The screw is the main component of the Decanter centrifuge. Its function is to transport the sediment deposited on the inside of the drum and smoothly discharge the sediment. It is not only the unloading device, but also determines the production capacity, service life and separation effect.
The type of screw is divided into counter-flow type and down-flow type according to the relative movement of liquid and solid in the drum.
The feeding chamber of the counter-flow Decanter centrifuge is located in the middle of the spiral, that is, near the boundary between the drying zone and the sedimentation zone, to ensure that the liquid phase has a sufficient sedimentation distance, but the solid phase can only stay for the time required to pass through the cone. Therefore, a high centrifugal force is required; entering the drum from here will cause the solid particles that have settled in this area to float again due to disturbance, and turbulence and additional vortices will be generated, which will reduce the separation effect.
The down-flow decanter Decanter centrifuge has a feed inlet at the end of the drum, which avoids counter-flow turbulence and ensures that the sediment is not disturbed. The entire length of the decanter centrifuge is settled, expanding the settlement area, and the residence time of the suspension in the machine. So that the separation effect is improved. The prolonged and undisturbed sedimentation can effectively reduce the amount of flocculant used, greatly improve the fluid flow state in the machine, and increase the centrifugal force by increasing the diameter of the drum, so it can significantly reduce the speed and save power consumption. At the same time, reduce noise and extend the life of the machine.
The down-flow screw structure of decanter centrifuge is especially suitable for difficult-to-separate materials with small solid-liquid density difference, poor solid-phase sedimentation performance, and low solid-phase content. However, the filtrate of the down-flow decanter centrifuge is discharged through the skimming tube. The solid particles that are not separated when the filtrate passes through the skimming tube will be separated and deposited in the skimming tube. The skimming tube channel will be blocked after a long time operation, so it needs to be washed regularly.
In recent years, with the increasing requirements for sludge dewatering, efficient screw structures have emerged. For example, weir plate technology, a special baffle is set at the spiral discharge end of the cone section of the decanter centrifuge, which can put the centrifuge in an ultra-deep liquid pool state to increase the slagging force on the mud cake, and only convey the lower sediment, and The sludge with high moisture content in the upper part is trapped on the outside of the crushing cone section to realize dehydration and make the sludge drier.