Process for separating CO2 from CO2 containing gas stream
The invention relates to gas separation, particularly to a process for separating CO 2 from a CO 2 containing gas stream with varying CO 2 concentration using a membrane-based separation system. The process for separating CO 2 comprises: (i) feeding the CO 2 containing gas stream into a membrane-based separation system comprising one or more membrane stages in-line, each membrane stage producing a CO 2 -depleted retentate stream and a rich CO 2 permeate stream, and (ii) recycling a part of the CO 2 -rich permeate stream from at least one membrane stage as a recycled stream, into a preceding feed stream of one or more membrane stages in the membrane-based separation system to adjust the CO 2 concentration of the feed stream. The process could stabilize the CO 2 concentration in the feed steam by recirculation of a fraction of the high purity CO 2 permeate to the feed of the membrane system, which would result in a lower incremental auxiliary load than other options such as compression of the entire gas stream.
1. A process for separating CO 2 from a CO 2 containing gas stream with varying CO 2 concentration in time comprising:
(i) feeding the CO 2 containing gas stream with varying CO 2 concentration into a membrane-based separation system comprising one or more membrane stages in-line, each membrane stage producing a CO 2 -depleted retentate stream and a CO 2 -rich permeate stream, and
(ii) recycling a part of the CO 2 -rich permeate stream of one or more membrane stages as a recycled stream, into a preceding feed stream of one or more membrane stages in the membrane-based separation system to adjust the CO 2 concentration of the feed stream to keep the CO 2 concentration in the feed stream to one or more of stages of the membrane-based separation system steady, the flow rate of the recycled stream is adjusted based on measurements of the CO 2 concentration of the feed stream, or the flow rate of the recycled stream is adjusted based on upstream parameters in accordance with which the CO 2 containing gas stream is generated including: operational parameters of the plant where the CO 2 containing gas stream is generated, or operational parameters related to upstream emissions controls of the CO 2 containing gas stream.
2. The process according to claim 1 wherein the CO 2 containing gas stream is a flue gas stream produced from power generation using fossil fuels.
3. The process according to claim 2 , wherein the fossil fuel is coal.
4. The process according to claim 1 further comprising using a part of the last CO 2 -rich permeate stream from the last membrane stage as the recycled stream.
5. The process according to claim 1 further comprising recycling at least a part of the recycled stream into the first feed stream of the first membrane stage.
6. The process according to claim 5 wherein the CO 2 concentration of the first feed stream is adjusted to 12 mol % or more by the recycled stream.
7. The process according to claim 6 wherein the CO 2 concentration of the first feed stream is adjusted to 12 mol % - 15 mol % by the recycled stream.
8. The process according to claim 1 wherein the flow rate of the recycled stream is 70 mol % or less based on total content of the last CO 2 -rich permeate stream.
9. The process according to claim 8 wherein the flow rate of the recycled stream is 25 mol % - 70 mol % based on total content of the last CO 2 -rich permeate stream.
10. The process according to claim 9 wherein the flow rate of the recycled stream is 30 mol % - 65 mol % based on total content of the last CO 2 -rich permeate stream.
11. The process according to claim 1 wherein the recycled stream enables the total content of the feed stream to be increased by 15 mol % or less.
12. The process according to claim 1 wherein overall CO 2 recovery rate is 50% or more.
13. The process according to claim 12 wherein the overall CO 2 recovery rate is 60% - 90%.
14. The process according to claim 1 wherein the concentration of CO 2 in the last permeate stream is 60 mol % or above.
15. The process according to claim 14 wherein the concentration of CO 2 in the last permeate stream is 90 mol % or above.
16. The process according to claim 14 wherein the concentration of CO 2 in the last permeate stream is 95 mol % or above.