Membrane process and system for high recovery of a nonpermeating gas utilizing a sweep gas

1. A method comprising:

(a) compressing a feed gas stream to form a pressurized feed gas stream;

(b) feeding the pressurized feed gas stream into at least one first stage membrane module, each of the at least one first stage membrane module having a first high pressure side and a first low pressure side, the first high pressure side extending from a first feed port to a first non-permeate port, the first low pressure side being in fluid flow communication with a first sweep port and a first permeate port;

(c) separating the pressurized feed gas stream in each of the at least one first stage membrane module into a first non-permeate stream and a first permeate stream;

(d) sweeping and discharging the first permeate stream from the first permeate port using a sweep gas that is fed in a first direction of flow that is countercurrent to a second direction of flow that the pressured feed gas stream is fed into the at least one first stage membrane module in step (a);

(e) discharging the first non-permeate stream from each of the at least one first stage membrane module through the first non-permeate port;

(f) compressing the first permeate stream in a first compressor to form a compressed first permeate stream;

(g) feeding the compressed first permeate stream to at least one second stage membrane module, each of the at least one second stage membrane module having a second high pressure side and a second low pressure side, the second high pressure side extending from a second feed port to a second non-permeate port, the second low pressure side being in fluid flow communication with a second sweep port and a second permeate port;

(h) separating the compressed first permeate stream in the at least one second stage membrane module into a second non-permeate stream and a second permeate stream;

(i) discharging the second non-permeate stream from each of the at least one second stage membrane module through the second non-permeate port;

(j) discharging the second permeate stream from each of the at least one second stage membrane module through the second permeate port;

(k) combining the second non-permeate stream with a compressed combined feed stream to form the pressurized feed gas stream;

(l) feeding the second permeate stream into at least one third stage membrane module, each of the at least one third stage membrane module having a third high pressure side and a third low pressure side, the third high pressure side extending from a third feed port to a third non-permeate port, the third low pressure side being in fluid flow communication with a third sweep port and a third permeate port;

(m) separating the second permeate stream in the at least one third stage membrane module into a third non-permeate stream and a third permeate stream;

(n) discharging the third non-permeate stream from each of the at least one third stage membrane module through the third non-permeate port;

(n) discharging the third permeate stream from each of the at least one third stage membrane module through the third permeate port;

(o) combining the third non-permeate stream with a raw feed gas stream to form a combined feed stream; and

(p) compressing the combined feed stream in a second compressor to form the compressed combined feed stream.

2. The method of claim 1 , wherein step (d) further comprises introducing the sweep gas at a pressure of less than 1.00 barg.

3. The method of claim 1 , wherein the sweep gas comprises less than 15% carbon dioxide.

4. The method of claim 1 , wherein the sweep gas comprises at least 85% methane.

5. The method of claim 1 , wherein the sweep gas provides a first molar flow rate of nitrogen that is less than or equal to 5% of a second molar flow rate of the pressurized feed gas stream.

6. The method of claim 1 , wherein the sweep gas comprises an off-gas.

7. The method of claim 6 , wherein the off-gas comprises an off-gas from a liquefaction process or a temperature swing adsorption process.

8. The method of claim 1 , wherein the sweep gas comprises a tail gas from a thermal swing adsorption (TSA) process.

9. The method of claim 7 , further comprising directing at least a portion of the off-gas to one or more selected from the group of: (1) the feed gas stream and (2) the first permeate stream.

10. The method of claim 1 , wherein the at least one first stage membrane module comprises a plurality of membrane modules arranged in series and/or parallel.

11. The method of claim 1 , wherein the at least one second stage membrane module comprises a plurality of membrane modules arranged in series and/or parallel.

12. The method of claim 1 , wherein the at least one third stage membrane module comprises a plurality of membrane modules arranged in series and/or parallel.

13. The method of claim 1 , wherein the feed gas stream is a product stream from an anaerobic digester.

14. The method of claim 1 , wherein the feed gas stream comprises at least 40% methane.

15. The method of claim 1 , wherein step (f) further comprises compressing the first permeate stream in the first compressor to a pressure of at least 10 barg to form the compressed first permeate stream.

16. The method of claim 1 , wherein the first non-permeate stream comprises at least 70% methane.

17. The method of claim 1 , wherein the third permeate stream comprises less than 1% methane.

18. A method comprising:

(a) compressing a feed gas stream to form a pressurized feed gas stream;

(b) feeding the pressurized feed gas stream into at least one first stage membrane module, each of the at least one first stage membrane module having a first high pressure side and a first low pressure side, the first high pressure side extending from a first feed port to a first non-permeate port, the first low pressure side being in fluid flow communication with a first sweep port and a first permeate port;

(c) separating the pressurized feed gas stream in each of the at least one first stage membrane module into a first non-permeate stream and a first permeate stream;

(d) discharging the first non-permeate stream from each of the at least one first stage membrane module through the first non-permeate port;

(e) feeding the first non-permeate stream into at least one stripping membrane module, each of the at least one stripping membrane module having a fourth high pressure side and a fourth low pressure side, the fourth high pressure side extending from a fourth feed port to a fourth non-permeate port, the fourth low pressure side being in fluid flow communication with a fourth permeate port;

(f) separating the first non-permeate stream in each of the at least one stripping membrane module into a fourth non-permeate stream and a fourth permeate stream;

(g) discharging the fourth permeate stream from the fourth permeate port;

(h) discharging the fourth non-permeate stream from each of the at least one stripping membrane module through the fourth non-permeate port;

(i) sweeping and discharging the fourth permeate stream from the fourth permeate port using a sweep gas that is fed in a first direction of flow that is countercurrent to a second direction of flow that the first non-permeate stream is fed into the at least one stripping membrane module in step (e);

(j) compressing the first permeate stream in a first compressor to form a compressed first permeate stream;

(k) feeding the compressed first permeate stream to at least one second stage membrane module, each of the at least one second stage membrane module having a second high pressure side and a second low pressure side, the second high pressure side extending from a second feed port to a second non-permeate port, the second low pressure side being in fluid flow communication with a second sweep port and a second permeate port;

(l) separating the compressed first permeate stream in the at least one second stage membrane module into a second non-permeate stream and a second permeate stream;

(m) discharging the second non-permeate stream from each of the at least one second stage membrane module through the second non-permeate port;

(n) discharging the second permeate stream from each of the at least one second stage membrane module through the second permeate port;

(o) combining the second non-permeate stream with a compressed combined feed stream to form the pressurized feed gas stream;

(p) feeding the second permeate stream into at least one third stage membrane module, each of the at least one third stage membrane module having a third high pressure side and a third low pressure side, the third high pressure side extending from a third feed port to a third non-permeate port, the third low pressure side being in fluid flow communication with a third sweep port and a third permeate port;

(q) separating the second permeate stream in the at least one third stage membrane module into a third non-permeate stream and a third permeate stream;

(r) discharging the third non-permeate stream from each of the at least one third stage membrane module through the third non-permeate port;

(s) discharging the third permeate stream from each of the at least one third stage membrane module through the third permeate port;

(t) combining the third non-permeate stream with a raw feed gas stream to form a combined feed stream; and

(u) compressing the combined feed stream in a second compressor to form the compressed combined feed stream.

19. The method of claim 18 , wherein step (i) further comprises introducing the sweep gas at a pressure of less than 1.00 barg.

20. The method of claim 18 , wherein the sweep gas comprises an off-gas from a liquefaction process or a temperature swing adsorption process.