REPRESSURIZATION OF ADSORPTION PURIFIERS FOR CRYOGENIC AIR SEPARATION

The repressurization and adsorption steps of a molecular sieve adsorption purifier upstream of a cryogenic air separation unit was analyzed with a one-dimensional equilibrium-stage model. Numerical solution of the differential mass and energy balances predicts that the effluent gas composition is briefly depleted in nitrogen and the effluent gas temperature undergoes a brief excursion due to preferential nitrogen adsorption on the freshly regenerated 13X molecular sieve. Temperature breakthrough data from an industrial adsorber confirm the theoretical predictions. The results of this analysis demonstrate that the temperature excursion can be used to monitor the performance of the adsorber. The magnitude of the temperature rise can be used to ascertain the amount of presorbed water on, or the extent of degradation of, the 13X molecular sieve and, hence, the subsequent capacity for carbon dioxide adsorption. Disparities in the temperature excursion profile at various locations at the outlet of the 13X molecular sieve bed can be used to detect flow maldistribution problems.