Design and scale-up of an oxidative scrubbing process for the selective removal of hydrogen sulfide from biogas

Abstract

Reliable and selective removal of hydrogen sulfide (H2S) is an essential part of the biogas upgrading procedure in order to obtain a marketable and competitive natural gas substitute for flexible utilization. A promising biogas desulfurization technology has to ensure high separation efficiency regardless of process conditions or H2S load without the use or production of toxic or ecologically harmful substances. Alkaline oxidative scrubbing is an interesting alternative to existing desulfurization technologies and is investigated in this work. In experiments on a stirred tank reactor and a continuous scrubbing column in laboratory-scale, H2S was absorbed from a gas stream containing large amounts of carbon dioxide (CO2) into an aqueous solution prepared from sodium hydroxide (NaOH), sodium bicarbonate (NaHCO3) and hydrogen peroxide (H2O2). The influence of pH, redox potential and solution aging on the absorption efficiency and the consumption of chemicals was investigated. Because of the irreversible oxidation reactions of dissolved H2S with H2O2, high H2S removal efficiencies were achieved while the CO2 absorption was kept low. At an existing biogas upgrading plant an industrial-scale pilot scrubber was constructed, which efficiently desulfurizes 180m3/h of raw biogas with an average removal efficiency of 97%, even at relatively high and strongly fluctuating H2S contents in the crude gas.