【作者】 蒋啸；

【导师】 岑可法； 周昊；

【作者基本信息】 浙江大学 ， 工程热物理， 2008， 博士

【摘要】 火力发电在我国的发电结构中占有主导地位,而燃煤火力发电在火力发电中占有绝对的比例,特别是煤粉燃烧火力发电。在能源日益紧张的今天,节能降耗要求越来越迫切。了解煤粉颗粒的燃烧特性特别是煤粉细度对燃烧特性的影响,不管是对于常规煤粉燃烧,还是对于开发新的燃烧技术和降低污染物NOx排放的炉内燃烧技术来说,具有重要的研究和现实意义。本文针对煤粉细度对煤粉燃烧特性的影响机理,进行了一系列探索性的研究。本文首先从煤粉燃烧效果的角度出发,通过研究不同粒径尺寸飞灰的可燃物特征,讨论了粒径尺寸对煤粉燃烧的作用规律。研究发现煤粉炉飞灰可燃物与粒径之间并不完全符合以前所获取的飞灰可燃物随飞灰细度减小单纯下降的线性关系认识,在一定条件下,存在拐点,典型的变化趋势为:随着粒径尺寸的减小,飞灰可燃物先减小后增加。特别是对于20μm以下的飞灰,其可燃物有升高趋势。应用热重分析法对不同颗粒直径煤粉样品的燃烧特性进行了研究,在分析煤粉主要着火与燃尽特征的基础上,进一步开展了煤粉热解和焦炭燃烧受颗粒直径影响的热重实验。根据煤粉热重试验结果,利用着火温度、燃尽温度、着火稳定性指标、可燃性指标和稳燃判别指数、平均燃烧速度和综合燃烧特性指数等煤粉燃烧特性参量对煤粉燃烧特性进行进行表征。研究结果表明,对于烟煤、贫煤和无烟煤,随着颗粒直径的减小,各项燃烧性能基本呈现增强的趋势。对于超细煤粉,特别是直径小于20μm的煤粉来说,颗粒直径的变化对煤粉燃烧特性的影响不大。无烟煤的着火和燃尽特性特别是燃尽特性受煤粉颗粒直径的影响较烟煤和贫煤更为明显。随着煤粉颗粒直径的减小,挥发份析出的速度加快,烟煤挥发份大量析出的时间更为集中。焦炭燃烧热重试验结果表明,焦炭燃烧受煤粉尺寸的影响更为显著。利用图像处理和分形理论,对颗粒直径对煤粉的形状特征和分形特征的影响展开了研究。研究的结果初步表明,颗粒尺度对煤粉的形状特征和分形特征的影响不明显。工业分析和元素分析的结果表明,不同细度煤粉的工业分析和元素分析结果差别不大,变化幅度一般不超过10%。表观活化能的测试结果表明,在低温段,随着颗粒直径的增加,煤粉的表观活化能逐渐增加,亦即细煤粉的燃烧性能优于粗煤粉。在高温段,贫煤和无烟煤随煤粉粒径增加,表观活化能升高;烟煤随煤粉粒径增大,表观活化能反而降低。煤种对表观活化能的影响更明显。本文借助大型CFD软件Fluent对不同细度煤粉在炉内燃烧过程进行了数值模拟研究。计算结果显示,随着煤粉颗粒直径的的增加,煤粉在炉内停留时间延长。停留时间变化的幅度可达30%以上。不同高度喷入的不同细度煤粉在炉内停留时间变化趋势并不完全一致。较细的煤粉在炉内在炉内较短的时间即达到比较高的燃尽度,而后焦炭燃尽率变化缓慢,而粗煤粉的燃尽率变化相对缓和。采用CBK模型模拟焦炭燃烧,煤粉随粒径增大,焦炭燃尽率升高。但超细煤粉特别是粒径10μm以下煤粉随粒径减小,焦炭燃尽率反而有升高的趋势。本文对酸浸处理粉煤灰工艺副产品进行了试验研究。提出了分步处理逐级利用的技术方案,即利用流化干燥技术脱除结晶水,然后对剩余物质氨解、硫解,回收硫酸氨和硫酸,返回酸浸工艺循环,最终剩余物氧化铝作为冶金原料。分步处理逐级利用大大降低了系统的能耗,提高了硫酸氨和硫酸的回收利用率。并对技术方案进行了试验研究,试验结果硫酸回收率达到90%以上,硫酸铵回收率达到70%以上。每吨硫酸铝氨热解后可回收得到0.2156吨硫酸、0.093吨硫酸铵和0.097吨的三氧化二铝。本文对宽粒径范围的煤粉燃烧特性进行了系统研究,为新燃烧技术和炉内污染物控制技术的开发提供了大量的基础数据,可以为技术开发和工程应用提供参考和指导。硫酸铝铵的循环利用工艺对粉煤灰酸浸提钒提铝等技术降低硫酸和硫酸氨耗量具有重要意义,并可有效防止新污染物的产生。更多还原

【Abstract】 Thermal power generation is a dominant part of power generation structure in China, in which, coal-fired thermal power generation is definitely the most common one, especially the coal powder burning thermal power generation. At present, energy saving and reduction of power consumption is more demanding with increasingly short energy resources. Finding out combustion characteristics of pulverized coal particles, especially the effect of coal powder fineness to combustion characteristics is theoretically and practically important to conventional coal powder burning technology, newly developed burning technology as well as in-furnace burning technology which is aiming at reducing emission of pollutant NOx. In this thesis, a series of exploring research is carried out to find out how coal powder fineness to influence the coal powder combustion characteristics.This thesis starts with analyzing coal powder burning effect. By analyzing characteristics of combustibles in fly ash with different size, the thesis discusses the influence of coal particle size on burning performance. The research finds out that relationship between combustibles in fly ash and diameter of coal particles is not completely conform with the linear relation we have made out that combustibles in fly ash is decreasing with fly ash fineness decreasing. As the research finds out that in certain circumstances, there is an inflection point and the typical changing tendency is as follows: with diameter of coal particles decreasing, combustibles in fly ash decreases first and then increases, especially to fly ash below 20μm , there is a tend for combustibles to increase.By applying TGA researching method, this thesis has analyzed combustion property of coal powder samples in different diameter. On the basis of analysis in ignition and burnout of coal powder, the thesis moves on to carry out the thermal-gravimetry study of effect of coal particles diameter on pyrolysis of pulverized coal and combustion of coke coal. Then the thesis uses parameters of coal powder burning characteristic such as ignition temperature, burnout temperature, ignition stability index, combustible index, combustion stability judging index, average combustion speed and comprehensive combustion property, etc to prove the study. The study shows that with coal particles diameter decreasing, soft coal, lean coal and blind coal takes on increasing trend in burning behavior; while to superfine pulverized coal powder, especially coal powder below 20μm , change of diameter of coal particles has little influence on coal powder combustion property; compared with lean coal and blind coal, the ignition and burnout characteristic, especially the burnout characteristic of soft coal is more easily influenced by diameter of coal particles; with coal particles diameter decreasing, release of volatile matters is speeded up and large amount of volatile matters in soft coal is released in s short time. Thermal-gravimetry study in coke coal burning shows that coke coal burning is more easily influenced by coal powder size.By using image processing and fractal theory, the thesis studies the effect of coal particle diameter on coal powder shape features and fractal characteristics. The preliminary result shows that coal particle diameter has little effect on coal powder shape features and fractal characteristics. The result also shows that the fineness of coal powder has little effect on the difference between the results of either industrial analysis or element analysis, the difference variation of results provided by industrial analysis and by element analysis is ranged with 10%. The test of apparent activation energy shows that in low temperature part, with diameter of coal particles increasing, apparent activation energy of coal powder is increasing gradually, i.e. combustion characteristics of fine coal powder is better than that of coarse coal powder; in high temperature part, with diameter of coal particles increasing, apparent activation energy of lean coal and blind coal increases, while apparent activation energy of soft coal is decreasing with increasing in diameter of coal particles. The above study result shows that type of coal powder has more obvious influence on corresponding apparent activation energy.By making use of CFD software FLUENT, the thesis has made numerical simulation study to combustion process of coal powder with different fineness in furnace. The result shows that with diameter of coal particles increasing, resident time for coal powder in furnace extends, and resident time variation extent can be up to and even more than 30%. In addition to that, resident time varies for coal powder injected from different highness. Finer coal powder burns quickly in a comparatively shorter time inside furnace, then the remained char burns out slowly; while the combustion rate of coarse coal powder changes more slowly. By applying CBK model to simulate coke coal burning, the study finds out that with diameter of coal powder increasing, burn-out rate of coke coal increases too, while to superfine coal powder especially the ones whose diameter is below 10μm, with diameter decreasing, burn-out degree of coke coal increases on the contrary.The thesis has also studied technological by-product of fly ash treated by acid and brought forward technical plan of processing step-by-step and utilizing level by level, i.e. using fluidized drying technology to remove crystal water, then by carrying out ammonolysis and thiolysis to the residue to get ammonium sulfate and sulphuric acid to get back to technological circulation of acid treatment, finally the residue aluminium oxide will be used as metallurgy material. Processing step-by-step and utilizing level by level has greatly reduced energy consumption, increased reclamation rate of ammonium sulfate and sulphuric acid. Through experimental study of technological plan, the result shows that reclamation rate of sulphuric acid is above 90% and ammonium sulfate is above 70%. 0.21t ammonium sulfate, 0.1t sulphuric acid and 0.114t Al₂O₃ can be reclaimed from 1 ton aluminum ammonium sulfate by pyrogenation.The thesis has carried out systematic study on combustion characteristics of wide sized distribution coal particles, which provided large amounts of basic statistics for new combustion technology and in-furnace pollutant controlling technology research and development, which can also be reference and informative to relevant technology development and project application. Circulation utilization technology of aluminum ammonium sulfate can be important to technology of treating fly ash by acid to extract vanadium and aluminium so as to reduce consumption of sulphuric acid and ammonium sulfate and effectively avoid producing new pollutants.更多还原