【作者】 郭永红；

【导师】 孙保民；

【作者基本信息】 华北电力大学（北京） ， 热能工程， 2006， 博士

【摘要】 燃煤电厂煤炭直接燃烧产生的NO_x不仅危害环境,也直接威胁着人类的健康,因此控制电站锅炉NO_x排放的技术应运而生,燃料再燃是其中比较有效的方法之一,针对可能需要增加第二种燃料及燃尽率差的缺点,提出了以超细化煤粉作为再燃燃料,本论文在863项目“超细化煤粉再燃低NO_x燃烧技术研究”的资助下对超细粉再燃进行了数值模拟和试验研究。论文以超细粉再燃低NO_x燃烧技术的三段燃烧综合体为研究对象,在中试试验的基础上对中试试验CRF炉、600MW示范机组四角切圆锅炉和330MW旋流燃烧器墙式锅炉进行超细粉再燃的数值模拟研究。首先对CRF炉进行常规燃烧与超细粉再燃NO_x生成的数值模拟与中试试验,试验结果超细粉再燃的NO_x脱除率为52.3~65.4%,数值模拟NO_x脱除率为58.20~75.06%。超细粉再燃与常规燃烧相比NO_x脱除率与再燃区NO_x还原率不成正比,它是由NO_x还原率与燃尽区NO_x新的生成综合决定的。其次600MW机组四角切圆燃煤锅炉的数值模拟所得NO_x脱除率为42.36~62.8%。对于大容量四角切圆锅炉的数值模拟,本文给出了一个可以有效减小伪扩散、流体流动方向与网格线方向一致、数目较少、计算精度较高的结构网格,该网格的数值计算结果清晰得捕捉到了四个角向火侧和背火侧靠近壁面处的小回流,而且计算温度与炉膛温度实测值较好的吻合。对NO_x的数值模拟,计算简单、耗时较少的耦合求解及软件自带常规模型的后处理求解均可以满足工程定性分析,但定量分析结果不理想,因此本文通过所用软件的用户自定义接口接入了一个NO_x的改进模型,该模型对NO_x的生成和还原在不同的氛围内采用不同的反应速率,且充分考虑了燃料再燃对NO_x的中间产物HCN的影响,因此计算结果比原软件自带常规模型更清晰的反映出NO_x生成和还原的变化,更适用于超细粉再燃技术。最后330MW机组旋流燃烧器墙式锅炉的数值模拟NO_x脱除率为50.57%。针对该锅炉可燃物损失大的问题,通过热解实验分析原因,提出改造方案,对原旋流燃烧器及改造方案的气固两相流进行了实验和数值模拟的验证,结果表明改造方案可以有效解决存在的问题,而且不会造成NO_x排放的增加。上述试验与数值模拟结果均表明,超细粉再燃较小的出口烟气温升对炉膛出口后受热面安全方面的影响较小,超细粉再燃对煤粉燃尽程度的影响较小。从超细粉再燃NO_x脱除率和其对锅炉安全及燃烧效率方面的影响来看,其工业应用是切实可行的。更多还原

【Abstract】 Pollutant NO_x emission by coal combustion in power plant is an increasing threatto environment and human health. Low-NO_x strategies have emerged as the timesrequire, and one of them is fuel reburning technique. For second fuel maybe beneeded and combustible efficiency maybe be minished, micronized coal is broughtforward as reburning fuel. In this paper, experiments and numerical simulations ofmicronized coal reburning technique have being studied supported by 863 project ofStudy on Low-NO_x Technique by Micronized Coal Reburning.In the paper three combustion zones of micronized coal reburning as a whole isresearch object. Based on laboratory-scale experimentation, numerical simulations ofmicronized coal reburning have been studied on bench-scale combustion researchfacility、full-scale 600MWe coal fired tangential utility boiler and full-scale330MWe swirling burner wall utility boiler.First NO_x of experiment and numerical simulation about general combustion andmicronized coal reburning in combustion research facility has been processed. NO_xdecreasing ratios are 52.3~65.4% in experiments and 58.20~75.06% in numericalsimulations. NO_x decreasing ratio of micronized coal reburning comparing withgeneral combustion is not proportionable to NO_x reduction ratio in reduction zone,which depends on both NO_x reduction ratio and NO_x increment in burnout zone.Numerical simulation of full-scale 600MWe coal fired tangential utilityboiler showed NO_x decreasing ratios are 42.36~62.8%. A structured grid partitionfor full scale coal fired tangential utility boiler has been given in this paper. It hasa small amount of grids and can decrease false diffusion effectively as it is inagreement with fluid flow direction. Accurate simulating results can be gainedwith the grid partition. Inverse flows are captured near the wall at four corners incombustion simulating through the above grid and temperatures simulating agreewell with them measured.NO_x numerical Simulation by coupled with combustion and post processinggeneral model provided by FLUENT can be satisfied by qualitative analysis, butcan’t meet quantitative requirement. So an improved NO_x model was connectedto software by user defined function. The model has the different NO_x formationand reduction rates in oxidizing and reducing atmosphere, and the effect ofreburning fuel on intermedia HCN of NO has been considered. Simulating resultsgiven by improved NO_x model reflect NO_x formation and reduction moredistinctly than by the former NO_x model. It is more applicable to micronized coalreburning technique.At last numerical simulation of full-scale 330MWe swirling burner wallutility boiler showed NO_x decreasing ratio is 50.57%. The combustible loss isbiggish in this boiler. Modifying cases have been suggested after analysis ofpyrolysis experiments. Experimental and numerical simulating data of gas-solidflow all predict the modifying cases can solve the existing problem effectivelyand NO_x emission can’t be increased.Above experiments and numerical studies argued that temperature rising at outcaused by micronized coal reburning technique has a little effect on heating surfacesafter furnace, and micronized coal ruburning has nearly same combustion efficiencyas general combustion. NO_x decreasing ratio and effects on boiler safety andcombustible efficiency all showed micronized coal reburning technique is practicable.更多还原