Engineering Design Considerations for Methane Fermentation of Energy Crops: Fundamental Considerations. Annual Report, Third Year, January 1-December 31, 1990.

摘要

The goal of the project was the development of the scientific and engineering basis for a cost-effective system to produce methane from energy crops. The emphasis was in two areas that provide the greatest systems cost reductions - purification of biogas to high quality methane and high conversion rates that would lead to small reactors. The two improvements in anaerobic digestion were further defined in the third and final year. Methane enhancement by recycling leachate to selectively absorb CO2 and strip it outside the digester achieved 95% methane at a reactor production rate of 1.3 v/v-d. Variables were examined to determine the most important parameters in controlling methane enhancement. Increasing alkalinity and carbon dioxides removal efficiency resulted in high methane concentrations and elevated reactor pH values. As the digester pH increased above 8.2, biomass conversion efficiency decreased significantly over the controls. The efficiency of the process could be related to the ratio of mass of alkalinity recirculated to volume of CO2 produced. Off-gas with 90% CH4 was obtained at a ratio of 10, and values above 22 resulted in 98% CH4.