Process and apparatus for treating methane-containing gas

A method of processing methane-containing gas, comprising the steps of:

• a) providing a methane-containing gas mixture comprising 20-60% by volume of CO2 and at least one compound from the group of volatile organic compounds (VOC),
• where the at least one VOC is selected from the group consisting of ketones, sulfur-containing hydrocarbons and terpenes,
• where the VOC concentration in the gas mixture is 10-10 000 ppm;
• b) compressing and cooling the methane-containing gas mixture from step a);
• c) feeding the compressed, cooled methane-containing gas mixture to an absorption apparatus, where the absorption apparatus comprises a liquid, reversibly VOC-absorbing absorbent;
• d) absorbing at least a portion of the VOCs and not more than 5% by volume of the CO2 by means of the absorbent, giving a methane-containing gas mixture having reduced levels of VOCs and CO2, and an absorbent laden with VOCs and CO2;
• e) feeding the absorbent laden with VOCs and CO2 from the absorption apparatus to a desorption apparatus;
• f) feeding the methane-containing gas mixture having reduced levels of VOCs and CO2 from the absorption apparatus to a separation apparatus comprising a membrane, in which the methane-containing gas mixture having reduced levels of VOCs and CO2 is separated into a pressure-reduced, CO2-enriched gas stream and an isobaric, methane-enriched gas stream;
• g) feeding a regeneration gas stream comprising at least a portion of the CO2-enriched gas stream from step f) to the desorption apparatus for regeneration of the absorbent laden with VOCs and CO2 to obtain an offgas stream comprising CO2 and the VOCs and an at least partly regenerated absorbent;
• and
• h) removing the offgas stream from the desorption apparatus and recycling the at least partly regenerated absorbent from the desorption apparatus into the absorption apparatus.