Research On Combustion Characteristics And Kinetics Of Typical Char In Oxy-fuel Conditions

Oxyfuel combustion is a promising combustion technology, which has great advantageson the removal of CO2, NOx, SO2, Hg and other trace elements. It has attracted the attentionof scholars around the world. Char combustion is the main process of pulverized coalcombustion. Studying the characteristics of char combustion is significant for the applicationof oxyfuel combustion and the development of critical equipments.Chars used to study combustion characteristics were usually obtained under an inertatmosphere. This type of chars’ generation process was seriously deviated from the actualprocess under the real oxyfuel conditions. For the current study, a method was proposed forpreparing chars of real conditions and chars of4steam coals were obtained. Then we studiedthe combustion characteristics and calculated Kinetic parameters of the chars to provide basicdata for the applications of the oxyfuel technology in the future.With4kinds of Chinese typical steam coals as the object of the research, chars closed tothe real oxyfuel process were prepared in the high-temperature entrained-flow reactor. Chars’generation process was described by means of numerical simulation, results were provedaccuracy according to experiments the simulation. Based on the principle of ash tracer, a kindof char which volatile release rate was more than80%and fixed carbon loss rate was smallwas deemed to be representative of the char from real process under the char-makingcondition of this research. This kind of char has developed pore structure. Infrared spectrashows that, hydroxyl groups in the surface of char were significantly higher than those of coalin the form of the distribution and quantity because of rich steam in the char-makingatmosphere and C=O/Car increased showing the opposite trend compared to the char of theconventional inert atmosphere because of high concentration of CO2in high temperatureconditions.In the part of combustion characteristics, the discipline of four chars burning rate withdifferent retention time was studied under different conditions (temperature from1073to1473℃，oxygen concentration from21%to50%) using a high-temperature drop tubefurnace(DTF). A database of combustion characteristics containing4kinds of typical charwas established. With the increase of coal rank, a higher oxygen concentration was requiredto reach the burnout rate resemble to air combustion. Considering to the CO2concentration atthe rear of the boiler,30%of O2concentration for JC-char was best under oxyfuel technologyrecommended by this paper. There is no need to increase the oxygen concentration to30%forthe other3kinds of chars. Burnout characteristics of high rank coal were more sensitive totemperature and oxygen concentration than those of low rank coal.Kinetics data of Char combustion are calculated by an improved Shrinking Core Model.In the kinetics data, the activation energy and pre-exponential factor of JC-char were the highest among4kinds of char and there was certain positive correlation between theactivation energy and pre-exponential factor of different char.