Deep-ocean Mining Technology: Development II

Jin S. Chung ISOPE*, Cupertino, California, USA

SUMMARY A brief observation of the developments in mining systems and technology in the past 2 to 4 years is presented. Discussions on the development of other deep-ocean resources that are somewhat similar to nodule production also include gas hydrates, Cobalt-rich manganese crusts, hydrothermal vents and deep-ocean water upwelling (DOW). Previous reviews of deep-ocean mining can be found in Chung (1985, 1994, 1997, 2003). The mining technology R&D schedule for manganese nodules appears to be in line with the International Seabed Authority (ISA) plan. R&D

activities in nodule mining since the ’90s are in their early learning stage relative to the major nodule mining technology R&D activities of the ’70s. The mining systems detailed in almost all recent publications resemble that of the OMCO’s total integrated mining system (TIS) and control (Brink and Chung, 1980): Ship-, pipe-, buffer- and connection-to-miner and miner, and transshipment (Fig. 1). • Surface ship system. Very little in the way of new work can be

found in recent surface ship system developments, including the heavy-lift heave compensator.

• Pipe dynamics and nodule (or solid) lift flows. China is preparing its 1,000-m-depth test, including the dynamics and launch and

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Fig. 1 Block diagram of TIS of integrating systems of production, ship and ocean transshipment/ transportation (Park, Min

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recovery behavior simulation of the pipe-buffer-flexible hose-miner. India tested its flexible pipe system to pump-lift sands from the 410-m seafloor. Relatively new investigations were conducted on nodule concentration distribution and characteristics in the flows.

• Buffer design and development have yet to appear at this stage, long after the OMCO’s original buffer test in the Pacific Ocean in 1976 and 1978.

• Buffer-to-miner link. All recent contractors use the OMCO’s flexible hose concept, where the buffer and link were revealed to the public for the first time. Now both China and Korea propose general concepts of flexible links in their experiment or simulation based on the conceptual flexible link.

• Miner. All recently joined contractors appear to prefer track belts. India tested a simple maneuvering control of small-scale track-belt miners in the 410-m-deep seafloor. The test included a hydraulic sand lift. China is preparing a 1,000-m-deep water test.

• There appears to be little new in the development of integrated system and control, except for all the concept sketches, which resemble that of an OMCO system (Brink and Chung, 1980).

• Most of the recent nodule mining R&D appears to be based on the collection of information previously published or presented by others since the ’70s. Very few new technical issues or problems appear to have been identified by the contractors themselves.

• Further, the contractors have been developing their subsystem components. But compatibility among the subsystem modules within the “integrated mining system and control” system doesn’t appear to be well checked out.

• More clearly defined guidelines or regulations at the early stages can save time and cost for the system, subsystem modules and technology developments, and avoid the repeat of concept or design modification for eventual commercialization.

Recently, more active R&D efforts on production or recovery of crusts, methane hydrates and sulphide are noticeable. The DOW area is making good progress. • Co-rich manganese crusts. Despite the early need for the

conceptual design of a crust mining system, there are very few such. One concept was based on the nodule mining system for the crust crushing and hybrid (continuous-line bucket and hydraulic-lift) mining/production system from the seafloor at the depth of 800 to 3,000 m. Recently a few concepts similar to land mining methods have been studied.

• Sulphide. Sulphide mining technology from 2,000-m seafloor may be similar to crust mining. One type of the miner is “drum cutter miner” operating as ROV.

• Gas hydrates. The preliminary phase of research on producing methane gas from the deep seabed started in Japan. Airlift for the recovery system of methane hydrates from the deep is a possible means. The lift system looks similar to the nodule-sediment-water slurry flow in the lift pipe.

• DOW upwelling is making good progress as part of Japan’s Marino-Forum 21 project for the creation of new fishing ground through the enhancement of marine primary production using artificial upwelling. The second phase, started in 2005, aims to confirm the effect of enhancing marine primary production, and to establish the technology for practical use of an ocean nutrient enhancer.

• Hydrothermal vents. Recently China has been developing sensors for the study of seafloor hydrothermal vents.

___________ *The ISOPE assumes no responsibility for the statements expressed by the author.

KEY WORDS: Manganese nodules, Co-rich manganese crusts, sulphide, gas hydrates, deep-ocean mining, production, integrated systems, technology, ship, dynamic positioning, long pipe, buffer, link, self-propelling, remote-controlled miner, track-keeping, control algorithm.

INTRODUCTION In the ’90s, International Seabed Authority (ISA) contractors started developing technology for the ocean mining of manganese nodules from the deep ocean floor in the Pacific Ocean. The recent state of technological developments among the contractors who joined around the ’90’s is observed and summarized in terms of readiness for the development of large-scale mining systems. Used as a baseline for review is the R&D work performed in the ’70s in deep-ocean mining technology and systems. The review includes discussions on the developments in the past 2 to 4 years. Recent technological developments do not yet appear to identify new issues. Technology developments in DOW and gas hydrate production are emerging, and they are included in this mining status, as their production can be similar to the lift systems for nodule and crust production. The seafloor disturbance by the miner and the moving collector discharge can be a major portion of environmental issues for the manganese nodule production, followed by sediment cleaning near the seafloor, and discharge from the ocean surface. This issue should be part of the mining system design (Chung, Schriever, Sharma and Yamazaki, 2002). Exploration is outside the scope of these observations. For the Co-rich manganese crust production, environmental issues associated with the seafloor disturbance by the miner are to be defined.

Fig. 2 TIS deep-ocean mining system (Brink and Chung, 1981; Chung, 1994; Chung and Cheng, 1996)

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The Total Integrated System (TIS) in Figs. 1 and 2 (Brink and Chung, 1981; Chung, 1994; Chung and Cheng, 1996; Park, Min and Chung, 1997) was upgraded from Lockheed/OMCO’s remotely controlled miner (RCM) ⎯ an integration of subsystems of production or mining from the seafloor, transport to the ocean surface, transport to land, and processing onshore or in the ocean. For the development of an economical, commercial system, specific commercial system models (e.g., TIS, Figs. 1 and 2) should first be defined. Commencement of the subsystem development should accompany compatibility among the subsystem modules. Otherwise, another costly learning cycle may repeat, which may force one to start new subsystem developments all over again. This review brings the TIS (Chung, 2003) up to date.

OCEAN SURFACE SYSTEM According to Brink and Chung (1980), the status of ship system and dynamic positioning with self-propelling miners is as follows: 1. The control system and computer simulation of the integrated ship,

pipe, pipe-handling, buffer and seafloor miner allow for the speedy change of concept tests and design when the subsystems consist of replaceable modules: Economical.

2. The efficient, nonconventional maneuvering capability such as the so-called crabbing reduces downtime, minimizes power consumption, and achieves higher nodule sweep efficiency by the miner.

3. The decision as to whether to process minerals on land or at sea, and as to what metals are of primary interest, greatly influences ship size, recovered mineral storage, ship system design, and shuttle ship requirements for transshipment and ocean transport.

4. Technological innovation is needed for the rapid deployment and retrieval of the pipe system within today’s storm-forecasting capability.

5. The hydrodynamic design of the ship system can be performed adequately with the existing technology.

Very little in the way of new work can be found in recent surface ship system developments for moonpool, nodule storage, preparation and transfer to the shuttle ship. The pipe-to-ship connection tends to use a

gimbal and heavy-lift heave compensator similar in concept to the 7500-ton-capacity shipboard, completely gimballed and heave-compensated platform of the Glomar Explorer (McNary, Person and Ozudogru, 1976). But most are still in the early stage of small-scale developments. The dynamics and control of the integrated ship-pipe-miner system play one of the key roles in system design and operation of both the economical nodule and crust recovery from the deep-ocean floor, and in the increase in nodule sweep efficiency (Brink and Chung, 1980): • Control of the system with active or passive control of the buffer or

pipe-joint thruster-control system, to keep the pipe-buffer system close to the miner as it maneuvers on the seafloor within the slant range.

• The crabbing motion of the ship to keep the thrusters’ fuel consumption to a minimum.

Some attempts have been made to apply recent algorithms other than the widely used PID control to the dynamic positioning control of the mining ship.

Fig. 4 Hydraulic and pneumatic nodule lift (Schick, 1980) PIPE/BUFFER SYSTEM Pipe and Buffer Behaviors and Position Control. A full understanding and simulation capability of the dynamic and static, coupled axial, bending and torsional behaviors of the pipe system (Chung, Cheng and Huttelmaier, 1994) are essential to the design of a TIS system and pipe. Whitney and Chung (1981) found that the axial stress is the design stress, not the bending for such a long pipe as their 5,846-m pipe, which has been recognized in the industry from the ’80s. Some of the key design and operational issues were discussed in Chung (2003). China is preparing its 1,000-m-depth test; the pipe’s 3-D dynamic and launch and recovery behaviors of the pipe-buffer-flexible hose-miner are simulated with ANSYS code, and the scale-model test of the pipe in a tank was conducted (Wang and Liu, 2005; Yu and Liu, 2005). Schick (1980) presented a comparison between hydraulic lift and airlift in terms of pipe diameter and nodule-mixture flow rates for the selection of a lift system for a 4,877-m-deep seafloor. The OMCO is still the first and only consortium to design and test a buffer in the Pacific Ocean in 1976 and 1978 (Fig. 3).

Fig. 3 OMCO’s RCM inside Hughes Glomar Explorer during at-sea test in Pacific Ocean, 1976: Flexible hose and buffer above Archimedean-screw miner

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Pipe System for Vertical Transport. Control of optimum nodule concentration in the nodule-water mixture is desired for optimum nodule (or solid) lift efficiency (Sobota et al., 2005 ; Li et al., 2005 ; Yoon et al., 2005) have been continuing tests and empirical simulation of water-nodule (solid) slurry. Sobota et al. (2005) and Jiang et al. (2005) are investigating nodule concentration distribution in the flows. But no specific pump power estimate method has been recently proposed for practical use, except that the pump power was estimated and used for India’s flexible pipe system to pump-lift sands from the 410-m seafloor (Deepak, 2001; Handschuh, 2001). India is planning to conduct a fully instrumented pump-lift test. Buffer development doesn’t yet appear to be at a hardware design level. So far the only detailed buffer information is the OMCO’s original patent, which was tested in the Pacific Ocean in 1976 and 1978. BUFFER-TO-MINER LINK SYSTEM This link, intended to transport nodules, sediments and water mixtures to the buffer at the bottom of the pipe, is not a strength member and is not vertical. Electromechanical cables along the link supply the power to the self-propelling miner and collector. All recent contractors use a form of the OMCO’s flexible hose concept (Brink and Chung, 1980), which revealed the buffer and link to the public for the first time. Now China (Yu and Liu, 2005) and Korea (Yoon, 2003; Hong, 2005) both propose general concepts of flexible links in their experiment or simulation based on the conceptual flexible link. SEAFLOOR MINER AND AT-SEA TESTS The mobility, reliability, safety, collection efficiency and sweep efficiency of the miner (or collector) system are the most important parameters in deep-ocean mining system design. The OMCO developed large-scale self-propelled “test” miner(s) with Archimedean screws (Fig. 3) and conducted at-sea track-keeping control tests of an RCM on the 4,877-m-deep seafloor in 1976 and 1978 in the Pacific Ocean with the mining ship Hughes Glomar Explorer. The RCM design was based on the most modern technology of the time. The at-sea test included deployment and retrieval of the RCM using the “7,500-t capacity heavy lift pipe and heave-compensating system onboard the ship, and the RCM’s self-propelled, maneuvering control at the 4,877-m depth. All recently joined contractors appear to prefer track belts. In 2000, India tested a simple control of small-scale track-belt miners (3.16-m long × 2.95-m wide) in the 410-m-deep seafloor off its Tuticorn coast (Deepak et al., 2001; Handschuh et al., 2001). The test included the miner’s maneuvering on the seafloor, and sand lift through a flexible hose 7.5 cm in size. China is preparing a 1,000-m-deep water test (Li, 2005). Controllers. PID control has been widely accepted in the ocean industry as mining ship, buffer and miner track-keeping controller (Brink and Chung, 1980) and dynamic ship positioning. Recently, newly developed controllers have been applied to the deep-ocean miner for its track-keeping on the seafloor, hoping to overcome problems from some uncertain or unknown real-time situations associated with automated track-keeping, the underwater physical environments and seafloor properties and characteristics, and the mining system

operations (Chung, 1999; Yeu, 2005; Wang, 2005). The controller can be allowed to carry out some tasks of decision-making in track-keeping control to overcome local uncertain and emergency situations. NOTES ON NODULE MINING SYSTEMS AND SUBSYSTEMS R&D activities in nodule mining since the ’90s are in their early learning stage relative to the major nodule mining technology R&D activities of the ’70s. Most recent nodule mining R&D projects tend to do their R&D and design based on the collection of the information previously published or presented by others since the ’70s. Very few new technical issues or problems appear to be identified in recent publications by the contractors themselves. All concept sketches resemble that of the OMCO (Brink and Chung. 1980). There appears little new in the development of an integrated system and control. Further, the contractors have been developing the subsystem components, while subsystem compatibility of the individual “integrated mining system and control” concepts are not yet definitively checked out, which may require modification. The subsystems consist of modules for easy replacement of individual modules, that is, modular design (Brink and Chung, 1980). However, the contractors’ publications seem to offer very few options of modular design. More clearly defined guidelines or regulations at the early stages can save time and cost for the system and technological development for commercialization. For the development of an economical or commercial system, specific commercial mining system models (e.g., TIS) should first be defined in a near complete form before the commencement of the subsystem development. Otherwise, another costly learning cycle may repeat, which may force one to start new subsystem developments all over again. Recently, more active R&D efforts on producing or recovering crusts, methane hydrates and sulphide are noticeable, and DOW is making good progress. Production of such deep-ocean resources is similar to the nodule lift system. Most of these resources for development are located within the individual EEZ. CRUST MINING (Fig. 5) Despite the early need of a conceptual design for the Co-rich manganese nodule mining system, very few such systems exist ― perhaps but the 3 concepts (Chung, 1994; one in Fig. 5, patent pending). The concept was based on the nodule mining system for the crust-crushing and hybrid (continuous-line bucket and hydraulic-lift) mining/production system from the seafloor at a depth of 800∼3,000 m. Crushed or broken crusts would require much more intensive seafloor preparation for lifting up to the ship than do the nodules. The concept uses a self-propelling miner with vibrators to crush the crusts for hydraulic-lift production from the 800∼3,000-m depth. One of the technical challenges is to mine the crust on a slope, as often Co-rich manganese crust deposits are plentiful on a steep slope (Yamazaki, Chung, and Tsurusaki, 1995). A few Co-rich crust-mining methods have been evolving. They include Co-rich crust crushing or cutting

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concepts and studies, notably in China (Ding et al., 2005; Xia et al., 2005). The proposed concepts are similar to land mining methods such as coal cutting and the cutter-suction head as used in shallow-water dredging for placer mining; they have not been studied yet for deep-ocean applications requiring crust scraping, grinding or crushing. Crust lift or production would require much more preparation at the deep-ocean floor level than shallow-water dredging. Further, some crusts are buried under sediment, unlike the nodules on the seafloor surface, and rich crusts are found on sloped seafloor and on steep seamount slopes. Such issues are a big challenge in crust mining. For the Co-rich manganese crust production, environmental issues associated with the seafloor disturbance by the miner are not well defined. The characteristics of crust properties and size, distributions above and below the sediment, seamount slope etc. would make it more complex to define the environmental issues than for the manganese nodules. Early definition of such environment issues can guide the designers of the crust mining systems. SULPHIDE. Production technology of sulphide from 2,000-m seafloor in Papua New Guinea (Heydon, 2005) may be similar to those for the crust mining production. One type of the possible miner is “drum cutter miner” operating as ROV. Drum cutter are used to cut coal for commercial production. GAS HYDRATES Research on the production of methane gas started in Japan. Sakamoto et al. (2003) analyzed the solid-liquid-gas mixture flow in the pneumatic or airlift system for recovery of Methane-Hydrate (MH) from the seabed. They calculated an unsteady gas-liquid 2-phase flow in single-dimension using a numerical procedure based on the finite method. From calculation and experiment, they investigated the possibility of using airlift for the deep-sea recovery system of MH. The behavior of multiphase flow in an artificial sample of marine sediment with gas hydrates (Hamaguch et al., 2003) was investigated. Both pneumatic and hydraulic lift systems look similar to the solid-(fines-)water flows such as the nodule-water slurry flow in the lift pipe. Interesting results on the strength of MH are noted (Nabeshima, Takai and Komai, 2005). DEEP-OCEAN WATER (DOW) UPWELLING DOW upwelling is making good progress as part of Japan’s Marino-Forum 21 project for the creation of new fishing ground by enhancing marine primary production through artificial upwelling (Ouchi, Otsuka and Omura, 2005). The first phase was undertaken from 2000 through 2004 to develop a prototype ocean nutrient enhancer. The research plan of the second phase, which started in April 2005, aims to confirm the effect of enhancing marine primary production, and to establish the technology for the practical use of an ocean nutrient enhancer. Small-scale R&D activities on DOW utilization are ongoing in Korea and Taiwan. A feasibility study and a strategic environmental assessment of the application of ocean thermal energy conversion (OTEC) as a renewable energy for pumping up DOW are planned for the practical use of an ocean nutrient enhancer. A consortium is planned, consisting of private companies, universities and national institutes in Japan.

HYDROTHERMAL VENTS Sensors are being developed in China for the study of deep seafloor hydrothermal vents (Yang et al., 2005). The U.S., Japan and European Union have already been active in deep-ocean research on hydrothermal vents.

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Fig. 5 A crust Mining System―hybrid mining systems: (a)continuous line bucket (CLB) system through pipe; (b) combinedCLB and hydraulic system (Chung, 1994)

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