Apparatus and method for drying building panels

Abstract

The present invention relates to an apparatus for drying building panels, comprising: a conveyor (40) for transporting wet building panels (60) along a drying path through several high temperature chambers (1, 2) (=HT: high temperature chambers) arranged upstream along the drying path of several low temperature chambers (N) (=LT: low temperature chambers); a distribution system (5) for distributing fluid into the HT and LT chambers for heating the main surfaces of the building panels and removing moisture from them as they pass through the chambers; and an exhaust system (7) configured to exhaust exhaust fluid from the apparatus along exhaust flow paths extending from the N chambers (1, 2, ...N) to the outside of the apparatus, wherein the fluid entering the HT chambers is heated by heating elements (11), and the fluid entering the LT chambers is heated by a heat pump / MVR system comprising a heat pump (8) for transferring heat from the exhaust fluid to an MVR cycle that transfers heat to a fluid in direct communication with the LT chambers.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and a method for drying building panels made of gypsum (= gypsum board or gypsum fiberboard) or cement or calcium silicate panels during their formation, which consumes less energy than state-of-the-art dryers, and a method for achieving the same level of drying with less energy consumption. The building panels to be dried are typically extruded on a conveyor through N chambers of a drying device.

[0002] Background of the Invention Building panels, such as panels made of gypsum (= gypsum board or gypsum fiberboard) or panels made of cement, fiber cement, or calcium silicate, are formed by mixing and reacting water with a base composition. For example, panels made of gypsum (CaSO4.2H2O), known as gypsum board, are formed by mixing and reacting plaster of Paris (CaSO4.1 / 2H2O) with water. The panels thus formed must be heated to promote the reaction and remove excess water. For example, the apparatus shown in Figure 1 includes a distribution system (5) configured to blow heated gas, typically air, onto both major surfaces of the panel as it passes through N chambers to increase its temperature and reduce its moisture content. Before the air reaches the panel in the chamber, it is heated by a heating element (11), which can typically be an air-fuel blower. The N chambers are divided into high-temperature (HT) chambers (1, 2), distributed to the HT drying zone where the air is heated at high temperature, and low-temperature (LT) chambers (N), distributed to the LT drying zone. An exhaust system (7) is provided to evacuate the cooling gas from the apparatus after it has contacted the surfaces of the panels in each chamber and has become saturated with moisture.

[0003] Even though continuous efforts are made to reduce the amount of water added to the base composition, drying costs still represent a significant portion of the total manufacturing cost. Given the importance of reducing CO2 emissions and rising energy costs, efforts have been made to increase the efficiency of drying equipment. For example, as shown in Figure 1, a heat exchanger (X75) is used to recover some heat from the exhaust air flowing through the exhaust system (7) before it is released into the atmosphere, transfer the heat to the fresh air flowing through the distribution system (5) before it reaches the chamber, and provide preheated air to the air-fuel burners used to heat the flowing air.

[0004] GB 1562031 describes a drying apparatus in which the air-fuel burners in the LT drying zone are replaced by heat exchangers that extract heat from the exhaust gases from the HT chamber and transfer it to a fresh air supply that is blown into the LT chamber. To increase heat transfer from the exhaust gases, the air blown onto the articles in the HT drying zone has a high temperature and moisture content. This has the effect of increasing the moisture content in the exhaust gases, but it also reduces the amount of water removed from the articles being dried.

[0005] WO 2019105888 describes a dryer and method for drying gypsum board in which heat from exhaust gases removed from an HT chamber is extracted by a heat exchanger and transferred to fresh air sources via heat exchangers arranged in series, each air source being coupled to an LT chamber. While this method is highly efficient, upgrading an existing dryer of the type shown in Figure 1 to a dryer according to WO 2019105888 is difficult because of the significant extra space required to achieve it.

[0006] U.S. Patent Application Publication No. 2010299956 describes a dryer that uses oil-to-air heat exchangers instead of air-to-fuel burners to heat the air blown into the chamber. Oil is heated in the furnace, circulated through various oil-to-air heat exchangers, and returned to the furnace. The dryer is equipped with an organic Rankine cycle system (ORC) to generate electricity using heat from the exhaust from the final LT chamber or furnace.

[0007] CN103708697 describes a mechanical vapor recompression (MVR) heat pump sludge drying system that includes a dryer and a vapor compressor. Wet sludge is dried by the dryer, which generates secondary steam, and the secondary steam is compressed in the vapor compressor to become recompressed steam. The recompressed steam is returned to the dryer. Thus, energy is saved by recovering the latent heat of the secondary steam. Similarly, CN109282615 describes an MVR band dryer for drying items.

[0008] It can be seen that various options have been considered in the art, all with the aim of reducing the energy consumption of the drying process. The present invention proposes an apparatus and method for drying building boards, such as gypsum boards and cement boards, during their production, which makes maximum use of the thermal energy available in the apparatus in order to substantially reduce energy consumption. A major advantage of the present invention is the ease and economic efficiency of upgrading existing drying apparatuses of the type shown in Figure 1 to obtain a drying apparatus according to the present invention, without reducing the capacity of the apparatus.

[0009] These and other advantages of the present invention are described below. Summary of the Invention The invention is defined in the accompanying independent claims. Preferred embodiments are defined in the dependent claims. In particular, the invention relates to an apparatus for drying building panels. A conveyor is configured to transport wet building panels along a drying path through a drying unit. The drying unit comprises N chambers, a distribution system, a heating element, and an exhaust system.

[0010] The drying unit comprises N chambers distributed in series along the drying path and in fluid communication with one another, with 1≦i≦N−1 and j=Ni, comprising i high temperature chambers (=HT chambers) located in a high temperature drying zone (HT) in the upstream part of the drying path and j low temperature chambers (=LT chambers) located in a low temperature drying zone (LT) downstream of the high temperature drying zone (HT) along the drying path.

[0011] The distribution system is in fluid communication with a fluid source at one end and with the N chambers at the other end. It is configured to circulate a flow of fluid along a fluid flow path extending from the fluid source into the N chambers. A heating element is configured to heat the fluid in the distribution system before it penetrates each HT chamber, i.e., the heating element is located upstream and adjacent to the access to the chamber at the other end of the distribution system. The drying unit also includes an exhaust system configured to exhaust exhaust fluid from the apparatus along an exhaust flow path extending from the N chambers to outside the apparatus.

[0012] The gist of the device of the present invention includes a heat pump / MVR system comprising a heat pump, an MVR cycle, and a specific heat exchanger.

[0013] The first heat pump heat exchanger is configured to transfer heat from an exhaust fluid flowing in the exhaust system to a low boiling point fluid of the heat pump. The heat pump includes a heat pump compressor configured to compress the low boiling point fluid to increase its temperature and to push the low boiling point fluid flow from the first heat pump heat exchanger to a second heat pump heat exchanger.

[0014] The second heat pump heat exchanger is configured to transfer the heat thus captured by the low boiling point fluid to a heating fluid, such as water / steam, having a higher boiling point than the low boiling point fluid of the heat pump. The heating fluid is configured to circulate in a mechanical vapor recompression (MVR) cycle, pushed by an MVR compressor configured to compress the heating fluid, thus increasing the temperature of the heating fluid, and push a flow of the heating fluid from the second heat pump heat exchanger to the MVR heat exchanger.

[0015] The MVR heat exchangers are configured to transfer heat from the heating fluid of the MVR cycle to the fluid in the distribution system directly before penetrating the respective LT chambers, i.e., immediately upstream and adjacent to the access to the chambers at the other end of the distribution system.

[0016] The coefficient of performance (COP) of a heat pump / MVR system consisting of a heat pump and an MVR cycle is defined as the ratio (Q / W) of useful heat (Q) provided by the combined heat transfer to the work (W) required to operate the heat pump compressor and the MVR compressor. For example, a heat pump / MVR system can be characterized by a COP comprised between 2 and 5, preferably between 2.5 and 4.

[0017] To recover as much heat as possible from the exhaust fluid and preheat the fluid in the distribution system, a preheating heat exchanger may be provided, configured to transfer heat from the exhaust fluid in the exhaust system to the fluid in the distribution system to increase the temperature of the fluid flowing through the distribution system. The preheating heat exchanger is preferably located in the exhaust system upstream of the first heat pump heat exchanger, where upstream is defined relative to the flow direction of the exhaust fluid in the exhaust system. The terms "upstream" and "downstream" are defined herein relative to the flow direction of the fluid in the corresponding fluid system, such as the fluid in the distribution system, the exhaust fluid in the exhaust system, the low-boiling-point fluid in the heat pump, or the heating fluid in the MVR cycle.

[0018] In a preferred embodiment, the heating element is an air-fuel burner and the fluid source is an air source. A portion of the air flowing through the distribution system is supplied to the air-fuel burner to fuel the air-fuel burner. Alternatively, the heating element can be an electric heater.

[0019] In a further preferred embodiment, the fluid source is a gas source, preferably an air source. The distribution system includes a distribution fan configured to push a flow of gas from the gas source toward the N chambers, and the HT chambers include a chamber fan configured to push a gas flow cycle through the heating element into the corresponding HT chamber and out through the gas flow cycle to the exhaust system. Similarly, the LT chambers include a chamber fan configured to push a gas flow cycle through the MVR heat exchanger into the corresponding LT chamber and out through the gas flow cycle to the exhaust system.

[0020] The temperature in the HT chamber may vary between 120°C and 260°C, preferably between 150°C and 250°C, with the maximum temperature in the middle section of the HT drying zone. The temperature in one or more LT chambers (N) has a lower average value than the average temperature in the HT chambers and may vary between 90°C and 170°C, preferably between 100°C and 160°C, with the maximum temperature in the upstream section of the LT drying zone, upstream being defined relative to the direction of the drying path.

[0021] The temperature of the low boiling point fluid of the heat pump in the second heat pump heat exchanger may be comprised between 90° and 110°, preferably equal to 100° C.±5° C. The temperature of the fluid of the MVR cycle in the MVR heat exchanger may be comprised between 120° C. and 180° C., preferably between 135° C. and 170° C., preferably equal to 150° C.±10° C.

[0022] In one embodiment, the heat pump / MVR cycle system includes an MVR distribution system heating loop that branches off from the MVR cycle downstream of the MVR compressor and rejoins the MVR cycle upstream of the MVR compressor after passing through a second MVR heat exchanger configured to transfer heat from a heated fluid in the MVR cycle to a fluid in the distribution system.

[0023] To further increase the heat transfer from the exhaust fluid to the fluid flowing in the distribution system, several options are available. For example, a fluid heat exchanger can be configured to transfer heat from the low-boiling-point fluid of the heat pump to the fluid in the distribution system. A second option is to provide the exhaust system with a fluid exhaust duct leading to a LT heat exchanger configured to transfer heat from the exhaust fluid in the exhaust system to the LT chamber. The LT heat exchanger is preferably located upstream of the first heat pump heat exchanger with respect to the flow direction of the exhaust fluid in the exhaust system.

[0024] The present invention also provides Providing a device as described above; extruding the wet building panel along a drying path through a chamber of a HT drying zone and subsequently through a chamber of a LT drying zone; flowing a fluid through a distribution system into each of the N chambers; Heating the fluid to a desired temperature using a heating element before infiltrating the HT chamber; exhausting the exhaust fluid from each of the N chambers via a fluid exhaust system; a method for drying a building panel, comprising: Heat is exchanged in a first heat pump heat exchanger from an exhaust fluid in the exhaust system to a low boiling point fluid in the heat pump after compression of the low boiling point fluid; Heat is exchanged in a second heat pump heat exchanger from the thus compressed low boiling point fluid to the heating fluid in the MVR cycle after compression of the heating fluid; Heat is exchanged in the MVR heat exchanger from the heated fluid thus compressed to a fluid in a distribution system that is in direct fluid communication with one or more LT chambers (N) in the low temperature drying zone (LT).

[0025] BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the nature of the present invention, reference should now be made to the following detailed description taken in conjunction with the accompanying drawings, in which: [Brief explanation of the drawings]

[0026] [Figure 1] 1 shows a typical drying device according to the prior art; [Figure 2] 1 is a diagram showing an embodiment of a drying device according to the present invention; [Figure 3] FIG. 1 illustrates an alternative embodiment of the present invention. [Figure 4] FIG. 10 illustrates a further alternative embodiment of the present invention. [Figure 5] FIG. 10 illustrates a further alternative embodiment of the present invention. [Figure 6] FIG. 10 illustrates a further alternative embodiment of the present invention. [Figure 7] FIG. 1 shows an example of a heat pump coupled to an MVR cycle according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] Detailed Description of the Invention The present invention relates to an apparatus for drying building panels made of gypsum (= gypsum board or gypsum fiberboard) or panels made of cement or calcium silicate during their manufacture. The apparatus comprises a conveyor (40) for transporting the building panels (60) along a drying path through N chambers (1, 2...N). A distribution system (5) distributes a drying fluid to each chamber, with a heating element (11) provided for heating the fluid in the distribution system before it reaches the chamber. An exhaust system (7) is provided for discharging the exhaust fluid from the chambers.

[0028] The present invention is not limited to any particular type of conveyor 40, so long as it allows for the conveyance of wet building panels 60 along a drying path through a chamber that exposes both major surfaces of the panels to a drying fluid. For example, the conveyor 40 may include rollers or a perforated sheet configured to support and transport the panels while exposing both major surfaces of the panels to a flow of hot gas, typically hot air.

[0029] The drying unit includes a total of N chambers (1, 2, ... N) distributed in series along a drying path and in fluid communication with one another. The N chambers consist of i high-temperature chambers (1, 2) (= HT chambers) located in a high-temperature drying zone (HT) in the upstream portion of the drying path, and j low-temperature chambers (N) (= LT chambers) located in a low-temperature drying zone (LT) downstream of the high-temperature drying zone (HT) along the drying path, where 1 ≤ i ≤ N - 1 and j = N i . While Figures 2-6 show a total of N = 3 chambers, i = 2 HT chambers (1, 2), and j = 1 LT chamber (N), it is clear that the numbers of chambers N, i, and j are not limited and can vary depending on the particular application.

[0030] The distribution system (5) is in fluid communication with a fluid source (5s), typically an air source, at one end and with N chambers (1, 2...N) at the other end. It is configured to circulate a fluid flow along a fluid flow path extending from the fluid source into the N chambers. Heating elements (11) configured to heat the fluid in the distribution system (5) are disposed within the distribution system (5) before the fluid penetrates the respective HT chambers (1, 2). The LT chambers (N) do not require a heating element for steady-state operation of the dryer. Typically, a shutdown heater is provided for use only during shutdown of a panel drying session (see shutdown burner (11s) in Figures 3-6).

[0031] An exhaust system (7) is configured to expel exhaust fluid from the apparatus along an exhaust flow path extending from the N chambers (1, 2...N) to the outside of the apparatus.

[0032] The subject of the present invention is a "heat pump / MVR system" used to recover heat from exhaust fluid flowing in an exhaust system (7) to substantially increase the temperature of fluid flowing in a distribution system (5). The heat pump / MVR system includes a heat pump (8) and a mechanical vapor recompression (MVR) cycle (9) coupled to respective heat exchangers (X78, X89, X95N) for efficiently transferring thermal energy from the exhaust fluid to the fluid in the distribution system (5). Specifically, the MVR heat exchangers (X95N) are configured to transfer heat from the heated fluid in the MVR cycle (9) to the fluid in the distribution system (5) before it penetrates the respective LT chambers (N). The MVR heat exchangers (X95N) in the LT chambers (N) have the same function as and replace the heating elements (11) used in the HT chambers (1, 2). In this way, while using the dryer in steady mode, the heating element (11) is not required to heat the fluid before it enters the LT chamber (N), and therefore energy consumption is reduced accordingly.

[0033] The first heat pump heat exchanger (X78) is configured to transfer heat from the exhaust fluid in the exhaust system (7) to a low boiling point fluid in the heat pump (8). The heat pump (8) comprises a closed loop duct for circulating the low boiling point fluid and a heat pump compressor (8c) configured to compress the low boiling point fluid to increase its temperature and push the flow of the low boiling point fluid in the closed loop duct from the first heat pump heat exchanger (X78) to the second heat pump heat exchanger (X89).

[0034] The second heat pump heat exchanger (X89) is configured to transfer the heat thus captured by the low boiling point fluid to a heating fluid, preferably vapor, having a boiling point higher than that of the low boiling point fluid of the heat pump (8). The heating fluid is configured to circulate in an MVR cycle (9). The MVR cycle (9) comprises an MVR compressor (9c) configured to compress the heating fluid, thus increasing its temperature, and to push the flow of heating fluid from the second heat pump heat exchanger (X89) to an MVR heat exchanger (X95N).

[0035] The MVR heat exchanger (X95N) is configured to transfer heat from the heated fluid of the MVR cycle (9) to a fluid in the distribution system (5) that is in direct fluid communication with one or more LT chambers (N) in the low-temperature dry zone (LT). By direct fluid communication, it is meant herein that the fluid in the MVR heat exchanger (X95N) is not separated from the interior of the LT chamber (N) by any fluid ducts (51, 52) or any other device of the apparatus. Heat can be transferred from the fluid to the building panel by at least forced convection of the fluid. In this embodiment, the fluid is preferably gas, more preferably air, which flows in contact with the two major surfaces of the building panel (60) immediately after being heated to a corresponding predetermined temperature by the MVR heat exchanger (X95N) in the LT chamber and the heating elements (11) in the HT chambers (1, 2).

[0036] Distribution system (5) and chambers (1, 2...N) The distribution system comprises ducts configured to circulate a flow of fluid from a fluid source (5s) along a fluid flow path extending into the N chambers. The circulating fluid is preferably a gas, more preferably air, which, after heating to a desired temperature, is blown onto the two major surfaces of the panel as it moves through successive chambers. Heat is thus transferred from the fluid to the major surfaces of the panel by forced convection.

[0037] The distribution system has an upstream end coupled to a fluid source (5s). The fluid is preferably gas. If the fluid is air, the air source can be ambient air at room temperature. A blower or fan (5f) is provided to drive the gaseous fluid from the fluid source (5s) into the distribution system (5). As shown in Figures 2-6, the distribution system (5) divides into N fluid supply ducts (51, 52...5N) for flowing fluid in parallel into each of N chambers (1, 2...N). When the fluid supply duct reaches the corresponding chamber, it forms a gas flow cycle with chamber fans (1f, 2f...Nf) for pushing the gas flow (e.g., air) along the gas flow cycle. The gas flow cycle within the HT chamber is configured to flow gas (e.g., air) through a heating element (11), such as an air-fuel burner, into the corresponding HT chamber (1, 2), licking both major surfaces of the panels to increase their temperature and remove moisture therefrom. Similarly, the gas flow cycle in the LT chamber is configured to pass gas (e.g., air) through an MVR heat exchanger (X95N) (instead of a heating element (11) as in the HT chamber) and into the corresponding LT chamber (N), licking both major surfaces of the panels to remove moisture therefrom. All or a portion of the gas (e.g., air) can run one or more cycles from the chamber to the heating element (11) or MVR heat exchanger (X95N) until its moisture content is deemed too high, at which point it can be forced out of the gas flow cycle into the exhaust system (7). Valves (5v, 7v) are provided in both the distribution system (5) and the exhaust system (7) to control the momentum and rate of gas (e.g., air) introduced into and exhausted from the gas flow cycle. The heating element (11) is used only in the HT chambers (1, 2) during steady-state operation of the dryer. As mentioned above, the LT chamber may be equipped with a shutdown burner (11s) that is used exclusively during the shutdown operation of the dryer at the end of a drying session after the heating element (11) in the HT chamber is turned off.At the end of the drying operation, once the last panel has passed through the HT chamber, the corresponding heating element (11) is turned off, and the temperature of the exhaust gas in the exhaust system (7) is no longer sufficient to heat the fluid flowing into the LT chamber (N) to the desired temperature. The shutdown burners (11s) are used exclusively for this purpose and are not used to heat the LT chamber during "normal" or steady-state use of the apparatus. Alternatively, the shutdown burners (11s) can be used to heat the fluid flowing into the LT chamber (N) during steady-state drying operations at only a fraction of their total heating capacity, such as 25% or less, preferably 10% or less. However, it is preferable that no heating element is used to heat the LT chamber during steady-state use of the apparatus. The apparatus may be equipped with a processing unit configured to control that the shutdown burners (11s) remain off or at only a fraction of their total heating capacity during steady-state use of the apparatus, and that the fluid flowing into the LT chamber is heated exclusively by the heat exchanger, including the MVR heat exchanger (X95N). The processing unit can be configured to control that the gas (e.g., air) is heated by a heating element (11) before entering the HT chambers (1, 2) and by an MVR heat exchanger (X95N) before entering the LT chamber (N).

[0038] The gas flow cycle in the LT chamber is similar to that in the HT chamber described above, but without the heating element (11). The gas flow cycle in the LT chamber instead flows through an MVR heat exchanger (X95N), increasing the temperature of the gas (e.g., air) each time it cycles through the gas flow cycle. A return exhaust duct (7h) can be provided to direct the exhaust fluid toward the LT chamber (N) and circulate it through the LT heat exchanger (X7N) shown in FIG. 4. Valve (7v) allows precise control of the amount of exhaust fluid introduced from the return exhaust duct (7h) into the LT heat exchanger (X7N), thereby controlling the temperature transferred to the fluid in the LT heat exchanger (X7N). Alternatively, as shown in Figures 3 and 6 where the fluid source is a gas source, the return exhaust duct (7h) is joined in fluid communication with the distribution system (5) adjacent to and upstream of the MVR heat exchanger (X95N) and configured to mix the exhaust gas with the fluid from the distribution system (5) and pass it into the LT chamber (N), through the MVR heat exchanger (X95N), and out through the LT chamber (N). The fluid exhaust duct (7h) is provided with a valve (7v) to control the ratio of the amount of exhaust fluid to the amount of fluid. This is important because the exhaust gas is loaded with a significant amount of moisture, and a careful balance of the moisture content of the gas sprayed onto the building boards moving through the LT chamber (N) is necessary to optimize the drying operation of the boards.

[0039] If the fluid is air, the heating element (11) is preferably an air-fueled burner supplied with a portion of the air flowing through fluid supply ducts (51, 52) leading to the HT chamber. Fuel (typically a gas such as acetylene, natural gas, or propane) is supplied to the air-fueled burner through duct (9g), as shown in Figures 2-6. Alternatively, the heating element (11) can be an electric heater or heat exchanger that receives a flow of a high-temperature fluid, such as hot oil, to raise the temperature of the fluid. In these cases, the fluid can be any gas, but air is readily available and is preferred.

[0040] To increase the temperature of the fluid flowing through the distribution system (5) before it reaches the chamber and the air-fuel burner, the fluid is preferably preheated in a preheating heat exchanger (X75) configured to transfer heat from the exhaust fluid in the exhaust system (7) to the fluid in the distribution system (5). The preheating heat exchanger (X75) is preferably located upstream of at least some, preferably all, of the fluid supply ducts (51, 52, ... 5N). The preheating heat exchanger (X75) is also preferably located upstream of the first heat pump heat exchanger (X78), which will be described in more detail below. The terms "upstream" and "downstream" are defined herein with respect to the flow direction of the fluid in the corresponding fluid system, such as the fluid in the distribution system (5), the exhaust fluid in the exhaust system (7), the low-boiling-point fluid in the heat pump (8), or the heating fluid in the MVR cycle (9). In this example, upstream is defined with respect to the flow direction of the exhaust fluid in the exhaust system (7). Preheating the fluid before it reaches the chambers and heating elements is advantageous because, on the one hand, less energy is needed to heat the fluid to the desired temperature by the heating elements (11) for the HT chambers (1, 2) and the MVR heat exchanger (X95N) for the LT chamber, and, on the other hand, the air-fuel burners are more efficient when supplied with warm air.

[0041] The temperature in the chambers (1, 2...N) can be controlled by controlling the fluid flow rate and the fluid temperature via the chamber fans (1f, 2f...Nf). The temperature of the fluid blown into the HT chambers (1, 2) can be controlled via the heating element (11), and the temperature of the fluid blown into the LT chamber (N) can be controlled via the MVR cycle and MVR heat exchanger (X95N). To dry the gypsum board, the temperatures (T1; T2) in the HT chambers (1, 2) can vary between low temperatures (T1L, T2L) and high temperatures (T1H, T2H), which can range from 120°C to 260°C, preferably from 150°C to 250°C, and are preferably the maximum temperature in the middle section of the HT drying zone. The temperature (TN) in the one or more LT chambers (N) has an average value lower than the average temperature in the HT chambers and can vary between a low temperature (TNL) and a high temperature (TNH), the high temperature (TNH) can range between 90°C and 170°C, preferably between 100°C and 160°C, being the maximum temperature in the upstream section of the LT drying zone, upstream being defined relative to the direction of the drying path.

[0042] Exhaust system (7) and heat exchanger (X75, X78, X7N) As shown in Figures 2-6, the exhaust system (7) comprises fluid exhaust ducts (71, 72...7N) for extracting fluid from the chambers when the temperature or water content is deemed to be outside predetermined boundaries. The fluid exhaust ducts (71, 72...7N) are coupled to the corresponding gas flow cycles at locations between the chamber fans (1f, 2f...Nf) and heating elements (11) for the HT chambers (1, 2) and the MVR heat exchanger (X95N) for the LT chamber (N).

[0043] The exhaust fluid leaving the chamber through the exhaust system (7) is cooler and more humid than the fluid entering the chamber through the distribution system (5), but still retains a significant amount of heat. The objective of the invention is to recover as much thermal energy as possible from the exhaust fluid by means of different heat exchangers (X75, X78, X7N).

[0044] The fluid in the fluid source (5s) is typically at room temperature and requires some preheating before reaching the chambers. If the fluid is air and the heating element (11) is an air-fuel burner, the effectiveness of the air-fuel burner is improved by supplying preheated air to the air-fuel burner. For this purpose, and as already mentioned, the device may include a preheating heat exchanger (X75) configured to transfer heat from the exhaust fluid in the exhaust system (7) to the fluid in the distribution system (5) in order to increase the temperature of the fluid flowing in the distribution system (5) before reaching the heating element (11), such as an air-fuel burner. The preheating heat exchanger (X75) is preferably located significantly upstream of the distribution system (5), where the fluid supply ducts (51, 52...5N) branch off to the respective chambers (1, 2...N). The preheating heat exchanger (X75) is preferably located in the exhaust system upstream of the first heat pump heat exchanger (X78), (upstream being defined here with respect to the flow direction of the exhaust fluid in the exhaust system (7)), which is configured to transfer heat from the exhaust fluid in the exhaust system (7) to the low boiling point fluid in the heat pump (8).

[0045] As shown in Figures 4 and 5, the exhaust system (7) may also include a LT heat exchanger (X7N) configured to transfer heat from the exhaust fluid in the exhaust system (7) to the LT chamber (N), the LT heat exchanger (X7N) not being dependent on the heating element (11) for steady-state use of the apparatus. The LT heat exchanger (X7N) is preferably located in the exhaust system (7) upstream of the first heat pump heat exchanger (X78).

[0046] Heat pump (8) and MVR cycle (9) The subject of the present invention is a heat pump / MVR system used to recover heat from the exhaust fluid flowing in the exhaust system (7) to substantially increase the temperature of the fluid flowing in the distribution system (5) before the fluid reaches the HT chambers (1, 2). It comprises a heat pump (8) in heat conducting contact with an MVR cycle (9) via a second heat pump heat exchanger (X89), as shown in Figure 7.

[0047] Heat Pumps(8) As shown in FIG. 7, the heat pump (8) includes a closed circuit for circulating a low-boiling-point fluid pumped by the heat pump compressor (8c). The low-boiling-point fluid can have a boiling point below -10°C, preferably below -20°C. For example, the low-boiling-point fluid can be a hydrofluorocarbon (HFC) such as tetrafluoroethane, a halogenated fluorocarbon (PFC), a halogenated fluorine olefin (HFO), or natural gas such as propane. The low-boiling-point fluid collects heat from the exhaust fluid flowing in the exhaust system (7) in the first heat pump heat exchanger (X78). As the heated low-boiling-point fluid passes through the heat pump compressor (8c), its pressure increases and its temperature follows the same trend. The heat thus stored by the low-boiling-point fluid is transferred to the heated fluid, preferably steam, flowing in the MVR cycle (9) through the second heat pump heat exchanger (X89). The pressure of the thus cooled low boiling point fluid is reduced by the expansion device (8e) to prevent or limit condensation before returning to the first heat pump heat exchanger (X89) and restarting the aforementioned cycle.

[0048] During heat transfer within the first heat pump heat exchanger (X78), the temperature of the wet exhaust fluid drops, forming condensed water (8w) with a temperature higher than that of the fluid from the fluid source (5s). To utilize the heat carried by the condensed water, the apparatus can include a condensing heat exchanger (X8w5) configured to transfer heat from the condensed water (8w) to the fluid flowing from the fluid source (5s) into the distribution system, as shown in Figures 4 and 5. Because the temperature of the condensed water is not very high, the condensing heat exchanger (X8w5) is preferably located upstream of the preheating heat exchanger (X75) on the heat distribution system (5). In addition to preheating the fluid, using the condensing heat exchanger (X8w5) also has the advantage of lowering the temperature of the condensed water (8w), which can then be used for other operations, such as forming new building boards (60), by adding water to the mixer upstream of the production line and sufficiently upstream of the drying device. This significantly reduces water consumption throughout the board production process.

[0049] Downstream of the second heat pump heat exchanger (X89) and upstream of the expansion device (8e) and the first heat pump heat exchanger (X78), the heat still remaining in the low boiling point fluid can be transferred to the fluid flowing in the distribution system (5) by flowing the low boiling point fluid through a fluid heat exchanger (X85) that is in thermal contact with the fluid in the distribution system (5), as shown in Figures 4 and 5.

[0050] The temperature of the low boiling fluid of the heat pump (8) in the second heat pump heat exchanger (X89) may usually be comprised between 90° and 110°, preferably equal to 100°C ± 5°C.

[0051] MVR Cycle (9) The heating fluid of the MVR cycle, preferably water / steam, picks up heat from the low boiling point fluid of the heat pump (8) in the second heat pump heat exchanger (X89).

[0052] The heated fluid flow is forced through an MVR compressor, which increases the pressure and, therefore, the temperature of the heated fluid. The compressed and heated heated fluid then flows through an MVR heat exchanger (X95N), which is configured to transfer heat from the heated fluid in the MVR cycle (9) to a fluid in the distribution system (5), which is in direct fluid communication with one or more LT chambers (N) in the low-temperature drying zone (LT). The MVR cycle can be an open cycle, which does not require an expansion device (9e) and produces condensed water that can be recovered. However, in this case, the MVR cycle must be periodically replenished with heated fluid that is not readily available from the process. For this reason, the MVR cycle (9) of the present invention is preferably a closed cycle, in which the condensate (typically water) formed during the transfer of heat from the heated fluid to the fluid flowing in the distribution system (5) is vaporized by passing the heated fluid through an expansion device (9e), as shown in Figure 7 (not shown in Figures 2-6 for clarity).

[0053] The MVR heat exchanger (X95N) is located in the distribution system (5) upstream from the fluid entry point into each LT chamber (N). In the preferred embodiment shown in Figures 2-6, the MVR heat exchanger (X95N) is located in the distribution system (5) at the level of the gas flow cycle of the corresponding LT chamber. The temperature of the heating fluid flowing through the MVR heat exchanger (X95N) can be between 120°C and 180°C, preferably between 135°C and 170°C, and is preferably equal to 150°C ± 10°C. Therefore, it can perform the same function in the LT chamber (N) as the heating element (11) in the HT chamber (1, 2), which brings the fluid to the required temperature of the corresponding LT chamber (N), which is lower than the temperature required in the HT chamber (1, 2). When the MVR heat exchanger replaces the heating element (11) of the HT chamber (1, 2) in the LT chamber (N), a lot of energy is saved. In fact, the energy required to operate the heating element (11) of the air-fuel burner or electric heater type or other heating element (11) is replaced by the energy required to operate the heat pump / MVR system, i.e., to operate the heat pump compressor (8c) and the MVR compressor (9c).

[0054] The temperature of the low-boiling-point fluid in the second heat pump heat exchanger (X89) can be around 90°C to 110°C, while the temperature required in the LT chamber can be around 90°C to 170°C. This temperature is too low to immediately heat the fluid entering the LT chamber to the desired temperature. Therefore, the heat pump (8) cannot be used alone to replace the heating element (11) in the LT chamber. Similarly, the MVR cycle contains a heating fluid with a higher boiling point than the low-boiling-point fluid in the heat pump (8), which is usually water / steam. The temperature of the exhaust gas flowing in the exhaust system (7) is not high enough to transfer enough heat to the heating fluid in the MVR cycle to reach the desired temperature at the level of the MVR heat exchanger (X95N) after compression of the heating fluid.

[0055] The coefficient of performance (COP) is defined as the ratio (Q / W) of the heat (Q) supplied by the MVR heat exchanger (X95N) to the work (W) required to operate the heat pump / MVR system, i.e., to operate the heat pump compressor (8c) and the MVR compressor (9c). It is a good indicator of the efficacy of a heat pump / MVR system. Tests have shown that the COP of a heat pump / MVR system can be between 2 and 5, preferably between 2.5 and 4 (to be efficient, a heat pump / MVR system must have a COP > 1).

[0056] In the embodiment shown in Figure 3, the MVR loop can include an MVR distribution heating loop (95) that branches off from the MVR cycle (9) downstream of the MVR compressor (9c) and rejoins the MVR cycle (9) upstream of the MVR compressor (9c). Meanwhile, the MVR distribution heating loop (95) passes through a second MVR heat exchanger (X95) configured to transfer heat from the heated fluid in the MVR cycle (9) to the fluid in the distribution system (5) upstream of the fluid supply ducts (51, 52, ... 5N). Because the heated fluid enters the MVR distribution system heating loop (95) downstream of the MVR compressor (9c), the heated fluid has a high pressure and a significantly higher temperature. Figure 5 shows an alternative embodiment in which the second MVR heat exchanger (X95) belongs to the same MVR cycle as the MVR heat exchanger (X95N). The temperature of the heating fluid at the level of the second MVR heat exchanger (X95) is lower than in the embodiment of FIG. 3, because the heating fluid has already transferred part of its heat to the gas flow cycle of the LT chamber (N) through the MVR heat exchanger (X95N) before reaching the second MVR heat exchanger (X95).

[0057] The fluid in the distribution system (5) can also collect heat directly from the heat pump (8) via a fluid heat exchanger (X85), as shown in Figures 4 and 5.

[0058] The preferred heat exchangers described herein can be selected and used in any combination. When placing several heat exchangers in the same duct, it is important to ensure that the temperature difference between the hot and cold fluids is high enough to transfer a significant amount of heat from the hot to the cold fluid.

[0059] Upstream of the heating element (11) and the MVR heat exchanger (X95N), the temperature of the fluid flowing in the distribution system (5) is lowest at the level of the fluid source (5s) and increases with each passing heat exchanger until it is highest when it reaches the fluid supply ducts (51, 52...5N). Therefore, the heat exchanger with the lowest temperature of the hot fluid is preferably located most upstream in the distribution system (5). In this case, as shown in Figure 5, the distribution duct may pass through one or more of the condensing heat exchanger (X8w5), the preheating heat exchanger (X75), the fluid heat exchanger (X85), and the second MVR heat exchanger (X95) before reaching the fluid supply ducts (51, 52) leading to the HT chambers (1, 2). They are preferably arranged along the distribution system in the following order:

[0060] The condensed water (8w) produced in the first heat pump heat exchanger (X78) flowing into the condensing heat exchanger (X8w5) has the lowest temperature of all the hot fluids. Consequently, if present, the condensing heat exchanger (X8w5) is preferably located most upstream in the distribution system (5).

[0061] The low boiling point fluid flowing through the heat pump (8) passes through the fluid heat exchanger (X85) at a lower temperature than when it passes through the second heat pump heat exchanger (X89), which may be between 120°C and 180°C. The fluid heat exchanger (X85), if present, can therefore safely be placed downstream of the condensing heat exchanger (X8w5), since the low boiling point fluid still carries sufficient heat.

[0062] The preheating heat exchanger (X75) is generally located upstream of the first heat pump heat exchanger (X78). Therefore, the temperature of the exhaust fluid flowing through the preheating heat exchanger (X75) is higher than the temperature of the exhaust fluid flowing through the first heat pump heat exchanger (X78). Depending on whether the temperature of the exhaust fluid in the first heat pump heat exchanger (X78) is higher or lower than the temperature of the low-boiling-point fluid flowing through the fluid heat exchanger (X85), the preheating heat exchanger (X75) is preferably located downstream or upstream of the first heat pump heat exchanger (X78). In the example of FIG. 5, the fluid heat pump (X85) is located downstream of the preheating heat pump (X75), suggesting that the temperature of the exhaust gas flowing through the preheating heat exchanger (X75) is lower than the temperature of the low-boiling-point fluid flowing through the fluid heat exchanger (X85).

[0063] The temperature of the heating fluid in the MVR distribution heating loop (95) is very high, around 120°C to 260°C, so the second MVR heat exchanger can be placed as far downstream in the distribution system as possible, before it reaches the fluid supply ducts (51, 52...5N).

[0064] Heat transfer As mentioned above, in the distribution system (5), the fluid can be preheated before being distributed to at least the HT chamber, and preferably also before reaching the LT chamber, via a fluid supply duct (51, 52...5N) with several heat exchangers, which can include any one of the preheating heat exchanger (X75), the second MVR heat exchanger (X95), the fluid heat exchanger (X85), the condensing heat exchanger (X8w5), and any combination thereof (see, for example, Figure 5). This is advantageous in that, on the one hand, the fluid is already warm when it reaches the heating elements (11) in the HT chambers (1, 2) and the MVR heat exchanger (X95N) in the LT chamber, and, on the other hand, if air-fuel burners are used, it is more efficient to supply them with warm air.

[0065] The fluid arriving at the HT chamber is heated to a high temperature by the heating element (11) in the corresponding gas flow cycle. The fluid can reach temperatures between 120°C and 260°C, preferably between 150°C and 250°C, with the maximum temperature being in the middle section of the HT drying zone. The heated fluid is then circulated in the gas flow cycle against the main surface of the panel (60) to raise the panel's temperature and remove moisture from it. During each cycle, a portion of the cooled and moistened fluid is discharged, while the remainder is recirculated and mixed with fresh fluid from the fluid source (5s). Alternatively, the entire fluid is recirculated between various cycles in a closed circuit until it is exhausted and replaced with fresh fluid introduced into the gas flow cycle. These operations can be controlled by valves (5v, 7v). In both cases, the exhaust fluid extracted from the HT chambers (1, 2) is still quite warm. As with previous attempts in the prior art, it is primarily the heat stored in the exhaust fluid that is recovered, but the device of the present invention benefits from it substantially more than prior art devices.

[0066] As shown in Figures 2-6, the device can include a preheating heat exchanger (X75) to transfer part of the heat of the exhaust fluid flowing in the exhaust system (7) directly to the fluid flowing in the distribution system (5). This is a simple and clearly preferred embodiment. However, the preheating heat exchanger (X75) alone is not sufficient to operate without a heating element (11) in the LT chamber (N).

[0067] The gist of the present invention is to transfer heat from the exhaust fluid flowing in the exhaust system (7) to the heat pump / MVR system, thereby making it possible to raise the temperature of the heating fluid in the MVR heat exchanger (X95N) to a value high enough to heat the fluid flowing in the fluid supply duct (5N) directly communicating with the LT chamber (N) to a predetermined temperature, replacing the heating element (11) required in prior art devices (see, for example, FIG. 1). In particular, the MVR heat exchanger (X95N) is located within the fluid in the distribution system (5) immediately upstream of where the fluid penetrates the respective LT chamber (N). If the fluid is a gas (e.g., air) and the fluid supply duct (5N) comprises a gas flow cycle, the MVR heat exchanger (X95N) is located within the gas flow cycle immediately upstream of the inlet leading to the corresponding LT chamber (N). This is achieved by adding the amount of energy (W) required to operate the heat pump compressor (8c) and the MVR compressor (9c), which is a small fraction (=1 / COP) of the heat (Q) thus recovered (note that COP=Q / W can be on the order of 2-6).

[0068] As shown in Figure 7, the heat pump / MVR system requires three heat exchangers.

[0069] the first heat pump heat exchanger (X78) is configured to transfer heat from an exhaust fluid in the exhaust system (7) to a low boiling point fluid in the heat pump (8); The second heat pump heat exchanger (X89) is configured to transfer heat from the high-temperature, high-pressure, low-boiling-point fluid to the low-temperature, low-pressure heating fluid of the MVR cycle (9); The MVR heat exchanger (X95N) is configured to transfer heat from the heated fluid of the high-temperature, high-pressure MVR cycle (9) to a fluid in a distribution system (5) that is in direct fluid communication with one or more LT chambers (N) in the low-temperature drying zone (LT). In particular, the MVR heat exchanger (X95N) can be coupled to the distribution system (5) at the level of the gas flow cycle in the LT chamber (see Figures 2 to 6).

[0070] First heat pump heat exchanger (X78) The low-boiling-point fluid flowing through the heat pump (8) becomes a gaseous state at low temperature and pressure when it enters heat transfer contact with the exhaust fluid in the first heat pump heat exchanger (X78). When the low-boiling-point fluid exits the first heat pump heat exchanger (X78), it has a higher temperature and maintains a low pressure from the heat collected from the exhaust fluid. The pressure and temperature increase as it passes through the heat pump compressor (8c) and reaches the second heat pump heat exchanger (X89) at a higher temperature and pressure. When the low-boiling-point fluid exits the second heat pump heat exchanger (X89), it is at a lower temperature and higher pressure due to the heat released to the heating fluid, and some of it may be condensed. The low-boiling-point fluid then expands through an expansion device (8e) shown in Figure 7 (not shown in Figures 2-6 for clarity) before being reintroduced into the first heat pump heat exchanger (X78) at a lower temperature and pressure.

[0071] Second heat pump heat exchanger (X89) The heating fluid flowing through the MVR cycle (9) becomes at least partially gaseous at low temperature and pressure as it enters heat transfer contact with a low-boiling-point fluid (high temperature and high pressure) in the second heat pump heat exchanger (X89). When the heating fluid exits the second heat pump heat exchanger (X89), it has a higher temperature and maintains a low pressure. The pressure and temperature increase as it passes through the MVR compressor (9c) and reaches the MVR heat exchanger (X95N) at a higher temperature and pressure. When the heating fluid exits the MVR heat exchanger (X95N), it is at a low temperature and high pressure, and some of it may be condensed. The condensate (typically water) is vaporized by passing the heating fluid through an expansion device (9e), as shown in Figure 7 (not shown in Figures 2-6 for clarity).

[0072] MVR heat exchanger (X95N) The gaseous heating fluid pushed out by the MVR compressor (9c) reaches the MVR heat exchanger at a higher temperature and pressure and transfers heat to the fluid flowing in the distribution system (5) which is in direct communication with the LT chamber (N).

[0073] In a preferred embodiment in which the fluid is gas, preferably air, the MVR heat exchanger (X95N) is positioned within the gas flow cycle of the LT chamber (N) at the corresponding location of the heating element (11) in the HT chamber (1, 2), i.e., downstream of the corresponding chamber fan (Nf) and upstream of where the fluid is introduced into the LT chamber (N). The heated fluid in the MVR heat exchanger (X95N) can have a temperature between 120 and 260 °C, which is quite sufficient to ensure a temperature of the fluid in the LT chamber (N) between 90 and 170 °C without the need for an additional heating element (11). As long as the COP of the heat pump / MVR system is greater than 1 (i.e., COP > 1), the use of the MVR heat exchanger (X95N) is advantageous over the use of a heating element (11), such as an air-fuel burner or electric heater, to heat the LT chamber (N). A COP > 1 is very easy to obtain for those skilled in the art with commercially available heat pumps (8) and MVR cycles (9).

[0074] Methods for drying building panels The present invention also relates to a method for drying building panels using the above-described apparatus. After being formed and cut into panels, the still-wet building panels (60) are extruded sequentially along a drying path through the chambers (1, 2) of the HT drying zone, followed by the chambers (N) of the LT drying zone. As the building panels move through the chambers (1, 2...N), a fluid, preferably a gas such as air, flows through a distribution system (5) into each of the N chambers (1, 2...N) and onto the major surface of the building panel. Before the fluid reaches the major surface of the building panel in the HT chambers (1, 2), the fluid is heated to a desired temperature by heating elements (11). The exhaust fluid is then removed from each of the N chambers via an exhaust system (7).

[0075] At least during steady-state drying operations, the fluid blown into the LT chamber (N) is heated exclusively using heat recovered from the exhaust fluid by exchanging heat in a first heat pump heat exchanger (X78) from the exhaust fluid in the exhaust system (7) to a low boiling point fluid in the heat pump (8), and after compression of the low boiling point fluid, exchanging heat in a second heat pump heat exchanger (X89) from the thus compressed low boiling point fluid to a heating fluid in the MVR cycle (9), and after compression of the heating fluid, exchanging heat in an MVR heat exchanger (X95N) from the thus compressed heating fluid to a fluid in the distribution system (5) that is in direct fluid communication with one or more LT chambers (N). This is achieved by:

[0076] This method produces the same quality of drying as prior art dryers, but consumes significantly less energy. Table 1 compares the performance of the prior art dryer according to Figure 1 with that of the inventive dryer according to Figure 2, which has the same components and the same temperature in the chamber. In both cases, the fluid is air, and the heating element (11) is an air-fuel burner. The inventive dryer includes a heat pump / MVR system not included in the prior art dryer. While the prior art dryer includes an air-fuel burner in the LT chamber, the inventive dryer relies solely on the MVR heat exchanger (X95N) to heat the air entering the LT chamber. Values ​​are nominal values, calculated and not measured. For the components selected for this simulation, the COP of the device in Figure 2, the heat pump / MVR system was 4.

[0077] [Table 1]

[0078] It can be seen that without the air-fuel burner in the LT chamber (N), the dryer of the present invention consumes 30% less natural gas! Of course, the heat pump compressor (8c) and MVR compressor (9c) consume power, but as long as the heat pump / MVR system has a COP>1, the total power consumption will be lower. In this example, with a COP=4 for the heat pump / MVR system, the dryer of the present invention consumes 23% less energy than the prior art dryer. In an era of increasing energy costs, this is a dramatic reduction.

[0079] Due to the lower consumption of natural gas due to the fewer number of air-fuel burners, CO2 emissions are reduced by approximately 30%. With global warming, significantly reducing CO2 emissions was a priority for the inventors. The amount of condensate recovered from the various heat exchangers is an indirect indicator of the effectiveness of heat transfer from the exhaust fluid (air) to the fluid (air) in direct communication with the LT chamber. From Table 1, it can be seen that more than three times the amount of condensate was recovered from the dryer of the present invention compared to the prior art dryer, indicating the superior level of heat transfer thus achieved.

[0080] The dryer of the present invention substantially reduces the energy requirements for drying wet building panels 60, with much lower CO2 emissions for similar results.

[0081] The building panels are cement board, calcium silicate board, fiber cement board, and preferably gypsum board. Ref# Feature 1, 2...N 1st, 2nd, ... Nth chamber 1, 2 High Temperature (HT) Chamber N Low Temperature (LT) Chamber Fans in the distribution system of the Nf LT drying zone 5 Distribution System 51, 52...5N Fluid supply duct 5f Fans in the distribution system 5s fluid source 5v distribution system valve 7. Exhaust system 7f Fan in the exhaust system 7h LT Return exhaust duct of the exhaust system leading to the drying zone 7v exhaust system valve 8. Heat Pump 8c Heat pump compressor 8e Inflatable Device 8w Condensate in the first heat pump heat exchanger (X78) 9 MVR cycles 9c MVR compressor 9g Fuel supply to fuel air burner 11 Fuel-air burner 11s Shutdown Burner 50 Preheating branch of distribution system 51, 52...5N Fluid supply ducts leading to chambers 1, 2...N Post-heated branching of 5(N+1) distribution system 51x, 52x: branches of the distribution system supplying the burners 11 of the first and second chambers 60 Building Panels 71, 72...7N Branches of the exhaust system leading from chambers 1, 2...N 95 MVR distribution heating loop High temperature zone including HT hT chambers (1, 2) LT Low temperature zone including LT chamber (N) MVR Mechanical Vapor Recompression TiH, i=1~N Maximum temperature in the chamber TiL, i=1~N Minimum temperature in the chamber X75 Preheating heat exchanger from exhaust system (7) to distribution system (5) X78 First heat pump heat exchanger from the exhaust system (7) to the heat pump (8) X7N LT heat exchanger shared from exhaust branch (7h) to fluid distribution in LT drying zone chamber (N) X85 Fluid heat exchanger from heat pump (8) to distribution system (5) X89 Second heat pump heat exchanger from heat pump (8) to MVR cycle (9) Condensation heat exchanger for condensate water from X8w5 X78 to distribution system X95 Second MVR heat exchanger for fluids flowing from the MVR cycle (9) to the distribution system (5) X95N MVR heat exchanger for fluid flowing from the MVR cycle (9) to the fluid supply duct (5N)

Claims

1. A device for drying building panels, - A conveyor (40) is provided for transporting the wet building panels (60) through the drying unit and along the drying path, and the drying unit is - A high-temperature chamber (1, 2) (=HT: high-temperature chamber) located in the high-temperature drying zone (HT) upstream of the drying path, and one or more low-temperature chambers (N) (=LT: low-temperature chamber) located in the low-temperature drying zone (LT) downstream of the high-temperature drying zone (HT) along the drying path, comprising N chambers (1, 2...N) distributed in series along the drying path and in fluid communication with one another, A distribution system (5) is configured to have fluid communication with a fluid source (5s) at one end and with the N chambers (1, 2...N) at the other end, and to circulate the fluid flow along a fluid channel extending from the fluid source into the N chambers, - A heating element (11) configured to heat the fluid in the distribution system (5) before it permeates into each of the HT chambers (1, 2), - An exhaust system (7) configured to discharge exhaust fluid from the apparatus along an exhaust passage extending from the N chambers (1, 2, ..., N) to the outside of the apparatus, and Equipped with, - It comprises a first heat pump heat exchanger (X78) configured to transfer heat from the exhaust fluid flowing within the exhaust system (7) to the low-boiling point fluid of the heat pump (8), - The heat pump (8) includes a heat pump compressor (8c) configured to compress the low-boiling-point fluid to raise its temperature and push the flow of the low-boiling-point fluid from the first heat pump heat exchanger (X78) to the second heat pump heat exchanger (X89), and the second heat pump heat exchanger (X89) is configured to transfer the heat thus taken in by the low-boiling-point fluid to a heating fluid having a higher boiling point than the low-boiling-point fluid in the heat pump (8). - The heating fluid is configured to circulate within a mechanical vapor recompression (MVR) cycle (9) which includes an MVR compressor (9c) configured to compress the heating fluid and thus increase the temperature of the heating fluid, and to push the flow of the heating fluid from the second heat pump heat exchanger (X89) to the MVR heat exchanger (X95N), - The MVR heat exchanger (X95N) is configured to transfer heat from the heated fluid of the MVR cycle (9) to the fluid in the distribution system (5) immediately before it penetrates into each of the LT chambers (N). An apparatus characterized by the following features.

2. The apparatus according to claim 1, wherein the heat pump / MVR system comprising the heat pump (8) and the MVR cycle (9) is characterized by a coefficient of performance (COP) that is between 2 and 5, preferably between 2.5 and 4, wherein the COP is defined as the ratio (Q / W) of useful heat (Q) supplied by the heat transfer combination to the work (W) required to operate the heat pump compressor (8c) and the MVR compressor (9c).

3. The apparatus according to claim 2, comprising a preheating heat exchanger (X75) configured to transfer heat from the exhaust fluid in the exhaust system (7) to the fluid in the distribution system (5) in order to raise the temperature of the fluid flowing in the distribution system (5), wherein the preheating heat exchanger (X75) is preferably located in the exhaust system (7) upstream of the first heat pump heat exchanger (X78), and upstream is defined with respect to the flow direction of the exhaust fluid in the exhaust system (7).

4. - The heating element (11) is an air fuel burner, - The fluid source (5s) is an air source, and a portion of the air flowing through the distribution system (5) is supplied to the air fuel burner. The apparatus according to claim 1.

5. - The heating element (11) is an air fuel burner, - The fluid source (5s) is an air source, and a portion of the air flowing through the distribution system (5) is supplied to the air fuel burner. The apparatus according to claim 2.

6. The apparatus according to claim 1, wherein the heating element (11) is an electric heater.

7. The apparatus according to claim 2, wherein the heating element (11) is an electric heater.

8. - The fluid source is a gas source, preferably an air source. - The distribution system (5) includes a distribution fan (5f) configured to push the gas flow from the gas source toward the N chambers (1, 2...N), - The HT chamber is equipped with chamber fans (1f, 2f) configured to push out the gas flow cycle that flows through the heating element (11) into the corresponding HT chambers (1, 2) and out of the gas flow cycle into the exhaust system (7), The LT chamber is equipped with a chamber fan (Nf) configured to push out the gas flow cycle that flows through the MVR heat exchanger (X95N) into the corresponding LT chamber (N) and out of the gas flow cycle into the exhaust system (7). The apparatus according to any one of claims 1 to 7.

9. - The temperature (T1, T2) inside the HT chambers (1, 2) changes between 120°C and 260°C, preferably between 150°C and 250°C, and is the maximum temperature of the intermediate section of the HT drying zone, and / or - The temperature (TN) in one or more LT chambers (N) has an average value lower than the average temperature in the HT chamber, varies between 90°C and 170°C, preferably between 100°C and 160°C, and is the maximum temperature in the upstream section of the LT drying zone, with the upstream being defined with respect to the direction of the drying path. The apparatus according to any one of claims 1 to 7.

10. The apparatus according to claim 1, wherein the temperature of the low-boiling point fluid in the heat pump (8) within the second heat pump heat exchanger (X89) is between 90°C and 110°C, and preferably equal to 100°C ± 5°C.

11. The apparatus according to claim 8, wherein the temperature of the fluid in the MVR cycle (9) within the MVR heat exchanger (X95N) is between 120°C and 180°C, preferably between 135°C and 170°C, and preferably equal to 150°C ± 10°C.

12. The apparatus according to any one of claims 1 to 7, comprising an MVR distribution system heating loop (95) that branches off from the MVR cycle (9) downstream of the MVR compressor (9c), passes through a second MVR heat exchanger (X95) configured to transfer heat from the heated fluid in the MVR cycle (9) to the fluid in the distribution system (5), and then returns to and rejoins the MVR cycle (9) upstream of the MVR compressor (9c).

13. The apparatus according to any one of claims 1 to 7, further comprising a fluid heat exchanger (X85) configured to transfer heat from the low-boiling point fluid of the heat pump (8) to the fluid of the distribution system (5).

14. The apparatus according to any one of claims 1 to 7, wherein the exhaust system (7) comprises a return exhaust duct (7h) leading to a corresponding LT heat exchanger (X7N) configured to transfer heat from the exhaust fluid in the exhaust system (7) to the LT chamber (N), and the LT heat exchanger (X7N) is preferably positioned upstream of the first heat pump heat exchanger (X78) with respect to the flow direction of the exhaust fluid in the exhaust system (7).

15. The apparatus according to any one of claims 1 to 7, wherein the fluid source is a gas source, the exhaust system (7) includes a return exhaust duct (7h) that fluidly communicates and connects with the distribution system adjacent to the MVR heat exchanger (X95N) upstream of the MVR heat exchanger (X95N), the exhaust gas is mixed with the fluid from the distribution system (5) and flows into the LT chamber (N), passes through the MVR heat exchanger (X95N), and flows out from the LT chamber (N), and the fluid exhaust duct (7h) is provided with a valve (7v) to control the ratio of the amount of exhaust fluid to the amount of fluid.

16. A method for drying building panels, - To provide the apparatus according to any one of claims 1 to 7, - The wet building panels (60) are pushed out along the drying path, passing through the chambers (1, 2) of the HT drying zone and then through the chamber (N) of the LT drying zone. - The fluid is to be flowed through the distribution system (5) into each of the N chambers (1, 2...N), - Before permeating into the HT chambers (1, 2), the fluid is heated to a desired temperature by the heating element (11), - To exhaust the exhaust fluid from each of the N chambers via the fluid exhaust system (7) Includes, - In the first heat pump heat exchanger (X78), after the compression of the low-boiling-point fluid, heat is exchanged from the exhaust fluid in the exhaust system (7) to the low-boiling-point fluid in the heat pump (8). - In the second heat pump heat exchanger (X89), after the heating fluid is compressed, heat is exchanged from the thus compressed low-boiling point fluid to the heating fluid in the MVR cycle (9). - Within the MVR heat exchanger (X95N), heat is exchanged from the compressed heating fluid in this manner to the fluid in the distribution system (5) which is in direct fluid communication with one or more LT chambers (N) in the low-temperature drying zone (LT). A method characterized by the following features.

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