Techno-economic Analysis of Hybrid Processes for Biogas Upgrading

Biogas upgrading is one piece in the framework of future energy supply. Commonly absorption and adsorption technology is applied for biogas upgrading where CO2, H2S, and water vapor have to be removed from CH4. Gas permeation technology offers an interesting alternative to conventional upgrading techniques. Combining gas permeation membranes and conventional separation equipment in membrane hybrid processes merges the advantages of both technologies. Hence, we analyze seven different membrane hybrid processes for biogas upgrading. A single gas permeation stage is combined with pressurized water scrubbing, amine absorption, cryogenic separation, and a particular process in which the permeate of the gas permeation stage drives a gas engine. Furthermore, we compare the specific upgrading costs to an individual three stage membrane process as well as to conventional separation processes. Simulation studies were performed in Aspen Plus to rigorously model the different hybrid process configurations. A full cost model determines operational and investment costs. The processes combining membranes and pressurized water scrubbing outperform the conventional pressurzied water scrubbing process in terms of specific upgrading costs. The application of a membrane remarkably reduces the upgrading costs for cryogenic separation. While the conventional process is far from being profitable, the hybrid process can compete with established biogas upgrading techniques. The three stage gas permeation process and both hybrid processes involving the pressurized water scrubbing technology have the lowest upgrading costs. Ultimately, it is important to note, that the results obtained in this study rely on the parameters set here. A site were heat is provided inexpensively and low grid injection pressures are required might favor the application of amine absorption processes.