Coal Bioprocessing

1
Coal Bioprocessing

• Drew Hill
• BKB Co., Ltd

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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 earths surface. Over the
  millions of years of intense heat and pressure
  compressed this organic matter into coal.

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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

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Categorizing Coal

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

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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

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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.

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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.

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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.

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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.

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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.

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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 Btus Reported in cost per million Btus
Coal 1.20
Oil 4.45
Natural gas 4.30
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Coal Mining

• Surface Mining
• Room and Pillar Mining
• Longwall Mining

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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 .

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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.

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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.

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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

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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)

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Categories of Coal Processing

• Gasification
• Liquefaction
• Beneficiation

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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.

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Gasification
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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

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Liquefaction

• Direct
• One phase
• Two phase
• Indirect

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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

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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

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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

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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

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Beneficiation

• Physical Cleaning
• Chemical Cleaning
• Biological Cleaning

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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.

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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.

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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.

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Beneficiation Biological Cleaning

• Bioleaching Two different mechanisms for
  biologically catalyzed oxidation of pyrite
  (sulfur combined with iron)
• Direct
• Indirect

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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

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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

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Bioleaching
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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

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Bioremediation of Mine Water

• Two main methods are used today
• Wetlands
• Bioreactors

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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

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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

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Bioreactors

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

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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

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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

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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

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References

• Coal's Past, Present, and Future. American Coal
  Foundation. 2003. lt http//www.acf-coal.org/aboutc
  oal/articles/coalppf.htmlgt
• Coals Journey. American Coal Foundation. 2003.
  lthttp//www.acf-coal.org/aboutcoal/articles/coaljo
  urney.htmlgt
• 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. lthttp//www.coaleducation.org/lessons/s
  ec/Illinois/cleanky.htmgt
• 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.

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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. lthttp//biology.bang
  or.ac.uk/bss014/documents/NESMI2003.pdfgt
• Coal All you really wanted to know. Earth
  Science Australia. lthttp//earthsci.org/energy/coa
  l/coal.htmgt
• Johnson, D.B. and Hallberg, K.B. (2002) Pitfalls
  of passive mine drainage. Re/Views in
  Environmental Biotechnology. 1335-343.
• 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. lthttp//cape.uwaterloo.ca/dept/personnel/pal
  .htmgt

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Thank You!

• BKB