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Application of Computational Mass Transfer (II): Chemical Absorption Process

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

Abstract

In this chapter, the two CMT models, i.e., \( \overline{{c^{{{\prime }2}} }} - \varepsilon_{{c^{\prime } }} \) model and Reynolds mass flux model (in standard, hybrid, and algebraic forms) are used for simulating the chemical absorption of CO2 in packed column by using MEA, AMP, and NaOH separately and their simulated results are closely checked with the experimental data. It is noted that the radial distribution of D t is similar to α t but quite different from μ t. It means that the conventional assumption on the analogy between the momentum transfer and the mass transfer in turbulent fluids is unjustified, and thus, the use of CMT method for simulation is necessary. In the analysis of the simulation results, some transport phenomena are interpreted in terms of the co-action or counteraction of the turbulent mass flux diffusion.

Keywords

Simulation of absorption CO2 absorption Turbulent mass transfer diffusivity Concentration profile 

Nomenclature

a

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

aeff

Effective area for mass transfer between the gas phase and liquid phase, 1/m

aw

Wetted surface area, m−1

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

Concentration variance, kg2 m−6

\( \overline{C} \)

Average concentration of mass fraction, kg m−3

Cμ, c1, c2

Model parameters in k − ε model equations, dimensionless

Cc0, Cc1, Cc2, Cc3

Model parameters in \( \overline{{c^{2} }} - \varepsilon_{c} \) model equations, dimensionless

\( C_{\text{p}} \)

Liquid-phase specific heat, J/kg/K

Ct0, Ct1, Ct2, Ct3

Model parameters in \( \overline{{t^{2} }} - \varepsilon_{t} \) model equations, dimensionless

D

Molecular diffusivity, ms−1

Deff

Effective diffusivity, ms−1

DG

Molecular diffusivity of CO2 in gas phase, m2 s−1

Dt

Turbulent diffusivity for mass transfer, 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

E

Enhancement factor, dimensionless

G

Gas-phase flow rate per unit cross-sectional area, kg m2 s−1

HA

Physical absorption heat of mol CO2 absorbed, J kmol−1

HR

Chemical reaction heat of mol CO2 absorbed, J kmol−1

Hs

Static holdup, dimensionless

Ht

Total liquid holdup, dimensionless

k

Turbulent kinetic energy, m2/s2

k2

Second-order reaction rate constant, m3 kmol s−1

kG

Gas-phase mass transfer coefficient, kmol m s kPa−1

kL

Liquid-phase mass transfer coefficient without chemical reaction, m s−1

kR,L

Liquid-phase mass transfer coefficient with chemical reaction, m s−1

L

Liquid flow rate per unit cross-sectional area, kg m2 s−1

R

Position in radial direction, m

Rc

The rate of reaction, kmol m3 s−1

r

Radius of the column, m

\( \overline{{t^{2} }} \)

Temperature variance, dimensionless

T

Liquid temperature, K

U

Liquid superficial velocity, m s−1

X

Molar concentration in the liquid bulk, kmol m−3

Xi

Molar concentration at interface, kmol m−3

x

Distance measured from column top (x = 0 at the column top), m

α, αeff, αt

Molecular, turbulent, and effective thermal diffusivities, respectively, m2 s−1

β

Volume fraction of liquid phase based on pore space, dimensionless

ε

Turbulent dissipation rate, m2 s−3

εc

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

εt

Turbulent dissipation rate of temperature fluctuation, s−1

Φ

Variable, dimensionless

νt

Turbulent diffusivity, m2 s−1

ρ

Liquid density, kg/m3

ρG

Gas-phase density, kg/m3

σ

Surface tension of aqueous solutions, dynes/cm, or N/m

σc, \( \sigma_{{\varepsilon_{c} }} \)

Model parameters in \( \overline{{c^{2} }} - \varepsilon_{c} \) model equations, dimensionless

σt, \( \sigma_{{\varepsilon_{t} }} \)

Model parameters in \( \overline{{t^{2} }} - \varepsilon_{t} \) model equations, dimensionless

σk, σε

Model parameters in k − ε model equations, dimensionless

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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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