Retrofit And Optimization Design Of Low Specific Speed Main Oil Pump Based On Performance Prediction

Low specific speed centrifugal pumps are widely used in the power plant, petroleum industry, chemical industry, urban water supply, agricultural irrigation and drainage, etc. A lot of problems, such as lower in efficiency, worse in operating stability, and overload easily at conditions of larger flow rate, were existed in this kind of pump generally. The main oil pump for the oil supply system of thermal power plant and nuclear power plant is typical double suction centrifugal pump with low specific speed. As the power source and key equipment of an oil supply system of steam turbine unit, the performance of main oil pump has very great influence on safe operation of the steam turbine unit. With the increasing unit capacity and size in structure of the turbine, the reliability and safety of the steam turbine are required to be accordingly improved in the oil supply system, so that it bring forward more challenges in the design of main oil pump.In order to meet the needs of oil system of large scale steam turbine, the working parameter of main oil pump demands not only the oulet pressure is 15-20 times higher than to the inlet pressure, but also demands larger flow and better adaptability in variable opearting conditions. Not merely require the main oil pump to have higher hydraulic efficiency, the characteristic curve is comparatively smooth, and have better cavitation performance. In order to meet requirements of an oil supply system of steam turbine unit, main oil pump generally adopt the single stage double suction centrifugal pump with super-low specific speed(often lower than 40). There often has the contradiction between its working parameters and the high-performance parameter requirement, so how to rationally solve and coordinate become a key problem in the hydraulic design for this kind of pump.The traditional research and development approach which mainly relying on model test is very difficult to meet these requirements, so it is very necessary to explore the optimization design method based on So it is very necessary to explore the optimization design method based on performance prediction to solve the research and development of this kind of low specific speed double suction oil pump. On the other hand, because a large number of low specific speed centrifugal pumps that are in service generally have low efficiency problems, such as main oil pumps for some 300MW and the belows steam turbine units need to carry on retrofit design. In order to solve the problem of retrofit design and lower cost, it is one of the effective ways by method of retrofit design based on performance prediction.The optimization design method for a low specific speed double suction centrifugal pump has been studied for improving efficiency and operation stability as the optimization objective based on the practical engineering requirements. Taken the retrofit design requirements of main oil pump for domestic 300MW steam turbine unit as a example, the hydraulic optimization design approach of low specific speed double suction centrifugal pump based on performance prediction is explored in this thesis. At first, performance prediction and verification with 3-D flow numerical simulation inside the whole flow passage of main oil pump for 300MW steam turbine unit was performed, then existed problems in the pump had analysed. The idea of flow passege re-design is analyzed and researched by numerical simulation of main oil pump for imported 600MW steam turbine unit. Taking its impeller vane shape as a reference, the preliminary plan of retrofit design is made according to the working requirement of 300MW main oil pump unit. And then, many loop calculations is made between "numerical simulation test and modifying geometric parameters and passage shape ", until obtain the passage to meet with requirements of working parameter and performance, finally finish the retrofit and optimization design of its passage. On the basis of 3-D numerical simulation on the whole flow passage, performance prediction method has been applied to retrofit and optimization design of double suction main oil pump flow passage components, by numerical test substituted for high-cost model test. In this paper, the method has been successfully used for practical engineering to solve the passage retrofit design of main oil pump. Not only improve the hydrodynamic performance, but also shorten the development cycle and reduce development costs.The subject of this thesis cooperated with large steam turbine manufacturer, on the basis of 3-D numerical simulation on the whole flow passage, performance prediction method has been applied to hydrodynamic optimization design of double suction main oil pump flow passage components. How to improve efficiency and operating stability of the whole operation range of low specific speed double suction main oil pump in the design process has been considered. And the research achievement has been applied on the localization of main oil pump for large steam turbine and the development of domestic independent innovation. It is very significant not only for independent innovation of electrical power equipment manufacture industry, but also for development of design theory and method of this kind centrifugal pump.