Thermophoresis effects on gas-particle phases flow behaviors in entrained flow coal gasifier using Eulerian model

doi:10.1016/j.cjche.2016.11.016

Abstract

Abstract: A numerical model based on the Eulerian-Eulerian two-fluid approach is used to simulate the gasification of coal char inside an entrained flow gasifier. In this model, effects of thermophoresis of coal char particles are thoroughly investigated. The thermophoresis is due to the gas temperature gradient caused by absorpted heat of coal char gasification. This work, firstly, calculates the gas temperature gradient and thermophoretic force at 1100℃,1200℃,1300℃ and 1400℃ wall temperatures. Then, the changes of particle volume fraction and velocity in the gasifier are studied in the simulation with thermophoresis or not. The results indicate that considering the particle thermophoresis has some effects on the calculation of particle volume fraction in the gasifier, especially at wall temperature of 1400℃, and the maximum particle volume fraction variance ratio reaches up to 1.38% on wall surface of the gasifier. These effects are mainly caused by large gas temperature gradient along the radial direction of the gasifier. For the particle velocity, the changes are small but can be observable along radial direction of the gasifier, which has good agreement with the distributions of radial gas temperature gradient and thermophoretic force. These changes above may have certain effects on gasification reaction rates in this Eulerian model. So the change of gasification reaction rates in the simulation with thermophoresis or not is studied finally.

Key words: Gasification, Thermophoresis, Eulerian model, Two-phase flow

摘要： A numerical model based on the Eulerian-Eulerian two-fluid approach is used to simulate the gasification of coal char inside an entrained flow gasifier. In this model, effects of thermophoresis of coal char particles are thoroughly investigated. The thermophoresis is due to the gas temperature gradient caused by absorpted heat of coal char gasification. This work, firstly, calculates the gas temperature gradient and thermophoretic force at 1100℃,1200℃,1300℃ and 1400℃ wall temperatures. Then, the changes of particle volume fraction and velocity in the gasifier are studied in the simulation with thermophoresis or not. The results indicate that considering the particle thermophoresis has some effects on the calculation of particle volume fraction in the gasifier, especially at wall temperature of 1400℃, and the maximum particle volume fraction variance ratio reaches up to 1.38% on wall surface of the gasifier. These effects are mainly caused by large gas temperature gradient along the radial direction of the gasifier. For the particle velocity, the changes are small but can be observable along radial direction of the gasifier, which has good agreement with the distributions of radial gas temperature gradient and thermophoretic force. These changes above may have certain effects on gasification reaction rates in this Eulerian model. So the change of gasification reaction rates in the simulation with thermophoresis or not is studied finally.

关键词: Gasification, Thermophoresis, Eulerian model, Two-phase flow

Chao Dai, Fan Gu. Thermophoresis effects on gas-particle phases flow behaviors in entrained flow coal gasifier using Eulerian model[J]. , 2017, 25(6): 712-721.

References

[1] D.H. Ahn, B.M. Gibbs, K.H. Ko, et al., Gasification kinetics of an Indonesian sub-bituminous coal-char with CO₂, at elevated pressure, Fuel 80(11) (2001) 1651-1658.
[2] S. Kajitani, S. Hara, H. Matsuda, Gasification rate analysis of coal char with a pressurized drop tube furnace, Fuel 81(5) (2002) 539-546.
[3] S. Kajitani, N. Suzuki, M. Ashizawa, et al., CO₂, gasification rate analysis of coal char in entrained flow coal gasifier, Fuel 85(2) (2006) 163-169.
[4] M.F. Irfan, M.R. Usman, K. Kusakabe, Coal gasification in CO₂, atmosphere and its kinetics since 1948:a brief review, Energy 36(1) (2011) 12-40.
[5] W. Vicente, S. Ochoa, J. Aguillón, et al., An Eulerian model for the simulation of an entrained flow coal gasifier, Appl. Therm. Eng. 23(15) (2003) 1993-2008.
[6] A. Toda, H. Ohnishi, R. Dobashi, et al., Experimental study on the relation between thermophoresis and size of aerosol particles, Int. J. Heat Mass Transf. 41(17) (1998) 2710-2713.
[7] P.S. Epstein, Zur Theorie des Radiometers, Ann. Phys. 54(7-8) (1929) 537-563.
[8] C.F. Schadt, R.D. Cadle, Thermal forces on aerosol particles, J. Phys. Chem. 65(10) (1961) 1689-1694.
[9] J.R. Brock, On the theory of thermal forces acting on aerosol particles, J. Colloid Sci. 17(8) (1962) 768-780.
[10] L. Talbot, R.K. Cheng, R.W. Schefer, et al., Thermophoresis of particles in a heated boundary layer, J. Fluid Mech. 101(101) (1980) 737-758.
[11] C. Chen, M. Horio, T. Kojima, Numerical simulation of entrained flow coal gasifiers. Part I:modeling of coal gasification in an entrained flow gasifier, Chem. Eng. Sci. 55(18) (2000) 3861-3874.
[12] L. Hao, C. Luo, M. Kaneko, et al., Unification of gasification kinetics of char in CO₂ at elevated temperatures with a modified random pore model, Energy & Fuels 17(4) (2003) 961-970.
[13] Q. Ni, A. Williams, A simulation study on the performance of an entrained-flow coal gasifier, Fuel 74(1) (1995) 102-110.
[14] C.J. Chen, C.I. Hung, W.H. Chen, Numerical investigation on performance of coal gasification under various injection patterns in an entrained flow gasifier, Appl. Energy 100(4) (2012) 218-228.
[15] C.T. Crowe, M. Sommerfeld, Multiphase flows with droplets and particles, Multiphase Flows With Droplets and Particles, CRC, 1998.
[16] H. Enwald, E. Peirano, A.E. Almstedt, Eulerian two-phase flow theory applied to fluidization, Int. J. Multiphase Flow 22(1345) (1996) 21-66.
[17] M.J. Pang, J.J. Wei, Analysis of drag and lift coefficient expressions of bubbly flow system for low to medium Reynolds number, Nucl. Eng. Des. 241(6) (2011) 2204-2213.
[18] O. Visuri, G.A. Wierink, V. Alopaeus, Investigation of drag models in CFD modeling and comparison to experiments of liquid-solid fluidized systems, Int. J. Miner. Process. s 104-105(s 104-105) (2012) 58-70.
[19] C. Shen, Thermophoresis of spherical particle and the dependence of the jump coefficients on the accommodation coefficient, Acta Mech. Sinica (1983).
[20] G.K. Batchelor, C. Shen, Thermophoretic deposition of particles in gas flowing over cold surfaces, J. Colloid Interface Sci. 107(1) (1985) 21-37.