A novel mini pressure swing adsorption plant for oxygen concentration

Abstract

The second wave of COVID-19 led to a severe scarcity of medical oxygen in the country, as cryogenic distillation plants could not entirely meet the exigent oxygen requirements for medical usage. Consequently, there has been a growing impetus to utilise the non-cryogenic air separation process for medical oxygen generation. In this regard, the pressure swing adsorption (PSA) process has emerged as a practical and suitable substitute for cryogenic distillation in separating oxygen from the air. The goal of the current work is to design, develop, and optimise a novel mini PSA plant that is pertinent to the conditions of a country like India. The device, thus developed, is configured to be portable and will provide at least 40 litres of oxygen per minute to support a minimum of 6 to 8 patients in a small hospital scenario. The device is rugged with medical-grade components and can handle both lithium-based and sodium-based zeolites. The overall procedure involved designing and testing multiple versions of the device, starting from tabletop models with LiX (X represents aluminosilicate) zeolite to a current experimental design with NaX zeolite as the adsorbent. A typical PSA cycle is essentially controlled by three parameters: pressurisation, purge, and equalisation times, which are the duration of different processes involved in the cycle. In the current work, we have carried out parametric studies on each version of the experimental setup by varying the above three times for the given input and output conditions. Each subsequent version of the device was evolved to address the issues faced by all the earlier designs. This finally led to the development of the device’s final version that provided a 92% enhanced oxygen stream at 40-45 litres per minute. It was observed from the different experimental trials that the critical design factors of the adsorption column are two: one, the length-to-diameter ratio (l/d) and the second, the dead volume. We observed experimentally that the ’l/d’ ratio should be between 4 and 6 to avoid both flow mal-distribution and large pressure drop inside the adsorbent column. Consequently, for the final experimental setup, the l/d ratio is 5.71. Note that the dead volume of the zeolite cylinder should be as low as possible (0.16% for the present experimental design) to avoid mixing trapped nitrogen with the oxygen-enriched air.