CN116558253A

CN116558253A - Air cushion type pulp dryer with transverse air blowing box

Info

Publication number: CN116558253A
Application number: CN202310127051.XA
Authority: CN
Inventors: P·T·海基莱; 理查德·索林
Original assignee: Valmet Technologies Oy
Current assignee: Valmet Technologies Oy
Priority date: 2022-02-04
Filing date: 2023-02-06
Publication date: 2023-08-08
Also published as: AT525833A3; FI130158B; FI20225098A1; AT525833A2; AT525833B1

Abstract

The invention relates to an air cushion type pulp dryer with a transverse air blowing box. The blow boxes (13) are arranged as superposed drying decks (11) with passages (15) for the pulp web (14) between them. The pulp web (14) is arranged to run horizontally in a zig-zag manner via the drying table (11). A part of the air blowing box (13) is positioned above the channel (15), and the rest of the air blowing box (13) is positioned below the channel (15). Between the two channels (15) there are two blow boxes (13) arranged together. The blow box (13) is a combined box (22) with both top nozzles (23) and bottom nozzles (24) and a bottom box (25) with only top nozzles (26), which is lower than the drying table (11). Furthermore, the blow box (13) is stationary.

Description

Air cushion type pulp dryer with transverse air blowing box

Technical Field

The invention relates to an air-cushion pulp dryer (airborne pulp dryer) with transverse blow boxes, wherein the blow boxes are arranged as superposed drying decks with a channel between them for a pulp web, which pulp web is arranged to run horizontally in a zigzag manner via the drying decks, and a part of the blow boxes is located above the channel and the rest of the blow boxes is located below the channel.

Background

In a pulp dryer, the pulp web runs zigzag between transverse blow openings arranged on stacked drying tables. Hereinafter, the air-blowing opening is referred to as a nozzle. The nozzles cover the width of the pulp web and are arranged as components of the blow box. In practice, several consecutive nozzles form a blow row. The hot drying air is blown through a nozzle arranged as a blow box. A so-called top box sprays air against the top surface of the pulp web. Accordingly, a so-called lower box sprays air underneath the pulp web. An air cushion type pulp dryer is disclosed in EP 3733964.

In the known pulp dryer, the blow boxes are located closely side by side on both sides of the pulp web in order to maximize the drying capacity of the pulp dryer. For maintenance, the top box includes a lifting function. In this way, each top box can be lifted so that, after the pulp web breaks, the pulp web can be reached for removal thereof. In addition to the lifting device itself, there must be additional space between the drying decks for the lifted top box. In addition, although there is an additional space between the drying tables, the air flow space for the exhaust air is narrow. In summary, pulp dryers have a limited capacity and pulp dryers include auxiliary equipment that adds to the cost and compromises occupational safety.

Disclosure of Invention

It is an object of the present invention to provide a new air cushion type pulp dryer with a transverse blow box, which pulp dryer is simple in construction, has fewer blow boxes but is more efficient than before. The characteristic features of the pulp dryer according to the invention are stated herein. In pulp dryers there are different types of blow boxes. On the other hand, more air can be sent to the pulp dryer. In addition, there is more room for exhaust. In this way, the hot air is uniformly and effectively diffused towards the pulp web, and the exhaust gas flows with low flow resistance. This significantly enhances the drying of the pulp web. There is more room for maintenance. In practice there is enough space so that the blow box can be stationary. In other words, broke (brook) may be removed without lifting the blow box as in the known art. Thus simplifying the construction of the pulp dryer without the need for lifting means. At the same time, the ergonomics and safety of the maintenance work become better. Furthermore, the drying table may be lower than before, which reduces the total height of the pulp dryer. On the other hand, more drying decks may be located in current pulp dryers.

Drawings

The invention is described in detail below with reference to the attached drawing figures, which illustrate some embodiments of the invention, wherein

Figure 1 schematically shows a side view of a pulp dryer according to the invention,

figure 2 shows a view of a pulp dryer according to the prior art in the machine longitudinal direction,

figure 3 shows a view of the pulp dryer according to the invention in the longitudinal direction of the machine,

figure 4a shows a side view of a part of a pulp dryer according to the invention,

figure 4b shows A-A view of figure 4a,

figure 4c shows a view B-B of figure 4a,

figure 5a shows a partial enlargement of figure 4b,

figure 5b shows a close-up view of figure 4c,

figure 5c schematically shows the flow of the supply air,

figure 5d schematically shows the flow of exhaust gases,

figure 6a shows one configuration of a blow box according to the invention,

figure 6b shows another configuration of a blow box according to the invention,

fig. 6c shows yet another configuration of a blow box according to the invention.

Detailed Description

Fig. 1 schematically shows a side view of a pulp dryer according to the invention. The pulp dryer has a closing hood 10 comprising a stack of drying stations 11. Each drying deck 11 has turning rolls 12 at both ends and a blow box 13 therebetween. In an air-cushion pulp dryer, the pulp web 14 runs horizontally in a zigzag manner via the drying table 11. Between the turning rolls 12, the air blown out of the blow box 13 supports the pulp web. The pulp web moves over the air layer. Typically, the pulp web enters from the top of the hood 10 and exits at the bottom of the other side end. The height of the drying deck is mainly dependent on the required air quantity and the width of the pulp web. The wider the pulp web, the higher the blow box and the higher the drying table. In practice, the drying decks are 250mm to 800mm high, and in a pulp dryer there are typically 10 to 30 drying decks.

Here, only a part of the blow box is shown. In practice, the lateral blow boxes arranged side by side fill the space between the turning rolls on both sides of the pulp web. The blow boxes 13 are arranged as stacked drying decks 11 with passages 15 for the pulp web 14 between them. As shown in fig. 2, a portion of the blow box 13 is located above the channel 15, and the rest of the blow box 13 is located below the channel 15. Thus, air is blown against both sides of the pulp web.

Air is sent at one end to the blow box by one or more fans. In fig. 1, seven stacked fans 16 are arranged as a fan tower. Here, the first blow box is open, while the next blow box is closed. Then, the next fan tower is located at the other side of the shroud. In practice, air is circulated through a fan tower. In addition, there is a heating and filtering device 17 in each fan tower as shown by the dashed rectangle in fig. 2 and 3. In this way, the air is continuously heated and filtered.

Fig. 2 shows a view of a pulp dryer according to the prior art in the machine longitudinal direction. Here, the fan 16 is on the left side, which blows hot air into the supply chamber 18 and thus into the blow box 13. Since the opposite end of the blow box is closed, the blown air is discharged via nozzles towards the pulp web 14. The air ejected from the nozzle is indicated by small arrows. The exhaust air then flows between the blow boxes 13 to the exhaust plenum 19 and thus to the adjoining fan towers. The upper two blow boxes 13 are shown in the production position. The next two blow boxes are in a maintenance position in which the so-called top box is lifted. The channel is then widened, for example, so that broke can be removed. For lifting the blow box 13, a lifting device 20 is provided.

Fig. 3 discloses a part of a pulp dryer according to the invention. Here, only the upper portion of the cover 10 is shown. Between the supply chamber 18 and the exhaust chamber 19 is a top plate 21 which restricts air flow out of the hood 10. By adjusting the amount and flow of the supply and exhaust air, the drying capacity of the pulp dryer is kept optimal and the energy losses are minimized.

According to the invention, between the two channels 15 there are two blow boxes 13 arranged together. First, there is a combination box 22, the combination box 22 having both a top nozzle 23 and a bottom nozzle 24 (fig. 5 c). Next, there is a bottom tank 25, the bottom tank 25 having only top nozzles 26 and being lower than the drying table 11. Here, the bottom box is below the pulp web, the top nozzle sprays air forming the underside of the pulp web, and the top nozzle is on the top surface of the bottom box. Thus, the known top box is lacking here. Finally, the blow box 13 is stationary. By this combination, a number of advantages are achieved. The combining box is so spacious that a large amount of air can be fed into the pulp dryer. Furthermore, by combining the boxes, air is simultaneously directed upwards and downwards towards the pulp web. However, since there is only a single low bottom tank, there is a clear exhaust path. In practice, the flow of exhaust gas is accelerated even in the funnel (fuel) thus formed. This facilitates air circulation and thus the efficiency of the pulp dryer. The flow of exhaust gas is indicated by arrows in fig. 4c, 5b and 5 d. With the new configuration, a large part of the double-sided drying efficiency is achieved, with sufficient space left between the blow boxes for the exhaust air and sufficient access to the pulp web for cleaning. In addition, the additional space is advantageous for maintenance. Finally, the blow box may be stationary. Thus, the known lifting device is not necessary. At the same time, the blow boxes of different drying stations may be closer than before. In this way the drying table becomes lower and the turning roll can therefore be smaller than before. Thus, the whole structure of the pulp dryer becomes more compact.

For example, as shown in fig. 5c, the combination tank 22 is a single tank having a top nozzle 23 and a bottom nozzle 24. The box has a simple structure and is easy to manufacture. On the other hand, the combining box 22 may be a combination of two boxes fixed on top of each other (on the top of each other) (fig. 6a to 6 c). In this way it is even possible to use known blow boxes and to combine them into a combined box. At the same time, the stiffness of the combined box increases, which reduces bending and vibration.

Since the blow box is stationary, especially the combined box may be higher than before. In practice, the maximum height H of the combining box 22 is 60% to 90% of the height H of the drying table 11, advantageously 70% to 95% of the height H of the drying table 11. At the same time, a maximum amount of air can be fed into the combiner box. The height of the bottom box can vary, as it is single. The bottom tank may be higher than before if more air is needed. In practice, however, the maximum height k of the bottom tank 25 is 20% to 70% of the height H of the drying table 11, advantageously 40% to 60% of the height H of the drying table 11. In this way, there is more space than known liftable gas boxes. In addition, the exhaust flow is relatively free, which is enhanced by the suction of the adjoining fan towers.

When the bottom tank 25 is arranged to taper (taper) in the longitudinal direction of the bottom tank 25, even more space is obtained. For example, when the open end is about half the height of the drying table, the closed end is about one-fourth the height. This facilitates maintenance and also enables sensing and visual monitoring. In other words, it can be seen from the side of the pulp dryer how the pulp web is to run. Furthermore, sensors may be installed if desired.

As a basic rule, the combination boxes 22 and the bottom boxes 25 are alternately arranged as shown in fig. 6 a. In other words, every other box is a box. However, this rule may vary. As in fig. 6b, there may be two combined boxes 22 after one bottom box 25. Alternatively, two combined boxes 22 may follow two bottom boxes 25 arranged side by side (fig. 6 c). By both variants the amount of air is increased, but still between the blow boxes without lifting. In the illustrated embodiment, each fan has six blow boxes. Further, six blow boxes are supported together at the open ends.

As mentioned before, each blow box 13 has an open feed head 27 and an opposite closed end 28. Instead of lifting means, the closed end 28 has a top bracket 29. The top bracket 29 is simple and it does not restrict the flow of exhaust gas. Here, the top bracket 29 is arranged on a square tube 30 in the machine longitudinal direction. This arrangement accommodates thermal expansion without distorting or deforming the blow box. In addition, the closed end 28 may be lifted out of the top bracket 29. This allows both assembly and maintenance. In addition, the blow box may leave or hide some during web breaks.

The nozzle is a hole or slit as its simplest formed blowing opening. Advantageously, in a part of the top nozzles 23, 26 there is a coanda shaping section 31 (fig. 5 d) for air blowing. This facilitates air flow along the pulp web and smoother running of the pulp web. In addition, a portion of the combiner box 22 has a planar bottom surface 32. These boxes are easy to manufacture, for example by bending a metal sheet.

As an example, the characteristics of an air-cushion dryer with a web width of 5, 6 meters, with the capacity to produce 1400 tons of air-dried pulp per day when the blow boxes are fixed, and each second top blow box is eliminated, are listed next. This means a total reduction of about 40% of the blow boxes. The outer dimensions of the pulp dryer will remain the same. However, as the drying table height can be scaled down, the turning roll diameter will be reduced from 475mm to 415mm. At the same time, the number of drying stations is increased from 25 to 29, which increases the drying length by 16%. This compensates for the fewer blow boxes. In addition, the number of blow boxes is reduced and new blow box arrangements can also be made from existing blow boxes. At the same time, the blow box lifting device becomes unnecessary. The pulp dryer will be simpler and more compact but easy to run and maintain. As a result, construction and operating costs are even reduced by 6% to 12%.

The air-cushion pulp dryer is characterized by contact-free drying, and the pulp web is run over the whole drying length by means of a high drying capacity blow box design. The pulp web runs directly in the pulp dryer without any risk of web breakage. The high overall efficiency of the circulating air flow with low pressure loss, combined with all-steel steam coils, improves drying process performance. By means of the new blow box, excellent runnability and enhanced drying are achieved. In addition, the pulp dryer has a high energy efficiency resulting in energy savings. Furthermore, the circulation of the gas flow has a low pressure loss. In summary, stable pulp web runnability is achieved with less production and maintenance costs and downtime.

Claims

1. An air cushion pulp dryer with transverse blow boxes, wherein the blow boxes (13) are arranged as stacked drying decks (11) with a channel (15) between them for a pulp web (14) which is arranged to run horizontally in a zigzag manner via the drying decks (11), and a part of the blow boxes (13) is located above the channel (15) and the rest of the blow boxes (13) is located below the channel (15), characterized in that between the two channels (15) there are two blow boxes (13) arranged together, namely a combination box (22) with both top nozzles (23) and bottom nozzles (24), and a bottom box (25) with only top nozzles (26), and that the bottom box is lower than the drying decks (11), and that the blow boxes (13) are stationary.

2. Pulp dryer according to claim 1, characterized in that the combined tank (22) is a single tank with a top nozzle (23) and a bottom nozzle (24).

3. Pulp dryer according to claim 1, characterized in that said combined box (22) is a combination of two boxes fixed on top of each other.

4. A pulp dryer according to any one of claims 1-3, characterized in that the maximum height (H) of the combining box (22) is 60-90% of the height (H) of the drying table (11), advantageously 70-95% of the height (H) of the drying table (11).

5. Pulp dryer according to any one of claims 1-4, characterized in that the maximum height (k) of the bottom box (25) is 20-70% of the height (H) of the drying table (11), advantageously 40-60% of the height (H) of the drying table (11).

6. Pulp dryer according to claim 5, characterized in that the bottom box (25) is arranged to taper in the longitudinal direction of the bottom box (25).

7. Pulp dryer according to any one of claims 1-6, characterized in that the combination boxes (22) and the bottom boxes (25) are alternately arranged.

8. A pulp dryer according to any one of claims 1-6, characterized in that after one bottom tank (25) there are two combined tanks (22).

9. A pulp dryer according to any one of claims 1-6, characterized in that after two bottom boxes (25) arranged side by side there are two combined boxes (22).

10. Pulp dryer according to any one of claims 1 to 9, characterized in that each blow box (13) has an open feed head (27) and an opposite closed end (28) with a top bracket (29).

11. Pulp dryer according to claim 10, characterized in that the closed end (28) can be lifted out of the top bracket (29).

12. Pulp dryer according to any one of claims 1-11, characterized in that a part of the top nozzles (23, 26) has a coanda forming section (31) for air blowing.

13. Pulp dryer according to any one of claims 1-12, characterized in that a part of the combining box (22) has a flat bottom surface (32).

14. Pulp dryer according to any one of claims 1 to 13, characterized in that the height (H) of the drying table (11) is 250mm to 800mm.

15. Pulp dryer according to any one of claims 1-14, characterized in that the pulp dryer comprises stacked fans (16) with heating and filtering means (17).