HYDRO 2018 Gdansk: Selecting A Dredge For Your Reservoir Maintenance

Barrage du Ksob, M’Sila, Algeria with a DOP dredge 350

This week, I am here in Gdansk for a presentation on the HYDRO 2018 Conference1 and assist at the Damen booth at the corresponding exhibition. The paper and the presentation are already prepared and I am very excited to do the presentation, but I can’t wait till tomorrow and I like to share the story now, already. So, you, as my favourite audience, will have my personal spoiler after so many teasers have been floating around2,3,4.

General modes of siltation at the usual location in a reservoir

The thing is, dam maintenance and reservoir restoration is something already long on my attention list. Back already in 2008, I wrote a paper on this subject for the CEDA Dredging Days5. Over and over we’ve conveyed the message on various platforms, that dredging might be a viable solution for sedimentation problems in reservoirs. Usually, the solution by dam owners and operators is to flush, sluice or store the sediment. This looks horrible from a dredging perspective, but it is also to the environment. You either smother or starve the downstream river with sediment. As a right minded dredge enthusiast, you see many possibilities to dredge such a project. Immediately we can identify what dredge to use on which location for which purpose.

Selection of applicable dredges for reservoir dredging

If you are very close to the dam and the length of the discharge line allows it, you might even not need a dredge pump. (No wear parts!) It is a so called siphon dredge. But as soon as there is some further transport involved, either distance or uphill, you need a dredge like a cutter suction dredge or a DOP dredge. For even further discharge, you might employ a booster for increased discharge pressure. If the distance becomes very far, you might have to resort to grabs and barges.

Water injection dredging principle and example (this example would be too big for a common reservoir)

As an intermediate solution you might even consider using a water injection dredge. Usually the reservoir is in the mountains and a bottom gradient will be present, enabling the required gravity flow. The actual dredge should have created a silt trap where it can collect the inflowing material from the water injection dredge. Than it can handle the material as usual.

Alternative uses for the dredged sediment a) silt farming as fertile additive b) gravel extraction for concrete

Off course, the dredged sediment belongs to the river and the best thing would be to gradually release the sediment after the dam. But there might be conditions, where it is beneficial to extract the valuable fraction of the sediment and use it for agriculture or as aggregate in the construction industry.

Dredge selection diagram for reservoirs

We noticed, that it is often difficult to convey to dam owners and operators which dredge to select for which job. Sediment is seen as a liability and not as an asset and they rather neglect issues associated with the sediment. So, I made an attempt to have a plain and simple selection diagram. That is the core of my manuscript. But my objective is, that we will see many beautiful dredges contributing to a sustainable and viable operation of hydropower dams and reservoirs.

New DOP dredge family

References

  1. HYDRO 2018: Progress through partnerships, Hydropower and Dams
  2. LinkedIn Teaser, Saskia den Herder
  3. Damen: Spotlight on Hydro Power Dam Maintenance
  4. LinkedIn Teaser, Olivier Marcus
  5. Multi Functional Small Dredging Solution For Maintenance Of Deep Irrigation Reservoirs And Hydro Power Dams, CEDA

See also

Dredging Exhibits At The National Maritime Museum Gdansk

Overview of the National Maritime Museum in Gdansk, Poland

Currently I am in Gdansk, Poland. Last week I had a CEDA event1 and next week I am at the Hydro 2018 Conference and Exhibition2. On both events I will report later. My colleague Saskia den Herder wrote a teaser for you3. Now, here, I had the weekend for myself and what better to do, than be a tourist, visit a maritime museum and write a blog about it. So, I will report you about interesting dredging exhibits I discovered at the National Maritime Museum in Gdansk4.

The National Maritime Museum comprises three major venues: the museum building itself5, the ‘SS Sołdek’6 and the old city ‘Crane’7. All equally interesting in their own way. Buy a combined ticket and you get the ferry between them for free. As general maritime museums go, they mainly focus on the history of shipping, shipbuilding and the interaction with the development of the city or country. Gdansk in itself has a very long history in shipbuilding, as the country was well forested for providing the building material for ships. In modern times, one might have heard of the ‘Lenin Shipyard’8, the birthplace of the free labour union ‘Solidarity’, which brought Poland out of the socialist led economy. And of course, where there is water, there are ships and where there are ships, there is Damen9,10.

Horse powered scoop ladder dredge

Between the many models and pictures I found some about dredges indeed. This one seems to be a very first attempt at mechanical dredging. The power was provided by two real horses. There were some sort of scoops or blades drawn over a chute. The wooden blades excavated the soil from the bottom. Water was expelled through holes in the blades. The drained material could be loaded in barges for further transportation. Only after translation later on, I learned that in fact this was an example of a Dutch dredge!

Picture and model of a steam powered bucket ladder dredge

I did find a picture and a model of a locally build dredge. It employs a German steam engine and was built on an oak hull. It already featured the classic iron buckets on a ladder. The development of the working principle did not change that much. The dredged material could be delivered to barges at the aft end for further transport.

Grab dredge ‘Homar’

Finally I came across this model. It is a grab dredge ‘Homar’11, built in 1971 and operated by PRCiP Sp.z o.o. (Dredging & Underwater Works Co Ltd) here in Gdansk12. OK, I don’t want to brag, but it looked vaguely similar to the one we saw when we were on a site visit with the CEDA to the Port of Gdansk13. We had a splendid view over the harbour from the port control tower. And there I already noticed they were doing some dredging works in the entrance channel. But for all what we could see, it could also have been its sister ship ‘Świdrak’. And that concludes a nice round up of dredging discoveries for the weekend.

Overview of the entrance channel as seen from the port control tower. Dredging works indicated.

References

  1. CEDA-MIG Joint Symposium on Advances in Dredging Technology 2018
  2. HYDRO 2018
  3. Dam maintenance – deep dredging, Saskia den Herder
  4. National Maritime Museum in Gdansk
  5. Granaries on Ołowianka Island, NMM
  6. Sołdek, NMM
  7. Crane, NMM
  8. Gdanks Shipyard (Lenin Shipyard), Wikipedia
  9. Damen Engineering Gdansk, Damen
  10. Damen Marine Components, Damen
  11. Homar, Dredgepoint
  12. PRCiP
  13. Port of Gdańsk

See also

Dual Stage Dredge Pump and Double Action Pump Drive for ¡VAMOS!

 

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

These days I have been very busy drafting a manuscript about our ¡VAMOS! project results1 for a dredging conference paper. As every writing process, there is so much to tell and so little space available. At a certain moment there follows a phase called: ‘kill your darlings’. You have to scrap parts that contribute less to the main message of the article. Still some of those orphans are worth sharing. So here is a part from the paper that might be interesting for you.

For those unfamiliar with ¡VAMOS!, it is a Viable Alternative Mining Operating System2, where we are cooperating in a 17 partner consortium to develop equipment and procedures for exploiting mineral reserves in disused or currently unavailable mines in the EU3. Many mines are disused, but still contain some reserves, that are unrecoverable due to an uneconomic stripping ratio4.

Schematic of typical vertical ore body in an opencast or submerged setting (Credit: ¡VAMOS!)

We developed a prototype mining vehicle (MV) and an accompanying launch and recovery vessel (LARV)5. Although the requirement for the slurry circuit on the MV are deceivingly similar to a normal dredge system, there is one fundamental difference in character: vertical transport. At the system architecture phase we assumed a dredging depth of at least 100 m. For clean water, this poses not so much of a problem, once pumping mixture is where the geodetical height difference comes into play. At 100 m a 1500 kg/m³ mixture requires an additional 5 bar of static head.

Influence of vertical riser on the head requirements of a dredge pump

The dredge pump has to cope with the large variation in head requirements. For the prototype machine, the only option is to vary the dredge pump speed. Still at a normal operating condition, we expected a head requirement for 10 to 16 bar. This is why we developed a dual stage dredge pump, it delivers double the head of a normal dredge pump.

The variation of the pump speed has been accomplished by various controllers working together. The power is generated on the LARV by a diesel engine driving a generator. A frequency drive supplies a hydraulic power pack on the MV. The power pack has a variable displacement pump for controlling the flow. At the dredge pump side there is also a variable displacement motor.

¡VAMOS! prototype drive train arrangement

With this setup in place, the dredge pump can vary between a slurry circuit just filled up with clean water and a fully filled riser with heavy mixture at the operating point. On top of that, there will always be the possibility, that the density increases even more. The flow will reduce and so will the power consumption. This enables the drive to increase the speed for extra oompf of the dredge pump to clear the riser. Where normally the dredge pump speed is controlled by the pump swash plate, the motor swash plate is so to speak the turbo boost. This is similar to a constant power drive for normal dredges, but the vertical riser makes the problem more pronounced.

So, not only the starting up of a dredge pump should be considered in the design of the drive train, but also the variations in operating point. Regarding the comments I received on my last post, yes indeed a production model of the ¡VAMOS! system would have an all-electric drive. Just be sure to have enough copper in the motor to cover every possible operating point.

Dual stage dredge pump with constant power drive mounted on a crowded MV equipment bay

References

  1. Successful demonstration of ¡VAMOS! technology in UK
  2. ¡VAMOS!
  3. Strategic Implementation Plan for the European Innovation Partnership on Raw Materials
  4. Developments in Mining Equipment and Pumps for Subsea and Inland Submerged Deposits, Kapusniak et al. WODCON 2013
  5. ¡VAMOS! reaches Design Freeze Milestone

See also