To produce O2 with a high purity of 99+% and a high productivity from various oxygen-rich
feeds, a parametric study was done on a six-step pressure swing adsorption (PSA) purifier using
carbon molecular sieve (CMS). The cyclic performances of the PSA process such as purity,
recovery, and productivity were compared under nonisothermal conditions. To study the effects
of N2 amount on the PSA purifier, various feeds with 90% O2 or more were experimentally and
theoretically applied for the PSA process. Since N2 plays a key role in product purity, the
maximum purity of the PSA was 99% O2 with 51.5% recovery from a higher nitrogen feed
(O2:Ar:N2; 90:4:6 vol %) and 99.8% O2 with 56.9% recovery from a lower nitrogen feed
(O2:Ar:N2; 95:4:1 vol %) within the experimental range. The adsorption step time and feed flow
rate served as key operating variables in the purification of the oxygen-rich feeds because the
concentration wave fronts of minor impurities such as N2 and Ar were controlled by kinetic
selectivity. To produce 99% O2 purity from feeds with various amounts of N2, the optimum
operating variables were set to maximize the recovery and productivity within the experimental
ranges. A high feed flow rate accompanied by a short adsorption step time could increase both
purity and productivity. Without any serious loss of recovery and productivity, the process could
purify the feed with higher than 91% O2 to the product with higher than 99% O2. The
nonisothermal model incorporating mass, energy, and momentum balance together with a
concentration-dependent rate model could accurately predict the performance results.
A parametric study was carried out to improve the cyclic performance of the three-bed pressure−vacuum
swing adsorption (PVSA) process, which consisted of two zeolite 10X beds for equilibrium separation and
one carbon molecular sieve (CMS) bed for kinetic separation. Since the adsorption pressure and the feed
flow rate of the zeolite 10X bed affected the concentration wave front of each component in the steps of
removing impurities in the CMS bed, they played an important role in the final purity and recovery of the air
separation. The pertinent step times in the nonisobaric steps, such as the pressurization and the pressure
equalization steps of the zeolite 10X bed, contributed to the improvement of both O2 purity and recovery. In
addition, the pressurization and the adsorption steps of the CMS bed served as key steps to purify the oxygen-rich feeds from the zeolite 10X bed. The increased pressurization step time leads to an increased adsorption
pressure in the CMS bed, and the increased adsorption time implies the prolonged step of removing impurities
in terms of kinetic separation in the CMS bed. Therefore, high O2 purity with high recovery and productivity
could be obtained from the low quality product of the zeolite 10X bed by the increased step times in these
two steps. However, increase of these step times might lead to a decrease in final O2 purity because the
breakthrough of impurities occurred through the extended adsorption step time of the zeolite 10X bed. The
effect of these step times on the final O2 purity from the CMS bed was, however, less sensitive than that
from the zeolite 10X bed. Furthermore, the recovery and the productivity could be increased simultaneously
with a decrease in purity in the variation of pressurization step time. Consequently, O2 of 97+% purity with
high recovery of 75+% and productivity of 5.8 × 10-5 cm3/g·s, was produced at a well-tuned operating
condition.
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