【作者】 沙龙；

【导师】 吴少华； 刘辉；

【作者基本信息】 哈尔滨工业大学 ， 热能工程， 2014， 博士

【摘要】 超超临界发电技术效率高，环保性能好，是当今世界洁净煤发电的主流技术之一。我国褐煤资源丰富，近年来动力用煤中褐煤的比例不断增加，但国内外都缺乏在1000MW等级锅炉上燃用我国年老褐煤的经验。因此，开发研制燃用我国褐煤的1000MW超超临界锅炉具有重要的现实意义和广阔的市场前景。国家“十一五”863计划立项开展了“1000MW超超临界褐煤锅炉关键技术研究”。1000MW超超临界锅炉广泛采用双切圆的燃烧方式，在炉内形成“冷、热角”，而褐煤灰熔点较低，极易在热角区域发生结渣。另一方面，褐煤锅炉的容积热负荷较低，炉膛尺寸较大，这将增大炉膛出口的烟气热偏差。本文针对这两个问题，采用理论分析、冷态单相流动试验和锅炉热态数值模拟等方法开展研究，并提出解决方案。采用数值模拟的方法对一台双切圆燃烧方式的1000MW超超临界褐煤锅炉炉膛出口热偏差进行研究，分析炉膛上部各种受热面热偏差的成因和特点。屏式辐射受热面的辐射热负荷分布与炉膛横截面尺寸有关，通常呈双峰分布，位于左、右两个半炉膛中心位置的管屏壁面热负荷最高；对于辐射-对流受热面，其中间区域烟气速度的叠加导致了较大的烟气回流区，烟气温度与速度最大值均出现在水平烟道中下部靠近两侧的位置；对流受热面热负荷的分布受流场速度分布影响最大，温度最大值也位于两侧墙附近，但截面温度分布相对均匀。对于这些受热面，烟气速度对截面热负荷分布影响很大，受热面上的热偏差与炉膛出口烟气残余旋转有很大关系。建立单相冷态试验台，运用冷态试验和1000MW超超临界褐煤锅炉热态数值模拟相结合的方法考察锅炉的燃尽风速、燃尽风水平摆角和部分燃尽风竖直摆角等因素对炉内空气动力场、炉内煤粉燃烧、烟气成分分布以及炉膛出口热偏差等方面的影响。研究结果表明，燃尽风比例的增加有利于空气分级燃烧的效果，但同时也会增大炉膛出口的烟气速度峰值，不利于烟气参数分布的均匀性，最佳燃尽风速为60m/s；燃尽风适当的反切摆动可以增强流场的湍动程度，弱化炉内烟气对前墙热角壁面的冲刷，大幅减小流场的旋转动量，有效减小烟气热偏差，最佳反切角度为10°；部分燃尽风喷口竖直向下摆动可以降低炉膛出口各截面上的速度最大值，并改变高速区的位置，但并不能有效减小整个水平烟道内的烟气热偏差，最佳摆动角度为竖直向下摆动10°。对炉内主燃区壁面的结渣趋势进行研究，发现易发生结渣的区域位于各燃烧器射流末端对同侧壁面的冲刷区域，上、下组燃烧器之间区域，上组燃烧器与燃尽风之间区域以及前墙壁面热角区域。后墙壁面热角区域并无明显结渣现象。前墙热角易发生结渣的主要原因是炉内的流场呈斜椭圆形，导致高温煤粉射流冲刷前墙壁面，而通过对炉膛冷角的一次风喷口进行反切，并不能十分有效地减轻煤粉结渣问题。研究结果表明，双切圆锅炉炉内斜椭圆形流场产生的根本原因在于燃烧器的非正方形布置与各燃烧器射流的不同程度偏斜。通过理论分析得到影响燃烧器射流偏斜的经验公式和关键因素，并对射流速度比值、射流冲击位置和射流冲击角度等因素进行试验验证。针对这些影响因素提出了一些工程实践中的优化和改造措施。提出半墙式半角式的燃烧器布置形式，搭建冷态试验台，对炉内的空气动力场进行测量，并与墙式燃烧器布置形式对比。同时通过数值模拟的方法对两种燃烧器布置形式下的炉内燃烧过程和壁面结渣趋势进行对比。对比结果证明，燃烧器采用半墙式半角式布置方式后，基本解决了斜椭圆形流场和前墙热角壁面结渣的问题，但形成的切圆流场偏向炉膛侧墙，且气流对部分壁面的冲刷情况有所加剧，整个流场的旋转动量增大，导致炉膛出口的烟气热偏差增大。通过整体调节燃烧器射流角度，对半墙式半角式燃烧器布置形式锅炉内的切圆流场位置进行优化，得到了更合理的流场分布并更有效的改善了各个炉膛壁面的结渣情况。通过反切燃尽风的方式来改善该燃烧器布置形式下炉膛出口的热偏差现象。由于主气流旋转动量较大，故燃尽风反切角度较大时也未在炉内形成气流反旋现象，燃尽风最佳反切角度为10°。本文研究结果解决了双切圆超超临界褐煤锅炉炉膛出口热偏差和炉内主燃区热角壁面结渣的问题，对该类锅炉工程设计具有重要的指导意义。更多还原

【Abstract】 Today, the ultra-supercritical power generation technology, which shows high power efficiency and good environmental protection performance, has become one of the main technologies in the field of clean coal power generation. In China, the lignite resource is rich, and in recent years, the proportion of lignite in power coal is on the increase, but at home and abroad the experience of1000MW level boiler burning Chinese old lignite is lack. Therefore, there is important practical significance and broad market prospect to exploit and develop the1000MW ultra-supercritical boiler which is suitable for Chinese lignite burning. The Eleventh Five-year Plan863project has carried out " Research on key technologies of1000MW ultra-supercritical lignite boiler ".1000MW ultra-supercritical boilers widely adopt the dual circle tangential firing combustion method, which causes the formation of "cold and hot corners". The melting point of lignite ash is low, so slagging could easily occur in the hot corner area. On the other hand, the volume heat load of lignite boiler is low, and the furnace size is larger, which will increase the gas thermal deviation at furnace outlet. Based on these two problems, this paper carried out research work by the means of theoretical analysis, cold single-phase flow experiments and hot numerical simulation, and then proposed solution methods.The thermal deviation at the furnace outlet of1000MW ultra-supercritical lignite boiler which adopts the dual circle tangential firing combustion method has been studied by method of numerical simulation. The causes and characteristics of the thermal deviation on all sorts of heating surfaces in the upper furnace have been investigated. The radiative heat load distribution of the platen heating surface is related with the cross section dimensions of the furnace, it shows bimodal distribution for the object of the study, and the heat loads of the panels at the central positions of the two furnace halves are highest; for the radiative-convective heating surfaces, due to the superposition of the gas velocity in the middle region, large area of gas recirculation region is formed here, and the maximums of gas temperature and velocity both appear in the locations which are in the middle-down of horizontal flue, close to the two sides; Heat load distribution on the convective heating surfaces is affected by the velocity distribution of the airflow field to the largest extent, the maximum temperatures also appear near the two side walls, but the cross section temperature distribution is more uniform. For these heating surfaces, the gas velocity has great influence on the heat load distribution, and the thermal deviations on the heating surfaces are relational with the gas residual rotation at the furnace outlet.A cold single-phase scale model of the boiler has been established. Cold experiments and hot numerical simulation on the1000MW ultra-supercritical lignite boiler were combined to study the over fire air parameters. Influence of over fire air velocity, over fire air horizontal swing angles and part over fire air vertical swing angles on the aerodynamic field in furnace, the pulverized coal combustion, the gas components distribution and the thermal deviation at the furnace outlet has been investigated. The results show that the larger over fire air proportion is beneficial to the effect of the air staged combustion, but at the same time, it can also increase the gas velocity peak at the furnace outlet, which is not conducive to the uniformity of gas parameters distribution. The best over fire air velocity is60m/s. Proper horizontal swing angles of over fire air could enhance the turbulence degree of the airflow field, weaken the scouring of airflow on the front wall, substantially reduce the rotating momentum of the airflow field, and effectively decrease the gas thermal deviation. The optimal over fire air horizontal swing angle is-10°. Part over fire air vertically swing downward could reduce the velocity maximum on each section of furnace outlet, and change the location of high velocity area. But it could not effectively reduce the thermal deviation in the whole horizontal flue. The best vertical swing angle is-10°.Slagging tendency on the water wall in the primary zone has been studied. The areas where slagging occurs easily are the area which is scoured by the jet on the same side, the area between the upper and the lower groups of burners, the area between the upper group of burners and the over fire air, and the hot corner area on the front wall. While the hot corner area on the rear wall shows no obvious slagging phenomenon. The main reason that slagging occurs easily in the hot corner area on the front wall is the airflow field in furnace shows oblique ellipse, which results in the scouring on the front wall by high temperature jets. While, by the horizontal swing of the primary air nozzles on cold corner could not effectively reduce the slagging problem.Research results show that the basic reason of the formation of the oblique elliptic airflow field in the dual circle tangential firing boiler is the rectangular arrangement of the burners and the different deviation degrees of the jets. By theoretical analysis, the empirical formula and the key factors that have effects on the jet deflection have been obtained. Experimental verification of the effect of the velocity ratio, the impacting position and the impacting angle on the jet deviation has been carried out. According to these factors, some optimization and modification measures in engineering practice have been put forward.The half-wall-half-corner burner arrangement form has been brought forward, and a cold model was built to measure the aerodynamic field in furnace, then the experimental results were compared with wall type burner layout form. At the same time, by the method of numerical simulation, the combustion process in furnace and the slagging tendency on the water wall in the two sorts of boilers were compared. Comparison results show that by using the half-wall-half-corner burner arrangement form, the problems of the oblique elliptic airflow field and the slagging on the hot corner of front wall have been basically solved. But the airflow field centers in this sort of boiler incline to the side walls, and the scouring to part of the water walls by the jets has been intensified, the rotating momentum of the whole airflow field increases, which leads to the increace of the thermal deviation at the furnace outlet.By wholly adjusting the jet angles, the airflow field location in the furnace of half-wall-half-corner burner arrangement type boiler has been optimized. More reasonable airflow field distribution has been obtained, and the slagging on each furnace wall has been reduced more effectively. By changing the over fire air horizontal swing angles, the thermal deviation at the furnace outlet in this sort of boiler has been decreased. Because of the large rotating momentum of the main airflow, the anti-cyclonic phenomenon was not formed in the furnace even though the over fire air horizontal reverse swing angle is big. The optimal over fire air horizontal swing angle is-10°.The study in this paper has solved the problems of the thermal deviation at the furnace outlet and the slagging on the hot corner in primary combustion zone in the1000MW dual circle tangential firing ultra-supercritical lignite boiler. The results have important guiding significance to the engineering design of this sort of boiler.更多还原