Method and apparatus for concentrating methane in anaerobic digestive fermentation gas

摘要

A methane concentration method for removing carbonic acid gas from an anaerobic digestive fermentation gas and concentrating and recovering methane by using an apparatus (10) including a pre-stage module (11) with a membrane (11a) and a post-stage module (12) with a membrane (12a) connected in series. According to this method, an anaerobic digestive fermentation gas is supplied under pressure to the pre-stage module (11) through a compressor (14). The gas passing through the pre-stage module (11) is discharged by a vacuum pump (16), while the gas remaining in the pre-stage module is supplied by a residual pressure to the post-stage module (12). The gas passing through the post-stage module is returned to the pre-stage module (11) through a recycling pipe (18), and the gas remaining in the post-stage module (12) is recovered as concentrated methane gas having a concentration of at least 90 % at a methane yield of at least 85 %.