Application of Computational Mass Transfer (I): Distillation Process

Chapter
Part of the Heat and Mass Transfer book series (HMT)

Abstract

In this chapter, the application of computational mass transfer (CMT) method in the forms of two-equation model and Rayleigh mass flux model as developed in previous chapters to the simulation of distillation process is described for tray column and packed column. The simulation of tray column includes the individual tray efficiency and the outlet composition of each tray of an industrial-scale column. Methods for estimating various source terms in the model equations are presented and discussed for the implementation of the CMT method. The simulated results are presented and compared with published experimental data. The superiority of using standard Reynolds mass flux model is shown in the detailed prediction of circulating flow contours in the segmental area of the tray. In addition, the capability of using CMT method to predict the tray efficiency with different tray structures for assessment is illustrated. The prediction of tray efficiency for multicomponent system and the bizarre phenomena is also described. For the packed column, both CMT models are used for the simulation of an industrial-scale column with success in predicting the axial concentrations and HETP. The influence of fluctuating mass flux is discussed.

Keywords

Simulation of distillation Tray column Packed column Concentration profile Tray efficiency evaluation 

Nomenclature

A

Surface area per unit volume of packed column, m−1

c1, c2, c3

Model parameters in transport equation for the turbulent mass flux

C

Concentration, kg m−3

\( \overline{C} \)

Average concentration, kg m−3

Cμ, C1ε, C2ε, C3ε

Model parameters in kε model equations

c′

Fluctuating concentration, kg m−3

\( \overline{{c^{{{\prime}2}} }} \)

Variance of fluctuating concentration, kgm−6

D

Molecular diffusivity, m2 s−1

Dt

Turbulent mass diffusivity, m2 s−1

de

Equivalent diameter of random packing, m

dH

Hydraulic diameter of random packing, m

dp

Nominal diameter of the packed particle, m

Eo

Overall efficiency

EMV

Murphree tray efficiency on gas basis

EML

Murphree tray efficiency on liquid basis

F

F factor, \( U_{\text{G}} \sqrt {\rho_{\text{G}} } \), m s−1 (kg m−3)0.5

g

Acceleration due to gravity, m s−2

G

Production term

H

Height of packed bed measured from column bottom, m

hf

Height of the liquid layer in tray column, m

hw

Weir height in tray column, m

KOL

Overall liquid-phase mass transfer coefficient in tray column, m s−1

k

Turbulent kinetic energy, m2 s−2

kG

Gas-phase mass transfer coefficient in packed column, kg m−2 s−1

kL

Liquid-phase mass transfer coefficient in packed column, kg m−2 s−1

L

Liquid flow rate per unit cross-sectional area, kg m−2 s−1

lw

Weir width, m

m

Distribution coefficient

r

Position in radial direction, m

R

Radius of the column, m

SC

Source term in species conversation equation, kg m−3 s−1

Sm

Source term in momentum equation, N m−3

t

Time, s

U

Superficial velocities, m s−1

U

Interstitial velocity vector, m s−1

\( u^{\prime}_{i} \)

Fluctuating velocity, m s−1

W

Weir length, m

x

Distance in x direction, m; mole fraction in liquid phase

y

Distance in y direction, m; mole fraction in gas phase

z

Distance in z direction, m

Z

Total height of packed bed, m

βL, βV

Volume fraction of liquid phase and vapor phase

αre

Relative volatility

ε

Turbulent dissipation rate, m2 s−3

\( {\boldsymbol{\varepsilon}}_{{c^{\prime}}} \)

Turbulent dissipation rate of concentration fluctuation, kg2 m−6 s−1

γ

Porosity distribution of the random packing bed

μ, μG

Liquid- and gas-phase viscosities, kg m−1 s−1

ρ, ρG

Liquid- and gas-phase densities, kg m−3

σ

Surface tension of liquid, N m−1

σk, σε

Correction factor in kε model equations

χ

Characteristic length of packing, m

\( \varPhi \)

Enhancement factor

Subscripts

G

Gas

i

Coordinates in different directions; component in solution

in

Inlet

L

Liquid

0

Interface

b

Bulk

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.School of Chemical Engineering and TechnologyTianjin UniversityTianjinPeople’s Republic of China

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