【作者】 何大林；

【导师】 童明伟；

【作者基本信息】 重庆大学 ， 动力工程及工程热物理， 2008， 硕士

【摘要】 本文分析了热力发电厂低压加热器的工作过程后,建立了热力发电厂蒸汽动力循环低压加热系统试验台,对一具体的引射混合式低压加热器进行了引射性能和加热性能的试验研究,并详细研究了中心喷射圆周引射型射水抽汽式引射混合式低压加热器的加热特性,按雷诺数的范围拟合出两种形式的加热器凝结换热过程的Nu准则式Nu=CRe~m Pr~nφ~k mL和Nu=CRe~m Pr~nφ~k。鉴于引射器性能的特殊性和影响因素众多,在引射混合式低压加热器设计过程中根据其内部流道变化规律,主要采用质量守恒原理和伯努利方程进行设计计算。通过对两种结构型式的引射混合式低压加热器进行试验,发现在热力发电厂低压加热系统中采用引射混合式低压加热器加热凝结水,通过选取适当的运行参数,完全可以消除凝结水沿抽汽管道进入蒸汽轮机的危险和将凝结水加热至除氧器运行要求。从该型加热器的试验结果可以得出,φ5mm直径喷嘴的该型加热器在入口水压大于0.25MPa时,即可在加热器的蒸汽吸入室产生0.04MPa的真空,φ3mm和φ4mm直径喷嘴在入口水压大于0.2MPa时即能产生大于0.08MPa的真空,远小于现有火电机组大于0.1MPa的低压抽汽压力;φ2mm和φ3mm直径喷嘴的加热器在入口水压小于0.25MPa范围内,将凝结水加热至大于105℃。引射混合式低压加热器具有较独特的蒸汽凝结性能和加热性能,简单分析了凝结水射流与蒸汽凝结换热的特性,指出在射流表面存在着蒸汽凝结换热的主要热阻——流动凝结液膜,在凝结水射流表面上蒸汽的凝结换热系数高达0.98～5.23MW/(m~2·K)。本文从引射器角度简单推导了对引射混合式低压加热器的结构和设计有较重要指导意义的引射特性基本方程式,定义了引射混合式低压加热器的引射效率ηe和加热效率η_h。通过实验数据的分析计算得出,φ2mm喷嘴的η_h=98.6%、η_e=19.8%,φ3mm喷嘴的η_h=95.6%、η_e=19.6%,φ4mm喷嘴的η_h=91.6%、η_e=13.5%,φ5mm喷嘴的η_h=90.3%、η_e=7.8%。引射混合式低压加热器性能试验研究结果表明:在热力发电厂中引射混合式低压加热器完全可以取代目前使用的表面式低压加热器。本文还对永荣矿务局6MW发电机组的低压加热器改造进行了可行性分析。更多还原

【Abstract】 After work process analysis about the Low-Pressure heater of the thermal power plant,a test-bed of low-pressure heating system in steam power cycle of the thermal power plant was established, an experimental investigation has been made on the ejecting and heating performance of a specific ejecting-mixing low-pressure heater, especially the heating performance of central jetting and circumferential ejecting water driven vapor ejecting-mixing low-pressure heater in detail, and Nu number formula of condensation heat transfer are fitted in two forms in the ranges of Reynolds number, i.e. Nu = CRe~m Pr~nφ~k m~L and Nu = CRe~m Pr~nφ~k.In view of the specific and multiple influence factors of the performance of ejector, during the design of the ejecting-mixing low-pressure heater, according to the law of its internal flow channel change, mainly mass conservation principle and Bernoulli equation are applied in design calculation. Based on the experiment on two type of structure of ejecting-mixing low-pressure heaters, it is found that if ejecting-mixing low-pressure heaters could be adopted in low-pressure preheating system to preheat condensate with the proper operation parameters, the possible danger could be cleared that condensate may flow into steam turbine along the extraction steam pipe, and condensate water would be heated up to meet the needs for deaerator. As the results of the experiment, the type of heater withφ5mm sized nozzle can generate a vacuum at 0.04MP in steam suction chamber when motive water inlet pressure is more than 0.25MPa, and the type of heater withφ3mm sized orφ4mm sized nozzle can generate a vacuum more than 0.08MP in steam suction chamber when motive water inlet pressure is more than 0.2MPa, while the low pressure extraction steam pressure in present power units is more than 0.1MPa. the type of heater withφ3mm sized orφ4mm sized nozzle can heat condensate up to more than 105℃.The ejecting-mixing low-pressure heaters present the unique performance of steam condensation and heating, according to the uncomplicated analysis of the performance of the steam condensation on the condensation water jet, it is pointed out that flowing condensation film exists on the surface of jet, which is the main heat resistance of steam condensation heat transfer, and the heat transfer coefficient of the steam condensation on the condensation water jet is as high as 0.98 ~ 5.23 MW / (m~2·K).This paper starts with the study of ejector theories, not only deduces the fundamental equations of ejecting performance for the structure design of ejecting-mixing low-pressure heaters, but also defines ejecting efficiency in terms ofη_eand heating efficiency in terms ofη_h. According to the calculation based on the experiment data, the value ofη_h atφ2mm sized nozzle equals 98.6% and the value ofη_e equals 19.8%, the value ofη_h atφ3mm sized nozzle equals 95.6% and the value ofη_e equals 19.6%, the value ofη_h atφ4mm sized nozzle equals 91.6% and the value ofη_e equals 13.5%, the value ofη_h atφ5mm sized nozzle equals 90.3% and the value ofη_e equals 7.8%.The results of experimental investigation on ejecting-mixing low-pressure heaters performance show that, ejecting-mixing low-pressure heaters can take the place of the present surface type low-pressure heaters in steam power cycle of power plant. And the feasibility analysis of reconstruction is made in the low-pressure heaters of 6MW power unit at Yongrong Mining Bureau.更多还原