Comparison of Conventional Biogas Upgrading Route and a Direct Methanation System

Traditional biogas upgrading systems focus on producing biomethane by means of carbon dioxide removal. Nevertheless, recent advancements have highlighted the potential for valorizing biogas CO₂ content by methanation without the need for its prior separation. This study compares the performance of a direct methanation system purposely designed to produce high-purity methane suitable for direct injection into a natural gas grid system to those of widely used conventional upgrading technologies, including water scrubbing, chemical absorption with monoethanolamine, membrane separation, and pressure swing adsorption. To this end, detailed mathematical models of the proposed system and conventional biogas upgrading units were developed using the commercial software AspenONE. The system’s performance is compared in terms of methane loss and purity, avoided carbon dioxide emissions, energy efficiency, and levelized cost of biomethane. Biogas direct methanation compares to conventional technologies regarding methane purity (96.96%) and energy efficiency (88%), surpassing them in terms of methane recovery (100%). From an economic perspective, direct methanation exhibited a slightly higher levelized cost of biomethane (0.58 €/Nm³) than conventional upgrading techniques, which average around 0.51 €/Nm³. As long as excess electric energy from renewable sources is used, biogas upgrading by direct methanation can be considered a technical and economical alternative to conventional upgrading routes.