Efficient Simulation and Acceleration of Convergence for a Dual Piston Pressure Swing Adsorption System

The dual piston pressure swing adsorption (DP-PSA) system offers the potential for the full characterization of adsorbent materials under a large range of experimental conditions. The analysis of these experiments requires an efficient tool for the simulation of the DP-PSA system to cyclic steady state (CSS). In this contribution, a simulation tool is developed and applied to a mathematical model of the DP-PSA system. The governing set of partial differential equations (PDEs) is solved with state-of-the-art discretization schemes, which are tailored to the character of the governing equations. PDEs with a strong hyperbolic character are discretized with the finite volume method (FVM) with a flux-limiting scheme; this guarantees the conservation of mass as well as correct tracking of the moving fronts. The mass transfer in the adsorbent materials is discretized with the orthogonal collocation on finite elements method which is a very efficient method for problems with steep, stationary gradients. The large system of differential algebraic equations (DAEs) is solved with the state-of-the-art DAE solver SUNDIALS. Even with these sophisticated discretization schemes, the computation times to reach CSS are long due to the nonlinear system behavior as well as the complex nature of the system. Several strategies to reduce the computation time are implemented: (i) conservative node refinement: initial simulation with lower resolution discretization; (ii) implementation of numerical acceleration schemes, e.g., the extrapolation method, which accelerate the convergence to CSS; (iii) restart from previous simulation runs. Each of the acceleration schemes reduces the required simulation time by at least a factor of 2, and the combination of the schemes accelerates the simulation by a factor of 10. Thus, the combined simulation tool allows the rapid simulation of the DP-PSA system