FI20225431A1

FI20225431A1 - Method in a pulp dryer

Info

Publication number: FI20225431A1
Application number: FI20225431A
Authority: FI
Inventors: Markku Kiuru; Veera Korpiniitty
Original assignee: Valmet Technologies Oy
Priority date: 2022-05-17
Filing date: 2022-05-17
Publication date: 2023-11-18
Also published as: CN117071316A; AT526181A3; AT526181B1; DE102023112845A1; FI130563B; AT526181A2

Abstract

The invention relates to a method in a pulp dryer. The method includes forming (10) a pulp web (14), and pressing (11), drying (12). Then the method includes sheet cutting (13) the formed pulp web (14) into sheets (24) and piling the sheets (24) into bales (32). The method also includes monitoring the production of the pulp web (14). According to the method, by the monitoring detecting any discontinuity of the production, but continuing the sheet cutting (13) of the remaining pulp web (14) until stopping the sheet cutting (13).

Description

METHOD IN A PULP DRYER AND CUTTING DEVICE FOR A PULP DRYER

The present invention relates to a method in a pulp dryer in- cluding forming a pulp web, and pressing, drying, and then sheet cutting the formed pulp web into sheets, and piling the sheets into bales, and monitoring the production of the pulp web. The invention also relates to a cutting device for a pulp dryer.

Forming of a pulp web is a lengthy process including differ- ent consecutive stages. In every stage and between them the pulp web may break or for some other reason the production must be stopped suddenly. During the web break, the pulp is run to the broke handling in the wet end and the dry end and broke is cleaned and the production is started again. There are operators monitoring the production.

The production stages before a drying box are more vulnerable for web breaks than in the drying box itself. In other words, in the forming and pressing the pulp web is still wet. Also the drying box is big, and it accommodates hundreds of meters of pulp web. However, the information about the web break on the forming or pressing comes to a sheet cutter following the

N pulp dryer with a delay or not at all. After the break, the

O 25 pulp web is run to a pulper after the drying box and the ro sheet cutter is stopped. If the delay was long, problems may ~ occur also in the sheet cutter. Also, a lot of pulp web must = run to the pulper to empty the pulp dryer before starting the = production again. 3 30 &

N The object of the invention is to provide a new method in a

N pulp dryer, which is more economical and safer than before, and easy to implement in the pulp dryer. Another object of the invention is to provide a new cutting device for a pulp dryer, which truncates a narrow pulp strip surely and guick- ly. The characteristic features of the method according to the invention are stated in the accompanying Claim 1. Corre- spondingly, the characteristic features of the cutting device according to the invention are stated in the accompanying

Claim 14. By the method, the amount of broke can reduced sig- nificantly. This increases the yield of the pulp and thereby improves the profits. Simultaneously the down time of the pulp dryer is shortened and stopping and restarting of the production can be done with low labor. Also, the stopping can be totally controlled. This shortens the down time further and prevents damage of the devices. The cutting device is ro- bust, and it is also easy to install to the pulp dryer.

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 principal side view of a pulp dryer,

Figure 2 shows a partial enlargement of Figure 1 showing a sheet cutter for a pulp web,

Figure 3a shows the beginning of the stopping of the sheet cutter according to the invention,

N Figure 3b shows separating of a narrow strip of the pulp web,

O 25 Figure 3c shows introducing a cutting device on the top of ro the strip, ~ Figure 3d shows the beginning of the spreading of the strip, z Figure 3d shows the end part of the spreading of the strip, = Figure 4 shows the sheet cutter of Figure 2 during stopping, i 30 Figure 5a shows a cutting device according to the invention

N during normal production,

N Figure 5b shows the cutting device of Figure 5a before break- ing,

Figure 5c shows the cutting device of Figure 5a right after breaking.

Figure 1 shows schematically a side view of a pulp dryer uti- lizing the method and the cutting device according to the in- vention. The pulp dryer includes consecutively a forming sec- tion 10, a press section 11, and a drying box 12, and finally a sheet cutter 13 for pulp web 14 just produced. In the form- ing section 10 agueous pulp is fed on a wire 15 by a headbox 16. On the forming section 10 a pulp web 14 is formed by re- moving water. Then the pulp web is pressed several times in the press section 11 thereby removing more water. After the press section 11 the pulp web 14 is led by an open draw to the drying box 12. Later on the forming section equals form- ing, the press section equals pressing, the drying box equals drying, and the sheet cutter equals sheet cutting. The same reference numbers are used accordingly.

The drying box 12 has a closed hood 17 including superposed drying decks. Only a small part of the drying box 12 is shown in Figure 1. Each drying deck has turn rolls at both ends and blow boxes between them. In the airborne drying box, the pulp web runs horizontally in a zigzag manner via the drying

N decks. Between the turn rolls, air blows from the blow boxes

O 25 support and dry the pulp web. So the pulp web moves on an air ro layer. Usually the pulp web enters from the top of the hood ~ 17 and exits at the bottom on the opposite end. The height of z the drying deck depends mainly on the amount of air needed = and the width of the pulp web. The wider pulp web, the taller i 30 blow box and higher drying deck. In practice, the drying deck

N is 250 - 800 mm high and there are typically 10 - 30 drying

N decks in one drying box.

In the sheet cutter, a uniform and full wide pulp web is first cut lengthwise and then in cross direction into sheets, which then are stacked into bales. Figure 1 and especially

Figure 2 shows the sheet cutter 13 in action. The sheet cut- ter is for a pulp web produced with a pulp dryer as described earlier. Between the drying box 12 and the sheet cutter 13 there is a pull press 18 and a pulper 19. The pull press draws the whole pulp web out of the drying box. Here, before the pull press 18 is a scanner 20 for determining the proper- ties of the pulp web 14 (Figure 1). If the pulp web breaks somewhere, the pulp web is run down to the pulper 19 and the remaining pulp web is drawn out of the drying box with the pull press. During the emptying of the drying box the sheet cutter is stopped and cleaned if necessary. There is also an- other pulper 19’ for the broke from the press section 11 and the drying box 12.

The sheet cutter 13 includes consecutively a slitter 21, a cross cutter 22 and a layboy conveyor 23 for overlapping cut sheets 24 before a bale table 25. The slitter 21 includes several parallel blades 26 arranged against a bottom slitter 27. When the pulp web 14 runs through the slitter 21, several strips are formed. From there the strips are pulled by a feed

N press 28 and further pushed to the cross cutter 22. In other

O 25 words, the slitter 21 cuts the pulp web 14 lengthwise into ro parallel strips, which are then crosscut into sheets 24 with ~ a rotating cutter roll 29 with cross cutting blade 30 and a = stationary counter blade 31. These sheets are then overlapped = with the layboy conveyor 23 to the bale table 25 as bales. i 30 The bale table descends little by little until the bales are ä completed.

The method is implemented in a pulp dryer, and the method in- cludes forming 10 the pulp web 14, and then pressing 11 and drying 12 the pulp web and finally sheet cutting 13 the formed pulp web 14 into sheets 24 and piled into bales 32.

The sheet cutting happens in the sheet cutter 13. Also, the method includes monitoring the production of the pulp web 14. 5 According to the invention, by the monitoring detecting any discontinuity of the production, but still continuing the sheet cutting 13 of the remaining pulp web 14 until stopping the sheet cutting 13. In other words, in spite of the discon- tinuity of the production, the sheet cutting is continued, and the sheets are baled. In this way, more bales are pro- duced thereby decreasing the broke. Also, less pulp remains in the drying box, which saves cleaning time of the pulp dry- er in the event of break. In practice, break detectors at the wet end start a stopping seguence which includes said contin- uing of the sheet cutting and stopping.

The method further includes monitoring the forming 10 and the pressing 11 of the pulp web 14. In other words, the forming section and the press section are monitored since these stag- es are the most vulnerable. When a web break occurs, the trigger for stopping the sheet cutter is detected. Again, in spite of the trigger, sheet cutting is still continued. But now the information of the trigger is known without delays,

N so the stopping of the production and the sheet cutter can be

O 25 done in a controlled way. 3 ~ The trigger may be a visual observation of the operator when = the web break is occurring. Then the operator starts the nec- = essary acts to run down the production. In addition or alter- i 30 natively, the method includes selecting as a trigger a signal

N from a control system 33 included in the pulp dryer. The web

N break can be detected with one or more sensor, probe or alike.

In practice, the method still includes continuing sheet cut- ting 13 until the next unfinished set of bales 32 is ready.

In other words, at least the unfinished bales are finished.

So, a proper set of bales are achieved, and they can be con- veyed to the market with full price. When the bales are ready, the sheet cutter is stopped, if necessary, and the production is started again later.

On the other hand, the method includes determining the amount of the remaining pulp web 14 and continuing sheet cutting 13 until the sets of bales 32 based on the determined amount are ready or as long the pulp web stays tensioned so that it will not travel sideways. For sheet cutting, the pulp web should have certain tension. In practice, here the properties of the pulp dryer are known beforehand. In other words, it can be determined how much pulp web is inside the drying box at the time of the web break. Then the sheet cutting and baling is continued for several set of bales until the drying box is almost empty. In practice, even up to three or four sets can be finalized, depending on the pulp dryer in question.

As mentioned earlier, the operator may start the stopping of the production. Advantageously, the stopping is arranged as

N an automated sequence. In practice, when the control system

O 25 detects the web break, all or at least majority of necessary ro actions are made automatically. At the end of the pulp dryer, ~ i.e. after the drying box, the steps are as follows.

Tr a — The method includes, during the stopping, first separating a i 30 narrow strip 34 from the full width pulp web 14. Usually, the

N separated strip 34 has a width of 50 - 300 mm. In practice,

N the method includes separating the strip 34 by water jet cut- ting or mechanical cutting. The position of a water cutter is pointed out with an arrow in Figure 1. In Figure 3a, the wa-

ter jet cutter 35 is moved to the edge of the pulp web 14.

Then the water jet cutter 35 starts cutting and the narrow strip 34 is separated (Figure 3b). Both the strip and the rest of the pulp web is still drawn to the cutter. Also the sheet cutting and baling may still continue. However, before actual the stopping, the method includes opening a reject gate 36 arranged after the sheet cutting 13. This is shown in

Figure 4, where the cut sheets 24 are directed down towards the pulper 19. Here, the narrow strip 34 is truncated, and it drops towards the pulper 19.

Next the method includes breaking the strip 34 before the sheet cutting 13 and spreading the strip 34 full again while pulling down before the sheet cutting 13. The strip 34 is broken between a pull press 18 arranged before the sheet cut- ting 13 and a feed press 28 included in the sheet cutting 13.

Here the method includes breaking the strip 34 on a feed roll 37 arranged between the pull press 18 and the feed press 28.

In this position, both the strip and the pulp web are under tension, which facilitates the breaking. Before the actual breaking, the method includes pressing towards the feed roll 37 a movable press wheel 38 having a width corresponding to the strip 34. In Figure 3c, the press wheel 38 is pressed

N against the feed roll 37. Thus, the narrow strip runs through

O 25 a nip formed by the press wheel and the feed roll. In this ro way the strip runs stably before breaking. ~ z Finally the method includes hitting the strip 34 before the = feed roll 37. In other words, the strip is broken by hitting, i 30 here by hitting the strip 34 with an actuator-operated blade

N 39. In Figure 3d the strip runs down to the pulper 19 while

N the rest of the pulp web 14 runs still to the sheet cutter 13. Then the water jet cutter 35 is moved toward the other edge of the pulp web, here from left to right. Thus, the nar-

row strip gradually widens while the rest of the pulp web narrows. During the widening, the strip runs down to the pulper. In Figure 3e, the strip is widened almost totally.

When the water cutter reaches the edge of the pulp web, the whole pulp web runs down to the pulper and nothing goes the sheet cutter, which can thereby be stopped or at least cleaned before starting the production again.

In Figure 5a the pulp web 14 runs normally via the feed roll 37. Here the cutting device include the press wheel 38 with the blade 39. This unit is supported with an articulated arm 40 to a bracket 41. The upper part of the unit it connected to the bracket 41 with a cylinder 42. Thus the press wheel 38 can be easily press towards the feed roll 37 by using the cylinder 42 (Figure 5b). Then, with an actuator 43, the blade 39 is pushed into the narrow strip 34 (Figure 5c) and the strip is truncated. In other words, the cutting device in- cludes a bracket 41 supporting a press wheel 38 and an actua- tor-operated blade 39 for truncating a narrow strip 34 sepa- rated from the full width pulp web 14. And more, the press wheel 38 is supported to the bracket 41 with an articulated arm 40 and a cylinder 42. The unit also includes a guard 49 which in this connection protects both the cutting equipment

N and the user from the blade. The shown cutting device is com-

O 25 pact and robust. It can be easily automated, and the narrow ro strip is cut surely. The actions of the device are quick, so ~ the stopping of the sheet cutter may be quick, but still con- z trolled. After stopping, the press wheel is lifted up. The = blade is preferably a serrated impact blade extending trans- i 30 verse across the separated narrow strip. In addition, the

N cutting device is even easy to install on older pulp dryers.

N

The layboy conveyor 23 includes several individual groups 44 of support rolls 45 set opposite to press wheels 46. For each feed roll there one set of press wheels. In this way, nips are formed between the support rolls and the press wheels.

When the support rolls are driven, the sheets move forward.

As shown in Figure 2, already at the first group 44, the sheets 24 are partly overlapping. With the next groups the sheets are overlapped further and finally at the bale table 25 the sheets are top of each other forming bales. After the bale table, the bales are wrapped and usually also tied up, and transported forward.

Here is also a reject gate 36 positioned under the layboy conveyor 23. At the stopping, the sheets will drop down to the reject gate 36 and thereby to the broke slide 47. With the method according to the invention the stopping of the sheet cutter is newly arranged, the slitter 21 and the cross cutter 22 can be arranged within safety fences 48. This im- proves the occupational safety and reduces litter. At the same time, also the cross cutter may be reversible. In the normal production, the speed of the sheets after the overlap- ping step is descending and therefore, the leading edge of each sheet settles on top of the trailing edge of the sheet in front resulting in the sheets to partly overlap each oth- er.

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Claims

1. Method in a pulp dryer, including forming (10) a pulp web (14), and pressing (11), drying (12), and then sheet cut- ting (13) the formed pulp web (14) into sheets (24), and pil- ing the sheets (24) into bales (32), and monitoring the pro- duction of the pulp web (14), characterized in that by the monitoring detecting any discontinuity of the production, but continuing the sheet cutting (13) of the remaining pulp web (14) until stopping the sheet cutting (13).

2. Method according to claim 1, characterized in that monitoring the forming (10) and the pressing (11) of the pulp web (14).

3. Method according to claim 1 or 2, characterized in that selecting as a trigger a signal from a control system (33) included in the pulp dryer.

4. Method according to any of claims 1 - 3, character- ized in that continuing sheet cutting (13) until the next un- finished set of bales (32) is ready.

N 5. Method according to any of claims 1 - 3, character- O 25 ized in that determining the amount of the remaining pulp web ro (14) and continuing sheet cutting (13) until the sets of ~ bales (32) based on the determined amount are ready. Tr a

— 6. Method according to any of claims 1 - 5, character- i 30 ized in that the stopping is arranged as an automated se- ä guence.

7. Method according to any of claims 1 - 6, character- ized in that during the stopping, separating a narrow strip

(34) from the full width pulp web (14), and breaking the strip (34) before the sheet cutting (13), and spreading the strip (34) full again while pulling down before the sheet cutting (13).

8. Method according to claim 7, characterized in that breaking the strip (34) between a pull press (18) arranged before the sheet cutting (13) and a feed press (28) including in the sheet cutting (13).

9. Method according to claim 8, characterized in that breaking the strip (34) on a feed roll (37) arranged between the pull press (18) and the feed press (28).

10. Method according to any of claims 9, characterized in that before the breaking, pressing towards the feed roll (37) a movable press wheel (38) having a width corresponding to the strip (34).

11. Method according to claim 9 or 10, characterized in that hitting the strip (34) before the feed roll (37).

12. Method according to any of claims 7 - 11, character- N ized in separating the strip (34) having a width of 50 - 300 O 25 mm. 3 ~

13. Method according to any of claims 1 - 12, character- z ized in that that before the stopping, opening a reject gate = (36) arranged after the sheet cutting (13). N

14. Cutting device for a pulp dryer, characterized in N that the cutting device includes a bracket (41) supporting a press wheel (38) and an actuator-operated blade (39) for truncating a narrow strip (34) separated from a full width pulp web (14).

15. Cutting device according to claim 14, characterized in that the press wheel (38) is supported to the bracket (41) with an articulated arm (40) and a cylinder (42). N N O N O <Q N I jami a O <r O N N O N