Design and optimization of membrane-based system for bio-methane purification
Xuehua Ruan · 2014
The production of compressed natural gas(CNG) from anaerobic fermentation gas is an important way for large scale use of biomass resources. A discrete simulation model for hollow fiber membrane is established by the finite element method in the process software UniSim Design, which is suitable for membrane separation with high permeation stage cut to purify bio-methane. The key operation condition, membrane feed pressure, which affects membrane process capacity, methane recovery ratio and CNG specific energy consumption, is studied by simulating the single-stage separation process of polyimide membranes. In this system, process capacity and methane recovery ratio are improved by increasing membrane feed pressure, but the lowest specific energy consumption is 0.46 kW·h·m?3 at membrane feed pressure of 2.70 MPa. After analyzing the change of methane content in permeate, a single-stage two-step membrane process is developed, with the advantages of compact process structure, low equipment investment, high methane recovery ratio and high production profit. For processing 1000 m3·h?1 feedstock, the methane recovery ratio is higher than 95%, with 500 m3·h?1 CNG yielded. The overall investment is 3.8×106 CNY, annual operation and depreciation cost is 1.5×106 CNY, and the annual gross economic profit can be 2.5×106 CNY at least.