The Ready Reckoner or Rule of Thumb Estimate of Landfill Gas Generation
First considerations before carrying out a full yield evaluation for landfill gas utilization projects:
For a 1Mt landfill, filled over the last ten years:
• 1m3 MSW yields 5 – 10 m3/t/y in the first 10 years of emplacement (Environment Agency, 2002)
• 5 – 10 Mm3/y LFG will be generated, which equates to somewhere between 5 x 106/365/24 = 570 m3/hr (lower bound) and, 1 x 107/365/24 = 1140 m3/hr (upper bound)
Two other rules of thumb also apply:
• It takes 1Mt to run a 1MW gas engine.
• A 1MW gas engine needs 530 – 630 m3/hr (depending on its efficiency).
(Source: GasSim and PPC Permitting: Current Practice, Future Practice; Conference Proceedings, Waste 2004, Stratford-upon-Avon, UK, September 2004)
Finally, the smallest EfW schemes which are normally economically viable in the UK, with the benefit from ROCS (or ROSCS in Scotland) are usually 500kW, and based upon a 500kW gas engine. (December 2004)
(Update 2007 - with the availability now of 300kW engines and good prices paid for the power possibly including ROCs, the 500kW minimum has dropped for many sites to 300kW, using these new engines.)
However, this is ONLY a rule of thumb based upon UK MSW, and actual yields will vary greatly. Expert modelling and advice is recommended. Economic circumstances also continually vary. Smaller purpose-designed gas engines and the innovatory use of micro-turbines are among the recent and interesting developments which may reduce the minimum size of EfW schemes still further for some sites.
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