The thermochemical route comprises biomass

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Unformatted text preview: ble, fruit, and garden waste, organic wet fraction of municipal solid wastes, manure, and sewage). The thermochemical route comprises biomass gasification in supercritical water, co-production of Fischer-Tropsch-SNG from biomass, and biomass gasification with downstream methanation. While anaerobic digestion and supercritical gasification processes are applied for conversion of wet biomass (70-95 wt.% water), the gasification / methanation processes are applied for conversion of relatively dry biomass streams (10-15 wt.% water). ECN-RX--04-085 4 ANAEROBIC DIGESTION Anaerobic digestion is a biological process in which organic wastes, in absence of air (anaerobic), are converted to biogas, i.e. a mixture of methane (55-75 vol.%) and carbon dioxide (25-45 vol.%). During anaerobic digestion, typically 30-60% of the solid input is converted to biogas, The co-products consist of an undigested residue and various water-soluble substances. Depending on the digestion system (wet or dry), the average residence time is between 10 days and 4 weeks. A simplified stoichiometric reaction for anaerobic digestion of biomass is: C6H10O5 + H2O → 3 CH4 + 3 CO2 Anaerobic digestion is a proven technology, generally available on a commercial basis, and being applied for small-scale decentralised treatment of “wet” organic wastes at their origin. The produced biogas, either raw or usually after some enrichment in CH4, can be used to generate heat and power through prime movers, at capacities up to 10 MWe, with excess power fed into the grid. In a gas engine, electric efficiencies of 30-35% (on LHV basis), and total efficiencies of 85% can be achieved. Higher electric efficiencies of up to 50% might be reached by using fuel cell systems instead of gas engines. Generally, the produced heat in a prime mover can be used optimally within the digestion process, and for other purposes such as space heating. The simultaneous demand for heat and power is the crucial factor for an efficient use of biogas in co-generation. Otherwise upgrading, i...
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This essay was uploaded on 03/18/2014 for the course ENG 316K taught by Professor Kruppa during the Spring '08 term at University of Texas.

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