Electricity, methane and liquid carbon dioxide production from landfill gas

Abstract

Landfill gas, which has a typical composition of 40–60% methane, 40–50% carbon dioxide, and a wide range of impurities, has historically been recovered solely for its heating value. After only minor impurity removal, landfill gas has been used as medium Btu industrial fuel or to generate electricity; after significant impurity and carbon dioxide removal, landfill gas has been used as a source of pipeline quality methane. For both cases, the value of the substantial amount of contained carbon dioxide has not been realized. This has been due to the impurities which present a significant obstacle to the economic production of merchant grade carbon dioxide. This paper presents two processes 1 1 Patent pending, The BOC Group, Inc. which make use of an oxygen fed combustion step to reduce both the quantity and variety of impurities which must be removed to meet carbon dioxide product specifications. The two processes produce carbon dioxide and electricity or carbon dioxide and pipeline quality methane, respectively. In both oxygen based coproduction processes, the combustion step is integrated into the overall process to maximize energy efficiency. The two processes are described and anticipated net liquid carbon dioxide manufacturing costs are presented.