【作者】 刘茂省；

【导师】 周俊虎； 岑可法； 刘建忠；

【作者基本信息】 浙江大学 ， 工程热物理， 2009， 博士

【摘要】 随着我国工业化进程的不断推进,大气污染问题已经成为摆在我们面前的严峻挑战之一。近几年随着SO2排放逐渐得到控制,氮氧化物排放逐渐成为主要的大气污染物。我国能源以煤炭为主,煤燃烧排放的氮氧化物成为氮氧化物主要来源之一,控制煤燃烧过程中氮氧化物生成意义重大。本文以探索煤燃烧过程中NOx生成控制最佳途径为研究目标,按照“固定床机理试验—>沉降炉模拟试验—>应用研究—>计算模型”的思路研究了煤粉燃烧过程中NOx的生成与控制规律。固定床试验主要研究煤粉燃烧和煤粉还原NOx过程机理,试验同时测量了燃烧过程中NO、HCN、NH3等的生成量,提出了通过对比燃料N向NO、HCN、NH3转化率与向N2转化率来综合评价燃烧过程中NOx控制效果的方法。本文试验条件下,氧浓度在1%～2%时,挥发份燃烧阶段NOx控制效果最佳,而且此气氛下挥发份还原烟气中NOx效果最佳；焦炭燃烧阶段NOx的生成和抑制受多种因素影响,其中氧浓度的影响最为明显,氧浓度的升高不利于焦炭燃烧过程中NOx的控制。在沉降炉上模拟了空气分级燃烧和煤粉再燃过程。在煤粉燃烧初期,富氧和欠氧条件下的燃烧过程相似,都有大量NO生成,燃烧后期NO会得到部分还原,欠氧条件下的NO还原率要高于富氧条件；采用空气分级燃烧技术控制NOx生成时,一次燃烧区域空气系数应取0.8左右,过低的空气系数会大大增大飞灰含碳量；综合考虑经济性和NOx排放控制,建议煤粉再燃技术再燃区空气系数取0.8～0.85。在大型电站锅炉上实施了空气分级燃烧和煤粉再燃,对比了技术改造前后锅炉的炉膛温度、蒸汽参数、NOx排放浓度、锅炉效率等,分析了运行方式对低NOx燃烧技术的影响规律。大型电站锅炉示范试验NOx脱除率超过50%。最后,建立了大型锅炉低NOx燃烧计算模型,模型包括煤粉热解和燃烧、炉膛传热计算、NOx生成与还原等计算模块。模型计算结果与大型电站锅炉试验结果吻合；采用模型计算优化了三次风、再燃风、燃尽风布置方式,计算结果对低NOx燃烧技术工程设计具有重大指导意义。更多还原

【Abstract】 With the industry development, the air pollution is becoming a austere challenge for people. In resent years, the emission of SO2 has been controlled gradually, and the nitrogen oxygen (NOx) emission becomes the main air pollution. In our country, coal is the primary energy, and the NOx emission during coal combustion is the main source of NOx. Its reduction is very significative.Aiming at exploring the best way to control the NOx emission during coal combustion, the NOx producing and reducing law during coal combustion is researched in this thesis. The experiment is carried out in a fixed-bed reactor firstly, then a drop tube reactor, and on the big boilers finally. An computing model is also made basing on the experiment result.In the fixed-bed reactor, the mechanism on NOx during the coal combusting and reburning is studied. The field quantity of NO, HCN and NH3 is measured and the conversion rate of the fuel-N to NO, HCN, NH3 and N2 is computed, which can represent the NOx reduction efficiency during coal combustion more exactly. At the experiment condition in this thesis, 1%-2% is the best concentration of oxygen at which the NOx emission is controlled best during the volatile combustion and NOx is reduced most by volatile during the volatile reburning. When the char combusting, the NOx emission and reduction is affected by many factors, in which the oxygen concentration effect is the most obvious. The higher the oxygen concentration, the more NOx emitted during char combustion.The air-staged combustion and reburning process is simulated in the drop tube reactor. In the initial stage of pulverized coal combustion, lots of NO is fielded at both air-rich atmosphere and fuel-rich atmosphere. The NO fielded will be reduced partially in the subsequent time. The reduction rate is higher at fuel-rich atmosphere than that at air-rich atmosphere. The optimal air coefficient in the first combustion zone is about 0.8 for air-staged combustion. Lower air coefficient will make the carbon content in fly ash increase quickly. Considering both the NOx controlling and the economic benefits, the optimal air coefficient in reburn zone is in the range of 0.8-0.85 for pulverized coal reburning. Both the air-staged combustion technology and the conventional pulverized coal reburning technology are utilized on large-scale plant boliers. The furnace temperature, the steam parameter, the NOx emission concentration and the boiler efficiency before and after the technical reformation is compared. The effect of the operation mode on the NOx control is also analyzed. The NOx reduction efficiency of the pulverized coal reburning technology exceeds 50% in the demonstration engineering.Finaly, a computing model is made up. It contains the pyrogenation and combustion model, the furnace temperature computing model and the NOx production and reduction model. The computing result of the model is consistent with the experiment. Using the engineering computing model, the nozzle position of the tertiary air, the reburn air and the burnout air is optimized. And the result can be used to direct the engineering design of the low NOx combustion technology.更多还原