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Landfill Gas: Overview


Landfill gas is generated by decomposing trash in landfills. Most municipal solid waste has already begun to decompose by the time it leaves a residence and can continue to decompose for 30 years or more. In order for trash to decompose, three elements must be present: heat, moisture and oxygen. As the trash decomposes and landfill gas is generated, the gas will travel to the point of least resistance within the trash, because the gas is lighter than air. Unfortunately, when a landfill does not have a gas collection system in place, the eventual point of least resistance is the atmosphere.

Landfill gas is comprised of roughly 55 percent methane, 40 percent carbon dioxide, 5 percent balance gases like nitrogen and traces of oxygen. Gases like methane and carbon dioxide are known as greenhouse gases and have the ability to deplete the ozone layer. Methane is a potent GHG and is generally recognized to be more than 21 times more potent than CO2. When captured and destroyed, much of the harmful effects are negated. When methane is utilized, the community wins. Landfills could provide up to 3 percent of the U.S. energy requirements when fully utilized. When a gas system is not in place, there are other harmful side effects that decomposing trash can have on the environment such as nuisance odors, vegetative destruction and groundwater contamination. When properly controlled, these harmful effects are mitigated.

The first step to mitigating these negative characteristics of a landfill is to install a landfill gas collection and control system. This involves the drilling of vertical wells throughout the landfill that will act as extraction points for the gas.

Next, horizontal “vacuum pipelines” connect each well into one larger “header pipeline” where all the gas will eventually travel. At the end of the header pipeline a gas collection and control skid is built.

This skid contains different components such as a blower, a condensate knockout, multiple pneumatic valves, data collection devices, a flare stack, and a computer that controls each device. The skid’s main function is to use the blower to create a vacuum on the landfill gas system to suck the gas out of the wells. The gas travels through the condensate knockout, to remove any moisture in the gas, then through various data collection devices so that the temperature and properties of the gas can be measured and then up to the “candle stick flare stack” where the gas is burned in an open flame at over 1,000 degrees Celsius. Since landfill gas burns cleanly, its harmful environmental effects can be prevented by doing this. At a later date, when the end use application is constructed, the excess gas not needed by the end user will still be burned in the flare. The pneumatic valves on the skid are used to control the volume of gas that travels to the flare and the volume that travels to the end user.

End-use applications for landfill gas are basically the same as any use for natural gas. Enerdyne has successfully used landfill gas to fuel generators, boilers and incinerators. Landfill gas can also be cleaned to the point that it is acceptable by natural gas pipeline standards and can also be used as an automotive fuel. There are less than 20 landfill gas-to-natural gas and landfill gas-to-automotive fuel applications in the world. The most common application is fueling generators.

Enerdyne brings an interesting dynamic to the table when involved in landfill gas-to-energy systems because a winning situation is created for all parties involved.