High-performance screening machines for the potash industry, Remscheid
Dipl.-Ing. Sigurd Schütz, RHEWUM GmbH
© Nelson Minar
Potash is an essential building block of life. Together with nitrogen and phosphorus, potash is the third essential one. It supports plant growth, enzyme activity, protein formation, photosynthesis, respiration and the improved absorption of nutrients. Almost 95% of all potash produced is used as a fertilizer. High-performance screening machines are indispensable in the potash production process.
Potash deposits, which are located at fixed positions and depths of up to 1400 m, are extracted by mechanised methods of underground mining. When underground extraction is no longer feasible due to the depth of the deposits and/or when water inflow problems hinder conventional underground mining, the extraction of salt domes is used. Solar evaporation of brine containing natural potash is the third method of extraction.
Screening technologies in the potash industry
Screening machines are required at various points in the processing chain. Starting with the extraction, because the mineral extracted from the mines is first crushed and then pre-classified. They are then used for compacting, granulate screening and loading. Screening machines are also used in wet processing, i.e. wet classification and dewatering. As screening machines have a considerably lower energy requirement compared to crushers, they can also relieve crushing stages (selective crushing) and thus avoid cost-intensive overgrinding in addition to the pure production of saleable product.The screening machines used are usually vibration and directly excited screening machines. Vibratory screens are used for high capacities with medium to coarse separation cuts. For critical product properties and separations below 3 mm, directly excited screening machines show their strengths.
Double frequency (DF) screens are a special type of vibratory screening machines. The drive principle of the DF machine is based on the use of two unbalanced motors with different speeds, which are mounted in the inlet and outlet. The feed material is loosened up in the inlet area by the higher amplitude and sorted according to size (segregation). In the outlet area, smaller oscillations are generated, which increase the screening accuracy by effectively separating out boundary grains. By changing the direction of rotation of the motors, the conveying speed and thus the screening capacity and the separation efficiency can be specifically influenced. Due to this drive principle, it was possible to create a compact screening unit compared to conventional screening technology.
|25 - 5 mm||4 x 400 t/h||Prescreening||DF|
|4 + 2 mm||180 t/h||Compacting||DF|
|4 + 2 mm||350 t/h||Loading||DF|
|1.0 mm||80 t/h||Crystallizate||WAU|
|0.2 mm||100 t/h||Flotation||WAU|
|1.0 mm||85 t/h||Wet-screening||RIUS 1+1|
|0.8 mm||80 t/h||Dewatering||ES|
Table: Examples of the different RHEWUM technologies
Direct excited screening machines
For finer separations below 2 mm up to 0.16 mm, directly excited screening machines are used. They are suitable for exact separations at high throughput rates. This machine type is a throw screen with direct excitation of the screen cloth. The screening unit is static. This allows fixed connections at inlets and outlets. Outside the screen housing, robust vibrators excite vibrations which are transmitted to the screen cloth via vibrating axles. The high-frequency excitation causes the material to be screened to be discharged at right angles from the screen fabric - the inclination of the fabric determines the transport. Thin-layer screening takes place on the screen fabric at high screening speed. An adjustable cleaning cycle reliably prevents possible plugging of the screenings. Due to the low moving masses (only the mesh vibrates) high accelerations are achieved on the screen lining. These help to overcome adhesive forces with moist or sticky material (e.g. rolling granulate).
Risk of condensate formation
During discontinuous operation or long downtimes, unwanted condensate formation can occur due to moist feed materials. In this case heating coils are often provided to keep the temperature in the screening chamber above the dew point. The heating coils are mounted either on the cover of the screening machine or on the static housing of the distribution device.
Wet classification of potassium requires - as with other materials - short sieve lengths, since with the separation of the liquid no more classification is possible. With the aid of a double feed within one machine, compact units with high screening capacities are possible.
Based on decades of experience in screening technology, especially in the potash industry, new materials and technologies open up even more effective and user-friendly processing of the valuable raw material potassium. This is all the more important against the backdrop of limited global resources and currently rising demand in growth markets.
If you are still looking for the right screening machine for your product, please contact us. Our screening experts will find a tailor-made solution for you.