FI117103B - Method and apparatus for drying wet webs - Google Patents

Description

Method and apparatus for drying wet webs

The present invention relates to the dewatering of water during papermaking and web formation, or after water-containing coating layers I, and generally to the dewatering of paper used in papermaking. adorable.

10 Paper and board webs are often coated with pigment slurry and binder dispersions and other additives. Most widely used pigments cr; calcium carbonate and precipitated calcium carbonate. The coating t is to improve the surface cleanliness, the new and the inking, the opacity and the glossiness of the products, and often also to improve the surface of the web.

Usually, the solids content of the coating suspension, also referred to hereinafter as "ρέ paste", is often close to 70% and the binder content is 3-15% of the final dry weight of the coating layer. The viscosity of the naphtha increases rapidly as the solids content increases, j <·. : Applying a paste to the web is difficult or impossible. Toi * · · • ♦, ···. as the concentration increases, the drying capacity of the coated web is required. The lower the solids content, the easier the oi process and the more expensive the drying process. The drying also takes ail: Y: The diffusion distance of the water molecules to the outer surface of the paper, from where they are wound, is long. Because drying times are longer, your drying compartments are long, especially in the case of thick coatings. Long 2

However, the drying of paper and board webs by infrared dryers is known, for example, during high-intensity infrared drying, but the very high energy effect can cause the coating water to boil, and the dissolved gases increase the coating coefficient. In order to avoid porosity, water diffusion from the pigment coating layer should be achieved rapidly to allow the water to boil. This becomes more difficult as the particle size of the pigments decreases. The particle size, the closer the particles are to each other and the more difficult or the vapor is to penetrate the particle layer.

10 To improve productivity, the web speed of paper and board machines is rapidly increasing. Increasing requirements for on-line and off-line coating equipment result in the need for higher drying rates of heat energy applied to the web within the prior period without damaging the base paper or coating, other means to improve dewatering.

It is known to remove water from various objects by means of ultrasonic treatment called electroacoustic effects. In these methods, the target is dewatered and the signal energy s 20 is the movement of the water molecules to separate them from the target.

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. ···. Ultrasonic drying of paper webs has been accomplished by sonication of *: ··: wet surface of the web with ultrasonic whip and similar treatment of the web (see RE White, Tappi J., vol. 47, no. 8, August 1964, and Tapf. 25 month 1986 / US Patent No. 4,561,953). These experiments showed that the t method worked, but that it was expensive.

used in combination with an electric field to remove water from sludge and sludge. In this method, the water is removed through a thin electrode, which makes the method suitable only for those which are in liquid phase or can be pumped. Since there are nearly 15 exposed permeable electrodes in contact with the species, these known methods cannot be applied to water dewatering webs or other moving dies.

In all the aforementioned articles, sources of acoustic energy at a suitable distance from the drying point have been observed up to 10 times higher drying speeds and humidity i from 40% to 15% by ultrasound, the known methods have not been implemented in practice. This is probably due in part to: The methods described in these TAPP1 articles were designed for on-site continuous sheet-by-sheet processes. The known methods also do not cause problems of continuous processing; dewatering by filtration is also continuous if used for solid motions

The object of the present invention is to eliminate the prior art; 20 da provides a new method for removing water from a moving web.

It is another object of the present invention to provide an apparatus for moving webs.

The present invention is based on the fact that a certain Taina is subjected to * bursting ultrasonic signal bursts to remove water from the web t; tea. The term “ultrasonic signal burst” clearly refers to the differences 4 as the energy increases and fog is formed. The fog formation is at the beginning of the vibration period. For this reason, the discharge pulses of the present invention are much more effective than regular smoothing. When the ultrasonic discharge starts, its effect on the ultrasonic emitter of water droplets is extremely large. One of the major concerns is the possible counteraction of the droplets formed on the surface and the resonance of the substance.

The basic idea of the present invention can be realized by arranging r over a plurality of rods. When using these rods, the mechanical strip ultrasonic vibration is applied to the moving web or to a moving, drying object in direct contact with another moving, drying object. Alternatively, if direct contact 15 is possible, the ultrasonic waves may be centered through the resonator on the web, and any mist or water droplets formed will be removed from the source.

The apparatus of the present invention for implementing the above-described method of removing water from a moving web has:, one ultrasonic radiator extending across the web in width. Radiated »• *. ·· *. in the direction of travel of the web is limited and its central axis is set o * · * ····: transverse to the direction of travel of the web. In addition, the apparatus includes a means for conducting the web through an ultrasonic radiator and means, such as for removing a mist formed by a fan: V: 25, in the vicinity of the web.

• · · • * · • t · TäcmälliQf ^ mmin cannttiina ocille nlowalla kökcinrinllo nn nääcaciallioo 5

The present invention provides considerable advantages. It saves energy, and the temperature gradient of the treated web is not a limiting factor for drying the paper, as in conventional drying 5 reduces the drying time or increases the web speed. In addition, the coating layer effectively compresses to provide a barrier between water and water vapor. The invention may be carried out in connection with modern drying methods, such as drying.

Other objects and features of the invention will become apparent from the following detailed description with reference to the accompanying drawings. However, it is to be understood that the drawings are intended only to illustrate the invention, in which reference the appended patents should be used.

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Fig. 1 is a diagrammatic view of a first embodiment of the invention in which the web rolls and ultrasonic beam rods are placed in close contact, Fig. 2 is a schematic diagram of a second embodiment of the invention web rollers and centering members, ·. ; Fig. 3 is a schematic diagram of a third embodiment of the invention. 4: shows a diagrammatic view of a fourth embodiment of the invention: * · the ultrasonic radiators are combined with the wire arrangements, and: V: 25 is a side elevational view of the rotating cylinder; pietsokldekerros.

In these cases, a separate, usually aqueous, phase is formed on the web or coating. When exposed to ultrasound water in the water phase in question, it forms microwaves or surface ripples. As a result, the mass, heat transfer at the air-web interface, and web \ increase. The thickness of the aqueous layer exposed to microwaves depends on the ultrasonic energy recovered but typically ranges from about 0.1 to 100

The above-mentioned prior art does not disclose any of the present methods of removing water from the Tainas and web 10 in small droplets generated by an ultrasonic energy source fluttering and contacting the underside of the object to be dried to contact the web to be treated with the ultrasonic hand.

The ultrasonic vibrator according to the present invention is applied by means of n ultrasonic beams or a centering radiator extending n upwards. The length of the area to which the energy effect is applied is short in the direction of web travel. Several consecutive radiators are used directly for pulsed delivery of ultrasonic vibration. The distance between the bars of the ultra 20 den or the ultrasonic source depends on the web no; * * », ··· * Preferably, the distance between the ultrasonic radiators is such that the e <· m :: 1 wave burst with droplets of water (or mist) is removed, and the following ultrasonic burst is applied to the e. Typically a radiator • ♦; y; the distance is 0.01-20 m, preferably about 0.1-10 m.

: T: The time between 25 sound bursts is about 0, C depending on the web speed

The energy of the ultrasonic vibration applied to the web is generally from 3 to 1000 W / cm 2, in particular from 5 to 100 W / cm 2. The frequency of 0.01 to 7 L is preferably maintained above 60 ° C during ultrasonic treatment, particularly at 95 ° C.

We've found that centered touch is almost as effective as 5 touches. For this purpose, the radiating rods or other radiating element 5) may be replaced by ultrasonic radiators equipped with a metaphile reflector to concentrate the center oscillation by a 10 to 200 fold vibration in direct contact with the ultrasonic source. Centers experience the effect of ultrasonic vibration in a very narrow direction of travel of 10 nanometers of the treated web, naturally dependent on the centering method used.

According to the invention, water droplets are removed by either airflow alone or by an airflow amplified by an ion blowing process.

As shown in the examples below, according to the first embodiment, a plurality of contact rods emitting ultrasound or centering ultrasonic radiators can be sequentially tracked along the web path, each radiator producing a lyre in the energy trees passing through the width of the radiator. Sticks you; 20 elongated members are mounted with their central axes or * · * ·. ···. substantially transverse to the direction of web travel.

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Ultrasonic beam rods may also be arranged alternately on the νε sides of the web. This makes it easier to control the correctness of the paper. This: »: The V-shape also provides a more regular orientation (unidirectional effect) of the filler material contained in the web: T: 25, since the molar is regularly dewatered.

• · · · · · 8 for cardboard webs. With regard to coated webs, greater drying speeds are required for the on-line and off-line coating machines required for papermaking processes. Coating layer to bring pigment particles as close to each other as possible or preferred. If the pigment layer can be squeezed and separated from the water, drying is much easier later. At the same time, it is also necessary to coagulate and compress the binder polymer portions of the binder polymer emulsified in the coating slurry d also uniformly throughout the coating layer. By removing water from the web in exactly the same way, an optimal distribution of binder and filler polymerization is achieved. This could help reduce the amount of polymers

All of the above features can be achieved by treating the head with ultrasonic energy in direct contact with the wet web t; 15 indirect touch. Ultrasonic waves are known to cause instability at interfaces, but the use of this phenomenon in web drying has not been observed before.

A denser coating can also be achieved by ultrasonically treating the top 20 instead of the usual drying process. This improves on *. : and its entire product.

It is a further feature and advantage of the present invention to provide such | : * ··· processing containing fiber deposits. The webs contain a tunnel that is not uniformly distributed throughout the web but forming

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: aggregates and areas where the number of fibers per unit volume is c than elsewhere in the web. These areas are the other parts of the web, perforated, 11

When the webs are subjected to ultrasonic treatment, the ultrasonic vibration homogenizes these denser areas and prevents premature surface drying. Curling does not occur during the drying of the ice support. The effect of ultrasound appears to be stronger than that of the t 5 material. Therefore, the denser parts of the material absorb e energy than the thinner areas. Powerful ultrasonic discharges can partially break the denser portions of the web and thus smooth the density differences.

It is preferred, although not obligatory, to perform the present web finishing at the very beginning of the wet web treatment. In many paper machine drying operations, the wet web passing the double wire I is removed in both directions. Usually this section is a vertical web running upwards. At this stage, ultrasonic vibration by the direct moth method is very easily performed.

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In the accompanying drawings, the following reference numerals are used: 1.43 web 2 film coating machine 20 3, 13, 24 wire roll 4, 14.24 wire roll «5 ultrasonic beam rods

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•: M: 7.17.27 Enclosure: / * (8.18.28 air intake \ v 25 9.19.29 air vent *** v: 16.26 reflective elements 31 inhtntplat 10 42 piezo-crystal segment

Fig. 1 illustrates a dewatering method according to the invention, a fluid coating machine 2. The web to be coated is guided to a film coating 5 roller, where the coating mixture applied to the transfer roller is subsequently secured to the web and guided by two guide rolls 3, 4 spaced apart. In this example, 4 is arranged horizontally on the same plane, but any arrangement is also possible. Ultrasonic emitter rods 5, which extend in the r 10 direction of water, are arranged between the guide rolls. An opposite housing is provided with a housing or cover 7 which collects emitted from the surface of the web. For this purpose, air is fed to the shell through a tube 8 and deflected from the shell through the tube 9.

Using this equipment is very simple. The radiator rod 15 is applied to the web of ultrasonic energy, and the water of the web forms droplets which pass through the surface of the nanoparticle and are collected in the air stream.

In the embodiment shown in Fig. 2, the radiator rods 5o of Fig. 1 are provided with ultrasonic radiators provided with centering suction 16.

20 / ·, · As shown in Fig. 3, the radiator rods, or in the case of Fig. 3, the:: *** / radiators 26 may also be arranged alternately on each side of the web * · * ·: · *: The opposite side of each radiator or reflector member • · * / »: 27-29 for ultrasound treatment to remove fog or leach <• * V .: 25. This makes it easier to adjust the paper's paper size. This filter also provides the fillers contained in the web, through the wire 32, supported by the guide rolls 31. The ultrasonic energy applied to the radiator members 34 disposed on either side of the web drops off the suction means 33. At this stage, ultrasonic color rays The keto method can be performed very easily. Direct contacts 5 be a rod or roll that rotates at the same pyrophoric velocity as the ra. It is surrounded by ultrasonic generating units which are electrically and

Also, the ultrasonic rod may be a rotating cylinder which passes at the same time web (Figure 5). Said cylinder 41 is provided with crystal segments 42 on the outer periphery 10.

In the following, the invention will be described with reference to the inventors

Example

Ultrasonic oscillation drying was compared with 20 air at normal airflow. The material was an aqueous suspension of PCC with a solids content of 69.92%. In the experiments, the oscillator source (radiator rod) was placed under the sample «« · * "in close contact with it. Ultrasonic oscillation frequency i · * *: / · {Ultrasonic sample dried 69.92% ------> 80.30% • * i * · Λ- *. ·. 25 Φ · ♦: The control sample was dried 69.92% -----> 70.56% .3 1

In all experiments, it was visually evident that when the ulti was initiated, evaporation, and in particular fine mist droplets, began immediately, and in fractional seconds the formation of mist droplets decreased. Fog formation can be easily measured by the laser beam * length is n-> m, since the beam's visibility from the side is always a misty area because of the light scattering from the droplets. If the fog is not es I can not see behind. Accordingly, the drying of the web is performed so that the web passes over a plurality of ultrasonic radiator rods, whereby the effect of res 10 at the beginning of the area of use of each beam is greatest.

Another option is a contactless system that requires ultrasonic centering. The centering is easily accomplished by the curved center of the beam at the level of the web. The hub is preferably manufactured under 15 direct-contact ultrasonic sources causing its vibration. Concentrations are 10 to 200 times, which means that the original oscillation range and range is 10 to 200 times smaller.

The energy intensity of the ultrasonic vibration energy applied to the web is o / ·: 1000 W / cm 2, in particular 5 to 100 W / cm 2.

• * «M t * ·· · Naturally, the same phenomenon can be applied to the coating of a coated web, which has no coating on a specific dry area of the paper, * * \ v 25 to the drying of uncoated paper. This method ***** * · * * also combines with any known drying method.

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Ultrasonic and Air Dryer: 0.39 g paper (relative moistened with 0.77 g -> dried per second.

5 Using an air dryer only: 0.40 g of paper -> moistened with 0 watt 0.43 g in 138 seconds.

The weight of the test paper per square meter was 80 g / m 2, the ambient temperature of the map fan temperature at the nozzle was 85 ° C and the paper level was 37 ° C.

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A heavier writing paper sheet of 127 g / m2 yielded the following fire

Ultrasonic: 1.27 g -> wetted 2.25 g -> 1.50 g in 15 90 seconds.

Using air blower only: 1.29 g -> moistened 2.16 g -> 1.39 g in 168 seconds.

20 /·.· Heavy Mass Sheet: 770 g / m2 • «• · '99 • ϊ **' · Ultrasonic: 3.16 g -> moistened 7.76 g -> SM 6.67 g • * v .: 25 in 189 seconds.

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With only a slight reduction in air, the total compression in the axial direction is low to low, reducing ultrasonic vibration more effectively compared to thicker sheets of water droplets. On the other hand, the more significant difference in the surface pigment layer is explained by the 5 refla elastic modulus of the inorganic pigment.

When the pigment slurry is ultrasonically dried, a hard, tightly packed pigment layer with a solids content as high as 85% at 70% PCC in the starting slurry is deposited on the glass vessel surface means that ultrasonic vibration also thickens the surface-coated pigment particles. This means better sidep use, better layer closure properties and better pressed mouths.

For example, at an ultrasonic frequency of 40,000 Hz, that is, at a sound speed of 1500 m / s, a wavelength of about 37 mm, and a Ki of 1000 kHz, a wavelength of 1.48 mm.

The particle displacement that ultrasound can at most produce 1 Λ • * 20 I f · • 44 * * ···· * A = v (max) / 0 =, where v (max) = vo x 1.42 and O = px 1000 kHz * · «« * A - wavelength in water.

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4 4 «* 4 • 4 4 V: 25 If the particle size is 0.1 microns = 1000 A then the best frequency for transferring 0.1 microns should then be 200 kHz.

4 • 4 4 4 4 9 444 4 15 are examples of preferred frequencies.

Water viscosity and surface tension and density depend on temperature: 5 Viscosity Surface tension Density μ Pas dynes / cm kg / m3 20 ° C 1 005 73 998 100 eC 284 62 954 10 Dependence of droplet size and internal droplet pressure;

Pst = 4 st / D where st = surface tension, 15 D = diameter and

Pst = pressure due to surface tension

We also know that 20 P, = P „+ Pd, where Pa = external dynamic pressure and m *

Pj = internal pressure • * • «* * • * With Pj> Pex« ♦ ♦ p ex • · · • * · * · where Pex = external pressure, 25 16 1 D (stm) = kx sti + 06) Vis { 02) dP 4 -4) where Vis = viscosity 5 As can be seen, the higher temperature is preferable the lower the surface drop required for the smaller droplet breakdown, it is preferable for the temperature of the web to be increased, e.g.

When the ultrasound has to change phase, the reflection takes quite a pa 10 and pressure potential.

The energy transfer from one phase to another can be expressed as: e = 4 Ζ, χΖ, ίΚΖ ^ ζη 15 where ZY and Z2 are the aft resistances of the different phases.

Z1 in air is 45 g / m2s and Z2 in water is 15 E + 4 g / m2s.

. ·. : 20 Z - density x velocity of sound in that medium, so e = 0.12 's II • »17 fine droplets are released in the form of mist. It is unstable that the resonant forces of the oscillations are at least local than the surface tension of the point in question.

5 The point of instability depends on the thickness of the free liquid phase, the elastic content, the mineral filler content and the quality and the heat content, and on the boundary conditions of the area to be dried. No straightforward mathematical conditions can be given easily, but experimentally you may find that by vibrating the water layer in the vessel, the evaporation is low until the 10 layer is sufficiently thin and then begins to vibrate so that energy drops high vapor clouds.

The concentrating ultrasonic radiator is most preferably made of aluminum and also the direct contact between the water and the metal surface is achieved with part 15 aluminum. Aluminum has the lowest sound impedance, which has the lowest sound energy absorbance in this metal. Any other metal can also be used.

One embodiment of the invention is a method of dewatering a coating slurry 20 and, after dewatering, attaching it to a coating; to the surface.

• ψ * * * • t •::. !!!: Based on our trial data, we have found that the present invention is a. : The drying intensity can be increased by up to 100% only by increasing the non-*.

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Thus, although the so-called presented and described herein, reference is made to novel combinations of m 18 steps of the invention which provide substantially the same within the scope of the invention. It is also perfectly intended and possible that the elements of the embodiment are already replaced. Thus, the principle of the invention relates to the assembly and compression of polymeric webs, coated metal webs and their. It is also to be understood that the drawings are not drawn to the correct scale, but are by nature only. It is intended that only the foregoing be limited to the scope of the accompanying drawings.

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Claims (15)

A method for removing water from a water-containing (1), characterized in that a plurality of success ultrasonic signal bursts are directed toward the web to effect dewatering of the web. A method according to claim 1, characterized in that the path (1) is passed by an ultrasonic radiator (5), which is; the width direction over the web and whose length in the web ('direction is limited; or solution the meadows are removed from the vicinity of the web. 3. A method according to claim 1 or 2, characterized in that the web (1) is shaken from one side by means of a high frequency direct contact device (5), and the simultaneously formed microwaves are removed from the other side of the web. 4. A method according to any one of claims 1-3, characterized in that the ultrasonic vibration is directed towards the web (1) by concentrating the vibration to 10-2 **** ** by means of an accumulating metal reflector. , which vibrates at d with the ultrasonic source. m λ m of an electric field and / or ion blasting process. Method according to any of claims 2 to 6, characterized in that the web (1) runs at least over two ultrasonic radiators (5). 5 8. Procedure in accordance with some of the foregoing | characterized in that the web has a pigment layer Ϊ the water, pigment particles and selectively of a soluble or emulsified I 9. A method according to claim 8, characterized in that the pigment layer is filled with such specific energy and frequency that it becomes unstable at the present water content at the moment the radiator is passed and the pigment layer is pressed. 10. A method according to some of the foregoing [characterized in that the vibration frequency is equal to 0.01 Method according to some of the foregoing [j characterized in that the temperature of the web is poured at a level <·: ··· 12. Method according to some of the foregoing \ characterized in that the web being treated is a hydrogen : V: cardboard path. • · » A method according to any of claims 1-11; ! *; The fact that it is easily processed is that heat is used in papermaking, e.g. a drying blanket or any other blanket. 15. A method according to any of claims 1-11, characterized in that the web being treated consists of a coating which method removes the water from the coating method in successive ultrasonic bursts and the batter from which water is brought into contact with the moving web. A method according to any one of claims 1 to 11, wherein the treatment is a coated web, wherein the coating is coated by means of the coating butter, and immediately after t the coated web is treated by ultrasonic vibration of the pigment particles of the cream, to separate and remove. water remove the water and coagulate a binder polymer. 17. Procedure in accordance with some of the foregoing | Characterized in that the ultrasonic vibration size 3-1000 W / cm2 is directed towards the web, preferably 5-100 W / cm2. • * t «« «* *** 18. Apparatus for removing water from a water holding in (1), characterized in that it comprises • * • V *: - at least one ultrasonic radiator (5) extending in its width direction and its length in the path of the web. (1) pipe: · :: limited,. means (3,4) for passing the path (1) past the ultrasonic radius 20. Device according to claim 18, characterized in that the ultrasonic radiator has a centrator for concentration of a 10-200-fold level by means of an accumulating metal ref vibrates upon direct contact with the ultrasonic source. 21. Device according to any of claims 18-20, c h a r a c t e r i z e d in that on the opposite side of the web is a shell to form an air stream in the vicinity of the web to remove the ultrasonic vibration formed. • · • · · • «· m · • · · · · · • # · • ·» • 1 • 1 • »» • «· •« «« «• ♦ · • ♦ ·« • 1 1 mm »