Oxy-fuel combustion characteristics of pulverized coal under the cction of CO₂/H₂O gasification at constant temperature

The burning behaviors of pulverized coal under different atmospheres (O₂/N₂, O₂/CO₂ and O₂/H₂O/CO₂) in the range of temperature (800-1 200 ℃) and oxygen concentration (2%-21%) were comparatively investigated using the isothermal thermal analysis system.The combustion characteristics of coal samples under the action of CO₂/H₂O gasification were mainly studied.The results indicate that at 800 ℃ the burning rate of Datong bituminous coal (DT) in O₂/N₂ is faster than that in O₂/CO₂ due to the different physical properties between N₂ and CO₂.The effect of CO₂ gasification is enhanced with the increase of temperature from 1 000 ℃ to 1 200 ℃ and as a result, the overall reaction rate of DT in O₂/CO₂ approaches and exceeds the burning rate in O₂/N₂.But the effect of gasification is weakened with the increase of oxygen concentration (e.g.≥10%), and the reaction rate of DT in O₂/CO₂ gradually lags behind that in O₂/N₂.Because the specific heat and the oxygen diffusion rate of H₂O are between those of N₂ and CO₂, the combustion rate of DT in the O₂/CO₂/H₂O is lower than that in O₂/N₂ but higher than that in O₂/CO₂ without the effect of gasification.At 2% oxygen concentration, the influence of CO₂ and H₂O synergistic gasification is enhanced by increasing temperature and thus the overall reaction rate in the O₂/H₂O/CO₂ is always higher than that in O₂/CO₂.But a higher oxygen concentration (e.g.10%) weakens the effect of synergistic gasification which leads to the similar burning processes in different atmospheres.With the effect of gasification, the overall reaction rate of Yangquan anthracite (YQ) increases more significantly compared to DT, which indicates that the gasification has remarkable influences on the reaction process of high-rank coal.