Nonequilibrium Computations For Multistage Extractors


Nonequilibrium descriptions of multistage extraction and distillation systems have been undertaken by a number of investigators. Deviation from equilibrium is recognized in distillation and has been found significant in extractors ranging from mixer-settlers to agitated columns and for a variety of chemical components. Two approaches have been taken to account for nonequilibrium. The efficiency method ratios the actual change accomplished to that possible at equilibrium. The two-phase method involves separate material balances for each phase and accounts for mass transfer across the interface between them. One direct method for solving a set of nonequilibrium material balance equations was presented by Holland[1]. It is applicable only to conventional distillation columns. Both the efficiency approach and the two-phase method lead to sets of materials balances in which variables interact with other variables which are not adjacent to them in sequential order. Since the coefficient matrix is not tridiagonal, the most common direct method applied to multistage problems, the Thomas algorithm, may not be used to obtain the solution to these material balances. To simplify material balance computations for liquidliquid extractors and vaporliquid absorbers a direct, non-iterative, computational algorithm is developed for steady-stage calculations. Iterative searches for composition dependent equilibrium may be included without interference and possible misdirection from nonequilibrium effects. When this procedure is used, nonequilibrium stage computations can be made routinely for all multistage systems. © 1978.


Chemical and Biochemical Engineering

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Article - Journal

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Publication Date

01 Jan 1978