1. Coal Bioprocessing
Drew Hill
BKB Co., Ltd

2. Outline Coal Relevance of Bioprocessing Coal Processing Conclusions
What is Coal
Relevance of Bioprocessing
Advantages of Bioprocessing
Why Remove Sulfur
Coal Processing
Gasification
Liquefaction
Beneficiation
Conclusions
References

3. What is Coal?
Over three hundred million years ago the vegetation of the earth died and drifted down to the bottom of the swamps. That dead vegetation formed peat, which is a soggy sponge like material, and as this material built up it was compressed under the earth’s surface. Over the millions of years of intense heat and pressure compressed this organic matter into coal.

4. Coal is Still Being Formed
The process of forming coal is still occurring today in the US in such places as
Great Dismal Swamp of North Carolina and Virginia
Okefenokee Swamp in Georgia
Everglades in Florida

5. Categorizing Coal
Coal is broken down into four categories according to the carbon content
Lignite (soft)
Subbituminous (medium-soft)
Bituminous (medium-hard)
Anthracite (hard)

6. Soft Coal
Lignite
This type of coal contains a lot of moisture and breaks apart easily. Of the four types, lignite contains the least amount of carbon. Also called brown coal, lignite is used mainly at electricity-generating plants

7. Medium Soft Coal Subbituminous
This type of coal has less moisture than lignite. Subbituminous coal is generally used to produce steam for electricity generation. Reserves of subbituminous coal are found mostly in the western United States and Alaska.

8. Medium Hard Coal Bituminous
This type of coal, which contains very little moisture, has high heat value. It is used to generate electricity and to produce coke, a coal residue used in the steel industry. Bituminous coal is the most plentiful type in the United States.

9. Hard Coal
Anthracite
This type of coal has the highest carbon content. Anthracite burns slowly and makes a good heating fuel for homes. The United States has about 7.3 billion tons of anthracite, most of which can be found in Pennsylvania.

10. Coal Use
Coal, being used to heat the tunnels of cavemen, has been a source of energy for as long as man can remember. In America the Native Americans were using coal as far back as the twelfth century for cooking and heating.

11. Coal Use
Coal continues today to be a major source of energy in the United Sates as the American Coal Foundation reports in Coal's Past, Present, and Future “Nine out of every ten tons of coal mined in the United States today is used to generate electricity. About 56 percent of the electricity used in this country is coal-generated electricity.”

12. Reported in cost per million Btu’s
Coal Abundance
The United States has a supply of coal that will last over three hundred years at the current usage rate which is promising as coal is more cost effective than oil or natural gas. Current prices of energy as listed by the American Coal Foundation in Coal's Past, Present, and Future are:
Reported in cost per million Btu’s
Coal
$1.20
Oil
$4.45
Natural gas
$4.30

13. Coal Mining
Surface Mining
Room and Pillar Mining
Longwall Mining

14. Surface Mining
During surface mining the land is bulldozed and leveled off. Next the topsoil is cleared and stored for later land reclamation. Next they drill smaller holes into the overburden, which is rock sitting above the desired coal. This overburden is exploded and removed so the desired coal can be picked up and placed into trucks to be separated and prepared for use .

15. Room and Pillar Mining
Room and pillar mining requires no blasting and is similar to what most people think of when they think mining as can be seen by the picture Coal: All you really wanted to know. Large holes are drilled in the ground using a large tungsten drill that follows the coal seam. As the coal is drilled away it is added to a conveyor belt and transported to the surface to the dump trucks. Once the desired depth is met roof bolts are placed to prevent collapsing and the drills are backed out.

16. Long Wall Mining
Longwall mining involves running a large tungsten cutting machine along a wall, between four hundred to six hundred feet, of the coal seam. The coal knocked off the wall falls on a large conveyor which transports the coal to the surface.

17. Advantages of Bioprocessing
Biological systems offer a number of advantages over conventional approaches, though their application is not appropriate in every situation
Potential for processing low-grade deposits
Re-processing earlier metal-containing wastes
Production of less chemically-active tailings
Lower energy inputs
Other environmental benefits such as zero production of noxious gases

18. Why Remove Sulfur
Acid rain is precipitation more acidic than normal rain and snow, which is slightly acidic with a pH of 5.6 because of the carbon dioxide dissolved in it
Sites downwind of industrial areas have had a pH close to 4.5 and sometimes as low as 2.1 (equivalent to lemon juice)

19. Categories of Coal Processing
Gasification
Liquefaction
Beneficiation

20. Gasification
Coal is combined with steam and air at high temperatures and high pressures
Produces “syngas” (made up primarily of H2 and CO)” and a solid ash waste product is remains at the bottom
After this the ash is removed and the gas is purified.

21. Gasification

22. Gasification
Primary impurities include gaseous ammonia and sulfur compounds as well as other particulates
Uses for syngas include
Chemical feedstock
Substitute natural gas, after adjusting the composition for conversion into products such as
Pure hydrogen
Methanol
Ammonia
Acetic anhydride
Various hydrocarbon fuels

23. Liquefaction
Direct
One phase
Two phase
Indirect

24. Liquefaction: Direct
Direct – Aim to add hydrogen to the organic structure of the coal, breaking it down only as far as is necessary to produce distillable liquids
Many different process, but common features
Dissolution of a high proportion of coal in a solvent at elevated temperature and pressure
Followed by the hydrocracking of the dissolved coal with H2 and a catalyst

25. Liquefaction: Direct
Direct One Phase – A single-stage direct liquefaction process gives distillates via one primary reactor or a train of reactors in series
Such processes may include
Integrated on-line hydrotreating reactor, which is intended to upgrade the primary distillates without directly increasing the overall conversion

26. Liquefaction: Direct
Direct Two Phase – A two-stage direct liquefaction process is designed to give distillate products via two reactors or reactor trains in series
Primary function of the first stage is coal dissolution and is operated either without a catalyst or with only a low-activity disposable catalyst
The heavy coal liquids produced in this way are hydrotreated in the second stage in the presence of a high-activity catalyst to produce additional distillate

27. Liquefaction: Indirect
Indirect liquefaction involves
First, the complete breakdown of the coal structure by gasification with steam
Next, the composition of the gasification products is then adjusted to give the required mixture of H2 and CO, and to remove sulfur-containing catalyst poisons
Finally, the resulting ‘synthesis gas’ is reacted over a catalyst at relatively low pressure and temperature

28. Beneficiation
Physical Cleaning
Chemical Cleaning
Biological Cleaning

29. Beneficiation: Physical Cleaning
Gravity Separation – During physical cleaning undesired substances such as dirt, rocks, and pyretic sulfur are removed from the coal. When added to water these impurities separate from the coal due to the difference in the density of coal and other substances.
Magnetic Separation – Use of hydrocyclones to centrifuge out unwanted particulates.

30. Beneficiation: Physical Cleaning
Froth Flotation – Coal is coated with a chemical, finely ground, and mixed with water. The chemical coating enables the coal to attach to the rising air bubbles in the mixture which allows nearly all inorganic matter to sink to the bottom of the flotation column.

31. Beneficiation: Chemical Cleaning
Chemical treatment involves the use of strong acids, bases or salts. It is usually applied at elevated temperatures, varying between 200ºC and 300ºC, and is characterized by limited selectivity.

32. Beneficiation: Biological Cleaning
Bioleaching – Two different mechanisms for biologically catalyzed oxidation of pyrite (sulfur combined with iron)
Direct
Indirect

33. Direct Bioleaching
Requires direct contact between the bacterium and the pyrite.
Generally not favored as with some coals the microorganisms are too large to fit inside the coal pores.
Reaction:
2 FeS2 + 7 O2 + 2 H2O → 2 FeSO4 + 2 H2SO4

34. FeS2 + 14 Fe3+ + 8 H2O → 15 Fe2+ + 16 H+ + 2 SO4
Indirect Bioleaching
The indirect method is more prominent due to the limiting size of the coal pores compared to the size of the microorganism.
Reactions
FeS Fe H2O → 15 Fe H+ + 2 SO4
2 Fe H+ + O2 → 2 Fe3+ + H2O

35. Bioleaching

36. Bioremediation of Mine Water
Acidic, sulfur rich wastewaters are produced from the mining process of coal
Contain many free metals such as iron, aluminum, manganese, and other metals
Generally, the mine water is controlled during the mining operation, as the water table level is kept low, but once the mines are abandoned the water table rebounds

37. Bioremediation of Mine Water
Two main methods are used today
Wetlands
Bioreactors

38. Wetlands Advantages Disadvantages Low maintenance
Solid-phase products of water treatment are retained within the wetland sediments
Disadvantages
Expensive to install
Require more land area than is available or suitable
Performance is less predictable than chemical treatment systems

39. Wetlands
Aerobic wetlands are used to treat net alkaline waters using the oxidation of ferrous iron, and subsequent hydrolysis of the ferric iron produced, which is a net acid-generating reaction seen below:
4Fe2+ + O2 + 4H+ → 4Fe3+ +2H2O
4Fe3+ + 4H2O → 4Fe(OH)3 + 12H+
Shallow systems
Work by surface flow
Macrophytes are rooted plants submerged, floating, or emergent present within a stream
Aesthetic reasons
Regulate water flow
Stabilizing the accumulating ferric precipitates

40. Bioreactors Occur in compost bioreactors Generate
Net alkalinity
Biogenic sulfide
Treat mine waters that are
Net acidic
Metal-rich

41. Bioreactors Compost for bioreactors are a mix of
Biodegradable materials such as manure
Slow degrading material, depending on local availability, such as
Peat
Sawdust
Straw

42. Bioreactors
First, contaminated water is forced through a layer of compost
To reduce iron and sulfate
Then, through a layer of limestone
To add alkalinity
Finally, into a sedimentation pond and/or an aerobic wetland
to precipitate and retain iron hydroxides

43. Conclusion
Biological systems offer a number of advantages over conventional approaches
Potential for processing low-grade deposits
Processing metal-containing wastes
Can remove finely dispersed sulfur
Control pH of mine water
Lower energy inputs

44. References
“Coal's Past, Present, and Future.” American Coal Foundation <
“Coal’s Journey.” American Coal Foundation <
United States. Department of Energy. Report to Congress: Coal Refineries: A Definition and Example Concepts
United States. Department of Energy. A Program to Deliver Clean, Secure, and Affordable Energy
“Kentucky Coal and Clean Coal Technologies.” Illinois Department of Commerce and Community Affairs, Office of Coal Development and Marketing. <
Prayuenyong, Pakamas “Coal biodesulfurization processes.” Songklanakarin J. Sci. Technol., 2002, 24(3):
Hone, H.J., Beyer, M., Ebner, H.G., Klein, J. and Juntgen, H “Microbial desulphurization of coal- Development and application of a slurry reactor.” Chemical Engineering Technology, 10:

45. References
D. Barrie Johnson. “Importance of microbiology in the development of sustainable technologies for mineral processing and wastewater treatment.” School of Biological Sciences, University of Wales, Bangor, LL57 2UW. U.K. <
“Coal: All you really wanted to know.” Earth Science Australia. <
Johnson, D.B. and Hallberg, K.B. (2002) “Pitfalls of passive mine drainage.” Re/Views in Environmental Biotechnology. 1:
Younger PL, Jayaweera A, Elliot A, Wood R, Amos P, Daugherty A, Martin A, Bowden L,
Aplin A, Johnson DB. “Passive treatment of acidic mine waters in subsurface-flow
systems: exploring RAPS and permeable reactive barriers.” Land Contamination and
Reclamatio.2003.
Pal, Rajinder. Research Interest. August 6, <

46. Thank You!
BKB