A technical and environmental analysis of carbon capture technologies applied to biogas: A simulation approach
Abstract
The conversion of biogas into biomethane and CO2 offers a potential solution for climate mitigation, avoiding the use of fossil carbon. While previous studies compared various carbon capture (CC) technologies for biogas upgrading, this research specifically addresses the co-production of biomethane and CO2 as high purity co-products. This work simulates, validates with literature and onsite data, and compares four CC technologies (Chemical Absorption (CA), Membrane Separation (MS), Cryogenic Separation (CS), and High-Pressure Water Scrubbing (HPWS)) at different scales, considering both technological and environmental impacts evaluated through the Life Cycle Assessment (LCA) method. ProSimPlus (R) software was employed to conduct process simulations, having as target biomethane for grid injection (> 96 % mol) and liquid CO2 (purity as high as possible). The analysis used data from a medium-scale biogas site (365.24 Nm(3)/h). The considered criteria were biomethane and CO2 purity and recovery rates, energy consumption, and environmental impacts. The comparison showed that all studied technologies met these targets, with CA technology demonstrating the highest purity and recovery rate (higher than 98 %), but with the highest energy consumption (electricity 0.8 kWh/Nm(3) biogas and heat 0.5 kWh/Nm(3) biogas). MS technology exhibited similar purity and recovery rates with significantly lower energy consumption (electricity about 0.2 kWh/Nm(3) biogas) than the other alternatives. Moreover, MS technology demonstrated the best environmental performance, with a global warming impact (GWP100) of 1.09 kg CO2-eq, outperforming CA, CS, and HPWS, which recorded values of 1.42 kg CO2-eq, 1.13 kg CO2-eq, and 1.12 kg CO2-eq respectively, impacts expressed per 1 kg liquid CO2. Furthermore, MS outperformed the other technologies for all 18 impact categories calculated with ReCiPe midpoint method. For example, MS demonstrated the lowest water consumption potential, freshwater ecotoxicity potential or photochemical oxidant formation potential-humans (1.94 10(-3) m(3), 3.15 10(-2) kg 1,4-DCB-eq, 6.64 10(-5) kg NOx-eq respectively) while CA the highest values for the same impact categories (6.27 10(-3) m(3), 7.62 10(-2) kg 1,4-DCB-eq, 5.4 10(-4) kg NOx-eq, respectively). The difference between the impact results of the four technologies is highly dependent on the used electricity mix: more carbonated is the electricity mix, more the difference between the four technologies is enhanced.
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