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.
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.