ABSTRACT

A numerical and experimental investigation has been done to understand the critical suction height (h) and flow influenced area around the Polymetallic nodules (PMNs) for hydraulic collection of the PMNs. The experimental investigation was carried out by using an educator driven suction pump for collecting polymetallic nodules. The studies were performed in a water tank to evaluate the critical bottom clearance for the vertical initial motion of the particles, which could accurately represent the hydraulic collecting features. The effect of bottom clearance was studied by varying the size fraction of the particles. For the investigation three different tests were conducted namely single particle test (SPT), cluster influence test (CIT), and area influence test (AIT). For the sucking of the particles, a suction pipe of 80 mm diameter was used. In the suction pipe two different average flow velocities; 2.7 m/s and 1.6 m/s were maintained. The numerical simulation for same experimental investigation was carried out by using ANSYS based DEM (Discrete Element Method) approach. The CFD-DEM numerical solver was used to simulate the flow field in the vicinity of the spherical particles before hydraulic collection. The outcome of the investigation helps us to design the critical height for suction pipe for the efficient collection of the PMNs in different conditions. Moreover, the study will be helpful to understand the intensity of disturbance at the seabed and investigate to design more efficient hybrid type nodule collection device.

INTRODUCTION

In the era of green energy and the electric vehicle the need of minerals has increased abruptly (Nitta et al., 2015; Sharma, 2017). The conventional mineral resources found at the earth are limited (Calas, 2017). In order to get rid of the problem, human kind is in searching of some different unconventional mineral resource. The ocean spread over the 70% of the earth's surface has been a potential source of petroleum and natural gases. Now, it is considered that deep ocean bed is a good source of Polymetallic nodules (PMNs) (Hein et al., 2020). These PMNs consist of some minerals such as Mn, Cu, Co, Ni and some rare earth elements (REE). Moreover, deep ocean bed can be considered as great resource of minerals, particularly deep-ocean deposits. And as a result, deep-ocean mining can be considered to be a key strategy for human sustainability (Sharma, 2011). The importance of this mining has been suggested by various researchers since the 1960s (Sparenberg, 2019). A conventional deep sea mining system consists of a mining vehicle, hydraulic lifting subsystem, buffer, and mother ship (Atmanand and Ramadass, 2017). The nodule collector device installed in a mining system plays an important role in deciding overall efficiency of the system. Being one of the core components, the nodule collector technique has always been paid great attention. The effective extraction of nodules from the deep-sea bed is required for an economically and environmentally acceptable mining operation (Chung, 2009; Hong et al., 1999). Three collection schemes are applied to the pick-up device after considering technological and economical aspect of the collector namely mechanical, hydraulic, and hybrid. The mechanical based nodule collector has been used by various deep-sea mining test programs including India conducted by National Institute of Ocean Technology (NIOT) (Sudarvelazhagan et al., 2022; Yates and Gupta, 1990). A typical mechanical based nodule collector system is used by NIOT, India as shown in Fig. 1. A mechanical rake has been used in the existing system (Fig. 1(b)) which will minimize the sea bed disturbance, loosen up the sediment and collect the Polymetallic nodules for crushing and transportation to the mother ship (Deepak et al., 2001). In current scenario, the overall efficiency of integrated deep sea mining system is very (Sharma, 2010). In view of future forecast of commercial mining the efficiency of the deep sea mining system should be increased. Moreover, it should have the minimum impact on the deep sea environmental ecosystem (Ramirez-Llodra, 2020; Sharma, 2017). As an alternate approach towards the augmentation in design configuration either a fused rake and suction type or any other hybrid type is planned to incorporate in the design. In order to achieve this, a system should be designed in such a way that it should have low weight and minimum rotating, oscillating and moving parts. For efficient and continuous run of the nodule collector and to counter the undulation of the sea bed, light weight and compact system need to be designed (Janarthanan C et al., 2022). The hydraulic nodule pick-up device is regarded as a proper commercial mining component with its simple structure, high reliability, acceptable pick-up efficiency, and mild disturbance to the seabed (Oebius et al., 2001). The results from sea trials conducted by ‘Ocean Management Incorporated’ in 1978 also showed that the hydraulic collection method has a higher nodule pick-up efficiency and better adaptability to variations in the bottom clearance than mechanical collection (Wang et al., 2022; Zhao et al., 2022). Additionally, it was discovered that hydraulic techniques are more flexible than other techniques in adapting to changes in bottom clearance (Zhao et al., 2018).

This content is only available via PDF.
You can access this article if you purchase or spend a download.