Method for drying panels, and dryer

Abstract

The invention relates to a method for drying panels in a drying device which comprises a first stage (A) and a second stage (B). Each of the two stages (A, B) has levels, and each of the panels is placed on surfaces formed at different levels and is guided through the drying device in each level of the two stages (A, B). In the first stage (A), the panels are brought into contact with drying air with a high temperature and are dried, and in the second stage (B), the panels are dried using drying air with a lower temperature. The invention is characterized in that the support surface (F1) provided in the levels of the first stage (A) for placing the panels is smaller than the support surface (F2) in the second stage (B), and the panels are guided in the second stage (B) at a second speed (v2) which is lower than the first speed (v1) in the first stage, wherein 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

[0001] Process for drying plates and dryer

[0002] When drying boards, especially cement and gypsum-based building boards, the boards are conveyed through a dryer and brought into contact with heated air.

[0003] The drying air can be supplied by longitudinal ventilation, transverse ventilation, or cross ventilation using nozzle boxes equipped with nozzles. With longitudinal ventilation, the drying air is supplied at one end of the dryer or, if it is divided into several zones, at one end of a zone and exhausted at the opposite end.

[0004] With cross ventilation, the air is introduced at several points along the sides of the dryer and discharged at the opposite sides, enabling more intensive drying within the dryer. Particularly intensive drying is achieved with cross ventilation via nozzles through the jet dryers in impingement flow.

[0005] In most cases, a recirculation process is used, in which a large portion of the drying air is circulated. In this case, most of the drying air is reheated after contact with the material being dried and thus reused. Only a small portion of the drying air is discharged to the outside as exhaust air, and a portion equivalent to the exhaust air is supplied from the outside as supply air.

[0006] Heating the drying air, for example, using burners or heating registers, requires fuel (i.e., primary energy), while supplying the air with fans requires electrical energy (i.e., secondary energy). The use of both primary and secondary energy must be reduced to enable more energy-efficient production of the above-mentioned panels.

[0007] DE 26 13 512 A1 discloses a drying process in which low primary energy consumption is achieved by utilising the condensation heat of the exhaust air. This process is designed in two stages. In the first drying stage, drying takes place at high temperature and high humidity, and in the second drying stage at low temperature and low humidity. The drying capacity of the first stage is two to three times that of the second stage and the second drying stage is heated from the exhaust air of the first drying stage via a heat exchanger. In both stages, the drying air is supplied using the recirculation process, namely in the first drying stage in the form of longitudinal ventilation and in the second drying stage in the form of cross ventilation with a large recirculation mass flow. However, the second stage requires a large recirculation mass flow and thus a high consumption of secondary energy.

[0008] When reducing primary energy consumption by also utilizing the condensation heat of the exhaust air, the general problem arises that the exhaust air's waste heat is only available at a low temperature level. A lower drying air temperature can be compensated for by larger air mass flows, but this leads to greater secondary energy consumption.

[0009] WO 95 / 04908 A1 discloses a method for drying boards conveyed through a dryer in tiers, in which the boards are brought into contact with drying air in two stages A and B, wherein in stage A drying is carried out using a recirculating air process with drying air of high temperature and at least medium humidity and with a drying performance 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 tiers of the dryer; at the same time, the drying air with low temperature and low humidity is passed in countercurrent to the exhaust air from stage A.

[0010] It is the object of the invention to further improve the method according to the preamble of claim 1.

[0011] According to the invention, this object is achieved as stated in claim 1.

[0012] By means of the method according to the invention, the transport speed of the panels to be dried is adapted to the respective energy consumption and the associated dehumidification of the panels, so that they are dried with minimal energy consumption.

[0013] The selection of the speed determined for each stage according to the desired drying progress results in a higher transport speed in stage A than in stage B for drying in stage A at a higher temperature than in stage B. This means that the speed of the boards emerging from stage A is reduced to the speed level of stage B in a separate conveyor arranged between stages A and B. At the same time, in order to avoid intermediate storage of boards in the area of ​​the conveyor, the conveyor distributes the boards over a larger area in stage B corresponding to the speed difference between stages A and B. This is achieved by dividing the boards into a larger number of floors or lanes in the area of ​​stage B than in stage A.Here, a conveyor device, for example a discontinuous conveyor, is used which, on the one hand, picks up boards at a higher speed on the side facing stage A and delivers them to a higher number of levels or tracks of stage B on the side facing stage B, with the conveyor preferably having a lower speed on this side. The conveyor has a tipping point at the transition to stage B in order to distribute the boards among the levels of stage B. In the case of a higher number of tracks, several boards are preferably transported next to one another on one level, for example in two to four tracks.

[0014] This measure creates, on the one hand, a compact entrance area of ​​the dryer with stage A, which can be passed through at high speed and high temperature, and which is also suitable for ensuring final activation of strengthening agents contained in the panels, such as starch.

[0015] On the other hand, the area and the speed within stage B are designed to achieve sufficient drying of the plates while at the same time making the best possible use of the energy from stage A. In order to achieve the best possible coordination between stages A and B, the invention provides that the product of the support surface of the plates, i.e. the area of ​​stage A actually occupied by the plates, with the speed that the plates have in stage A, is equal to the product of the speed of the plates in stage B with the support surface occupied by the plates in stage B. As a result, this leads to a larger support surface for the plates in stage B, combined with a longer residence time for the plates in stage B. In stage B, the plates are dried at a lower temperature.The energy consumption in stage B for heating the panels is greatly reduced compared to the energy consumption required for heating in stage A because in stage B heat from heat recovery is used for drying.

[0016] To achieve rapid drying in stage A, the boards are preferably heated by an impingement flow of hot air. The impingement flow is preferably generated by nozzle boxes equipped with a plurality of nozzles, from which an air stream is applied to the boards perpendicular to the transport direction.

[0017] While the nozzle boxes enable good drying results for the panels in a short period of time, they require a high energy input to generate the required airflow. On the other hand, the nozzle boxes also take up considerable space within stage A, which typically has several sections, with the nozzle boxes in each section arranged one above the other, corresponding to the number of levels in stage A.

[0018] According to the invention, a design of stage A with longitudinal ventilation is possible, as is the use of nozzle boxes.

[0019] Since, according to the invention, no nozzle boxes are required in stage B because cross-air flow, where required, is generated by appropriate fans, the distance between the levels on which the panels to be dried are located can be smaller than in stage A. To form transport paths, the transport rollers are arranged closer to one another.

[0020] In stage B, for example, a drying facility is provided with a conveyor system comprising a plurality of successively extending fields or sections in the conveying direction for conveying continuous panels to be dried, in a plurality of levels per field, with conveyor devices arranged in the levels as roller conveyors. A drive system drives a plurality of endless chains, each of which is assigned at least one drive. Preferably, the roller conveyors on all levels of a field can each be driven by at least one single chain.

[0021] The roller conveyors guide the panels over one another in a very compact manner. Since stage B requires a greater length than stage A due to the longer drying time of the panels to be dried, a larger number of panels per height of stage B and / or per width of stage B is possible, thus creating a very high overall space utilization in stage B, while at the same time, the air from stage A is optimally utilized to transfer its residual heat into the panels via at least one heat exchanger.

[0022] For this purpose, a drive system is used that is adapted to a low-temperature dryer and to the large number of boards, particularly plasterboards, that are processed simultaneously in the low-temperature dryer over a large number of levels, for example, 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 boards, particularly plasterboards, in a low-temperature dryer can be achieved with the same dryer length as in a high-temperature dryer.

[0023] Due to this concept of connecting a stage A, which is preferably at least partially equipped with nozzle boxes, existing dryer systems with several sections, each equipped with nozzle boxes, can also be converted into a dryer according to the invention by continuing to use at least some of these sections, forming stage A, and adding an additional stage B to stage A. By increasing the number of levels in stage B with a corresponding reduction in the transport speed, continuous operation between stages A and B is maintained, while at the same time the thermal energy still available from stage A is utilized in stage B. In the low-temperature dryer formed by stage B, the support rollers of the transport system used there are mounted on rolling bearings.Graphite-based plain bearings required in high-temperature dryers are eliminated. This allows the use of roller bearings with lower coefficients of friction than plain bearings, for example, by using support rollers with internal roller bearings. This results in significant energy savings in the Stage B low-temperature dryer because the roller bearings used in Stage B generate much lower friction than the plain bearings in Stage A.

[0024] It is thus shown that particularly large energy savings are possible when the dryer arrangements according to the invention are installed in an existing plant.

[0025] To convert an existing system into a dryer according to the invention, it must be supplemented with a conveyor system and a low-temperature stage (stage B). In other cases, some sections of stage A of an existing dryer are removed, and a conveyor system and a low-temperature stage B are added.

[0026] Advantageous further developments of this method emerge from the subclaims and the description, in particular in conjunction with the drawings.

[0027] Preferably, the plates are transferred between the first stage A and the second stage B via a transfer or transfer device, in particular via a continuous conveyor or a discontinuous conveyor; in this case, the plates are slowed down from the speed at which they move in stage A until they reach the second, lower speed in stage B.

[0028] During the transition between stages A and B, the panels are raised or lowered to different levels in the transfer device or the continuous conveyor or the discontinuous conveyor and transferred to the levels of the second stage B. It is understood that the transfer device is preferably also enclosed, like stages A and B.

[0029] In order to achieve rapid drying in stage A, the panels are dried at least essentially by using nozzle boxes.

[0030] In order to optimise the use of the waste heat generated in particular in stage A, the plates are dried by at least one internal heat exchanger and / or by at least one external heat exchanger in the first stage A and / or in the second stage B.

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

[0032] Preferably, the plates are dried in the first stage A by drying air at a temperature of 130 to 300 °C, while the plates in the second stage B are dried by drying air at a temperature of 20 to 90 °C.

[0033] The exhaust air from the drying process of the first stage A can advantageously be reused by passing it into a heat exchanger to preheat the drying air of the second stage B. An even higher efficiency of the drying process according to the invention can be achieved if the panels are 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.

[0034] Preferably, the panels in stages A and B are conveyed through sections by means of separate conveyors for each stage A and B and / or each section. Alternatively, the conveyors are each driven by direct-drive motors, or they are at least partially interconnected by gears.

[0035] The invention also provides a dryer for drying boards in a first and a second stage A, B, each of which is equipped with a conveyor device for conveying the boards arranged in tiers through the dryer, wherein the first stage (A) has at least one zone, wherein the first stage A has a supply device, a discharge device and a recirculation duct with conveying means and a heating device for recirculation air, as well as means for supplying supply air and means for discharging exhaust air, and wherein the second stage B is equipped to take over the boards from the first stage A and is equipped with a supply device for drying air and a discharge device for drying air and a heating device.

[0036] The object of the invention is to design the dryer in such a way that the plates are dried with a low energy consumption.

[0037] According to the invention, this object is achieved in that a transfer device, a continuous conveyor or a discontinuous conveyor is arranged between the first and the second stage A, B, by means of which the boards can be slowed down from the conveying speed in the first stage A to the conveying speed of the second stage B and raised or lowered to the height of the levels of the conveyor device of the second stage B or distributed onto adjacent tracks within the levels of the second stage B. The boards are dried in each of the two stages at a speed and at a temperature that ensures a rapid throughput of the boards through the dryer while at the same time ensuring efficient energy utilization.

[0038] This optimizes the use of both primary and secondary energy. In particular, the primary energy used is maintained by utilizing waste heat and the condensation heat of the exhaust air, without increasing the demand for secondary energy by recirculating large air mass flows.

[0039] In particular, high flow rates for air circulation are avoided in the second stage, so that this dryer has only a low consumption of secondary energy.

[0040] Advantageous further training results from the subclaims.

[0041] A dryer is advantageous in which the first and second stages A, B each comprise at least one section and are equipped with means for the flow of circulating air transversely to the conveying direction of the plates.

[0042] For design reasons, the first stage A of the dryer is preferably divided into several sections, which are at least partially equipped with nozzle boxes for cross ventilation by means of impingement flow of hot air.

[0043] Advantageously, the second stage B of the dryer is equipped with means for the flow of circulating air against and / or in the conveying direction of the plates.

[0044] In a further advantageous embodiment of the dryer, the second stage B is equipped with guide means for helically guiding the recirculating air or with at least one exhaust air fan in conjunction with at least one recirculating air fan. Alternatively, guide means, for example in the form of baffles, are provided.

[0045] The dryer preferably comprises at least one heat exchanger. Roller conveyors or conveyor belts are preferably provided as conveying devices for transporting the boards to be dried in the dryer.

[0046] In stage B, the exhaust air from stage A, which is highly rich in water vapor and is passed through the heat exchanger, is cooled so much by the low-temperature drying air that part of the water vapor condenses.

[0047] By also utilising the condensation heat, which is made possible by the low temperature of the drying air cooling the heat exchanger and the at least medium humidity of the exhaust air of stage A, the primary energy is used intensively.

[0048] When the drying air is directed countercurrently to the exhaust air passing through the heat exchanger in stage A, cooler drying air encounters already cooled exhaust air. This ensures the greatest possible condensation of the water vapor contained in the exhaust air and further improves the utilization of primary energy. The more intensive use of primary energy leads to significant savings in primary energy.

[0049] Overall, drying performance in stage B is at most half of that of stage A.

[0050] Each stage A, B is equipped with a conveyor device for conveying boards arranged in tiers through the dryer. The dryer can be designed as a roller conveyor dryer or a belt dryer, with the conveyor device comprising several roller conveyors or conveyor belts arranged one above the other.

[0051] The conveying device arranged between stage A and stage B is preferably enclosed so that the heat energy from stage A is not lost when the plates move to stage B.

[0052] The plate dryer according to the invention can be constructed in a compact manner; it is not necessary to provide a base plate for the dryer; rather, it is sufficient if the side walls of the dryer are placed directly on the floor of a factory hall without the need to lay an additional base plate for the dryer.

[0053] For additional transient loads, additional heating devices can be installed in stage B.

[0054] The invention is explained in more detail below using exemplary embodiments. They show:

[0055] Fig. 1 shows a dryer with two stages A and B and a conveyor installed between the stages A and B, in a first embodiment,

[0056] Fig. 2 the dryer with the two stages A and B and the conveyor in a second embodiment,

[0057] Fig. 3 the dryer with the two stages A and B and the conveyor in a third embodiment,

[0058] Fig. 4a a dryer in a side view and

[0059] Fig. 4b shows the dryer according to Fig. 4a in a plan view.

[0060] A dryer 1 (Fig. 1 ) comprises two stages A and B for drying boards which are fed to the dryer 1 in the direction of an arrow C. These boards are in particular building material boards, for example plasterboard or

[0061] plasterboard.

[0062] Each of the two stages A and B is preferably divided into sections 2. This applies in particular to section A, which is preferably designed as a jet dryer. This means that at least in the majority of the sections of stage A, nozzle boxes are arranged, from which hot air is blown in an impingement flow onto the plates. This creates a temperature of 130 to 300 °C within sections 2 of stage A. Stage A preferably has a pre-drying section 3 on the inlet side. The pre-drying stage 3 is supplied from a heat exchanger 4 with heated fresh air via a supply line 6 equipped with a closable flap 5. This fresh air supply serves not only to heat the plates but also to seal stage A against other air currents and to prevent outside air from entering stage A.

[0063] Fresh air heated by a fan 8 is distributed via a line 7 branching off from the supply line 6 to individual lines 9, 10, 11. From these, the fresh air is directed to heating devices 12, 13, and 14, respectively, which are arranged, for example, in a ceiling box above the nozzle boxes. As shown in Fig. 1, the heating devices 12 to 14 are each assigned to two sections 2 of stage A. It is understood that other assignments may be made in another embodiment. For example, in another embodiment, 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 sections 2 or jointly for each section, at least one recirculation fan 15 to 17 is provided to generate a cross-flow of the heated air in sections 2 as recirculation air. Alternatively, two recirculation fans 15 to 17 are arranged in each section 2.

[0064] From stage A, the pre-dried boards are transported to stage B via a conveyor device 18. Since stage B has a higher number of levels than stage A, the boards are introduced into the levels of stage B by the conveyor device 18 at correspondingly smaller intervals from one another, but at a correspondingly reduced speed. This allocation is achieved, for example, by the conveyor device 18, as a transfer device, having a larger radius of curvature of its conveyor belt on the side facing stage A, which also results in a higher relative speed of the conveyor belt on this side. On the side facing stage B, the conveyor belt then has a lower rotational speed resulting from a smaller radius of curvature, whereby a relatively higher number of boards can be distributed across the larger number of levels of stage B.The conveyor system 18 is preferably insulated against heat loss to the outside, like stages A and B. Heating devices and fans for recirculation or air exchange can also be arranged in it.

[0065] For example, stage A has six to sixteen tiers, while stage B has eighteen to forty-eight tiers, with stage B operating at a plate conveying speed that is, for example, only two-thirds of the conveying speed in stage A. Instead of having a higher number of tiers, the tiers in stage B are wider than in stage A, so that instead of a single lane of plates in stage A, two lanes of plates are conveyed within one tier of stage B. In another embodiment, in stage A, two lanes are conveyed side by side on one tier, while in stage B, three lanes are conveyed on one tier.

[0066] Stage B is also supplied with heated fresh air from heat exchanger 4. Lines 19 to 24 serve this purpose. Of these, lines 19, 21, and 23 are each equipped with a closure flap 25, 26, and 27, respectively.

[0067] Fans can also be arranged in lines 19 to 24. At the inlet of sections 2, the air flowing into sections 2 from lines 19 to 24 is heated by heating devices 29 to 31. 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 insufficient heat is yet available from stage A and heat exchanger 4 is not yet receiving any warm exhaust air or is not receiving enough warm exhaust air from stage A. The heating devices are also required when the system is shut down and insufficient warm air is no longer available from stage A to enter stage B.Heating devices 29 to 31 can also be used in the event that the panels to be dried have a higher moisture content than expected, as well as when switching between different panel formats, which can lead to a lack of thermal energy in stage B. Thus, heating devices 29 to 31 are provided in particular for transient loads in stage B.

[0068] It is understood that, depending on the length of stage B, a plurality of lines can be provided for supplying air, in particular warm air from the heat exchanger 4 or from another heat exchanger, in order to recover the evaporation enthalpy of the water evaporated from the plates.

[0069] Optionally, recirculation fans are also provided in stage B, which are constructed and arranged like the recirculation fans in stage A. Both radial and axial fans are possible.

[0070] Just like the recirculation fans, exhaust fans 32, 33 are also arranged along the entire length of stage B, of which only the exhaust fans 32, 33 are shown as examples in Fig. 1. Moist air is removed from stage B via these and chimneys 34, 35.

[0071] In addition, there is also an exhaust fan 36 in connection with a chimney 37 at the end.

[0072] An internal heat exchanger can be provided in both stage A and stage B, for example above the nozzle boxes in stage A in a ceiling box or above the conveyor device in stage B, also in a ceiling box provided for this purpose.

[0073] The heat exchanger 4 is connected to sections 2 of stage A via exhaust air ducts 38 and a central exhaust air duct 39. Warm, moisture-saturated air is passed through the exhaust air ducts 38, 39 via an exhaust air fan 40 to the heat exchanger 4, where it condenses and releases its moisture as water.

[0074] Heat exchanger 4 draws in fresh air via a fresh air fan 41. It expels used air to the environment via a chimney 42. In another embodiment (Fig. 2), several internal heat exchangers 43, 44 are present in various sections of stage B. These heat exchangers are supplied either directly or indirectly with hot air, for example with flue gases from a combined heat and power plant or from gas turbines or other warm gas streams from other processes. Such gases can also be additionally fed to heat exchanger 4. Or they are fed to a further heat exchanger 45, which is connected in series with heat exchanger 4 and serves to further heat the gases fed to stages A, B via lines 6, 7, 19, 20, 21, 22, 23, 24.

[0075] In a further embodiment (Fig. 3), the heat exchanger 4 is connected only to stage B with regard to the air supply; such an arrangement is present, for example, when stage B is subsequently connected to an existing dryer, i.e., to an already existing stage A.

[0076] A dryer 1 according to one of the embodiments shown in Figs. 1 to 3 comprises, in one embodiment (Figs. 4a, b), a plurality of burners 50 in stage A, each of which is mounted in the ceiling area or on the ceilings of sections 2 of stage A for heating the air in sections 2. The air heated by the burners 50 is circulated in a circular motion perpendicular to the conveying direction of the plates in stage A via recirculation fans 51.

[0077] Stage B is equipped with hot air inlets 52, which are also mounted on the top of individual sections 2. The hot air inlets 52 are mounted, for example, in pairs on the ceilings of sections 2, as can be seen in Fig. 4b.

[0078] In stage B, exhaust air fans 53 are also arranged in some sections 2. The exhaust air fans 53 are preferably mounted laterally on the ceilings of sections 2, with inlets for warm air, which is supplied either from the heat exchanger 4 and / or from the heat exchanger 45, preferably being provided opposite the exhaust air fans 53 on the other side of the ceilings of sections 2. The fans 53 are preferably mounted in stage B in such a way that air flows are created in the longitudinal direction of stage B. In this case, an air flow in the conveying direction (arrow D) of the plates is preferably generated in the front part of stage B facing the transfer device, while in the rear part an air flow counter to the conveying direction of the plates (arrow E) is generated.

Claims

Patent claims 1. A method for drying panels in a drying apparatus comprising a first stage (A) and a second stage (B), wherein the two stages (A, B) each have levels and the panels are placed on surfaces formed in each level and passed through the drying apparatus in the respective levels of the two stages (A, B), wherein the panels are brought into contact with high-temperature drying air and dried in the first stage (A) and are dried with lower-temperature drying air in the second stage (B), characterized in that the support area (F1) available for placing the panels in the levels of the first stage (A) is smaller than the support area (F2) in the second stage (B), and that the panels are passed through the second stage (B) at a second speed (v2) which is lower than the first speed (v1) in the first stage.where the product of the first contact area (F1) with the first velocity (v1) is equal to the product of the second contact area (F2) with the second velocity (v2).

2. Method according to claim 1, characterized in that the plates in the second stage (B) are guided in a higher number of levels, which run above each other or next to each other.

3. Method according to claim 1 or 2, characterized in that the plates are transferred between the first stage (A) and the second stage (B) via a transfer device, a continuous conveyor or a discontinuous conveyor, wherein the plates are slowed down until they reach the second speed (v2).

4. Method according to one of claims 1 to 3, characterized in that the plates in the transfer device or the continuous conveyor or the discontinuous conveyor are raised or lowered to different levels and transferred to the levels of the second stage (B). A method according to any one of claims 1 to 4, characterized in that the plates in the region of the first stage (A) are dried at least substantially by the use of nozzle boxes. A method according to any one of claims 1 to 5, characterized in that the plates are dried in the first (A) or in the second stage (B) by at least one internal heat exchanger (27) and / or by at least one external heat exchanger (4, 43, 44, 45). A method according to any one of claims 1 to 6, characterized in that the plates in the first stage (A) are heated by means of circulating air through a burner directly, or by means of superheated steam or thermal oil, or indirectly by electricity, or by means of low-temperature heat. A method according to any one of claims 1 to 7, characterized in that the plates in the first stage (A) are dried by drying air at a temperature of 130 to 300 °C.A method according to any one of claims 1 to 8, characterized in that the plates are dried in the second stage (B) by drying air at a temperature of 20 to 90 °C. A method according to any one of claims 1 to 9, characterized in that the exhaust air from the first stage (A) is directed into a heat exchanger (31) for preheating the drying air of the second stage (B). A method according to any one of claims 1 to 10, characterized in that the plates are 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). A method according to any one of claims 1 to 11, characterized in that the plates in the stages (A, B) are each conveyed through sections (2) by means of separate conveying devices for each stage (A, B). Dryers for drying panels in a first (A) and a second (B) stage, each equipped with a conveying device for conveying the panels arranged in tiers through the dryer, wherein the first stage (A) has at least one zone, wherein the first stage (A) has a feed device, a discharge device and a recirculation duct with conveying means and a heating device for recirculation, as well as means for supplying supply air and means for discharging exhaust air, and wherein the second stage (B) is equipped for receiving the panels from the first stage (A) and with a supply device for drying air and a discharge device for drying air and a heating device, characterized in that a transfer device, a continuous conveyor or a discontinuous conveyor is arranged between the first (A) and the second stage (B).by means of which the plates can be slowed down from the conveying speed (v1) in the first stage (A) to the conveying speed (v2) of the second stage (B) and raised or lowered to the height of the levels of the conveying device of the second stage (B) or distributed onto adjacent tracks of the conveying device of the second stage (B). Dryer according to claim 13, characterized in that the first (A) and the second stage (B) each comprise at least one section and are equipped with means for the flow of recirculated air transverse to the conveying direction of the plates. Dryer according to claim 13 or 14, characterized in that the first stage (A) of the dryer has several sections which are at least partially equipped with nozzle boxes for transverse ventilation by means of an impact flow of hot air. Dryer according to any one of claims 13 to 15, characterized in thatthat the second stage (B) is equipped with means for the flow of recirculated air against and / or in the conveying direction of the plates. A dryer according to claim 16, characterized in that the second stage (B) is equipped with guide means for the helical guidance of the recirculated air or with at least one exhaust fan in conjunction with at least one recirculating air fan. A dryer according to any one of claims 13 to 17, characterized in that it comprises at least one heat exchanger (4, 43, 44, 45). A dryer according to any one of claims 13 to 17, characterized in that the conveying devices comprise roller conveyors or conveyor belts. A dryer according to any one of claims 13 to 19, characterized in that the plates in the stages (A, B) can be transported in several parallel tracks within the levels.

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