Thermal Gravimetric Study Of The Kinetic Model SCT During Pulverized Coal-char Combustion And Experimental Determination Of The Specific Heat By Applying DSC

Suspended pulverized coal combustion systems are widely implemented on large-scale utility boilers at present. The burn-out ratio of pulverized coals is an important parameter which deals a lot with the efficiency of boiler. A simple and effective model will help optimizing the combustion process, and also do a lot of help for the boiler design. The Active Specific Surface Area(ASSA) of chars during its combustion process is an intrinsic reaction kinetic parameter, which reflects the various reactivities of different coal types. As an important thermal property of coal-chars, the value of specific heat extremely influences the delay time prior to its ignition.Three kinds of raw coals were selected for studying the variations of Active Specific Surface Area during pulverized coal combustion under atmospheric pressure. Nine kinds of coal char samples were obtained in Drop Tube Furnace(DTF). Pore size distribution, micro-morphology of the samples were investigated by N2-BET and FESEM. With TG experiments under 3 types of atmosphere and 3 types of heating rates , it has been found that Active Specific Surface Area(ASSA) Ae, Critical Active Energy(CAE) Ec and the frequency factor k0 varied during combustion. Several profiles were obtained appling the reaction kinetic model based on Simple Collision Theory(SCT) developped by Prof. Fu Peifang.The results showed that: during the char samples combustion, the Active Surface Area(ASA) increases with the burnout-ratio, and its change rate achieved the peak simultaneously with combustion rate. The change rate of ASSA increased with the burn-out ratio increasing and arrived at the maximum when the burn-out ratio was 90% around, and then decreased rapidly. The change rates of ASSA at high heating rates(30℃/min,50℃/min) were significantly higher than that at lower heating rate(10℃/min).The CAE of the char samples increased rapidly from (100~200)kJ/mol in the middle stage of conversion to 300kJ/mol around at the last stage (burnout ratio>85%). The frequency factor k0 showed the same trend with CAE as rising with the burnout ratio, and its variation range was (10-6~1011)kg/(m2sPa) associate with char types. Below 500℃, the specific heat values of char samples monotonically increased from around 0.9 J/g℃to (1.4~1.7) J/g℃with the same trend of theoretical data which was slightly smaller. The specific heat values of chars prepared at 1100℃were all higher than that of chars prepared at 1300℃. The volatile content Vdaf of raw coals influence the specific heat value difference between chars prepared at different temperature levels.