Landfill Gas

At landfill sites, the anaerobic digestion of the organic component of waste occurs naturally, but more slowly than in specially designed digesters. Landfill gas containing methane and carbon dioxide (typically in the ratio of 65%:35%) is released into the atmosphere if no controls are put in place.

 

 

To avoid the environmentally harmful effects of this, landfill gas can be collected and used as an energy source for heat and/or power. Wells are inserted into the waste to collect the gas through a series of perforated pipes. A suction pump collects the gas, which is then cleaned and used as a source of energy.

Currently, there are five landfill gas recovery facilities in operation in Ireland.

Power generation from landfill gas
 
Power generation from landfill gas
 

Facts

Almost two million tonnes of municipal solid waste (MSW) were generated in Ireland in 1998, over 90% of which was consigned to landfill. At landfill, bacteria cause the organic fraction of deposited waste to decompose, under partially anaerobic conditions, producing a biogas. This biogas consists primarily of methane and carbon dioxide in the ratio of 2:1, with small quantities of some other gases also present.

 

Landfill Gas Image

Methane is highly flammable and is one of the major greenhouse gases responsible for climatic change as it has 21 times the global warming capacity of carbon dioxide. However, landfill gas (LFG) emissions can be minimized through effective recovery systems, which harness the gas and use it as a renewable and valuable fuel. In addition to electrical power generation, LFG can also be used for combined heat and power (CHP), kiln firing and as a heating or vehicle fuel. LFG is similar to 'natural' or fossil gas and can be fed into the 'natural' gas network. Because LFG has different characteristics (calorific value and specific gravity) to 'natural' gas, burners designed for use with 'natural' gas will require some modifications prior to using LFG.

The technology used for landfill gas is mature and well established. In order to avoid any shortfalls in LFG production careful resource assessment is essential prior to establishing a recovery plant. The landfill site must be evaluated in relation to size, location, composition of waste, age and estimated tonnage. The rate of LFG production can then be calculated using computer models.

 
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