POLYBED PSA process

The feed to this process is typically steam reformer or catalytic reformer net gas, but is not limited to them. Feed pressures up to 1,000 psig have been commercially demonstrated. Figure 4.12 shows a schematic of the Polybed PSA process [ 182]. The recovery of H2 ranges between 60% and 98% depending upon the feed gas compositions and pressures. Typical feed and product temperatures are 40 120°F. The H2 purity can be 99.9999+%. 

SCHEMATIC OF POLYBED PSA PROCESS FLOW SHEET (Production of H2 from SHROG)... 

Early work on the u.se of PSA processes for the purification of hydrogen was conducted by the Union Carbide Corporation, and the advanced technology that they developed is now licensed by UOP as the Polybed PSA Process. The process utilizes a relatively large number of adsorption beds (3 to 12) in a specific sequence of steps to provide improved separation efficiency (Fuderer and Rudelstorfer, 1976). The basic steps for hydrogen purification are described as follows (UOP, 1991 A) ... 

The Polybed PSA process has been an outstanding success. The wide variety of applications and the number of units operating on each feed source as of September 1989 are listed in Table 12-23. According to a report in the Gas Process Handbook (UOP, 1996), over 500 Polybed PSA units were in operation or under construction at that time. A photograph of a large UOP Polybed PSA unit is shown in Figure 12-33. 

Because RPSA is appHed to gain maximum product rate from minimum adsorbent, single beds are the norm. In such cycles where the steps take only a few seconds, flows to and from the bed are discontinuous. Therefore, surge vessels are usuaHy used on feed and product streams to provide unintermpted flow. Some RPSA cycles incorporate delay steps unique to these processes. During these steps, the adsorbent bed is completely isolated and any pressure gradient is aHowed to dissipate (68). The UOP Polybed PSA system uses five to ten beds to maximize the recovery of the less selectively adsorbed component and to extend the process to larger capacities (69). 

Hydrogen Polybed PSA A version of the Polybed process, for purifying hydrogen from various industrial processes. Developed by the Union Carbide Corporation in 1975 and now licensed by UOP. More than 400 units were operating worldwide in 1992. 

The POLYBED PSA system is clean and non-polluting. The only materials leaving the unit are product and a tail gas which is used for fuel or subsequent processing. The system requires no water, combustion air, or fuel, and discharges nothing to the atmosphere. Existing commercial units are distinguished by their clean appearance and freedom from odor and corrosion problems. 

Despite these problems, PSA is often used for oxygen and hydrogen purification, and a recent runner-up Kirkpatrick Award for Union Carbide s Polybed hydrogen process (T ) attests to the fact that it is now both practical and economical to perform bulk separations on feed streams in excess of one million cubic feet per hour. 

Recently two widely divergent process variations of PSA have been commercialized by Union Carbide Corporation The first of these is called POLYBED PSA, which Is used for hydrogen recovery (17-21) Plants with capacities of up to about 1 2 x 10 NM /day of hydrogen have been built Hydrogen recoveries of 86 percent vs 70-75 percent for other PSA processes have been demonstrated, as well as purities of 99 999 mole percent (20) POLYBED PSA involves the use of five or more beds, with extensive gas Interchanges and pressure equalizations between the beds One process embodiment (17) is shown In Figure 3 ... 

Thus POLYBED PSA can be thought of as a process which alms for maximum recovery of the less-adsorbed component in very high purity at the expense of a complex flowsheet Its growing commercial acceptance suggests that it competes quite successfully with cryogenic separation in many cases ... 

As mentioned before, POLYBED PSA and PSPP represent quite different approaches to improving the basic PSA process Table II shows the pluses and minuses of these approaches compared to a basic PSA process ... 

Pressure swing adsorption (PSA) on zeolite molecular sieves (see Section 4.3.2.6) may be also used for hydrogen recovery from purge gas [761]. The process, originally developed by Union Carbide under the name HYSIV, is now marketed as Polybed PSA by UOP [970], [973], [974], PSA technology is also offered by Linde and other companies. If required, the process also offers the possibility to supply pure hydrogen from... 

Fig. 9 Schematic drawings of (A) nine column polybed PSA and (B) SMB process with two distillation columns.

The Polybed pressure swing adsorption (PSA) process developed by UOP, can produce hydrogen of any purity, typically 90% to 99.9999+ %. Impurities removed include N2, CO, CH4, C02, H20, Ar, C2-C8+, CH3OH, NH3, and H2S. Typical feed and product temperature is 40—120°F. This process also can be used for other separations such as methane from ethane, C02 from nitrogen, etc. [182],... 

G.Q. Miller and M.J. Mitariten, Process Considerations for POLYBED PSA and POLYSEP Membrane Systems, First Annual Technical Seminar on Hydrogen Plant Operations, San Francisco, CA, June 23-25, 1993, p. 1. 

UOP, 1991 A, Polybed PSA Systems, Publication of UOP Process Plants and Systems, EP3015B, March. 

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