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.