Innovations In The New MAD Series To Increase Uptime And Reduce Fuel Consumption

Innovative Marine Aggregate Dredge for gravel dredging
Innovative Marine Aggregate Dredge for gravel dredging

This week, there will be a lot of interesting presentations at the CEDA Dredging Days 2019 in Rotterdam1. I would like to draw your attention to one particular presentation that I was involved with at certain moments in the project, though not in writing the paper. Kudos to my colleagues Frank & Frank to write the interesting manuscript2.

The topic of the presentation will be the change of perspective for the concept of marine aggregate dredging. Historically, the marine aggregate dredging takes place relatively close to shore. With the depletion of the deposits and the increase in demand, other locations further out at sea are coming into focus. As Damen, with a heritage in the design of offshore operating vessels, it was a natural choice to cross breed the offshore supply vessels with the marine aggregate dredges. The resulting offspring: the MAD series of hopper dredges3. Frank de Hoogh will elaborate on the seakeeping abilities of this innovative design.

Other dredging related innovations are the suction tube and ancillary equipment, the screening towers and the process sensors. Of those, I have some personal anecdotes on the screening towers and the density sensor. For all other interesting stories, you’ll have to attend the presentation.

The screening towers are fundamental to the efficiency of the process. If the screening is improved, shorter dredge cycles are possible and a better product can be landed onshore. Also, if the requirement for the product change, the screens have to be adapted to the new specifications. Ideally, this changing has to be done at one unloading phase, otherwise you miss a complete dredge cycle. A lot of effort has been done to optimise the design. But the real test was to actually build, modify and test the complete screening tower, before it was even installed on the vessel. So, we had this construction right here at our doorstep for a thorough evaluation.

Screening towers for fit and fat testing at our yard
Screening towers for fit and fat testing at our yard

One other component, that I was even more involved with, was the non-radioactive density sensor. There are regulations in place to phase out nuclear density sensors4 and a lot of alternatives are available. Back in the !VAMOS! project5, we had the opportunity to test a unit of an electro tomography system. The results indicated a good reliability and a worthy replacement for the traditional nuclear sensor6. Because of the tomography picture, there was an additional benefit: we received an early warning on the slurry behaviour. We could actually see when we were too close to the deposition limit in the pipe line. This enabled us to work with higher densities at lower velocities, resulting in better efficiency and less wear. As the rough process conditions in the mining pit were similar to the marine aggregate dredging industry, we proposed to use this on this MAD also. How we further developed and tested this system is for you to hear and see at the presentation.

Testing the non-radioactive density sensor
Testing the non-radioactive density sensor

Due to the physical processes involved in slurry transport, the mixture does not behave like a normal Newtonian fluid. It is some non-linear viscous substance. At high speeds and low concentrations, it is similar to the carrier water. Slowing down, there is a certain critical speed, where there is a minimum hydraulic gradient. At that flow condition, the specific power consumption of moving a cubic meter of soil is the lowest. So, although working at critical speed is dangerous, it has its advantages: low fuel consumption and less wear. Actually seeing the mixture approaching this critical speed from the deposition is an interesting feature of this new density measuring sensor.

Explanation on slurry flow conditions, critical speed and specific power consumption
Explanation on slurry flow conditions, critical speed and specific power consumption

References

  1. CEDA Dredging Days 2019, CEDA
  2. Next generation marine aggregate dredger as platform for innovation and basis for fleet renewal, CEDA
  3. Damen unveils Marine Aggregate Dredger, Damen
  4. Regeling bekendmaking rechtvaardiging gebruik van ioniserende straling, Staatscourant
  5. Project ¡VAMOS! Let’s Go Real!
  6. Real time production efficiency based on combination of non-nuclear density and magnetic flow instrumentation, WEDA

See also

Project ¡VAMOS! Let’s Go Real!

¡VAMOS! equipment on trial at Lee Moor, Devon, UK.

One month ago, we concluded the ¡VAMOS! project with a presentation at the European Commission headquarters in Brussels1. A relieving event after an amazing project. It all started long, long ago, when several people from the early partners came together and their creative minds forged a brilliant concept: let’s apply the experience from the off-shore mining machines to submerged inland mines, to retrieve minerals, which currently are not profitable to exploit2.

There were three major questions in the project:

  1. What will the production rates be in relation to the minerals that can be expected?
  2. How do we find out, where the valuable mineral is in a submerged environment?
  3. Is the alternative system indeed as easy to handle and environmentally safe as envisioned?

All these issues have been addressed in various work packages. As this was not a desk study or a lab experiment, we needed real hardware to test in field trials. A mining vehicle, a hybrid ROV and a barge to launch the others. The engineering and building was interesting in itself, but the real test was in the two field trials. All the equipment and the people had to perform there. And after all these years since I helped writing the project proposal, it worked! I love it when a plan comes together!

All three research questions can be answered positive. We know how to handle such a system and the hardware required. It will definitely look different than the test vehicle. Here we optimized the engineering for the test, not for production or operation. But we definitely know how to configure the components in a viable operating system. The cutting system was tested to the limits, and production rates estimated. This machine was too light as a production model, but the cutting technology will be able to handle the hardest mineral, as long as weight and power can be applied. As there is no direct vision under water, we developed a data fusion system, where measurements from video, laser, sonar and GPS where the environment was presented in meticulous detail and the vehicle completely modelled in geometry, position and movement. At the pit floor, we were literally driving in virtual reality. The machine created some turbidity, deteriorating vision, but it happened to be less persistent than initially thought. The influence from precipitation runoff into the pit caused more turbidity. All together, we also prepared several business cases for this system against a conventional solution and there are certainly opportunities for a ¡VAMOS! solution.

Results from ¡VAMOS! (a) Cutting tests (b) Virtual vision (c) Equipment handling (d) Viability example (Credit: ¡VAMOS!).

The EU was also very interested whether clients were lining up for the real product. However, investments in the mining industry are slow, long term projects. Our main objective was to find out the operational parameters and present this as a viable alternative to conventional system. And that is what we’ve achieved. And the technology has matured enough, that when there is an opportunity for such a requirement, we are confident, that the tested components can be scaled to production size and readily applied. As a research project, we are finished. At each partner, we will still be working on the test results and improving our technology further. For the interested customer: we are ready to offer a production model. ¡VAMOS!: let’s go for real!

A happy team after concluding the ¡VAMOS! project.

References

  1. The outcomes and the future of the ¡VAMOS! project, ¡VAMOS!
  2. Developments in Mining Equipment and Pumps for Subsea and Inland Submerged Deposits, WODCON 2013

See also

Discussion at LinkedIn post

Sunken Treasures From ¡VAMOS! At Silvermines

Overview of the ¡VAMOS! test operation in the Magcobar Pit, Silvermines, Ireland

Last week, I was at a test site for the ¡VAMOS! project. It was in the abandoned Magcobar Pit1. Well, only in ancient times, people have been digging for silver at this location. In 1963 the site was opened for a large scale operation to mine Baryte2. A mineral used in the oil industry. After the veins ran out in the open cast mine, they continued underground, extending the tunnels almost to the next mine in an adjacent area. Then they had to stop operation altogether and the pit got filled with water from a small river that now enters in an attractive waterfall. So far the historic perspective of this site. Currently the forgotten mine is bustling with activity. So many people and equipment was brought in from all corners from Europe, it looked like a circus has come to town.

The ¡VAMOS! road show on its way to Silvermines, Ireland

When I came there, the team had already set up camp and assembled the Launch and Recovery Vessel. The Mining Vehicle was ready to be deployed and we could commission and test the special drive we had provided for the project3. Another item we had to commission was the dewatering facility. Well, it is a fancy name for a dump area. Basically, it is a reclamation area, where we can collect the material that has been cut by the mining vehicle and was pumped through the discharge line to the shore. We had one pond for collecting the cuttings and one pond for containing the fines. Eventually all effluent water was skimmed trough an overflow box.

Overview of the dewatering facility

As there might still be some very fine material contained in the overflow water, we wanted to dispose the water at a lower level than where we were going to do the cutting tests with the mining vehicle. This would ensure clear visibility and an undisturbed background turbidity for the effects measurements. A submerged pipe line for dredging is a well-known component in the dredging industry. If e.g. a discharge line of a cutter suction dredge has to cross a busy fairway, the discharge line is submerged under water, so the traffic can pass without interruption.

Example layout of a submerged dredge line

There are several issues to pay attention to. Selecting the right diameter is the first to consider. You definitely don’t want to block the submerged dredge line. In order to reduce the critical velocity and increase the mixture velocity, the diameter of the submerged pipe is usually chosen a bit smaller than the rest of the pipe. Furthermore, you don’t want any air get trapped in the submerged line. Air inside the line will make the pipes float again, usually at the most inconvenient moment and probably damage the line. Positioning the submerged line can be done by actually having the air in the line slowly escape. The line will lose buoyancy and settle on the bottom. Injecting compressed air will float the line again.

Deployment of a submerged dredge line

The mining we are doing at the Magcobar Pit is solely for scientific purposes. The material we gather and sample will not be used. But, we hope our technology will revive some disused mines again to their former glory. At least get some people back at work. There are a lot of little villages that fully depended on the activity of the mine. The little town of Silvermines is still remembering those good old times with a little monument to commemorate a glorious past4.

Memorial for the mining industry in the town of Silvermines

References

  1. ¡VAMOS! preparing for second field tests in Ireland, ¡VAMOS!
  2. Baryte, Wikipedia
  3. Dual Stage Dredge Pump and Double Action Pump Drive for ¡VAMOS!, Discover Dredging
  4. Silvermines, Wikipedia

See also