Happy 2019!

Post card picture of a Damen CSD500 at work.

Happy New Year! First of all, I would like to wish you: health, happiness and a year full of dredging action. And there will certainly be some dredging action. We will start this year with closing our ¡VAMOS! project and we will close off with another CEDA Dredging Days1, just as with which this blog started one year ago with a new year’s resolution.

Further topics will include the upcoming WODCON conference in Shanghai2, more CEDA Dredging Management Commission, some interesting book reviews and whatever happens along the way. Maybe I can get back on working on articles that explain interesting phenomena in dredging technology. Or just some funny experiences I had in our beautiful profession. There are so many memorable moments worth sharing for the general benefit.

And George Santayana has warned us to learn from the past: ‘Those who cannot remember the past are condemned to repeat it.’3 I don’t fancy that this site will be a monumental source of reference for posterity. There are much better institutes to store and share dredging knowledge. e.g. the CEDA comes to mind. It’s ‘a forum for all stakeholders involved in the dredging industry’4 and there are many working groups were the current knowledge is shared and stored in publications.

A much better place to look at a condensation of knowledge over a longer time span is the National Dredging Museum5. You might have noticed, that I am very fond of museums. I like to dwell through their expositions, relive the past and see the origins of current technologies. When I am trying to hatch some new sort of gizmo or gadget to perform a very peculiar dredging requirement, I can relate to all those branches of the technology tree, that are out there and see if there is something that can be combined in a new contraption.

Model of a ‘Krabbelaar’ or ‘Scratcher’ at the National Dredging Museum.

Sometimes you can recognize some technology in an exhibit, that was ahead of its time. Take this ‘Krabbelaar’ or ‘Scratcher’. It loosens the top layer of the sediment and expected it to flush out at the outgoing tide. Considering the enormous forces for cutting and internal friction, that have to be delivered by sail power, I doubt the production would make a viable business case. Nowadays, you would employ a dredge plough behind a tug6. Modern propulsion delivers the thrust needed for all requirements. Ploughing, scraping and smoothing has become much easier and modern hydrological simulations will give a better idea about the possible production and where the sediment will end up.

Example of a modern dredge plough, fitted on a Damen Stan Tug 1606.

Possibly our modern dredge plough technology will be surpassed by even better concepts. Maybe, regulations or fuel economy would direct us back again to a sustainable form of dredging management and the old scratcher makes a comeback in a modern form. And then, you know to find the origins in the National Dredging Museum.

I think, it is very important, we cherish our dredging heritage. For ourselves and for our posterity. Just as we support our trade associations, we should support the dredging museum. So, now I come back to my ‘new’ new year’s resolution: I will become patron7 to the National Dredging Museum. It is not much, but if it inspires you to do the same, we can make a difference together.

Collection of dredges.

References

  1. CEDA Dredging Days 2019, CEDA
  2. WODCON XXII, CEDA
  3. George Santayana, Wikipedia
  4. Our mission and strategy, CEDA
  5. National Dredging Museum
  6. Scrabster Harbour takes delivery of Damen Stan Tug 1606, Damen
  7. Sponsoring 2018, National Dredging Museum

See also

Ploughs, Beams and Rakes, IADC

 

 

 

Alternative Fuel Systems on TSHD Samuel de Champlain

Trailing Suction Hopper Dredge ‘Samuel de Champlain’

The Trailing Suction Hopper Dredge ‘Samuel de Champlain’ has been in the news. She will get a mid-life upgrade with new engines running on LNG1,2. This is good news for the environment as the vessel will have lower emissions of greenhouse gasses. And it is good news for Damen as we see this old lady back again. Already more than ten years ago, we had her also as a customer concerning a gas related retrofit3. That time I was involved in the development and commissioning of that particular system.

Degassing installation on board ‘Samuel de Champlain’

The most peculiar feature of this degassing installation on this ship was that it had to work on the submerged dredge pump. Even as the pump had plenty of NPSH available at that depth, the gas content at certain locations was able to choke the pump. The submerged location posed special requirements on the operational pressures and the dimension of the sludge tank.

Off course, the most simple solution would be to have some gas ejectors on the drag arm and just blow the foam from the degassing scoop overboard altogether. However, that mixture contains (possibly contaminated) silt also, which is unscrupulously released to the environment. The Damen system has some extra components, such as a sludge tank, where the foam is separated in silt and gas. And a separation tank, where the gas is extracted from the clean water. Gas is than released to the atmosphere and the water returned to sea. As the sludge from the sludge tank is injected back to the slurry pipes, it ends up in the hopper and is disposed of with the rest of the silt.

Diagram of a typical Damen degassing system

An often heard complaint is, that the gas is still released to the atmosphere. That is right, but with the other systems it is released in the sea and comes in the atmosphere in bubbles. On top of that, one could also look at the natural process of gas formation4. If it is not dredged the gas would eventually get released by nature itself. With the autumn and winter storms, the bottom gets disturbed enough to release the contained gasses and enter the atmosphere naturally. The dredge only releases the gasses in a concentrated form, where nature does this gradually.

Another question I was asked regularly (and fitting to the opening article): ‘Can we capture the gas to drive the engines?’ That in itself is a good question, as it disposes the gasses beneficially. The degassing installation on board is capable of removing 800 kg/h of gasses from the mixture. If it were LNG, it would provide about a quarter of the energy requirements of this vessel. But, it is not LNG, only part is combustible methane, the rest doesn’t burn or forms sulphuric acid. Yuk! Certainly not something to pour in your expensive engine. It might be easier to just flare the whole mixture4. At least the potent greenhouse gas methane is converted to the less severe carbon dioxide. Any thought anyone?

It was fun to contemplate on this during the return trip from the commissioning. It was already running late (which commissioning doesn’t?) and we were 20 miles out at sea. The captain didn’t want to stop the dredge and he put us in the dingy to return to port. With calm seas and a fast RIB, this was a thrill ride to remember.

Return trip after a job well done

References

  1. TSHD Samuel De Champlain to be converted to LNG in a European firs; Damen Magazine
  2. Damen Wins Contract for First European TSHD LNG/MGO Conversion; DredgingToday
  3. Retrofit Degassing Lifts Dredger Efficiency; Maritime Journal
  4. Gas flare; Wikipedia

See also

A Reservoir of Dredging Opportunities

Glendo Reservoir in Glendo State Park, Wyoming, USA (Credit: Wikipedia)

OK, sorry, above picture was not taken by us, but could have been in our annual picture book. At this place we had only one mission and that was to watch the 2017 solar eclipse. It took more, than two years of preparation and we were rewarded. With great care we inspected the statistics on cloud cover maps and local geography for the best place to watch this event. The Rocky Mountains in the west block the clouds, the dry planes on the east have a clear horizon, combined with a favourable timing, we selected Glendo State Park, Wyoming, USA to pitch our camp and watch.

Eclipse party at Glendo State Park, Wyoming, USA

We pitched our tents at one of the campsites in the park. This time, the soil had a much higher SPT than at Bad Bear Campground. Although at the top of a hill overlooking the reservoir, the trees prevented to take a good picture of the lake. Hence the Wikipedia picture. The lake was built for power generation, irrigation and recreation. The dam was constructed between 1954 and 1958 as a zoned earth fill structure. Projected lifespan was for a 100 year accumulation. Mmh, clean greenhouse gas free hydroelectricity was eternal, wasn’t it? Well, not so much.1 The dam blocks of some part of the watershed and this will always be a disruption of the natural sediment transport.

General modes of siltation at the usual location in a reservoir

Due to the creation of this artificial lake, there are several areas that have specific siltation problems. At the upper end of the lake, where the river slowly stalls, the bigger particles will settle in the immediate vicinity of the entrance. Smaller, lighter particles will be carried longer, even all the way to the dam. Usually there is a facility near the dam to prevent (re)suspended particles to enter the gates. A common solution is to have a silt trap, a deeper area in front of the dam. The suspended solids behave like a denser fluid and tend to sink in the lower areas and the cleaner, lighter water is skimmed away for sluicing through the dam. Without any action, the reservoir fills up eventually. By now, a lot of reservoirs are already not performing anymore to their specifications.

Total capacity of all reclamation reservoirs over time (Credit: US Bureau of Reclamation)

There are several options to perform reservoir maintenance.2 The most spectacular method is flushing. The reservoir is drained quickly, over a special by pass channel.3 The idea is, that as the water table is lowered, the cross section of the water body decreases and the velocity increases. Hopefully, the current increases enough to pick up material and by pass it along the dam.

Flushing of a reservoir dam (Credit: US Army Corps of Engineers)

As a right minded dredger, I am always a bit disappointed that there is no dredge present to solve the sedimentation problem in a more sophisticated way. In a way, I have some experience in actually building a power dam dredge. But that will be another historical narrative.

Let me conclude this series of reviews from our annual picture album with the one single picture that was the cause and culmination of our special holiday in the United States: the Great American Eclipse.

2017 Solar Eclipse at Glendo State Park, Wyoming

References

  1. Hydroelectric power’s dirty secret revealed, New scientist
  2. Formulating Guidelines for Reservoir Sustainability, USBR
  3. Annual sediment flushing exercise scheduled at Cherry Creek Reservoir, USACE

See also