The effect of reliable prediction of final pressure during pressure equalization steps on the performance of PSA cycles

The present work aims at modeling the performance of isothermal PSA cycles for the production of H₂ from refinery fuel gas by introducing a more reliable calculation of the final pressure during the pressure equalization steps. The latter calculation is performed based on the law of conservation of mass in a system comprehending the depressurizing and pressurizing beds in contact. Single adsorbent (zeolite 5A) dual and six-bed PSA processes have been considered. The PSA cycle performance is compared with a conventional model considering an arithmetic mean for the final pressure during the pressure equalization steps (old model). It is shown that the new model predicts lower values for product purity and recovery when compared with the old model. The error in the estimation of the product recovery is larger than the corresponding value for product purity and may exceed 9%. It is shown that the error in the calculation of purity and recovery strongly depends on the number of beds. The error in the calculation of product recovery increases approximately two-fold increasing the number of beds from 2 to 6. Therefore, the present study shows that implementation of a more robust method for the evaluation of final pressure during the equalization steps is imperative for the development of new models of industrial PSA processes, especially for the number of beds exceeding 2.