Numerical Simulation,Hydraulic Optimization And Experimental Research Of Low Consistency Pulp Pump

According to the statistical results,China is the biggest paper and board production country in the word now.The pulp pump is the heart of the paper mill,which is responsible for transport pulp during all the process of producing paper and board.In recent years,the government advocates saving energy and reducing pollution.Also,with the development of the paper industry,the demand for highly efficient pulp pumps increases year by year.However,the pump factory in our country still can not produce highly efficient pulp pump now.which means our country must spend much of money to import a great number of pulp pump from abroad.At present,most of the low consistency pulp pump is opened or semi-opened centrifugal pump.The shroud and hub are replaced with two plates.The clearance between impeller and plates is adjustable.The clearance improve because of the wear of the surface of impeller after the pump running for a period of time.And the plates can help avoiding the performance of pump grow worse after the clearance changed.According to study,the clearance between impeller and plates can help improve the ability of transporting air in pulp.However,the head and efficiency are usually much lower than normal centrifugal pumps.In this paper,the following work was completed to investigate this kind low consistency pulp pump:(1)The standard experiences was conducted on standard test rig to test the performance of original pump.The experimental results showed that the head and efficiency are low.And the flow rate is larger than rated flow rate at the optimal operating point.(2)The numerical simulation based on CFX software was completed to simulate the flow in original pump.And the computational results and experimental results were compared.The results show that the head and efficiency of the original pump are much lower than the required head and efficiency.Besides,the computational results showed that the head and efficiency drop after taking the clearance into consideration.(3)The size parameters of six groups of models were counted.The inlet equivalent diameter coefficient,impeller outer diameter coefficient and the outlet width coefficient were calculated.Also,the ratio of rated head to test head were calculated to study the effect of each coefficient on the performance of the pump.The statistics show that the inlet equivalent coefficient of each model is almost the same.The exit angle of most impellers is relatively large.When the wrapping angle of blade and the outlet blade angle are small,the experimental head of the model pump is significantly lower than the rated head.(4)The impeller and volute of original pump were optimized to improve the performance of the pump.The Design of Experiments(Do E)method was further applied to improve the originally designed pump.During process of optimization,impellers with different out blade angle and big wrapping angle of blade was designed.And a smaller volute was design.These impellers and volute were combined into new models.The performance of these models were calculated.The computational results show that the head increases while the efficiency decreases with the increase of the outlet blade angle of impellers.In addition,the efficiency and head of the new models which are equipped with small volute are significantly higher than models equipped with original volute.Therefore,it can equip the pump with an impeller with larger outlet blade angle and smaller volute for achieving higher head and efficiency.(5)The pressures on the suction surface and the pressure surface were extracted respectively.And the distribution of pressure on impeller were studied.The comparison results show that the difference of pressure on the suction surface and pressure surface increased with the increasing of outlet blade angle.This means the performance of impeller improved.The influence of the outlet blade angle on the hydraulic performance of the model were confirmed.(6)Another medel wre optimized according to the previous optimization experience.The head of the medel increased three meter,and the efficiency increased 7% after optimization.(7)The hexahedral grid were used to generate the mesh of computational domain.The distribution of the flow in the clearance was analyzed.The results showed that the fluid flows from the pressure surface to suction surface with the increasing of flow rate.In the clearance,the velocity of the fluid first increases and then decreases.The pressure at the blade tip and the outlet of impeller are relatively higher.Therefore,the blades were worn at the top of the impeller and the outlet of impeller.In the area near the suction surface of the blade,there is a vortex near the clearance.From the inlet to the outlet,the vortex develops from the boundary to the middle of the flow channel.The pressure difference of the two sides of the clearance is small at the inlet and outlet.The pressure difference on the blade increases with the increasing of flow rate.After the air enters from the inlet,the air moves from the pressure surface to the suction surface with the increasing of the pressure difference.And the pressure distribution on the blade tends to be uniform.(8)The best optimized model was manufactured.And the experiment was conducted on the pulp pump test rig.The test results show that the efficiency of the optimized pump was obviously improved.The flow rate is smaller than the rated flow rate at the optimal operating point.The head increased 0.6m,and the efficiency increased 14.8% after optimization.