The decanter centrifuge is mainly composed of two key components: the drum and the spiral discharger (helix for short). During the feeding process, these two components rotate at high speed in the same direction with a certain differential speed. The material is first continuously introduced into the inner cylinder of the spiral through the feed pipe, and then accelerated and enters the drum.
Under the action of centrifugal force, the heavier solid phase in the material will be deposited on the drum wall to form a sediment layer. The lighter liquid phase forms an inner liquid ring, which is located on the inner side of the solid phase. At this time, the spiral discharger begins to play a role, and it continuously pushes the solid phase (sediment) deposited on the drum wall to the conical end of the drum. This pushing process is achieved by the direct contact and conveying of the mule blades and the sediment. The spiral blades have various forms, such as continuous integral type, continuous belt type and disconnected type, which can be selected according to different material characteristics and separation requirements.
With the continuous pushing of the spiral, the sediment finally reaches the conical end of the drum and is discharged out of the machine through the slag discharge port. At the same time, the lighter liquid phase continuously overflows from the overflow port at the large end of the drum and is discharged from the machine through the discharge port.
In this process, the differential speed between the drum and the screw is one of the key factors. This differential speed (i.e., the slip rate) is usually controlled in the range of 0.6%~4%, and the specific value depends on the difficulty of material separation. For materials that are easy to separate, the slip rate can be appropriately higher; while for fine and sticky materials that are difficult to separate, a smaller slip rate should be taken.
In addition, the number of heads of the screw discharger is also an important parameter. The double-headed screw has a higher slag conveying efficiency than the single-headed screw, but it will cause greater agitation to the fluid in the machine. Therefore, when separating fine and sticky low-concentration materials, in order to avoid excessive agitation in the machine and increase the solid content in the separated liquid, it is usually more ideal to use a single-headed screw.
In general, the feeding process of the sedimentation type horizontal screw centrifuge is a complex and delicate process, which depends on the coordinated work of the drum and the screw, appropriate differential speed control, and the selection of appropriate spiral blade form and number of heads. The reasonable combination and precise control of these factors ensure that the decanter centrifuge can complete the solid-liquid separation task efficiently and stably.