SIMULATION OF BINARY GAS SEPARATION IN HOLLOW-FIBER ASYMMETRIC MEMBRANES BY ORTHOGONAL COLLOCATION

Modeling of hollow fiber asymmetric membrane modules can provide usefu l guidelines to achieve desirable separations of gas mixtures. In this work the performance of a countercurrent flow separator was analyzed through a parametric study of the most important system variables as f unctions of basic design and operational parameters. Results refer to CO2-N-2 separation from power station flue gases as a typical, potenti al process. The appropriate model equations were solved by orthogonal collocation to approximate differential equations, and to solve the re sulting system of non-linear algebraic equations by the Brown method. This technique compared to other applied computational procedures mini mized the computational time and effort and improved solution stabilit y. This is very important if the pressure and concentration profiles a long the permeator, both in the residue and the permeate streams, need to be determined. These profiles influence strongly the permeator per formance and, under certain conditions such as moderate and high feed pressure, they may result in lower than expected permeate purity. The simulation results also indicate that the role of the basic design par ameters may be of equal if not higher importance to membrane selectivi ty. Thus industrial permeator performance, as it is expressed by stage cut and permeate purity, is not very sensitive to membrane permselect ivity beyond a modest value of 40-50, especially at moderate and high (15-20 bar) feed pressures. A desirable gas separation may then be ach ievable with a reasonably permeable, albeit not very selective membran e, provided that design and operating variables are selected appropria tely. (C) 1998 Elsevier Science B.V.