JPH06248593A - Method for non-contacting air drying of web material and nozzle blowing box and pulp dryer by means of said method - Google Patents

Abstract

PURPOSE: To provide a novel method which can improve heat transfer from dry air to a web to be dried and a novel nozzle-blow-box. CONSTITUTION: To a web W to be dried from underneath the web air blowings perpendicular to the web and air blowings parallel to plane of the web are applied. By means of these blowings heat is transferred to the web W and the web is supported by air free of contact and the run of the web through a dryer is stabilized. In order to improve heat transfer in comparison with a plane carrier face by providing to a nozzle-carrier face lateral areas, where the air flow velocity of parallel to the plane of the web W to be dried and to be air-supported in connection with the nozzle-carrier face is initially kept substantially invariable, after that the air flow velocity is lowered suddenly or gradually in a direction of air discharge, the air flow velocity is lowered at the lateral areas of the nozzle-carrier face. Decrease of heat transfer due to side flow is reduced and the run of web is stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for air drying a relatively high basis weight web material such as a pulp web, and more particularly to the web to be dried from below, with an air blowout substantially perpendicular to the web and Air is blown substantially parallel to the plane of the web, heat is sent to the web by both blows, the web is supported by air without contact, and the running of the web through the dryer is stabilized Air drying of the web material It is about the method.

Further, the present invention relates to a nozzle blowing box of an air dryer which blows air to a web material to be dried, and particularly, by blowing air, heat is transferred from dry air to the web, and there is no contact. The running of the web is stabilized by air support, and the nozzle blowing box has a box portion provided with a nozzle support surface arranged facing the web, and in the center of this support surface in the running direction of the web. A V-shaped groove intersecting with each other is provided, the groove has a shape that is open toward the web, and a series of nozzle holes is provided in the opposing wall, and the nozzle is supported and stabilized toward the outside of the nozzle hole. The present invention relates to a nozzle blowing box in which air is blown out in an opposite direction to each other, and flat nozzle supporting surface portions are provided on the same plane on both sides of a V-shaped groove. It is intended.

Further, the present invention relates to a pulp dryer used when using the air drying method for a web material according to the present invention and / or when using the nozzle blowing box according to the present invention.

[0004]

Background of the Invention In the paper and pulp industry, blowout boxes are commonly used in paper dryers. The nozzle support surface of this blow-out box is made of a flat plate, and blow-out holes are punched in this plate. Such nozzles are to be dried by blowing air and are located on one or both sides of the air-supported web. Further, the nozzle supporting surface is usually formed with holes in many rows in the running direction of the web. The blown air flows through the space between the web and the nozzle support surface and is collected and escaped through the suction slot between the nozzle blow boxes.

In conventional air dryer direct blow nozzle boxes for paper, board, or pulp webs, the blowoff of air is directed perpendicular to the web material to be dried. The problem heretofore is the cross-flow of air flowing between the web material to be dried and the nozzle support surface. The term "cross flow" as used herein refers to a flow of air that is parallel to the plane of the nozzle support surface and the plane of the web, and parallel or opposite to the running direction of the web. The "cross-flow" problem is unavoidable because the air blow has to escape from the processing gap. In a conventional blow-out nozzle box, such a cross flow causes poor heat transfer, and the obstacle becomes larger as the velocity of the exhaust air flow increases. Furthermore, the pressure loss that occurs in the blowing nozzle box also increases as the velocity of the cross flow increases. On the other hand, in view of the running property of the web material to be dried in the blowing nozzle box, a negative pressure region is formed on the supporting surface of the blowing nozzle box to stabilize the running of the web material, and a stable web material without distortion. It is desirable to address the problem of cross flow by taking into account the geometry of the blowing surface and its nozzle opening so as to guarantee the running of the nozzle.

For the closest prior art to the present invention, see Freight's Swedish Patent No. 8,106,152 (corresponding US Pat. No. 4,505,053) and K.K. Kriga International Patent Application W
O88 / 08950 (corresponding US Pat. No. 5,016,363).

In the blow-out nozzle box disclosed in the Swedish patent, a triangular opening, the so-called "fisheye", is punched into its flat nozzle support surface, the front edge of the opening or the triangle. The bottom has a sharp edge. A sharp edge is not a major drawback as long as the amount of air expelled from the nozzle is sufficient. Sometimes the amount of air that the nozzle receives is significantly reduced. For example, when the air drying filter is blocked, the web comes into contact with the nozzle support surface. The sharp edges described above, for example, loosen the pulp web and make it flat.
In this case, the quality of the final product is deteriorated and waste is left in the dryer. Wastes remaining in the dryer hinder the passage of the pulp web. This is referred to as the manufacture of "cigars" because the shape of the material separated from the surface of the pulp web is cigar-shaped.

The present invention firstly relates to a nozzle blowing box used in a pulp dryer, in which the web runs above the nozzles and the supporting surface of the blowing box. The function of blowing air is to transfer heat from the blowing air to the web and to support the web in a contactless manner. In consideration of the running property of the web, it is desirable to blow out the air in parallel with the plane of the nozzle. In this case, the web is 3
It is stably supported at intervals of 6 mm. However, in this case, in the conventional nozzle blowing box, the velocity of the exhaust air flowing through the space between the web and the nozzle becomes high. Therefore, heat transfer is deteriorated and a significant pressure loss occurs. The nozzles can be made sufficiently narrow in order to reduce the adverse effects caused by the high velocity of the exhaust air, but this increases the number of nozzles and considerably increases the manufacturing cost of the dryer.

[0009]

SUMMARY OF THE INVENTION The present invention overcomes these shortcomings of the prior art and provides a novel method and a novel nozzle blow-off box that can improve heat transfer from dry air to the web to be dried. The purpose is to provide. Such an improvement in heat transfer can be achieved sufficiently effectively with a small dryer, so that, for example, the construction cost of a pulp dryer and the cost of mechanical equipment can be reliably reduced.

Another object of the present invention is to reduce the deterioration effect of heat transfer due to cross flow and stabilize the running of the web.

[0011]

SUMMARY OF THE INVENTION To solve the above problems, the method of the present invention is air supported with respect to a nozzle support surface to improve heat transfer as compared to a planar support surface. The nozzle supporting surface is provided with a side wall so that the flow velocity of the air running parallel to the plane of the web to be dried is kept substantially constant at the beginning and thereafter becomes stepless and / or stepwise lower in the air outflow direction. Therefore, the main feature is to reduce the flow velocity of the air in the side region of the nozzle support surface.

The nozzle blowing box of the present invention continuously and / or non-steps the support surface further away from the web material to be supported.
Alternatively, the extended portion of the nozzle supporting surface portion is formed by gradually separating. In the area of the extended support surface portion, the flow velocity of the air is lower than that of the flat nozzle support surface portion for the stable support, and the nozzle support surface is provided with a plurality of further nozzle holes, and is supported thereby. The main feature is that it is blown out substantially vertically from the nozzle blow-out box onto the plane of the web material.

According to the present invention, the reduction in heat transfer due to cross flow is minimized by lowering the lateral regions of the nozzle to a level lower than the center of the plane, thereby reducing the velocity of cross flow. Furthermore, the cross flow is preferably directed so that it does not directly impinge on the direct air jet stream at the nozzle plane or in the lower flanks.

In the present invention, the lower side area of the nozzle supporting surface portion is based on the fact that the efficiency of heat transfer is deteriorated when the flow velocity of the exhaust air flowing through the web and the nozzle supporting surface is high. The narrower the gap between the web and the nozzle support surface, the higher the flow velocity of the exhaust air. The more air is generated, the more the velocity of the exhaust air increases from the center of the nozzle toward both ends. By lowering the lateral area of the nozzle support surface according to the invention, the flow velocity of the air in this lateral area can be reduced.

The nozzle blow-out box of the present invention is a combination of a nozzle and a positive / negative pressure, and the magnitude of the cross flow for generating the negative pressure is approximately selected in relation to the amount of air blown directly. .

The characteristic of the hole-nozzle region of the present invention on the nozzle support surface is that the exhaust air blows out from the nozzle hole even if the gap between the web and the nozzle support surface is very small enough to operate the nozzle of the present invention. If the jet stream of air is not substantially impeded to a certain extent, the heat transfer efficiency is essentially unaffected by the gap. On the other hand, when the rows of nozzle holes are provided over many rows, the air discharged from the nozzles passes through the end of the space between the web and the nozzles, and if the speed increases The higher the height, the more the exhaust air impedes the jet of air blown out from the nozzle holes, resulting in poor heat transfer efficiency.

In a preferred embodiment of the nozzle blowing box of the present invention, air is jetted from the wall of the V-shaped groove located at the center of the nozzle supporting surface, and the air jet flows on both sides of the V-shaped groove. Curved points extending from each side of the wall to the flat portion of the support surface are intersected with each other. Since this air jet is directed tangentially to the bending point, it changes direction at the bending point due to the Coanda effect and becomes parallel to the flat surface portion of the supporting surface. A negative pressure region is formed between the web and the nozzle support surface according to Bernoulli's law, whereby the position of the web is maintained at a constant distance from the support surface, and is generally about 3 to 6 mm. Maintains a stable distance. Attempts have also been made to avoid direct collisions between the jet of jets and the jet of air in the horizontal direction on the horizontal portion of the support surface.

[0018]

According to the present invention, from below the web to be dried,
The air is blown substantially perpendicular to the web and the air is blown substantially parallel to the plane of the web, and heat is sent to the web by both of these blows, the web is contactlessly supported by air, and the web passes through the dryer. Driving is stabilized. To improve heat transfer compared to a flat support surface,
A side area in which the velocity of the air running parallel to the plane of the air-supported web to be dried with respect to the nozzle support surface is initially kept substantially constant and then sharply and / or gradually decreases in the direction of air outflow. Is provided on the nozzle support surface, the flow velocity of air is reduced in the lateral region of the nozzle support surface.

[0019]

The present invention will now be described in detail with reference to several examples shown in the accompanying drawings and test results related to the examples.

FIG. 1 is a schematic longitudinal sectional view in the machine direction of a pulp dryer using the method according to the present invention and a set of nozzle blowing boxes. The pulp dryer has a set of nozzle blow-out boxes 30 according to the present invention inside, and a closed hood 12 arranged to face the box,
It consists of a set of direct blow box 40,
The web W to be dried is conveyed in a contactless air-supported manner through a processing gap 25 formed by the set of boxes. The pulp web W _in or its equivalent fed through such a drier is passed through the wet press 10 and the roll 11, its tension is adjusted, and is fed to the hood 12 through the inlet 12a. In the hood 12, the web W to be dried is guided by the guide roll 13 and is pulled forward in the horizontal direction or pulled backward and continues to run. The dried web W is taken out from the outlet 12b at the bottom of the hood 12 and further aligned roll 14
And through the drive roll 15 (W
_out ). The webbing belt or loop path is shown by the dash-dotted line 16.

In FIG. 1, the circulation of the dry air generated in the hood 12 is indicated by arrows A ₁ . ． ． It is indicated by A ₂ . Arrow A ₁ and related air duct
17 indicates that the replacement air is introduced from the heat recovery section,
Arrow A _{2 The} associated air-duct 18 indicates the delivery of discharged air to the heat recovery section.

FIG. 2 shows a modular structure of a pulp dryer using the method according to the present invention and a nozzle blowing box, the basic principle of which is shown in FIG.
Similar to that of. The dryer / blower module is composed of a blower tower 21 and a blower having an impeller 22. This module structure has a heat radiator 24 through which blown air flows into the gap between the upper and lower nozzles, the web gap 25. In addition, this module structure has an air filter 26
including. On the operating side of the blower module there is a maintenance bridge 28, which is associated with an inspection gate 27 for the blower motor and an inspection door 29 for the blower module. FIG. 2 shows the circulation of dry air as shown by the arrow, and the nozzle blowing boxes 30, 40 according to the present invention.
, And the web gap 25 and the like between them are shown.

With reference to FIGS. 1 and 2, the method and nozzle blowing boxes 30 and 40 according to the present invention have been shown as an application example for one application field in the above description, but the method and nozzle blowing box according to the present invention are shown. It can be applied to many other fields, as well. Other than the pulp dryer, for example, application to boards and paper webs can be considered. The pulp dryer is the most effective and basic field of application of the present invention, but in other fields, different effects are expected depending on the purpose.

FIG. 3 shows a set of nozzle blowing boxes 30 according to the present invention and a set of direct blowing type boxes 40 on the opposite side. In the following, with respect to the nozzle blowing box 30, they are preferably placed below the horizontally running web W, so they will be simply referred to as "lower boxes". Each lower box 30
There is a free space 30a between them, and correspondingly, there is a free space 40a between the direct blow boxes 40, and the blown air is these free spaces 30a and 40a, and further FIG.
It is sent by the blower 22 through the heat radiator 24 shown in FIG. As shown in FIG. 3, the web W to be dried, typically a pulp web, runs horizontally through a web gap 25. Web gap 25
Is defined by a lower box 30 disposed with a uniform space on the lower horizontal surface, and a direct blow box 40 disposed with a uniform space disposed on the upper horizontal surface. With respect to the lower box 30, the web W is usually heavy (weighing about 2000 g / sq.m by weight of wet pulp web), which is supported by the blowouts B ₂ and B ₃ . A blowout B ₁ perpendicular to the plane of the web W is added to the web W through a nozzle hole 42 provided in the horizontal lower wall of the direct blow box 40,
The web W is dried from above by the blowout B ₁ .

FIGS. 4, 6 and 8A, 8B show the construction of the lower box 30 in more detail. At the center of the support surface 31 of the lower box 30, a transverse groove 32, that is, a groove 32 that intersects the lateral direction of the web W, is provided, and this groove is open toward the web W. The opening angle a of the V-shaped groove 32 is generally a = 50 ° to 90 °, preferably a = 60 ° to 80 °. V-shaped groove 32
Sloped wall, which is preferably planar and has a radius of curvature R
The curved portion 31b is connected to the horizontal portion 34 of the support surface at an intermediate angle b. As can be seen from FIG. 6, the angle a
And the angle b, a relationship of a + 2b = 180 ° is established. A plurality of blowing holes 33 are provided in rows on both wall surfaces of the inclined flat surface of the V-shaped groove 32. In the blowing hole 33, the jet B _{3 of} air blown from the blowing hole 33 is directed tangentially to the curved portion 31b, and the jet B _{3 of} air bends along the flat portion 34 of the support surface 31 in the curved portion 31b by the Coanda effect. , The jet B ₃ is arranged so as to be parallel to the plane portion 34. Blowing hole 33
Are alternately provided in a zigzag pattern on opposite sides of the V-shaped groove 32, and the jets B ₃ are arranged so as to intersect with each other in opposite directions. Therefore, one set of the jet B ₃ is parallel to the traveling direction of the web W and its plane, and the other set is the web W 3.
However, the direction is opposite to the traveling direction of the web W. According to Bernoulli's law, the jet B ₃ generates a negative pressure region between the web W and the supporting surface 31, whereby the web W maintains a constant distance H from the supporting surface, and generally H = 3. It is stabilized by keeping a distance of about 6 mm.
In this case, air drying of the web W is generally the most efficient.

On both sides of the support surface 31, there is a side area portion 35 which is lowered over the length L ₁ in the running direction of the web, the height of which is a central plane portion 34 of the support surface 31. Lower than the height of the web W. In FIG. 6, the side area portion 35 is a sloping plane ramp, the distance of which in relation to the central plane section 34 is indicated by h ₂ at the end of the box 30.

In the nozzle blowing box according to the present invention, at the web processing gap 25 under the web W, the air velocity is initially substantially constant with respect to the flat portion of the support surface 31, and thereafter toward the end of the lower box 30. Support surface portions 35; 35 as they go toward the space 30a of the web processing gap 25 of
For b, 35d, and 35e, the speed decreases gradually or continuously. This significantly increases heat transfer, as can be seen from the test results shown in FIGS. 9 and 10. The increase in heat transfer is mainly due to the lower bearing surface 35; 35b, 35d, 3
In 5e, this is based on the fact that the air flow velocity parallel to the plane of the web W is significantly reduced, which in particular increases the heat transfer of the direct blow B ₂ .

In the pulp dryer, as shown in FIGS.
The lower box 30 and the direct blowing box 40 shown in are placed in a vertical relationship so as to face each other. Therefore,
The faces 41 and 31 are substantially parallel to each other and generally form a horizontal plane. The face 41 of the direct blowing box 40 is formed with a rounded edging portion 43 at the end thereof, and the end of the face 31 of the lower box 30 is provided with a corresponding rounded edging portion 31.
a is formed.

Lower box 30 and direct blowing box 40
Nozzle holes 42 and 36 are provided on the surfaces 31 and 41 which face each other. A preferred example of the distribution of nozzle holes 36 in lower box 30 is shown in FIG. 8A. Nozzle holes 42; 36 to web W
The vertical blowouts B ₁ ; B ₂ are performed toward, which accelerates the drying of the web W. Since flow velocity in the support surface 35 in order to cross the basin between the web supporting surface is increased is reduced, balloon vertical air towards the lower surface of the web, i.e. directly balloon B ₂ is made longer time.

FIG. 8B is a view for explaining a preferred embodiment of the shape and size of the V-shaped groove 32 described above.
The shape of FIG. 8B is symmetrical about the transverse vertical center plane KK. The jets F ₁ and F _{2 of} air blown from opposite directions are tangential to the curved portion 31b connected to the end of the V-shaped groove 32, and change direction due to the Coanda effect to become parallel to the flat portion 34. This is the starting point for the design of the V-shaped groove 32. Air is a flat surface between the groove 32 and the flat surface 34.
Especially rounded so that it is guided along 34.

7A to 7E show various examples of the support surface of the lower box 30. The nozzle box 30A shown in FIG. 7A is composed of a support surface 31, in which a flat surface portion 34 is provided on both sides of a V-shaped groove 32, and a flat inclined portion 35 following the flat surface portion 34 is provided.

FIG. 7B shows a particularly effective blow box 30B.
Is shown. In the box 30B, a flat surface portion 34b of the supporting surface and a step portion 37 following the flat portion 34b are provided on both sides of the V-shaped groove 32. The step portion 37 has a surface perpendicular to both the first flat surface portion 34b of the supporting surface and the flat surface portion 35b following the step portion 37. The initial portions 34b of the support surfaces 31 on both sides are parallel to each other and on the same horizontal plane. Similarly, the support surface
The lateral regions of 31, namely the plane portions 35b, are also parallel to each other and on the same horizontal plane. FIG. 7B is also for explaining a preferred dimensional example of the box 30B. According to FIG. 7B, the height h ₂ of the stepped portion 37 is 10 mm, and can be changed within a range of approximately h ₂ = 7 to 15 mm.

FIG. 7C shows the nozzle box 30C in its basic form. In this box, the support surface 31c is a flat surface over both sides of the V-shaped groove 32. To be precise, this nozzle box 30C is not according to the present invention but is shown for comparison with the present invention, and the comparison result will be apparent from FIGS. 9 and 10 described later.

FIG. 7D shows a blow box 30 according to the present invention.
D is shown. This box 30D has a relatively long flat supporting surface portion 34d and a relatively short and steep sloped side area.
Has 35d. FIG. 7D also shows a preferred box size.

FIG. 7E shows a modification of the blow box shown in FIG. 7B. The box 30E is provided with a relatively long flat supporting surface portion 34e, a step portion 37 following the step portion 37, and a relatively short supporting surface portion 35e following the step portion 37.
FIG. 7E also shows a structural example of box 30E.

FIG. 8A shows the relative position of the nozzle holes 33 of the V-shaped groove 32 and the staggered arrangement, and the jet B _{3 in the} opposite direction is blown out in an intersecting manner by such arrangement. The openings 36 in the nozzle support surface 31 are arranged in four rows, but are arranged in a staggered manner so that the jets B ₂ and B ₃ do not collide with each other. The mutual spacing of the nozzle holes 33 is generally in the range of 20 to 50 mm, and the mutual spacing of the nozzle openings 36 is generally in the range of 40 to 100 mm.

The dimensions of the blow box shown in FIGS. 6 and 7 are as follows. With respect to the dimensions of FIG. 6, the angle a between the plane walls of the V-shaped groove 32 is approximately a = 50.
The angle b of the Coanda surface 31b in the range of 90 ° to 90 °
Is approximately in the range of b = 45 ° to 65 °, and
The depth h ₁ of the V-shaped groove 32 is approximately in the range of h ₁ = (2 to 5) × Φ, where Φ is the diameter of the nozzle hole 33 in the wall of the V-shaped groove 32. Is. Diameter of nozzle hole 33 Φ
Is selected in relation to the diameter of the nozzle hole 36 on the support surface, and the amount of air in the jet B ₃ blown out from the nozzle hole 33 is the total blowout amount of the nozzle blowout box (jet B ₂ and B ₃ ).
It is selected to be 30% to 60% of the air amount, preferably 35% to 45%. With respect to the length L ₁ in the running direction of the web, the side regions 35, 35b, 35d, 35e of the supporting surface 31 of the nozzle blowing box may have any shape that bends gradually or rapidly, but L ₁ = (0 ．
1 to 0.3) × L, preferably L ₁ = (0.2 to 0.25) × L, where L is the total length of the support surface of the nozzle blowing box 30 and L≈300 to 5
Select to the range of 00 mm, and the side areas 35, 35b, 35 of the supporting surface 31
When the heights of d and 35e are compared with the plane of the nozzle support surface, the maximum difference h ₂ is selected in the range of h ₂ = 7 to 15 mm, and preferably h ₂ ≈10 mm.

9 and 10 are graphical representations of the test results obtained for the nozzles shown in FIGS. 7A-7E. 9 and 10, the vertical axis represents the relative heat transfer coefficient α.
_R is shown, and the horizontal axis is the distance from the support surface 31, in particular, the flat portion 34 thereof to the web W. Alphabet A-E on each box 30A-E in FIGS. 7A-7E
Corresponds to A-E in FIGS. 9 and 10.

FIGS. 9 and 10 were tested on the nozzle shown in FIGS. 7A to 7E, but the heat transfer was tested by blowing warm air onto a flat metal surface using a static test device. Is. The efficiency of heat transfer was obtained by measuring the heat transfer rate of the metal plate using a thermometric detector. In FIGS. 9 and 10, the measured relative heat transfer coefficient α _R is a function of the distance H between the web and the support surface 31 of the nozzle box, varying the blowing speed as a parameter. According to this result, when the distance H is equal to the normal air transmission distance (3 to 6 mm) of the pulp web, the heat transfer coefficient is reduced by lowering the side areas 35, 35b, 35d, 35e of the supporting surface 31. Of a simple flat support surface (Fig. 7
It is increased by about 5% to 10% as compared with the supporting surface 31c) of C. Further, if the distance H is made larger than that, the effect corresponding to it cannot be obtained. Increased heat transfer coefficient is shown in the lower areas 35,35b of the bearing surface 31 (Figs. 7A and 7B)
Highest in case of. The measurement result of FIG. 9 is obtained when the jet velocity W _puh of the jets B ₂ and B ₃ is W _puh = 26 m / s, and the measurement result of FIG. 10 is that the jet velocity W _puh of the jets B ₂ and B ₃ is W _{When puh} = 34 m / s, the temperature T _{puh of the} blown air is T _puh = 15 in any case.
This is when the temperature is 0 ° C. As is apparent from FIGS. 9 and 10, the difference in the relative heat transfer coefficient α _R in each case is correct and remarkable at the optimum air transfer web distance H = 3 to 6 mm.

The simulations and measuring methods used in the measurements of FIGS. 9 and 10 are published in Helsinki Syndrome, an alternative method for pulp and paper drying, held in Helsinki, 4-7 June 1991. "Air-
Wheel Dryer Heat Transfer ",
P. High proof and I.I. It is described in detail in the literature by Joki Oinen.

Based on the above-described measurements, the most effective embodiment of the invention so far is the nozzle box 30A shown in FIG. 7A. According to the measurement results of FIGS. 9 and 10, the support surfaces 34b, 35b having the steep stepped portion 37 as shown in FIG. 7B are optimal from the viewpoint of heat transfer, but considering the overall surface, Nozzle box 30A shown in 7A is preferred. The nozzle box 30A has a continuous downward sloped side area portion 35 of the support surface, and since the shape of the blowing surface does not include an acute angle, the risk of forming "shiger" is low. Therefore, so far, the nozzle box shown in FIG.
It can be said that 30A is the most suitable embodiment of the present invention. In this case, the distance from the horizontal surface portion 34 of the support surface 31 to the pulp web W is
For example, it is about 5 mm.

Although the present invention has been described with reference to several embodiments, the present invention is not limited to these embodiments.
Many modifications and variations are possible within the scope of the inventive concept as defined in the claims.

[0043]

As described above, according to the present invention, the lateral area of the nozzle supporting surface of the nozzle blowing box is lowered so that the velocity of the cross flow decreases as the cross sectional flow area between the web and the supporting surface increases. As a result, the efficiency of heat transfer of the air jet blown out from the direct blowing opening provided in the downwardly lowered nozzle supporting surface portion and / or the straight nozzle supporting surface portion is improved.

The nozzle blowing box of the present invention is suitable for use in drying a web such that one side or both sides of the web can be dried in the case of a low basis weight web (200 g / sq.m or less).
It is also suitable for use in web drying where both the bottom and top of the web are dried. For heavier webs such as pulp webs (200 g / sq.m or less), the nozzle spout box of the present invention may be a lower nozzle used with a direct spout box that acts as an upper nozzle, or a bottom nozzle that only dries on one side. Most suitable for boxes.

Another advantage achieved by the shape of the blowing support surface of the nozzle blowing box of the present invention is that the cross flow of air is guided by the rounded surface of the central V-shaped groove and outside the V-shaped groove. It is that there is a smooth blowing surface where the end of the supporting surface part is not square when flowing out.

According to the invention, the heat transfer to the web is improved by 5% to 10%, as shown by the measurements. With this improvement, the dryer can be downsized, and the cost of the dryer, the cost of installing the machine room, and indirectly or indirectly, the number of production interruptions can be reduced to improve the operating rate of the dryer. The advantages mentioned above are particularly important when the pulp dryer is large and complex.

[Brief description of drawings]

1 is a schematic longitudinal section in the machine direction of a pulp dryer using the method according to the invention and of a set of nozzle blowing boxes.

FIG. 2 is an axial side view showing a modular structure of a pulp dryer using the method according to the present invention and a nozzle blowing box.

FIG. 3 is a schematic vertical cross-sectional view in the machine direction of a set of nozzle blowing boxes according to the present invention and a set of direct blowing type boxes on the upper side thereof.

FIG. 4 is an axial side view for explaining a nozzle blowing box according to the present invention and a principle of the blowing.

FIG. 5 is an axial side view of the structure of an upper direct blowing type box, that is, a direct blowing box.

FIG. 6 is an explanatory diagram of an embodiment showing the details of the support surface of the nozzle blowing box according to the present invention and the blowing nozzle of the supporting surface together with the most important dimensional parameters.

FIG. 7 is an explanatory view of an example showing various examples in which the shape and size of the nozzle support surface of the nozzle blowing box according to the present invention are different, and a basic nozzle blowing box.

8A is a view of the nozzle blowing box shown in FIG. 4 or 5 as seen from the side of the nozzle supporting surface, and FIG. 8B is a view showing a preferable shape and size of the V-shaped groove of the nozzle. It is the expanded schematic longitudinal cross-sectional view in the machine direction of the V-shaped groove | channel which shows an example.

FIG. 9 is a graph showing the relationship between the relative heat transfer coefficient and the web distance for each of the nozzles shown in FIGS. 7A to 7E at the first air blowing speed.

FIG. 10 is a graph diagram showing a case corresponding to FIG. 9 in the case of a second air blowing speed higher than the first air blowing speed.

[Explanation of symbols]

10 Wet press 11 Roll 12 Closed hood 13 Guide roll 13 14 Roll 15 Drive roll 16 Web threaded belt 17 Air duct 18 Air duct 18 21 Blower tower 22 Wing wheel 24 Heat radiator 25 Web gap 26 Air-filter-27 Inspection gate for blower motor 28 Maintenance bridge 29 Inspection door for blower module-30 Nozzle blowing box 30a Free space 31b Curved part 31 Support surface 32 Cross groove 33 Blowing hole 34 Horizontal surface 35 of support surface 35 Side area 35b Flat surface 35d Inclined side area 35e Support surface 36 Nozzle hole 37 Step 40 Direct blowing box 40a Free space 40a 41 Surface 42 Nozzle hole 43 Edged portion W Web B ₁ Direct blowing B ₂ Direct blowout B ₃ jet flow

Claims (16)

[Claims] 1. A method of air drying a relatively high basis weight web material, such as a pulp web, wherein the web to be dried is blown from below, substantially perpendicular to the web and substantially in the plane of the web. Air is blown in parallel to each other, heat is sent to the web by both of these blows, the web is supported in a non-contact air manner, and the running of the web through the dryer is stabilized. In order to improve the heat transfer compared to the surface, the velocity of the air, which is air-supported with respect to the nozzle support surface and runs parallel to the plane of the web to be dried, is initially kept substantially constant, after which the outflow of air By providing a side region on the nozzle support surface that is steplessly and / or stepwise lowered in the direction, the flow velocity of the air is reduced at the side region of the nozzle support surface. Air drying method for Eve material. 2. The method for air drying a web material according to claim 1, wherein a plurality of nozzle blowing boxes are provided below the web, and each of the nozzle blowing boxes has a head surface forming a supporting surface for supporting the web. Having an air blow in a direction parallel to the running direction of the web and an air blow in an opposite direction to the running direction of the web, intersecting toward the outside of the groove located in the center of the supporting surface, and perpendicular to the web. Air is blown toward the web outside the nozzle holes provided on the support surface, and the vertical air blow is directed toward the lower surface of the web, and the web and the support surface in the side areas of the web and the support surface. A method for air-drying a web material, characterized in that it is carried out for a long time by increasing the cross-sectional basin between and. 3. The method for air drying a web material according to claim 1 or 2, wherein the nozzle supporting surface is provided with a side region which is steplessly and / or stepwise lowered in the air outflow direction. A method for air drying a web material, characterized in that it optimizes the transfer of heat to the web of dry air and adjusts the running height in air of the web to be dried which is air supported with respect to the nozzle support surface. 4. The air-drying method for a web material according to claim 1, wherein the air blowing is performed so as to intersect with each other in opposite directions from a groove portion located at the center of the nozzle supporting surface. Respectively toward the outside of the nozzle hole in a direction substantially tangential to the guide surface where the curvature of the nozzle supporting surface begins, and by providing the guide surface, the air blowing direction changes due to the Coanda effect. A method for air drying a web material, characterized in that the air is run in the vicinity in parallel with the plane basic part and with the plane of the web. 5. The method of air drying a web material according to claim 1, wherein the air blowing is performed so that the nozzle supporting surfaces intersect in opposite directions and are parallel to the plane of the web. The amount of air blown out of is 30% to 60%, preferably 35% to 45% of the total amount of air blown out of the nozzle blowing box. 6. The method for air drying a web material according to claim 1, wherein the air blowing is performed so that the nozzle supporting surfaces intersect in opposite directions and are parallel to the plane of the web. Slows down over a distance of length L ₁ parallel to the running of adjacent webs on the side of the support surface of the nozzle blowing box, where L ₁ =
(0.1 to 0.3) × L, preferably L ₁ = (0.2
To 0.25) × L, where L is the total length of the support surface of the nozzle blowing box and L = 300 to 500 mm. 7. The method for air drying a web material according to claim 1, wherein the air blown out from the nozzle blow-out box is outside the drying support gap via a space provided between the nozzle blow-out boxes. A method for air-drying a web material, which comprises: 8. The method for air drying a web material according to claim 1, wherein an upper direct blowing box is provided on the opposite side of the nozzle blowing box located below the air-supported web to be dried. A method for air-drying a web material, characterized in that the web is blown toward the outside of the upper direct blowing box substantially perpendicularly to the plane of the web to dry the web from both sides. 9. A nozzle blowing box of an air dryer for blowing air to a web material to be dried, wherein the blowing of the air transfers heat from the dry air to the web and a non-contact air support. The traveling of the web is stabilized by the above, and the nozzle blowing box has a box portion provided with a nozzle supporting surface arranged facing the web, and intersects in the traveling direction of the web at the center of the supporting surface. A V-shaped groove is provided, the groove has a shape that is open toward the web, and a series of nozzle holes is provided on the opposite wall of the groove for supporting and stabilizing it toward the outside of the nozzle hole. Air is blown out in opposite directions, and a nozzle blow box in which flat nozzle support surface portions are provided in the same plane on both sides of the V-shaped groove should be supported. The extension portion of the nozzle support surface portion is formed by forming a support surface portion that satisfies the positional relationship such that it further separates from the web material steplessly or stepwise, and the support portion is formed in the region of the extended support surface portion. And the flow velocity of air for stabilization is lower than the flow velocity of air with respect to the flat nozzle supporting surface portion, and the nozzle supporting surface is further provided with a plurality of nozzle holes, and the flat surface of the supported web material. A nozzle blow-out box characterized in that a blow-out substantially perpendicular to the above is further performed from the nozzle blow-out box through the another nozzle hole. 10. The nozzle blowing box according to claim 9, wherein the extension portions of both plane walls of the V-shaped groove are formed by a curved Coanda guide surface, and the guide surface is continuous with the plane portion of the support surface. The nozzle holes provided on both plane walls of the V-shaped groove are arranged so that the main direction of the air blown out from the nozzle holes is substantially tangential to the curved Coanda guide surface. A nozzle blow-out box, which is characterized by being installed. 11. The nozzle blowing box according to claim 9, wherein an angle a between both plane walls of the V-shaped groove is a = 50 ° to 90 °, and the V-shaped groove is formed. Has a depth h ₁ of h ₁ = (2 to 5) × Φ,
Here, Φ is the diameter of the nozzle hole in the wall of the V-shaped groove, which is a nozzle blowing box. 12. The nozzle blow-out box according to claim 9, wherein, with respect to the length L ₁ of the material web in the traveling direction, the side area of the support surface of the nozzle blow-out box is gradually or suddenly increased. L ₁ = (0.1 to 0.3)
× L, preferably L ₁ = (0.2 to 0.25) × L, where L is the total length of the support surface of the nozzle blowing box and L = 300 to 500 mm. Nozzle characterized in that the maximum value h ₂ of the difference when the height of the side area of the surface is compared with the flat surface of the nozzle supporting surface is selected in the range of h ₂ = 7 to 15 mm, and preferably h ₂ ≈10 mm. Speech bubble box. 13. The nozzle blowing box according to claim 9, wherein the nozzle holes of the V-shaped groove are spaced apart from each other on both plane walls facing each other of the V-shaped groove. The nozzles are provided alternately in a zigzag pattern, and the constant interval is in the range of 20 to 50 mm. The nozzle holes on the plane of the nozzle supporting surface are arranged in a zigzag pattern with respect to the nozzle holes of the V-shaped groove, 3 to 5 rows crossing the running direction of the web, and further provided with a constant interval in both the running direction of the web and the crossing direction, where the constant interval is in the range of 40 to 10 mm. Nozzle blowing box characterized by that. 14. A pulp dryer using the air-drying method for a web material according to any one of claims 1 to 8 and / or using a nozzle blowing box according to any one of claims 9 to 13, The pulp dryer has a plurality of nozzle blowing boxes arranged in a straight line at a distance from each other, and air for supporting, drying and stabilizing the web material is mainly processed through a gap between the boxes. The pulp to be dried by arranging the plurality of nozzle blowing boxes one by one on the same horizontal plane in the running direction of the web, and by arranging the boxes in a plurality of vertical arrangements. The web was supported by air inside the hood of the pulp dryer, and the web was turned back and forward in each stage. Therefore, the pulp dryer is characterized in that the traveling direction of the web is switched by a reversing roller. 15. The pulp dryer according to claim 14, wherein a direct blowing box is provided above the web material on the opposite side of the nozzle blowing box, and is provided on a plane of the direct blowing box facing the web. A pulp dryer characterized in that it blows from a nozzle hole substantially perpendicularly to the web, and an intermediate space through which air blows directly upward is provided between the direct blowing boxes. 16. The pulp dryer according to claim 15, wherein the nozzle blow-out box located below the web and the direct blow-out box located on the opposite side of the web have equal lengths in the running direction of the web.
Further, the pulp dryer is arranged so as to face each other with a uniform interval.