MXPA98009479A - System of convection-radiation for treatment of a band treatment - Google Patents

Abstract

Installation for the thermal treatment of a band that continuously moves in relation to infrared radiating elements and air blowing elements on said band, the installation comprises a succession of blower elements separated from each other by at least one infrared radiant element, each blower element comprising on each of its sides, a suction element that extends in proximity with an infrared radiating element

Description

CONVECTION-RADIATION SYSTEM FOR THERMAL TREATMENT OF A CONTINUOUS BAND The present invention relates to a convection-radiation system for the thermal treatment of a continuous band. It is known that the continuous bands or the deposits made on said continuous webs must be subjected to thermal treatments. Frequently, said thermal treatments must be carried out without contact, in order to maintain the quality of the surface condition of the band or the deposit made on it. This applies, for example, to paper webs that have to be subjected to a wet treatment, such as the treatment for obtaining coated paper. In order to treat these continuous bands thermally without contact, two different techniques are currently used: either the heating of the continuous band by means of infrared radiating elements, or the heating by means of hot air blowing elements. The infrared radiating elements have a very high power density (power per unit area), which makes it possible to obtain a thermal treatment by means of a relatively small voluminous installation. However, the use of these radiating elements requires the use of means to support the continuous band; said support means, under no circumstances, should be in contact with the paper web. Heating systems with hot air have the disadvantage of having a density and power much weaker than those using infrared radiating elements; its voluminosity, therefore, is very important in relation to that of an infrared radiation system that performs the same thermal treatment. On the contrary, this type of installation does not need auxiliary means to support the band; This function is ensured by the air which, moreover, can create waves in the road to increase its rigidity in a direction perpendicular to its trajectory. An example of an installation of this type has been described in the international application WO 95/14199. In order to associate the advantages of both techniques described above, attempts have been made to combine them. One such attempt has been described in European patent 0 291 832 or in US 5,261,166. However, the solution described in the cited patent is not perfect, at least for the reasons stated below: the blowing devices are not perfectly protected from the radiation coming from the infrared emitters; - the blown air can alter the good functioning of the infrared radiation emitter. It is the object of the present invention to remedy the drawbacks of the prior art, by creating a drying system of a continuous band, which has a low volume, which provides a high density of heating power and which contributes with a solution for supporting the band keep going. The invention thus contemplates a thermal treatment installation of a band that moves continuously, in relation to the infrared radiation elements and air blowing elements on said band. According to the invention, this installation is characterized in that it comprises a succession of blower elements separated from each other by means of a radiant infrared element; each blower element on each side comprising a suction element extending in the vicinity of an infrared radiating element. The installation according to the invention thus combines infrared radiating elements with blowing and aspirating elements. The volume of the installation is greatly reduced, in this way, due to: - the infrared radiating elements that provide a high power density; - blown air volumes, which are at least 30% lower than those circulating in a facility that does not use hot air. The blowing elements allow to support the band without contact, without using auxiliary means, but creating on the band undulations that ensure its mechanical rigidity in a direction perpendicular to its trajectory. The suction elements arranged between the rows of infrared radiating elements, on each side of a blower element, allow: - to suck out the air laden with water vapor coming from the band, when it is desired to dry it; the air blown by the blowing elements, as well as the combustion gas coming from the infrared radiating elements, when they operate with gas; - Effectively protect the blowing elements of the radiation coming from the infrared radiating elements, to result in the dimensional stability of the blowing systems, it is necessary to have their proper functioning. The configuration of the blower-aspirator modules is such that they do not alter the operation of the infrared radiating elements. According to a preferred version of the invention, the blower elements are separated from each other by two parallel rows of infrared radiating elements. Preferably, each blower element comprises, near the band, at least one air blowing slot, transverse to the direction of travel of the band. Other features and advantages of the invention will appear further in the description that follows. In the attached drawings, given by way of non-limiting examples: Figure 1 is a schematic view in longitudinal section of an installation for heat treatment according to the invention. Figure 2 is an enlarged view of the lower part of a blower element and of two adjacent suction elements. Figure 3 is a view similar to Figure 1, which is related to a variant of the installation mode for heat treatment. Figures 4 and 5 are views similar to Figures 1 and 3, which refer to two other variants. The preferred version of the invention, as illustrated in FIG. 1, relates to an installation for the thermal treatment of a band 1, which can be moved at a speed that can reach or exceed 2000 m / minute. According to the invention, the heat treatment installation comprises a succession of blower elements 2 separated from each other by at least one infrared radiating element 3. Each blower element 2 comprises, on each side, a suction element 4, which extends next to an infrared radiating element 3. The radiant surface of the radiating elements 3 extends parallel to the strip 1. The blowing elements 2 and the suction elements 4 are constituted by substantially parallelepiped chests extending vertically and in the direction of the length of the band. The blower elements 2 are connected to means (not shown) to create an air overpressure. The suction elements 4 are connected to means (not shown) to create a depression. In the illustrated example, the blower elements 2 are separated from each other by two parallel rows of infrared radiating elements 3. Each blower element 2 comprises, near the band, at least one, and preferably two, air blowing slots 8. (see Figure 2), cross-sectional with respect to the direction of travel D of the strip 1. As seen in more detail in Figure 2, each suction element comprises, near the strip 1, a suction mouth 9, forming an acute dihedral with the wall of the adjacent end 10 of the blowing element 2. The distance between the lower part of the dihedral and the band 1 is between 5 and 50 mm, in the preferred version, said distance is between 10 and 25 m. In addition, the edge 11 of the suction mouth 9 closest to the band 1 is connected to the side wall 12 of the suction element 4, by means of a bent wall 13. The arrangement of a suction mouth 9 allows the once: - obtain an effective aspiration of air charged with water vapor, in case of a drying operation; of the air blown by the modules 2, of the combustion gases, in the case where the infrared elements work with gas, or of the cooling air of the electrical connections, in the case that the radiating elements are electric infrared emitters; - avoid any disturbance in the operation of the infrared radiating elements 3; - protecting the blowing modules 2 against the radiation emitted by the radiating elements 3; maintaining the efficiency of the blowing modules without altering the air pressure cushion created by them on the strip 1. In the example of FIGS. 1 and 3, the infrared radiating elements 3 and the blowing elements 2 and aspirating elements 4 are located at each side of the band 1. In the case of the installation shown in figure 3, the elements 3, 2 and 4 are arranged symmetrically on one side and the other of the band 1. In the preferred version of figure 1, the elements 3 , 2 and 4, located on one side of the band 1, are offset, in the direction of displacement D of the band 1, with respect to the elements 3, 2 4 located on the other side of the band 1. This deviation or alteration is such that the infrared radiating elements 3, located on one of the sides, are arranged, in relation to the blower elements 2 and the aspirators 4 located on the other side. This staggered arrangement has the effect of creating ripples on the band 1 that make it mechanically rigid in a direction perpendicular to its displacement. In the example of figure 4, on one of the sides of the band 1, a succession of radiating elements 3 and of blowing elements 2 and aspirators 4 are arranged, while on the other side only blower elements 2 and aspirators 4 are arranged. In the case of this configuration, there can be no aspirating elements 4. The distribution of the infrared radiating elements 3 and / or of the blowing elements 2 and aspirators 4 can vary along the direction D of displacement of the band 1. This The division takes into account the fact that the band may need non-constant power densities along its route. The thermal treatment installation that is being described works as follows: The band 1 to be treated is continuously moved in the D direction, between two superimposed series of elements 3, 4, 2. The air blown by the blower elements 2 (see the arrows F in figure 2) keeps the band 1 at a distance from the successive elements 3, 4, 2 and thus supports the band during its journey in the installation, without auxiliary support devices. The infrared radiating elements 3, which have a large power density, transfer the energy to the band. The suction elements 4, arranged on one side and the other of each blower element 2, aspirate through their suction mouth 9 the combustion gases emitted by the radiating elements 3, if they operate with gas; water vapor emitted by band 1, if it is drying (see arrows Fi in figure 2) and air coming from blower elements 2 (see arrows F2). In another practical embodiment, when the radiating elements only exist on one side, on the opposite side to the radiating elements 3 can be arranged reflectors, in order to improve the thermal efficiency of the system. In this case, the reflectors are arranged, alternately with the blower elements, so as to guarantee the support of the paper.

In the same way, additionally, these reflectors can serve as suction elements. Finally, in another arrangement, these reflectors can be arranged between the blower elements and the aspirators. In all cases, the arrangement of the radiating elements, blowers and aspirators can be such that a non-rectilinear path of the strip is obtained. The main advantages of the installation that has just been described are the following: - the installation has a high power per unit area, thanks to the radiating elements 3 and the blower elements 2 and vacuum cleaners 4, due to the fact of its compact shape and of its reduced voluminosidad, do not affect much the total voluminosidad of the installation; - the blower elements 2 allow to support the band 1 without rollers or any other auxiliary means; in the entire path of the band in the installation, or in part of said path; - the arrangement of the suction elements 4, on each side of a blower element 2, allows to efficiently suck the water vapor emitted by the band, in case it is in the evaporation phase, and the combustion gases emitted by the radiating elements 3, if they work with gas, as well as the air blown by the elements 2, which do not alter, therefore, the operation of the infrared elements. It should be understood that the invention is not limited to the application examples that have just been described, and numerous modifications can be made therein without departing from the scope of the invention.

Claims (16)

NOVELTY OF THE INVENTION REGVINDICATIONS

1. - System of thermal treatment by convection-radiation of a band that moves with respect to infrared radiant elements and air blowing elements on said band; comprising a succession of blow elements separated from each other by at least one infrared radiating element; said system characterized in that each blower element comprises, on each side, a suction element that extends close to an infrared radiating element.

2. Installation according to claim 1, further characterized in that each blower element comprises, near the band, at least one air blowing slot, transverse with respect to the direction of travel of the band.

3. Installation according to any of claims 1 and 2, further characterized in that each suction element comprises, near the band, a suction mouth forming a sharp dihedral with the adjacent end wall of the blower element.

4. Installation according to claim 3, further characterized in that the edge of the suction mouth closest to the band is connected to the side wall of the suction element 4, by means of a bent wall.

5. Installation according to any of claims 1 to 4, further characterized in that infrared radiating elements and blower elements and aspirators are located on each side of the band.

6. Installation according to claim 5, further characterized in that said elements are arranged symmetrically on either side of the band.

7. Installation according to claim 5, further characterized in that the aforementioned elements, located on one side of the band, are offset, in the sense of the displacement of the band, with respect to the elements located on the other side of the band.; so that the infrared radiating elements located on one of the sides are arranged in relation to the blower and aspirator elements located on the other side.

8. Installation according to any of claims 1 to 4, further characterized in that on a side of the band is arranged a succession of radiating elements and blower elements and vacuum cleaners; while on the other side only blower elements are arranged.

9. Installation according to claim 8, further characterized in that reflectors are arranged between the blowing elements on the side opposite the radiating elements.

10. Installation according to claim 9, further characterized in that the reflectors serve as suction elements.

11. Installation according to any of claims 1 to 4, further characterized in that on a side of the band is arranged a succession of radiating elements and blower elements and vacuum cleaners; while on the other side only blower and suction elements (4) are arranged.

12. Installation according to claim 11, further characterized in that reflectors are arranged between the blower elements and vacuum cleaners on the side opposite the radiant elements.

13. Installation according to any of claims 1 to 12, further characterized in that the distribution of the infrared radiating elements and / or the blower elements and aspirators varies along the direction of travel of the band.

14. - Installation according to any of claims 1 to 13, further characterized in that the infrared radiating elements are radiant burners that run on gas.

15. Installation according to any of claims 1 to 14, further characterized in that the infrared radiating elements are radiant emitters that work with electricity.

16. Installation according to any of claims 1 to 15, further characterized in that the arrangement of the radiating elements, blowers and vacuum cleaners, allows to obtain a non-rectilinear path of the band.