Integrated Design and Control of Pressure Swing Adsorption Systems
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In the last few decades, pressure swing adsorption (PSA) has evidenced substantial growth in terms of size, versatility and complexity. In addition to handling multi-component separation and purification, it offers tremendous flexibility at the design stage, requiring careful selection of key decision variables including number of beds, number of pressure equalization steps per cycle, cycletime, bed length and bed diameter. Further challenges are posed by the fact that the PSA operation is periodic in nature and never attains a true steady state. Integrated design and control of PSA system, incorporating its highly nonlinear and dynamic nature remains a challenging task and is the focus of this study. Towards this goal, a detailed first principle based model is first developed for a double bed, 6 step PSA system. In the next step, the full scale integrated design and control dynamic optimization problem is formulated and solved incorporating all operational constraints. The key design objective for the PSA system separating 70 % H2 - 30 % CH4 mixture into high purity hydrogen, is to maximize the H2 recovery, while fast tracking the H2 purity to a set point value of 99.99 % for disturbances in feed temperature and feedrate. The results of detailed comparative studies shows that the optimal design obtained from integrated design and control case provides better hydrogen recovery and disturbance rejection as compared to sequential design and control case. 2011 Elsevier B.V.