What is Landfill Gas
As garbage decomposes, microbes break down material into molecules. Some of these molecules are in liquid form and are collected in the leachate system. Other molecules are gaseous and are collected by the gas to energy system. The landfill gas is approximately half methane and half carbon dioxide, with other trace elements. This gas is not only odorous, but it contains greenhouse gasses. At the Short Mountain Landfill, the landfill gas
is collected and utilized to produce electricity.
How the Process Works
The landfill gas is collected by placing horizontal wells in the garbage as the waste mass is constructed. (See photo left) These wells are comprised of long HDPE perforated pipes connected to a well head. Each well feeds into a main header pipe that draws the gas to the power plant under a vacuum. The gas is then used to fuel combustion engines in the plant which turn generators and produce electricity. The wells are placed in vertical layers every 30’ and the wells are spaced 150’ horizontally. This configuration is designed to provide coverage over the entire waste mass to collect as much gas as possible. If areas of landfilled garbage do not get adequate coverage from these horizontal wells, vertical gas wells can be drilled into the garbage from the top.
The Gas to Energy Plant
The Landfill Gas to Energy Plant (shown in photo) is owned and operated by the Emerald People Utility District (EPUD). The plant contains four large combustion engines that burn landfill gas for producing electricity. EPUD and Lane County work together to increase the gas collection by improvements in operations and by constructing final covers over completed areas of the landfill. Currently, enough gas is collected to power over 1200 homes. The electricity generated at Short Mountain Landfill is fed into the EPUD power grid. On average, 2.5 MW, or 2,500,000 Watts is created each year. Remember that a light bulb is about 60 Watts! Many landfills have flares in addition to gas to energy facilities which burn excess gas. Short Mountain is fortunate enough to have the capacity to utilize 100% of the gas collected.