1 Combined Heat and Mass Transfer Model in Amines System Xiao Luo and Hallvard F. Svendsen Norwegian University of Science and Technology (NTNU) Trondheim, NORWAY

2 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

3 Motivation In CO 2 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

4 General description Vapor bulk Liquid bulk N CO2 N H2O N Amines Interface QLQL QSQS Water Amines CO 2 Other Gases H 2 O Vap Amines Vap XIAO LUO, Combined Heat and Mass Transfer Model in Amines System

5 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

6 Fick’s Law Diffusion in binary mixtures: 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

7 Maxwell-Stefan Equation Derivation of Maxwell-Stefan equation –Sum of driving force = Sum of friction force –Theoretic significance 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

8 Mass transfer theories Penetration Theory (Higbie, 1935) –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); XIAO LUO, Combined Heat and Mass Transfer Model in Amines System 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 ;

9 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

10 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

11 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

12 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

13 Experimental validation Falling film apparatus –Mass transfer at interface –Heat transfer at interface –Considering the influence of momentum transfer near the wall WallG-L Interface LiquidGas XIAO LUO, Combined Heat and Mass Transfer Model in Amines System N H2O N CO2 N Amines TGTG TLTL Heat transfer

14 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

15 THANK YOU FOR YOUR ATTENTION XIAO LUO, Combined Heat and Mass Transfer Model in Amines System