JP2006336994A - Rotary kiln - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control an increase in the amount of scattering of the subject of processing in an area near the exit of a rotary drum in a rotary kiln where agitating blades are installed on the inner surface of the rotary drum. <P>SOLUTION: In the rotary kiln where the agitating blades are provided on the inner surface of the rotary drum and in parallel with an axis of rotation, the agitating blades are higher at the entrance side than at the exit side of the drum. A plurality of the agitating blades may be provided along the circumferential direction of the rotary drum. In the rotary kiln, the subject of processing gets drier or more carbonized and is more likely to scatter as it gets closer to the exit of the rotary drum. With the agitating blades made high at the entrance side and low at the exit side of the rotary drum, the amount that the subject of processing is lifted by the agitating blades is decreased to reduce scattering. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rotary kiln used for drying foods, wastes, cement raw materials and the like, or pyrolyzing industrial wastes such as general wastes, sludges and food wastes, or firing cement raw materials.

  In a rotary kiln that is used by rotating a drum in a horizontal state, it is known to install a stirring blade on the rotating drum in order to improve heating efficiency (see, for example, Patent Document 1). Patent Document 1 discloses a configuration in which a plurality of stirring blades are installed in the inner circumferential direction of a rotating drum.

JP-A-8-233234 (Abstract)

  A rotary kiln having a structure in which a plurality of stirring blades are installed on the inner surface of a rotating drum in order to increase the amount of heat transfer generally has a problem that the amount of scattering of the object to be processed increases near the outlet. Although a solid product and a gaseous product are discharged from the rotary kiln, if a large amount of the solid product is mixed in the gaseous product, it is necessary to treat the exhaust gas. Further, for example, in an external heating type rotary kiln, in general, combustible gas such as carbon monoxide and methane is included in exhaust gas, and thus, this is often burned and used as a heat medium for the rotary kiln. However, in this case, if scattered substances are mixed in the gas, the burner may become clogged during combustion.

  It is an object of the present invention to provide a rotary kiln having a structure in which a stirring blade is provided on the inner surface of a rotary drum, which promotes heat transfer and can suppress an increase in the amount of scattering of an object to be processed near the drum outlet. It is to provide.

  The present invention resides in that in a rotary kiln in which a stirring blade is provided on the inner surface of the rotating drum in parallel or substantially in parallel with the rotating shaft, the height of the stirring blade is increased on the inlet side of the drum and lower on the outlet side.

  A plurality of stirring blades can be provided in the circumferential direction of the rotating drum. Further, the stirring blade may be formed by a single long plate continuous from the inlet side to the outlet side of the rotating drum, or a plurality of short stirring blades may be continuously connected from the inlet side to the outlet side of the rotating drum. It may be arranged intermittently or intermittently.

  In general, as the rotary kiln approaches the outlet of the rotating drum, drying or carbonization of the workpiece progresses, and the workpiece becomes easily scattered. As in the present invention, the height of the stirring blade is increased on the inlet side of the rotating drum and lower on the outlet side, thereby promoting heat transfer to the workpiece and increasing the amount of the workpiece to be lifted by the stirring blade. It can be reduced and scattering can be suppressed.

  The rotary kiln of the present invention changes continuously or stepwise such that the height of the stirring blade is high on the inlet side of the rotating drum and low on the outlet side.

  It is desirable that the height of the stirring blade is lower than the minimum layer height of the workpiece to be set in all regions in the rotating drum. In particular, it is desirable to make it 0.5 times or more and less than 1 time with respect to the minimum layer height of the set workpiece.

  In the rotary kiln, in general, considering the operation efficiency and the like, the layer height of the workpiece to be supplied to the rotary drum or the contact length of the workpiece to be in contact with the inner surface of the rotary drum is often limited. By setting the height of the stirring blade to be lower than the layer height of the object to be processed, the effect of suppressing the scattering of the object to be processed can be enhanced.

  It is desirable to install a plurality of stirring blades in the circumferential direction of the rotating drum. In this case, the spacing between the stirring blades is preferably set shorter than the minimum contact length of the workpiece to be in contact with the drum inner surface. Thereby, mixing of a to-be-processed object is accelerated | stimulated more.

  When a plurality of short stirring blades are arranged in the rotating drum rotating shaft direction and a plurality of circumferential stirring blades are also arranged, the number of circumferential stirring blades is small on the inlet side of the rotating drum and many on the outlet side. It is desirable to do. Thereby, further mixing promotion can be achieved.

  The angle formed by the surface of the stirring blade facing the drum rotation direction and the inner surface of the rotating drum is smaller at the drum inlet side than at the drum inlet side to the outlet side, and the angle at the outlet side. It is desirable to enlarge it. By providing the stirring blades in such an inclined manner, the effect of suppressing the scattering of the object to be processed is enhanced.

  The stirring blade can be composed of a plurality of heat transfer tubes arranged in the direction of the rotation axis of the rotating drum and fins provided on the outer periphery of the heat transfer tube. A heat medium can flow through the heat transfer tube. In this case, the length of the fin is preferably long on the inlet side of the rotating drum and short on the outlet side. By configuring the stirring blade with a heat transfer tube, the heating efficiency can be improved.

  In the present invention, when a plurality of stirring blades are provided in the circumferential direction of the rotating drum and a plurality of stirring blades are provided in the rotation axis direction, the interval between the circumferential stirring blades is set in advance. It is extremely desirable to make the length smaller than the minimum length of the contact portion between the processed product and the rotating drum, and to reduce the number of circumferential stirring blades on the drum inlet side and increase it on the outlet side.

  The present invention relates to a rotary kiln in which stirring blades are installed on the inner surface of a rotating drum that rotates in a horizontal state in parallel with the rotation shaft, and a plurality of stirring blades are provided in the circumferential direction of the rotating drum and from the inlet to the outlet of the rotating drum. A rotary kiln is proposed in which a sheet is provided and the number of circumferential stirring blades is small on the inlet side of the rotating drum and larger on the outlet side.

  Further, in a rotary kiln in which a plurality of stirring blades are installed in the circumferential direction of the inner surface of a rotating drum that rotates in a horizontal state and in parallel with the rotating shaft, the contact portion between the workpiece to be processed and the rotating drum that has a predetermined interval between the stirring blades We propose a rotary kiln that is narrower than the minimum length.

  Furthermore, in a rotary kiln in which a plurality of stirring blades are installed on the inner surface of a rotating drum that rotates in a horizontal state in parallel to the rotation axis, a plurality of stirring blades are arranged in the circumferential direction of the rotating drum and from the inlet to the outlet of the rotating drum. Provide a plurality of sheets, the interval between the circumferential stirring blades is set smaller than the predetermined minimum length of the contact portion between the workpiece and the rotating drum, and the number of circumferential stirring blades is set at the inlet side of the rotating drum. We propose a rotary kiln with a small number of exits.

  Hereinafter, although the Example which applied this invention to the external heating type rotary kiln is described using drawing, this invention is not limited to the external heating type rotary kiln described below.

  FIG. 1 is a schematic configuration diagram showing an overall image of a rotary kiln according to the present invention. The rotary kiln of the present embodiment includes a rotating drum 1, a heated gas jacket 2 that is a flow path of the heated gas 54, a screw feeder 3 for supplying the workpiece 51, a solid product 52 generated from the workpiece 51, and It consists of an outlet foot 4 for separating the gaseous product 53 and a stirring blade 5 installed on a rotating drum. The rotating drum 1 has a cylindrical shape and rotates in a horizontal state around the rotation axis. A screw feeder 3 is connected to one end of the rotating drum 1, and the other end is inserted into the outlet foot 4. A heated gas jacket 2 is disposed on the outer periphery of the rotating drum 1.

  The stirring blade 5 is formed by connecting plates having different heights into a single plate shape, and the height of the rotary drum at the inlet side is high, and the height gradually decreases toward the outlet side. Yes. The height may be lowered continuously rather than stepwise. The stirring blades 5 are provided in parallel with the rotating shaft of the rotating drum 1, and eight are provided at equal intervals in the circumferential direction of the rotating drum.

  FIG. 2 shows a state in which the height of the stirring blade and the layer height of the workpiece change from the inlet to the outlet of the rotating drum. It is almost equal to the layer height of the workpiece.

  When the rotary kiln is used in a drying process, for example, the closer to the outlet of the rotating drum, the lower the moisture content of the workpiece and the apparent specific gravity. Moreover, when using it for thermal decomposition processes, such as a waste and a food basket, carbonization progresses, and a to-be-processed object pulverizes, so that the exit of a rotating drum is approached. As a result, the object to be processed is more likely to scatter as it goes downstream. However, if the height of the stirring blade on the outlet side is lowered as in the present embodiment, the amount of the object to be processed lifted by the stirring blade is reduced, and at the same time, the drop height difference is reduced. Thereby, scattering of a to-be-processed object is suppressed.

In the case where the stirring blades are provided substantially perpendicularly to the inner surface of the rotating drum as in this embodiment, the rotating drum diameter is D (m), the rotating drum length is L (m), and the rotational speed of the rotating drum is Is N (rpm), the supply speed of the workpiece is F (kg / min), the bulk density of the workpiece is ρ (kg / m ³ ), and the repose angle of the workpiece is β (°). The layer height h (m) of the object to be processed can be obtained by the following equation.

h = D / (0.74 / F × D ⁴ × N × cot β × ρ / L) ^{1 / 2.05}
By replacing the length L of the rotating drum with the distance from the entrance of the rotating drum, the layer height h at each position can also be obtained.

  FIG. 3 shows the improvement rate of the heat transfer coefficient k for each region of the rotating drum when the stirring blade according to the present embodiment is provided on the basis of the case where there is no stirring blade. For comparison, FIG. 16 shows an improvement rate of the heat transfer coefficient k when a stirring blade having a constant height is provided on the basis of the case where there is no stirring blade. Here, the heat transfer coefficient k is obtained by the following equation, where Q is the amount of heat applied to the rotating drum, A is the area of the heating part of the rotating drum, and ΔT is the temperature difference between the inlet and outlet of the rotating drum. It is done. Further, the temperature difference ΔT is set such that the inner wall temperature of the rotary drum at the inlet is Tw1, the inner wall temperature of the rotary drum at the outlet is Tw2, the temperature of the workpiece at the inlet is Tm1, and the temperature of the workpiece at the outlet is Tm2. Sometimes it is calculated by the following formula.

k = Q / A × ΔT
ΔT = ln {(Tw1−Tm1) − (Tw2−Tm2) / [(Tw1−Tm1) / (Tw2−Tm2)]}
3 and 16, if the heat transfer coefficient when the stirring blade is installed is, for example, 15% higher than the heat transfer coefficient when the stirring blade is not installed, the improvement rate of the heat transfer coefficient k is It is expressed as 15%. In the case of FIG. 16, the improvement rate of the heat transfer coefficient is as high as about 15% near the inlet of the rotating drum, but decreases toward the drum outlet, about 5% near the middle and about 2% near the outlet. Yes. On the other hand, in the present invention, as shown in FIG. 3, the heat transfer coefficient is improved in all regions of the rotating drum, about 15% near the inlet and middle of the rotating drum, and about 17% near the outlet. It was confirmed that this was done efficiently.

  In this embodiment, the angle formed between the surface of the stirring blade facing the drum rotation direction and the inner surface of the rotating drum changes between the drum inlet side and the outlet side, and the height of the stirring blade is the drum inlet side. The case where it is high and low on the exit side will be described. 4A and 4B are cross-sectional views of the rotating drum, where FIG. 4A is a cross-sectional view near the inlet, and FIG. 4B is a cross-sectional view near the outlet. By increasing the angle formed by the stirring blade and the inner surface of the rotating drum, the amount of the object to be processed that is lifted by the stirring blade is reduced, and the drop height difference is reduced. Therefore, on the inlet side where the processing amount of the object to be processed is large and the layer height is high, the height of the stirring blade is increased and the angle θ is decreased, and on the outlet side, the height of the stirring blade is decreased and the angle θ is increased. It is desirable to do. Thereby, scattering of a to-be-processed object can further be suppressed.

  The case where a stirring blade is comprised with a heat exchanger tube is demonstrated. 5A and 5B are cross-sectional views of the rotary drum, where FIG. 5A shows a cross-sectional view near the entrance of the rotary drum, and FIG. 5B shows a cross-sectional view near the exit. The stirring blade is composed of a plurality of heat transfer tubes 6 through which a heat medium is arranged in the direction of the rotation axis of the rotary drum, and fins 7 are provided on the outer periphery of the heat transfer tubes. The length of the fin 7 is long in the vicinity of the inlet of the rotating drum and is shorter toward the outlet. The number of heat transfer tubes is the same in the vicinity of the inlet and the outlet of the rotating drum, but the height of the stirring blade in the direction of the rotating shaft is adjusted by changing the length of the fin. According to the present embodiment, since the heat transfer area increases, the heating efficiency can be greatly improved.

  In the present embodiment, a case will be described in which a plurality of stirring blades are provided in the inner circumferential direction of the rotating drum, and the stirring blades are constituted by a single long plate continuous from the inlet to the outlet of the rotating drum. FIG. 6 shows the overall structure of the rotary kiln, and FIG. 7 shows a developed view of the inner surface of the rotary drum. FIG. 8 is a sectional view taken along line AA in FIG. FIG. 9 shows the distance between the stirring blades obtained by dividing the circumference of the rotating drum by the number of stirring blades and the length of the contact portion between the workpiece and the rotating drum from the inlet to the outlet of the rotating drum. This area is shown in FIG. FIG. 10 shows a contact state between the workpiece near the outlet of the rotating drum and the stirring blade.

  In the present embodiment, as shown in FIG. 7, the stirring blade is composed of a single long plate. As shown in FIG. 8, a plurality of stirring blades are radially arranged around the rotating shaft of the rotating drum at substantially equal intervals.

  The rotary kiln tends to have a large amount of processed material at the inlet portion of the rotating drum and less at the outlet portion, and the contact length of the processed material contacting the inner surface of the rotating drum rotates as shown in FIG. It is longer near the drum entrance and shorter near the exit. If the interval between the stirring blades arranged in the circumferential direction of the rotating drum is smaller than the length of the portion where the workpiece is in contact with the inner surface of the rotating drum as shown in FIG. Two or more stirring blades always come into contact with the object, so that the object can be prevented from slipping and mixing can be promoted.

  FIG. 11 shows the improvement rate of the heat transfer coefficient k of the rotary kiln according to the present embodiment with reference to the heat transfer coefficient k when no stirring blade is installed. This area is shown in FIG. The improvement rate of the heat transfer coefficient was higher near the middle and near the outlet than the inlet of the rotating drum.

  In the present embodiment, the case where the height of the stirring blade is made constant from the inlet to the outlet of the rotating drum has been described, but when the height of the stirring blade on the inlet side is increased and the height of the stirring blade on the outlet side is decreased. It goes without saying that can also be applied.

  The case where the number of stirring blades is small on the inlet side of the rotating drum and increased on the outlet side will be described. FIG. 12 is a schematic view showing the overall configuration of the rotary kiln, and FIG. 13 is a development view of the inner surface of the rotary drum. FIG. 14 shows the distance between the stirring blades in the drum circumferential direction and the length of the arc of the portion where the workpiece contacts the inner surface of the rotating drum in each region from the inlet to the outlet of the rotating drum. FIG. 15 shows the improvement rate of the heat transfer coefficient k according to this example when the case where no stirring blade is installed is used as a reference.

  In this embodiment, a short stirring blade is arranged from the inlet to the outlet of the rotating drum. The closer to the inlet, the fewer the number of stirring blades. As shown in FIG. 14, the distance between the stirring blades is smaller than the length of the arc in which the workpiece and the rotating drum are in contact with each other in the entire area of the rotating drum, and it can be seen that there is no portion where slip occurs. Further, since the number of stirring blades is reduced as the position is closer to the entrance of the rotating drum, it is possible to avoid blockage and catching of the workpiece at the entrance. For this reason, it is possible to set the height of the stirring blade as a whole high and promote mixing. Also in this example, as shown in FIG. 15, the improvement rate of the heat transfer coefficient was improved in the entire region of the rotating drum.

  Needless to say, this embodiment can be applied when the height of the stirring blade on the inlet side is high and the height of the stirring blade on the outlet side is low.

The schematic block diagram of the rotary kiln by the Example of this invention. The rotary kiln of FIG. 1 is the figure which showed the space | interval of the stirring blade of the circumferential direction, and the circular arc length of the contact part of a to-be-processed object and a rotating drum over the range from a rotating drum entrance to an exit. The figure which showed a mode that the heat transfer coefficient improvement rate of the rotary kiln of FIG. 1 changed toward the exit from an entrance of a rotating drum. Sectional drawing of the rotary kiln provided with the stirring blade inclined. Sectional drawing of the rotary kiln which comprised the stirring blade with the heat exchanger tube and the fin. The schematic block diagram of the rotary kiln by another Example. FIG. 7 is a development view of the inner surface of the rotary drum of the rotary kiln shown in FIG. 6. AA line sectional view of the rotary kiln shown in FIG. The figure which showed the space | interval of the stirring blade of the rotary kiln shown in FIG. 6, and the circular arc length of the contact part of a to-be-processed object and a rotating drum in the range from the entrance of a rotating drum to an exit. The figure which showed typically the state which a stirring blade and a to-be-processed object contact about the rotary kiln shown in FIG. The figure which showed a mode that the heat transfer coefficient improvement rate of the rotary kiln shown in FIG. 6 changed toward the exit from an entrance of a rotating drum. Schematic which shows another Example of the rotary kiln by this invention. FIG. 13 is a development view of the inner surface of the rotary drum of the rotary kiln shown in FIG. 12. The figure which showed a mode that the space | interval of the stirring blade in the rotary kiln shown in FIG. 12, and the circular arc length of the contact part of a to-be-processed object and a rotating drum change toward the exit from an entrance of a rotating drum. The figure which showed a mode that the heat transfer coefficient improvement rate of the rotary kiln shown in FIG. 12 changed toward the exit from an entrance of a rotating drum. The figure which showed the heat-transfer coefficient improvement rate at the time of providing the stirring blade of fixed height on the basis of the case where a stirring blade is not provided about the entrance of a rotating drum, an intermediate position, and the exit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Rotary drum, 2 ... Heated gas jacket, 3 ... Screw feeder, 4 ... Outlet foot, 5 ... Stirrer blade, 6 ... Heat transfer tube, 7 ... Fin, 51 ... To-be-processed object, 52 ... Solid product, 53 ... Gaseous product, 54 ... heated gas.

Claims (12)

  In a rotary kiln in which a stirring blade is installed on the inner surface of a rotating drum that rotates in a horizontal state in parallel or substantially parallel to the rotating shaft, the height of the stirring blade is continuously or stepwise from the inlet to the outlet of the rotating drum. The rotary kiln is characterized by a low height.   The rotary kiln according to claim 1, wherein a plurality of the stirring blades are provided in a circumferential direction of the rotating drum.   2. The number of the stirring blades in the circumferential direction of the rotating drum according to claim 1, wherein a plurality of the stirring blades are provided in the circumferential direction of the rotating drum and from the inlet to the outlet of the rotating drum. Is a rotary kiln characterized by having a small amount on the inlet side of the rotating drum and a large amount on the outlet side.   2. The rotary kiln according to claim 1, wherein the height of the stirring blade is lower than a minimum layer height of the set workpiece.   5. The rotary kiln according to claim 4, wherein the height of the stirring blade is 0.5 times or more and less than 1 time with respect to the minimum layer height of the set workpiece.   In Claim 1, the stirring blade is inclined so that the angle between the surface of the front stirring blade facing the drum rotation direction and the inner surface of the rotating drum is small on the inlet side of the rotating drum and large on the outlet side. Rotary kiln characterized by being provided.   In Claim 1, the said stirring blade is comprised by the several heat exchanger tube arrange | positioned in the rotating shaft direction of the said rotating drum, it has a fin in the outer periphery of the said heat exchanger tube, and the inside of the said heat exchanger tube is a heat medium. The rotary kiln is characterized in that the fin is long on the inlet side of the rotating drum and short on the outlet side.   The rotary kiln according to claim 2, wherein a distance between the stirring blades is narrower than a predetermined minimum length of a contact portion between the workpiece and the rotary drum.   In Claim 1, the said stirring blade is provided with two or more sheets in the circumferential direction of the said rotating drum and toward the exit from the inlet of the said rotating drum, and the space | interval of the stirring blade in the circumferential direction of the said rotating drum is preset. A rotary kiln characterized by being narrower than the minimum length of the contact portion between the workpiece to be processed and the rotating drum, wherein the number of stirring blades in the circumferential direction of the rotating drum is small on the inlet side and large on the outlet side .   In a rotary kiln in which stirring blades are installed on the inner surface of a rotating drum that rotates in a horizontal state in parallel or substantially in parallel with a rotating shaft, a plurality of the stirring blades are provided in the circumferential direction of the rotating drum and from the inlet to the outlet of the rotating drum. A rotary kiln comprising a plurality of the stirring blades in the circumferential direction, wherein the number of the stirring blades in the circumferential direction is small on the inlet side of the rotating drum and increased on the outlet side.   In a rotary kiln in which a plurality of stirring blades are installed in the circumferential direction of the inner surface of a rotating drum that rotates in a horizontal state in parallel or substantially parallel to the rotating shaft, the interval between the stirring blades is set in advance between the workpiece to be processed and the rotating drum. A rotary kiln characterized by being smaller than the minimum length of the contact portion.   In a rotary kiln in which a plurality of stirring blades are installed on the inner surface of a rotating drum that rotates in a horizontal state in parallel or substantially in parallel with a rotating shaft, a plurality of the stirring blades are disposed in the circumferential direction of the rotating drum and are exited from the inlet of the rotating drum. A plurality of the agitating blades in the circumferential direction are made narrower than a predetermined minimum length of the contact portion between the workpiece and the rotating drum, and the number of the agitating blades in the circumferential direction is set to the rotating drum. The rotary kiln is characterized by being small on the entrance side and more on the exit side.

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