Abstract

Biogas upgrading aims to increase the methane concentration in biogas by removing carbon dioxide. Upgraded biogas can then be used as a renewable energy resource. Among the technologies used for biogas upgrading, High Pressure Water Scrubbing (HPWS) is one of the most widespread. HPWS is identified as fulfilling all the requirements for farm-scale anaerobic digesters, presenting several levers to reduce operational and installation costs. One possible remedy is to optimize operating parameters to reach targeted gas specifications, without applying excessive treatment or energy consumption. The purpose of this study is to develop an efficient modeling tool that can predict methane purity and its recovery for different operating conditions of gas and liquid. This original model integrates the decrease of gas flow along the packing height and the concomitant absorption of carbon dioxide and methane. The model is based on mass transfer and hydrodynamics to explain and anticipate the performance of HPWS in order to facilitate its implementation on the field. Model results retrieved from a homemade environment on Excel are compared to those of experiments conducted on a farm-scale biogas upgrading plant and show very good agreement. The model demonstrates great adaptability regarding variations of parameters. It can thus be used to anticipate HPWS performance and to optimize running parameters in order to reach targeted purities while making energy consumption more flexible. Water regeneration is identified as the key parameter for compliance with gas injection standards, achieving a purity over 97% and a recovery ratio of 93% at a desorption pressure of 0.2 bar. Results highlight that a rate-based model giving access to molar fraction variation along the column is crucial to adjust operating parameters in order to reach optimal economic and environmental performances. More accurate operating conditions could be the key to lowering costs of production and attaining financial viability for biogas upgrading at farm scale.

https://www.sciencedirect.com/science/article/abs/pii/S0306261922002082