Experimental and Modeling Analysis of Dual-Reflux Pressure Swing Adsorption Process

Abstract

A laboratory-scale dual-reflux pressure swing adsorption process unit comprised of two beds with intermediate feed position was built and tested for concentrating dilute gaseous feed of methane in nitrogen using Norit RB1 activated carbon. Experimental investigations revealed that the change in blowdown or pressurization step time, feed or purge step time, and heavy product flow rate did not have a significant effect on process performance (in terms of methane purity). However, the process performance was found to be quite sensitive to changes in light reflux flow rate. These experimental results were used to validate the predictions of a mathematical model developed in the frame of the commercial software Aspen Adsim, thus providing an effective tool to elucidate process behavior.

Capture of low grade methane from nitrogen gas using dual-reflux pressure swing adsorption

“…Methane recovery to the heavy product was highest in Runs 1, 3, 5, 19 and 20. The experiments of Bhatt et al [24] were conducted with a similar carbon adsorbent and a feed composition of 5 mol% CH 4 and produced average CH 4 and N 2 products of 58 mol% and 98 mol% purity, respectively. The results of the separations reported by Bhatt et al are also shown in Fig.…”

“…The light reflux and heavy product flow rates were varied in each experiment, which changed the separation performance as indicated by the arrows. The results obtained by Bhatt et al are also plotted[24].…”

“…Recently, Bhatt et al have performed an experimental investigation of DR-PSA with a split-column design, where each adsorbent bed is separated into two columns in series [24]. DR-PSA processes have features similar to a continuous distillation process; for example when both gas species are competing for adsorption sites the phase equilibria (vapor-solid) is akin to vapor-liquid equilibria [23], and the use of heavy (extract) and light (raffinate) refluxes through the adsorbent beds is similar to the use of liquid and vapor refluxes in a distillation process.…”

Influence of the main operating parameters on the DRPSA process design based on the equilibrium theory

“…1; Saleman et al 2015;Zhang et al 2016;May et al 2017) and the light recycle ( ̇n LR in Fig. 1; Bhatt et al 2014;Shen et al 2017;Zhang et al 2016;Tian et al 2017;Li et al 2016) have been identified as major operating parameters to tune the product purity. On the other hand, the effect of changing the pressure ratio, , has not been systematically investigated, even though it can be expected to affect significantly the DR-PSA process performances.…”

“…Similar efforts towards the design of the best process conditions have been made on the modelling side. Different models have been proposed, ranging from detailed models requiring numerical solutions (Rossi et al 2019a, b;Zou et al 2017;May et al 2017;Bhatt et al 2014;Thakur et al 2011) to simplified semi-analytical models based on the so called Equilibrium Theory (Bhatt et al 2018(Bhatt et al , 2017(Bhatt et al , 2013Kearns and Webley, 2006a, b). In the latter case, the design conditions which allow the complete separation of binary mixtures in the case of linear isotherms have been investigated (Bhatt et al 2013(Bhatt et al , 2015(Bhatt et al , 2017(Bhatt et al , 2018 and two key process parameters have been identified: the capacity ratio C , proportional to the ratio between the number of moles injected during the adsorption step and the volume of the column, and the dimensionless feed injection position z feed .…”