On Selecting a Point for Injection of a Separated Mixture into a Multicomponent-Rectification Column
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 5, September, 2020
HEAT AND MASS TRANSFER IN DISPERSED AND POROUS MEDIA ON SELECTING A POINT FOR INJECTION OF A SEPARATED MIXTURE INTO A MULTICOMPONENT-RECTIFICATION COLUMN A. I. Balunov,a I. A. Sukin,b and A. M. Tsirlinb
UDC 621.1
Consideration has been given to the problem on selecting a point for injection of a separated mixture into a multicomponent-rectification column in accordance with the dissipation minimum condition during the mixing of reflux and mixture streams. An estimate for the minimum entropy production in mixing has been found. The manner in which the irreversibility of the process of mixing at the injection point affects the region of permissible regimes of the column has been shown. An algorithm for calculating the concentration profile of the mixture′s components over the column height has been proposed. Keywords: rectification, optimization thermodynamics, entropy production, point of injection of a separated mixture, dissipation. Introduction. Problems of optimum organization of the process of rectification are the focus of an enormous number of studies [1–12]. Here, account of the irreversibility of the process in the column is taken due to the correction of its reversible characteristics (passage from the minimum rate of flow of the reflux to an operating rate and from the theoretical separation stage to a real plate) by coefficients found experimentally and verified by the experience of many years. Most of the studies are devoted to a simplified model of binary rectification [1–3]. In [13, 14], an "ideal" form of an operating line has been obtained from the results of [15], for which the process′s irreversibility characterized by the entropy production is minimum at fixed output and integral heat- and mass-transfer coefficients. Since the problem was posed of establishing the upper bound of the potential of the column, assumptions simplifying the calculation and extending the applicability of results were made so as that each assumption did not enhance the irreversibility of the process. It is only in this case that we can state that the indices of the real column do not exceed the found ones. Such assumptions overstate the estimates, but these estimates are much more realistic than those obtained on the basis of reversible processes. Furthermore, on the basis of reversible estimates, we cannot obtain such an index as the limiting output at all. In the mentioned works, the authors made the following assumptions: 1) mass transfer is equimolar, 2) in each cross section over the column height, the pressures and temperatures of the vapor and liquid streams are similar (they may vary from one cross section to another), 3) the effects of diffusion between neighboring cross sections are negligibly small and flow regimes are close to an ideal-displacement regime, 4) the heat of the outgoing streams is transferred to the streams entering the column; here, the irreversibility of this heat transfer may be neglected, and 5) the stream o
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