Powder production method and solid powder

Abstract

To produce a powder product which has a low percentage content of concave powder and hollow powder, and has a high percentage content of solid powder.SOLUTION: A method for producing powder for heating air sent from a blower 13 and generating hot air, and drying a droplet of a stock solution sprayed into a drying chamber 10 by a rotary atomizer 20, with hot air supplied into the drying chamber 10 includes selecting the temperature of the hot air supplied into the drying chamber 10 from a range from 100°C to 30°C, determining an air blow quantity per unit time of the blower 13, on the basis of the temperature of the hot air and the maximum diameter of the drying chamber 10, and determining air speed of the hot air supplied into the drying chamber 10, on the basis of the temperature of the hot air and the maximum diameter of the drying chamber 10, and dries the droplet of the stock solution sprayed into the drying chamber 10 while performing control to keep the temperature of the hot air, the air blow quantity per unit time of the blower 13, and the air speed of the hot air supplied into the drying chamber 10, and thereby generates solid powder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing powder using a spray dryer, and in particular to a method for producing powder that enables a dramatic increase in the solid powder content by using low-temperature hot air of 100°C to 30°C. [Background technology]

[0002] In general spray dryer equipment, the raw liquid is dried using relatively high-temperature hot air to maintain a consistent quality of the powder product being manufactured. For example, in small spray dryer equipment used for research and development, the temperature of the hot air at the entrance of the drying chamber is set to about 140°C to 200°C. In addition, in small, medium, and large spray dryer equipment used for mass production of powder products, the temperature of the hot air at the entrance of the drying chamber is set to about 220°C to 300°C.

[0003] However, hot air temperatures above 140°C are too high to instantly dry the raw material. Powders that are overdried due to high temperatures lose bulk and become hard, resulting in low quality. Furthermore, electricity, liquefied natural gas (LNG), liquefied petroleum gas (LPG), kerosene, heavy oil, and other heat sources are used to heat the air and generate hot air. The higher the hot air temperature, the greater the consumption of these heat sources. Conventionally, generating excessively hot air temperatures above 140°C wasted heat. Furthermore, the higher the temperature of the hot air supplied to the drying chamber inlet, the higher the temperature of the hot air discharged from the spray dryer equipment. When the spray dryer equipment is installed indoors, the hot air discharged from the equipment can heat the indoor space to high temperatures. Workers involved in the production of powder products must constantly work under high temperatures.

[0004] Therefore, the present applicant proposed in JP 2022-189024 A (Patent Document 1) a spray dryer system that enables the production of powder using hot air at a constant temperature of 120°C or less. This spray dryer system includes a first means for uniformizing the temperature distribution of the hot air supplied into the drying chamber, a second means for uniformizing the droplet diameter of the stock solution sprayed into the drying chamber, a third means for maintaining a constant temperature distribution within the drying chamber, a fourth means for ensuring at least the residence time of the powder required for drying within the drying chamber, and a fifth means for maintaining a constant pressure within the drying chamber. These first to fifth means strictly control the temperature distribution of the hot air, the droplet diameter of the stock solution, the temperature distribution within the drying chamber, and the residence time of the powder within the drying chamber, making it possible to produce powder using hot air at a low temperature of 120°C or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-189024 Summary of the Invention [Problem to be solved by the invention]

[0006] Powder was produced using the spray dryer equipment disclosed in JP 2022-189024 A, with the temperature of the hot air supplied into the drying chamber set to 100°C. As a result, it was found that the produced powder had three types of forms, as shown in Figures 11(a) to 11(d). Figures 11(a) and 11(b) show concave powder with depressions formed on the surface. Figure 11(b) shows hollow powder with no depressions on the surface and voids formed inside. Figure 11(d) shows solid powder with no depressions on the surface and a solid interior.

[0007] When powders produced using a spray dryer contain a mixture of three types of powder forms, i.e., concave, hollow, and solid, the bulk density (weight / volume) of the powder becomes unstable. Powders with unstable bulk density are difficult to mold into compacts of uniform density by pressing. This can lead to problems such as the formation of minute voids inside the compacts or cracks or chips on the exterior of the compacts. Such problems are more likely to occur with smaller compacts, such as tablets.

[0008] The inventors believe that the reason for the formation of the three types of powder—concave, hollow, and solid—is as follows: Droplets of the raw liquid sprayed into the drying chamber contain dispersed particles of the powder material. The moisture in the droplets sprayed into the drying chamber gradually evaporates from the surface exposed to the hot air, reducing the volume of the droplets. The particles contained in the evaporated moisture migrate to the droplet's surface. Therefore, the faster the moisture on the droplet's surface evaporates, the higher the density of the particles that migrate to the droplet's surface, and a dried particle shell forms on the droplet's surface. As a result, even if the droplets continue to dry, their volume no longer shrinks, and the pressure inside the droplets from which the moisture has evaporated decreases. If there is a weak part in the shell of the dried particle on the droplet's surface, this part will be depressed, resulting in the formation of a concave powder. If there is no weak part in the shell of the dried particle on the droplet's surface, a hollow powder with voids remaining inside will be formed. On the other hand, if a shell of dried particles does not form on the surface of the droplets, the volume of the droplets shrinks as the droplets dry, resulting in the production of a solid powder filled with particles. It is believed that the reason for the production of solid powder by the spray dryer equipment of JP 2022-189024 A is that the relatively low temperature of 100°C hot air slowly evaporates the moisture on the surface of the droplets, preventing the formation of a shell of dried particles on the surface of the droplets, resulting in the reduction of the droplet volume. However, the powder produced by the spray dryer equipment of JP 2022-189024 A had a high content of hollow powder and a low content of solid powder.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a method for manufacturing powder that enables the production of powder products with a low content of concave powder and hollow powder and a high content of solid powder, and that can be formed into a molded body of uniform density by press processing. [Means for solving the problem]

[0010] (1) In order to achieve the above object, the powder manufacturing method of the present invention is a powder manufacturing method that heats air sent from a blower to generate hot air, and dries droplets of a raw liquid sprayed into a drying chamber by a rotary atomizer with the hot air supplied into the drying chamber, the method comprising: selecting a temperature of the hot air supplied into the drying chamber from a range of 100°C to 30°C; determining the air flow rate per unit time of the blower based on the temperature of the hot air and the maximum diameter of the drying chamber; and determining the air velocity of the hot air supplied into the drying chamber based on the temperature of the hot air and the maximum diameter of the drying chamber, and is characterized in that a solid powder is produced by drying the droplets of the raw liquid sprayed into the drying chamber while controlling to maintain the temperature of the hot air, the air flow rate per unit time of the blower, and the air velocity of the hot air supplied into the drying chamber.

[0011] (2) Preferably, in the powder manufacturing method of (1) above, the maximum diameter of the drying chamber is 960 mm or more, and the air volume per unit time of the blower is 1.0 m 3 / min or more, and the wind speed of the hot air supplied into the drying chamber is 12.0 m / s or more.

[0012] (3) Preferably, in the powder manufacturing method of (1) above, the air volume per unit time of the raw liquid supplied to the rotary atomizer is set within a range of 1.0 L / h to 2.0 L / h, and the rotation speed of the rotary atomizer is set to 30,000 rpm or less.

[0013] (4) To achieve the above object, the solid powder of the present invention is characterized by being produced by any one of the powder production methods (1) to (3) above. [Effects of the Invention]

[0014] In the powder manufacturing method of the present invention, by controlling the hot air supplied to the drying chamber at a low temperature selected from the range of 100°C to 30°C and by controlling the air volume per unit time of the blower and the speed of the hot air supplied to the drying chamber to constant values, it is possible to manufacture a powder product with a high content of solid powder. The air volume per unit time of the blower is determined based on the temperature of the hot air and the maximum diameter of the drying chamber. The residence time of the powder required for drying is determined depending on the air volume. The speed of the hot air supplied to the drying chamber is also determined based on the temperature of the hot air and the maximum diameter of the drying chamber. The air volume per unit time that comes into contact with the raw liquid sprayed into the drying chamber is determined depending on the hot air speed. By setting the hot air temperature, the air volume per unit time of the blower, and the speed of the hot air supplied to the drying chamber to optimal values ​​and controlling them to maintain these values, it is possible to manufacture a powder product with a low content of concave and hollow powder and a high content of solid powder. Furthermore, the solid powder produced by the powder production method of the present invention can be formed into a compact with uniform density by pressing. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing a spray dryer facility used in a powder production method according to an embodiment of the present invention. [Figure 2] FIG. 2 is an exploded view showing a first embodiment of an air disperser constituting the spray dryer facility of FIG. [Figure 3] FIG. 3 is a schematic diagram showing the air disperser of FIG. [Figure 4] FIG. 4 is a schematic view showing a second embodiment of the air disperser constituting the spray dryer facility of FIG. [Figure 5] 5A and 5B are schematic diagrams showing the up-and-down movement of the lower parts constituting the air disperser of FIG. 4, with FIG. 5A showing the lower parts in a lowered state and FIG. 5B showing the lower parts in a raised state. [Figure 6]FIG. 6 is a schematic diagram showing a third embodiment of the air disperser constituting the spray dryer facility of FIG. [Figure 7] 7A and 7B are schematic diagrams showing the up-and-down movement of the lower parts constituting the air disperser of FIG. 6, with FIG. 7A showing the lower parts in a lowered state and FIG. 7B showing the lower parts in a raised state. [Figure 8] FIG. 8 shows a mixer provided in the spray dryer equipment of FIG. 1, where FIG. 8(a) is a front view and FIG. 8(b) is a cross-sectional view taken along line AA of FIG. 8(a). [Figure 9] FIG. 9 is a cross-sectional view showing a rotary atomizer provided in the spray dryer equipment of FIG. [Figure 10] FIG. 10 shows the upper distributor, lower distributor, and rotating wheel provided in the rotary atomizer of FIG. 9, where FIG. 10(a) is an exploded view, FIG. 10(b) is an assembly view, FIG. 10(c) is a plan view of the rotating wheel, and FIG. 10(d) is a schematic diagram showing the flow of the concentrate. [Figure 11] Figure 11 shows three types of powder produced by the spray dryer equipment of JP 2022-189024 A, where Figures 11(a) and (b) show concave powder, Figure 11(b) shows hollow powder, and Figure 11(d) shows solid powder. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, a method for producing powder according to an embodiment of the present invention will be described with reference to FIGS.

[0017] 1. Overview of spray dryer equipment The powder manufacturing method of this embodiment is carried out using a spray dryer apparatus 1 shown in FIG. 1. The spray dryer apparatus 1 includes a drying chamber 10, a cyclone 40, and a bag filter 50. The spray dryer apparatus 1 employs a two-point collection system, whereby the produced powder product is collected at two points: the bottom of the cyclone 40 and the bottom of the bag filter 50. The powder produced in the drying chamber 10 is sucked into the cyclone 40 from the bottom of the drying chamber 10. The cyclone 40 separates the sucked powder using centrifugal force, and collects powder with excellent fluidity. Relatively light or fine powder is sucked from the cyclone 40 into the bag filter 50 and collected in the bag filter 50.

[0018] An air disperser 11 is installed on the ceiling of the drying chamber 10. A rotary atomizer 20 is attached to the center of the air disperser 11. As shown in FIGS. 2 and 3, the air disperser 11 includes a housing 111 and a lower part 112. The housing 111 has a donut-shaped outer shape with a circular opening in the center. An annular air passage 111a is formed inside the housing 111. This air passage 111a surrounds a circular first opening 111b provided in the center of the housing 111. Meanwhile, the lower part 112 has a wall portion in the shape of an inverted truncated cone. The wall portion of the lower part 112 is inserted into the first opening 111b of the housing 111, and an annular hot air outlet is formed between this wall portion and the first opening 111b. The hot air supplied to air passage 111a inside housing 111 swirls along the shape of air passage 111a and is discharged from the annular hot air outlet toward the wall portion of lower part 112 in the shape of an inverted truncated cone.

[0019] A rotary atomizer 20 shown in FIG. 9 is suspended from the lower end opening of the lower part 112. The rotary atomizer 20 has a disk-shaped rotary wheel 27 that is rotated at high speed by a motor 22. When the stock solution is supplied to the inlet 27b (see FIG. 10(c)) of the rotating wheel 27 that is rotating at high speed, the stock solution is accelerated on the disk surface and is dispersed at high speed from a lattice-shaped outlet provided on the periphery of the disk. As a result, the stock solution turns into droplets and is sprayed into the drying chamber 10. The droplets of the stock solution sprayed into the drying chamber 10 then come into contact with a swirling flow of hot air supplied into the drying chamber 10 from the hot air outlet of the air disperser 11, and are dried and granulated.

[0020] In the powder manufacturing method of this embodiment, the raw solution is dried to produce powder using low-temperature hot air selected within the range of 100° C. to 30° C. This low-temperature drying technique can be widely applied to spray dryer equipment 1 having a drying chamber 10 with a maximum diameter of approximately 960 mm to 8000 mm and a water evaporation rate of approximately 1 kg / h to 1200 kg / h.

[0021] 2. Means for achieving low-temperature drying 2 to 7 show air dispersers 11 according to first to third embodiments. The air dispersers 11 according to the first to third embodiments are all configured to be able to control the speed of hot air supplied into the drying chamber 10. That is, the speed of hot air can be optimally adjusted according to the temperature of the hot air selected from the range of 100°C to 30°C and the maximum diameter of the drying chamber 10. Hereinafter, the air dispersers 11 according to the first to third embodiments will be described with reference to FIGS. 2 to 7.

[0022] 2-1. Air disperser according to the first embodiment 2 and 3 show an air disperser 11 according to a first embodiment of the present invention. The air disperser 11 of the first embodiment includes an attachment 113 as a means for adjusting the wind speed of hot air supplied into the drying chamber 10.

[0023] 2, attachment 113 is an annular metal plate having a circular second opening 113a. Diameter R2 of the second opening is smaller than diameter R1 of first opening 111b of housing 111 and is larger than the outer diameter of the portion of the inverted truncated cone-shaped wall of lower part 112 that is inserted into first opening 111b.

[0024] As shown in FIG. 3, attachment 113 is attached to the upper edge of first opening 111b of housing 111 with its central axis aligned with that of first opening 111b. This positions attachment 113 between housing 111 and lower part 112, uniformly changing the width of the hot air outlet around its entire circumference. Specifically, the outer diameter of the annular hot air outlet formed inside housing 111 is reduced from diameter R1 of first opening 111b to diameter R2 of second opening 113a. This increases the velocity of hot air supplied from the hot air outlet into drying chamber 10, increasing the amount of air per unit time that contacts the raw liquid sprayed into drying chamber 10. As a result, it becomes possible to dry the raw liquid sprayed into drying chamber 10 using hot air that is cooler than conventional methods.

[0025] Preferably, a plurality of attachments 113 having different diameters R2 of the second openings 113a are prepared, and the attachment 113 that provides the optimum air speed for drying the raw liquid is selectively used depending on the hot air temperature selected from the range of 100°C to 30°C and the maximum diameter of the drying chamber 10.

[0026] 2-2. Air disperser according to the second embodiment 4 and 5 show an air disperser 11 according to a second embodiment of the present invention. The air disperser 11 of the second embodiment includes a plurality of hydraulic cylinders 114 and bellows 115 as means for adjusting the wind speed of hot air supplied into the drying chamber 10.

[0027] As shown in FIG. 4, multiple hydraulic cylinders 114 constitute a drive mechanism for raising and lowering the lower part 112 relative to the housing 111. Each hydraulic cylinder 114 is installed vertically with its cylinder tube facing upward and its piston rod facing downward. The tip of the piston rod is connected to a stepped portion in the center of the housing 111. Meanwhile, the rear end of the cylinder tube is connected to a flange portion that protrudes outward from the upper edge of the lower part 112. Each hydraulic cylinder 114 supports the lower part 112 so that it can be raised and lowered relative to the housing 111. It is preferable that the number of hydraulic cylinders 114 is three or more. For example, three hydraulic cylinders 114 are installed on the stepped portions of the housing 111 at 120° intervals, and the flange portion of the lower part 112 inserted into the first opening 111b is supported at three points.

[0028] Bellows 115 is formed of a cylindrical bellows that is elastic and airtight. The lower end of bellows 115 is airtightly joined to a stepped portion in the center of housing 111. Meanwhile, the upper end of bellows 115 is airtightly joined to a flange portion of lower part 112. Bellows 115 covers the upper outer periphery of lower part 112 that protrudes from the center of housing 111, sealing the gap between housing 111 and lower part 112. Bellows 115 expands and contracts when lower part 112 is raised and lowered by multiple hydraulic cylinders 114, preventing leakage of hot air supplied from air passage 111a of housing 111 to the hot air outlet.

[0029] In air disperser 11 of this embodiment, first opening 111b of housing 111 and the inverted truncated cone-shaped wall portion of lower part 112 inserted therein form an annular hot air outlet (see W1 in FIG. 5).

[0030] 5(a) shows the lower part 112 in a lowered state. When the piston rods of the multiple hydraulic cylinders 114 are contracted, the lower part 112 is in a lowered state. When the lower part 112 is lowered, the inverted truncated cone-shaped wall portion of the lower part 112 approaches the first opening 111b, and the width W1 of the annular hot air outlet becomes narrower. This increases the speed of the hot air supplied from the hot air outlet into the drying chamber 10.

[0031] Here, the guide cone 112b shown in Fig. 4 is not fixed to the wall of the inverted truncated cone shape of the lower part 112. Therefore, as shown in Fig. 5(a), when the lower part 112 is lowered, the wall of the inverted truncated cone shape of the lower part 112 approaches the inner surface of the guide cone 112b, and the width W2 of the flow path of the hot air formed between them becomes narrower. This increases the speed of the hot air flowing toward the rotary wheel 27 (see Fig. 4) of the rotary atomizer 20.

[0032] 5(b) shows the lower part 112 in a raised state. When the piston rods of the multiple hydraulic cylinders 114 are extended, the lower part 112 is raised. When the lower part 112 is raised, the inverted truncated cone-shaped wall portion of the lower part 112 moves away from the first opening 111b, and the width W1 of the annular hot air outlet increases. This slows down the speed of the hot air supplied from the hot air outlet into the drying chamber 10.

[0033] 5(b), when the lower part 112 is raised, the wall of the inverted truncated cone shape of the lower part 112 moves away from the inner surface of the guide cone 112b, widening the width W2 of the hot air flow path formed between them. This reduces the speed of the hot air flowing toward the rotary wheel 27 (see FIG. 4) of the rotary atomizer 20.

[0034] As described above, according to the air disperser 11 of the second embodiment, it is possible to uniformly change the width W1 of the hot air outlet and the width W2 of the flow path of the hot air toward the rotary wheel 27 over the entire circumference by raising and lowering the lower part 112 inserted into the first opening 111b of the housing 111. This makes it possible to adjust the air speed to an optimum value for drying the stock solution according to the temperature of the hot air selected from the range of 100°C to 30°C and the maximum diameter of the drying chamber 10.

[0035] 2-3. Air disperser according to the third embodiment 6 and 7 show an air disperser 11 according to a third embodiment of the present invention. The air disperser 11 of the third embodiment includes a plurality of hydraulic cylinders 114, an annular guide 116, and a packing 117 as means for adjusting the wind speed of hot air supplied into the drying chamber 10.

[0036] The plurality of hydraulic cylinders 114, which are drive mechanisms for raising and lowering the lower parts 112, have the same configuration as in the second embodiment described above, and so are given the same reference numerals and detailed description thereof will be omitted.

[0037] As shown in FIG. 6, the annular guide 116 and the packing 117 are a sealing mechanism that replaces the bellows 115 of the second embodiment. The annular guide 116 is a bearing member having an inner diameter slightly larger than the outer diameter of the upper part of the lower part 112. An annular groove for accommodating the packing 117 is provided on the inner periphery of the annular guide 116. The annular guide 116 is fixed to a stepped portion in the center of the housing 111 with its central axis aligned with the first opening 111b of the housing 111. On the other hand, the packing 117 is a sliding lip packing having a cross section that is, for example, U-shaped, V-shaped, L-shaped, or J-shaped.

[0038] When lower part 112 is inserted into first opening 111b of housing 111, the upper outer peripheral surface of lower part 112 faces the inner peripheral surface of annular guide 116. The lifting and lowering movement of lower part 112 by multiple hydraulic cylinders 114 is guided by annular guide 116. Meanwhile, packing 117 seals the gap between housing 111 and lower part 112 through its self-sealing action. That is, the pressure in the internal space formed between housing 111 and lower part 112 increases due to the hot air supplied from air passage 111a. This pressure causes packing 117 to deform over its entire circumference and come into close contact with the upper outer peripheral surface of lower part 112. This self-sealing action of packing 117 prevents leakage of hot air supplied from air passage 111a to the hot air outlet, even when lower part 112 is lifted and lowered.

[0039] 7(a) and 7(b), according to the air disperser 11 according to the third embodiment, by raising and lowering the lower part 112 inserted into the first opening 111b of the housing 111, it is possible to uniformly change the width W1 of the hot air outlet and the width W2 of the flow path of the hot air toward the rotary wheel 27 over the entire circumference. This makes it possible to adjust the air speed to an optimum value for drying the stock solution according to the temperature of the hot air selected from the range of 100°C to 30°C and the maximum diameter of the drying chamber 10.

[0040] 2-4. Measures 1 to 5 for achieving more precise control The spray dryer equipment 1 used in the powder production method of this embodiment is equipped with first to fifth means for dramatically increasing the solid powder content by using low-temperature hot air of 100°C to 30°C.

[0041] 2-4-1. First method The first means makes the temperature distribution of the hot air supplied into the drying chamber 10 more uniform. The hot air is generated by the first filter 12, the blower 13, the air heater 14, and the second filter 15 shown in FIG. 1 and is supplied to the air disperser 11 through the duct 81.

[0042] The blower 13 sends outside air into the duct 81 through the first filter 12. Dust and other impurities contained in the air are removed by the first filter 12, and the purified air is sent into the duct 81. The air sent into the duct 81 is heated by the air heater 14 to become hot air at a predetermined temperature. The hot air is purified by the second filter 15. A HEPA filter (High Efficiency Particulate Air Filter) is preferably used as the second filter 15. The HEPA filter has a particle collection efficiency of 99.97% or more for particles with a particle size of 0.3 μm at a rated air volume, and has an initial pressure loss of 245 Pa or less. The hot air purified by the second filter 15 is supplied to the inlet 11a of the air disperser 11 through the duct 81.

[0043] Here, the spray dryer equipment 1 of this embodiment includes, as the above-mentioned first means, at least one mixer 16, a temperature sensor 11b, and a first control unit 71. Such first means can make the temperature distribution of the hot air supplied into the drying chamber 10 closer to uniform.

[0044] The mixer 16 is provided at least at the hot air inlet 11a of the air disperser 11. As shown in FIGS. 8(a) and 8(b), the mixer 16 has a main body 16a made of a metal plate and multiple agitating blades 16d. The main body 16a is circular, corresponding to the shapes of the flanges provided at the outlet of the duct 81 and the inlet 11a of the air disperser 11 shown in FIG. 1. Multiple through holes 16b for inserting bolts are provided at equal intervals in the main body 16a. An opening 16c having the same diameter as the inner diameter of the outlet of the duct 81 and the inlet 11a of the air disperser 11 is formed in the center of the main body 16a. Multiple agitating blades 16d are provided at equal intervals around the circumference of the opening 16c.

[0045] The hot air supplied from duct 81 flows in the air blowing direction indicated by the arrow in Figure 8(b) and passes through mixer 16. At this time, the hot air is agitated by multiple agitating blades 16d. As a result, the temperature distribution of the hot air that passes through mixer 16 and is supplied to inlet 11a of air disperser 11 becomes more uniform. Thereafter, the hot air swirls along the shape of the air passage inside the housing of air disperser 11 and is discharged toward the inverted truncated cone-shaped wall portion of lower part 112.

[0046] The reason for the non-uniform temperature distribution of the hot air supplied to the inlet 11a of the air disperser 11 is that the temperature distribution in the duct 81 between the outlet of the air heater 14 and the inlet 11a of the air disperser 11 is non-uniform. The outer peripheral wall of the duct 81 is affected by the temperature of the external environment, resulting in non-uniform temperature distribution in the cross-sectional direction of the duct 81. As a result, non-uniform temperature distribution in the cross-sectional direction of the hot air flowing through the duct 81 occurs. This non-uniformity in the temperature distribution of the hot air is eliminated by the multiple mixing blades 16d of the mixer 16. The length and inner diameter of the duct 81 are set according to the processing capacity of the spray dryer equipment 1, and are, for example, 2 mm long and 100 mm inner diameter. In this case, the diameter of the opening 16c of the mixer 16 is also 100 mm. To minimize unnecessary heat dissipation, the shorter the length of the duct 81, the better. If the duct 81 is made longer, it is preferable to add another mixer 16 along the duct. Furthermore, in order to make the temperature distribution in the cross-sectional direction of the duct 81 uniform, the outer wall of the duct 81 may be covered with a heat insulating material.

[0047] As shown in Fig. 1, temperature sensor 11b is provided in housing 111 immediately after inlet 11a of air disperser 11, and detects the temperature of the hot air whose temperature distribution has been made uniform by mixer 16. Temperature information detected by temperature sensor 11b is sent to first control unit 71. First control unit 71 variably controls the heat generation amount of air heater 14 based on the temperature information from temperature sensor 11b. As a result, the temperature of the hot air at inlet 11a of air disperser 11 is kept constant within the range of 100°C to 30°C.

[0048] Here, a commercially available temperature indicating controller can be used as the first control unit 71. In this embodiment, the temperature sensor 11b detects the temperature of the hot air whose temperature distribution has been made uniform by the mixer 16, so the accuracy of the temperature information transmitted from the temperature sensor 11b is high. As a result, the first control unit 71 can also control the heat generation amount of the air heater 14 with high accuracy.

[0049] The first means described above makes uniform the temperature distribution of the hot air for drying the stock solution sprayed into the drying chamber 10. As a result, even if the temperature of the hot air is low within the range of 100°C to 30°C, the droplets of the stock solution sprayed into the drying chamber 10 are exposed to hot air at a constant temperature and are dried uniformly.

[0050] 2-4-2.Second method The second means keeps the droplet diameter of the stock solution sprayed into the drying chamber 10 close to constant. The stock solution is stored in a stock solution tank 31 shown in FIG. 1. The stock solution stored in the stock solution tank 31 is transferred by a stock solution pump 32 and supplied to the rotary atomizer 20 through a pipe 82. In order to improve the solid powder content, the flow rate per unit time of the stock solution supplied to the rotary atomizer 20 is preferably set within a range of 1.0 L / h to 2.0 L / h. The rotary atomizer 20 sprays the stock solution supplied from the stock solution pump 32 into the drying chamber 10.

[0051] As shown in FIG. 9, the rotary atomizer 20 includes a motor 22 mounted above a base plate 21. The rotating shaft of the motor 22 is connected to a spindle 23. The spindle 23 passes vertically through the center of the base plate 21. The lower end of the spindle 23 is rotatably held by a bearing on a lower flange 25. Meanwhile, a concentrate pipe 24 passes obliquely through the right side of the base plate 21 in the figure. The upper end of the concentrate pipe 24 forms an inlet 24a for the concentrate. The lower end of the concentrate pipe 24 forms an outlet 24b for the concentrate. The outlet 24b of the concentrate pipe 24 communicates with a through-hole 25a provided in the lower flange 25. An upper distributor 26A is attached to the underside of the lower flange 25.

[0052] As shown in FIGS. 10(a) and 10(b), the upper distributor 26A is housed within the lower distributor 26B. A rotary wheel 27 is disposed below the lower distributor 26B. A first flow path 261, a second flow path 262, and a third flow path 263 are formed in the upper distributor 26A. Meanwhile, a fourth flow path 264 is formed in the lower distributor 26B. The first flow path 261 and the second flow path 262 are annular recesses surrounding the upper edge of the third flow path 263. The third flow path 263 and the fourth flow path 264 have the same inner diameter. As shown in FIGS. 10(b) and 10(c), when the upper distributor 26A is housed within the lower distributor 26B, the first flow path 261, the second flow path 262, the third flow path 263, and the fourth flow path 264 form a single flow path that is continuous with the concentrate inlet 27b of the rotary wheel 27.

[0053] As shown in FIG. 9 , the lower end of the spindle 23 penetrates the centers of the upper distributor 26A and the lower distributor 26B and is connected to the mounting hole 27a of the rotary wheel 27. The first flow path 261 of the upper distributor 26A receives the concentrate from the outlet 24b of the concentrate pipe 24 through the through-hole 25a of the lower flange 25. The concentrate supplied to the first flow path 261 flows through the first flow path 261, the second flow path 262, the third flow path 263, and the fourth flow path 264, as shown in FIG. 10(d), and is uniformly supplied to the concentrate inlet 27b of the rotary wheel 27. The rotary wheel 27 is rotated at high speed by the motor 22, and centrifugal force sprays the concentrate droplets horizontally. For example, the rotary wheel 27 has a diameter of 50 mm and is rotated at a high speed of 30,000 rpm or less. The lower the rotation speed of the rotary wheel 27, the larger the diameter of the sprayed droplets and the larger the particle size of the generated powder. By setting the rotation speed of the rotating wheel 27 to be lower than 30,000 rpm, solid powder is more likely to be produced.

[0054] The components of the rotary atomizer 20 from the lower side of the base plate 21 to the lower distributor 26B are covered with an inverted truncated cone-shaped jacket skirt 28. The internal space of the jacket skirt 28 is filled with a heat insulating material.

[0055] Here, the spray dryer equipment 1 of this embodiment is equipped with at least one of the pulsation reduction mechanisms 32a and 33 shown in Fig. 1 as the second means described above. The pulsation reduction mechanism 32a is incorporated into the stock solution pump 32. On the other hand, the pulsation reduction mechanism 33 is provided in the piping 82 between the outlet of the stock solution pump 32 and the inlet 24 of the stock solution pipe 24 of the rotary atomizer 20. The pulsation reduction mechanisms 32a and 33 reduce the pulsation of the stock solution transferred by the stock solution pump 32, thereby keeping the instantaneous flow rate of the stock solution supplied to the rotary atomizer 20 closer to a constant value and keeping the droplet diameter of the stock solution sprayed from the rotary atomizer 20 closer to a constant value within a range of 10 µm to 100 µm.

[0056] The pulsation reduction mechanism 32a incorporated in the concentrate pump 32 may be, for example, a tube pump equipped with two or more rollers, with the pulsation generated when the first roller separates from the tube being canceled out by the acceleration action of the second roller. Alternatively, for example, the concentrate pump 32 may be a multiple reciprocating pump equipped with two or more diaphragms, with the timing at which each diaphragm starts to reciprocate offset. When two diaphragms are used, the timing at which the diaphragms start to reciprocate is offset by 180 degrees. When three diaphragms are used, the timing at which the diaphragms start to reciprocate is offset by 120 degrees. The greater the number of diaphragms, the greater the reduction in concentrate pulsation.

[0057] On the other hand, the pulsation reduction mechanism 33 provided in the pipe 82 may be, for example, an air chamber or an accumulator provided in the pipe 82. The air chamber uses the air pressure in the air chamber to suppress the pulsation of the concentrate pump 32. The accumulator is configured so that nitrogen gas is sealed in a spherical container isolated by a rubber membrane. The sealed nitrogen gas repeatedly expands and contracts via the rubber membrane, thereby absorbing the pulsation of the concentrate.

[0058] According to the second means described above, the pulsation of the stock solution transported by the stock solution pump 32 is reduced, and the instantaneous flow rate of the stock solution supplied to the inlet 24a of the stock solution pipe 24 of the rotary atomizer 20 can be made nearly constant. As a result, a constant amount of stock solution per unit time is supplied to the first flow path 261 of the upper distributor 26A, and is uniformly supplied to the stock solution inlet 27b of the rotary wheel 27 by the flow shown in FIG. 10(d). As a result, the diameter of droplets of the stock solution sprayed from the rotary atomizer 20 approaches a constant value within the range of 10 μm to 100 μm. 10 μm to 100 μm is the range of the diameter of droplets of stock solution that can be dried using low-temperature hot air within the range of 100°C to 30°C.

[0059] 2-4-3.Third method The third means maintains a constant temperature distribution within the drying chamber 10. The spray dryer equipment 1 of this embodiment is provided with a heat-retaining air layer 10a shown in FIG. 1 as the third means. The heat-retaining air layer 10a forms an air layer that covers the outer wall of the drying chamber 10. The heat-retaining air layer 10a maintains a constant temperature distribution within the drying chamber 10 by dissipating or absorbing heat into the air layer to compensate for the temperature difference that occurs in the temperature distribution within the drying chamber 10.

[0060] 2-4-4.Fourth means The fourth means ensures the residence time of the powder required for drying in the drying equipment, which affects the quality of the powder product. The spray dryer equipment 1 of this embodiment includes a second control unit 72 shown in FIG. 1 as the fourth means. The second control unit 72 controls the air flow rate of the blower 13 to a preset value, thereby causing the powder to reside in the drying chamber 10 and the cyclone 40 for a fixed time within a range of 20 to 60 seconds. 20 to 60 seconds is the range of residence time required to sufficiently dry a stock solution with droplet diameters of 10 μm to 100 μm using low-temperature hot air within a range of 100°C to 30°C.

[0061] When the spray dryer equipment 1 is composed of the drying chamber 10 and the bag filter 50, the second control unit 72 may control the air volume of the blower 13 so that the residence time of the powder in the drying chamber 10 is 20 to 60 seconds. When the spray dryer equipment 1 includes a third drying equipment in addition to the drying chamber 10 and the cyclone 40, the second control unit 72 may control the air volume of the blower 13 so that the residence time of the powder in the drying chamber 10, the cyclone 40, and the third drying equipment is 20 to 60 seconds.

[0062] 2-4-5.Fifth means The fifth means maintains a constant pressure inside the drying chamber 10. The spray dryer equipment 1 of the embodiment includes a pressure sensor 10b and a third control unit 73 shown in FIG.

[0063] As shown in FIG. 1, the exhaust port of the bag filter 50 is connected to the inlet of the exhaust fan 60 via a duct 81. The exhaust fan 60 exhausts the hot air used to produce the powder to the outside of the spray dryer equipment 1. The exhaust air volume of the exhaust fan 60 affects the pressure inside the drying chamber 10. The pressure sensor 10b detects the pressure inside the drying chamber 10 and transmits the pressure information to the third control unit 72. The third control unit 72 variably controls the exhaust air volume of the exhaust fan 60 based on the detection result of the pressure sensor 10b. This maintains a constant pressure inside the drying chamber 10. [Example]

[0064] Examples of the method for producing powder of the present invention will be described below with reference to Tables 1 and 2. Using a spray dryer facility having the same configuration as that shown in Fig. 1, a stock solution having the composition shown in Table 1 below was dried to produce a dextrin powder product. [Table 1]

[0065] Powder manufacturing methods were carried out under eight different conditions as shown in Table 2 below. In all powder manufacturing methods, the maximum diameter of the drying chamber was 960 mm. Powder manufacturing methods in which the temperature of the hot air supplied into the drying chamber was controlled to 150°C, 140°C, 130°C, and 120°C were designated as Comparative Examples 1, 2, 3, and 4, respectively. Powder manufacturing methods in which the temperature of the hot air supplied into the drying chamber was controlled to 100°C, 90°C, 80°C, and 70°C were designated as Examples 1, 2, 3, and 4, respectively. The air flow rate of the blower was increased by 1.0 m / s in inverse proportion to the temperature of the hot air supplied into the drying chamber, 150°C to 70°C. 3 / min~1.7m 3 / min, up to 0.1m 3 / min in increments. By increasing the airflow rate of the blower, the wind speed of the hot air supplied into the drying chamber also increases in inverse proportion to the temperature of the hot air supplied into the drying chamber, which is 150°C to 70°C. The rotation speed of the rotary atomizers in Comparative Examples 1 to 4 was kept constant at 30,000 rpm. The rotation speed of the rotary atomizers in Examples 1 to 4 was reduced in increments of 2,000 rpm from 26,000 rpm to 20,000 rpm. [Table 2]

[0066] The powder products produced in each of Comparative Examples 1 to 4 and Examples 1 to 4 were collected, and a certain amount of powder sample was taken from each powder product. The cross section of each of the powder samples in Comparative Examples 1 to 4 and Examples 1 to 4 was observed using a scanning electron microscope to confirm the shape of the powder most commonly contained in the powder sample. As a result, the powder samples in Comparative Examples 1 to 4 all had a high content of hollow powder. On the other hand, the powder samples in Examples 1 to 4 all had a high content of solid powder. [Explanation of symbols]

[0067] 1. Spray dryer equipment 10 Drying room 10a Air layer 10b Pressure sensor 11 Air Disperser 11a Entrance 11b Temperature sensor 111 Housing 111a Wind path 111b 1st opening 112 Lower parts 112a Upper guide vane 112b Guide Cone 112c Lower guide vane 113 Attachment (wind speed adjustment means) 113a 2nd opening 114 Hydraulic cylinder (drive mechanism) 115 Bellows (sealing mechanism) 116 Circular guide 117 Packing (sealing mechanism) 12 First filter 13 Blower 14 Air heater 15 Second filter 16 Mixer 16a Main body 16b Through hole 16c aperture 16d stirring blade 20 Rotary atomizer 21 Base Plate 22 Motor 23 Spindle 24 Concentrate Pipe 24a Entrance 24b exit 25 Lower flange 25a through hole 26A Upper Distributor 26B Lower Distributor 261 First Channel 262 Second Channel 263 Third Channel 264 4th Channel 265 Storage section 27 Spinning Wheel 27a Mounting hole 27b Stock solution inlet 28 Jacket Skirt 31 Concentrate tank 32 Concentrate pump 32a Pulsation reduction mechanism 33 Pulsation reduction mechanism 40 Cyclone 50 Bag Filter 60 Exhaust fan 71 First Control Section 72 Second Control Section 73 Third Control Section 81 Duct 82 Piping

Claims

1. A method for producing powder, comprising heating air sent from a blower to generate hot air, and drying droplets of a raw material sprayed into a drying chamber by a rotary atomizer with the hot air supplied into the drying chamber, The temperature of the hot air supplied into the drying chamber is selected within a range of 100°C to 30°C; determining an air flow rate per unit time of the blower based on the temperature of the hot air and the maximum diameter of the drying chamber; determining a wind speed of the hot air supplied into the drying chamber based on a temperature of the hot air and a maximum diameter of the drying chamber; A method for producing powder, characterized by producing a solid powder by drying droplets of the raw liquid sprayed into the drying chamber while controlling to maintain the temperature of the hot air, the air flow rate per unit time of the blower, and the wind speed of the hot air supplied into the drying chamber.

2. The maximum diameter of the drying chamber is 960 mm or more, and the air volume per unit time of the blower is 1.0 m ３ 2. The method for producing powder according to claim 1, wherein the hot air supplied into the drying chamber has a speed of 12.0 m / s or more.

3. 2. The method for producing powder according to claim 1, wherein the flow rate per unit time of the raw solution supplied to the rotary atomizer is set within a range of 1.0 L / h to 2.0 L / h, and the rotation speed of the rotary atomizer is set to 30,000 rpm or less.

4. A solid powder produced by the method for producing powder according to any one of claims 1 to 3.

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