ABSTRACT

Deep-sea mining pumps play a vital role in deep-sea mining operations. Typically, these pumps are multi-stage centrifugal pumps designed to deliver adequate hydraulic power. Given the complex and fluctuating concentration and size distribution of ore particles, understanding the internal transport characteristics under different conditions is crucial for ensuring the smooth operation of the lifting system. In this study, we employed the discrete element method and computational fluid dynamics (CFD-DEM) to numerically investigate the operational behavior of deep-sea mining pumps under non-rated and non-normal conditions. Additionally, we analyzed the slurry characteristics within the pump when it operates under unfavorable conditions.

INTRODUCTION

The oceans are rich in mineral resources, and the seabed several thousand meters below is rich in many minerals that are scarce on land: manganese nodules, cobalt-rich crusts, polymetallic sulfides, and so on(Toro, et al. 2020). Among them, manganese nodules are rich in metal elements, which can be used for the development of various high-tech industries and are important metals for the new energy industry. (Hein, et al. 2020)Marine mineral resources promise to be the answer to metal shortages for future industrial development, and the most promising commercial mining currently is based on solid-liquid two-phase flow hydraulic lifting(Sharma 2022, Yang and Liu 2020), a process in which ore is collected by mining trucks, crushed and conveyed to a buffer, and then a slurry mixed with large quantities of ore particles is lifted to the water surface using a hard pipe and a multi-stage pump(Kang and Liu 2021). Multi-stage pumps provide pressure energy for the slurry throughout the lifting pipeline(Hong and Hu 2022). The slurry, which contains a large number of particles, has a complex movement within the multi-stage pumps, with both random collisions of particles and vane-controlled forced flow, and the development of centrifugal pumps has always been a priority for deep-sea mining(Zou 2007). Historically, sea trial failures have been common due to insufficient research on centrifugal pumps(Hu, et al. 2021). In 1978, OMI and OMA Group conducted sea trials for deep-sea polymetallic nodule mining at 5,200 m and 4,570 m, respectively(Hu, et al. 2022). 650 tons of minerals were collected by OMI using a six-stage centrifugal pump designed and developed by the KSB Group, and the wear failure of the lifting pumps was found to be a problem during the trials. 550 tons of nodules were lifted by OMA in 18 hours, with a maximum capacity of 50 tons per hour, but the motor stalled because one of the blades of the suction pump broke(Wang, et al. 2022). In 1986, Ebara Japan manufactured an eight-stage lift pump of the same type based on a two-stage pump that had been successfully tested. The pump structure consisted of two symmetrically arranged four-stage pumps at the top and bottom, with the pump motor located in the middle of the two pumps, and the pump was designed to have a flow rate of 450 m3/h and a total hydraulic head of 376 meters, which was found to have a backflow clogging problem during the test(Chung and Tsurusaki 1994). Korea conducted a 2000m depth sea trail with a two-stage pump in 2015(Yoon, et al. 2011). In June 2016, China's Changsha Research Institute of Mining and Metallurgy successfully developed a five-stage slurry pump with a high specific rotational speed and successfully conducted a 300m lifting pumping pipe test in the South China Sea(Filer and Gabriel 2018). Overall, hydraulic pipe-lifting systems driven by multistage centrifugal pumps remain the dominant technical solution for vertical transportation in deep-sea polymetallic nodule mining. Deep sea mining pumps still need a lot of R&D efforts, the current R&D is mainly based on the design of clear water pumps for the modification of the internal slurry movement and transport, reflux clogging and other issues of the research are still relatively lacking.

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