燃煤电厂亚临界压力下垂直并联管组流量分配特性

Flow distribution characteristics of vertical parallel pipe groups under subcritical pressure in coal-fired power plants

为研究亚临界压力下垂直并联管组内工质质量流量分配特性及其压降分布等情况,建立了亚临界压力垂直并联管组流量分配及压降计算数学模型,对某1000 MW超临界锅炉机组在亚临界直流工况下的并联管组进行相关水动力计算,计算分析了不同长度下垂直光管和垂直内螺纹管并联管组中工质质量流量分配特性及压降变化。结果表明:在水冷壁管结构及初始工质参数相同的条件下,不同长度并联管组中各水冷壁管第1相变点所在位置高度相同;并联管组出口工质皆为汽水混合物,出口工质温度相同,不同管长出口工质温度随管长的增加略降低;不同长度垂直光管并联管组中具有良好的自补偿特性,管组中工质质量流量与所受热负荷呈正流量补偿特性;不同长度垂直内螺纹并联管组内工质质量分布不同,随管长增加,并联管组保持良好的正流量补偿特性,管长增加到一定程度后,并联管组中的正流量补偿特性逐渐减弱直至消失,进而转化为负流量补偿特性。

In order to study the mass flow distribution characteristics and pressure drop distribution of working medium in the vertical parallel tube group under subcritical pressure,a mathematical model for flow distribution and pressure drop calculation of the vertical parallel tube group under subcritical pressure was established.For a 1000 MW supercritical boiler unit,the parallel tube group under subcritical once through working condition was subjected to relevant hydrodynamic calculation,the mass flow distribution characteristics and pressure drop of the working medium in the parallel tube group of vertical smooth tube and vertical internally threaded tube with different lengths were calculated and analyzed.The results show that under the same structure and initial working fluid parameters of the water wall tubes,the position and height of the first phase change point of each water wall tube in different length parallel tube groups are the same.The outlet working medium of the parallel tube group is steam water mixture,and the outlet working medium temperature is the same.The outlet working medium temperature of different tube lengths decreases slightly with the increase of tube length.The parallel tubes with different lengths of vertical smooth tubes have good self compensation characteristics,and the mass flow of working medium in the tube group has a positive flow compensation characteristic with the heating load.The mass distribution of working fluid in the parallel tube groups with different lengths of vertical internal thread is different.With the increase of tube length,the parallel tube groups maintain good positive flow compensation characteristics.When the tube length increases to a certain extent,the positive flow compensation characteristics in the parallel tube groups gradually weaken until they disappear,and then turn into negative flow compensation characteristics.