Coarse screening system

Abstract

The present invention relates to a roughing system comprising: a first roughing stage comprising a first screen rake and a first pump providing pressure to the first screen rake upstream of the first screen rake, wherein the first screen rake has a screen extending upwardly from a base and a rotor rotating around the outside of the screen, wherein the first screen rake has a discharge opening arranged inside the screen, the first roughing stage provides a good pulp to downstream equipment through the discharge opening of the first screen rake, and a suction inlet and a sludge outlet are arranged outside the screen; a discharge tank receiving sludge from the sludge outlet of the first screen rake through a feed pipe; a discharge tank; a high density cleaner for separating heavy impurities in the pulp, wherein the sludge outlet of the first screen rake directly outputs sludge to the feed pipe of the high density cleaner, the overflow pipe of the high density cleaner outputs good pulp to the feed pipe of the discharge tank, and the underflow pipe of the high density cleaner discharges heavy impurities.

Description

Technical Field

[0001] This invention relates to a coarse screening system. Background Technology

[0002] In order to utilize recycled fibers to produce different types of paper and paperboard, pulping different types of waste paper followed by several washing and screening steps is widely used in the papermaking industry. These steps consume a significant amount of energy both on the equipment and pump sides. Pumping in the aforementioned production lines may consume up to 50% of the total energy consumption. Figure 2 The diagram illustrates the process layout of a pumping and coarse screening system in the prior art. An embodiment with a rotary drum pulper is shown as an example, although it is clear that a low-concentration pulper could be used instead. A pulping stage is schematically shown, in which waste paper and water are mixed and dissolved under shear force by passing through the rotary drum shown here or through a rotor in the tank of a low-concentration pulper. Large impurities (including light and heavy impurities) that cannot pass through the screen openings (typically 10-18 mm) of the pulping and deslagging equipment are removed in the pulper. After the pulping process, to protect the downstream coarse screening system from abrasion, a high-concentration cleaner (e.g., a hydrocyclone) is installed where coarse and heavy impurities need to be removed. The good pulp passing through the high-concentration cleaner then enters the discharge tower for soaking (e.g., approximately 1 hour). Here, the pulp flow rate entering the discharge tower and the predetermined residence time of the pulp in the discharge tower determine the volume of the discharge tower. The coarse screening system installed after the unloading tower primarily removes light impurities (such as small plastic fragments that can pass through the pulper orifices) and dissolves residual paper scraps (fiber bundles) to minimize fiber loss.

[0003] In the aforementioned process layout, the large-sized hydrocyclones and discharge towers result in relatively high energy consumption on both the equipment and pump sides. All the slurry suspension needs to be pumped to a high-concentration cleaner (typically two stages), and the good slurry from the high-concentration cleaner must be introduced into the discharge tower, which requires additional pressure due to its height. After passing through the discharge tower, all the slurry is again pumped to the coarse screening system, resulting in high pumping pressure. Therefore, it is desirable to provide a coarse screening system that can improve the process and significantly reduce the energy consumption of the entire coarse screening system, including pumping.

[0004] The applicant's patent application filed on September 1, 2021, with application number 202111021322.0 and entitled "Pulping Machine," discloses a pulping machine comprising: a screen extending upward from the bottom of the pulping machine and a rotor rotating around the outside of the screen. The pulp outlet is located inside the screen, while the pulp inlet and pulp residue outlet are located outside the screen. The rotor blades extend cantilevered from a rotor base located at the top of the screen into the area of ​​the screen, and the rotor blades are not interconnected within the area of ​​the screen. The rotor blades possess stiffness suitable for working with the outer surface of the screen to achieve a dispersing effect. Compared to "outward-flow" pulping machines with the pulp outlet located outside the screen, it is hoped that the advantages of this "inward-flow" pulping machine can be used to improve current coarse screening systems, thereby achieving the goals of reducing wear, improving dispersing, reducing costs, and reducing energy consumption. Summary of the Invention

[0005] To address the above technical problems, the present invention provides a coarse screening system that coarsely screens slurry received from a pulper and provides high-quality slurry to downstream equipment. The coarse screening system includes: a first coarse screening stage, comprising a first pulp screener and a first slurry supply pump located upstream of the first pulp screener and providing pressure to the first pulp screener; wherein the first pulp screener has a screen extending upwards from the bottom and a rotor rotating around the outside of the screen; wherein the slurry outlet of the first pulp screener is arranged inside the screen, and the high-quality slurry from the first coarse screening stage is provided to the downstream equipment through the slurry outlet of the first pulp screener; the slurry inlet and slurry outlet are arranged outside the screen; and the rotor blades of the rotor extend from the top of the screen. The rotor base extends cantilevered into the area of ​​the screen, and the rotor blades are not connected to each other within the area of ​​the screen. The rotor blades have stiffness suitable for working with the outer surface of the screen to achieve a dispersing effect. A discharge tank is included. A high-concentration cleaner is used to separate coarse and heavy impurities from the slurry. The slurry residue outlet of the first screen pulper outputs slurry residue to the feed pipe of the high-concentration cleaner. The overflow pipe of the high-concentration cleaner outputs good slurry to the feed pipe of the discharge tank. The underflow pipe of the high-concentration cleaner discharges coarse impurities. Depending on the composition of the slurry and impurities, due to the screening effect of the first coarse screen, the flow rate of good slurry from the high-concentration cleaner accounts for 10-40%, preferably 15-30%, of the total discharge flow rate of the pulper. Therefore, the volume of the discharge tank (in m³) is... 3 The good pulp flow rate corresponds to that of the high-concentration cleaner in the pulp and sludge line located in the first coarse screening stage, rather than the total discharge flow rate of the pulper under the prior art, that is, significantly reduced to the total discharge flow rate of the pulper (unit: m³). 3The product of one-third of the slurry's ( / min) and the predetermined residence time (in min) of the slurry in the discharge pool.

[0006] Coarse impurities are discharged from the waste collector of the high-concentration cleaner.

[0007] Preferably, the coarse screening system further includes a second coarse screening stage, which is arranged downstream of the discharge pool and includes a second pulping machine and a second pulping pump located upstream of the second pulping machine to provide pressure to the second pulping machine. The good pulp from the second coarse screening stage is provided to the downstream equipment through the pulping outlet of the second pulping machine. The discharge pool receives the good pulp from the good pulping outlet of the high-concentration cleaner downstream of the first pulping machine through a feed pipe and outputs the pulp to the second coarse screening stage through an underflow pipe.

[0008] In the coarse screening system of this invention, the first coarse screening stage employs a pulp screener based on the internal flow principle. In this "internal flow" pulp screener, since the inlet is located on the outside of the screen and the outlet is located on the inside, the good pulp flows towards the inside of the screen, while the pulp residue is blocked on the outside of the screen and preferably leaves the pulp screener tangentially from the pulp residue outlet, which is also designed on the outside of the screen. This reduces the wear on the inside of the screen caused by the centrifugal force generated by the rotor rotation, which typically occurs in the prior art, because heavy impurities that would cause severe wear to the screen are no longer located inside the screen but leave the outside of the screen tangentially under the action of centrifugal force.

[0009] Since the wear caused by heavy impurities on the screen can be significantly reduced in an in-flow pulping mill as described above, it is not necessary to require the pulp from the pulper to first pass through a hydrocyclone to remove heavy impurities before meeting the requirements of the downstream coarse screening stage, as is required in the prior art. Therefore, the first coarse screening stage with an in-flow pulping mill is arranged upstream of the high-concentration cleaner and closer to the pulper outlet in the coarse screening system of the present invention.

[0010] The pulp received from the pulper first passes through a first coarse screen, and then only the pulp residue from the first coarse screen is supplied to a downstream high-concentration cleaner (e.g., a hydrocyclone) through the outlet of the first pulp screen. Compared to the prior art where the pulp received from the pulper first passes through the high-concentration cleaner, instead of the entire flow passing through the high-concentration cleaner, only, for example, 20-30% (preferably diluted to a concentration of less than 4%) of the pulp residue reaches the high-concentration cleaner. This facilitates the use of a smaller high-concentration cleaner.

[0011] Similarly, in the coarse screening system according to the invention, no large loading / unloading towers are required. Typically, the slurry needs to be settling in such large loading / unloading towers for one hour to soak the shredded paper and reduce fiber loss. Now, a significantly smaller unloading tank can be used downstream of the high-concentration cleaner to replace the unloading towers of the prior art. Due to the significant reduction in volume of the unloading tank compared to the unloading tower (only about 25-35% of the latter's volume), the settling time of the slurry in the unloading tank is also significantly reduced. This significantly reduces investment costs, saves floor space, and reduces pumping energy consumption. The reduced height of the unloading tank of the present invention compared to the unloading towers of the prior art also leads to a further reduction in the required pumping power.

[0012] Furthermore, since the pulp screening machine itself has a certain outlet pressure, there is no need to arrange a pumping device between the first coarse screening stage and the high-concentration cleaner. Instead, the pulp residue can be directly output from the pulp residue outlet of the first pulp screening machine (preferably diluted to a concentration of <4%) to the feed pipe of the high-concentration cleaner. It is particularly preferred that the pulp residue flows directly to the high-concentration cleaner tangentially along the pulp screening machine.

[0013] This invention only requires that the first coarse screening stage be arranged immediately after the pulper, but the number of coarse screening stages can be arbitrarily set as needed, and is not limited to an arrangement of two, three, or more coarse screening stages. In a preferred embodiment of the coarse screening system according to the invention, the coarse screening system further includes a third coarse screening stage, which dilutes the pulp residue received from the second coarse screening stage with pulp received from the overflow pipe of the discharge tank and performs coarse screening, discharging the pulp residue from the coarse screening system and providing good pulp to the downstream equipment. It should be understood that, depending on the requirements for pulp quality, the good pulp can also be cascaded back upstream.

[0014] Since the first coarse screening stage has completed the main dewatering task with the first screening machine based on the internal flow principle, the second coarse screening stage can be either internal flow type, external flow type, or disc screening machine under existing technology.

[0015] In other words, according to a preferred embodiment of the coarse screening system of the present invention, the second coarse screening stage has a screen extending upward from the bottom and a rotor rotating inside the screen, wherein the inlet and outlet of the second coarse screening stage are arranged inside the screen, and the outlet is arranged outside the screen. This conventional "outflow" coarse screening stage has lower energy consumption and is preferred for a second coarse screening stage that does not primarily undertake the task of dewatering.

[0016] In another alternative implementation, the second coarse screening stage, using a "disc screen," has a screen arranged on the bottom surface and a rotor located above the screen. The outlet of the second coarse screening stage is located below the screen, while the inlet and outlet are located above the screen. However, this implementation results in higher energy consumption for the second coarse screening stage compared to the "outflow" type.

[0017] Of course, the second coarse screening stage can also be designed as an "internal flow" stage, just like the first coarse screening stage. The second screening mill of the second coarse screening stage has a screen protruding upwards from the bottom and a rotor rotating around the outside of the screen, wherein the pulp outlet of the second screening mill is arranged inside the screen, and the pulp inlet and pulp outlet are arranged outside the screen. The "internal flow" second coarse screening stage still has significant advantages in terms of screen wear and provides additional descaling effect. Attached Figure Description

[0018] The present invention will now be described in detail with reference to the accompanying drawings. In the drawings:

[0019] Figure 1 The coarse screening system according to the present invention is schematically illustrated;

[0020] Figure 2 The diagram schematically illustrates a coarse screening system in the prior art. Detailed Implementation

[0021] Figure 1 A coarse screening system according to the present invention is schematically illustrated. For comparison, Figure 2 The accompanying drawings schematically illustrate a coarse screening system of the prior art. For clarity, similar reference numerals are used in the drawings to denote the same or similar technical features in the present invention and the prior art.

[0022] like Figure 1 As shown, the pulp screened by the rotary drum pulper 10 is supplied to the first screening machine 20 of the first coarse screening stage via the first feed pump 21. The good pulp from the first screening machine 20 is combined with the good pulp from the downstream second screening machine 30 and third screening machine 40 and directly supplied to downstream equipment. The pulp residue from the first screening machine 20 is directly supplied to the hydrocyclone 50, which acts as a high-concentration cleaner. The high-concentration cleaner 50 is used to separate coarse and heavy impurities from the pulp. Figure 1 In the process shown, before the slurry from the first screening machine 20 is fed to the feed pipe of the hydrocyclone, dilution water W can be added as needed. However, the process of adding dilution water does not reduce the pressure of the slurry. On the contrary, the inlet pressure of the hydrocyclone can be increased during the process of adding dilution water by means of techniques known in the art.

[0023] The first coarse screen stage can be immediately following the rotary drum pulper 10 because the first pulper 20 of the first coarse screen stage is based on the internal flow principle. Here, the first pulper 20 has a screen protruding upward from the bottom and a rotor rotating around the outside of the screen. The pulp outlet of the first pulper 20 is arranged inside the screen, and the good pulp from the first coarse screen stage is supplied to the downstream equipment through the pulp outlet of the first pulper 20. The pulp inlet and pulp outlet are arranged outside the screen. The rotor blades of the rotor cantilever from the rotor base located at the top of the screen to the area of ​​the screen, and the rotor blades are not connected to each other in the area of ​​the screen. The rotor blades have stiffness suitable for achieving a dispersing effect together with the outer surface of the screen.

[0024] Because the "internal flow" slurry screener reduces the wear on the inner side of the screen under centrifugal force, the first coarse screen stage can handle slurry with more coarse and heavy impurities. Therefore, the first coarse screen stage can be arranged before the hydrocyclone. The screening effect of the first coarse screen stage greatly reduces the amount of slurry that the hydrocyclone needs to process.

[0025] The overflow pipe of the hydrocyclone outputs good slurry to the feed pipe of the discharge tank 60, while the underflow pipe of the hydrocyclone typically discharges heavy impurities through a waste collector. The slurry output from the underflow pipe of the discharge tank 60 is pressurized by the second slurry pump 22 and supplied to the second screening machine 30, while the overflow pipe supplies slurry to the third screening machine 40. The slurry residue from the second screening machine 30 is diluted and supplied to the third screening machine 40.

[0026] In the above embodiments of the coarse screening system of the present invention, the specific form of the second pulp screener 30 is not limited. It can be an internal flow type or an external flow type, or it can be a disc pulp screener.

[0027] Figure 2 The diagram schematically illustrates a coarse screening system in the prior art. Compared to the embodiments of the present invention described above, because a pulp screening machine based on the internal flow principle is not used, the inlet pulp of the first pulp screening machine in the prior art needs to be treated by a high-concentration cleaner 150 and a discharge tower 170. Figure 2In the illustrated embodiment, two hydrocyclones 150 are cascaded. The underflow pipe of the first-stage hydrocyclone, which receives the good pulp from the pulper 110, supplies slurry residue to the second-stage hydrocyclone, which receives the screen residue from the pulper 110. Diluent water is added upstream of the latter's feed pipe. The good pulp from the second-stage hydrocyclone is typically cascaded back to the upstream pulper, but in certain situations, it can also be fed downstream to the discharge tower. The first-stage hydrocyclone 150 overflows to the discharge tower 170. After settling for approximately one hour, the slurry is pressurized by the slurry pump 122 and supplied to a downstream coarse screening system with three coarse screening stages. The first, second, and third screeners, as well as the discharge pool and slurry pump between the second and third screeners, are indicated by reference numerals 120, 130, 140, 160, and 122, respectively.

[0028] The preferred embodiments of the present invention have been disclosed above; however, the spirit and scope of the present invention are not limited to the specific content disclosed. Those skilled in the art can develop more embodiments and specific applications based on the teachings of the present invention, and these embodiments and specific applications also fall within the spirit and scope of the present invention. The specific embodiments of the present invention are illustrative rather than limiting in their application to the claims.

[0029] List of reference numerals

[0030] 10 Pulping machine

[0031] 20 First screening machine

[0032] 21 First Grouting Pump

[0033] 30 Second screening machine

[0034] 22 Second Grouting Pump

[0035] 40 Third screening machine

[0036] 50 High-concentration cleaner

[0037] 60 Unloading Pool

[0038] 110 Pulper

[0039] 120 First screening machine

[0040] 121 First Grouting Pump

[0041] 130 Second Screening Machine

[0042] 122 Second Grouting Pump

[0043] 140 Third screening machine

[0044] 150 High-Concentration Cleaner

[0045] 160 Unloading Pool

[0046] 170 Unloading Tower

Claims

1. A coarse screening system for coarsely screening pulp received from a pulper and providing good pulp to downstream equipment, characterized in that, The coarse screening system includes: A first coarse screening stage, comprising a first pulp screener and a first pulp supply pump located upstream of the first pulp screener and providing pressure to the first pulp screener, wherein the first pulp screener has a screen extending upward from the bottom and a rotor rotating around the outside of the screen, wherein the pulp outlet of the first pulp screener is arranged inside the screen, and the good pulp of the first coarse screening stage is provided to the downstream equipment through the pulp outlet of the first pulp screener, while the pulp inlet and pulp outlet are arranged outside the screen, wherein the rotor blades of the rotor cantileverly extend from the rotor base located at the top of the screen to the area of ​​the screen, and the rotor blades are not connected to each other in the area of ​​the screen, wherein the rotor blades have stiffness suitable for achieving a dispersing effect together with the outer surface of the screen; Unloading pool; A high-concentration cleaner is used to separate coarse and heavy impurities in slurry. The slurry residue outlet of the first slurry screener directly outputs slurry residue to the feed pipe of the high-concentration cleaner. The overflow pipe of the high-concentration cleaner outputs good slurry to the feed pipe of the unloading pool. The underflow pipe of the high-concentration cleaner discharges coarse impurities.

2. The coarse screening system according to claim 1, characterized in that, The coarse screening system also includes a second coarse screening stage, which is arranged downstream of the unloading pool and includes a second pulp screening machine and a second pulp supply pump located upstream of the second pulp screening machine to provide pressure to the second pulp screening machine. The good pulp from the second coarse screening stage is supplied to the downstream equipment through the pulp outlet of the second pulp screening machine. The discharge tank receives good slurry from the good slurry outlet of the high-concentration cleaner downstream of the first screening machine via a feed pipe, and outputs the slurry to the second coarse screening stage via an underflow pipe.

3. The coarse screening system according to claim 2, characterized in that, The coarse screening system further includes a third coarse screening stage, which dilutes the slurry residue received from the second coarse screening stage with the slurry received from the overflow pipe of the discharge pool and performs coarse screening, discharging the screened slurry residue from the coarse screening system while providing good slurry to the downstream equipment.

4. The coarse screening system according to claim 2 or 3, characterized in that, The second screening machine of the second coarse screening stage has a screen protruding upward from the bottom and a rotor rotating around the outside of the screen, wherein the slurry outlet of the second screening machine is arranged inside the screen, and the slurry inlet and slurry outlet are arranged outside the screen.

5. The coarse screening system according to claim 2 or 3, characterized in that, The second coarse screening stage has a screen protruding upward from the bottom and a rotor rotating inside the screen, wherein the inlet and outlet of the second screening machine are arranged inside the screen and the outlet is arranged outside the screen.

6. The coarse screening system according to claim 2 or 3, characterized in that, The second screening machine of the second coarse screening stage has a screen arranged on the bottom surface and a rotor located above the screen, wherein the slurry outlet of the second screening machine is arranged on the lower side of the screen, and the slurry inlet and slurry outlet are arranged on the upper side of the screen.

7. The coarse screening system according to any one of claims 1 to 3, characterized in that, The pulp residue outlet of the first screening machine directly outputs pulp residue diluted to a concentration of less than 4% to the feed pipe of the high-concentration cleaner.

8. The coarse screening system according to any one of claims 1 to 3, characterized in that, The underflow pipe of the high-concentration cleaner discharges coarse impurities through a waste collector.

9. The coarse screening system according to any one of claims 1 to 3, characterized in that, The volume of the discharge pool corresponds to approximately one-third of the total slurry flow rate discharged from the pulper and the product of the predetermined residence time of the slurry in the discharge pool.

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