Double décanteur Twin-cône
"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.
