WERF: COMPARISON OF FULL-SCALE BIOGAS ENERGY RECOVERY ALTERNATIVES

In this study, technical aspects of biogas pretreatment and energy conversion at wastewater treatment plants were examined. Data were compiled from survey results, literature data and industry professionals. The efficiencies of various gas pretreatment technologies and a gas treatment train schematic are presented. The energy conversion efficiencies, maximum contamination limits, and the minimum biogas required to use each energy conversion technology are also presented.The potential energy recovered is a function of the efficiencies of the energy conversion technology(s), natural gas supplementation (if applicable), biogas production rate and distribution of fuel (biogas and natural gas) to the energy conversion technologies, which may vary seasonally. Model plants were used to predict energy recovery potential with respect to plant energy consumption, for different plant sizes. Plant size was found to have little impact on energy consumption and biogas production on a flow basis. A medium sized (100,000 m3/day) model plant was selected for close examination of energy recovery potential. All cogeneration technologies were predicted to produce at least one-third of the plant electricity demands. Using gas engines for mechanical direct drive versus electricity production resulted in higher energy efficiency but there may be trade-offs of practicality. All technologies except steam turbines and molten carbonate fuel cells were predicted to produce enough heat for summer digester heating. Plants using cogeneration technologies likely require a boiler fueled with natural gas to supplement winter heating.