Evaluation of systems for purification of fuel gas from anaerobic digestion. Engineering report

Abstract

Fuel gas obtained from the anaerobic digestion of waste materials usually needs to be treated before being transmitted in existing pipeline systems. The purification scheme involves the removal of carbon dioxide, hydrogen sulfide, and moisture from the digester gas to meet pipeline specifications. Gas treatment systems for the handling of 0.1, 1.0, and 3.0 MM Scfd of raw feed gas and product delivery pressures of 125 and 1000 psia were considered in this study. From the results of an economic and technical analysis of these systems, physical absorption systems, particularly water scrubbing, were found to be the most economical system for the treatment of digester gas with the flow streams considered. The Fluor Solvent process was economically comparable with the water scrubbing process for high pressure applications, but the value presented had a large uncertainty. The commercial chemical absorption systems were less economical due to high heat requirements for solvent regeneration. Among the chemical absorption processes, the hot potassium systems were found to be more economical than the amine system. The molecular sieve adsorption process was economically similar to the chemical absorption process. The GE membrane separation process was economically comparable for both high and low pressure apllications, but thismore » system has not been evaluated in real-life conditions. Since no kinetic and equilibrium data were available for the phosphate buffer system, estimates had to be assumed. Using what were believed to be very conservative estimates, this chemical absorption process was found to be economically competitive with the water scrubbing process for treating gas with a delivery pressure of 125 psia.The cost analyses in this study were based on the assumption of no recovery of the CO/sub 2/ by-product. It was found that credits for the recovery of the CO/sub 2/ could be significant.« less