Improving high-pressure water scrubbing through process integration and solvent selection for biogas upgrading

Biogas plays a vital role in many renewable and sustainable energy strategies, where CO2 removal is required to produce biomethane (i.e., biogas upgrading). New ideas and technologies have been proposed to improve the process efficiency of biogas upgrading with liquid absorbents, and ionic liquids have been identified as promising candidates. Meanwhile, there is an urgent need to effectively utilize low-quality waste heat in industry. In this study, two strategies (i.e., waste heat integration and desorption unit modification) were proposed and compared with the original high-pressure water scrubbing; in addition, the effects of the temperatures of the heat source and solvents on the energy usage and cost were further investigated. The results showed that the total cost of the process integrated with waste heat recovery decreased by 6.2% compared with the original high-pressure water scrubbing, and the higher temperature of the waste heat source corresponded to a lower cost. The comparison of different solvents further confirmed that ionic liquid-based solvents were promising, with a potential cost reduction of 24.7%; the properties of the solvent, such as the CO2 absorption capacity, selectivity, and viscosity had significant influences on the total cost, and a new and single index comparative absorption factor was proposed to reflect the overall impact of these properties on the cost.