Structure and dehydration principle
The centrifuge is mainly composed of a drum, a spiral, a differential system, a liquid level baffle, a drive system and a control system. The centrifuge uses the density difference between the solid and liquid phases to accelerate the sedimentation speed of the solid phase particles under the action of centrifugal force to achieve solid-liquid separation. The specific separation process is that the sludge and flocculant liquid are sent into the mixing chamber of the drum through the inlet pipe, where they are mixed and flocculated; due to the high-speed rotation and friction resistance of the rotor (spiral and drum), the sludge is accelerated inside the rotor and forms a cylindrical liquid ring layer; under the action of centrifugal force, the solid particles with higher density settle to the inner wall of the drum; then the relative speed difference between the spiral and the drum is used to push the solid phase to the conical end of the drum, and the mud residue is dehydrated and dried after being pushed out of the liquid surface, and then pushed to the slag discharge port for discharge; the supernatant is discharged from the large end of the drum to achieve solid-liquid separation.
Drum speed
The adjustment of drum speed is usually achieved through variable frequency motor or hydraulic motor. The higher the speed, the greater the centrifugal force, which helps to increase the solid content of the mud cake. However, when the speed is too high, the sludge flocs will be destroyed, which will reduce the dehydration effect. At the same time, higher speeds have higher requirements on materials, increase machine wear, and increase power consumption, vibration and noise levels accordingly.
Speed difference
The speed difference directly affects the slag discharge capacity, mud cake thickness and filtrate quality. Increasing the speed difference is conducive to improving the slag discharge capacity, but the sediment dehydration time is shortened, the water content of the mud cake after dehydration is large, and the spiral disturbance to the liquid pool in the clarification area is large, and the filtrate quality is relatively poor. Reducing the speed difference increases the sediment thickness, increases the sediment dehydration time, and reduces the moisture content of the mud cake after dehydration. At the same time, the spiral disturbance to the material in the clarification area is also smaller, and the filtrate quality is relatively better, but it will increase the load of the spiral pusher. It should be prevented that the sediment in the centrifuge cannot be discharged in time due to the reduction of the slag discharge amount, which causes the material blocking phenomenon.
Otherwise, it is easy to cause a large amount of mud in the filtrate. At this time, the feed amount must be reduced, or the speed difference must be increased. Therefore, the speed difference should be determined according to the material properties, processing volume, processing requirements and centrifuge structural parameters. It is generally believed that the dehydration time of the mud cake in the drying area should be controlled between 4 and 6 seconds, and the effect of increasing the time is not obvious.
Liquid ring layer thickness
The thickness of the liquid ring layer is an important parameter for process optimization, which directly affects the effective sedimentation volume and drying zone length of the centrifuge, and thus affects the treatment effect of the centrifuge. Generally, it is achieved by manually adjusting the height of the liquid level baffle in the shutdown state. When adjusting, it is necessary to ensure that the height of each liquid level baffle is consistent, otherwise it will cause violent vibration during the operation of the centrifuge. Some foreign manufacturers can also realize automatic adjustment of the thickness of the liquid ring layer.