【作者】 黄志军；

【导师】 郑楚光； 邹春；

【作者基本信息】 华中科技大学 ， 热能工程， 2013， 博士

【摘要】 电力生产中以煤炭为主的化石燃料的燃烧排放了大量的二氧化碳，温室气体的快速增加导致了温室效应和全球变暖，其引发的全球气候变化和环境问题已经给人类带来了越来越大的影响。国际社会对此给予了越来越多的关注，达成了一系列以《京都议定书》为代表的国际间碳减排合作协议，并加速了燃煤电厂碳减排技术的发展。在众多针对燃煤电厂烟气中CO₂的收集和储存的技术中，使用氧气与循环烟气混合后替代空气参与燃烧的煤粉燃烧技术（也被称为富氧燃烧或O₂/CO₂循环燃烧），是当前在技术和经济上最能被工业界所接受的一项碳减排燃烧技术。与煤粉在空气下的燃烧相比，煤的O₂/CO₂循环燃烧技术由于没有N2的参与，炉膛尾部烟气中CO₂浓度能够达到90%以上，便于进行捕集和回收，且烟气容积的大量减少降低了热损失和处理成本。已有研究表明，煤粉在O₂/CO₂气氛下燃烧的燃烧特性与污染物排放特性均不同于传统空气下的燃烧，如火焰温度降低、稳定性变差等。通过采用新型的燃烧器及合理的配风技术，能够使火焰温度和炉膛传热特性与空气下燃烧时接近，并且在污染物的脱除方面有很大的减排潜力。在本文研究之前国内对这项技术的中型和大型试验研究尚无，对于该项技术在试验运行参数、O₂/CO₂燃烧器开发、燃烧特性和污染物生成机理等方面的研究还非常缺乏。本文采用热天平（TGA）与红外烟气分析仪联用，对三种煤及其煤焦进行了不同O₂浓度下的O₂/N2和O₂/CO₂气氛下的燃烧实验，并对燃烧产生的烟气进行了红外实时监测分析，对比了两种气氛下煤的燃烧反应特性，得到了处在化学动力学控制区域范围内动力学参数，并采用多种计算方法相结合找出了最概然机理函数。通过对比烟气浓度随温度的变化规律，分析了高浓度CO₂对煤的反应速率的影响以及污染物生成规律的影响。设计并搭建了以竖直燃烧炉为主体的国内首台中试规模O₂/CO₂循环燃烧综合试验台，对煤在空气下和O₂/CO₂气氛下的燃烧进行了多工况试验，对比分析了煤粉在不同O₂浓度及不同烟气循环方式下的燃烧特性和温度场。寻找最佳烟气循环率及其它运行参数，以使空气下和O₂/CO₂循环燃烧条件下的炉内温度场和传热状况相近，且炉膛出口烟气中CO₂达到回收标准。根据O₂/CO₂循环燃烧的特点，采用数值模拟和试验研究相结合的方法，对O₂/CO₂旋流燃烧器的设计方法进行了探索。对改进后的燃烧器进行了冷态空气动力场试验，确定了气流扩展角及回流区大小。在中试台架上进行的热态试验用来研究燃烧器在空气下和O₂/CO₂循环燃烧条件下的燃烧特性及污染物排放特性。研究表明，改进后O₂/CO₂旋流燃烧器具有良好的可调性，氧-煤混合度和燃烧性能有明显的提高。这些研究对今后O₂/CO₂燃烧器的研究和设计有非常强的指导意义。利用CFD软件对整个炉膛全尺度建模，选取了合适的湍流流动、燃烧与传热的数学模型对煤粉在空气和O₂/CO₂气氛下的燃烧进行了计算，并对模拟结果与实测数据进行了对比分析，数据吻合度良好，说明模拟能够反映真实的燃烧过程。并在FLUENT软件上对变更烟气循环参数后的燃烧过程进行了探讨，对实际运行给出了建议和指导。另外，FLUENT软件在燃烧器设计过程中，在确定燃烧器的关键参数如旋流强度和叶片安装角度上起到了重要的作用。对中试台架上煤在空气下和O₂/CO₂循环燃烧条件下燃烧时炉内污染物生成规律进行了理论分析和试验研究，研究了NOx和SO₂的浓度分布及排放规律，探索了在O₂/CO₂循环燃烧条件下进行炉内喷钙实现对NOx和SO₂进行联合脱除的方法。并使用FLUENT和CHEMKIN对O₂浓度不同的O₂/N2和O₂/CO₂气氛下的燃烧进行了模拟计算和机理分析，研究了用CO₂置换N2后NOx和SO₂的生成机理的变化规律，考察了温度、氧气浓度、气氛、循环方式等因素对污染物排放的影响。试验和模拟的结果吻合度良好，O₂/CO₂循环燃烧条件下污染物的排放量与空气下相比大大降低。另外，改进后的燃烧器的污染物脱除率有明显的提高，改进效果显著。更多还原

【Abstract】 Electric power production from coal-based fossil fuel combustion results in theemission of greenhouse gases which are dominant contributed by CO₂. The rapidincreasing amount of greenhouse gases exerts profound influence on the globalenvironment, and global warming and climate changes it caused become progressivelyworse. Public awareness and legislation lead to a series of international cooperativeagreements on reduction of greenhouse gas emissions which are represented by Kyotoprotocol and the Intergovernmental Panel on Climate change. It also accelerates thedevelopment of the technologies on Carbon capture and storage （CCS）. Compared withother current possibilities, however, oxy-fuel combustion is the most reliable andeconomical choice which was characterized by coal burned in pure oxygen and recycledflue gas （O₂/RFG） instead of air.Current available research findings show that CO₂concentration of exhaust gasesis over90%during the process of coal oxy-fuel combustion, so it is possible to utilizeand treat it without separation. Furthermore，the expense of pollutant disposal andthermal loss decrease because of the relatively small amount of flue gas volume.However, the flame temperature is lower and its stability is poorer while compared withthe combustion process in air atmosphere. The pollutant emission characteristic isdifferent too. But the flame temperature and furnace heat-transfer characteristic isenhanced effectively by adopting advanced burners or by adjusting air distribution. Ithas great potential on simultaneous removal of multi-pollutant. However, few studiesfocuses on these aspects such as the mechanism of coal oxy-fuel combustion andpollutant formation characteristics, operation parameters, O₂/CO₂burner designing, etc.Especially, the research that experimental investigation on pilot-scale or full-scale testfacility still seems insufficient in depth and scope before this paper.Thermogravimetric-Infrared Interconnection method （TG-FTIR） was employed inthe online measurement of combustion process of three kinds of coal and its char inO₂/N2and O₂/CO₂atmosphere with different proportion of O₂, particularly inmeasurement of CO concentration. Reaction kinetic parameters of the coals were obtained by analyzing the reaction curves and the combustion products under O₂/N2andO₂/CO₂atmosphere, and the corresponding most probability mechanism function wasacquired by using two different simulation calculation methods too. The influence ofhigh concentration CO₂on the reaction rates of the coals and the formation of pollutantswas researched by analyzing the composition of flue gas.The first domestic pilot-scale oxy-fuel combustion test facility was designed andbuilt in this work. The facility was characterized by a0.3MW vertical combustor. Aseries of combustion experiments have been carried out in this system in air, O₂/CO₂and O₂/RFG atmosphere. The combustion characteristics and temperature fields werecomparative analyzed at different oxygen concentration and different flue gasecirculation ratio. Optimum operation parameters were determined to obtain the similarflame temperature and heat transfer under air and O₂/RFG atmosphere and to gain aready-to-recovery stream of flue gas. According to the characteristics of O₂/CO₂recycled combustion, a type of O₂/CO₂swirl burner was designed by using numericalsimulation method combined with experimental approach. It got an insight into themethodology of designing O₂/CO₂burner. The cold-state experiment was carried out totest the aerodynamic performance of the burner and adjusted the flow expansion angleand the central recirculation region. The combustion tests under air and O₂/RFGatmosphere were carried out to examine the performance of the burner in respect ofcombustion characteristics and pollutant formation characteristics. Studies showed theimproved swirl burner has the virtue of operational flexibility and better combustionperformances when it was applied to oxy-fuel combustion conditions. It presentedimportant references for future researching and designing of O₂/CO₂burner.FLUENT was used to simulate the coal combustion process on the pilot test facility.The appropriate flow, combustion and heat transfer model were chosed to obtain thereasonable results which were compared with measured data. The simulation results hada good agreement with the experimental data. This demonstrates that numericalsimulation could reflect the real combustion process. FLUENT was used to analyze thecombustion process when the operational parameters changed, for example, thecirculation ratio. The analytical results can guide the future operation of the experiments.Moreover, FLUENT was useful on determining the best swirl strength and blade fitting angle in designing process of O₂/CO₂burner.Theoretical analysis and experimental studies of the pollutant formationmechanism during coal oxy-fuel combustion process were conducted on the pilot testfacility. The formation and emission mechanism of NOxand SO₂was investigated underair and O₂/CO₂atmosphere. The in-furnace limestone injection technology wasconducted to explore the possibilities of NOxand SO₂co-capture during O₂/CO₂recycled coal combustion process. Numerical simulation was carried out to simulate thecombustion process under air and O₂/CO₂atmosphere by using the commercial softwareFLUENT and CHEMKIN. Simulation results were analyzed to discover the mechanismof pollutant formation and decomposition. A lot of facters （such as temperature, O₂concentration, reaction atmosphere, recycling mode） were taken into account to analyzetheir influences on pollutant emission characteristics. The numerical simulation resultsand experimental results agree well, and the pollutant emission index of oxy-fuelcombustion was significantly lower than AIR condition. In addition, the pollutantremoval rate of the improved burner was marked increased.更多还原