Environmental Engineering Reference
In-Depth Information
concluded that the existing data from several landfills did not provide evidence showing
significant dioxin formation during landfill gas combustion. Because of the potential imminent
health threat from other components of landfill gas, landfill gas destruction in a properly
designed and operated control device, such as a flare or energy recovery unit, is preferable to
uncontrolled release of landfill gas. Scientists continue to review new information on by-
product emissions from landfill gas control devices as it becomes available.
•
Boilers
Boilers
are among the cheapest options. They produce thermal energy or heat, not
electricity. Boilers are generally less sensitive to landfill gas contaminants and therefore
require fewer cleanups than other alternatives. Boilers have the lowest NO
x
and carbon
monoxide emissions of the combustion technologies. Landfill gas use in boilers brings in the
issue of piping the gas to local industries. While boilers themselves may not require much
cleanup of the gas, the pipelines do require some cleanup, since corrosive compounds in the
gas (particularly the acids and hydrogen sulfide -- H
2
S) can damage the pipelines. Among the
concerns with this option are the integrity of the pipeline, liability issues, and the economic
support of neighboring polluting industries which might use the gas.
•
Internal Combustion Engines
Internal combustion engines
are the dirtiest technology for burning landfill gas. They
emit the most carbon monoxide and NO
x
and they may be the largest dioxin source of the
available technologies.
•
Gas Turbines
Gas turbines
are somewhere in the middle in terms of carbon monoxide and NO
x
emissions. There isn't enough data on dioxin emissions from landfill gas turbines to provide
an extensive comparison.
•
Fuel Cells
Fuel cells
are the most expensive technology, and they are still largely experimental. EPA
describes fuel cells as "potentially one of the cleanest energy conversion technologies
available." In order not to poison the fuel cells, halogenated contaminants must first be
removed and destroyed, for example by pyrolysis.
•
Conversion of Methane to Methyl Alchol
One option is to convert the methane recovered from landfills into
methyl alcohol
or
methanol. Other novel ideas include converting the carbon dioxide in landfill
gas to dry ice
for sale to industry.
2. Non-combustion technologies
Non-combustion technologies were developed in the 1990s as an alternative to
combustion, which produces compounds that contribute to smog, including nitrogen oxides,
sulfur oxides, carbon monoxide, and particulate matter. Non combustion technologies fall into
two groups: energy recovery technologies and gas-to-product conversion technologies.
Regardless of which non combustion technology is used, the landfill gas must first undergo
