Modelling of slag deposition and flow characteristics of coal combustion under oxy-firing condition in a 550 MW tangentially fired furnace

Abstract

In this paper, the development of three dimensional slagging combustion model for coal-firing in a 500MW tangentially fired industrial furnace under oxy-fuel condition is presented. The model incorporates the Eulerian-Lagrangian model for the gas-particles flow and the particles-wall interaction sub-model for predicting the deposition and conversion characteristics of char/ash particles. A commercial CFD package coupled with some user-defined functions were used for consideration of char particle combustion and tracking, particle capturing and deposition and other related phenomenons. Validation of the model was achieved by comparing the available slag thickness data for coal-water slurry combustion under oxy-fuel condition in a 5MW small scale furnace. The slag thickness deposited on the furnace wall was found to be in good agreement with the available data. Species distributions such as O2, CO2, H2O, flame temperature distribution and flow dynamics were presented at different heights. Coal particles appeared to be combusted at a relatively higher rate in the near burner region and burn in situ because of enriched O2 concentration. The deposited slag thicknesses on the vertical wall of reaction zone were found in the range of 0–1.0mm. Due to the effect of gravitational force, the molten slag flows downward and velocity was slow (maximum 0.05mm/s) because of higher viscosity and greater surface tension properties. Overall, this study provides an understanding of how the ash/char particles are deposited on the refractory wall and its dynamics in an industrial furnace.