Biogas Upgrading by a Combination of Innovative Treatments Based on Carbonation of Waste Incineration Residues

This paper reports the results of experimental tests carried out in a biogas upgrading pilot plant installed in a landfill site based on an innovative process for bio- methane production that allows to permanently store the separated CO2 and that makes use of waste incineration residues. The proposed upgrading method is based on the idea of coupling two processes developed in a previous project. The first process consists in the direct removal of carbon dioxide from the biogas through direct carbonation of bottom ash, while the second in CO2 absorption with alkali solutions that are regenerated through contact with air pollution control residues. The results of the experi- mental tests showed that the process is able to effectively produce biomethane (i.e. a gas with a CH4 content [96 % vol.). The advantages of applying the combined process instead of one of the two techniques in terms of the decrease of residues requirement was assessed. For the combined process the specific requirements of residues resulted, respectively of 84 kg of bottom ash and 0.6 kg of air pollution control residues per each Nm3 of biomethane produced, allowing to achieve almost twofold and a 20-fold reduction of the requirements, respectively, if separate processes were applied. Economic assessment indicated that the combined process may prove to be less costly with respect to direct carbonation if the treated BA cannot be reused.