The use of an industrial by-product as a sorbent to remove CO2 and H2S from biogas

• Evidences of biogas purification for bio-CNG using industrials by-products were shown.
• Steel-slag were tested and shown good removal of H2S and CO2.
• Moistening was the most influencing parameter on the removal performances.

Raw biogas, produced by anaerobic digestion of organic matter, is a methane-rich combustible gas. The CH4 content can be upgraded to reach the natural gas composition for vehicle fuel use (bio-CNG) or injection into the gas grid. This upgrading is performed by CO2 removal and pollutants treatment (H2S, water, etc.). The accelerated carbonation on BOF slag, a by-product from the steel industry containing calcium and iron oxides, was studied as a solution. The purpose of this work was to study the potential of slags to remove simultaneously CO2 with CaO (carbonation) and H2S with Fe2O3 (sulfuration) under atmospheric conditions. Firstly, batch experiments have confirmed the reactivity among CO2, H2S and slag. Removal capacities of 63 gCO2/kgBOF and 140 gH2S/kgBOF were estimated. The effect of the amount of water in the mix biogas/slag was studied on treatment performances, and an optimal L/S range between 0.05 and 0.2 Lwater/kgBOF was found. Secondly a field scale column experiment has been performed to treat the biogas of a pilot digester. This test under dynamic conditions using a BOF slags filter has given promising results (73 gCO2/kgBOF).