Study On Floating Objects Moving,Being Intercepted By And Passing Trash Racks,Blocking A Pump For Pumping Stations

Trash racks are often set up at pumping stations to intercept floating objects.The head loss caused by trash increases the pump head,reduces the flow,increases the operating cost,exacerbates the pump cavitation and cavitation,and generates vibration and noise.The leaked floaters enter the pump,entangles in the water pump,affects the flow in the pump,and hinders the impeller and the pump shaft from rotatingTo solve the above problems,this paper uses three methods:experimental research,theoretical analysis and numerical simulation.The movement of typical floating objects in front of the trash racks is studied by the test method.Numerical simulation is used to explore the motion characteristics,stress conditions and the state before reaching racks.The floating objects passing through or being intercepted by racks are tested.Analyze the mechanism of floating objects crossing the rack or intercept,and calculate the probability of floating objects crossing the racks.Analyzing floating objects'movement law and reaching location of the impeller.Analyze the entanglement mechanism in the pump.The numerical simulation method is used to calculate the influence of different blocking degrees in front of the pollution barrier and in the pump on the performance of the pump.Provide optimization solutions for the design of the cleaning machine,the trash racks and the flow components in the pump.The main work and achievements of this paper are as follows(1)Determined the equation of motion of the floating object in water and the maximum velocity Vfmax of the columnar floating object in the steady flow.The velocity equation of the moving center of mass of the column floater is determined(2)For floating objects with the same object-spacing ratio ?(the ratio of the float length to the space between the racks)and water flow velocity,the probability of peanuts passing the trash racks is slightly lower than dead branches,plastic bags are higher than old cloths,and columnar rigid floaters are higher than sheet flexible floaters.Based on 80%interception rate,?cotton cloth is 2.3,?plastic bag is 4.15,?peanuts is about 7,?dead branches is about 8.(3)Through experiments and numerical simulation,the critical submergence depth in front of the floating debris grid and the critical submergence level at the inlet of the floating debris inlet passage are determined.(4)Old cloth floating objects,in the middle of the impeller,are easy to wind on the blade shaft.Floating objects such as plastic bags,at the hub,are easily wound around the blade shaft,guided vane,jammed between the hub and the blade,or hub's middle hole position.Floating objects such as dead branches are not easy to form entanglement when entering the impeller,and will be interrupted by the impeller.(5)Compared with no floating object entanglement,when the wheel entanglement is 4.375%and 8.75%,the overall performance curve of the pump is shifted to Small flow side and the highest efficiency is reduced.Under the design conditions(H=6.277 m),the flow rate decreased by 13.1%and 26.9%,the power decreased by 6.4%and 20.3%,and the efficiency decreased by 6.68 and 7.46 percentage point,respectively.Under low lift conditions(H=3.222 m),the flow decreases by 12.9%and 27.4%,the power decreases by 6.2%and 24.9%,and the efficiency decreases by 6.62and 4.32 percentage point,respectively.(6)The water pump over-flow component adopts non-wrap design.The flow surface needs to be smooth,and the water-facing surface is streamlined.Increasing the blade shaft diameter.Reasonably design the interval of trash rack according to lmax(the maximum flexible float size allowed by the impeller)and a certain grid crossing probability f(p).According to the impact of different blockage of floating objects in front of the grid on the performance of the pump device,reducing the cleaning cost,and ensuring the safe operation of the pump unit.