Numerical modeling of a steam-assisted tubular coal gasifier

Understanding the heat and mass transfer phenomena in a coal gasifier is very useful for the assessment of gasifier performance and optimization of the design and operating parameters. In this paper, performance of an entrained flow air blown laboratory scale gasifier is numerically simulated with Fluent software. In the model, the continuous phase conservation equations are solved in an Eulerian frame, while those of particle phase are solved in a Lagrangian frame, with coupling between the two phases carried out through interactive source terms. The dispersion of the particles due to turbulence is predicted using a stochastic tracking model, in conjunction with the k–e equations for the gas phase. The coal gasification model adopted includes devolatilization, combustion of volatiles, char combustion and gasification. The gasification performance inside the gasifier has been predicted for different air ratios as well as for different air and steam inlet temperatures. The overall temperature inside the gasifier is found to increase when the degree of air/steam pre-heating is increased, resulting in acceleration of the different reaction steps in the gasifier. The overall gasification performance indices such as carbon conversion, heating value of the exit gas and cold gas efficiency have been predicted. The predicted results show good agreement with available experimental data in literature.

[1]  A. P. Watkinson,et al.  A PREDICTION OF PERFORMANCE OF COMMERCIAL COAL GASIFIERS , 1991 .

[2]  G. J. Germane,et al.  Char oxidation at elevated pressures , 1995 .

[3]  R. Essenhigh,et al.  Determination of global kinetics of coal volatiles combustion , 1991 .

[4]  I. W. Smith,et al.  The combustion rates of coal chars: A review , 1982 .

[5]  Wolfgang Schäfer,et al.  A computer model of entrained coal gasification , 1988 .

[6]  A. Sarofim,et al.  Coal devolatilization at high temperatures , 1977 .

[7]  B. Hjertager,et al.  On mathematical modeling of turbulent combustion with special emphasis on soot formation and combustion , 1977 .

[8]  L. Douglas Smoot,et al.  Controlling mechanisms in gasification of pulverized coal , 1987 .

[9]  Rakesh Govind,et al.  Modeling and simulation of an entrained flow coal gasifier , 1984 .

[10]  Caixia Chen,et al.  Numerical simulation of entrained flow coal gasifiers. Part I: modeling of coal gasification in an entrained flow gasifier , 2000 .

[11]  C. Westbrook,et al.  Simplified Reaction Mechanisms for the Oxidation of Hydrocarbon Fuels in Flames , 1981 .

[12]  J. Aguillón,et al.  An Eulerian model for the simulation of an entrained flow coal gasifier , 2003 .

[13]  Masayuki Horio,et al.  Numerical simulation of entrained flow coal gasifiers. Part II: effects of operating conditions on gasifier performance , 2000 .

[14]  P. Cheng.  Two-dimensional radiating gas flow by a moment method , 1964 .

[15]  Hiroaki Watanabe,et al.  Numerical simulation of coal gasification in entrained flow coal gasifier , 2006 .

[16]  L. D. Smoot,et al.  Entrained flow gasification of coal: 1. Evaluation of mixing and reaction processes from local measurements , 1985 .

[17]  M. Baum,et al.  Predicting the Combustion Behaviour of Coal Particles , 1971 .

[18]  Despina Vamvuka,et al.  Modelling of an entrained flow coal gasifier. 1. Development of the model and general predictions , 1995 .

[19]  Kalyan Annamalai,et al.  Interactive processes in gasification and combustion—II. Isolated carbon, coal and porous char particles , 1993 .

[20]  W. E. Ranz,et al.  Evaporation from drops , 1952 .

[21]  Kenneth Littlewood,et al.  Gasification: Theory and application , 1977 .

[22]  L. Douglas Smoot,et al.  Effect of coal type on entrained gasification , 1986 .

[23]  Alan Williams,et al.  A simulation study on the performance of an entrained-flow coal gasifier , 1995 .

[24]  S. A. Morsi,et al.  An investigation of particle trajectories in two-phase flow systems , 1972, Journal of Fluid Mechanics.

[25]  L. Smoot,et al.  Carbon conversion in an atmospheric-pressure entrained coal gasifier , 1986 .