【作者】 刘峰；

【导师】 傅培舫； 周怀春；

【作者基本信息】 华中科技大学 ， 热能工程， 2009， 硕士

【摘要】 我国西部地区处于高海拔环境,压力较平原地区低。研究煤粉在低压下的燃烧规律,在理论上能深化压力对着火稳燃、结焦和燃尽机理的认识;对预防灭火和控制结焦,针对西部环境特点,改进燃烧器和锅炉的结构尺寸,提高煤的燃尽率具有重要学术价值和应用价值。因此,研究粉煤焦在低压下的燃烧、热解、反应动力学及其相关机理有着重要的意义。本文选取了六种具有代表性的煤样,通过连接在热综合分析仪上的真空泵使实验系统达到低压状态并由真空隔膜阀和真空压力表来调节压力及读取低压示数。实验分别以三种压力(常压、表压-25kPa和表压-35kPa)和氧气气氛通过TG及DTG实验数据首先得到了煤粉在不同压力下的着火温度及着火时间、燃尽温度、最大燃烧速度所对应的温度、燃烧特性指数及煤粉燃烧速度,然后以粉煤焦SCT模型为研究手段,分计别算得到了累计活性表面积、活性比表面积和临界活化能等反应动力学参数,并由氧气分子的平均自由程及努森扩散系数来说明了压力对燃烧的影响。实验结果表明:实验煤样在不同压力下的燃烧,随着压力的下降,煤粉燃烧的着火温度及着火时间、燃尽温度和最大燃烧速度所对应的温度均依次推迟,煤粉燃烧特性指数也相应减小。通过SCT模型可以看到累计活性表面积和活性表面积与燃尽度成正比,均随燃尽度的增大而增大。低压下的累计活性表面积的变化率及活性比表面积的变化率与常压下的变化趋势相同,均随燃尽度的增加先增大到峰值再减小,有所不同的是压力越低,累计活性表面积的变化率及活性比表面积的变化率也就越小。这就说明在低压环境下,煤粉燃烧的反应活性比常压燃烧要差。对于同种煤样不同压力下所求得的活化能表现为随着燃尽度的增大,在反应前期和后期较中期要大,由于低压抑制了煤粉燃烧的反应活性,使得在反应前期及后期所需的活化能比常压下的要大,且压力越低活化能越大。更多还原

【Abstract】 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.更多还原