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

Novel Density Measurement By A Little Dredging Engineer

 

Design of an experiment to test a novel density measurement.
Design of an experiment to test a novel density measurement.

Innovative ideas need an open mind, not hindered by trodden paths of thought that limit one’s ability to be creative. And whose mind is open and flexible enough to trust such a task? Children! In order to keep me sharp, I sometimes discuss tricky problems at the dinner table with my daughter. Lately I presented her with the problem of density measurement in a slurry pipeline. There is a well-known technology: nuclear radiation dissipation detection. But there are already two words in that concept that we are asked to replace with a safer and more environmentally friendly alternative1. Her solution was to measure how much particles would stick on a glue lathered rod held in the mixture flow. During one of my daughter’s holidays from school, we took the opportunity to test her novel concept.

Preparations for the density measurement experiment.
Preparations for the density measurement experiment.

If this is going to be a novel measuring technique, we should prove, that there is a relation between the amount of particles sticking to the glue and the density of the mixture. This had to be tested in a controlled experimental environment: a bucket. We filled it with a known amount of water and by adding sand to it, we gradually increased the density. There were several types of glue to be tested, which we applied to short pieces of PVC tube. Glues we considered were: hobby glue, mounting kit, wall paper glue, contact adhesive and duct tape. There was one reference tube with no glue. We kept the samples in the mixture for 30 seconds, while vigorously stirring the slurry with a mixing drill.

Density measurement in progress.
Density measurement in progress.

Before and after the sample was dipped in the slurry, we measured the mass of the sample on a scale. The difference in mass should represent the amount of particles that stuck to the glue. These differences were recorded and plotted in a graph. Surprise! There is a distinctive trend in the data points that would support our hypothesis on the relation between mixture density and particle capture.

Results of the density measurement.
Results of the density measurement.

Some remarks on these results. There is a wide variation in trend lines. Some of the samples became lighter than they started. Probably, because they dissolved in the mixture. The measurements for the 600 and 1200 grams of diluted sand is notable. This is probably related to an observer variability. The strongest relation between mixture density and grain capture is with contact adhesive and duct tape. Interestingly, the best predictor for the average capture over the glue types was the reference tube. Probably, the water clinging to the tube already contained enough particles to result in a measurable signal.

It was fun to do this exercise and the results are interesting. But, I doubt we can make a viable product out of this concept. In the dredging industry, we prefer a non-invasive technology, the sample rod would be knocked out in seconds. Several manufacturers are already developing alternatives2,3. In our ¡VAMOS! project, we tested one concept, that seems very promising and you will definitely hear more about it in due time. It is time to say good bye to the nuclear density sensor and adopt technologies that are future proof. Our children will be grateful if we leave them a better world.

Non-radioactive density measurement (Credit: ¡VAMOS!).
Non-radioactive density measurement (Credit: ¡VAMOS!).

References

  1. Regeling bekendmaking rechtvaardiging gebruik van ioniserende straling, Staatcourant NL
  2. Magnetic resonance multiphase flowmeters, Krohne
  3. ITS exhibiting at Europort and CEDA Dredging Days 2017, ITS

See also

Production management, Damen

Discussion at LinkedIn post