Design and Selection Process of Vertical Transport Systems SS: Ocean Mining; chairman Julien Denegre
Authors: Verichev Stanislav , Van Bloois Jan Willem , van de Ketterij Robert Gerard 
Published: July 2010

With solutions for the cutting process at large depths on the drawing table, we have started to focus on the question how to bring mined material from the sea bottom to the surface. Here we shortly outline different transportation concepts, some of which are already well known within the dredging industry. Other transportation concepts are less known. Due to the economical considerations, continuous transport seems to be most promising. Therefore, most of the concepts are focused on the hydraulic transportation of mined material. We address the hydraulic transportation methods and describe the possible hardware involved i.e. the different pump types with their characteristics, potential advantages and disadvantages.

Hydraulic transportation has several advantages and will in most cases prove to be the most economical transportation solution. It also introduces a set of potential risks thaough that have to be abated in order to make vertical transportation feasible. We will address the foreseeable significant problems that might be met in the course of the vertical transport of slurries from the large depths.

Additionally we consider the problem of the energy input for the centrifugal pumps. For potential solutions, we review the experience gathered in the offshore industry. Several potential solutions such as hydraulic drives, electrical drives or mechanical drives are available. We will discuss how close the solutions approach the requirements of the vertical transportation system, and where we expect further development be required before it is ready for use for deep sea mining applications.

Introduction

Nowadays, industry is returning back to the consideration of the relatively old concept of mining subsea deposits, which are known to be rich of minerals [3,5,24,29]. Large quantities of mineral reserves like zinc, copper, silver, lead, manganese, phosphate and diamonds are present at the ocean floor (see Figure 1). The main motivators are, of course, relatively high grades and possibility to produce relatively high volumes per unit time. The most likely subsea mining scenario will consist of a remotely operated bottom tracked vehicle attached to a surface vessel by means of a hydraulic pipe lift system and an electrical umbilical. Regrettably, due to legal problems and a fall in price of these specific metals (mainly manganese), the exploitation of these nodules never took off and technology to mine manganese nodules has never been deployed in a production situation. November 1994 UNCLOS (United Nations Convention Law of the Seas) came into force and in this treaty the EEZ (Economic Exclusive Zone) is defined. EEZ is a 200 nautical miles zone in which coastal states have the exclusive rights for exploration and exploitation. This development caused additional attention for offshore mining because the disagreements about management of the sites and the distribution of the revenues had now been solved. Besides technological developments this contributed to today's attention that is paid to seabed massive sulphide deposits as resource for (among others) copper and zinc. The most attractive reserves are the so-called Seabed Massive Sulphide (SMS) deposits. These are rock concretions formed by hydrothermal activity and can mostly be found on the continental slope of the Atlantic and Pacific oceans. Among other minerals they are rich in zinc and copper and due to rising prices of these resources and technological development it becomes increasingly interesting to mine them. Exploitation of these deposits is mainly limited by the technology for their recovery or delivery to the surface. The most probable design of the deep sea miming system comprises Seafloor Mining Tool (SMT), Vertical Transport System (VTS), and Mining Support Vessel (MSV) (see Figure 2).