JP2023181690A - Dryer for asphalt plant - Google Patents

Abstract

To provide a dryer of an asphalt plant capable of suppressing scattering of sparks to a bug filter arranged downstream of the dryer.SOLUTION: A dryer of an asphalt plant is equipped with a mixed combustion type burner 2 provided with both a liquid fuel injection nozzle 14 and a solid fuel injection nozzle 16, a combustion chamber 3, a cylindrical kiln main body 4 having a variable rotating speed, and a controller 43 for controlling the combustion amount of the burner 2 and the rotating speed of the kiln main body 4. In addition, a plurality of scraping blades 28 for scraping up aggregate and a damming body 42 for damming and retaining a part of the flow of the aggregate are circumferentially provided on the inner peripheral wall of the kiln main body 4, and the controller 43 performs control for adjusting the number of revolutions of the kiln main body 4 based on the injection amount of the solid fuel increased and decreased according to the combustion amount of the burner 2.SELECTED DRAWING: Figure 1

Description

The present invention relates to a dryer for heating and drying aggregate in an asphalt plant that produces an asphalt mixture that is a road paving material, and more particularly to a dryer for heating and drying aggregate in an asphalt plant that uses powdered solid fuel.

In asphalt plants, fossil fuels are used as fuel for burners installed in dryers that heat and dry aggregates, such as powdered solid fuel produced by crushing waste, thinned wood, etc. It is being used to co-combust fuels with liquid fuels or gaseous fuels such as heavy oil or city gas, thereby reducing the amount of fossil fuels used and reducing the environmental impact.

As shown in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2005-16200), the present applicant has disclosed that wood-based fine powder, which is a powdered solid fuel, is placed in the combustion area of a burner that burns fossil fuels such as liquid fuel or gaseous fuel. The company has filed an application for a dryer for asphalt plants that reduces the amount of fossil fuel used by blowing in and co-combusting the wood powder, which corresponds to the calorific value of the supplied wood fine powder.

In addition, as shown in Patent Document 2 (Japanese Patent Laid-Open No. 2015-87047), a solid fuel injection means and an auxiliary combustion burner for assisting the combustion of solid fuel are provided at one end of the kiln body, which has casters around the inner peripheral surface. , the hot air supply duct is provided with a secondary combustion chamber on the other end side for burning and decomposing the scattered unburned matter flowing down with the combustion gas from the kiln main body, and supplies hot air to the heating drying device disposed downstream. The application is for a hot air generating furnace that is connected to the upper part of a secondary combustion chamber and uses solid fuel as its main fuel.

Japanese Patent Application Publication No. 2005-16200 Japanese Patent Application Publication No. 2015-87047

However, solid fuel has inferior combustibility compared to liquid or gaseous fuels, and in the conventional device described above, for example, the dryer described in Patent Document 1, a part of the wood-based fine powder blown into the combustion area of the burner does not burn out and remains as sparks. If the sparks are discharged from the dryer, they may adhere to the filter cloth of the bag filter installed downstream and cause the filter cloth to burn out, so some kind of measure is desired to prevent the sparks from scattering downstream in the dryer.

In addition, in the hot air generating furnace described in Patent Document 2, the combustion ash of the solid fuel burned in the kiln main body is recovered in the downstream secondary combustion chamber, and combustion air is supplied to the combustion ash. When re-burning the fugitive unburned matter remaining in the burner, in some cases some of it may not burn out and scatter as sparks downstream, for example to a heating drying device such as a dryer, or to a bag filter installed further downstream. Therefore, some kind of measure is desired to prevent sparks from scattering to the bag filter on the downstream side in the heating drying device.

In view of the above points, an object of the present invention is to provide a dryer for an asphalt plant that uses powdered solid fuel and is capable of suppressing the scattering of sparks to a bag filter disposed downstream of the dryer. shall be.

In order to solve the above problems, the dryer for an asphalt plant according to claim 1 of the present invention includes a burner that is provided with a liquid or gaseous fuel injection nozzle for flame formation and a powdery solid fuel injection nozzle; a combustion chamber disposed in front of the burner; a cylindrical kiln body tilted and rotatably supported in front of the combustion chamber and having a variable rotation speed; a combustion amount of the burner; and a rotation speed of the kiln body. a controller for controlling the flow of aggregate, and a plurality of scraping blades for scraping up aggregate on the inner peripheral wall of the kiln body, and a dam for damming and retaining a part of the flow of aggregate in the kiln body. The kiln body is characterized in that a stop body is provided around the kiln body, and the controller adjusts the rotational speed of the kiln body based on the amount of solid fuel injected that increases or decreases depending on the combustion amount of the burner.

Further, in the dryer for an asphalt plant according to a second aspect of the present invention, the controller adjusts the rotational speed of the kiln main body to increase as the amount of solid fuel injected by the burner increases.

The dryer for an asphalt plant according to claim 3 is characterized in that the controller stops the injection of solid fuel in the burner when the amount of aggregate supplied to the kiln body becomes less than a predetermined amount. There is.

According to the dryer for an asphalt plant according to claim 1 of the present invention, the amount of sparks increases or decreases depending on the amount of solid fuel injected in the burner, and the amount of sparks can be adjusted by adjusting the rotation speed of the kiln main body. As a result of being able to form a suitable aggregate veil inside the kiln body, the sparks scattered inside the kiln body can be effectively brought into contact with the aggregate veil and extinguished, thereby preventing the sparks from reaching the bag filter downstream of the dryer. It is possible to suppress the scattering of.

Further, according to the dryer for an asphalt plant according to claim 2, even if the amount of scattered sparks within the kiln body increases due to an increase in the amount of solid fuel injected, the rotational speed of the kiln body is increased and the kiln is operated. By increasing the number of aggregate bales formed within the main body, it is possible to reliably cause sparks to come into contact with the aggregate bales and fall, thereby extinguishing the fire.

Further, according to the dryer for an asphalt plant according to claim 3, the amount of aggregate supplied to the kiln body is small compared to the veil of aggregate formed within the kiln body even if the rotation speed of the kiln body is adjusted. In a situation where a large gap is likely to occur, by forcibly stopping the solid fuel injection regardless of the burner combustion amount, it is possible to reliably prevent sparks from scattering to the bag filter.

FIG. 1 is a partially cutaway schematic explanatory diagram of a dryer for an asphalt plant according to the present invention. It is an enlarged view with a part of a burner and a combustion chamber notched. It is an enlarged view with a part of the kiln main body cut away. It is an AA sectional view with a part of the kiln main body omitted. It is a BB sectional view with a part of the combustion chamber omitted. 5 is a sectional view showing a state when aggregate is supplied into the kiln main body of FIG. 4. FIG. It is an enlarged view with a part cut away which shows another Example of a kiln main body. FIG. 8 is a cross-sectional view taken along the line CC in FIG. 7 with a part of the kiln main body omitted.

The dryer for an asphalt plant according to the present invention includes a co-firing type burner in which a fossil fuel liquid or gaseous fuel injection nozzle for flame formation and a powdery solid fuel injection nozzle are installed together, and a front part of the burner. A cylindrical kiln body is provided with a combustion chamber disposed in front of the combustion chamber, and a cylindrical kiln body which is tilted and rotatably supported in front of the combustion chamber and whose rotational speed is variable.

The combustion chamber has a horizontal configuration with a circular longitudinal section and fireproof casters installed around the inner wall surface, and the ignited (combusted) solid fuel introduced into the combustion chamber is oriented in the tangential direction of the combustion chamber. A plurality of stirring air supply pipes for supplying stirring air from the combustion chamber are connected at predetermined intervals along the axial direction of the combustion chamber.

The powdered solid fuel injected from the solid fuel injection nozzle may be a solid fuel that is expected to reduce environmental impact and is relatively easily procured, such as solid fuel made by pulverizing rice husks or the like into powder ( biomass fuel) can be suitably employed. However, as mentioned above, when using solid fuel made by pulverizing rice husks, some of it remains in the combustion chamber (near the bottom) and is exposed to high temperatures of about 1,000°C or more for about 10 minutes or more. If this continues, there is a possibility that cristobalite, which has been suggested to be carcinogenic, may be produced. Therefore, by introducing outside air from the tangential direction of the combustion chamber through the stirring air supply pipe so as to swirl it along the inner wall surface, combustion It is preferable to adopt a configuration that can effectively agitate the solid fuel burning indoors to reduce retention in the combustion chamber and suppress the generation of harmful substances.

The kiln body has a plurality of scraping blades for scraping up aggregate on its inner peripheral wall, and a roughly ring-shaped blade having a predetermined height that dams and retains a part of the aggregate flow inside the kiln body. A dam body is installed around the area. A plurality of rows of the damming bodies are provided around the kiln body at positions that do not interfere with the raking blades and extending from approximately the center in the longitudinal direction of the kiln main body to the downstream side in the flowing direction of the hot air.

By disposing the damming body around the kiln body, even if the number of rotations (rotational speed) of the kiln body changes, the amount of aggregate retained within the kiln body does not change significantly, and the amount of aggregate retained at the bottom of the kiln body is maintained at a predetermined level. As a result of being able to maintain a thick aggregate layer, an amount of aggregate at least commensurate with the raking capacity of the raking blades (an appropriate amount for dropping the aggregate in a bale shape into the kiln main body) is transferred to the bottom of the kiln main body. It is possible to secure the

The kiln also includes a controller that controls the combustion amount of the co-combustion type burner (each injection amount of liquid or gaseous fuel and solid fuel) and the rotation speed of the kiln main body. The controller adjusts the rotation speed of the kiln main body based on the injection amount of solid fuel, which increases and decreases with the injection amount of liquid or gaseous fuel, according to the combustion amount of the burner, and controls the rotation speed of the kiln main body downstream from the combustion chamber. The sparks from the solid fuel that are scattered are effectively brought into contact with the veil of aggregate formed inside the kiln body to extinguish the fire, and are then discharged as sparks to the bag filter located downstream. The structure is designed to suppress

When the aggregate is heated and dried in the dryer of the asphalt plant having the above configuration, first, only the fossil fuel is injected singly from the liquid or gaseous fuel injection nozzle of the burner, ignited and combusted, and the combustion chamber and the kiln body are The inside of the kiln is preheated, and when preheating is completed, the supply of aggregate into the kiln body begins.

The aggregate supplied into the kiln body is temporarily retained in the kiln body by the damming body, and the amount of the retained aggregate is a predetermined amount. When the amount of accumulated aggregate is such that a veil of aggregate can be formed to the extent that it can be dropped to extinguish the fire, the controller calculates the injection amount of solid fuel according to the burner combustion amount, and is blown into the flame region formed by combustion of the liquid or gaseous fuel to ignite and burn it. At this time, the amount of liquid or gaseous fuel injected is reduced by an amount corresponding to the calorific value of the amount of solid fuel injected.

When the ignited solid fuel is introduced into the front combustion chamber, it is effectively agitated by stirring air supplied along the inner wall surface of the combustion chamber, and remains on the inner wall surface (near the bottom) of the combustion chamber. The hot air generated by the combustion (mixed combustion) of these solid fuels and liquid or gaseous fuels is led downstream to the kiln main body.

At this time, a sufficient amount of aggregate remains in the kiln body due to the damming body, so the bale formed inside the kiln body due to the raking and falling of the aggregate by the raking blades , there is no large gap where the aggregate and hot air can blow through without coming into contact with each other, and the aggregate is efficiently heated and dried.

On the other hand, in the combustion chamber, a portion of the solid fuel with poor combustibility may not be completely burnt out and may remain in the form of sparks and scatter toward the downstream kiln main body. Even in that case, as mentioned above, there are multiple bales of aggregate with no large gaps formed inside the kiln main body, so the sparks come into contact with the bales of aggregate without leaking and fall, and the kiln The fire is absorbed into the aggregate layer that accumulates at the bottom of the main body and is extinguished. At this time, the aggregate contained in the aggregate layer staying at the bottom of the kiln body is still in the process of heating and drying, and the temperature is relatively low and it also contains some moisture, so the aggregate layer Sparks trapped in the fire are effectively extinguished.

Preferably, the controller adjusts the number of rotations (rotational speed) of the kiln main body to increase as the amount of solid fuel injected by the co-firing burner increases. For example, if the amount of solid fuel injected increases by increasing the burner combustion amount or increasing the co-firing ratio of solid fuel, the amount of sparks scattered inside the kiln body will also increase, but the kiln will By increasing the rotational speed of the main body, the number of bales of aggregate formed within the kiln main body can be increased, and the increased sparks can reliably come into contact with and fall to the bales of aggregate to extinguish the fire without leaking. .

Furthermore, preferably, the controller stops the injection of solid fuel in the mixed combustion type burner when the amount of aggregate supplied to the kiln body becomes less than a predetermined amount. When the amount of aggregate supplied decreases and the amount of aggregate retained in the kiln body decreases, the scraping blades can only scrape up a small amount of aggregate that is less than the scraping capacity, even if the rotation speed of the kiln body is increased. However, there is a possibility that only a veil will form with large gaps that allow sparks to blow through. In such a case, the injection of solid fuel is forcibly stopped regardless of the amount of combustion in the burner, and control is performed to give priority to preventing sparks from scattering to the bag filter. At this time, the injection amount of liquid or gaseous fuel is increased by an amount corresponding to the calorific value of the solid fuel whose injection has been stopped.

In this way, a predetermined amount or more of aggregate is retained in the kiln body to ensure a constant aggregate layer at the bottom of the kiln body, and the rotation speed of the kiln body is adjusted to increase or decrease depending on the amount of solid fuel injected. By forming a veil of aggregate in proportion to the amount of sparks scattered inside the kiln body, the sparks scattered with hot air can be effectively extinguished by coming into contact with the aggregate and falling, making it easier to use the dryer. It is possible to suppress the scattering of sparks (burnout of the filter cloth) to the bag filter disposed downstream.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

1 in Fig. 1 is a dryer of an asphalt plant, which uses liquid fuel such as kerosene or heavy oil (or gaseous fuel such as city gas or LPG) and solid fuel in powder form obtained by crushing rice husks, etc. A burner 2 of a co-combustion type that co-combusts a combination of the following: a combustion chamber 3 having a circular longitudinal section; a rotary kiln body 4 having a rotary kiln structure that heats and dries the aggregate that becomes the material of the asphalt mixture; and purifying the exhaust gas discharged from the kiln body 4. It consists of a bag filter 5 for processing, an exhaust fan 6, a chimney 7, etc.

The burner 2 includes a cylindrical burner body 8, a throat 9 having a substantially truncated cone shape is connected to the tip of the burner body 8, and combustion air is supplied to the base end through a blow duct 10. A blower 11 for use is connected. The drive motor 12 of the blower 11 is equipped with an inverter (not shown) for adjusting the rotation speed, and by adjusting the rotation speed of the drive motor 12 with the inverter, the amount of combustion air corresponding to the burner combustion amount is adjusted. It is possible to suck it through the intake port 13 and supply it to the burner body 8.

A liquid fuel injection nozzle (or gaseous fuel injection nozzle) 14 for injecting liquid fuel (or gaseous fuel) for flame formation is provided approximately at the center (cylindrical axial center) of the burner body 8, and the liquid fuel injection nozzle 14 injects liquid fuel (or gaseous fuel) for flame formation. An annular flame-holding plate 15 having a diameter slightly larger than the inner diameter of the burner body 8 is provided in the throat 9 at a position in front of the nozzle 14 . Further, around the liquid fuel injection nozzle 14, a plurality of, for example about 4 to 8 (6 in this embodiment) solid fuel injections are arranged concentrically at predetermined intervals around the liquid fuel injection nozzle 14. It is equipped with a nozzle 16.

17 in the figure is a liquid fuel supply device that supplies liquid fuel such as kerosene or heavy oil to the liquid fuel injection nozzle 14, and supplies fuel from a liquid fuel tank (not shown) to the liquid fuel injection nozzle 14. A feed pipe 18 that includes a built-in fuel supply pump (not shown) and sends liquid fuel from the fuel supply pump to the liquid fuel injection nozzle 14, and a feed pipe on the upstream side of the fuel supply pump from the liquid fuel injection nozzle 14. A return pipe 19 for returning liquid fuel to 18 is provided. Further, a flow rate adjustment valve (not shown) is interposed in the return pipe 19 in the liquid fuel supply device 17, and the opening degree of the valve is adjusted to adjust the return amount of the liquid fuel, thereby controlling the liquid fuel injection nozzle. The injection amount of liquid fuel from 14 is adjusted.

Each of the solid fuel injection nozzles 16 has a substantially L-shaped bent tube structure, and its tip (injection port) penetrates the flame stabilizing plate 15 and is connected to the tip (injection port) of the liquid fuel injection nozzle 14. The base end extends forward so that the powdered solid fuel injected from the solid fuel injection nozzle 16 can be blown into the flame region formed in the throat 9 in front of the liquid fuel injection nozzle 14. It is bent at a substantially right angle toward the center of the burner body 8 and connected to the distributor 20 .

21 in the figure is a solid fuel storage bin that stores powdered solid fuel, and at its lower end there is a rotary valve 22 that can continuously cut out an amount of solid fuel according to the amount of solid fuel to be injected. A lower discharge part of the rotary valve 22 is connected to a solid fuel pressure feed pipe 23, and the solid fuel cut out by the rotary valve 22 is air-forced to the distributor 20 by air from a pressure fan 24, The solid fuel can be supplied substantially equally to the plurality of solid fuel injection nozzles 16 via the distributor 20.

The pressure fan 24 is equipped with an inverter (not shown) for adjusting the amount of air blown, and the amount of air blown is commensurate with the amount of solid fuel cut out from the rotary valve 22 at the bottom of the solid fuel storage bin 21 according to the amount of solid fuel injected. It is adjusted and controlled so that

In addition, as shown in FIG. 2, in the combustion chamber 3 installed in front of the burner 2 and having a horizontal configuration and having a circular longitudinal section, heat-resistant (heat storage) casters 25 are installed around the inner wall surface of the combustion chamber 3. In order to make it possible to maintain a high temperature atmosphere inside the combustion chamber 3, and to prevent the burning solid fuel from accumulating on the inner wall surface (near the bottom) of the combustion chamber 3, it is possible to maintain a high temperature atmosphere inside the combustion chamber 3. A plurality of stirring air supply pipes 26 for supplying outside air are connected at predetermined intervals along the axial direction of the combustion chamber 3, for example, about 2 to 6 (3 in this embodiment).

The base end of the stirring air supply pipe 26 is connected to an outside air supply fan 27 equipped with an inverter (not shown) for adjusting the amount of air blown, and the amount of solid fuel injected increases or decreases depending on the combustion amount of the burner 2. Based on this, the amount of air blown is adjusted to be just the right amount so that the solid fuel does not accumulate on the inner wall surface (near the bottom) of the combustion chamber 3. Note that if the air is blown into the combustion chamber 3 more than necessary, the temperature of the hot air will decrease and fuel efficiency will deteriorate, so it is preferable to control the amount of air blown to be just the right amount as described above.

Further, the cylindrical kiln main body 4 which introduces hot air from the combustion chamber 3 to heat and dry the aggregate is provided with a number of scraping blades 28 for scraping up the aggregate around the inner periphery thereof. At the same time, it is tilted and rotatably supported by support rollers 30 on the machine base 29, and is rotated at a predetermined speed (rotation number) by a drive motor 31. The kiln main body 4 is of a counter-flow type in which the direction of flow of hot air from the burner 2 and the direction of flow of aggregate are opposite to each other.

Further, a hot hopper 32 connected to the combustion chamber 3 is provided at one end of the kiln main body 4, and a cold hopper 34 connected to the exhaust flue 33 is provided at the other end. The cold hopper 34 is equipped with an aggregate discharge port 36 equipped with an aggregate temperature sensor 35, and the cold hopper 34 is equipped with a conveyor scale 37 for measuring the aggregate supplied to the kiln main body 4. A conveyor 38 is provided. The exhaust flue 33 is equipped with an exhaust gas temperature sensor 39 that detects the temperature of the exhaust gas, and also has a bag filter 5 that collects and cleans the dust in the exhaust gas, and an exhaust fan 6 for discharging the exhaust gas. and the end is connected to the chimney 7.

Further, a static pressure sensor 40 for detecting static pressure is provided at the upper end corner of the hot hopper 32, and the static pressure value detected by the static pressure sensor 40 is a predetermined negative pressure value, for example, approximately equal to atmospheric pressure. Alternatively, a static pressure/exhaust air volume controller 41 is provided to adjust and control the rotation speed of the exhaust fan 6 so that the pressure is maintained at a level slightly lower than atmospheric pressure, and the kiln body 4 is rotatably provided at both ends. While preventing hot air from blowing out to the outside from the gap between the parts, excess outside air that causes deterioration of fuel efficiency is prevented from entering into the kiln main body 4 as much as possible.

Further, on the inner circumferential wall of the kiln body 4 on the downstream side in the flow direction of the hot air from approximately the center in the longitudinal direction, a dam body 42 that partially dams the flow of aggregate and retains the aggregate is interfering with the raking blades 28. The aggregates supplied into the kiln main body 4 are temporarily dammed by the respective damming bodies 42, and the aggregates are arranged around the kiln body 4 in multiple rows (three rows in this embodiment) at predetermined intervals and at predetermined intervals. A certain amount of aggregate is retained at the bottom of the kiln body 4 extending from approximately the center of the body 4 to the downstream side in the flow direction of the hot air to ensure an aggregate layer with a predetermined thickness.

As shown in FIG. 4, the damming body 42 has a substantially ring shape disposed along the inner circumferential wall of the kiln main body 4, and its height size is set such that, for example, an aggregate layer of a predetermined thickness can be secured. The ring-shaped dam 42 is divided into an appropriate number of parts and fixed to the inner circumferential wall of the kiln main body 4 with a gap D of about 75 mm, for example, so that the kiln can be heated after the aggregate supply is finished. The aggregate remaining in the main body 4 gradually passes through the gap D and is discharged from the kiln main body 4, so that no aggregate remains in the kiln main body 4.

Further, as shown in FIG. 6, the raking blades 28 formed into a substantially J-shaped cross section are in a state where the blades are filled with the aggregate of the aggregate layer E near the bottom of the kiln main body 4 due to the rotation of the kiln main body 4. As the kiln body 4 is raked up, some of the raked aggregate begins to fall from the blade tip side at a relatively early stage when the kiln body 4 has rotated about 90 degrees upward from the bottom position (0° position), and about The aggregate continues to fall over a relatively wide range up to a position slightly exceeding 180°, and is configured to form an aggregate veil F on one surface in the radial direction inside the kiln body 4.

Reference numeral 43 in the figure is a controller for controlling each device/equipment of the dryer 1, which receives input signals from the exhaust gas temperature sensor 39, aggregate temperature sensor 35, conveyor scale 37, etc., and receives input signals from the liquid fuel supply device 17. , the drive motors 12 and 31 for driving the blower 11 and the kiln main body 4, the input/output section 44 that inputs and outputs control signals to the rotary valve 22, the pressure fan 24, the outside air supply fan 27, etc. It has a control section 45 that drives and controls each device, device, etc.

The control unit 45 includes a co-firing ratio control unit and a kiln rotation speed control unit, and the co-firing ratio control unit is configured to preliminarily control liquid fuel (for example, kerosene or heavy oil) and solid fuel (for example, pulverized fuel) to be used. Each unit calorific value of processed rice husk) is set and registered. When the aggregate temperature detected by the aggregate temperature sensor 35 is input to the controller 43, the burner combustion amount is calculated based on the aggregate temperature, and the calculated burner combustion amount is calculated in terms of liquid fuel. The calorific value is calculated, and then the injection amount of solid fuel is calculated so that the co-combustion ratio of solid fuel becomes 30% in terms of calorific value, and the injection amount of the remaining liquid fuel is calculated. I have to.

The mixed combustion ratio control section further includes a solid fuel supply control section and a liquid fuel supply control section, and the solid fuel supply control section includes a rotary valve 22, While controlling the pressure feeding fan 24, the outside air supply fan 27, etc., the liquid fuel supply control section controls the liquid fuel supply device 17, the drive motor 12, etc. so that the calculated injection amount of liquid fuel is achieved. There is.

On the other hand, the kiln rotational speed control section of the control section 45 adjusts the rotational speed of the kiln main body 4 based on the calculated injection amount of solid fuel, and removes sparks scattered from the combustion of the solid fuel into the kiln main body 4. Control is performed so that the aggregate veil formed in the container 4 contacts and falls without leaking and extinguishes the fire. Depending on the combustion amount of the burner 2, the amount of solid fuel injected as well as the amount of liquid fuel increases or decreases, and the amount of scattered sparks also increases or decreases accordingly. The number of rotations of the kiln body 4 is increased or decreased in order to form a veil of aggregate (which cannot pass through the kiln body 4 as it is).

Note that the rotational speed of the kiln main body 4 does not necessarily have to be always high enough to form a large number of veils of aggregate. When the number of bales of aggregate increases, the chances of contact with the hot air from the burner 2 increase and the heating efficiency improves, resulting in an unnecessary drop in exhaust gas temperature, and in some cases, the temperature inside the exhaust flue 33 or bag filter 5 increases. Condensation may occur, leading to problems such as corrosion of the flue and blockage of the filter cloth.

Therefore, after conducting combustion experiments in advance and taking into account the heating efficiency of aggregates, exhaust gas temperature, etc. in addition to the amount of sparks scattered, An appropriate rotation speed of the main body 4 is determined and registered as a reference rotation speed, and when the burner combustion amount (injection amount of solid fuel) increases or decreases, the rotation speed is adjusted to increase or decrease based on the reference rotation speed. It is preferable to do so. Incidentally, it is preferable that the adjustment amount of increase/decrease in the rotational speed of the kiln main body 4 with respect to the increase/decrease in the burner combustion amount is also determined and registered in advance through combustion experiments or the like.

Then, using the dryer 1 of the asphalt plant having the above configuration, for example, powdered rice husk as a solid fuel and heavy oil as a liquid fuel are co-combusted to heat and dry aggregate, which is a material of an asphalt mixture. When doing so, first, heavy oil is supplied from the liquid fuel supply device 17 to the burner 2, and is ignited and burned to preheat the inside of the combustion chamber 3 and the kiln body 4. During this time, the burner 2 is in a heavy oil burning operation. Next, when preheating is completed, supply of aggregate to the kiln main body 4 is started.

The aggregate supplied into the kiln main body 4 is temporarily retained in the kiln main body 4 by the dam 42, and the aggregate retention amount (for example, the amount is measured by the conveyor scale 37 of the aggregate input conveyor 38). (amount of aggregate supplied per predetermined time) is at least a predetermined amount, for example, an amount that can form a veil of aggregate that can extinguish by contacting and falling the sparks of rice husks scattered within the kiln main body 4 without leaking. Then, the controller 43 calculates the injection amount of rice husks from the preset co-firing ratio of heavy oil and rice husks and the burner combustion amount.

Then, rice husks corresponding to the calculated injection amount are cut out from the rotary valve 22, and are injected from each solid fuel injection nozzle 16 through the distributor 20 by air blowing from the pressure fan 24, and the heavy oil injected from the liquid fuel injection nozzle 14 is It is blown into the combustion region formed in the throat 9 by combustion to cause ignition combustion (co-combustion). At this time, the injection amount of heavy oil is reduced by an amount corresponding to the calorific value of the injection amount of rice husks.

When the ignited rice husks are introduced into the front combustion chamber 3, they are effectively stirred by stirring air supplied in a swirling manner from the tangential direction of the combustion chamber 3 via the stirring air supply pipe 26, and the combustion chamber 3 The hot air is burned without staying on the inner wall surface (near the bottom), and the hot air generated by the combustion (mixed combustion) of these rice husks and heavy oil is led to the kiln main body 4 downstream. The rice husks burned in the combustion chamber 3 are not exposed to high temperatures of about 1,000° C. or higher for more than about 10 minutes, which is the condition for cristobalite formation, and are burnt suitably.

In the kiln main body 4 into which the hot air is introduced, a predetermined amount of aggregate (sufficient amount for bale formation) is retained by the damming body 42, so that, for example, the raking blades 28 The aggregate begins to fall relatively early after rotating upward by about 90 degrees from the position, and continues to fall over a relatively wide range until the position slightly exceeds about 180 degrees. As a result, there are no large gaps in the aggregate veil formed inside the kiln body 4 where the aggregate and hot air can blow through without coming into contact with each other, and the aggregate is efficiently heated and dried. .

On the other hand, in the combustion chamber 3, some of the rice husks with poor combustibility may not be completely burnt out and may scatter into the kiln body 4 as sparks. Even in that case, as described above, a plurality of bales of aggregate with no large gaps are formed in the kiln main body 4, so that the sparks come into contact with the bales of aggregate without leaking and fall. The fire is absorbed into the aggregate layer that remains at the bottom of the kiln body 4 during heating and drying (in a state where the temperature is relatively low and contains some moisture) and is effectively extinguished.

Even if the sparks once extinguished in the aggregate layer are scraped up (into the hot air) together with the aggregate by the scraping blades 28, they will not be re-ignited (reaching the ignition temperature), and the fly ash will not ignite again (reach the ignition temperature). The exhaust gas is extracted from the kiln main body 4 along with dust, introduced into the bag filter 5 through the exhaust flue 33, captured by the built-in filter cloth, and the purified exhaust gas is released into the atmosphere from the chimney 7. .

Note that when the amount of aggregate supplied from the aggregate input conveyor 38 into the kiln main body 4 becomes less than a predetermined amount, the controller 43 outputs a control signal to stop the rotary valve 22, and the rice husk is removed from the burner 2. The injection may be stopped.

When the aggregate supply amount decreases and the amount of aggregate retained in the kiln body 4 decreases, the raking blades 28 can only scrape up a small amount of aggregate that is less than the raking capacity, and in some cases, the raking blades 28 As a result, even if the aggregate does not start falling even if 28 rotates upwards from the bottom position of the kiln body 4 by more than 90 degrees, there is a large gap where sparks can blow through even if the rotational speed of the kiln body 4 is increased. There is a possibility that only a veil that has been formed can be formed. In such a case, it is preferable to forcibly stop the injection of rice husks regardless of the combustion amount of the burner 2 and take control to give priority to preventing sparks from scattering to the bag filter 5.

Further, even if the exhaust gas temperature sensor 39 provided in the exhaust flue 33 detects an exhaust gas temperature higher than a predetermined temperature, it is assumed that the sparks in the combustion state have passed through the kiln main body 4, and the burner The injection of rice husks at step 2 may be stopped.

In this embodiment, the measured value of the conveyor scale 37 of the aggregate input conveyor 38 was used as the amount of aggregate supplied into the kiln main body 4, but the value is not limited to this. The cutout amount for each type of aggregate from an aggregate hopper (not shown) installed in the kiln body 4 may be used, and any method can be used as long as the amount of aggregate supplied into the kiln body 4 can be determined. .

In addition, the arrangement method of each raking blade 28 is not limited to the form of this embodiment, and as shown in FIGS. The blades 28 may be arranged at different levels by being shifted by a predetermined angle in the circumferential direction of the kiln main body 29.

With the above arrangement, the falling start positions of the aggregate of each of the raking blades 28 located in the front and rear with each damming body 42 in between are shifted by a predetermined angle, and as a result, bones are formed in the kiln main body 4. Large gaps are less likely to form in the bale of wood, making it possible to further suppress sparks from scattering to the downstream bag filter 5, and reducing the amount of rice husk (solid fuel) used in the mixed combustion type burner 2. It can also be expected to increase the co-firing rate.

Further, the co-firing type burner 2 is not limited to the form of this embodiment, but can be various types of co-firing type as long as it is capable of co-firing powdered solid fuel and liquid (gaseous) fuel. A burner can be used.

2...Burner 3...Combustion chamber 4...Kiln body 5...Bag filter 6...Exhaust fan 14...Liquid fuel injection nozzle 16...Solid fuel injection nozzle 28...Scraping blade 33...Exhaust flue 37...Conveyor scale 38...Aggregation input Conveyor 42...damming body 43...controller

Claims (3)

a burner equipped with a liquid or gaseous fuel injection nozzle for flame formation and a powdered solid fuel injection nozzle; a combustion chamber disposed in front of the burner; and a rotatably tilted support in front of the combustion chamber; and a cylindrical kiln body with a variable rotation speed, and a controller that controls the combustion amount of the burner and the rotation speed of the kiln body, and the inner peripheral wall of the kiln body has a plurality of aggregate scrapers. A raking blade for lifting and a damming body for damming and retaining a part of the flow of aggregate in the kiln main body are provided around the kiln body, and the controller increases or decreases the amount of aggregate in accordance with the combustion amount of the burner. A dryer for an asphalt plant, characterized in that the rotation speed of the kiln main body is adjusted based on the injection amount of solid fuel. 2. The dryer for an asphalt plant according to claim 1, wherein the controller adjusts the rotational speed of the kiln main body to increase as the amount of solid fuel injected by the burner increases. 3. The dryer for an asphalt plant according to claim 1, wherein the controller stops injection of solid fuel in the burner when the amount of aggregate supplied to the kiln body becomes less than a predetermined amount.

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