CO2/CH4 separation by hot potassium carbonate absorption for biogas upgrading

In biogas upgrading to biomethane, the release of CO off-gas into the atmosphere is generally regarded as a carbon-neutral emission, but a significant loss of CH can occur in this step: considering the global warming potential of this latter compound, methane slip can worsen or even nullify the CO savings associated to biomethane. This study investigates a novel approach for biogas upgrading to biomethane, aimed at reducing the methane loss. A plant based on hot potassium carbonate was fed with 150-200 Nm h of biogas from municipal waste. CO is removed in a KCO absorption column, with negligible CH absorption. An assessment of biomethane quality was performed to check its compliance with recent National and European standard specifications. Results show that a methane slip below 0.1% can be achieved with this technology, thus significantly reducing the greenhouse gas emissions associated to biomethane industry. This leads to a lower capital expenditure because no off-gas post-treatment is required. Heat and electricity consumption were monitored, and operational expense resulted to be lower than membrane separation in the specific case study, by applying life cycle cost (LCC) methodology.