(554d) Advanced Novel Hybrid PSA/TSA Thermal Adsorptive Processes for Air Purification

Pre-purification of air prior to an air separation units (ASU) is a major unit operation responsible for removal of water, CO2, Oxides of Nitrogen and Hydrocarbons. The operation of the pre-purification unit has a major role in stability, operation, overall economics and safety of an ASU. Pre requisite for such adsorption units, C2H2, with low solubility in liquid oxygen has to be fully removed prior to cryogenic distillation system for safety concerns.

First generation (1970â??s) of the adsorptive air purification utilised conventional thermal swing adsorption (TSA) systems, utilised high proportions or all NaX molecular sieve. The optimal design of a TSA system requires a pre-cooling system, which lowers the water loading duty of the system to minimise the adsorbent utilisation, regeneration power and the vessel size. Such a system typically operate with an on-line time in the range 2-8 hrs. Extensive hardware and regeneration power requirements for a TSA system adversely impact its economics.

More recently, Air Products starting from basic Skarstromâ??s 2 bed PSA Cycle, has developed and commercialised on over 500 industrial applications worldwide new generations of pioneering PSA, Thermal PSA (TPSA) and Thermally Enhanced PSA (TEPSA) to meet the requirements of the modern Air Separation plants across different product lines and varied applications. Objective throughout has been to reduce capital cost and regeneration energy requirements. Parallel, Air Products has developed new generation of proprietary advanced materials to meet the varied demands and match mass transfer characteristics and requirements of the hybrid cycles. Combined, the new cycles and adsorbents have resulted in significant reduction in both capital and power footprint of these units by around 50% compared with industry standard (TSA) and take advantage of synergies to retrofit older units for improved throughput and power reduction.

A major feature of Hybrid PSA/TSA is use of pioneering advanced proprietary low cost activated alumina for partial removal of water and CO2 and ability to take full advantage of PSA effect removals thus minimise the use of more costly NaX materials. We shall therefore report our progress on modelling H2O and CO2 isotherms and simultaneous breakthrough characteristics.

 

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