Study On Combustion Characteristic Of Pulverized Coals Under Low Pressure Of High-altitude By Using Thermogravimetry

Because of high-altitude environment in the western China, the pressure is lower than the plain areas. It's necessary for us to study on the law of coal combustion under low-pressure. First of all, our understanding of pressure'action on the stable combustion and burn-out can be deepened; Secondly, in view of the western coal's combustion characteristics, improving the adaptive structure size of burner and advancd burn rate of coal have an important value of academic and application. Therefore, it's an important significance for us to study on pulverized coal combustion, pyrolysis and reaction kinetics under low pressure conditon.Six kinds of raw coal were selected for studying coal combustion characteristics under low-pressure conditon. In order to acquire the state of low pressure, we connected the vacuum pump to the TGA, and that the vacuum valve and vacuum pressure gauge can help us regulate pressure and read the number of low-pressure. TG and DTG experiments were carried out under three different pressure (atmospheric pressure, gauge pressure -25kPa and gauge pressure -35kPa) and the atmosphere of oxygen. Though experements we can obtain the ignition temperature and ignition time, burnout temperature, combustion temperature under the maximum velocity, combustion characteristics index of pulverized coal, burnout rate and velocity of combustion under different conditions. And then the cumulative active surface area, specific active surface area and critical active enery are calculated by the means of the SCT model. Then effects of pressure on the combustion are illustrated based on oxygen molecule mean free path and the Knudsen diffusion coefficient.Experimental results showed that: The ignition temperature and ignition time, burnout temperature and maximum velocity of combustion correspongding to the combustion temperature are delayed as the pressure decreased, besides the combustion characteristics of pulverized coal index reduced accordingly. The cumulative active surface area and active specific surface area were in direction of the burnout rate, both increased as the burnout rate increased. Under low pressure condion, the change rate of cumulative active surface area and the change rate of active specific surface area had the same trend, firstly both increased to the peak and then decreased as the burnout rate increased. For the same kinds of coal samples, the critical active enery at the first and last stage were larger than that at the middle stage as the burnout rate increased, due to the low-pressure inhibit the reactivity of pulverized coal combustion, this maked the critical active enery at first and last stage were greater than atmospheric pressure, and the lower the pressure was the less the critical active enery was.