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Twin-Cone Decanter Centrifuge
 The needs of Industry demands smaller, more economical equipment with higher throughputs. In the past, decanters were designed using the physical limitations of a standard style decanter while optimizing the geometry of the bowl for the fine incompressible solids. This usually means designing for a smaller load to achieve the desired results.
Technological advances have put into operation considerably smaller solid bowl decanters for higher throughput.
In order to achieve acceptable final moisture values, the decanter centrifuge should be operated at the highest G-force obtainable, while still considering safety and maintenance in the design. For reasons of safety and stability, the size of the centrifuge is limited, so that in small bowl cones, large solids volumes have to be processed.
In designing the Twin-Cone Decanter, the demand for optimum dewatering has been the goal, while also taking into account capital costs and maintenance.
The slurry is fed via the feed pipe to the center of the machine and deposited in the cylindrical portion. It is then accelerated by the increased gravity of the rotating bowl, which is of nominal diameter to achieve clarification (initial separation by sedimentation). The solids are transported up the short conical area of the first cone by the scroll (screw conveyor) and deposited in the second, larger diameter cone area.
In the first cone, the desired effect of pre-concentrating is achieved, thus scalping off the majority of the liquid, leaving only the surface moisture (i.e., standard decanter style). The clarification area pool level and corresponding beach length are adjustable via the weir height adjustment, just as in standard decanters.
The pre-concentrated solids are discharged into the second, substantially large drying cone as mentioned above. In this cone, higher gravity is exerted due to the same speed but larger diameter [ G-force=(rpms/30)2 * (diameter in mm/2)]. In this large cone, there is a greater surface area to spread the solids, and hence a thinner cake. This larger diameter and increase in surface area also means that the volume between the scroll flights is less.
Now, you have accomplished in one machine what would have previously taken two centrifuges. You have pre-concentrated the solids in the smaller first stage, thereby discharging clear effluent and dewatering the cake of the capillary moisture, and then re-distributed the cake on a larger diameter of much higher gravity to break the surface tension of the liquid and discharge the driest possible particle by mechanical means. All this without increasing the rotor (main shaft) speed.
The second drying cone of the Twin-Cone Decanter now also gives the processor a second added benefit, which is the ability to wash the fine solids separately from the mother liquor area. The second cone also has an adjustable weir that will allow clear discharge of the washed solids.
Another consideration in the second cone area is that the effluent from this area can be reintroduced into the centrifuge feed if any solids are carried over the second weir, thus achieving total solids capture and maximum dewatering.
Also, in cases where product washing is desired, the mother liquor and the wash liquor streams are discharged separately.
Another benefit of the two cones: In most cases when a decanter is stopped, a residual amount of liquid is discharged via the solids or small cone end, which is usually undesirable. However, the Twin-Cone Decanter, this is eliminated by the second cone area where the discharged liquid will naturally flow out the weir openings.
Advantages of a Twin-Cone Decanter*
- Clarification and drying in two sections, different in concept and size.
- Separate and optimum adjustments of sump heights in both sections. One side for clarification, the second for drying.
- No trade-off between clarification and drying (i.e. sump pool level adjustments).
- Incorporating the "advancing scroll" design in which the solids are always conveyed towards the discharge end and not remixing with the mother liquor. This allows the use of the highly efficient "Cyclo-Gear" instead of planetary or hydraulic drive systems. This eliminates the problem associated with planetary gear sets and hydraulic systems.
- The drying cone area is designed with a very large diameter for the optimum dewatering of the surface moisture. This is achieved without the expense of sizing the entire centrifuge for the drying diameter. With high solids capacities, the larger drying cone offers high volume and less product accumulation loading before the scroll flights. This corresponds to a thinner cake and an easier migration path for the residual liquid, thus achieving the maximum dewatering of the solids.
- In a regular decanter, the drying takes place on the relatively small cone diameter in relation to the cylinder diameter (i.e., decreasing G-force) and increasing solids loading (cake thickness). In the Twin-Cone Decanter, the pre-concentrated solids are discharged into a substantially larger diameter where they are post
- dewatered with higher G-force and lower scroll loading (ie: cake thickness).
- Allows for a different number, shape, and pitch of the scroll flights in each cone area: the clarification and drying bowls.
- The settling of the solids under gravity takes place in a smaller diameter cylinder section. Since this is where the most volume (hence weight) is taken out of the process, this allows for smaller motors and results in lower power consumption. This is true since the diameter of the cylinder enters square into the power consumption for the acceleration of a given mass. A smaller diameter results in a substantial energy savings of approximately 36%. This of course translates in to both capital and operational savings.
- No residual outflow of mother liquid from the bowl into the solids discharge area when the centrifuge comes to a stop.
- Product washing in the second cone area. Mother liquor and wash liquor are discharged separately.
* Actual capacities depend on the properties of material and their separation characteristics.
Additional Features
Lower residual moistures possible over conventional designs
Twin-Cone design allows solids to settle and dewater twice
Increasing G-force beach zones
Internal wash capability
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