Carbonation And Sulfation Of High-calcium Ash Under Oxy-Fuel Combustion Conditions

Global warming has threatened the development of human beings. Since power plants are the largest point sources of CO2 emission, it's in urgent need to carry out some technologies to reduce this kind of emission. Oxy-fuel combustion has been the most promising choice by now. Slagging and fouling problem of the boiler has always been a difficult issue in coal-fired power plants. Thus, for the application of oxy-fuel combustion technology, having a good knowledge of the effect of ash deposition under changing conditions is particularly important.Calcium compounds in the ash have always been regarded as the important components of the deposition. A typical flue gas under oxy-fuel combustion always contains a high concentration of CO2, as well as impurities such as water(H2O), SO2 and so on. These gaseous impurities may have an effect on the carbonation and the sulfation of the calcium compounds in coal ash, which will increase the strength and hardness of ash. Therefore, a deep understanding of these reaction mechanisms is the solid basis for developing new technologies, which can solve the deposit problems under oxy-fuel combustion. So this thesis focuses on these kinds of reaction.Based on the atmospheric TG reactor, a high-calcium ash was conducted to a typical flue gas atmosphere under oxy-fuel combustion. A chemical test was carried out then, in order to define the precise extent of reaction. The experiments focus on the influence of SO2 and H2 O on carbonation and sulfation under high concentration of CO2, and conclusions were obtained as followings:(1) Without the addition of SO2 and H2 O, the carbonation degree of coal ash increased a lot compared to the initial sample, where the temperature was 650?and the volume percentage of CO2 was 80%. It means that this kind of ash has a great potential of carbonation.(2) With the addition of H2 O but no SO2, the carbonation degree rose along with the increasing concentration of water vapor. The main mechanism that water vapor promotes the carbonation reaction is that the presence of H2 O offers more possibility for the solid-phase ion diffusion.(3) With the addition of both SO2 and H2 O, the carbonation reaction was faster than the sulfation reaction of this high-calcium ash. As for the sulfation, the direct sulfation plays a dominant role.(4) With the addition of both SO2 and H2 O, sulfation degree rose along with the increasing concentration of water vapor. H2 O still promotes solid-phase ion diffusion.