Effect of CO₂ and H₂O gasification on the combustion characteristics of coal and char under O₂/CO₂atmosphere

The burning behaviors of Datong coal and char under O₂/N₂, O₂/CO₂ and O₂/H₂O/CO₂ atmosphere were comparatively investigated by thermogravimetric analyzer. The influence of CO₂ and H₂O gasification on the oxy-fuel combustion characteristics of coal and char were mainly studied. The results indicate that at 5% oxygen concentration the burning rate of pulverized coal in each atmosphere decreases in the order of O₂/N₂, O₂/CO₂ and O₂/H₂O/CO₂. When the oxygen concentration reduces to 2%, owing to the CO₂ and H₂O gasification, the overall reaction rate of pulverized coal increases in the same order at high temperatures. The burning rate of char is slower in O₂/CO₂ than that in O₂/N₂ at 5% oxygen concentration, but as the burning process is delayed, the overall reaction rate of char in O₂/H₂O/CO₂ rises significantly due to the action of gasification. At 2% oxygen concentration, the overall reaction rate of char in O₂/CO₂ is higher than the burning rate of char in O₂/N₂ with the rise in temperature. The overall reaction rate of char in O₂/H₂O/CO₂ further increases because the H₂O gasification plays a major role in CO₂ and H₂O co-gasification. The kinetic analysis shows that at 5% oxygen concentration the apparent activation energy in the atmosphere increases in the order of O₂/N₂, O₂/CO₂ and O₂/H₂O/CO₂. However, the apparent activation energy of different atmospheres declines with the decrease of oxygen concentration.