Landfill Gas

Landfill gas is created during the anaerobic decomposition of organic substances in municipal solid waste (MSW) and commercial and industrial (C&I) wastes. Depending upon the landfill design and its management, as well as waste composition, compaction, moisture and several other factors, thousands of landfills are available on worldwide to collect and utilize this valuable renewable energy source for power generation. If landfill gas is allowed to escape to atmosphere, methane contained within it’s a powerful greenhouse gas, 21 times more so than carbon dioxide. Therefore, its prevention of escape to atmosphere and its utilization as a renewable fuel source is win-win situation.

Landfill Gas Collection

For a landfill restoration that prevents greenhouse gas from migrating into the atmosphere while avoiding offensive smells and smouldering fires, the gas must be continuously extracted under controlled conditions. Perforated tubes are drilled into the landfill body and interconnected by a pipework system. Using a blower, the gas is sucked from the landfill. A well-designed gas collection system will flexibly capture the gas from various spots and handful high temperatures, leachate, condensates and air content – thus ensuring a cost-efficient collection as well as stable gas quality. Several engineering companies specialise in this field and offer their services on a worldwide basis.

Landfill gas generation schematic

 

Landfill Gas Composition

Landfill gas composition and production rates are primarily affected by the waste that has been deposited in the landfill site. MSW contains 150-250 kg of organic carbon per tonne which micro-organisms convert to landfill gas via anaerobic processes. The gas formation is influenced by a number of factors such as waste composition, landfill storage height and density, air temperature, atmospheric pressure and precipitation levels. Gas production starts one to two years after the waste is deposited in the landfill and lasts 15-25 years. The continuously decreasing gas volume can be compensated by the disposal of additional waste during this period. With a calorific value of 3.5 to 5.5 kWh Nm3(35-55% methane), landfill gas constitutes a high-value fuel for gas engines that can be effectively used for power generation.

ComponentComposition (by volume)
Methane (CH4)35-55%
Carbon dioxide (CO2)30-44%
Nitrogen (N2)5-25%
Oxygen (O2)0-6%
Water vapourSaturated

Consequently, 1 million tonnes of MSW generate 1.7-2.5 million m3 of collectable methane, enough to fuel a gas engine capacity of 850-1,250 kWeproducing 6,500 to 10,000 MWh of electricity per year. That roughly corresponds to the average power demand of 1,500-2,200 EU households.

Source: http://www.clarke-energy.com/landfill-gas/