Biogas quality upgrade by simultaneous removal of CO2 and H2S in a packed column reactor

Biogas from anaerobic digestion of biological wastes is a renewable energy resource. It has been used to provide heat, shaft power and electricity. Typical biogas contains 50-65% methane (CH4), 30-45% carbon dioxide (CO2), moisture and traces of hydrogen sulphide (H2S). Presence of CO2 and H2S in biogas affects engine performance adversely. Reducing CO2 and H2S content will significantly improve quality of biogas. In this work, a method for biogas scrubbing and CH4 enrichment is presented. Chemical absorption of CO2 and H2S by aqueous solutions in a packed column was experimentally investigated. The aqueous solutions employed were sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2) and mono-ethanolamine (MEA). Liquid solvents were circulated through the column, contacting the biogas in countercurrent flow. Absorption characteristics were examined. Test results revealed that the aqueous solutions used were effective in reacting with CO2 in biogas (over 90% removal efficiency), creating CH4 enriched fuel. H2S was removed to below the detection limit. Absorption capability was transient in nature. Saturation was reached in about 50 min for Ca(OH)2, and 100 min for NaOH and MEA, respectively. With regular replacement or regeneration of used solutions, upgraded biogas can be maintained. This technique proved to be promising in upgrading biogas quality.