Nonequilibrium modeling of three-phase distillation

A nonequilibrium (NEQ) model for a complete three-phase distillation in tray columns is described. The model consists of a set of mass and energy balances for each of the three possible phases present. Mass and heat transfer between these phases is modeled using the Maxwell–Stefan equations. Equilibrium is only assumed at the phase boundary between two phases. The equilibrium stage model is a special case of the general model. The method of solving the NEQ model equations described here consists of first solving the equilibrium two phase model, using this solution to obtain a converged solution for the equilibrium three-phase problem by means of a differential arc length continuation method, and subsequently using this as a starting guess for the nonequilibrium three-phase model with Newton’s method. Incorporated into the algorithm model is a liquid phase stability check and phase split calculation to evaluate the thermodynamic stability of all liquid phases present in the distillation column each iteration. We have found that the component Murphree efficiencies tend to be lower and more highly variable in the two-liquid phase region than they are in the single liquid region. There may be a jump discontinuity in component efficiencies as we move from homogeneous to heterogeneous liquid phase regions of composition space. EQ models modified by efficiency factors should not, in general, be used for the simulation of three-phase distillation processes. NEQ models should be preferred in general.

[1]  U. Block,et al.  Development and application of a simulation model for three-phase distillation , 1976 .

[2]  R. Krishna,et al.  The Maxwell-Stefan approach to mass transfer , 1997 .

[3]  Michael F. Malone,et al.  Conceptual design of distillation systems , 2001 .

[4]  Rajamani Krishna,et al.  Real-world: Modeling of distillation , 2003 .

[5]  J. W. Kovach.  Heterogenous azeotropic distillaion-homotopy-continuation methods , 1987 .

[6]  Multicomponent three-phase azeotropic distillation. 1. Extensive experimental data and simulation results , 1990 .

[7]  M. Michelsen.  The isothermal flash problem. Part II. Phase-split calculation , 1982 .

[8]  Harvey D. Mendelson.  The prediction of bubble terminal velocities from wave theory , 1967 .

[9]  B. Cairns,et al.  Multicomponent three-phase azeotropic distillation. 3. Modern thermodynamic models and multiple solutions , 1990 .

[10]  R. Reid,et al.  The Properties of Gases and Liquids , 1977 .

[11]  Massimo Morbidelli,et al.  Distillation models for two partially immiscible liquids , 1981 .

[12]  H. Kooijman,et al.  The ChemSep book. , 2001 .

[13]  B. Cairns,et al.  Multicomponent three-phase azeotropic distillation. 2. Phase-stability and phase-splitting algorithms , 1990 .

[14]  E. Eckert,et al.  Some aspects of rate-based modelling and simulation of three-phase distillation columns* , 2000 .

[15]  J. D. Seader.  The B.C. (Before Computers) and A.D. of Equilibrium-Stage Operations. , 1985 .

[16]  Warren D. Seider,et al.  Simulation of three-phase distillation towers , 1981 .

[17]  Hamid Reza Mortaheb,et al.  Hydrodynamics and mass transfer in heterogeneous distillation with sieve tray column , 2002 .

[18]  M. Lockett.  Distillation Tray Fundamentals , 1986 .

[19]  Ross Taylor,et al.  Modeling Mass Transfer in Three-Phase Distillation , 1994 .

[20]  M. Michelsen.  The isothermal flash problem. Part I. Stability , 1982 .

[21]  K. K. Bool,et al.  Three-phase flash and distillation , 1985 .

[22]  Rajamani Krishna,et al.  Nonequilibrium cell model for multicomponent (reactive) separation processes , 1999 .

[23]  Ernest J. Henley,et al.  Separation Process Principles , 1998 .

[24]  Composition Trajectories for Heterogeneous Azeotropic Distillation in a Bubble-Cap Tray Column: Influence of Mass Transfer , 2003 .

[25]  Ross Taylor,et al.  A nonequilibrium stage model of multicomponent separation processes. Part I: Model description and method of solution , 1985 .

[26]  Günter Wozny,et al.  A nonequilibrium model for three-phase distillation in a packed column: modelling and experiments , 2000, Comput. Chem. Eng..

[27]  William R. Smith,et al.  General optimality criteria for multiphase multireaction chemical equilibrium , 1993 .

[28]  Ross Taylor,et al.  Multicomponent mass transfer , 1993 .

[29]  Ignacio E. Grossmann,et al.  Systematic Methods of Chemical Process Design , 1997 .

[30]  Günter Wozny,et al.  Experimental Investigations of Three-Phase Distillation in a Packed Column , 2002 .

[31]  Christopher L.E. Swartz,et al.  Finite‐element steady state simulation of multiphase distillation , 1987 .

[32]  M. Morbidelli,et al.  An approximate mathematical model for three-phase multistaged separators , 1982 .

[33]  Rajamani Krishna,et al.  Mass Transfer in Multicomponent Mixtures , 2006 .