【作者】 王连勇；

【导师】 蔡九菊；

【作者基本信息】 东北大学 ， 热能工程， 2009， 博士

【摘要】 我国大部分中小型燃煤工业炉窑(不包括电厂锅炉)采用直燃煤工艺,燃烧效率低,环境污染严重。为了解决直燃煤工艺引发的环境问题,近些年中小型燃煤工业炉窑开始采用煤气化技术,其中传统的固定床气化炉约占90%。固定床气化炉的出炉煤气热值低、焦油含量高,这样的热脏煤气不宜直接燃用。若采用炉外净化工艺,由于煤气净化设备复杂,运行费用高,且易造成二次污染,所以不适合我国大量而分散的中小型燃煤工业炉窑。为了从根本上解决燃煤工业炉的煤转换效率低、煤气热值低、焦油含量高等问题,论文开发了“煤高温空气气化ˉˉ高温贫氧燃烧一体化实验系统”和煤无焦油气化技术。一方面利用燃气炉窑排出的高温烟气预热空气,将高温空气作为煤气化炉的高温气化剂使煤高效气化：另一方面使焦油在煤气化过程中裂解并转化为可燃气体,实现洁净燃烧。论文工作为煤气化炉的结构设计和操作优化提供了理论依据,为我国中小型燃煤工业炉窑的节能减排开辟了新途径。1.论文自行设计了煤高温空气气化炉,首次成功实现空气高度预热的煤常压固定床气化工艺。研究了气化操作参数对气化指标的影响规律。结果表明：在保持气化温度不变的条件下,空气预热温度由500℃提高到800℃时,煤气热值提高幅度达32.5%。气化当量比和汽碳比对气化指标的影响本质上是通过改变气化温度来实现的,且气化当量比和汽碳比均存在一个最佳操作区域。在保证气化炉内不结焦的前提下,应采用较大的气化当量比和较小的汽碳比并提高空气预热温度。空气预热温度越高,煤气热值、气化效率等气化指标越好,而不同的空气预热温度又对应不同的最佳气化当量比,空气预热温度越高,最佳气化当量比越小。2.论文将煤高温空气气化和高温贫氧燃烧技术相结合,开发了煤高温空气气化ˉ高温贫氧燃烧一体化实验系统。一体化系统实验结果表明：气化空气流量随鼓风机开度增加和排烟机开度减小而逐渐增加,助燃空气流量则随排烟机开度增加和鼓风机开度减小而逐渐增加。实验得到气化空气和助燃空气的分流量范围分别为0-68.5 Nm3/h和0-122.5Nm3/h,可以分别满足气化和燃烧过程的需要；一体化系统使燃气加热炉烟气显热得到充分利用,使煤高温空气气化过程比常温空气气化过程的气化效率和热效率分别提高7.3%和6%,整个一体化系统比常规燃用热发生炉煤气的工业炉窑热效率提高约30个百分点,充分体现了一体化系统的优越性。3.利用TG-MS联用仪研究了煤焦油热裂解时的热失重特性和气相产物的逸出规律,阐述了焦油热裂解机理。结论如下：(1)焦油在100℃左右出现缓慢失重,从200℃开始出现剧烈失重,323℃左右失重速率最大,达到16.38%/℃,之后失重速率逐渐降低,当温度升高至800℃时失重速率缓慢增大,在877℃、1084℃和1235℃左右分别出现三个失重峰,1300℃时热分解基本结束,固体残留物约占49.8%。(2)焦油的热解过程中,H20的析出可以分为三个区间,分属于吸附水的脱出和羟基之间发生缩聚反应产生的热解水以及稳定含氧官能团的断键,其中在316℃左右析出最明显。H2在400～1050℃之间大量析出,从1050℃开始,H2进入缓慢生成阶段。CH4、C2H4和C2H2的析出均存在一个类似高斯分布的峰,其析出峰的强度差异说明焦油裂解产生的小分子碳氢化合物以CH4和C2H4为主。C3、CO和CO2均在800℃以上的高温下析出明显。4.论文对煤高温空气固定床气化炉的结构进行了改造,利用改造后的气化炉在典型的工况下进行了无焦油气化实验研究,并在此基础上提出了喉口型双火层固定床气化炉结构,开发了煤高温空气无焦油气化炉。结果表明：(1)二次空气的加入对降低煤气中焦油的含量作用明显。对上吸式气化炉,采用在干馏段加入二次空气的方法仅能给煤气中的焦油裂解提供一个高温环境,但这需要以燃烧部分煤气为代价,煤气热值反而降低,不能获得去除焦油和提高煤气热值的双重效果。对改造后的气化炉,二次空气的加入,提高了气化炉内上部氧化层的最高温度和还原层的整体温度,加剧了焦油的裂解反应、Boudouard反应和水煤气反应,不仅大大降低了煤气中焦油含量,而且使煤气中CO和H2浓度升高,提高了煤气热值和气化效率,改善了气化过程。(2)气化炉的双火层结构和三段供风方式使出炉煤气中焦油含量大大降低,煤气热值明显提高,煤气中焦油含量最低可达10mg/Nm3,煤气热值高达6466.9kJ/Nm3,完全可满足各种燃烧器和加热工艺要求,实现了煤无焦油气化。(3)炉箅空气的加入可提高碳转化率,降低炉渣含碳量,但炉箅空气比例过大,对降低煤气中焦油含量不利。(4)适量水蒸汽的加入可降低煤气中焦油含量,因为它可与某些焦油成分发生反应,但水蒸汽量过大会导致床层温度下降,反而会使煤气中焦油含量升高。更多还原

【Abstract】 Traditional direct coal combustion technology has been adopted in moat medium and small-sized coal fired industrial furnaces in China, which not only leads to low energy efficiency but also results in environmental pollution. In recent years, gasification technology has been adopted by some factories for environmental protection. Fixed bed gasifier account for almost 90% of the total gasifiers. The gas produced by conventional fixed bed gasifier has low heating value and high tar concentration. The kind of gas doesn’t suit direct combustion. If the hot gas is cleaned outside the gasifier and turn into cold gas without tar, the cost of equipments and running will increase and the secondary pollution will be produced. So it doesn’t suit the large numbers of medium and small-sized coal fired industrial furnaces. In order to solve the above problems, The integrated system for coal high temperature air gasification and high temperature air combustion and the coal tar-free gasifier was developed in the thesise. The high temperature air preheated by waste heat of high temperature flue gas is used for coal gasification as gasification agent in the integrated system. The tar crack and turn into fuel gas inside the gasifier during coal gasification and the clean combustion is realized. The study mentioned above not only is the theoretical foundation for the structural design of gasifier and the optimization of operational parameters, but also brings forward a new way for the energy saving and emission reduction of medium and small-sized coal fired industrial furnaces in China.1. The high temperature air as gasifying agent gasification of coal was applied successfully the first in a fixed bed gasifier by self-designed. The effects of operational parameters on gasification performance were studied. The experimental results show that the gas heating value increase 32.5% with the air pemperature increasing from 500℃to 800℃. The effects of ER and the steam/carbon ratio on coal gasification performance are realized by changing the gasification temperature, and the two parameters have an optimum operating range for a certain gasification process. It’s of significance to optimize the process parameters such as ER and the steam/carbon ratio for high temperature air gasification process. It is avail for gasification performance to adopt higher ER, lower steam/carbon ratio and higer air temperature in the condition of no slag bonding in gasifier. The different air temperature carries with them corresponding ER. The higher the air temperature is, the lower ER.2. The integrated system for coal high temperature air gasification and high temperature air combustion was developed through combining the high temperature air gasification with high temperature air combustion technology. The cold state experimental results indicate that the flow rate of gasificaiton air is increased with an increase in the opening degree of fan and a decrease in the opening degree of a fume exhaust fan. The flow rate of combustion air is increased with an increase in the opening degree of fume exhaust fan and a decrease in the opening degree of fan. The regulation range of the gasification air and combustion air are between 0～68.5Nm3/h and 0～122.5Nm3/h, which may satisfy the gasification and combustion’s needs, respectively. The hot state experimental results indicated that Integrated system made the most of the sensible heat of the gas-fired furnace’s flue gas. The gasification efficiency and thermal efficiency of the high temperature air gasification is 7.3% and 6% higher than the normal temperature air gasification. The thermal efficiency of the Integrated system is 29.14% higher than the normal hot gas-fired furnaces. It adequately shows the advantage of the Integrated system.3. Simultaneous TG-MS was used to investigate thermo-gravimetric behavior of tar and the the releasing characteristics of gaseous products during the pyrolysis. We expatiate the mechanism of tar thermal cracking. The results show that:(1) The pyrolysis behavior of tar is slow at 100℃and become quicker after 200℃, and is the quickest at 323℃, then, it slow down. When the temperature is higher than 800℃, it slowly quicken and appeares three apices at 877℃,1084℃,and 1235℃. The pyrolysis behavior of tar is over at 1300℃and the solid residue is about 49.8%.(2) The release of H2O has three stage during pyrolysis of tar, and is from adsorbed water emersion, pyrolysis water produced by condensation polymerization of hydroxy groups and the chemical bond of functional group broken, respectively. It mostly release at 316℃. H2 release between 400～1050℃obviously, then it slow down. The release rules of CH4, C2H4, and C2H2 are similar, which all have an apice which is similar to Gaussian distribution. The difference of three apices’ intensity show that the hydrocarbon release by tar pyrolysis primarily are CH4, C2H4. C3, CO and CO2 all release above 800℃obviously.4. In order to investigate the influencing factors of tar-free gasification, the high temperature air gasifier was mended. Using the mended gasifier, a series of tar-free gasification experiments were carried out in different typical operating conditions. Based on this experimental investigation, the throated twin-fire fixed bed gasifier structure was put forward and a high temperature air tar-free gasifier was developed. The results show that:(1) The injection of secondary air is an effective way to reduce the primary tar concentration in gas. The method which solely inject secondary air at pyrolysis region of gasifier can merely offer a high temperature condition for tar pyrolysis, but it is at a cost of combustion of a part of gas for updraft gasifier. It can’t get the double effect of the reduction of tar and the increase of heating value of gas. The injection of the secondary air raises the highest temperature in upper oxidation layer and the temperature in reduction layer for the throated twin-fire structure of gasifier. This can enhance reaction rate of tar pyrolysis, Boudouard reaction and water-gas reaction, and improve the concentration of CO and H2, heating value of gas and gasification effeciency. Consequently, the gasification is ameliorated.(2) The throated twin-fire gasifier and the three-stage air-feeding measure can reduce the tar concentration and raise the heating value of gas. The tar concentration and the heating value of gas can get 10mg/Nm3 and 6466.9kJ/Nm3, respectively.(3) The injection of the grate air leads to a comparable high carbon conversion ratio and also to an ash with a low carbon content. The more than ever grate air is adverse to reduce tar concentration. This kinds of gas can satisfy all kinds of burners and heating process. The tar-free gasification is realized.(4) An amount of steam avail to reduce tar concentration, but more than ever ateam will decrease the gasification temperature and increase the tar concentration in gas.更多还原