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Developing the largest size dredge pump in dredging industry

As the demand for larger dredgers rises, there is a growing need for developing largest size dredge pump that can reach up to 1,800 mm suction diameter.

The largest size dredge pump is one of the main components of the dredger, and it is critical to achieving production. Dredge pumps also have the biggest power consumer during operation so efforts to reduce the pump’s power needs through smarter design are critical.

Engineering challenges of dredge pumps

Dredge pumps involve more complex engineering challenge than water pumps. They must carry water filled with mixture of several types of soils like mud, fine sand, coarse sand, gravel, stones, and other debris. The mixture of those materials with pumped water doesn’t behave as homogenous fluid as the soil tends to settle down and slide on the pipe bed depending on the flow speed. Another challenge is that pump parts wear quickly. Clogged impellers and breaking vanes also pose risks to pump performance.

Dredge Yard’s largest size dredge pump design

In 2011, Dredge Yard began developing a new range of dredge pumps ranging from 200mm to 1,400mm – the largest size dredge pumps in the dredging industry. These pumps are designed to counter wear problems inherent in dredge pumps. Impellers are designed in multiple categories of 3, 4 and 5 vanes. To resist wear, the pump parts are made from high chromium iron having a hardness of 60HRC. Unfortunately these materials don’t have high elongation properties and are not impact resistant. For this reason, some dredge pumps are built with an outer casing.

The large pumps are connected in series, reaching a final pressure of 30 bar by the 3rd pump. The pumps often weight more than 100 tons for one complete assembly including wet parts, outer casing, plates, shaft, bearing assembly and pedestal.

Size, weight and component resistance, among other factors, create an imposing challenge for dredge pump designers. Demand has recently grown in the market for even bigger dredgers. Dredge pump size must increase from 1,400 mm to 1,600 mm – even 1,800 mm. Larger suction pipes and dredge pumps must be designed to fill the dredgers in less than 2 hours.

New design methods are needed to adapt to the market efficiently. Pumps must be tested and analyzed for their efficiency and performance. Foundries with casting capacity of 50 tons and heavy steel machinery 6 meters in diameter are required when casting and machining the pump case.

Performance analysis of the largest size dredge pump

The size of these dredger pumps makes building a test and analysis laboratory extremely difficult if not impossible. The manufacturer must design and manufacture the pump as a prototype and deliver the prototype to the dredger without testing and performance checks. All performance will be tested in the dredger when it starts working. The design has to be flawless, performance oriented and reliable before its production. Engineers at Dredge Yard test dredge pump performance with computational fluid dynamics (CFD) instead of physical testing. CFD software calculates and simulates the pump performance measurements like flow rate, aeration, cavitation, pumping head, efficiency, power required, and net positive suction head (NPSH).

CFD codes, can provide steady-state simulation, also known as multi-frame reference (MRF) simulation or “frozen blade” simulation, which put the impeller in a reference frame that rotates at the pump speed, while solving for the rest of the pump in the stationary lab frame.

3-D modeling

After achieving the hydraulic design, a basic 3-D pump model is made in several CAD programs. Once the basic design is completed Dredge Yard runs several trials on major FEA calculations on the model to ensure getting the right stiffness and strength of the pump. This model incorporates pressures output from the CFD analysis to determine the wall loadings.

The gap between the impeller and front plate must be tightly controlled in terms of geometric tolerance. If deformation widens the gap, efficiency will drop significantly. The 3-D modeling and FEA process is repeated as needed to ensure the highest safety margin and lowest weight. At 1,800 mm a dredge pump weights approximately 200 tons. Any weight savings from the FEA calculation could be significant.

Design work continues on the 1,800 mm dredge pump. Dredge Yard aims to finalize the development in 2016 and build the pumps for the dredging and mining market.

One of the examples of a geometric tolerance that needs to be tightly controlled is the gap between the impeller and the front plate. If there is a deformation in that area and the gap widens, the efficiency will drop significantly. Besides the impeller gap effect, the stiffening of the pump structure will assure a symmetrical tension on the pump case and plates. As the pump case is of a volute shape and pressure is not evenly spread, deformation could be asymmetric which is not desirable in pump structures.

The 3-D models takes into account such performance measurements as flow rate, head and cavitation for many of the pump’s components.

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New trend: upgrading & converting dredgers

Modification, conversion and upgrading

Engineering is continuously providing new technologies and solutions with time. It is therefore creating new options for users to be well-efficient and highly proficient. In the recent times, modification, conversion and upgrading of existing dredgers are proving to be good solutions for users. These solutions increase capacity and capabilities with a reasonable amount of investment. Companies which cannot invest in a new dredger can convert their existing dredger, barges to a more functional and efficient dredger.

Upgrading of existing dredger systems is quite practical as it offers re-usability and functionality of the old dredger with low investment.

Conversion of existing vessel into dredger can help in increasing the capacity and capability of the dredging companies in much lesser time with a huge saving in investment.

A dredger also needs to be modified when the supplied dredger does not meet the requirements. Slight changes in the parts or system can then make it appropriate for the project requirements.

All type of dredgers can be subject for modifications that can vary from replacing a single pump with more efficiency to the whole suction/discharge system of the dredger or literally converting existing barges and vessels into dredgers.

Upgrading Dredge Pumps

Dredge pump or sand-slurry pump is considered as the heart of the dredger and plays the most vital role on the efficiency of a dredger.

 Dredge Yard’s Senior Design EngineerManish Jangir, says: “Latest tools in the market like CFD and optimum design calculating software have widen the paths of having an efficient pump design for the same old pump without changing any fitting parameters or the connections like the flange.

After achieving the final design of the pump, the manufacturing is done by using the latest production techniques, molding software for casting, and strict metallurgical testings.

Suction and delivery lines upgrades

Suction and delivery lines of a dredger are the means of transport of slurry and the line design and components vary between dredgers. The efficiency of the dredger depends on the pump and the pumps efficiency certainly depends on the pipe line. And the maintenance cost depends on the quality and capability of the components. The major components involved in the pipe lines are: pipe pieces, gate valves, suction mouth, swivel bend, bow coupling, turning glands, ball joint couplings, etc.

New trending components

Kabi Eisa, Production Manager at Dredge Yard describes the double wall dredge pipe as the newest trending product in the dredging market. He also adds that the double wall pipes are highly wear resistant due to their special design where three layers of material have been used. It consists of wear liner, concrete and steel pipe where wear liner being the layer that will be in contact with the sand or slurry.

Double Wall Dredge Pipe

Dredge Gate Valves are highly sophisticated components and for proper functioning, maintenance, it is very important to select the right type with right material and pressure handling capability for long life.

Upgrading split suction trailing hopper dredger

“For example, the dredger in the image didn’t have a discharge line and could only offload the material through its bottom doors. Dredge Yard developed the complete suction and discharge line on the ship which includes several pipes, bends, dredge valves, and bow coupling. The nominal diameter of pipe is 750 mm.” says Michel Debo, Dredge Yard’s Operational Manager.

Converting hopper barge into trailing suction hopper dredger

Another example shows a barge in Brazil, capacity 800 m3, which is in process of conversion into trailing suction hopper dredger. A complete trailing suction system has been installed on the barge. The system consists of drag head, turning gland, gantries, sliding piece, pipes, bends, valves, pump and bow coupling.

Discharge line on TSHD

Many hopper dredgers are upgraded by adding complete discharge line on the ship as pipes, bends, valve and bow coupling structure.

Modifying or converting old vessels will always be considered the most convenient alternative due to the cost cuts, less time involved in the makeover of an old ship than building a new one and the possibility of customizing the vessel according to the customers’ needs.

 

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