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.

There are many types of decanter centrifuges, and each type has different characteristics and scope of application. Therefore, it is a very important issue to properly select the appropriate decanter centrifuge according to certain process requirements and technical conditions. The selection of decanter centrifuge is mainly considered from two aspects. The first is the nature, composition of the separated materials, and the second is the technological requirements and economic rationality of the separation process:

I. Consider from the nature and composition of materials

The primary basis for selection is the type of heterogeneous system that is separated. For example, for the separation of emulsions in a liquid-liquid system, the first consideration is to use a centrifugal separator. For liquid-solid systems, when the liquid phase of the suspension is a loose material with a low degree of solidity, large solid phase concentration, and coarse particle size (> 100um), various filter decanter centrifuges can be considered. Generally speaking, this kind of decanter centrifuge can get drier filter residue and better washing conditions. Secondly, it is necessary to further select the appropriate form for specific conditions.
If the suspension is a material with a large liquid phase viscosity and a fine solid particle size, it is easy to block the filter cloth or screen, but it is difficult to regenerate. Therefore, a centrifugal sedimentation decanter centrifuge should be used. When the solid phase concentration is large (5% to 10%), a spiral discharge sedimentation decanter centrifuge can be used. If the solid phase concentration is less than 1%, a tubular high-speed decanter centrifuge or a chamber decanter centrifuge can be used. If the solid phase concentration is 1% — 5%, a disc decanter centrifuge can be used. The automatic slag-discharging dish decanter centrifuge can obtain flowing concentrated sediment, so it is often used for solid-phase concentration. For liquid-liquid-solid three-phase systems, generally the solid content is not high, you can use a dish decanter centrifuge.

2, from the technical requirements of the separation process

The process requirements of the separation process directly affect the selection of the decanter centrifuge. For example, the separation process requires intermittent or continuous operation. The minimum particle size of the separation, the liquid content of the filter residue, the clarity of the filtrate, the discharge method, whether the solid particles are allowed to be destroyed, and washed Requirements, the length of the operating cycle and whether automatic control is required, the degree of automatic control, etc.
In addition, there are still requirements for sealing, anti-corrosion and explosion-proof.
In short, it is necessary to choose a decanter centrifuge that is inexpensive, applicable (that is, in line with process requirements), simple to manufacture, and easy to maintain. Choose according to the main contradictions that need to be resolved and make economic comparisons. Both technical possibilities and economic rationality must be considered. Of course, according to human operation, there are also manual operation and automatic operation. Users can choose according to their needs.

The thickness of the liquid-ring layer is an important parameter for the optimization of Decanter centrifuge, which directly affects the effective settling volume of the decanter centrifuge and the length of the drying area (shore area), and then affects the sludge dewatering treatment effect. Generally, it is realized by manually adjusting the height of the liquid level baffle in the stop state. When adjusting, the height of each liquid level baffle must be consistent, otherwise it will cause severe vibration during the operation of the decanter centrifuge, and some foreign manufacturers’ products can realize automatic adjustment of liquid-ring layer thickness.

By increasing the thickness of the liquid-ring layer will increase the sedimentation area and the residence time of the material in the Decanter centrifuge will increase accordingly. The quality of the filtrate will be improved as well. On the contrary, by lowering the thickness of the liquid-ring layer can obtain a higher mud cake of solid content, but this will be at the basic of the filtrate quality lost.

Therefore, the height of the liquid level baffle should be adjusted reasonably to achieve the best combination of mud cake degree and filtrate quality. In general, many decanter centrifuge suppliers have adjusted the liquid level baffle in advance when the machine leaves the factory. However, due to different conditions on the site, if the operating status of the decanter centrifuge is not ideal, you can communicate with the equipment engineer to make adjustment to the on-site liquid level baffle.

GN can not only provide users with Decanter Centrifuges, but also provide users with turnkey solutions for dewatering process, including solutions for material transportation, classification and dewatering. Rely on GN’s rich production line of separation and conveying equipment, more and more reliable and advanced equipment will be manufactured for users all over the world.

Difference between solid-liquid & solid-liquid-liquid separation by decanter centrifuge

In the processing and selection of decanter centrifuge, it is sometimes necessary to judge whether solid-liquid two-phase separation can be completed in case of accident due to the difference of properties of materials to be separated, or whether liquid can be divided into light liquid and heavy liquid needs solid-liquid three-phase separation. This delineates the need for solid-liquid separation using two-phase separation or solid-liquid-liquid three-phase separation of decanter centrifuges.

The two-phase decanter centrifuge consists of frame, cover, main bearing, drum, screw, differential, drive system and control system. The drum and the screw rotate at the same direction and high speed at different speeds. The material enters the inner cylinder of the screw through the feed pipe and enters the drum from the feed port.

Under the action of centrifugal force, the heavy solid-phase materials are deposited on the wall of the drum to form a sediment layer, and the spiral continuously pushes the deposited solid-phase materials to the cone end of the drum, which is discharged out of the machine through the slag discharge port. The lighter liquid phase materials form an inner liquid ring, which overflows the drum continuously from the overflow port at the big end of the drum, and is discharged out of the machine through the discharge port.

The three-phase decanter centrifuge is mainly used for solid-liquid-liquid separation, that is, separation of one solid phase (high density) and two liquid phases with different densities. The drum and the screw rotate at the same direction and high speed at different speeds. The material enters the inner cylinder of the screw through the feed pipe and enters the drum from the feed port.

Under the action of centrifugal force, the solid phase material is deposited on the wall of the drum to form a sediment layer, and the two liquid phase materials form a light liquid phase ring and a heavy liquid phase ring respectively. From the wall of the drum, the solid phase layer, the heavy liquid phase layer and the light liquid phase layer are successively formed inward.

The solid materials deposited on the drum wall are continuously pushed to the cone end of the drum by the screw and discharged out of the machine through the slag discharge port. The light liquid phase and heavy liquid phase overflow continuously from different overflow ports at the big end of the drum, so as to realize three-phase separation.

GN 3 Phase Decanter Centrifuge Shipped to Middle East for Oily Wastewater Treatment

News from GN company this week: Recently, 1 set of 3-Phase Decanter Centrifuge have been manufactured and ready to start serving for a project in Middle East for Oily Wastewater Treatment.

GN 3-Phase Decanter Centrifuge is mainly designed for Solid-liquid-liquid three-phase separation of materials.With our over 10 years of experience in the separation industry, it is the most advanced type machine for 3 phase separation. It is designed for 24 hours continuous and smooth operation throughout the day. It is mainly composed of driving system, decanter bowl, screw conveyor inside the bowl, cover box, skid and VFD control panel.

To make sure the 3-Phase Decanter Centrifuge will provide a reliable performance and the parts and components of all the equipment will run smoothly for a long term operation, our technical department, production department and quality control department have paid a lot of attention to the material selection, material preparation, every step of production and the inspection for this set of equipment in each step.

If you need any support about the operation and maintenance of GN’s equipment like 3-Phase Decanter Centrifuge, please feel free to contact GN company for our engineers’ best experience and knowledge in the relevant industry. We will do our best to assist your project because just in this way we can establish a stable and long term cooperation. And we can provide on-line support and site instruction for specific situation if needed.

As a leading manufacturer of separation equipment and conveying equipment, GN always pay high attention to the product quality and consider the long-term benefits for our users. We would also like to introduce GN as a professional manufacturer in decanter centrifuge field, GN pays a lot of attention in the selection of raw materials, high-quality centrifugal casting or forging stainless steel materials are used, and for wearing parts, hard alloy protection is used.

By the way, if you are interested in our products, please check the following items of our company on Alibaba:

Decanter centrifuge

3-Phase Disc centrifuge

Sludge dewatering Screw press

Oil water separator

Centrifugal pump

Vacuum Pump

Submersible pump