Correlation Analysis between Working Conditions and the Performance of a Small-Scale Pressure Swing Adsorption Oxygen Production Process

Abstract

Working conditions determine the efficiency of a pressure swing adsorption (PSA) process employing a given adsorbent. The correlation between working conditions and the performance of a small-scale PSA air separation system was comprehensively and quantitively analyzed by experiments and models. Results showed that product recovery could be improved by decreasing the superficial inlet velocity, and the maximum productivity was achieved under optimal superficial velocity conditions of 0.35–0.6 m·s–1 due to a high product recovery and feed rate. Based on the analysis of the mass flow of the cyclic adsorption process, the product recovery and productivity are related with a simple equation of superficial velocity, and the correlation model is in satisfactory agreement with the experimental results. The quantitative relationships between the superficial velocity and performance can be used for designing the adsorber and adsorption process.

Mass and Heat Transfer of Pressure Swing Adsorption Oxygen Production Process with Small Adsorbent Particles

“…The assumptions of the model employed to simulate the mass, heat transfer and performance of the RCPSA oxygen production process are as follows: (1) air is regarded as ideal gas; (2) the feed composition is approximated as a gas mixture of N 2 and O 2 with ratio of 79:21 [16,17,23]; (3) radial gradients of concentration and temperature are negligible; (4) it is necessary to have a uniform particle diameter for adsorbents and adsorption bed porosity; (5) multicomponent Langmuir isotherm could be described as the adsorption equilibrium [24]; (6) linear driving force (LDF) model is employed to characterize the rate of mass transfer between gas and solid phase [25]; (7) the pressure drop is controlled by Ergun's equation [26]; (8) the heat conduction of the bed wall and heat transfer resistance of the wall external convection are negligible.…”

“…The cyclic sequence of the RCPSA oxygen production process is presented in Figure 1. Four beds (labeled bed1, bed2, bed3 and bed4) are employed to conduct rapid cycle and each bed goes though the same cycle steps sequentially [7]. Notably, bed1 and bed3 (bed2 and bed4) are connected for transferring gas and energy during pressure equalization and purge steps.…”

“…Rapid cycle (total cycle time ≤ 10 s) PSA (RCPSA) employing adsorbents with small LiLSX zeolite particles (~0.5 mm in diameter) is particularly suitable for a small-scale oxygen concentrator, since rapid cycle permits the bed to be operated more frequently and therefore enhances the productivity [6][7][8][9][10]. Qadir et al [10] experimentally and numerically analyzed the dynamic breakthrough profiles and separation performance of two-bed RCPSA-based oxygen concentrator, and high productivity of 370 L•(h•kg) −1 with oxygen recovery of 40% is achieved though the enhanced process with adsorption pressure of 350 kPa.…”

“…Rao and Farooq [15] came to a similar result on the effect of axial dispersion on the PSA process using very small adsorbent particles (5A with diameter of 63-75 µm). Zhu et al [7] analyzed the influence of mass transfer models on the PSA air separation performance. There is a satisfactory agreement between the model and experimental results of product recovery and productivity when the film resistance, macropore diffusional resistance and axial dispersion effect are determined as the dominant resistance for small LiLSX particles.…”

“…However, most of the above studies use the simple assumption of mass transfer rate solely controlled with macropore diffusion for small LiLSX particles, which induces significant inaccuracies when numerically predicting the separation performance [7]. The assumption of macropore diffusion is recognized as the dominant mass transfer resistance and traditionally provides a reasonable performance estimation for adsorption involving large zeolite particles [13,16,[18][19][20][21][22].…”