oEPA
United States
Environmental Protection Agency
430F98083
 Air and Radiation
 6202J
Draft
April 1998
            EPA Coalbed Methane Outreach Program Technical Options Series

             GENERATING ELECTRICITY WITH COAL MINE
                  METHANE-FUELED MICRO TURBINES
TurboGenerator™ Power System, photo courtesy of AlliedSignal
                         MicroTurbine™, photo courtesy of Capstone
                Micro turbines are about a third the size of comparable diesel generators
  APPLICATIONS AND BENEFITS INCLUDE. ..

     * Off-grid self-generation of electricity at remote gas production sites
     4 Available in 30 kW to 2000 kW systems
     4 Use with cogeneration technologies such as discharge heat recovery
     * Low air and noise emissions
     * Low installation and maintenance costs
     + • Ideal for gob gas use, as they can operate on gas with a heating value as low as 350 Btu
     * Recovery and use of methane reduces greenhouse gas emissions

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    Micro turbines
    have only one
  moving part, which
  drastically reduces
    maintenance
Micro turbines use air-
 bearing technology
  that eliminates the
  need for lubricants
Micro turbines have a
 high power-to-weight
   and volume ratio
 compared to diesel
     generators
Why Consider Using Micro Turbines  To Generate  Electricity
With Coal Mine Methane?
A      large portion of the methane emitted from coal mines comes from gob
      areas  (collapsed   rock  over  mined  out  coal),   where  methane
      concentrations typically vary from 30 to 80%.   Gas with  a methane
      concentration less than 95% is usually not suitable for pipeline injection.
Coal mines frequently do not use medium-quality gas from gob wells and-instead
vent the gas to the atmosphere, contributing to global  warming.  However, gas
with a methane concentration exceeding 35%  can in fact be used as a fuel for
on-site electricity generation, Given their large energy requirements, coal mines
can  recover methane and generate electricity with micro turbines to  realize
significant economic savings and reduce greenhouse gas emissions,

The micro turbine is a new technology developed from the  aerospace industry
that may be an ideal option for on-site electricity generation at coal mines.  The
micro turbine consists of a small,  air-cooled gas turbine connected to a high-
speed generator and compressor on a single shaft,  This simple design results in a
system with  a high power output,  minimal  noise  generation, and efficient
operation. Diesel, gasoline or kerosene can be used as alternate fuels to insure
continuous electricity production  in  the  event that  the  methane supply is
disrupted.

Micro turbines  are a compact, quiet, clean, and reliable power source. Their
compact size allows them to be located at remote gob well sites or inside mine
buildings, and  can reduce the level  of investment and maintenance typically
associated with conventional generators.  Because the generating capacity can
be sized from 30 kW to 2000 kW by integrating multiple-unit systems, .a mine can
easily scale  the project according to its  needs.  The  micro turbine's 22-30%
efficiency rating  improves with the  use of exhaust heat for pre-heating  and
adsorptive cooling.

Currently, two  manufacturers, Capstone Turbine Corp. and AlliedSignal Power
Systems Inc.  state that micro turbines will be available by late 1998. Advertised
uses for micro turbines include off-grid power  generation,  load management
standby power generation,  and cogeneration,  According to projections from
AlliedSignal and Capstone, installed costs for micro turbines  will range from $US
350/kWto$700/kW,
Focfs About Micro Turbine Power Plants...
•   Provide off-grid power to remote areas
•   Exhaust temperatures for a single 30 kW system exceed 500° F with an air flow
    of 35.2 Ib (16.0 kg) per minute; a  75 kW system has a  470° F exhaust
    temperature and an air flow of 91.2 Ib (41.5 kg) per minute
•   Mines can recover exhaust energy over ,250,000 Btu/hr for heating or drying
•   Quiet operation (at least one model is less than 60 decibels @ 33 feet)
•   Multi-unit  systems  can  be  designed according  to  site-specific  power
    demands
•   Natural gas, diesel, gasoline or fuel oil can be used as a backup fuel

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    In todays changing power market, the trend toward distributed generation will allow
    consumers to determine their own power generation sources.  At coal mines, these
    mini power plants can help shift the source of power from centralized power stations
    to on-site units, satisfying a host of power-generating needs.  Micro turbines are both
  a  short and long  term solution to meeting a  coal mine's electricity needs, while
  reducing greenhouse gas emissions.
                         How A MICRO TURBINE OPERATES
     COMPRESSOR
    AIR INTAKE
                                                           PREHEATED AIR
                                        COMBUSTOR
A micro turbine is a small, recuperated combustion turbine that operates with a high-speed generator, compressor
and turbine located on the same shaft. Pressurized gas is preheated with turbine exhaust increasing the overall
efficiency of the system.  Benefiting from  new technology, the core unit operates on floating air bearings
eliminating the need for oil lubrication or cooling systems.
               COMPARISON OF MICRO TURBINE WITH OTHER
                     POWER GENERATION TECHNOLOGIES

Capacity (kW)
Efficiency
Typical Installed Cost ($US/kW)
Maintenance cost ($US/kW-h)
MICRO TURBINE
30-2000
22%-30%
350-700
0.003-0.01
1C ENGINE
10-4000
1 2%-20%
600-1000
0.015-0.025
FUEL CELL
3-3000
40%-65%
900-3000
0.005-0.01 '
GAS TURBINE
1 000-50000
21%-42%
650-1000
0.003-0.008

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 For More Information.
  Rapidly changing  electricity markets "are
  creating new opportunities for on-site power
  generation using coal mine methane.  Micro
  turbines may be  a cost-effective power
  generation option  for gassy underground
  coal mines.

  To obtain more information about generating
  electricity using micro turbines contact:

  AlliedSignal Power Systems Inc.
  2525 W. 190th Street
  Torrance, CA 90504-6099
  Telephone: (800) 406-2267
  Fax:       (310)512-1561
  e-mail:     turbogen@alliedsignal.com
  Web site:   www.alliedsignal.com/turbogen

  Capstone Turbine Corp.
  6025 Yolanda Avenue
  Tarzana, CA91356
  Telephone: (818) 774-9600
  Fax:       (818)774-0228
  Web site:   www.capstoneturbine.com
 Or contact EPA's Coalbed  Methane Outreach Program for  information about this and
 other profitable uses for coal mine methane:
  Coalbed Methane Outreach Program
  U.S. EPA (6202J)
  401 M Street, SW
  Washington, DC 20460 USA
      (202) 564-9468 or 564-9481
  Fax: (202)565-2077
  e-mail: fernandez.roger@epamail.epa.gov
        schultz.karl@epamail.epa.gov

       http://www.epa.gov/coalbed
M E  T  H  A N
OUTREACH
PROGRAM
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The mention of products or services in this case study does not constitute an endorsement by EPA

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