Separation Cascade

Research on removal of noble gases by permeation method with dimethyl silicon membranes was carried out in Oak Ridge National Laboratory [160]. On the basis of experimental work, the calculations for different industrial cascades separating krypton and xenon from the space of molten salt and sodium cooled breeder reactor or from the off gas from a plant processing spent reactor fuel were performed. 

Cascade separations have been advanced by other researchers (18,19,20,21,22). Commerlcal units, such as the Du Pont Permasep... 

Consider an extracting-scrubbing cascade separating components A and B, with constant distribution coefficients and Dg. The concentrations x, and the recovery p of component A are specified. Components A and B are not present in the entering organic and in the entering scrub solution. 

Such a countercurrent cascade separates feed containing zp fraction of desired component flowing at rate F into product containing yp fraction of desired component flowing at rate P and waste, or tails, containing xw fraction of desired component flowing at rate W. These six compositions and flow rates are called the external variables of the cascade. 

FIGURE 6.19 Schematic of air-stream (cascade) separator. 1, Gate valve 2, cascading (zigzag) channel 3, container with air suction 4, gate valve 5, blower 6, cyclone 7, filter with particle container. 

Gas extraction extends the possibilities of separation processes like distillation, absorption and liquid-liquid extraction to the isolation and purification of components of low volatility. Furthermore, it enables separation of components with very similar properties if used in the countercurrent mode. Process temperatures in gas extraction are determined by the critical temperature of the solvent and not, as is the case of distillation of any kind, by the liquid-vapor transition of the feed mixture. As compared to liquid-liquid extraction, gas extraction makes easily possible to operate a two cascade separation column, applying a stripping and an enriching section. Combined, these possibilites allow gas extraction to be operated at very moderate temperatures and as a separation process for difficult separations. 

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