Biogas heating value

CHP plant Air feed 15% excess Electric efficiency 0.42 Heat efficiency 0.38 Biogas heating value 33.3 MJ kg" 18.52% in CHP flue gas (from mass balance)... 

The initial biogas recovered is an MHV gas and is often upgraded to high heat value (HHV) gas when used for blending with natural gas suppHes. The aimual production of HHV gas ia 1987, produced by 11 HHV gasification facihties, was 116 x 10 m of pipehne-quaUty gas, ie, 0.004 EJ (121). This is an iacrease from the 1980 production of 11.3 X 10 m . Another 38 landfill gas recovery plants produced an estimated 218 x 10 m of MHV gas, ie, 0.005 EJ. Additions to production can be expected because of landfill recovery sites that have been identified as suitable for methane recovery. In 1988, there were 51 sites ia preliminary evaluation and 42 sites were proposed as potential sites (121). 

Digestion may continue for about 10 days to a few weeks. The bacterial action generates heat but in cold climates additional heat is normally required to maintain a process temperature of about 35°C. A digester can produce 400 cubic meters of biogas with a methane content of 50% to 75% for each dry ton of input. This is about two thirds of the fuel energy of the original fuelstock. The effluent which remains when digestion is complete also has value as a fertilizer. 

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