USE OF AN INTERNALLY STAGED PERMEATOR IN THE ENRICHMENT OF METHANE FROM BIOGAS

An internally staged membrane permeator of a bench scale type has been employed in a study of methane enrichment from biogas. The permeator contains two membranes of the same type; therefore, the overall driving force between feed and permeate side in the permeator is divided into two parts through these two membranes. Theoretical studies were conducted using mathematical models based on perfect mixing and cocurrent flow patterns. The effects of operating variables such as feed pressure, overall stage cut and flow patterns in the permeator on the extent of separation and membrane area requirement have been examined. The observed experimental results from bench scale studies agree well with theoretical predictions based on perfect mixing model. Simulation results show that the optimal performance of the permeator can be obtained by properly selecting the stage cut parameter, E(phi) and stagepressure parameter, E(r), which are functions of individual stage cut and intermediate pressure respectively. A comparative study between the internally staged permeator and a conventional single-stage permeator indicates that, under the same energy consumption, the former offers higher product recovery, but requires much larger membrane area.