We Choose To Adopt Energy Transition, But How Will We Succeed?

President John F. Kennedy speaking at Rice University on September 12, 1962 (Credit: NASA)
President John F. Kennedy speaking at Rice University on September 12, 1962 (Credit: NASA)

‘We choose to go to the moon.’ Was the famous speech at Rice University of President John F. Kennedy to express his ambition to send his nation to the Moon1. At the time, his call was far from clearly achievable. But it was a very clear roadmap and it quickly gained traction. The success of the Apollo project is well known. Neil Armstrong did land on the Moon within a decade and the American flag is still planted on its surface.

Panel discussion at the CEDA Dredging Days 2019 with Mike van der Vijver
Panel discussion at the CEDA Dredging Days 2019 with Mike van der Vijver

At the CEDA Dredging Days 20192, there was an interesting panel discussion on ‘Energy transition: the views in our dredging community’3. Panel members were: Eric de Deckere, Michael Deruyk, Kaj Portin and Klaas Visser. The discussion was moderated by Mike van der Vijver from MindMeeting. As an introductory teaser to the audience, he posited the claim: ‘Excessive ambition drives breakthroughs’. The question is: ‘Is the dredging industry ambitious enough to convert to a new fossil free energy source?’ The audience was polled for their opinion on a scale from one to ten and the response ranged from three to eight. The three represented the position, that the industry is not doing much. What is visibly done, are only single purpose, company specific solutions that are not adopted by the community. On the other hand, there was also a very positive signal with an eight for ambition. The sense of urgency is very well present in the community. Most companies are developing plans and cooperating in working groups, such as the CEDA Working Group on Energy Efficiency4. Also, the government is pitching in with initiatives on zero emission maintenance dredging, where the dredging community is actively participating in putting forward proposals.

So, why is there still no zero emission dredge? What is the ambition lacking? The hint is the opinion that the effort is not focussed. The strong motivation in Kennedy’s speech was that there was a very clear picture what to do. What do we do: ‘Put a man on the Moon’. When: ‘By the end of the decade’. How: ‘Bring him safely back’. Ambition with a clear plan can indeed achieve great things. Ambition without motivation will only bring daydreaming and lethargy.

Block diagram of influencers for energy transition in the dredging community
Block diagram of influencers for energy transition in the dredging community

To achieve something, we need motivation. And who is responsible for pulling this off? Mike polled the audience again for: 1) Government, 2) Public opinion, 3) Companies, 4) Technology. There was not a clear picture here either. All positions are valid. Another driver is the reward for the effort. The Apollo project effectively created part of our modern society. What would the energy transition yield for the dredging community: ‘Learning by challenge’, ‘Flexibility and resilience in energy generation’, ‘Low maintenance and higher independence’?

At this website I can’t change the world, but addressing most issues mentioned, I can only put forward my idea on the ‘How’ motivation. We know how to apply power. As long as the power arrives electrically, we can use it. Essentially, we have to generate electricity with a flexible power source. The investment lifetime of a dredge often exceeds 30 years, but under the current circumstances, the power plant only lasts ten. The solution would be to have some separate module for power generation. Either locally, near the dredge, or remote at the end of the pipeline. As every project and application will be different, it will be a challenge to design the specific solution. But I am looking forward in developing the solutions below with any interested customer5.

Transition schedule to convert to fossil fuel free dredging equipment
Transition schedule to convert to fossil fuel free dredging equipment

References

  1. We choose to go to the Moon, Wikipedia
  2. CEDA Dredging Days 2019, CEDA
  3. Programme 7 November 2019, Panel Discussion, CEDA
  4. CEDA Working Group on Energy Efficiency, CEDA
  5. Innovation at Damen Dredging Equipment, Damen

See also

Sensing My Audience, Feedback On How To Drive DOP Pumps

DOP pump and power pack, ready for commissioning.

This website provides me a platform to share my knowledge about dredging as far as my experience reaches. Sometimes, I do training sessions with colleagues or clients. They give me the opportunity, as an academically educated dredger, to experience how our figments of imagination work out in real life. People from different countries and lifestyle share their experience with our products. I really enjoy those sessions, they give me feedback on my normal work. Some of the topics on this website are directly related to the topics I present on those sessions. One of the recurring issues might not be that obvious at first hand. So, this post results from this feedback, aptly concerning the feedback loop in a load sensing circuit in a hydraulic drive system, specifically for a DOP.

The most common arrangement for the traditional DOP drive is to have a separate (preferably co-purchased) hydraulic power pack1. The power pack we supply is specifically designed to drive the dredge pump in the DOP. This requires the extra investment of a hydraulic power pack. Whereas most hydraulic cranes and excavators, that can handle the DOP pump by weight, will also be able to divert some hydraulic power to an auxiliary connection or so called Power Take-Off or Aux PTO. Especially when the excavator is working with a standard suction head, not much motion and forces are required for other functions. So, naturally clients tend to propose to use their DOP driven on the hydraulic PTO. This could be possible, but only under very strict conditions. And here comes the advice after commissioning hundreds of those units: ‘Don’t use the load sensing feature of the hydraulic PTO!’ Why? Let’s study the hydraulic diagrams.

Hydraulic diagram DOP pump and power pack.

The standard arrangement of a DOP is quite straightforward. As long as you do connect them in the right fashion. By controlling the angle of the swash plate, you control the delivered flow from the hydraulic pump and the rotational speed changes accordingly. Any load changes at the dredge pump result in pressure changes in the circuit, without changing the pump speed.

Typically, excavators do have a different power characteristic. When freely raking the stick, they encounter little resistance at preferably a high speed to reduce cycle time. When they hit the ground, the resistance or load increases and they typically lower the flow to maximize power delivery. They do this by connecting the pump line to a control line that influences the angle of the swash plate. Effectively, this results in a feedback control loop.

Infographic feedback control loop in a load sensing circuit.

And here comes the trick. Feedback control loops are designed to be stable. But the varying load at the dredge pump, in combination with the masses in the hydraulic lines, the springs in the rubber hoses and the damping of the flow losses, make the sensitivity of the control loop irrelevant. The signal from the dredge pump load is lost and becomes out of sync with the required action at the LS port of the pump. Any random static will make the swash plate rattle and usually in an instant, the drive stops. Other than maybe a blocked dredge line, no harm is done and service calls to our colleagues2 will resolve the issue: ‘modern excavators will allow you to turn of the Load Sensing feature’. Or, purchase said dedicated hydraulic power pack.

Damen hydraulic power pack mounted on a crane.

I would like to acknowledge Wim Roeterdink for his advice and review of this post. He is an expert on hydraulics engineering and he is always available for assistance in your particular hydraulics problem.

References

  1. Hydraulic power packs, Damen
  2. Service, Damen

See also

Parker hydraulic pumps

Perspective on Commissioning – Connecting the DOP’s

DOP pump and power pack, ready for commissioning

A DOP pump1 and it’s drive go together like a horse and carriage, you can’t have one without the other. Basically one product, but two units. Whether hydraulic or electric driven. OK, in some cases, you could use the extra power take off from the excavator or crane, but you still have to hook them up, before they can do any useful work.

And connecting the DOP to its drive is an elementary job, that can cause some headaches, when not done carefully. The modern electric drives require some more certified wizardry, that is beyond the scope of this post. Hydraulic power packs have their own peculiar quirks, that are worth mentioning here.

Usually, the hydraulic hoses come supplied with Snap-tite® connections2. These are quick and prevent most oil spills in the environment. They come with a disadvantage in price and resistance. Ultimately, the DOP should be connected to the power pack like this:

Hydraulic diagram DOP pump and power pack

So, even with such a simple diagram, still things can go horribly wrong. Off course, don’t switch the ‘Pump’ and ‘Return’ line, you will blow some seals on the motor. Most common is a failed connection of the Snap-tite®. When it is not completely tight, the internal valve is not completely open and you have a lot of resistance. So a lot of power on the power pack gets converted to heat on the connection and no performance on the DOP pump. Another common problem is the resistance in the leak line. This can cause terrible things on the hydraulic motor.

One client followed all the instructions in the manual and all advise from the service department, but still could not coach his new DOP to work. Lots of flow at the power pack, but almost no pressure. And the impeller could still be turned by hand. (Warning: never put your hand in an impeller when there is power on the drive!) One of our engineers went over to have a look on board. Well, here is an impression of the situation on deck.

Situation on board during commissioning

He quickly began cleaning up the mess on deck and uncovered how the hydraulic hoses were actually connected.

How the DOP pump was connected (not), actually

Well, that makes sense! Now it was easy to see, why the DOP was not working. Solution, connect the lines correctly and dredge away. Oh, and educate the crew about a tidy workplace.

Ship shape and ready to rumble

Well, after this first basic lesson in connecting the DOP, you are ready to connect your own DOP project. It’s easy as child’s play.

Connect the dots to set up a DOP project yourself (pdf version)

References

  1. Hydraulically driven submersible dredge pump DOP, Damen
  2. Quick Disconnect and Valve Division, Parker Snap-tite

See also