Pyrolysis and Thermal
Gasification of Municipal Solid WasteGasification
and pyrolysis can produce a gas for fuel. The
process operates at a high temperature and in the
absence of air. Under special conditions, a
liquid fuel or chemical feedstock can also be
made. The gas may be used in existing boilers or
furnaces, or can fire combustion turbines to
generate electricity.
Pyrolysis is the thermal decomposition
of organic material at elevated temperatures in
the absence of air or oxygen. The process, which
requires heat, produces a mixture of combustible
gases, primarily methane, complex hydrocarbons,
hydrogen, and carbon monoxide, and liquids and
solid residues.
Gasification of MSW is a special type
of pyrolysis where thermal decomposition takes
place in the presence of a small amount of oxygen
or air. The gas which is generated
can then be burned in industrial boilers or
cleaned up and used in combustion turbines for
electric generators.
The gasification process has been used
commercially with coal and wood chips. It was
used with MSW in the United States in the 1970s,
but those plants have been shut down because of
operating and financial problems. Some
gasification plants were built and operated in
Europe in the early 1980s. Los Angeles had a
system designed to use dried sewage sludge. The
gas was burned to drive a 10 megawatt steam
turbine-generator.
Environmental Permitting Issues for
Pyrolysis and Thermal Gasification Facilities
Thermal gasification facilities share some of
the same environmental problems associated with
mass burn incinerators including:
| Meeting air quality requirements Classification
of the ash as a hazardous material
Disposal of ash and other by-products
Possible conflict with adjacent land
uses
Disturbances to biological resources
Use of large amounts of water for
cooling purposes (if wet cooling towers
are used)
Transportation impacts from numerous
truck trips from the refuse source to the
facility
Health, safety, odor, and traffic
impacts
Possible hazardous materials leakage
Conflicts between using MSW for
electricity generation and waste
reduction techniques, composting, and
recycling
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According to the California
Energy Commission, it is not economical to
transport the gas produced by such facilities
over long distances, so power generation
equipment must be sited near gasification
facilities. The gas produced by pyrolysis or
thermal gasification can be scrubbed to remove
contaminants prior to combustion, so air
emissions may be easier to control than with mass
burn incinerators. However, scrubbing the gas at
high temperature is currently under research and
the technology has yet to be demonstrated on a
large scale. And the gas from pyrolysis and
gasification of MSW may contain hazardous organic
compounds that are difficult to remove. Finally,
the organic material for gasification which
comprises 61% of MSW—
paper, cardboard, wood, yard waste, and food
scraps—
is also the fraction most valuable for
composting.
more info:
April 1, 2002: BREDL releases
report: Waste Gasification
- impacts on the environment and public health (.pdf) | BREDL
report: Incineration and
Gasification: A Toxic Comparison
(posted 4/12/02)(.pdf)
check these sites:
California Energy Commission
http://www.energy.ca.gov/development/biomass/msw.html
National Renewable Energy
Laboratory
http://rredc.nrel.gov/biomass/doe/nrel/waste_data/msw/msw_data_sum/options.html
Blue Ridge Environmental Defense League
http://www.BREDL.org
BLUE RIDGE ENVIRONMENTAL DEFENSE LEAGUE
www.BREDL.org
~ PO Box 88 Glendale Springs, North Carolina
28629 ~ Phone (336) 982-2691 ~ Fax (336) 982-2954
~ BREDL@skybest.com
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