Purge to feed ratio

Effect of Purqe/Feed on Separation. The purge to feed ratio effect is shown in Figure 6 for a cycle time of 12 minutes and a feed rate of 190 SCCM. 

The effect of increasing feed rate is not as marked as changing the purge to feed ratio or cycle time however, it is evident that at the lowest feed rate the product concentration is highest in hydrogen sulfide. The overlap of the 190 and 280 SCCM flow rates shows that there is little if any difference in separating capacity at these flows. 

Figure 8 also shows the mass balance model predictions for two runs. The mass balance model does a reasonable job of predicting the product concentration for the low cycle time. Here the predicted values are lower than the experimental values, differing by a factor of approximately two. However, for a cycle time of 12 minutes, the prediction falls short of the experimentally determined value. The critical value of y 3 1.0 was used in the model calculations. If 1.3 were used for the purge to feed ratio as suggested by Skarstrom (4), or a value closer to 3 as found in these experiments, the agreement would be slightly better for both runs. 

The Purge-to-feed ratio (that is purge gas flowrate) is one of the most important operating variables in PSA whose increase leads to an increase in purity and a significant decrease in recovery. It has been employed as an optimization variable in case studies I and III. 

Pressure Ratio Ph/Pl Purge-to-Feed Ratio P/F PcD (atm) O2 Product Recovery (%) Sorbent Selection Parameter, S... 

Figure 16. Oxygen concentration profiles at the end of the steps. Cycle time 240s. Product oxygen concentration 0.05%. Purge to feed ratio 0.05. Purge purity 10 ppm O2.

Figure 11. Gas phase concentration profiles of nC, and nCb in the bed at cyclic steady state at the end of a) pressurization b) high-pressure feed c) blowdown d) low-pressure purge step. Temperature profiles are also shown. Feed conditions are 84.6Kg/h of a mixture containing 13.9 % nCj and 4.6 % nC6 mole fraction. The purge to feed ratio is 0.465. Fligh-pressure feed is 15 bar. Low-pressure purge is at 2 bar.

In order to study the performance of the system a plot of purity and recovery of the iso rich fraction versus the purge to feed ratio is shown in Figure 12. Recovery is practically a linear function of purge to feed ratio. Purity decreases significantly when purge to feed ratio is lower than 0.46. 

Figure 12. Recovery and purity versus the iso fraction purge to feed ratio for a PSA separation of n/iso-paraffins based on patent data of Minkkinen et al. [3]. Simulations are performed with equilibria, kinetic and a fixed bed model shown in this work.

Fig 119 Comparison of calculated and experimental dependence of dew points of product gas on volumctnc purge to feed ratio... 

Figure 7.1.15. Critical purge-to-feed ratio. (After Chan et aL (1981).)...

The performance of scheme A was assessed and compared to that of a standalone PSA unit for the separation of a 50/50% (v/v) H2/CH4 mixture. The effects of various operating parameters, such as permeation throughput, total feed amount per cycle, purge-to-feed ratio, and adsorption and blowdown pressures, were analyzed through detailed process simulation. The PSA... 

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