Numerical analysis of coal size influencing the performance and slag flow characteristics of gasifier based on a comprehensive model

A comprehensive char gasification model based on random pore model with correction factor eta is established to depict the char conversion process for entrained-flow gasification. The new comprehensive model uses advanced correlations for char gasification process parameters, including the correlations of a simplified multicomponent molecular diffusion, the evolution of particle size and density, char specific surface area and char thermal deactivation. A one-dimensional slag flow model coupled with the particle capture model is used to describe the deposition, flow and heat transfer process of the molten slag on the wall of HNCERI (Huaneng Clean Energy Research Institute) gasifier. The species mole fractions, carbon conversion efficiency, outlet temperature and the wall heat loss of the gasifier under the baseline are compared with the operating data. The simulation results indicate that the comprehensive model has sufficient accuracy to model the multiphase reactions and slag flow characteristics of HNCERI gasifier. The effect of coal size on exit gas temperature, detailed char heterogeneous reactions, gasification performance and slag flow characteristics of the gasifier are studied. Results show that, as coal size increases from 10 mu m to 320 mu m, the volume average rate of C + CO2 drops from 0.0095 to 0.0035 kmol/m(3).s and C + H2O increases from 0.0064 to 0.012 kmol/m(3).s at the first stage, and the carbon conversion efficiency at the first stage decreases from 99.72 % to 93.42 % while that at the second stage increases from 65 % to 93 %. The increase of coal size with values<80 mu m has none significant influence on the formation of slag in the gasifier. With coal size further increasing, the formation of slag is highly promoted and thereby results in a rapid increasing thickness of the solid and liquid slag at the slag tap hole. An optimum coal size might be<80 mu m for the first stage while an appropriate increase of coal size at the second stage is beneficial to improve carbon conversion efficiency.

Automated summary

A comprehensive char gasification model based on a random pore model with a correction factor eta is established in this study to depict the char conversion process for entrained-flow gasification. The model uses advanced correlations for char gasification process parameters, as well as a one-dimensional slag flow model coupled with a particle capture model to describe the deposition, flow and heat transfer process of the molten slag. The simulation results indicate that the comprehensive model has sufficient accuracy to model the multiphase reactions and slag flow characteristics of the gasifier. Additionally, the study investigates the effect of coal size on exit gas temperature, detailed char heterogeneous reactions, gasification performance and slag flow characteristics of the gasifier.