Drying method, drying device and manufacturing method for powder and granular material

Abstract

In order to provide a drying method for achieving an ideal fluidized state of processed material and for performing continuous processing under reduced pressure, with which a high drying efficiency can be achieved, in this particulate matter drying method a median diameter (D50) of particulate matter raw material being processed lies in a range of 1 μm to 1000 μm, and under a reduced pressure of absolute pressure 4 to 30 kPa the particulate matter raw material is fluidized and dried by being heated using a heat medium at a temperature 15 to 120°C higher than the boiling point of a solvent in the particulate matter raw material under said reduced pressure.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for drying powder or granular material, and more particularly to a method and apparatus for drying powder or granular material by continuous treatment under reduced pressure, and further to a method for producing powder or granular material with a specific dryness. [Background technology]

[0002] Drying operations can be broadly classified by the heat transfer method and the method of contact with the object to be treated, and various methods exist depending on the combination of these methods and on the method of transporting the object to be treated. Heat transfer methods include direct heating, indirect heating, and heating by electromagnetic waves. Methods of contact with the object to be treated include static, airflow, stirring, and fluidized bed methods. In drying operations, efforts are made to efficiently apply heat energy to promote the evaporation of water and solvents (remaining moisture in the object to be treated and all liquids used as solvents or dispersion media in manufacturing processes; hereinafter simply referred to as "solvents"). Various methods have also been considered, such as reducing the pressure to lower the boiling point of the solvent.

[0003] The drying process is the final step in the manufacturing of industrial materials, and therefore has a significant impact on product quality. Therefore, simply pursuing drying efficiency is not enough; it is also necessary to minimize the content of volatile components, such as volatile organic compounds (VOCs). Meeting these strict requirements contributes to increasing the commercial value of industrial products made from the treated powder.

[0004] Therefore, various drying systems have been investigated to improve drying efficiency and increase the commercial value of processed materials. For example, a fluidized bed drying system is an example of a drying system used for industrial product materials.

[0005] Fluidized-bed drying systems use hot air blown upward from a perforated or other dispersion plate to fluidize the powdered or granular raw materials, ensuring efficient contact with the hot air and the movement of evaporants, facilitating the removal of volatile components such as VOCs. Another advantage is that the device itself has no moving parts, making maintenance easy. Furthermore, fluidized-bed drying systems can continuously process large amounts of powder, for example, by dividing the device into multiple drying chambers, feeding a fixed amount of powder to the first drying chamber, moving it through the gap under the partition plate to the next drying chamber, and then overflowing and discharging it from the final drying chamber.

[0006] On the other hand, issues with fluidized bed drying systems include the large size of the equipment and the generation of large amounts of exhaust gas. Generally, VOCs resulting from monomers and other substances contained in the raw materials of the powder being treated are mixed into the exhaust gas during drying operations, not only when drying organic solvents but also when drying water. Therefore, a regenerative thermal combustion deodorizer (hereinafter referred to as "RTO") capable of removing VOCs is installed in the exhaust process of the drying system. However, the high exhaust flow rate of fluidized bed drying systems presents the issue of high equipment and running costs for the RTO.

[0007] Drying at high temperatures is not suitable for drying substances with low thermal decomposition points, low softening temperatures, or low melting points. Another example of a drying system used to dry such treated powders is a reduced-pressure drying system that performs drying under vacuum or reduced pressure.

[0008] The reduced-pressure drying system evaporates and dries the solvent in the powder to be treated without heating the powder to high temperatures by drying under vacuum or reduced pressure, which has the advantage of easily reducing residual components such as VOCs. However, under reduced pressure, it is difficult to efficiently transfer a large amount of heat using only hot air heating, so drying is carried out by raising the temperature to near the boiling point of the solvent to be dried, in addition to using conductive heat transfer from the dryer casing, etc. Another issue with reduced-pressure drying systems is that it is difficult to continuously introduce and discharge the powder to be treated, making them unsuitable for large-scale processing.

[0009] One of the most efficient heat transfer methods capable of mass processing is to use hot air as in a fluidized bed drying system. However, applying reduced pressure to the fluidized bed drying system described above means that it is difficult to achieve a vacuum or reduced pressure environment with the fluidization and heat transfer that occur with hot air.

[0010] As described above, fluidized bed drying systems have high drying efficiency, can continuously process large amounts of material, and produce high-quality material with volatile components such as VOCs removed. However, they have the drawback of being large in size and placing a heavy burden on the environment. On the other hand, reduced pressure drying systems are an effective method for processing materials that are not suitable for high temperature drying, and are also suitable for removing volatile components such as VOCs, but they have the drawback of being difficult to process continuously and unsuitable for large-scale processing.

[0011] In light of the above situation, a system that takes advantage of the advantages of reduced pressure drying and allows for continuous processing has been investigated. For example, Patent Document 1 discloses a continuous vacuum drying method for granular materials, in which granular materials placed in a vacuum state in a preliminary vacuum chamber are continuously fed into a rotating drum rotating in the vacuum chamber, the granular materials are dried by moving them along a ribbon-shaped screw provided on the inner surface of the rotating drum, and then the granular materials are removed in a vacuum release chamber after being returned to normal pressure. Patent Document 2 discloses a moisture-containing material drying device including a dryer main body section into which a moisture-containing material is supplied under reduced pressure and which transports the moisture-containing material in a fixed direction while heating it, and a storage hopper section which is provided downstream along the moisture-containing material transport direction of the dryer main body section so that its interior communicates with the interior of the dryer main body section and which has an opening / closing mechanism that can airtightly close and open a discharge port through which the moisture-containing material is discharged.

[0012] Furthermore, Patent Documents 3 and 4 disclose drying systems that focus on fluidizing the material to be treated in order to increase heat transfer efficiency.

[0013] Patent Document 3 discloses a method for drying high-moisture materials in which a sealed drying chamber equipped with a heating jacket and agitator blades capable of fluidizing the material is maintained under reduced pressure, and the moisture content of the material is maintained within a range that allows fluidization. Although Patent Document 3 explains that fluidization improves the heat transfer coefficient, it also states, "When drying is performed using the method of the present invention, the material undergoes various changes in properties during drying. Therefore, the relationship between moisture content and properties was investigated, particularly when the material was strongly agitated in the drying chamber. As a result, it was confirmed that when the moisture content was approximately 40% or less, the material began to fluidize with strong agitation, and when the moisture content was approximately 30% or less, strong agitation fluidized the material in a manner similar to fluidization in a fluidized bed." As such, this technology merely fluidizes the material by applying a stirring force within a specific moisture content range. Furthermore, the processing conditions disclosed are 66°C and 200 Torr, which are approximately equivalent to the saturated vapor pressure of water.

[0014] Patent Document 4 discloses a method for producing dried SPG using a dryer having at least an inlet for 3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane (hereinafter referred to as "SPG") powder wetted with a solvent, an outlet for dried SPG powder, a means for fluidizing the wet powder, and a jacket on the outer wall of the dryer, and indirectly heating the wet powder by passing a heating medium at a temperature range from the boiling point of the solvent to 190°C through the jacket. However, Patent Document 4 also states that "the powder fluidization means may be a stirring blade that rotates around an axis, or the dryer itself may rotate, or the dryer body may vibrate. Examples of stirring blades include paddle blades, anchor blades, and ribbon blades." The term "fluidization" in Patent Document 4 has a technical meaning of stirring and flowing the treated powder due to the action of stirring or rotational force. Furthermore, Patent Document 4 states that "the temperature of the heating medium is preferably at least 15°C higher than the boiling point of the solvent, and by increasing the temperature by at least 15°C higher than the boiling point of the solvent, a dry SPG with a solvent content of 0.5% by weight or less can be obtained," but there is no mention or suggestion of the relationship between reduced pressure or heating temperature and "fluidization," and all of the examples are carried out at normal pressure. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Publication No. 56-127168 [Patent Document 2] Japanese Patent Publication No. 2011-163602 [Patent Document 3] Japanese Patent Publication No. 6-50659 [Patent Document 4] Japanese Patent Publication No. 2003-55383 Summary of the Invention [Problem to be solved by the invention]

[0016] However, the drying methods disclosed in Patent Documents 1 and 2 simply enable continuous processing under reduced pressure, but do not include any improvement in the heat transfer mechanism, and therefore are not drying systems with a practical level of drying capacity capable of mass processing. Furthermore, the fluidization of the material to be treated disclosed in Patent Documents 3 and 4 involves applying a stirring force or a rotational force to the material to be treated, in other words, the material to be treated is scattered due to movement, and does not achieve the ideal fluidization of the material to be treated, which will be described in detail later. Therefore, a dramatic improvement in heat transfer efficiency cannot be expected.

[0017] The present invention has been made in consideration of the problems inherent in the background art described above, and its object is to provide a method and apparatus for drying powder or granular material that realizes an ideal fluidized state of the material to be treated and performs continuous processing under reduced pressure to obtain high drying efficiency, as well as a method for efficiently producing powder or granular material with a specified dryness. [Means for solving the problem]

[0018] In order to achieve the above object, the present invention provides the following [1] to [ 6 The present invention provides a method and apparatus for drying powder and granular material, as well as a method for producing powder and granular material. [1] A method for drying powder or granular material, in which powder or granular raw material is continuously supplied, a heating medium is supplied to a stirring means under reduced pressure, and the powder or granular raw material is dried by heating while being stirred, wherein the median diameter (D50) of the powder or granular raw material is in the range of 1 μm to 1000 μm, and the powder or granular raw material is heated under reduced pressure of 4 to 30 kPa absolute pressure with a heating medium at a temperature 15 to 120° C. higher than the boiling point of the solvent in the powder or granular raw material under the reduced pressure. The solvent evaporates and the resulting gas A method for drying powder or granular material, characterized in that the powder or granular material is fluidized and dried. [2] The fluidization of the powder raw material is in a state where the powder surface inclination angle (θ) is 20 degrees or less. The method for drying powder or granular material according to [1] above, Here, the powder surface inclination angle (θ) is the angle between the horizontal plane and a line connecting the most elevated point (α) of the powder surface on the upstream side of rotation and the most depressed point (β) of the powder surface on the downstream side of rotation within a perfect circle formed by the trajectory of the outermost periphery of the stirring means during the drying operation of powdered or granular raw materials. [3] 2. The method for drying powder or granular material according to claim 1, wherein the moisture content of the powder or granular raw material is 10 to 70% by mass. [4] 2. The method for drying powder or granular material according to claim 1, wherein the powder or granular material has a median diameter (D50) in the range of 150 μm to 700 μm and a moisture content of 20 to 60 mass %. [5] a supply port provided at an upper part of one end of the casing and a discharge port provided at a lower part of the other end of the casing, the casing being connected to a pressure reducing means so that the pressure inside the casing can be reduced, a hollow shaft being rotatably suspended within the casing, a hollow stirring means being disposed on the hollow shaft at a predetermined interval, and a heating medium being supplied to the hollow shaft and the hollow stirring means so that the powder or granular material is heated while being stirred under reduced pressure; a valve casing having an inlet opening at an upper side and an outlet opening at a lower side at the supply port and the outlet of the casing, and a valve rotatably provided within the valve casing to a position where it closes the inlet and a position where it closes the outlet, and an air lock valve is provided so that the powder or granular material can be supplied and discharged in an airtight state by rotating the valve. [6] A method for producing powder or granular material, characterized in that powder or granular material having a moisture content of 1.0 mass % or less is produced by the method for drying powder or granular material described in [1] or [2] above. [Effects of the Invention]

[0019] The powder / granular material drying method and drying apparatus according to the present invention described above can be used to construct a drying system with practical drying capacity capable of mass processing. Furthermore, the powder / granular material manufacturing method according to the present invention can be used to manufacture dried powder / granular material with minimal volatile components such as VOCs. [Brief explanation of the drawings]

[0020] [Figure 1] These are diagrams conceptually showing the relationship between the stirring means in a dryer and the powder surface, where (A) shows the powder surface in a typical fluidized state due to stirring, and (B) shows the powder surface in an ideal fluidized state. [Figure 2] This is a conceptual diagram showing a method for measuring the powder surface inclination angle (θ) of the powder surface in a fluidized state. [Figure 3] 1 is a partially cutaway side view showing an embodiment of a drying apparatus used in a drying method of the present invention. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a portion taken along line XX in FIG. 3. [Figure 5] FIG. 1 is a conceptual diagram of an air lock valve. [Figure 6] FIG. 10 is a diagram showing the process of transferring processed material through an air lock valve. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] FIG. [Figure 10] FIG. 9 is an enlarged cross-sectional view of a portion taken along line YY in FIG. 8. [Figure 11] FIG. 10 is a perspective view showing a state in which the stirring means is arranged on the shaft. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present inventors have not only made continuous processing possible in reduced-pressure drying, but have also completed the present invention by fundamentally reconsidering the heat transfer mechanism in reduced-pressure drying. The present invention is characterized in that the powder or granular raw material to be processed has a median diameter (D50) in the range of 1 μm to 1000 μm, and the powder or granular raw material is heated under a reduced pressure of 4 to 30 kPa absolute with a heating medium at a temperature 15 to 120°C higher than the boiling point of the solvent in the powder or granular raw material under the reduced pressure, thereby achieving ideal fluidization of the powder or granular material and enabling continuous drying processing.

[0022] Here, in explaining "fluidization" in the present invention, it will be helpful to understand the formation of a fluidized layer in powder.

[0023] In a fluidized bed drying system, hot air is blown up from a dispersion plate such as a perforated plate. If the amount of air blown up is small, the powder will remain in the fixed bed. As the amount of air is increased, at some point the surface of the powder bed will begin to bubble due to air bubbles. At this point, fluidization in the broad sense begins. If the amount of air is increased further, the particles will rise and begin to move up and down, and the height of the powder surface will increase compared to when it is in a fixed bed.

[0024] Channeling and bubbling are examples of phenomena occurring in fluidization in a broad sense. Channeling refers to the phenomenon in which the generated or supplied gas does not disperse uniformly throughout the powder bed, but intermittently blows through parts of the bed. Bubbling refers to the phenomenon in which the generated or supplied gas at the bottom or within the powder bed rises in the form of bubbles.

[0025] When considering the fluidization state of the powder to be treated from the viewpoint of drying operation, the ideal fluidization state in a fluidized bed drying system is one in which the gas is uniformly dispersed in the powder bed in terms of contact with hot air and the movement of evaporated materials. In this case, the powder bed will have a relatively smooth powder surface, although this will depend on the amount of gas generated or supplied.

[0026] On the other hand, the fluidization disclosed in Patent Documents 3 and 4 listed in the Background Art is a state in which a stirring force or a rotational force is applied to powder or granular material, in other words, a state in which the powder or granular material is scattered due to its movement, which is different from the above-mentioned ideal fluidization state in which the gas and the processed powder or granular material are uniformly dispersed.

[0027] Patent Document 4 discloses that in a conduction heat transfer dryer in which a heating medium is passed through an agitator, the heat transfer efficiency is improved by fluidizing the material to be treated through agitation. Regarding the effects of changes in the state of powder and granular material due to agitation, the movement of the powder to be treated causes it to become dispersed, increasing the number of contacts between the powder and the heat transfer surface, thereby improving the efficiency of heat exchange and facilitating smooth evaporation of the solvent. However, according to the inventors' research, the above-described fluidization by agitation is not only insufficient to achieve a fluidized state, but also causes the powder layer to oscillate during agitation, exposing the heat transfer surface and creating large cavities within the powder layer, reducing the heat transfer surface in contact with the powder, and therefore is not a fundamental solution to improving heat transfer efficiency.

[0028] Figure 1(A) conceptually shows the relationship between the agitator and the powder surface inside the dryer. In this figure, for ease of understanding, the agitator is shown as a perfect circular disk, but even if an asymmetrical agitator is used, it is sufficient to think of it as showing the perfect circle formed by the trajectory of the outermost periphery when rotating around the rotation axis. As shown in the figure, if the stirring means is divided into regions a to d vertically and horizontally, near region b on the upstream side of rotation, the powder being treated is lifted as the stirring means rotates, causing the powder surface to rise due to momentum. In contrast, near region c on the downstream side of rotation, the powder surface drops downward, causing unevenness of the powder surface. The unevenness of the powder surface increases further as the rotation speed increases. Furthermore, when a scraping member or the like is used to promote stirring, in addition to unevenness of the powder surface, periodic fluctuation of the powder surface may also occur.

[0029] When the above-mentioned unevenness and oscillation occur, the heat transfer surface is exposed in region c. Furthermore, large cavities are instantaneously and continuously generated within the powder bed, preventing the heat transfer surface from contacting the treated powder where the cavities occur. If the rotation speed of the agitator is significantly reduced to prevent this unevenness and oscillation, the heat exchange efficiency between the treated powder and the heat transfer surface decreases, resulting in a decrease in heat transfer efficiency. Even if the input amount of treated powder is increased without changing the rotation speed of the agitator to raise the powder surface, unevenness and oscillation of the powder surface still occur. Furthermore, in this case, the number of contacts between the treated powder and the heat transfer surface per unit time and per unit weight decreases, resulting in a decrease in heat transfer efficiency. This decrease in heat transfer efficiency was more pronounced in a single-shaft conduction heat transfer dryer than in a conduction heat transfer dryer with multiple agitation shafts.

[0030] The present invention fundamentally solves the above problems by creating a state in which the processed powder spontaneously fluidizes without the application of kinetic energy such as stirring force or rotational force. The fluidized state in the present invention is characterized by the powder layer rising uniformly and fluidizing, the powder surface remaining flat without shaking even when stirred, and the powder surface tilting due to stirring being small; as shown in Figure 1(B), the powder surface is flat with little shaking, and the tilt angle of the powder surface is small.

[0031] When the fluidized state is defined as in Table 1, the fluidized state of the present invention refers to a state in which the powder surface state during operation of the dryer is rank 5 or rank 4. [Table 1] The powder surface inclination angle (θ) in the table is the angle between the horizontal plane and a line connecting the most elevated point (α) of the powder surface on the upstream side of rotation and the most depressed point (β) of the powder surface on the downstream side of rotation within the perfect circle formed by the locus of the outermost periphery of the agitator when the agitator is rotated during the drying operation of the treated powder (see Figure 2).In addition, when the powder surface is unstable and vibrating violently, the powder surface inclination angle (θ) is determined by taking a video and determining the powder surface inclination angle (θ) for each frame, and the maximum value is taken as the powder surface inclination angle. The rotation conditions of the stirring means are a linear velocity at the outermost periphery of 0.03 to 0.8 m / s, preferably 0.25 to 0.63 m / s, but the powder surface inclination angle (θ) of the present invention is not limited to the above rotation conditions and is defined by the state of the powder surface during operation of the dryer.

[0032] In the cases of ranks 1 to 3 in Table 1, even if the input amount is increased and the powder surface is raised, at a linear speed of the stirring means within the above range, scattering of powder particles occurs during stirring, the powder surface becomes disturbed and not flat due to stirring, and the powder surface inclination angle (θ) does not become 20 degrees or less, and it was confirmed that the state does not reach ranks 4 or 5.

[0033] On the other hand, when the powder to be treated is subjected to heat treatment under reduced pressure (absolute pressure 30 kPa or less) by passing a heating medium at a temperature 15°C or more higher than the boiling point of the solvent in the material under reduced pressure through an agitator, the liquid inside the powder bed instantly evaporates, generating gas, and the powder bed reaches a fluidized state of ranks 4 and 5. This fluidized state facilitates the movement of the generated gas even under reduced pressure, and the powder not only moves but also maintains contact with the heating means, dramatically increasing heat transfer efficiency and achieving processing capabilities not possible with conventional vacuum dryers. In particular, the improved processing capacity due to the fluidized state is particularly pronounced in single-shaft conduction heat transfer dryers, making them suitable for compact equipment.

[0034] Drying using a combination of reduced pressure and heating has been practiced in the past, but the technical intent was to lower the boiling point of the solvent through reduced pressure, thereby enabling efficient drying at lower temperatures. Therefore, even if excessive heat is applied at normal pressure, when the pressure is reduced to a certain level or below, the material is treated at a temperature close to the boiling point of the solvent, and considering the objective of drying at a lower temperature, it can be said that there are inhibiting factors that make excessive heating after reducing the pressure unacceptable.

[0035] Even at normal pressure, depending on the temperature, fluidization in the broad sense occurs due to boiling of the solvent, but the gas generated by evaporation is uneven and is accompanied by intermittent channeling, and the fluidization state remains at rank 1 in the above-mentioned fluidization ranking, which is different from the fluidization state of the present invention.

[0036] To achieve the fluidized state of the present invention, a reduced pressure of 30 kPa or less is required. Releasing this reduced pressure causes the powder to cease fluidization and begin to oscillate due to agitation, demonstrating that the fluidized state of the present invention is not due to agitation. Furthermore, to ensure that the liquid inside the powder bed instantly evaporates, generating gas, and uniformly fluidize the powder bed, a reduced pressure of 30 kPa or less and heating with a heating medium at a temperature at least 15°C higher than the boiling point of the solvent under reduced pressure are required. The upper limit of the heating temperature must be determined taking into account the decomposition point and melting point of the processed material. In the examples, it was confirmed that the fluidization of the present invention is possible up to a difference (ΔT) between the heating medium temperature and the boiling point of the solvent under reduced pressure of 120°C. From the perspective of thermal stability of the processed material, the ΔT is preferably in the range of 15 to 100°C, and more preferably in the range of 15 to 70°C. At temperatures below 15°C, fluidization in the broad sense occurs, but gas generation is insufficient, resulting in channeling. For stable fluidization, a temperature of 20°C or higher is preferable, and taking this into consideration, ΔT is preferably in the range of 20 to 100°C, and most preferably 20 to 70°C.

[0037] The powdered or granular raw material to be treated by the drying method of the present invention is not limited in any way and can be widely used for drying synthetic resins, foods, chemical products, etc. However, the median diameter (D50) of the powdered or granular raw material to be treated should be in the range of 1 μm to 1000 μm. If the D50 exceeds 1000 μm, the treated powder will be too heavy, even under the heating conditions under reduced pressure, making spontaneous fluidization difficult. On the other hand, if the D50 is below 1 μm, the amount of fine powder of approximately 1 μm or less will be large, and the powder will have strong cohesive properties, making continuous fluidization difficult. From this perspective, the median diameter (D50) of the powdered or granular raw material to be treated is preferably in the range of 100 μm to 800 μm, more preferably in the range of 150 μm to 700 μm. Furthermore, from the viewpoint of uniform fluidization, the moisture content of the powdered or granular raw material to be treated is preferably 10 to 70 mass %, more preferably 20 to 60 mass %, and even more preferably 20 to 50 mass %. If the moisture content is less than 10% by mass, fluidization will end in a short time, and sufficient improvement in drying processing capacity will not be observed. If the moisture content exceeds 70% by mass, uniform fluidization will be difficult to achieve. If the powdered or granular raw material to be processed does not have the median size or moisture content described above, it is preferable to perform pretreatment to adjust the powdered or granular raw material to the median size or moisture content described above. In this case, the pretreatment is not limited in any way, and a wide variety of known grinding methods and moisture adjustment methods can be used.

[0038] The moisture contained in the powder to be treated may be any liquid commonly used as a solvent or dispersion medium in the manufacturing process, including water remaining in the material to be treated and liquids commonly used as solvents or dispersion media. Examples of such liquids include water, lower alcohols such as methanol, ethanol, propanol, and isopropanol, polyhydric alcohols such as glycerin, ethylene glycol monoethyl ether, propylene glycol, and 1,3-butylene glycol, lower ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, lower esters such as ethyl acetate and isopropyl acetate, and lower ethers such as diethyl ether and diisopropyl ether. Mixtures of two or more of these may also be used. When multiple solvents are used, the fluidized state of the present invention can be achieved if at least one of the solvents satisfies the above-mentioned conditions: a reduced pressure of 4 to 30 kPa absolute and heating at a temperature 15 to 120°C higher than the boiling point of the solvent under reduced pressure. When an azeotropic mixture is formed, the azeotropic point corresponding to the ratio is used as the reference.

[0039] The heating means for the powder to be treated is preferably a conduction heat transfer dryer configured to include a hollow shaft and a hollow agitator, and to indirectly heat the powder to be treated by circulating a heating medium therethrough. In addition to the heating means, heating may be performed from the casing. Furthermore, the agitator may be a disk-shaped agitator, a paddle-shaped agitator, or a screw-shaped agitator. However, a disk shape is preferred, as it ensures the widest heat transfer surface in contact with the powder to be treated, and a scraper or pin may be provided as needed. Furthermore, a conduction heat transfer dryer with a single agitator is preferred, as this significantly improves processing capacity compared to a conduction heat transfer dryer with multiple agitators, and allows for a more compact device.

[0040] In the present invention, it is preferable that the fluidized state of the present invention occurs along at least one-fifth of the path length where the heating means and the powder to be treated come into contact. When most of the moisture (solvent) evaporates and constant rate drying is completed, the fluidized state of the present invention does not occur, and therefore, in a part of the downstream region of the path length, the process shifts to falling rate drying, and the fluidized state of the present invention does not occur.

[0041] Next, one embodiment of a drying apparatus used in the drying method according to the present invention will be described in detail with reference to the drawings.

[0042] 3 is a side view showing a part of the drying device cut away, and FIG. 4 is an enlarged cross-sectional view of a part taken along line XX in FIG. In these figures, reference numeral 1 denotes the casing of the drying device, which is a relatively horizontally long container. The casing 1 is placed in a slightly inclined position on a support stand 2. A supply port 3 for the material to be treated is provided at the top of the front end of the casing 1, and a discharge port 4 for the material to be treated is provided at the bottom of the rear end. An exhaust port 5 is also provided at the top of the casing 1.

[0043] A supply port 3 for the material to be treated provided in the casing 1 is connected to a raw material hopper 7 via an airlock valve 6, which continuously charges the material to be treated. A discharge port 4 is connected to a recovery hopper 9 via an airlock valve 8, which also continuously discharges the material to be treated. An exhaust port 5 provided in the casing 1 is connected to an exhaust / decompression unit 10.

[0044] 5, the airlock valve 6 (or 8) is configured to include a valve casing 13 having an inlet 11 opening upward and an outlet 12 opening downward, and a valve 14 rotatably disposed within the valve casing 13 between a position where the inlet 11 is closed and a position where the outlet 12 is closed. When only the outlet 12 is closed by the valve 14 (the state shown in FIG. 6A), the material P to be treated is taken into the valve casing 13 from the raw material hopper 7 (or the casing 1 of the drying apparatus) through the inlet 11. The valve 14 is then rotated to a state where both the outlet 12 and the inlet 11 are closed by the valve 14 (the state shown in FIG. 6B), and then to a state where only the inlet 11 is closed (the state shown in FIG. 6C), and the material P to be treated taken into the valve casing 13 is then introduced into the casing 1 of the drying apparatus (or discharged into the recovery hopper 9) through the outlet 12.

[0045] The exhaust decompression unit 10 serves to exhaust steam from the inside of the casing 1 of the drying apparatus and reduce the pressure inside. This exhaust decompression unit 10 can be composed of, for example, a dust removal device such as a bag filter that removes dust contained in the exhaust from the casing 1, a condenser that cools and condenses the steam contained in the exhaust, a pressure reduction means that reduces the pressure inside the casing 1, and a deodorization device that removes odors contained in the exhaust. Here, the pressure reduction means can be a pump, an aspirator, etc., and the deodorization device can be a metal catalyst, a filter, activated carbon, etc. It is preferable that the exhaust decompression unit 10 be equipped with at least the pressure reduction means and the deodorization device.

[0046] A hollow shaft 20 passes through the front and rear of a casing 1 of the drying device and is rotatably supported by bearings 21 and 22 provided at the front and rear of the casing 1. A sprocket 23 is provided at the front of the hollow shaft 20, and the rotation of a motor 24 is transmitted to the hollow shaft 20 via a chain meshed with the sprocket 23. Note that a direct drive in which the motor is directly connected may be used, or a hydraulic motor may also be used as the motor.

[0047] A heating medium supply pipe 26 is connected to the front end of the hollow shaft 20 via a rotary joint 25, and a heating medium discharge pipe 28 is connected to the rear end of the hollow shaft 20 via a rotary joint 27. Furthermore, as shown in FIG. 4 , a partition plate 29 is provided in the hollow shaft 20, dividing the interior of the hollow shaft 20 in half in the axial direction. The partition plate 29 divides the interior of the hollow shaft 20 into a primary chamber 20a and a secondary chamber 20b. The primary chamber 20a is connected to the front end of the hollow shaft 20, and the secondary chamber 20b is connected to the rear end of the hollow shaft 20. Although this state is not specifically shown, the above configuration can be realized by sealing the front end of the secondary chamber 20b at the front end of the hollow shaft 20 and the rear end of the primary chamber 20a at the rear end of the hollow shaft 20 with crescent-shaped end plates, respectively.

[0048] A large number of hollow stirring means 30, 30... are arranged at regular intervals on the hollow shaft 20. As shown in Figures 7 to 10, this hollow stirring means 30 is formed in a disk shape with a thickness that is thin compared to its diameter. More specifically, it has concentric protrusions 31, 31 that are gently curved in the left-right direction in a side view in the center, and openings 32, 32 are formed at the tip of each of the protrusions 31, 31, forming a thin, approximately hollow disk shape with both plate surfaces parallel to each other.

[0049] As shown in the figure, a plurality of scraper blades 33 are attached at equal intervals to the outer periphery of the disk-shaped hollow stirring means 30. In the illustrated embodiment, a scraper blade 33 is attached to each stirring means 30, but depending on the physical properties of the material to be processed, a scraper blade (not shown) may be attached across two or more adjacent stirring means 30, 30. Conversely, there may be no scraper blade.

[0050] 4, 8, and 10, a partition plate 34 is attached inside the hollow stirring means 30, and the partition plate 34 divides the internal space 35 of the stirring means 30. The heating medium flows from the primary chamber 20a of the hollow shaft 20 through the communication hole 36 into the internal space 35 of the hollow stirring means 30, circulates in a fixed direction within the internal space 35, and flows out through the communication hole 37 into the secondary chamber 20b of the hollow shaft 20. In the case of a relatively small device, a single partition plate 34 may be used, but in the case of a larger device, the internal space 35 of the stirring means 30 may be divided into smaller sections by multiple partition plates 34, and the number of partition plates 29 dividing the hollow shaft 20 may be increased accordingly, and communication holes 36, 37 may be provided to connect each divided internal space 35 to the primary chamber 20a and the secondary chamber 20b divided by the hollow shaft 20, as described above.

[0051] As shown in FIG. 11 , a number of hollow agitators 30 having the above-described configuration are arranged at regular intervals on the hollow shaft 20 so that their scraping blades 33 are aligned in the same direction. The spacing between the agitators is ensured by the abutment of the tips of the protrusions 31 of adjacent agitators 30 when the hollow shaft 20 is inserted through the opening 32 of the agitator 30. The number of hollow shafts 20 is not limited to one and may be, for example, two or more. However, as described above, a single hollow shaft 20 is preferred from the viewpoints of significantly improving processing capacity and achieving a compact device. Furthermore, all hollow agitators 30 arranged on the hollow shaft 20 may be disc-shaped as described above. However, depending on the physical properties (thermal strength change) of the material to be processed, agitators of other shapes may be appropriately combined and attached to the hollow shaft 20. However, disc-shaped agitators are preferred at least in the area where the fluidized state of the present invention is to be formed, from the viewpoint of ensuring a sufficient heat transfer surface, as described above.

[0052] Next, the case where powdered or granular raw material is dried using the above-mentioned drying apparatus will be described. First, the interior of the casing 1 of the drying device is placed under a predetermined reduced pressure and heated condition. To this end, the hollow shaft 20 is rotated by a motor 24 via a sprocket 23, and a heating medium, such as steam or hot water, is sent to the hollow shaft 20 via a rotary joint 25. The heating medium sent to the hollow shaft 20 flows from the primary chamber 20a of the hollow shaft 20 into the internal space 35 of the hollow agitator 30, heating the agitator 30, and then passes through the secondary chamber 20b of the hollow shaft 20 and is discharged from the heating medium discharge pipe 28 via a rotary joint 27 connected to the rear of the hollow shaft. The exhaust / decompression unit 10 is then activated to draw air through the exhaust port 5 provided in the casing 1, placing the interior of the casing 1 under reduced pressure. Through the above operations, the interior of the casing 1 is placed under reduced pressure of 4 to 30 kPa absolute and heated to a temperature 15 to 120°C higher than the boiling point of the moisture (solvent) in the powdered or granular raw material under the reduced pressure.

[0053] Next, the powdered or granular raw material to be processed (which may be powder or granules) is continuously fed into the casing 1 through the supply port 3 of the drying device. The powdered or granular raw material to be fed preferably has a median diameter (D50) in the range of 1 μm to 1000 μm and a moisture content of 10 to 70 mass %. If the powdered or granular raw material to be processed does not have the above median diameter or moisture content, it is preferable to carry out pretreatment as described above to adjust it to the above median diameter or moisture content. The powdered or granular raw material fed into the casing 1 is heated while being stirred by the stirring means 30, and drying proceeds. During this process, the powdered or granular raw material is heated under a reduced pressure of 30 kPa or less absolute pressure to a temperature at least 15°C higher than the boiling point of the solvent under said reduced pressure. This causes the solvent to instantly evaporate from within the powder or granular layer, generating gas, and the powder layer enters a fluidized state of ranks 4 and 5 described above. This makes it easier for the generated gas to move, and since the powder or granular material is not only moving but also maintaining contact with the heating means, the heat transfer efficiency is dramatically increased, resulting in efficient drying.

[0054] The powdered and granular raw material fed into the casing 1 is subjected to the efficient drying process described above as it gradually flows down inside the casing 1 due to the pressure caused by the filling height of the powdered and granular raw material subsequently fed into the feed port 3 and the inclination of the casing 1, and then moves to the discharge port 4, where it is discharged in an airtight state through the air lock valve 8 and collected in the collection hopper 9. The collected powdered and granular material has a moisture content of 1.0% by mass or less and is a dried powdered and granular material with volatile components such as VOCs reduced as much as possible.

[0055] The above describes embodiments of the method for drying powder or granular material according to the present invention, the drying apparatus used in the drying method, and the method for producing powder or granular material with a moisture content of 1.0 mass % or less. However, the present invention is not limited to the above-described embodiments, and it is natural that various modifications and changes can be made within the scope of the technical concept of the present invention described in the claims. [Example]

[0056] Examples of the drying method according to the present invention will be described below, but the present invention is not limited to these examples in any way.

[0057] The NVD-3 type (single-axial conduction heat transfer dryer, heat transfer area 3.4 m) manufactured by Nara Machinery Manufacturing Co., Ltd., shown in Figures 3 and 4, 2 The airlock valves shown in Figure 5 were attached to the supply and discharge ports of a 150 L dryer (150 L capacity), and a drying device capable of continuous processing under reduced pressure was fabricated. The stirring means was disk-shaped and had a diameter of 300 mm.

[0058] Example 1 Water was added to commercially available polyester ketone (D50: 648 μm, melting point: 300 to 360° C.) to prepare a wet raw material with a moisture content of 20 mass %. Using the above drying device, continuous drying treatment was carried out according to the following procedure. Steam was used as the heating medium, and the temperature was set to 180°C. The pressure inside the device was reduced to 20 kPa. At this time, the boiling point of water was 60°C, and ΔT was 120°C. The peripheral speed of the outermost periphery of the disc was set to 0.3 m / s, and the wet raw material was fed at a rate of 90 kg / h (based on dry powder), and continuous reduced-pressure drying was started. Thirty minutes after the drying process had stabilized, the wet raw material was fluidized within the device, and the powder surface was flat and smooth. The fluidization rank at this point was "Rank 5" in Table 1. Furthermore, fluidization of "Rank 4" or higher was observed within the upstream 80% of the path length. Thirty minutes after the start, the drying process was continued for two hours, and 180 kg (dry powder basis) of a product powder with a moisture content of 0.3 mass % was obtained.

[0059] Examples 2 to 15 and Comparative Examples 1 to 5 The wet raw materials shown in Table 2 were prepared and subjected to continuous drying treatment using the above drying device under the conditions shown in Table 3.

[0060] [Table 2]

[0061] [Table 3]

[0062] The results of the drying treatment of each wet raw material are shown in Table 4. [Table 4] In Comparative Example 1, the powder surface was disturbed and not flat due to stirring, and the moisture content of the product was 8 mass %, which was very poor compared to the Examples. Intermittent and localized gas blow-through (channeling) occurred in Comparative Examples 2 and 3. The moisture content of the product was 3 mass %, which was inferior to that of the Examples. In Comparative Example 4, intermittent and localized gas blow-through (channeling) occurred. The moisture content of the product was 23 mass %, which was very poor compared to the Examples. In Comparative Example 5, the powder surface was disturbed and not flat due to stirring. The moisture content of the product was 3% by mass, which was inferior to the Examples. [Industrial Applicability]

[0063] The powder / granular material drying method, drying apparatus, and manufacturing method according to the present invention can be used for drying and manufacturing powder / granular materials in a wide range of fields, such as synthetic resins, foods, and chemical products. [Explanation of symbols]

[0064] 1: casing of drying device, 2: support base, 3: supply port, 4: discharge port, 5: exhaust port, 6, 8: air lock valve, 7: raw material hopper, 9: recovery hopper, 10: exhaust pressure reduction unit, 11: inlet port, 12: outlet port, 13: valve casing, 14: valve, P: material to be treated, 20: hollow shaft, 20a: primary chamber, 20b: two-way chamber, 21, 22: bearings, 23: sprocket, 24: motor, 25, 27: rotary joint, 26: supply pipe, 28: discharge pipe, 29: partition plate, 30: hollow stirring means, 31: protrusion, 32: opening, 33: scraping blade, 34: partition plate, 35: internal space, 36, 37: communication holes

Claims

1. A method for drying powder or granular material, which comprises continuously supplying powder or granular raw material, supplying a heating medium to a stirring means under reduced pressure, and heating the powder or granular raw material while stirring, characterized in that the powder or granular raw material has a median diameter (D50) in the range of 1 μm to 1000 μm, and is heated under a reduced pressure of 4 to 30 kPa absolute pressure with a heating medium at a temperature 15 to 120° C. higher than the boiling point of a solvent in the powder or granular raw material under said reduced pressure, and fluidizing the powder or granular raw material with gas generated by evaporation of the solvent, thereby carrying out the drying process.

2. A method for drying powdered or granular material as described in claim 1, characterized in that the fluidization of the powdered or granular raw material is in a state where the powder surface inclination angle (θ) is 20 degrees or less. Here, the powder surface inclination angle (θ) is the angle between the horizontal plane and a line connecting the highest point (α) of the powder surface on the upstream side of rotation and the lowest point (β) of the powder surface on the downstream side of rotation within a perfect circle formed by the locus of the outermost periphery of the stirring means during the drying operation of the powder or granular raw material.

3. A method for drying powdered or granular material as described in claim 1, characterized in that the moisture content of the powdered or granular raw material is 10 to 70 mass%.

4. A method for drying powdered or granular material as described in claim 1, characterized in that the median diameter (D50) of the powdered or granular raw material is in the range of 150 μm to 700 μm, and the moisture content of the powdered or granular raw material is 20 to 60 mass%.

5. A drying apparatus for use in the method for drying powdered or granular material according to claim 1 or 2, comprising a casing, a supply port provided at the top of one end of the casing, and a discharge port provided at the bottom of the other end of the casing, the casing being connected to a pressure reducing means so that the interior can be reduced in pressure, a hollow shaft being rotatably suspended within the casing, hollow stirring means being arranged on the hollow shaft at a predetermined interval, and a heating medium being supplied to the hollow shaft and the hollow stirring means so that the powdered or granular raw material is heated while being stirred under reduced pressure, the drying apparatus comprising: a valve casing having an inlet opening at the top and an outlet opening at the bottom of the supply port and outlet of the casing, and a valve rotatably provided within the valve casing between a position where the inlet is closed and a position where the outlet is closed, and an air lock valve which can supply and discharge powdered or granular material in an airtight state by rotating the valve.

6. A method for producing powder and granular material, characterized in that powder and granular material having a moisture content of 1.0 mass% or less is produced by the method for drying powder and granular material described in claim 1 or 2.

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