Kinetic Models for Coal Hydrogasification and Analyses of Hydrogasification Characteristics in Entrained-Flow Gasifiers

Abstract

Coal hydrogasification (CHG) is a promising technology for clean and efficient coal utilization. However, the kinetic mechanism of CHG has not been fully understood, and multidimensional numerical simulations of CHG in entrainedflow gasifiers are still rarely reported. To evaluate and optimize hydrogasification parameters in an entrained-flow-bed gasifier, it is necessary to develop a reasonable CHG kinetic model and carry out the corresponding numerical simulations. In this work, a CHG kinetic model, including five homogeneous reactions and three heterogeneous reactions, is established. Thereinto, for the heterogeneous reactions, a novel combined random pore and shrinking-core model with pressure correction (CRPSC−PC) is put forward to predict the char−gas reaction process. When the CHG model is set up, it is then loaded to the commercial computational fluid dynamics (CFD) package, Fluent, via the user-defined function (UDF), and the simulation results are validated against literature-available experimental data for entrained-flow coal hydrogasifiers. Good agreements between the simulation results and the experimental data are detected, which indicates that the model is reliable and can be used to predict the effects of different operating parameters on entrained-flow CHG. Finally, the CHG properties in the cylindrical entrained-flow gasifiers are analyzed on the basis of the experiments reported in the literature, and the CH 4 concentration in the gasification product is found to increase with the increasing H 2 O concentration of the gasification agent, the increasing inlet temperature of the gasification agent when the H 2 O concentration is high, and the increasing gasification pressure when the H 2 concentration is high.

Numerical modeling of a 500 kW air-blown cyclone gasifier

“…The reaction rate for benzene should therefore be updated as soon as suitable experimental data becomes available. The value used in the present simulations is almost the same reaction rate as in Yan et al [20] for benzene steam reforming.…”

“…It is virtually impossible to model the decomposition of the mixture in detail in a complex flow situation. In order to find a compromise between detailed modeling of the multitude of tar species and reactions involving those species in the real syngas and the need for short computational times, it is assumed in the model, in accordance with Yan et al [20], that tar consist only of benzene. In that work coal hydrogasification in an entrained flow gasifier is simulated and the results show that the simplified tar model leads to accurate predictions of the composition of the product gas.…”

Simulation of Gas Generation from the Paleogene Enping Formation in the Baiyun Sag in the Deepwater Area of the Pearl River Mouth Basin, the South China Sea

“…When the experiment adopts a constant heating rate ( D ), then the following expression is applied: From eqs –, we can obtain the following expression: After integrating the above equation ( T 0 → T ), we noted that X i ( T o ) = 0 and X i ( T ) = X i . Thus, the following equation was developed: The total amount of gas generation of N parallel reactions is expressed according to the following equation: The iterative method was used to determine the chemical kinetic parameters ( E i , A i , and X i G ) for the N parallel first-order reactions. − This approach enables the best fitting of the theoretical gas yield of kerogen calculated using eq and the simulated gas yield of kerogen at each temperature point. The calculation can be accomplished using two-dimensional basin modeling software.…”

Numerical Simulation of Biomass Gasification in an Entrained Flow Cyclone Gasifier

“…Therefore, modeling of tar is problematic and impossible to decompose the mixture in detail. According to the model used by Yan et al, 23 the tar is simplified to consist of only C 6 H 6 (benzene). It has been shown that this simplification leads to precise predictions for the yields of the product gas.…”