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Combined Heat and Mass
Transfer Model in Amines
System
Xiao Luo and Hallvard F. Svendsen
Norwegian University of Science and Technology (NTNU)
Trondheim, NORWAY
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Contents
• Literature work
–
–
–
–
Motivation
Multi-component system
Influence of convection
Combined heat and mass transfer
• Work plan
• Expectation
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Motivation
• In CO2 absorption processes large mass and heat transfer
driving forces occur several places, absorber bottom, water
wash section and in the desorber.
• Good fundamental models for the combined heat and mass
transfer including chemical reaction and convective mechanisms
are still lacking.
• A proper description of the transfer processes is vital for
improved absorption process simulation and optimization.
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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General description
Interface
NCO2
Vapor bulk
CO2
Water
NH2O
Other Gases
H2OVap
AminesVap
Liquid bulk
Amines
NAmines
QL
CO2
QS
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Multi-components system
• Conventional approaches to mass transfer in multi-component
mixtures are based on an assumption that the transfer flux of
each component is proportional to its own driving force.
• Ross Taylor & R. Krishna, (1993)
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Fick’s Law
• Diffusion in binary mixtures:
n 1
J i  ct  Dik xk
k 1
• Multi-component Fickian Diffusion Coefficients
– Obtained from composition profiles measured in a diffusion apparatus.
– Wilke (1950), Dunlop, 1972; Cussler, (1976);
– Tyrrell and Harris, (1984);
– Schiesser, (1991)
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Maxwell-Stefan Equation
• Derivation of Maxwell-Stefan equation
– Sum of driving force = Sum of friction force
– Theoretic significance
d ln  i xi 
dP
d
2
RT
 Vi
 M i r  FZi

dz
dz
dz
n
xi N j  x j Ni
j 1
ct Dij
 RT 
• Driving force including
–
–
–
–
–
Gravity driving force (usually ignored)
Chemical potential driving force; Frank, (1994);
Pressure driving force
Centrifugal driving force
Electrical potential driving force; Schneider, R. (1999)
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Mass transfer theories
• Penetration Theory (Higbie, 1935)
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–
–
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Small fluid eddy; Retention time τ
Samanta, A. (2007); Tobiesen, F. A. (2007);
van Elk, E. P. (2007); Zhang, X. (2004);
Mandal, B. P. (2001); Bhat, R. D. Vas, (1998);
• Surface renewal theory (Danckwerts, 1951)
– Based on Penetration Model; Statistical age distribution function Φ(θ)
– Li, Zhengxing (2007); Shen, Shuhua (2007);
– Rahimpour, M. R. (2004); Pacheco, M. A. (2000);
• Film theory (Lewis & Whitman, 1924)
– Steady state; Thickness of film δ;
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Combined heat and mass transfer
• Heat transfer including
– Sensible heat by difference in temperature between two phases
– Latent heat by evaporation or condensation
– Heat produced by solvation and chemical reactions
– Y. T. Kang & Y. Fujita (2001); I. Alatiqi (1993)
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Modeling separately
• Model in liquid phase
– Similar property of amines
– Water > 90 mol%
– Seen as binary mixture
– Using Fick’s Law
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Modeling separately
• Model in gas phase
– More complicated
– Differences between each components
– Using Maxwell-Stefan Equation
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Combined model
• Assumptions
– Equilibrium at the interface
– Driving force is caused by chemical potential (Liquid)
– Consider fugacity driving forces (Gas)
– Convective contributions
– ……
• Combine such models above by using Henry’s Law
at the interface
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Experimental validation
G-L Interface
Wall
• Falling film apparatus
– Mass transfer at interface
Gas
NH2O
– Heat transfer at interface
NCO2
– Considering the influence
NAmines
Liquid
of momentum transfer near
the wall
TG
Heat transfer
TL
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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Expectation
• More accurate
– Reduce the number of assumptions of existing models
• More scientific
– Modify the parameters which only depend on experimental data or
empirical equations.
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System
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THANK YOU
FOR YOUR ATTENTION
XIAO LUO, Combined Heat and Mass Transfer Model in Amines System