|It is important to distinguish that landfill gas
and natural gas or methane gas are different. Landfill gas only contains
about 50% of methane when natural gas contains approximately 80-99% methane.
The remaining composition is mostly carbon dioxide, then small amounts of
nitrogen and oxygen. In the gases EPA has found 94 different NMOC (non-methane
organic compounds.) These include chemicals like benzene, toluene,
chloroform, vinyl chloride, carbon tetrachloride, and 1,1,1 trichloroethane.
At least 41 of these are halogenated compounds. Halogenated chemicals
(chemicals containing halogens - typically chlorine, fluorine, or bromine)
combust in the presence of hydrocarbons and recombine into highly toxic compounds
such as dioxins and furans, the most toxic chemicals ever studied. Burning
at high temperatures doesn't solve the problem as dioxins are formed at low
temperatures and can be formed as the gases are cooling down after the combustion
To get rid of these gases several processes can be taken. It can be flared, put through a boiler to makes heat, or to produce electricity it can be put through an internal combustion engine, a gas turbine, or a fuel cell. The methane can also be converted to methyl alcohol. Lastly, one can clean it up enough to pipe it to other industries or into the natural gas lines .
||Shrouded flares are enclosed in
an isolated cylindrical shroud which can be anywhere from 16 to 60 feet
tall. Here the dioxins can be regulated.
||Candle flares are open to the air
and can not be monitored for dioxins or other toxic emissions. Shrouded
ones can increase dioxins by providing a constant temperature in the range
that they form.
||Cheap, easy to clean because of
their low sensitivity to landfill gas. Produce heat not electricity. Low
NO and carbon monoxide emissions
||Corrosive compounds in the gas (acids
and hydrogen sulfide) damages the pipelines.
||Dirtiest; Emit the most carbon monoxide
|| Filtering process that is very
||Expensive; And is self defeating
||Converting the carbon dioxide into
dry ice can be economically profitable.
||Converting methane to methyl alcohol
is self defeating because the halogenated filtered organics are sent to a
|| Requires a lot of cleaning and
filtering. It may degrade the quality by actually adding contaminants to
TYPICAL CONSTITUENTS AND COMPOUNDS FOUND IN LANDFILL GAS
Typical Constituents Found in Municipal Solid Waste Landfill Gas
* Exact percentage distribution will vary with the age of the landfill.
Typical Concentrations of Some Trace Compounds Found in Landfill Gas
SOURCE: G. Tchobanoglous, H. Theisen and S. Vigil, "Integrated Solid Waste Management, Engineering Principles and Management Issues," McGraw-Hill, New York, 1993. Shown here as reproduced in J.Wilcos, Ph.D., and W.Clister, "Waiting is Over: Landfills Have Clean Air Act Rules," Solid Waste Technologies, March/April 1996.
Provided by Dan Knapp of Urban Ore, Berkley, California