Design And Study Of A Hydraulic Collecting System Of Deep Sea Manganese Nodule Miners

Various mineral deposits such as manganese nodules,cobalt-rich crusts,and hydrothermal sulphides are present in the deep sea.The reserves are huge and the economic prospects are broad.Therefore,deep sea mining is regarded as an important way for humans to obtain mineral resources in the future.The development of deep sea mining technology is of great strategic significance.In recent years,the development of deep sea mining is in the ascendant.China,Germany,India,South Korea,Japan,Canada,Belgium,the European Union and many other countries and organizations are engaged in the research of deep-sea mining technology.Several deep-sea mining prototypes have been developed and various sea trials have been conducted.Deep sea mining currently faces two main challenges,namely the economics of commercial mining and the environmental protection of large-scale mining.Some studies have suggested that deep-sea mining operations may cause disturbances to the seafloor and discharge sediment,which may pose a threat to deep-sea benthic biological communities and even deep-sea ecology.The International Seabed Authority also places restrictions on the environmental impact of deep sea mining technology.In this context,the thesis proposes an environmentally-friendly hydraulic collecting scheme suitable for deep-sea manganese nodule miner based on innovative thinking,and uses numerical simulation methods to study several key aspects of the scheme.An Eulerian liquid-solid two-phase flow model is used to numerically simulate the sediment discharge process of the existing hydraulic collecting system.The diffusion characteristics of sediment particles under different discharge conditions are studied.An evaluation index is established,which indicates the effects of sediment particles on the surrounding waters.The impact of variables such as the emission speed and concentration on the index is analysed.The results show that adopting a lower emission speed and a certain emission concentration is beneficial to reduce the impact on the environment.It is deduced from this that if there is a technology capable of concentrating,storing,and discharging the sediment-water mixture with a controlled intensity,it can effectively reduce the impact on the subsea ecological environment.Based on the above study,a new type of circulating hydraulic collecting system is proposed.The system is mainly composed of hydraulic nodule collector,nodulesediment separator,water-sediment separator,etc.The system can not only achieve nodule-sediment separation to reduce the proportion of sediment impurities in the nodules,but also achieve controlled discharge of the sediment to effectively reduce the impact on the seabed environment.In order to study the working performance of the key parts of the system,multiphase flow models based on Eulerian method and Discrete Element Method are established for the sediment particles and manganese nodules,respectively.First of all,a design of seabed-attached type hydraulic nodule collector is proposed,based on the existing principle of water-jet collector.The internal flow field characteristics and manganese nodule kinematic characteristics are studied.Effects of different working conditions on the above characteristics and on the performance of the collector are analysed.The results show that high-intensity and energy-concentrated water jets are beneficial to improve collecting performance of the collector.Secondly,based on the differences between the kinematic characteristics of manganese nodules and sediment particles,a design of gravity type nodule-sediment separator is proposed,and the kinematic behaviour of manganese nodules and sediment particles in the upper horizontal passage and the lower vertical passage are studied,respectively.The impact of different conveying conditions on the separation effect is analysed.The results show that the separator can achieve an effective separation effect with appropriate working parametersFinally,a free-settling water-sediment separator and a water-sediment separator based on the principle of the U-baffle inertial separator are proposed.The relationship between the separation effect of the two separator and the speed and concentration of the mixed flow,as well as some improvement are respectively studied.The results show that the separation effect of the two separators is affected by the flow rate and concentration.Both separators can achieve good performance under certain conditions.