【作者】 王炯；

【导师】 张力；

【作者基本信息】 重庆大学 ， 动力工程及工程热物理， 2010， 博士

【摘要】 我国每年排放约占当年煤炭产量的百分之十以上的煤矸石,目前已累计堆积达数十亿吨。煤矸石长期堆存,污染大气、地面水源或下渗损害地下水质,占用大量土地。中国煤层气可采资源量约10万亿立方米,累计探明煤层气地质储量1023亿立方米,可采储量约470亿立方米,目前我国每年由煤炭生产而释放大量煤层气,其中被利用的仅占很少部分。对煤矸石与煤层气进行高效混烧能源化利用,可以节约资源,减少温室气体排放。采用流化床技术利用低、劣质燃料是国内外研究的热点。目前国内外对不同相态的燃料在循环流化床中的混烧还很少进行系统研究,因此在深入研究煤矸石热解与燃烧特性的基础之上,进行煤层气与煤矸石CFB内多相流动与混烧特性的数值模拟与试验研究,弄清不同相态的燃料在CFB内的流动、传热及燃烧特性,可以为研究和开发煤层气与煤矸石CFB混烧技术奠定坚实的理论基础。论文使用热分析天平,在不同气氛下进行煤矸石的热解与燃烧特性实验,获得了煤矸石的着火点、活化能等特性参数。首次建立了适应低热值煤层气高效燃烧的燃烧器物理模型与数学模型,通过数值模拟,优化了燃烧器结构,并通过实验验证了数值模拟的结果。以现有的45t CFB锅炉为基础,首次建立不同相态燃料在CFB锅炉内混烧的物理模型与数学模型,对煤层气与煤矸石CFB混烧进行数值模拟,深入分析了混烧的流场、温度场以及CO2及CH4的浓度变化,获得了高效燃烧的最佳工况。在数值模拟的基础上,首次对某煤矿45t CFB锅炉进行了煤层气混烧的改造,对锅炉进行了冷态试验、热态试验,测试了不同混烧比时的炉膛沿高度方向的温度变化,以及炉膛出口处CH₄的浓度,并测试了锅炉热效率。研究结果为开发煤层气与煤矸石CFB混烧技术奠定了坚实的理论基础。煤矸石的热解与燃烧动力学特性研究表明:煤矸石中挥发分含量越高,越容易发生热解;热解终温增加,煤矸石的热解失重率增大;样品粒径越大,热解特征温度越高,热解失重率降低;升温速率增加, DTG峰值增大,失重率降低;煤矸石高灰分的特点导致了其燃尽性能很差,不易燃尽;煤矸石综合燃烧性与挥发分含量关系密切,挥发分越高,综合燃烧性能越好。低甲烷浓度煤层气燃烧器数值模拟研究表明:部分预混式燃烧器燃烧效率最高,扩散式燃烧器燃烧效率最低,完全预混式燃烧器介于两者之间。部分预混式燃烧器射流刚性最好,燃烧温度相对较高。总体来看,部分预混式燃烧器配渐扩口,且扩散角为6.88°时能获得相对高的燃烧效率。低浓度煤层气燃烧器冷态与热态试验表明:完全预混式燃烧器燃气侧流动阻力最大,扩散式燃烧器最小。完全预混式燃烧器,部分预混式燃烧器,扩散式燃烧器在不同热负荷下均能稳定燃烧,不回火、不脱火,具有较宽的负荷调节能力。部分预混式燃烧器燃烧时火焰刚性好,燃烧温度最高,高温段距离长,火焰宽度最小,火焰扩散角最小。扩散式燃烧器火焰长度最长,火焰宽度最大,火焰扩散角最大。完全预混式燃烧器的火焰长度最短。低浓度煤层气燃烧器冷态与热态试验表明:扩散式燃烧器压力损失最小,完全预混式燃烧器压力损失最大。部分预混式燃烧器火焰温度最高,火焰刚性好,完全预混式燃烧器的火焰长度最短扩散式燃烧器火焰最长,宽度最大。通过实验结果与模拟结果的比对,可看出两者结果吻合较好,部分预混式燃烧器综合性能最优。低热值煤层气与煤矸石CFB混合燃烧数值模拟研究表明:混烧比为10:0时,炉膛内速度整体分布比较均匀,随着煤层气混烧比例的增加,流场偏斜加剧,煤矸石与煤层气混烧比达到6:4时,偏斜程度最大。当燃料全部为煤矸石时,燃烧器内温度分布比较均匀。喷入煤层气,导致燃烧器内流场发生偏斜,从而造成局部高温。随混烧比的增加,在距布风板高度5 m左右出现CH₄的浓度峰值,随炉膛高度的增大,CH4浓度明显下降。综合模拟结果,混烧比不宜大于8:2,一、二次风比益选用6:4。煤层气与煤矸石循环流化床混烧试验研究表明:布风板阻力随一次风量增大而增大,布风板阻力特性曲线基本上近似为一条二次曲线。随着流化风量的增加,曲线有明显的压力变化拐点,该拐点对应的风量为即临界流化风量。由热态试验数据可知,密相区温度较高,稀相区温度较低,稀相区温度变化较小,温度较为均匀,这有利于在密相区未燃尽的颗粒在稀相区继续燃烧。随着煤层气混烧比的增加,锅炉的效率增加,从混烧比为10:0时的82.6%增长到混烧比为8:2时的84.1%。本文通过对煤层气及煤矸石在CFB内混烧特性的深入研究,为进一步研究、开发相关技术打下了坚实的基础,在资源综合利用与环境保护方面有着十分广阔的工程应用前景。更多还原

【Abstract】 China’s annual heavily emissions gangue, which is about ten percent of coal production, has aggregated piled up billions of tons at present. Long-term stockpiling of coal gangue needs amounts of land and leads to air and water pollution. Coal bed methane（CBM） resources in China is about 10 trillion cubic meter, of which proved reserves is 102.3 billion cubic meter and recoverable reserves is 470 billion cubic meter. Now, only a small part of CBM is used. Therefore, the efficient utilization of coal gangue and CBM is able to save resources and reduce greenhouse gas emission.It is hot topic at China and abroad that using fluidized bed to utilize low-grade fuel. In present, there are few systematic researchs on the co-combustion with different phases of the fuel in circulating fluidized bed. So that, based on the in-depth study of pyrolysis and combustion characteristics of coal gangue , the simulation and experimental research of multi-fluid flow and co-combustion characteristics of CBM and coal gangue were done. The study of different phases fuel in CFB the flow,heat transfer and combustion characteristics lays a solid theoretical foundation for further developing the CBM and coal gangue CFB firing technology.The experiments of the pyrolysis and combustion of coal gangue in different atmospheres were done by thermal analyser. The ignition of coal gangue, activation energy and other parameters were obtained. Physical and math models of burner adapting low calorific thermal value CBM combustion were built for the first time. The burner has been optimum designed by numerical simulation methods and the results were verified by experimentation. The physical and mathematical models which described the mixing burning of different phases fuel in CFB were established based on the subsistent 45t CFB for the first time. Numerical simulations were done for mixing burning of CBM and coal gangue. Flow field, temperature and concentration changes of CO2 and CH₄ were analyzed in depth. The best work condition was obtained.The renovation of a 45t CFB for mixing burning of CBM was carried out based on the results of numerical simulations for the first time. The cold and hot tests of the boiler were done. The variation laws of temperature in vertical direction, the concentration of CH₄ at the outlet of the furnace and boiler efficiency were test. The results have established the theory bases for the development of technology of mixing burning of coal bed methane and coal gangue in CFB. The pyrolysis and combustion of coal gangue kinetics characteristics study shows that the higher the volatile content in coal gangue, the more prone to thermal decomposition; final pyrolysis temperature increased, the pyrolysis of coal gangue weight loss rate increases; Larger sample size,the higher characteristic temperature pyrolysis, pyrolysis mass loss rate decreased; heating rate increases, DTG peak increased, weight loss reduced;the characteristics of high ash coal gangue lead to poor performance of its burn; combustion of coal gangue comprehensive close relationship with the volatile content, the higher the volatile, integrated combustion performance is better.Numerical simulation study on low-calorific value coal bed methane burner indicates that burning efficiency of part-premixed burner is highest, burning efficiency of diffusion burner is lowest, premixed burner is in between part-premixed burner and diffusion burner. Partially premixed burner has good jet rigid, combustion temperature is relatively high, in general, part of the premixed burner with gradually expanding, and the diffusion angle of 6.88°has a relatively high combustion efficiency.Low concentrations of methane burner cold and hot test showed that: diffusion burner pressure loss is minimum, fully premixed burner pressure loss is very bigt. Partially premixed burner flame temperature is maximum, fully premixed burner flame length is the shortest, diffusion burner flame length is longest. Comparing experimental results with the simulation results, we can see a good agreement between both, partially premixed burner has the best overall performance.Low calorific value coal methane and coal gangue CFB combustion simulation results show that when the ratio of coal gangue and coal bed methane is 10:0, the overall speed of the combustion chamber is relatively evenly distributed, with the increasing of coal bed methane, flow deflection increase, when the co-combustion ratio is 6:4, the degree of flow deflection is the highest. When all the fuel is coal gangue, the overall temperature of the combustion chamber is relatively evenly distributed. When the coal bed methane is injected, flow field deflection occurs, resulting in local high temperature. With the increasing of coal methane, the peak of the concentration of CH₄ occurs when the height away from the air distribution plate 5m,With the height increasing of the combustion chamber, CH₄ concentration significantly reduced. Comprehensive simulation results show that the ratio of coal gangue and coal bed methane is improper when more than 8:2, a beneficial use of primary and secondary air ratio 6:4. The experimental studies of coal bed methane and coal gangue co-combustion in Circulating fluidized bed show that air flow resistance of the air distribution plate increases with air volume increasing. The resistance characteristic curve of the air distribution plate is basically similar to a quadratic curve. With the increasing flow of air, an inflection point can be seen on the the pressure curve clearly, and the inflection point corresponds to the critical flow air volumeo f the air. It can be conclused from the thermal test data of high temperature in dense region, low and unifom temperature in dilute phase region that unburned particles in dense area can continue combustion in dilute phase region. With the increasing of the ratio of methane co-combution from 10:0 to 6:4, boiler efficiency increase from 82.6% to 84.1%.The study of the co-combustion characteristics of the coal bed methane and coal gangue in CFB is useful for further research and development relative technology. It has a very broad application prospect in comprehensive utilization of resources and environmental protection.更多还原