and 4) the impact of APCC processes on 

the potential for production of very low sulfur coals. 

2.0 MODES OF SULFUR OCCURRENCE IN COAL 

Sulfur occurs in coal in three basic forms: organic, pyritic, 

and sulfate. Organic sulfur is chemically bound to the organic 

structure of coal. Because of this chemical bond, physical cleaning 

methods are ineffective at removing organic sulfur. In most U. S. 

coals, organic sulfur accounts for 0.3 to 1.5 percent of the total 

weight of the coal. This corresponds to up to 80 percent of the total 

sulfur in some low sulfur coals, but can be as little as 25 percent on 

the total sulfur in some high sulfur coals. Sulfate generally 

represents less than 0.1 weight percent and has little impact on total 

sulfur levels (the major exceptions in the U. S. are in the Interior 

and Northern Great Plains regions where levels of up to 0.5 percent 

can occur). 

Pyritic sulfur occurs in coal as discrete particles of pyrite and 

marcasite (both of which are mineral polymorphs of iron sulfide, FeS-) 

and to a lesser extent as sulfides of copper, zinc, and lead. These 

mineral particles can range from microscopic grains dispersed 

throughout the coal matrix to large fragments several inches across. 

In most U.S. coals, pyritic sulfur ranges from 0.1 to 5.0 weight 
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percent. On a relative basis, pyritic sulfur can range from 20 

percent to 80 percent of the total sulfur content; the low end of this 

range is generally associated with coals that are also low in organic 

sulfur while the high end is generally found in coals that are high in 

organic sulfur. 

The ability to separate pyritic sulfur from coal depends on both 

the physical size of the sulfide particles and their distribution 

throughout the coal matrix. In general, small sulfide particles are 

harder to remove than large particles. Existing coal cleaning 

methods, most of which are limited to cleaning coals that have been 

crushed to a particle size of 28 mesh* and larger, are capable of 

removing almost all of the pyritic sulfur that occurs as fairly large, 

discrete nodules. However, sulfide particles smaller than this size 

remain attached to the lighter organic fraction and are more difficult 

to remove. By using separating fluids with low specific gravities 

(e.g., s.g.=1.3-1.4), additional amounts of pyrite can be removed. At 

these low specific gravities, however, a significant portion of the 

original heating content of the coal is also lost, thus resulting in 

unfavorable economics. As a percentage of the total sulfur in coal, 

sulfur reductions economically achievable with conventional PCC 

processes range from near zero (for as-mined coals in which pyrite 

content is already low) up to roughly 50 percent. 

3.0 ADVANCED PHYSICAL CLEANING PROCESSES 

Research and development efforts are underway by DOE and private 

industry to develop APCC processes capable of removing greater amounts 

of fine-grained pyrite. To achieve these higher removal efficiencies, 

* Mesh sizes are used to define the size of particles able to pass 

through a wire screen of defined spacing between wires. Mesh sizes 

used in this memo and corresponding particle sizes are: 

14 mesh = 1.19 mm (0.0469 inches), 

28 mesh = 0.595 mm (0.0234 inches), 

100 mesh = 0.149 mm (0.0059 inches), and 

200 mesh = 0.074 mm (0.0029 inches). 
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the coal is ground to particle sizes smaller than conventional PCC 

processes can handle (i.e., 28 mesh). Some APCC processes have been 

tested at particle sizes of 200 mesh and smaller. This additional 

grinding allows more complete separation of particles containing 

fine-grained pyritic sulfur and ash from those containing mainly coal. 

However, at these small particle sizes, PCC methods based solely on 

differentiating the specific gravity of particles are relatively 

ineffective due to constraints associated with both the physics of 

small particles and the cost of handling finely ground material. To 

overcome these limitations, APCC processes use a variety of techniques, including heavy organic compounds combined with centrifugal 

force, alteration of surface properties through use of surfactants, 

and use of differences in the magnetic and electrostatic properties. 

Table 1 summarizes several advanced physical coal cleaning processes. 

Because APCC processes are expected to be two- to three-times 

more expensive per ton of cleaned coal than existing PCC processes, 

most advanced cleaning processes are envisioned as part of an integrated cleaning plant in which material larger than 28 mesh is cleaned 

using conventional processes followed by further crushing and APCC of 

a portion of the plant's total throughput as needed to meet coal 

product specifications. By combining conventional and advanced PCC 

processes into a single plant, it is possible to operate the conventional equipment at lower specific gravities than would otherwise 

be economical in order to recover a very low ash and sulfur product. 

4.0 SULFUR REDUCTION POTENTIAL OF APCC 

As discussed above, the performance of APCC processes relative to 

conventional processes is dependent upon the liberation of additional 

pyrite as a result of finer grinding. In concept, the finer the 

grind, the more complete the separation of pyritic sulfur from coal. 

As discussed earlier, however, none of the physical cleaning 

processes—whether conventional or advanced—are able to remove 
TABLE 1.. DESCRIPTION OF SELECTED APCC PROCESSES 

EBQCESS. 

Heavy Media 

Cyclone (HMO 

Advanced Flotation 

Heavy Liquid 

Electrostatic 

Separation 

011 Agglomeration 

DESCRIPTION 

Uses finely ground magnetite (325 mesh) dispersed 1n water to produce 

a high specific gravity fluid. Separation of sulfur and coal 1s 

enhanced by centrifugal forces produced 1n cyclone. Used on 

28 X 150 mesh material. Multiple vendors. 

Uses finely divided bubbles and surfactants to selectively remove 

ash and pyrite 1n sequential cleaning steps. Used on 100 X 0 mesh 

material. Developers include BCRNL, Bechtel, Michigan Tech. 

Uses heavy organic liquids (e.g., freon, perchloroethylene) and 

cyclones to separate coal from ash and pyrite based on specific 

gravity. Some heavy liquid processes also use agglomeration as a 

precleaning step to separate hydrophobic coal from hydrophilic clay. 

Used on 100 X 0 mesh material. Developers Include Dow Chemical and 

Otlsca. 

Uses differences 1n electrostatic properties of nonconductive coal 

versus conductive pyrite and ash to collect coal on an electrically 

charged drum. Two different variants of process exist, one for 

28 X 400 mesh "fine" coal and the other for 140 X 0 mesh "ultraflne" 

coal. Developed by Advanced Energy Dynamics. 

Uses fuel oil or other solvents to selectively coat and agglomerate 

hydrophobic coal. Used on 100 X 0 mesh material. Developers include 

National Research Council of Canada, Otlsca, and University of 

Pittsburgh. 

TJ 
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organic sulfur regardless of how finely the coal is ground. As a 

result, SO- reductions from a coal containing half pyritic sulfur and 

half organic sulfur are at most 50 percent. 

Table 2 presents data on sulfur removal versus coal particle size 

and Btu recovery for several major U. S. coal seams. While 

washability data does not directly translate to sulfur removals with 

specific cleaning processes, they do give an indication of the 

relative significance of additional grinding and Btu recovery. For 

the listed coals, the additional SO- reduction achieved (at 90 percent 

Btu recovery) by reducing particle top size from 3/8 inch (comparable 

to particle top sizes in several conventional processes) to 14 mesh 

(closer to that used in conjuction with advanced processes) ranges 

from 2 to 7 percent. Depending on the mode of pyrite occurrence in an 

individual coal, grinding to smaller particle sizes (e.g., less than 

100 mesh) may liberate additional sulfur from some coals. The "70 

percent Btu recovery, -14 mesh" column is an approximation of the 

practical upper limit on SO- reduction achievable; for the Northern 

Appalachia and Illinois Basin coals, these SO- reductions correspond 

to removing 75 to 90 percent of the pyritic sulufr in the as-received 

coal. APCC processes may be able to achieve comparable SO- reduction 

while recovering a higher percentage of the original Btu content. 

Table 3 presents data from tests on three Northern Appalachian 

coals using several different APCC processes discussed in Table 1. 

Note the variability in performance achieved with different processes, 

indicating the sensitivity of these processes to coal specific 

characteristics. Inclusion of the Upper and Lower Freeport seams in 

this table is significant because they are generally among the most 

highly washable coals in the U. S. Maximum SO- reductions with each 

coal range from 49 percent for the Pittsburgh seam to 77 percent with 

the Lower Freeport. 

Direct comparison of data from Tables 2 and 3 for the Pittsburgh 

and the two Freeport seams in not possible because of difference in 

as-received coal characteristics for the evaluated samples. However, 
TABLE 2. S02 REDUCTION VERSUS PARTICLE SIZE AND BTU RECOVERY BASED ON WAHABILITY DATA FOR SELECTED 

U.S. COALS3 

Coal Reg1on/Seam 

Northern Appalachia 

Pittsburgh 

Upper Freeport 

Lower Freeport 

Upper K1ttan1ng 

M1d/Low K1ttan1ng 

Southern Appalachia 

Illinois Basin 

Western Interior 

West 

ROM 

5.8 

3.9 

3.6 

3.5 

4.8 

1.6 

6.5 

9.0 

1.1 

90% 

- I 1 / * 

4.2 

2.3 

2.1 

1.8 

2.8 

1.3 

4.2 

6.2 

0.8 

— lh ^O /MUn+n 

Btu Recovery 

=!/fi -14 Mesh 

3.9 3.6 

1.9 1.6 

1.5 1.4 

1.5 1.4 

2.3 2.2 

1.2 1.2 

4.1 4.0 

5.9 5.8 

0.9 0.8 

7056 

-14 Mesh 

3.0 

1.2 

1.1 

1.1 

1.8 

1.2 

3.5 

4.6 

0.8 

90* 

-lV2 

26 

39 

40 

43 

38 

15 

34 

30 

15 

Btu Recovery 

-

3/8 -14 Mesh 

31 38 

50 57 

56 62 

50 52 

44 47 

16 18 

35 38 

35 38 

15 19 

70S 

-14 Mesh 

47 

65 

68 

59 

54 

19 

45 

52 

23 

-l1/? = I1/?" • -

3/fl = 3 Actual particle sizes: -1V2 = 1V2" X 100 mesh; - /8 =

 J/fl /8"« X 100 mesh; -14 mesh = 14 mesh X 0 

Reference 5 
TABLE 3. S02 REDUCTION PERFORMANCE FOR SELECTED APCC PROCESSES 

00 

Pittsburgh 

lb S02/MM Btu 

X S02 Reduction 

X Btu Recovery 

Upper Freeport 

lb S02/MM Btu 

X S02 Reduction 

X Btu Recovery 

Lower Freeport 

lb S02/MM Btu 

X S02 Reduction 

X Btu Recovery 

ROM 

F£E£ 

5.6 

— 

4.7 

— 

7.5 

HMC/ 

FLOTATION 

3.2 

43 

89 

1.8 

63 

86 

2.1 

72 

84 

ADVANCED 

FLOTATION 

3.4 

39 

89 

2.1 

55 

93 

2.6 

65 

89 

HEAVY 

LIQUID 

3.1 

44 

92 

1.6 

66 

89 

2.0 

74 

87 

ULTRAFINE 

ELECTROSTATICS 

2.8 

49 

94 

1.1 

74 

92 

1.7 

77 

90 

OIL 

AGGLOMERATION 

3.7 

34 

92 

2.3 

52 

90 

2.9 

61 

90 

aSee Table 1 for description of Processes 

Reference 3 
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for the Pittsburgh seam (for which total sulfur levels on both tables 

are similar, but not necessarily the split between organic and puritic 

sulfur), several of the APCC processes were able to achieve 5 to 10 

percent greater SO- reductions than shown in the "90 percent Btu 

recovery, -14 mesh" column of Table 2. These SO- reductions are 

comparable to the change in Table 2 between 70 and 90 percent Btu 

recovery with -14 mesh coal. 

5.0 USE OF APCC TO PRODUCE VERY LOW SULFUR COALS 

Even if all of the pyritic sulfur could be removed by APCC 

processes, an SO- emission limit of 1.2 lb/million Btu would require a 

coal with less than roughly 0.7 percent organic sulfur (assuming a 

coal heating value of 11,700 Btu/lb). At a emission rate of 0.8 lb 

SO-/million Btu, the maximum organic sulfur level is 0.5 percent. 

Coals with these low organic sulfur levels are found primarily in the 

Pottsville Formation of Alabama, eastern Kentucky, southern West 

Virginia, and Virginia; the Freeport and Kittaning seams of Ohio, 

Pennsylvania, and northern West Virginia; and various western coals 

from Colorado, Montana, North Dakota, Utah, and Wyoming. Because many 

of these western coals have pyritic sulfur levels of less than 0.1 

percent and as-mined SO- emission rates below 0.8 lb/million Btu, coal 

cleaning would be of limited value. This section, therefore, focuses 

on coals from Northern and Southern Appalachia. 

As shown in Table 2, cleaned coals from several major seams in 

these regions have average SO- emission rates at or slightly above 1.2 

lb/million Btu. However, some individual coals have lower sulfur 

contents or are more washable than these average values. To estimate 

the potential for producing very low sulfur coals, washability data in 

Reference 5 was reviewed. A threshold value of 1.2 lb S0-/million Btu 

at 70 percent Btu recovery and a 14 mesh top size was used to estimate 

SO- reductions possible with APCC. A top size of 3/8 inch and 90 

percent Btu recovery was used to represent conventional PCC processes. 
Coal seams of interest in Northern Appalachia are the Upper and 

Lower Freeport and the three members of the Kittaning. Based on 

coal samples collected from these seams in Pennsylvania, roughly 60 

percent of the Freeport coals and 20 percent of the Kittaning coals 

meet or exceed the 1.2 lb criteria for APCC. With conventional PCC 

processes (i.e., at 90 percent Btu recovery), the percentages for each 

set of seams decreases to roughly 20 and 15 percent, respectivley. 

The lowest SO- emission rate with APCC is roughly 0.8 lb/million Btu 

for both sets of seams. With conventional PCC the lowest emission 

limit is roughly 0.9 lb/million Btu. Percent reductions in S0-

emissions associated with cleaning these coals range from 50 to 70 

percent for both PCC and APCC. 

In Southern Appalachia, the coals from Virginia were examined. 

All of the Virginia coals listed in Reference 5 achieve SO- emission 

rates of 1.2 lb/million Btu or lower at 90 percent Btu recovery (in 5 

of the 8 samples listed, the 1.2 lb level was met without washing). 

The lowest SO- emission rate at both 70 and 90 percent Btu recovery is 

roughly 0.8 lb/million Btu. Because most of these samples have 

as-received pyritic sulfur levels of less than 0.3 percent, S0-

reductions associated with cleaning were generally less than 20 

percent. 

Based on the above discussion, the potential for APCC processes 

to produce very low sulfur coals appears limited to specific coals 

which are inherently low in organic sulfur. Based on the data 

reviewed, use of APCC has the potential to expand the supply of 

Northern Appalachian coals with less than 1.2 lb S0-/million Btu, but 

does not appear likely to significantly increase the supply of these 

coals with less than 0.8 lb S0-/mil1ion Btu. Because of the low 

pyritic sulfur content in other low sulfur coals, such as those from 

Southern Appalachia and the West, the potential impact of APCC on very 

low sulfur coal supply appears small. 

10 
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6.0 REFERENCES 

1. Kilgroe, J. D. and J. Strauss. Coal Cleaning Options for S0-

Emission Reduction. Power Magazine Conference of Acid Rain, 

Washington, D. C , 1985, 53 pp. 

2. Holt, E. C. An Engineering/Economic Analysis of Coal Preparation 

Plant Operation and Cost. EPA-600/7-78-124, U. S. Department of 

Energy and U. S. Environmental Protection Agency, Washington, 

D. C , 1978, 296 pp. 

3. Boron, D. J., M. P. Matoney, and M. C. Albrecht. Advanced 

Physical Coal Cleaning: An Evaluation of Five Select Processes. 

Proceedings of the Third Annual Pittsburgh Coal Conference, 

University of Pittsburgh, September 8-12, 1986, pp. 13-18. 

4. Cavallaro, J. A., R. P. Killmeyer, A. W. Deurbrouck, and K. Rhee. 

An Overview of PETC's Chemical, Physical, and Surface-Enhanced 

Beneficiation Program. Pittsburgh Energy Technology Center, 

U. S. Department of Energy, 1986, 29 pp. 

5. Cavallaro, J. A., M. T. Johnston, and A. W. Deurbrouck. Sulfur 

Reduction Potential of the Coals of the United States. RI 8118, 

U. S. Bureau of Mines, Pittsburgh, Pennsylvania, 1976, 323 pp. 

Hucko, R. E., Pittsburgh Energy Technology Center. An Overview of 

U.S. Department of Energy Coal Preparation Research. Society of 

Mining Engineers of AIME, Preprint Number 84-105. 

5. Hucko, R. E., Pittsburgh Energy Technology Center. Recent 

Initiatives in Coal Cleaning Research at the U.S. Department of 

Energy. Society of Mining Engineers of AIME, Preprint Number 86-56. 

6. Simmons, Frederick J., and Douglas V. Keller, Jr., Otisca 

Industries, Ltd., Two Ton-per-day Production of Otisca T-Process 

Ultra-Clean Coal/Water Slurry, 10th International Coal Preparation 

Congress, September 1-5, 1986. 

7. Keller, Douglas V., Jr., Otisca Industries Ltd., telephone 

conversation with Edward Moretti, Radian Corporation, December 8, 

1986. 

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