The optimal control of a periodic adsorber: Part II. Theory

Abstract

and higher flow rates, for which adsorption rate limitations may become significant. Second, unless the permeability is constant, the optimal timing of the control sequence will vary and unless corrections for this are made in the control, suboptimal operation will result. To avoid this problem, adsorbent particles that resist abrasion and maintain a constant flow resistance should be used. The round particles used in this research were found to be satisfactory.Another factor that affects the operation of the adsorber is the length of the column. Unlike most chemical process equipment, decreased length increases the capacity of this system (within certain limits). To achieve the same product composition for shorter lengths, higher frequencies are required. Since the optimal frequency increases as the inverse of the square of the length (Kowler, 1969), shorter lengths would require faster operation. This result is valid for flow rates for which adsorption rate limitations can be neglected. In fact, since the optimal frequency increases so quickly as length decreases, the performance of the controlling solenoid valves may limit the achievement of the optimal frequency for shorter lengths. Despite these limitations, it is clear that attempts should be made to use shorter lengths of column to increase capacity and decrease equipment costs at the same time.Having found (theoretically) the optimal feed bound-ary cyclic control of (maximum pressure, zero flow, minimum pressure) and having gained a better understanding of the design parameters, a cyclic adsorption system can now be more properly designed. For the separation of gas mixtures for which there exists an adsorbent with a high relative volatility, the cyclic adsorption process may well be of commercial value.

Gas separation by pressure swing adsorption: A pore‐diffusion model for bulk separation

“…Other commercial applications are oxygen or nitrogen (but not both in the same process) production from air, octane improvement (using Union Carbide ISOSIV Process), and solvent recovery (Cassidy and Holmes, 1984;Keller, 1983). A variation of PSA, first described by Turnock and Kadlec (1971), and Kowler and Kadlec (1972), involves a one-column process driven by a square feed pressure variation applied to one end of the column, with slow withdrawal of a product stream from the opposite end. A process similar to this but using a different pressure cycle, i.e., a short feed and a long exhaust which result in better separation, has recently been commercialized for medical oxygen purposes (Jones and Keller, 1981).…”

“…Most of them considered the adsorption of a single, dilute adsorbate (Pigford et al, 1969; Sweed and Wilhelm, 1969; Wankat, 1981; Hill et al 1981Hill et al ,1982Hill et al , 1983. Kadlec et al (1971Kadlec et al ( ,1972 modeled a single-column process similar to PSA for separating 28.4% N2 in CHI. In this work, bulk separation is studied both experimentally and theoretically for a mixture of 50/50 H2/CH4.…”

Scaling rules and intensification of thermal swing adsorption

“…Such scaling analyses have been carried out for adsorption (Wankat, 1987), chromatography (Wankat and Koo, 1988), isothermal PSA (Kowler and Kadlec, 1972;Suh and Wankat, 1990), and for adiabatic PSA processes (Rota and Wankat, 1990). This note extends these analyses to TSA processes.…”

“…The goal is to keep pressure drop and separation constant while improving absorbent productivity. A dimensional analysis method (Kowler and Kadlec, 1972;Suh and Wankat, 1990;Rota and Wankat, 1990) will be presented.…”

Pore‐diffusion model for cyclic separation: Temperature swing separation of hydrogen and methane at elevated pressures

“…There is an increasing number of important industrial applications being found for temperature and pressure swing separation processes. Designs and performance models have been made and illustrated with various examples (Pigford et al, 1969(Pigford et al, ,1971; Kadlec et al, 1972Kadlec et al, ,1973Wankat et al, 1975Wankat et al, ,1978Hill et al, 1980Hill et al, ,1982. In these models it has been assumed that the adsorbed phase is in instantaneous equilibrium with the ~~ Correspondence concerning this paper should be addressed to R. T. Yang bulk flow phase of the fluid.…”