JPH0118771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a stirring plate and a rotating arm of a multi-stage furnace used for firing powdery raw materials such as pellets of briquette coal.

(Prior art) When dry distilling and activating (hereinafter referred to as firing) granular raw materials such as pellets of briquette coal (hereinafter simply referred to as raw materials) in a multi-stage furnace, each raw material and its entire surface must be uniformly fired. To do this, the raw materials are stirred on the hearth. Whether each raw material is fired uniformly depends on whether the firing time of all raw materials, that is, the residence time in the multistage furnace is constant, and whether the surface of the raw materials is fired uniformly. Whether or not this happens depends on the quality of the stirring on the hearth.

Conventionally, stirring and feeding (also referred to as conveyance) of raw materials on the hearth of a multi-stage furnace is carried out by using a plurality of flat stirring plates 1 of the same shape mounted on a rotary arm 3 at the same pitch p, as shown in Fig. 1. In addition, this is achieved by attaching the rear end of the stirring plate 1 located on the front side in the rotation direction and the tip of the next stirring plate 1 so that they are in a positional relationship that draws the same rotation locus. In such cases, two undesirable phenomena occur in the stirring and feeding actions. One of them is that, as shown in FIG. 1, the stirring plates 1 of the same shape are attached to the rotating arm 3 at the same intersection angle γ, so that as shown in the enlarged view near the stirring plates of FIG. Tip side F of stirring plate 1
In this case, the contact angle θ' with the raw material 6 is smaller than the intersection angle γ, but at the intersection of the rotating arm 3 and the stirring plate 1, the contact angle θ' becomes equal to the intersection angle γ, and conversely, the contact angle θ' with the stirring plate 1 is equal to the intersection angle γ. Then, the contact angle θ' becomes larger than the intersection angle γ. In the areas where the contact angle θ' is large, the frictional resistance between the raw material 6 and the stirring plate surface is strong, so slippage is poor.
Therefore, some of the raw materials are transported to the stirring plate 1.
As the raw material moves in the circumferential direction, it moves only gradually in the radial direction, so the speed of movement from the center of the hearth to the outer periphery is slow, and the residence time of the raw material in the furnace becomes longer, resulting in proper firing of the raw material. If the time is exceeded, over-firing will occur. Another phenomenon is that the moving distance, that is, the circumferential length, of the stirring plate 1 attached to the outer circumference of the rotary arm 3 is larger than that of the stirring plate 1 attached to the inner circumference. but,
Since the volume of the raw material 6 displaced in the radial direction by the stirring plate 1 is equal per rotation, as shown in FIG. ) The thickness T of the valley portion is considerably different between the center side (inner circumferential side) Ti and the outer circumferential side To of the rotating shaft 2. In other words, the cross-sectional area of the raw material layer is larger on the inner circumferential side because the circumference is shorter, and the interval P (corresponding to the bottom of the cross section) between adjacent valleys of the raw material layer is constant, so the raw material is smaller than on the outer circumferential side. The valleys of the layer become thicker.
On the other hand, on the outer circumferential side, since the circumference is large, the cross-sectional area of the raw material layer becomes small, and the troughs of the raw material layer become thin due to the same spacing. The degree of firing varies depending on the thickness of the troughs in the raw material layer, and since the structure is such that the subsequent stirring plate passes through the peaks formed by the previous stirring plate in the rotating direction, the raw material A part of the raw material at the peaks of the layer collapses into the valleys on the outer and inner sides (hereinafter, the former is referred to as back mixing phenomenon, and the latter is referred to as jump mixing phenomenon), and the raw materials that are back mixed are fired repeatedly. is,
The firing time for raw materials that are jump mixed is shortened. This phenomenon causes large variations in residence time (firing time) between raw materials, resulting in uneven product quality and, in turn, a decrease in product yield.

(Object of the Invention) In view of the above-mentioned current situation, the present invention aims to solve the above-mentioned problems by improving the stirring plate and its arrangement on the rotating arm.

(Structure of the Invention) That is, in a stirring plate that is attached to a rotating arm that rotates above a hearth centering around a rotating shaft in a multi-stage furnace and moves over the hearth to stir and convey the granular material on the hearth, The stirring plate has a curved shape in a plan view, and the curved shape is such that the moving direction at an arbitrary point on the stirring plate in a plan view and the tangential direction to the stirring plate at the arbitrary point are different from each other. By using a stirring plate that has a curved shape with the same intersecting angle θ, all the raw materials can be sent out in the radial direction, and the granular raw materials on the hearth in a multi-stage furnace can be stirred. In the rotary arm to which a stirring plate is attached, the stirring plate has a curved shape in plan view, and the curved shape corresponds to the direction of movement of any point on the stirring plate with respect to the hearth in plan view. , a plurality of stirring plates each having a curved shape having the same intersection angle θ with the tangential direction to the stirring plate at any of the above points are attached to a rotating arm by moving the stirring plate with respect to the axis of the arm. The stirring plates are attached at intervals so that the thickness of the troughs of the raw material layer formed by the stirring plates are equal, and the stirring plate next to the troughs of the raw material layer formed by the rear end of the stirring plate located on the front side in the rotation direction is By using a rotating arm that is sequentially attached to the rotating arm so that the tip is located, the thickness of the valley part of the raw material layer can be made constant, back mixing and jump mixing can be prevented, and all The firing time of the raw materials is to be kept constant.

Hereinafter, the two closely related inventions described above will be described in more detail by examples with reference to the drawings. For convenience of explanation, the shape of the stirring plate will be explained first, and then the arrangement of the stirring plate on the rotating arm will be explained.

FIG. 3 is a plan view showing an embodiment of the stirring plate according to the present invention. In the figure, 1 is a stirring plate having a curved shape in a plan view, 2 is a rotating shaft, A is an arbitrary point on the stirring plate 1, line B is the moving direction of the stirring plate 1, and line C is the stirring plate 1. The tangent direction at any point A above, θ is the direction of movement of the stirring plate 1 relative to the hearth at any point A on the stirring plate 1 (line diagram B) and the tangent at that point (line diagram C). intersection angle (same as contact angle),
r (variable) is the radius of curvature at each arbitrary point of stirring plate 1, R ₀ is the length from point O at the inner end of stirring plate 1, and R ₁ is O at the outer end of stirring plate 1. The length from the point O indicates the center point of rotation (rotation axis). The curved shape of the stirring plate 1 according to the present invention in a plan view is defined by the movement (advancement) direction of the stirring plate 1 with respect to the hearth at any point A in the plan view (line diagram B).
and the tangent direction (diagram C) to the curve of the stirring plate at any point A on the horizontal plane (hearth). 15mmL, angle of repose α≒32° and θ
≒20~30° is preferable. ) is formed by a curve (spiral curve) that is the same at each arbitrary point on the curve. That is, in each stirring plate 1, the curve of the stirring plate 1 and the curvature constituting the curve change depending on the position where the stirring plate 1 is attached to the rotating arm in the radial direction of rotation and the position in the circumferential direction.

However, as a result of the inventor's experiments, the above curve approximates the above curve in actual use, for example, the distance from the rotation center O to the attachment position of the stirring plate 1 to the rotating arm is (See Figure 5)
It has been confirmed that almost the same effect is obtained even when the arc is formed by an arc with r' (constant curvature)≒1 to 1.2R. Therefore, it is safe to understand that the curved shape forming the above-mentioned curved shape also includes a curved shape that approximates the above-mentioned curved shape.

FIG. 4 shows the shape and cross section of a suitable raw material layer.
In the figure, 6 is the raw material, 4 is the hearth, Tm is the allowable value of the thickness of the valley of the raw material layer, Pa, Pb, Pc are the raw material layer pitch, that is, the interval between adjacent valleys of the raw material layer, Ra,
Rb and Rc represent the distance from the rotation center O of the raw material layer, and α represents the angle of repose of the raw material.

Regarding the length of the stirring plate, in Fig. 4, the raw material volume per rotation determined from the rotational speed of the rotary arm 3 and the raw material flow rate, the allowable value Tm of the thickness of the valley part of the raw material layer, and the The shape and dimensions of the raw material layer are determined by the distance Ra from the rotation center O of the raw material layer and the angle of repose α of the raw material, and the raw material layer pitch Pa
is obtained. Similarly, the dimensions of the next raw material layer are determined by setting Rb=Ra+Pa, and the pitches of adjacent raw material layers are determined in sequence. In this case, it can be considered that the angle of repose α of the raw material 6 and the thickness Tm of the valley of the raw material layer are equal over the entire hearth. In the case of the embodiment, the length of displacing the raw material 6 handled by one stirring plate 1 in the radial direction is equivalent to 1/4 of the raw material layer pitch per stirring plate, since each rotation is shared by four stirring plates. All you have to do is have a displacement length. However, after the stirring plate passes, there is the above-mentioned back-mixing phenomenon in which a part of the raw material at the mountain part of the raw material layer collapses, so the length of this collapse (Dimension l in Figure 6)
and the length of the above 1/4 pitch length (hereinafter,
Let the feed pitch (referred to as Lp) be the displacement length of the stirring plate 1. Therefore, in FIG. 3, R ₁ =R ₀ =Lp
The length of the stirring plate 1 is determined. In addition, in Fig. 6, the moving distance S of the raw material layer is the feed pitch mentioned above.
This corresponds to the difference between Lp and the falling length l, that is, the above 1/4 length.

Next, the arrangement of the stirring plate 1 on the rotating arm will be explained. Figure 5 is a cross-sectional plan view of a multi-stage furnace showing the arrangement of the stirring plate on the hearth on the rotating arm, which stirs and feeds the raw materials toward the outer circumference of the hearth, and Figure 6 shows the attachment of the stirring plate to the rotating arm. 7 is a perspective view showing the positional relationship between the rear end of the stirring plate on the front side in the rotational direction and the front end of the stirring plate on the rear side in the front and back positional relationship in the rotational direction of the rotating arm. FIG. In the figure, 1 is a stirring plate, 2 is a rotating shaft of a multi-stage furnace, 3 is a rotating arm, 4 is a hearth of a multi-stage furnace, 5 is an outer wall of a multi-stage furnace, and 7 is a discharge port. One end of a rotating arm 3 is attached to the rotating shaft 2 of the multi-stage furnace, and a plurality of stirring plates 1 (in this embodiment, 2 to 3 plates/rotating arm) are attached to the lower end surface of the rotating arm 3. It is worn. That is, to explain the arrangement of the stirring plates that stir and feed the raw materials in the outer circumferential direction shown in FIG.
is attached to the rotary arm 3 so that the tip of the stirring plate substantially coincides with the outer periphery of the rotary shaft 3 and is set at an intersecting angle β with the axis of the rotary arm. The intersecting angle β corresponds to the intersecting angle θ of the stirring plate 1 in FIG. 3, and is the same value for all stirring plates. As shown in FIGS. 5 and 6, the second stirring plate 1b in the rotational direction first has its tip in the rotational direction located in the valley of the raw material formed by the rear end of the first stirring plate 1a. It is attached to the rotary arm 3 so that it is located at the appropriate intersection angle β as described above. Thereafter, the third stirring plate 1c, fourth stirring plate 1d, . . . are also attached in the same manner.

The above description has mainly been given to the case where the raw material is stirred and sent from the inner circumferential side to the outer circumferential side, but the same concept can be applied to the case where the raw material is stirred and sent from the outer circumferential side to the inner circumferential side. However, the contact surface between the stirring plate and the raw material is a concave surface.

(Operations and Effects of the Invention) Since the stirring plate is constructed from the above-mentioned curve and is always in contact with the raw material at a constant contact angle (same as the intersection angle θ), it is possible to The raw material is sent in the radial direction (not in the circumferential direction) without rotating about the stirring plate, either near the front end or the rear end of the plate in the rotating direction. In addition, by setting the mounting position of the stirring plate as described above, during stirring and feeding, the raw material forms valleys with approximately the same thickness on the inner and outer sides of the hearth as shown in Figure 4. Form. Further, since the positional relationship between the preceding stirring plate and the next stirring plate is appropriate, phenomena such as back mixing and jump mixing do not occur. Therefore, in the conventional stirring in a multi-stage furnace, the distribution of the firing time of the raw materials was shown in Figure 8 (with a large standard deviation), but the distribution of the firing time of the raw materials was as shown in Figure 9 (with a large standard deviation). The distribution state has become dramatically smaller. That is, the variation in firing time between each raw material is dramatically reduced, the yield of the product is dramatically improved, and the overall residence time in the hearth can be shortened, resulting in energy savings. In addition, the band-shaped body indicated by hatching in FIGS. 8 and 9 above indicates the planned residence time period.

As explained above, the present invention ideally performs the stirring and feeding (conveying) action of raw materials on the hearth, dramatically improving the yield of products, and making it possible to improve the average firing time t (8th, 9th (see figure), shorten
This is an excellent invention that contributes to energy savings in the firing process.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional multistage furnace showing the arrangement of the rotating arm on the hearth and the stirring plate attached to it, and Figure 2 is an enlarged perspective view showing the thickness of the raw material layer on the hearth in Figure 1. 3 is a plan view showing an embodiment of the stirring plate according to the present invention, FIG. 4 is an enlarged perspective view showing the shape of an appropriate raw material layer, and FIG. 5 is a plan view showing an embodiment of the stirring plate according to the present invention. A plan view of a cross section of a multi-stage furnace showing the arrangement of the stirring plate on the rotating arm in the feeding hearth, FIG. A perspective view showing the relationship between the rear end of the stirring plate on the front side and the front end of the stirring plate on the rear side, FIG. 7 is a side sectional view taken along line X-X in FIG. 5, and FIG. 8 is a conventional stirring plate. FIG. 9 is a distribution diagram showing the distribution of firing times of raw materials in a multi-stage furnace having a stirring plate and a rotating arm according to the present invention; FIG. FIG. 10 is an enlarged view showing the action of a conventional stirring plate near the stirring plate. A...Arbitrary point, B, C...Diagram, θ...Angle of intersection, α...Angle of repose, β...Angle of intersection, R...Radius, r
... Radius of curvature, O ... Center of rotation, 1 ... Stirring plate, 2 ... Rotating shaft, 3 ... Rotating arm, 4 ... Hearth, 5 ... Outer wall, 6 ... Raw material, 7 ... Exhaust Exit.

Claims (1)

[Scope of Claims] 1. A stirring plate that is attached to a rotating arm that rotates above the hearth around a rotating shaft in a multi-stage furnace and that moves over the hearth to stir and convey the granular material on the hearth, The stirring plate has a curved shape in a plan view, and the curved shape is such that the moving direction at an arbitrary point on the stirring plate in a plan view and the tangential direction to the stirring plate at the arbitrary point are different from each other. A stirring plate for a multi-stage furnace, characterized in that the intersecting angles θ are the same. 2. In a rotary arm to which a plurality of stirring plates are attached for stirring the granular raw material on the hearth in a multi-stage furnace, the stirring plate has a curved shape in plan view, and the curved shape is as follows in plan view. A plurality of stirring plates each having a curved shape such that the intersection angle θ between the moving direction at an arbitrary point on the stirring plate and the tangential direction to the stirring plate at the arbitrary point are the same, on a rotating arm, The arm is attached at a distance from the axis of the arm so that the thickness of the trough of the raw material layer formed by the movement of the stirring plate is equal, and is formed by the rear end of the stirring plate located on the front side in the rotational direction. A rotary arm of a multi-stage furnace, characterized in that the rotary arms are sequentially attached to the rotary arms so that the tips of the next stirring plates are located in the valleys of the raw material layer.