Our Interview About New Pump Designs In The Latest Damen Nieuws

Headline of our interview in ‘Damen Nieuws’
Headline of our interview in ‘Damen Nieuws’

Another magazine dropped on my doormat, albeit a digital edition of ‘Damen Nieuws’1. The internal magazine for Damen colleagues. It featured an article with Suman Sapkota and me. Suman is our pump design specialist2 and at a Damen wide R&D convention he presented a poster on his pump design workflow within Damen Dredging Equipment. This caught the attention of the editorial board and we were interviewed on what we actually do for a living. Although we can’t share the exact details of the article or the poster, it is still an interesting message that we can highlight here.

Pump design workflow (inspired by Suman Sapkota)
Pump design workflow (inspired by Suman Sapkota)

The design of a dredge pump is based on the required specifications(1). The most important properties of the pump are: efficiency, NPSH, wear and ball passage. The first important property we try to fix is the ball passage3. We do use our own geometry generator(2) that assist us in creating a pump with a big ball passage. Unlike normal pumps, dredge pumps have to cope with debris and boulders that have to pass the impeller. The bigger chunks that can pass, the more uptime the dredge will have. Once we are satisfied with the geometry, we feed this through a file format converter(3). The resulting 3D file can be used on several platforms. This will enable us to create the digital solid for the engineering4, but it also gives us the negative volume, also known as fluid. Then to do mathematical operations on the digital fluid, we have to divide the volume into tiny cells. This process is called meshing.(4) When the mesh is available, the fluid flow through the mesh can be simulated with computational fluid dynamics.(5) All the fluid properties of every cell are calculated and the results are shared with the adjoining cells. This can be repeated until all properties of the cells don’t change very much anymore, a stable solution. Integrating all the properties of the cells give the resulting performance of the pump.

Balancing the four dredge pump performance properties
Balancing the four dredge pump performance properties

The estimated performance can be evaluated against the four properties.(6) The head times the capacity divided by the power required will give the efficiency. That is one of the items we wanted to know, as it relates to how much fuel will be consumed. The other parameter obtained from the CFD is the NPSH, or roughly: the suction performance. Wear cannot be estimated yet, but we are working on that2. Although the calculated turbulence might give a clue what wear to expect. If the properties are not satisfying our requirements we make an iteration in the geometry for improving the performance. However, changing the geometry will usually result in a smaller ball passage. If the parameters are OK to our requirements we have a pump design.(7) Manufacturing it is a completely different game.5

The design process of the dredge pump takes quite some effort and we are continually looking to improve the workflow6. Eventually we would like to be able to cater for all special requirements each individual customer might have.

Working for a dredge manufacturer, I am happy we design and produce our own pumps. It gives us the confidence, that when we supply dredges, they are as we like them to be. Another benefit is in discussions with the customer. It is easier when we can sit at the table as experts on their equipment assit them in finding a solution for their dredge.

Pump experts immersing themselves in checking the design of their pumps
Pump experts immersing themselves in checking the design of their pumps

References

  1. Damen Nieuws, Juni 2020, Damen
  2. Graduation Suman Sapkota: Where wear parts were worn down, Discover Dredging
  3. On The Relation Of Maximum Ball Passage And Recirculation Losses In Dredge Pumps, WODA
  4. Graduation Of Carsten Markus: Designing And Casting Of Impellers
  5. Don’t Play Games With Your Wear Part Planning
  6. Innovation, Damen

See also

When does your pump suck?

Regular pump inspection

One of the key process indicators for the performance of your dredge pump, is the capability to work with low suction pressure. The parameter involved is called ‘Required Net Positive Suction Head’. Which translates more or less to: ‘the head value at a specific point required to keep the fluid from cavitating.1’ Effectively, this is the extra pressure above the vapour pressure. From the pump inlet to the blade, there still is a pressure drop. And the geometry and the form of the blade influence this pressure drop. The operator will notice this as when the blade wears down, the pressure drop becomes greater and the required suction pressure goes up. Resulting in less performance and less production. Regular inspection of the pump will warn the operator of prospective deterioration.

Test arrangement NPSHr

Normally, the measurement of the NPSHr requires a valve in the suction pipe and a valve in the discharge pipe to control the flow. Every time you want a data point, you have to adjust both valves and iteratively return to the same flow conditions, albeit with a different suction pressure. This usually takes a lot of time and one hour per data point is not uncommon. Klaas Slager presented an alternative method at the CEDA Dredging Days2. His method is more suitable for testing the NPSHr as installed in a dredge. It does not involve the dredge valves and is quicker to execute. It is optimised to check if the NPSHr wanders off nominal and thus will yield an indication on the condition of the pump. If the internal pressure drop increases, there is less differential pressure available in the suction pipe for the dredging process. Less concentration or less capacity, or less in the combination of the two: less production.

NPSHr measurement processing

Instead of varying the flow conditions, he proposes to vary the pump speed. This will influence both flow and suction pressure at the same time. However, by cleverly applying the affinity laws and presenting the operating conditions in a dimensionless scale, the cavition is immediately visible. A quick post processing will reveal any wandering of the NPSHr conditions. As this can be implemented in the PLC and executed during start-up every day, the operator will receive a daily update on the suction condition of his pump and can plan actions accordingly. This will prevent unnecessary delays and downtime.

Worn down suction side of a dredge pump deteriorates NPSHr

This concludes my scheduled series of posts about the CEDA Dredging Days. There was much more to discover. The interactive session was fun. There were a couple of interesting presentations. And I’ve seen some innovations at the exhibition. So, I will write some more reports, although at a more leisurely pace of about once a week. Later on, the other promised topics will be covered3. I’ll keep you posted.

References

  1. NPSH
  2. Presentation Klaas Slager
  3. Discover Dredging: A new personal website for dredging enthusiasts

See also

CEDA Dredging Days