Dredge pump is the main machine used by large cutter suction dredger in dredging engineering, It plays an important role in dredging engineering. and its performance directly affects the efficiency of the dredging project. Usually, large cutter-suction dredger using the centrifugal pump as a dredge pump, Its working principle is to use an impeller to rotate under the driving device of the diesel engine to produce centrifugal force, so that the fluid in the pipeline is forced to rotate and push by the blade, so that the fluid pressure increases at the outlet of the dredge pump, thus producing centrifugal force. Head, to achieve the purpose of conveying fluid. At the same time, the suction chamber at the inlet of the impeller forms a local vacuum, which generates suction and inhales the fluid continuously. The shaft power of the dredge pump will increase with the increase of flow rate. There is an optimal efficiency point at the rated speed of the dredge pump, which is called the optimal operating point. From the economic point of view, the dredge pump should be operated at the optimal operating point as far as possible. When the dredge pump works at the non-rated speed, the impact loss of fluid flowing in and out of the impeller will increase. Usually, the high-efficiency zone is chosen and the difference is less than 5% for the suitable working condition of the dredge pump. The shaft power of the dredge pump is the power transferred from the prime mover to the pump. Due to the hydraulic loss, volume loss, and mechanical friction loss of the dredge pump during operation, its effective power is lower than that of the shaft.
1.1 Main parameters characteristics of dredge pump
The main parameters of large cutter suction dredger dredge pump include flow, head, speed, NPSH, power and efficiency, mud capacity and concentration, maximum allowable particle size, and so on. The speed of the dredge pump has a great influence on the characteristic of the dredge pump. The NPSH can effectively show the cavitation performance of the dredge pump. The power of the dredge pump includes input power and output power. The input power is the power output from the diesel engine and other driving devices to the shaft of the dredge pump. the output power of the dredge pump is referred to as the slurry through the dredge pump, the power of the dredge pump is transmitted to the slurry. The difference between the input power and output power of the dredge pump is the lost power of the dredge pump.
1.2 Clearwater characteristics of the dredge pump
In the actual dredging project, in order to improve the efficiency of the dredger dredge pump and achieve the best working conditions. To achieve this goal, it is necessary to master the performance characteristics of the dredge pump, which mainly needs to understand the relationships between the dredge pump parameters and fluid density. Usually, the manufacturer of the dredge pump will provide the clear water characteristic curve of the dredge pump.
The Head gradually decreases with the increase of flow rate. the power of the dredge pump increases with the increase of flow rate, and the efficiency of the dredge pump increases with the increase of flow rate. but when reached a certain limit, will gradually decline, the dredge pump will have the best work condition point, in actual engineering, should make the dredge pump work in the best condition point.
1.3 Slurry characteristics of dredge pumps
Although the manufacturer may provide a curve of the clear water characteristics of the dredge pump, in the actual dredging project, the fluid material delivered by the dredge pump is slurry. The slurry is a mixture of water and soil under the action of the dredger cutter. The characteristics of slurry are influenced by drawings, soil density, particle size, concentration, gravity, and so on. Generally speaking, when the dredge pump carries out slurry transportation, the relationship between various working parameters should have the same property as the clear water characteristic curve, and only certain changes will occur in the quantity of transportation. The degree of change will change as the characteristics of the slurry change.
- The particle size of mud and sand in slurry has great influence on the head and working efficiency of dredge pump. The smaller the particle size of mud and sand in the slurry, the higher the head and working efficiency of the dredge pump.
- At the same speed and flow rate, the efficiency of slurry transportation by dredge pump is slightly lower than that of clear water transportation; at the same speed, the head and efficiency of the dredge pump will decrease simultaneously with the increase of fluid concentration, and the degree of head decline is lower than that of working efficiency decline.
- The vacuum allowed by the dredge pump will be decreased when the slurry is transferred.
- when delivering slurry, the dredge pump needs more input power because the density of mud is higher than that of clean water, and the speed and flow rate of dredge pump remain unchanged. In dredging engineering, the input power of the dredge pump will increase with the increase of slurry When the slurry concentration delivered by the dredge pump is too high, the dredge pump may be overloaded and the damaged.
- The impeller parameters of the dredge pump will affect the performance of the dredge Under the condition of constant fluid concentration, the larger the outside diameter of the impeller, the lower the performance of the dredge pump.