Pulper with means for heating the pulp web

Abstract

The invention relates to a pulp machine having a device for heating a pulp web. The device comprises a water distribution device (19) for hot water and a steam distribution device (20) for steam, both arranged above the pulp web (16). The device further comprises a suction device (21) arranged below the pulp web (16). The water distribution device (19) comprises a water tank (22) and the steam distribution device (20) comprises a steam tank (23). The water tank (22) is separate from the steam tank (23) and arranged in front of the steam tank (23). Furthermore, the suction device (21) comprises a suction tank (24).

Description

Technical Field

[0001] The invention relates to a pulping machine having a device for heating a pulp web, the device comprising a water distribution device for hot water and a steam distribution device for steam, both of which are arranged above the pulp web, and a suction device arranged below the pulp web. Background Art

[0002] WO 9955958 A1 discloses an apparatus for heating a fibrous material strip (actually a pulp web). Essentially, the pulp web is dried with hot air in a pulp dryer. Prior to this, the pulp web is pressed to remove water. To improve drainage during the pressing process, the pulp web is preheated. In known techniques, hot water and steam are distributed over the pulp web to increase its temperature. The higher the pulp web temperature, the lower the viscosity of the water, thereby improving drainage during the pressing process. Furthermore, water can be removed by suction.

[0003] There are a number of problems with the known technology. Hot water is distributed simultaneously with steam and air. This disrupts the flow of each medium, reducing the efficiency of the entire device. In addition, there is a large hood that requires a lot of space and conducts heat away. The large hood is a box with long sides, which is challenging to position and seal (causing leaks). Secondly, the steam is distributed away from the pulp web and fills the entire open space within the hood. As a result, the steam mixes with the air and water, which disrupts effective heat transfer. At the same time, the steam escapes from the hood, also reducing efficiency. What's more, the suction below is weak and suffers from a lack of replacement air because it is always below the hood. In addition to the low efficiency of the device, because the pulp web is located away from the first press, it has time to cool down before being pressed. Summary of the Invention

[0004] The object of the present invention is to provide a novel pulping machine having a device for heating a pulp web that is more efficient and easier and more precise to adjust than previous devices. The pulping machine according to the present invention is characterized as follows. The pulping machine according to the present invention has a device for heating a pulp web, the device comprising: a water distribution device for hot water and a steam distribution device for steam, both of which are arranged above the pulp web; and a suction device arranged below the pulp web, the water distribution device comprising a water box, the steam distribution device comprising a steam box, wherein the water box is separate from and arranged before the steam box, and the suction device comprising a suction box. Furthermore, the water box and the steam box are positioned in the machine direction in the region of the suction box. Furthermore, the pulping machine has a top forming unit, the water box being arranged after the top forming unit. Furthermore, the distance between the top forming unit and the water box in the machine direction is 15 mm to 2500 mm, preferably 200 mm to 1000 mm. Furthermore, the water tank has a supply flow rate of 1 l / m / s to 4 l / m / s, preferably 1.5 l / m / s to 2.5 l / m / s. Furthermore, the water tank is a distribution water tank. Furthermore, the suction box has a length in the machine direction of 1000 mm to 4000 mm, preferably 1500 mm to 2500 mm. Furthermore, the suction box comprises several consecutive chambers in the machine direction, each chamber having its own suction connection. Furthermore, each chamber has a different increasing vacuum level compared to the previous chamber. Furthermore, the first vacuum level starts at -20 kPa and the last vacuum level ends at -50 kPa. Furthermore, the distance between the water tank and the steam box in the machine direction is 200 mm to 1500 mm, preferably 400 mm to 1200 mm. Furthermore, the steam box has a length in the machine direction of 500 mm to 2000 mm, preferably 1000 mm to 1600 mm. Furthermore, the steam box has a flat diffuser positioned 1 mm to 20 mm above the pulp web, preferably 10 mm to 15 mm. Furthermore, a lump breaker in contact with a suction roll is provided after the device. Furthermore, the temperature of the hot water during the distribution process is 70°C to 99°C, preferably 85°C to 95°C. This device effectively utilizes the advantages of each heating device. Furthermore, the environmental impact can be minimized. Thus, the pulp web can be heated more than before using less energy. The device has several adjustment options. Thus, one device can be installed in different types of pulping machines. Furthermore, the efficiency of the device can be improved in various ways. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present invention will now be described in detail with reference to the accompanying drawings, which illustrate some embodiments of the present invention, in which:

[0006] Figure 1 shows a side view of a portion of a pulping machine according to the invention,

[0007] Figure 2 A variant of the pulping machine according to the invention is shown.

[0008] Figure 3 Shown Figure 1 A partial enlarged view of the device.

[0009] Figure 4 The device is shown as seen from above the top of the pulp web. DETAILED DESCRIPTION

[0010] Figure 1 The beginning of a pulping machine is shown schematically. First comes the forming section 10, followed by the press section 11, and then the pulp dryer 12 (only partially shown). The forming section 10 comprises a wire 13 arranged in a loop. The pulp suspension is fed onto the wire 13 via a headbox 14. Below the wire 13 are several foils or suction boxes 15 for removing water, thereby forming a pulp web 16. Most of the water is removed in the forming section.

[0011] Here, the press section 11 first comprises a combi press 17, followed by a shoe press 18. Both presses have two press felts. Following the first shoe press, there can also be another shoe press. Most of the time, the pulp web is supported by a wire or press felt. However, there is an open draw between the presses, as well as between the shoe press 18 and the pulp dryer 12. After the shoe press, the pulp web 16 has a sufficiently high dryness of approximately 50% or more, and the remaining water evaporates in the pulp dryer 12.

[0012] Here, the forming section 10 includes an apparatus for heating a pulp web 16. The apparatus comprises a water distribution device 19 for hot water and a steam distribution device 20 for steam, both of which are arranged above the pulp web 16. Furthermore, the apparatus comprises a suction device 21 arranged below the pulp web 16. In the present invention, the water distribution device 19 comprises a water box 22, and the steam distribution device 20 comprises a steam box 23, wherein the water box 22 is separate from the steam box 23 and is arranged before the steam box 23. In other words, there are two separate devices or boxes spaced apart, with the water box in front and the steam box in the back. Furthermore, the suction device 21 comprises a suction box 24.

[0013] The combination of these boxes achieves numerous advantages. Each box can be adjusted and optimized independently. Furthermore, the flow of each medium remains undisturbed. When hot water is supplied first, it flows into the pulp web. The hot water effectively raises the pulp web's temperature throughout the process. Subsequently, steam contributes to the heating of the pulp web's surface. In other words, the hot water first penetrates the pulp web by suction. Simultaneously, some air is drawn from at least the top surface of the pulp web. Then, steam is supplied, condensing deeper into the surface of the pulp web. Surprisingly, the suction box below the wire continuously spans the gap between the water box and the steam box. This improves the penetration of water and steam into the pulp web, and when the pulp web includes a middle layer and a bottom layer, this results in a more efficient transfer of total heat to the pulp web across the entire thickness of the fiber mat. Consequently, the maximum amount of distributed heat is delivered to the pulp web, effectively heating it.

[0014] Advantageously, the water box 22 and steam box 23 are positioned in the machine direction in the area of ​​the suction box 24. This facilitates the flow of each medium. Furthermore, the surrounding, moist, warm air between the water box and steam box becomes a significant displacement air source that penetrates the web structure. This enables more efficient water removal and prepares the pulp web to absorb and condense steam deeper into the pulp web, providing better overall heat transfer. Preferably, the suction box is activated slightly earlier than the water box. Thus, when the pulp web is under vacuum before hot water is dispensed, hot water is immediately drawn into the pulp web. Simultaneously, water is effectively removed from the pulp web.

[0015] In addition to removing water downward, it is advantageous to use the top forming unit 25 in the front. Water is then also removed from above, which intensifies the removal of water. Therefore, the dryness of the pulp web before pressing increases and the forming section becomes shorter. In the present invention, the water tank 22 is arranged directly behind the top forming unit 25. The top surface of the pulp web is then in an open state, assisting the hot water in impregnating the pulp web. In other words, the hot water flows easily into the pulp web. Advantageously, the water tank is located as close as possible behind the top forming unit. In this way, it is possible to prevent outside air from flowing into the pulp web. Not only that, the hot water flows freely with the help of suction. In the present invention, in the machine direction, the distance D between the top forming unit 25 and the water tank 22 is 15 mm-2500 mm, preferably 200 mm-1000 mm ( Figure 3 ). In practice, the water tank is positioned as close as possible to the top forming unit. In this way, as little outside air as possible comes into contact with the pulp web. Instead of air, hot water will penetrate into the pulp web. Figure 2 In the example, the beginning of the forming section 10 is arranged as a gap former, with Figure 1 The hybrid former is shorter than the conventional one.

[0016] In practice, water lubrication is provided on the front wall of the water tank to keep its surface clean. The actual hot water flows out along a distribution surface at the rear edge of the water tank at an angle of approximately 45 degrees. This distribution surface preferably has a more gradual angle at its ends. As a result, the hot water flows more in the direction of the pulp web and its speed matches that of the pulp web. The distribution surface is preferably machined and shaped. This helps to distribute the water film as evenly as possible across the pulp web. Water can be supplied to only one selected side. On the other hand, dual-sided water supply is also possible in wide machines or with large amounts of water.

[0017] The amount of hot water depends on the grammage of the pulp web. In principle, the supply rate to the water tank 22 is 1-4 liters / m / s, preferably 1.5-2.5 liters / m / s. This unit indicates how many liters of hot water are supplied per second per meter of pulp web width. At this rate, the entire pulp web is heated by approximately 5 degrees Celsius without unnecessary rewetting. The added water is largely removed from the pulp web before pressing via a long, efficient suction box. Therefore, only a small amount of additional water is required, and the pulp web is effectively heated. The hot water also removes sticky components and fines, which can cause problems in later stages of the process (such as dust removal) and other runnability issues. This improves the runnability of the pulp web, reduces talc consumption, and improves pulp quality. During the dispensing process, the hot water temperature is 70-99°C, preferably 85-95°C. As a result, the hot water effectively penetrates the entire thickness of the pulp web, truly heating it. The upper temperature limit can be easily reached by using steam to heat the water in the water tank. If the amount of hot water needs to be increased, more than one water tank can be arranged in series.

[0018] The location of the water boxes, especially the profiling water boxes, is advantageous. This allows the moisture profile of the pulp web to be adjusted before pressing. At the same time, the forming section can be operated as efficiently as possible, and the moisture profile can then be adjusted immediately before the press section. The final product is then uniform, without the need for additional adjustments.

[0019] In practice, the suction box 24 has a length in the machine direction of 1000 mm to 4000 mm, preferably 1500 mm to 2500 mm. With such a long suction box, water removal is efficient, and hot water flows into the pulp web, raising its temperature. Furthermore, the pulp web is also subjected to a vacuum before the hot water is distributed to it. Advantageously, the suction box 24 comprises several chambers 26a, ..., 26n arranged in series in the machine direction, each chamber having its own suction connection 27a, ..., 27n. This allows water removal to be adjusted as needed. According to the present invention, each chamber 26a, ..., 26n has a different increasing vacuum level compared to the previous chamber. For example, the first vacuum level starts at -20 kPa, while the last vacuum level ends at -50 kPa. For example, if there are five chambers, the vacuum levels could be -20 kPa, -25 kPa, -30 kPa, -40 kPa, and -50 kPa. It is also possible to have a large single-chamber suction box with the same vacuum level or exactly the same vacuum level in at least two chambers or boxes. In this way, the vacuum level is increased step by step without damaging the pulp web, but effectively extracting water and steam.

[0020] exist Figure 4 In the drawing, there are five chambers 26a-26e arranged side by side. Only a portion of the width of the wire 13 on the drive side is shown here. The pulp web 16 lies on the wire 13, and the suction box 24 is located below the wire 13. The wire 13 and the pulp web 16 are partially cut away, and the dewatering element 28 is shown as part of the suction box 24. Each suction connection 27a-27e initially extends directly out of the pulping machine and then bends downwards, for example, to a vacuum system.

[0021] The suction box reaches slightly longer than the steam box. This prevents steam from escaping because replacement air from the surrounding environment enters the suction box. The replacement air, together with the vacuum, pulls heat into the pulp web.

[0022] The suction box can be a single unit with several chambers. Alternatively, there can be two or more suction boxes arranged side by side. For example, each of the first two suction boxes has two chambers, and then the third suction box has three chambers. Advantageously, the suction box has a slit cover with a ceramic dewatering element. Such a suction box is compact and the vacuum is evenly distributed. Moreover, the service life of the ceramic dewatering element 28 is very long even if the net rubs against the ceramic dewatering element. The width of the chamber in the applicant's own suction box (i.e. the length in the machine direction) is 400 mm. The length of a suction box with five chambers is then 2000 mm.

[0023] According to the present invention, the distance P between the water box 22 and the steam box 23 in the machine direction is 200 mm to 1500 mm, preferably 400 mm to 1200 mm. This short gap gives the hot water time to penetrate the pulp web before the steam box. Furthermore, due to the gap, a portion of the suction box is open, effectively allowing the hot water to pass through the pulp web. Furthermore, the outside air slightly cools the surface of the pulp web. This facilitates condensation of the steam, which heats the pulp web surface. Assuming that hot liquid and air penetrate the pulp web together, this displacement air flowing toward the pulp web plays a significant role in improving the efficiency of the water box and steam box. The more hot water there is, the longer the gap becomes. Furthermore, it is the steam (not the water in it) that heats the pulp web.

[0024] Since the water box is separate from the steam box, a gap or free space is created on top of the pulp web, which brings advantages as mentioned before. Air can flow freely, but there may be equipment for distributing replacement air with conditioned heat and / or humidity.

[0025] The water box is short and compact. In contrast, the length T of the steam box 23 in the machine direction is 500 mm to 2000 mm, preferably 1000 mm to 1600 mm. This ensures that the steam is distributed efficiently and has time to heat the pulp web. While the hot water heats the entire pulp web, the steam primarily heats the top surface. The steam heats the pulp web by approximately 15 degrees Celsius. Consequently, together with the hot water, the pulp web temperature exceeds 70°C, advantageously exceeding 75°C, compared to approximately 50°C before the device. This effectively increases the dryness after the press section by 0.5% to 1%. Furthermore, the preheated pulp web begins to dry more quickly in the pulp dryer. Furthermore, the present invention reduces the specific steam consumption in the pulp dryer (and also in the entire pulp mill).

[0026] Advantageously, the steam box 23 has a flat diffuser plate 29 positioned 1 mm to 20 mm, preferably 10 mm to 15 mm, above the pulp web 16. This flat plate distributes the steam evenly and can be installed very close to the pulp web. As a result, the steam heats efficiently, and a small amount of outside air flows in from the sides as replacement air. This prevents the steam from escaping into the surroundings. The optimal pulp web temperature increase is achieved when the steam releases most of its energy and transforms from the gas phase to the liquid phase (so-called condensation). The steam emerges from the diffuser plate and condenses to the greatest extent possible, releasing its latent heat into the pulp web.

[0027] Finally, this device is followed by a lump breaker 30 in contact with a suction roll 31. The suction roll beneath the pulp web also transfers heat to the pulp web. The lump breaker 30 brings water to the top felt 32 and refurbishes it immediately before the actual combination press 17 and the subsequent transfer to the shoe press 18. The lump breaker 30 breaks up prematurely formed and / or oversized pulp lumps. Here, the heat is further diffused into the pulp web, and the temperature drops by several degrees. After the combination press 17, the pulp web is sufficiently dry and therefore durable enough to be transferred to the shoe press 18. With the device according to the invention, the pulp web is heated more efficiently from the top surface, but the press distributes the heat evenly throughout the pulp web.

Claims

1. A pulping machine having a device for heating a pulp web, the device comprising: a water distribution device (19) for hot water and a steam distribution device (20) for steam, both of which are arranged above the pulp web (16); and a suction device (21) arranged below the pulp web (16), characterized in that the water distribution device (19) comprises a water box (22), the steam distribution device (20) comprises a steam box (23), wherein the water box (22) is separate from the steam box (23) and is arranged before the steam box (23), and the suction device (21) comprises a suction box (24); the pulping machine has a top forming unit (25), and the water box (22) is arranged after the top forming unit.

2. The pulping machine according to claim 1, characterized in that The water box (22) and the steam box (23) are positioned in the machine direction on the region of the suction box (24).

3. The pulping machine according to claim 1 or 2, characterized in that: In the machine direction, the distance D between the top forming unit (25) and the water tank (22) is 15 mm to 2500 mm.

4. The pulping machine according to claim 1 or 2, characterized in that: In the machine direction, the distance D between the top forming unit (25) and the water tank (22) is 200 mm to 1000 mm.

5. The pulping machine according to claim 1 or 2, characterized in that: The supply flow rate of the water tank (22) is 1 l / m / s-4 l / m / s.

6. The pulping machine according to claim 1 or 2, characterized in that: The supply flow rate of the water tank (22) is 1.5 l / m / s-2.5 l / m / s.

7. The pulping machine according to claim 1 or 2, characterized in that: The water tank (22) is a distribution water tank.

8. The pulping machine according to claim 1 or 2, characterized in that: The length L of the suction box (24) in the machine direction is 1000 mm to 4000 mm.

9. The pulping machine according to claim 1 or 2, characterized in that: The length L of the suction box (24) in the machine direction is 1500 mm to 2500 mm.

10. The pulping machine according to claim 1 or 2, characterized in that: The suction box (24) comprises several consecutive chambers (26a, ... 26n) in the machine direction, each chamber having its own suction connection (27a, ... 27n).

11. The pulping machine according to claim 10, characterized in that The plurality of consecutive chambers (26a, ... 26n) in the machine direction have different rising vacuum levels.

12. The pulping machine according to claim 11, characterized in that The first vacuum level starts at -20 kPa and the last vacuum level ends at -50 kPa.

13. The pulping machine according to claim 1 or 2, characterized in that: The distance P between the water box (22) and the steam box (23) in the machine direction is 200 mm to 1500 mm.

14. The pulping machine according to claim 1 or 2, characterized in that: The distance P between the water box (22) and the steam box (23) in the machine direction is 400 mm to 1200 mm.

15. The pulping machine according to claim 1 or 2, characterized in that: The length T of the steam box (23) in the machine direction is 500 mm to 2000 mm.

16. The pulping machine according to claim 1 or 2, characterized in that: The length T of the steam box (23) in the machine direction is 1000 mm to 1600 mm.

17. The pulping machine according to claim 1 or 2, characterized in that: The steam box (23) has a planar diffuser plate (BP) positioned 1 mm - 20 mm above the pulp web (16).

18. The pulping machine according to claim 1 or 2, characterized in that: The steam box (23) has a flat diffuser plate (BP) positioned 10-15 mm above the pulp web (16).

19. The pulping machine according to claim 1 or 2, characterized in that: Following the device there is a lump breaker (30) in contact with a suction roll (31).

20. The pulping machine according to claim 1 or 2, characterized in that: The temperature of the hot water during the dispensing process is 70°C-99°C.

21. The pulping machine according to claim 1 or 2, characterized in that: The temperature of the hot water during the dispensing process is 85°C-95°C.

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