Investigation On Backflow Characteristics In A Deep-sea Mining Lifting Pump During The Stopping Process

With the rapid development of industrial technology,the land-based mineral resources are becoming increasingly scarce,and the exploitation of deep-sea mineral resources has become a strategic goal for many countries.In the"14th Five-Year Plan"and the"2035Visionary Goal Proposal"by Chinese government,it is explicitly stated that it is necessary to accelerate the development and utilization of marine mineral resources.The lifting pump of deep-sea mining carries the risk of emergency pump shutdown during operation due to sudden reasons such as faults or power outages.Emergency shutdown of the pump is easily to cause blockage of mineral particles in the settling process,resulting in the inability of the entire system to restart properly.In order to explore the internal shutdown and backflow characteristics of the deep-sea mining lifting pump,this paper takes a two-stage deep-sea mining lifting pump as the research object,uses the combination of experimental test and numerical simulation to study the backflow characteristics of the lifting pump.Based on the wheelbase and blade combination between the pump stages,the optimization method of the backflow characteristics of the solid-liquid two-phase flow lifting pump is explored.The specific research work and achievements is summarized as follows:1.A more systematic summary of the current status of research on the experimental testing and numerical simulation of deep-sea mining lifting pumps at home and abroad,as well as the current research methods and results on the stopping backflow characteristics of lifting pumps,and points out the problems of the current research and the future development trend.2.A visual closed test bench was built and the visualization shot of the spherical particle(ρ=1.5g/cm~3、C_v=5%)backflow in the guide vane after the model pump stopped was carried out by using the high-speed photography system,and the movement trajectory of the particle in the guide vane at all levels was obtained.The test results are:(1)There are three kinds of typical trajectories of spherical particles in each guide vane during the backflow process,and there are significant differences in the trajectories of particles in each guide vane.(2)The secondary guide vane is dominated by the type I motion trajectory,the particles flow back into guide vane from the working face,and flow back out of the guide vane along the working face,with the occurrence probability of 36.67%.(3)The type II trajectory is the main trajectory in the first stage guide vane,the particles flow back into the first guide vane from the middle of the outlet,after running along the speed direction for a distance,they collide with the working surface,continue to flow downward after reflection,and flow out from the inlet after contact with the blade,with the occurrence probability of 53.33%.(4)Due to the inlet angle of the secondary impeller blades,particles are more likely to collide with the first stage guide vane.3.The CFD-DEM coupled calculation method was used to simulate particle backflow with different physical parameters,the influence of the concentration,density and particle size of spherical particles on the particle backflow performance in the model pump was analyzed;the influence of spherical,square and cylindrical particles on the particle backflow performance in the model pump was also studied.The main simulation results are:(1)During the backflow process,particles in both the secondary and primary pumps are prone to accumulate on the working surface of the guide vanes and the connection between the impeller and the guide vanes.Additionally,particles can also accumulate in the passageway of the impeller in the primary pump.(2)When the spherical particles backflow,as the particle concentration,density and particle size increase,the particle backflow pass rate gradually decreases,and the backflow performance of the lifting pump gradually decreases.(3)When the different shapes particles are backflow,the spherical particles have the highest backflow pass rate,with the best backflow performance in the pump.Conversely,square particles have the poorest refluxing performance,with a particle backflow pass rate of only 31.58%.(4)The collision of particles in the pump is mainly in the form of collision between particles and particles,the collision between particles and overflow components mainly occurs in the first stage pump;with the increase of particle concentration,density and particle size,the main collision position of particles and overflow components collision gradually changed from the first stage pump to the secondary pump,in which particles and secondary guide vane collision rate increases most obviously.4.Taking improving the particle backflow performance as the optimization objective,the influence of pump stage wheelbase and blade combination on the backflow performance of the model pump was studied using numerical simulation methods.The main simulation results are:(1)With the increase of the wheelbase between the pump stages,the number of particles accumulated and the number of collisions in the first pump stage gradually decreases,the number of particles the particle backflow pass rate gradually increases,and the performance of particle backflow increases significantly.(2)As the number of blades increases,the total number of particle collisions in the lifting pump gradually decreases;The particle reflux rate has been improved,with the number of guide vanes and the number of impeller blades increase,the particle backflow pass rate increased by 2.56%and 4.48%respectively,the increase in the number of impeller blades has a more pronounced improvement in reflux performance.