Electric crawler uses waterjets to pick up nodules from ocean floor
Royal IHC has developed a fully electric crawler with a hydraulic collector as part of its deepsea mining solution. With hydraulic ‘we mean we collect the nodules with waterjets,’ says Wiebe Boomsma, Manager R&D at Royal IHC. ‘The jets create a negative relative pressure which sucks up the sediment.’
Deepsea mining requires a full mining value chain to take off: the right licences and permits, deposits, the harvesting technology (vehicle, transport system, mining vessel), processing and refining of the materials and the right logistics. Over the past twelve years, Royal IHC has been developing an integrated deepsea mining solution, comprising a crawler and riser system as well as mining vessel designs to harvest polymetallic nodules from water depths of up to six kilometres.
SWZ|Maritime spoke to Boomsma and his colleague Laurens de Jonge, Manager Marine Mining at Royal IHC, to discuss the deepsea mining landscape as well as the mining solution developed by the company. In the first article published two weeks ago, we looked at deepsea mining landscape in general. Last week’s article discussed the riser system. This third article takes a closer look at the collector that was designed.
Laurens de Jonge (left) and Wiebe Boomsma.
The original plan was to investigate deepsea mining with a group of Dutch companies, but in the end it became a European cluster. ‘With European partners and subsidies we worked on sustainable solutions,’ explains Boomsma. ‘The first programme was Blue Mining, which focused on the development of a riser system to bring the resources to the sea surface. The second programme started while Blue Mining was still underway: Blue Nodules, which developed the collector needed to pick up the nodules from the ocean floor.’
Designing the collector
Blue Nodules looked at the collector that harvests the nodules as part of a vehicle or crawler. The first of these was the Apollo I, a small version of a crawler to test design choices. Its successor is the larger Apollo II.
The full scale collector will be a sixteen-metre modular design
‘We started with simulations and computational fluid dynamics (CFD) to create a model,’ describes Boomsma. ‘We then did small-scale tests and our first validations. Then we did a large-scale (1:1) test at Deltares in the Water and Soil Flume. The full scale collector will be a sixteen-metre modular design. For the test, we used a one-metre section of this model.’
‘A hydraulic collector was chosen because it was much more robust than a mechanical one,’ says Boomsma. ‘Even with a whole list of improvements, it would never be as robust as the hydraulic one, which is something you simply need at a depth of five kilometres.’
De Jonge adds: ‘The idea behind the mechanical collector was to see if you could harvest selectively on the seabed, because you want to avoid picking up a lot of sediments. However, this turned out to be very tricky, especially because the nodules have different sizes and are embedded in clay, which is sticky.’
Boomsma: ‘We started with a kind of comb with the idea that the clay would then fall through it, but the deepsea sediments turned out to be too sticky. You’d end up with a kind of bulldozer and pick up as much sediment as with the hydraulic one.’ ‘Because you also have a lot more moving parts than with a hydraulic one, the clay would stick to everything with consequences for operation, wear and tear and maintenance,’ De Jonge points out.
Boomsma goes on to explain that with hydraulic ‘we mean we collect the nodules with waterjets. The jets create a negative relative pressure which sucks up the sediment and the nodules and the slurry is then transported further. So there is no mechanical contact between the excavation tool and the seabed.’
The vehicle does not use hydraulic oil and is therefore fully electrically driven. It is now suitable up to a water depth of 500 metres.
Boomsma: ‘There are three limitations. First is the currently used E-pod (the electronic pod, an air chamber where all the electronics are located). As long as we are testing at a maximum depth of 500 metres, it makes no sense to use a very heavy E-pod with a high wall thickness of aluminium, which would entail the necessary costs. Secondly, we are now running at a relatively low voltage and that will be upgraded to 4.2 kilovolt if we go deeper. Furthermore, the umbilical that powers the vehicle will have to be longer. For the rest, everything is suitable for six kilometres.’
In principle, the vehicle is not limited to a width of sixteen metres. It all depends on whether you can still launch it from the ship (consider the A-frame, width of the ship and dynamics). De Jonge: ‘It is also about weight. Underwater it weighs practically nothing, but above water the umbilical needs to be able to lift the unit on board. As each one-metre wide collector can adjust its distance to the seabed, the seabed is not a limiting factor.’
200 kilogrammes per second
With the sixteen-metre model, you can harvest eight square metres per second which comes down to approximately 200 kilogrammes of nodules per second. De Jonge: ‘Because the nodules are on the surface, we in fact have a 2D mine. That is why we measure in square metres and not in volume.’ The ratio of sediment/nodules is about fifty-fifty.
Aluminium and plastic
The vehicle is mainly made of aluminium. The black parts on the vehicle are made of high-density polyethylene (HDPE), plastic in fact. De Jonge: ‘It’s nice and tough and easy to handle. Moreover, it is easy to repair because you can weld it. That’s why we didn’t choose composites, because if it breaks, it’s really broken. We don’t need its strength for these tests either.’
Testing at sea
IHC did two tests in 2018 and 2019 on the research vessel Sarmiento de Gamboa, a Spanish ship in Spanish waters (300 metres water depth). Boomsma: ‘We planned two test runs because if a problem would be encountered during the first tests, there would still be time to make improvements or make the necessary repairs. And although the tests were very successful, there were a few mishaps.’
De Jonge: ‘The Apollo II is remote controlled from the ship. After the first launch, we found out the heading sensors stopped working below 100 metres water depth. On deck, they worked just fine. So, we had to control the crawler manually using a pinger for direction. Let’s just say the path we travelled was a winding one.’
Let’s just say the path we travelled was a winding one
Last summer, the second run took place. ‘We used a different underwater sensor this time,’ tells De Jonge. ‘We drove perfectly straight lines this time. Just set the course on the autopilot and drive.’
Watch a video of the first test run below.
This is the third in a series of four articles about deepsea mining. The final article will be published next week and will describe what is needed above water to make deepsea mining a reality. The full article has also been published in SWZ|Maritime’s January issue.