Simulation and optimization of pressure-swing adsorption systems for air separation

Ling Jiang, Lorenz T. Biegler, V. Grant Fox
2003 AIChE Journal  
Over the past twenty years, Pressure Swing Adsorption (PSA) processes have gained increasing commercial acceptance as an energy efficient separation technique. After a start-up time, the system reaches cyclic steady state (CSS), at which the conditions in each bed at the start and end of each cycle are identical. The traditional way to reach CSS is via successive substitution, which starts from the initial conditions and applies dynamic simulation of the bed performance cycle after cycle until
more » ... he bed conditions repeat periodically. Successive substitution mimics the process performance but suffers from very slow convergence rates. To accelerate CSS convergence, we implement a direct determination approach using a Newton-based method with accurate sensitivities to achieve fast and robust convergence. Trust region methods and scaling are used to handle ill-conditioning and model nonlinearities. When design specifications are imposed, this approach is easily extended to include control constraints. This eliminates trial-and-error experiments and determines all the operating parameters simultaneously. In addition, we modify a standard flux limiter in order to deal with non-differentiable terms and ensure computational accuracy and efficiency. Finally, we design optimal PSA processes by means of state-of-the-art rSQP-based optimization algorithms. The simultaneous tailored approach incorporates detailed adsorption models and specialized solution methods. Here, CSS convergence is achieved only at the optimal solution and the timeconsuming CSS convergence loop is eliminated. Applications of several non-isothermal VSA O2 bulk gas separation processes are presented to illustrate all of these approaches.
doi:10.1002/aic.690490508 fatcat:zospiealubafnjs7ia2lqtuvfm