【作者】 吕俊复；

【导师】 岳光溪；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2005， 博士

【摘要】 超临界循环流化床锅炉具有超临界蒸汽循环发电效率高以及循环流化床低成本洁净燃烧的综合优势,受到人们的重视。本文提出了26.17MPa、604oC、一次再热800MWe 超临界燃煤循环流化床锅炉基本方案:单炉膛双裤衩腿结构,采用无中间混合的设置节流管圈的一次垂直上升光滑管膜式水冷壁,选用成本相对较低的管壁较厚光滑管,使水冷壁质量流速相对较高,B-MCR 负荷下为1428kg/(m~2-s),可保证各种负荷下的安全性并提高防磨性能。采用6 个高温绝热旋风分离器、冷却式机械分配阀、换热床,以及带循环泵的内置式启动系统,锅炉在40~91%T-MCR 为滑压运行;40%T-MCR 以下为定压运行。NOX 排放浓度不大于200mg/Nm3,石灰石炉内脱硫效率>90%,CO 排放浓度不大于100mg/Nm3。B-MCR 下锅炉效率为93.12%。为研究水冷壁水动力,根据导热式热流计实验测量结果,建立了基于局部物料悬浮浓度的半经验换热模型,并考虑了受热面结构的影响。与测量结果的比较表明该模型具有较高的准确度。构造了固体物料悬浮浓度分布经验型三维模型,根据部分实际测量结果获得了模型参数,其中的循环流率以改进的一维流动物料平衡模型计算。该模型预测结果具有较好的精度。基于有限元传热分析,对截面积分别为3m×6m,5m×10m,7m×14m 等实际循环流化床锅炉上进行水冷壁换热系数分布测量,以检验传热模型,比较表明传热模型预测值与有限元测量结果比较吻合,几乎所有的点均在5%误差范围内。并改进了鼓泡床埋管传热模型用于流化床换热器的传热计算,与实际运行的换热床受热面进行比较,预测结果与实际运行结果的相对误差在7%之内,表明模型的可靠性。建立循环流化床锅炉水冷壁在超临界和亚临界区域的工质流动和传热模型。对不考虑集箱效应、考虑集箱效应以及调整节流管圈三种情况,分别计算了6 个负荷下的水冷壁水动力。设置节流管圈并考虑集箱效应条件下的计算结果表明,角部管子出口的工质温度、内外壁温以及鳍片中心温度最高,60%T-MCR 下温度偏差最大;流量偏差在B-MCR 下最大,炉墙中心管子的工质流量最小;各种负荷下,管外壁和鳍片中心最高温度低于水冷壁的材料SA-213T11 的最大许用温度为100oC以上。更多还原

【Abstract】 Supercritical pressure circulating fluidized bed (SCCFB) is more and more attractive because of its unique combination of higher power generation efficiency with lower cost emission control. The conceptual design of a 26.17MPa, 604℃and once reheat 800MWe SCCFB fired high sulphur coal was suggested, of which the furnace is single with pants leg, and the membrane water wall of once through vertical smooth tube with throttle while without intermediate mixing. The tubes with thickness of 8mm for erosion protection are safe at various load conditions because of the relative higher mass flow rate of 1428kg/(m~2-s) under B-MCR. In the combustion system, there are 6 insulated cyclones, 6 water cooled mechanical distribution valves and 6 external heat exchangers (EHE). An internal start-up system with recalculating pumps was also suggested. It operates with sliding pressure at 40~91%T-MCR, while with fixing pressure at higher than 91%T-MCR or lower than 40%T-MCR. With the limestone particles added, the desulphurization efficiency is higher than 90%. The efficiency of the boiler is 93.12% at B-MCR. And emission of NOX and CO can be kept lower than 200mg/Nm3 and 100mg/Nm~3, respectively. In order to investigate the hydrodynamics in water wall, a semi-empirical local heat transfer (HT) model was developed according to the experimental results from the present measurements of conduct heat probe, where the effect of the membrane structure is considered. The model prediction agrees well with the experimental results from literatures. Then an empirical 3-dimensions solid suspension density (SD) model was established, which is necessary for HT model. The parameters of the SD model are defined from field measurements. However, the circulating material rate in SD model is predicted with an improved 1-demision material balance model. The SD model prediction consists well with the other experimental results. The heat transfer coefficient of bed to wall was measured in the furnace of real CFB boilers with cross section of 3m×6m,5m×10m,7m×14m based on the finite element method to check HT model. The HT model results of which solid suspension density is predicted with SD model agree well with these measured results, with less than 5% error. Besides, a heat transfer model of EHE is also suggested by improving the previous heat transfer model of the immersed tube of bubbling fluidized bed with 7% error compared with the data from a real boiler EHE. A water hydrodynamic (HD) model of water wall panel was proposed in supercritical and subcritical region. With HD model, the hydrodynamics and heat transfer of water wall were predicted in three cases of without (1) or with (2) the consideration of header effect and with throttles (3) in six loads. The model results show that for case 3 the temperature of water at the outlet of the tube near the furnace corner is highest as well as that of the inner or outer tube wall and the fin middle. The highest temperature difference occurs at 60%T-MCR. While the biggest mass flow rate difference occurs at B-MCR with the lowest mass flow rate in the tube near middle of the water wall. The highest temperature of the tube and fin at any load is less than the permitted working temperature over 100 oC for the designed tube material of SA-213T11. The heat flux of SCCFB is more uniform besides much less than that of supercritical pulverized coal boilers. The heat flux decreases with the increase of the distance to the distributor. The horizontal heat flux distribution is related to the horizontal position of tube and boiler load. The heat flux difference at the top of the tube is highest, which is about 20% at B-MCR. And it is found that if the solid suspension density is over 20kg/m3, the impact of it is no longer sensitive on the bed to the wall heat transfer coefficient. The general model combining the suggested models with the common heat transfer models of back pass was built to predict the SPCFB thermal performance of various loads including the material balance. The results show that the main steam and reheat steam temperature can reach the rated value for sliding pressure operating ranging from 40%T-MCR to B-MCR. Finally, the further investigations of SPCFB were suggested, such as the design comparison, material balance, dynamic model of SPCFB, etc.更多还原