Coal Bioprocessing

1. Coal Bioprocessing Drew Hill BKB Co., Ltd

2. Outline • Coal • 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. 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:

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. 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 FeS2 + 14 Fe3+ + 8 H2O → 15 Fe2+ + 16 H+ + 2 SO4 2 Fe2+ + 2 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 • 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. 2003. < http://www.acf-coal.org/aboutcoal/articles/coalppf.html> • “Coal’s Journey.” American Coal Foundation. 2003. <http://www.acf-coal.org/aboutcoal/articles/coaljourney.html> • United States. Department of Energy. Report to Congress: Coal Refineries: A Definition and Example Concepts. 1991. • United States. Department of Energy. A Program to Deliver Clean, Secure, and Affordable Energy. 2001. • “Kentucky Coal and Clean Coal Technologies.” Illinois Department of Commerce and Community Affairs, Office of Coal Development and Marketing. <http://www.coaleducation.org/lessons/sec/Illinois/cleanky.htm> • Prayuenyong, Pakamas “Coal biodesulfurization processes.” Songklanakarin J. Sci. Technol., 2002, 24(3): 493-507. • Hone, H.J., Beyer, M., Ebner, H.G., Klein, J. and Juntgen, H. 1987. “Microbial desulphurization of coal- Development and application of a slurry reactor.” Chemical Engineering Technology, 10: 173-176.

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. <http://biology.bangor.ac.uk/~bss014/documents/NESMI%2003.pdf> • “Coal: All you really wanted to know.” Earth Science Australia. <http://earthsci.org/energy/coal/coal.htm> • Johnson, D.B. and Hallberg, K.B. (2002) “Pitfalls of passive mine drainage.” Re/Views in Environmental Biotechnology.1:335-343. • 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, 1998. <http://cape.uwaterloo.ca/dept/personnel/pal.htm>

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