An Experimental Research On Heating Performance Of Ejecting-Mixing Low-Pressure Heater

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.