直接空冷机组排汽管道内雾化补水的数值研究

摘要

In order to reduce the heat load of the condenser and the unit cold source loss and improve the unit vacuum and thermal economy ,changing make-up water method from entering hot well directly to entering hot well after it was atomized at the appropriate location within the exhaust pipe .Taking an example of exhaust pipe of NK 600-24.2/566/56,applying the heat and mass transfer theory for air-water two-phase flow ,establishing the model of atomized make-up water for direct air-cooled unit .performing a numerical simulation about atomizing effect of different nozzle arrangement ,nozzle position ,spray direction,spray pressure and nozzle diameter by using CFD software and analyzing the temperature fields of exhaust of the best spraying effect .The results showed that: the smaller the nozzle diameter is and the higher the spray pressure is ,the more help to improve the degree of atomization ,strengthen the effect of heat and mass transfer for air-water and increase the amount of condensed steam .When the nozzles diameter is 0.3mm,spray pressure is 0.35MPa,the nozzles are arranged in the pipe centerline of 0.5m,1.5m,2.5m in a symmetrical manner on the x=4m cross section,and the spray angle with the positive x-axis in yz plane is 120°,the amount of steam condensation reaches a maximum of 0.079kg/s.%为降低空冷凝汽器的热负荷和机组冷源损失，提高机组真空和热经济性，将补水方式由直接进入热井改为在排汽管道内适当位置雾化后再进入热井。以NK600－24．2／566／566机组排汽管道为例，应用汽水两相流的传热传质理论，建立了直接空冷机组雾化补水模型。利用CFD软件对不同喷嘴位置、喷嘴角度、喷雾压力及喷嘴孔径下的雾化效果进行了数值摸拟，得到了最佳的喷嘴布置方案，并分析了最佳喷雾效果时排汽的温度场。结果表明：喷嘴孔径越小、喷雾压力越高，越有利于提高雾化程度，加强汽、液的传热传质效果，增加排汽的凝结量。当喷嘴孔径为0．3mm、喷雾压力为0．35MPa、喷嘴在x＝4m截面上以对称方式布置在管道中心线0．5m、1．5m、2．5m处，且喷雾方向在yz平面内与x轴正向夹角为120°时，蒸汽凝结量最大，约为0．079kg／s。