A fluidized bed drying method applicable to heat-sensitive materials

Abstract

The present invention relates to the technical field of fluidized bed drying, and specifically relates to a fluidized bed drying method suitable for heat-sensitive materials. The method is carried out in a fluidized bed dryer suitable for heat-sensitive materials, and the material is dried by using an inlet air temperature above the critical temperature of the material to be dried, and the inlet air temperature can keep the bed temperature of the fluidized bed lower than the critical temperature of the material to be dried; through the cooling effect of the cooling medium in the cooler, the surface temperature of the cooler is kept below the bed temperature of the fluidized bed; the critical temperature is the minimum value among the temperatures at which the material undergoes oxidation, decomposition, polymerization, deactivation and / or melting. The present invention realizes drying the material by using an inlet air temperature above the critical temperature of the material to be dried, greatly improves the evaporation intensity per unit area of the fluidized bed dryer, thereby greatly reducing the equipment volume, equipment investment, energy consumption and tail gas emissions.

Description

Technical Field

[0001] The present invention relates to the technical field of fluidized bed drying, and particularly relates to a fluidized bed drying method suitable for heat-sensitive materials. Background Art

[0002] The fluidized bed drying technology refers to that solid raw materials (usually powder-like crystals, wet materials, etc.) enter the fluidized bed through a feeding system or manually. Process gas is introduced into the air inlet chamber of the fluidized bed and passes through the gas distribution plate into the fluidized bed material layer, so that the raw materials form a specific fluidization state on the gas distribution plate of the fluidized bed.

[0003] A typical fluidized bed dryer has a fluidization chamber. Hot air enters from the bottom, passes through the material layer, and then discharges from the top. In engineering, based on the ordinary fluidized bed dryer, internal heating fluidized bed dryers, fluidized bed granulation dryers, vibrating fluidized bed dryers, etc. have been developed. For existing fluidized bed dryers, reference can be made to: CN201992951U - A fluidized bed drying and cooling machine with an internal coil heat exchanger, CN201565289U - A large-scale spray granulation fluidized bed dryer, CN103344093A - A vertical continuous fluidized bed granulation drying device and method, CN203605647U - A vibrating fluidized bed dryer.

[0004] From the perspective of thermal properties, heat-sensitive materials generally have a relatively low critical temperature turning point. During the drying operation, when the material temperature is above the critical temperature, the material will undergo undesirable physical, chemical, and biological property changes, resulting in a decline in product quality or performance. Therefore, when using existing fluidized bed dryers to dry heat-sensitive materials, the inlet air temperature usually has to be limited to be lower than the critical temperature. Due to the low inlet air temperature, the evaporation intensity per unit area (referring to the unit area of the air distribution plate) of the fluidized bed dryer is low, which causes a large increase in equipment volume, energy consumption, equipment investment, and tail gas emissions.

[0005] In most cases, the drying of materials can generally be divided into two stages: constant-rate drying and falling-rate drying. In the constant-rate drying stage, the temperature of the material is near the wet-bulb temperature of the inlet air, far lower than the dry-bulb temperature of the inlet air, and also lower than the critical temperature of most heat-sensitive materials commonly found in industry. Theoretically, it is allowed to use an inlet air temperature much higher than the wet-bulb temperature for drying, and the dried material in the fluidized bed can still be kept below the critical temperature while remaining in a fully fluidized state. However, production practice often deviates from the theoretical analysis, that is, when the inlet air temperature exceeds the critical temperature, the product quality and performance often decline. The inventors of the present invention have found based on many years of actual production experience that for the drying of highly heat-sensitive materials, when the inlet air temperature is above the critical temperature, it is easy to cause problems such as oxidation, decomposition, polymerization, deactivation, and / or melting of the material in direct contact with the air distribution plate and the wall surface of the fluidization section connecting the inlet air chamber. The reasons are as follows: First, the air distribution plate is the area directly affected by the heat transfer of the hot air, and the surface temperature of the air distribution plate is very close to the inlet air temperature. For the wall surface of that part of the fluidization section connected to the inlet air chamber, due to the combined action of the heat conduction of the high-temperature wall surface of the inlet air chamber and the convective heat transfer of the hot air near the upper surface of the air distribution plate, the wall surface temperature of this section is also close to the inlet air temperature. When the inlet air temperature is above the critical temperature of the material, the temperature in both of these two regions will be equal to or exceed the critical temperature. Second, during the drying process, the material stays in contact with the upper surface of the air distribution plate and the wall surface of the fluidization section connected to the inlet air chamber for a relatively long time, giving the material the opportunity to be heated above the critical temperature, especially at the air distribution plate. Because the hole opening rate of the air distribution plate (i.e., the ratio of the opening area of the distribution holes on the air distribution plate to the total area of the air distribution plate) is generally between 1% and 20%, in the area near the air distribution plate, there is a certain distance from when the fluidizing air jets out from the gas distribution holes in a jet shape to when it evenly diffuses into the mainstream air flow. So, the mixing and disturbance of the material and air near the air distribution plate are in an unstable state. Some particles will directly contact the air distribution plate and stay on the air distribution plate for a relatively long time, and thus have a relatively high possibility of being heated above the critical temperature by the air distribution plate. Coupled with the fact that there is a concentration of large particles at the lower part of the bed layer, and even some material agglomerates cannot be fluidized and thus stay on the air distribution plate, it is even easier to be heated above the critical temperature by the air distribution plate or the nearby wall surface of the fluidization section. This causes problems such as oxidation, decomposition, polymerization, deactivation, and / or melting of some materials, resulting in a decline in product quality or performance, and further limiting the increase in the inlet air temperature. Summary of the Invention

[0006] The object of the present invention is to provide a fluidized bed drying method suitable for heat-sensitive materials, which realizes drying heat-sensitive materials with an inlet air temperature above the critical temperature of the dried material, and can prevent heat-sensitive materials from undergoing oxidation, decomposition, polymerization, deactivation, and / or melting problems due to being above the critical temperature during the drying process, thereby greatly increasing the evaporation intensity per unit area of the fluidized bed dryer.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A fluidized bed drying method applicable to heat-sensitive materials, which is carried out in a fluidized bed dryer applicable to heat-sensitive materials. The fluidized bed dryer applicable to heat-sensitive materials includes a bed body and a cooler. An air inlet chamber, a fluidization section, and a separation section are sequentially arranged in the bed body from bottom to top. An outlet is provided on the bed body. The cooler includes a cooling air distribution plate, which is arranged between the air inlet chamber and the fluidization section. A hot air passage is provided on the cooling air distribution plate. A cooling cavity is arranged inside the cooling air distribution plate, and a cooling medium is passed through the cooling cavity. During the drying process, the material is dried with an inlet air temperature above the critical temperature of the material to be dried, and the inlet air temperature can keep the bed temperature of the fluidized bed lower than the critical temperature of the material to be dried. Through the cooling effect of the cooling medium in the cooler, the surface temperature of the cooler is kept below the bed temperature of the fluidized bed. The critical temperature is the minimum value among the temperatures at which the material undergoes oxidation, decomposition, polymerization, inactivation, and / or melting.

[0008] In the present invention, the temperature at which oxidation occurs refers to the temperature at which the components of the material undergo an oxidation reaction resulting in the denaturation of the material. For example, potassium sorbate will gradually undergo surface oxidation and turn yellow above 125°C. The temperature at which decomposition occurs refers to the temperature at which a compound is decomposed into simpler compounds or elements by heating. When various crystals with crystal water are heated and lose one or more molecules of crystal water, this is the case. For example, during the drying process of copper sulfate pentahydrate, two molecules of crystal water are lost when heated to 45°C, four molecules of crystal water are lost at 110°C, and all crystal water is lost at 200°C. For the drying of copper sulfate pentahydrate products, the temperature at which decomposition occurs is 45°C. Another example is that industrial-grade ammonium carbonate decomposes into carbon dioxide, ammonia, and water above 58°C. The temperature at which polymerization occurs generally refers to the temperature at which low-molecular compounds are converted into high-molecular compounds through chemical bond connection. For example, during the drying process of aspartic acid, a polymerization reaction occurs to form polyaspartic acid when staying above 105°C for a long time. The temperature at which inactivation occurs refers to the temperature at which a biologically active material loses its biological activity. For example, for active yeast feed, the microorganisms such as yeast it contains will cause partial or all of the microorganisms to die and become unable to survive when the temperature exceeds 50°C. The temperature at which melting occurs refers to the temperature at which the physical state of a solid material changes from solid to liquid. For example, the melting point of fertilizer-grade urea is between 105 and 110°C.

[0009] In the present invention, the inlet air temperature is obtained through tests or product trial production and needs to meet two conditions: one is above the critical temperature of the material to be dried, and the other is that the bed temperature of the fluidized bed can be maintained below the critical temperature of the material to be dried. Under the inlet air temperature conditions of the present invention, restricted by the wet bulb temperature, the bed temperature of the fluidized bed can be maintained below the critical temperature of the material to be dried, thereby preventing problems such as oxidation, decomposition, polymerization, deactivation, and / or melting of the material in the fluidized bed due to being above its critical temperature.

[0010] Compared with the prior art, the beneficial effects of the fluidized bed drying method for heat-sensitive materials in the present invention are as follows: When drying the material with an inlet air temperature above the critical temperature of the material to be dried, through the cooling effect of the cooling medium in the cooler, the surface temperature of the cooler is maintained below the bed temperature of the fluidized bed, that is, below the critical temperature of the material, to prevent the material in the fluidized bed dryer from overheating due to contact with the cooling air distribution plate. Therefore, the fluidized bed dryer allows the material to be dried with an inlet air temperature above the critical temperature of the material to be dried, resulting in a significant increase in the evaporation intensity per unit area of the fluidized bed dryer, thereby greatly reducing the equipment volume, equipment investment, energy consumption, and tail gas emissions. Under the condition of the same evaporation capacity, the fluidized bed dryer has a higher evaporation intensity, a smaller equipment volume, less tail gas emissions, and lower energy consumption.

[0011] Furthermore, the cooler further includes a cooling jacket through which a cooling medium passes, and the cooling jacket is provided on the wall surface of the bed body in the fluidization section. Even if the heat conduction from the high-temperature wall surface of the inlet air chamber to the wall surface of the fluidization section is completely blocked by the cooling air distribution plate, when drying the material with an inlet air temperature above the critical temperature of the material to be dried, the convective heat transfer of the hot air near the upper surface of the cooling air distribution plate will still cause the wall surface temperature of the fluidization section to approach the inlet air temperature. With this technical solution, by introducing a cooling medium into the cooling jacket, the wall surface temperature of the fluidization section connected to the inlet air chamber is always maintained below the critical temperature of the material, preventing the material in the fluidized bed dryer from overheating due to contact with the high-temperature wall surface of the fluidization section.

[0012] Preferably, the cooling jacket extends upward from the cooling air distribution plate by 20 to 300 mm. Due to the intense heat and mass transfer in the fluidized bed dryer and the intense backmixing of the materials in the bed body in the height direction, starting from the cooling air distribution plate upward, the bed temperature will rapidly drop to the bed temperature in the mainstream area, and most areas of the entire bed layer maintain a uniform operating temperature in the height direction. From production practice, the height of this temperature decay layer does not exceed 300 mm, and generally, the temperature transition from the inlet air temperature to the bed temperature in the mainstream area will be completed within 150 mm. Therefore, it is not necessary to be higher than 300 mm, which will also lead to an increase in the cost of the cooling jacket; when it is lower than 20 mm, the process of this temperature reduction may not be completed, and there is still a possibility of overheating of the materials, and too small a size is not conducive to the processing and production of the cooling jacket.

[0013] Preferably, the cooling jacket extends upward from the cooling air distribution plate by 150 mm.

[0014] Preferably, the cooling air distribution plate includes a plurality of unit components arranged at intervals in the horizontal direction on the bed body, and a hot air channel is formed between the unit components, and a cooling cavity is provided in the unit components.

[0015] Preferably, distribution manifolds are also provided on both sides of the cooling air distribution plate, and the distribution manifolds on both sides are respectively connected to both ends of each unit component. With this technical solution, the distribution manifolds on both sides of the cooling air distribution plate are respectively used for introducing and discharging the cooling medium into the unit components.

[0016] Further, the unit component includes an upper pressing strip, a lower pressing strip and a bending part, and the upper pressing strip and the lower pressing strip are connected through the bending part; the upper pressing strip of the unit component is stacked above the lower pressing strip of its adjacent unit component behind, and the outlet of the hot air channel faces the discharge port and is parallel to the cooling air distribution plate. Since the hot air faces the discharge port and is parallel to the cooling air distribution plate, this technical solution has a strong ability to discharge large pieces or large particles of materials.

[0017] Further, the fluidized bed dryer applicable to heat-sensitive materials further includes a cooling medium supply system and a temperature detection module; the cooling medium supply system is used to supply a cooling medium to the cooler; the temperature detection module includes a bed temperature detection unit and a cooler temperature detection unit, the bed temperature detection unit is used to obtain the bed temperature of the fluidized bed, and the cooler temperature detection unit is used to obtain the surface temperature of the cooler or the cooling medium temperature at the outlet of the cooler or the cooling medium temperature at the inlet of the cooler.

[0018] Further, a controller is also included, and the controller is used to control the cooling capacity provided by the cooling medium supply system to the cooler according to the temperature value obtained by the temperature detection module, so as to keep the surface temperature of the cooler below the bed temperature of the fluidized bed.

[0019] Furthermore, the cooling medium supply system includes a coolant tank, a circulation pump, and a heat exchanger. The coolant tank, the circulation pump, and the heat exchanger are sequentially connected through a cooling medium pipeline and form a circulation system with the cooler; a refrigerant inlet valve is provided on the heat exchanger, and the circulation pump, the temperature detection module, and the refrigerant inlet valve are all connected to the controller; the bed temperature detection unit is arranged in the fluidization section, and the cooler temperature detection unit is arranged at the outlet of the cooler. The controller is used to control the flow rate of the circulation pump and / or the opening degree of the refrigerant inlet valve according to the temperature value obtained by the temperature detection module.

[0020] Preferably, the outlet of the hot air channel is perpendicular to the cooling air distribution plate, so that the hot air forms an upward airflow perpendicular to the cooling air distribution plate; alternatively, the outlet of the hot air channel faces the discharge port and forms an acute angle with the cooling air distribution plate, so that the hot air has a side blowing force towards the discharge port direction, which is beneficial to quickly discharging large pieces or large particles of materials in the fluidized bed dryer and avoiding the normal bed fluidization being damaged due to a large amount of large pieces or large particles of materials deposited on the cooling air distribution plate.

[0021] Preferably, the cross-sectional area of the hot air channel gradually decreases from bottom to top. With this technical solution, the particulate materials leaking from the cooling air distribution plate can smoothly pass through the hot air channel, avoiding the particulate materials being stuck in the hot air channel.

[0022] Preferably, the fluidized bed dryer is a fixed fluidized bed dryer, a fluidized bed granulation dryer, or a vibrating fluidized bed dryer. Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of the fluidized bed dryer applicable to heat-sensitive materials in Embodiment 1.

[0024] Figure 2 It is a schematic structural diagram of the cooler in Embodiment 1.

[0025] Figure 3 It is a top view of the cooling air distribution plate in Embodiment 1.

[0026] Figure 4 It is a sectional view of the cooling air distribution plate in Embodiment 1.

[0027] Figure 5 It is a sectional view of the cooling air distribution plate in Embodiment 2.

[0028] Figure 6 It is a top view of the cooling air distribution plate in Embodiment 3.

[0029] Figure 7 It is a sectional view of the cooling air distribution plate in Embodiment 3.

[0030] Figure 8 It is a sectional view of the cooling air distribution plate in Embodiment 4.

[0031] Figure 9 It is a schematic structural diagram of a fluidized bed dryer suitable for heat-sensitive materials in Example 5.

[0032] Figure 10 It is a schematic structural diagram of the cooler in Example 5.

[0033] Figure 11 It is a top view of the cooling air distribution plate in Example 5.

[0034] Figure 12 It is a sectional view of the cooling air distribution plate in Example 5.

[0035] Figure 13 It is a sectional view of the cooling air distribution plate in Example 6.

[0036] Figure 14 It is a sectional view of the cooling air distribution plate in Example 7.

[0037] Figure 15 It is a schematic structural diagram of a fluidized bed dryer suitable for heat-sensitive materials in Example 8.

[0038] Wherein: 1-unit assembly, 2-hot air channel, 3-cooling chamber, 4-upper pressing strip, 5-lower pressing strip, 6-bending part, 7-bed body, 8-air inlet chamber, 9-fluidization section, 10-separation section, 11-cooling jacket, 12-cooling air distribution plate, 13-coolant tank, 14-circulation pump, 15-heat exchanger, 16-cooler temperature detection unit, 17-controller, 18-cooling medium pipeline, 19-refrigerant inlet valve, 20-blower, 21-air heater, 22-cyclone dust collector, 23-induced draft fan, 24-first cooling medium pipe orifice, 25-second cooling medium pipe orifice, 26-distribution main pipe, 27-first communication flow channel, 28-second communication flow channel, 29-spray gun, 30-return pipe, 31-vibrating motor, 32-spring seat, 33-control valve, 34-bed layer temperature detection unit. Detailed implementation manners

[0039] The following embodiments further illustrate the present invention, but the present invention is not limited thereto.

[0040] Embodiment 1

[0041] Figures 1 to 4 Embodiment 1 of the present invention is shown.

[0042] As Figure 1 shown, a fluidized bed dryer suitable for heat-sensitive materials. The fluidized bed dryer in this embodiment is a fixed fluidized bed dryer, and includes a bed body 7, a blower 20, an air heater 21, a cyclone dust collector 22, an induced draft fan 23, a cooler, a cooling medium supply system, and a temperature detection module.

[0043] Inside the bed body 7, an air inlet chamber 8, a fluidization section 9, and a separation section 10 are successively arranged from bottom to top. An outlet is provided at the end of the bed body 7. The blower 20 and the air heater 21 are successively connected to the air inlet of the air inlet chamber through pipelines to provide hot air for drying materials; the cyclone dust collector 22 and the induced draft fan 23 are successively connected to the air outlet of the separation section 10 through pipelines to discharge tail gas.

[0044] The cooler includes a cooling jacket 11 and a cooling air distribution plate 12.

[0045] As Figure 2 shown, the cooling air distribution plate 12 is arranged between the air inlet chamber 8 and the fluidization section 9. As Figure 3 、 Figure 4 shown, hot air channels 2 are evenly distributed on the cooling air distribution plate 12 for guiding hot air from the air inlet chamber 8 into the fluidization section 9. A cooling cavity 3 is arranged inside the cooling air distribution plate 12, and a cooling medium is passed through the cooling cavity 3. Two first cooling medium nozzles 24 communicating with the cooling cavity 3 are arranged on the cooling air distribution plate 12. Figure 2 The left first cooling medium nozzle 24 in is used for the input of the cooling medium, and the right first cooling medium nozzle 24 is used for the output of the cooling medium. The hot air channels 2 are circular straight holes, and their extending direction is perpendicular to the cooling air distribution plate 12, so that the hot air forms an upward airflow perpendicular to the cooling air distribution plate 12 through the hot air channels 2.

[0046] The cooling jacket 11 is arranged on the wall surface of the bed body 7 of the fluidization section 9 and extends 150 mm upward from the air distribution plate 12. A cooling medium is passed through the cooling jacket 11. Two second cooling medium nozzles 25 communicating with its inner cavity are arranged on the cooling jacket 11. Figure 2 The left second cooling medium nozzle 25 in is used for the input of the cooling medium, and the right second cooling medium nozzle 25 is used for the output of the cooling medium.

[0047] The cooler is connected to a cooling medium supply system, which is used to supply cooling medium to the cooler. In this embodiment, the cooling medium supply system is respectively connected to the cooling jacket 11 and the cooling air distribution plate 12. Specifically, the cooling medium supply system includes a coolant tank 13, a circulation pump 14, a heat exchanger 15, and a control valve 33. The coolant tank 13, the circulation pump 14, and the heat exchanger 15 are sequentially connected through a cooling medium pipeline 18 and respectively form a circulation system with the cooling jacket 11 and the cooling air distribution plate 12. The control valve 33 is respectively arranged at the inlets of the cooling jacket 11 and the cooling air distribution plate 12 to respectively control the supply amount of the cooling medium for the cooling jacket 11 and the cooling air distribution plate 12. The refrigerant of the heat exchanger 15 can be air, water or other media. In this embodiment, water is used as the refrigerant for the heat exchanger 15, and a refrigerant inlet valve 19 is provided on the heat exchanger 15.

[0048] The temperature detection module includes a bed temperature detection unit 34 and a cooler temperature detection unit 16. The bed temperature detection unit 34 is used to obtain the bed temperature of the fluidized bed. Specifically, the bed temperature detection unit 34 is arranged in the fluidization section 9 and is located 100 - 300 mm above the cooling air distribution plate 12. Since the bed of the fluidized bed has an isothermal characteristic, that is, the bed temperature of the fluidized bed is basically the same, the temperature obtained by the bed temperature detection unit 34 at this position represents the bed temperature of the fluidized bed (in this height area, the material is both close to the cooling air distribution plate 12 and has left the area with a drastic temperature change near the cooling air distribution plate 12, and the measured temperature is the highest temperature in the area where the temperature is uniform in the height direction of the fluidized bed layer). The cooler temperature detection unit 16 is used to obtain the surface temperature of the cooler. Those skilled in the art can understand that the surface of the cooler refers to the surface of the cooler in contact with the material. Specifically, in this embodiment, one cooler temperature detection unit 16 is provided on the surface of each of the cooling jacket 11 and the cooling air distribution plate 12, which can respectively obtain the surface temperatures of the cooling jacket 11 and the cooling air distribution plate 12. The bed temperature detection unit 34 and the cooler temperature detection unit 16 are thermocouples, which directly measure the temperature and convert the temperature signal into a thermoelectric signal, and are converted into the temperature of the measured medium through an electrical instrument (secondary instrument) outside the bed body 7.

[0049] Through calculation or experiment, the corresponding relationship between the surface temperature of the cooler and the cooling capacity provided by the cooling medium supply system is determined in advance. When the cooling medium supply system provides cooling capacity to the cooler according to this corresponding relationship, it can ensure that the surface temperature of the cooler is below the bed temperature of the fluidized bed and prevent the cooling medium supply system from consuming too much energy due to providing too much cooling capacity. The cooling medium supply system can change the cooling capacity in various ways, such as changing the flow rate of the circulation pump 14 and / or the opening degree of the refrigerant inlet valve 19 and / or the opening degree of the control valve 33.

[0050] This embodiment also provides a fluidized bed drying method using the above fluidized bed dryer for drying heat-sensitive materials. In this embodiment, the heat-sensitive material to be dried is citric acid monohydrate, which begins to decompose at 50-70°C and loses its crystal water at 50-70°C, becoming anhydrous citric acid.

[0051] In the existing fluidized bed drying method, since no cooling measures are taken for the air distribution plate and the inner wall of the fluidization section, when drying the material with an inlet air temperature above the critical temperature of the material to be dried, under the heat transfer (or heating) action of the high-temperature inlet air, the wall surface temperature of the air distribution plate and the fluidization section connecting the inlet air chamber will reach or even exceed the critical temperature of the material, and the material has the opportunity to contact the upper surface of the air distribution plate and the wall surface of the fluidization section connecting the inlet air chamber for a long time. Therefore, it is easy for this part of the material to be heated by the upper surface of the air distribution plate and the wall surface of the fluidization section of the inlet air chamber and reach or even exceed the critical temperature. Therefore, in order to prevent citric acid monohydrate from decomposing at a temperature above the critical temperature, the inlet air temperature needs to be limited to below 50°C, which results in a low evaporation intensity per unit area of the fluidized bed dryer, and greatly increases the operating costs such as equipment investment, energy consumption, plant investment, and tail gas emissions.

[0052] The fluidized bed drying method of this embodiment includes the following steps:

[0053] S1. Sequentially turn on the induced draft fan 23, the blower 20, and the air heater 21, then turn on the circulation pump 14, control the inlet air temperature below 50°C, and start feeding the bottom material to the required layer height.

[0054] S2. After the feeding of the bottom material is completed, turn on the heat exchanger 15, gradually increase the inlet air temperature to 75°C, and at the same time feed the wet material and gradually increase it to the normal flow rate to start drying the material.

[0055] 75°C is the inlet air temperature obtained through experiments or product trial production. At 75°C, due to the limiting effect of the wet bulb temperature, the bed temperature of the fluidized bed can be maintained below the critical temperature of the material to be dried, thereby preventing citric acid monohydrate in the fluidized bed from decomposing at a temperature above its critical temperature.

[0056] During the drying process, the bed temperature of the fluidized bed is obtained by the bed temperature detection unit 34, and the surface temperatures of the cooling jacket 11 and the cooling air distribution plate 12 are obtained by the cooler temperature detection unit 16. The operator selects the higher value of the surface temperatures of the cooling jacket 11 and the cooling air distribution plate 12 as the judgment criterion, and changes the cooling capacity provided by the cooling medium supply system to the cooler according to the judgment criterion and the preset corresponding relationship, so as to keep the surface temperature of the cooler below the bed temperature of the fluidized bed, that is, below the critical temperature of monohydrate citric acid. The critical temperature of monohydrate citric acid refers to the lowest temperature at which monohydrate citric acid decomposes and loses its crystal water, that is, 50 °C, so as to ensure that monohydrate citric acid will not decompose due to overheating during normal production.

[0057] In this embodiment, the fluidized bed dryer suitable for heat-sensitive materials allows the use of an inlet air temperature of 75 °C to dry monohydrate citric acid, which increases the evaporation intensity per unit area of the fluidized bed dryer by 50%. Under the condition of the same evaporation capacity, the equipment volume and tail gas emission of the fluidized bed dryer are reduced by 1 / 2, and the energy consumption is reduced by 50%, so that the equipment investment, energy consumption, and tail gas emission are all greatly reduced.

[0058] Embodiment 2

[0059] Figure 5 Embodiment 2 of the present invention is shown. The difference from Embodiment 1 is that the extending direction of the hot air channel 2 in this embodiment forms an acute angle with the cooling air distribution plate 12, and its outlet faces the discharge port, so that the hot air has a side blowing force towards the discharge port direction, which is beneficial to quickly discharge large pieces or large particles of materials in the fluidized bed dryer, and avoid damaging the normal bed fluidization due to the large amount of deposition of large pieces or large particles of materials on the cooling air distribution plate 12.

[0060] Embodiment 3

[0061] Figure 6 、 Figure 7 Embodiment 3 of the present invention is shown. The difference from Embodiment 1 is that the cross-sectional shape of the hot air channel 2 in this embodiment is rectangular, and the hot air channel 2 is in a tapered shape with a smaller upper part and a larger lower part, that is, the cross-sectional area of the hot air channel 2 gradually decreases from bottom to top. Based on this design, the particulate materials leaking from the cooling air distribution plate 12 can smoothly pass through the hot air channel 2, avoiding the particulate materials being stuck in the hot air channel 2.

[0062] Embodiment 4

[0063] Figure 8Embodiment 4 of the present invention is shown. The difference from Embodiment 3 is that the extending direction of the hot air channel 2 in this embodiment forms an acute angle with the cooling air distribution plate 12, and its outlet faces the discharge port, so that the hot air has a side blowing force towards the discharge port, which is beneficial to quickly discharge large pieces or large particles of materials in the fluidized bed dryer, and avoid damaging the normal bed fluidization due to the large amount of deposition of large pieces or large particles of materials on the cooling air distribution plate 12.

[0064] Embodiment 5

[0065] Figures 9 to 12 Embodiment 5 of the present invention is shown.

[0066] As Figure 5 shown, a fluidized bed dryer suitable for heat-sensitive materials. The fluidized bed dryer in this embodiment is a fluidized bed granulation dryer, which includes a bed body 7, a blower 20, an air heater 21, a cyclone dust collector 22, an induced draft fan 23, a cooler, a cooling medium supply system, a temperature detection module, and a controller 17.

[0067] An air inlet chamber 8, a fluidization section 9, and a separation section 10 are sequentially arranged in the bed body 7 from bottom to top, and a discharge port is arranged at the end of the bed body 7. The blower 20 and the air heater 21 are sequentially connected to the air inlet of the air inlet chamber through pipelines for providing hot air for drying materials; the cyclone dust collector 22 and the induced draft fan 23 are sequentially connected to the air outlet of the separation section 10 through pipelines for discharging tail gas. A spray gun 29 and a return pipe 30 are arranged on the bed body 7. The spray gun 29 is used to spray atomized liquid materials onto the surface of the particulate materials in a fluidized state in the fluidization section 9. Under the action of coating and agglomeration, the liquid materials are agglomerated on the surface of the particles. The return pipe 30 is connected to the discharge end of the cyclone dust collector 22. After the fine particulate matters entrained in the tail gas are separated by the cyclone dust collector 22, they return to the bed body 7 through the return pipe 30 to participate in granulation.

[0068] The cooler includes a cooling jacket 11 and a cooling air distribution plate 12.

[0069] As Figure 10 shown, the cooling air distribution plate 12 is arranged between the air inlet chamber 8 and the fluidization section 9.

[0070] There are multiple unit components 1, and the multiple unit components 1 are arranged at intervals on the bed body 7 substantially along the horizontal direction. A hot air channel 2 is formed between the unit components 1. A cooling cavity 3 is arranged in the unit component 1, and a cooling medium is passed through the cooling cavity 3. There are two distribution main pipes 26, and the two distribution main pipes 26 are respectively connected to both ends of each unit component 1.

[0071] In this embodiment, the cross-sections of the unit component 1 and the cooling chamber 3 are both equilateral triangles, forming a hot air channel 2 that gradually decreases from bottom to top. The particulate material leaking from the cooling air distribution plate 12 can smoothly pass through the hot air channel 2 without being stuck. The outlet of the hot air channel 2 is perpendicular to the cooling air distribution plate 12, and the hot air forms an upward airflow perpendicular to the cooling air distribution plate 12 through the hot air channel 2. Those skilled in the art can conceive that the unit component 1 and the cooling chamber 3 with equilateral triangle cross-sections in this embodiment can also be replaced with regular trapezoidal structures (either upright or inverted).

[0072] The cooling jacket 11 is provided on the wall surface of the bed body 7 in the fluidization section 9 and extends 150 mm upward from the air distribution plate 12. A cooling medium is passed through the cooling jacket 11. In this embodiment, two cooling jackets 11 are symmetrically arranged on the left and right. The cooling jacket 11 is provided with a second cooling medium pipe orifice 25 communicating with its inner cavity. Figure 10 The second cooling medium pipe orifice 25 on the left cooling jacket 11 in the figure is used for the input of the cooling medium, and the second cooling medium pipe orifice 25 on the right cooling jacket 11 is used for the output of the cooling medium.

[0073] As Figure 11 、 Figure 12 shown, distribution headers 26 are also provided on both sides of the cooling air distribution plate. The upper surface of the distribution header 26 is provided with a first communication flow channel 27 communicating with the cooling jacket 11, and the side of the distribution header 26 is provided with a second communication flow channel 28 communicating with each unit component 1. The cooling jacket 11 and the cooling air distribution plate 12 form a series structure through two distribution headers 26. Refer to Figure 10 In the figure, during operation, the cooling medium sequentially flows through the second cooling medium pipe orifice 25 on the left, the left cooling jacket 11, the left first communication flow channel 27, the left distribution header 26, the left second communication flow channel 28, the unit component 1, the right second communication flow channel 28, the right distribution header 26, the right first communication flow channel 27, the right cooling jacket 11, and the second cooling medium pipe orifice 25 on the right.

[0074] The cooler is connected to a cooling medium supply system, and the cooling medium supply system is used to supply a cooling medium to the cooler. Specifically, the cooling medium supply system includes a coolant tank 13, a circulation pump 14, and a heat exchanger 15. The coolant tank 13, the circulation pump 14, the heat exchanger 15, and the cooler are sequentially connected through a cooling medium pipeline 18. The refrigerant of the heat exchanger 15 can be air, water, or other media. In this embodiment, water is used as the refrigerant for the heat exchanger 15, and the heat exchanger 15 is provided with a refrigerant inlet valve 19.

[0075] The circulating pump 14, the temperature detection module, and the refrigerant inlet valve 19 are all connected to the controller 17. The temperature detection module includes a bed temperature detection unit 34 and a cooler temperature detection unit 16. The bed temperature detection unit 34 is used to obtain the bed temperature of the fluidized bed. Specifically, the bed temperature detection unit 34 is arranged in the fluidization section 9 and is located 100 - 300 mm above the cooling air distribution plate 12. The cooler temperature detection unit 16 is arranged on the cooling medium pipeline 18 upstream of the coolant tank 13 and can obtain the temperature of the cooling medium at the outlet of the cooling air distribution plate 12.

[0076] The controller 17 is used to control the cooling capacity provided by the cooling medium supply system to the cooler according to the temperature of the cooling medium in the cooling medium pipeline 18. Specifically, through calculation or experiment, the corresponding relationship between the temperature of the cooling medium at the outlet of the cooling air distribution plate 12 and the cooling capacity provided by the cooling medium supply system is determined in advance. When the cooling medium supply system provides cooling capacity to the cooler according to this corresponding relationship, it can ensure that the surface temperature of the cooler is below the bed temperature of the fluidized bed and prevent the cooling medium supply system from consuming too much energy due to providing too much cooling capacity. The cooling medium supply system can change the cooling capacity in various ways, such as changing the flow rate of the circulating pump 14 and / or the opening degree of the refrigerant inlet valve 19.

[0077] Embodiment 6

[0078] Figure 13 Embodiment 6 of the present invention is shown. Different from Embodiment 5, in this embodiment, the cross-sections of the unit component 1 and the cooling chamber 3 are both quadrilateral, and the length of the bottom side of the quadrilateral is less than the length of the top side, forming a hot air channel 2 that gradually decreases from bottom to top. The particulate material leaking from the cooling air distribution plate 12 can smoothly pass through the hot air channel 2 without being stuck. The outlet of the hot air channel 2 faces the discharge port and forms an acute angle with the cooling air distribution plate 12. The hot air has a side blowing force towards the discharge port direction, which is beneficial to quickly discharging large pieces or large particles in the fluidized bed dryer and avoiding the normal bed fluidization being damaged due to a large amount of large pieces or large particles depositing on the cooling air distribution plate 12.

[0079] Embodiment 7

[0080] Figure 14 Embodiment 7 of the present invention is shown. Different from Embodiment 5, in this embodiment, the unit component 1 includes an upper pressing strip 4, a lower pressing strip 5, and a bending part 6. The upper pressing strip 4 is connected to the lower pressing strip 5 through the bending part 6; the upper pressing strip 4 of the unit component 1 is laminated above the lower pressing strip 5 of its adjacent unit component 1. The outlet of the hot air channel 2 faces the discharge port and is parallel to the cooling air distribution plate 12. Compared with the form in Embodiment 2 where the outlet of the hot air channel 2 faces the discharge port and forms an acute angle with the cooling air distribution plate 12, this embodiment has a stronger ability to discharge large particles or lumps.

[0081] Example 8

[0082] Figure 15 Example 8 of the present invention is shown.

[0083] As Figure 8 shown, a fluidized bed dryer suitable for heat-sensitive materials. The fluidized bed dryer in this embodiment is a vibrating fluidized bed dryer, which includes a bed body 7, a blower 20, an air heater 21, a cyclone dust collector 22, an induced draft fan 23, a cooler, a cooling medium supply system, a temperature detection module, and a controller 17.

[0084] An air inlet chamber 8, a fluidization section 9, and a separation section 10 are sequentially arranged in the bed body 7 from bottom to top, and a discharge port is provided at the end of the bed body 7. The blower 20 and the air heater 21 are sequentially connected to the air inlet of the air inlet chamber through pipelines to provide hot air for drying materials; the cyclone dust collector 22 and the induced draft fan 23 are sequentially connected to the air outlet of the separation section 10 through pipelines to discharge tail gas. Spring seats 32 are provided at the bottom of the bed body 7, and vibration motors 31 are provided on both sides of the bed body 7. During the drying process, mechanical vibration is provided by the vibration motors 31 to help fluidize the materials, which not only facilitates boundary layer turbulence and strengthens heat and mass transfer, but also ensures that the dryer operates under relatively stable fluid mechanics conditions.

[0085] The cooler includes a cooling air distribution plate 12, and the structure of the cooling air distribution plate 12 in this embodiment is the same as that in Embodiment 1.

[0086] The cooler is connected to the cooling medium supply system, and the cooling medium supply system is used to supply cooling medium to the cooler. Specifically, the cooling medium supply system includes a coolant tank 13, a circulation pump 14, and a heat exchanger 15. The coolant tank 13, the circulation pump 14, the heat exchanger 15, and the cooler are sequentially connected through a cooling medium pipeline 18. The refrigerant of the heat exchanger 15 can be air, water, or other media. In this embodiment, water is used as the refrigerant for the heat exchanger 15, and a refrigerant inlet valve 19 is provided on the heat exchanger 15.

[0087] The circulation pump 14, the temperature detection module, and the refrigerant inlet valve 19 are all connected to the controller 17. The temperature detection module includes a bed temperature detection unit 34 and a cooler temperature detection unit 16. The bed temperature detection unit 34 is used to obtain the bed temperature of the fluidized bed. Specifically, the bed temperature detection unit 34 is arranged in the fluidization section 9 and is located 50 - 300 mm above the cooling air distribution plate 12. The cooler temperature detection unit 16 is arranged on the cooling medium pipeline 18 upstream of the coolant tank 13 and can obtain the temperature of the cooling medium at the outlet of the cooling air distribution plate 12.

[0088] The controller 17 is used to control the cooling capacity provided by the cooling medium supply system to the cooler according to the temperature of the cooling medium in the cooling medium pipeline 18. Specifically, through calculation or tests, the corresponding relationship between the temperature of the cooling medium at the outlet of the cooling air distribution plate 12 and the cooling capacity provided by the cooling medium supply system is determined in advance. When the cooling medium supply system provides the cooling capacity to the cooler according to this corresponding relationship, it can ensure that the surface temperature of the cooler is below the bed temperature of the fluidized bed and prevent the cooling medium supply system from consuming too much energy due to providing excessive cooling capacity. The cooling medium supply system can change the cooling capacity in various ways, such as changing the flow rate of the circulation pump 14 and / or the opening degree of the refrigerant inlet valve 19.

[0089] The above-described embodiments are merely descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A fluidized bed drying method applicable to heat-sensitive materials, characterized in that, The material is dried in a fluidized bed dryer suitable for heat-sensitive materials. The fluidized bed dryer suitable for heat-sensitive materials includes a bed body (7) and a cooler. In the bed body (7), an air inlet chamber (8), a fluidization section (9), and a separation section (10) are sequentially arranged from bottom to top. An outlet is provided on the bed body (7). The cooler includes a cooling air distribution plate (12). The cooling air distribution plate (12) is arranged between the air inlet chamber (8) and the fluidization section (9). A hot air channel (2) is provided on the cooling air distribution plate (12). A cooling cavity (3) is arranged inside the cooling air distribution plate (12), and a cooling medium is passed through the cooling cavity (3). During the drying process, the material is dried with an inlet air temperature above the critical temperature of the material to be dried, and the inlet air temperature can keep the bed temperature of the fluidized bed lower than the critical temperature of the material to be dried. Through the cooling effect of the cooling medium in the cooler, the surface temperature of the cooler is kept below the bed temperature of the fluidized bed. The critical temperature is the minimum value among the temperatures at which the material undergoes oxidation, decomposition, polymerization, inactivation, and / or melting.

2. The fluidized bed drying method applicable to heat-sensitive materials according to claim 1, characterized in that, The cooler further includes a cooling jacket (11). A cooling medium is passed through the cooling jacket (11). The cooling jacket (11) is arranged on the wall surface of the bed body (7) of the fluidization section (9).

3. The fluidized bed drying method applicable to heat-sensitive materials according to claim 2, characterized in that, The cooling jacket (11) extends upward from the cooling air distribution plate (12) by 20 - 300 mm.

4. The fluidized bed drying method applicable to heat-sensitive materials according to claim 3, characterized in that, The cooling jacket (11) extends upward from the cooling air distribution plate (12) by 150 mm.

5. The fluidized bed drying method applicable to heat-sensitive materials according to claim 1, characterized in that, The cooling air distribution plate (12) includes a plurality of unit components (1) arranged at intervals in the horizontal direction on the bed body (7). The hot air channel (2) is formed between the unit components (1), and the cooling cavity (3) is arranged inside the unit components (1).

6. The fluidized bed drying method applicable to heat-sensitive materials according to claim 5, characterized in that, Distribution manifolds (26) are further provided on both sides of the cooling air distribution plate. The distribution manifolds (26) on both sides are respectively connected to both ends of each unit component (1).

7. The fluidized bed drying method applicable to heat-sensitive materials according to claim 5, characterized in that, The unit component (1) includes an upper pressing strip (4), a lower pressing strip (5), and a bending part (6). The upper pressing strip (4) is connected to the lower pressing strip (5) through the bending part (6). The upper pressing strip (4) of the unit component (1) is stacked above the lower pressing strip (5) of its adjacent unit component (1) behind. The outlet of the hot air channel (2) faces the outlet and is parallel to the cooling air distribution plate (12).

8. The fluidized bed drying method applicable to heat-sensitive materials according to any one of claims 1 to 7, characterized in that, The fluidized bed dryer suitable for heat-sensitive materials further includes a cooling medium supply system and a temperature detection module. The cooling medium supply system is used to supply the cooling medium to the cooler. The temperature detection module includes a bed temperature detection unit (34) and a cooler temperature detection unit (16). The bed temperature detection unit (34) is used to obtain the bed temperature of the fluidized bed. The cooler temperature detection unit (16) is used to obtain the surface temperature of the cooler or the temperature of the cooling medium at the outlet of the cooler or the temperature of the cooling medium at the inlet of the cooler.

9. The fluidized bed drying method applicable to heat-sensitive materials according to claim 8, characterized in that, It further includes a controller. The controller is used to control the cooling capacity provided by the cooling medium supply system to the cooler according to the temperature value obtained by the temperature detection module, so as to keep the surface temperature of the cooler below the bed temperature of the fluidized bed.

10. The fluidized bed drying method applicable to heat-sensitive materials as described in claim 9, characterized in that, The cooling medium supply system includes a coolant tank (13), a circulation pump (14), and a heat exchanger (15). The coolant tank (13), the circulation pump (14), and the heat exchanger (15) are sequentially connected through a cooling medium pipeline (18) and form a circulation system with the cooler; a refrigerant inlet valve (19) is provided on the heat exchanger (15), and the circulation pump (14), the temperature detection module, and the refrigerant inlet valve (19) are all connected to the controller (17); the bed temperature detection unit (34) is arranged in the fluidization section (9), the cooler temperature detection unit (16) is arranged at the outlet of the cooler, and the controller (17) is used to control the flow rate of the circulation pump (14) and / or the opening degree of the refrigerant inlet valve (19) according to the temperature value obtained by the temperature detection module.

11. The fluidized bed drying method for heat-sensitive materials according to any one of claims 1 to 6, characterized in that, The outlet of the hot air channel (2) is perpendicular to the cooling air distribution plate (12); alternatively, the outlet of the hot air channel (2) faces the discharge port and forms an acute angle with the cooling air distribution plate (12).

12. The fluidized bed drying method for heat-sensitive materials according to any one of claims 1 to 6, characterized in that, The cross-sectional area of the hot air channel (2) gradually decreases from bottom to top.

13. The fluidized bed drying method for heat-sensitive materials according to any one of claims 1 to 7, characterized in that, The fluidized bed dryer is a fixed fluidized bed dryer, a fluidized bed granulation dryer, or a vibrating fluidized bed dryer.

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