Improved ODE integrator and mass transfer approach for simulating a cyclic adsorption process

Abstract

This paper introduces two methods specifically tailored to minimise the CPU time required to simulate a Rapid Pressure Swing Adsorption (RPSA) process to Cyclic Steady State (CSS) using a Full Pellet Model (FPM) approach to mass transfer. The first technique introduces the ODE integrator BzzOde (developed in c++) to an existing fortran90 source code (presently using the integrator VODE) for the simulation of an adsorption process. CPU comparisons using two analytical solutions and a four-step RPSA cycle show BzzOde provides significant computational improvements over VODE. Coupled with the introduction of BzzOde is the Mass-transfer Model Switch (MMS), which automatically activates the computationally demanding FPM only after the simpler Linear Driving Force (LDF) model has established CSS. This concept provides a better estimate of the initial conditions passed to the FPM by extrapolating CSS profiles obtained with the LDF model. While significant reductions in CPU time were observed for a non-isothermal RPSA simulation employing the MMS, the initial mole fraction for the bed had a major impact on the improvements afforded with the MMS for the equivalent isothermal simulation. All numerical simulations were performed using a successive substitution approach to CSS convergence.