【作者】 李社锋；

【导师】 方梦祥； 王勤辉； 倪明江；

【作者基本信息】 浙江大学 ， 热能工程， 2010， 博士

【摘要】 能源紧缺、环境污染是整个人类社会面临的两个重大问题,低挥发份燃料的高效综合利用日益受到重视。本文对多联产半焦和石煤等低挥发份燃料的着火燃烧特性、CFB燃烧及污染物排放特性、循环流化床飞灰回燃特性进行了研究,从而为工业应用提供指导。采用SEM、氮吸附、压汞、固体压片红外光谱相结合的方法研究了多联产半焦的物理化学特性,结果表明：半焦和原煤相比,孔隙结构更发达,尤其是小尺度的大孔显著增多；氢键缔合的-OH或-NH、=CH等官能团减少,脂肪族CH、CH2和CH3减少,饱和酯、醛类、酮类、羧酸、烯烃、芳环及杂环化合物等物质减少,C-O基团化合物及乙烯类物质减少,甲基／亚甲基的数量比增大,含氧基团与芳香度含量之比降低。利用常压、加压热天平研究了不同半焦的着火燃烧机理,结果表明：随着热解温度或升温速率的升高,半焦的着火温度(Ti)升高,燃烧产物释放特性指数(r)减小,燃烧稳定性(Rw)降低,燃尽性能(Cb)提高,活化能(Ea)降低；随着反应压力的提高,半焦的着火温度降低,燃烧产物释放特性指数r增大,燃烧稳定性提高,燃尽温度先升后降,活化能先降后升,在压力0.8MPa时燃尽温度最高,活化能最低；粒径增大,则半焦着火温度升高,燃烧产物释放特性指数增大,燃烧稳定性先升后降,燃尽特性非单调变化,活化能非单调提高；焦煤比增大,则其着火温度先降后升,燃烧产物释放特性指数减小,燃烧稳定性降低,燃尽性能提高,活化能升高。另外,DAEM模型计算结果显示,半焦的活化能Ea随着质量损失率的增加而降低。在小型CFB试验台上进行了半焦燃烧及污染物排放特性试验,结果表明：焦煤比越大,S02、NO、N20的排放浓度越低；从850℃到940℃,随着温度的升高,NO排放量逐渐升高,N20排放量逐渐降低,但降低的趋势变缓；提高过量空气系数会导致NO、N20排放量增大；增大二次风率可降低NO、N20的排放；风量增大,炉膛烟气表观流速提高,NO排放浓度减小,N20排放浓度增大。针对有些循环流化床锅炉存在飞灰含碳量高和石灰石利用率低的问题,进行了劣质燃料水活化飞灰回燃特性研究。飞灰回燃不仅可以降低飞灰含碳量,而且可以提高脱硫剂的利用率。本文在小型循环流化床实验台上进行了一系列的飞灰回燃试验,研究了灰煤比(Ca/S比)、运行温度、飞灰活化方式、循环倍率、表观烟气速度等因素对脱硫效率和飞灰含碳量的影响,寻求合理运行参数,得到的试验结果可以指导工业运行。在前入研究的基础上,结合循环流化床流动特性、煤焦反应、污染物的生成与分解规律,建立了考虑飞灰再燃的CFB燃烧总体数学模型,并利用该模型对试验工况进行了模拟,分析显示计算结果与试验结果基本吻合。同时,运用该模型对CFB燃烧进行了预测,得到了采用飞灰回燃时,CFB系统的运行特点,为工业生产提供理论依据。最后,对CFB焙烧石煤灰渣提钒进行了初步探索,在一台小型流化床燃烧试验台上研究了不同配方灰渣料团的焙烧特性,着重考察了焙烧温度、焙烧时间、表观烟气速度、添加剂种类对焙烧成球率的影响,并对飞灰、底渣、床料进行收集采样,利用多种酸溶液对各种样品浸取提钒,研究了焙烧温度、焙烧时间、浸取方式对转浸率的影响。结果表明：采用水泥为添加剂,温度为930℃,焙烧时间为90 min,可得较高焙烧成球率和转浸率,钒总回收率约为55.1%。更多还原

【Abstract】 Nowadays, energy shortage and environmental pollution are the two major problems that human are facing to, and efficient utilization of low-grade fuels has been highlighted for more special attention. The ignition and combustion mechanisms, combustion characteristics and pollution emission of multi-generation-semicoke and stone coal in CFB combustor were investigated systematically and intensively in the thesis. Furthermore, the characteristics of fly ash recycle in CFB combustor was also studied, which could play a guidancing role in industrial operation.The investigation on physicochemical characteristics of semi-coke was conducted with employing Scanning Electron Microscope (SEM), nitrogen adsorption, mercury porosimetry, infrared spectroscopy. And the results demonstrate that compared with parent coal, semi-coke has the following conspicuous changes:pore structure has been developed strongly, and the amount of pores increases significantly, especially for small-scale large pores. Many functional groups, such as OH, NH, CH, CH2 and CH3, reduce. Moreover, the contents of some chemical compounds, including saturated polyesters, aldehydes, ketones, alkenes, aromatic rings, heterocycles oxo-compounds, are all decreased too. CH3 to CH2 mole ratio increases, while the content ratio of oxygen-containing groups to aromaticity decreases.Atmospheric and pressurized thermogravimetry were employed to study the pyrolysis-ignition-combustion mechanisms of different semi-cokes, and the results show:With the increased gasification temperature or heating rate, ignition temperature (Ti) is increased, volatile release index (r) is decreased, combustion stability (Rw) is reduced, burnout performance (Cb) is enhanced, and activation energy (Ea) of semicoke is decreased. With the increased reaction pressure, Tt drops, r increases, Rw improves, Cb drops down after increasing, Ea rises after falling. When reaction pressure at 0.8MPa, burnout temperature is maximized, and Ea is minimized. With the increased average diameter of semi-coke particles, Ti and r increase, Rw fall after rising, Cb changes non-monotonically, Ea increases non-monotonically. With the increased char-to-coal ratio, Ti increases after falling, r and Rw decrease, Cb improves, Ea increases. Besides, calculation results from Distributed Activation Energy Model (DAEM) show that activation energy of semi-coke decreases with the increased mass loss rate. Experiments were carried out in a bench scale CFB combustor to investigate the combustion and pollution emission characteristics of semi-coke. It was found that the emission concentrations of SO2, NO and N2O would be decreased with the increased char to coal mass ratio. With the increased temperature from 850℃to 940℃, the emission concentration of NO is raised while that of N2O is cut down. With the increased excess air coefficient or the decreased secondary air rate, the emission concentrations of SO2, NO and N2O would be increased. With the increased superficial gas velocity, NO emission concentration decreases, while N2O emission concentration increases.At present, high carbon content of fly ash and low utilization ratio of limestone are the two main problems existing in some CFB boilers. The combustion of recycled fly ash could not only reduce the carbon content, but also increase the utilization ratio of limestone. Experiments on the combustion of the recycled fly ash, obtained from Guizhou Thermal Power Plant burning local anthracite coal, were conducted in a bench-scale CFB combustor. Effects of ash to coal mass ratio (Ca/S. molar ratio), furnace temperature, reactivation mode of fly ash, solid circulation rate and superficial gas velocity on the desulfurization efficiency and carbon content of fly ash were investigated to find the reasonable operation parameters, which could guide the industrial operation.Based on many chievements of other preivious study, a general mathematical model has been developed to simulate CFB combustion with the consideration of fly ash recycle. The characteristics of hydrodynamic of CFB, coal-char combustion, pollutions emission combustion are considered extremely as well. The simulation results show a good agreement with the experimental results, and the model could reasonably simulate semi-coke combustion in CFB boiler with fly ash recycling, which would play a significant role in guiding industrial operation to reflect the operating characteristics of CFB system.Finally, a preliminary test was performed in a bench scale fluidized bed combustor to study the roasting characteristics of several kinds of stone coal pellets, focusing on the effects of roasting temperature, roasting time, superficial gas velocity and various additives on the pellet-remaining ratio after roasting. Fly ash, bottom ash and bed material were collected. V2O5 was extracted from the fly ash and bottom ash by deionized water, acid solutions of 2% Na2CO3, 6% H2SO4 and 10% H2SO4, while the effects of roasting temperature, roasting time, leaching mode on leaching rate were analyzed. The test results showed that with cement as additive, temperature at 900℃and roasting time-90 minutes, the excellent pellet-remaining ratio after roasting and leaching rate were obtained, and the vanadium recovery rate was as high as 55.1%.更多还原