Tools for the Deep

The dredging industry is gearing up to deliver the tools and know-how for winning minerals from the deep sea. The first deep sea mining projects are almost ready for operation. Equipment manufacturers work hard to provide machines that can work under the immense pressure in the deep waters. A glance into the technology needed and the initiatives undertaken to get down to the ocean floor.

The atmosphere is vibrant in the dredging industry as soon as the topic of deep sea mining is mentioned. 2012 is the threshold to a new industry, possibly sourcing unimaginable wealth of minerals and energy. Gold and copper are discovered in grand amounts, just as rare earth minerals that are essential to modern day electronics, as they are required to produce long lasting batteries and electronic connectors in smartphones and tablet computers. There is even more: large energy resources may be found in hydromethane clathrate, phosphate is found in sub-sea rocks and diamonds are won from the sea bed.

Solwara project

Dredgers anticipate the first deep sea mining operations, soon to begin with the Solwara project at 1,600 metres of depth in the Bismarck Sea north of the isle of Papua New Guinea. Results of the first operations will teach a lot about operations at such depths. Canadian company Nautilus gained the license to start mining for minerals there. United Nations organisation International Seabed Authority indicated fifteen areas in international waters that may be exploited for deep sea mining. Companies and governmental institutions from different nations have been granted licences to work there.

Geologists exploring the ocean floor have discovered a variety of minerals. Rocks like manganese nodules contain a lot of minerals in highconcentrations.Theyaretypicallyfoundina layer of very fine sediment at depths of four to six kilometres. It is quite hard to harvest these rocks without causing the sediment to whirl up and overcloud the waters for years. There is also the cobalt rich crust, a layer of rock that is typically found on the slopes of sub-sea mountains. It is hard and hard to get to. The rock needs to be broken to harvest the minerals, but it is situated on steep parts at the bottom of the ocean at depths from 2,000 to even 7,000 metres. Machines cannot drive over the steep slopes, while structures hanging from ropes do not have the weight to employ enough power to break the rock. These two deep-hidden types of mineral reserve will only be ready for exploitation after deep sea mining techniques have evolved, progressing on first experiences.

The type of mineral reserve marine geologists and dredgers think they can harvest, are the seafloor massive sulphites (SMS). These are rocks, very rich with minerals for all kinds of metals. They are found in areas of the ocean where there is a lot of seismic activity. The rocks have grown as chimneys around so-called black smokers.

These underwater hot fountains are created due to water leaking through the cracks of earth shell towards the hot magma. The water heats up and is blasted up towards the cold ocean water, much like a volcano. The cold water causes the minerals to settle down around the chimneys. In volcanic areas, the sea bed is covered with rocks from these chimneys, broken off after the black smoker was no longer active. This kind of mineral rocks can be found at depths from 1,500 to 4,000 metres. The Solwara project is planned to harvest SMS.

Even greater depths

Engineers and construction companies of deep sea equipment are planning ahead towards new projects at even greater depths than the 1,600 metres of the Solwara project. Anticipating success, Nautilus has announced to start preparations for a second project in the Pacific somewhere between Hawaii and Mexico, operating at about 4,500 metres below surface. “We have the components to build machines that can operate 6,000 metres below surface”, product manager dredge technology Eugène Slaats of Bosch Rexroth assures. “As a supplier to yards and equipment manufacturers that build deep sea dredging machinery, we can offer either hydraulics and electronics that still work under 600 times the atmospheric pressure. That is the pressure at 6,000 metres depth. For operating in these extreme circumstances, we developed pressure-compensated hydraulics that withstand the pressure. We tested them in a hyperbaric chamber, increasing pressure gradually. At the chamber’s maximum pressure of 600 bar, all components still worked as they should.” Pressure compensation works with a quite simple principle: a membrane with a spring transfers the outside water pressure to the hydraulic oil within the system. The spring reassures that the inside pressure is always about one bar higher than the outside pressure, so no sea water will get into the system. Electro-hydraulic manifolds are encapsulated and also filled with fluids, which are likewise pressure-compensated. “It is crucial to bleed all the air when filling the covers around the hydraulic valves with fluids”, Slaats’ colleague Johannes Schunder explains. “Air is so easily compressible, having air bubbles left in the system would mean a loss of compensation pressure. To be sure that no air is captured in small hollows, we redesigned a lot of parts of the hydraulic valves.”

“Service and maintenance intervals for equipment working so deep under water should be minimised as much as possible,” Schunder understands. “If a crawler with a cutting head for breaking rocks is failing at about 2,000 metres below surface, heaving the 250 ton vehicle back on board of the control ship for service is a complex, time demanding and costly operation. Even if you could move the structure at 20 metres a minute, which is fast in water and at enormous lengths of cable, it still takes about two hours to only get the thing to the surface. Therefore we use the most durable materials and apply special coatings that have proven to provide maximum corrosion resistance. For some parts super duplex stainless steel is used, an extra strong metal that is even more corrosion resistant than the grade 316 stainless steel commonly known.”

Comparable to open mining at land

In practice, dredging specialists expect the sea bed operations to resemble open mining at land. A multitude of equipment and machinery will be applied. Crawlers will ride over the rock-clad ocean floor on tracks and eventually even out a trail for their operations and moving about. Other ROVs (remote operated vehicles) will crush rocks or collect particles. A large pump will lift all the harvested minerals and sediment that has come loose along a big hose to the surface, where it will be deposited in barges that anchor alongside the main operating vessel that lies at the surface above all the mining activity. Companies like Seatools, IHC Merwede and Damen are developing a variety of equipment for mineral harvesting in deep oceans. Being experienced manufacturers of underwater equipment for dredging, these companies have their own expertise in developing hydraulics and electronics that perform at depths. Never before has any dredging company in the world employed such extensive operations at such great depths as is planned with deep sea mining.

Damen has come up with a multifunctional tool: the RORO dredger. This is a flexible dredging system that can operate at depths down to 200 metres. That is of course not the immense depth of the ocean floor, but in coastal areas it can be applied for mining as well as dredging. The RORO dredger is a modular system that can be installed as a complete and self-powered system on any vessel. A draghead and a submersible dredgepump are lowered from the vessel, connected with a suction pipe that rolls from a ten metre diameter winch. The sediment or minerals pumped up are hovered into a barge that docks alongside the vessel on which the RORO deep dredge is installed. “This is the only product for operation in deeper waters that is presently ready available”, public relations manger Saskia den Herder of Damen Dredging Equipment explains her company’s advantage. “We developed it as the need for the right kind of sands for house or road construction demands that dredgers operate in deeper water. As barges collecting the sand of minerals dock alongside continuously, the dredging can go on non-stop. That saves time and also saves the need to navigate up and down from the winning area to the place where the sand or minerals need to be deposited.”

Joint projects

Damen, IHC Merwede and other manufacturers engage in the Joint Industry Project ‘Deep Sea Mining’ organised at MARIN research institute to investigate technological solutions for operating in the deep waters. ROVs with all kinds of different cutter heads and robotic arms are being studied.

The outcome of the project will enable all of the participants to develop equipment employing the newly discovered technologies.

IHC Merwede and Belgian dredging company DEME have joined forces in OceanflORE. As it is yet unknown for mining companies that have gained a license for deep sea mining how profitable operations will be, the consortium is offering mining operation at a cost-per-ton basis. “The companies in this new industry are young start-ups”, general manager Kris van Nijen explains from his Singapore office. “Often they don’t have the capacity to heavily invest in equipment. We do just that at OceanflORE. For our first clients and prospects we are now investigating the requirements of specific sites. With today’s knowledge, it seems feasible to say that for every location of deep sea mining, special equipment needs to be developed. We perform baseline monitoring to map the ocean bed at the location of the exploitation. Then we research possibilities of getting the minerals up while doing least possible damage to the marine environment.”

Founding partner IHC Merwede can develop the equipment needed, while DEME has the fleet and workforce to actually operate the project. There is already experience with sub sea mining. IHC Merwede delivered the crawlers for the underwater winning ground of De Beers: sub sea diamond mining off the coast of Namibia. “We are of course closely watching progression at Nautilus with their Solwara project. We are also involved in other preparations for deep sea mining. I expect deep sea mining to be common practice within ten years.”

Hans Buitelaar