Enhanced hydrogen recovery utilizing gas separation membranes integrated with pressure swing adsorption unit and/or cryogenic separation system
Processes and systems for recovering hydrogen include feeding a gas stream, comprising hydrogen and additional gases, to a pressure swing adsorption (PSA) system and feeding a membrane permeate stream comprising hydrogen to the PSA system. In the PSA system, a portion of the hydrogen is separated from the additional gases to recover a hydrogen product stream and a PSA tail gas stream comprising unseparated hydrogen and the additional gases. The PSA tail gas stream is fed to a membrane separation unit for separating hydrogen from the additional gases and to recover (i) the membrane permeate stream comprising hydrogen fed to the PSA system and (ii) a membrane tail gas stream comprising the additional gases. Processes and systems herein may additionally include a refrigeration system for partially condensing one or both of the feed gas stream and the PSA tail gas stream, enhancing the efficiency of the membrane separation unit.
1 . A process for recovering hydrogen, the process comprising:
feeding a gas stream, comprising hydrogen and additional gases, to a pressure swing adsorption system;
feeding a membrane permeate stream comprising hydrogen to the pressure swing adsorption system;
in the pressure swing adsorption system, separating a portion of the hydrogen from the additional gases to recover a hydrogen product stream and a pressure swing adsorption tail gas stream comprising unseparated hydrogen and the additional gases;
heating the pressure swing adsorption tail gas stream to a temperature in a range of 35° C. to 45° C. prior to feeding to the membrane separation unit;
feeding the pressure swing adsorption tail gas stream to a membrane separation unit;
in the membrane separation unit, separating hydrogen from the additional gases to recover (i) the membrane permeate stream comprising hydrogen fed to the pressure swing adsorption system and (ii) a membrane tail gas stream comprising the additional gases; and
cooling the pressure swing adsorption tail gas stream to a temperature in the range of −60° C. to −98° C. to partially condense and flash separate the pressure swing adsorption tail gas stream to recover a PSA tail gas condensate stream and a PSA tail gas vapor stream, and feeding the PSA tail gas vapor stream as the pressure swing adsorption tail gas stream fed to the membrane separation unit.
2 . The process of claim 1 , further comprising compressing the pressure swing adsorption tail gas stream upstream of the membrane separation unit.
3 . The process of claim 1 , further comprising compressing the membrane permeate stream upstream of the pressure swing adsorption system.
4 . The process of claim 1 , further comprising partially condensing the gas stream, recovering a condensate stream and a vapor stream, and feeding the vapor stream as the gas stream fed to the pressure swing adsorption system.
5 . The process of claim 4 , wherein the partially condensing the gas stream comprises cooling the gas stream to a temperature of −37° C. to −60° C.
6 . The process of claim 1 , wherein the gas stream is fed to the pressure swing adsorption system at a pressure in a range from 25 to 35 barg.
7 . The process of claim 1 , wherein the pressure swing adsorption tail gas stream is recovered from the pressure swing adsorption system at a pressure in a range of 1 to 5 barg and is compressed to a pressure of 10 to 20 barg prior to being fed to the membrane separation unit.
8 . The process of claim 1 , wherein the membrane permeate stream is recovered from the membrane separation unit at a pressure in a range from 1 to 2 barg and is compressed to a pressure in a range from 25 to 35 barg for feed to the pressure swing adsorption system.
9 . The process of claim 1 , wherein the membrane tail gas stream is recovered at a pressure in a range of 8 to 18 barg.
10 . The process of claim 1 , wherein the membrane separation unit recovers 70% to 90% of the hydrogen in the PSA tail gas.
11 . The process of claim 1 , wherein an overall hydrogen recovery is in the range of 96 to 99%.
12 . A system for recovering hydrogen, the system comprising:
a flow line for feeding a gas stream, comprising hydrogen and additional gases, to a pressure swing adsorption system;
a flow line for feeding a membrane permeate stream comprising hydrogen to the pressure swing adsorption system;
the pressure swing adsorption system, configured for separating a portion of the hydrogen from the additional gases to recover a hydrogen product stream and a pressure swing adsorption tail gas stream comprising unseparated hydrogen and the additional gases;
a flow line for feeding the pressure swing adsorption tail gas stream to a membrane separation unit;
the membrane separation unit, configured for separating hydrogen from the additional gases and to recover (i) the membrane permeate stream comprising hydrogen fed to the pressure swing adsorption system and (ii) a membrane tail gas stream comprising the additional gases;
a refrigeration/separation system configured for cooling the pressure swing adsorption tail gas stream to a temperature in the range of −60° C. to −98° C. to partially condense and flash separate the pressure swing adsorption tail gas stream to recover a PSA tail gas condensate stream and a PSA tail gas vapor stream, and configured to heat the pressure swing adsorption tail gas stream to a temperature in a range of 35° C. to 45° C. prior to feeding to the membrane separation unit;
a flow line for feeding the PSA tail gas vapor stream as the pressure swing adsorption tail gas stream fed to the membrane separation unit.
13 . The system of claim 12 , further comprising a compressor for compressing the pressure swing adsorption tail gas stream upstream of the membrane separation unit.
14 . The system of claim 12 , further comprising a compressor for compressing the membrane permeate stream upstream of the pressure swing adsorption system.
15 . The system of claim 12 , further comprising a refrigeration/separation system for partially condensing the gas stream, recovering a condensate stream and a vapor stream, and a flow lines for feeding the vapor stream as the gas stream fed to the pressure swing adsorption system.
16 . The system of claim 12 , the refrigeration/separation system comprising:
a cross-exchanger configured to exchange heat between the gas stream, the pressure swing adsorption tail gas stream, the vapor stream, the PSA tail gas vapor stream, a mixture of the condensate stream and the PSA tail gas condensate stream, and a refrigerant, producing a partially condensed gas stream;
a cross-exchanger configured to exchange heat between the pressure swing adsorption tail gas stream and the PSA tail gas vapor stream, producing a partially condensed pressure swing adsorption tail gas stream;
a vapor-liquid separator configured to receive the partially condensed gas stream, the vapor-liquid separator including a vapor outlet for recovering the vapor stream and a liquid outlet for recovering the condensate stream; and
a second vapor-liquid separator configured to receive the partially condensed pressure swing adsorption tail gas stream, the second vapor-liquid separator including a vapor outlet for recovering the PSA tail gas vapor stream and a liquid outlet for recovering the PSA tail gas condensate stream.