【作者】 乌晓江；

【导师】 张忠孝；

【作者基本信息】 上海理工大学 ， 热能工程， 2007， 博士

【摘要】 随着我国经济的快速发展,能源与环境正日益成为限制我国经济发展的主要瓶颈。鉴于我国能源资源富煤缺油少气的特点,高压、大容量气流床气化技术便成为我国煤炭清洁、高效转化的重要途径和发展方向之一。鉴于我国煤炭资源的自身特点(灰含量高,灰熔点普遍偏高),本文通过研究高温下煤焦气化反应机理、小试装置、数值模拟和气化条件下灰的熔融特性等手段对我国高灰熔点煤在固态排渣温度范围的气化特性进行了较系统的研究,为进一步开发适合我国高灰熔点煤的固态排渣气流床气化工艺提供必要的基础数据和理论指导。首先在对我国主要动力矿区煤灰熔融特性进行广泛调研的基础上,利用TGA-51H型高温热天平,采用等温热重法对抽样选出的煤种在1100℃～1400℃温度范围内进行了煤焦-O2/CO2/H2O气化反应动力学特性研究。研究结果表明:高温下煤焦的气化反应特性不同于低温时的反应特性,在1200℃～1300℃时气化反应逐步由化学反应控制过渡到扩散控制;当温度超过煤灰熔点温度时,由于灰的熔融行为(分散尺度,聚集状态)导致了高温下高、低灰熔点煤所表现出的不同特性;高升温速率制得的煤焦由于挥发份的快速析出导致煤焦表面空隙度远大于低升温速率时煤焦表面的空隙度,反应活性大大增强,比低升温速率时约高出1～2个数量级;煤种本身的反应活性与煤中挥发份、氢以及固定碳含量有很大关系,气化反应速率与表征煤化程度参数β具有良好的线性关系;低温时压力对气化反应速率的影响明显大于其在高温时对气化反应速率的影响;随着压力的升高气化反应由化学反应动力学控制向扩散控制转变的转变温度降低;当压力低于1.6MPa时,随着压力的增加反应速率明显增加,而在压力大于1.6MPa以上时,压力的影响越来越小。在25kg/h规模的加压气流床气化实验系统上,对我国高灰熔点煤在固态排渣温度范围内(<1400℃)的气化特性进行实验研究。研究结果表明:高温有利于气化反应向吸热方向进行,随着O/C摩尔比的增加,气化温度升高,碳转化率升高,但过多氧的存在,使得合成气中CO2和H2O的含量升高,有效成分CO、H2含量降低,从而导致冷煤气效率下降。最佳气化温度在1300～1350℃之间,相应的碳转化率和冷煤气效率较高,且此时气化炉底部、旋风分离器内的灰渣在整体上仍以固态形式存在,只有部分低熔点成分发生熔融,熔融部分一般在几μm到十几μm之间,而布袋除尘器中的灰渣并没有发生熔融现象;因此,对于高灰熔点煤,在1300～1350℃气化时的结渣性较弱。在煤焦气化反应动力学研究的基础上,结合25kg/h加压气流床气化炉内的燃烧、气化反应特性,建立了一维稳态动力学数学模型。该模型较为真实地反映了气化炉内的反应过程,模型计算值与实验值对比后显示,本模型对煤粉加压气流床气化过程的模拟是成功的。利用SEM-EDX对高、低灰熔点煤在煤焦-H2O气化反应过程中不同阶段的灰表面形貌进行分析。研究结果表明:气化条件下灰的熔融变化过程不同于其在燃烧条件下的熔融变化过程,燃烧情况下灰的熔融过程是与燃烧同时进行,而气化条件下灰的熔融过程主要发生在气化反应的中、后期;气化条件(还原性气氛)下,煤灰开始出现熔融主要是由灰中的含Fe物质引起的,灰中含Fe物质先发生熔融,随后含Ca物质才开始发生熔融;煤灰开始发生熔融的温度一般要比由灰锥法测得的温度低100～150℃左右;相同条件下,氧化性气氛(O2)下灰的熔融温度要比其在还原性气氛下(煤焦-CO2/煤焦-H2O)的熔融温度要高;同是还原性气氛条件下,煤焦-H2O气氛下灰的熔融温度比其在煤焦-CO2气氛下的要高,与CO含量有关。更多还原

【Abstract】 With the rapid development of our national economy, the energy and environment are increasingly become the limitation of our national economy development. Considering our characteristics of energy structure with rich coal, short of petroleum and natural gas, the entrained flow coal gasification technology with high pressure and large scale has become one of the important means and directions in clean coal and coal conversion technology in the future. For the purpose of developing new entrained flow coal gasification with dry ash out to fit our high ash fusion temperature coal, the coal char gasification reaction characteristics at high temperature, coal gasification characteristics in 25kg/h lab-scale coal gasification experimental system, one dimensional mathematical model simulation and coal ash fusion characteristics under coal gasification condition was researched and paper has been researched to supply necessary basic data and theory guidance.Firstly, based on the extensive investigation of coal ash fusion characteristics of main coal mining area in China, the coal char-O2/CO2/H2O gasification reaction characteristics of selected coal samples were studied with isothermal thermogravimetry method by using TGA-51H. The results were shown that the coal char gasification reaction characteristics at high temperature were different from the condition of at low temperature, the reaction control step is transferred from chemical reaction control zone to pore diffusion control zone at around 1200℃～1300℃. When the temperature was higher than coal ash fusion temperature, the coal ash fusion behaviour, mainly the distribution form changed, is caused to the differences above. The coal char which was produced with high heating rate has much higher gasification reactivity than those that with low heating rate because high voidage in coal char surface which is produced in the stage of fast coal pyrolysis. The gasification reaction velocity of coal char with high heating rate is above 1~2 order of magnitude than those that with low heating rate. The inherent gasification reactivity of coal type is much related to the contents of volatile, hydrogen and fix carbon in coal and is linear with the value of parameterβwhich represent the coal rank. The effect of pressure on gasification reaction rate at low temperature is much higher than that at high temperature. The transition temperature from chemical reaction control to pure diffusion control decreases with the increasing of pressure. The reaction rate increases evidently with the increasing pressure when the pressure is lower than 1.6MPa while when the pressure is above 1.6MPa the effect of pressure is become smaller and smaller.The gaification characteristics of coal with high ash fusion temperature were studied by using 25kg/h lab-scale entrained flow gasification experimental system at temperature range below 1400℃which was suitable for dry ash out. The results were shown that the gasification temperature increases with the increasing of O/C molar ratio. The high temperature is favourable to the gasification reaction to move for the direction of absorption but higher content of oxygen can get higher content of CO2 and lower content of CO and H2. The cold gas efficiency will decrease when the O/C molar is too high. Under the experimental conditions the optimal gasification temperature range is from 1300℃to 1350℃, corresponding higher the cold gas efficiency and carbon to gas conversion. Under this condition, the ash in the bottom of gasifier and cyclone is existed as solid in the view of overall except some little parts are melted in the size of severalμm. And the ash in the bag filter has not melted. Due to the melted part is accounted for very little percentage within the whole ash. The tendency of slagging is small and will not meet slagging and jam problems on the discharging of coal ash.Based on the research of kinetic of coal char gasification reaction and coal gasification characteristics, one dimensional mathematic simulation of 25kg/h pressured entrained flow gasifier had been set up. The model can truly reflect the process in the entrained flow gasifier. The simulation of entrained flow coal gasification was indicated success by comparison between model value and experimental value.The ash melting characteristics at different stages of coal char-H2O gasification reaction process was studied by using SEM-EDX. The results were shown that quite different the ash melting process under combustion condition, under gasification condition the coal ash melting is mainly started at the middle and latter process of coal gasification. Under coal gasification condition, the starting melting part is mainly caused by minerals which contain Fe element and after that the minerals which contain Ca element are begin to melt. The staring melt temperature is usually 100～150℃lower than initial deformation temperature(IDT) which is got by ASTM test. Under both reducing conditions, the starting belting temperature of coal ash under coal char-H2O reaction condition is higher than that under coal char-CO2 reaction condition, the reason is concerned of the content of CO.更多还原