Extraction cascade, counter-current

Stripping can equally be done in single-stage, cross-flow, or counter-current systems. To illustrate how the overall concepts remain valid, the performance of a countercurrent cascade accepting as feed the scrubbed extract... 

The GS enriching process is a counter-current gas-liquid extraction done at a pressure of 2000 kPa in a sieve tray tower with the upper half operating at 30 C and the lower at 130 C. ( 5) In the top half of the tower, feedwater extracts deuterium from the upflowing cold H2S, reaching a maximum at the centre of the tower. The recycled lean H2S entering the lower hot half of the tower strips deuterium from the water, which then leaves the system depleted in deuterium. A cascade of several stages is used to reach the desired feed concentration for the final water distillation or finishing unit. Transfer between cascades can be either by gas or liquid from the centre of the tower. 

In order to evaluate the plutonium purification process with TBP, a calculation code has been developed for the system composed of TBP, nitric acid and plutonium on the basis of a batchwise counter-current extraction cascade (28). The code computes not only number of theoretical stages required, but also concentration profile for steady or transient state. The profiles of calculated... 

This unit can simulate any type of separation processes, as distillation, absorption, stripping, or extraction columns, modelled as cascade of counter-current equilibrium stages. The model Radfrac in Aspen Plus is particular powerful. It is first built on the inside-out algorithm that increased dramatically the robustness in simulating distillation-based operations (Boston, 1980). Columns with multiple feeds, side streams products, stage heaters or coolers, can be treated, as illustrated in Fig. 3.13. The following capabilities are generally available ... 

Countercurrent multiple contact. This method involves the use of a cascade of stages, extracting solvent and solution to be extracted entering at opposite ends of the cascade. Extracts and raffinates flow counter-currently. The operation is more analogous to gas absorption than to any distillation practice. It is necessarily continuous but may be simulated in batch fashion, in the laboratory for example, as pseudo countercurrent multiple contact. ... 

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