Low Temperature Membrane System for Biogas Upgrading

A system comprising:

• (a) a compressor for compressing a feed gas stream to form a pressurized feed gas stream, the pressurized feed gas stream comprising CH4 and being fully saturated with water;
• (b) a chiller for cooling the pressurized feed gas stream to a target operating temperature of between 0 and 20 degrees C. to form a condensed water stream and a saturated gas stream;
• (c) at least one membrane dryer, each of the at least one membrane dryer having a high pressure side and a low pressure side, the high pressure side extending from a feed port to a non-permeate port, the low pressure side being in fluid flow communication with a sweep port and a permeate port;
• the at least one membrane dryer provided for separating the saturated gas stream to form a dried gas stream and a water vapor stream, and for sweeping and discharging the water vapor stream from the low pressure side using a sweep gas stream, the dried gas stream having a water content of less than 2000 ppm;
• (d) a first separation stage for separating the dried gas stream into a first non-permeate stream and a first permeate stream, the first non-permeate stream having a greater percentage of methane than the first permeate stream, the first separation stage comprising at least one first stage membrane module;
• (e) a second separation stage for separating the first non-permeate stream into a second non-permeate stream and the sweep gas stream, the second non-permeate stream having a greater percentage of methane than the sweep gas stream, the second separation stage comprising at least one second stage membrane module;
• (f) a third separation stage for separating the first permeate stream into a third non-permeate stream and a third permeate stream, the third non-permeate stream having a greater percentage of methane than the third permeate stream, the third separation stage comprising at least one third stage membrane module;
• and
• (g) a first mixing junction for combining the third non-permeate stream with the water vapor stream to form a recycle stream to be combined with the feed gas stream.