JP2005009712A - Rotary kiln and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotary kiln and its operation method for stably obtaining a uniform foam by rapidly and uniformly heating a heated material into a certain temperature range. <P>SOLUTION: This rotary kiln comprises a shell 4 having a supply port 2 for the heated material at one end and a discharge port 3 for discharging the heated material, at the other end, and rotated around an axis; and a heating chamber 5 provided with outside heating burners 6 for heating the outside part of the shell. The rotary kiln is provided with an inside heating burner B for heating the inside of the shell. In the rotary kiln of such constitution, the combustion amount of the inside heating burner is made constant, and the combustion amount of the outside heating burners is controlled by measuring the outer surface temperature of the shell. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rotary kiln. More specifically, the present invention relates to a rotary kiln suitable for foaming a foamed material that is foamed by heating and an operation method thereof.
[0002]
[Prior art]
A rotary kiln is an apparatus that performs various heat treatments such as drying, firing, and dry distillation on a heated object to be heated supplied in a rotating cylindrical shell. Since the shell is provided in a state slightly inclined from the horizontal, the object to be heated is sequentially moved in the axial direction along the rotation of the shell and subjected to a desired heat treatment.
[0003]
In such a rotary kiln, an externally heated rotary kiln that heats the object to be heated indirectly by heating the outer portion of the shell, and an internal heat type that directly heats the object to be heated by heating the inside of the shell There is a rotary kiln.
[0004]
The externally heated rotary kiln does not cause temperature unevenness due to direct contact of flame or hot air with the object to be heated, so that the object to be heated can be subjected to uniform heat treatment. There are advantages such as being able to decide freely regardless of the type of heating means and combustion gas. However, such an externally heated rotary kiln performs heat treatment of an object to be heated only by conduction heat from the shell, and therefore has a problem that thermal efficiency is lower than that of an internally heated rotary kiln.
[0005]
On the other hand, the internal heating type rotary kiln has a very high thermal efficiency because the heating burner can be installed near the supply port or the discharge port of the shell to directly heat the object to be heated. However, since the high-temperature combustion gas from the burner directly contacts the object to be heated, there is a drawback that temperature unevenness is likely to occur in the object to be heated.
[0006]
By the way, foams made from natural glassy minerals or waste glass as a raw material due to their light weight and water absorption properties are used as building materials or horticultural materials that are excellent in reducing the weight of aluminum and plastic, or having excellent heat insulation properties. Widely used.
[0007]
As the raw material of the foam, for example, natural glassy minerals such as obsidian, pearlite and pine sebite, and waste glass such as commonly used window glass are known.
[0008]
Natural vitreous minerals themselves contain water, and when the minerals begin to soften by heating, the contained moisture becomes vapor and the volume increases, resulting in a so-called foaming phenomenon. In the case of artificial glass such as waste glass, a foam can be obtained by adding a foaming agent such as SiN or SiC to the raw material powder and granulating and heating as necessary.
[0009]
As a manufacturing method of these foams, a method of heating at 900 to 1000 ° C. using an externally heated rotary kiln, an electric furnace or a hot air furnace has been tried, but seizure occurs in the apparatus, There were problems such as variations in quality due to changes in heating time and heating temperature.
[0010]
More specifically, for example, when the heating temperature of the object to be heated is low, foaming is incomplete, so that only a foam having a high specific gravity and a small particle diameter can be obtained. If the temperature is too high, it will be excessively foamed, resulting in a foam with a small specific gravity and a weak particle size, and when foaming proceeds at a higher temperature, the foams will fuse together and the particle shape will be If the heating rate is slow and the temperature of the object to be heated is slow, moisture will evaporate before the glass is softened and foaming will not be possible. Temperature management was a very important issue.
[0011]
In particular, this tendency is remarkable in nacre, and rapid heating and strict temperature control for adjusting the heating temperature to a narrow range are required to stably obtain a desired foam.
[0012]
Taking the foaming treatment of pearlite as an example, for a certain product, when the maximum heating temperature is 1030 ° C., the resulting foam has a bulk specific gravity of 0.20 g / cm ^2. The specific gravity was 0.22 g / cm ² , and 0.35 g / cm ^{2 at} 900 ° C. Since the control range of the bulk specific gravity of this product was 0.18 to 0.22 g / cm ² , in this case, the heating temperature must be controlled within ± 10 ° C. Further, in order to keep the entire object to be heated within this control range and obtain a homogeneous product, the entire object to be heated must be rapidly and uniformly heated.
[0013]
However, it has been difficult to obtain such a homogeneous foam in a rotary kiln.
[0014]
[Problems to be solved by the invention]
This invention is made | formed in view of the above situations, and the subject of this invention is to obtain a stable homogeneous foam by heating to-be-heated material to a certain temperature range rapidly and uniformly. It is to provide a rotary kiln that can be operated and its operation method.
[0015]
[Means for Solving the Problems]
In the externally heated rotary kiln, the object to be heated is heated on the surface portion of the shell inner wall. Therefore, in the fluidized bed M of the heated object supplied as shown in FIG. 3, the portion a that contacts the shell inner wall surface of the fluidized bed M is rapidly heated, but the surface portion b of the fluidized bed M has a shell. Compared with the part a which contacted the inner wall, the heating rate becomes slower. Therefore, the foamed state of the heated object in the entire fluidized bed varies, and a foam having uniform properties cannot be obtained. Therefore, in the rotary kiln according to the present invention, in addition to heating from the outer part of the shell, the main purpose is to provide an internal heat burner that directly heats the object to be heated toward the inside of the shell.
[0016]
In other words, the rotary kiln of the present invention has a supply port for an object to be heated at one end and a discharge port for discharging the object to be heated at the other end, and a shell that rotates around an axis and an outer portion that heats the outer part of the shell. A rotary kiln comprising a heating chamber provided with a heat burner is characterized by comprising an internal heat burner for heating the inside of the shell.
[0017]
Moreover, it is preferable to have the stirring blade erected on the inner peripheral surface of the shell in the concentric direction. The object to be heated moves toward the discharge port while being agitated by the rotation of the shell, but the object to be heated can be more efficiently agitated by having a stirring blade standing on the inner wall of the shell. The entire object can be heated evenly and rapidly.
[0018]
In the rotary kiln of the present invention, the external heat burner that heats the outer portion of the shell is preferably a burner that includes a heat storage portion that preheats the combustion air of the burner.
[0019]
By using such a heat storage burner, the combustion efficiency can be increased and a great energy saving can be realized.
[0020]
The rotary kiln operating method of the present invention has a supply port for an object to be heated at one end and a discharge port for discharging the object to be heated at the other end, and heats a shell rotating around an axis and an outer portion of the shell. In an operation method of a rotary kiln having a heating chamber having an external heat burner and an internal heat burner for heating the inside of the shell, a combustion amount of the internal heat burner is made constant and an outer surface temperature of the shell is measured. Thus, the combustion amount of the external heat burner is controlled.
[0021]
By adopting such an operation method, the temperature inside the shell can be accurately controlled to the target temperature, and a homogeneous foam can be obtained throughout.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
[0023]
FIG. 1 is a schematic longitudinal sectional view of a rotary kiln according to the present invention, and FIG. 2 is a schematic side view of a part AA of FIG.
[0024]
The rotary kiln 1 includes a shell 4 made of stainless steel or the like having a supply port 2 to be heated and a discharge port 3 for a heated object, and an external heat burner for heating the outer surface of the shell 4. 6 and a heating chamber 5 having 6.
[0025]
The shell 4 is disposed so as to penetrate the heating chamber 5 in the length direction. In the vicinity of both ends of the shell 4, annular tires 7 and 7 are integrally attached to the outer peripheral surface of the shell 4, and the shell 4 is rotatably supported by the receiving rollers 8 and 8 at these portions. Rotation means (not shown) can gently rotate around the axis. The axis of the shell 4 is installed with an inclination (gradient is 1/100 to 3/100) so that the discharge side is slightly lowered.
[0026]
The heating chamber 5 is formed of a steel plate outer shell 9 and a refractory heat insulating material 10 and is fixed on a base frame (not shown). The heating chamber 5 is provided with a burner 6 for external heat and an exhaust port 11 for combustion gas. The burner 6 is installed in the lower part of the shell 4 which penetrates in consideration of thermal efficiency. Combustion gas generated inside the heating chamber 5 is sent from a combustion gas exhaust port 11 to a chimney (not shown) and discharged outside the furnace.
[0027]
The outer peripheral surface of the shell 4 and the heating chamber 5 are provided with a slight gap and are almost sealed with a sealing material (not shown) to prevent heat dissipation by the external heat burner 6. In addition, the temperature in the heating chamber 5 is automatically controlled so as to become a set temperature by an automatic controller (not shown) connected to the thermometer 12 (FIG. 2).
[0028]
The supply port 2 of the shell 4 is provided with a supply device 13 for supplying an object to be heated, and the object to be heated can be put into the shell 4 through the supply device 13.
[0029]
Further, a hood 14 is attached to the discharge port 3 of the shell 4 to prevent intrusion of outside air into the shell. The shell 4 and the hood 14 are provided with a slight clearance with a sealing material (not shown). It is almost sealed. A chute for taking out an object to be heated discharged from the discharge port 3 of the shell 4 is provided at the lower portion of the hood 14. A rotary valve 15 is provided in the middle of the chute to prevent intrusion of outside air.
[0030]
On the inner peripheral surface of the shell 4, a plurality of stirring blades 16 are erected in the direction of the center of the shell 4. By providing such a stirring blade, the object to be heated can be more efficiently stirred, and the object to be heated can be uniformly and rapidly heated. In addition, there is no limitation in particular in the shape of a stirring blade, a number of sheets, a standing position, etc., In consideration of stirring efficiency, it can provide suitably in the range which does not prevent the movement of a to-be-heated material. The stirring blade is preferably formed of a heat resistant metal such as stainless steel.
[0031]
In the rotary kiln in the present embodiment, an internal heat burner B that directly heats an object to be heated toward the inside of the shell 4 is provided in the vicinity of the supply port 2 of the shell 4. The internal heat burner B preferably uses a gas such as LPG or a petroleum-based fuel such as light oil as a heat source, and is installed so that the flame of the burner is parallel to the axis of the shell or slightly downward from the parallel. It is desirable to install it so that the object to be heated is directly exposed to flame. The combustion gas generated by the heating burner B passes through the exhaust port 3 of the shell 4, passes through the exhaust port 17 of the hood 14, and is discharged out of the kiln from a chimney (not shown).
[0032]
In the rotary kiln of the present invention, the external heat burner 6 that heats the outer portion of the shell 4 is preferably a heat storage burner including a heat storage section that preheats the combustion air of the burner. For example, the burner itself collects the exhaust gas burned in the burner, the heat storage chamber is stored by the exhaust temperature, and the combustion air passes through the heat storage chamber and burns as preheated air by switching the damper incorporated in the burner after a predetermined time A regenerative burner that can be used. In the burner having such a mechanism, by repeating the movement of the damper at short time intervals, continuous heat storage combustion becomes possible and significant energy saving can be realized. Adopting such a regenerative burner as the internal heat burner B is not suitable because the atmosphere gas in the shell contains a lot of dust. However, it can be suitably employed as the external heat burner 6 of the heating chamber 5 having a clean combustion atmosphere.
[0033]
Next, the operation method of the rotary kiln which consists of the above structure is demonstrated.
[0034]
First, a certain amount of an object to be heated is supplied from the supply device 13 into the rotating shell 4. Since the shell 4 is installed with a slight inclination toward the discharge port 3, the object to be heated becomes a fluidized bed and gradually flows to the heating unit as the shell 4 rotates. Since the outer peripheral surface of the shell 4 is heated, the portion in contact with the inner wall surface of the fluidized bed is rapidly heated to a predetermined temperature. On the other hand, the surface portion of the fluidized bed is rapidly heated by the flame F of the heating burner B. The fluidized bed is not stirred by the rotation of the shell having the stirring blades, but is sent to the discharge port 3 through the shell and is discharged from the discharge port 3 to the chute of the hood 14.
[0035]
Here, it is desirable to control the heating temperature of the object to be heated by the following method.
[0036]
Controlling the temperature of the internal heat burner B means controlling the amount of combustion of the internal heat burner. Thereby, since the flame temperature of the internal heat burner fluctuates, the temperature of the combustion gas filled in the shell and the amount of generated combustion gas change. For this reason, the temperature distribution in the shell fluctuates, and stable heating conditions cannot be maintained. As a result, the object to be heated cannot be heated uniformly. Therefore, in the present embodiment, the combustion amount of the internal heat burner B is set to a constant amount within a certain range, and the temperature control is performed to control the external heat burner 6 of the heating chamber 5.
[0037]
The temperature control of the heating chamber 5 is normally performed by the atmospheric temperature of the heating chamber, but at this atmospheric temperature, the control delay is larger than the temperature change in the shell. Therefore, it is desirable to control by the temperature change of the outer surface of the shell. If the combustion amount of the external heat burner is controlled by the temperature change of the outer surface, this control delay can be reduced. In the present embodiment, a side hot hole 18 (FIG. 2) is drilled at an appropriate location on the furnace wall of the heating chamber 5, and the outer surface temperature of the shell 4 is measured by the infrared radiation thermometer 12, so that the heating burner 6 Combustion control is performed. The above temperature control is desirably performed at the highest temperature portion of the shell. A plurality of thermometers may be provided corresponding to appropriate positions in the longitudinal direction of the shell to control the temperature distribution in the longitudinal direction of the shell.
[0038]
It is desirable that the combustion amount of the internal combustion burner be constant as described above when the processing amount of the workpiece (the amount of raw material input) is constant. However, when increasing or decreasing the processing amount, it is desirable to set the combustion amount of the internal combustion burner in proportion to the processing amount.
[0039]
[Test example]
(Test Example 1)
Using the rotary kiln shown in FIG. 1, a foam test was performed using pearlite as an object to be heated.
[0040]
The dimensions of the main part of the rotary kiln were: shell inner diameter: 300 mm, effective length of the shell in the heating furnace: 2.5 m, shell inclination: 4 °, and shell rotation speed was 3 rpm.
[0041]
The pearlite that is the object to be heated was a pulverized powder having a particle size of 1 to 3 mm, and the moisture content was approximately 2% or less by preheating.
[0042]
The nacre was put into the shell at a constant supply rate of 54 kg / h. The combustion amount of the internal heat burner was constant at 43,000 kcal / h, and the combustion amount of the external heat burner was controlled so that the outer surface temperature of the shell was constant at 1030 ° C. A normal type burner was used for both the internal heat burner and the external heat burner. The average combustion amount of the external heat burner was 81,000 kcal / h.
[0043]
By the above method, foaming was applied to nacre, and a foam having an average bulk specific gravity of 0.20 g / cm ² was obtained. Since the target value of the bulk specific gravity of this foam was 0.18 to 0.22 g / cm ² , the target value could be satisfied.
(Test Example 2)
In the same manner as in Test Example 1, the foaming test of pearlite was conducted with the rotary kiln shown in FIG.
[0044]
In this test, a regenerative burner was used as the external heat burner instead of the normal type burner.
[0045]
As in Test Example 1, nacre is introduced into the shell at a constant supply rate of 54 kg / h, the combustion amount of the internal heat burner is constant at 43,000 kcal / h, and the outer surface temperature of the shell is constant at 1030 ° C. The combustion amount of the external heat burner was controlled so that
[0046]
By the above method, foaming was applied to nacre, and a foam having an average bulk specific gravity of 0.20 g / cm ² was obtained. Since the target value of the bulk specific gravity of this foam was 0.18 to 0.22 g / cm ² , the target value could be satisfied.
[0047]
The average combustion amount of the external heat burner was 46,000 kcal / h, which was about 43% energy saving compared with the combustion amount of the normal type burner of Test Example 1.
[0048]
【The invention's effect】
In the rotary kiln of the present invention, the internal heating burner for directly heating the object to be heated is attached to the externally heated rotary kiln, so that the object to be heated can be uniformly and rapidly heated. Therefore, natural glassy minerals such as nacre and obsidian, and foamable raw materials such as artificial glass powder can be uniformly foamed in a desired shape, which is effective for stabilizing the quality of the foam.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view showing a main configuration of a rotary kiln of the present invention.
FIG. 2 is a schematic side view including a partial AA cross section of FIG. 1;
FIG. 3 is a schematic cross-sectional view of a shell for explaining a heated portion of a fluidized bed of an object to be heated.
[Explanation of symbols]
1: Rotary kiln 2: Supply port 3: Discharge port 4: Shell 5: Heating chamber 6: External heat burner 12: Thermometer 13: Supply device 16: Stirrer blade B: Internal heat burner F: Frame M: To be heated Fluidized bed a, b: heating section

Claims (4)

A heating port having a supply port for the heated object at one end and a discharge port for discharging the heated object at the other end, rotating around the axis, and an external heat burner for heating the outer portion of the shell In the rotary kiln
A rotary kiln comprising an internal heat burner for heating the inside of the shell. 2. The rotary kiln according to claim 1, wherein the shell has a stirring blade erected on an inner peripheral surface of the shell in a direction of a circle. The rotary kiln according to claim 1, wherein the external heat burner is a burner including a heat storage unit that preheats combustion air of the burner. A heating chamber having a supply port for the object to be heated at one end and a discharge port for discharging the object to be heated at the other end, rotating around the axis, and an external heat burner for heating the outer portion of the shell; In the operation method of the rotary kiln having an internal heat burner for heating the inside of the shell,
A method for operating a rotary kiln characterized by controlling the combustion amount of the external heat burner by measuring the outer surface temperature of the shell with the combustion amount of the internal heat burner being constant.

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