The prospects of using landfill gas (LFG) as a high-grade fuel in the immediate future, in view of environmental regulations, the Kyoto Protocols, and energy prices, are discussed. Adsorption cycles suggested in the late 1980s by Sircar and co-workers for treating LFG are reviewed: one produced CO2-free methane and the other produced both CO2-free methane and methane-free CO2. Neither of those could be used to produce pipeline quality gas from LFG, due to contaminants such as nitrogen. Two new three-stage flowsheets are discussed as a means to separate pipeline-grade methane from LFG. One is a hybrid membrane-PSA system. The other is a TSA-PSA system. The third stage of both of these systems is crucial to obtaining pipeline quality gas, i.e., a PSA unit to extract the nitrogen and other light gases from methane. A novel PSA cycle is suggested and explained in terms of: a model by which the recovery, power requirements, and adsorbent bed size can be estimated.
