SIMULATION OF RAPID PRESSURE SWING ADSORPTION AND REACTION PROCESSES

A general model for non-isothermal adsorption and reaction in a rapid pressure swing process is described. Several numerical discretisation methods for the solution of the model are compared. These include the methods of orthogonal collocation, orthogonal collocation on finite el ements, double orthogonal collocation on finite elements, and cells-in -series. Computationally, orthogonal collocation on finite elements is found to be the most efficient of these. The model is applied to air separation for oxygen production. Calculations confirm the formation o f a concentration shock when an adsorbent bed is pressurised with air. The form and propagation of the shock over short times is found to be in excellent agreement with the exact similarity transformation solut ions derived for an infinitely long bed. For air separation, novel exp erimental measurements, showing an optimum particle size for maximum p roduct oxygen purity, are accurately described by the model. Calculati ons indicate that a poor separation results from ineffective pressure swing for beds containing very small particles, and from intraparticle diffusional limitations for beds containing very large particles. For adsorption coupled with reaction, finite rate and reversible reaction s are considered. These include both competitive and non-competitive r eaction schemes. For the test case of a dilute reaction A half arrow r ight over half arrow left B + 3C, with B the only adsorbing species, b ed pressurisation calculations are found to be in excellent agreement with the solutions obtained by the method of characteristics.