【作者】 江爱林；

【导师】 赵在理；

【作者基本信息】 武汉理工大学 ， 轮机工程， 2005， 硕士

【摘要】 随着电网容量增大和用电结构的变化,电网峰谷差日益增加,一大批高参数、大容量的火力发电机组不得不参加变负荷甚至启停调峰运行。参与调峰的机组里面特别是高参数、大容量的锅炉汽包直径和壁厚都比较大,在机组启停和变负荷过程中,尤其是机组事故情况下,较快的升压、降压速度和温度变化会使汽包材料所承受的机械应力和热应力发生很大的变化,而频繁交变的机械应力和热应力将使金属材料产生的疲劳损伤增大,缩短锅炉汽包的使用寿命。为此,人们高度重视并积极开展了锅炉汽包的相关研究工作。其中,计算锅炉汽包的瞬态温度场和瞬态应力场分布,以及在此基础上进行汽包裂纹的扩展计算与预测,对于确保汽包的安全运行具有直接的指导意义。 本文以株洲电厂300MW锅炉汽包作为研究对象,在获得试验数据的基础上,对该汽包的瞬态温度场、瞬态应力场、强度计算和裂纹扩展预测等方面开展了多学科的交叉研究。文章主要从以下几个方面进行了探讨。 首先,本文建立了含下降管和封头的锅炉汽包的整体计算模型,并计算了汽包吊带和自重对汽包应力的影响。通过对计算结果进行对比分析以后确定了汽包的计算模型,然后利用采集的数据作为计算的边界条件,采用三维有限元理论,运用国际通用大型温度场、结构分析软件ANSYS,计算了该模型下汽包的瞬态温度场、热应力、机械应力、总应力（热和机械的耦合应力）。 其次,通过对计算结果的分析,找出了汽包应力最大值的位置,求出了危险点机械应力和总应力与蒸汽压力的比例关系,并对各工况的应力进行了综合比较。 论文最后运用ANSYS计算的σ_eqv并结合断裂力学的半椭圆形表面裂纹公式和COD法计算了危险区域不同长度裂纹的断裂强度因子随时间的变化,并根据材料的断裂韧性确定了裂纹的临界尺寸。 本文创新点为:以现场试验数据和事故情况采集的数据作为汽包应力、裂纹计算的基础,特别是对汽包温度进行了准确测量,把汽包水位的变化也加以一并考虑,避免了以往因数学模型的边界条件失真而带来的计算结果的欠准确性:首次采用节点耦合模型计算了吊带对锅炉汽包机械应力和热应力的影响;汁算了汽包运行时的温度场、应力场以及它们的变化规律;计算了汽包最危险更多还原

【Abstract】 Along with the increase of electric power plant capacity and the change of power consumption, the peak-valley difference of electrical network increases day by day, a lot of thermoelectricity generator units with high running parameters and large capacity have to take part in changing the loads and even to startup-halt for adjusting the peak output. The diameter and wall thickness of the boiler drum is relative big. During the process of starting or stopping and altering loads, especially under the accident, the pressure rising or dropping and temperature varying will make mechanical and thermal stress of the drum greatly change. The varying of the stress will result in fatigue damage to drum material and shorten the service life of the drum. For this reason, people had paid great attention to this and a lot of research work about drum was carried out. Among these work, the distribution of transient temperature field and stress field, the calculation and prediction of crack propagating are significant to ensure boiler in good condition and safety running.The thesis takes 300MW boiler drum of Zhuzhou Power Plant as object. Based on test data, the multi-disciplinary research across transient temperature field, transient stress field, predicting crack propagating etc was carried out. The thesis mainly carried on the discussion in the followed respects.Firstly, author built a calculating model with drop pipe, end cover of the drum, and calculated the effect by hanging strip and gravity of the drum to the stress field. The model was completed after comparing and analyzing the result of calculation. Then utilized the test data as border condition of the model. The three-dimensional finite element unit was adopted; ANSYS software were used and the transient temperature field, thermal stress, mechanical stress, total stress of the drum were calculated to the model.Secondly, the position of maximum stress of the drum was found out through the analysis of calculating result, some proportionate regulation between mechanical stresses or total stresses and steam pressure also found out. The results were compared synthetically to the different operating mode.Finally, the change of crack strength factors to cracks which have differentlength size in dangerous area was calculate and compared with that it was calculated by use of half oval surface crack formula. The COD method was applied and the critical size of crack was defined according to the fracture toughness of the material by Von misses stress calculated.The innovation in this thesis are as follows:1. The running parameters and test data of the drum during typical and accident operation was used as boundary condition for stress calculating and crack analyzing. Especially accurate measurement to the temperature of drum and considered the change of the water level in the drum were carried on, which have avoided the error owing of the distortion of border condition.2. Adopted the nodal coupling model to calculate the machinery stress and thermal stress of the drum to make sure the effect by the hanging strip for the first time.3. Calculated transient temperature and stress field and varying regularity underchanges load varying and other disturbance.4. Found out the position of maximal total stress and dangerous point in the drum. Calculated the critical size of crack and the yearly crack-propagating value at the point. This is important for periodicity checking and the treatment to cracks appeared in the drum.更多还原