OPTIMIZATION OF MODULE CONFIGURATION IN MEMBRANE GAS SEPARATION

Mathematical models have been developed to optimize three configuratio ns for membrane gas separation modules. The three systems include the single stage, the two stage, and the continuous membrane column (CMC). Analysis of the three systems is carried out for the case of enrichin g a binary mixture of methane and carbon dioxide, where the reject str eam is the desired product. The cost optimization function includes th e capital cost for compressors and membranes as well as the energy ope rating cost. The cost function is solved subject to a set of equality and inequality constraints. The equality constraints include the modul e balance equations and the permeation fluxes across the membrane. The inequality equations include constraints on mole fractions in permeat e and reject streams, operating pressure, membrane area, and the amoun t of methane recovered in reject stream. Model equations for the three systems are solved using GINO, a program for nonlinear optimization. A quasi-Newton search method is selected and found quite efficient for solution of the equations. Over the range of parameters considered in the analysis, results show that the two stage configuration has a low er production cost than the other two systems. In addition, the operat ing cost for the CMC and the single stage systems are found to be comp arable. Irrespective of this, the optimum amount of methane recovered is the highest for the CMC system. Although the optimum operating cost s for the CMC and the single stage systems are higher than the two sta ge system, comparison should consider other factors including higher m ethane recoveries generated by the CMC system and the simplicity of de sign and operation for the single stage system.