filter coalescer, (b) carbon bed, (c) particulate filter, and (c) heater. The heated gas is then routed to the first membrane stage, which separates the inlet gas into two streams: ➊ LP permeate stream: the membranes preferentially permeate CO 2 , and the resulting LP permeate stream, enriched in CO 2 , is compressed and sent to the second
Stage-1
HP residue CO < 7%
Membrane
Pretreatment
Feed gas 29% CO
Permeate Stage-1
Recycle
Compressor
Membrane
Pretreatment
Stage-2
Permeate product CO > 90%
Figure 3 Two-stage membrane process scheme
membrane stage for further CO 2 recovery. ➋ HP residue stream, depleted in CO 2 and more concentrated in the heavy hydrocarbons, is routed to the sales pipeline at high pressure. The permeate from the first stage is further compressed via a recycle compressor and routed to the second-stage membrane for further processing. After passing through the pretreatment section, the second membrane stage further separates the inlet HP gas into two streams: ➊ LP permeate, enriched in CO 2 , is the final product CO 2 stream and routed to the CO 2 liquefaction unit. ➋ With a reduced CO 2 content, the HP residue
stream is recycled back to the front of the first- stage process. A CO 2 removal multi-stage membrane plant is illustrated in Figure 4 (compressor not shown). Description of CO 2 liquefaction CO 2 liquefaction is a process to separate CO 2 from the mixture of hydrocarbons, mostly methane, where two streams will be generated: one is the CO 2 , and the other is residue or natural gas. The residue is recycled back to the membrane system for further separation. The dried gas enters the CO 2 liquefaction unit, where it is chilled by heat integration with the fractionation column (furnishing reboiler duty for the column). The gas is then further chilled
Figure 4 Onsite installation of multi-stage membrane CO 2 removal unit
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