Gas separation system with auto-refrigeration and selective recycle for carbon dioxide capture and compression

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, at least one stream splitter, a plurality of heat exchangers, a plurality of mixers, at least a first expander, and a throttle valve;
• (b) delivering the mixed gas stream to the compression module;
• (c) (I) compressing and cooling the mixed gas stream through each of the plurality of compressors and intercoolers in sequence to form a compressed gas stream;
• (c) (II) generating output streams from each of the plurality of heat exchangers and the first expander, the output streams each including liquid carbon dioxide and a gaseous stream;
• (d) removing the liquid carbon dioxide from each of the said output streams in first, second, and third flow separators to generate from each selected flow separator a first, second, and third, respectively, liquid carbon dioxide stream and a first, second, and third, respectively, separated gaseous stream;
• (e) mixing in a first mixer of the plurality of mixers the first and the third liquid carbon dioxide streams generated in step (d) to form a first mixed liquid carbon dioxide stream and sending at least a first portion of the first mixed liquid carbon dioxide stream through to a second mixer to mix with the second liquid carbon dioxide stream to form a second mixed liquid carbon dioxide stream;
• (f) throttling at least a portion of the second mixed liquid carbon dioxide stream from step (e) in the throttle valve;
• (g) passing at least a portion of the throttled second mixed liquid carbon dioxide stream from step (f) through the plurality of heat exchangers to form a carbon dioxide product stream and removing the carbon dioxide product stream from the processing structure;
• (h) (I) splitting the first separated gaseous stream in a first one of the at least one stream splitter to form first and second portions of a split stream;
• (h) (II) using the second separated gaseous stream to cool the first portion of the split stream;
• (h) (III) using the third separated gaseous stream to cool the compressed gas stream to form a liquid carbon dioxide portion of the output stream of a first one of the plurality of heat exchangers;
• (h) (IV) removing the second separated gaseous stream from the processing structure;
• (i) recycling the third separated gaseous stream to at least one of the compressors selected from a second compressor and a compressor thereafter in the sequence in the compression module;
• and
• (j) expanding in the first expander a second portion of the split stream from the selected stream splitter in step (h) (I), to recover energy and to provide cooling to the processing structure.