Membranes Purge cycles

Figure 1 Flowsheet of hybrid membrane-PSA process. Steps pressurization (PR = PRi + PR2). high-pressure adsorption (HPA), co- and counter-current blowdown (CD, BD), Purge (PG) A stream enriched in less adsorbed component, B-. stream enriched in strongly adsorbed component. Pressure histories of the integrated cycle at CSS.

Figure 9 shows a schematic flow diagram and an example of the hybrid H2 PSA-SSF membrane concept. The fresh feed to the PSA process is SMROG. The PSA process cycle is an abridged version of the Poly-bed process with only two co-current depressurization steps, having a H2 recovery of 77.6%. The countercurrent depressurization effluent gas is fractionated. The initial part of this gas, which is richer in H2, is directly fed to a SSF membrane at a pressure of 3 bar. The H2 purge effluent gas is compressed to 3 bar and fed to the same membrane. The H2 enriched high pressure effluent gas from the membrane is recompressed and recycled as feed gas to the PSA process. This increased the overall H2 recovery of the hybrid process to 84.0% [23]. 

Ultimately, the PSA cycle proceeds with the following steps co-current blowdown (CD) to recover the residual amount of A that was pushed to the end of the bed during the HPA step counter-current blowdown (BD) and purge (PG) to recover species B and to regenerate the bed for the next cycle. During these steps, the membrane module operates with the other PSA bed. Although the operation of each bed is batch-wise, the system as a whole is a continuous one that is operated under cyclic steady-state conditions. Unlike conventional membrane operation, in which the pressures are kept constant, here the permeation occurs cyclically due to its coupling to the PSA cycle. 

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