煤粉锅炉燃烬风配风率和相对高度对炉膛出口烟温影响

发布时间：2018-04-26 04:39

本文选题：分级燃烧 + 数值模拟　；参考：《上海发电设备成套设计研究院》2017年硕士论文

【摘要】：我国是世界燃煤大国,而其中电厂发电占了约60%的煤炭使用比例。由燃煤带来的环境问题日益突出,在其排放的各种污染物中,氮氧化物(NOx)对环境的影响最为明显,因此控制NOx排放量为电厂清洁排放的首要指标。目前广泛采用的是在原一次风、二次风基础上增设燃烬风来降低NOx排放。燃烬风的配风率和相对高度对于炉膛出口烟温有着重要的影响,而炉膛出口烟温的变化关系到锅炉整体性能的计算和运行的经济性,是锅炉能否实现设计性能的一个重要参数,对锅炉安全经济运行具有直接的影响。过去采用的炉膛出口温度计算方法只考虑了一次风的变化而忽略了二次风的配风比,由于采用空气分级燃烧以后二次风需抽调一部分比例的风量来在炉膛主燃区上方形成补燃区域,因此改变二次风的配风比以及结构以后对炉膛出口的温度有着明显的影响。随着CFD技术的发展,对于炉膛出口温度的计算方法修正可以不再局限于实验法,可节约大量的时间和人力成本。本文以实际改造案例为基础,对超临界锅炉燃烬风配风率和相对高度的变化进行数值模拟,研究这些因素对炉膛出口烟温的影响,初步分析并总结燃烬风配风率和相对高度对炉膛出口烟温的变化规律,探讨相应的计算方法。希望能为锅炉的设计或改造提供有益的参考。研究借助FLUENT对珠海电厂一期600MW超临界锅炉进行模拟,以锅炉BMCR工况数据为基础,选取不同燃烬风率和相对高度位置对整个炉膛进行燃烧模拟,并与实际工程改造数据相比对,期望找出燃烬风率和相对高度变化对炉膛出口烟温影响的回归分析表达式,即燃烧条件影响系数的计算方法。燃烬风相对高度对炉膛出口温度的影响主要体现在分离燃烬风层和主燃区上层燃烧器之间的间隔,本文提出了表征该影响因素的新的当量比,与燃烬风率共同构成了新的燃烧条件影响系数算法。该算法表明:燃烬风相对高度对炉膛出口温度变化有一个正负斜率区间,当燃烬风相对高度低于一定值时,炉膛出口温度与燃烬风率为负斜率线性关系,当燃烬风相对高度高于一定值时,炉膛出口温度与燃烬风率为正斜率线性关系。改进后的燃烧条件影响系数总体为原燃烧条件影响系数的0.9倍左右,即加设燃烬风后炉膛燃烧火焰中心会有所抬高,并且炉膛出口温度会随燃烬风率和相对高度的变化而变化。实际工程初步验证,结果表明该计算方法具有一定可信度。
[Abstract]:China is a big coal-burning country in the world, and about 60% of the coal is used by power plants. The environmental problems caused by coal combustion are becoming more and more prominent. Among the pollutants emitted, no _ x (no _ x) has the most obvious impact on the environment. Therefore, controlling the NOx emission is the primary index of clean emission in power plants. At present, it is widely used to reduce NOx emissions by adding cinder wind on the basis of primary and secondary air. The air distribution rate and relative height of the burning cinder have an important influence on the flue gas temperature at the outlet of the furnace, and the change of the flue gas temperature at the outlet of the furnace is related to the calculation of the overall performance of the boiler and the economy of its operation, and is an important parameter of whether the boiler can realize the design performance. It has direct influence on the safe and economical operation of boiler. In the past, the furnace outlet temperature calculation method only considered the change of primary air and neglected the ratio of secondary air to air distribution. Since it is necessary to adjust a part of the air volume of the secondary air after the air staged combustion to form a supplementary combustion area above the main combustion zone of the furnace, the change of the air distribution ratio of the secondary air and the structure of the secondary air have an obvious influence on the temperature of the furnace outlet. With the development of CFD technology, the calculation method of furnace outlet temperature can not be limited to the experimental method, and can save a lot of time and labor costs. In this paper, based on the actual reconstruction cases, the variation of the air distribution rate and the relative height of the burning cinder of supercritical boiler is simulated, and the influence of these factors on the flue gas temperature at the outlet of the furnace is studied. The variation law of air distribution ratio and relative height of burning cinder on flue gas temperature at furnace outlet is analyzed and summarized preliminarily, and the corresponding calculation method is discussed. It is hoped that it can provide useful reference for boiler design or renovation. In this paper, the 600MW supercritical boiler of Zhuhai Power Plant is simulated by FLUENT. Based on the boiler BMCR working condition data, the combustion simulation of the whole furnace is carried out at different burning cinder rates and relative height, and compared with the actual engineering reconstruction data. It is expected to find out the regression expression of the influence of the burning cinder rate and the relative height on the flue gas temperature at the outlet of the furnace, that is, the calculation method of the influence coefficient of the combustion condition. The influence of the relative height of cinder air on the outlet temperature of furnace is mainly reflected in the interval between the upper burner of separating the cinder layer and the upper layer of the main combustion zone. In this paper, a new equivalent ratio characterizing the influence factor is proposed. Together with the cinder rate, a new algorithm for calculating the influence coefficient of combustion conditions is proposed. The algorithm shows that there is a positive and negative slope range between the relative height of burning cinder and the temperature of furnace outlet. When the relative height of burning cinder is lower than a certain value, the linear relationship between furnace outlet temperature and cinder rate is linear. When the relative height of burning embers is higher than a certain value, the linear relationship between furnace outlet temperature and cinder rate is linear. The influence coefficient of the improved combustion condition is about 0.9 times of that of the original combustion condition, that is, the combustion flame center of the furnace will be raised with the addition of cinder air, and the furnace outlet temperature will change with the change of the cinder rate and the relative height. The experimental results show that the method is reliable.
【学位授予单位】：上海发电设备成套设计研究院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM621.2

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