An air flow circulation mill main machine

Abstract

The airflow circulating mill main machine discloses a circulating mill main machine, a gas hole is arranged on a centrifugal fan of the circulating mill main machine, high-pressure airflow sprayed from the gas hole pushes or assists in pushing the rotation of a mill impeller, the impact and friction crushing mechanism of the circulating mill is retained, the crushing mechanism of mutual impact of material particles is increased, the process of spraying compressed air from the nozzle is approximately adiabatic expansion, a large amount of heat is consumed, the operation temperature is reduced, the advantages of the circulating mill and airflow crushing are retained, the shortcomings of the two are overcome, and the adaptability is wider.

Description

Technical Field

[0001] This invention relates to an airflow circulating mill main unit, 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. Before this invention, circulating mills used a combination of two techniques to address the wall adhesion problem: first, the impact of high-speed fluidized material on the wall adhesion material prevents its stable formation; second, the return of dry powder (recycled material) from auxiliary devices is mixed with the existing material and newly added material to reduce the 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 mainly 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.

[0008] Air jet milling is an ultra-fine grinding technology that uses compressed air to impact materials, causing them to collide and pulverize. Its most significant advantage is that the compressed air is ejected from the nozzle through a near-adiabatic expansion process, which consumes a large amount of heat and keeps the operating temperature low. The disadvantages of air jet milling are that it is difficult to process fibrous materials such as Ganoderma lucidum and plastics, and it is also difficult to expand the single-machine capacity. Its energy consumption is relatively high. Its advantages and disadvantages are in stark contrast to those of the circulating mill. Summary of the Invention

[0009] The purpose of this invention is to address the problems described in the background art by inventing an airflow circulating mill host, which overcomes the shortcomings of existing airflow pulverizers and circulating mills, and promotes the advantages of both.

[0010] The technical measures taken to achieve the purpose of this invention are as follows: an airflow circulating mill host is formed by setting air holes on the centrifugal fan of the circulating mill host, and the air holes are set so that the high-speed airflow ejected from the air holes can drive or assist in driving the impeller of the centrifugal fan to rotate.

[0011] The circulating mill main unit consists of a centrifugal fan and a circulating pipe. The centrifugal fan has at least one outlet. The centrifugal fan volute is provided with a coarse material outlet. The impeller inlet is provided with a circulating pipe interface in the axial projection area on the front cover and / or rear cover. The coarse material outlet, the circulating pipe inlet, the circulating pipe outlet, and the circulating pipe interface are connected in sequence to form a circulating channel.

[0012] The principle of the above-mentioned circulating mill host technical solution is that the fluidized material in the diffuser chamber, due to high-speed rotation, and the material with a sufficiently large particle size and / or sufficiently high moisture content, converges to the inner wall of the vortex shell under the action of centrifugal force. This process is a kind of classification. The circulation channel sends the classified coarse material back to the mill to realize the circulation operation.

[0013] To expand the air intake space and facilitate the connection of the 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 circulating mill main unit. The circulation pipe interface or a second type of circulation pipe interface on the front cover is located on the air intake conical pipe.

[0014] To achieve better grading results, a grading zone is also set up in the diffuser chamber. The grading zone is the outer area of ​​the second curved segment formed by the curved segment of the centrifugal fan casing extending forward from the vortex tongue. It will be more effective to set the coarse material outlet at the intersection of the curved segment of the vortex casing and the outer straight segment.

[0015] When the 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 first type of circulation pipe interface to enter the impeller. Furthermore, the inlet end of the blades needs to extend towards the impeller center and be fixedly connected to the shaft sleeve so that all impeller components can function as a single unit. The blade portion formed by the inlet end of the blades extending towards the impeller center and being fixedly connected to the shaft sleeve is referred to as the kinetic energy recovery blade in this project. Sometimes, it is more convenient to locate the coarse material outlet on the edge of the front or rear cover.

[0016] The air vents on the centrifugal fan can be located on the front cover and / or the rear cover and / or the air inlet duct. The air vents are configured such that the high-speed airflow ejected from the air vents can impact the inlet end of the blades or the kinetic energy recovery blades to drive or assist in driving the impeller to rotate. Alternatively, the high-speed airflow ejected from the air vents can impact the outlet end of the blades to drive or assist in driving the impeller to rotate.

[0017] The airflow circulating mill main unit disclosed in this invention, by setting air holes on the centrifugal fan of the circulating mill main unit, uses the high-pressure airflow ejected from the air holes to drive or assist in driving the mill impeller to rotate. It retains the impact and friction crushing mechanism of the circulating mill, and also adds the crushing mechanism of material particles colliding with each other that is unique to airflow crushing. At the same time, the process of compressed air being ejected from the nozzle is approximately adiabatic expansion, which consumes a large amount of heat and reduces the operating temperature. It retains the advantages of the circulating mill and airflow crushing, and also overcomes the disadvantages of both, making it more adaptable. Attached Figure Description

[0018] Figure 1 This is a structural diagram of an existing centrifugal fan; Figure 2 It is the rear of the airflow circulating mill main unit in Example 1; Figure 3 The airflow circulation mill main unit in Example 1 has a hidden centrifugal fan front cover; Figure 4 It is the circulating mill main unit with an air inlet conical pipe in Example 2; Figure 5 Example 3 is a circulating mill host with two outlets. Specific Implementation

[0019] Example 1: An airflow circulating mill main unit, see [link to example]. Figure 2 and Figure 3 , Figure 2 This shows the back of the circulating mill main unit. Figure 3 The display shows the front of the circulating mill main unit, with the centrifugal fan front cover concealed. The circulating mill main unit consists of a centrifugal fan and a circulation pipe 21. The centrifugal fan comprises two main components: a casing and an impeller. The impeller consists of 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 air inlet of the impeller is a circular hole in the center of the front disc. The rear disc is fixed to the bushing, which 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. The volute is composed of an outer straight section 22, a curved section 24, and an inner straight section 23. The intersection of the curved section 24 and the inner straight section 23 is called the volute tongue 27. The centrifugal fan has one outlet... The outlet of the centrifugal fan is formed by the outer straight section 22 of the front cover and the inner straight section 23 of the rear cover and the volute. The area outside the impeller axial projection line on the front and rear covers inside the casing is called the diffuser. The volute is provided with a coarse material outlet 20. The impeller inlet is located in the axial projection area on the rear cover with a circulation pipe interface 25. The coarse material outlet 20, the inlet of the circulation pipe 21, the outlet of the circulation pipe 21, and the circulation pipe interface 25 are connected in sequence to form a circulation channel. The centrifugal fan is provided with air holes, which are designed so that the high-speed airflow ejected from the air holes can drive or assist in driving the impeller of the centrifugal fan to rotate.

[0020] The coarse material outlet can also be located on the side of the front or rear cover as needed; in this embodiment, since the circulation pipe interface 25 is located on the rear cover, in order to allow the material from the 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, and the blades extend towards the center of the impeller and are fixedly connected to the bushing to form kinetic energy recovery blades.

[0021] 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's volute, formed by the curved section 24 extending forward from the volute tongue 27; the coarse material outlet 20 is located at the intersection of the curved section 24 and the outer straight section 22 of the volute.

[0022] In this embodiment, the grading zone enhances the grading effect within the centrifugal fan diffuser chamber. Furthermore, since the pressure at the centrifugal fan outlet is lowest within the diffuser chamber, and there is no second curve section in the centrifugal fan, a large portion of the airflow directly exits from the impeller outlet in front of the vortex 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 curve section of the vortex significantly reduces the proportion of short-circuit airflow, thus improving the wall-adhesion problem.

[0023] Example 2: Airflow circulating mill main unit with air inlet conical tube, see [link / reference] Figure 4 In this embodiment, the front cover of the casing also includes an air inlet duct 30. The large end of the air inlet duct 30 is connected to the inlet of the centrifugal fan, and the small end of the air inlet duct is the air inlet of the airflow circulation mill host. The air inlet duct 30 is provided with a circulation pipe interface 29. The coarse material outlet, the circulation pipe inlet, the circulation pipe outlet, and the circulation pipe interface 29 are connected in sequence to form a circulation channel.

[0024] Example 3: A circulating mill main unit with two outlets, see [link / reference] Figure 5 In this embodiment, the airflow circulating mill main unit adopts a horizontal arrangement. Figure 5The exhibit showcases the airflow circulation mill main unit with the centrifugal fan's front cover concealed. The centrifugal fan has two outlets and two circulation pipes. The centrifugal fan's volute 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 enclosed by the front cover, the outer straight section 32 of the first volute section, the rear cover, and the inner straight section 31 of the second volute section. The other outlet of the centrifugal fan is enclosed by the front cover and the second section... The outer straight section 39 of the volute shell, the rear cover, and the inner straight section 38 of the first volute shell are enclosed. The front cover also includes an air inlet cone 36. The air inlet cone 36 is provided with two circulation pipe interfaces. One circulation channel is formed by connecting the coarse material outlet 33 on the first volute shell, the inlet of the circulation pipe 34, the outlet of the circulation pipe 34, and one circulation pipe interface on the air inlet cone 36 in sequence. The other circulation channel is formed by connecting the coarse material outlet 41 on the second volute shell, the inlet of the circulation pipe 40, the outlet of the circulation pipe 40, and another circulation pipe interface on the air inlet cone 36 in sequence.

Claims

1. A circulating mill main unit, comprising a centrifugal fan and a circulation pipe, wherein the centrifugal fan includes two main components: a casing and an impeller; the impeller consists of 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 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 consists of 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 tongue; the centrifugal fan outlet is formed by the front cover, the outer straight section of the volute, the rear cover, and the inner straight section of the volute; the area outside the impeller outer edge projected along the impeller axial direction on the front and rear covers inside the casing is called the diffuser chamber; characterized in that... The centrifugal fan is equipped with air holes, which are designed so that the high-speed airflow ejected from the air holes can drive or assist in driving the impeller of the centrifugal fan to rotate.

2. The airflow circulating mill main unit according to claim 1, characterized in that, The volute casing is provided with a coarse material outlet, and the impeller inlet has a circulation pipe interface in the axial projection area on the front or rear cover. The coarse material outlet, the circulation pipe inlet, the circulation pipe outlet, and the circulation pipe interface are connected in sequence to form a circulation channel.

3. The airflow circulating mill main unit according to claim 1, characterized in that, The coarse material outlet is located on the side of the front or rear cover.

4. The airflow circulating mill main unit according to claim 1, characterized in that, The impeller rear disc has a round hole in the middle.

5. The airflow circulating mill main unit according to claim 1, characterized in that, The inlet end of the blade extends towards the center of the impeller and is fixedly connected to the bushing to form a kinetic energy recovery blade.

6. The airflow circulating mill main unit according to claim 1, characterized in that, The front cover also includes an air inlet conical pipe. The first type of circulation pipe interface on the front cover is located on the air inlet conical pipe. The large end of the air inlet conical pipe 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 first type of circulation mill main unit.

7. The airflow circulating mill main unit according to claim 1, characterized in that, The diffuser chamber is further provided with a grading zone, which is the outer area of ​​the second curved segment formed by the curved segment of the centrifugal fan volute extending forward from the volute tongue; or the diffuser chamber is further provided with a grading zone, which is the outer area of ​​the second curved segment formed by the curved segment of the centrifugal fan volute extending forward from the volute tongue, and the coarse material outlet is located at the intersection of the curved segment of the volute and the outer straight segment.

8. The airflow circulating mill main unit according to claim 1, characterized in that, The air vents are located on the front or rear cover or on the air inlet duct as described in claim 6. The air vents are configured such that the high-speed airflow ejected from the air vents can impact the inlet end of the blades and drive or assist in driving the impeller to rotate.

9. The airflow circulating mill main unit according to claim 1, characterized in that, The air vents are located on the front or rear cover or on the air inlet duct as described in claim 6. The air vents are configured such that the high-speed airflow ejected from the air vents can impact the kinetic energy recovery blades as described in claim 5, thereby driving or assisting in driving the impeller to rotate.

10. The airflow circulating mill main unit according to claim 1, characterized in that, The air vents are located on the front or rear cover, and the air vents are configured such that the high-speed airflow ejected from the air vents can impact the outlet end of the blades, thereby driving or assisting in driving the impeller to rotate.

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