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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