Jet mill comprising recycled stream

Abstract

The jet mill is provided with a grinding cavity; the material nozzle is configured to spray particles to be ground into the grinding cavity; a main discharge port configured to discharge the ground particles from the grinding chamber; the grinding nozzle is configured to spray grinding gas into the grinding cavity; and, a recirculation outlet, which may be configured to collect a portion of the milled particles from within the milling chamber. A delivery conduit effectively connects the recirculation outlet with the grinding nozzle such that a portion of ground particles from within the grinding chamber can be recirculated to the grinding nozzle via the recirculation outlet and the delivery conduit, and in a material flow of the mixed particles and the grinding gas, the mixed particles and the grinding gas return to the grinding cavity through the grinding nozzle.

Description

Technical Field

[0001] The present invention generally relates to an air jet mill and a method for grinding particles in the air jet mill. Background Technology

[0002] In the production of pigment-grade titanium dioxide (TiO2) particles, TiO2 particles that have been initially prepared by chlorination or sulfuric acid processes are usually pulverized to obtain smaller particle sizes suitable for pigments. Figure 1 and Figure 2 A conventional steam jet mill (also known as a "micronizer") is shown for pulverizing TiO2 particles to a desired particle size and particle size distribution (also known as "micronization"). This conventional cyclone jet mill includes a generally planar circular grinding chamber surrounded by a manifold with multiple grinding steam ejectors that inject grinding steam into the grinding chamber. Typically, each grinding steam ejector is oriented at the same angle to the radial direction, i.e., tangential to the centerline, to push a relatively uniform airflow clockwise or counterclockwise along the grinding chamber. The grinding chamber is topped with a cover comprising a single material nozzle for injecting a material stream mixed with input steam and unground granular material into the grinding chamber. This material nozzle is typically oriented tangentially to the centerline and at an acute angle to the horizontal plane, thus injecting the material and input steam streams in a clockwise or counterclockwise direction along the grinding steam. As the granular particles swirl along the outer periphery of the grinding chamber, they collide with the grinding steam injected from the grinding steam ejectors, ultimately pulverizing the granular particles. The smaller, pulverized particles eventually migrate towards the center of the grinding chamber, where an outlet allows the pulverized particles to be discharged from the grinding chamber along with the waste steam. An example of a conventional cyclone jet mill can be found in U.S. Patent No. 7,150,421.

[0003] While conventional steam jet mills are perfectly capable of grinding particles to the desired particle size and size distribution, they consume significant energy and are relatively inefficient due to the need to maintain a high flux of steam to grind a given amount of TiO2 particles to the desired size. Therefore, there is a pressing need for a grinding system that reduces the amount of steam or other grinding gases required to grind a given amount of particles to the desired particle size and / or size distribution, thereby lowering both production input costs and environmental impact (e.g., carbon footprint) by using less energy. Summary of the Invention

[0004] To address one or more of the aforementioned limitations, this invention provides a novel airflow pulverizer and a novel method for grinding particles.

[0005] In a non-limiting aspect of the invention, an air jet mill is provided. In a portion of this aspect, the air jet mill may include a grinding chamber; a material nozzle configured to inject particles to be ground into the grinding chamber; a main outlet configured to discharge ground particles from the grinding chamber; a grinding nozzle configured to inject grinding gas into the grinding chamber; and a recirculation outlet configured to collect a portion of the ground particles from the grinding chamber. A conveying conduit can effectively connect the recirculation outlet to the grinding nozzle, such that a portion of the ground particles from the grinding chamber can be recirculated to the grinding nozzle via the recirculation outlet and the conveying conduit, and returned to the grinding chamber by the grinding nozzle in a material flow containing mixed particles and grinding gas.

[0006] In another non-limiting aspect of the invention, a method for grinding particles in an air jet mill is provided. The air jet mill may include a grinding chamber, a material nozzle, and a grinding nozzle. In some aspects of the method, a flow of particles may be injected into the grinding chamber through the material nozzle. Grinding gas may be injected into the grinding chamber through the grinding nozzle. A portion of the grinding gas, mixed with partially ground particles, may be recycled to the grinding nozzle. The recycled grinding gas and partially ground particles may be mixed with the grinding gas, and the resulting mixture of recycled grinding gas, partially ground particles, and grinding gas may be injected into the grinding chamber through the grinding nozzle.

[0007] In some optional configurations, the grinding nozzle may include a mixing chamber; a first inlet configured to introduce a material flow of grinding gas into the mixing chamber; a second inlet configured to introduce a material flow of particles into the mixing chamber; and an injection port configured to introduce a material flow of mixed particles and grinding gas from the mixing chamber into the grinding chamber. The delivery conduit can effectively connect the recirculation outlet to the second inlet of the grinding nozzle.

[0008] In some optional configurations, the grinding nozzle may include a venturi tube configured to receive a material flow of mixed particles and grinding gas. For example, in some arrangements, the venturi tube may be effectively positioned between the mixing chamber and the injection port, such that the material flow of mixed grinding gas and particles from the mixing chamber is sprayed back into the grinding chamber after passing through the venturi tube.

[0009] In some optional configurations, the recirculation outlet may be located along the radial peripheral wall of the grinding chamber.

[0010] In some optional configurations, the grinding nozzle may be oriented to inject the material flow of the mixed particles and grinding gas tangentially into the grinding chamber along a vortex.

[0011] In some optional configurations, the recirculation outlet may be oriented substantially radially to the central axis of the vortex.

[0012] In some optional configurations, at least two or more of the grinding nozzles may be distributed along the radial outer periphery of the grinding chamber.

[0013] In some optional configurations, at least two or more of the recirculation outlets may be distributed along the radial periphery of the grinding chamber.

[0014] In some optional configurations, the material nozzle is disposed within a cover that covers the grinding chamber.

[0015] In some optional configurations, two or more of the material nozzles may be oriented to spray particles radially inward into the grinding chamber from the radial outer periphery of the grinding chamber.

[0016] In some optional configurations, a grinding gas injection port may be provided on the radial outer periphery of the grinding chamber and configured to inject grinding gas into the grinding chamber. The grinding nozzle may be connected to the grinding gas injection port.

[0017] In some optional configurations, the mixed recirculated grinding gas, partially ground particles, and grinding gas can be accelerated via a venturi tube to further pulverize the partially ground particles.

[0018] In some optional configurations, the grinding chamber may have a peripheral wall with the centerline of the vortex facing radially outward. The material nozzle may inject the particle material stream into the grinding chamber at a position between the peripheral wall and the centerline of the vortex.

[0019] In some optional configurations, the grinding nozzle can spray the grinding gas and some of the grinding particles along the peripheral wall.

[0020] In some optional configurations, a portion of the abrasive gas, mixed with some of the abrasive particles, can be recycled to two or more of the abrasive nozzles.

[0021] In some configurations and methods, the cyclone air jet mill and / or method of the present invention can provide faster and / or more efficient grinding of small particles (TiO2 pigment particles), saving up to 50% or more of energy compared to conventional air jet mills. Other advantages, uses, and / or features will become apparent after careful reading of the following detailed description and accompanying drawings. Attached Figure Description

[0022] Figure 1 This is a side cross-sectional view of a conventional steam jet mill used for grinding titanium dioxide particles.

[0023] Figure 2 for Figure 1 Top cross-sectional view of a conventional steam jet mill;

[0024] Figure 3 A schematic top view of an airflow pulverizer according to a non-limiting exemplary embodiment of the present invention;

[0025] Figure 4 for Figure 3 An axial cross-sectional view of one of the grinding nozzles of an air jet mill; and

[0026] Figure 5 for Figure 3 Top cross-sectional view of an airflow pulverizer. Detailed Implementation

[0027] The following description is intended to illustrate the contents shown in the accompanying drawings and / or various contemplated embodiments of the contents shown in the accompanying drawings and / or various contemplated embodiments related to the contents shown in the accompanying drawings. The embodiments shown in the accompanying drawings are non-limiting examples and do not in themselves limit the invention. Any feature shown and / or described in one embodiment may be combined with any or more features shown and / or described in another embodiment, and any feature shown in any embodiment may be omitted in other embodiments. Any dimensions shown in the accompanying drawings are merely exemplary dimensions and are not intended to limit the scope of the invention. The use of "a" and "an" is an open-ended, inclusive expression and, unless otherwise stated, is not limited to only one feature, but may include more than one feature.

[0028] According to some non-limiting aspects of the invention, an air jet mill for grinding particles, such as titanium dioxide (TiO2) pigment particles, is configured to recycle at least some of the partially ground pigment particles from the grinding chamber within the air jet mill, via one or more grinding nozzles, and back to the grinding chamber. By recycling the partially ground particles via the grinding nozzles, the air jet mill can, in some configurations, reduce the energy required to grind the particles to the desired particle size, and / or shorten the time required to grind the particles to the desired particle size. For example, in an air jet mill configuration that uses steam to grind the particles (“micronization”), it is believed that recycling the partially ground particles via the grinding nozzles can reduce the steam consumption required to grind the particles to the desired particle size by about 25% to 50%, which significantly saves energy and reduces the environmental impact of using the air jet mill. In some arrangements, depending on the specific configuration and operating parameters of a given air jet mill, the savings in steam energy input can be higher than 50% or lower than 25%.

[0029] Now turn to the attached image. Figure 3 and Figure 5 An airflow pulverizer 10 according to a non-limiting exemplary embodiment of the present invention is shown, and Figure 4 A grinding nozzle 18 included in an air jet mill 10 is shown according to a non-limiting example. The air jet mill 10 has a grinding chamber 12 formed inside a body. In this embodiment, the body is generally cylindrical, having generally cylindrical sidewalls, and a top and bottom end that together enclose the grinding chamber 12. However, the body may also have other shapes. The grinding chamber 12 forms a hollow cavity inside the body, configured to allow vortices of gas and / or particles to swirl about an axis while particles and vapor and / or other gases are injected into the grinding chamber at high speed. In this embodiment, the grinding chamber 12 is generally cylindrical, generally corresponding to the shape of the body, and has a cylindrical outer peripheral sidewall 34, a bottom wall, and a cover 36, wherein the cylindrical outer peripheral sidewall 34 is radially spaced from and surrounds the central vertical axis of the grinding chamber, and the cover 36 covers the top opening into the grinding chamber. However, the grinding chamber 12 may be a non-circular shape, such as elliptical or polyhedral.

[0030] At least one material nozzle 14 is provided for spraying particulate material, such as TiO2 pigment particles, into the grinding chamber 12 during the grinding process. In this embodiment, the air jet mill 10 includes two material nozzles 14. Each material nozzle 14 is preferably configured to spray the particles to be ground along a vortex formed in the grinding chamber 12. In this embodiment, each nozzle 14 extends through the cover 36 at a downward angle and is arranged off-center from the centerline of the grinding chamber 12 and approximately tangent to the radius of the centerline, so that the airflow of the sprayed particles is aligned with the counterclockwise direction (top view) and the direction of the vortex formed within the grinding chamber. In other arrangements, the material nozzles 14 may be arranged differently and / or there may be only one or more nozzles. The material nozzles 14 are effectively connected to one or more feeding devices for particles to be ground in the air jet mill 10. The particle feeding device may be located remotely from the air jet mill and may be effectively connected to the nozzle 14, for example, via a delivery pipe connected to an external flange of the nozzle.

[0031] At least one main outlet 16 is configured to discharge fully ground particles from the grinding chamber 12 after the particles have been crushed to the desired particle size. In this embodiment, the main outlet 16 is disposed in the cover 36 and extends upward near the central axis of the vortex, preferably aligned with the central axis of the grinding chamber 12. In this configuration, as the particles are ground to a smaller particle size, they migrate slowly radially inward in the vortex due to the reduction in mass, and are eventually discharged via the main outlet 16 along with the gas and / or grinding vapor. However, the main outlet may also be configured in other ways, such as extending downward from the bottom wall of the grinding chamber 12, or some other configuration.

[0032] At least one grinding nozzle 18 is configured to inject grinding gas (also known as milling gas), such as grinding steam, into the grinding chamber 12 to pulverize the particles within the grinding chamber to a smaller particle size. In this embodiment, the air jet mill includes four grinding nozzles 18; however, fewer or more than four grinding nozzles may also be used. Unlike previous air jet mills, the grinding nozzles 18 are configured to not only inject grinding gas but also simultaneously inject the particles to be ground along with the grinding gas. In this way, the grinding nozzles 18 can grind the particles both as they flow through the nozzles themselves and as they impact other particles within the grinding chamber 12. Therefore, by injecting a mixture of grinding gas (e.g., steam) and particles (e.g., TiO2 pigment particles) via the grinding nozzles 18, the air jet mill provides additional pulverization sites compared to conventional air jet mills, enabling faster particle pulverization. Figure 4 As most preferably shown, the grinding nozzle 18 has a first inlet 22 and a second inlet 24, wherein the first inlet 22 is used to receive grinding gas from a pressurized source of grinding gas, and the second inlet 24 is used to receive an airflow of particles to be ground and / or re-ground. The first inlet 22 and the second inlet 24 introduce their respective grinding gas and particle material flows into a mixing chamber 20 within the body of the grinding nozzle 18, where the grinding gas and particles are mixed together. Downstream of the mixing chamber 20 is a jet nozzle 26 configured to inject the mixture of particles and grinding gas from the mixing chamber 20 into the grinding chamber 12. The jet nozzle 26 is connected to the body of the air jet mill and configured to inject the mixture of particles and grinding gas from the mixing chamber 20 into the grinding chamber 12. In this embodiment, the jet nozzle 26 is connected to a flange on the outside of the body, and the jet port extends through the peripheral walls of the body and the grinding chamber 12. However, in other arrangements, the nozzle 26 may extend itself through the body of the air jet mill, or be configured to inject a mixture of grinding gas and particles into the grinding chamber 12. In other embodiments, the recirculated particles and (pure) grinding gas may be mixed upstream of the grinding nozzle 18 rather than directly in the grinding nozzle, and then conducted via the grinding nozzle 18.

[0033] Preferably, at least one or more grinding nozzles 18 are arranged to inject a mixture of grinding gas and particles tangentially relative to the central axis of the grinding chamber in a vortex direction, thereby generating and / or helping to maintain a vortex flow of gas and particles within the grinding chamber 12 during operation. In this embodiment, four grinding nozzles 18 are each arranged to inject their respective material flow tangentially in a counterclockwise direction (top view perspective) to generate a counterclockwise vortex within the grinding chamber, and the four grinding nozzles are spaced approximately at a generally even angular interval of about 90° along the outer periphery and peripheral wall 34 of the body. However, any one or more grinding nozzles 18 may have different orientations and / or different spacing. The act of injecting the mixture of grinding gas and particles together via the grinding nozzles 18 provides at least some additional grinding of the particles, at least in terms of the impact between the injected particles and the particles already swirling in the vortex. However, to provide more grinding action within the grinding nozzle 18, a venturi tube 32 can be optionally provided between the mixing chamber 20 and the injection port 26. This causes a pressure drop in the particles of the grinding gas flowing from the mixing chamber 20 to the injection port 26 at the venturi tube, causing agglomerated particles to disperse and / or to collide with each other at higher speeds to break up the agglomerated particles, or to provide additional grinding action. Therefore, if the grinding nozzle is designed to have a venturi form similar to the material nozzle, the additional grinding / crushing action obtained by using the grinding nozzle can be further enhanced. In this way, by means of the generated negative pressure, TiO2 pigment particles can be drawn out of the grinding chamber through the suction line and then accelerated back into the grinding chamber through the ejector (grinding nozzle).

[0034] The grinding nozzle 18 can be connected to the grinding chamber 12 using any convenient mechanism. In this embodiment, a grinding gas injection port 38 is provided on the radially outer surface of the peripheral wall 34, providing a through-hole for entering the grinding area within the grinding chamber 12 through the peripheral wall. Each grinding gas injection port 38 includes a flange on the radially outer surface of the peripheral wall 34, and a matching flange on the injection port 26 of the grinding nozzle can be connected to this flange, for example, by bolts and / or welding. In other embodiments, the injection port 26 of the grinding nozzle can at least partially penetrate the peripheral wall 34 to directly input a material flow of grinding gas (with or without recirculated particles) into the grinding chamber 12. Other configurations can also be used to effectively connect the grinding nozzle 18 to the grinding chamber 12 to deliver a material flow of grinding gas and, optionally, recirculated particles.

[0035] At least one recirculation outlet 28 is configured to collect grinding gas and partially ground particles from the grinding chamber 12 for recirculation to at least one grinding nozzle 18. In this embodiment, the air jet mill 10 has four recirculation outlets 28, corresponding to the number of grinding nozzles 18. However, other configurations for recirculating grinding gas and partially ground particles from the grinding chamber 12 to one or more grinding nozzles 18 are also possible. Each recirculation outlet 28 provides an opening through the peripheral wall 34 and sidewalls of the body of the air jet mill. In this embodiment, each recirculation outlet 28 is radially aligned with the central axis of the grinding chamber 12 to collect grinding gas and particles moving along the peripheral wall of the grinding chamber. In other arrangements, any one or more recirculation outlets may be non-radially aligned with the central axis. For example, any one or more recirculation outlets 28 may be tangentially aligned, for example, in a clockwise or counterclockwise direction opposite to the grinding nozzles 18.

[0036] The delivery conduits 30 effectively connect each recirculation outlet 28 to the second inlet 24 of the corresponding grinding nozzle 18, thereby conveying and recirculating the mixed grinding gas and partially ground particles from the recirculation outlets to the second inlet. In this embodiment, each delivery conduit 30 is a flexible or rigid pipe with both ends directly connected to the corresponding recirculation outlet 28 and second inlet 24. However, in other arrangements for collecting and / or conveying the mixed grinding gas and partially ground particles from the recirculation outlet 28 to the grinding nozzle 18, manifolds or other types of delivery conduits may be used.

[0037] According to some aspects of the invention, in a non-limiting example method using an air jet mill, such as the air jet mill 10 described above, a stream of material to be pulverized to a smaller particle size (unpulverized particles) is injected into the grinding chamber through one or more material nozzles 14. Typically, the particles are unground / unpulverized particles, but may also be particles that may have undergone preliminary simple pulverization and require additional pulverization / grinding. For ease of reference, particles ejected from the material nozzles 14 may be referred to as unpulverized particles, even if they have undergone preliminary pulverization at some other time / place; the term "unpulverized" as used herein is understood to mean that they have not yet been pulverized in this particular air jet mill during this process. The material nozzles 14 may be arranged to eject the particles in the direction of a vortex formed within the grinding chamber 12. The material nozzles 14 may be arranged to eject the grinding gas in the direction of the vortex, thereby generating and / or contributing to the formation or maintenance of a vortex vortex within the grinding chamber. The grinding gas is also injected into the grinding chamber through one or more grinding nozzles 18. The grinding gas can be simultaneously injected with the material from the material nozzle 14, causing the injected particles and gas to swirl along the grinding chamber 12 in a vortex. As the particles swirl along the vortex in the grinding chamber 12, they are pulverized to a smaller particle size. Lighter and smaller fully ground particles tend to migrate towards the center, rising with the waste grinding gas and exiting through the main outlet 16, while larger and heavier particles that are only partially pulverized are more likely to move radially outward from the grinding chamber 12. As the partially pulverized particles move along the outer periphery of the grinding chamber, at least some of the partially pulverized particles enter the recirculation outlet 28 by suction from the grinding nozzle 18 and / or by centrifugal force and / or positive pressure within the grinding chamber, and are conveyed via corresponding delivery pipes 30 to the second inlet 24 of the corresponding grinding nozzle 18. The recirculated partially ground particles are then mixed in the mixing chamber 20 with the material flow of grinding gas entering the first inlet 22 and injected back into the grinding chamber 12 via the injection port 26 to collide with other particles already swirling within the grinding chamber, thereby providing additional grinding impact. If the grinding nozzle includes a venturi tube 32, the particles are further ground by flowing through the venturi tube. Ultimately, as the partially ground particles are ground to very small diameters until they become fully ground, they also migrate radially inward and exit through the main outlet 16. In this manner, compared to conventional air jet mills without a circulation system, the particles receiving grinding in the air jet mill 10 undergo stronger grinding behavior per unit input grinding energy due to the recirculation created by the air jet mill 10.

[0038] The embodiments described above and illustrated in the accompanying drawings are merely examples and are not intended to limit the invention. As previously stated, the invention may include any one or more of the various features described and / or shown herein in any feasible combination, including fewer or more than all the features described and / or shown in the respective embodiments, and / or different combinations of the features described and / or shown in the respective embodiments. Therefore, the invention is intended to be defined by the following claims, rather than by the foregoing description and exemplary embodiments.

Claims

1. An airflow pulverizer (10), comprising: Grinding chamber (12); Material nozzle (14) is configured to spray the particles to be ground into the grinding chamber; The main outlet (16) is configured to discharge the ground particles from the grinding chamber; A grinding nozzle (18) is configured to inject grinding gas into the grinding chamber; A recirculation outlet (28) is configured to collect a portion of the ground particles from the grinding chamber; as well as The delivery pipe (30) effectively connects the recirculation outlet to the grinding nozzle. Some of the ground particles from the grinding chamber can be recycled to the grinding nozzle via the recirculation outlet and the conveying pipe, and then returned to the grinding chamber by the grinding nozzle in the material flow of mixed particles and grinding gas.

2. The airflow pulverizer according to claim 1, wherein, The grinding nozzle (18) includes: Mixing chamber (20); The first inlet (22) is configured to introduce the material flow of grinding gas into the mixing chamber; A second inlet (24) is configured to introduce a flow of particulate material into the mixing chamber; and The injection port (26) is configured to introduce a material flow of mixed particles and grinding gas from the mixing chamber into the grinding chamber; The delivery pipe (30) effectively connects the recirculation outlet to the second inlet of the grinding nozzle.

3. The airflow pulverizer according to claim 2 or any of the preceding claims, wherein, The grinding nozzle includes a venturi tube (32), wherein the venturi tube (32) is configured to receive a material flow of mixed particles and grinding gas.

4. The airflow pulverizer according to claim 1 or any of the preceding claims, wherein, The recirculation outlet (28) is disposed along the radial peripheral wall (34) of the grinding chamber.

5. The air jet mill according to claim 1 or any of the preceding claims, wherein, The grinding nozzle (18) is oriented to inject the material flow of the mixed particles and grinding gas tangentially into the grinding chamber (12) along a vortex.

6. The air jet mill according to claim 1 or any of the preceding claims, wherein, The recirculation outlet (28) is oriented substantially radially to the central axis of the vortex.

7. The airflow pulverizer according to claim 1 or any of the preceding claims, comprising a plurality of grinding nozzles (18) wherein the grinding nozzles (18) are distributed along the radial outer periphery of the grinding chamber (12).

8. The airflow pulverizer according to claim 1 or any of the preceding claims, comprising a plurality of recirculation outlets (28), wherein the recirculation outlets (28) are distributed along the radial outer periphery of the grinding chamber (12).

9. The air jet mill according to claim 1 or any of the preceding claims, wherein, The material nozzle (14) is located in the cover (36) covering the grinding chamber (12).

10. The airflow pulverizer according to claim 1 or any of the preceding claims, comprising a plurality of material nozzles (14), wherein the material nozzles (14) are oriented to spray particles radially inward into the grinding chamber (12) from the radial outer periphery of the grinding chamber.

11. The airflow pulverizer according to claim 1 or any of the preceding claims, comprising a grinding gas injection port (38), wherein the grinding gas injection port (38) is disposed on the radial outer periphery of the grinding chamber and configured to inject grinding gas into the grinding chamber (12), wherein, The grinding nozzle (18) is connected to the grinding gas injection port.

12. A method for grinding particles in an air jet mill (10), wherein the air jet mill (10) includes a grinding chamber (12), a material nozzle (14), and a grinding nozzle (18), the method comprising: The material flow of particles is sprayed into the grinding chamber (12) through the material nozzle (14); Grinding gas is injected into the grinding chamber (12) through the grinding nozzle (18); A portion of the grinding gas, which contains some of the ground particles, is recirculated from the grinding chamber (12) to the grinding nozzle (18). The recirculated grinding gas and partially pulverized particles are mixed with the grinding gas; as well as The mixed recirculated grinding gas, partially crushed particles, and grinding gas are injected into the grinding chamber (12) through the grinding nozzle (18).

13. The method according to claim 12, wherein, The step of injecting the mixed recirculated grinding gas, partially ground particles, and grinding gas includes accelerating the mixed recirculated grinding gas, partially ground particles, and grinding gas via a venturi tube (32) to further pulverize the partially ground particles.

14. The method according to any one of claims 12 to 13, wherein, The grinding chamber (12) has a peripheral wall that is radially outward from the center line of the vortex, and a material nozzle (14) that sprays the material flow of the particles into the grinding chamber at a position between the peripheral wall and the center line of the vortex.

15. The method according to any one of claims 12 to 14, wherein, The grinding chamber (12) has a peripheral wall that is radially outward from the centerline of the spin vortex, and a grinding nozzle (18) that sprays the grinding gas and some of the grinding particles along the peripheral wall; And optionally, The airflow pulverizer includes a plurality of grinding nozzles (18), wherein the recirculation step includes: recirculating a portion of the grinding gas containing partially ground particles to at least some of the plurality of grinding nozzles (18), preferably each grinding nozzle (18).

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