Effect of biogas-to-biomethane upgrading on power efficiency and emissions reduction in wastewater treatment plants

Abstract

This study investigates the feasibility of transitioning from biogas to biomethane as a fuel source for power generation in wastewater treatment plants. Using real operational data from the As-Samra Wastewater Treatment Plant in Jordan, the biogas upgrading process was modeled using water scrubbing and methanation techniques. Simulations were performed with Aspen Plus®, TRNSYS, and MATLAB® to analyze the biogas upgrading process, generator performance, and emissions. The results revealed that optimizing water flow rates and feed pressure during scrubbing enhanced methane purity to over 80% at the scrubbing stage, prior to the methanation step. After catalytic methanation, the final biomethane purity exceeded 90%. However, increasing the water flow temperature negatively affected the methane concentration in the produced biomethane, necessitating greater hydrogen addition during the methanation stage. Key operational parameters, such as reactor temperature and pressure, were also analyzed, achieving maximum methane recovery of 2500 kg/h at 15 bar and 350 °C. Replacing biogas with biomethane in generators increased power output from 5 MW to 7.9 MW due to biomethane’s higher calorific value, which led to a 50% increase in the heat release rate. Emissions analysis showed a 55% reduction in CO 2 mole fraction (from 9.5% to 4.2%), reflecting the lower CO 2 content in the upgraded fuel compared to raw biogas. • Transitioning from biogas to biomethane enhances power generation efficiency. • Water scrubbing and methanation improve methane percentage and recovery rates. • Biomethane use increases generator output from 5 MW to 7.9 MW. • Biomethane reduces the mole fraction of biogenic CO 2 per unit of energy by 55%. • Optimizing reactor conditions maximizes methane recovery and system performance.