The Effect Of H₂O On Combustion Properties Of Coal During Oxy-fuel Combustion

Excessive emissions of CO2 caused the Greenhouse effect, which brought global warming, global warming seriously threats the survival environment of the human, thus the capture of CO2 is urgent needed. Oxy-fuel combustion is a new technology of combustion, which can effectively capture CO2 and has a broad application prospect. The oxy-fuel combustion flue gas contains high concentration of CO2 and H2 O, because of the different properties of CO2/H2 O and N2, the combustion properties of air combusion and oxy-fuel combusion were different. This paper did pyrolysis and combustion experiments of coal in the drop tube furnace and thermo-gravimetric respectively, mainly focused on the effect of H2 O on combusion process during wet-oxy-fuel combustion, researched the influence of H2 O on combustion characteristics of pulverized coal from the two process of coal combustion respectively. Moreover, studied the catalytic effect of AAEM on the gasification reaction in the combustion process.H2O could affect the reactivity of coal during wet-oxy-fuel combustion. H2 O was added to the pyrolysis atmosphere to see the effect of H2 O on the reactivity of char during de-volatilization. The result was that H2 O did not have effect on the reactivity of char. Then, a certain amount of H2 O was added to the combustion atmosphere, data from isothermal combustion and non-isothermal combustion showed : coal oxy-fuel combustion at 21%O2 was accelerated by adding water vapor at 800 centigrade, and the combustion rate was increased with increasing water vapor concentration;adding water vapor also could decrease combustion activation energy.Using isothermal thermo-gravimetric analysis, the effects of typical alkali and alkaline earth elements Na and Ca on the coal combustion reactivity under various wet recycle oxy-fuel combustion conditions were investigated. Both Na and Ca had a catalytic effect on the gasification and oxidation reactions, thus improving coal combustion rate. By comparison, the catalytic effect of Ca was better than Na under the conditions investigated. The data on coal samples containing different concentrations of Na showed that, at low concentrations, the catalytic effect was enhanced with increasing Na concentration. However, at high concentrations, the catalytic effect of Na did not change significantly with the increase of its concentration. Comparing the experimental results under different temperature, the catalytic effect of Na had a better temperature window,in this experiment,the catalytic effect was better at higher temperature. During wet recycle oxy-fuel combustion, the amount of water added had a best value, at this value,the acceleration of pulverized coal combustion was the best.