Simulation and Optimization of Urban Small-Scale Centralized Bio-Gas Purification Process Based on Methyl Diethanolamine Absorbent

This study addresses the energy-intensive challenge of small-scale biogas upgrading by optimizing a chemical absorption process employing methyl diethanolamine (MDEA). Focusing on a typical distributed application of 300 Nm³/d, we developed an integrated simulation-optimization framework using Aspen HYSYS 14.0 to systematically evaluate the effects of critical operating parameters—absorption pressure, MDEA concentration, flow rate, temperature, number of trays, and reboiler duty—on methane purity and energy consumption. The key finding is the identification of an optimal parameter set: absorption pressure of 1200 kPa, MDEA concentration of 20 mol%, lean flow rate of 2.5 kmol/h, temperature of 298.15 K, 20 absorber trays, 10 regenerator trays, and a reboiler duty of 4 kW, which enabled the product gas to achieve a high CH₄ concentration of 97 mol%, compliant with pipeline standards. A detailed energy consumption analysis revealed that the reboiler is the most energy-intensive unit, accounting for 75.40% of the total 5.29 kW energy consumption, followed by the gas compressor (23.38%). The specific energy consumption for CH₄ recovery and the Energy Consumption Index (ECI) were quantified at 0.8852 kWh/kg CH₄ and 6.82, respectively. This work provides a validated optimization strategy and critical energy breakdown, offering practical guidance for enhancing the technical and economic viability of small-scale, centralized biogas purification systems.