Effects of nonisobaric and isobaric steps on O₂ pressure swing adsorption for an aerator

The effects of nonisobaric and isobaric steps on a two-bed O₂ pressure swing adsorption (PSA) packed with zeolite 5A were investigated. In addition, the operating conditions in the O₂ PSA were studied to supply the various O₂ concentrations to the oxygen aerator efficiently. Because the velocity variation along the bed and the related Mass Transfer Zone (MTZ) shape at the isobaric and nonisobaric steps were affected by the diffusion rate, the concentration-dependent rate parameter in a modified linear driving force (LDF) model was evaluated from the Darken equation related to the loading ratio correlation isotherm model. The LDF coefficients had a significant effect on the prediction of the O₂ purity and recovery at the low flow rate region. However, the higher the feed flow rate, the lower the LDF parameter effect. It was also noted that the effects of each step time in the isobaric and nonisobaric steps on the PSA performance were subtle in the O₂ purity and recovery except for the blowdown step. Also, there was the optimum step time to maximize the O₂ purity and recovery in the adsorption and pressurization steps, while the increase of O₂ purity and recovery with the pressurization equalization step time showed asymptotic curvature. The idle time at the pressurization step had a negative effect on the PSA performance, while the short idle time at the pressure equalization step led to improved product purity. However, it was negligible for the effect of the idle time at the blowdown step on the PSA performance. The successive variation between high and low P/F ratios caused the continuous variation of O₂ purity and recovery to nearly the same extent as the results under each constant P/F ratio condition. Therefore, to save the operating cost of the oxygen aerator system, the desired oxygen concentration for the aerator can be supplied simply by controlling the feed rate or purge rate.