Modeling the adsorption of mixed gases based on pure gas adsorption properties

N Tzabar,H J Holland,H J M Ter Brake,C H Vermeer

doi:10.1088/1757-899x/101/1/012169

N Tzabar, H J Holland + Show 2 more

Open Access

https://doi.org/10.1088/1757-899x/101/1/012169

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Abstract

Sorption-based Joule-Thomson (JT) cryocoolers usually operate with pure gases. A sorption-based compressor has many benefits; however, it is limited by the pressure ratios it can provide. Using a mixed-refrigerant (MR) instead of a pure refrigerant in JT cryocoolers allows working at much lower pressure ratios. Therefore, it is attractive using MRs in sorption- based cryocoolers in order to reduce one of its main limitations. The adsorption of mixed gases is usually investigated under steady-state conditions, mainly for storage and separation processes. However, the process in a sorption compressor goes through various temperatures, pressures and adsorption concentrations; therefore, it differs from the common mixed gases adsorption applications. In order to simulate the sorption process in a compressor a numerical analysis for mixed gases is developed, based on pure gas adsorption characteristics. The pure gas adsorption properties have been measured for four gases (nitrogen, methane, ethane, and propane) with Norit-RB2 activated carbon. A single adsorption model is desired to describe the adsorption of all four gases. This model is further developed to a mixed-gas adsorption model. In future work more adsorbents will be tested using these four gases and the adsorption model will be verified against experimental results of mixed-gas adsorption measurements.

Highlights

Joule-Thomson (JT) cryocoolers that are driven by sorption compressors are free of vibrations and have potentially a long lifetime, thanks to the absence of moving parts
Using a mixed-refrigerant (MR) instead of a pure refrigerant in JT cryocoolers allows working at much lower pressure ratios
The process in a sorption compressor goes through various temperatures, pressures and adsorption concentrations; it differs from the common mixed gases adsorption applications

Summary

Introduction

Joule-Thomson (JT) cryocoolers that are driven by sorption compressors are free of vibrations and have potentially a long lifetime, thanks to the absence of moving parts. A JT cryocooler that operates with a pure gas has an intrinsic low efficiency due to the irreversible heat transfer at its recuperative heat exchanger and the isenthalpic expansion at the restriction. This irreversibility can be dramatically decreased by using mixed gases as the working fluid. A study on sorption compressors for gas mixtures has been reported [14,15], investigating binary mixtures of nitrogen-methane and nitrogen-ethane on Chemviron activated carbon. This paper presents a method to determine the adsorption of mixed gases out of pure gases adsorption characteristics This method will be further incorporated in a sorption compressor simulation for driving JT cryocoolers

Pure gas adsorption measurement procedure

Findings

Conclusions