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Coal Bioprocessing


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Title: Coal Bioprocessing

Coal Bioprocessing
  • Drew Hill
  • BKB Co., Ltd

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

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.

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

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

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

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.

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

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.

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.

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

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

Reported in cost per million Btus Reported in cost per million Btus
Coal 1.20
Oil 4.45
Natural gas 4.30
Coal Mining
  • Surface Mining
  • Room and Pillar Mining
  • Longwall Mining

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 .

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.

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.

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

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)

Categories of Coal Processing
  • Gasification
  • Liquefaction
  • Beneficiation

  • 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

  • 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

  • Direct
  • One phase
  • Two phase
  • Indirect

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
  • 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

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

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
  • 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

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

  • Physical Cleaning
  • Chemical Cleaning
  • Biological Cleaning

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.

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.

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

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

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

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

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

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

  • 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
  • Performance is less predictable than chemical
    treatment systems

  • 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

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

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

  • 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

  • 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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    Foundation. 2003. lt http//
  • Coals Journey. American Coal Foundation. 2003.
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    Congress Coal Refineries A Definition and
    Example Concepts. 1991.
  • 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. lthttp//
  • 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

  • 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
  • Coal All you really wanted to know. Earth
    Science Australia. lthttp//
  • 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//

Thank You!
  • BKB
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