Method for drying plate and dryer

Abstract

The invention relates to a method for drying sheets in a drying system comprising a first stage (A) and a second stage (B), in which the two stages (A, B) each have a hierarchy and the sheets are placed on a surface formed layer by layer and are guided through the drying system in the respective hierarchy of the two stages (A, B), the invention relates to a method for producing a sheet material, in which the sheet material is brought into contact with high-temperature drying air in a first stage (A) and is dried and in which the sheet material is dried with less high-temperature drying air in a second stage (B), characterized in that in at least one of the two stages (A, B), hot air is supplied to the sheet material from a means for recovering heat, said means being arranged outside the two stages, and wherein hot air is supplied directly to the at least one stage.

Description

Technical Field

[0001] The present invention relates to a method for drying a sheet material and a dryer for this purpose. Background Art

[0002] When drying a sheet material (especially a building sheet material containing cement and gypsum), the sheet material conveyed through the dryer comes into contact with hot air.

[0003] The drying air can be supplied in the form of longitudinal ventilation, transverse ventilation, or transverse ventilation using a nozzle box equipped with nozzles. In the case of longitudinal ventilation, the drying air is supplied from one end of the dryer, or if the dryer is divided into multiple zones, from one end of a certain zone, and discharged from the opposite end.

[0004] Through transverse ventilation, air enters from multiple points on the side of the dryer and is discharged from the opposite side, so that drying inside the dryer is more sufficient. Very good drying effects can be achieved through transverse ventilation in which the air passes through the spray dryer in an impinging jet manner.

[0005] In most cases, a circulation process is adopted, so that most of the drying air is circulated. In this case, most of the drying air needs to be reheated after contacting the material to be dried, so that it can be reused. Only a small part of the drying air is discharged to the outside as exhaust gas, and a part corresponding to the exhaust gas is input from the outside as supply air.

[0006] Fuel (i.e., primary energy) is required to heat the drying air, such as using a burner or a heating regulator, and electric energy (i.e., secondary energy) is required to supply air using a fan. The use of primary energy and secondary energy must be reduced in order to produce the above-mentioned sheet material more energy-efficiently.

[0007] DE 26 13 512 A1 discloses a drying method in which low primary energy consumption is achieved by utilizing the condensation heat from the exhaust gas. This process has a two-stage design. In the first dryer stage, drying is carried out at high temperature and high humidity, and in the second dryer stage, drying is carried out at low temperature and low humidity, where the drying capacity of the first stage is two to three times that of the second stage, and the second dryer stage is heated from the exhaust gas of the first dryer stage by inserting a heat exchanger. In both stages, the drying air is supplied in a recirculation process, that is, in the form of longitudinal ventilation in the first dryer stage and in the form of transverse ventilation in the second dryer stage, and the mass flow rate of the recirculated air is large. However, a large amount of circulating air is required in the second stage, so the energy consumption of secondary energy is high.

[0008] When using the condensation heat of the exhaust gas to reduce the primary energy consumption simultaneously, a problem usually occurs, that is, the waste heat of the exhaust gas can only be utilized at a low temperature. Although the lower dry air temperature can be compensated by a larger air mass flow, this will lead to an increase in secondary energy consumption.

[0009] WO 95 / 04908A1 discloses a method for drying a sheet conveyed through a dryer in layers, wherein the sheet is contacted with drying air in two stages A and B, wherein the drying in stage A is carried out in a circulating air process, wherein the temperature of the drying air is high, the humidity is at least medium, and the drying capacity is two to four times higher than that in stage B. In stage B, the exhaust gas from stage A passes through a heat exchanger arranged in the shelves of the dryer; at the same time, the drying air with low temperature and low humidity flows in a reverse direction to the exhaust gas from stage A.

[0010] According to WO 2019 / 105888A1, at least two devices for heat recovery are used, wherein the two devices are arranged in series, and wherein the heat from the first device is used for further heating by a burner before being introduced into the first stage of the dryer. Summary of the Invention

[0011] The object of the present invention is to further improve the method described in the preamble of claim 1.

[0012] According to the present invention, this object is achieved as disclosed in claim 1.

[0013] According to the present invention, hot air is supplied to the sheet in at least one of the two stages (A, B) by a device for heat recovery, wherein the device is arranged outside the two stages, and wherein the hot air is directly supplied to the at least one stage.

[0014] In this way, the use of primary energy and secondary energy is optimized. In particular, the primary energy used is maintained by utilizing the waste heat and the condensation heat of the exhaust gas, without increasing the demand for secondary energy by circulating a large amount of air.

[0015] A further advantageous improvement of the method results from the dependent claims and the description, especially when combined with the drawings.

[0016] Preferably, the sheet is heated at least in the first stage by: hot air generated by a heat exchanger, a heat pump, a wet separator, a burner directly or through hot steam or through heat transfer oil or indirectly through electricity or through low calorific value heat.

[0017] According to the present invention, heat is supplied to the sheet at least in the second stage, wherein at most a single device for heat recovery is provided.

[0018] Preferably, according to the method of the present invention, the transport speed of the board to be dried is also adapted to the corresponding energy absorption and associated dehumidification of the board, so that the board to be dried is dried with a minimum energy input.

[0019] The present invention provides a method with low primary energy consumption and secondary energy consumption. By utilizing the waste heat and the condensation heat of the exhaust gas, the primary energy used in the present invention remains low. Compared with the methods known in the prior art, the mass flow rate of the drying air is reduced in this way, thus reducing the consumption of secondary energy, because the mass flow rate of the recirculating air is reduced.

[0020] The present invention particularly utilizes the waste heat from other processes occurring near the drying equipment, such as the waste heat from a waste incineration plant or a combined heat and power plant; according to the present invention, low calorific value heat obtained as waste heat from other exothermic processes can also be used.

[0021] The waste heat of a combined heat and power plant can also be used. This technology generates heat and electricity simultaneously. Generating heat and electricity simultaneously using fuel in a single device is more efficient and cost-effective than generating heat and electricity separately in two different devices (COGEN technology or combined heat and power). Combined heat and power is 40% more efficient than generating heat and electricity separately. Combined heat and power preferably uses renewable fuels for operation. The electricity generated in this way can also be used in the system for transporting boards and operating fans.

[0022] In one embodiment, the dryer system according to the present invention is coupled to a solar and / or photovoltaic system. Alternatively, the dryer according to the present invention uses the heat from a geothermal system.

[0023] Generally, the pre-stage A and the post-stage B have the same number of tiers, arranged one above the other for guiding and transporting the boards. Generally, each tier also has the same height and the same distance from each other, so that the boards can be transferred from stage A to stage B without interruption. This is particularly applicable if the boards are transported at the same transport speed in both stages. However, this does not exclude the possibility of selecting different transport speeds in the two stages.

[0024] Thus, according to an embodiment of the present invention, different transport speeds can be used for the boards to be dried in two stages. Selecting the speed of each stage according to the desired drying progress will also result in the transport speed of stage A being higher than that of stage B, because the drying temperature of stage A is higher than that of stage B. This means that on the independent conveyor located between stage A and stage B, the speed of the board leaving stage A will be reduced to the speed level of stage B. At the same time, in order to avoid intermediate storage of the boards in the conveyor area, the conveyor distributes the boards over a larger area in stage B according to the speed difference between stage A and stage B. This is achieved by distributing the boards over more tiers or tracks in the area of stage B compared to stage A. For this purpose, a conveyor device (such as a discontinuous conveyor device) is used that picks up the boards at a higher speed on the side facing stage A and unloads the boards onto more tiers or tracks of stage B on the side facing stage B, and this conveyor device preferably has a lower speed on this side. The conveyor has an inclination point when transitioning to stage B in order to distribute the boards to the respective tiers of stage B. In the case of a larger number of channels (for example, two to four channels), multiple boards are preferably transported side by side on one tier.

[0025] This measure creates, on the one hand, a compact inlet area of the dryer in stage A, which can be passed through at high speed and high temperature and is also suitable for ensuring the final activation of the curing agent (such as starch) contained in the boards. Combining strong heating with high humidity in the pre-stage A promotes the swelling of the curing agent contained in the building boards to be dried. In this way, high-quality boards can be produced.

[0026] If two stages with different conveyor speeds for the boards are implemented, the area and speed within stage B can be adjusted to achieve sufficient drying of the boards while making the best use of the energy from stage A.

[0027] In order to achieve rapid drying in stage A, the boards are preferably heated by the lateral flow of hot air without using a nozzle box. This allows the boards to be easily heated without the need for the structural work involved in installing a nozzle box. The boards are preferably heated in the front part of the dryer during the recirculation of air. Due to the high air humidity of the boards, the dew point is preferably between 60°C and 99°C, most preferably between 75°C and 90°C.

[0028] The heat supplied to the boards in stage A is preferably at least partially generated by a device for heat recovery, in particular by a heat pump. At least some sections of stage A are additionally equipped with heaters, especially the front section of stage A. Alternatively, stage A can also be completely heated using the heaters installed therein.

[0029] The full heating in the first stage generates high air humidity in this stage, which means that the dew point rises to a temperature between 75°C and 99°C, where the dew point is preferably between 75°C and 90°C. The air humidity is between 200 and 600 grams per kilogram of air.

[0030] To simplify the design of stage A, the sections of stage A can also be placed directly on the level of the industrial building without the need for a separate level for the dryer. This allows stage A to be implemented in a lightweight structure; if stage A consists of a large number of modules arranged one after another in the production direction, these modules can be easily installed and removed, for example, to repair or replace the fans installed in the zones, especially in the top area.

[0031] Although the nozzle boxes can dry the sheets well in a short time, they require a high energy input to generate the required air flow. On the other hand, the nozzle boxes also occupy a considerable amount of space within stage A, which usually has multiple sections, and the nozzle boxes are stacked on top of each other in each section according to the number of levels of stage A.

[0032] According to the present invention, a longitudinal ventilation design for stage A is as possible as the use of nozzle boxes.

[0033] Both stages are divided into zones or sections. For example, in stage A and stage B, the drying equipment is provided with a conveyor system that has a plurality of zones or sections extending one after another in the conveying direction for conveying the sheets to be dried, and the sheets to be dried pass through in multiple levels for each zone, where the conveying means are arranged in the levels and designed as roller conveyors. Preferably, a separate conveyor chain is provided for the sheets in each zone; however, the sheets can also be driven by a conveyor chain shared by these zones in multiple zones. For example, the conveyor chain drives the sheets on five zones.

[0034] Due to the longer drying time of the sheets to be dried, stage B requires a larger drying area; therefore, it is longer than stage A.

[0035] In stages A and B of the dryer, a drive system is used that is suitable for dryers operating at low temperatures and for simultaneously processing a large number of sheets (especially gypsum boards) at low temperatures in a large number of levels (for example, 16 to 60 levels). By using a large number of levels in combination with the drive system according to the present invention, a longer residence time of the sheets (especially gypsum boards) can be achieved in a low-temperature dryer, while the length of the dryer is the same as that of a high-temperature dryer.

[0036] Therefore, it can be seen that installing the dryer device according to the present invention in existing equipment can achieve particularly large energy savings.

[0037] To optimize the utilization of the waste heat generated especially in stage A, the sheets are dried in the first stage A and / or in the second stage B by means of at least one external heat exchanger and / or alternatively by means of an internal heat exchanger.

[0038] It is also advantageous if, in the first stage A, the sheets are heated directly by passing the circulating air through the burner, or indirectly by means of superheated steam, hot oil or electricity, or by means of low calorific value heat. In stage B, the sheets are heated by low calorific value heat, which can come from the heat recovery of stage A or from another process that releases heat at a low temperature, such as from a combined heat and power plant or a heat pump.

[0039] Preferably, in the first stage A, the sheets are dried by drying air at a temperature of 90 to 160 °C, especially 120 to 140 °C. The choice of a low temperature allows the sheets to be gently dried. No gypsum anhydrite is formed in the sheets.

[0040] When the sheets are dried in these temperature ranges in the first stage A, the hot air absorbs a large amount of moisture, and the temperature and circulation speed of the air are preferably selected such that the dew point of the hot air is between 60 °C and 99 °C.

[0041] The drying zone of the first stage A either has cross ventilation or, alternatively or additionally, has longitudinal ventilation. If a high temperature is to be achieved, stage A is preferably heated indirectly by means of a heat pump, for example up to 50%. Alternatively, the zones of stage A are heated by a burner or indirectly.

[0042] In the second stage B, the sheets are dried with drying air at a temperature of 20 to 90 °C, preferably 30 to 90 °C.

[0043] The exhaust gas discharged during the drying process of the first stage A can be advantageously reused by entering the heat exchanger to preheat the drying air of the second stage B.

[0044] If the sheets are first dried in a pre-drying stage upstream of the first stage A, then dried in the first stage A, and finally dried in the second stage B, a higher efficiency of the drying process according to the invention can be achieved.

[0045] Preferably, the sheets are conveyed through the sections in stages A and B by means of separate conveyor devices for each stage A, B and / or each section. Alternatively, the conveyor devices are each driven by a direct drive motor, or the conveyor devices are at least partially interconnected by using gears.

[0046] The present invention also provides a dryer for drying sheets in a first stage A and a second stage B, each stage being equipped with conveyor means for conveying the sheets arranged in layers through the dryer, wherein the first stage (A) comprises at least one zone, wherein the first stage A has a supply device, a discharge device and a circulating air duct having a conveying device and a heating device for circulating air, as well as a device for supplying supply air and a device for discharging exhaust air, and wherein the second stage B is equipped with a device for receiving the sheets from the first stage A, a supply device for supplying drying air; alternatively, the heating device may also be provided in the second stage.

[0047] In particular, in the second stage, a high conveying capacity for circulating air is avoided, so that the dryer only has a low secondary energy consumption.

[0048] Preferably, the housing of the dryer is equipped with doors for each dryer stage A, B. Preferably, the dryer, especially in stage B, does not have its own levels, but is built on the floor leveling layer of the factory hall.

[0049] Advantageously, each of the first stage A and the second stage B in the dryer comprises at least one section or zone equipped with means for causing the circulating air to flow transversely to the conveying direction of the sheets, especially in the first stage A.

[0050] For design reasons, the first stage A of the dryer is preferably divided into a plurality of sections, at least some of which are equipped with means for transverse ventilation; in particular, fans are provided in the front zone of stage A, especially in the top region; however, if the circulating air generated by the fans is subsequently guided into the interior of the zone, the fans can also be installed externally, especially above the upper cover of the region. For this purpose, air guiding elements are preferably provided in the zone. For example, transverse ventilation is achieved by hot air impinging on the surface.

[0051] Preferably, in stage B, i.e., in the later stage, only longitudinal ventilation is provided, which does not exclude the provision of additional and / or proprietary means for transverse ventilation in stage B. In stage B, the temperature of the sheets is between 30 °C and 90 °C; during the drying of the sheets in stage B, the air humidity is between 5 g / kg and 30 g / kg (i.e., per kilogram of air).

[0052] Advantageously, means are provided for causing the circulating air to flow against and / or along the conveying direction of the sheets for the second stage B of the dryer.

[0053] In another advantageous embodiment of the dryer, the second stage B is provided with guiding means for guiding the circulating air in a spiral manner or is provided with at least one exhaust fan. Auxiliary guiding means are provided, for example in the form of guiding the sheets.

[0054] Preferably, a drum conveyor or a conveyor belt is provided as a conveying device for transporting the boards to be dried in the dryer.

[0055] Furthermore, the primary energy is utilized fully by using the condensation heat that is possible due to the relatively low temperature of the drying air for cooling the heat exchanger and the at least medium humidity of the exhaust air in stage A.

[0056] When the drying air flows countercurrently to the exhaust air from stage A through the heat exchanger, the colder drying air meets the already cooled exhaust air. This ensures that the water vapor contained in the exhaust air condenses as much as possible and further improves the utilization of the primary energy. A more intensive use of the primary energy can save a large amount of primary energy.

[0057] Overall, the drying capacity of stage B is at most 60% of that of stage A.

[0058] Each of stage A and stage B is equipped with a conveyor device for conveying the boards arranged in layers into the dryer. The dryer can be designed as a drum conveyor dryer or a belt dryer, wherein the conveyor device has a plurality of drum conveyors or conveyor belts stacked on one another.

[0059] The shelves are spaced at a distance between 100 mm and 150 mm, preferably 130 mm.

[0060] For additional transient loads, additional heating devices can be installed in stage B. Description of the Drawings

[0061] The invention is explained in more detail below using embodiments. A single drawing shows a dryer having two stages A and B and a heat pump. Detailed Description of the Invention

[0062] The dryer 1 (see figure) includes two stages A and B for drying the boards fed into the dryer 1 in the direction of arrow C. These boards are in particular building material boards, such as gypsum boards or gypsum wallboards.

[0063] Each of the two stages A and B is preferably divided into sections or zones 2. At least some of the zones 2 of stage A, in particular the front zones 2, are each equipped with a circulation fan 15 for generating a flow transverse to the board conveying direction.

[0064] Preferably, stage A has a sealing section 3 on the inlet side. The sealing section 3 is supplied via a supply line 6 equipped with a closable flap 5 with fresh air heated by the heat pump 4 or the heat exchanger 4; this fresh air supply is used not only for heating the boards, but also for sealing stage A against other airflows and external air entry into stage A.

[0065] The fresh air heated by the fan 8 is distributed to the respective ducts 9, 10, 11, 12, 13, 14 via a duct 7 branching off from the air supply duct 6 and via another duct 80. The fresh air reaches from there the heating devices 15 installed in some zones 2, which are arranged in a box in the top area, for example above the level for conveying the sheets. The heating devices 15 are preferably direct heating devices (such as burners) or indirect heating devices (such as steam heaters or electric heaters). At least one circulation fan 16 is provided within the zone 2 or jointly for several zones in order to generate a lateral flow of heated air within the zone 2 as recirculating air. Alternatively, two circulation fans 16 are provided for each zone 2. The moisture-rich air returns from the zone 2 via the outlet 38 to the heat exchanger 4, where the moisture condenses out.

[0066] The pre-dried sheets are transported from stage A to stage B, which is designed as a longitudinal dryer.

[0067] Stage B is also supplied with heated fresh air from the heat exchanger 4. Ducts 19 to 26 are used for this purpose.

[0068] Fans can also be installed in the ducts 19 to 26. At the inlet of section 2 of stage B, the air flowing into section 2 from the ducts 19 to 26 is heated by the heating devices 29 to 31. The heating devices 29 to 31 are switched on when additional heating energy is required; this is the case when starting up the system if stage A does not yet have sufficient heat and the heat exchanger 4 has not yet received the hot exhaust or stage A does not have sufficient hot exhaust. The heating devices are also required when the system is switched off and the hot air provided by stage A is not sufficient to enter stage B. The heating devices 29 to 31 can also be used when the moisture content of the sheets to be dried is higher than expected and in the case of a changeover between different sheet formats, which can lead to insufficient thermal energy in stage B. Therefore, the heating devices 29 to 31 are specifically provided for the transient loads of stage B.

[0069] It should be understood that a plurality of ducts for supplying air (in particular hot air from the heat exchanger 4 or from another heat exchanger) can be provided according to the length of stage B in order to recover the enthalpy of vaporization of the water evaporated from the sheets.

[0070] Normally, stage B does not require circulation fans; however, if such circulation fans must be provided, they are constructed and arranged in the same way as the circulation fans in stage A. Both radial fans and axial fans can be used.

[0071] Like the circulation fans, the exhaust fans 32 to 35 are distributed over the entire length of stage B. The moist air is discharged from stage B through these fans and the chimneys 36 to 39.

[0072] Additional internal heat exchangers can be provided in both phase A and phase B, for example, in the top box above the nozzle box in phase A or above the conveyor device in phase B (also in a top box provided for this purpose).

[0073] The heat exchanger 4 is connected to the zone 2 of phase A via the exhaust pipe 38 and the central exhaust pipe 39. The hot, moisture-saturated air is conveyed to the heat exchanger 4 through the exhaust pipes 38, 39 and the exhaust fan 40, and condenses in the heat exchanger 4, releasing its moisture in the form of water.

[0074] The heat exchanger 4 draws in fresh air through the fresh air fan 41. The heat exchanger 4 releases the used air into the environment through the chimney 42. A condensate separator 43 is provided between the fresh air fan 41 and the heat exchanger 4.

[0075] Phase B is designed as a longitudinal drying zone; at least in the front region of phase B, the air is guided countercurrent to the conveying direction of the sheet according to the intensity of the air supply via lines 19 to 26 relative to the used air drawn by the fans 32 to 34.

[0076] Due to the temperature preferably not exceeding 160°C overall in the dryer, all kinds of building sheets, especially gypsum sheets, but also cement sheets, are dried very gently with low energy consumption in the dryer according to the invention, whereby high-quality sheets can be produced.

[0077] The relatively low height of the large number of tiers also enables the sheets to be dried very effectively because a large number of sheets can be dried simultaneously in a small space. If the sheets are also conveyed in several adjacent channels, the production efficiency is further increased.

Claims

1. A method for drying a sheet in a drying apparatus including a first stage (A) and a second stage (B), wherein the two stages (A, B) each have a level, the sheets are placed layer by layer on the level surfaces respectively and the sheets are passed through the drying apparatus in the corresponding levels of the two stages (A, B), wherein the sheets are contacted with hot drying air and dried in the first stage (A), and are dried using drying air at a lower temperature in the second stage (B), characterized in that, Hot air from a device for heat recovery is supplied to the sheet in at least one of two stages (A, B), wherein the device is arranged outside the two stages, and wherein the hot air is directly supplied to the at least one stage.

2. The method according to claim 1, wherein The sheet is heated in at least the first stage by hot air generated by a heat exchanger, a heat pump, a wet separator, a burner directly or via hot steam or via heat transfer oil or indirectly via electricity or via low calorific value heat.

3. The method according to claim 1 or 2, characterized in that The moisture contained in the air condenses at a dew point between 60 °C and 99 °C in the first stage (A).

4. The method according to claim 3, wherein The moisture contained in the air condenses at a dew point between 75 °C and 90 °C in the first stage (A).

5. The method according to any one of claims 1 to 4, characterized in that, The moisture per kilogram of air in the air is between 5 g / kg and 30 g / kg in the second stage (B).

6. The method according to any one of claims 1 to 5, characterized in that The sheet is dried at least in the first stage (A) by circulating air.

7. The method according to any one of claims 1 to 6, characterized in that, The sheet is dried at least in the first stage (A) by drying air at a temperature between 120 °C and 160 °C.

8. The method according to any one of claims 1 to 7, characterized in that, The sheet is dried at least substantially by using a nozzle box in the region of at least the first stage (A).

9. The method according to any one of claims 1 to 8, characterized in that, The sheet is dried by drying air at a temperature between 20 °C and 90 °C in the second stage (B).

10. The method according to any one of claims 1 to 9, characterized in that, The exhaust gas from the first stage (A) is fed into a heat exchanger (31) for preheating the drying air in the second stage (B).

11. The method according to any one of claims 1 to 10, characterized in that, The sheet is first dried in a sealing stage (3) or a pre-drying stage upstream of the first stage (A), then dried in the first stage (A), and finally dried in the second stage (B).

12. A dryer for drying a sheet in a first stage (A) and a second stage (B), characterized in that, At least one of the two stages (A, B) can be supplied with hot air from a device for heat recovery, wherein the device is arranged outside the two stages, and wherein the hot air can be directly supplied to the at least one stage.

13. The dryer according to claim 12, characterized in that, The device for heat recovery includes a heat exchanger, a heat pump, a wet separator, and / or a burner for directly or indirectly heating the hot air by hot steam or by hot oil or by indirect electric heating or by low calorific value heat, wherein at most a single device for heat recovery is provided.

14. The dryer according to claim 12 or 13, characterized in that, The sheet in the first stage (A) can be heated by hot air flowing transversely to the conveying direction, and in the second stage (B) by hot air flowing in the longitudinal direction.

15. The dryer according to any one of claims 12 to 14, characterized in that, The second stage B is equipped with a device for causing the circulating air to flow against and / or along the conveying direction of the sheet.

16. The dryer according to one of claims 11 to 14, characterized in that, A condensate separator (43) is arranged upstream of at least one heat exchanger (4).

17. The dryer according to one of claims 12 to 16, characterized in that, It has at least 16 levels in which the sheet is dried and transported.

18. The dryer according to any one of claims 12 to 17, characterized in that, The levels are spaced 150 mm or less apart.

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