Dilution method for a pressure sorter
By adding dilution water to the reject zone at a specific ratio and using rotor blades with ribs, the pressure screen addresses thickening issues, enhancing sorting efficiency and reducing energy consumption and investment costs.
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Patents
- Current Assignee / Owner
- ANDRITZ CHINA
- Filing Date
- 2022-01-28
- Publication Date
- 2026-06-24
AI Technical Summary
Existing pressure screens experience undesirable thickening effects on the screen surface, leading to capacity limitations and increased power consumption due to high consistency near the reject outlet, which is not effectively addressed by current methods of adding dilution water, especially when exceeding 40% of the reject stream, causing inefficiencies and motor overload.
A dilution process where dilution water is added to the reject zone at a rate of 0.8 to 3.5 times the reject stream, with rotor blades featuring ribs to enhance distribution, ensuring effective consistency reduction in the sorting area and stable operation with a rejection rate below 5%, thereby reducing energy consumption and investment costs.
The proposed method achieves reduced rejection rates and lower energy consumption by effectively distributing dilution water, minimizing blockages and motor load, while maintaining sorting efficiency.
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Abstract
Description
[0001] The present invention relates to a dilution process for pressure screens. Pressure screens with rotors and basket screens or screen plates are frequently used to remove impurities from fibrous suspensions. In such a screening process, there is a certain thickening effect on the screen surface (e.g., in the case of perforated or slotted basket screens or perforated or slotted screen plates) due to a certain filtering effect. The most commonly used screens are basket-shaped screens through which the material flows from the inside out (outflow principle). This means that a rotor is arranged in the perforated or slotted basket screen, which is spaced apart from the screen surface and continuously cleans it.
[0002] A wide variety of rotors are available on the market. However, all rotors aim to generate pressure and suction pulses on the screen surface.
[0003] Thickening occurs with increasing height of the basket. Normally, the consistency increases with decreasing height (i.e., closer to the reject outlet). The reject material thus has the highest consistency, while the usable material has the lowest. This is currently considered an undesirable effect, as it not only limits capacity but also increases power consumption and energy use. Due to the increasing consistency towards the reject outlet, less fiber can pass through the basket. Furthermore, energy consumption increases due to the higher friction.
[0004] Current technology offers measures to reduce the aforementioned thickening. This involves either adding dilution water to the reject zone or adding dilution water directly to the sorting area in specific sections.
[0005] DE 10 2004 039 712 A1 discloses a sorter in which a dilution fluid is added to the reject stream to prevent the clogging of a throttling point in the reject stream line.
[0006] WO 03 / 104549 A1 describes a sorter in which dilution water is added directly in a ring shape in the area of the sieve.
[0007] US Patent 8,869,989 B2 describes a sorter with a special rotor that has openings for suspension and interference strips to generate pressure pulses.
[0008] Adding water to the sorting area typically involves a complex setup. Water is usually added to the reject zone at a dilution rate of 20% to 40% of the reject flow. If the dilution rate exceeds 40% of the reject flow, the motor load is typically increased due to the restricted flow rate in the sorting area, as the dilution water is added to the reject chamber located below the sorting area (basket). In this scenario, the dilution only reduces the consistency within the reject chamber of the pressure screen, not within the sorting area itself, between the rotor and the basket. In other words, when the dilution water flows towards the sorting area, its high consistency makes it difficult for it to penetrate deeper into the sorting area to reduce the consistency there.Therefore, it is known from the prior art that adding more than 40% of the reject stream with water causes the dilution water to primarily take a "shortcut" to the reject outlet. That is, the water flows into the reject outlet instead of into the sorting area. Furthermore, a large number of screen baskets tends to become overloaded. Fig. 2Figure 1 shows another embodiment of a pressure screen that includes a device for adding dilution water. In this embodiment, the dilution water is added directly to the screening area of the pressure screen, with the total amount of dilution water added representing 40% to 70% of the reject stream. However, if the amount of dilution water is increased further, it mainly "shoots" directly through the screen basket and ends up in the good material zone. As a result, it is not used effectively to reduce the consistency in the screening area. Furthermore, this arrangement is complicated and expensive.
[0009] Therefore, it is necessary to provide a simple and cost-effective continuous dilution process without negatively impacting the sorting operation.
[0010] In the present invention, the dilution water is added to the reject zone, as is already common practice. However, the amount of dilution water added makes a significant difference. As described above, a dilution water quantity exceeding 40% of the reject stream complicates the sorting process. Performance increases, and blockages and motor overload are observed. However, the applicant has recently discovered that when the amount of dilution water is even greater than the amount of the reject stream, the thickening factor decreases further, and the motor load also drops.
[0011] This discloses a dilution process for a pressure screen that solves the aforementioned technical problems. The pressure screen comprises a rotor that rotates within the screen and is arranged at a specific distance from it. The supplied fibrous materials are fed into the sorting zone formed by the distance between the rotor and the screen. A portion of the supplied materials passes through the screen into the good material zone and forms the good material. The remaining supplied materials are discharged in a reject zone as a reject stream, wherein the amount of dilution water added to the reject stream is 0.8 to 3.5 times, preferably 1.6 to 2.2 times, greater than the amount of the reject stream, depending on the sorting stage and the supplied material.
[0012] This reduces the rejection rate. This means that smaller or fewer downstream stages can be used, resulting in lower energy consumption and reduced investment costs. Furthermore, the large quantity of dilution water reduces consistency in the sorting area, thereby decreasing the risk of blockages.
[0013] The advantageous effect also depends on the rotor shape. In a preferred embodiment of the present invention, structure(s) are provided on the rotor to improve the distribution of the dilution water in the sorting area. It has been found that ribs on the front and back of the rotor blades can improve the distribution of the dilution water in the sorting area, so that the rotor can be operated very stably even with a rejection rate of less than 5%. Fig. 1shows a schematic view of a cross-section of a pressure sorter, where the dilution water is added to the reject zone. Fig. 2 shows a schematic view of a cross-section of a pressure sorter, in which the dilution water is added to the sorting zone by means of several specifically designed pipelines. Fig. 3A to Fig. 3C These are schematic views showing the front and back of the wings with the ribs, as well as a rotor with a multitude of wings.
[0014] The Figure 1Figure 1 shows the cross-section of the pressure sorter 100, where the dilution water D is added to the reject zone 20 of the pressure sorter 100, as is already the case with known pressure sorters. However, the amount of dilution water D, which is added to the reject stream by means of a device adapted for adding dilution water (not shown), is 0.8 to 3.5 times greater than the amount of the reject stream.
[0015] Figure 1 Figure 1 shows a rotor 40 rotating within the screen and spaced apart from the screen 60. The supplied materials F are fed into the sorting zone 10, which is formed by the space between the rotor 40 and the screen 60. A portion of the supplied materials F passes through the screen 60 into the good material zone 30 and forms the good material A. The remaining supplied materials F are discharged in the reject zone 20 as the reject stream R.
[0016] In this embodiment according to Figure 1 are the in Figure 2The pipes shown for adding dilution water to the sorting area are omitted. Figure 2 The dilution water is also fed to the sorting area. With the devices according to the invention, the same or even better sorting effects and lower energy consumption are achieved compared to conventional systems.
[0017] Out of Fig. 1 and Fig. 2 It is evident that a large number of blades are arranged on rotor 40 to improve the flow conditions in the sorting area. As shown in the Figures 3A to 3C As shown, 40 ribs 50 are arranged on the front and back of the rotor's wings 70 to improve the distribution of the dilution water D in the sorting area.
[0018] The above description specifies the preferred embodiments of the present invention, but the basic concept and scope of the present invention are not limited to the specific content disclosed herein. A person skilled in the art in this field can freely combine and further develop the above embodiments according to the teachings of the present invention to create more embodiments and applications. REFERENCE MARK LIST
[0019] 10 Sorting area 20 Reject zone 30 Good material zone 40 Rotor 50 Rib 60 Sieve 70 Blade 100 Pressure sorter 200 Pressure sorter F Input materials A Good material R Reject D Dilution water
Claims
1. Dilution method for a pressure screen (100, 200) comprising a rotor (40) rotating within a screen (60) and spaced from the screen (60), wherein fibrous material (F) are fed into a screening section (10) formed by the distance between the rotor (40) and the screen (60), wherein a portion of the supplied fibrous material (F) passes through the screen (60) into a accepts section (30) and forms the accepts (A) and the remaining supplied fibrous material (F) is discharged in a reject section (20) as a reject flow (R), wherein the dilution water (D) is added directly into the reject flow (R), characterised in that the amount of dilution water (D) added into the reject flow is 0.8 to 3.5 times the amount of the reject flow (R).
2. Dilution process for a pressure screen (100, 200) according to claim 1, characterised in that the amount of dilution water (D) added to the reject flow (R) is 1.6 to 2.2 times the amount of the reject flow (R).
3. Dilution method for a pressure screen (100, 200) according to claim 1 or 2, characterised in that structures are provided on the rotor (40) by means of which the distribution of dilution water (D) in the screening section (10) is improved.
4. Dilution method for a pressure screen (100, 200) according to claim 3, characterised in that the rotor (40) has blades (70) and in that ribs (50) are provided on the front side and / or the rear side of the blades (70), whereby the distribution of the dilution water (D) in the screening section (10) is improved.