The GEA Niro CONTEXTM features true continuous counter-current extraction.
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The solids (in a suitable form) are fed by gravity or metered by volume to the lower end of the process-vessel and are transported upwards through the extractor by 2 counter-rotating mirrored helicoidal screws with a controlled slip. The solids pass in the form of 2 overlapping cylinders, rotating at about half the rate of the screws.
The fresh extraction liquid enters at the top-end and flows by inclination-controlled gravity down as a submerged stream in the bottom half of the cross-sectional area through the slowly rotating solid in true, well-controlled countercurrent extraction with close to ideal plug-flow in both phases. The speed of the screws is adjusted to give the neccesary residence time for the solid. The flow of liquid is adjusted independently to give an optimum concentration of the extract. |
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The extract leaves at the lower end through special self-cleaning filters and a level-control reservoir. The extracted solid is slightly squeezed at the top end and continuously discharged.
Adjustment and automatic control is very simple. Scale-up from pilot plant tests is well proven.
Extraction is diffusion- and equilibrium-controlled. The solid is only submerged in the liquid half of the time, but the rate-limiting diffusion takes place all the time. The counterflow ensures the best possible equilibrium limit. Therefore, a high yield and a high extract concentration can be obtained simultaneously: the overall efficiency equals 3 to 5 ideal conter-current equilibrium/separation-stages and the yield is typically adjusted to an overall optimum of around 90% of total extractables.
The equipment has been successfully used for many beverages, pharmaceuticals and generally all kinds of difficult vegetable materials such as leaves, stems and roots. The solid must be cut, milled, rolled or shredded as finely as possible to maximize extraction speed, however with a limit of typically max. 10% smaller than 1 mm due to the built-in filter and the resistance to the gravity-controlled percolation of the liquid - which could be water or a suitable organic liquid.
The pilot plant has a working volume of 27 litres (0.027 m3). Commercial units with up to 2.700 litres(2.7 m3) and capacities up to the 500-1000 kg/h raw material are available, with solids residence times in the ½ to 2 hour range.
Maximum Extraction Time:
- Approx. 2 hours (for reasons of size and cost)
- Extract flow velocity may limit scale-up
Size of Raw Material:
- Generally, 'As fine as possible' to facilitate minimum extraction time and maximum capacity
Mechanical limits:
- Max. size approx. 5 cm
- Min. size approx. 0.9 mm
