Scale-up analysis of a twin-bed PSA pilot plant

Abstract

Small-scale pressure swing adsorption (PSA) plants, also referred to as pilot plants, are commonly exploited for studying separation processes in favour of the development of mathematical models and scale-up strategies. The applicability of a lately presented mathematical model, which was developed based on experimental data acquired from a high-purity twin-bed N2-PSA pilot plant, is verified in this paper for the design of large-scale systems by an analysis of the mass transfer zone development at different PSA cycle times. Effects of the PSA scale-up factor, adsorber aspect ratio, packed-bed density, and flow resistances along the piping system on the process performance are studied numerically. These considerations are particularly relevant for the scale-up of bank-type PSA units as well as for skid-mounted systems fitted to local space limitations, where the standard scale-up concept of keeping the gas velocity constant often cannot be fully realised. It is demonstrated that the sensitivity of the PSA performance to studied factors increases along with the required product purity level. Therefore, recommendations for adequate dimensions of pilot plants depending on the desired gas purity level can be derived. Limitations of the gas velocity through the adsorber shall be observed to generate reliable simulation data. The agreement between experimental results obtained from an industrial-scale system on one hand, and the outcome of a dynamic simulation on the other hand, is confirmed—provided that realistic pressure profiles are generated by a proper adjustment of flow resistances along the piping.