Low-consumption apparatus and method for drying building panels

Abstract

Low-consumption apparatus and method for drying building panels The invention comprises a conveyor (40) for conveying 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) comprising a LT distribution section configured to distribute heated drying gas into the LT chambers and remove moisture from them as they move through the chambers, connected in series by a connecting duct (5L) to the HT distribution section configured to distribute heated drying gas into the HT chambers and to heat the main surfaces of the building panels in this way, and a gas distribution system (5) extending from the HT chambers (1, 2) to the outside of the device. and an exhaust system (7) configured to discharge exhaust fluid from the apparatus along an exhaust flow path, wherein the fluid entering the HT chamber is heated by a heating element (11), and the fluid entering the LT chamber is heated by an LT heat exchanger (X95N) heated by the exhaust gas, and the heat pump / MVR system includes a heat pump (8) that transfers heat from the exhaust fluid to an MVR cycle, which transfers heat to the drying gas in a connecting duct (5L) that preheats the drying gas before it reaches the heating element (11).

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 warm dry gas, usually air, onto both major surfaces of the panel as it passes through N chambers to increase the panel's 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 usually 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 a low-temperature (LT) chamber (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, comprising a conveyor for transporting wet building panels along a drying path through N chambers distributed in series and in fluid communication with one another along the drying path. The dryer comprises one or more high temperature chambers (=HT chambers) arranged in a high temperature drying zone (HT) in the upstream part of the drying path, and one or more low temperature chambers (=LT chambers) arranged in a low temperature drying zone (LT) downstream of the high temperature drying zone (HT) along the drying path.

[0010] The distribution system is in fluid communication with a dry gas source, preferably an air source, at one end and with the N chambers at the other end. The distribution system is configured to circulate a flow of dry gas along dry gas flow paths extending from the dry gas source into the N chambers. A heating element is provided and configured to heat the dry gas in the distribution system (5) before it penetrates each of the HT chambers.

[0011] The exhaust system is configured to discharge exhaust gases from the apparatus along an exhaust flow path extending from the HT chambers through corresponding LT heat exchangers (X75N) provided in the LT chambers and through return exhaust ducts leading to the outside of the apparatus. An LT heat exchanger (X75N) is provided in each LT chamber and configured to transfer heat from the exhaust gases flowing in the corresponding return exhaust ducts to the drying gas as it flows through the corresponding LT chamber.

[0012] the distribution system comprises an LT distribution section for distributing the drying gas into the LT chamber and an HT distribution section for distributing the drying gas into the HT chamber, the LT distribution section and the HT distribution section being connected in series downstream of the LT distribution section by a connecting duct; The LT distribution section comprises one or more dry gas supply ducts leading in parallel to one or more corresponding LT chambers; The HT distribution section comprises one or more dry gas supply ducts leading in parallel to one or more corresponding HT chambers.

[0013] The apparatus includes a first heat pump heat exchanger (X78) configured to transfer heat from exhaust gas flowing in the exhaust system to a low boiling point gas in 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 flow of the low boiling point fluid from the first heat pump heat exchanger (X78) to a second heat pump heat exchanger (X89).

[0014] 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 having a boiling point higher than the low boiling point fluid of the heat pump, and configured to circulate in a mechanical vapor recompression (MVR) cycle comprising an MVR compressor configured to compress the heating fluid, thus increasing its temperature, and push the flow of heating fluid from the second heat pump heat exchanger (X89) to the MVR heat exchanger (X95L), which is configured to transfer heat from the heating fluid of the MVR cycle to dry gas in the distribution system downstream of the LT distribution section and upstream of the HT distribution section.

[0015] The heat pump and MVR cycle together form a heat pump / MVR system characterized by a coefficient of performance (COP) preferably comprised between 2 and 5, preferably between 2.5 and 4. The COP 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.

[0016] In a preferred embodiment, the dryer includes a preheating heat exchanger (X75) configured to transfer heat from the exhaust gas in the exhaust system to the drying gas in the distribution system in order to increase the temperature of the drying gas flowing in the distribution system before it reaches the LT chamber. in the distribution system (5) upstream of the LT distribution section, and in the exhaust system (7) downstream of the LT heat exchanger (X75N) and preferably upstream of the first heat pump heat exchanger (X78); and "upstream" and "downstream" are defined herein relative to the direction of fluid flow within the corresponding distribution or exhaust system.

[0017] When the heating element is an air-fuel burner, the drying gas source is preferably an air source, and a portion of the air flowing through the distribution system is supplied to the air-fuel burner. Alternatively, the heating element may be an electric heater or a high-temperature fluid heat exchanger.

[0018] The distribution system can include a distribution fan configured to push a flow of dry gas from the dry gas source toward the N chambers. The HT chambers preferably include a chamber fan configured to push the dry gas flow cycle through the heating element into the corresponding HT chamber and back to the heating element for the next cycle or out of the dry gas flow cycle to an exhaust system. The fan is configured to push the dry gas flow through the LT chamber between the radiant surface of the LT heat exchanger (X75N) that collects heat and the major surface of the building panel that transfers heat to and collects moisture from them, through the LT chamber into the connecting duct, and through the MVR heat exchanger (X951) before reaching the HT distribution section.

[0019] The temperature in the HT chamber can vary, for example, between 120°C and 260°C, preferably between 150°C and 250°C. The temperature in one or more LT chambers has a lower average value than the average temperature in the HT chamber and can vary between 90°C and 170°C, preferably between 100°C and 160°C. The temperature of the low-boiling-point fluid of the heat pump in the second heat pump heat exchanger (X89) can be between 90°C and 110°C, preferably equal to 100°C ± 5°C. The temperature of the heating fluid of the MVR cycle (9) in the MVR heat exchanger (X95L) can be between 120°C and 180°C, preferably between 135°C and 170°C, preferably equal to 150°C ± 10°C. The heating fluid in the MVR cycle is preferably water / steam.

[0020] The heat pump / MVR system may include additional heat exchangers to increase the temperature of the dry gas in the distribution system. In one embodiment, the MVR cycle includes an MVR distribution system heating loop that branches off from the MVR cycle downstream of the MVR compressor and passes through a second MVR heat exchanger (X95b) configured to transfer heat from a heating fluid in the MVR distribution system heating loop to the dry gas in the distribution system before joining back into the MVR cycle upstream of the MVR compressor. A gas heat exchanger (X85) may be provided and configured to transfer heat from the low boiling point fluid of the heat pump to the dry gas in the distribution system.

[0021] In one embodiment, a branch duct branches off from the return exhaust duct and is configured to mix the exhaust gas with the dry gas from the LT distribution section and allow the exhaust gas to flow into and out of the LT chamber, and the branch duct and the exhaust duct are provided with valves to control the ratio of the amount of exhaust gas from the exhaust system to the amount of dry gas from the LT distribution section flowing into the LT chamber.

[0022] 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 dry gas through a distribution system into each of the N chambers; Heating the drying gas to a desired temperature using a heating element before infiltrating the HT chamber; exhausting exhaust gases from each of the N chambers via an exhaust system; a method for drying a building panel, comprising: Heat is exchanged in a first heat pump heat exchanger (X78) from the exhaust gas in the exhaust system to the low boiling point fluid in the heat pump after compression of the low boiling point fluid; After compression of the heating fluid, heat is exchanged in the second heat pump heat exchanger (X89) from the thus compressed low boiling point fluid to the heating fluid in the MVR cycle; · Heat is exchanged in the MVR heat exchanger (X95L) from the heated fluid thus compressed to the dry gas in the distribution system exiting from the LT distribution section, before the dry gas is heated by a heating element before penetrating the respective HT chamber.

[0023] The building panel may be a panel made of a material containing gypsum, or cement, or calcium silicate as a main component in an amount of at least 50% by weight.

[0024] 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]

[0025] [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. 10 illustrates a further alternative embodiment of the present invention. [Figure 8] FIG. 1 shows an example of a heat pump coupled to an MVR cycle according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] 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, calcium silicate, or fiber cement 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 heated drying gas to each chamber, with heating elements (11) provided to heat the drying gas in the distribution system before it reaches the chamber. An exhaust system (7) is provided to discharge exhaust gas from the chambers.

[0027] 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 drying gas. 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 drying gas, typically hot air.

[0028] 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.

[0029] The distribution system (5) is in fluid communication with a drying gas 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 flow of drying gas along a drying gas flow path extending from the drying gas source into the N chambers. A heating element (11) configured to heat the drying gas in the distribution system (5) is disposed within the distribution system (5) before the drying gas penetrates each of the 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 the shutdown burner (11s) in Figures 3-6). The distribution system (5) includes an LT distribution section for distributing drying gas into the LT chamber (N) and an HT distribution section coupled in series downstream of the LT distribution section for distributing drying gas into the HT chambers (1, 2).

[0030] The LT distribution section includes one or more dry gas supply ducts (5N) connected in parallel to one or more corresponding LT chambers (N). The HT distribution section includes one or more dry gas supply ducts (51, 52) connected in parallel to one or more corresponding HT chambers (1, 2).

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

[0032] The exhaust system (7) includes return exhaust ducts (7h) connected in parallel to the corresponding LT chambers. An LT heat exchanger (X75N) is provided in each LT chamber (N) and configured to transfer heat from the exhaust gas flowing in the corresponding return exhaust duct (7h) to the drying gas as it flows through the corresponding LT chamber (N).

[0033] The gist of the present invention is to provide a heat pump / MVR system comprising a heat pump (8) and an MVR cycle (9). The "heat pump / MVR system" recovers heat from exhaust gas flowing through an exhaust system (7) to substantially increase the temperature of dry gas flowing through a distribution system (5) before the dry gas reaches the dry gas supply ducts (51, 52) of the HT distribution section. 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, X95L) for efficiently transferring thermal energy from the exhaust gas to the dry gas in the HT distribution section of the distribution system (5). Specifically, the MVR heat exchangers (X95L) are configured to transfer heat from the heating fluid of the MVR cycle (9) to the dry gas in the distribution system (5) after the dry gas exits the LT distribution section and flows toward or through the HT distribution section, before penetrating the respective HT chambers (1, 2).

[0034] The MVR heat exchangers (X95L) downstream of the LT distribution section and upstream of the HT chambers (1, 2) increase the temperature of the drying gas flowing in the distribution system (5) towards the HT chambers (1, 2) before it reaches the corresponding heating elements (11). This has the effect that less energy must be supplied by the heating elements (11) to heat the drying gas to the desired temperatures (T1, T2) required in the HT chambers (1, 2). The exhaust gases exiting the HT chambers in the exhaust system (7) still retain significant heat, which is used to heat the drying gas flowing in the LT chambers (N) as follows:

[0035] The first heat pump heat exchanger (X78) is configured to transfer heat from the exhaust gas in the exhaust system (7) to a low-boiling-point fluid in the heat pump (8). The heat pump (8) includes 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 low-boiling-point fluid through the closed-loop duct from the first heat pump heat exchanger (X78) to the second heat pump heat exchanger (X89). The LT heat exchanger (X75N) is preferably located upstream of the first heat pump heat exchanger (X78) with respect to the flow direction of the exhaust gas in the exhaust system (7).

[0036] 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 the MVR heat exchanger (X95L).

[0037] The MVR heat exchanger (X95L) is configured to transfer heat from the heating fluid of the MVR cycle (9) to the drying gas in the distribution system (5) downstream of the LT distribution section and upstream of the HT distribution section. The MVR heat exchanger (X95L) is configured to transfer significant heat to the drying gas flowing toward the HT chambers (1, 2), which is beneficial because it allows the use of heating elements (11) with smaller dimensions and power to heat the already warm drying gas to the desired temperature required in the HT chambers (1, 2). Tests have shown that the temperature of the drying gas arriving at the inlet of the heating element (11) of the HT chamber in a dryer according to the present invention, equipped with the above-defined MVR heat exchanger (X95L), as shown in Figure 1, is 30 to 40°C higher than in a prior art dryer without an MVR heat exchanger (X95L). For example, if the required temperature of the drying gas in the first chamber (1) is T1=260°C and the temperature of the drying gas reaching the corresponding heating element (11) is 110°C without the MVR heat exchanger and 140°C with the MVR heat exchanger (X95L), then the heat that must be transferred to the air to reach the set temperature of 260°C is 20% less than without the MVR heat exchanger.

[0038] Heat can be transferred from the drying gas to the building panel by at least forced convection of the drying gas and also by radiation. In this embodiment, the drying gas is preferably air, which flows in contact over the two main surfaces of the building panel (60) immediately after being heated to a corresponding predetermined temperature by the heating elements (11) in the HT chambers (1, 3) and the LT heat exchanger (X75N) in the LT chamber (N).

[0039] Distribution systems (5) and exhaust systems (7) The distribution system includes ducts configured to circulate a flow of dry gas from a dry gas source (5s) along a dry gas flow path extending into the N chambers. The circulating dry gas is preferably air, which, after heating to a desired temperature, is blown onto the two major surfaces of the panels as they move through successive chambers. Thus, heat is transferred from the dry gas to the major surfaces of the panels by forced convection, and moisture is removed from the panels.

[0040] The distribution system has an upstream end coupled to a dry gas source (5s). When the dry gas is air, the air source can be ambient air at room temperature. A blower or fan (5f) is provided to drive the dry gas from the dry gas source (5s) through the distribution system (5). The distribution system (5) is divided into an HT distribution section for distributing the dry gas into the HT chambers (1, 2) and an LT distribution section for distributing the dry gas into the LT chambers (N) coupled in series downstream of the LT distribution section. The LT distribution section includes one or more dry gas supply ducts (5N) connected in parallel to the corresponding one or more LT chambers (N). Similarly, the HT distribution section includes one or more dry gas supply ducts (51, 52) connected in parallel to the corresponding one or more HT chambers (1, 2).

[0041] The LT distribution section includes j dry gas supply ducts (N) connected in parallel to j corresponding LT chambers (N), and the HT distribution section includes i dry gas supply ducts (51, 52) connected in parallel to i corresponding (=(Nj)) LT chambers (1, 2). A communication duct (5L) connects the LT distribution section to the HT distribution section in series. An MVR heat exchanger (X95L) is disposed on the communication duct (5L) between the LT distribution section and the HT distribution section.

[0042] The dry gas supply duct (5N) of the LT distribution section connects immediately downstream of each LT chamber (N) and allows dry gas to flow countercurrently to the drying path of the building panels (60) in heat exchange contact with the LT heat exchanger (X75N). As shown in Figures 2-7, the dry gas can be preheated in a preheating heat exchanger (X75) between the exhaust system (7) upstream of the LT chamber (N) and the distribution system. After reaching the upstream end of the corresponding LT chamber (N) (upstream of the drying path), the dry gas exits the LT chamber and merges with the connecting duct (5L) and the MVR heat exchanger (X95L) to acquire some heat from the heat pump / MVR system before reaching the HT distribution section.

[0043] In contrast to the dry gas supply duct (N) of the LT distribution section, when the dry gas supply ducts (51, 52) of the HT distribution section reach the corresponding HT chambers (1, 2), they form a dry gas flow cycle, each equipped with a chamber fan (1f, 2f) for pushing a dry gas flow (e.g., air) along the dry gas flow cycle. The dry gas flow cycle in the HT chamber is configured to flow dry 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 raise their temperature and remove most of the moisture therefrom.

[0044] In the HT distribution system, all or a portion of the drying gas (e.g., air) can be cycled one or more times from the chamber to the heating element (11) until its moisture content is deemed too high, at which point it can be pushed out of the drying 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 the drying gas (e.g., air) introduced into and exhausted from the drying 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 can be equipped with a shutdown burner (11s) (shown dotted in the diagram) 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 empty HT chamber is turned off. At the end of the drying run, 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 drying gas flowing into the LT chamber (N) to the required 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 drying gas flowing into the LT chamber (N) during steady-state drying runs with only a small portion of their total heating capacity, such as 25% or less, preferably 10% or less, of the shutdown burners' (11s) total heating capacity. However, it is preferable that no heating elements are used to heat the LT chamber during steady-state use of the apparatus. The apparatus may comprise a processing unit configured to control that the shutdown burners (11s) remain off or at only a fraction (e.g., 25% or less, or 10% or less) of their total heating capacity during steady-state use of the apparatus, and that the drying gas entering the LT distribution section and the LT chamber is heated exclusively by heat exchangers, including a preheating heat exchanger (X75) upstream of the LT chamber (N) relative to the drying gas flow direction in the distribution system (5).

[0045] The dry gas flows into the corresponding HT chambers (1, 2) several times along the dry gas flow cycle. Once it has removed enough moisture from the building panels (60) to reach a high moisture content, it is exhausted from the cycle through the exhaust system (7). The exhaust gas still retains significant heat. For example, the temperature of the exhaust gas outside the HT chambers can be around 170°C to 200°C, typically 180°C ± 10°C. Each HT chamber has exhaust gas ducts (71, 72) that exit the corresponding dry gas flow cycle and all join within a central exhaust duct that leads to a return duct (7h). Each return duct (7h) joins the corresponding LT heat exchanger (X75N) of the corresponding LT chamber (N). After exiting the LT heat exchanger (X75N), the exhaust gas preferably flows through a preheating heating element (X75) to preheat the dry gas entering the distribution system (5) before entering the LT chamber (N). The gist of the present invention is that at this stage, instead of releasing the exhaust gas into the atmosphere, the exhaust gas flows through a first heat pump heat exchanger (X78), where it releases a portion of its thermal energy to the low-boiling-point fluid of the heat pump (8). At this stage, a significant amount of condensed water (8w) is formed by condensation of the cooling-high-water-content exhaust gas. The condensed water (8w) can be used to form new building plates. Before being added to the base composition, the heat retained in the condensed water (8w) is preferably pushed through a condensation heat exchanger (X8w5) to heat the dry gas flowing directly from the dry gas source (5s) before reaching either the preheating heat exchanger (X75) or the LT heat exchanger (X75N).

[0046] As shown in Figures 2, 3, and 7, the valve (7v) precisely controls the amount of exhaust gas introduced from the return exhaust duct (7h) into the LT heat exchanger (X75N), thereby controlling the temperature transferred to the drying gas in the LT heat exchanger (X75N). In the embodiment shown in Figure 7, the return exhaust ducts (7h) are fluidly connected to the distribution system (5) upstream of the entry point of each corresponding LT chamber (N) and include branch ducts (7h5) configured to mix the exhaust gas with fluid from the distribution system (5) and enter the LT chamber (N). The drying gas exhaust duct (7h) and branch duct (7h5) are provided with valves (7v) to control the ratio of the amount of exhaust gas to the amount of drying gas. This is important because the exhaust gas contains a significant amount of moisture, and a careful balance of the moisture content of the resulting gas mixture sprayed against the building boards traveling through the LT chamber (N) is necessary to optimize the drying operation of the boards. The valves (5v, 7v) of the distribution system (5) and the exhaust system (7) can be controlled by a processor, which is preferably configured to control the flow rate in a closed loop via control of the fans (1f, 2f, 5f, 7f) and valves (5v, 7v) depending on the temperature of the drying gas flowing through the corresponding chambers (1, 2...N).

[0047] When the drying gas is air, the heating element (11) is preferably an air-fuel burner supplied with a portion of the air flowing through the drying gas 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-fuel 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 high-temperature fluid, such as hot oil, to raise the temperature of the drying gas. In these cases, the drying gas can be any gas, but air is readily available and is preferred.

[0048] To increase the temperature of the dry gas flowing in the distribution system (5) before it reaches the LT chamber (N), the dry gas is preferably preheated in a preheating heat exchanger (X75) configured to transfer heat from the exhaust fluid in the exhaust system (7) to the dry gas in the distribution system (5). The preheating heat exchanger (X75) is preferably located upstream of the LT chamber (N) with respect to the flow direction in the distribution system (5) and preferably upstream of the first heat pump heat exchanger (X78) with respect to the flow direction in the exhaust system (7).

[0049] Unless otherwise defined, the terms "upstream" and "downstream" are defined herein relative to the direction of fluid flow in the corresponding fluid system, such as the dry gas in the distribution system (5), the exhaust gas in the exhaust system (7), the low boiling point fluid in the heat pump (8), or the heated fluid in the MVR cycle (9).

[0050] Preheating the drying gas before it reaches the LT chamber is advantageous because the only remaining heat source for bringing the drying gas flowing through the corresponding LT chamber (N) to the required temperature is the corresponding LT heat exchanger (X75N). The preheating heat exchanger (X75) can heat the drying gas stream from room temperature to about 100±10°C before it penetrates the corresponding LT chamber (N), and can be further heated to the desired temperature by contact with the LT heat exchanger (X75N), for example, reaching a temperature of about 110±10°C upon exiting the LT chamber.

[0051] The temperature in the LT chamber (N) can be controlled by controlling the dry gas flow rate in the distribution system (5) via the fan (5) in the distribution system and by controlling the temperature of the dry gas flowing through the LT chamber (N). The latter can be achieved by controlling the exhaust gas flow rate in the preheating heat exchanger (X75) and the LT heat exchanger (X75N). The temperature in the HT chamber can be controlled via the heating element (11). Thanks to the heat pump / MVR system, a smaller heating element (11) can be used, and the heat pump / MVR system increases the temperature of the dry gas flowing through the distribution system (5) before it reaches the heating element (11).

[0052] 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), where the high temperatures (T1H, T2H) 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 temperatures (TN) in one or more LT chambers (N) have an average value lower than the average temperature in the HT chambers and can vary between low temperatures (TNL) and high temperatures (TNH), where the high temperatures (TNH) can range from 90°C to 170°C, preferably from 100°C to 160°C, and are the maximum temperature in the upstream section of the LT drying zone, with upstream being defined relative to the direction of the drying path.

[0053] Heat exchanger (X75, X78, X75N) As shown in Figures 2-7, the exhaust system (7) includes gas exhaust ducts (71, 72) for extracting dry gas from the HT chamber when the temperature or moisture content of the dry gas entering the HT chamber along the dry gas flow cycle is deemed to fall outside predetermined boundaries. The gas exhaust ducts (71, 72) are coupled to the corresponding dry gas flow cycle at a location between the chamber fans (1f, 2f) and the heating elements (11) of the HT chambers (1, 2).

[0054] The exhaust gases leaving the HT chamber through the exhaust system (7) are cooler and more humid than the dry gases entering the chamber through the distribution system (5), but still retain a significant amount of heat. The exhaust gases can be at temperatures of the order of 180±20°C, depending on the temperatures (T1, T2) required in the HT chambers (1, 2). The aim of the invention is to recover as much thermal energy as possible from the exhaust gases by means of different heat exchangers (X75, X78, X75N).

[0055] Unlike the HT chambers (1, 2), the drying gas flowing into the LT chambers (N) is not heated by the heating element (11) (at least not during normal operation). Instead, it is heated exclusively by heat transfer from the exhaust gas in the optional preheating heat exchanger (X75) located upstream of the LT chamber (N) relative to the flow direction in the distribution system (5), which then flows through the LT chamber (N) with the LT heat exchanger (X75N). As mentioned above, the LT chamber (N) may be equipped with a shutdown heating element (11s) that is used only during shutdown of the drying operation. This can be controlled by a processor. Each LT heat exchanger (X75N) has channels configured to circulate the exhaust gas, which releases heat to a radiant surface located inside the corresponding LT chamber (N), thereby heating the drying gas flowing through the LT chamber. The drying gas flows through the LT chamber (N) in the opposite direction to the drying path followed by the building panels (60), so that the drying gas enters the LT chamber (N) at its lowest temperature, contacts the substantially completely dried panels, and accumulates heat as it flows through the LT chamber, exiting it at its highest temperature, where the panels have a lower moisture content but are higher than the LT chamber outlet. For example, if the drying gas is preheated in the preheating heat exchanger (X75), it can enter the different LT chambers at a temperature on the order of 100°C ± 10°C and exit the chamber at a higher temperature on the order of 110°C ± 10°C. Heating of the drying gas is moderate because much of the thermal energy obtained from the radiant surface of the LT heat exchanger (X75N) is transferred to the panels (60).

[0056] After flowing through the LT heat exchanger (X75N) and optionally the preheating heat exchanger (X75), the exhaust gas has lost significant heat but is still relatively warm. For example, the exhaust gas may still be at a temperature above 70°C, such as 75-85°C. Releasing the exhaust gas into the atmosphere at such a temperature would be a waste of energy. Some of the thermal energy further carried by the exhaust gas is transferred to the heat pump / MVR system by flowing it through the first heat pump heat exchanger (X78), described below.

[0057] 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 gas flowing in the exhaust system (7) to substantially increase the temperature of the dry gas flowing in the distribution system (5) before it 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 8.

[0058] Heat Pumps(8) As shown in FIG. 8, the heat pump (8) includes a closed circuit for circulating a low-boiling-point fluid pumped by a 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 gas 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 a heated fluid, preferably steam, flowing in the MVR cycle (9) through a 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.

[0059] During heat transfer in the first heat pump heat exchanger (X78), the temperature of the wet exhaust gas decreases, forming condensed water (8w) that has a higher temperature than the dry gas from the dry gas source (5s). To utilize the heat carried by the condensed water (8w), as shown in FIGS. 3-7, the apparatus can include a condensing heat exchanger (X8w5) configured to transfer heat from the condensed water (8w) to the dry gas flowing from the dry gas source (5s) into the distribution system (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) relative to the flow direction in the distribution system (5). In addition to preheating the dry gas, using the condensing heat exchanger (X8w5) also has the advantage of lowering the temperature of the condensed water (8w) so that it can be used directly for other tasks, such as forming new building boards (60), by adding the condensed water (8w) to a mixer upstream of the production line and sufficiently upstream of the drying device. This significantly reduces water consumption throughout the board manufacturing process.

[0060] As shown in FIG. 6, downstream of the second heat pump heat exchanger (X89) and upstream of the expansion device (8e) (not shown for clarity) and the first heat pump heat exchanger (X78), the heat still remaining in the low boiling point fluid can be transferred to the dry gas 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 dry gas in the distribution system (5).

[0061] 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.

[0062] 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).

[0063] The heating fluid flow is forced through the MVR compressor, which increases the pressure and therefore the temperature of the heating fluid. The compressed and heated heating fluid flows through the MVR heat exchanger (X95L), which transfers heat from the heating fluid of the MVR cycle (9) to the dry gas in the distribution system (5) at the level of the connecting duct (5L) connecting the upstream of the LT distribution section to the downstream of the HT distribution section. 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 replenished at regular intervals with heating 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, and the condensate (typically water) formed during the heat transfer from the heating fluid to the dry gas flowing in the distribution system (5) is vaporized by passing the heating fluid through an expansion device (9e), as shown in Figure 8 (not shown in Figures 2-7 for clarity).

[0064] The MVR heat exchanger (X95L) is located in the distribution system (5) upstream from the entry point of the dry gas into each HT chamber (1, 2) at the level of the connecting duct (5L). Tests have shown that the temperature of the heating fluid flowing through the MVR heat exchanger (X95L) can be between 120°C and 180°C, preferably between 135°C and 170°C, and preferably equal to 150°C ± 10°C. Therefore, the MVR heat exchanger (X95L) can raise the temperature of the dry gas flowing through the distribution system (5) by 30°C to 40°C. This can contribute 20 to 75% of the heat transferred to the dry gas to reach the required temperature before entering the HT chambers (1, 2). This represents a significant energy saving and allows a smaller heating element (11) to be used to heat the preheated dry gas to its required temperature. Furthermore, if the dry gas 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.

[0065] The energy required to operate the air-fuel burner or electric heater type heating element (11) or other heating elements (11) to heat the dry gas by an additional 30-40°C 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). Operating the heat pump / MVR system consumes energy, but it is significantly less than the energy required to operate the heating element (11), as long as the coefficient of performance (COP), as described below, remains greater than 1.

[0066] The coefficient of performance (COP) is defined as the ratio (Q / W) of the heat (Q) supplied by the MVR heat exchanger (X95L) 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).

[0067] In the embodiment shown in FIG. 6, the distribution system (5) can include a bypass duct (5b) that bypasses the LT chamber (N) and directs the dry gas directly to the connecting duct (5L). A valve (5v) is provided to control the proportion of dry gas that flows through the bypass duct (5b) and through the LT chamber (N). As shown in FIG. 6, the bypass duct (5b) can begin downstream of any number of heat exchangers (X8w5, X85, X75), but in all cases can begin upstream of the LT heat exchanger (X75N). 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 bypass heat exchanger (X95b) configured to transfer heat from the heating fluid in the MVR cycle (9) to the dry gas in the bypass duct (5b). Because the heating fluid enters the MVR distribution heating loop (95) downstream of both the MVR compressor (9c) and the MCR heat exchanger (X95L) but upstream of the expansion device (9e), it is still at a high pressure and a fairly high temperature, which is lower than the inlet of the MVR heat exchanger (X95N) because the heating fluid has already transferred some of its heat through the MVR heat exchanger (X95N) to the dry gas flowing in the connecting duct (5L). The MVR heating loop (95) is preferably provided with a valve (9v) to control the proportion of heating fluid flowing through the MVR heating loop (95). The valve (9v) can be controlled by a processor.

[0068] As shown in Figure 6, the dry gas in the distribution system (5) can also collect heat directly from the heat pump (8) via the fluid heat exchanger (X85) described above.

[0069] The preferred heat exchangers described herein can be selected and used in any combination. When several heat exchangers are placed in the same duct of the distribution system (5) or exhaust system (7) or heat pump / MVR system, 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 fluid to the cold fluid.

[0070] Upstream of the heating element (11), the temperature of the dry gas flowing in the distribution system (5) is lowest at the level of the dry gas source (5s), which is generally at room temperature, and increases with each passing through the heat exchangers (X8w5, X85, X75, X75N, X95b, X95L) until it is highest when it reaches the dry gas supply ducts (51, 52). Conversely, the temperature of the exhaust gas is highest when it leaves the dry gas flow cycle of the HT chambers (1, 2), flows through the corresponding exhaust gas ducts (71, 72), and decreases with each passing through the heat exchangers (X75N, X75, X78).

[0071] Therefore, the heat exchanger with the lowest temperature hot fluid is preferably located most upstream in the distribution system (5), while the dry gas is cooler to maintain a substantial temperature gradient between the hot and cold sources. In this case, as shown in Figure 6, the ducts of the distribution system (5) can pass through one or more of the following heat exchangers before reaching the dry gas supply ducts (51, 52) of the HT distribution section leading to the HT chambers (1, 2): a condensing heat exchanger (X8w5), a fluid heat exchanger (X85), a preheating heat exchanger (X75), and a second MVR heat exchanger (X95). They are preferably arranged along the distribution system in the following order:

[0072] 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).

[0073] 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.

[0074] The preheating heat exchanger (X75) is generally arranged upstream of the first heat pump heat exchanger (X78) in the flow direction within the exhaust system (7). Therefore, the temperature of the exhaust gas flowing through the preheating heat exchanger (X75) is higher than the temperature of the exhaust gas flowing through the first heat pump heat exchanger (X78). Depending on whether the temperature of the exhaust gas 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 arranged downstream or upstream of the first heat pump heat exchanger (X78). In the example of FIG. 6, the fluid heat exchanger (X85) is arranged upstream of the preheating heat pump (X75) in the flow direction within the distribution system (5), suggesting that the temperature of the exhaust gas flowing through the preheating heat exchanger (X75) is higher than the temperature of the low-boiling-point fluid flowing through the fluid heat exchanger (X85). However, this must be taken into account in the design of the dryer.

[0075] The temperature of the heating fluid in the MVR distribution heating loop (95) is very high, around 100°C to 240°C, therefore the bypass heat exchanger (X95b) can be placed most downstream in the LT distribution section before reaching the MVR heat exchanger (X95L), which is the last heat exchanger on the distribution system (5) before reaching the connecting duct (5L) and the HT chambers (1, 2).

[0076] Heat transfer As mentioned above, heat is recovered from the exhaust gases flowing in the exhaust system (7) and transferred to the dry gases in the distribution system (5) through several heat exchangers. via direct conduction with both the dry gas and the exhaust gas flowing in heat transfer communication through separate channels in a heat exchanger, as in the preheating heat exchanger (X75); or By radiation and forced convection from dry gas flowing against the radiating surface of the LT heat exchanger (X75N), which is heated by exhaust gas flowing through the channels of the LT heat exchanger (X75N). can be realized, or The heat of the exhaust gases can be transferred to the dry gases indirectly via the warm condensate (8w) generated in the condenser heat exchanger (X8w5), or, as is specific to the present invention, The heat of the exhaust gas can be indirectly transferred to the dry gas via a heat pump / MVR system.

[0077] The dry gas flowing through the LT chamber (N) is heated exclusively by heat transferred directly or indirectly from the exhaust gas, both upstream of the LT chamber with the heat exchangers (X8w5, X85, X75) and within the LT chamber (N) with the LT heat exchanger (X75N). The heating element (11) is not used to heat the dry gas flowing through the LT chamber (N) except during line shutdown. The shutdown heating element (11s) can be used to heat the dry gas flowing through the LT chamber (N) when the heating element (11) in the HT chamber is switched off after the last panel (60) exits the HT chambers (1, 2). This already results in significant energy savings. The present invention further advances the energy savings of the heat pump / MVR system.

[0078] The gist of this invention is to transfer heat from the exhaust gas flowing through the exhaust system (7) to a heat pump / MVR system when the exhaust gas is normally released into the atmosphere. The heat pump / MVR system allows the temperature of the heating fluid in the MVR heat exchanger (X95L) to be raised to a value high enough to heat the dry gas flowing through the connecting duct (5L) to a higher temperature. The temperature increase can be 30-40°C, preferably 33-37°C, above the temperature of the dry gas as it leaves the LT chamber (N). This temperature increase is useful when the heating element (11) heats the dry gas to the required temperature before it enters the HT chambers (1, 2).

[0079] For example, when the dry gas leaves the LT chamber and reaches the MVR heat exchanger (X95L), it is at a temperature of about 110°C ± 10°C. The temperature of the dry gas can increase by 30-40°C by flowing through the MVR heat exchanger (X95L), resulting in a temperature of the dry gas downstream of the MVR heat exchanger (X95L) of about 130-140°C ± 10°C.

[0080] The drying gas arriving at the HT chamber is heated to a high temperature by the heating element (11) in the corresponding drying gas flow cycle. The required drying gas temperature before entering the HT chambers (1, 2) can be 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. Referring to the drying gas temperature example above, in prior art dryers, the drying gas would need to be heated from, for example, 110°C to approximately 250°C, i.e., the drying gas temperature would need to increase by 250-110=140°C. In the dryer according to the present invention, the drying gas can arrive at the heating element (11) at a temperature of, for example, 140°C, reducing the temperature increase required to reach the required temperature to 110°C, i.e., 79% of the temperature increase required in prior art dryers. This corresponds to a significant energy saving.

[0081] After being heated to the required temperatures (T1, T2) by the heating element (11), the dry gas circulates in a dry gas flow cycle against the main surfaces of the panels (60) as they move through the HT chambers (1, 2) along the drying path, raising the temperature of the panels (60) and removing moisture from them. During each cycle, a portion of the thus cooled and humidified dry gas is exhausted, while the remainder is recirculated and mixed with fresh, preheated dry gas from the dry gas source (5s). Alternatively, the entire dry gas recirculates between various cycles in a closed circuit until it is exhausted and replaced with fresh dry gas introduced into the dry gas flow cycle. This operation can be controlled by valves (5v, 7v). In either case, the exhaust gas extracted from the HT chambers (1, 2) is still quite warm, possibly around 180°C ± 20°C, depending on the temperature in the HT chambers (1, 2) and the amount of moisture contained in the panels. As with previous attempts in the prior art, it is primarily the heat stored in the exhaust gases that is recovered, but the device of the present invention takes advantage of it substantially more than the prior art devices.

[0082] As shown in Figure 8, the heat pump / MVR system requires three heat exchangers.

[0083] The first heat pump heat exchanger (X78) is configured to transfer heat from the exhaust gases in the exhaust system (7) to a low boiling point fluid in the heat pump (8) when the exhaust gases are typically disposed of in a prior art dryer.

[0084] 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 (X95L) is configured to transfer heat from the high-temperature, high-pressure heating fluid of the MVR cycle (9) to the dry gas flowing in the connecting duct (5L) of the distribution system (5).

[0085] As shown in Figures 2-7, the apparatus can include a preheating heat exchanger (X75) for transferring part of the heat of the exhaust gas flowing in the exhaust system (7) directly to the drying gas 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); the LT heat exchanger (X75N) placed in heat transfer contact with the LT chamber (N) is essential to operate without a heating element (11) in the LT chamber (N).

[0086] First heat pump heat exchanger (X78) The low-boiling-point fluid flowing through the heat pump (8) becomes gaseous at low temperature and pressure as it enters heat transfer contact with the exhaust gas 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 gas. 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 2-7 for clarity) before being reintroduced into the first heat pump heat exchanger (X78) at a lower temperature and lower pressure.

[0087] 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 (at high temperature and 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 (X95L) at a higher temperature and pressure. When the heating fluid exits the MVR heat exchanger (X95L), 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 8 (not shown in Figures 2-6 for clarity).

[0088] MVR heat exchanger (X95L) 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 dry gas flowing in the connecting duct (5L) below the LT chamber (N) relative to the flow direction in the distribution system (5). As described above, heating the dry gas flowing through the MVR heat exchanger in the connecting duct (5L) reduces the energy supplied by the heating element (11) to heat the dry gas to the required temperatures (T1, T2) before entering the HT chambers (1, 2).

[0089] In a preferred embodiment where the drying gas is air and the heating element (11) is an air-fuel burner, a portion of the air flowing in the drying gas supply ducts (51, 52) can be diverted at (9g) to feed the air-fuel burner. Raising the temperature of the air in the MVR heat exchanger (X95L) before it reaches the air-fuel burner is beneficial as it increases the effectiveness of the air-fuel burner compared to feeding it with cooler air.

[0090] 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), drying gas, preferably air, first flows through a distribution system (5) into each of the LT chambers, then through a connecting duct (5L) and an MVR heat exchanger (X95L) into the HT chambers (1, 2). The drying gas flows over the major surfaces of the building panels (60) through the N chambers (1, 2, ... N), increasing their temperature and reducing their moisture content. Before the drying gas reaches the major surfaces of the building panels in the HT chambers (1, 2), it is heated to the desired temperature by a heating element (11). Exhaust gas is then removed from each of the HT chambers via an exhaust system (7).

[0091] At least during steady-state drying operation, the drying gas blown into the LT chamber (N) is heated via the LT heat exchanger (X75N), preferably upstream of the LT chamber (N), exclusively using heat recovered from the exhaust gas by one or more of the preheating heat exchanger (X75) or the condensing heat exchanger (X8w5).

[0092] 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 drying gas is air, and the heating element (11) is an air-fuel burner. The inventive dryer includes a heat pump / MVR system, which is not included in the prior art dryer. Both dryers are equipped with a preheating heat exchanger (X75). Values ​​are nominal values, as they were calculated and not measured. For the components selected for this simulation, the COP of the device in Figure 2, the heat pump / MVR system had a COP of 2.5.

[0093] [Table 1]

[0094] By increasing the temperature of the gas in the MVR heat exchanger before feeding it to the heating element (11), it can be seen that the dryer of the present invention reduces natural gas consumption by 8%! 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=2.5 for the heat pump / MVR system, the dryer of the present invention consumes 5% less energy than a prior art dryer. In an era of increasing energy costs, this is a dramatic reduction.

[0095] Due to the lower consumption of natural gas due to the use of smaller air-fuel burners, CO2 emissions are reduced by approximately 8%. With global warming, 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 gas (air) to the gas (air) flowing in the distribution system (5). From Table 1 it can be seen that more than 2.5 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.

[0096] The dryer of the present invention reduces the energy requirements for drying wet building panels 60, with a lower CO2 footprint for the same results.

[0097] The building panels are cement board, calcium silicate board, fiber cement board, and preferably gypsum board.

[0098] 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 Dry gas supply duct 5b Bypass duct 5f Fans in the distribution system 5L Connecting duct connecting HT distribution section and LT distribution section in series 5s Dry Gas 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 7h5 Branch Duct 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 Dry gas 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) X75N LT heat exchanger shared from exhaust branch (7h) to drying gas flowing 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 from the MVR cycle (9) to the dry gas flowing in the distribution system (5) X95b Bypass heat exchanger from the MVR cycle (9) to the dry gas in the bypass duct (5b) X95L MVR cycle (9) to dry gas in dry gas supply duct (5N) MVR heat exchanger

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 total of N chambers (1, 2...N) distributed in series along the drying path and in fluid communication with one another, comprising one or more high-temperature chambers (1, 2) (=HT: high-temperature chamber) located in a high-temperature drying zone (HT) upstream of the drying path, and one or more low-temperature chambers (N) (=LT: low-temperature chamber) located in a low-temperature drying zone (LT) downstream of the high-temperature drying zone (HT) along the drying path, A distribution system (5) is configured to have fluid communication with a drying gas source (5s), preferably an air source, at one end, and with the N chambers (1, 2...N) at the other end, and to circulate the flow of the drying gas along a drying gas flow path extending from the drying gas source into the N chambers, - A heating element (11) configured to heat the dry gas in the distribution system (5) before it permeates into each of the HT chambers (1, 2), - An exhaust system (7) is configured to discharge exhaust gas from the device along an exhaust flow path extending from the HT chambers (1, 2), passing through a return exhaust duct (7h) which ultimately leads to a corresponding LT heat exchanger (X75N) located outside the device, and Equipped with, - The LT heat exchanger (X75N) is provided in each LT chamber (N) and is configured to transfer heat from the exhaust gas flowing through the corresponding return exhaust duct (7h) to the dry gas as it flows through the corresponding LT chamber (N). - The distribution system (5) comprises an LT distribution section for distributing dry gas into the LT chamber (N), and an HT distribution section for distributing dry gas into the HT chambers (1, 2), which is connected in series downstream of the LT distribution section by a connecting duct (5L). ○ The LT distribution section comprises one or more dry gas supply ducts (5N) connected in parallel to one or more corresponding LT chambers (N), ○ The HT distribution section comprises one or more dry gas supply ducts (51, 52) connected in parallel to one or more corresponding HT chambers (1, 2), - The apparatus includes a first heat pump heat exchanger (X78) configured to transfer heat from the exhaust gas flowing through the exhaust system (7) to the low-boiling point gas 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) comprising an MVR compressor (9c) configured to compress the heating fluid and thus increase the temperature of the heating fluid, thereby pushing the flow of the heating fluid from the second heat pump heat exchanger (X89) to the MVR heat exchanger (X95L), - The MVR heat exchanger (X95L) is provided at the level of the connecting duct (5L) and is configured to transfer heat from the heated fluid of the MVR cycle (9) to the dry gas in the distribution system (5) downstream of the LT distribution section and upstream of the HT distribution section. 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. In order to raise the temperature of the dry gas flowing through the distribution system (5) before it reaches the LT chamber (N), a preheating heat exchanger (X75) is provided, configured to transfer heat from the exhaust gas in the exhaust system (7) to the dry gas in the distribution system (5), wherein the preheating heat exchanger (X75) - Within the distribution system (5), upstream of the LT distribution section, - Within the exhaust system (7), downstream of the LT heat exchanger (X75N), preferably upstream of the first heat pump heat exchanger (X78) The arrangement is such that “upstream” and “downstream” are defined here with respect to the direction of fluid flow in the corresponding distribution system (5) or exhaust system (7). The apparatus according to claim 2.

4. - The heating element (11) is an air fuel burner, - The dry gas 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 3.

5. The apparatus according to any one of claims 1 to 3, wherein the heating element (11) is selected from among an electric heater and a high-temperature fluid heat exchanger.

6. - The distribution system (5) includes a distribution fan (5f) configured to push out the flow of dry gas from the dry gas source toward the N chambers (1, 2...N), - The HT chamber is equipped with chamber fans (1f, 2f) configured to push out the dry gas flow cycle that flows through the heating element (11) into the corresponding HT chambers (1, 2) and out of the dry gas flow cycle into the exhaust system (7), - One or more of the fans (5f) are configured to push out a dry gas flow through the LT chamber (N) between the radiating surface of the LT heat exchanger (X75N) that collects heat and the main surface of the building panel that transfers heat to them and collects moisture from them, and from the LT chamber (N) to the connecting duct (5L), passing through the MVR heat exchanger (X95N) before reaching the HT distribution section. The apparatus according to claim 4.

7. - 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 / or - The temperature (TN) in one or more LT chambers (N) has an average value lower than the average temperature in the HT chamber, and varies between 90°C and 170°C, preferably between 100°C and 160°C. The apparatus according to claim 6.

8. The apparatus according to claim 7, 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.

9. The apparatus according to claim 8, wherein the temperature of the heating fluid in the MVR cycle (9) within the MVR heat exchanger (X95L) is between 120°C and 180°C, preferably between 135°C and 170°C, and preferably equal to 150°C ± 10°C.

10. The apparatus according to claim 9, 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 bypass heat exchanger (X95b) configured to transfer heat from the heating fluid in the MVR distribution system heating loop (95) to the dry gas in the distribution system (5), and then returns to and rejoins the MVR cycle (9) upstream of the MVR compressor (9c).

11. The apparatus according to claim 10, further comprising a gas heat exchanger (X85) configured to transfer heat from the low-boiling-point fluid of the heat pump (8) to the dry gas of the distribution system (5).

12. The apparatus according to claim 11, wherein a branch duct (7h5) branches off from the return exhaust duct (7h), the branch duct is configured to allow exhaust gas to flow into the LT chamber (N) where dry gas from the LT distribution section is mixed, and to allow exhaust gas to flow out of the LT chamber (N), and the branch duct (7h5) and the exhaust duct (7h) are provided with valves (7v) to control the ratio of the amount of exhaust gas from the exhaust system to the amount of dry gas from the LT distribution section.

13. The apparatus according to claim 12, wherein the heating fluid in the MVR cycle is water / steam.

14. A method for drying building panels, - To provide the apparatus according to any one of claims 1 to 4, - 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 dry gas is flowed through the distribution system (5) into each of the N chambers (1, 2...N), - Before penetrating into the HT chambers (1, 2), the drying gas is heated to a desired temperature by the heating element (11), - To exhaust the exhaust gas from each of the N chambers via the 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 gas 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). - In the MVR heat exchanger (X95L), heat is exchanged from the thus compressed heating fluid to the dry gas in the distribution system (5) flowing out of the LT distribution section, before the dry gas is heated by the heating element (11) before it penetrates into the respective HT chambers (1, 2). A method characterized by the following features.

15. The method according to claim 14, wherein the building panel (60) is a fibrous cement panel, or a panel made from a material containing gypsum, cement, or calcium silicate as the main component in an amount of at least 50% by weight.

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