亚临界压力下垂直并联管组简化水动力计算研究

STUDY ON SIMPLIFIED HYDRODYNAMIC CALCULATION OF VERTICAL PARALLEL TUBE GROUP UNDER SUBCRITICAL PRESSURE

以某1000 MW超超临界锅炉机组下炉膛水冷壁为研究对象,在现有回路划分法的基础上创新性地引入等效管节距与等效工质质量流量建立了亚临界压力简化水动力计算模型,并对该锅炉垂直并联水冷壁管水动力特性进行计算分析。结果表明:简化水动力计算方法相较于简化前水动力计算,在保证计算结果精度的同时,提高了模型的计算效率;对于垂直并联管组中弱受热回路中,因其重位压降所在比例大于摩擦阻力压降所占比例,因此对应该回路内工质质量流量与所受热负荷值呈正相关;对于强受热回路,考虑其管内工质汽化程度较高,工质平均密度下降,工质质量流速增加,这使得该回路内工质的摩擦阻力压降的增大程度大于重位压降的减小程度,因此对应该回路内工质质量流量与其所受热负荷呈负相关性;对应30%BMCR和50%BMCR负荷下因其各回路内工质质量流量偏差较小,加之内螺纹管的强化换热作用,使得在上述两工况下垂直并联管组各回路沿炉膛高度方向水冷壁管安全稳定运行。

Taking the lower furnace water wall of a 1000MW ultra supercritical boiler unit as the research object,based on the existing circuit division method,the equivalent pipe pitch and equivalent working medium mass flow rate are innovatively introduced to establish a simplified hydrodynamic calculation model for subcritical pressure,and the hydrodynamic characteristics of the vertical parallel water wall tubes of the boiler are calculated and analyzed.The results show that the simplified hydrodynamic calculation method improves the calculation efficiency of the model while ensuring the accuracy of the calculation results compared with the hydrodynamic calculation before simplification;For the weak heating circuit in the vertical parallel tube group,because the proportion of its gravity pressure drop is greater than that of friction resistance pressure drop,the mass flow rate of working medium in the corresponding circuit is positively correlated with the heat load value;For a strong heating circuit,considering the high degree of vaporization of the working medium in the pipe,the decrease of the average density of the working medium and the increase of the mass flow rate of the working medium,the increase of the frictional resistance pressure drop of the working medium in the circuit is greater than the decrease of the pressure drop of the heavy position,therefore,the flow rate of the working medium in the circuit is negatively related to the heat load it is subjected to;Under the corresponding load of 30%BMCR and 50%BMCR,due to the small mass flow deviation of working medium in each loop,and the enhanced heat exchange effect of the internally threaded tubes,the water wall tubes in each loop of the vertical parallel tube group operate safely and stably along the furnace height direction under the above two working conditions.