HK1114899B - External heating rotary kiln and its operating method - Google Patents

Description

External heating rotary kiln and operation method thereof

Technical Field

The present invention relates to an externally heated rotary kiln used as a carbonization furnace, a pyrolysis furnace, a heat treatment furnace or the like, and a method of operating the same.

Background

The externally heated rotary kiln includes an outer cylinder surrounding a rotary kiln (kiln inner cylinder) that rotates about an axis. The rotary kiln is heated from the outside by the heating gas caused to flow in the outer cylinder, so that the heat treatment is performed while the material to be treated is axially conveyed in the rotary kiln. The externally heating rotary kiln is also called an indirect heating rotary kiln because the rotary kiln is configured such that the heating gas does not contact the substance to be treated, and is widely used as a carbonization furnace or other furnaces such as a pyrolysis furnace, a heat treatment furnace, and a drying furnace.

Utilizing the above-described characteristics of the externally heated rotary kiln, studies have been made to thermally decompose organic waste, such as sewer sludge, into fuel. Specifically, organic waste is charged into an external rotary kiln and thermally decomposed in a low-oxygen atmosphere without mixing heating gas to recover pyrolysis gas and carbide, and the obtained fuel gas and solid fuel are utilized. In the case where the fuel gas is to be obtained, the heating temperature is set as high as possible to efficiently vaporize the organic substances. On the other hand, in the case where a solid fuel is to be obtained, it is necessary to complete thermal decomposition at a temperature lower than the gasification temperature so that combustible substances remain in the carbide. Therefore, temperature control in rotary kilns is critical.

As a method for controlling the temperature in the rotary kiln rotating around the shaft, the following methods have been proposed: a method in which a pipe is installed along the rotary kiln axis to control the output of a heating coil and the heating power of a heating gas combustion device based on the temperature detected by a temperature sensor installed in the pipe (see JP11-211040 a); and a method of controlling the amount of combustion air based on the temperature detected by a thermocouple provided at the outlet of the rotary kiln (see JP 2903045B). However, since the gas temperature in the rotary kiln is measured in any of these methods, the carbonization temperature of the processed substance is not necessarily displayed, and there is a fear that an error occurs due to a change in the balance of radiation and convection in the kiln or a substance adhering to the temperature sensor. In addition, the inlet properties of organic wastes including sewage sludge, such as the treated amount and water content, fluctuate so greatly that stable control of carbonization temperature is difficult to achieve.

Disclosure of Invention

The present invention has been made in view of the above-mentioned actual circumstances, and therefore it is an object of the present invention to provide an externally heated rotary kiln in which the temperature in the rotary kiln rotating about an axis can be accurately measured in association with (corresponding to) the temperature of a substance to be processed, whereby stable control of the heating temperature can be performed, and also to provide an operating method of the externally heated rotary kiln.

In order to solve the problems in the conventional art, the present invention provides an externally heated rotary kiln including a kiln inner cylinder rotating around an axis and an outer cylinder for causing a heating gas to flow around the kiln inner cylinder, the externally heated rotary kiln performing a heating process while a material to be treated is axially transported in the kiln inner cylinder, characterized in that: the kiln interior cylinder is rotatably supported on a movable side end portion and a fixed side end portion which are movable in the axial direction, and a device for measuring the axial thermal elongation of the kiln interior cylinder and a plurality of noncontact thermometers for measuring the shell temperatures at a plurality of positions in the axial direction of the kiln interior cylinder from the outer wall portion of the outer cylinder are provided.

In a preferred mode of the present invention, the thermal elongation measuring means includes an integral thermal elongation measuring means for measuring an integral thermal elongation in an axial direction of the kiln interior cylinder. Further, the thermal elongation measuring device includes at least one partial thermal elongation measuring device for measuring thermal elongation in an intermediate portion in the kiln inner cylinder axial direction from the outer cylinder peripheral wall portion.

Further, as an operation method of the above-described externally heated rotary kiln, the present invention uses the following operation method: in the case where the difference between the transition shell temperature obtained by dividing the thermal elongation obtained from the measurement value of the thermal elongation measuring device by the linear expansion coefficient of the material of the kiln inner cylinder and the average shell temperature obtained from the measurement value of the noncontact thermometer becomes not less than a predetermined value, compressed air is injected onto the outer surface of the kiln inner cylinder to remove dust adhering to the outer surface of the kiln inner cylinder.

In addition, as an operation method of the externally heating rotary kiln, the present invention uses the following operation method: in the case where the difference between the transition shell temperature obtained by dividing the thermal elongation obtained from the measurement value of the thermal elongation measuring device by the linear expansion coefficient of the material of the kiln interior cylinder and the average shell temperature obtained from the measurement value of the contact thermometer becomes not less than a predetermined value, or in the case where this state continues for a predetermined time, a signal for prompting maintenance of the kiln interior cylinder is generated.

Further, the present invention is an operation method of an externally heated rotary kiln in which an amount of a heating gas flowing in an external cylinder is increased or decreased based on an average shell temperature obtained from a measurement value of a non-contact thermometer, so that the average shell temperature is maintained at a predetermined temperature region, characterized in that: in the case where a state where the difference between the transition shell temperature and the average shell temperature, which is obtained by dividing the thermal elongation obtained from the measurement value of the thermal elongation measuring device by the linear expansion coefficient of the material of the kiln inner cylinder, is not less than the predetermined value for a predetermined time, the average shell temperature is calibrated according to the temperature difference, and the amount of the heating gas flowing in the outer cylinder is adjusted using the calibrated average shell temperature.

In another mode of the externally heated rotary kiln of the present invention, the outer cylinder is divided into a plurality of zones, a non-contact thermometer is provided in each zone, and a heating gas amount adjusting means for adjusting a heating gas flow rate and a temperature control means for controlling the heating gas amount adjusting means based on a measured value of the shell temperature in each zone are further provided. In a preferred mode, the thermal elongation measuring means includes a zone thermal elongation measuring means for measuring thermal elongation in each zone from the outer cylinder peripheral wall portion. In another preferred mode, the thermal elongation measuring device includes a heated gas distributing device for distributing the heated gas of one system to each section at a predetermined flow rate ratio, and a heated gas total flow rate adjusting device for adjusting a heated gas total flow rate of one system.

As another mode of the externally heated rotary kiln, the present invention provides an externally heated rotary kiln comprising a kiln inner cylinder rotating around an axis and an outer cylinder for causing a heated gas to flow around the kiln inner cylinder, the externally heated rotary kiln performing a heating process while a material to be treated is axially transported in the kiln inner cylinder, characterized in that: a plurality of noncontact thermometers for measuring the shell temperature from the outer wall portion of the outer cylinder at a plurality of positions in the axial direction of the kiln inner cylinder are provided.

As another mode of the externally heated rotary kiln, the present invention provides an externally heated rotary kiln comprising a kiln inner cylinder rotating around an axis and an outer cylinder for causing a heated gas to flow around the kiln inner cylinder, the externally heated rotary kiln performing a heating process while a material to be treated is axially transported in the kiln inner cylinder, characterized in that: the kiln interior cylinder is rotatably supported on a movable side end portion and a fixed side end portion which are movable in the axial direction, and a device for measuring the axial thermal elongation of the kiln interior cylinder is provided.

According to the externally heated rotary kiln of the present invention, a means for measuring the axial thermal elongation of the kiln inner cylinder and a plurality of non-contact thermometers for measuring the shell temperature at a plurality of positions in the axial direction of the kiln inner cylinder from the outer wall portion of the outer cylinder are provided. Therefore, by dividing the thermal elongation obtained from the measurement value of the thermal elongation measuring device by the linear expansion coefficient of the kiln interior cylinder material, an accurate kiln shell temperature (transition shell temperature) can be detected which excludes the measurement error caused by radiation and convection variations in the kiln and substances adhering to the kiln interior cylinder or the temperature sensor.

Further, since the kiln shell temperature is the temperature of a portion in direct contact with the substance to be treated in the kiln, the kiln shell temperature is closely related to the thermal decomposition temperature of the substance to be treated, and the heating state is well reflected. By performing temperature control based on such a kiln shell temperature, the heating temperature can be stably controlled. Therefore, in the case where the externally heated rotary kiln of the present invention is used as a carbonization furnace for providing fuel carbide from, for example, organic waste, the carbonization temperature can be maintained at an appropriate temperature according to the required residual proportion of combustible components, so that high-quality carbonized fuel can be stably obtained.

Also, the transition shell temperature of the thermally elongated base (base) is compared with the average shell temperature of the non-contact thermometer, whereby the adhesion of dust on the outer surface of the kiln inner cylinder and the corrosion state of the kiln inner cylinder can be detected. The following methods were used: an operation method in which compressed air is injected onto the outer surface of the kiln interior cylinder in a case where the temperature difference becomes not less than a predetermined value to remove dust adhering to the outer surface of the kiln interior cylinder; an operating method in which a signal for causing maintenance of the kiln interior shell is generated in the case where the temperature difference continues for a predetermined time; and a method in which the average shell temperature is calibrated by emissivity or the like according to the temperature difference, whereby the operation of the rotary kiln is continued as usual.

Further, in a manner that the outer cylinder is axially divided into a plurality of zones, a noncontact thermometer is provided in each zone, and a heating gas amount adjusting means for adjusting the flow rate of the heating gas in each zone and a temperature control means for controlling the heating gas amount adjusting means based on the measured value of the shell temperature in each zone are further provided, the shell temperature can be controlled so that the shell temperature is different in each zone based on the measured value of the shell temperature in each zone. Further, in addition to the temperature control in each region, since the calibration of the temperature region is controlled as compared with the average shell temperature of the noncontact thermometer for the conversion shell temperature of the thermal elongation base, more reliable temperature control can be performed, and thus a high-quality heating process can be realized.

Drawings

FIG. 1 is a sectional view showing the external appearance of an externally heated rotary kiln according to a first embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1;

FIG. 3 is a flowchart showing the control of the externally heated rotary kiln;

fig. 4 is a sectional view showing the external appearance of an externally heated rotary kiln according to a second embodiment of the present invention.

Detailed Description

The invention will now be described with reference to embodiments shown in the drawings.

Fig. 1 shows an example in which an externally heated rotary kiln 1 according to the present invention is used as a carbonization furnace. In fig. 1, the rotary kiln 1 includes an inner cylinder 11 (kiln shell) and an outer cylinder 12 (muffle) for causing a flow of heating gas around the inner cylinder 11. The inner cylinder 11 is supported on a movable-side end 13 and a fixed-side end 14 that are movable in the axial direction so as to be rotatable about an axis. In a movable side end portion 13 forming an inlet portion of the inner cylinder 11, a screw conveyor 10 for filling the substance to be treated is provided, and in a fixed side end portion 14 forming an outlet portion of the inner cylinder 11, a runner 15 for discharging the substance to be treated is provided.

More specifically, in the movable-side end portion 13 of the inner cylinder 11, an annular frame 131 that rotatably supports the inner cylinder 11 is provided, both sides of the annular frame 131 are rotatably supported at the upper end portion of a support member 132, and the support member 132 is swingably erected on the mounting surface 130. The distance between the support points of the support member 132 is set to be much larger than the thermal elongation of the kiln inner cylinder 11, described in detail later, and the up-and-down movement of the movable-side end portion 13 caused by the oscillation of the support member 132 is kept sufficiently small.

Further, the movable-side end 13 and the fixed-side end 14 of the inner cylinder 11 form an airtight seal between the rotating portion 11 and the non-rotating portions 13, 14. In addition, in the connecting portion between the movable-side end portion 13 and the auger 10, an expansion portion 133 is provided which absorbs the axial displacement of the movable-side end portion 13.

In the movable side end 13 of the inner cylinder 11, a measuring device 114 for measuring the thermal elongation of the entire heated portion, that is, the overall thermal elongation D of the inner cylinder 11, is provided. The measuring device 114 measures the displacement of the indicator P provided in the movable side end portion 13 of the inner cylinder 11 by using a dial fixed to the mounting portion of the rotary kiln 1. The measuring means 114 may be a position sensor for measuring the displacement of the indicator P by means of electromagnetic means or similar means, such as a differential transformer. Further, instead of the sensor for detecting continuous displacement, a probe for detecting that a preset predetermined displacement has been reached may be provided, or a laser rangefinder may be used to detect displacement.

On an inner wall portion of the inner cylinder 11, a plurality of fins (or spirals, not shown) inclined with respect to the circumferential direction are provided. The inner cylinder 11 is rotated at a predetermined rotation speed by a driving source (not shown), and the treated substance filled from the inlet side can be transferred to the outlet side through the inner cylinder while being heated. In some cases, instead of providing the fins, the inner cylinder 11 is supported to be rotatable about an axis slightly inclined with respect to the horizontal, whereby the treated material is transferred to the outlet side by the inclination and rotation of the inner cylinder 11.

The outer cylinder 12 is fixed to the mounting portion by a support member (not shown) in a state that allows the inner cylinder 11 to rotate and move in the axial direction and provides sealing between the outer cylinder 12 and the inner cylinder 11. The entire inner surface of the outer cylinder 12 is covered with an insulating material, and as shown in fig. 2, one side of the inner space (one side of the inner cylinder 11) is partitioned by a partition wall 120 over the entire length of the outer cylinder 12. The heating gas introduction part 121 is defined at a lower side of the partition part, the heating gas delivery part 122 is defined at an upper side of the partition part, and a heating gas flow passage capable of passing from the introduction part 121 to the delivery part 122 is formed. The introduction portion 121 of the outer cylinder 12 is connected to a supply pipe 20, and the heating gas is supplied from the heating gas combustion furnace 2 through the supply pipe 20. On the other hand, the conveying portion 122 of the outer cylinder 12 is connected to the heating gas amount adjusting damper 3 and the induced draft fan 4 via the heating gas conveying pipe 21.

In the upper part of the outer cylinder 12, three sight glasses 123 are provided to be axially separated from each other, each sight glass 123 being provided with a measuring device 124 for measuring a partial displacement, i.e. a partial thermal elongation D1, D2, D3 of the inner cylinder 11. The measuring means 124 is composed of a sight glass or a camera which is provided on the sight glass 123 of the outer cylinder 12 so as to face the indicators P1, P2, P3 provided on the outer circumferential surface of the inner cylinder 11, and measures the displacement of the indicators P1, P2, P3 relative to the measuring position by means of a dial provided in the field of view of the sight glass, or measures the displacement of the indicators P1, P2, P3 relative to the measuring position on the basis of the position on the image obtained by the camera.

Further, at a position adjacent to the conveying portion 122 in the upper portion of the outer cylinder 12, six windows 125 are provided so as to be axially separated from each other. Each window 125 is provided with a non-contact thermometer 126, the non-contact thermometer 126 facing the outer circumferential surface of the inner cylinder 11 rotating around the axis to measure the kiln shell temperatures T11 to T32 (Tn). As the noncontact thermometer 126, a radiation thermometer may be used. In this case, combustion gas containing soot and dust is used as the heating gas flowing in the outer cylinder 12 described later, so that an infrared wavelength of 3, 9 μm is preferably used as the response wavelength of the radiation thermometer, and an infrared wavelength of 3.9 μm is not affected by soot, dust and combustion gas. Further, the use of a two-color thermometer of a wavelength around 1.0 μm is also suitable because it is less affected by combustion gas, smoke and dust, and is less susceptible to emissivity (emissivity), even if the outer surface of the inner cylinder 11 corrodes.

Next, in the case where the rotary kiln 1 is used as a carbonization furnace for thermally decomposing organic waste such as sewage sludge into fuel, the operation method of the externally heating rotary kiln 1 is explained based on the above-described embodiment.

The heating gas is supplied from the heating gas combustion furnace 2 into the outer cylinder 12 of the rotary kiln 1 by the induced air action of the induced draft fan 4, so that the inner cylinder 11 located in the outer cylinder 12 is heated from the outer circumferential surface by the heating gas. The heating power of the heating gas combustion furnace 2 is kept constant, and the heating gas supplied from the heating gas combustion furnace 2 is kept at a predetermined high temperature. However, the amount of heat required for heating the inner cylinder 11 varies according to fluctuations in the load introduced into the kiln inner cylinder 11, such as variations in the characteristics of the material to be treated, the amount of treatment, and the moisture content.

Therefore, the opening degree of the heating gas amount damper 3 and the number of rotations of the induced draft fan 4 are controlled by the temperature control device 5 based on the control logic shown in fig. 3, so that the kiln shell temperatures T11 to T32(Tn) measured by the noncontact thermometers 126 provided at six positions in the axial direction are maintained in the predetermined temperature region.

In fig. 3, from among the kiln shell temperatures T11 to T32 at the six measurement positions, the temperature at any one position or the temperatures at a plurality of arbitrary positions (at the maximum six positions) is selected by the selector switch 50. In the case where the temperature of one place is selected, the selected kiln shell temperature is used as the process value, and in the case where the temperatures of a plurality of places are selected, the average value of the kiln shell temperatures obtained by the averaging process 51 is used as the process value, and the PID control is performed using the process value so that this process value PV is maintained at the set value SV.

In the PID control, a proportional control action (P control action) proportional to the difference between the kiln shell temperature process value PV and the set value SV affected by the delay process 52, an integral control action (I control action) proportional to the difference duration, and a derivative control action (D control action) proportional to the difference change speed are combined, the output of the PID control is inverted (reversed) (53) and used as an opening command, and the opening of the heating gas amount adjusting damper 3 is adjusted by the command. Further, the opening degree command of the heating gas amount damper 3 is affected by the delay processing 54, and is converted into a processing value in the rotation number control of the induced draft fan 4. PID control is performed such that this process value PV is maintained at the set value SV, the output of PID control is inverted (55) and used as a rotation number command of the induced draft fan 4 by which the rotation number of the induced draft fan 4 is adjusted.

Therefore, the basic temperature control is performed by the opening degree adjustment of the heating gas amount damper 3, the backup control is performed such that the opening degree of the heating gas amount damper 3 is maintained within a predetermined range, and by the backup control, stable control can be performed against the inlet load variation. Further, in the above-described control, the delay process 54 in the rotation number control of the induced draft fan 4 is set to be larger than the delay process 52 in the opening degree adjustment of the heating gas amount damper 3, whereby a short time temperature change can be realized only by the opening degree adjustment of the heating gas amount damper 3 without performing the rotation number control of the induced draft fan 4, and a long time temperature change is realized by the rotation number control of the induced draft fan 4. Therefore, more stable temperature control can be performed.

On the upstream side of the rotary kiln 1, whose temperature is controlled as described above, a dryer (not shown) is provided. The dried sludge 71, which has been agitated and dried by the dryer so that the moisture therein is controlled to a predetermined value, is introduced into the inner cylinder 11 of the rotary kiln 1 through the screw conveyor 10. The dried sludge 71 introduced into the inner drum 11 is heated in the course of being transferred toward the outside along with the rotation of the inner drum 11. Therefore, the remaining moisture is evaporated first, and the thermal decomposition of the organic component is performed after the moisture evaporation is completed. Therefore, when the pyrolysis gas is generated, the organic component is carbonized and discharged from the launder 15 as the carbide 72 (solid fuel) having a predetermined carbonization degree.

On the other hand, pyrolysis gas 73 generated by the thermal decomposition is introduced into a dry gas combustion furnace (not shown) through the flow groove 15 and is combusted together with auxiliary fuel or combustion gas heat-exchanged in the heating gas delivery pipe 21. Some of the combustion gas flows back to the heating gas combustion furnace 2, is combusted together with the auxiliary fuel in the heating gas combustion furnace 2, and is used to heat the rotary kiln 1. Since the heating gas is a combustion gas, it contains soot, dust and soot. If dust adheres to the outer circumferential surface of the inner cylinder 11, an error may occur between the temperatures T11 to T32(Tn) measured by the non-contact thermometer 126 and the actual kiln shell temperature.

Therefore, based on the measured value of the overall thermal elongation D obtained by the measuring device 114 provided in the movable-side end portion 13 of the inner cylinder 11, the average value of the kiln shell temperatures (transition shell temperatures) is determined, and this value is compared with the aforementioned average value (Tn) of the kiln shell temperatures T11 to T32, whereby the state of dust adhering to the kiln shell can be detected.

Let the overall thermal elongation of the kiln shell interior cylindrical body 11 be D (mm,. DELTA.L), the length of the heated portion of the kiln shell interior cylindrical body 11 be L (m), the linear expansion rate of the kiln material be α (mm/m. DEG C.), and the transition shell temperature Ts (. degree.C.) obtained by dividing the overall thermal elongation D/L (Δ L/L) by the linear expansion rate α of the kiln material be expressed as D (mm,. DELTA.L), and be expressed as

Ts＝D/αL

The difference between the transition shell temperature Ts and the average shell temperature Tn is expressed as

ΔT＝(D/αL)-Tn

And becomes not less than the set value, or in the case where this state continues for a predetermined time, it can be judged that dust is adhered to the kiln shell. In this case, the compressed gas may be injected from a nozzle 127 (fig. 2) provided on the outer cylinder 12 onto the outer surface of the kiln inner cylinder 11 to remove dust, or a signal for promoting maintenance of the inner cylinder 11 is generated.

Further, in the case where dust adheres to the kiln shell, although the average shell temperature Tn based on the non-contact thermometer 126 is lower than the transition shell temperature Ts based on the thermal elongation of the entire kiln inner shell 11, such difference does not immediately hinder the operation of the rotary kiln 1 itself. Therefore, in the case where the temperature difference Δ T becomes not less than the set value (or in the case where this state continues for a predetermined time), the average shell temperature is calibrated by the emissivity of the noncontact thermometer or the like based on the temperature difference Δ T, and the amount of the heating gas flowing into the outer cylinder 12 through the heating gas amount adjustment damper 3 or the induced draft fan 4 is controlled using the calibrated average shell temperature, whereby the operation of the rotary kiln 1 can be performed as usual.

Further, based on the measured value of the measuring device 124 for measuring the partial thermal elongations D1, D2, D3 of the inner cylinder 11, the kiln shell temperature of the portion (converted partial shell temperature) is determined, and this value is compared with the kiln shell temperatures T11 to T32 based on the non-contact thermometer 126 (in the example shown in fig. 1, the average value T1 of T11 and T12, the average value T2 of T21 and T22, and the average value T3 of T31 and T32), whereby the error of the measured value of each of the portions P1, P2, and P3 of the kiln inner cylinder 11 and the state of adhering dust can be detected. Among the partial thermal elongations D1 to D3, D2 and D3 must use values obtained by subtracting the partial thermal elongations D1, D2 on the fixed side end portion 14 side from the displacement actually measured.

In the case where the present invention is carried out in the rotary kiln 41 provided with a plurality of regions having different heating temperatures in the axial direction as shown in fig. 4, the above-described measuring device 124 for measuring the thermal elongations D1, D2, D3 of the inner cylinder 11 portion is advantageous. Hereinafter, a rotary kiln 41 of a second embodiment will be described with reference to this fig. 4. Since the rotary kiln 41 of the second embodiment has the same basic structure as the rotary kiln 1 of the first embodiment, reference numerals are applied to the same elements, and their explanations are omitted.

In fig. 4, with the rotary kiln 41, the interior of the outer cylinder 12 is divided into three zones Z1 to Z3 by partition walls 42 and 43, heating gas is distributively supplied from the heating gas combustion furnace 2, and heating gas amount regulating dampers 31 to 33 for regulating the flow rates of the heating gas in the zones Z1 to Z3 are also provided, respectively.

Further, with the rotary kiln 41, in each of the zones Z1 to Z3, one measuring device 124 for measuring partial thermal elongation (D1, D2, D3) and two non-contact thermometers 126(T11 to T32) are provided. The opening degree of each heating gas amount damper 31 to 33 is controlled based on the measured values T1, T2, T3 (the average value T1 of T11 and T12, the average value T2 of T21 and T22, the average value T3 of T31 and T32) of the kiln shell temperature in each zone Z1 to Z3. The amount of heated gas flowing through each zone Z1 to Z3 is thereby adjusted so that the kiln shell temperature in each zone Z1 to Z3 can be maintained at a different set temperature.

The transition shell temperatures Ts1, Ts2, Ts3(D1/α L1, D1/α L2, D1/α L3, where L1, L2 and L3 are the length of each zone, respectively) in each zone Z1 to Z3 are determined based on the partial thermal elongations D1, D2, D3 in each zone Z1 to Z3, which values are compared with the measured values T1, T2, T3 of the kiln shell temperatures in each zone Z1 to Z3 to determine the temperature differences Δ T1, Δ T2, Δ T3. Therefore, the temperature error and the dust adhesion state in each of the zones Z1 to Z3 can be detected. At this time, needless to say, the aforementioned method of comparing the conversion shell temperature Ts determined by the overall thermal elongation D with the average value of the kiln shell temperatures T11 to T32 may be performed simultaneously.

Further, in a state where the opening degree of each of the heating gas amount damper 31 to 33 is maintained at a predetermined ratio, the number of revolutions of the induced draft fan 4 may be controlled such that the kiln shell temperature of any zone, for example, the kiln shell temperature T3 (average of T31 and T32) of the outlet zone Z3 located at the most downstream side is maintained at a predetermined temperature zone. In this case, the measuring means 124 for measuring the partial thermal elongation may be provided only in the outlet zone Z3.

The foregoing is a description of embodiments of the invention. The present invention is not limited to the above-described embodiments, and various modifications and variations can be made based on the technical idea of the present invention. For example, in the above embodiment, a rotary kiln provided with six non-contact thermometers 126 and three measuring devices 124 for measuring the thermal elongation of the axial portion is shown. However, the number of these elements may be set as appropriate. Further, in the second embodiment, a rotary kiln provided with three zones having different temperatures of the kiln shell in the axial direction is shown. However, the number of regions is not limited to three, and the length of each region may be different.

Claims (10)

1. An externally heated rotary kiln comprising a kiln inner cylinder that rotates about an axis and an outer cylinder for causing a heated gas to flow around the kiln inner cylinder, the externally heated rotary kiln performing a heating process while a material to be treated is axially transported in the kiln inner cylinder, characterized in that:

the kiln interior cylinder is rotatably supported on a movable side end portion and a fixed side end portion which are movable in the axial direction, and a device for measuring the axial thermal elongation of the kiln interior cylinder and a plurality of noncontact thermometers for measuring the shell temperature at a plurality of positions in the axial direction of the kiln interior cylinder from an outer wall portion of the outer cylinder are provided.

2. The externally heated rotary kiln as recited in claim 1, further comprising: the thermal elongation measuring device comprises an integral thermal elongation measuring device for measuring the integral thermal elongation in the axial direction of the kiln inner cylinder.

3. The externally heated rotary kiln as recited in claim 1, further comprising: the thermal elongation measuring device includes at least one partial thermal elongation measuring device for measuring thermal elongation in an intermediate portion in the kiln inner cylinder axial direction from the outer cylinder peripheral wall portion.

4. The method of operating an externally heated rotary kiln as claimed in claim 1, wherein: in the case where the difference between the transition shell temperature, which is obtained by dividing the thermal elongation obtained from the measurement value of the thermal elongation measuring device by the linear expansion coefficient of the material of the kiln inner cylinder, and the average shell temperature, which is obtained from the measurement value of the noncontact thermometer, becomes not less than a predetermined value, compressed air is injected onto the outer surface of the kiln inner cylinder to remove dust adhering to the outer surface of the kiln inner cylinder.

5. The method of operating an externally heated rotary kiln as claimed in claim 1, wherein: the signal for prompting maintenance of the kiln interior cylinder is generated in a case where a difference between a transition shell temperature obtained by dividing a thermal elongation obtained from a measurement value of a thermal elongation measuring device by a linear expansion coefficient of a material of the kiln interior cylinder and an average shell temperature obtained from a measurement value of a noncontact thermometer becomes not less than a predetermined value, or in a case where such a state continues for a predetermined time.

6. The method of operating an externally heated rotary kiln as set forth in claim 1, in which the amount of the heating gas flowing in the outer cylinder is increased or decreased based on an average shell temperature obtained from the measurement values of the non-contact thermometer, so that the average shell temperature is maintained in a predetermined temperature region, characterized in that: in the case where a state where a difference between a transition shell temperature and the average shell temperature is not less than a predetermined value continues for a predetermined time, the average shell temperature is calibrated according to the temperature difference, and the amount of the heating gas flowing in the outer cylinder is adjusted using the calibrated average shell temperature, the transition shell temperature being obtained by dividing a thermal elongation obtained from a measurement value of the thermal elongation measuring device by a linear expansion coefficient of the material of the kiln inner cylinder.

7. The externally heated rotary kiln as recited in claim 1, further comprising: the outer cylinder is divided into a plurality of zones, the noncontact thermometer is disposed in each zone, and heating gas amount adjusting means for adjusting the heating gas flow amount in each zone and temperature control means for controlling the heating gas amount adjusting means based on a measured value of the shell temperature in each zone are further provided.

8. The externally heated rotary kiln as recited in claim 7, further comprising: the thermal elongation measuring device includes a zone thermal elongation measuring device for measuring thermal elongation in each zone from the outer cylinder peripheral wall portion.

9. An externally heated rotary kiln as claimed in claim 7 or claim 8, wherein: the thermal elongation measuring apparatus includes a heated gas distributing means for distributing a heated gas of one system to each section at a predetermined flow rate ratio, and a heated gas total flow rate adjusting means for adjusting a heated gas total flow rate of one system.

10. An externally heated rotary kiln comprising a kiln inner cylinder that rotates about an axis and an outer cylinder for causing a heated gas to flow around the kiln inner cylinder, the externally heated rotary kiln performing a heating process while a material to be treated is axially transported in the kiln inner cylinder, characterized in that:

the kiln interior cylinder is rotatably supported on a movable side end portion and a fixed side end portion that are movable in the axial direction, and means for measuring the axial thermal elongation of the kiln interior cylinder is provided.