Reduction of Cutter Spillage
Type:
Presented during:
CEDA Dredging Days 2021
Authors:
B. Yousef
Abstract
Dredging process contains two major activities, namely: cutting and pumping of various soil materials.
One of the major problems for the environment and for the dredging process is the spillage of cutter suction dredgers. To compensate the spillage, operators are increasing the cutting depth, which results in overcut/undercut of the soil. Several studies and calculations are made to estimate the spillage percentage. A recent article in Terra Et Aqua #153 estimates a spillage of up to 80% depending on speed and other factors.
In order to reduce the spillage, we have come up with a closed type cutter head. This cutter head is welded on a tube, having the suction mouth in the centre of the cutting system. An electric ring motor is placed around the suction tube. The purpose of this cutter head is to contain the cut material inside the cutter and lead the flow to the suction tube.
This process is achieved by the closed blades design and the Archimedes screw principal. In addition, the cutter blade leading edge is designed as an aerofoil, which leads to the acceleration of the cut particles towards the inside of the cutter instead of outside.
This innovation is done in 3 stages as follows:
Stage 1: CFD simulation, which is done inhouse to decide the shape of the cutter and to simulate the flow through the cutting system.
In the CFD calculation we have simulated both the conventional and the new cutting system. In the picture hereafter you see a CFD presentation for both systems. The difference between the two systems is more than doubled in flow rate. This is mainly because of two effects:
1) The cutting blades are based on a Archimedes screw principle, pumping the medium in axial direction rather than radial direction.
2) the medium is directed to a centred pipe with less abstraction.
In the conventional cutting system, the shaft, bearing, drive, cooling, flushing etc is placed in the middle of the cutter head. Consequently less space is left for the suction mouth that is crammed between the shaft arrangement and the cutter outer ring. The remaining part of the system is a straight bulk head. Note: this flow simulation is without the dredge pump. This simulation represents only the flow generated by the cutter head.
Stage 2: Scaled model, using a 3D printed cutter, electric motor drive, water pump and sand aquarium to test the cutter and simulate part of the reality. In the picture hereafter you can see the setup. Stage 3: A prototype with a 550mm suction pipe is made for testing purposes only. This prototype is equipped with two ring motors around the suction tube of total 48000 Nm torque. The prototype was tested on a CSD500 dredger in the coastal waters of the Arabian Gulf. Loose soil that is less cohesive and produces more spillage was chosen for testing the cutter. During the testing, the influence of the new blade design, suction velocity, material inflow to the pipe, electric motor performance, and several other parameters are monitored and recorded....
Keywords: Cutter Head, Cutter Spillage, Efficiency Dredging Process, Environment.