HYBRID MEMBRANE AND PRESSURE SWING ADSORPTION NITROGEN REMOVAL SYSTEM
A process for removing nitrogen from a feed gas containing at least nitrogen and methane comprises a) introducing the feed gas into a first membrane stage to produce a first permeate enriched in methane and a first residue enriched in nitrogen; b) forwarding the first residue into a second membrane stage to produce a second permeate enriched in methane and a second residue enriched in nitrogen; c) forwarding the second residue into pressure swing adsorption (PSA) beds to produce an high pressure overhead stream containing nitrogen and a low pressure offgas stream containing methane therein; d) combining the second permeate enriched in methane and the low pressure offgas stream containing methane to form a combined gas and forwarding the combined gas to the feed gas for recycle; e) collecting a first permeate enriched in methane as a product; and f) venting out the high pressure overhead stream containing nitrogen.
1 . A process for removing nitrogen from a feed gas containing at least nitrogen and methane, the process comprising the steps of:
a) introducing the feed gas into a first membrane stage to produce a first permeate enriched in methane and a first residue enriched in nitrogen;
b) forwarding the first residue enriched in nitrogen into a second membrane stage to produce a second permeate enriched in methane and a second residue enriched in nitrogen;
c) forwarding the second residue enriched in nitrogen into pressure swing adsorption (PSA) beds to produce an high pressure overhead stream containing nitrogen and a low pressure offgas stream containing methane therein;
d) combining the second permeate enriched in methane and the low pressure offgas stream containing methane to form a combined gas and forwarding the combined gas to the feed gas for recycle;
e) collecting a first permeate enriched in methane as a product; and
f) venting out the high pressure overhead stream containing nitrogen.
2 . The process of claim 1 , further comprising the step of:
compressing the feed gas before feeding the feed gas to the first membrane stage.
3 . The process of claim 1 , further comprising the step of:
compressing the combined gas before forwarding the combined gas to the feed gas for recycle.
4 . The process of claim 1 , further comprising the steps of: if the feed gas containing exceeding 6 mol % but not greater than 10 mol % of nitrogen,
splitting the feed gas into a first and a second feed streams;
forwarding the first feed stream to the first membrane stage, wherein the first feed stream is merged with the combined gas before forwarding the first feed stream to the first membrane stage;
forwarding the second feed stream to the second membrane stage, wherein the second feed stream is merged with the first residue enriched in nitrogen from the first membrane stage before forwarding the second feed stream to the second membrane stage; and
moderating a ratio of the feed gas in the first and second feed streams, respectively.
5 . The process of claim 4 , further comprising the step of:
compressing the feed gas before splitting the feed gas.
6 . The process of claim 4 , further comprising the step of:
compressing the combined gas before forwarding to the first membrane stage.
7 . The process of claim 1 , further comprising the steps of: if the feed gas containing exceeding 10 mol % but not greater than 20 mol % of nitrogen,
a) splitting the feed gas into a first and second feed streams;
b) forwarding the first feed stream to the second membrane stage, wherein the first feed stream is merged with the first residue enriched in nitrogen from the first membrane stage before forwarding the first feed stream to the second membrane stage;
c) forwarding the second feed stream to the pressure swing adsorption (PSA) beds, wherein the second feed stream is merged with the second residue enriched in nitrogen from the second membrane stage before forwarding the second feed stream to the pressure swing adsorption (PSA) beds; and
d) moderating a ratio of the feed gas in the first and second feed streams, respectively.
8 . The process of claim 7 , further comprising the step of:
compressing the feed gas before splitting the feed gas.
9 . The process of claim 7 , further comprising the step of:
compressing the combined gas before forwarding to the first membrane stage.
10 . A membrane system for removing nitrogen from a feed gas containing at least nitrogen and methane, the system comprising:
a) a first membrane stage, fed with the feed gas, configured to produce a first permeate enriched in methane and a first residue containing nitrogen;
b) a second membrane stage, fed with the first residue containing nitrogen, configured to produce a second permeate enriched in methane and a second residue enriched in nitrogen;
c) a pressure swing adsorption (PSA) system containing PSA beds, fed with the second residue enriched in nitrogen, configured to produce an high pressure overhead stream containing nitrogen and a low pressure offgas stream containing methane therein; and
d) a combined gas, formed by combining the second permeate enriched in methane and the low pressure offgas stream containing methane,
wherein the combine gas is forwarded to the feed gas for recycle, the high pressure overhead stream containing nitrogen is vent out, the first permeate enriched in methane is collected as a product.
11 . The membrane system of claim 10 , further comprising:
a compressor, configured to compress the feed gas before the feed gas is fed to the first membrane stage.
12 . The membrane system of claim 10 , further comprising:
a compressor, configured to compress the combined gas before the combined gas is forwarded to the feed gas for recycle.
13 . The membrane system of claim 10 , further comprising: if the feed gas containing exceeding 6 mol % but not greater than 10 mol % of nitrogen,
a splitter, configured to split the feed gas into a first and a second feed streams; and
two control valves, each installed along the first and second feed streams, respectively, configured to moderate a ratio of the feed gas in the first and second feed streams,
wherein the first feed stream is fed to the first membrane stage and the second feed stream is fed to the second membrane stage.
14 . The membrane system of claim 13 , further comprising:
a compressor, configured to compress the feed gas before the feed gas is forwarded to the splitter.
15 . The membrane system of claim 13 , further comprising:
a compressor, configured to compress the combined gas before the combined gas is forward to the first membrane stage.
16 . The membrane system of claim 10 , further comprising: if the feed gas containing exceeding 10 mol % but not greater than 20 mol % of nitrogen,
a splitter, configured to split the feed gas into a first and a second feed streams; and
two control valves, each installed along the first and second feed streams, respectively, configured to moderate a ratio of the feed gas in the first and second feed streams,
wherein the first feed stream is fed to the second membrane stage and the second feed stream is fed to the pressure swing adsorption (PSA) system.
17 . The membrane system of claim 16 , further comprising:
a compressor, configured to compress the feed gas before the feed gas is forwarded to the splitter.
18 . The membrane system of claim 16 , further comprising:
a compressor, configured to compress the combined gas before the combined gas is forward to the first membrane stage.
19 . The membrane system of claim 10 , wherein the first membrane stage and the second membrane stage each comprise rubbery-type hollow-fiber membranes.
20 . A process for removing nitrogen from a feed gas containing at least nitrogen and methane, when the feed gas containing exceeding 10 mol % but not greater than 20 mol % of nitrogen, the process comprising the steps of:
a) splitting the feed gas into a first and second feed streams;
b) moderating a ratio of the feed gas in the first and second feed streams, respectively;
c) forwarding the first merged gas to the second membrane stage, wherein the first feed stream is merged with a first residue enriched in nitrogen from a first membrane stage before forwarding the first merged gas to the second membrane stage;
d) forwarding the second merged gas to pressure swing adsorption (PSA) beds to produce an high pressure overhead stream containing nitrogen and a low pressure offgas stream containing methane therein, wherein the second feed stream is merged with a second residue enriched in nitrogen from the second membrane stage before the second merged gas to pressure swing adsorption (PSA) beds, and;
e) combining a second permeate enriched in methane from the second membrane stage and the low pressure offgas stream containing methane from the PSA beds to form a combined gas and forwarding the combined gas to the first membrane stage as a first stage feed gas;
f) compressing the combined gas before forwarding the combined gas to the first membrane stage;
g) collecting a first permeate enriched in methane as a product; and
h) venting out the high pressure overhead stream containing nitrogen.