Circulating mill main machine

Abstract

According to the circulating mill disclosed by the invention, the internal circulating pipe interface is arranged in the area between the axial projection line of the impeller air inlet on the front cover or the rear cover and the axial projection line of the centrifugal fan inlet along the impeller, so that new problems brought by a grading problem solution constructed for solving the high pressure problem in the circulating mill in the background art are eliminated; and the pressure in the circulating mill is reduced, so that the rotating resistance of the impeller is reduced, and the energy consumption of the mill is reduced.

Description

Technical Field

[0001] This invention relates to a circulating mill host, belonging to the fields of circulating fluidized bed technology, drying and grinding technology, and energy-saving and environmental protection technology. Background Technology

[0002] Centrifugal fans are gas pressurization and conveying devices. To clarify the relevant terminology for centrifugal fans in this case, a brief description of the centrifugal fan structure is provided below. (See attached image) Figure 1 and Figure 2 It typically consists of two main parts: the casing and the impeller. The impeller generally consists of a front disc 9 and blades 8 on the side near the centrifugal fan inlet 7, a rear disc 12 on the side near the input shaft 13, and a bushing 14. The air inlet 6 of the impeller is a circular hole in the middle of the front disc 9. The rear disc 12 is fixedly connected to the bushing 14, and the bushing 14 is mounted on the input shaft 13. The casing consists of a front cover 10 with the centrifugal fan inlet 7, a volute 15, and a rear cover 11 on the side near the input shaft. The volute 15 generally consists of an outer straight section 4, a curved section 5, and an inner straight section. The centrifugal fan is composed of segment 2. The intersection of curved segment 5 and the inner straight segment 2 of the volute is called the volute tongue 1. The outlet 3 of the centrifugal fan is formed by the front cover 10, the outer straight segment 4 of the volute, the rear cover 11, and the inner straight segment 2 of the volute. The area outside the projection line of the impeller outer edge on the front and rear covers along the impeller axial direction inside the casing is called the diffuser. The minimum distance between the inner surfaces of the outer straight segment 4 and the inner straight segment 2 of the volute is called the outlet width of the centrifugal fan. The distance between the inner surfaces of the front cover 10 and the rear cover 11 is called the outlet height of the centrifugal fan.

[0003] In powder engineering, classification technology is widely used. After classification, materials are obtained into two types of materials with different fineness. For ease of description, the circulating mill project refers to the two types of materials with different particle sizes obtained after classification as coarse material and fine material, respectively. When classifying with a sieve, the material on the sieve is coarse material and the material under the sieve is fine material. The ash discharge port of the cyclone classifier discharges coarse material, while the exhaust airflow carries away fine material.

[0004] A circulating fluidized bed mill, also known as a centrifugal mill or circulating fluidized bed mill, is a technology that uses a centrifugal fan and its high-speed airflow to fluidize materials and achieve drying and / or grinding through high-speed circulation within a circulating channel. In a circulating mill, large particles are mainly crushed by impeller impact, while ultrafine powders are crushed primarily through friction between the material and the surfaces of the blades and volute during high-speed flow. This crushing action continuously disperses the material into a fluidized state, resulting in a high-speed circulating flow. The mass-energy exchange area increases geometrically, the gas-solid boundary layer thins, and the exchange rate of water (mass) and heat (energy) between the material and the airflow is maximized, leading to a very fast drying speed. This circulating mill project focuses on the drying and grinding of fresh agricultural products, exploring factors affecting drying and grinding efficiency. Due to the presence of wall adhesion issues, these influencing factors are more easily exposed and can be addressed specifically, with the aim of developing a highly efficient drying and grinding solution. The three core technical challenges in drying and grinding fresh agricultural products are reliability, economy, and grading. Fresh agricultural products, after being crushed by the impeller, become a slurry that adheres to the machine and stops circulating, a process known as "wall adhesion." Once this wall adhesion stabilizes, the circulation channel will eventually become blocked, causing equipment failure and preventing the drying and grinding process from being achieved. Wall adhesion is essentially a reliability issue. Before 2024, circulating mills used a combination of two technologies to address reliability: first, the impact of high-speed fluidized material on the wall adhesion prevented its stable formation; second, the return of dry powder (return material) from auxiliary devices was mixed with the existing material to reduce moisture content and improve wall adhesion performance. The former is fundamental, while the latter is a strengthening measure. With the latter's support, even if liquid is added, increasing the amount of return material can definitely solve the wall adhesion problem. Economy mainly concerns energy consumption, and grading involves separating and discharging qualified material from the circulation channel.

[0005] The inventions disclosed in CN107694135B and WO2020057617 are circulating mills. CN107694135B relies on the combined effect of centrifugal force and the drag force exerted on the particles by the classifying airflow to achieve classification. When the drag force is greater than the centrifugal force, the particles are carried out by the classifying airflow through the space between the classifying blades. When the drag force is less than the centrifugal force, the particles enter the circulation pipe and reach the mill inlet for circulating drying and grinding. Under the condition of fixed rotational speed and impeller diameter, the centrifugal force depends on the particle diameter and moisture content, while the drag force depends on the velocity of the classifying airflow. The velocity of the classifying airflow depends on the pressure difference between the inlet and outlet of the circulating mill. The magnitude and direction of this pressure difference depend on the difference between the outlet diameter on the middle cover and the inlet diameter on the front cover. The larger the difference, the greater the pressure difference. When the difference is positive, the airflow flows from the main inlet to the outlet; when the difference is negative, the airflow flows from the main outlet to the inlet. The problems with CN107694135B are as follows: First, the staged airflow weakens the impact of fluidized material on the inner surface of the volute corresponding to the staged blades, making this area almost a dead zone, where wall deposits can easily and stably form. This defect is due to the solution to the staged problem. Second, the circulation pipe of a single circulating mill is a bent pipe, which is more prone to wall deposit formation. Two circulating mills or centrifugal fans need to be used in series to make the circulation pipe a straight pipe, which increases the equipment cost.

[0006] Invention patent WO2020057617 improved upon this, disclosing six types of circulating mills. The common feature of these six mills is that they rely on the pressure difference between the inlet and outlet of the centrifugal fan and the cyclone classification effect within the feed pipe to achieve classification. In the first, second, third, and sixth types of circulating mills, the circulating pipe becomes a straight pipe, improving the wall adhesion within the circulating pipe and eliminating the near-dead zone area found in CN107694135B. However, the classification problem solution in WO2020057617 increases the internal pressure, hindering impeller rotation and increasing mill energy consumption. This is because the air velocity in the feed pipe, which serves as the outlet of the circulating mill, generally exceeds 50 m / s, making the resistance to cyclone classification very large. The auxiliary mill further pressurizes the mill on top of the high pressure at the main mill outlet. A similar problem exists in CN107694135B, where centrifugal force hinders the classification airflow, also increasing the internal pressure of the mill. In addition, the kinetic energy recovery technology proposed in WO2020057617 has very little practical significance because the kinetic energy recovery device itself also consumes energy.

[0007] The internal circulation pipe proposed in CN107694135B is of great significance to the circulating mill project because, within an acceptable economic range, the flow velocity of the fluidized material in the constructed internal circulation channel can be increased to a level sufficient to solve the wall adhesion problem. However, the setting of its internal circulation interface brings two new problems. First, the airflow from the internal circulation pipe interface is equivalent to setting a gate in the feed pipe, which hinders the airflow from entering the main unit from the feed pipe. Second, the fluidized material from the internal circulation pipe interface contains particles, droplets, foam, etc. with high moisture content. After the high moisture content particles collide with the inner wall of the feed pipe, the newly generated droplets, foam, etc. will adhere to the area near the impact point between the fluidized material from the internal circulation pipe interface and the feed pipe, especially in the low velocity area, and harden rapidly. They will continuously capture powder and gradually grow, eventually clogging the feed pipe. Summary of the Invention

[0008] The purpose of this invention is to address the problems described in the background art by inventing a circulating mill main unit with lower energy consumption and solving the new problems caused by the internal circulation pipe interface setting method in CN107694135B.

[0009] The technical measures taken to achieve the purpose of this invention are as follows: a circulating mill main unit includes a centrifugal fan and an internal circulation pipe. The centrifugal fan casing is provided with at least one coarse material outlet, and the front cover or rear cover is provided with an internal circulation pipe interface. The coarse material outlet, the inlet of the internal circulation pipe, the outlet of the internal circulation pipe, and the internal circulation pipe interface are connected in sequence to form an internal circulation channel. The inlet area of ​​the centrifugal fan is smaller than the air inlet area of ​​the impeller. The internal circulation pipe interface is located in the area between the impeller air inlet projection line along the impeller axis and the centrifugal fan inlet projection line along the impeller axis on the front cover or rear cover.

[0010] Depending on the specific needs, the projection line of the impeller inlet along the impeller axis and the projection line of the centrifugal fan inlet along the impeller axis can be either tangent or concentric.

[0011] To facilitate the disassembly and assembly of the impeller, the front cover includes a front cover assembly and an impeller chamber cover plate. The front cover assembly has an impeller mounting hole that is concentric with the impeller and has a diameter larger than the outer diameter of the impeller. The centrifugal fan inlet and the internal circulation pipe interface are located on the impeller chamber cover plate. The inner side of the impeller chamber cover plate is connected to the outer side of the front cover assembly and is concentric with the impeller mounting hole.

[0012] To facilitate the disassembly and assembly of the internal circulation pipe and the air inlet pipe, the impeller chamber cover plate consists of a cover plate and an air inlet plate. The cover plate has an air inlet plate mounting hole concentric with the impeller. The centrifugal fan inlet and the internal circulation pipe interface are located on the air inlet plate. The inner side of the air inlet plate is connected to the outer side of the cover plate and is concentric with the air inlet plate mounting hole.

[0013] The principle of this invention is that, due to high-speed rotation, fluidized materials in the diffuser chamber, with sufficiently large particle sizes and high moisture content, rapidly converge to the inner wall of the volute under the influence of significant centrifugal force. Smaller particles with lower moisture content, experiencing less centrifugal force, converge to the inner wall of the volute more slowly, thus achieving a classification effect. The circulation channel returns the classified coarse material back to the mill for recirculation, while some fine material is carried out of the main unit by the exhaust airflow. Specifically, the internal circulation pipe interface is located on the front or rear cover in the area between the centrifugal fan inlet and the impeller air inlet along the impeller axial projection line, solving two new problems arising from the internal circulation pipe interface setting method described in CN107694135B in the background art.

[0014] When the internal circulation pipe interface is located on the rear cover, a circular hole is required in the center of the impeller rear disc to allow fluidized material from the internal circulation pipe interface to enter the impeller. Furthermore, the blades need to extend towards the impeller center and be fixed to the bushing so that all impeller components function as a single unit. The blades extending towards the impeller center and being fixed to the bushing constitute the kinetic energy recovery blades. The internal circulation pipe interface is designed to effectively impact the kinetic energy recovery blades, thus assisting in driving the impeller's rotation. Sometimes, it is more convenient to locate the coarse material outlet on the edge of the front or rear cover. Locating the coarse material outlet near the intersection of the curved section and the outer straight section will yield better results.

[0015] To achieve efficient recovery and utilization of energy from the high-speed fluidized material and airflow in the internal circulation channel, the internal circulation pipe interface can be configured such that the fluidized material from the internal circulation channel can effectively impact the inlet end of the blades, thereby assisting in driving the impeller rotation. Alternatively, the rear part of the blade inlet end can extend towards the center of the impeller to form a kinetic energy recovery blade, and the internal circulation pipe interface can be configured such that the fluidized material from the internal circulation channel can effectively impact the kinetic energy recovery blades, thereby assisting in driving the impeller rotation.

[0016] To expand the air intake area and facilitate the connection of the internal circulation pipe, the front cover also includes an air intake conical pipe. The larger end of the air intake conical pipe is connected to the inlet of the centrifugal fan, and the smaller end of the air intake conical pipe is the air inlet of the circulation mill. The interface of the internal circulation pipe is located on the air intake conical pipe.

[0017] The present invention also provides a Yunjie powder, which is a powder processed by a circulating mill using the aforementioned circulating mill host as the host.

[0018] The circulating mill disclosed in this invention eliminates new problems caused by the graded solution to solve the high pressure problem in the circulating mill described in the background art by setting the internal circulation pipe interface in the area between the impeller air inlet projection line along the impeller axis and the centrifugal fan inlet projection line along the impeller axis on the front or rear cover. This reduces the pressure in the circulating mill, thereby reducing the impeller rotation resistance and achieving the goal of reducing mill energy consumption. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of an existing centrifugal fan. Figure 2 This is a cross-sectional view of an existing centrifugal fan; Figure 3 This is a schematic diagram of the rear structure of the circulating mill in Example 1; Figure 4 This is a schematic diagram of the circulating mill structure in Example 1, which conceals the front cover of the centrifugal fan; Figure 5 This is a schematic diagram of the circulating mill with an air inlet conical tube in Example 2; Figure 6 This is a schematic diagram of the circulating mill with two outlets in Example 3; Figure 7 This is a schematic diagram of embodiment 4 in which the internal circulation pipe interface and air inlet are directly located on the front cover; Figure 8 This is a schematic diagram of the internal circulation pipe interface and air inlet located on the impeller chamber cover plate in Embodiment 4; Figure 9 This is a schematic diagram of the internal circulation pipe interface and air inlet located on the air inlet plate in Embodiment 4; Figure 10 This is a complete schematic diagram of the circulating mill main unit with the internal circulation pipe interface and air inlet located on the air inlet plate in Embodiment 4. Detailed Implementation

[0020] Example 1: A circulating mill, see [link to example]. Figure 3 and Figure 4 , Figure 3 The image shown is of the back of the circulating mill. Figure 4 The front of the circulating mill is shown with the centrifugal fan front cover hidden. The circulating mill consists of a centrifugal fan and an internal circulation pipe 21. The centrifugal fan includes two main components: the casing and the impeller. The impeller consists of a front disc and blades on the side near the centrifugal fan inlet, a rear disc and a bushing on the side near the input shaft. The air inlet of the impeller is a round hole in the middle of the front disc. The rear disc is fixed to the bushing, and the bushing is mounted on the input shaft. The casing consists of a front cover with a centrifugal fan inlet, a volute, and a rear cover on the side near the input shaft.

[0021] The volute is composed of an outer straight segment 22, a curved segment 24, and an inner straight segment 23. The intersection of the curved segment 24 and the inner straight segment 23 is called the volute tongue 27. The centrifugal fan has an outlet, which is formed by the front cover, the outer straight segment 22 of the volute, the rear cover, and the inner straight segment 23 of the volute. The area outside the impeller outer edge on the front and rear covers along the impeller axial projection line is called the diffuser. The minimum distance between the inner surfaces of the outer straight segment 22 and the inner straight segment 23 of the volute is called the outlet width of the centrifugal fan, and the distance between the inner surfaces of the front and rear covers is called the outlet height of the centrifugal fan. The volute has a coarse material outlet 20, and the impeller inlet has an internal circulation pipe interface 25 in the axial projection area on the rear cover. The coarse material outlet 20, the inlet of the internal circulation pipe 21, the outlet of the internal circulation pipe 21, and the internal circulation pipe interface 25 are connected in sequence to form an internal circulation channel.

[0022] The coarse material outlet 20 can also be located on the side of the front cover or the rear cover as needed. In this embodiment, since the inner circulation pipe interface 25 is located on the rear cover, in order to allow the material from the inner circulation pipe to enter the impeller, the rear disc of the impeller is provided with the same round hole as the impeller inlet on the front disc. The blades extend towards the center of the impeller and are fixedly connected to the bushing to form kinetic energy recovery blades.

[0023] The centrifugal fan's diffuser chamber is also equipped with a grading zone, which is the outer area of ​​the second curved section 28 of the centrifugal fan casing formed by the curved section 24 of the centrifugal fan casing extending forward from the volute tongue 27; the coarse material outlet 20 is located at the intersection of the curved section 24 of the volute casing and the straight section 22 on the outer side of the volute casing.

[0024] In this embodiment, the grading zone enhances the grading effect within the centrifugal fan's diffuser chamber. Furthermore, because the pressure at the centrifugal fan outlet is lowest within the diffuser chamber, and there is no second curved section in the centrifugal fan, a large portion of the airflow directly exits from the impeller outlet in front of the volute tongue and reaches the centrifugal fan outlet, becoming short-circuit airflow. While short-circuit airflow does not negatively impact the centrifugal fan used for ventilation, as it is a major component of the circulating mill, the presence of short-circuit airflow reduces the amount and velocity of non-short-circuit airflow. Material in the non-short-circuit airflow tends to settle and adhere to the wall. The second curved section of the volute significantly reduces the proportion of short-circuit airflow, thus improving the wall-adhesion problem.

[0025] Example 2: Circulating mill with air intake conical tube, see [link / reference] Figure 5 In this embodiment, the front cover of the casing also includes an air inlet conical pipe 30. The large end of the air inlet conical pipe 30 is connected to the inlet of the centrifugal fan, and the small end of the air inlet conical pipe is the air inlet of the circulating mill. An internal circulation pipe interface 29 is provided on the air inlet conical pipe 30. The coarse material outlet, the inlet of the internal circulation pipe, the outlet of the internal circulation pipe, and the internal circulation pipe interface 29 are connected in sequence to form an internal circulation channel. In this embodiment, the inlet of the centrifugal fan is concentric with the impeller.

[0026] Example 3: A circulating mill with two outlets, see [link / reference] Figure 6 In this embodiment, the circulating mill is arranged horizontally. Figure 6 The display shows a circulating mill with the front cover of the centrifugal fan concealed. The centrifugal fan has two outlets and two internal circulation pipes. The centrifugal fan casing consists of two sections: the first section comprises an outer straight section 32, a curved section 37, an inner straight section 38, and a second curved section 43; the second section comprises an outer straight section 39, a curved section 44, an inner straight section 31, and a second curved section 35. One outlet of the centrifugal fan is formed by the front cover, the outer straight section 32 of the first centrifugal fan casing, the rear cover, and the inner straight section 31 of the second centrifugal fan casing. The other outlet of the centrifugal fan is formed by the front cover and the outer straight section 39. The rear cover and the inner straight section 38 form a front cover, which also includes an air inlet duct 36. The air inlet duct 36 is provided with two internal circulation pipe interfaces. One internal circulation channel is formed by connecting the coarse material outlet 33 on the first section of the volute, the inlet of the internal circulation pipe 34, the outlet of the internal circulation pipe 34, and one internal circulation pipe interface on the air inlet duct 36 in sequence. The other internal circulation channel is formed by connecting the coarse material outlet 41 on the second section of the volute, the inlet of the internal circulation pipe 40, the outlet of the internal circulation pipe 40, and another internal circulation pipe interface on the air inlet duct 36 in sequence. In this embodiment, the impeller air inlet and the centrifugal fan inlet are concentrically arranged.

[0027] Example 4: Method for setting up the internal circulation pipe interface (see attached document). Figure 7 , Figure 8 , Figure 9 and Figure 10 The circulating mill shown has two coarse material outlets on its volute casing, and correspondingly two internal circulation channels. These two internal circulation channels enable more efficient classification. Figure 7 The internal circulation pipe interface 50 is located on the front cover 53 in the area between the impeller inlet's axial projection line 51 and the centrifugal fan inlet's axial projection line 52. Clearly, with this arrangement, the impeller and centrifugal fan inlet are not concentric. The internal circulation pipe interface area is maximized when the impeller inlet's axial projection line 51 is tangent to the centrifugal fan inlet's axial projection line. (Appendix) Figure 8 In this design, the front cover includes a front cover assembly 55 and an impeller chamber cover plate 56. The front cover assembly has an impeller mounting hole concentric with the impeller and with a diameter larger than the impeller's outer diameter. The centrifugal fan inlet 58 and the internal circulation pipe interface 57 are located on the impeller chamber cover plate 56. The inner side of the impeller chamber cover plate 56 is connected to the outer side of the front cover assembly 55 and is concentric with the impeller mounting hole. (See attached image) Figure 9In the impeller chamber cover, there is a cover plate 60 and an air inlet plate 63. The cover plate 60 has an air inlet plate mounting hole concentric with the impeller. The centrifugal fan inlet 62 and the internal circulation pipe interface 61 are located on the air inlet plate 63. The inner side of the air inlet plate 63 is connected to the outer side of the cover plate 60 and is concentric with the air inlet plate mounting hole. The projection line of the impeller air inlet along the impeller axis is tangent to the projection line of the centrifugal fan inlet along the impeller axis. (Attached) Figure 10 The image shows the complete circulating mill main unit, with the internal circulation pipe interface using an attached... Figure 8 As shown in the diagram, the circulating mill main unit has two internal circulation pipes, namely internal circulation pipe 70 and internal circulation pipe 71. Internal circulation pipes 70 and 71 merge at their ends and connect to an internal circulation interface. The internal circulation pipe interface is configured such that the fluidized material airflow from the internal circulation channel can effectively impact the inlet end of the blades, thus assisting in driving the impeller rotation. Sometimes, to efficiently recover the energy of the fluidized material and airflow in the internal circulation pipe, the rear part of the blade inlet end extends towards the impeller center to form a kinetic energy recovery blade. This further facilitates the effective impact of the fluidized material and airflow from the internal circulation channel on the kinetic energy recovery blade, thereby assisting in driving the impeller rotation.

[0028] Example 5: A type of clean powder, which is a powder processed by a circulating mill using the aforementioned circulating mill host as the host. In practical engineering applications, circulating mills generally consist of a circulating mill host and auxiliary devices. Typical auxiliary devices include dust collectors, etc. For specific components, please refer to the background art documents CN107694135B and WO2020057617.

Claims

1. A circulating mill main unit, comprising a centrifugal fan and an internal circulation pipe, wherein the centrifugal fan consists of two main components: a casing and an impeller. The impeller comprises a front disc and blades on the side near the centrifugal fan inlet, a rear disc on the side near the input shaft, and a bushing. The air inlet of the impeller is a circular hole in the center of the front disc. The rear disc is fixedly connected to the bushing, and the bushing is mounted on the input shaft. The casing comprises a front cover with a centrifugal fan inlet, a volute, and a rear cover on the side near the input shaft. The volute is composed of an outer straight section, a curved section, and an inner straight section. The intersection of the curved section and the inner straight section is called the volute. The centrifugal fan outlet is formed by a front cover, an outer straight section of the volute, a rear cover, and an inner straight section of the volute. The area outside the impeller's outer edge projected along the impeller's axial direction on the front and rear covers inside the casing is called the diffuser chamber. The volute has at least one coarse material outlet. The front or rear cover has an internal circulation pipe interface. The coarse material outlet, the internal circulation pipe inlet, the internal circulation pipe outlet, and the internal circulation pipe interface are sequentially connected to form at least one internal circulation channel. The centrifugal fan inlet area is smaller than the impeller inlet area. Its characteristic is that... The internal circulation pipe interface is located in the area between the impeller air inlet along the impeller axial projection line on the front or rear cover and the centrifugal fan inlet along the impeller axial projection line.

2. The circulating mill host according to claim 1, characterized in that, The projection line of the impeller air inlet on the front or rear cover along the impeller axial direction is tangent to the projection line of the centrifugal fan inlet along the impeller axial direction.

3. The circulating mill host according to claim 1, characterized in that, The centrifugal fan inlet is concentric with the impeller.

4. A circulating mill main unit according to claim 1, 2, 3, or 4, characterized in that, The front cover includes a front cover assembly and an impeller chamber cover plate. The front cover assembly has an impeller mounting hole that is concentric with the impeller and has a diameter larger than the outer diameter of the impeller. The centrifugal fan inlet and the internal circulation pipe interface are located on the impeller chamber cover plate. The inner side of the impeller chamber cover plate is connected to the outer side of the front cover assembly and is concentric with the impeller mounting hole.

5. A circulating mill main unit according to claim 5, characterized in that, The impeller chamber cover plate consists of a cover plate and an air inlet plate. The cover plate has an air inlet plate mounting hole concentric with the impeller. The centrifugal fan inlet and the internal circulation pipe interface are located on the air inlet plate. The inner side of the air inlet plate is connected to the outer side of the cover plate and is concentric with the air inlet plate mounting hole.

6. A circulating mill main unit according to claim 1, characterized in that, The internal circulation pipe interface is configured such that the fluidized material airflow from the internal circulation channel can effectively impact the inlet end of the blades and assist in driving the impeller to rotate.

7. A circulating mill main unit according to claim 1, characterized in that, The rear part of the blade inlet extends towards the center of the impeller to form a kinetic energy recovery blade. The internal circulation pipe interface is configured so that fluidized material and airflow from the internal circulation channel can effectively impact the kinetic energy recovery blade and assist in driving the impeller to rotate.

8. A circulating mill main unit according to claim 1, characterized in that, The front cover also includes an air inlet conical pipe. The circulation pipe interface on the front cover is located on the air inlet conical pipe. The larger end of the air inlet conical pipe is connected to the inlet of the centrifugal fan, and the smaller end of the air inlet conical pipe is the air inlet of the circulation mill.

9. A circulating mill main unit according to claim 1, characterized in that, The diffuser chamber is also equipped with a grading zone, which is the outer area of ​​the second curved segment of the centrifugal fan casing formed by the curved segment of the centrifugal fan casing extending forward from the volute tongue.

10. A type of clean powder, which is powder processed by a circulating mill using the circulating mill main unit as described in claim 1, 2, 3, 4, 5, 6, 7, 8, or 9 as the main unit.

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