Powder mixer with appropriate clearance

Abstract

To provide a powder mixer equipped with appropriate clearance. [Solution] A powder kneader having one or more rotating blades such that the rotational axis of the rotating blades is substantially horizontal, wherein there exists a point of appropriate clearance where the clearance d between a point on the inner surface of the casing of the powder kneader and the rotating blade whose tip is closest to the point on the inner surface of the casing is in the range of D × 0.90 ≤ d ≤ D × 1.15 with respect to the radius r of the adjacent rotating blade, and the area consisting of the point of appropriate clearance occupies 50% or more of the area of ​​the inner surface of the casing below the horizontal plane passing through the rotational axis of the rotating blades.

Description

[Technical Field]

[0001] This invention relates to a powder mixer equipped with appropriate clearance. [Background technology]

[0002] In recent years, a technology has been put into practical use in which a portion of the raw coal for blast furnace coke production is mixed with petroleum-based or coal-based binding and filler materials using a powder mixer, and then molded and blended.

[0003] However, in powder mixers used in molded coal blending technology, casing wear due to coal powder is a problem. When the casing wears down, it becomes more prone to breakage.

[0004] In light of the above problems, a method is known in which a self-lining layer of powder is formed by providing a clearance between the rotational trajectory traced by the tip of the rotating blade and the casing, thereby preventing wear of the casing.

[0005] For example, Patent Document 1 provides a twin-screw mixer in which two mixing shafts, driven to rotate in opposite directions, are mounted in a parallel arrangement inside the casing, and multiple stirring blades with blades at their tips are provided protruding from each of the two mixing shafts, and a gap is provided between the inner surface of the outer plate of the casing and the rotational trajectory traced by the tips of the stirring blades to form a self-lining layer that is generated when the mixed material adheres to the inner surface of the casing, thereby preventing wear of the casing and providing a twin-screw mixer that can be greatly improved in durability. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2011-25112 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, regarding the numerical value of the clearance, the estimation method thereof is not known. In order to estimate the clearance that can generate self-aligning in an actual machine, it is first necessary to estimate the theoretically calculated clearance (appropriate clearance).

[0008] The present invention has been made in view of the above-described situation, and an object thereof is to provide a powder kneader having an appropriate clearance.

Means for Solving the Problems

[0009] The gist of the present invention is as follows.

[0010] (1) A powder kneader provided with one or more rotating blades such that the rotation center axis of the rotating blades is substantially horizontal, and the clearance d between a point on the inner surface of the casing of the powder kneader and the rotating blade among the rotating blades whose tip is closest to the point on the inner surface of the casing is within the range of the formula (5) with respect to the radius r of the adjacent rotating blade, and there exists a clearance appropriate point, and the area composed of the clearance appropriate points occupies 50% or more of the area of the inner surface of the casing below the horizontal plane passing through the rotation center axis of the rotating blade. A powder kneader having an appropriate clearance, characterized in that.

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[0011] According to the present invention, a powder kneader with appropriate clearance can be provided. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing a model for predicting the flow velocity distribution from the balance of shear forces. [Figure 2] This is a magnified view of the cell in the model shown in Figure 1, which is explained in the cell division process. [Figure 3] This is a cell-enlarged view of the model in Figure 1, which is explained in the flow velocity assumption process. [Figure 4] This graph shows the dependence of the coefficient of friction on the shear rate. [Figure 5] This is a magnified view of the cell in the model shown in Figure 1, which is explained in the process of calculating the appropriate clearance. [Figure 6] This graph shows the relationship between the flow velocity of the mixed material and the distance from the tip of the rotating blade towards the inner surface of the casing. [Figure 7] This is a schematic diagram illustrating a self-lining verification test. [Figure 8]This graph shows the relationship between the appropriate clearance and the diameter of the rotating blades. [Figure 9] This is a schematic diagram of an actual powder mixing machine with clearance applied. [Modes for carrying out the invention]

[0013] The inventors have discovered a method for estimating the appropriate clearance for a powder mixer.

[0014] The following describes in detail an embodiment of a method for estimating the appropriate clearance between the rotational trajectory of the rotating blades and the casing in a powder kneader according to the present invention. The clearance estimation method of this embodiment comprises a cell division step S1, a flow velocity assumption step S2, a shear velocity calculation step S3, a shear stress calculation step S4, and a flow velocity calculation step S5.

[0015] (Cell splitting process S1) The inventors diligently studied methods for estimating the appropriate clearance and devised the model shown in Figure 1. The model shown in Figure 1 consists of a rotating blade 1, a casing 2 housing the rotating blade 1, and an annular region between the rotating blade 1 and the casing 2. The rotating blade 1 rotates clockwise around the central axis, C. Figure 1 is a model that predicts the flow velocity distribution in the model diameter direction of the powder being stirred in the casing 2 from the balance of shear forces. In the cell division process S1, in the model of Figure 1, the annular region B between the rotation trajectory of the rotating blade 1 and the casing 2 is divided into n (n≧3) annular cells with a width Δr. Figure 2 is an enlarged view of the cells in the model of Figure 1. As shown in Figure 2, the i-th cell from the inner circumference is called cell A. i Let i = 1, 2, 3...n. Also, for convenience, let cell A0 be a circular cell with width Δr that is inside cell A1.

[0016] (Flow velocity assumption step S2) For each of the cells divided in the cell division process S1, we assume a flow velocity in the direction along the circumference. Specifically, as shown in Figure 3, the i-th cell A from the inner circumference side i VAi and cell A i Cell A one inside i-1 Let the flow velocity in the circumferential direction be V Ai-1 Cell A one outside cell Ai i+1 Let the flow velocity in the circumferential direction be V Ai+1 and set. Each cell is an annular rigid body when viewed from the C-axis direction, and the moving velocity at the center line in the width direction of each cell is defined as the flow velocity of each cell. There is no velocity difference inside the cell. Since the flow velocities of each cell are different, a shear stress occurs between cells.

[0017] (Shear rate calculation step S3) Cell A i and cell A i-1 The shear rate γ Ai-1⇔Ai between them can be obtained by the following formula (1). Also, as shown in FIG. 3, the boundary passing through the midpoint of △r is defined as the cell boundary.

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[0018] (Shear stress calculation step S4) In order to apply the model of FIG. 1 in practice, it is necessary to clarify the relationship between the shear rate and the shear stress. Therefore, the inventors conducted a shear test to investigate the friction coefficient of the powder at different shear rates. The shear test was conducted under the following conditions. Sample: Coal / road tar mixture Test method: Constant volume shear test Shear zone thickness: 1 mm Temperature: 65 °C The shear rate [1 / s] was changed to 0.8, 0.3, and 1.

[0019] Figure 4 shows the dependence of the coefficient of friction on the shear rate obtained in the shear test described above. The horizontal axis represents the shear rate, and the vertical axis represents the coefficient of friction. The coefficient of friction increased with increasing shear rate. The graph in Figure 4 is approximated by the following equation (2).

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[0020] Next, the shear stress τ(γ) can be determined by multiplying the friction coefficient obtained in (2) by the powder pressure P. This is expressed by the following equation (3).

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[0021] (Flow velocity calculation step S5) Shear force is calculated by multiplying the area of ​​the shear surface (the contact surface acting on the shear stress) by the shear stress. In the models shown in Figures 1 and 2, cell A i and cell A i+1 shear rate γ between Ai⇔Ai+1 The shear force generated by (left side of equation (4)) and cell A i and cell A i-1 shear rate γ between Ai-1⇔Ai The shear force generated by this (right-hand side of equation (4)) is A i It balances out in a steady state where it neither accelerates nor decelerates. The reason for this will be explained in detail. Cell A iThe rotating blade 1 rotates in the circumferential direction, transmitting its rotational force to the outer cells through frictional forces between cells. After sufficient time has elapsed since the rotating blade 1 began rotating, and the rotational force of the rotating blade 1 has been sufficiently transmitted to each cell in the casing 2, each cell is rotating at a constant velocity without acceleration or deceleration. Therefore, in each cell, the shear force acting from the innermost cell and the shear force acting on the outermost cell are balanced. This is expressed by the following equation (4). The area of ​​the shear surface is the product of the circumference of the cell and the depth of the cell, but since the depth of each cell is the same, it is canceled out on both sides. Here, τ(γ Ai⇔Ai+1 ) is the shear rate γ Ai⇔Ai+1 In this case, r represents the shear stress and the radius of the rotational trajectory traced by the rotating blade 1.

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[0022] Since the aforementioned shear force balances out at all adjacent cell boundaries, V satisfies the following equation (5). Ai By determining (1 ≤ i ≤ n), we can find the flow velocity of each cell in the casing 2 at the point when the rotational force of the rotating blade 1 has been sufficiently transmitted to each cell. The flow velocity of the cells will be explained in detail below.

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[0023] Finally, cell A at the outermost periphery of casing 2 n Convergence calculations are performed so that the flow velocity becomes 0. The appropriate clearance calculation step S6 is performed as shown in Figure 5. At this time, r is the diametrical coordinate with the center of the rotating blade and casing as 0, A i is the i-th cell, R i (=r+i△r) is A i This represents the coordinates inside the box. Furthermore, V i to A i The rotation speed, F i to A i is A i-1 Shear stress and Ai Let F be the average of F1 to Fn, which is the product of the inner circumference length of F1 to Fn (n=80). i The expression is given by the following equation (6). In this case, 1 ≤ i ≤ 79 and V i We vary the value of equation (7) and calculate the convergence so that it is minimized and holds for all i (i=1, 2, 3...n). At this time, the constraints are V0 = rotational speed of the blade tip, 1 ≤ i ≤ 79, V i+1 ≤V i , V 80 = 0. Also, V i This can be calculated using equation (1).

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[0024] (Self-lining verification test) To confirm the consistency between the model described above and the actual phenomenon, a self-lining verification test was conducted as shown in Figure 7. During this test, the flow of the powder was evaluated at various clearances (5, 15, and 25 mm) by changing the size of the container.

[0025] Similar to the calculation conditions in Figure 6, the diameter of the rotating blade was set to 150 mm and the rotation speed of the rotating blade was set to 32 rpm. The motor performance was a rated output of 120 W and a rated torque of 2.2 Nm. The area inside the interface where the powder flow stagnates was defined as the fluidized bed, and the area outside was defined as the stagnant bed. The thicknesses of the fluidized bed and the stagnant bed were determined. The results are shown in Table 1 below, and the experimental value for the appropriate clearance in this mixing system was approximately 9 mm. This result was in good agreement with the estimated value of the appropriate clearance by the model shown in Figure 6.

[0026] [Table 1]

[0027] Furthermore, considering that powder mixers of various sizes are used in industrial applications, the relationship between the diameter of the rotating blades and the appropriate clearance was predicted using this model. The results are shown in Figure 8 below, and it was estimated that for powder mixers of all sizes, the appropriate clearance is 0.115 times the radius of the rotating blades. It should be noted that this model did not show any change in the appropriate clearance depending on the rotation speed. If the clearance of a powder mixer is smaller than the appropriate clearance, sliding occurs between the inner surface of the casing and the powder, causing wear on the casing. Conversely, if the clearance of a powder mixer is larger than the appropriate clearance, problems such as reduced powder mixing performance or the equipment becoming unnecessarily large may occur. In Figure 6, the horizontal axis at 0.009 represents the optimal clearance (powder velocity = blade tip velocity × 0.01) and also the interface between the flowing and stagnant areas confirmed in experiments. Using this optimal clearance (horizontal axis 0.009) as a baseline, decreasing the horizontal axis to 0.008, 0.007, and 0.006 increases the powder velocity near the casing surface shown on the vertical axis, thereby increasing the casing wear rate. Conversely, as the horizontal axis approaches 0.010, the calculated powder velocity is expected to fall below 1 / 1000 of the blade tip velocity, becoming almost zero. If the clearance is designed and manufactured with a value of 0.006, which is smaller than the horizontal axis value of 0.009 in Figure 6, the powder velocity will be approximately 10 times that of the appropriate clearance (0.009), leading to increased casing wear. It is expected that the wear will stop when the clearance approaches 0.009. Therefore, the clearance of a powder mixer for industrial use is preferably 90% to 115% of the appropriate clearance, and more preferably 95% to 110%. When designing the clearance of a powder mixer to be slightly smaller than the appropriate clearance, the outer circumference of the rotating blades should be extended radially outward from that point, and this point should be within the range from the inner surface of the casing to the center of the casing plate thickness. This corresponds to a value of 90% or more of the appropriate clearance. When designing to be slightly smaller, it is more preferable to have a clearance of 95% or more of the appropriate clearance. Also, when designing the clearance of a powder mixer to be slightly larger than the appropriate clearance, the outer circumference of the rotating blades should be extended radially outward by 110% from that point, and this point should be within the range from the inner surface of the casing to the center of the casing plate thickness. This corresponds to a value of 110% or less of the appropriate clearance. When designing to be slightly larger, it is more preferable to extend the length by 105% or 100%.

[0028] (A powder mixer with appropriate clearance) Next, we will explain an example of how the calculated appropriate clearance was implemented in the actual machine.

[0029] <Example of application to a horizontal powder mixer> The powder kneader with appropriate clearance according to this embodiment is a powder kneader equipped with one or more rotating blades such that the rotational axis of the rotating blades is substantially horizontal, and there exists an appropriate clearance point such that the clearance d between a point on the inner surface of the casing of the powder kneader and the rotating blade whose tip is closest to the point on the inner surface of the casing is within the range of equation (9) with respect to the radius r of the adjacent rotating blade, and the area consisting of the appropriate clearance point occupies 80% or more of the area of ​​the inner surface of the casing below the plane passing through the rotational axis of the rotating blades. Alternatively, the area consisting of the appropriate clearance point may be 50% or more of the area of ​​the inner surface of the casing below the horizontal plane passing through the uppermost end of the rotating blades. However, D is the appropriate clearance and is calculated as D = 0.115 × r.

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[0030] If a powder mixer has two or more rotating blades, the radius r of the adjacent rotating blade is defined as the rotating blade with the longest rotational axis. Equation (9) shows that the clearance d of the actual machine is between 90% and 115% of the appropriate clearance.

[0031] <Example of application to a vertical powder mixer> The powder mixer with appropriate clearance according to this embodiment is a powder mixer equipped with one or more rotating blades such that the angle θ between the rotational axis of the rotating blades and the horizontal plane is 0° < θ ≤ 90°, and there exists an appropriate clearance point such that the clearance d between a point on the inner surface of the powder mixer casing and the rotating blade whose tip is closest to the point on the inner surface of the casing is within the range of equation (9) with respect to the radius r of the adjacent rotating blade, and the area consisting of the appropriate clearance point occupies 80% or more of the area of ​​the inner surface of the casing below the horizontal plane passing through the uppermost tip of the rotating blades. Alternatively, the area consisting of the appropriate clearance point may be 50% or more of the area of ​​the inner surface of the casing below the horizontal plane passing through the center of the rotational axis of the uppermost tip of the rotating blades. However, D is the appropriate clearance and is calculated as D = 0.115 × r.

[0032] The rotational axis of the rotating blade being approximately vertical means that it includes an angular range of 0° to 10° with respect to the vertical. More preferably, it includes an angular range of 0° to 10°. If a powder mixer is equipped with two or more rotating blades, the radius r of the adjacent rotating blade is defined as the rotational axis of the blade with the longest rotational axis. Equation (9) shows that the clearance d of the actual machine is 90% to 115% of the appropriate clearance.

[0033] (Examples) The present invention will be described in more detail by reference to examples. The present invention is not limited in any way by these examples. Figure 9 is a schematic diagram of a real powder mixer 4 with clearance applied. There are two rotating blades 1 at the bottom of the casing 2. The bottom surface of the casing 2 is a cylindrical surface coaxial with the rotating blades 1. Above the axis of the rotating blades 1, the side walls of the casing 2 extend vertically. Multiple nozzles 3 are installed on the ceiling wall of the casing 2. A feeder (not shown) is installed behind the rotating blades 1 in the illustration. A discharge port (not shown) is located in front of the rotating blades 1 in the illustration. The materials to be mixed in both of these powder mixers 4 are coal and oil. The coal to be mixed is supplied from the feeder. The oil is supplied from the nozzle, and the processed mixture is discharged from the opening. In the example, a clearance within the range calculated using formula (9) from the appropriate clearance D was applied. In the comparative example, a clearance outside the range calculated using formula (9) from the appropriate clearance D was applied. In both the example and the comparative example, the amount of casing wear was evaluated after a certain period of test operation. Table 2 shows the design values ​​(rotating blade radius r, clearance d), appropriate clearance D, processing volume of the material to be kneaded, and wear amount for the examples and comparative examples.

[0034] [Table 2]

[0035] As shown in Table 2, in the example, no wear was detected even when the daily processing rate of the material being kneaded was high. On the other hand, in the comparative example, wear was detected even when the daily processing rate of the material being kneaded was low. [Industrial applicability]

[0036] According to the present invention, by using this model, it is possible to provide an appropriate clearance for a powder mixer. Furthermore, it is possible to provide a powder mixer equipped with an appropriate clearance. In this powder mixer, sliding between the coal powder and the casing wall is suppressed, and a significant extension of the lifespan can be expected. Therefore, the present invention has high industrial applicability. [Explanation of Symbols]

[0037] 1. Rotating blade 2 Casing 3 nozzles 4. Powder Mixer

Claims

1. A powder kneader having one or more rotating blades such that the rotational axis of the rotating blades is substantially horizontal, wherein there exists a point of appropriate clearance where the clearance d between a point on the inner surface of the casing of the powder kneader and the rotating blade whose tip is closest to the point on the inner surface of the casing is within the range of equation (5) with respect to the radius r of the adjacent rotating blade, and the area consisting of the point of appropriate clearance occupies 50% or more of the area of ​​the inner surface of the casing below the horizontal plane passing through the rotational axis of the rotating blades. [Math 1] However, D is the appropriate clearance, and is calculated as D = 0.115 × r.

2. A powder kneader equipped with one or more rotating blades such that the angle θ between the rotational axis of the rotating blades and the horizontal plane is 0° < θ ≤ 90°, wherein there exists a point of appropriate clearance where the clearance d between a point on the inner surface of the casing of the powder kneader and the rotating blade whose tip is closest to the point on the inner surface of the casing is within the range of equation (5) with respect to the radius r of the adjacent rotating blade, and the area consisting of the point of appropriate clearance occupies 50% or more of the area of ​​the inner surface of the casing below the horizontal plane passing through the center of the rotational axis of the uppermost tip of the rotating blades. [Math 2] However, D is the appropriate clearance, and is calculated as D = 0.115 × r.

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