Cyclone

Abstract

[Problem] A purpose of the invention is to improve dust collection efficiency while reducing pressure loss in a cyclone. [Solution] A cyclone 1, 11, 21 according to the invention includes: an outer cylinder 3 provided at an upper portion of a rotating cylinder 2; an inner cylinder 4 provided concentrically within the outer cylinder 3; a flow straightening member 5 in a space immediately below the inner cylinder 4, in which a plurality of planar flow straightening plates, each having a curved surface formed in at least a lower half thereof, are provided at equal angular intervals around an axis of the inner cylinder 4, and the curved surface of each planar flow straightening plate is provided in the same direction as a swirling flow flowing around an inner circumference of the inner cylinder 4; an inlet tube 6 provided tangentially to an outer circumference of the outer cylinder 3; a drop port 8 provided at a lower portion of the rotating cylinder 2; and a re-scattering prevention member 9, 19, 29 provided at a lower end portion of the flow straightening member 5. The re-scattering prevention member may have a cylindrical, inverted conical or inverted truncated conical shape.

Description

Cyclone

[0001] The present invention relates to a cyclone that separates dust by centrifugal force by creating a swirling flow of dust-containing gas.

[0002] A cyclone is a dust collection device that uses centrifugal force. It has a simple structure with no internal drive unit and can be used regardless of the temperature of the dust-containing gas, so it is used in various fields of the chemical industry. In recent years, there has been an increasing demand for low-pressure drop cyclones from the perspective of energy conservation.

[0003] For example, in cement calciners, cyclones are used in suspension preheaters used to preheat raw materials, and the cyclones account for most of the pressure loss in the preheaters of cement calciners. Reducing the pressure loss in the cyclones increases production volume and reduces the power consumption of the fans, leading to reduced cement production costs.

[0004] Patent Document 1 discloses a low pressure loss cyclone in which pressure loss is significantly reduced by a straightening member in which the outer and inner swirl cylinders are arranged concentrically, and a plurality of inverted triangular planar straightening plates, each with a curved surface in the lower half, are arranged at the lower end of the inner cylinder at equal angular intervals around the axis of a conical straightening member, with the curved surface of each planar straightening plate facing the swirling flow flowing around the outer periphery of the conical straightening member.

[0005] Japanese Patent No. 2609168 Japanese Patent No. 3336440

[0006] When evaluating cyclone performance, dust collection efficiency is an important factor along with pressure loss, and a decrease in dust collection efficiency is undesirable because it increases the load on downstream exhaust gas treatment equipment (such as bag filters). Furthermore, in cement firing equipment, a decrease in the cyclone's dust collection efficiency increases the amount of heat carried out outside the preheater system and the amount of dust circulating within the preheater, causing problems such as an increase in heat consumption.

[0007] Generally, there is a trade-off between the pressure loss and dust collection efficiency of a cyclone, and it is not easy to meet the requirement of low pressure loss while maintaining dust collection efficiency.

[0008] The low-pressure-loss cyclone in Patent Document 1 can reduce pressure loss, but it also has the problem of reducing dust collection efficiency. Furthermore, the invention in Patent Document 2 aims to improve dust collection efficiency compared to the low-pressure-loss cyclone in Patent Document 1, but the straightening member is installed in a space close to the conical portion. As a result, re-entrained dust is sucked into the inner cylinder, and there have been cases in which dust collection efficiency has deteriorated in actual equipment.

[0009] The present invention has been made in view of the above circumstances, and has as its object to improve the dust collection efficiency while reducing the pressure loss of a cyclone.

[0010] In order to achieve the above object, the present invention provides a cyclone comprising an outer cylinder provided on top of a swirling cylinder, an inner cylinder provided concentrically within the outer cylinder, a straightening member provided in the space directly below the inner cylinder, in which a plurality of planar straightening plates each forming a curved surface in at least the lower half are arranged at equal angular intervals around the axis of the inner cylinder, with the curved surface of each planar straightening plate oriented in the same direction as the swirling flow flowing around the inner circumference of the inner cylinder, an inlet cylinder provided tangentially to the outer circumference of the outer cylinder, a drop port provided at the bottom of the swirling cylinder, and a re-entrainment prevention member provided at the lower end of the straightening member.

[0011] Dust-laden gas that flows into the cyclone is separated into gas and dust by centrifugal force in the outer cylinder, and the dust passes through the wall of the cone and is discharged from the outlet at the bottom of the cyclone. Meanwhile, the gas reverses direction midway through the cone and is discharged from the inner cylinder while rotating upward.

[0012] At this time, the gas that reverses and rises rotates at high speed, and its central axis does not remain in a fixed place but moves unsteadily around the central axis of the inner cylinder, exhibiting a behavior called precession.

[0013] This precession disturbs the flow of dust and gas descending inside the cyclone, causing the dust to be re-entrained and leading to a deterioration in dust collection efficiency.

[0014] According to the present invention, the re-entrainment prevention member provided at the lower end of the straightening member suppresses the precession of the inverted gas inside the cyclone, and the re-entrainment prevention member also prevents dust re-entrained from the conical section from being directly sucked into the inner cylinder, thereby making it possible to improve the dust collection efficiency while reducing the pressure loss of the cyclone.

[0015] In the cyclone, the re-entrainment prevention member may be cylindrical, inverted conical, or inverted truncated conical.

[0016] In the cyclone, the re-entrainment prevention member may be cylindrical, inverted conical, or inverted truncated conical.

[0017] Fig. 1 is a schematic cross-sectional view showing a first embodiment of a cyclone according to the present invention. Fig. 2 is a schematic cross-sectional view showing a second embodiment of a cyclone according to the present invention. Fig. 3 is a schematic cross-sectional view showing a third embodiment of a cyclone according to the present invention. Fig. 4 is a schematic cross-sectional view showing an example of a conventional cyclone.

[0018] Next, an embodiment of the present invention will be described. To facilitate understanding of the configuration and operation of the cyclone according to the present invention, a conventional cyclone will first be described.

[0019] FIG. 4 shows an example of a conventional cyclone. This cyclone 31 constitutes, for example, a suspension preheater for a cement burning apparatus, and comprises an outer cylinder 3 provided on top of a swirling cylinder 2, an inner cylinder 4 of diameter (outer diameter) d provided concentrically within the outer cylinder 3, a flow straightening member 5 provided at the lower end of the inner cylinder 4 (the space directly below the inner cylinder 4), an inlet cylinder 6 provided tangentially to the outer periphery of the outer cylinder 3, and a drop opening 8 provided at the bottom of the swirling cylinder 1.

[0020] The flow straightening member 5 is a flow straightening plate (spiral cone) described in Patent Documents 1 and 2, which is attached to the inner cylinder 4 at equiangular intervals around the axis of the inner cylinder 4, with a plurality of planar flow straightening plates each forming a curved surface in at least the lower half thereof, and such that the curved surface of each planar flow straightening plate faces in the same direction as the swirling flow flowing around the inner circumference of the inner cylinder 4. As for the flow straightening member 5, in addition to the planar flow straightening plate directly attached to the inner cylinder 4 as described above, there are also flow straightening members 5 which are attached to the inner cylinder 4 via a conical flow straightening plate. Furthermore, the shape of each planar flow straightening plate can be a vertically elongated rectangle or an inverted triangle.

[0021] In the cyclone 31 having the above-described configuration, a dust-containing gas G is supplied tangentially from the inlet tube 6 into the outer tube 3, generating a swirling flow inside the outer tube 3. The swirling flow moves from the top to the bottom of the outer tube 3, and dust D suspended in the gas is thrown out toward the wall of the outer tube 3 by centrifugal force, falls along the inner wall surface, and is discharged to the outside through the drop port 8.

[0022] Dust particles smaller in particle size than the dust separated by the swirling flow near the inner wall surface of the outer cylinder 3 form a swirling flow together with the gas and move to the space directly below the inner cylinder 4. This dust-laden gas is then guided by the surface of the curved planar straightening plate of the straightening member 5, where it gradually changes from a swirling flow to an upward flow, converting the tangential velocity of the swirling flow into a velocity in the axial direction only, and moves through the inner cylinder 4 to the next process.

[0023] In the conventional cyclone 31, although the pressure loss is reduced by the rectifying member 5, the gas vector changes from the tangential direction to an upward direction toward the inner cylinder 4 near the rectifying member 5, making it easier for the dust-containing gas to be sucked into the inner cylinder 4 and also making it easier for the dust to be re-scattered near the rectifying member 5 due to the precession of the reverse gas inside the cyclone 31, thereby reducing the dust collection efficiency.

[0024] Therefore, in the first embodiment of the cyclone according to the present invention, as shown in Figure 1, a re-entrainment prevention member 9 is provided at the lower end of the straightening member 5. The provision of this re-entrainment prevention member 9 is a feature of the present invention. Since the components other than the re-entrainment prevention member 9 are the same as those of the cyclone 31 shown in Figure 4, the other components are assigned the same reference numerals as in Figure 4 and their description will be omitted.

[0025] The re-entrainment prevention member 9 is cylindrical and has a dimension of approximately 0.5 to 1.1 d relative to the outer diameter d of the inner cylinder 4, and a height h of approximately 0.8 to 1.2 d. By disposing the re-entrainment prevention member 9 at the lower end of the rectifying member 5, the precession of the reverse gas inside the cyclone is suppressed, and the re-entrainment prevention member 9 can prevent dust re-entrained from the conical portion from being directly sucked into the inner cylinder 4, making it possible to improve the dust collection efficiency while reducing pressure loss in the cyclone.

[0026] A comparative test was conducted on the pressure loss and dust collection efficiency of the cyclone 1 according to the present invention and a conventional cyclone. The cyclone 1 according to the present invention was used as an example, a conventional cyclone without the flow straightening member 5 was used as comparative example 1, and the cyclone 31 having the flow straightening member 5 at the lower end of the inner cylinder 4 was used as comparative example 2, and the pressure loss and dust collection efficiency of the cyclones were compared. The results are as follows.

[0027] Example: Pressure loss 290 Pa, dust collection efficiency 97.5% Comparative Example 1: Pressure loss 490 Pa, dust collection efficiency 97.5% Comparative Example 2: Pressure loss 300 Pa, dust collection efficiency 96.7%

[0028] As described above, it can be seen that the present invention achieves a significantly lower pressure loss than Comparative Example 1, and also achieves a lower pressure loss than Comparative Example 2 and an improved dust collection efficiency.

[0029] The present invention is not limited to the first embodiment described above, and can be implemented by partially modifying the configuration or partially adding other configurations within the scope of the gist. For example, instead of the cylindrical re-entrainment prevention member 9, an inverted cone-shaped re-entrainment prevention member 19 (height h: approximately 0.8 to 1.2 d) shown in FIG. 2 may be used as a second embodiment, or a truncated cone-shaped re-entrainment prevention member 29 (height h: approximately 0.8 to 1.2 d) shown in FIG. 3 may be used as a third embodiment. In either embodiment, dust collection efficiency can be improved, as in the first embodiment. Furthermore, re-entrainment prevention members with shapes different from these may be used.

[0030] The illustrated embodiments are merely examples and are not intended to limit the technical scope of the present invention.

[0031] 1, 11, 21 Cyclone 2 Swirling cylinder 3 Outer cylinder 4 Inner cylinder 5 Flow straightening member 6 Inlet cylinder 8 Drop port 9, 19, 29 Re-scattering prevention member

Claims

1. A cyclone comprising: an outer cylinder provided above a swirling cylinder; an inner cylinder provided concentrically within the outer cylinder; a straightening member provided in the space directly below the inner cylinder, which comprises a plurality of planar straightening plates, each of which has a curved surface in at least its lower half, arranged at equal angular intervals around the axis of the inner cylinder, with the curved surface of each planar straightening plate oriented in the same direction as the swirling flow flowing around the inner circumference of the inner cylinder; an inlet cylinder provided tangentially to the outer circumference of the outer cylinder; a drop port provided at the bottom of the swirling cylinder; and a re-entrainment prevention member provided at the lower end of the straightening member.

2. A cyclone according to claim 1, wherein the re-entrainment prevention member is cylindrical, inverted conical or inverted truncated conical.

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