【作者】 张晓辉；

【导师】 孙绍增；

【作者基本信息】 哈尔滨工业大学 ， 热能工程， 2008， 博士

【摘要】 结合我国目前经济发展及能源利用状况,开发出具有低成本、高效、安全的燃烧法脱除NO_x排放技术已成为控制污染物排放的一个重要目标。本文以此为出发点,对电站锅炉燃煤过程中的NO析出影响因素展开机理研究,并通过在不同负荷机组上进行工业验证,开发出立体分级低NO_x燃烧系统。首先对我国某高挥发分烟煤展开热重—红外光谱仪联用（TG-FTIR）机理试验研究,采用Coasts-Redfern积分法对热解动力学参数进行求解,发现当n=1时其相关系数最佳,建立了升温速率为20、40和80K/min时的热解动力学模型,动力学模型模拟结果与试验结果吻合较好;同时,深入研究了热解条件对挥发分析出产物及含量的影响,确定了在不同升温速率下的CH₄、CO等主要析出产物及含氮化合物（NH3）占原煤的质量份额。随后,把热重试验结果,与FG-DVC模型的计算结果进行对比,二者吻合较好,说明该热解模型可以用于描述我国烟煤的热解过程及产物。对真实燃烧条件下的挥发分组分及含量进行计算,采用GRI3.0反应机理的PFR反应器模型,对不同化学当量比下的燃料N生成NO的转化率“CR”进行计算。发现随着化学当量比的增加,NO转化率逐渐降低。得出在燃烧法脱除NO_x所采用的高化学当量比燃烧条件下,NO_x完全转化达到稳定需要较长时间,约为0.2s左右,并据此确定了对于高挥发分烟煤,为了达到降低NO_x排放的目的,由主燃烧区至燃尽区的停留时间不能少于0.32s的结论。从而确立了面向电站锅炉的立体分级燃烧系统方案。分别对中储仓式和直吹式制粉系统锅炉机组开展工业试验研究,在保证机组稳定运行基础上,NO_x排放浓度取得大幅度降低,其中50MW中储仓式制粉系统锅炉机组可将NO_x排放量控制在450mg/m3以下;对200MW直吹式制粉系统锅炉机组进行改造后,可将NO_x排放量有效控制在350mg/m3以下,最低可降至250mg/m3左右,取得了巨大的经济及社会效益,从而在不同容量机组上验证了前期机理研究方案的可靠性。最后,采用验证后的模型和计算方法对不同容量机组上的燃烧及NO_x排放进行模拟,采用结合FG-DVC热解模型的FLUENT后处理平台,对NO_x排放水平进行模拟计算,结果与试验值吻合较好,验证了模型的稳定性和可靠性。为低NO_x燃烧技术改造结果的预报奠定了模拟研究基础。本研究工作对推广及应用立体分级低NO_x燃烧技术,降低电站锅炉NO_x排放,提高燃烧效率,降低能耗提供理论依据及技术参考。更多还原

【Abstract】 It is a primary goal of China, on the basis of its situation, to develop low-NO_x combustion technologies of low cost, high efficiency and good safety. To reach this goal, this dissertation investigated factors that affect NO_x control in utility boiler units and developed stereo-staged low-NO_x combustion technology for pulverised coal. which was validated via retrofit in a number of boilers.Firstly, experimental study was made on pyrolysis of bituminous coal with TG-FTIR. Coasts-Redfern quadrature is used to get the kinetic parameters of coal pyrolysis and it is found that the results are best correlated when reaction order equals to 1. Kinetic model for coal pyrolysis at the heating rates of 20, 40 and 80K/min respectively were proposed, and the modelling results agree well with experimental results. Effects of pyrolysis conditions on volatile components and their yields were studied, and mass fraction of the primary pyrolysis products （CH4, and CO et al） and N-component （NH₃） at different heating rates were determined.Secondly, it was confirmed that the FG-DVC model can be used to describe pyrolysis course of bituminous coal from China, since TG-FTIR data agree with FG-DVC modeling results well. The model was used to simulate the volatile components and yields. These data were used to GRI 3.0 chemical reaction mechanism combined with PFR reaction model to calculate transformation proportion （CR）, which refers to Fuel-N converted into NO, at different equivalence ratios （ER）. CR decreases with the increase of ER. The reaction time for stable Fuel-N conversion is about 0.2s by comparison with the experimental results. It is concluded that the suitable residence time for the fuel from primary combustion zone to the over-fire air zone should be 0.32 s at least. The parameters for the stereo-staged combustion technology can be established from this conclusion.Thirdly, the industry experimental investigations were carried out on 50 MW and 200 MW units, NO_x emission was decreased remarkably. In the 50MW units, it is no more than 450 mg/m³ by adopting stereo-staged combustion technology, and the result is 350 mg/m³ in the 200 MW units, with the minimum NO_x emission being 250 mg/m³, and enormous economic and social benifit are attained. The reliability of former mechanism is therefore validated in different utility boilers. At last, combustion and NO_x emission were simulated by using the models and computation method validated as above. It is shown that when NO emission was simulated on the FLUENT platform with pyrolysis data from FG-DVC model, NO_x emission agrees better with experimental results than using the pyrolysis data from FLUENT.This work provides theoretical and technical foundation for reducing NO_x emission from utility boiler, while improving combustion efficiency and saving energy consumption.更多还原