Groton Fuel Cell
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Operating a Fuel Cell Using Landfill Gas |
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Fuel Cell Demonstration Fact Sheet
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C. E. Trippel and W. L. Stillinger, Northeast Utilities Service
Company
J. L. Preston, Jr. and J. C. Trocciola, International Fuel
Cells Corporation
R. J. Spiegel, U.S. Environmental Protection
Agency
|
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An ONSI PC25TM, 200 kW (nominal capacity) phosphoric acid fuel cell operating
on landfill gas (LFG) is installed at the Town of Groton Flanders Road landfill
in Groton, Connecticut. This joint project by the Connecticut Light & Power
Company (CL&P) which is an operating company of Northeast Utilities, the
Town of Groton, International Fuel Cells (IFC), and the United States
Environmental Protection Agency (EPA) is intended to demonstrate the viability
of installing, operating and maintaining a fuel cell operating on LFG at a
landfill site. The goals of the project are to evaluate the fuel cell and gas
pretreatment unit (GPU) operation, test modifications to simplify the design,
and demonstrate the reliability of the entire system.
In 1990, the EPA contracted with IFC to design and
build a landfill
GPU that would allow LFG to be used by a fuel cell. Upon successful
demonstration of the GPU, the fuel cell was installed at the Penrose Landfill in
Los Angeles to demonstrate the system operation. The energy recovery system
operated for approximately three months, and concluded operations in February
1995. In order to verify operation on a different composition LFG and in
different climatic conditions, the energy recovery system was shipped to the
East Coast. Discussions between all parties resulted in the Town of Groton
landfill being chosen as a site to continue operation of the fuel cell and GPU
system. The EPA is the current owner of the fuel cell and GPU and is providing
technical expertise for the project. CL&P is funding the project and is
providing the engineering, design, and construction for the installation as well
as the operation and maintenance for the 12 to 18 month demonstration period.
IFC is providing technical expertise for the operation of the fuel cell and GPU
system. The Town of Groton is providing the
site as well as the collected LFG and operation of an existing LFG flare
at no cost to CL&P.
The LFG is collected from an 18.2 (45 acre) closed landfill.
Based on the estimated volume of solid waste in the Groton landfill, a
calculated 5.8 million m3 (204 million ft3) of LFG would be produced annually.
Before the installation of the fuel cell system at Groton, the LFG was collected
and burned in a flare at a rate of approximately 0.189 m3/s (400 cfm).
The fuel cell system uses a maximum of 0.0378 m3/s (80 scfm) of landfill gas
while the remaining gas continues to be burned by the flare. Where LFG is
emitted into the atmosphere without recovery and use, methane has a global
warming potential much greater than that of carbon dioxide (CO2).
Some of the non-methane constituents of LFG, such as hydrogen sulfide
(H2S), are odoriferous and potentially harmful to the environment.
The fuel cell emissions are primarily water vapor and CO2.
Emissions of nitrogen oxides (NOx) and sulfur dioxide (SO2), which
result from the combustion of LFG, are virtually eliminated. Due to its higher
efficiency, the quantity of CO2 emitted from the fuel cell is less
than the amount created through combustion conversion electrical generators such
as the combustion turbine and internal combustion engine. A comparison of
typical emission rates is:
| Typical Emission Rates (g/kWh) |
| |
Combustion Turbine |
Internal
Combustion Engine |
Fuel Cell |
| NOx |
0.694 |
0.417 |
0.004 |
| SO2 |
0.077 |
0.054 |
0 |
| CO2 |
889.041 |
621.421 |
435.449 |
System Description at the Groton Landfill
The LFG is collected from the closed and capped landfill through a series of
wells and is drawn out of the landfill by the flare blower. This maintains an
absolute pressure of 99.8 kPa (14.5 psia) on the collection system. An LFG compressor draws LFG from a collection
header and compresses the gas to 276 kPa (40 psig) for use in the GPU. Two
H2S absorbers, using activated carbon as the
absorbing medium, are installed on the suction side of the compressor to remove
the H2S from the gas stream before compression. A moisture
separator before the H2S absorbers removes any bulk moisture
present in the gas. The H2S absorbers are installed in a
parallel/series arrangement where normal operation is in series but either
absorber can be removed from service while the other is in service. This is
useful for carbon changeout during operation or testing the removal
effectiveness of an individual absorber.
The gas is discharged from the gas compressor and into the
GPU where moisture and volatile organic compounds (VOCs) including
sulfides and halogenated compounds are removed. The GPU has dual cleanup trains,
so when one train is in service cleaning the gas the other is being regenerated
with a portion of the cleaned gas. The regeneration gas,
in the quantity of 0.0118 m3/s (25 scfm), is combusted in an enclosed
flare. The cleanup train consists of an alumina plus mole sieve dryer
vessel which removes the moisture from the gas, a carbon vessel which absorbs
hydrocarbons and VOCs, and a refrigeration unit and heat exchanger which are
used to cool the gas to 274.3 K (34oF) prior to entering the cleanup train. The
gas leaves the GPU consisting of methane, CO2, and trace amounts of
nitrogen and oxygen. The dew point of the gas is 244.3 K (-20oF). The specific
composition of the Groton LFG leaving the GPU is:
- Methane - 57.1%
- Carbon dioxide - 41.0%
- Nitrogen - 1.5%
- Oxygen - 0.4%
The fuel cell has been modified for operation on LFG to accept the higher
flow rate required because of the reduced methane content in the LFG. These
modifications include a larger fuel control valve and fuel control venturi plus
resizing of two fixed orifices. Minor modifications were also made to the
control settings.
Site
The total site encompasses an area 13.12 m (43 ft) wide by 41.15 m (135 ft)
long and is enclosed by a chain link fence. Located at the south end of the site
are the existing LFG flare and a newly installed underground storage tank to collect
condensate that comes from the landfill with the gas as well as from the
GPU. The GPU control room houses the GPU control panel, refrigeration unit purge air compressor,
nitrogen bottles for actuating the GPU pneumatic valves, and project
documentation. The GPU flare is used to combust the regeneration gas. The
gas pretreatment unit building is a pre-engineered building with aluminum siding
and insulated walls and roof. The space inside the building is considered a
Class 1, Division 2 location, and all electrical equipment and fixtures are
explosion proof. Enclosed in the gas pretreatment unit building is the LFG
moisture separator, H2S absorber vessels, gas compressor, GPU
and refrigeration unit. A combustible gas
detector is used to monitor the interior atmosphere and ultimately shut down the
gas compressor if gas is detected.
A compressed natural gas (CNG) bottle
rack is required to supply start up burner fuel for the fuel cell and for
the GPU flare. The fuel cell and cooling module are in the
standard configuration for a typical installation. A
nitrogen bottle rack external to the fuel cell is used to increase
bottle capacity and facilitate bottle changeout. The switchgear contains the
distribution bus and breakers for the fuel cell and all other site equipment.
The step-up transformer takes the 480 volt power from the fuel cell output and
increases it to 13,800 volt for use on the utility grid. The equipment and site
layout are designed for unmanned operation. Remote data monitoring of the fuel
cell and GPU controller will be utilized.
Project Status
Construction was completed in mid-June 1996, and system start-up and testing
were in progress in late August 1996. Before start-up start-up of the fuel cell,
the GPU was started and operated for 200 hours, and gas quality suitable for
fuel cell operation was verified. Operation of the fuel cell at the Groton site
on landfill gas has been achieved with an output of 165 kW obtained to date. The
power generated is enough to supply over 100 homes and is fed into the local
utility grid. Continued testing and refinement of the system is expected to
achieve a continuous net fuel cell output of 140 kW.
Conclusion
The operation of fuel cells on landfill gas presents an opportunity to use a
waste gas that is harmful to the environment to generate electricity more
cleanly and efficiently than other methods currently used. The use of other bio
gases, such as from waste water treatment plants and livestock wastes, in fuel
cells is possible as a result of the work performed using LFG as a fuel. This
project brings bio gas conversion using fuel cells one step closer to commercial
application.
