A recirculating mill main machine

Abstract

The circulating mill main machine discloses a new classification problem solution in the circulating mill main machine by arranging the discharge port on the front cover and / or the rear cover, eliminates the cause of high pressure in the circulating mill main machine, reduces the pressure in the circulating mill main machine, further reduces the rotating resistance of the impeller, realizes the purpose of reducing the energy consumption of the mill, and meanwhile, the reduction of the pressure in the main machine also slows down the reduction amplitude of the fluidized material speed in the diffuser chamber, increases the impact force of the fluidized material on the wall-hanging material in the volute, and is beneficial to the improvement of the wall-hanging problem in the volute.

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] The centrifugal fan is an important component in this invention. To clarify the relevant terminology for the centrifugal fan in this case, a brief description of the centrifugal fan structure is provided below. (See attached image) Figure 1 It typically consists of two main parts: the casing and the impeller. The impeller generally consists of a front disc 9 (near the air inlet 7), blades 8, a rear disc 12 (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, which is mounted on the input shaft 13. The casing consists of a front cover 10 with a centrifugal fan inlet 7, a volute 15, and a rear cover 11 (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 section 2 is composed of curved section 5 and inner straight section 2, which is called vortex tongue 1. The outlet 3 of the centrifugal fan is surrounded by front cover 10, outer straight section 4 of the vortex shell, rear cover 11 and inner straight section 2 of the vortex shell. The area outside the projection line of the impeller outer edge inside the casing along the impeller axial direction on the front and rear covers is called the diffuser chamber. The minimum distance between the inner sides of the outer straight section 4 and the inner straight section 2 is called the outlet width of the centrifugal fan. The inner distance between the front cover 10 and the rear cover 11 is called the outlet height of the centrifugal fan.

[0003] This case also involves grading technology. After grading, the material is divided into two materials with different fineness. For ease of description, the two materials with different particle sizes obtained after grading are referred to as coarse material and fine material, respectively. When grading 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 grading device discharges coarse material, and the exhaust airflow carries away fine material.

[0004] A circulating fluidized bed mill, also known as a circulating mill or circulating fluidized bed mill, consists of a main mill unit and auxiliary devices. The main mill unit is the primary site for drying and grinding, while the auxiliary devices perform functions such as material-gas separation. The circulating mill utilizes a centrifugal fan and its high-speed airflow to fluidize the material, achieving drying and grinding through high-speed circulation within the circulating channel. In the main mill unit, large particles are primarily crushed by impeller impact, while ultrafine powders are crushed mainly through friction between the material and the surfaces of the blades and volutes 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 rapid drying. This study 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 identified and can be addressed specifically, aiming to develop a highly efficient drying and grinding solution.

[0005] 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. The circulating mill uses a combination of two technologies to address this problem: first, the impact of high-speed fluidized material on the wall adhesion prevents its stable formation; second, the return of dry powder from auxiliary devices (recycled material) mixes with the existing material and newly added 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 recycled material can definitely solve the wall adhesion problem. Economy primarily concerns energy consumption, and grading involves separating and discharging qualified material from the circulation channel.

[0006] The inventions disclosed in CN107694135B and WO2020057617 are related to circulating mills. The circulating mill in CN107694135B achieves classification by the combined action of centrifugal force and the drag force exerted on the particles by the classifying airflow. 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 circulating pipe and reach the mill inlet for circulating drying and grinding. Under the condition of a 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, in turn, depends on the pressure difference between the inlet and outlet of the circulating mill main unit. 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 this difference, the greater the pressure difference. When the difference is positive, the airflow flows from the main unit inlet to the outlet; when the difference is negative, the airflow flows from the main unit 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 vortex shell corresponding to the staged blades, making this area a near 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 main unit is a bent pipe, which is more prone to wall deposit formation. Four circulating mill main units need to be used in series to make the circulation pipe a straight pipe.

[0007] Invention patent WO2020057617 improved upon this, disclosing six types of circulating mill main units. The common feature of these six circulating mill main units 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 mill main units, two main units are connected in series to make the circulation pipe a straight pipe, improving the wall adhesion within the circulation 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 the mill's energy consumption. This is because the air velocity in the feed pipe with the circulating mill outlet 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 the centrifugal force's obstruction of the classification airflow also increases the internal pressure of the mill. Summary of the Invention

[0008] The purpose of this invention is to address the problem described in the background art of high internal pressure in circulating mill main units, which hinders impeller rotation and increases mill energy consumption, and to invent a circulating mill main unit with lower energy consumption.

[0009] The technical measures taken to achieve the purpose of this invention are as follows: A circulating mill host is composed of a centrifugal fan and a circulating pipe. The impeller inlet is provided with a circulating pipe interface in the axial projection area on the front cover and / or the rear cover. The outlet of the centrifugal fan, the inlet of the circulating pipe, the outlet of the circulating pipe, and the circulating pipe interface are connected in sequence to form a circulating channel. The discharge port of the circulating mill host is located on the front cover, outside the axial projection area of ​​the impeller on the front cover; or / and the discharge port of the circulating mill host is located on the rear cover, outside the axial projection area of ​​the impeller on the rear cover. The discharge ports are distributed circumferentially around the impeller inlet.

[0010] To expand the air intake space and facilitate the connection of the circulation pipe, the front cover is also provided with an air intake conical pipe. The large end of the air intake conical pipe is connected to the inlet of the centrifugal fan, and the small end of the air intake conical pipe is the air inlet of the circulating mill main unit. The circulation pipe interface on the front cover is located on the air intake conical pipe.

[0011] The circulating mill main unit also includes an air collecting hood, which collects the discharge ports on the front or rear cover. The air collecting hood has at least one outlet. The air collecting hood on the front cover consists of an inner side plate, an outer side plate, and a cover. The inner side plate is cylindrical, the outer side plate is shaped like the volute of a centrifugal fan, and the cover is shaped like the front cover of a centrifugal fan. The cover has a hole in the middle, which fits over one end of the inner side plate. One end of the outer side plate connects to the outer edge of the cover, and the other ends of the inner and outer side plates connect to the outside of the front cover and cover the exhaust port. The outlet of the air collecting hood on the front cover is formed by the portion extending from the front cover of the centrifugal fan, the outer straight section of the outer side plate, the outlet portion of the cover, and the inner straight section of the outer side plate. The rear cover's air collecting hood consists of an inner side plate, an outer side plate, and a cover. The inner side plate is cylindrical, the outer side plate resembles the vortex casing of a centrifugal fan, and the cover resembles the front cover of a centrifugal fan. The cover has a hole in the middle, which fits onto one end of the inner side plate. One end of the outer side plate connects to the outer edge of the cover, and the other ends of the inner and outer side plates connect to the outside of the rear cover and cover the exhaust port. The outlet of the air collecting hood on the rear cover is formed by the portion extending from the rear cover of the centrifugal fan, the outer straight section of the outer side plate, the outlet portion of the cover, and the inner straight section of the outer side plate. The outlet of the air collecting hood on the front cover and the outlet of the air collecting hood on the adjacent rear cover are converged into a single circulating mill main unit outlet via an exhaust tee.

[0012] The air collection hood is also equipped with a grading zone. The grading zone inside the air collection hood on the front cover is the outer area of ​​the second curved segment formed by the curved segment of the outer side plate of the air collection hood on the front cover extending forward from the vortex tongue. The grading zone inside the air collection hood on the rear cover is the outer area of ​​the second curved segment formed by the curved segment of the outer side plate of the air collection hood on the rear cover extending forward from the vortex tongue.

[0013] The circulating mill main unit also includes a second type of circulating pipe. A coarse material outlet is provided on the outer side plate of the air collecting hood on the front or rear cover. The inlet of the impeller has a second type of circulating pipe interface in the axial projection area on the front or rear cover. The coarse material outlet, the inlet of the second type of circulating pipe, the outlet of the second type of circulating pipe, and the interface of the second type of circulating pipe are connected in sequence to form a second type of circulating channel.

[0014] The circulating mill main unit disclosed in this invention provides a new solution to the classification problem within the circulating mill main unit by setting the discharge port on the front cover and / or rear cover. This eliminates the cause of high pressure within the circulating mill main unit as described in the background art, reduces the internal pressure of the circulating mill main unit, thereby reducing the impeller rotation resistance and achieving the goal of reducing mill energy consumption. At the same time, the reduction in pressure within the main unit also slows down the decrease in the velocity of the fluidized material in the diffuser chamber, increasing the impact force of the fluidized material on the material adhering to the wall inside the volute, which is beneficial to improving the problem of material adhering to the wall inside the volute. Attached Figure Description

[0015] Figure 1 This is a structural diagram of an existing centrifugal fan; Figure 2 It is the circulating mill host in Example 1; Figure 3 It is the circulating mill main unit with air inlet conical tube in Example 2; Figure 4 It is the circulating mill main unit with an air collecting hood in Example 3; Figure 5 It is the circulating mill main unit with air collection hoods on both the front and rear covers in Example 4. Specific Implementation

[0016] Example 1: A circulating mill main unit, see [link to example]. Figure 2 , Figure 2The upper left and upper right figures show the front and rear of the circulating mill main unit. This main unit consists of a centrifugal fan and a circulation pipe 50. The centrifugal fan comprises two main components: an impeller 57 and a casing. The impeller consists of a front disc and blades on the side near the centrifugal fan inlet 58, and a rear disc and bushing on the side near the input shaft. 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, which is mounted on the input shaft. The casing consists of a front cover 54 with the centrifugal fan inlet 58, a rear cover 52 on the side near the input shaft, and a volute 53. The outlet 51 of the centrifugal fan consists of a straight section on the outer side of the front cover 54 and the volute 53, and a straight section on the inner side of the rear cover 52 and the volute 53. The area outside the impeller's outer edge projected along the input axial direction on the front and rear covers, enclosed by line segments, is called the diffuser chamber. The impeller inlet on the front cover has a circulation pipe interface 59, a centrifugal fan outlet 51, a circulation pipe inlet 50, and a circulation pipe outlet 50. The circulation pipe interface 59 is connected in sequence to form a ring channel. The impeller inlet on the front cover 54 is provided with a discharge port 56 for the circulating mill main unit outside the axial projection area on the front cover. The impeller inlet on the rear cover 52 is also provided with a discharge port 55 for the circulating mill main unit outside the axial projection area on the rear cover. The discharge ports 56 and 55 are distributed circumferentially around the impeller inlet.

[0017] Figure 2 The centrifugal fan of the circulating mill main unit shown in the lower left figure has two outlets, and there are two circulation pipe interfaces 61 and 62 on the front cover. There are two circulation pipes. Figure 2 The centrifugal fan of the circulating mill main unit shown in the lower right figure has four outlets, and there are four circulation pipe interfaces on the front cover. There are four circulation pipes.

[0018] The circulating mill main unit described in this embodiment makes a new constructive contribution to solving the three core technical problems of drying and pulverizing fresh agricultural products. By setting the discharge port on the front and rear covers, on the one hand, the internal pressure of the centrifugal fan is reduced, thereby reducing the impeller rotation resistance and achieving the goal of reducing energy consumption; on the other hand, it also slows down the decrease in the flow velocity of fluidized material in the diffuser chamber, increases the impact force of fluidized material on the material adhering to the wall inside the vortex shell, and helps to solve the problem of adhering to the wall inside the vortex shell. Furthermore, setting the discharge port on the front cover and / or rear cover also creates a different solution to the classification problem than CN107694135B and WO2020057617. The pressure inside the diffuser is greater than the pressure outside the discharge port. The pressure difference between the two drives the airflow to flow out through the discharge port. Under the action of centrifugal force, the material with large particle size and high moisture content crosses the discharge port and gathers on the inner wall of the vortex shell, flowing along the impeller rotation direction. It then re-enters the centrifugal fan through the circulation channel to achieve circulation. Particles with a particle size and low moisture content are less affected by centrifugal force and flow out through the discharge port with the airflow to achieve classification.

[0019] Example 2: A circulating mill main unit with an air inlet conical tube, see [link / reference] Figure 3The circulating mill host with four second-type circulating pipes described in Example 2 is formed by adding an air inlet conical pipe 65. The large end of the air inlet conical pipe 65 is connected to the inlet 68 of the centrifugal fan, and the small end 66 of the air inlet conical pipe is the air inlet of the circulating mill host. There are four circulating pipe interfaces on the air inlet conical pipe 65, one of which, 67, is connected to the outlet of a circulating pipe. The circulation channel is formed by the outlet of the centrifugal fan, the inlet of the circulating pipe, the outlet of the circulating pipe, and the circulating pipe interface connected in sequence.

[0020] Example 3: A circulating mill main unit with an air collecting hood, see [link / reference] Figure 4 In this embodiment, there are two circulation pipes 76 and 83. The interfaces of the two circulation pipes are located in the axial projection area of ​​the impeller inlet on the rear cover. The front cover is provided with an air collecting hood, which is composed of an inner side plate 71, an outer side plate 75 and a cover 72. The inner side plate 71 is a cylinder, the outer side plate 75 is similar to the volute of a centrifugal fan, and the cover 72 is similar to the front cover of a centrifugal fan. The cover 72 has a hole 73 in the middle, and the hole 73 in the middle of the cover is fitted onto one end of the inner side plate 71. One end of the outer side plate 75 is connected to the outer edge 74 of the cover 72. The other ends of the inner side plate 71 and the outer side plate 75 are connected to the outside 77 of the front cover and cover the exhaust port. The outlet of the air collecting hood on the front cover is formed by the part 79 extending from the front cover of the centrifugal fan, the outer straight section 80 of the outer side plate, the cover 72 and the inner straight section 78 of the outer side plate. The air collecting hood on the front cover also has a grading zone, which is the outer area of ​​the second curved segment 70 formed by the curved segment of the outer side plate of the air collecting hood on the front cover extending forward from the vortex. This embodiment also has a second type of circulation pipe and an air inlet cone. The coarse material outlet 81 is located at the intersection of the curved segment and the straight segment on the outer side plate. The air inlet cone is provided with a second type of circulation pipe interface. The coarse material outlet, the inlet of the second type of circulation pipe 82, the outlet of the second type of circulation pipe 82, and the second type of circulation pipe interface are connected in sequence to form a second type of circulation channel.

[0021] Example 4: A circulating mill main unit with air collection hoods on both the front and rear covers, see attached... Figure 5 The circulating mill main machine housing with air inlet conical pipe described in Example 2 is formed by adding air collecting hoods to the front and rear covers. The air collecting hood on the front cover has four outlets 86, 88, 91 and 92. The rear cover is also provided with a discharge port. The air collecting hood on the rear cover also has four outlets 85, 87, 89 and the one behind outlet 91 is covered. The air collecting hood outlet 88 on the front cover and the air collecting hood outlet 89 on the adjacent rear cover are converged into a circulating mill main machine outlet by an exhaust tee 90.

Claims

1. A circulating mill main unit, comprising a centrifugal fan and a circulating pipe (50), wherein the centrifugal fan comprises two main components: a casing and an impeller, the impeller comprising a front disc and blades on the side near the air inlet, a rear disc and a bushing on the side near the input shaft, the impeller inlet being a circular hole in the middle of the front disc, the rear disc being fixedly connected to the bushing, and the bushing being 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 comprising an outer straight section, a curved section, and an inner straight section, the intersection of the curved section and the inner straight section The outlet (51) of the centrifugal fan is formed by the outer straight section of the front cover, the outer straight section of the vortex shell, the rear cover, and the inner straight section of the vortex shell. The area outside the impeller outer edge on the front and rear covers along the impeller axial projection line inside the casing is called the diffuser. The impeller inlet has a circulation pipe interface (59) in the axial projection area on the front or rear cover. The outlet (51) of the centrifugal fan, the inlet of the circulation pipe (50), the outlet of the circulation pipe (50), and the circulation pipe interface (59) are connected in sequence to form a circulation channel. The discharge port (56) of the circulating mill host is located outside the axial projection area of ​​the impeller on the front cover; or / and the discharge port (55) of the circulating mill host is located outside the axial projection area of ​​the impeller on the rear cover.

2. The circulating mill host according to claim 1, characterized in that, The front cover also includes an air inlet conical pipe (65), and the circulation pipe interface (67) on the front cover is located on the air inlet conical pipe (65). The large end of the air inlet conical pipe (65) is connected to the inlet (68) of the centrifugal fan, and the small end (66) of the air inlet conical pipe is the air inlet of the circulating mill host.

3. The circulating mill host according to claim 1, characterized in that, The discharge ports are distributed circumferentially around the impeller inlet.

4. The circulating mill host according to claim 1, characterized in that, The housing also includes an air collecting hood on the front cover, which gathers the discharge ports on the front cover together, and the air collecting hood on the front cover has at least one outlet; or / and the housing also includes an air collecting hood on the rear cover, which gathers the discharge ports on the rear cover together, and the air collecting hood on the rear cover has at least one outlet.

5. A circulating mill main unit according to claim 4, characterized in that, The air collection hood outlet on the front cover and the air collection hood outlet on the adjacent rear cover are combined into a single circulating mill main unit outlet via an exhaust tee.

6. A circulating mill main unit according to claim 4, characterized in that, The air collecting hood on the front cover consists of an inner side plate (71), an outer side plate (75), and a cover (72). The inner side plate (71) is cylindrical, the outer side plate (75) is shaped like a centrifugal fan volute, and the cover (72) is shaped like a centrifugal fan front cover. The cover (72) has a hole (73) in the middle. The hole (73) in the middle of the cover fits onto one end of the inner side plate (71). One end of the outer side plate (75) is connected to the outer edge (74) of the cover (72). The other ends of the inner side plate (71) and the outer side plate (75) are connected to the outside of the front cover (77) and cover the exhaust port. The outlet of the air collecting hood on the front cover is the part (74) extending from the centrifugal fan front cover. 9) The outer straight section (80) of the outer side plate, the cover (72) and the inner straight section (78) of the outer side plate are enclosed; the air collection hood on the rear cover is composed of an inner side plate, an outer side plate and a cover. The inner side plate is a cylinder, the outer side plate is shaped like a centrifugal fan vortex, the cover is shaped like a centrifugal fan front cover, the cover has a hole in the middle, the hole in the middle of the cover is fitted onto one end of the inner side plate, one end of the outer side plate is connected to the outer edge of the cover, the other end of the inner side plate and the outer side plate are connected to the outside of the rear cover and cover the exhaust port. The outlet of the air collection hood on the rear cover is enclosed by the part extending from the rear cover of the centrifugal fan, the outer straight section of the outer side plate, the cover and the inner straight section of the outer side plate.

7. A circulating mill main unit according to claim 6, characterized in that, The circulating mill main unit also includes a second type of circulating pipe (82). A coarse material outlet (81) is provided on the outer side plate of the air collecting hood on the front cover. The inlet of the impeller has a second type of circulating pipe interface in the axial projection area on the front cover or the rear cover. The coarse material outlet (81), the inlet of the second type of circulating pipe (82), the outlet of the second type of circulating pipe (82), and the second type of circulating pipe interface are connected in sequence to form a second type of circulating channel.

8. A circulating mill main unit according to claim 6, characterized in that, The circulating mill main unit also includes a second type of circulating pipe. A coarse material outlet is provided on the outer side plate of the air collecting hood on the rear cover. The inlet of the impeller has a second type of circulating pipe interface in the axial projection area on the front cover or the rear cover. The coarse material outlet, the inlet of the second type of circulating pipe, the outlet of the second type of circulating pipe, and the interface of the second type of circulating pipe are connected in sequence to form a second type of circulating channel.

9. A circulating mill main unit according to claim 4, characterized in that, The front cover also has a grading zone inside the air collecting hood. The grading zone is the outer area of ​​the second curved segment (70) formed by the curved segment of the outer side plate of the air collecting hood extending forward from the vortex.

10. A circulating mill main unit according to claim 4, characterized in that, The rear cover also has a grading zone inside the air collecting hood. The grading zone is the outer area of ​​the second curved segment formed by the curved segment of the outer side plate of the air collecting hood on the rear cover extending forward from the vortex tongue.

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