WO2018189363A1

WO2018189363A1 - Continuous furnace for heating material by means of microwaves

Info

Publication number: WO2018189363A1
Application number: PCT/EP2018/059504
Authority: WO
Inventors: Volker Reichardt
Original assignee: Dieffenbacher GmbH Maschinen- und Anlagenbau
Priority date: 2017-04-13
Filing date: 2018-04-13
Publication date: 2018-10-18
Also published as: EP3610700A1; DE102017108092A1

Abstract

The invention relates to a continuous furnace (4) for heating material (2) by means of microwaves, comprising a treatment chamber (7) for heating the material (2), wherein one or more openings (6) for introducing the radiation (5) via waveguides into the treatment chamber (7) are arranged in the treatment chamber (7) and/or the microwave generators are arranged directly in the treatment chamber (7), at least one continuously circulating conveyor belt (1, 8) for transporting the material (2) through the continuous furnace (4), and a plate (10) over which the conveyor belt (1, 8) is pulled in the treatment chamber (7). The invention is characterised in that the plate (10) lies on at least one or more supports (11) and/or the plate (10) is overlapped or surrounded on its edges by a holder (14) and/or the plate (10) is made up of segments (15).

Description

Continuous furnace for heating material by means of microwaves

The invention relates to a continuous furnace for heating material by means of microwaves according to claim 1.

In the production of material plates, in particular wood-based panels of lignocellulosic material, it is known to preheat the material scattered to a non-woven before pressing in a press. Due to the higher heat at the beginning of the compression, the press needs less time to completely heat the fleece. Accordingly, the press can be made shorter or operated faster. Have proven particularly hot air or

Steam preheating or the use of high-frequency radiation, such as microwaves, for preheating in microwave continuous ovens, referred to in the following continuous furnace. The physical principle is based on the

Conversion of electromagnetic energy into thermal energy in the absorption of microwaves by the material to be heated.

For example, it is known from DE 197 18 772 A1 to expose the material scattered to a nonwoven fabric to microwaves before being introduced into a heated, preferably continuously operating press so as to accelerate a subsequent heating and pressing operation. The heating with microwaves has the advantage that the desired heat is generated directly in the product by the

Microwaves penetrate into the product, be absorbed and stimulate existing water molecules or other electric dipoles to vibrate. In contrast, when using hot plates or

Heißluftvorwärmsystemen or the like, the heat applied substantially from the outside, whereby a complete penetration of the product to be manufactured with this heat can not always be guaranteed. In the case of products preheated by means of microwaves, such a heat distribution is to be ascertained in the heated press in which the core of a product also reaches a desired temperature, without critical temperatures already being exceeded during pressing on the areas lying further outside. Compared to the use of steam preheating systems, the use of microwaves has the advantage that no additional moisture is introduced into the material to be compacted during preheating. Due to the additional moisture which is introduced with the Dampfvorwärmsystemen, the material is to be dried prior to application to the conveyor belt such that the maximum moisture content of the material before pressing by adding moisture, such as steam, is not exceeded. This leads already in the pretreatment of the material to an intensive drying of the material and a high

Power consumption.

When using microwaves or high frequency radiation in one

Continuous furnace for heating the material can be dispensed with intensive drying of the material under maximum moisture in advance, which has a positive effect on the energy balance.

In known microwave ovens, as they are used in the field of catering or in the household, is usually a hermetically demarcated

Treatment chamber is provided, which is to be sealed off to the outside with respect to the leakage of microwaves.

In contrast, in the continuous furnace described here, the material to be treated is irradiated to one for the radiation, in particular microwaves,

deposited permeable conveyor belt and transported by this through the treatment room, wherein the material to be treated is uniformly irradiated both from below and possibly from above with microwaves.

The problem here may be that the conveyor belt due to the

Requirements of transparency for microwave radiation from plastic, such as polyester, so that it moves over a the

Wall chamber down covering plate to electrostatic if necessary

Charges can come because such plates also from one

Microwave permeable plastic, such as polypropylene, so that for homogeneous heating of the material and radiation below the Material and thus introduced below the floor area in the treatment room and can be absorbed by the material.

In the case of the relative movement of the conveyor belt relative to these floor areas, it may be due to triboelectric effects for the separation of charges and thus to an electrostatic charge. This transmits and also affects the material to be treated. As a result, individual charged particles of the material tend to be from the mat or fleece, in particular from the latter

Surface, during transport through the continuous furnace to solve.

Such dissolved particles then settle within the treatment room, especially at exposed locations. Here form corresponding agglomerates. These can lead to malfunctions of various kinds, be it that they disturb a uniform distribution of microwaves within the treatment room, whether they grow and detach from a certain size and fall back on the material cake, what in this undesirable

Irregularities, or even cause them to ignite in unfavorable constellations.

It can also be problematic that the transparent to the radiation plate over which the conveyor belt runs, should be made particularly solid with a corresponding thickness due to the width of the continuous furnace of up to 3.5 m, so that they are the burden of the Material resting on the conveyor belt also withstands. In addition, the plate in the treatment room also warms up and due to the selected material of a strong

Thermal expansion may be subject. This can lead to a deformation de plate, which in turn affects the conveyor belt running above it and the material lying thereon and there can lead to a deformation of the present in the form of a mat or nonwoven material.

Object of the present invention is therefore to overcome the disadvantages mentioned above. Another object of the present invention is to improve the distribution of

To improve microwave radiation within the continuous furnace.

Yet another object of the present invention is to improve the transport of the material through the continuous furnace.

Yet another object of the present invention is to provide such

Accumulation of electrostatically charged particles within the

Prevent treatment room.

These and other objects are achieved by a

Continuous furnace for heating material by means of microwaves, comprising a treatment space for heating the material, wherein in the treatment space, one or more openings for the introduction of radiation via waveguides in the

Treatment room are arranged and / or the microwave generator in

Treatment room are arranged directly, at least one endlessly circulating

Conveyor belt for transporting the material through the continuous furnace, and a plate over which the conveyor belt is pulled in the treatment room, wherein the plate is located on at least one or more carriers and / or the plate is overlapped or encompassed by a holder at its edges and / or the plate is made up of segments ..

The invention is based on the finding that the support receives the support from the plate, as a result of which the plate can also be made thinner. By means of the carrier, sagging of the plate can be prevented, so that the material, preferably present as fleece or mat, can be transported more uniformly and without bending through the continuous furnace. By resting the plate on the carriers, there is also a thermal connection between the carriers and the plate, whereby any occurring heat distribution fluctuations can be dissipated and the heat distribution can be homogenized as a whole. By arranging the carriers between the microwave generators or the openings for the entry of the radiation into the treatment space and the plate, these can also influence and improve the distribution of the radiation in the treatment space, especially between the floor and the plate. The invention is based on the finding that, in particular when using sheets made of plastic, which is microwave transparent, the

find electrostatic charges substantially on their surfaces, i. on the top or bottom of each plate. By these plates lie on at least one carrying them and the charge-conducting carrier and thereby form a basically electrically conductive contact, these electrical charges

be compensated. Whether it be that excess charges are discharged, be it the missing charges are supplied. In this way, the

Compensated electrostatic charges to a large extent and so the above-mentioned problems can be effectively avoided.

The supports preferably extend substantially parallel to one another and are arranged parallel to one another. Preferably, at least a part of the carriers are aligned perpendicular and / or parallel to the production direction. The arrangement as well as orientation can be influenced by the width and the length of the continuous furnace.

In particular, the carriers do not run only at the edge of the floor areas, but in particular over the central areas bounded by the edges.

Alternatively or in combination, the carriers include a spacer and a rail, the rail being in contact with the plate. As a result, the carriers are on the one hand not solid, whereby a better distribution of the radiation, in particular the microwaves, is achieved in the treatment room.

Preferably, the spacer elements and the rails are made of the same material or of different materials. The distribution of radiation in the

Treatment room can be influenced by the choice of materials. Alternatively, the materials can also be selected so that they specifically influence the distribution of the radiation in the treatment room.

Preferably, the carriers do not cover the openings, so that they can release the radiation freely into the treatment room. Direct reflection of the radiation in the opening is thus avoided. The said openings for microwaves are included preferably arranged in the areas between the above-mentioned parallel rails.

Preferably, the carriers are arranged equidistant and thus distributed in the treatment room. This can be especially true for the distribution of radiation in the

Treatment room be beneficial.

A further embodiment provides that the carriers are formed from a material with low thermal expansion. Low thermal expansion to mean in this case that the material of the carrier by direct heating by

Absorption of the radiation as well as by indirect heating via contact heat and / or heat radiation only slightly, preferably by less than 5%, especially by less than 3%, most preferably by less than 2%, in relation to the size at room temperature.

The supports are preferably constructed of a material which is transparent to the radiation or of a metallic material, for example of aluminum or steel. Transparent materials for the radiation offer the advantage that they do not affect the distribution of the radiation in the treatment room, but, because they are mostly plastics, difficult to connect to the wall, in particular to the bottom of the continuous furnace. Metallic materials can influence the radiation distribution, also positively.

A further embodiment is characterized in that the contact surface of the plate on the carriers is less than 20%, preferably less than 12%, particularly preferably less than 8%, most preferably less than 5%. By a small contact surface the largest possible area is available through which the radiation can penetrate into the material and heats the material, in particular if the carriers are constructed of a material which is not transparent to the radiation.

Preferably, the plate is overlapped or encompassed by a holder at its edges. By the holder bending of the plate, for example by thermal expansion or the like, is avoided. The bracket, which are usually made of steel or aluminum, also serves as a guide device for the plate. These Brackets also allow electrostatic charges on the

To compensate conveyor belt facing side of the plate, so these charges causing electrons or dissipate.

Alternatively or in combination, the holder forms with the plate

Overlap range of 2 cm to 20 cm, preferably from 5 to 15 cm, whereby a secure guidance of the plate by the holder, which is preferably arranged completely circumferentially around the plate, is ensured. By the brackets thereby overlap the edges of the plate, joints are also avoided at the edges, in which otherwise could accumulate particles and as pollution etc. can lead to malfunction.

Preferably, the holder tapers in a wedge shape from the housing of the continuous furnace to the plate. The running over the plate and the bracket conveyor belt can thus conform to the shape and angular transitions, which could lead to damage to the conveyor belt can be avoided.

A further embodiment is characterized in that the plate is mounted floating between the carrier and the holder. Thus, the plate is free to expand, for example when heated by the material being heated and heated above it.

Preferably, the plate is connected at a fixed point with the support or the holder or the housing of the continuous furnace. The fixed point allows targeted control of the thermal expansion of the plate in one or more specific

Directions.

A further embodiment of the invention provides that the plate

Segments is constructed. Especially when building the system or even when changing the plate provides a segmented plate has the advantage that the individual segments can be removed and replaced separately.

Preferably, the segments of the plate overlap and preferably have

overlapping segment noses on. Due to the overlap, the space between the Wall and the bottom of the continuous furnace and the plate closed and there are no openings in the plate, through which material can penetrate into the area below the plate and ignite there.

Alternatively or in combination, the segments of the plate are interconnected, preferably via tongue and groove. On the one hand, a kind of overlapping of the individual segments occurs due to the connection, on the other hand the stability of the plate as a whole is improved by the connection of the segments. Preferably, the segments of the plate can also be welded.

Preferably, expansion joints are arranged between the segments.

In particular, the plate has a thickness of less than 30 mm, preferably less than 20 mm, particularly preferably less than 15 mm. A thinner plate also allows for easier handling due to its lower weight.

A further embodiment of the invention provides that the plate a

Base plate and a wear plate, which rests on the base plate includes. Due to the transport belt running over the plate, wear can occur on this plate. By the execution of the plate as a split plate comprising a base plate and a wear plate can be changed in a visible wear only the wear plate, wherein the base plate is arranged in a continuous furnace. The change of the plate can thus be done faster, reducing the downtime for such a change is shortened.

Preferably, the wear plate is made thinner than the base plate. The change of the wear plate can thus be done without large equipment and fast.

In a preferred embodiment, the wear plate has a thickness of less than 8 mm, preferably less than 5 mm, particularly preferably less than 3 mm. Further advantages and features of the invention will become apparent from the dependent claims, which can be combined with each other in any combination, and the

following description. Showing:

Fig. 1 is a schematic diagram of a device according to the invention;

3 shows a partial view of the continuous furnace in the region of the conveyor belt; and

FIG. 2 shows a partial view of the treatment space in perspective view; FIG.

Fig. 4 is a partial view of a constructed of segments plate.

1 shows a schematic diagram of a continuous furnace 4 for heating material 2, in particular lignocellulosic material 2, as it

for example, in the wood-based material industry for the production of

Wood-based panels is used. Lignocellulosic material 2, like

For example, chips or fibers, is scattered on an endlessly circulating conveyor belt 1 to a mat or a non-woven and fed in the production direction 3 a here shown only symbolically continuous furnace 4. The continuous furnace 4 comprises a treatment chamber 7, in which the material 2, which is present here in the form of a mat or a fleece, with radiation 5, in particular with

Microwave radiation is irradiated from below and / or above.

If necessary, while the top of the material 2 by means of another

Conveyor belt 8 are covered, which runs at the same speed as the material 2 through the treatment chamber 7. The upper transport belt 8, which rests on the material 2, on the one hand has the function of protecting the surface of the mat material 2 as it passes through the continuous furnace 4, and on the other hand, it also prevents particles, such as product fibers, Dust etc., easily detach from the surface of the material 2.

In the treatment chamber 7, the radiation 5 is preferably introduced above and / or below the material 2 in order to ensure a uniform heating of the material 2. The radiation 5 can be generated by means of microwave generators (not shown) outside the continuous furnace 4 and by means of waveguides

Openings 6 are coupled into the treatment chamber 7 of the continuous furnace 4. Alternatively, the radiation 5 can also be generated within the treatment space 7 be, which can be dispensed waveguide and the corresponding openings 6. The radiation generator for generating the radiation 5 within the treatment chamber 7 or the openings 6 for the entry of the radiation 5 into the treatment chamber 7 are preferably arranged at a distance from the material 2 around a spatial, in particular even, propagation of the radiation 5 in the complete treatment chamber 7 to enable.

In the production direction 3 before and / or after the treatment chamber 7 absorption chambers 9 are arranged in the example shown here, which prevents that in the treatment chamber 7 introduced radiation 5, in particular

Microwave radiation, in an undesirable manner from the one shown here

Continuous furnace 4 can escape. In the absorption chambers 9, the residual radiation, which has not been absorbed by the material 2, is conducted onto absorption elements 17, for example water reservoirs or plates made of ceramic materials, at which the residual radiation is converted into heat and destroyed.

In the region of the treatment chamber 7, the lower conveyor belt 1 runs with its underside over a permeable plate 5 or microwaves plate 7, so that the lower conveyor belt 1, which is loaded with the weight of the mat, does not sag. The distance between the openings 6 and the microwave generators and the continuous material 2 ensures that the radiation 5 in the

Spread and distribute treatment room 7.

Since the conveyor belt 1, 8 and the plate 10 made of different plastics, it comes due to triboelectric effects to an electrostatic charge. The thereby occurring on the conveyor belt 1, 8 charges are discharged from this part of the material 2, which thus also charges electrostatically or already, for example, by the scattering of the material 2 to a mat, has an electrostatic charge. Individual particles of material 2,

in particular, as far as they are arranged on the edge, detach from the material 2 due to this electrostatic charge or due to the electric field generated by the charge separation and then fly in particular in the

Treatment room 7. There, these particles can accumulate and thus lead to significant malfunctions. In Fig. 2 shows a part of a cross section transverse to the production direction 3 through the treatment chamber 7 of the continuous furnace 4. The present as a mat or nonwoven material 2 rests on the conveyor belt 1, which in the treatment room 7 on the plate 10 in the production direction 3, which into the picture plane, is moved. The plate 10, which consists of a, for the entering into the treatment chamber 7 radiation 5 transparent material, lies on the carriers 1 1, which are supported on the bottom of the continuous furnace 4. The carriers 1 1 are in

present case of a spacer elements 13 and a rail 12 constructed, which is in contact with the plate 10. The design of the carrier 1 1 with spacer 13 and rail 12 results in a better propagation possibility of the radiation 5 in the treatment chamber 7 and the radiation 5 is not channeled, for example, when using metallic carriers 1 1, between the carriers 1 1. The carrier 1 1 and the spacers 13 and the rails 12 may be made of a metallic material, such as steel or aluminum, which also by the movement of the conveyor belt 1 on the plate 10 resulting charges can be dissipated. Alternatively, the carrier 1 1 or the

Rails 12 and the spacer elements 13 also from a transparent material for the radiation 5, such as a plastic such as polyethylene or polypropylene, be constructed. Especially when using

Spacers 13 made of these materials, however, proves the connection of these to the wall of the continuous furnace 4 as difficult.

The peripheral edges of the plate 10 are each overlapped by a holder 14, which has a portion which can also be seen as an overlap of the holder 14 with the plate 10, and which presses firmly on the top of said plate 10. By means of this overlapping region, electrostatic charges which collect on the upper side of the plate 10 can be compensated for by the supply or removal of electrons. At the same time, these sections yield the

Possibility that the plate 10 can expand due to heat and the resulting dimensional changes, in particular a length and

Width expansion, located in below the sections mentioned

Groove areas can be compensated. By these joint areas are below the sections of the holder 14, they are also preserved from contamination. The plate 10 is thus floating between the carriers 1 1 and the Bracket 14 stored and clamped and can expand freely here. The overlap region of the holder 14 and the plate 10 is designed such that the plate 10 is always overlapped by the holder 14 and the plate 10 can extend below the holder 14. Alternatively, the plate may be connected at a fixed point to the carrier 1 1 or the holder 14, so that the expansion can preferably take place in one direction, for example the production direction 3. The possibility of expansion of the plate 10 below the holder 14 results in a change in the contact surface between the plate 10 and conveyor belt. 1 In particular, stresses within the plate 10 and bulges thereof are avoided in a strong expansion.

FIG. 3 shows a detail of the treatment space 7 in a perspective view, which shows the bottom plate of the continuous furnace 4 with the

Openings 6 and the carrier 1 1 shows. On an illustration of the plate 10, which rests on the carriers 1 1, was omitted because of the overview. It can be seen in particular the transversely to the production direction 3 extending, as rails 12, which are mounted on spacer elements 13, formed carriers 1 1. These rails 12 as well as the spacer elements 13 may be metallic and in a direct, electrically conductive contact with the plate 10. It is thus possible to compensate for the accumulating on this underside of the plate 10 electrostatic charges via an addition or removal of electrons. The spacers 13 hold the mutually parallel rails 12 of the carrier 1 1 in a distance between the bottom of the continuous furnace 4 and the plate 10, so that the radiation 5 can propagate freely in this area.

In the bottom plate of the continuous furnace 4 preferably crosswise, in particular longitudinally or transversely to the direction of production 3 arranged openings 6 are provided through which guided via waveguides and generated from outside of the continuous furnace 4 magnetron radiation 5 is introduced into the treatment chamber 7. By caused by the spacers 13 distance between the plate 10 and the bottom plate of the continuous furnace 4, the radiation 5 can distribute more evenly and thus occurs not only punctiform in a guided over the plate 10 2 material. By the arrangement of carriers 1 1 shown here is the smallest possible disturbance of uniform radiation, especially in Shape of microwaves, achieved in conjunction with an optimized support of the plate 10. The carrier 1 1 are preferably evenly arranged, in particular with an equal distance, wherein the openings 6 are not covered by the carriers 1 1. Alternatively or in combination with the openings 6, microwave generators may be arranged at intended locations, by means of which the radiation 5 is generated directly in the treatment space 7.

4, an embodiment of the plate 10 is shown, which is constructed of segments 15 which overlap in one area and allow continuous support of the conveyor belt 1 running over it. The individual segments 15 rest on carriers 11, which in turn are constructed of spacer elements 13 and rails 12. The segments 15 have segment lugs 16, which interlock the two segments 15 such that the individual segments 15 can expand to a certain extent when heated. In the region of the overlap of the segment lugs 16, a sealing material can also be introduced, so that no material can penetrate into the space below the plate 10 or the segments 15 and possibly ignite. The sealing material should be compressible so that it can be compressed with an expansion of the segments 15, without affecting the surface of the plate 10, for example, by leaking sealing material. The plate 10 may be constructed of a plurality of segments 15. The segments 15 may overlap in and / or across the direction of production 3, depending on their size.

Reference list P1551:

1 conveyor belt

2 material

3 production direction

4 continuous furnace

5 radiation

6 opening

7 treatment room

8 conveyor belt

9 absorption chamber

10 plate

1 1 carrier

12 rail

13 spacer elements

14 bracket

15 segment

16 segment nose

17 absorption element

Claims

claims

1 . Continuous furnace (4) for heating material (2) by means of microwaves, comprising a treatment space (7) for heating the material (2), wherein in

Treatment space (7) one or more openings (6) for introducing the radiation (5) via waveguides in the treatment chamber (7) are arranged and / or the microwave generators in the treatment chamber (7) are arranged directly

at least one endlessly circulating transport belt (1, 8) for transporting the material (2) through the continuous furnace (4), and a plate (10) over which the transport belt (1, 8) is pulled in the treatment space (7),

characterized in that the plate (10) on at least one or more carriers (1 1) is located and / or the plate (10) at its edges by a holder (14) overlapped or comprises and / or the plate (10) Segments (15) is constructed.

2. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the carriers (11) extend substantially parallel to one another.

3. continuous furnace (4) according to one or more of the preceding claims,

characterized in that at least a part of the carrier (1 1) are aligned perpendicular and / or parallel to the production direction (3).

4. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the supports (11) comprise a spacer element (13) and a rail (12), the rail (12) being in contact with the plate (10).

5. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the spacer elements (13) and the rails (12) are made of the same material or of different materials.

6. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the carriers (1 1) do not cover the openings (6).

7. continuous furnace (4) according to one or more of the preceding claims, characterized in that the carrier (1 1) are arranged equidistantly.

8. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the carriers (1 1) are formed of a material with low thermal expansion.

9. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the carriers (1 1) are made of a material transparent to the radiation (5) or a metallic material, preferably aluminum or steel.

10. Continuous furnace (4) according to one or more of the preceding claims,

characterized in that the bearing surface of the plate (10) on the carriers (1 1) is less than 20%, preferably less than 12%, more preferably less than 8%, most preferably less than 5%.

1 1. Continuous furnace (4) according to one or more of the preceding claims,

characterized in that the holder (14) with the plate (10) forms an overlap region of 2 cm to 20 cm, preferably from 5 to 15 cm.

12. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the holder (14) tapers in a wedge shape from the housing of the continuous furnace (4) to the plate (10).

13. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the plate (10) between the carrier (1 1) and

Holder (14) is floating.

14. Continuous furnace (4) according to one or more of the preceding claims,

characterized in that the plate (10) at a fixed point to the support (1 1) or the holder (14) or the housing of the continuous furnace (4) is connected.

15. continuous furnace (4) according to one or more of the preceding claims, characterized in that the segments (15) of the plate (10) overlap and preferably overlapping segment lugs (16).

16. continuous furnace (4) according to one or more of the preceding claims,

characterized in that the segments (15) of the plate (10) are interconnected, preferably via tongue and groove.

17. continuous furnace (4) according to one or more of the preceding claims,

characterized in that expansion joints are arranged between the segments (15).

18. Continuous furnace (4) according to one or more of the preceding claims,

characterized in that the plate (10) has a thickness of less than 30 mm, preferably less than 20 mm, more preferably less than 15 mm.

19. Continuous furnace (4) according to one or more of the preceding claims,

characterized in that the plate (10) has a base plate and a

Wear plate, which rests on the base plate includes.

20. Continuous furnace (4) according to one or more of the preceding claims,

characterized in that the wear plate is made thinner than the base plate.

21. Continuous furnace (4) according to one or more of the preceding claims,

characterized in that the wear plate has a thickness of less than 8 mm, preferably less than 5 mm, more preferably less than 3 mm.