FI71367C - PROOF OF EFFECTIVE EFFECTIVENESS WITH AVIABILITY AND ENTRY MACHINERY - Google Patents

Description

71367 1 Method and apparatus for improving dewatering on a paper machine Förfarande och anordning för effektivering av avvattning i en pappersmaskin 5

The invention relates to a method for enhancing dewatering in a paper machine forming section and / or press section, wherein the web 10 to be formed is subjected, preferably on the opposite side of felt or other web-supporting fabric or surface, to hot water vapor so that a substantial portion of said steam condenses. wherein in a method for enhancing steam treatment, the condensing density of steam in the treatment interval 15 is increased by preventing air from entering the treatment interval by a blocking flow.

The invention further relates to a device for carrying out the method according to the invention, comprising a steam supply device having a steam supply surface with a small clearance against the web to be treated, such as a perforated plate, a plate made of sintered material or the like. , comprising a nozzle box, the interior of which opens into a nozzle slot bounded on one side preferably by a planar wall, the extension of which is a curved guide surface, the extension of which in turn is a foil surface parallel to the plane of the web.

Dewatering by evaporation from paperlralna is very energy intensive and therefore expensive and uneconomical. Therefore, an attempt is made to remove water from the rai-30 pin as much as possible before the drying section by mechanical means. The final step in this event is the press section, where water is removed from the web by pressing it between the rollers. In this case, it is known that the water is removed much more easily when the temperature is raised, because the viscosity of the water and the compressive modulus of the web are thus reduced at the same time as the surface tension. In this way, considerable increases in the dry matter content of the web after the press section and thus savings in the use of drying energy have been achieved.

5 In the applicant's Finnish advertisement publication No. 50651 (cf. U.S. Pat.

No. 4 209 361) has made it possible to further increase the speed of paper machines, because in addition to efficient dewatering, this so-called The "Sym-Fress" press section (trademark) has the advantage that virtually eliminates paper web breaks. However, as the speeds of the paper machine have been increased, the free stretches of the web after the press section have formed as a bottleneck, either from the blasting section to the warping section or in the first free gaps of the drying section.

It is therefore an object of the present invention to provide a method and apparatus by which the runnability of a paper machine can be improved by enhancing the dewatering of the press section so that the ralna leaves the press section even drier and more durable.

Referring to the prior art of the invention, reference is made to Applicant's U.S. Patent No. 4,163,688, which discloses a method and apparatus for enhancing dewatering in a press section of a paper machine, the method being primarily characterized by a "Sym-Pre8s" press section between the first and second nips. over the sector of the suction roll on the felt, the web 25 is treated by subjecting it from the direction of its outer surface to a substantially large sector of the suction roll under the action of hot water vapor, the treatment taking place mainly so that a significant portion of the treatment vapor condenses by transferring its evaporation heat to the web.

30 As is well known, a thin layer of air follows lime moving surfaces. This is also the case for the paper web going to the steam box. As will be shown in detail later in the computation, the mucus entrained in the web has a decisive effect on the condensation in the treatment interval of the steam supply box.

35

The above-mentioned air problems have already been recognized in the past. Attempts have been made to solve these problems by means of a kind of curtain jet which is directed from the sharp-edged slits in the planar surface perpendicular to the web 11 3 71367 1. However, these curtain jets have not achieved a satisfactory result in preventing air from entering the processing space of the steam supply box. This may be due to the fact that when the curtain jets are applied very sharply to the web, they cause strong turbulence. In any case, these known curtain jets have not been able to create a sufficiently effective protective barrier to prevent air from entering the treatment interval of the steam supply box.

It has also been recognized as a problem that when steam escapes very strongly from the edge area of the steam box, this causes water droplets to condense, which when dropped onto the web may completely damage the web.

It is an object of the present invention to provide a method and apparatus by which the effect of the above drawbacks can be decisively reduced. It is a further object to provide a method and apparatus applicable to a steam supply box which can be advantageously used to adjust the transverse moisture profile of a web.

In order to achieve these and later objectives, the method of the invention is mainly characterized in that a substantially machine-direction blocking flow is blown to prevent air from entering the steam treatment gap at least in the direction of web travel before the treatment interval.

The device according to the invention, in turn, is mainly characterized in that said foil surface delimits at least in the direction of travel of the steam supply box on the front side of the web to be treated together with the web at which the blocking flow can be blown from the nozzle box.

30

As will be explained in detail computationally later, even if the device according to the invention were able to prevent air flow into the steam box treatment interval by about 70%, a corresponding increase of about 70% in the steam box power precisely through an increase in condensing frequency.

____ - ΤΓ 71367

Air or steam or a mixture thereof can be used as the shielding gas to be blown by means of the foil nozzles used according to the invention. The use of air is advantageous in that it does not cause dripping or compaction problems. On the other hand, using steam may achieve a somewhat better air barrier effect. The use of steam also has the advantage that steam is inherently available in connection with the steam box and said steam jets also provide some heating effect for the web, although this is not the main object of the present invention.

10

In the following, the invention will be described in detail with reference to some application examples of the invention shown in the figures of the accompanying drawing, to the details of which the invention is not narrowly limited. In addition, the drawing has figures explaining the physical background of the invention.

Figure 1 schematically illustrates embodiments of the invention in various positions on a paper machine.

20 Figure 2 illustrates a cross-direction of the paper machine and on the Figure 1 seen in the direction of the arrow A according to the invention a steam supply box.

Figures 3 and 4 illustrate the air and water balance of the space element of the steam box treatment interval.

Figure 5 shows a schematic cross-section of a steam supply box applying a method and device according to the invention to be fitted to a suction roll.

30

Figure 6 shows a schematic side view of a steam supply box according to the invention provided with a single-sided air barrier, which is applied in connection with a flat wire.

Figure 7 shows a steam supply box with double-sided air baffles.

Figure 8 illustrates the principle of operation of the foil nozzle used in the invention.

5,71367

The following is a brief description of the various steps of the method according to the invention and the main structural features of the steam supply box according to the invention. First, it is repeated that the purpose of the steam supply box is to provide an even drier press product, i.e. a paper-5 web W after the press section of the paper machine. The fact that more water is removed from the web W using the steam box or boxes is due to a decrease in the viscosity of the water in the web W and a decrease in the compressive modulus of the web W due to the increase in temperature caused by the steam treatment. Fibrous materials 10 which contain relatively little lignin as well as relatively heavy Tains have a predominant effect on the reduction of water viscosity, while lignin-containing and e.g. woody and unbleached Tains have the effect of In this regard, reference is made to the article by Lars Andersson and Ernst L. Back, Swedish Forest Products Research Laboratory "The effect of temperature up to 90 ° C on dewatering of wet paper webs, evaluated in a press Simulator".

Reference is first made to Figures 6 and 7, which show in cross-section two steam supply devices 101 and 103 according to the invention, the preferred position of which on a paper machine is shown in Figure 1. According to Figure 6, the web W on the forming wire 10 is subjected to The steam supply device 101 25 consists of a steam supply box 31 extending over the entire width of the web W, which is bounded on the web W by a perforated plate 39. Steam is supplied to the web W According to the invention, a foil nozzle device is arranged in the device 101 30 on the inlet side of the web W to prevent air from entering the vapor space V between the web supply box 31 and the web W. The device according to the invention consists of a import equipment (not shown). Immediately before the perforated plate 39 of the steam box 31, the foil nozzle device has a foil surface 37 in its plane, which extends after the surface having the radius of curvature R as a wall 37 '. The wall 37 'to limit the other side via foilisuutinlaitteen nozzle slot 35. Said slot 35 6 71367 blown Coanda-effect by using foilipintaa 37 fol-lowing air and / or steam jets towards the web W traveling in the opposite direction. The jets prevent air from passing with the web W into the evaporation gap V. Fig. 7 shows a steam supply device 103, respectively, with foil nozzle boxes 34a and 34b according to the invention at both its inlet and outlet edges. The blocking jets E 1 acting on the inlet side of the web W operate as described above. In addition, the blocking jets E1 blown on the outlet side of the web W act in such a way that also on this side air cannot pass between the evaporation space 10. According to Fig. 7, the blocking jets E1 and on both sides of the web V.

Figure 1 shows different locations of a steam-15 feeder applying the method according to the invention in the web-forming and press section of a paper machine. According to Figure 1, the web W is formed on a flat wire 10, from which it is detached by running between the rollers 11 and 12 in the suction zone 15a of the pick-up roll 15 and transferred to the pick-up fabric 14. The first steam supply device 101 according to the invention is arranged on the horizontal top of the forming wire 10 on top of the leveling box 13. The second steam supply device 102 according to the invention is arranged at the suction zone 11a of the breast roll 11. The third device 103 according to the invention is adapted to run the pick-up felt 14 before the first press nip N 1.

25

The press part shown in Fig. 1 is a so-called "Sym-Press" press section, where the web W passes in a closed export through three nips and through.

The first pressing nip is formed between the lower roll 16 with the hollow surface 16 'and the suction roll 17. As a lower fabric, the nip has a felt 19 guided by the guide rollers 18. A fourth device 104 according to the invention is located in the suction zone 17a of the suction roll 17. The second pressing nip is formed at the suction zone 176 of the suction roll 17 against the embodiment 28 provided with a smooth surface 28 '. The pick-up fabric 14 acts as a press fabric in the second nip, after which said fabric 14 differs from the strip W. The fifth device 105 according to the invention is located in the sector 28 between the second and third press nips and the design. A third press nip is formed between the hollow surface roll 20 and the design 28. The third nip has a press fabric 21 71367 guided by the guide rollers 22. The web W is detached from the design 28 by a guide roll 23 and applied to the drying section of a paper machine as is known per se, showing only the drying cylinder 24 and the drying fabric 26 and its guide roll 25 in Fig. 1.

5

Although Figure 1 shows the steam supply device 101-105 according to the invention in five different positions, it is to be understood that in practice it is seldom necessary or advantageous to use so many successive devices. For the construction and operation of the device 104, reference is made to Applicant's U.S. Patent No. 4,163,688 (issued August 7, 1979).

With regard to the different placement options for the steam supply devices shown in Figure 1, the following is further stated. In the arrangement of the steam supply device 101 on the wire section on top of the suction box, the amount of water to be heated is quite large, but on the other hand there is generally enough space for a long steaming area. When the device 101 is placed on the opposite side of the leveling box 13, good steam penetration into the web W is obtained. When the steam supply device 102 is placed above the suction sector 11a of the turning roll 11 of the wire 10, the amount of water to be heated is also quite large and the suction zone 11 is generally only about 200-350 mm. The amount of water to be heated in the position of the steam supply device 103 is still quite large because the dry matter content of the web W is about 16 ... 20%. If necessary, a suction device can be placed at the steam supply device 103 on the opposite side of the pick-up felt 14 to promote the penetration of steam.

The position of the steam supply device 104 is particularly advantageous, since the amount of water to be heated is quite reasonable with a dry matter content of the web W of about 30%. Due to the suction zone 17a of the suction roll 17, the environmental disadvantages of the steam box 104 are quite small. The disadvantage, on the other hand, is that the space is limited, so the evaporation length cannot be very large.

30 With regard to the device 105, it is noted that the amount of water to be heated is quite small, and condensate removal may become difficult, and at the design 28 there is no suction box opposite the device 105. On the other hand, the application of the method and device according to the invention in a position in which the suction device on the opposite side is absent is particularly advantageous. When using both the device 104 and the device 105, there is also the advantage that the web VJ is steam-treated on both sides, whereby, in addition to the efficiency of dewatering, 8 71367 paper-technical advantages are also obtained. In this regard, reference is made to the applicant's earlier FI patent application No. 803021 (filed September 25, 1980).

As shown in Fig. 2, the steam supply pipe 42 is connected in connection with the steam supply-5 valve 50 to the steam distribution pipe 51, to which steam enters schematically from the devices shown as block 52, which inherently belong to a paper machine. In connection with the pipe 42, control devices 54 are arranged, which control the actuator 53 of the steam volume control valve 50.

Fig. 5 shows a steam supply device 105 arranged on the suction sector 17a of the press suction roll 17. The suction roll 17 is known per se provided with a perforation 17 'and an inner suction chamber 17a. The steam supply device 104 'shown in Fig. 5 differs from the corresponding position device 104 shown in Fig. 1 only in that in Fig. 5 the device 104' 15 is shown provided with foil nozzle boxes 34a and 34b on both its inlet and outlet sides. As shown in Figure 5, the supply pipe 42 of the steam supply box 104 'acts as its load-bearing structure. Attached to the steam supply pipe 42 by a support structure 43 is a jacket plate 44 and a front plate 39 corresponding to the curvature of the suction roll 17, through which perforation steam jets 20 are fed on the surface of the roll 17 against the web W passing over the suction chamber 17a.

The steam supply pipe 42 and said jacket plate 44 define a space 38 into which steam is supplied from the pipe 42 through nozzle holes 47. In connection with the nozzle holes 47, which are spaced along the length of the tube 42 at suitable intervals, steam volume adjusting spindles 48 are arranged, which can be adjusted by means of adjusting screws 49. The steam supply box 104 'includes an outer sheath 45 and a thermal insulator 46 therein. 38 before they discharge through the plate 39 as flows F1 against the web W. Instead of the perforated plate 39, a corresponding front plate made of transparent pores, e.g. sintered material, can be used.

According to the present invention, foil nozzle boxes 34a, respectively, are arranged on both the front and rear edges of the jacket 44 of the steam supply device 104 '.

34b, the interiors 36 of which open through the nozzle slots 35 to the vaporization 119 71367 V. The foil nozzle boxes 34a and 34b have a foil surface 37 which substantially coincides with the cylindrical surface defined by the outer surface of the front plate 39.

According to the invention, the blocking jets are fed through the nozzle slots 35 and to the foil surfaces 37, respectively. On the inlet side of the steam supply box 104 ', the blocking jets are opposite to the running direction of the web W and on the outlet side the blocking jets are in the downstream direction.

10

In the following, with reference to Figures 3 and 4, the physical possibilities of the blocking jets E1 »E2 according to the invention in preventing the entry of air into the evaporation interval V will be described.

15 In treatment interval V, the density of the condensing water vapor stream can be calculated from equation n; k · «h · in tt1 a) im” 20 where k = mass transfer coefficient = molar mass of water 18.0 kg / kmol X ^ ^ = molar fraction of dry air in the boundary layer right on the surface of the condensate X. = molar fraction of dry air in the air flow far from im »25 condensate surface .

The mass transfer coefficient can be further represented by the equation t 1-n k = a · - (2) 30 Pm where a = heat transfer coefficient C = molar specific heat of moist air pm = X. C. + X. c. i pmi n pmh C. = 29 kJ / kmol (air) pmi '35 Cpmh = 34 "(steam)

Le = Lewis number = D / (X / oc)

P

D = diffusion coefficient λ = thermal conductivity of moist air 10 71 367 p = density of moist air c = specific heat of moist air

P

n = 0.35-0.5; the same power that occurs when calculating the heat transfer coefficient at the power of the Prandtl number 5 Nu = A · Rem Pr ° Thus, formula (1) can also be represented by a · M, pc,. X., • tt n f Pv i-n nl n. t imlv / ^ \ "h -c— <λ> D ln (—5 <3) io Pm im00 l-n Ximl

In particular, the terms D and ln (—-) are considered in the prior art X # steam box solutions and in the solution according to the present invention, in which the flow of air entraining the web and the felt into the treatment space is substantially prevented. Changes in other terms can be very ignored.

As is known, a thin layer of air follows all moving surfaces.

There is no sliding between the air and the moving surface, but the air particles which contact the moving surface travel at the same speed as the surface, in this case the web.

The air and water balance of the state element AV of the processing interval V can be shown according to Fig. 3. Looking at Fig. 3, it is seen that moist air and not steam is blown onto the moving surface (web 25) from the previously known steam boxes, as illustrated in Fig. 4.

Next, consider the computational importance of the air entrained by the web W for the condensing density in the case where the feed surface 39 of the steam box is located 10 mm from the web W. The speed W of the web W is 15 m / s and the temperature 50 ° C.

The amount of air pumped with the web is of sufficient accuracy.

_ -.e m ne. ! * 03 kg ki air s 1,086 m3 = 0.07 kg ki / sm Steam is blown from the steam box 0.18 kg / sm.

Il 11 71367

When the humidity of the air entrained with the web is 0.086 kg I ^ O / kg ki, the humidity of the generated moist air is x = —-1 --- = 2.66 kg H-O / kg ki 5 0.07

When, by means of the present invention, using the blocking jets E1 and / or E2, the air flow accompanying the web W is e.g. blocked by e.g. 70%, the situation changes as follows: m 0.021 · 0.086 + 0.18 n „,„ „„,.

10 x2 = -q-'0'21-1— = 8.66 kg H 2 O / kg ki

Below is a comparative table based on the above: -1--1 15 Variable Known steam box Steam box according to the invention x 2.66 8.66 kg H 2 O / kg ki: D 47.3 · 10'6 50.3 * 10-6 m2 / s! 7 1 nl-n i ° '4 ° »4 i 20 D 2.54 · 10 ~ 3 2.64 · 10 3 (m2 / s) 0.6! | X.. 0.804 0.753 1 imi i

Ximoo! 0.211 0.081 μ X. 1; j

In (^ -) I 1.34 2.16 25 i ™ 00 '

; I

j m2 = 1.68 m -1

j - - - - --- - -1 ----- - - - ---- - 1

In other words, when the air flow to the steam box is blocked by 70%, the power of the 30 boxes through the increase of the condensing density increases to 68 Z.

A particularly important embodiment of the invention is such that the blocking jets E1, E2 according to the invention are used to control the transverse moisture profile of the web, either exclusively or in addition to the control in the steam box. With the method and device according to the invention, the adjustment of the moisture profile can be carried out very simply by passing more air past the blocking devices in the drier areas of the web W. Thus, the heating power of the 71 367 12 steam box decreases in these areas, which also results in a decrease in the dewatering power in the subsequent pressing steps. Through this, the humidity level in these areas rises to the average humidity level.

5

As device solutions, the control of the humidity profile can be implemented e.g. by dividing the foil nozzle boxes 34a, 34b by machine-directed partitions into several different compartments and adjusting the pressure of the shielding gas to be blown into these compartments. In one case, it may also be possible to implement such profile adjustment by adjusting the width and / or position of the nozzle slots 35.

The basics of the operation of the foil-15 nozzle according to the invention will now be described in more detail with reference to Fig. 8.

One starting point for the invention has been the physical facts which emerge, for example, from reference D.W. Mc Glaughlin, I. Greber The American Society of Mechanical Engineers, Advances in Fluids 1976, "Experiments 20 on the Separation of a Fluid Jet from a Curved Surface," pp. 14-29.

This reference explains the flow jet detachment mechanisms from a curved wall and the various parameters that affect it. Essential to the present invention are the results that emerge from the reference on page 21 of FIG. 5 is a graph showing a curve swarm in a coordinate system with a detachment angle as a vertical axis as a horizontal axis. w

Reynoldsm chapter. The curve parameter is the ratio - = nozzle gap width

R

the ratio of water to the radius of curvature of the surface. It is clear from these research results that with the flow parameter present in the nozzle structures, the tracking angle ip is generally between 45 ° and 70 °.

30

According to Figure 8, the nozzle gap 35 abuts the walls 37 'and 38 *. The width of the nozzle gap is marked with w. The extension of the wall 37 'is a curved part 37R, the sector of which is marked with an angle α. The curved part 37R is followed by a foil surface 37, at which a protective barrier is formed to prevent air 35 from entering the treatment zone. When the nozzle gap width w, the blowing velocity v and the angle u of the gas jets E 1 are suitably selected, the jets spray the foil surfaces 37R and 37 without detaching therefrom, as will be apparent from the above. According to Fig. 8, the nozzle gap 35 is already inclined at an angle β 11 l13 71 367 towards the blowing direction of the blocking jets. Thus, a smaller angle α is required to ensure that the jets follow the curved surface 37R without detaching therefrom and that the flow is substantially laminar.

5

One advantageous effect of the jets on achieving the desired goals is that they eject the steam in the surface area of the web W from the treatment space V. This ejection effect is illustrated by arrows E.

B

10

As stated above, it is preferable that the angle α is between 45 and 70 °, depending on the flow parameters. In some cases, the angle n can be larger, always almost 90 °, where the angle β is 0. Such a solution is shown in Fig. 6.

15

In some cases, several short spaced successive nozzle slots 35 may be used to blow a similar shielding gas or a different shielding gas.

If air is used as the shielding gas to be blown from the foil nozzles, the foil nozzle boxes 34a, 34b are connected to a blower to which air is taken from a suitable location from the paper machine so that it has a suitable temperature and humidity space. If steam is used as the treatment gas, it can be taken through the pipe 55 as shown in Fig. 2. In this case, the valve 50 is e.g. a three-way valve. When a mixture of air and steam is used as the treatment gas, the air and steam can be introduced separately into the foil nozzle boxes 34a, 34b or mixed with the steam and air before being introduced into the nozzle boxes 34a, 34b.

The following are claims which, within the scope of the inventive idea defined by it, may vary the various details of the invention.

Claims (10)

A method for effecting the dewatering in the forming portion and / or the pressing portion of a paper machine, wherein the method (W) to be formed is most preferably applied to the opposite seam of a blanket or some other tissue (10,14) or surface (28). ') which carries the web, in a state in which it is exposed to the effect of hot water vapor in such a manner, that a noticeable portion of said steam is condensed in the structure (W) of the web, thereby passing on its extension heat to the web (W), whichever Process condensation density of the treatment interspace (V), in order to effect the evaporation treatment, is increased by preventing air from escaping to the treatment interspace (V), characterized in that in order to prevent the air entry to the meadow processing space, ) substantially in the machine direction in the running direction of the web (W) at least before the processing gap (V). 1 Patent Claim 71367 2. A process according to claim 1, characterized in that the process uses air, aqueous or a mixture of these as protective gas. 20 Method according to claim 1 or 2, characterized in that the method is applied in a feeding device (101; 102; 103; 104; 105) at one or more of the following positions: on the forming wire (10) p1 opposite to the side of a flat suction slide ( 13) or correspondingly, at the suction zone (11) of the forming wire (10), the rotary roller (11), 30 µl of the pick-up tissue (14) against the web (W) before the first press nip (N a suction roll (17) between the first and second press nip (ΝΝ, ΝΝ) of a closed press portion (16,17,28,20), and / or in a sector covered by the web (W) by a smooth surface of a roller (28) in the closed press portion (16,17,28,20), most preferably between the second and third press nips (N 2 N 2). 18 71 367 1 Method according to any one of claims 1-3, characterized in that the method is applied in the running direction of the web (W) only on the front edge of the supply drawer (102; 104) in such a way that the blocking current (E ^) is directed in the opposite direction. direction towards the running direction of the web (W). 5 5. A method according to any one of claims 1-4, characterized in that said blocking current (ΕΕ,) används) is used for controlling the transverse moisture profile of the web (W) running through the meadow treatment. 10 6. A method according to claim 5, characterized in that the transverse moisture profile of the web (W) retrieved for meadow treatment is controlled by controlling the amount and / or quality of the air barrier gas measured in the transverse direction of the web (W). .ex. the mixing relationship between the meadow and the air. 15 Apparatus for carrying out the method according to any one of claims 1-6, which apparatus comprises a feeding tube (101,102,103, 104,104 ', 105) having a feeding surface (39,40) against the web (W) to be treated at a small distance. therefrom, such as a neck plate, a plate 20 of sintered material or the like and wherein the inner space (38) of the device's feeder (31; 44) is joined to feeding devices (42.50, 51.52), the device comprising foil nozzle devices, comprising a nozzle drawer (34a; 34b), from whose inner space (36) opens a nozzle hall (35), one side of which is most preferably confined to a planar wall (37 '), a curved guide surface (37R) constituting a extension thereof, the extension of which in turn consists of a foil surface (37) located in the direction of the web (W) of the web, characterized in that said foil surface (27) limits in the running direction of the treated web (W) together with the on-site path (W) a hole space at least on the front side of the meadow feeder, to which a blocking current (E 2, E 2) can be blown from the nozzle casing (34a, 34b). Apparatus according to claim 7, characterized in that the foil nozzle device is located only on the front side of the meadow feeding device (102; 104) in relation to the running direction of the web (W). n