Optimization of pilot-scale 3-stage membrane process using asymmetric polysulfone hollow fiber membranes for production of high-purity CH4 and CO2 from crude biogas

Abstract

In this work, we report on the design, construction and optimization of a pilot scale 3-stage membrane plant operated by a single compressor for production of high-purity CH4 and CO2 from crude biogas. In our previous works, we developed asymmetric polysulfone hollow fiber membranes with high CO2/CH4 separation properties and a numerical simulation program for a 3-stage membrane process for biogas separation. Herein, utilizing a pure gas permeation test, we report the effects of feed pressure and temperature on gas separation properties of the developed membrane modules. We also report the effects of various operating conditions on CH4 purity and recovery at the retentate, which were investigated using mixed gases as a function of stage-cut. Using a simulation program and the gas permeation data, we designed and constructed a 3-stage membrane plant that can treat 100 Nm3/h of crude biogas (65–75 vol% CH4, balanced CO2). It was confirmed that, in the constructed 3-stage pilot plant, the final purity and recovery ratios for CH4 and CO2 of the 3-stage membrane plant were significantly influenced by the operation conditions. Under optimized operation conditions, the 3-stage membrane plant exhibited outstanding biogas separation performance; high CH4 purity and good recovery (98.4% and 98.7%, respectively) were observed, together with high CO2 purity and recovery (97.2% and 97.0%, respectively). This study demonstrates the commercial applicability of the 3-stage membrane pilot plant using polysulfone hollow fiber membranes for simultaneous production of high purity CH4 and CO2 from crude biogas.