Auto-refrigerated gas separation system for carbon dioxide capture and compression

Abstract

A system and method for capturing and separating carbon dioxide from mixed gas streams. The gas stream is processed in a structure including a compression module comprising a plurality of compressors, intercoolers and inter-stage condensate separators. The flow path from the compression module includes a plurality of flow separators, gas stream splitters, heat exchangers and at least a first mixer and a first expander. The gas stream is sequentially compressed and cooled to form process condensate and separate it from the compressed gas stream. The gas stream is further dried and cooled to liquefy carbon dioxide and separate it from the non-condensable portion. Selective expansion of liquid carbon dioxide streams provides cooling for the system, and further energy efficiency is achieved by selective recycling of portions of gas streams, allowing for compact equipment and economical operation, while providing for high purity product streams of carbon dioxide.

1 . A method for separating carbon dioxide from a mixed gas stream, the method comprising the steps of:
 (a) providing a processing structure including a compression module comprising at least a plurality of compressors, a plurality of intercoolers with inter-stage condensate separators, the processing structure further including a plurality of flow separators, a plurality of gas stream splitters, a plurality of heat exchangers and at least a first mixer and a first expander;   (b) delivering the mixed gas stream to the compression module;   (c) compressing and cooling the mixed gas stream through each of the plurality of compressors and intercoolers in sequence and ones of the plurality of heat exchangers to generate an output stream including liquid carbon dioxide and a gaseous stream;   (d) selectively removing the liquid carbon dioxide from the output stream in selected ones of the plurality of flow separators to generate from each selected flow separator a liquid carbon dioxide stream and a separated gaseous stream;   (e) selectively mixing in the first mixer at least two of the liquid carbon dioxide streams generated in step (d) to form a mixed liquid carbon dioxide stream;   (f) passing the mixed liquid carbon dioxide stream through one of the heat exchangers to form a mixed carbon dioxide stream and removing the said mixed carbon dioxide stream from the processing structure;   (g) splitting selected ones of the separated gaseous streams to further cool the split streams to form liquid carbon dioxide and selectively repeating step (d) to separate the liquid carbon dioxide from other gases and selectively removing the other gases from the processing structure;   (h) selectively recycling the separated gaseous stream from at least one of the flow separators to at least one of the compressors selected from a second compressor and a subsequent compressor in the sequence in the compression module;   (i) selectively expanding at least portions of the separated gaseous stream and selectively expanding at least portions of the split stream to recover energy and to provide cooling to the processing structure;   (j) throttling selected portions of the separated liquid carbon dioxide stream from step (d) and/or step (e) to provide cooling to the processing structure; and   (k) repeating selected ones of steps (c) to (j) in a manner selected from periodically and continuously.   
     
     
         2 . A method according to  claim 1 , further comprising a start-up operation wherein step (e) further comprises diverting a selected portion of the mixed liquid carbon dioxide stream through a second mixer and a second one of the heat exchangers before removing the diverted portion from the processing structure in step (f). 
     
     
         3 . A method according to  claim 1 , further comprising prior to step (c) the step of
 (b.1) pre-treating the mixed gas stream by removing at least one of water, particulate matter, mercury and other heavy metals, hydrogen chloride, hydrogen fluoride, nitrogen oxides, sulphur oxides and other sulphur derivatives from the mixed gas stream.   
     
     
         4 . A method for separating carbon dioxide from a mixed gas stream, the method comprising the steps of:
 (a) delivering the mixed gas stream to a processing structure;   (b) compressing the mixed gas stream in at least two compression stages and subjecting the mixed gas stream to cooling and separating steps after each compression stage to produce a compressed gas stream;   (c) passing the compressed gas stream through a first heat exchanger to form a first two-phase flow;   (d) separating the first two-phase flow into a first liquid stream comprising at least 90% carbon dioxide and a first gas stream including residual carbon dioxide;   (e) splitting the first gas stream into a first gas stream branch and a second gas stream branch;   (f) passing the first gas stream branch through a second heat exchanger to form a second two-phase flow;   (g) separating the second two-phase flow into a second liquid stream comprising at least 90% carbon dioxide and a second gas stream including impurities and residual carbon dioxide;   (h) passing the second gas stream including impurities and residual carbon dioxide, in sequence through the second heat exchanger and the first heat exchanger to form a fourth gas stream comprising impurities and residual carbon dioxide;   (i) expanding the second gas stream branch to produce a third two-phase flow;   (j) separating the third two-phase flow into a third liquid stream comprising at least 90% carbon dioxide and a third gas stream including residual carbon dioxide;   (k) passing the third gas stream through the first heat exchanger and recycling it back to an intermediate stage of the compressor;   (l) passing the third liquid stream through a pressurizing means to raise the pressure of the third liquid stream to match the pressure of the first liquid stream, and thereafter mixing the first liquid stream with the third liquid stream in a first mixer to form a mixed fourth liquid stream;   (m) passing the second liquid stream through the second heat exchanger;   (n) mixing the mixed fourth liquid stream with the second liquid stream to form a fifth liquid stream;   (o) passing the fifth liquid stream through a throttle valve to form a first cold throttled stream including a gaseous portion and a liquid portion;   (p) passing the first cold throttled stream through the second heat exchanger and the first heat exchanger, in sequence, to form a product stream comprising at least 90% carbon dioxide.   
     
     
         5 . A method according to  claim 4 , further comprising after step (o) the step of:
 (o.1) passing the first cold throttled stream to a first additional separator to remove the gaseous portion of the first cold throttled stream to form a sixth gas stream, the liquid portion of the first cold throttled stream forming a sixth liquid stream;   (o.2) passing the sixth liquid stream through the second heat exchanger and the first heat exchanger, in sequence, to form a product stream comprising at least 90% carbon dioxide; and   (o.3) recycling the sixth gas stream back to an intermediate stage after the first and before the last of the at least two compression stages of step (b).   
     
     
         6 . A method according to  claim 4 , further comprising after step (o) the step of:
 (o.4) passing the first cold throttled stream to a first additional separator to remove the gaseous portion of the first cold throttled stream to form a sixth gas stream, the liquid portion of the first cold throttled stream forming a sixth liquid stream;   (o.5) passing the sixth liquid stream through the second heat exchanger and the first heat exchanger, in sequence, to form a product stream comprising at least 90% carbon dioxide;   (o.6) passing the sixth gas stream to a first additional compressor to form a compressed sixth gas stream; and   (o.7) mixing the compressed sixth gas stream with the compressed gas stream of step (b).   
     
     
         7 . A method according to  claim 4 , further comprising after step (b), the step of:
 (b.1) drying the compressed gas stream to form a dried compressed gas stream having a dew point temperature at least one degree C. lower than a lowest operational temperature of each of the steps of the method.   
     
     
         8 . A method according to  claim 4 , wherein the pressurizing means in step (l) comprises a pump. 
     
     
         9 . A method according to  claim 7 , further comprising after step (h) the step of:
 (h.1) expanding the fourth gas stream in a vent stream turbo-expander to recover energy and to form a vent stream comprising impurities and residual carbon dioxide.   
     
     
         10 . A method according to  claim 9 , further comprising after step (h.1) splitting the vent stream into a first vent stream branch and a second vent stream branch. 
     
     
         11 . A method according to  claim 10 , further passing the first vent stream branch through the first heat exchanger to use the residual cooling capacity of the said stream. 
     
     
         12 . A method according to  claim 10 , further comprising after step (b) and before step (c), passing the compressed gas stream through a first additional heat exchanger; and passing the first vent stream branch through the first additional heat exchanger. 
     
     
         13 . A method according to  claim 10 , further comprising after step (e) and before step (i), passing the second gas stream branch through a second additional heat exchanger, and passing the second vent stream branch through the second additional heat exchanger. 
     
     
         14 . A method according to  claim 4 , further comprising after step (p) the step of:
 (p.1) raising the pressure of the product stream to higher set pressure to form a pressurized product stream.   
     
     
         15 . A method according to  claim 4 , further comprising expanding the second gas stream branch in a main turbo-expander to recover energy, and to produce the third two-phase flow. 
     
     
         16 . A method according to  claim 4 , further comprising expanding the second gas stream branch in sequence through a Joule-Thompson throttle valve and a chiller to produce the third two-phase flow. 
     
     
         17 . A method according to  claim 4 , further comprising a start-up operation comprising the steps of:
 (A) performing steps (a) to (l) of the method;   (B.1) splitting the mixed fourth liquid stream into a main portion stream and a remaining portion stream;   (B.2) expanding the remaining portion stream through the first throttle valve and the first heat exchanger, in sequence, to produce a first product stream comprising at least 90% carbon dioxide;   (B.3) when step (g) commences producing a second liquid stream, mixing the second liquid stream of step (g) with the main portion stream to form a mixed second liquid stream and thereafter passing the mixed second liquid stream in sequence through the second throttle valve, the second heat exchanger, and the first heat exchanger to produce a second product stream comprising at least 90% carbon dioxide;   (C) continuing performing steps (B.1) to (B.3) until step (d) and step (g) produce the first and the second liquid streams at their respective steady state levels; and thereafter   (D) continuing performing steps (a) to (l) of the method and performing steps (m) to (p) of the method.   
     
     
         18 . A method according to  claim 17 , further comprising after step (B.2) the step of:
 (B.2.1) raising the pressure of the first product stream to higher set pressure to form a first pressurized product stream; and after step (B.3) the step of:   (B.3.1) raising the pressure of the second product stream to higher set pressure to form a second pressurized product stream.   
     
     
         19 . A method according to  claim 18 , further comprising matching the pressure of the first pressurized product stream and the second pressurized product stream. 
     
     
         20 . A method for separating carbon dioxide from a mixed gas stream, the method comprising the steps of:
 (a) delivering the mixed gas stream to a processing structure;   (b) compressing the mixed gas stream in at least two compression stages and subjecting the mixed gas stream to cooling and separating steps after each compression stage to produce a compressed gas stream;   (c) passing the compressed gas stream through a first heat exchanger to form a first two-phase flow;   (d) separating the first two-phase flow into a first liquid stream comprising at least 90% carbon dioxide and a first gas stream including residual carbon dioxide;   (e) splitting the first gas stream into a first gas stream branch and a second gas stream branch;   (f) passing the first gas stream branch through a second heat exchanger to form a second two-phase flow;   (g) separating the second two-phase flow into a second liquid stream comprising at least 90% carbon dioxide and a second gas stream including impurities and residual carbon dioxide;   (h) passing the second gas stream, including impurities and residual carbon dioxide, in sequence through the second heat exchanger and the first heat exchanger to form a fourth gas stream comprising impurities and residual carbon dioxide;   (i) expanding the second gas stream branch to produce a third two-phase flow;   (j) separating the third two-phase flow into a third liquid stream comprising at least 90% carbon dioxide and a third gas stream including residual carbon dioxide;   (k) passing the third gas stream through the first heat exchanger and recycling it back to an intermediate stage of the compressor;   (l) passing the third liquid stream through a pressurizing means to raise the pressure of the third liquid stream to match the pressure of the first liquid stream, and thereafter mixing the first liquid stream with the third liquid stream in a first mixer to form a mixed fourth liquid stream;   (m) passing the second liquid stream through the second heat exchanger;   (n) mixing the mixed fourth liquid stream with the second liquid stream to form a fifth liquid stream;   (o) passing the fifth liquid stream through the second heat exchanger;   (p) splitting the fifth liquid stream into a first liquid stream branch and a second liquid stream branch;   (q) passing the first liquid stream branch through a first-branch throttle valve to form a first cold throttled stream branch having a gaseous portion and a liquid portion;   (r) passing the second liquid stream branch through a second-branch throttle valve to form a second cold throttled stream branch having a gaseous portion and a liquid portion;   (s) passing the first cold throttled stream branch through the first heat exchanger to form a first product stream comprising at least 90% carbon dioxide; and   (t) passing the second cold throttled stream branch through the second heat exchanger and the first heat exchanger in sequence to form a second product stream comprising at least 90% carbon dioxide.   
     
     
         21 . A method according to  claim 20 , further comprising after step (q) the step of:
 (q.1) passing the first cold throttled stream branch to a first-branch additional separator to remove the gaseous portion of the first cold throttled stream branch to form a seventh gas stream, the liquid portion of the first cold throttled stream branch forming a seventh liquid stream;   (q.2) passing the second cold throttled stream branch to a second-branch additional separator to remove the gaseous portion of the second cold throttled stream branch to form an eighth gas stream, the liquid portion of the second cold throttled stream branch forming an eighth liquid stream;   (q.3) passing the seventh liquid stream through the first heat exchanger to form a first product stream comprising at least 90% carbon dioxide;   (q.4) passing the eighth liquid stream through the second heat exchanger and the first heat exchanger, in sequence, to form a second product stream comprising at least 90% carbon dioxide;   (q.5) mixing the seventh gas stream with the eighth gas stream to form a first recycle gas stream; and   (q.6) recycling the first recycle gas stream back to an intermediate stage after the first and before the last of the at least two compression stages of step (b).   
     
     
         22 . A method according to  claim 20 , further comprising after step (q) the steps of:
 (q.7) passing the first cold throttled stream branch to a first-branch additional separator to remove the gaseous portion of the first cold throttled stream branch to form a seventh gas stream, the liquid portion of the first cold throttled stream branch forming a seventh liquid stream;   (q.8) passing the second cold throttled stream branch to a second-branch additional separator to remove the gaseous portion of the second cold throttled stream branch to form an eighth gas stream, the liquid portion of the second cold throttled stream branch forming an eighth liquid stream;   (q.9) passing the seventh liquid stream through the first heat exchanger to form a first product stream comprising at least 90% carbon dioxide;   (q.10) passing the eighth liquid stream through the second heat exchanger and the first heat exchanger in sequence to form a second product stream comprising at least 90% carbon dioxide;   (q.11) passing the seventh and eighth gas streams through a first additional compressor to form a compressed recycle gas stream; and   (q.12) mixing the compressed recycle gas stream with the compressed gas stream of step (b).   
     
     
         23 . A method according to  claim 20 , further comprising after step (b), the step of:
 (b.1) drying the compressed gas stream to form a dried compressed gas stream having a dew point temperature at least one degree C. lower than a lowest operational temperature of each of the steps.   
     
     
         24 . A method according to  claim 20 , wherein the pressurizing means in step (l) comprises a pump. 
     
     
         25 . A method according to  claim 20 , further comprising after step (h) the step of:
 (h.1) expanding the fourth gas stream in a vent stream turbo-expander to recover energy and to form a vent stream comprising impurities and residual carbon dioxide.   
     
     
         26 . A method according to  claim 25 , further comprising after step (h.1) splitting the vent stream into a first vent stream branch and a second vent stream branch. 
     
     
         27 . A method according to  claim 26 , further passing the first vent stream branch through the first heat exchanger to use the residual cooling capacity of the said stream. 
     
     
         28 . A method according to  claim 26 , further comprising after step (b) and before step (c), passing the compressed gas stream through a first additional heat exchanger; and passing the first vent stream branch through the first additional heat exchanger. 
     
     
         29 . A method according to  claim 26 , further comprising after step (e) and before step (i), passing the second gas stream branch through a second additional heat exchanger, and passing the second vent stream branch through the second additional heat exchanger. 
     
     
         30 . A method according to  claim 20 , further comprising after step (s) the step of:
 (s.1) raising the pressure of the first product stream to higher set pressure to form a first pressurized product stream; and after step (t) the step of:   (t.1) raising the pressure of the second product stream to higher set pressure to form a second pressurized product stream.   
     
     
         31 . A method according to  claim 30 , further comprising matching the pressure of the first pressurized product stream and the second pressurized product stream. 
     
     
         32 . A method according to  claim 20 ,  further comprising expanding the second gas stream branch in a main turbo-expander to recover energy, and to produce the third two-phase flow. 
     
     
         33 . A method according to  claim 20 , further comprising expanding the second gas stream branch in sequence through a Joule-Thompson throttle valve and a chiller to produce the third two-phase flow. 
     
     
         34 . A method according to  claim 20 , further comprising prior to step (b) the step of:
 (a.1) pre-treating the gas stream by removing at least one of water, particulate matter, mercury and other heavy metals, hydrogen chloride, hydrogen fluoride, nitrogen oxides, sulphur oxides and other sulphur derivatives from the gas stream.   
     
     
         35 . A method according to  claim 20 , further comprising after step (m) the step of:
 (m.1) passing the first cold throttled stream through a first additional separator to remove the gaseous portion of the first cold throttled stream to form a fifth gas stream; and the liquid portion of the first cold throttled stream to form a fifth liquid stream;   (m.2) passing the fifth gas stream through the first heat exchanger and recycling the fifth gas stream back to an intermediate stage after the first and before the last of the at least two compression stages of step (b); and   (m.3) passing the fifth liquid stream through the first heat exchanger to form a third product stream comprising at least 90% carbon dioxide.   
     
     
         36 . A method according to  claim 20 , further comprising a start-up operation comprising the steps of:
 (A) performing steps (a) to (l) of the method;   (B.1) splitting the mixed fourth liquid stream into a main portion stream and a remaining portion stream;   (B.2) expanding the remaining portion stream through the first throttle valve and the first heat exchanger, in sequence, to produce a third product stream comprising at least 90% carbon dioxide;   (B.3) when step (g) commences producing a second liquid stream, mixing the second liquid stream of step (g) with the main portion stream to form a mixed second liquid stream and thereafter performing step (p) to step (t) of  claim 20 ;   (C) continuing performing steps (B.1) to (B.3) until step (d) and step (g) produce the first and the second liquid streams at their respective steady state levels; and thereafter   (D) continuing performing steps (a) to (l) of the method and performing steps (m) to (t) of the method.   
     
     
         37 . A method according to  claim 36 , further comprising after step (s) the step of:
 (s.1) raising the pressure of the first product stream to a higher set pressure to form a first pressurized product stream; and after step (t) the step of:   (t.1) raising the pressure of the second product stream to a higher set pressure to form a second pressurized product stream; and after step (B.2) the step of:   (B.2.1) raising the pressure of the third product stream to a higher set pressure to form a third pressurized product stream.   
     
     
         38 . A method according to  claim 37 , further comprising selectively matching the pressure of the first pressurized product stream, the second pressurized product stream and the third pressurized product stream. 
     
     
         39 . A method according to  claim 4 , further comprising selectively removing oxygen from selected ones of each of the product streams before removing the selected product stream from the processing structure. 
     
     
         40 . A system for separating carbon dioxide from a mixed gas stream, the system comprising a processing structure including:
 (a) a compression module comprising at least a plurality of compressors and a plurality of intercoolers with inter-stage condensate separators, the module being constructed and arranged to compress and cool the mixed gas stream through each of the plurality of compressors in sequence to generate a first processing structure stream comprising an output stream;   (b) a plurality of heat exchange means for further cooling the output stream to form liquid carbon dioxide and for cooling of selected ones of a plurality of additional processing structure streams;   (c) a plurality of flow separation means for selectively removing the liquid carbon dioxide from gaseous portions of selected ones of the processing structure streams to generate at least one liquid carbon dioxide stream and at least one separated gaseous stream;   (d) a plurality of splitting and transfer means for splitting selected ones of the separated gaseous streams and liquid carbon dioxide streams;   (e) at least a first mixing means for selectively mixing at least two liquid carbon dioxide streams to form a mixed liquid carbon dioxide stream;   (f) recycling means for selectively recycling the separated gaseous stream from at least one of the flow separation means to at least one of the compressors selected from a second compressor and a subsequent compressor in the sequence in the compression module;   (g) at least one expander means to selectively expand at least portions of the separated gaseous stream to recover energy and to provide cooling to the processing structure; and   (h) at least one throttle means to selectively throttle selected portions of at least one liquid carbon dioxide stream.   
     
     
         41 . A system according to  claim 40 , further comprising a second mixer means for receiving and transferring a selected portion of the mixed liquid carbon dioxide stream in a start-up operation. 
     
     
         42 . A system according to  claim 40 , further comprising at least one pre-treatment means for removing from the mixed gas stream at least one of water, particulate matter, mercury and other heavy metals, hydrogen chloride, hydrogen fluoride, nitrogen oxides, sulphur oxides and other sulphur derivatives from the mixed gas stream. 
     
     
         43 . A system according to  claim 40 , further comprising oxygen removal means for selectively removing oxygen from at least one carbon dioxide stream.