Apparatus and method for drying building boards

Abstract

A drying device for a building board having at least one drying zone, wherein the at least one drying zone comprises a plurality of radiant elements each having a heating medium circulating within a duct (1), and each radiant element has a temperature variation of up to 30 °C.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for drying building boards, preferably gypsum-based or cement-based building boards, particularly gypsum boards.

Background Art

[0002] Various building boards, such as gypsum-based building boards, for example, gypsum fiber boards or gypsum boards, or cement-based building boards, for example, cement fiber boards, are typically manufactured in a continuous process. The finished boards generally have a thickness of 6 mm to 60 mm and can have, for example, planar dimensions of up to about 1.5 m × 3 m. During manufacture, an endless sheet having a width of up to 3 m can be produced. Depending on the dryer, this endless sheet can be cut to a length of 2 m to 4 m for the drying process. For example, the manufacturing process of gypsum fiber boards is different from that of gypsum boards, but both processes have in common that they mix stucco (calcium sulfate hemihydrate) with water and additives to form a slurry. The slurry is spread on a web to form a large sheet. When the slurry has hardened to a certain extent and sufficient gypsum (calcium sulfate dihydrate) has been formed, the boards can acquire their shape and be cut to size. Cement-based building boards, such as cement fiber boards, can be formed in the same way. The building boards then pass through a drying device where the setting can be completed and excess water evaporates. The water is usually evaporated by convective heating, and hot air passes along the surface of the boards to remove the water vapor. Other building boards, particularly other dry lining building boards, such as clay-based building boards, can be manufactured in a batch process and often include a drying step in a drying device.

[0003] Typical drying devices for building boards include several drying units, often three units, namely a pre-drying (or pre-heating) unit, a main drying unit (or high-temperature drying), and a final drying unit. The pre-drying unit is the most upstream unit of the drying device, and the final drying unit is the most downstream unit of the drying device. The temperature of the pre-drying unit is typically set at a lower temperature than the main drying unit. Similarly, the temperature of the final drying unit can also be set at a lower temperature than the main drying unit. Each unit can have one or more drying zones. The pre-drying unit (i.e., one or more first drying zones) is configured to moderately increase the temperature of the board and start evaporating water from the board before entering the main drying unit. The main drying unit (i.e., subsequent zones) is configured to evaporate moisture from the substrate and thereby dry the substrate. The final unit is configured to end the drying process while simultaneously avoiding firing the outermost layer of the board. Typically, a temperature range is assigned to each unit. For example, the pre-drying unit can have a temperature range of 40°C to 180°C, preferably, for example, 70°C to 150°C. Alternatively, heated air at 70°C to 180°C can be supplied to the pre-drying unit. This heated air or hot air can originate from one or more drying zones, preferably one or more drying zones of the main drying unit. As an example, the main drying unit can have a temperature range of 100°C to 330°C, preferably, for example, 100°C to 300°C, more preferably, for example, 200°C to 280°C. Alternatively, heated air at 180°C to 330°C can be supplied to the main drying unit. The final unit can have a temperature range of, for example, 50°C to 180°C, preferably, for example, 100°C to 180°C. Alternatively, heated air at, for example, 80°C to 180°C can be supplied to the final unit. The drying unit can typically include 1 to 60 drying zones with lateral ventilation, or 1 to 5 drying zones with longitudinal ventilation, or a combination of drying zones with both longitudinal and lateral ventilation. The number of drying zones generally depends on the type of ventilation, i.e., lateral ventilation or impingement ventilation typically requires more drying zones than longitudinal ventilation.

[0004] Thus, a typical drying apparatus for building boards comprises a plurality (i.e., more than one number, e.g., 2, 3, 4, 5, 6, or up to 80 depending on their size) of drying zones.

[0005] The drying apparatus can further be adjacent to the first and / or second adjustment sections. The first adjustment section can be provided upstream of the pre-drying unit, i.e., upstream of the first drying zone of the pre-drying unit. The first adjustment section can, for example, appropriately adjust the state from the state outside the drying apparatus to the state inside the drying apparatus by controlling the moisture and / or temperature surrounding the building board. This adjustment can include passive heating, for example, by utilizing the exothermic reaction in the building board. A second adjustment section can be provided downstream of the final drying unit, i.e., downstream of the last drying zone of the final drying unit. The second adjustment section can, for example, adjust the state from the state inside the drying apparatus to the post-drying state by allowing the building board to cool to approximately room temperature.

[0006] Each drying zone is supplied by at least one heating means and at least one ventilation means. The drying zone typically further comprises an input end and an output end of the building board, and optionally ducts that enter and exit the zone. To increase the capacity of the drying apparatus for building boards, the drying apparatus is usually configured to form a plurality of decks such that the various drying zones of the drying unit comprise a plurality of decks, and each deck has support means for the building board. The support means are typically arranged as conveying means such that a plurality of building boards can pass through the drying apparatus stacked essentially vertically on top of each other within the deck or in a rack. Multiple decks are preferred when spatial and energy requirements are a concern.

[0007] In the prior art, the heating means typically comprises direct heating means such as one or more fossil fuel burners (e.g., natural gas burners), or indirect heating means such as one or more hot oil heat exchangers. The heating means can also comprise other direct heating means such as one or more renewable fuel burners (e.g., biogas or hydrogen burners), and / or other indirect heating means such as one or more gas-gas heat exchangers (e.g., air-air or air-steam) or one or more gas-liquid heat exchangers, e.g., air-water, air-hot oil, air-glycol solution) or one or more radiant elements. All of these heating means are used to heat air, which is then circulated through the drying zone. The terms "gas-liquid" and "liquid-gas" are used interchangeably with respect to this disclosure. Similarly, when one or both of the general terms are specified, the order is irrelevant. For example, "air-water" means the same type of heat exchanger as "water-air". The ventilation means can comprise an air inlet port and an air outlet or suction port configuration, and the movement of air is effected, for example, by a ventilation fan. The air inlet and air outlet ports can be located at or near both ends of the drying zone. By providing the air inlet port essentially opposite the air outlet port, a directional air movement within the drying zone can be provided. This air movement is typically in the conveyance direction, countercurrent or transverse to the conveyance direction. Thus, the ventilation means can further comprise a configuration for ventilation that is countercurrent to the direction of travel of the building board, also called parallel flow longitudinal ventilation, or countercurrent to the direction of travel, also called countercurrent longitudinal ventilation, or transverse to the direction of travel, also called transverse ventilation. A drying zone with impingement ventilation, i.e., impingement heating, or transverse ventilation is often shorter than a drying zone with (parallel or countercurrent) longitudinal ventilation. The ventilation (air flow) means can instead or in addition comprise a nozzle box or air jet box that generates an air jet for impingement ventilation. It may also be possible to combine different ventilation means within the same drying unit. A drying unit with impingement ventilation or transverse ventilation is often shorter than a drying zone with (parallel or countercurrent) longitudinal ventilation. A drying zone with impingement ventilation or transverse ventilation can be, for example, from 2 m to 6 m.(Concurrent or countercurrent) The drying zone with vertical ventilation can be, for example, 30 m to 70 m. The drying device can comprise, for example, 10 to 40 drying zones with either impingement ventilation or cross ventilation, and one drying zone with vertical ventilation. Further, the drying unit can have, instead of one drying zone with vertical ventilation, for example, 10 to 40 drying zones with impingement ventilation or cross ventilation.

[0008] In the case of gypsum-based building boards, the hardening of gypsum is an exothermic process. This means that the gypsum-based boards enter a drying device with a temperature of about 25 to 45 °C. Thereafter, the gypsum-based building boards are heated more or less uniformly to a temperature of about 80 to 110 °C, preferably about 90 to 100 °C, in the first drying zone to promote drying. Due to the high moisture content of the boards at the start, the boards can be dried at a relatively high temperature (e.g., 200 °C or higher) without the risk of burning the outermost part of the gypsum-based building boards. Burning results in brittle edges and, if present, reduces the adhesion of the liner. The evaporation of the moisture present in the boards keeps the temperature of the gypsum boards themselves below 100 °C. A similar description can be made for cement, which also hardens exothermically. As the moisture content of the boards decreases, the cooling effect of evaporation also decreases. Therefore, the latter half of the drying device operates at a lower temperature to avoid burning the outermost layer of the boards.

[0009] There are various methods for reducing the amount of energy required to dry building boards such as gypsum-based building boards. Many of these methods focus on reducing the amount of water in the gypsum slurry. Other methods include means for reusing the exhaust steam mixture from one drying zone in another drying zone, which often causes problems of excessive relative humidity that can induce condensation. Some methods also address the recovery of energy from the exhaust gas mixture by other heat recovery means such as heat exchangers or heat pumps. However, with the increasing demand to reduce CO 2 emissions, further improvements are still needed.

Summary of the Invention

[0010] Accordingly, the object of the invention described in the claims is to provide an apparatus for drying building boards, in particular gypsum-based building boards, comprising an alternative to convective drying that can be used with energy sources other than fossil fuels. A further object is to provide a drying apparatus with low energy consumption and / or high heat transfer capacity. Preferably, an existing drying apparatus can be reconstructed into an apparatus with low energy consumption and / or high heat transfer capacity without increasing its construction volume. This means that the construction volume of the reconstructed drying apparatus is maintained or even reduced while the drying efficiency is maintained or even increased. A further object is to provide an apparatus with low investment costs and the same or smaller space requirements with respect to deck height compared to manufacturing lines known from the state of the art. Preferably, the distance between decks can be maintained or even reduced. It is also an object to provide a method for drying building boards, in particular gypsum-based building boards, with high drying efficiency at low energy consumption.

[0011] These objects are achieved by a drying apparatus having the features of claim 1 and a method having the steps of claim 17.

[0012] Typically, the drying apparatus comprises a plurality of drying units, each composed of one or more drying zones and configured as described in the introduction section.

[0013] The term "building board" is meant to denote a flat sheet or slab used in structures for assembling walls, floors or ceilings. This type of structure can be referred to as dry lining or dry construction. Examples of building boards include gypsum-based building boards, cement-based building boards, and clay-based building boards. Building boards can have a thickness of 6 mm to 60 mm, a width of about 0.5 m to 3 m, and / or a length of about 0.5 m to 4 m. For the purposes of this invention, the term "building board" preferably refers to a building board in an unfinished state, specifically in a state where it is shaped but not yet dried and / or cured, i.e., the state it would be in within a drying device.

[0014] The term "radiating element" is meant to denote a heating element that transfers thermal energy to the building board, particularly but not limited to via radiation such as electromagnetic waves. Despite the exact terminology, this term is also meant to encompass heating elements that operate via conduction, particularly a combination of both radiation and conduction.

[0015] The present invention encompasses a drying device for a building board comprising at least one drying zone, wherein each drying zone comprises a plurality of radiating elements each provided with a heating medium circulating within a duct, and each radiating element has a temperature variation of up to 30°C. Using a heating medium circulating within a duct is particularly relevant when the radiating elements themselves have a large surface area relative to the volume of the drying zone (for example, a surface area of 20 m 3 per 1 m 2 to 100 m 2 of the drying zone, or a surface area of 30 m 3 per 1 m 2 to 50 m 2It has the advantage that a heating medium can be used at a relatively low temperature (such as 60 to 130 °C, etc.) in terms of surface area, etc. This also means that it is easier to use alternative heating means such as heat recovered from the drying device itself, for example. Unexpectedly, it is found that it is not necessary to increase the distance between adjacent decks of the drying zone with radiation elements compared to the distance between decks of a conventional drying zone with the same drying efficiency but without radiation elements. By arranging a plurality of radiation elements with a temperature variation of up to 30 °C, preferably up to 20 °C, more preferably up to 10 °C in the drying zone, more uniform drying can be achieved. The drying zone in a conventional drying device can have a temperature variation or a temperature drop of about 150 °C. Such a temperature variation or temperature drop in this range is not acceptable, for example, in a drying zone operating in the vicinity of 80 °C to 120 °C. The drying temperature in the drying zone can be lowered with a temperature variation of up to 30 °C, preferably up to 20 °C, more preferably up to 10 °C.

[0016] Preferably, the temperature variation of up to 30 °C is the temperature drop between the supply line to the drying zone and the return line from the drying zone. The heating medium is circulated from the heating means to the radiation elements. The heating medium enters the drying zone, specifically the radiation elements, via the supply line and exits the drying zone, specifically the radiation elements, via the return line. Ideally, the heating medium exiting the drying zone is circulated and returned to the heating means.

[0017] Preferably, the radiation elements are arranged in a horizontal layer. By arranging the radiation elements in a horizontal layer, the building board can be conveyed through the drying zone below and / or above the horizontal layer of the radiation elements.

[0018] Alternatively or in addition, the drying device is configured with a plurality of decks, each deck comprising conveying means and a horizontal layer of radiation elements, preferably with the horizontal layer of radiation elements arranged above the conveying means, more preferably with the horizontal layer of radiation elements arranged at least 40 mm above the conveying means. The drying device is more efficient when the building boards can pass through drying zones that are essentially "stacked" vertically on top of each other. Two decks double the efficiency compared to only one deck. Three decks triple the efficiency, and so on. The number of decks can vary, for example, between 6 and 24. From 8 to 18 decks are preferred, and from 10 to 16 decks are particularly preferred. Positioning the radiation elements at a distance of at least 40 mm above the conveying means allows two potentially colliding building boards to push up without damaging the radiation elements.

[0019] Preferably, the horizontal layer comprises parallel ducts or parallel duct segments, which are fluidly interconnected, for example, by non-parallel connecting pieces. The non-parallel connecting pieces can be U-shaped so as to be able to change the flow direction by 180°. The non-parallel connecting pieces are preferably located in the drying zone. More preferably, the parallel ducts or parallel duct segments are arranged transversely to the conveying direction. Most preferably, the ducts of the radiation elements have a length not exceeding 900 m, preferably in the range of 4 m to 800 m for the ducts of the radiation elements. A length in the range of 320 m to 750 m is particularly suitable, more preferably a length of 450 m to 550 m. The ducts of the radiation elements refer only to the part of the ducts located in the drying zone, i.e., the distance from the supply line to the return line. By limiting the length of the ducts of the radiation elements, the temperature drop can be limited. Alternatively or in addition, the radiation elements are arranged such that there is no temperature difference in the vertical direction. This can be achieved by overlapping or staggering the radiation elements in different racks and / or by alternating the flow directions in adjacent horizontal layers.

[0020] When heating a building board, typically moisture evaporates from the building board. This typically increases the relative humidity and may slow down or reduce further evaporation. If the moisture condenses, it may also damage the building board. Therefore, it is desirable to remove this excess moisture present in the form of water vapor. Gases such as air containing water vapor can be removed from the drying zone through the suction port by a circulation fan. To avoid negative pressure or partial vacuum, gases such as air must also be introduced into the drying zone, for example through an inlet port. When the inlet port and the suction port are located at both ends of the drying zone, there is a directional movement of the gas. This movement of the gas such as air can remove the moisture evaporated from the building board. Preferably, the drying zone further includes a gas movement with a flow rate of 3 to 10 m / s in a direction opposite to the conveying direction or along the conveying direction. Preferably, the gas movement is an air movement, and more preferably further includes a water vapor movement.

[0021] Preferably, at least one drying zone further includes convective heating. By supplementing the drying process by introducing a heated gas such as heated air, the drying process can be further improved. A gas with a temperature of 50°C to 120°C, preferably air, is sufficient. Since the space for gas movement is restricted by the radiation element, the cross-sectional area in the gas is reduced. To achieve the same flow rate, less (heated) gas such as (heated) air is required. Further, the radiation element may cause turbulence in the gas movement, which can be advantageous for drying the building board.

[0022] The heating medium within the duct can be steam, water, a water glycol solution, or hot oil. The water glycol solution typically includes a solution of water, ethylene, or diethylene glycol. Preferably, the heating medium is steam, water, a water glycol solution, or hot oil. Steam, particularly steam having a temperature of 180°C to 230°C, is useful in one or more drying zones of the main drying unit as described at the beginning. The disclosed heating medium is more efficient than air used in conventional convective heating because it has a higher specific heat capacity. Generally, more uniform drying can be achieved using the radiant elements of the present invention as compared to convective drying with vertical ventilation.

[0023] Preferably, the heating medium is at least partially heated with heat recovered from the drying apparatus. Preferably, at least 40% of the heating medium, more preferably at least 80% of the heating medium, and most preferably 95% to 100% of the heating medium is heated with heat recovered from the drying apparatus.

[0024] Preferably, the duct of the radiant element is a finned duct, optionally with a non-finned connection piece. Similarly, parallel ducts or parallel duct segments can be finned ducts or finned duct segments.

[0025] Finned ducts, also known as finned tubes, are typically used in heat exchangers to increase the surface area. Finned ducts can have radial, spiral, or longitudinal fins. The fins can be formed from the duct material, for example, by extrusion. The fins can also be connected or attached to the duct by, for example, tension, brazing, welding (including laser welding, spot welding, resistance welding, and welding with filler materials), or soldering. When connected by tension, the fins are generally wound or wrapped spirally around the duct. These spirally wound fins are often located within the grooves of the duct and are often called embedded fins. Embedded fins have good surface contact with the duct, thereby improving the thermal conductivity from the duct to the fins. Other spirally wound fins have L-shaped feet to increase contact with the underlying duct. Still other fins have overlapping feet. In other types of finned tubes, square or rectangular fins are welded to the base duct. These ducts offer minimal resistance to gas flow. Further, the straight path suppresses fouling and simplifies cleaning.

[0026] The fins can be essentially flat or can have a wavy or corrugated structure to further increase the surface area of the fins. Also, the wavy or corrugated structure can also result in higher gas or air turbulence between and / or around the fins.

[0027] There are different surface treatments for the duct or finned duct. For example, the duct or finned duct can be hot-dip galvanized, polyurethane-coated, or zinc-plated. In particular, hot-dip galvanizing or zinc plating can improve the connection between the fins and the duct. This is especially true when the fins are spot-welded. The extensive metal-metal contact improves the thermal conductivity of the duct or tube.

[0028] Preferably, the finned duct has an inner diameter or nominal core diameter, also known as the nominal bore, of 35 mm to 55 mm.

[0029] Preferably, the fin extends at least 15 mm, more preferably at least 20 mm, from the bare duct, i.e., the duct without fins. For example, in the case of a wound fin, this means that the fin strip has a height of at least 15 mm, preferably at least 20 mm. Alternatively or in addition, the fin extends up to 35 mm, preferably up to 30 mm, most preferably up to 25 mm, from the bare duct.

[0030] Preferably, the duct has a wall thickness of 2.5 mm to 3.5 mm.

[0031] Preferably, the finned duct has a fin pitch or fin spacing (i.e., the distance between adjacent fins) of 5 mm to 30 mm, more preferably 10 mm to 20 mm. Preferably, the fins have a frequency of 50 to 500 fins per meter of duct. This fin pitch or fin frequency enhances efficiency because it prevents the fins from getting easily fouled or clogged, which would occur if the fin pitch were too narrow.

[0032] Preferably, the fins have a thickness of 0.2 mm to 1.5 mm. Further, the fins can be serrated or perforated.

[0033] Preferably, the finned duct has a heat transfer surface of 1 to 2 m 2 / m, more preferably 1.5 m 2 / m to 1.8 m 2 / m.

[0034] The finned duct may comprise connection pieces or sections that are not finned, and may also comprise ends that are not finned. A connection piece / section / end that is not finned does not mean that it indicates the space between two regularly or evenly spaced fins. By regularly spaced, it refers to fins that are essentially equidistant. Instead, a connection piece / section / end that is not finned means that it indicates a space or length that is larger than the length of the space that can accommodate at least three regularly spaced fins. These pieces, sections or ends can be flat pieces, sections or ends. Instead of or in addition to this, these pieces, sections or ends can also be peeled-off pieces, sections or ends, which means that the fins have been peeled off or removed from the duct.

[0035] Instead of or in addition to this, a plurality of radiant elements are arranged in a sub-circuit such that they share one heat source, and / or each radiant element preferably operates at the same temperature such that the radiant elements have a parallel inflow and the heating medium is supplied at the same flow temperature in all the radiant elements.

[0036] Preferably, any connection duct outside the drying zone or outside any heat recovery means is insulated to prevent heat loss to the surroundings.

[0037] Preferably, the width of the drying device is in the range of 2 to 6 meters, more preferably 3 to 5 meters. The width of the drying device can be such that several building boards can be arranged side by side across the width. Preferably, the height of the drying device is 4 to 8 meters, more preferably 5 to 6 meters. The height of the drying device can be such that several building boards can be arranged in horizontal layers stacked on top of each other.

[0038] The drying device can comprise a series of drying zones such as a first drying zone and a second drying zone downstream of the first drying zone, preferably further comprising a third drying zone downstream of the second drying zone, more preferably further comprising a fourth drying zone downstream of the third drying zone, most preferably comprising a fifth drying zone downstream of the fourth drying zone, and potentially up to an eightieth drying zone downstream of the seventy-ninth drying zone. Any one from the first, second, third, fourth, fifth drying zones up to the eightieth drying zone respectively comprises a plurality of radiant elements each provided with a heating medium circulating within a duct, and each radiant element has a temperature variation of up to 30 °C.

[0039] The drying device typically comprises a pre-drying unit, a main drying unit, and a final drying unit, with each unit having one or more drying zones. Any, some, or all of the drying units (i.e., the pre-drying unit, the main drying unit, or the final drying unit) can each comprise a plurality of radiant elements each provided with a heating medium circulating within a duct, and each radiant element has a temperature variation of up to 30 °C. Any, some, or all of one or more drying zones of the drying units (i.e., the pre-drying unit, the main drying unit, or the final drying unit) can comprise a plurality of designated radiant elements.

[0040] One or more drying zones of the pre-drying unit generally operate at a lower temperature than, for example, subsequent drying zones of the main drying unit and are used to gradually warm the building board before drying at a higher temperature. Preferably, some, any or all of the drying zones of only the pre-drying unit comprise a plurality of radiant elements. The radiant elements within one or more drying zones of the pre-drying unit can be maintained at 60°C to 130°C, preferably 65°C to 95°C. The pre-drying unit typically operates at a lower temperature compared to, for example, subsequent drying zones of the main drying unit. This makes it easier to heat the drying medium of the radiant elements, for example, using heat recovered from warmer drying zones of the main drying unit. When the building board still has a relatively high moisture content, it is advantageous to have a low drying temperature achieved, for example, by maintaining the radiant elements at 60°C to 130°C, preferably 65°C to 95°C at the start of the drying process. This is related to the fact that the evaporation rate is relatively constant when the moisture content is 15% to 50%, but the evaporation rate drops sharply when the moisture content is less than about 15%. For example, a low drying temperature such as achieved by maintaining the radiant elements at 60°C to 130°C, preferably 65°C to 95°C is inefficient at a moisture content of 15% or less, and for this reason, it is not practical to lower the temperature towards the end of the drying process.

[0041] The conveying means can comprise a plurality of rollers. The rollers have the advantage that water vapor can escape from under the building board. When conveying means such as a conveyor belt is used, it is necessary to consider water permeability. It is advantageous not to position the ducts of the radiant elements directly under the rollers, as such gas flow is optimized and the pressure drop is minimized. It is also advantageous not to position the radiant elements between the rollers. Ideally, one or two parallel ducts or parallel duct segments are positioned in the gaps below and / or above two rollers. Also, for sufficient air flow, it is advantageous to have a gap of 5 mm to 20 mm between the fins of adjacent finned ducts.

[0042] Preferably, the drying device further comprises heat recovery means, and preferably, the heat recovery means comprises a heat pump and / or a heat recovery column and / or a gas-gas heat exchanger and / or a gas-liquid heat exchanger.

[0043] More preferably, the heating medium is heated by a heat pump, preferably by an absorption heat pump or a compression heat pump or a hybrid heat pump. In the case of an absorption heat pump, the heating medium is preferably heated in the absorber cycle of the absorption heat pump.

[0044] Another aspect of the present invention includes a method of drying a building board in a drying device comprising at least one drying zone, the method comprising: - providing conveying means in at least one drying zone; - providing a plurality of radiation elements in at least one drying zone; - circulating a heating medium through the ducts of the radiation elements; - conveying the building board through the drying zone; and a method, wherein each radiation element has a temperature variation of at most 30°C.

[0045] Preferably, the drying device used in the method corresponds to any of the preferred embodiments of the drying device disclosed above.

[0046] Yet another aspect of the present invention relates to the use of radiation elements, each comprising a heating medium in a duct, for drying a building board. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention will be further described with reference to the drawings. However, it is not intended to limit the scope of the present invention and the general teachings according to the selected embodiments in the drawings.

[0048]

Figure 1

Claims

1. A drying apparatus for building boards, comprising at least one drying zone, wherein the at least one drying zone comprises a plurality of radiating elements, each having a heating medium circulating within a duct, and each radiating element having a temperature fluctuation of up to 30°C.

2. The drying apparatus according to claim 1, wherein the radiating elements are arranged in a horizontal layer.

3. The drying apparatus according to claim 1, wherein the drying apparatus is configured to consist of a plurality of decks, each deck comprising a conveying means and a horizontal layer of radiating elements, preferably the horizontal layer of radiating elements is positioned above the conveying means, and more preferably the horizontal layer of radiating elements is positioned at least 40 mm above the conveying means.

4. The drying apparatus according to claim 1, wherein the horizontal layer comprises parallel ducts or parallel duct segments, and the parallel duct segments are fluidly interconnected.

5. The drying apparatus according to claim 1, wherein the drying zone further includes air movement with a flow velocity of 3 to 10 m / s opposite to the conveying direction.

6. The drying apparatus according to claim 1, wherein the at least one drying zone further includes convective heating.

7. The drying apparatus according to claim 1, wherein the heating medium is steam, water, aqueous glycol solution, or hot oil.

8. The drying apparatus according to claim 1, wherein at least 40%, preferably at least 80%, and most preferably 95% to 100% of the heating medium is heated by heat recovered from the drying apparatus.

9. The drying apparatus according to claim 4, wherein the parallel duct or the parallel duct segment is a finned duct or a finned duct segment.

10. The drying apparatus according to claim 1, wherein the duct is a finned duct and optionally includes a connecting piece without fins.

11. The drying apparatus according to claim 1, wherein the plurality of radiating elements are arranged in a subcircuit such that they share a single heat source, and / or each radiating element operates at the same temperature.

12. The drying apparatus according to claim 1, comprising a pre-drying unit, a main drying unit, and a final drying unit, each unit having one or more drying zones, and any, part, or all of the drying units comprising a plurality of radiating elements each having a heating medium circulating in a duct, and each radiating element having a temperature fluctuation of up to 30°C.

13. The drying apparatus according to claim 12, wherein part, any, or all of the drying zone of the pre-drying unit alone is provided with a plurality of radiating elements.

14. The drying apparatus according to claim 1, wherein the conveying means comprises a plurality of rollers.

15. The drying apparatus according to claim 1, further comprising a heat recovery means, preferably the heat recovery means comprising a heat pump and / or a heat recovery column and / or a gas-gas heat exchanger and / or a gas-liquid heat exchanger.

16. The drying apparatus according to claim 1, wherein the heating medium is heated by the heat pump, preferably by an absorption heat pump, a compression heat pump, or a hybrid heat pump.

17. A method for drying building boards in a drying apparatus having at least one drying zone, - A step of providing a conveying means in at least one of the drying zones, - A step of providing a plurality of radiating elements in at least one of the drying zones, - A step of circulating the heating medium through the duct of the radiating element, - A process of transporting building boards through the aforementioned drying zone, Includes, A method in which each radiating element has a temperature variation of up to 30°C.

18. The method according to claim 17, wherein the drying apparatus is the drying apparatus described in any one of claims 1 to 16.

19. The use of radiant elements, each equipped with a heating medium within a duct, for drying building boards.

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