Method for recovering heat from a drying device for building boards

Abstract

A method for recovering heat from a drying device for building boards, the drying device comprising a plurality of drying zones, the method comprising: removing an exhaust steam mixture from at least one of the drying zones; transferring the exhaust steam mixture at a temperature of 50°C to 200°C to a heat recovery column (1); passing water and the exhaust steam mixture through the interior (6) of the heat recovery column (1) in a non-countercurrent flow, the interior (6) being defined with respect to two or more theoretical stages; A method comprising the above steps.

Description

Technical Field

[0001] The present invention relates to a method for recovering heat, i.e., thermal energy, from a drying device for building boards, preferably gypsum-based or cement-based building boards, particularly gypsum boards.

[0002] The production of building boards, which consume a large amount of energy, involves two processes: the firing of raw materials (e.g., gypsum or limestone) before forming the boards and the drying of the newly formed boards.

[0003] Various building boards, such as gypsum-based building boards, e.g., gypsum fiber boards or gypsum boards, or cement-based building boards, e.g., cement fiber boards, are typically manufactured in a continuous process. The finished boards generally have a thickness of 6 mm to 60 mm and can have, for example, planar dimensions of up to approximately 1.5 m × 3 m. During production, an endless sheet with a width of up to 3 m can be manufactured. Depending on the dryer, this endless sheet can be cut to a length of 2 m to 4 m for the drying process. For example, the manufacturing process of gypsum fiber boards may differ from that of gypsum boards, for example, but both examples have in common that stucco (calcium sulfate hemihydrate) is mixed with water and additives to form a slurry. The slurry is spread on a web to form a large sheet. When, for example, the stucco slurry is set to a certain extent and sufficient gypsum (calcium sulfate dihydrate) is formed, the boards can acquire their shape and be cut to size. Cement-based building boards, such as cement fiber boards, can be formed in the same way. The building boards then pass through a drying device where the setting can be completed and excess water evaporates. The water is usually evaporated by convective heating, and hot air passes along the surface of the boards to remove the water vapor. Other building boards, particularly other dry lining building boards, such as clay-based building boards, etc., can be manufactured in a batch process and often include a drying step in a drying device.

[0004] A typical drying device for building boards comprises several drying units, often three units, namely a pre-drying (or preheating) unit, a main (or high-temperature) drying unit and a final drying unit. The pre-drying unit is the most upstream unit of the drying device, and the final drying unit is the most downstream unit of the drying device. The temperature of the pre-drying unit is typically set at a lower temperature than that of the main drying unit. Similarly, the temperature of the final drying unit can also be set at a lower temperature than that of the main drying unit. Each unit can have one or more drying zones. The pre-drying unit (i.e., one or more first drying zones) is configured to moderately increase the temperature of the board and start evaporating the water from the board before entering the main drying unit. The main drying unit (i.e., subsequent zones) is configured to evaporate moisture from the substrate and thereby dry the substrate. The final unit is configured to end the drying process while simultaneously avoiding firing the outermost layer of the board. Typically, a temperature range is assigned to each unit. For example, the pre-drying unit can have a temperature range of 40°C to 180°C, preferably, for example, 70°C to 150°C. Alternatively, heated air at 70°C to 180°C can be supplied to the pre-drying unit. This heated air or hot air can originate from one or more drying zones, preferably one or more drying zones of the main drying unit. As an example, the main drying unit can have a temperature range of 100°C to 330°C, preferably, for example, 100°C to 300°C, more preferably, for example, 200°C to 280°C. Alternatively, heated air at 180°C to 330°C can be supplied to the main drying unit. The final unit can have a temperature range of, for example, 50°C to 180°C, preferably, for example, 100°C to 180°C. Alternatively, heated air at, for example, 80°C to 180°C can be supplied to the final unit. The temperature of each drying unit can be constant and / or can follow a predetermined temperature profile within its respective temperature range. The drying unit can typically comprise 1 to 60 drying zones with lateral ventilation, or 1 to 5 drying zones with longitudinal ventilation, or a combination of drying zones with both longitudinal and lateral ventilation.The number of drying zones generally depends on the type of ventilation, i.e., cross ventilation or impingement ventilation typically requires more drying zones than longitudinal ventilation.

[0005] Thus, a typical drying device for building boards comprises a plurality (i.e., two or more, for example, 2, 3, 4, 5, 6, or up to 80) of drying zones.

[0006] The drying device can further be adjacent to a first and / or a second adjustment section. The first adjustment section can be provided upstream of the pre-drying unit, i.e., upstream of the first drying zone of the pre-drying unit. The first adjustment section can, for example, appropriately adjust the state from the external state of the drying device to the state inside the drying device by controlling the moisture and / or temperature surrounding the building board. This adjustment can include passive heating, for example, by utilizing the exothermic reaction in the building board. A second adjustment section can be provided downstream of the final drying unit, i.e., downstream of the last drying zone of the final drying unit. The second adjustment section can, for example, adjust the state from the state inside the drying device to the post-drying state such that the building board can cool down to approximately room temperature.

[0007] Each drying zone is supplied by at least one heating means and at least one ventilation means. The drying zone typically further comprises an input end and an output end of the building board and, optionally, ducts entering and exiting the zone. To increase the capacity of the drying device for building boards, the drying device is usually configured in a plurality of decks such that the various drying zones of the drying unit comprise a plurality of decks, and each deck comprises support means for the building board. The support means are typically arranged as conveying means such that a plurality of building boards can pass through the drying device stacked essentially one above the other within the deck or in a rack. Multiple decks are preferred when spatial and energy requirements are a concern.

[0008] In the prior art, the heating means typically comprises direct heating means such as one or more fossil fuel burners (e.g., natural gas burners), or indirect heating means such as one or more hot oil heat exchangers. The heating means can also comprise other direct heating means such as one or more renewable fuel burners (e.g., biogas or hydrogen burners), and / or other indirect heating means such as one or more gas-gas heat exchangers (e.g., air-air or air-steam) or one or more gas-liquid heat exchangers, e.g., air-water, air-hot oil, air-glycol solution) or one or more radiant elements, all of which are used to heat a gaseous medium such as air that is subsequently circulated through the drying zone. The terms “gas-liquid” and “liquid-gas” are used interchangeably with respect to this disclosure. Similarly, when one or both of the general terms are specified, the order is irrelevant. For example, “air-water” means the same type of heat exchanger as “water-air”. The ventilation means can comprise the configuration of an air inlet port and an air discharge or suction port, and the movement of air is effected, for example, by a ventilation fan. The air inlet and air discharge ports can be located at or near both ends of the drying zone. By providing the air inlet port essentially opposite the air discharge port, a directional air movement within the drying zone can be provided. This air movement typically follows the conveying direction or is countercurrent or transverse to the conveying direction. Thus, the ventilation means can comprise a configuration for ventilation in the conveying direction of the building board, also called co-current longitudinal ventilation, or countercurrent to the advancing direction, also called countercurrent longitudinal ventilation, or transverse ventilation transverse to the advancing direction, also called cross ventilation. A drying zone that includes impingement ventilation, i.e., impingement heating, or cross ventilation is often shorter than a drying zone with (co-current or countercurrent) longitudinal ventilation. The ventilation (air flow) means can instead or in addition comprise a nozzle box or an air jet box that generates an air jet for impingement ventilation. It may also be possible to combine different ventilation means within the same drying unit. A drying zone with impingement or cross ventilation can have a length of, for example, 2 m to 6 m. A drying zone with (co-current or countercurrent) longitudinal ventilation can have a length of, for example, 30 m to 70 m.Thus, the drying unit can have, for example, 10 to 40 drying zones with impingement or cross ventilation instead of one drying zone with longitudinal ventilation.

[0009] Regarding gypsum-based building boards, it should be noted that the solidification of gypsum, i.e., the formation of calcium sulfate dihydrate from calcium sulfate hemihydrate, is an exothermic process. This means that gypsum-based building boards enter the drying device at a temperature of about 25 to 45 °C. Subsequently, the gypsum-based boards are heated more or less uniformly to a temperature of about 80 to 110 °C, preferably about 90 to 100 °C, in the first drying unit in order to accelerate the drying process. Due to the high moisture content of the boards at the start, the boards can be dried at a relatively high temperature (e.g., 200 °C or higher) without the risk of firing the outermost layer of the gypsum board. Firing results in brittle edges and, if present, reduces the adhesion of the liner. The evaporation of the moisture present in the board keeps the temperature of the gypsum board itself below 100 °C. A similar description can be made for cement, which also hardens exothermically. As the moisture content of the board decreases, the cooling effect of evaporation also decreases, which is why the final unit typically operates at a lower temperature to avoid firing the outermost layer of the board.

[0010] There are various methods for reducing the amount of energy required to dry building boards, especially gypsum-based building boards. Many of these focus on reducing the amount of water in the slurry. Other methods include means of reusing the warm exhaust steam mixture from one drying zone in other drying zones, which often causes problems with excessive humidity (and the possibility of condensation). Some also address recovering energy from the exhaust steam mixture by means of a heat exchanger without specifying generally required steps or explicit features. However, with the increasing demand to reduce CO 2 emissions, further improvements are still needed.

[0011] Accordingly, the object of the invention described in the claims is to reduce the energy consumption of a drying device for building boards, in particular gypsum-based building boards.

[0012] This object is achieved by the method according to claim 1, which method comprises: · removing the exhaust steam mixture from at least one drying zone; · transferring the exhaust steam mixture at a temperature of 50°C to 200°C to a heat recovery column; · passing water and the exhaust steam mixture through the interior of the heat recovery column in a non-cocurrent flow, the interior being defined with respect to two or more theoretical stages, preferably 3 to 5 theoretical stages, more preferably 4 to 5 theoretical stages, most preferably 4 theoretical stages; and comprising.

[0013] The exhaust steam mixture is understood to be a drying gas, i.e., a gaseous drying medium such as heated air, together with the water evaporated from the building board during the drying process. Typically, the exhaust steam mixture is a mixture of air and water vapor. This exhaust steam mixture can be discharged from any of the drying zones of the drying device. Typically, the drying device comprises a plurality of drying units each composed of one or more drying zones and is configured as described in the introduction section. The exhaust steam mixture can be removed from one drying zone or accumulated from part or all of the drying zones. The condensation heat recovery technology that can capture latent heat is more efficient than the heat recovery technology that captures only sensible heat. Therefore, the exhaust steam mixture is typically most useful near the dew point, which varies depending on the moisture content, i.e., the water vapor content. The dew point is the temperature to which the water vapor has to be cooled until it becomes saturated. When cooled below the dew point, the moisture capacity decreases and the suspended water vapor condenses to form liquid water, also known as dew. The dew point is proportional to the moisture content, i.e., the higher the moisture content, the higher the dew point. At temperatures well above the dew point, only sensible heat can be transferred, i.e., recovered. If the exhaust steam mixture is not saturated with water when it enters the heat recovery column, the available sensible heat can evaporate the water, i.e., the second heat transfer medium, introduced into the column in a non-cocurrent flow to the exhaust steam mixture. This can essentially result in the loss of energy in the heat recovery column, especially a direct heat exchanger such as a condensation heat recovery column. The preferred temperature of the exhaust steam mixture is 60°C to 160°C, more preferably 70°C to 100°C. The exhaust steam mixture has a moisture content of at least 200 g per kg of air, i.e., dry air, preferably at least 250 g per kg of air, more preferably >300 g per kg of air, for example, from 350 g to 850 g, even more preferably from >300 g to 600 g per kg of air, most preferably from >300 g to 650 g per kg of air, especially from >300 g to 550 g per kg of air, and is most effective at this moisture content.

[0014] The term "building board" means a flat sheet or slab used in a structure for assembling walls, floors or ceilings. This type of structure can be called a dry lining or a dry structure. Examples of building boards include gypsum-based building boards, cement-based building boards, and clay-based building boards. Building boards can have a thickness of 6 mm to 60 mm, a width of about 0.5 m to 3 m, and / or a length of about 0.5 m to 4 m. For the purposes of this invention, the term "building board" preferably refers to a building board in an unfinished state, specifically in a state where it is shaped but not yet dried and / or cured, i.e., the state it would be in within a drying device.

[0015] The terms "upstream" and "downstream" are used to describe the relative positions of two components or features in a heat recovery process, as well as in a sub-process, with respect to each other. Here, heat recovery starts with the removal of the exhaust vapor mixture from the drying zone. Thus, the removal of the exhaust vapor mixture is upstream of any heat recovery means. The terms "upstream" and "downstream" are also used to describe the relative positions of two components or features within the drying process itself. For example, the pre-drying unit is located upstream of the main drying unit with respect to the direction of travel of the building board. Similarly, the main drying unit is located upstream of the final drying unit.

[0016] The heat recovery column is an example of a heat recovery means. The heat recovery column is a type of direct heat exchanger in which the exhaust vapor mixture comes into direct contact with water, thereby transferring sensible heat and / or latent heat, preferably latent heat. These columns are most efficient when they operate in a non-parallel flow, also called a cross-flow, i.e., a countercurrent or cross-flow, or a combination of both. Countercurrent columns are typically used as scrubbers for distillation or chromatography purposes. Different purposes have different requirements. Most columns that have been used for heat recovery so far lack the efficiency to play the most important role in energy conservation. A heat recovery column for recovering heat from a drying device for building boards preferably has a height of 6 m to 15 m and a height of 1.8 m2 ~50 m 2 、 preferably 4 m 2 ~20 m 2 and has an installation area, i.e., a base area, of ~20 m to 50 m, preferably 4 m. The installation area of the heat recovery column can have any shape, such as circular or rectangular. Preferably, the heat recovery column is a condensation heat recovery column. The condensation heat recovery column has the advantage of being able to recover latent heat.

[0017] The term "interior" refers to the internal mechanism or system hidden from view, i.e., the internal structure. In this disclosure, the term "interior" refers to the internal mechanism that can be defined at the theoretical stage. In a heat recovery column without an internal structure, typically, water is injected into the column from above and steam is supplied to the column from below. As the steam rises, it comes into contact with the falling water. The steam warms the falling water and a portion of the steam condenses. To be more efficient, the heat recovery column can have means for increasing the contact between the water and the steam, or means for separating the steam into pressure-temperature equilibrium, or both. These means are achieved by the internal structure, which can also be defined at the theoretical stage. Each theoretical stage corresponds to a theoretical equilibrium, but the actual packed column follows a continuous vapor equilibrium curve. The present invention can be envisioned with an internal structure defined with respect to two or more theoretical stages, preferably 3 to 5 theoretical stages, more preferably 4 to 5 theoretical stages, and most preferably 4 theoretical stages. By separating the exhaust steam mixture into different temperature equilibria, heat transfer and condensation are optimized. As the exhaust steam mixture rises, heat is continuously transferred to the water, causing its temperature to drop. Also, since a portion of the water vapor in the exhaust steam mixture has condensed, its moisture content decreases. At the same time, the temperature of the water dripping through the column rises. Since warm air can hold more water vapor than cold air, the top separation means can effectively extract the remaining moisture content from the exhaust steam mixture. The theoretical stages of the heat recovery column can also be separated into two heat recovery columns arranged in series, preferably directly in series, i.e., end-to-end, without any intervening devices.

[0018] Preferably, the water entering the heat recovery column has a temperature of 10°C to 70°C, more preferably 40°C to 60°C. Preferably, the water exiting the heat recovery column has a temperature 10°C to 20°C higher than the water entering the heat recovery column.

[0019] In the present invention, the heat recovery column can accommodate water at 20 to 300 m 3 / h, preferably 100 to 300 m 3 / h. A column with an installation area of 2 m 2 corresponds to a capacity of approximately 20 m 3 / h. A column with an installation area of 50 m 2 corresponds to a capacity of approximately 300 m 3 / h. Intermediate values can be approximated by interpolation. Due to condensation, excess water is generated that can be purged at 0.5 to 12 m 3 / h, preferably 8 to 15 m 3 / h. The purged water of 0.5 m 3 / h approximately corresponds to a capacity of 20 m 3 / h, and the purged water of 15 m 3 / h approximately corresponds to a capacity of 300 m 3 / h. The purged water can be reused in the production of building boards.

[0020] Preferably, the method of recovering heat further includes a step of cleaning (e.g., by wet scrubbing, centrifugal force such as a cyclone separator, electrostatic precipitation or filtration) the exhaust vapor mixture before passing it inside the heat recovery column. This can be done to remove or reduce debris, and / or to dust the exhaust vapor mixture, and / or to purify the exhaust vapor mixture. The exhaust vapor mixture exiting the dryer may contain debris such as particles up to about 5 mm in size, e.g., small pieces of paper, fiber (e.g., cellulose or glass), gypsum dust or gypsum particles. Too much debris can ultimately clog the interior and / or reduce the efficiency of heat transfer inside. The cleaning step can be carried out in a separate duct, chamber or column (such as a wet scrubber or wet separator), or can be included in the heat recovery column and located in the upstream (i.e., lower) section inside. Preferably, the cleaning step includes wet scrubbing with a scrubbing medium, e.g., water, and the scrubbing medium is preferably injected into the chamber, column or section. The wet scrubbing can operate in a co-current or non-co-current flow. When the cleaning step is carried out in a separate column or chamber, a co-current flow is preferred because this co-current flow provides more constructive versatility. When the cleaning step is located in the lower section inside the heat recovery column, a non-co-current flow is preferred. Generally, since the system typically operates in thermodynamic equilibrium, there is only a negligible amount of heat transfer during the cleaning step. Preferably, the scrubbing medium can be circulated between the column, chamber or section. Debris is typically removed from the system.

[0021] A method of recovering heat from a drying apparatus for building boards can further include recovering heat using additional heat recovery means such as a gas-gas heat exchanger, a gas-liquid heat exchanger, and / or a heat pump, which can be located either upstream or downstream of the heat recovery column. Preferably, the method further includes passing the exhaust vapor mixture through a heat exchanger, preferably a gas-gas heat exchanger, before passing the exhaust vapor mixture into the interior of the heat recovery column, preferably before washing the exhaust vapor mixture. Thus, the gas-gas heat exchanger is located upstream of the heat recovery column. The gas according to this disclosure means a gas medium such as air, steam, water vapor, or an exhaust vapor mixture, and the gas phase of the working medium. The liquid according to this disclosure means a liquid medium such as water, a water-glycol solution, or hot oil, and the liquid phase of the working medium. A gas-gas heat exchanger, such as an air-air heat exchanger or an air-exhaust vapor mixture heat exchanger, can be used to preheat the (cooler) ambient air coming in with the (warmer) exhaust vapor mixture. This preheated incoming air can be directed, for example, to any drying zone where it can be further heated by additional heat recovery means (such as a gas-gas heat exchanger or a gas-liquid heat exchanger) or a burner. The exhaust vapor mixture can have a temperature of 90°C to 180°C when entering the gas-gas heat exchanger and a temperature of 60°C to 120°C when exiting the gas-gas heat exchanger, especially when the gas-gas heat exchanger is located upstream of the heat recovery column. Any heat recovery means located upstream of the heat recovery column can precool the exhaust vapor mixture to a temperature near its dew point. By precooling the steam to a temperature near its dew point, the available sensible heat of the exhaust vapor mixture can be effectively used before entering the heat recovery column. A heat pump can be used to transfer heat from the water heated in the heat recovery column to a third heat transfer medium. In this regard, the exhaust vapor mixture can be regarded as the first heat transfer medium, and the water entering and exiting the heat recovery column can be regarded as the second heat transfer medium. Preferably, the heat pump is located downstream of the heat recovery column.For example, a gas-liquid heat exchanger such as an air-water heat exchanger can be used to transfer further heat from the water exiting the heat recovery column, preferably also from the heat pump, to warm, for example, the incoming ambient air before it enters the gas-gas heat exchanger. Preferably, the gas-liquid heat exchanger is positioned in the cycle of water that exits the heat recovery column as warm water and enters the heat recovery column as cold water. More preferably, the gas-liquid heat exchanger is positioned between the heat pump and the water entering the heat recovery column. Most preferably, the gas-liquid heat exchanger is simultaneously positioned upstream of the gas-gas heat exchanger.

[0022] Heat recovery can be · circulating water through the heat pump and back to the heat recovery column · transferring heat from the water to a third heat transfer medium present within the heat pump to heat the third heat transfer medium to at least 10°C improved using a method that further includes this.

[0023] By circulating water through the heat pump, the heat from the water is used to heat the third heat transfer medium by at least 10°C depending on the type of heat pump, i.e., to raise the temperature of the third heat transfer medium by at least 10°C, more preferably up to 200°C, most preferably to 20°C - 30°C or 30°C - 130°C, preferably 30°C - 80°C, more preferably 30°C - 50°C. The third heat transfer medium can be air, water, steam, a water-glycol solution, or hot oil. Ideally, this causes the temperature of the third heat transfer medium to rise above the temperature of the water. Preferably, the second heat transfer medium (water) has a temperature of 50°C - 90°C, preferably 50°C - 80°C when entering the heat pump and a temperature of 30°C - 65°C, preferably 45°C - 60°C when exiting the heat pump.

[0024] Preferably, the method involves passing a water and exhaust steam mixture through an interior defined with respect to the theoretical stage, the interior comprising one or more packings, sometimes referred to as a packed bed. The one or more packings or packed bed can be random packings or structured packings. Preferably, the one or more packings are structured packings. Structured packings having a porosity of >94%, preferably 95% - 99%, more preferably 97% - 99% have been particularly effective. Porosity is defined as the ratio of the total volume that is free space available for fluid flow. Water can wet the surface of the packing, but the exhaust steam mixture can pass through this wetted surface where heat and mass transfer can occur. Structured packings typically comprise thin corrugated sheets or gauzes designed to force the fluid through a complex path. The corrugated sheets can be further perforated and / or embossed. This design is intended to provide a large surface area for contact between the water and the exhaust steam mixture. Ideally, the voids can be structured so as to avoid water clogging. Structured packings can be made of various materials such as plastics (e.g., polypropylene), metals, or ceramics. The material must be able to withstand a temperature of at least 70°C. Among the aforementioned materials, plastics (e.g., polypropylene) and metals are preferred mainly for cost-effectiveness. Structured packings offer the following advantages compared to random packings, namely, higher efficiency, reduced liquid holdup, and higher capacity for the same column height.

[0025] Alternatively or in addition, the structured packing has a specific surface area of 80 m 2 / m 3 ~500 m 2 / m 3 , preferably 100 m 2 / m 3 ~200 m 2 / m 3 , more preferably 100 m 2 / m 3 ~150 m 2 / m 3 .

[0026] Alternatively or in addition, the structured packing can comprise a corrugated sheet or a pleated sheet (such that the sheet is non-planar with ridges or bends), preferably the corrugated sheet or the pleated sheet is oriented at an inclination angle of at least 60°, preferably 70° to 90°, with respect to the base of the column, i.e., with respect to the horizontal. The corrugated sheet or the pleated sheet can be further arranged in a plurality of layers, and each layer is oriented at 140° to 180° with respect to the lower layer. The height of the pleat (or twice the amplitude of the corrugation) can be 15 mm to 35 mm, preferably 18 mm to 30 mm. The angle of the wave can be 45° to 60°.

[0027] Alternatively or in addition, the structured packing can comprise channels, preferably the channels are arranged at an inclination angle of at least 60°, more preferably 70° to 90°, with respect to the base of the column, i.e., with respect to the horizontal. The channels can be formed by corrugated sheets stacked with an offset or stacked with a spacer or a distance piece. The steep inclination angle has the advantage that the surface of the packing is kept relatively clean. Water can pass through the structured packing at a rate sufficient to wash away debris such as gypsum particles and / or paper particles, and / or other contaminants that may be present in the exhaust steam mixture.

[0028] Preferably, the heat pump is an adsorption heat pump, a compression heat pump or a hybrid heat pump. The adsorption heat pump has the advantage of not requiring much electrical energy to operate the system. The adsorption heat pump typically raises the temperature by 10°C to 30°C, usually 20°C to 30°C. The compression heat pump has the advantage that it can raise the temperature of the third heat transfer medium by 30°C to 130°C, preferably 30°C to 80°C, most preferably 40°C to 50°C.

[0029] In the case of an adsorption heat pump, a lithium bromide or ammonia water heat pump containing lithium bromide or ammonia water as an adsorbent is preferred. The adsorption heat pump can include an evaporator unit, a generator unit, an adsorber unit, and a condenser unit. The evaporator unit and the adsorber unit are connected by a vapor passage, and the condenser unit and the generator unit are connected by a vapor passage. The temperature of the evaporator unit can typically be higher than the temperature of the condenser unit. This configuration has the advantage that the heat pump can be driven by a medium temperature, for example, between 50°C and 90°C.

[0030] More preferably, the method includes circulating water through the evaporator unit and then through the generator unit of the heat pump and returning it to the heat recovery column. In this configuration, water entering the heat pump at a temperature between 50°C and 90°C can be used to heat a third heat transfer medium above the temperature of the water. In particular, water entering the adsorber unit at a temperature between 60°C and 90°C can heat the third heat transfer medium by at least 10°C.

[0031] The compression heat pump can preferably be a high-temperature heat pump in which the working medium is heated to a maximum absolute temperature of about 80°C to 130°C, or a super-high-temperature heat pump in which the working medium is heated to a maximum absolute temperature of about 130°C to 200°C. Preferably, for an absolute temperature of about 80°C to 130°C, ammonia, butane, or propane, preferably ammonia, is used as the working medium, or for a maximum absolute temperature of 130°C or higher, for example, up to 200°C, helium or CO 2 is used.

[0032] A hybrid heat pump, also called a compression adsorption heat pump, combines the technologies of an adsorption heat pump and a compression heat pump. The hybrid heat pump uses a working medium, for example, a mixture of ammonia and water. The hybrid heat pump typically includes a desorber, a separator, a pump, a compressor, an adsorber, and an expansion element. The hybrid heat pump has the advantage of requiring less electrical energy while providing an equally high temperature rise compared to a compression heat pump.

[0033] The method of recovering heat can further include circulating water from the heat recovery column to a gas-liquid heat exchanger upstream of the heat pump, downstream of the heat pump, or parallel to the heat pump. For this purpose, a liquid-gas heat exchanger, preferably a water-air heat exchanger, can be located upstream or downstream of the heat pump, and the heat pump can be any of the aforementioned adsorption heat pumps, compression heat pumps, or hybrid heat pumps. The gas-liquid heat exchanger, preferably a water-air heat exchanger, can also be located in a cycle parallel to the disclosed heat pump cycle. If the heat pump cannot process hot water at a temperature of 50 °C to 90 °C, specifically 60 °C to 80 °C, it is advantageous to locate the gas-liquid heat exchanger upstream of the heat pump. This can apply, for example, when using a compression heat pump with ammonia as the working medium. Locating the gas-liquid heat exchanger downstream of the heat pump can be advantageous for any type of heat pump to recover additional heat from a second heat transfer medium (e.g., water). Locating the gas-liquid heat exchanger in a parallel cycle can be advantageous for saving (electrical) energy when using a compression heat pump or a hybrid heat pump. Essentially, the temperature conditions can be optimized for any type of heat pump having a gas-liquid heat exchanger located upstream, downstream, and / or parallel to the heat pump.

[0034] Alternatively or in addition, the method further includes heating one or more drying zones of the drying zone, preferably the preliminary drying unit and / or one or more drying zones of the final drying unit, with a third heat transfer medium. Heating one or more drying zones of the preliminary drying unit and / or the final drying unit with a third heat transfer medium is particularly advantageous when a heat pump having a relatively low temperature rise (up to about 30 °C) is used, since these drying units typically operate at a lower temperature compared to the main drying unit. When a heat pump having a relatively high temperature rise of 30 °C to 130 °C is used, any, some, or all of the drying units can be heated with a third heat transfer medium. Brief Description of the Drawings

[0035] The present invention is further illustrated in the figures. However, it is not intended to limit the scope of the present invention and the general teachings according to the selected embodiments in the figures.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0036] The flow paths of water and exhaust steam mixture through the heat recovery column (1) and related cycles are schematically shown in Figure 1. The water drips downward as the exhaust steam mixture rises and spreads inside. The internal packing geometry such as structured packing can vary. The heat recovery column can be divided into upper, middle, and lower sections for illustrative purposes. The upper section includes a water distributor (4) (such as a water injection nozzle), an air outlet duct (5), and a mist eliminator (not shown). The middle section includes an internal (6) such as structured packing, and the lower section includes a sump basin (7), as well as a drain for this basin (8) and a supply duct (3) for the exhaust steam mixture. The water distributor (4) is positioned at a sufficient height from the internal (6) so that the distributed water can wet the internal surface area. The internal (6) is dimensioned to fit snugly into the body of the column. The exhaust steam mixture is circulated through the column using a blower. Ideally, any connecting ducts outside any heat recovery means are insulated to prevent heat loss to the surroundings. The water collected in the basin (7) is pumped back to the original column via further means for heat recovery (2) or heat transfer (2). Examples of further heat recovery or heat transfer means (2) include, but are not limited to, one or more liquid-gas heat exchangers, heat pumps, multiple radiant elements. The radiant elements can include a heat transfer medium circulating within the duct. The flow of water is indicated by solid arrows. The flow of the exhaust steam mixture is indicated by dashed arrows. A gas-gas heat exchanger (not shown) can be positioned upstream of the heat recovery column, whereby heat transfer from the exhaust steam mixture to, for example, the incoming ambient air can precede the heat recovery described in the column (1). A cleaning step (e.g., by centrifugal force such as in a cyclone separator, wet separation using, for example, injected water, electrostatic precipitation, or filtration) is not shown but is not excluded as a further option. This cleaning step can be performed inside the lower, i.e., upstream side of the illustrated heat recovery column. Alternatively, this cleaning step can be performed in a separate duct, chamber, or column (e.g., a wet scrubber or wet separator) positioned upstream of the illustrated heat recovery column.In this technical field, wet scrubbers are known to remove dust particles by capturing the dust particles in droplets. Wet scrubbers generally operate on the principle of direct contact between a liquid (here, for example, water) and a gas (here, an exhaust vapor mixture).

[0037] In Figure 2, a heat pump (10) is incorporated into the water cycle with the heat recovery column (1). The column is configured as described for Figure 1. The heat pump (10) can be a compression heat pump, an adsorption heat pump, or a hybrid heat pump. The heat pump (10) shown in this specification can also represent a two-stage heat pump or two heat pumps arranged in series. An example of an adsorption heat pump is shown in Figure 4.

[0038] In Figure 3, in addition to the heat pump (10), a liquid-gas heat exchanger (11) is incorporated into the water cycle with the heat recovery column (1). The column is configured as described for Figure 1. The heat pump (10) shown in this specification can be a compression heat pump, an adsorption heat pump, a hybrid heat pump, a two-stage heat pump, or two heat pumps arranged in series. An example of an adsorption heat pump is shown in Figure 4.

[0039] Figure 4 shows an example of a heat pump, i.e., an adsorption heat pump (10), that can be used in combination with the heat recovery column (1). This type of heat pump can raise the temperature of a third heat transfer medium (17) by at least 10 °C. The driving energy source is heat. Electrical energy is only required for auxiliary devices such as pumps and cooling fans. The illustrated heat pump is an adsorption heat pump, such as a lithium bromide heat pump, comprising a condenser unit (12), a generator unit (13), an absorber unit (14), and an evaporator unit (15). Typically, all four units operate at low pressure, meaning the low pressure indicates a pressure of less than 1 bar. The low pressure can also indicate a vacuum. The evaporator unit (15) and the absorber unit (14) are connected by a vapor passage (19), and the condenser unit (12) and the generator unit (13) are connected by a vapor passage (19). The illustrated heat pump comprises three heat transfer medium cycles, specifically, a cycle of a second heat transfer medium (16), a cycle of a third heat transfer medium (17), and a cycle of a fourth heat transfer medium (18). Considering the entire heat recovery process, there are additional heat transfer media. For example, the exhaust vapor mixture can also be regarded as the first heat transfer medium, while the water passing through the heat recovery column can be regarded as the second heat transfer medium (16). This water can further pass through the aforementioned heat pump (10). Specifically, as shown in the figure, the water can pass through both the evaporator unit (15) and the generator unit (13). In the evaporator unit (15), the injected water is evaporated. The newly generated water vapor travels to the absorber unit (14) and is adsorbed by the concentrated lithium bromide salt solution, which is an exothermic process. The heat generated by this exothermic process is transferred to a third heat transfer medium (17), such as liquid water, water vapor, a water glycol solution, etc. The diluted lithium bromide solution is pumped to the generator unit (13), where it is reconcentrated by the heat released by the water, which is the second heat transfer medium (16), guided through the generator unit. The resulting water vapor, i.e., steam, is condensed in the condenser unit (12) by the fourth heat transfer medium (18). An ammonia adsorption heat pump functions similarly.

[0040] Heat pumps, i.e., adsorption heat pumps, and related processes can be exemplified in a temperature range. A second heat transfer medium (16), for example water, enters the evaporator unit (15) at 70 °C ± 10 °C and exits the generator unit (13) at 60 °C ± 10 °C. A third heat transfer medium (17) enters the adsorber unit (14) at 85 °C ± 10 °C and exits the same unit at 95 °C ± 10 °C. A fourth heat transfer medium (18) enters the condenser unit (12) at 26 °C ± 10 °C and exits the same unit at 30 °C ± 10 °C. The temperature range of the fourth heat transfer medium (18) depends on the ambient temperature and relative humidity and thus varies according to the geographical location.

[0041] FIG. 5 schematically shows an example of a drying device (20) for building boards. The illustrated drying device includes a first drying zone (21), a second drying zone (22) downstream of the first drying zone, a third drying zone (26) downstream of the second drying zone (22), a fourth drying zone (27) downstream of the third drying zone (26), a fifth drying zone (28) downstream of the fourth drying zone (27), and a sixth drying zone (29) downstream of the fifth drying zone (28), and any one, part, or all of the first, second, third, fourth, fifth, or sixth drying zones delivers the exhaust mixture to the heat recovery column (1). This is illustrated by arrow (24) with respect to the fifth drying zone. The illustrated zones may be included in a pre-drying unit, a main drying unit, or a final unit. Any one, part, or all of the first, second, third, fourth, fifth, or sixth drying zones can receive a third heat transfer medium (17) and dry the building boards within that zone. This is illustrated by arrow (23) with respect to the first drying zone. It may be particularly useful to circulate the third heat transfer medium through a plurality of radiant elements each having a duct for the third heat transfer medium. Alternatively or in addition, any one, part, or all of the first, second, third, fourth, fifth, or sixth drying zones can receive a fifth heat transfer medium, such as air heated by, for example, a gas-liquid heat exchanger, and dry the building boards within that drying zone. Although only six drying zones are shown, FIG. 5 is intended to show that the drying device (20) can include a plurality of drying zones, up to 80 drying zones. The building boards can enter the drying device at the input end of the first drying zone and exit the drying device at the output end of the drying zone having the highest sequence number. In FIG. 5, the drying zone with the highest sequence number is the sixth drying zone. The direction arrow (25) depicts the continuous movement of the building boards through the drying device. The drying device of the present invention can include only three, four, five, or six drying zones, or 20 to 80 drying zones, particularly when at least some of the drying zones have impingement and / or cross ventilation.

Explanation of reference numerals

[0042] 1 Heat recovery column 2 Heat recovery or heat transfer means 3 Supply duct for exhaust steam mixture 4 Water distributor 5 Air outlet duct / port / outlet 6 Interior, e.g., structured packing 7 Sump 8 Drain duct 9 Return water duct 10 Heat pump 11 Liquid-gas heat exchanger 12 Condenser unit 13 Generator unit 14 Adsorber unit 15 Evaporator unit 16 Water as the second heat transfer medium 17 Third heat transfer medium 18 Fourth heat transfer medium 19 Passage for steam 20 Drying device 21 First drying zone 22 Second drying zone 23 Heat transfer means, e.g., radiant element with a third heat transfer medium 24 Exhausted exhaust steam mixture 25 Conveying direction 26 Third drying zone 27 Fourth drying zone 28 Fifth drying zone 29 Sixth drying zone

Claims

1. A method for recovering heat from a drying apparatus for building boards, wherein the drying apparatus comprises a plurality of drying zones, the method comprising: - removing an exhaust steam mixture from at least one of the drying zones; - transferring the exhaust steam mixture at a temperature of 50°C to 200°C to a heat recovery column (1); - passing water and the exhaust steam mixture through the interior (6) of the heat recovery column (1) in a non-cocurrent flow, wherein the interior (6) is defined with respect to two or more theoretical stages; A method comprising the steps of.

2. - circulating the water (16) through a heat pump (10) and returning it to the heat recovery column (1); - transferring heat from the water (16) to a third heat transfer medium (17) in the heat pump (10) and heating the third heat transfer medium to at least 10°C; The method according to claim 1, further comprising the steps of.

3. The method according to claim 1 or 2, further comprising the step of washing the exhaust steam mixture before passing it through the interior of the heat recovery column.

4. The method according to any one of claims 1 to 3, further comprising the step of passing the exhaust steam mixture through a heat exchanger, preferably a gas-gas heat exchanger, before passing it through the interior of the heat recovery column, preferably before washing the exhaust steam mixture.

5. The method according to any one of claims 1 to 4, wherein the interior (6) is provided with structured packing, preferably the structured packing has a porosity of more than 94%.

6. The method according to claim 5, wherein the structured packing is provided with channels, preferably the channels are arranged at an inclination angle of at least 60°, preferably 75° to 90°, with respect to the base of the column / horizontally.

7. The method according to any one of claims 1 to 6, further comprising the step of purging excess water from the circulation.

8. The heat pump (10) is an adsorption heat pump comprising an evaporator unit (15), a generator unit (13), an adsorber unit (14), and a condenser unit (12), wherein the evaporator unit (15) and the adsorber (14) unit are connected by a steam passage (19), and the condenser (12) and the generator (13) unit are connected by a steam passage (19). The method according to any one of claims 2 to 7.

9. The method according to any one of claims 2 to 8, further comprising the step of circulating the water (16) through the evaporator unit (15) and then through the generator unit (13) of the heat pump and back to the heat recovery column (1).

10. The method according to any one of claims 2 to 7, wherein the heat pump is a compression heat pump or a hybrid heat pump.

11. The method according to any one of claims 2 to 10, further comprising the step of circulating the water from the heat recovery column to a gas-liquid heat exchanger located upstream of the heat pump, downstream of the heat pump, and / or in a cycle parallel to the heat pump cycle.

12. The drying device comprises a pre-drying unit, a main drying unit, and a final drying unit, each unit having one or more drying zones, and the method further comprises the step of heating the drying zones of the drying device (20) with the third heat transfer medium (17), preferably a part of the drying zones of the pre-drying unit, either some or all. The method according to any one of claims 2 to 11.

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