Research On The Performance And Structure Strength Of Boiler Water Circulating Pump

Boiler water circulating pump is used to convey the high temperature and high pressure boiler water in the thermal power plant,which is the main dynamic component of the boiler water circulation.The stability of pump system and efficiency of boiler unit are affected by the performance and strength of the pump.Therefore,studying the performance and structural strength of boiler water circulating pump is to provide the theoretical guidance for improving the hydraulic and structure design to ensure to operate safely and stably.In this paper,the 365WLB-965 type boiler water circulating pump is a kind of single-stage single-suction centrifugal pump,which carries high temperature and high pressure water(360?,36.6MPa)and the hemispherical casing made by forging method is the main bearing part.The hydraulic performance and the structure strength are affected by casing,guide vane,impeller and fluid pressure,temperature,respectively.Firstly,the steady flow field was calculated to get the whole flow field of pump by ANSYS-CFX.Secondly,the steady result was used as initial condition to calculate the unsteady flow field to get the pressure fluctuation.And then,according to the unsteady results,the temperature field and static-strength field were calculated by Workbench software to get the distribution of stress and temperature of the pump casing.Besides,the orthogonal test design method was applied to design and improve the guide vane performance.Considering the actual installation of pump,the performance of different outlet-pipe angles were compared and analyzed.The primary research results are as follows:1.The steady flow field of boiler water circulating pump was calculated,and then the internal flow condition of pump at different flow rates was compared and analyzed.It is observed that the pressure gradient and velocity gradient are obvious in the impeller and guide vane,and the flow in the guide vane is disorganized.There is a large number of vortexes in the hemispherical pump body,and the number of vortexes increases with the decrease of the sphere radius.With the increase of flow rate,the internal flow is more stable in the pump.2.The unsteady flow field was calculated.The results show:(1)The internal pressure fluctuation is mainly caused by the action of rotating domain and stationary domain,fluid vortex and the interaction of fluid-solid.(2)The main frequency of pressure fluctuation in the impeller and guide vane is several times larger than axial frequency of the guide vane and the impeller blade respectively.The more closer the interaction between impeller and the vane was,the greater the pressure fluctuation was.(3)As the influence of the interaction between the rotating and static domain gradually decreases and the effect on the fluid-solid impact gradually increases,the pressure fluctuation amplitude at the radial inlet of the pump body decreases firstly and then increases.In the four axial section positions of pump sphere(two spaced 90degrees),the pulsation is smaller at the top near the outlet tube,and the pulsations of the other three sides are similar.the whole pressure pulsation of the pump body is very small.3.Nine hydraulic models of guide vane were designed through the orthogonal method.Hydraulic performance and internal flow condition were compared.Extreme analysis and relative impact index of the head and efficiency were obtained.At last,the best design parameters were obtained that inlet angle ?3=16.2?,diffuse angle?=8?,throat area F3=37×50mm2.Comparing the original guide vane,the flow vortexes of optimized guide vanes decrease very much,and the flow becomes more smooth.Both head and efficiency are greatly improved.4.The installation of pump is a uncertain problem in the actual situation which is related to outlet pipe angle.To explore and analyze the problem of the outlet pipe angle,four different angles were calculated and analyzed.According to the comparison of the hydraulic performance,internal flow field and pressure fluctuation at four different conditions,the results show: compared to other three angles,the head and efficiency decrease slightly when the angle is 130?.There are a large number of dead water zones in the outlet pipe,and both the pressure fluctuation amplitude and the whole pressure pulsation coefficient are larger than those of other three angles,and there is no obvious regularity.The big angle is not advised because of the decrease of performance and unsteady flow at the big outlet pipe angle.5.The steady-state thermal module and static structural module were used to analyze the temperature field and static structural field of casing in the workbench.The results show:(1)The temperature field of the pump is further away the insulation body,the higher the temperature and the heat flux distribution are inverse to the temperature.(2)When the temperature load is only taken into account,the thermal stress is affected by the bolt connection constraint between the insulation body and the casing where the stress becomes larger sharply,and the thermal deformation gradient of the pump is obvious,the deformation is minimized at the constraint place.(3)When only considering the fluid pressure,the stress at the inlet and outlet pipes is largest,the pump body deformation at the constraint is the smallest,and the stress maximum decreases with the increase of the flow rate.(4)When the temperature load and the pressure load are considered together,the casing total stress at the constraint becomes larger sharply and the total stress of the pump body is a little lower than the thermal stress,the total deformation is slightly larger than the thermal deformation,and the spherical deformation and stress is more uniform than other areas.(5)The comparison results show that the spherical body total stress and total deformation are uniform at three different conditions,which indicates that the spherical pump casing is fit for supporting high temperature and high pressure.The total deformation of the pump body is mainly dominated by thermal deformation,and the total stress is mainly dominated by mechanical stress.The total spherical deformation of the casing is below 1.37 mm,which is less than the minimum clearance 5mm between the pump body and its adjacent parts.So there is no interference,and the structure design is reasonable.