Combustion Characteristics Of Coal And Char In Oxy-fuel Technology

With the development of global warming, the environment of human being living has been gradually threatening. Researches show that Carbon Dioxide is the most prominent factor of which resulted in the greenhouse effect. Meanwhile, the carbon dioxide stays longer in the atmosphere than any other greenhouse gases, which draws a particular attention from all fields in the society. Coal combustion can generate a large amount of carbon dioxide. The methods of the carbon dioxide capture and treatment include: Pre-Combustion Capture, Oxy-fuel combustion technology and the Post-Combustion Capture. Among them, the oxy-fuel combustion technology is considered as the most economic method to control carbon dioxide in plant station. Therefore, the scholars at home and abroad have done a lot of theoretical and experimental researches on the oxy-fuel combustion technology.The thesis particularly researched the combustion characteristics and the transition of the minerals in the coal with different density fractions under the oxy-fuel combustion. In the experiment, the raw coal was divided into three different density fractions: the heavy, the medium and the light. With the help of the drop tube furnace, we did the experiment under different oxygen contents and different temperatures. We analyzed the particle size distribution and the chemical components of those formed ash particles. The results indicates that in the situation of 20% and 30% oxygen contents, the burn-out rate of all 3 density coals have nothing to do with the atmosphere under the modes of oxy-fuel combustion and the N₂/O₂ combustion. The transition mechanisms of ash formation during combustion is the same in the both atmosphere, on contrast, the relative contents of the mineral crystal phase in the ashes are different. Meanwhile, particle size of the formed ash doesn't have obvious change under the two combustion modes, while in the lower temperatures, it is a little smaller under the oxy-fuel combustion atmosphere.Considered the direct effect of the char reaction time on the whole coal combustion process, we studied the physical structure of the formed char, the reactivity and the differences of the combustion characteristics between the combustion under the O₂/CO₂ atmosphere and the O₂/N₂ atmosphere. The results showed the ignition point and the temperature of completing combustion of the char generated under the O₂/CO₂ atmosphere is a little preacted, while the highest weight loss rate is higher compared with the O₂/N₂ atmosphere. In the temperature range of 500-750℃, the reactivity of the formed char is faster under the O₂/N₂ atmosphere, while in the other experimental temperature range, the reactivity of the formed char is similar in both atmosphere. In the O₂/CO₂ atmosphere, the specific surface area and the total pore volume of the char generated from the coal with three different density fractions is increased compared with the O₂/N₂ atmosphere. The swelling rate of char is commonly higher in the O₂/CO₂ atmosphere.