| Д. Борохович И. Круш Ю. Ободан Kroosh Technologies Ltd. Israel | УДК 622.74 ОПЫТ ПРИМЕНЕНИЯ ТЕХНОЛОГИИ KROOSH ДЛЯ ПРОСЕИВАНИЯ НЕРУДНЫХ СЫПУЧИХ МАТЕРИАЛОВ Розглядено основи багаточастотної вібраційної технології Kroosh. Аналізуються показники грохотування в декількох застосуваннях нерудної промисловості. Basics of Kroosh multifrequency vibratory technology are described. Screening performance is analyzed for several applications in aggregate industry. |
Dedicated to the bright memory of Academician V.N. POTURAEV
1. What is Kroosh Technology?
Kroosh technology is a vibration technology that comprises a combination of methods and devices for multi-frequency impact on bulk, liquid, or viscous media. Since this article focuses on solving bulk material screening problems, we will briefly explain the basic principles of Kroosh technology, as embodied in the so-called multi-frequency screens from Kroosh Technologies Ltd., trade name Ultimate ScreenerTM (ULS).
The technology is based on the principle of applying a frequency spectrum corresponding to the specific bulk material passing through the screen to the bulk material passing through it. As a result, the bulk material acquires the properties of a liquid. This appears as a turbulent fluidized flow of a layer of bulk material across a screen. In this state, segregation in the layer is sharply activated, and small particles pass through the layer to the mesh and then through the mesh openings in a very short time.
It is clear that only a body in direct contact with a bulk solid located on a screen can exert force on it. This body is the mesh. The mesh, which transmits high-energy, broad-spectrum vibrations to the bulk solid, itself oscillates in a multi-frequency mode and, depending on the task at hand, experiences acceleration peaks ranging from tens to hundreds of g’s. In addition to transmitting these accelerations to the bulk solid, they ensure continuous self-cleaning of the mesh during screen operation. This is the second fundamental feature of Kroosh technology.
The multi-frequency mesh oscillation mode is created by a system developed by Kroosh Technologies Ltd. A mechanical ULS screen system, which, in combination with the mesh and bulk solids, forms a nonlinear vibration system with one-way couplings. This ULS screen vibration system is calculated and designed to implement a natural physical phenomenon known as a “strange attractor.” A “strange attractor” is a physical effect that maintains the vibration system in a given mode, regardless of the influence of external factors changing during its operation. The “strange attractor” effect determines the strong nonlinear nature of the vibration system and stabilizes the system’s dynamic behavior.
The combination of the ideas presented here, practically implemented in ULS screen designs, has created the opportunity to begin screening bulk materials in previously inaccessible areas, and to ensure a multiple increase in the specific screen performance and high-quality products in existing technological processes. The article demonstrates this using examples of industrial screening using the “dry” method of screenings from crushed carbonate and igneous rocks and fine screening of quartz sand.
2. Solving the problem of crushing screenings in the non-metallic industry
In the non-metallic industry, crushing carbonate and igneous rocks produces screenings smaller than 5 mm. These screenings are currently considered waste and are practically unused, as they cannot be economically fractionated using the available technology. Difficulty processing screenings from crushing on traditional screens arises both in ongoing production and when screening waste from waste heaps.
In the former case, screening on fine meshes leads to rapid clogging. In the latter case, additional difficulties arise due to the moisture content of the material, with mesh clogging occurring at 2-3% moisture content. Waste is stored in waste heaps, which, in addition to economic issues, also creates significant environmental problems. When crushing igneous rocks with cone crushers, screenings account for over 25%. Centrifugal crushers, which produce cubic crushed stone, the demand for which is constantly growing, simultaneously produce screenings, the content of which in the crushed crushed stone reaches up to 50%. Carbonate rock screenings, on average across the industry, account for up to 40% of the processed rock mass.
According to expert estimates from various sources, in Russia alone, which has approximately 5,000 non-metallic crushed stone production facilities, the annual waste dump volumes of igneous rocks exceed 12 x 106 m³, and carbonate rocks, an additional 10 x 106 m³. At Granit, the largest enterprise in the Republic of Belarus, the waste dumps contain 5 x 106 tons of screenings with a particle size of 0-8 mm.
A similar situation is observed in Ukraine. It should be noted that a small proportion of screenings is used in road construction, and screening beneficiation is limited to the extraction of dust particles <0.16 mm. The “wet” beneficiation method is primarily used, which requires the use of large volumes of water and the need for treatment facilities to clarify it. Despite this, hundreds of millions of tons of material, already mined to the surface but unsuitable for use due to the backwardness of their processing technology, continue to lie in waste heaps. At the same time, the modern building materials industry urgently needs to expand the range of high-quality narrow fractions from crushed screenings, which are increasingly used in road construction, the production of concrete mixtures and plaster mortars, the production of dry building mixes, granite chips for roofing, paving slabs, water filters, small architectural forms, etc.
Table 1 shows the results of obtaining such fine fractions from crushed screenings using the dry method on ULS screens under industrial conditions. In the examples given, with the exception of Case 4, the main product is the oversize fraction. Dolomite screening solves a specific problem, in which the screen ensures the output of products with the mass and quality ratios specified by the customer (Fig. 1). The product –6+1.4 mm, which is used for concrete production, retains up to 30-40% of the fraction smaller than 1.4 mm, which allows for partial cement savings and improves the plastic properties of the concrete. Excess fine fractions present in the source material are screened at the specified throughput (6-10 t/h) and used to prepare plaster mortars. The product –0+1.4 mm contains virtually no fraction larger than 1.4 mm.
High screening quality indicators are achieved, in addition to the specific dynamic characteristics of ULS screens, due to the design’s ability to regulate parameters over a wide range, such as oscillation frequency, centrifugal force of vibrators, mesh tension force, screen inclination angle and mesh cell size.
3. Fine “dry” sifting of quartz sand
The extraction and processing of quartz sand in most cases requires fractionation of the wet material. This is achieved by using a wet screening process, followed by dewatering and drying of the resulting products. When extracting dry sand, which is possible in some climates, direct dry screening is used, or dry screening after preliminary drying. In this case, the lower limit of the size that can be achieved with traditional screens is the -0.6+0 mm fraction. This satisfies the needs of the building materials industry, but proves insufficient in the face of increased raw material requirements in a number of industries, in particular,
Table 1. Results of fractionation of crushed screenings on ULS screens using the dry method
| № | Name of material, location of screen installation | Material moisture/clay content, % | Screening products (fractions), mm | Mesh surface area, m² | Screen capacity, t/h | Efficiency, % |
| 1 | Chalk, Processing Plant | dry | -3+1.25,-1.25+0 | 2.0 | 16,0 | 99.7* |
| 2 | Limestone, Quarry | 8.7 | -5+3, -3+0 | 1.3 | 18.1 | 93.4* |
| 3 | Limestone, Quarry | 8.7 | -3+1, -1+0 | 1.3 | 4.75 | 60.7* |
| 4 | Dolomite, Quarry | 2.5 | -6+1.4, -1.4+0 | 2.2 | 48.5 | 99.4** |
| 5 | Granite, Processing Plant | 1.8/10.84.5/5.6 | -20+5, -5+0- | 1.3- | 3418 | 92.5*82.8* |
*) Extraction of fines into under-sieve product.
**)Extraction of large particles into the oversize product
Table 2. Results of screening quartz sand using ULS screens with fine meshes.
| Type of screen | Separation boundary, µm | Cell size, µm | Product, µm | Nutrition, kg/h*m² | Product yield, kg/h*m² | Coarsening/Refining, % |
| round | 12 | 45 | +45 | 200 | 110 | /4.4 |
| rectangular | 75 | back |