Method and dryer for drying panels

Abstract

The present invention relates to a method for drying panels in a drying device comprising a first stage (A) and a second stage (B), each of the two stages (A, B) having levels, each of the panels being placed on a surface formed in a different level and guided through the drying device in each level of the two stages (A, B). In the first stage (A), the panels are dried by contacting them with drying air having an elevated temperature, and in the second stage (B), the panels are dried using drying air having a lower temperature. The invention is characterized in that the support surface (F1) provided in the level of the first stage (A) for placing the panel is smaller than the support surface (F2) in the second stage (B), the panel is guided in the second stage (B) with a second speed (v2) slower than the first speed (v1) in the first stage, and the product of the first support surface (F1) and the first speed (v1) is equal to the product of the second support surface (F2) and the second speed (v2).

Description

[Background technology]

[0001] When drying panels, particularly those containing cement and gypsum, the panels are exposed to hot air as they are conveyed through the dryer.

[0002] Dry air can be supplied in the form of longitudinal ventilation, transverse ventilation, or transverse ventilation using a nozzle box equipped with nozzles. With longitudinal ventilation, dry air is supplied at one end of the dryer, or at one end of a zone if it is divided into multiple zones, and exhausted at the opposite end.

[0003] With cross ventilation, the material is fed at multiple points on the side of the dryer and discharged on opposite sides, allowing for more intensive drying within the dryer, particularly with cross ventilation through nozzles passing through the jet dryer in the impinging stream.

[0004] In most cases, a recirculation process is used in which a large proportion of the dry air is circulated, where most of the dry air is reheated after contact with the material to be dried and is then reused, and only a small proportion of the dry air is discharged to the outside as exhaust air, while a corresponding proportion of the exhaust air is pumped in from the outside as supply air.

[0005] Fuel, i.e. primary energy, is needed to heat the drying air, e.g. using burners or heating registers, and electrical energy, i.e. secondary energy, is needed to supply the air, using fans. The use of primary and secondary energy must be reduced to allow a more energy-efficient production of the above mentioned panels.

[0006] DE 26 13 512 A1 discloses a drying method in which low primary energy consumption is realized by using the heat of condensation from the exhaust air. The process has a two-stage design. Drying takes place at high temperature and high humidity in the first dryer stage and at low temperature and low humidity in the second dryer stage, whereby the drying capacity of the first stage is two to three times higher than that of the second stage, which is heated from the exhaust air of the first dryer stage with the intervention of a heat exchanger. In both stages, drying air is supplied in a recirculation process, i.e. in the form of longitudinal ventilation in the first dryer stage and in the form of cross ventilation with a large mass flow of recirculated air in the second dryer stage. However, the second stage requires a large mass flow of circulating air and thus a high consumption of secondary energy.

[0007] If the primary energy consumption is reduced by also using the heat of condensation of the exhaust air, the overall problem arises that the waste heat of the exhaust air is only available at low temperature levels. The lower temperature of the dry air can be compensated for by a higher air mass flow, but this leads to a higher consumption of secondary energy.

[0008] WO 95 / 04908 A1 discloses a method for drying boards conveyed in stages through a dryer, in which the boards are contacted with drying air in two stages A and B, the dryer being run in stage A with circulating air treatment, with drying air of high temperature and at least moderate humidity, having a drying capacity two to four times higher than in stage B. In stage B, the exhaust air from stage A is passed through a heat exchanger arranged in the shelves of the dryer; at the same time, dry air of low temperature and low humidity is passed in countercurrent to the exhaust air from stage A. Summary of the Invention

[0009] It is an object of the present invention to further improve the method according to the preamble of claim 1.

[0010] According to the present invention, this object is solved as disclosed by claim 1.

[0011] By means of the method according to the invention, the speed of transport of the panels to be dried is adapted to their respective energy absorption and associated dehumidification, so that the panels are dried with a minimum energy input.

[0012] The speed selection determined for each stage according to the desired drying progress also results in a faster speed of transport in stage A than in stage B, in order to dry at a higher temperature in stage A than in stage B. This means that the speed of the panels leaving stage A is brought down to the level of the speed of stage B in a separate conveyor located between stages A and B. At the same time, in order to avoid intermediate storage of the panels in the area of ​​the conveyor, the conveyor distributes the panels over a wider area in stage B according to the difference in speed between stages A and B. This is done by distributing the panels over a greater number of levels or tracks in the area of ​​stage B compared to stage A. A conveyor device, for example a discontinuous conveyor, is used here, which on the one hand picks up the panels at a faster speed on the side facing stage A and discharges them on the side facing stage B onto a greater number of levels or tracks of stage B, so that the conveyor on this side preferably has a slower speed. The conveyor has a slope at the transition to stage B to distribute the panels to the tiers of stage B. In the case of a larger number of lanes, multiple panels are preferably transported next to each other on one tier, for example in two to four lanes.

[0013] On the one hand, this approach creates a compact entrance area for the dryer at stage A that can be passed through at high speed and temperature, which is also favorable to ensure final activation of the coagulant contained within the panel, such as starch.

[0014] On the other hand, the area and speed in stage B are designed to achieve sufficient drying of the panel while at the same time making the best possible use of the energy from stage A.

[0015] In order to achieve the best possible coordination between stages A and B, the invention provides that the contact area of ​​the panel, i.e. the area actually occupied by the panel in stage A, times the speed of the panel in stage A, is equal to the product of the speed of the panel in stage B times the contact area occupied by the panel in stage B. As a result, this leads to a larger contact surface of the panel in stage B, in combination with a longer residence time of the panel in stage B. In stage B, the panel is dried at a lower temperature. The energy input in stage B for heating the panel is greatly reduced compared to the energy input required for heating in stage A, because the heat from the heat recovery is used for drying in stage B.

[0016] To achieve rapid drying in step A, the panels are preferably heated there by an impinging stream of hot air. The impinging stream is preferably generated by a nozzle box, which is equipped with many nozzles, from which the air streams are applied to the panels at right angles to the direction in which they are transported.

[0017] On the one hand, the nozzle box allows good drying results for the panels in a short time, but requires a high energy input to generate the required air flow, and on the other hand, the nozzle box also occupies a significant amount of space within stage A, which usually has several sections, the nozzle boxes being arranged one above the other in each of the sections according to the number of tiers of stage A.

[0018] According to the invention, it is also possible to design stage A with longitudinal ventilation and to use a nozzle box.

[0019] According to the invention, since no nozzle boxes are required in stage B since a cross flow of air is generated by a corresponding fan, if necessary, the distance between the levels on which the panels to be dried rest can be smaller than in stage A. The transport rollers are arranged closer together to form a transport path.

[0020] Thus, in step B, the drying device is provided with a conveyor system having several bays or sections extending in succession in the conveying direction, for example by means of conveying devices arranged in layers in the form of roller conveyors, for conveying the successive panels to be dried in several layers per bay. The drive system drives several endless chains, each of which is assigned to at least one drive. Preferably, the roller conveyors in all layers of the bays can be driven in each case by at least one single chain.

[0021] Roller conveyors are used to guide the panels one above the other in a very compact manner. Since stage B requires a longer length than stage A due to the longer drying time of the panels to be dried, a higher number of panels per stage B height and / or per stage B width is possible on the other side, so that an overall very high utilization of space is created in stage B, while at the same time the exhaust air from stage A is optimally utilized to introduce its residual heat into the panels by means of at least one heat exchanger.

[0022] For this purpose, dryers operating at low temperatures and drive systems adapted to a large number of panels, in particular gypsum boards, are used, which are simultaneously processed in the low-temperature dryer over a large number of levels, for example from 16 to 60 levels. By using a large number of levels in conjunction with the drive system according to the invention, a longer residence time of the panels, in particular gypsum boards, can be realized in a low-temperature dryer having the same dryer length as a high-temperature dryer.

[0023] Due to this concept of connecting stages A, preferably at least partially equipped with a nozzle box, existing dryer systems having several sections, each equipped with a nozzle box, can also be converted into a dryer according to the invention by continuing to use at least some of these sections, so that they form stage A, and by attaching an additional stage B to stage A, so that the continuous operation between stages A and B is maintained by increasing the number of layers in stage B with a corresponding reduction in the speed of transport, while the still available thermal energy from stage A is simultaneously utilized in stage B. In the low-temperature dryer formed by stage B, the idlers of the transport system used there are supported by roller bearings. The graphite-based plain bearings required for the high-temperature dryers are not required; the fact that roller bearings have a lower coefficient of friction than plain bearings can be utilized here, so that, for example, idlers with internal roller bearings are used. This saves a considerable amount of energy in the low-temperature dryer of stage B, since the roller bearings used in stage B generate much less friction than the plain bearings in stage A.

[0024] It can therefore be seen that particularly large energy savings are possible when a dryer arrangement according to the invention is installed into an existing system.

[0025] To convert an existing system into a dryer according to the invention, a conveyor system and a cold stage (Stage B) must be added. In other cases, sections of Stage A of the existing dryer are removed and a conveyor and cold stage B are added.

[0026] Advantageous embodiments of the method are set forth in the dependent claims and in the description, particularly in conjunction with the drawings.

[0027] Preferably, the panels are transported between the first stage A and the second stage B via a transfer or transport device, in particular via a continuous or discontinuous conveyor; in this case the panels are decelerated from the speed at which they move in stage A until they reach a slower speed in the second, stage B.

[0028] During the transition between stages A and B, the panels are raised or lowered to a different level in a transfer or transport device, or continuous or discontinuous conveyor, and transferred to a level of the second stage B. It will be appreciated that preferably the transfer device is also enclosed as are stages A and B.

[0029] To achieve rapid drying in stage A, the panel is then at least substantially dried by use of a nozzle box.

[0030] For optimal utilization of the waste heat, especially generated in stage A, the panels are dried in the first stage A and / or in the second stage B by means of at least one internal heat exchanger and / or by means of at least one external heat exchanger.

[0031] It is also advantageous if the panels are heated in a first stage A directly with circulating air by a burner, or with superheated steam or thermal oil, or indirectly electrically, or with heat from low-temperature sources. In stage B, the panels are heated by heat from low-temperature sources, either from the heat recovery of stage A, or from another process in which heat is released at low temperature, for example from a combined heat and power plant or a heat pump.

[0032] Preferably, the panel is dried in a first stage A with dry air at a temperature of between 130°C and 300°C, while the panel is dried in a second stage B with dry air at a temperature of between 20°C and 90°C.

[0033] Advantageously, exhaust air from the drying process of the first stage A can be recycled by passing it through a heat exchanger to preheat the drying air of the second stage B.

[0034] An even higher efficiency of the drying process according to the invention can be realized if the panel is first dried in a pre-drying stage upstream of the first stage A, then in the first stage A and finally in the second stage B.

[0035] Preferably, the panels are transported through the sections in stages A, B using a separate transport device for each stage A, B and / or each section. Alternatively, each of the transport devices are driven by a direct drive motor or they are at least partially interconnected by the use of gears.

[0036] The invention also provides a dryer for drying panels in a first stage A and a second stage B, each of which is equipped with a conveyor device for transporting the panels arranged in tiers through the dryer, the first stage (A) having at least one section, the first stage A having a supply device, a discharge device and a recirculation device, a circulating air duct with a discharge device and a conveying means, and a heating device for the circulating air, as well as means for supplying supply air and means for discharging exhaust air, and the second stage B is equipped with a supply device for dry air and a discharge device for dry air and a heating device for taking over the panels from the first stage A.

[0037] It is an object of the present invention to design a dryer so that panels are dried with low energy input.

[0038] According to the invention, this object is solved in that a transport device, a continuous conveyor or a discontinuous conveyor, is arranged between the first stage A and the second stage B, by means of which the panels can be slowed down from the conveying speed in the first stage A to the conveying speed of the second stage B and can be raised or lowered to the height of the level of the conveying device of the second stage B or distributed onto adjacently extending tracks within the level of the second stage B.

[0039] The panels are dried in each of the two stages at a speed and temperature that ensures rapid throughput of the panels through the dryer while simultaneously utilizing energy efficiently.

[0040] This optimizes the use of both primary and secondary energy: in particular, the primary energy used is maintained by also utilizing waste heat and the heat of condensation of the exhaust air, without increasing the demand for secondary energy by circulating large air mass flows.

[0041] In particular, large conveying volumes for circulating air are avoided in the second stage, so that the dryer consumes only low amounts of secondary energy.

[0042] Advantageous further embodiments are given in the dependent claims.

[0043] Dryers in which the first stage A and the second stage B each have at least one section and are equipped with means for directing circulating air transversely to the conveying direction of the panels are advantageous.

[0044] For design reasons, the first stage A of the dryer is preferably divided into several sections, at least some of which are equipped with nozzle boxes for cross-flow ventilation with impinging streams of hot air.

[0045] It is advantageously provided that the second stage B of the dryer is equipped with means for flowing circulating air against and / or in the direction of conveyance of the panels.

[0046] In a further advantageous embodiment of the dryer, it is provided that the second stage B is equipped with induction means for helically inducing the circulating air or at least one exhaust air fan in conjunction with at least one circulating air fan. Alternatively, induction means, for example in the form of induction panels, are provided.

[0047] Preferably, the dryer comprises at least one heat exchanger.

[0048] A roller conveyor or a conveyor belt is preferably provided as a conveying device for transporting the panels to be dried within the dryer.

[0049] In stage B, the exhaust from stage A, which has a high water vapor content and is passed through a heat exchanger, is cooled by cool dry air to such an extent that some of the water vapor condenses.

[0050] Primary energy is also used intensively by exploiting the heat of condensation, which is made possible by the low temperature of the dry air cooling the heat exchanger and the at least moderate humidity of the exhaust air from stage A.

[0051] If dry air is routed countercurrent to the exhaust air from stage A, it is routed through a heat exchanger, where the cooler dry air meets the already cooled exhaust air. This ensures the greatest possible condensation of the water vapor contained in the exhaust air, further improving the use of primary energy. A more intensive use of primary energy leads to considerable savings in primary energy.

[0052] Overall, stage B is dried at a drying capacity not exceeding half that of stage A.

[0053] Each stage A, B is equipped with a conveyor device for transporting the sheets arranged in tiers through the dryer, which may be designed as a roller conveyor dryer or as a belt dryer, whereby the conveyor device has several roller conveyors or conveyor belts arranged one above the other.

[0054] The conveyor device located between stages A and B is preferably enclosed so that thermal energy from stage A is not lost as the panels pass to stage B.

[0055] The panel dryer according to the invention can be set up in a compact manner; it is not necessary to provide a base panel for the dryer, rather it is sufficient if the side walls of the dryer are set up directly on the floor of the factory hall, without the need to place an additional base panel for the dryer.

[0056] Additional heating devices may be installed in stage B for additional transient loads. [Brief description of the drawings]

[0057] The invention is explained in more detail below using embodiment examples, which are illustrated by:

[0058] [Figure 1] FIG. 1 is a diagram of a dryer having two stages A and B and a conveyor installed between stages A and B in a first embodiment. [Diagram 2] FIG. 13 is a diagram of a dryer having two stages A and B and a conveyor in a second embodiment. [Diagram 3] FIG. 13 is a diagram of a dryer having two stages A and B and a conveyor in a third embodiment. [Figure 4a] FIG. 2 is a diagram of the dryer in a side view. [Figure 4b] FIG. 4b is a top view of the dryer according to FIG. 4a. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] The dryer 1 (FIG. 1) comprises two stages A and B for drying panels which are fed to the dryer 1 in the direction of the arrow C. These panels are in particular building material panels, for example gypsum sheets or gypsum wallboards.

[0060] Each of the two stages A and B is preferably divided into several sections 2. This applies in particular to stage A, which is preferably designed as a nozzle dryer. This means that at least in a greater number of sections of stage A, nozzle boxes are arranged from which hot air is blown onto the panels in an impinging stream. This generates temperatures of 130°C to 300°C in section 2 of stage A.

[0061] Preferably, stage A has at its inlet side a pre-drying section 3. The pre-drying stage 3 is supplied with outside air heated therein by a heat exchanger 4, via a supply line 6 equipped with an openable flap 5; in addition to heating the panels, this supply of outside air also serves to seal stage A against other air flows and against the intrusion of outside air into stage A.

[0062] Via a pipe 7 branching off from the supply pipe 6, the heated outside air is distributed by means of a fan 8 to the individual pipes 9, 10, 11. From each of these, the outside air reaches a heating device 12, 13 or 14, which is arranged, for example, in the ceiling box above the nozzle box. As shown in FIG. 1, each of the heating devices 12 to 14 is assigned to two sections 2 of stage A. It will be understood that in alternative embodiments, other assignments can also be made. For example, in alternative embodiments, one heating device is provided for each section. The heating devices 12 to 14 are preferably direct heating devices, such as burners, or indirect heating devices, such as steam or electric heaters. Within the section 2 or together for each section, at least one recirculation fan 15 to 17 is provided to generate a cross flow of hot air in the section 2 as recirculated air. Alternatively, two recirculation fans 15 to 17 are arranged for each section 2.

[0063] The pre-dried panels are transported from stage A to stage B via a conveyor 18. As stage B has a larger number of levels than stage A, the conveyor 18 delivers the panels to the levels of stage B at a smaller distance from each other but at a correspondingly reduced speed. This distribution is achieved, for example, by the conveyor 18 as a transport device having a larger radius of curvature of its conveyor belt on the side facing stage A, which also results in a relatively higher speed of the conveyor belt on this side.

[0064] On the side facing stage B, the conveyor belt then has a slower speed of rotation resulting from a smaller radius of curvature, which results in a relatively larger number of panels being distributed over the larger number of stages of stage B. As with stages A and B, the conveyor 18 is preferably insulated against heat loss to the outside. Heating devices and fans for air circulation or exchange may also be arranged therein.

[0065] For example, stage A may have 6 to 16 levels, while stage B may have 18 to 48 levels, with stage B being operated at a speed of transport of panels that is, for example, only two-thirds of the speed of transport of stage A. Instead of a larger number of levels, the levels of stage B may be wider than stage A, so that instead of a single lane of panels in stage A, two lanes of panels are transported within one level of stage B. In another embodiment, two lanes are transported side-by-side on one level in stage A, while three lanes are transported on one level in stage B.

[0066] Stage B is also supplied with heated outside air from the heat exchanger 4. Ducts 19 to 24 are used for this purpose, of which ducts 19, 21 and 23 are each provided with a sealing flap 25, 26 and 27 respectively.

[0067] Fans may also be arranged in the ducts 19 to 24. At the entrance to section 2, the air flowing from ducts 19 to 24 to section 2 is heated by heating devices 29 to 31. The heating devices 29 to 31 are switched on when additional heating energy is required; this is the case when the system is started up when there is not yet enough available heat from stage A and the heat exchanger 4 has not yet received warm exhaust air from stage A or receives exhaust air that is not warm enough. Heating devices are also needed when the system is shut down and there is insufficient provision of warm air entering stage B from stage A. The heating devices 29 to 31 may also be used when the panels to be dried have a higher moisture content than expected, which may lead to a lack of thermal energy in stage B, and when changing between different panel formats. The heating devices 29 to 31 are therefore provided especially for transient loads in stage B.

[0068] It will be appreciated that a number of conduits for supplying air, in particular warm air from heat exchanger 4 or from another heat exchanger, may be provided along the length of stage B to recover the enthalpy of evaporation of the water evaporated from the panel.

[0069] Optionally, a recirculation fan is also provided in stage B, constructed and arranged in the same manner as the recirculation fan in stage A. Both centrifugal and axial fans are possible.

[0070] Just like the recirculation fans, exhaust air fans 32, 33 are also distributed over the length of stage B, of which only exhaust air fans 32, 33 are shown by way of example in Figure 1. Moist air is removed from stage B via these fans and chimneys 34, 35.

[0071] Additionally, there is an exhaust fan 36 at the end along with a chimney 37 .

[0072] An internal heat exchanger may be provided in both stages A and B, for example in stage A in a ceiling box above the nozzle box, or in stage B in a ceiling box above the conveying device which is also provided for this purpose.

[0073] Heat exchanger 4 is connected to stage A, section 2 via exhaust duct 38 and central exhaust duct 39. Warm, moisture-saturated air is delivered to heat exchanger 4 via exhaust ducts 38, 39 and exhaust air fan 40 where it condenses and releases its moisture as water.

[0074] The heat exchanger 4 draws in outside air via an outside air fan 41. It releases the used air to the environment via a chimney 42.

[0075] In another design example (FIG. 2), there are several internal heat exchangers 43, 44 in various sections of stage B, which are supplied with hot air, either directly or indirectly, for example using flue gas from a cogeneration plant or from a gas turbine, or other hot gas streams from other processes. Such gases can also be additionally fed to the heat exchanger 4, or they are fed to a further heat exchanger 45, which is connected in series with the heat exchanger 4 and serves to further heat the gases, which are fed to stages A, B via lines 6, 7, 19, 20, 21, 22, 23, 24.

[0076] In a further embodiment (FIG. 3), the heat exchanger 4 is connected only to stage B with respect to the air supply; such an arrangement exists, for example, when stage B is connected to an existing dryer, i.e. subsequent to an already existing stage A.

[0077] In one embodiment (FIGS. 4a, 4b), the dryer 1 shown in FIGS. 1 to 3 has multiple burners 50 in stage A, each mounted in the ceiling area or above the ceiling of section 2 of stage A, to heat the air in section 2. A circulation fan 51 circulates the air heated by the burners 50 in a circular motion perpendicular to the conveying direction of the panels in stage A.

[0078] Stage B is equipped with hot air inlets 52, which are also attached to the top surface of the individual sections 2. The hot air inlets 52 may be mounted in pairs on the top surface of the sections 2, as can be seen, for example, in Figure 4b.

[0079] In stage B, exhaust fans 53 are also arranged in some of the sections 2. The exhaust fans 53 are preferably mounted laterally on the ceiling of the sections 2, where preferably an inlet for warm air supplied either by the heat exchanger 4 and / or by the heat exchanger 45 is provided opposite each other to the exhaust fans 53 on the other side of the ceiling of the sections 2.

[0080] Preferably, the fan 53 is arranged in stage B such that an air flow is created in the longitudinal direction of stage B. Preferably, an air flow in the conveying direction of the panels (arrow D) is generated in the front part of stage B facing the transfer device, while an air flow against the conveying direction of the panels (arrow E) is generated in the rear part.

Claims

1. 1. A method for drying panels in a drying device comprising a first stage (A) and a second stage (B), each of the two stages (A, B) having a tier, each of the panels being placed on a surface formed in a tier and passed through the drying device in the respective tier of the two stages (A, B), the panels being dried in the first stage (A) by contacting with hot dry air and in the second stage (B) by using dry air of a lower temperature, the method comprising: a first support surface available in the tier of the first stage (A) for placing the panels being smaller than a second support surface in the second stage (B); the panels being passed through the second stage (B) at a second speed slower than the first speed in the first stage, the product of the first speed and the first support surface being equal to the product of the second speed and the second support surface.

2. 2. The method of claim 1, wherein the panels in the second stage (B) are guided in a greater number of tiers extending above and below each other or next to each other.

3. 3. The method of claim 1 or 2, wherein the panels are transported between the first stage (A) and the second stage (B) via a transfer device, a continuous conveyor, or a discontinuous conveyor, whereby the panels are decelerated until they reach the second speed.

4. 4. The method according to claim 3, wherein the panels are raised or lowered to different levels in the transport device or the continuous or discontinuous conveyor and transferred to the levels of the second stage (B).

5. 3. The method according to claim 1 or 2, wherein the panel in the area of ​​the first stage (A) is at least substantially dried by use of a nozzle box.

6. 3. The method according to claim 1 or 2, wherein the panel is dried in the first stage (A) or in the second stage (B) by means of an internal heat exchanger and / or by means of at least one external heat exchanger.

7. 3. The method according to claim 1 or 2, wherein the panel is heated in the first stage (A) directly using circulating air by a burner, or using superheated steam or thermal oil, or indirectly electrically, or using heat from a low-grade heating source.

8. 3. The method according to claim 1 or 2, wherein the panel is dried in the first step (A) by dry air at a temperature between 130°C and 300°C.

9. 3. The method according to claim 1 or 2, wherein the panel is dried in the second step (B) by dry air at a temperature between 20°C and 90°C.

10. 3. The method according to claim 1 or 2, wherein the exhaust air of the first stage (A) is fed to a heat exchanger to preheat the dried air of the second stage (B).

11. 3. The method according to claim 1 or 2, wherein the panel is first dried in a pre-drying stage upstream of the first stage (A), then in the first stage (A) and finally in the second stage (B).

12. 3. The method according to claim 1 or 2, wherein the panels are transported through sections, within the stages (A, B) in each case, by means of a separate transport device for each stage (A, B).

13. A dryer for drying panels in a first stage (A) and a second stage (B), each of said first stage (A) and second stage (B) carrying a conveying device for conveying said panels arranged in hierarchical manner through said dryer, said first stage (A) having at least one section, said first stage (A) having a supply device, an exhaust device and a recirculation device, a circulating air duct having an exhaust device and a conveying means, and a heating device for the circulating air, as well as means for supplying the supply air and means for exhausting the exhaust air, said second stage (B) being a drying device for drying panels from said first stage (A), A dryer equipped with a supply device for drying air and an exhaust device for drying air and a heating device, wherein a transport device, a continuous conveyor or a discontinuous conveyor is arranged between the first stage (A) and the second stage (B) to take over the panels, whereby the panels can be slowed down from the conveying speed in the first stage (A) to the conveying speed of the second stage (B), raised or lowered to the height of the floor of the conveying device of the second stage (B) or distributed to adjacently extending tracks of the conveying device of the second stage (B).

14. 14. The dryer of claim 13, wherein each of the first stage (A) and the second stage (B) has at least one section and includes means for directing the circulating air in a direction transverse to the conveying direction of the panels.

15. 15. The dryer according to claim 13 or 14, wherein the first stage (A) of the dryer has a number of sections at least partially equipped with nozzle boxes for cross-flow ventilation with impinging streams of hot air.

16. 15. A dryer as claimed in claim 13 or 14, wherein the second stage (B) comprises means for flowing the circulating air against and / or in the direction of the transport of the panels.

17. 17. The dryer of claim 16, wherein the second stage (B) comprises at least one exhaust air fan in combination with induction means for helically inducing the circulating air or at least one circulating air fan.

18. 15. The dryer of claim 13 or 14, wherein the dryer comprises at least one heat exchanger.

19. 15. The dryer of claim 13 or 14, wherein the transport device comprises a roller conveyor or a conveyor belt.

20. 15. The dryer according to claim 13 or 14, wherein the panels in the stages (A, B) can be transported in a plurality of trucks running side by side within the level.

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