Simulation of an Enriching Reflux PSA Process with Parallel Equalization for Concentrating a Trace Component in Air

• Published in: Industrial & engineering chemistry research Vol. 45; no. 18; pp. 6243 - 6250
• Main Authors: Yoshida, Masayuki, Ritter, James A., Kodama, Akio, Goto, Motonobu, Hirose, Tsutomu
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 30.08.2006
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie0604573

The utility of a simple numerical model, based on the LDF approximation and the frozen solid phase assumption, was developed to predict the performance of an enriching reflux (ER) pressure swing adsorption (PSA) cycle with parallel equalization (PEQ) for concentrating a trace component. The utility of this model was successfully demonstrated with the enrichment of Xe from air using 13X zeolite and a two-bed, 6-step, ER PSA cycle with PEQ. With the LDF mass transfer coefficient (Ka) ranging from 2.0 to 3.0 kg m-3 s-1, the model predictions of the enrichment factor (Y HP/Y F) compared well with the experimental results over a wide range of conditions. Both the modeling and experimental results showed that ambient Xe in air could be enriched up to 80 times by the ER PSA cycle with PEQ. The enrichment factor that could be obtained from the more conventional stripping reflux PSA cycle was theoretically limited to 12.5, i.e., the high to low pressure ratio, with the actual value usually being much less than half of this limit. A constant value of Ka = 2.0−3.0 kg m-3 s-1 also sufficed when predicting the performance of the ER PSA cycle with PEQ for different high to low pressure ratios, feed flow rates, and heavy product flow rate to feed flow rate ratios. For the effect of the half cycle time (t c) on the enrichment factor, Ka was allowed to decrease in proportion to t c -0.5, which led to a reasonable value for the diffusion coefficient of Xe in 13X zeolite of 5.14 × 10-11 m2 s-1. Both the modeling and experimental results showed that PEQ provided enrichment factors of more than twice that obtainable from heavy product end equalization. The modeling results also revealed that the frozen solid phase assumption epitomized the parallel equalization concept, in that it resulted in no disturbance in the axial concentration profile in the beds, a condition that could only be approached experimentally through PEQ. Finally, the modeling results indicated that PEQ had the same effect on the process performance as increasing Ka.