Modelling of a selective absorption process for rare gas removal from reprocessing off-gas

A mathematical model for a selective absorption process for rare gas recovery from the dissolver off-gas will be presented. The process is a conventional gas absorption-desorption procedure using circulating CC12F2 solvent at cryogenic temperatures. A high product purity is achieved with an additional intermediate stripping step for the removal of coabsorbed carrier gases. The mathematical model is based on the stage theory. The absorber and the final desorber can be described by simple equations, because the operating conditions are constant over the packed length. For the intermediate stripper the whole system of material and energy balance equations has to be solved for each stage. An iterative procedure has been developed, which allows the determination of flow and concentration profiles for each gas component. A selfconsistent temperature profile terminates the iteration. The model requires experimental distribution data of the various gas components, operating conditions and design parameters such as the number of stages in the packed zones, which must be determined experimentally. Optimum operation conditions have been predicted by the model and verified in the pilot plant