Techno-economic analysis of biogas upgrading via amine scrubber, carbon capture and ex-situ methanation

Abstract

Biogas upgraded to biomethane can provide a renewable gaseous transport fuel and is one of the proposed solutions in meeting the renewable energy supply in transport targets set under the EU Renewable Energy Directive. The upgrading process for biogas involves the removal of CO2. Amine scrubbing is one traditional method of upgrading that is applied due to its low methane slippage and its capability to provide a high purity renewable methane product. However, new technologies such as power to gas (P2G) can also upgrade biogas through biological methanation by combining the CO2 in biogas with H2 to produce renewable methane. The H2 for P2G can be produced through electrolysis of renewable electricity. Through simulation software – SuperPro Designer, the economics of different pathways for upgrading biogas from a grass silage and slurry fed digester are analysed and compared in this paper. Three scenarios were investigated: biogas upgrading through amine scrubbing (scenario 1); biogas upgrading through amine scrubbing with CO2 directed to ex-situ biological methanation (scenario 2) and biogas upgrading through ex-situ biological methanation only (scenario 3). The results show that at a net present value of zero, the minimum selling price (MSP) per m3 of renewable methane for scenario 1, 2 and 3 is €0.76; €1.50 and €1.43, respectively (with an electricity price to produce H2 of €0.10/kWh and a grass silage production cost of €27/t). The electricity price has a significant effect on the cost of renewable methane in both scenarios 2 and 3. The MSP reduces to €1.09 and €1.00 per m3 of renewable methane, respectively for scenarios 2 and 3, if the electricity price is reduced to €0.05/kWh. Since the renewable methane MSP from scenario 2 is higher than scenario 3, it is suggested that direct biogas injection to the methanation reactor is financially more attractive than capturing CO2 from biogas and feeding it to the methanation step. The MSP of renewable methane from both scenarios 2 and 3 are significantly higher than that of scenario 1. However, when considering climate change mitigation, balancing of the electricity network and storage of surplus electricity, utilising P2G can offset some of these costs. The cost of H2 is a significant factor in determining the cost of renewable methane.