Simulation of continuous-contact separation processes: unsteady-state, multicomponent, adiabatic absorption

Abstract

A rigorous algorithm has been developed for the unsteady-state simulation of multicomponent, adiabatic absorption in packed columns. The simulation uses an implicit integration scheme to solve the partial differential model equations which may include both nonideal vapor-liquid equilibrium relationships and nonlinear mass-transfer expressions. All physical parameters used in the model are obtained from empirical correlations available in the literature. Simulation predictions, both dynamic and final steady-state, compared favorably with experimental results.The numerical simulation of continuous-contact separation devices is a topic that has long been neglected. In a previous article (Hitch et al., 1986), we pointed out that until recently most research efforts in the area of the design and analysis of separation processes have concentrated on

Dynamic Simulation of Continuous-Contact Separation Processes with the Moment Transformation Method

“…Liquid holdup is usually calculated from an empirical correlation for a specific packing type. Although holdup and pressure drop correlations apply strictly in the steady state only, they are frequently used in dynamic simulations. ,,, It can be assumed that the changes in holdup and pressure drop during the transients are so small that the correlations apply with good accuracy. This applies during transients from one steady state to another but not necessarily during startup and shutdown periods as the column may be initially completely dry.…”

“…Mathematically, continuous-contact separation processes are modeled by partial differential equations for mass, momentum, and energy transport in both phases. These equations can be solved using a number of techniques, such as the finite difference method, , the finite volume method, or polynomial approximations such as orthogonal collocation. , The probably most popular rate-based method, the nonequilibrium stage model of Krishnamurthy and Taylor, , is a finite volume model in the sense that the column is divided into a finite number of slices and the mole fractions and temperatures are averaged within those slices. All these models can be used for both steady state and dynamic simulations.…”

Nonlinear model predictive control of a packed distillation column

“…A mixing-cell type of model was employed, and mass transfer was described using the filmfactor concept. Hitch et al (1987) extended their earlier work (Hitch et al, 1986) to include the dynamic behavior of packed absorbers by introducing accumulation terms into the material and energy balances. The finite-difference method was used to discretize the partial differential equations in the time dimension.…”