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Ewout van Duursen 25 Years: Monitoring the Hopper Process

Ewout van Duursen (l) and colleague installing monitoring software on TSHD Tommy Norton

Regularly, I do write about the adventures of a student internship or graduation that I am involved in. And it really helps those young aspiring engineers to be in the limelight of attention. Today there is a different story on my website, the 25 year work anniversary of my esteemed colleague Ewout van Duursen1. A fitting opportunity to celebrate his achievements during his long career at Damen Dredging Equipment. Ewoud’s specialties are drive systems and programming. And especially in applications for trailing suction hopper dredges. One of the products he has been working on tirelessly are hopper process monitoring systems2.

Dredge master console with hopper process monitoring installed

A good TSHD monitoring system will show a number of processes for operating a trailing suction hopper dredge.

Trailing suction pipe visualisation
Pump performance monitoring
Hopper loading monitoring and draught measurement
Survey and positioning
Recording and reporting

One aspect I want to highlight is the hopper loading and draught measurement. There are some details that might be confusing at first.

Screen shot of a sample hopper loading process

Take for instance a nominally 1000 cube hopper. It may be rectangular 32 m long, 9 m wide and 4 m deep, without any obstructions for simplicity. The mathematical capacity would be 1152 m³. But you don’t want to have the cargo spilling over the coaming. The maximum water level might be 0.5 m below the coaming making the volume 1008 m³. The maximum height of the telescopic overflow may be 0.7 m below the coaming level, as the water draws down about 0.2 m from stagnation level to the rim of the overflow. This measurable volume is now 950 m³.

Diagram of various hopper loading volumes

And the cargo does not only have volume, it also has a mass. And as Archimedes already discovered, mass displaces its weight in volume of water. During design of the vessel and the hopper, the loaded sand is assumed to have a certain density, e.g. 1.6 ton/m³. But the density for the hopper may only be 1.5 ton/m³, as one has to accommodate for the transport water that also enters the hopper. So, you can’t fill the 950 m³ with 1521 ton of sand. The vessel can only carry 1426 ton of total cargo. This is 713 m³ sand of 1.6 ton/m³ and 237 m³ mixture of 1.2 ton/m³. It sounds disappointing when your 1000 cube hopper only carries 713 m³ of valuable sand. The 1.5 ton/m³ hopper density is rather low and the vessel is probably more intended for silt and mud with a lower in situ density. With mud of 1.5 ton/m³ density, you can load the hopper to the rim. And when you encounter heavier sand with e.g. a density of 1.8 ton/m³, don’t try to fill the hopper with this 713 m³ mentioned before. You’ll sink your ship. A good hopper loading monitoring system will enable you to monitor filling of the hopper to the maximum safe cargo capacity.

Heavy weather dredging (Retrieved from YouTube 18/10/2012, unknown source)

References

CEDA Industry News: Snap Back Story out of the Old Stone Box

Cutter wheel dredge ‘Sylvia’ at work on the TIWAG Langkampfen power dam reservoir

You might have read the CEDA Industry News1 publication of September and the LinkedIn announcement2. Or, have been present at Session 10, The Story of Safety3 of the CEDA Dredging Days 2024, where I initially recounted my story of misfortune. For the uninitiated, I’ll shortly recount it over here, although the focus will be more on the design problem back than.

Me telling this story at the Safety Session of the CEDA Dredging Days 2024 (Credit: CEDA)

When I was fresh out of university, working for my previous employer, I was assigned to advise during the commissioning of a bucket wheel dredge in Austria. Here at my website, I’ve already mentioned a very peculiar problem we had with starting the dredge on Monday morning4. The whole dredge was a funny contraption, trying to fulfil the specific requirements set by the customer. The task of the dredge was to clean out the sediment caught in a silt trap5 in front of a power dam to prevent the material flushing through the delicate turbines. Furthermore, the fine sediment should be removed from the system to be sold for beneficial use, but the larger boulders that came along should be rejected from the system. Unless they were very large and stay in place for forming the liner of the silt trap.

General modes of siltation at the usual location in a reservoir

The proposed method was to use a bucket wheel to gobble up the larger stones, but leave the even bigger ones down at the pit floor. Additional advantage of the bucket wheel is that they tend to have a very low resuspension rate which is beneficial for reducing the turbidity in the river and save the dam turbines. However, the larger stones taken by the bucket wheel will not pass the dredge pump. A proven solution to filter out stones for the dredge pump is a so called stone collection box. They come in various executions, but this one was a large cylindrical vessel with a cover on top. Inside was a cage that connected to the inlet and outlet of the vessel. When the cage was filled, the lid was lifted by the crane and the attached cage came out. The cage was swung over to a barge alongside and the stones were unloaded through a trap door. Sounds straightforward, right?

General arrangement of the ladder and suction system on bucket wheel dredge ‘Sylvia’

The thing is, when you have anything in the suction pipe section, it will create a pressure loss and the pressure in front of the dredge pump becomes lower. Or higher vacuum, as you wish. This is already a problem for an inboard pump when you are working at sea level, even more so when working at altitude. The NPSHr is easily reached. In order to have enough NPSHa, even when the stone collecting box was filling up, it was decided to have a submerged dredge pump for increasing the pre-pressure. Consequently, the stone collecting box would also be placed on the ladder, in front of the dredge pump.

Explanation on NPSHr and NPSHa in mountains and submerged, including stone box

All in itself no problem. The disadvantage is that a submerged stone collecting box should be very strong, big and heavy to withstand the under pressure, although there is very little room around the ladder, the ladder itself becomes quite heavy and bulky and the submerged frontal area increased dramatically, increasing the total drag of the dredge in the fast flowing river current. To mitigate this, the ladder winch, the service crane and the 25 ton forward wire winch were all stacked over each other, so each could do it’s job independently. Although none of us ever did a collision check in the design phase of the dredge. In actual operation, they all were in each others way. When lifting the cover of the stone collecting box, it got caught by the forward wire. When lifting it further, it slipped of the side by the strong drag forces on the wire. I was to first to experience our negligence and got hit on my head when I was to eager to inspect the contents of the box. I blacked out, fell in the frigid water in the ladder well and woke up washed up on the ladder. My colleagues rushed me to the hospital, where I ended up between all sorts of winter sports injuries. Fortunately for me, I am able to recount my story and share it here and through the CEDA Industry News.

Annotated overview of the accident site where the wire slipped from the cover onto my head.

References

Second Thoughts On The Energy Transition Panel At the Latest CEDA Dredging Days

Energy transition panel discussion CEDA Dredging Days 2021 (Credit: CEDA)

The CEDA Dredging Days are long gone1. Maybe some of you still have a faint memory of the innovative online event. After this event I was quite occupied and not able to do a proper review. I did even miss the opportunity for the traditional new years welcome post. My apologies, more to that another time. Concerning the Dredging Days. I still kept some nagging thoughts about the Energy transition panel discussion that I want to share with you. And the recent invitation for participating in the CEDA Commission on Decarbonisation is another good motivation2.

On the second day of the conference there was a session with a panel discussion on the ‘Energy transition in the dredging industry’. Several experts in the dredging community were invited to present their perspective on the energy transition. From the legislation side (Dagmar Nelissen, CE Delft), clients (Joris Vijverberg, Rijkswaterstaat), suppliers (Benny Mestemaker, Royal IHC) and contractors (Sven Kramer, Van Oord). The panel was moderated by Paul Vercruijsse from the CEDA Working Group on Energy Efficiency3.

The take-aways of the panellists were amongst others: ‘No single solution for all, Transitional fuels should be flexible, Transition should be facilitated by regulation, There might be a financial objection to change.’ Along these lines, there were polls on the perspective of the audience. The response to two of the polls surprised the panellists.

Results on the polls for rate of transition (l) and preferred energy carrier (r) (Credit:CEDA)

As I was present there, I have my own perspective on the discussion. First the rate of transition. The panel was surprised that the audience was expecting a transition ahead of the IMO planning. I was responding to our own national situation. Currently I see so some initiatives to convert dredges and projects to electric drives, that it could be possible4,5,6. But I expect to see a next generation of newbuilds soon that will be virtually or completely decarbonized.

Well to propeller emissions (Credit: CEDA)

The other surprise is was the preference for hydrogen as the final fuel of the future. Although all the alternatives do have better performance, are easier to store or downright cheaper according to the experts in the panel. That might be very well, but I think the answer is in the presentation by Benny Mestemaker. It will simply be the fuel with the lowest emission to supply and use. In the end we will have to go to that dot on the horizon. And I do see other advantages where my opinion differs from the experts. The complaints of the panel was the complete lack of infrastructure for hydrogen at both the project sites and the vessels themselves.

Concerning the infrastructure near the project site. Yes, there are no installations yet. However, the thing is. You can find renewably generated hydrogen everywhere. As long as you have access to sun, wind and water. And that is exactly where most dredging projects are happening. Off course, there is no factory yet, but that is outdated philosophy. There will be movable plants available that will create a new market. e.g. I am very hopeful of initiatives like ‘Solar Duck’7. They can roam the projects delivering tailor made hydrogen production, right where you need it.

Floating solar power plant (Credit: SolarDuck)

Concerning the vessels. Yes, the installation to sail the vessel on hydrogen will take up a lot of valuable cargo space. But, that is no technical problem. We’ve had technologies that required an even bigger chunk of the vessel deadweight: coal burning steam ships. The big equalizer is: there was no other solution. Everybody was using it. And that is the same here. I think there will be no other solution than to use hydrogen, as it is completely emission free. One of my perspectives on design choices: select the solution that you know will solve the problem!
Transition schedule to convert to fossil fuel free dredging equipment

Transition schedule to convert to fossil fuel free dredging equipment

References

Comment

CEDA will provide access to the panel discussion shortly. Dredging Days attendees can still (re-) watch it on the conference platform.

Category: Dredge design

Ewout van Duursen 25 Years: Monitoring the Hopper Process

References

See also

CEDA Industry News: Snap Back Story out of the Old Stone Box

References

See also

Second Thoughts On The Energy Transition Panel At the Latest CEDA Dredging Days

References

See also

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