FI20225098A1

FI20225098A1 - Airborne pulp dryer with cross-directional blow boxes

Info

Publication number: FI20225098A1
Application number: FI20225098A
Authority: FI
Inventors: PERTTI HEIKKILä; Richard Solin
Original assignee: Valmet Technologies Oy
Priority date: 2022-02-04
Filing date: 2022-02-04
Publication date: 2023-03-21
Also published as: FI130158B; AT525833A3; CN116558253A; AT525833A2; AT525833B1

Abstract

The invention relates to an airborne pulp dryer with cross-directional blow boxes. The blow boxes (13) are arranged as superposed drying decks (11) having in between a passage (15) for a pulp web (14). The pulp web (14) is arranged to run horizontally in a zigzag manner via the drying decks (11). A part of the blow boxes (13) are situated above the passage (15) and the rest of the blow boxes (13) are situated below the passage (15). Between two passages (15) there are two kinds of blow boxes (13) arranged alongside. The blow boxes (13) are namely combo boxes (22) having both top nozzles (23) and bottom nozzles (24), and bottom boxes (25) having top nozzles (26) only and being lower than the drying deck (11). Also the blow boxes (13) are stationary.

Description

ATRBORNE PULP DRYER WITH CROSS-DIRECTIONAL BLOW BOXES

The present invention relates to an airborne pulp dryer with cross-directional blow boxes, wherein the blow boxes are ar- ranged as superposed drying decks having in between a passage for a pulp web arranged to run horizontally in a zigzag man- ner via the drying decks, and a part of the blow boxes are situated above the passage and the rest of the blow boxes are situated below the passage.

In the pulp dryer the pulp web runs zigzag between cross- directional blow openings arranged on superposed drying decks. Later on the blow openings are called as nozzles. The nozzles cover the width of the pulp web and are arrange as the parts of the blow boxes. In practice, several consecutive nozzles form a blow row. Hot drying air is blown though the nozzles, which are arranges as blow boxes. So-called top box- es jet air towards the top surface of the pulp web. Corre- spondingly so-called lower boxes jet air towards the under- side of the pulp web. One airborne pulp dryer is disclosed in

EP3733964.

In the known pulp dryer the blow boxes are situated tightly

N side by side and on both side of the pulp web to maximize the

O 25 drying capacity of the pulp dryer. For maintenance, the top

N boxes include lifting functionality. In this way, each top x box can be lifted and thereby reach to pulp web for removal = after the break of the pulp web. In addition to the lifting

N devices themselves, between drying decks there must be extra 3 30 room for the top boxes lifted. Also, in spite of the extra

N room between drying decks, air flow space for exhaust air is

N tight. In total, the capacity of the pulp dryer is limited, and the pulp dyer includes auxiliary eguipment which raise costs and impair occupational safety.

The object of the invention is to provide a new kind airborne pulp dryer with cross-directional blow boxes, which pulp dry- er is simple, but more effective than before even with less blow boxes. The characteristic features of the pulp dryer ac- cording to the invention are stated in the accompanying

Claims. In the pulp dryer there are different types of blow boxes. On the other hand, more air can be fed into the pulp dryer. And more, there are more space for exhaust air. In this way hot air is spread evenly and effectively towards the pulp web and exhaust air flows with low flow resistance. This intensifies the drying of the pulp web notably. Also there are more room for maintenance. In practice, there is so much room that the blow boxes may be stationary. In other words, broke can be removed without lifting the blow boxes like in the known technology. So the lifting devices are unnecessary which simplifies the structure of the pulp dryer. Simultane- ously, the ergonomics and safety of the maintenance work get much better. And more, the drying decks may be lower than be- fore which reduces the total height of the pulp dryer. On the other hand, more drying decks can be situated in a current pulp dryer.

N The invention is described below in detail by referring to

O 25 the enclosed drawings, which illustrate some of the embodi-

N ments of the invention, in which 3 = Figure 1 shows schematically a side view of a pulp dryer ac-

N cording to the invention, 3 30 Figure 2 shows a view in the machine direction of a pulp

N dryer according to the prior art,

N Figure 3 shows a view in the machine direction of a pulp dryer according to the invention,

Figure 4a shows a side way of the of a part of the pulp dryer according to the invention,

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

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

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

Figure 5b shows a partial enlargement of Figure 4c,

Figure 5c shows schematically flowing of supply air,

Figure 5d shows schematically flowing of exhaust air,

Figure 6a shows one configuration of the blow boxes according to the invention,

Figure 6b shows another configuration of the blow boxes ac- cording to the invention,

Figure 6c shows still another configuration of the blow boxes according to the invention.

Figure 1 shows schematically a side view of a pulp dryer ac- cording to the invention. The pulp dryer has a closed hood 10 including superposed drying decks 11. Each drying deck 11 has turn rolls 12 at both ends and blow boxes 13 between them. In the airborne pulp dryer, the pulp web 14 runs horizontally in a zigzag manner via the drying decks 11. Between the turn rolls 12 air blowing from the blow boxes 13 supports the pulp web. So the pulp web moves on an air layer. Usually the pulp

N web enters from the top of the hood 10 and exits at the bot-

O 25 tom on the opposite end. The height of the drying deck de-

N pends mainly on the amount of air needed and the width of the x pulp web. The wider pulp web, the taller blow box and higher = drying deck. In practice, the drying deck is 250 - 800 mm

N high and there are typically 10 - 30 drying decks in one pulp 2 30 dryer.

S

Here only a part of the blow boxes are shown. In practice, the cross-directional blow boxes arranged side by side fill out the space between the turn rolls on both side of the pulp web. The blow boxes 13 are arranged as superposed drying decks 11 having in between a passage 15 for the pulp web 14.

Like shown in Figure 2, a part of the blow boxes 13 are situ- ated above the passage 15 and the rest of the blow boxes 13 are situated below the passage 15. So, air is blown towards both sides of the pulp web.

Air is fed to the blow boxes at one end with one or more fans. In Figure 1 there are seven superposed fans 16 arranged as a fan tower. Here the first blow boxes are open-ended while the next blow boxes are close-ended. Then the next fan tower is at the opposite side of the hood. In practice, air is circulated through the fan towers. Also there are heating and filtering means 17 in each fan tower shown as dashed rec- tangles in Figures 2 and 3. In this way, air is constantly heated and filtered.

Figure 2 shows a view in the machine direction of a pulp dry- er according to the prior art. Here the fan 16 is on the left side, and it blows hot air to a supply chamber 18 and thereby into the blow boxes 13. Since the opposite ends of the blow boxes are closed, the blown air discharges via the nozzles towards the pulp web 14. Air jetting from the nozzles is rep-

AN resented with small arrows. Then the exhaust air flows be-

O 25 tween the blow boxes 13 to an exhaust chamber 19 and thereby

N to the adjoining fan towers. The upper two blow boxes 13 are x shown in the production position. The next two blow boxes are = in the maintenance position where the so-called top box is

N lifted up. Then the passage wideness enabling the removal of 3 30 broke, for example. For lifting the blow boxes 13 there are

N lifting means 20.

N

Figure 3 discloses a part of the pulp dryer according to the invention. Here only the upper part of the hood 10 is shown.

Between the supply chamber 18 and the exhaust chamber 19 there is a ceiling 21, which limits the air flow out of the hood 10. By regulating the amounts and flows of supply and exhaust air, the drying capacity of the pulp dryer is kept 5 optimum and energy loss is minimized.

According to the invention between two passages 15 there are two kinds of blow boxes 13 arranged alongside. First there are combo boxes 22 having both top nozzles 23 and bottom noz- zles 24 (Figure 5c). Next there are bottom boxes 25 having top nozzles 26 only and being lower than the drying deck 11.

Here, the bottom box is under the pulp web and the top noz- zles jet air form underside of the pulp web while the top nozzles are on the top surface of the bottom box. So, the known top boxes are missing here. Finally, the blow boxes 13 are stationary. With this combination many advantages are achieved. The combo boxes are spacious, so a large amount of air can be fed into to the pulp dryer. Also, with the combo box air is fed simultaneously up and down towards the pulp web. However, since there is only single bottom box, which is low, there is a clear way for exhaust air. In practice, the flow of the exhaust air even accelerates in the funnel thus formed. This aids the air circulation and there by the effi-

N ciency of the pulp dryer. The flows of exhaust air are repre-

S 25 sented with arrows in Figure 4c, 5b and 5d. With the new con-

N figuration, the majority of the double-sided drying efficien- x cy is achieved, but leaving sufficient space for exhaust air = between the blow boxes and adequate access to the pulp web

N for cleaning. Also, the extra room facilitates the mainte- 3 30 nance. And finally, the blow boxes may be stationary. So, the

N known lifting means are needless. Simultaneously, the blow

N boxes of the different drying decks may be much closer than before. In this way, the drying decks become lower and there-

by the turn rolls may be smaller than before. Thus, the whole structure of the pulp dryer becomes more compact.

As shown in Figure 5c for example, the combo box 22 is a sin- gle box having top nozzles 23 and bottom nozzles 24. This kind of box is simple in structure and easy to manufacture.

On the other hand, the combo box 22 may be a combination of two boxes fixed on the top of each other (Figures 6a - 6c).

In this way, even the known blow boxes may be utilized and combined as a combo box. At the same time, the stiffness of the combo box increases, which reduces bending and vibra- tions.

Since the blow boxes are stationary, especially the combo boxes may be higher than before. In practice, the maximum height h of the combo box 22 is 60 — 90%, advantageously 70 -— 95% of the height H of the drying deck 11. Simultaneously, the maximum amount of air can be fed into combo boxes. Since the bottom box is single, its height can vary. If more air is needed, the bottom box may be higher than before. However, in practice the maximum height k of the bottom box 25 is 20 - 70%, advantageously 40 - 60% of the height H of the drying deck 11. In this way, there is more room than with the known

N liftable blow boxes. In addition, the exhaust air flows more

O 25 freely which is intensified by the suction of the adjoining

S fan towers.

S

= Even more space is achieved, when the bottom box 25 is ar-

N ranged to taper in the longitudinal direction of the bottom 3 30 box 25. For example, when the open end is about the half of

N the height of the drying deck, is the closed end about quar-

N ter of the height. This facilitates the maintenance, but also enables sensing and visual monitoring. In other words, from the side of the pulp dryer it is possible to see how the pulp web runs. Also, sensors may be installed if needed.

As a basic rule, the combo boxes 22 and the bottom boxes 25 are arranged alternately, like shown in Figure 6a. In other words, every other is a combo box. However, this rule may vary. Like in Figure 6b, there can be two combo boxes 22 af- ter one bottom box 25. Alternatively, there can be two combo boxes 22 after two bottom boxes 25 arranged side by side (Figure 6c). With these two variants the mount of air is in- creased, but it is still possible the reach between the blow boxes without lifting. In the shown embodiments there are six blow boxes per one fan. Also, the six blow boxes are support- ed together at the open ends.

As mentioned earlier, each blow box 13 has an open feed head 27 and a 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 limit the flow of exhaust air. Here, the top bracket 29 lies on a square tube 30 arranged in the machine direction. This arrangement adapts thermal expansion without twisting or deformation of the blow box. Also, the closed end 28 is liftable out from the top bracket 29. This

AN enables both assembly and maintenance. Also, during web

O 25 breaks, the blow boxes may pop up or dodge a little bit.

S x The nozzles are holes or slits as their simplest forming blow = openings. Advantageously, in a part of the top nozzles 23, 26

N has a coanda shaping 31 for air blows (Figure 5d). This fa- 3 30 cilitates the air flow along the pulp web and smoother run-

N ning of the pulp web. In addition, a part of the combo boxes

N 22 has a flat bottom surface 32. These boxes are easy to man- ufacture, by bending sheet metal, for example.

As an example, next 1s listed features of an airborne dryer with web width of 5,6 meters and capacity 1400 air-dried tons of pulp per day when the blow boxes are fixed, and every sec- ond top blow box is eliminated. This means about 40% fewer blow boxes in total. The outer dimensions of the pulp dryer will stay the same. However, the turning roll diameter will reduce from 475 mm to 415 mm, since the drying deck height can be scale down. Simultaneously, the number of the drying decks increases from 25 to 29 which increases the drying length 16%. This compensates for the fewer blow boxes. Also, the amount of blow boxes reduces, and the new blow box con- figuration could also be made out of existing blow boxes. At the same time, the blow box lifting equipment become unneces- sary. The pulp dryer will be simpler and more compact, but easy to run and maintain. As one result, building and running costs are reduced even 6 — 12%.

The airborne pulp dryer features contactless drying and the pulp web run with a high drying capacity blow box design across the whole drying length. The pulp web runs straight inside the pulp dryer without any risk of web breaks. The high total efficiency with low pressure losses of circulation air flow, combined with all-steel steam coils improve the

N drying process performance. With the new blow boxes excellent

S 25 runnability and enhanced drying is achieved. Also, the pulp

N dryer has high-energy efficiency causing energy savings. And x more, circulation of airflows has low pressure losses. In to- = tal, a steady pulp web runnability is achieved with fewer

N production and maintenance costs and shutdowns.

O

D

N

Claims

1. Airborne pulp dryer with cross-directional blow box- es, wherein the blow boxes (13) are arranged as superposed drying decks (11) having in between a passage (15) for a pulp web (14) arranged to run horizontally in a zigzag manner via the drying decks (11), and a part of the blow boxes (13) are situated above the passage (15) and the rest of the blow box- es (13) are situated below the passage (15), characterized in that between two passages (15) there are two kinds of blow boxes (13) arranged alongside namely combo boxes (22) having both top nozzles (23) and bottom nozzles (24), and bottom boxes (25) having top nozzles (26) only and being lower than the drying deck (11), and the blow boxes (13) are stationary.

2. Pulp dryer according to claim 1, characterized in that the combo box (22) is a single box having top nozzles (23) and bottom nozzles (24).

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

N 4. Pulp dryer according to any of claims 1 - 3, charac- O 25 terized in that the maximum height (h) of the combo box (22) N is 60 — 90%, advantageously 70 - 95% of the height (H) of the x drying deck (11). x a

© 5. Pulp dryer according to any of claims 1 - 4, charac- 3 30 terized in that the maximum height (k) of the bottom box (25) N is 20 - 70%, advantageously 40 - 60% of the height (H) of the N drying deck (11).

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

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

8. Pulp dryer according to any of claims 1 - 6, charac- terized in that there are two combo boxes (22) after one bot- tom box (25).

9. Pulp dryer according to any of claims 1 - 6, charac- terized in there are two combo boxes (22) after two bottom boxes (25) arranged side by side.

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

11. Pulp dryer according to claim 10, characterized in that the closed end (28) is liftable out from the top bracket (29). N S 25

12. Pulp dryer according to any of claims 1 - 11, charac- N terized in that a part of the top nozzles (23, 26) has a x coanda shaping (31) for air blows. x a ©

13. Pulp dryer according to any of claims 1 - 12, charac- 3 30 terized in that a part of the combo boxes (22) has a flat N bottom surface (32). N

14. Pulp dryer according to any of claims 1 - 13, charac- terized in that the height (H) of the drying deck (11) is 250 - 800 mm.

15. Pulp dryer according to any of claims 1 - 14, charac- terized in that the pulp dryer includes superposed fans (16) having heating and filtering means (17). N N O N N I + O I a a © O O O N N O N