FI130498B

FI130498B - Pulp machine having an arrangement for heating a pulp web

Info

Publication number: FI130498B
Application number: FI20215983A
Authority: FI
Inventors: Timo Kari; Jukka Leino; Veli-Matti Levonmaa; Janne Suonperä
Original assignee: Valmet Technologies Oy
Priority date: 2021-09-20
Filing date: 2021-09-20
Publication date: 2023-10-10
Also published as: AT525492A2; AT525492B1; FI20215983A1; AT525492A3; CN115839039A

Abstract

The invention relates a pulp machine having an arrangement for heating a pulp web. The arrangement includes water distribution means (19) for hot water and steam distribution means (20) for steam both arranged above the pulp web (16). The arrangement includes further includes suction means (21) arranged below the pulp web (16). The water distribution means (19) include a water box (22) and the steam distribution means (20) include a steam box (23). The water box (22) is separate from the steam box (23) and arranged before the steam box (23). Further the suction means (21) include a suction box (24).

Description

PULP MACHINE HAVING AN ARRANGEMENT FOR HEATING A PULP WEB

The invention relates to a pulp machine having an arrangement for heating a pulp web, the arrangement including water dis- tribution means for hot water and steam distribution means for steam both arranged above the pulp web, and suction means arranged below the pulp web.

WO9955958A1 discloses a device for heating a band of fibrous material, in practice a pulp web. Basically, the pulp web is dried in a pulp dryer with hot air. Before this, the pulp web is pressed in order to remove water. To intensify the drain- age during pressing, the pulp web is heated beforehand. In the known technology, hot water and steam are distributed on the pulp web to increase the temperature. The warmer the pulp web, the lower the viscosity of water, which improve the drainage during pressing. Also, water is removed by suction.

There are many problems with the known technology. Hot water is distributed simultaneously with steam and air. This dis- turbs the flows of each medium and thereby reduces efficiency the whole device. Also, there is a large hood which needs a lot of space and conducts heat away. The large hood is a — long-edged box which is challenging to position and seal

O 25 which causes leaking. Second, the steam distribution is far 2 from the pulp web and steam fills the entire open space in

S the hood. Thus steam mixes with air and water which inter- z feres with efficient heat transfer. At the same time, steam

N escapes from the hood which also reduces efficiency. And 3 30 more, suction underneath is low, and it is affected because

N it is all the way under the hood causing the lack of replace-

N ment air. In addition to the poor efficiency of the device, the pulp web has time to cool down before pressing, since it is arranger far from the first press.

It is an object of the invention to provide a novel pulp ma- chine having an arrangement for heating a pulp web, which ar- rangement has better efficiency than before, and which is easier and more accurate to adjust. The characteristic fea- tures of the pulp machine according to this invention are stated in the accompanying Claims. With the arrangement, the benefits of each heating means can be utilized effectively.

Also, the influence of the environment can be minimized.

Thus, the pulp web can be heated more than before with less energy. The arrangement has several ways to be adjusted. In this way one kind of arrangement can be arranged in different kinds of pulp machine. Also, the efficiency of the arrange- ment can be increased in many ways.

The invention is described below in detail by referring to the enclosed drawings which illustrate some of the embodi- ments of the invention, in which

Figure 1 shows a side view of a part of a pulp machine ac- cording to the invention,

Figure 2 shows a modification of the pulp machine according to the invention, — Figure 3 shows a partial enlargement of the arrangement of

O 25 Figure 1, 2 Figure 4 shows the arrangement from above on the top of the

S pulp web. x a n Figure 1 shows as a diagram the beginning of the pulp ma- 3 30 chine. First there is a forming section 10 following a press

N section 11 and then a pulp dryer 12 (only partly shown). The

N forming section 10 includes a wire 13 arranged as a loop.

Pulp suspension is fed onto the wire 13 through a headbox 14.

Under the wire 13 there is plurality of foil or suction boxes

15 for removing water and thereby forming a pulp web 16. The majority of water is removed on the forming section.

Here the press section 11 includes first a combi press 17 following a shoe press 18. Both presses have two press felts.

There can be another shoe press after the first one. The most of time the pulp web is support by a wire or a press felt.

However, between the presses there is an open draw as well between the shoe press 18 and the pulp dryer 12. After the shoe press the dry content of the pulp web 16 is high enough, about 50% or more, and the rest of water is evaporated in the pulp dryer 12.

Here the forming section 10 includes an arrangement for heat- ing the pulp web 16. The arrangement includes water distribu- tion means 19 for hot water and steam distribution means 20 for steam both arranged above the pulp web 16. In addition, the arrangement includes suction means 21 arranged below the pulp web 16. In the present invention, the water distribution means 19 include a water box 22 and the steam distribution means 20 include a steam box 23, wherein the water box 22 is separate from the steam box 23 and arranged before the steam box 23. In other words, there are two separate devices or — boxes spaced apart and the water box is first and then the

O 25 steam box after. In addition, the suction means 21 include a 3 suction box 24.

N

E With the combination of the above mentioned boxes many ad-

N vantages are achieved. Each box can be adjusted and optimized 3 30 independently. Also the flows of each medium are undisturbed.

N When hot water is fed first, water flows into the pulp web.

N Hot water increases the temperature of the pulp web effi- ciently throughout. After this, steam boosts the heating at the surface of the pulp web. In other words, first hot water penetrates through the pulp web with suction. Simultaneously some air is sucked at least in the top surface of the pulp web, and then steam is fed which condenses deeper in the sur- face of the pulp web. Surprisingly the suction box below the wire continues over the gap between said water and steam box- es. This improves water and steam penetration into the pulp web which makes the total energy transfer more efficient to the pulp web throughout the whole thickness of the fibrous mat as the pulp web including the middle layer and bottom part. Thus maximum amount of the distributed heat is brought to the pulp web, which heats the pulp web efficiently.

Advantageously, the water box 22 and the steam box 23 are situated in the machine direction on the area of the suction box 24. Then the flows of each medium are boosted. Moreover the surrounding moist warm air between water and steam boxes becomes an important replacement air penetrates to the web structure. This enables more efficient water removal and pre- pares the pulp web to take and condense steam deeper into the pulp web giving better overall heat transfer. Preferably, the suction box starts a bit before than the water box. Thus, hot water is immediately sucked into the pulp web, when the pulp web is under vacuum before hot water is distributed. At the — same time, water is removed efficiently out of the pulp web.

O 25 2 In addition to remove water downwards, it is advantageous to

S use a preceding top forming unit 25. Then water is removed z also from above, which intensify the water removal. Thus the

N dry content of the pulp web increases before pressing and the 3 30 forming section becomes shorter. In the present invention,

N the water box 22 is arranged right after the top forming unit

N TPU. Then the top surface of the pulp web is open aiding hot water to impregnate the pulp web. In other words, hot water flows into the pulp web easily. Advantageously, the water box is as soon as possible after the top forming unit. In this way, outer air is prevented to flow into the pulp web. De- spite of this, hot water flows freely with aid of suction. In the present invention, in the machine direction the distance 5 D between the top forming unit 25 and the water box 22 is 15 = 2500 mm, preferably 200 - 1000 mm (Figure 3). In practice, the water box is situated as close as possible to the top forming unit. In this way, as little as possible outer air is coming into contact with the pulp web. Instead of air, hot water will impregnate into the pulp web. In Figure 2, the be- ginning of the forming section 10 is arranged as a gap for- mer, which is still shorter compared to the hybrid former of

Figure 1.

In practice, a water lubrication is provided on the front wall of the water box to keep the surface of the front wall clean. The actual hot water overflows along a distribution surface on the trailing edge of the water box at an angle of about 45 degrees. The distribution surface preferably has a gentler angle at its end. Thus hot water flows more in the direction of the pulp web and its speed is made to correspond to the speed of the pulp web. The distribution surface is preferably machined. This helps to distribute as even an — agueous film as possible on the pulp web. The water supply

O 25 can be on one selectable side only. On the other hand, with a 2 wide machine or with a large amount of water also a double-

S sided supply is possible. x a n The amount of the hot water depends on the grammage of the 3 30 pulp web. In principle, the water box 22 has a feed flow of 1

N - 4 1/m/s, preferably 1,5 - 2,5 1/m/s. This unit means how

N many liters hot water is fed per width meter of the pulp web per second. With this flow the whole pulp web is heated up about 5 degrees without rewetting the pulp web needlessly.

With a long and efficient suction box, the added water is mostly removed from the pulp web before pressing. So the pulp web is heated efficiently, with only low additional water.

Hot water also washes off sticky ingredients and fines that will cause problems in the later stages of processes like dusting and other runnability problems. This helps the runna- bility of the pulp web, decreases the consumption of the talc, and improves the quality of the pulp. The temperature of the hot water during the distribution is 70 - 99 C°, pref- erably 85 - 95 C°. Thus hot water really heats the pulp web efficiently through the whole thickness of the pulp web. The upper temperatures can be easily reached by using steam in heating water in the water box. If necessary to increase the amount of the hot water, more than one water box may be ar- ranged consecutively.

The situation of the water box is advantageous for the water box, especially for a profiling water box. In this way, the moisture profile of the pulp web can be adjusted before the pressing. Simultaneously, the former section can be run as efficiently as possible and then the moisture profile can be adjusted just before the press section. Then the final prod- uct is uniform without extra adjustments.

O 25 In practice, the suction box 24 has a length L of 1000 - 4000 2 mm, preferably 1500 - 2500 mm in the machine direction. With

S such long suction box the water removal is efficient and hot z water will flow into the pulp web and thereby raising the

N temperature. Also the pulp web is under a vacuum before hot 3 30 water is distributed on the pulp web. Advantageously, the

N suction box 24 includes several consecutive chambers

N 26a, . .26n in the machine direction each having a suction con- nection 27a,..2/n of their own. In this way the water removal can be adjusted as needed. According to the invention, the chambers 26a,..26n have different vacuum levels ascending compared to the previous one. For example, the first vacuum level starts from -20 kPa while the last ending up to -50 kPa. If there are five chambers, the vacuums can be -20 kPa, -25 kPa, -30 kPa, -40 kPa, and -50 kPa, for example. There can also be a big single chamber suction box with the same vacuum level or guite same vacuum in at least two chamber or boxes. In this way, the vacuum increases step by step without harming the pulp web but sucking water and steam efficiently.

In Figure 4 there are five chambers 26a - 26e arranged side by side. Here only part of the width of the wire 13 is shown at the drive side. The pulp web 16 is on the wire 13 while the suction box 24 is under the wire 13. Ihe wire 13 and the pulp web 16 is partly cut out showing the dewatering elements 28 being part of the suction box 24. First each suction con- nection 27a - 27e run straight out of the pulp machine and then they bend down to the vacuum system, for example.

The suction box reaches a bit longer than the steam box. Then steam 1s prevented to escape since replacement air from the surroundings into the suction box. Replacement air together with vacuum pull heat into the pulp web.

O 25 The suction box may be a single unit with several chambers. 2 Alternatively, there can be two or more suction boxes arrang-

S es side by side. For example, there can be first two suction z boxes each having two chambers and then the third suction box

N with three chambers. Advantageously, the suction box has a 3 30 slit covers with ceramic dewatering elements. Such suction

N box is compact, and vacuum is evenly spread. Also, the ceram-

N ic dewatering elements 28 are long lasting even the wire rubs against the ceramic dewatering elements. The width, i.e. the length in the machine direction, of the chamber in the appli-

cant’s own suction box is 400 mm. Then the length of the suc- tion box with five chambers is 2000 mm.

According to the invention, in the machine direction the dis- tance P between the water box 22 and the steam box 23 is 200 - 1500 mm, preferably 400 - 1200 mm. By this short gap hot water has time to impregnate into the pulp web before the steam box. In addition, a part of the suction box is open due the gap, which efficiently drags hot water through the pulp web. Also, the outer air cools the surface of the pulp web a little bit. This contributes the condensation of steam and thereby heats up the surface of the pulp web. This replace- ment air flow to the pulp web has an important role to boost the efficiency of both water and steam boxes when provided hot liquid penetrates the web together with the air. The more hot water the longer gap. Also, steam heats the pulp web, not water in it.

As the water box is separate from the steam box, a gap or free space is formed on top of the pulp web which brings ad- vantages as described earlier. Air can flow freely, but there can be equipment for distribute replacement air with regulat- ed heat and/or humidity.

O 25 The water box is short and compact. The steam box 23 instead 2 has a length T of 500 - 2000 mm, preferably 1000 - 1600 mm in

S the machine direction. In this way, steam can be distributed z sufficiently, and steam has time to heat the pulp web. While

N hot water heats the pulp web throughout, steam heats mainly 3 30 the top surface of the pulp web. Steam heats the pulp web

N about 15 degrees. Thus, together with hot water, the tempera-

N ture of the pulp web is over 70 C°, advantageously over 75

C*, when before the arrangement it is about 50 C°. In prac- tice, this rises the dry content 0,5 - 1 % after the press section. Also, the preheated pulp web starts quickly to dry in the pulp dryer. Moreover the specific steam consumption gets lower with the invention in the pulp dryer like vise in the whole pulp machine.

Advantageously, the steam box 23 has a plane diffuser plate 29 positioned 1 - 20 mm, preferably 10 - 15 mm above the pulp web 16. The plane plate distributes steam evenly and it can be installed very close to the pulp web. Thus, steam heats efficiently, and a little bit of outer air is flown from the sides acting as replacement air. This prevents steam form es- caping to the surroundings. The optimum pulp web temperature increase is obtained when the steam gives up the most energy in the vapor to liquid phase, also known as condensation.

Steam comes out of the diffuser plate, and it condenses to a maximum extent and gives up its latent heat to the pulp web.

Finally, after the arrangement there is a lump breaker 30 in contact with a suction roll 31. The suction roll below the pulp web also transfers heat to the pulp web and the lump breaker 30 takes water into a top felt 32 and takes it for refurbishment immediately before the actual combi press 17 and next transfer to the shoe press 18. The lump breaker 30 — breaks up pulp lumps which are formed too early and/or are

O 25 excessively large. Here heat spreads further into the pulp 2 web and the temperature drops few degrees. Following the com-

S bi press 17, the pulp web is sufficiently dry and, thus, du- = rable to be led to shoe press 18. With the arrangement ac-

N cording to the invention, the pulp web heats up more effi- 3 30 ciently from the top surface, but the presses even out the

N heat throughout the whole pulp web.

N

Claims

1. Pulp machine having an arrangement for heating a pulp web, the arrangement including water distribution means (19) for hot water and steam distribution means (20) for steam both arranged above the pulp web (16), and suction means (21) arranged below the pulp web (16), characterized in that the water distribution means (19) include a separate water box (22) and the steam distribution means (20) include a separate steam box (23), wherein the water box (22) is separate from the steam box (23) and arranged before the steam box (23) spaced apart so that in the machine direction the distance P between the water box (22) and the steam box (23) is 200 - 1500 mm, preferably 400 - 1200 mm, and the suction means (21) include a suction box (24).

2. Pulp machine according to claim 1, characterized in that the water box (22) and the steam box (23) are situated in the machine direction on the area of the suction box (24).

3. Pulp machine according to claim 1 or 2, characterized in that there is a top forming unit (25), after which the wa- ter box (22) is arranged. N S 25

4. Pulp machine according to claim 3, characterized in N that in the machine direction the distance D between the top © forming unit (25) and the water box (22) is 15 - 2500 mm, z preferably 200 - 1000 mm. a & 23 30

5. Pulp machine according to any of claims 1 - 4, char- N acterized in that the water box (22) has a feed flow of 1 — 4 N 1/m/s, preferably 1,5 - 2,5 1/m/s.

6. Pulp machine according to any of claims 1 - 5, char- acterized in that the water box (22) is a profiling water box.

7. Pulp machine according to any of claims 1 - 6, char- acterized in that the suction box (24) has a length L of 1000 = 4000 mm, preferably 1500 - 2500 mm in the machine direc- tion.

8. Pulp machine according to any of claims 1 - 7, char- acterized in that the suction box (24) includes several con- secutive chambers (26a,..26n) in the machine direction each having a suction connection (27a,..27n) of their own.

9. Pulp machine according to claim 8, characterized in that the chambers (26a,..26n) have different vacuum levels ascending compared to the previous one.

10. Pulp machine according to claim 8 or 9, characterized in that, characterized in that the first vacuum level starts from -20 kPa while the last ending up to -50 kPa.

11. Pulp machine according to any of claims 1 - 10, char- N acterized in that the steam box (23) has a length T of 500 - O 25 2000 mm, preferably 1000 - 1600 mm in the machine direction. 5 ©

12. Pulp machine according to claim 1 - 11, characterized z in that the steam box (23) has a plane diffuser plate (29) N positioned 1 - 20 mm, preferably 10 - 15 mm above the pulp 3 30 web (16). S

13. Pulp machine according to any of claims 1 - 12, char- acterized in that after the arrangement there is a lump breaker (30) in contact with a suction roll (31).

14. Pulp machine according to any of claims 1 - 13, char- acterized in that the temperature of the hot water during the distribution is 70 - 99 C°, preferably 85 - 95 C°. N N O N K I © Oo I Ao a 0 00 O 0 N O N