Asphalt plant dryer
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- NDC CORPORATION
- Filing Date
- 2022-06-13
- Publication Date
- 2026-08-05
Smart Images
Figure 0007900956000001 
Figure 0007900956000002 
Figure 0007900956000003
Abstract
Description
Technical Field
[0001] The present invention relates to a dryer for heating and drying aggregates of an asphalt plant that manufactures asphalt mixtures as road paving materials, and particularly to a dryer for heating and drying aggregates of an asphalt plant that uses powdery solid fuel.
Background Art
[0002] In an asphalt plant, as fuel for a burner provided in a dryer for heating and drying aggregates, for example, powdery solid fuel generated by crushing and carbonizing waste, thinned wood, etc. is co-fired with liquid fuels such as heavy oil or gaseous fuels such as city gas, which are fossil fuels, in order to reduce the amount of fossil fuel used and reduce the environmental load.
[0003] As shown in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-16200), the applicant has filed an application for a dryer of an asphalt plant in which woody fine powder, which is powdery solid fuel, is blown into the combustion region of a burner that burns fossil fuels such as liquid fuel or gaseous fuel and co-fired to reduce the amount of fossil fuel used corresponding to the calorific value of the supplied woody fine powder.
[0004] Also, as shown in Patent Document 2 (Japanese Patent Application Laid-Open No. 2015-87047), an input means for solid fuel and an auxiliary burner for assisting the combustion of solid fuel are provided on one end side of a kiln body with casters provided on the inner peripheral surface, and a secondary combustion chamber for burning and decomposing scattered unburned components flowing down with combustion gas from the kiln body is provided on the other end side. A hot air supply duct for supplying hot air to a heating and drying device arranged downstream is connected to the upper part of the secondary combustion chamber, and an application has been made for a hot air generator that uses solid fuel as the main fuel.
Prior Art Documents
Patent Documents
[0005]
Patent Document 1
[0006] However, solid fuels have inferior flammability compared to liquid or gaseous fuels. In conventional devices such as the dryer described in Patent Document 1, some of the woody fine powder blown into the burner's combustion area may not burn completely and may be discharged from the dryer as sparks. These sparks could adhere to the filter cloth of a bag filter installed downstream, potentially burning the filter cloth. Therefore, some measure is needed to prevent sparks from scattering downstream within the dryer.
[0007] Furthermore, in the hot air generator described in Patent Document 2, when the combustion ash of the solid fuel burned in the kiln body is recovered in a downstream secondary combustion chamber, and combustion air is supplied to this combustion ash to re-burn the remaining unburned, spritze material, some of which may not burn completely and may scatter as sparks downstream to a heating and drying device such as a dryer, or to a bag filter installed further downstream. In such cases, some measures are needed to prevent sparks from scattering to the bag filter downstream of the heating and drying device.
[0008] In view of the above, the present invention aims to provide an asphalt plant dryer that uses powdered solid fuel and can suppress the scattering of sparks to a bag filter installed downstream of the dryer. [Means for solving the problem]
[0009] To solve the above problems, the asphalt plant dryer according to claim 1 of the present invention is equipped with a liquid or gaseous fuel injection nozzle for flame formation and a powdered solid fuel injection nozzle. mixed-fired type A burner, a combustion chamber positioned in front of the burner, a cylindrical kiln body rotatably tilted and supported in front of the combustion chamber, and having a variable rotation speed, and the burner The burner is the injection volume of liquid or gaseous fuel and solid fuel in a burner.The kiln is equipped with a controller that controls the amount of combustion and the rotation speed of the kiln body, and the inner circumferential wall of the kiln body is provided with a plurality of scraping blades for scraping aggregate and a damming body that blocks and retains a portion of the flow of aggregate inside the kiln body, and the controller controls the burner The rotation speed of the kiln body is increased as the amount of solid fuel injected increases. Its defining characteristic is its ability to be adjusted.
[0011] Furthermore, claims 2 In the dryer of the asphalt plant described above, the controller is characterized in that when the amount of aggregate supplied to the kiln body falls below a predetermined supply amount, the injection of solid fuel in the burner is stopped. [Effects of the Invention]
[0012] According to the asphalt plant dryer described in claim 1 of the present invention, by adjusting the rotation speed of the kiln body in response to the amount of sparks which increases or decreases depending on the amount of solid fuel injected in the burner, a bale of aggregate corresponding to the amount of sparks can be formed inside the kiln body. As a result, sparks scattered inside the kiln body can be effectively brought into contact with and dropped onto the bale of aggregate to extinguish the fire, and the scattering of sparks to the bag filter downstream of the dryer can be suppressed.
[0013] Also , solid Even if the amount of sparks scattered inside the kiln increases with the increase in the amount of fuel injected, the sparks can be reliably extinguished by increasing the rotation speed of the kiln body and thereby increasing the number of aggregate bales formed inside the kiln body, causing them to come into contact with and fall onto the aggregate bales.
[0014] Furthermore, claims 2 According to the dryer of the asphalt plant described, if the amount of aggregate supplied to the kiln body is insufficient, and even after adjusting the rotation speed of the kiln body, relatively large gaps tend to form in the aggregate bale inside the kiln body, then the scattering of sparks to the bag filter can be reliably prevented by forcibly stopping the injection of solid fuel regardless of the burner's combustion rate. [Brief explanation of the drawing]
[0015] [Figure 1] The figure is a schematic explanatory view of a part of the dryer of an asphalt plant according to the present invention, with a part cut out. [Figure 2] The figure is an enlarged view of a part of the burner and the combustion chamber, with a part cut out. [Figure 3] The figure is an enlarged view of a part of the kiln body, with a part cut out. [Figure 4] The figure is a sectional view taken along the line A - A, with a part of the kiln body omitted. [Figure 5] The figure is a sectional view taken along the line B - B, with a part of the combustion chamber omitted. [Figure 6] The figure is a sectional view showing the state when aggregate is supplied into the kiln body of FIG. 4. [Figure 7] The figure is an enlarged view of a part showing another embodiment of the kiln body, with a part cut out. [Figure 8] The figure is a sectional view taken along the line C - C, with a part of the kiln body of FIG. 7 omitted.
Embodiments for Carrying Out the Invention
[0016] In the dryer of the asphalt plant according to the present invention, there is provided a co - firing burner in which a liquid or gaseous fuel injection nozzle, which is a fossil fuel for flame formation, and a powder - shaped solid fuel injection nozzle are provided side by side, a combustion chamber arranged in front of the burner, and a cylindrical kiln body that is rotatably and inclinedly supported in front of the combustion chamber and has a variable rotational speed.
[0017] The combustion chamber has a horizontally - placed configuration with a vertically - sectioned circular shape in which refractory casters are provided around the inner wall surface. A plurality of stirring air supply pipes for supplying stirring air from the tangential direction of the combustion chamber to the powder - shaped solid fuel in the ignition (combustion) state introduced therein are connected at predetermined intervals along the axial direction of the combustion chamber.
[0018] As the powdery solid fuel injected from the solid fuel injection nozzle, a solid fuel (biomass fuel) obtained by pulverizing, for example, rice husks into a powdery state, which can be expected to reduce environmental impact and can be relatively easily procured, can be preferably adopted. However, as described above, when a solid fuel obtained by pulverizing rice husks is adopted, if a part of it stays in the combustion chamber (near the bottom) and is continuously exposed to a high temperature of about 1,000 °C or more for about 10 minutes or more, there is a possibility that cristobalite, which is suspected to be carcinogenic, may be generated. Therefore, by introducing outside air from the tangential direction of the combustion chamber along the inner wall surface through the stirring air supply pipe so as to swirl, it is preferable to adopt a configuration that can effectively stir the solid fuel burning in the combustion chamber, reduce the stay in the combustion chamber, and suppress the generation of harmful substances.
[0019] The kiln body is provided with a plurality of scraping blades for scraping up aggregates on its inner peripheral wall and a substantially ring-shaped retaining body having a predetermined height for retaining a part of the flow of the aggregates in the kiln body. The retaining body is provided in a plurality of rows around the kiln body from near the approximate center in the longitudinal direction of the kiln body to the downstream side in the flowing direction of the hot air at a position where it does not interfere with the scraping blades.
[0020] By providing the retaining body around the kiln body, even if the rotation speed (rotation rate) of the kiln body is changed, an aggregate layer with a predetermined layer thickness can be retained at the bottom of the kiln body without significantly changing the amount of aggregates retained in the kiln body. As a result, at least an amount of aggregates corresponding to the scraping capacity of the scraping blades (an appropriate amount for dropping the aggregates in the kiln body in a veil shape) can be ensured at the bottom of the kiln body.
[0021] Furthermore, the kiln is equipped with a controller that controls the combustion amount of the mixed-combustion burner (the injection amounts of liquid or gaseous fuel and solid fuel) and the rotation speed of the kiln body. The controller adjusts the rotation speed of the kiln body based on the injection amount of solid fuel, which increases or decreases along with the injection amount of liquid or gaseous fuel according to the combustion amount of the burner. This configuration effectively extinguishes the sparks of solid fuel that scatter from the combustion chamber downstream to the kiln body by causing them to come into contact with and fall onto the veil of aggregate formed inside the kiln body, and further suppresses the discharge of sparks as they are into the bag filter located downstream.
[0022] When heating and drying aggregate in the dryer of the asphalt plant with the above configuration, first, fossil fuel alone is injected from the liquid or gaseous fuel injection nozzle of the burner to ignite and burn, preheating the combustion chamber and the kiln body. Once preheating is complete, the supply of aggregate into the kiln body is started.
[0023] The aggregate supplied into the kiln body is temporarily retained within the kiln body by the damming body. When the amount of retained aggregate reaches a predetermined amount, for example, an amount sufficient to form a veil of aggregate that can extinguish sparks from solid fuel scattered inside the kiln body by contacting and dropping them without leakage, the controller calculates the amount of solid fuel to be injected according to the burner combustion rate, and injects this calculated amount of solid fuel into the flame area formed by the 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 equivalent to the heat generated by the amount of solid fuel injected.
[0024] When the ignited solid fuel is introduced into the combustion chamber at the front, it is effectively agitated by the agitated air supplied along the inner wall of the combustion chamber, and burns favorably without accumulating on the inner wall (near the bottom) of the combustion chamber. The hot air generated by the combustion (co-combustion) of these solid fuels and liquid or gaseous fuels is then guided to the kiln body downstream.
[0025] At this time, a sufficient amount of aggregate is retained inside the kiln body by the damming body, so that there are no large gaps in the bale formed inside the kiln body by the scraping and dropping of the aggregate by the scraping blades, allowing the hot air to pass through without contacting the aggregate, and the aggregate is efficiently heated and dried.
[0026] On the other hand, in the combustion chamber, some of the solid fuel, which has poor flammability, may not burn completely and may scatter downstream as sparks. Even in that case, as mentioned above, multiple bales of aggregate with no large gaps are formed inside the kiln body, so the sparks will come into contact with and fall onto the bales of aggregate without fail, and will be taken into the aggregate layer that remains at the bottom of the kiln body and extinguished. At this time, the aggregate contained in the aggregate layer that remains at the bottom of the kiln body is still in the process of being heated and dried, and its temperature is relatively low, and it also contains some moisture, which helps to effectively extinguish the sparks taken into the aggregate layer.
[0027] Preferably, the controller is adjusted so that the rotation speed of the kiln body increases as the amount of solid fuel injected by the mixed-combustion burner increases. For example, if the amount of solid fuel injected increases by increasing the burner combustion rate or increasing the ratio of solid fuel mixed in, the amount of sparks scattered inside the kiln body will also increase. By increasing the rotation speed of the kiln body accordingly, the number of aggregate bales formed inside the kiln body can be increased, and the increased sparks can be reliably brought into contact with and dropped onto the aggregate bales without escaping, thereby extinguishing the fire.
[0028] Furthermore, preferably, the controller stops the injection of solid fuel from the mixed-combustion burner when the amount of aggregate supplied to the kiln body falls below a predetermined amount. When the amount of aggregate supplied decreases and the amount of aggregate remaining in the kiln body decreases, the scraping blades can only scrape up a small amount of aggregate that is not enough to reach the scraping capacity, and even if the rotation speed of the kiln body is increased, it is possible that only a veil with large gaps that allow sparks to pass through will be formed. In such cases, the injection of solid fuel is forcibly stopped regardless of the amount of combustion in the burner, and control is taken to prioritize preventing sparks from scattering onto the bag filter. At this time, the amount of liquid or gaseous fuel injected is increased by an amount equivalent to the calorific value of the solid fuel whose injection has been stopped.
[0029] In this way, by retaining a certain amount or more of aggregate inside the kiln body to secure a certain aggregate layer at the bottom of the kiln body, and by increasing or decreasing the rotation speed of the kiln body according to the amount of solid fuel injected, a veil of aggregate equal to the amount of sparks scattered inside the kiln body is formed. As a result, sparks scattered with the hot air can be effectively extinguished by coming into contact with and falling onto the aggregate, and the scattering of sparks to the bag filter located downstream of the dryer (burning of the filter cloth) can be suppressed. [Examples]
[0030] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0031] Figure 1 shows a dryer for an asphalt plant, which consists of a mixed-combustion burner 2 that co-combusts liquid fuels such as kerosene or heavy oil (or gaseous fuels such as city gas or LPG) with powdered solid fuels obtained by crushing, for example, rice husks; a combustion chamber 3 with a vertical circular cross-section; a kiln body 4 with a rotary kiln structure that heats and dries aggregates that will be used as materials for the asphalt mixture; a bag filter 5 that purifies the exhaust gas discharged from the kiln body 4; an exhaust fan 6; a chimney 7, etc.
[0032] The burner 2 comprises a cylindrical burner body 8, a substantially truncated cone-shaped throat 9 connected to the tip of the burner body 8, and a blower 11 for supplying combustion air connected to the base end via an air supply duct 10. The drive motor 12 of the blower 11 is equipped with an inverter (not shown) for adjusting the rotational speed, and by adjusting the rotational speed of the drive motor 12 with the inverter, it is possible to draw in a combustion air amount commensurate with the burner's combustion amount from the air intake port 13 and supply it to the burner body 8.
[0033] The burner body 8 is equipped with a liquid fuel injection nozzle (or gaseous fuel injection nozzle) 14 at approximately the center (cylindrical axis) for injecting liquid fuel (or gaseous fuel) to form a flame, and an annular flame-holding plate 15, slightly larger in diameter than the inner diameter of the burner body 8, is provided in the throat 9 located in front of the liquid fuel injection nozzle 14. Furthermore, around the liquid fuel injection nozzle 14, there are multiple solid fuel injection nozzles 16 arranged concentrically around the liquid fuel injection nozzle 14 at predetermined intervals, for example, about 4 to 8 (6 in this embodiment) of solid fuel injection nozzles 16.
[0034] In the figure, 17 is a liquid fuel supply device that supplies liquid fuel such as kerosene or heavy oil to the liquid fuel injection nozzle 14. It incorporates a fuel supply pump (not shown) that sends fuel from a liquid fuel tank (not shown) to the liquid fuel injection nozzle 14, a supply pipe 18 that sends liquid fuel from the fuel supply pump to the liquid fuel injection nozzle 14, and a return pipe 19 that returns liquid fuel from the liquid fuel injection nozzle 14 to the supply pipe 18 upstream of the fuel supply pump. Furthermore, a flow rate adjustment valve (not shown) is interposed in the return pipe 19 within the liquid fuel supply device 17, and the amount of liquid fuel returned is adjusted by adjusting its opening, thereby adjusting the amount of liquid fuel injected from the liquid fuel injection nozzle 14.
[0035] Each of the solid fuel injection nozzles 16 has a roughly L-shaped curved pipe structure, and its tip (injection port) extends forward beyond the tip (injection port) of the liquid fuel injection nozzle 14 by penetrating the flame holder plate 15, so that the powdered solid fuel injected from the solid fuel injection nozzle 16 can be blown into the flame area formed in the throat 9 in front of the liquid fuel injection nozzle 14, while its base end is bent at roughly a right angle toward the center of the burner body 8 and connected to the distributor 20.
[0036] In the figure, 21 is a solid fuel storage bin for storing powdered solid fuel, and its lower end is equipped with a rotary valve 22 capable of continuously dispensing an amount of solid fuel corresponding to the amount of solid fuel to be injected. The lower discharge part of the rotary valve 22 is connected to a solid fuel pressurized pipe 23, and the solid fuel dispensed by the rotary valve 22 is air-pressurized by air from a pressurized fan 24 and supplied to the distributor 20, which can then be supplied substantially equally to a plurality of solid fuel injection nozzles 16.
[0037] The aforementioned pressure fan 24 is equipped with an inverter (not shown) for adjusting the airflow rate, which adjusts and controls the airflow rate to match the amount of solid fuel dispensed from the rotary valve 22 at the bottom of the solid fuel storage bin 21, according to the amount of solid fuel injected.
[0038] Furthermore, as shown in Figure 2, the combustion chamber 3, which is horizontally positioned with a circular vertical cross-section and installed in front of the burner 2, is equipped with heat-resistant (heat-storing) casters 25 around its inner wall surface to maintain a high-temperature atmosphere inside the combustion chamber 3. At the same time, to prevent the burning solid fuel from accumulating on the inner wall surface (near the bottom) of the combustion chamber 3, multiple agitated air supply pipes 26, which supply outside air from the tangential direction of the combustion chamber 3 along the inner wall surface, are connected at predetermined intervals along the axial direction of the combustion chamber 3, for example, about 2 to 6 pipes (3 pipes in this embodiment).
[0039] The base end of the agitated air supply pipe 26 is connected to an outside air supply fan 27 equipped with an inverter (not shown) for adjusting the airflow rate. Based on the amount of solid fuel injected, which increases or decreases according to the combustion rate of the burner 2, the fan adjusts the airflow rate to be just right, so that the solid fuel does not accumulate on the inner wall surface (near the bottom) of the combustion chamber 3. It is preferable to control the airflow rate to be just right, as blowing more air into the combustion chamber 3 than necessary will lower the hot air temperature and worsen fuel efficiency.
[0040] Furthermore, the cylindrical kiln body 4, which heats and dries the aggregate by introducing hot air from the combustion chamber 3, has numerous scraping blades 28 for scraping up the aggregate on its inner circumference, and is rotatably tilted and supported by support rollers 30 on the machine base 29, and is rotated at a predetermined speed (rotational speed) by a drive motor 31. The kiln body 4 employs a counter-flow design in which the direction of flow of hot air from the burner 2 and the direction of flow of the aggregate are opposite.
[0041] Furthermore, a hot hopper 32 connected to the combustion chamber 3 is provided at one end of the kiln body 4, and a cold hopper 34 connected to the exhaust flue 33 is provided at the other end. An aggregate discharge port 36 equipped with an aggregate temperature sensor 35 is provided at the lower end of the hot hopper 32, while an aggregate input conveyor 38 equipped with a conveyor scale 37 that can weigh the aggregate to be supplied to the kiln body 4 is provided in the cold hopper 34. The exhaust flue 33 is equipped with an exhaust gas temperature sensor 39 for detecting the exhaust gas temperature, and also includes a bag filter 5 for collecting and purifying dust in the exhaust gas, and an exhaust fan 6 for exhaust gas discharge, with its end connected to the chimney 7.
[0042] Furthermore, the hot hopper 32 is equipped with a static pressure sensor 40 at its upper corner to detect static pressure, and 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 static pressure value detected by the static pressure sensor 40 is maintained at a predetermined negative pressure value, for example, approximately the same as atmospheric pressure or slightly lower than atmospheric pressure. This prevents hot air from blowing out from the gaps at both ends of the rotatably mounted kiln body 4, while also preventing excess outside air, which can cause a deterioration in fuel efficiency, from entering the kiln body 4 as much as possible.
[0043] Furthermore, multiple rows (three rows in this embodiment) of damming bodies 42 are installed around the inner circumferential wall on the downstream side in the direction of hot air flow, extending from approximately the center of the longitudinal direction of the kiln body 4, at predetermined intervals and in positions that do not interfere with the scraping blades 28. These damming bodies 42 temporarily dam the aggregate supplied into the kiln body 4, causing a certain amount of aggregate to accumulate at the bottom of the kiln body 4 extending from approximately the center to the downstream side in the direction of hot air flow, thereby ensuring an aggregate layer of a predetermined thickness.
[0044] As shown in Figure 4, the damming body 42 is roughly ring-shaped and is installed around the inner circumferential wall of the kiln body 4. Its height is approximately 250 mm, for example, to ensure a predetermined aggregate layer thickness. The ring-shaped damming body 42 is divided into an appropriate number of sections and fixed to the inner circumferential wall of the kiln body 4 with gaps D of approximately 75 mm between them. This allows the aggregate remaining in the kiln body 4 after the aggregate supply is completed to gradually pass through the gaps D and be discharged from the kiln body 4, preventing any aggregate from remaining inside the kiln body 4.
[0045] Furthermore, as shown in Figure 6, the scraping blades 28, which are formed in a roughly J-shape in cross-section, are configured such that when the scraping blades fill with aggregate from the aggregate layer E near the bottom of the kiln body 4 as the kiln body 4 rotates, some of the scraped aggregate spills out from the tip of the blades relatively early, when the kiln body 4 has rotated upward by about 90° from the bottom position (0° position). The aggregate continues to fall over a relatively wide area, reaching a position slightly exceeding 180°, and a bale F of aggregate can be formed on one radial surface inside the kiln body 4.
[0046] In the figure, 43 is a controller for controlling each device and equipment of the dryer 1, and has an input / output unit 44 that inputs and outputs input signals from the exhaust gas temperature sensor 39, aggregate temperature sensor 35 and conveyor scale 37, etc., and control signals to the liquid fuel supply device 17, blower 11 and drive motors 12 and 31 for driving the kiln body 4, rotary valve 22, pressure fan 24 and outside air supply fan 27, etc., and a control unit 45 that drives and controls each device and equipment that constitutes the dryer 1.
[0047] The control unit 45 is equipped with a co-firing ratio control unit and a kiln rotation speed control unit, and the co-firing ratio control unit has pre-set and registered the unit calorific value of the liquid fuel (e.g., kerosene or heavy oil) and solid fuel (e.g., crushed rice husks) to be used. 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, the calorific value in liquid fuel terms is calculated for the calculated burner combustion amount, and then the injection amount of solid fuel is calculated so that a predetermined co-firing ratio in terms of calorific value is obtained, for example, a solid fuel co-firing ratio of 30%, and the injection amount of the remaining liquid fuel is also calculated.
[0048] Furthermore, the mixed combustion ratio control unit is further equipped with a solid fuel supply control unit and a liquid fuel supply control unit. The solid fuel supply control unit controls the rotary valve 22, pressure fan 24, and outside air supply fan 27, etc., to achieve the calculated solid fuel injection amount, while the liquid fuel supply control unit controls the liquid fuel supply device 17, drive motor 12, etc., to achieve the calculated liquid fuel injection amount.
[0049] Meanwhile, the kiln rotation speed control unit of the control unit 45 adjusts the rotation speed of the kiln body 4 based on the calculated amount of solid fuel injected, controlling it so that sparks scattered as the solid fuel burns are completely extinguished by contacting and falling into the veil of aggregate formed inside the kiln body 4. The amount of solid fuel injected increases or decreases along with the amount of liquid fuel injected according to the amount of combustion of the burner 2, and consequently the amount of sparks scattered also increases or decreases. Therefore, the rotation speed of the kiln body 4 is increased or decreased to form a veil of aggregate that matches the amount of sparks scattered (so that the sparks cannot pass directly through the kiln body 4).
[0050] Furthermore, the rotation speed of the kiln body 4 should not be kept high at all times to ensure that a large number of aggregate bales are always formed. When the number of aggregate bales increases, the opportunities for contact with the hot air from the burner 2 increase, improving heating efficiency. However, this can result in an unnecessary decrease in exhaust gas temperature, which in some cases can cause condensation inside the exhaust flue 33 or bag filter 5, potentially leading to problems such as corrosion of the flue or blockage of the filter cloth.
[0051] Therefore, it is preferable to conduct combustion experiments in advance, taking into account not only the amount of sparks scattered but also the heating efficiency of the aggregate and the exhaust gas temperature, to determine the appropriate rotation speed of the kiln body 4 at a predetermined standard burner combustion amount (solid fuel injection amount) and to set and register this as the standard rotation speed. When the burner combustion amount (solid fuel injection amount) increases or decreases, the rotation speed should be adjusted by increasing or decreasing it based on the aforementioned standard rotation speed. It is also preferable to determine and register in advance, through combustion experiments, the amount by which the rotation speed of the kiln body 4 should be adjusted in response to the increase or decrease in the burner combustion amount.
[0052] Then, when using the dryer 1 of the asphalt plant with the above configuration to heat and dry aggregate, which is the material for the asphalt mixture, by, for example, co-firing powdered rice husks (a solid fuel) and heavy oil (a liquid fuel), heavy oil is first supplied from the liquid fuel supply device 17 to the burner 2 and ignited to preheat the combustion chamber 3 and the kiln body 4. During this time, the burner 2 operates exclusively on heavy oil. Next, once preheating is complete, the supply of aggregate to the kiln body 4 is started.
[0053] The aggregate supplied into the kiln body 4 is temporarily held in the kiln body 4 by the damming body 42, and when the amount of aggregate held (for example, the amount of aggregate supplied per predetermined time measured by the conveyor scale 37 of the aggregate input conveyor 38) exceeds a predetermined amount, for example, an amount that can form a veil of aggregate sufficient to extinguish the sparks of rice husks scattered inside the kiln body 4 by contacting and dropping them without leakage, the controller 43 calculates the amount of rice husks to be injected from the pre-set mixing ratio of heavy oil and rice husks and the burner combustion amount.
[0054] Then, the amount of rice husks corresponding to the calculated injection amount is dispensed from the rotary valve 22 and injected from each solid fuel injection nozzle 16 via the distributor 20 using air blown from the pressure fan 24. This is then blown into the combustion region formed in the throat 9 by the combustion of the heavy oil injected from the liquid fuel injection nozzle 14, causing ignition and combustion (co-combustion). At this time, the amount of heavy oil injected is reduced by an amount corresponding to the heat generated by the amount of rice husks injected.
[0055] When the ignited rice husks are introduced into the combustion chamber 3 at the front, they are effectively agitated by the agitating air supplied in a swirling manner from the tangential direction of the combustion chamber 3 via the agitating air supply pipe 26, and burn without accumulating on the inner wall surface (near the bottom) of the combustion chamber 3. The hot air generated by the combustion (co-firing) of these rice husks and heavy oil is then led to the kiln body 4 downstream. Furthermore, the rice husks burning in the combustion chamber 3 are not exposed to high temperatures of approximately 1,000°C or higher for approximately 10 minutes or more, which are the conditions for the formation of cristobalite, and thus burn favorably.
[0056] Inside the kiln body 4 into which hot air is introduced, a predetermined amount of aggregate (sufficient for bale formation) is retained by the damming body 42. Therefore, for example, aggregate begins to fall relatively early, when the scraping blades 28 rotate upward by about 90° from the bottom of the kiln body 4, and continues to fall over a relatively wide area until it reaches a position slightly exceeding 180°. As a result, the bale of aggregate formed inside the kiln body 4 does not have large gaps that would allow the hot air to blow through without contacting the aggregate, and the aggregate is efficiently heated and dried.
[0057] On the other hand, in the combustion chamber 3, some of the rice husks, which have poor combustibility, may not burn completely and may scatter as sparks into the kiln body 4. Even in that case, as described above, multiple bales of aggregate with no large gaps are formed inside the kiln body 4, so the sparks will come into contact with and fall onto the bales of aggregate without any leakage, and will be taken into the aggregate layer that is partially heated and dried (at a relatively low temperature and containing some moisture) that remains at the bottom of the kiln body 4, and will be effectively extinguished.
[0058] Once extinguished within the aggregate layer, the sparks, even when raked upwards (into the hot air) along with the aggregate by the raking blades 28, do not reignite (reach the ignition temperature). Instead, they are discharged from the kiln body 4 as fly ash along with dust, introduced into the bag filter 5 via the exhaust flue 33, captured by the built-in filter cloth, and the purified exhaust gas is released into the atmosphere through the chimney 7.
[0059] Furthermore, if the amount of aggregate supplied into the kiln body 4 from the aggregate input conveyor 38 falls below a predetermined amount, the controller 43 may output a control signal to stop the rotary valve 22, thereby stopping the injection of rice husks into the burner 2.
[0060] When the aggregate supply decreases and the amount of aggregate remaining in the kiln body 4 decreases, the scraping blades 28 can only scrape up a small amount of aggregate that is not enough to reach the scraping capacity. In some cases, even if the scraping blades 28 rotate upward by more than approximately 90° from the bottom of the kiln body 4, the aggregate may not start to fall. As a result, even if the rotation speed of the kiln body 4 is increased, only a bale with large gaps that allow sparks to pass through may be formed. In such cases, it is advisable to forcibly stop the injection of rice husks regardless of the combustion rate of the burner 2 and to prioritize preventing sparks from scattering onto the bag filter 5.
[0061] Furthermore, if the exhaust gas temperature sensor 39 provided in the exhaust flue 33 detects an exhaust gas temperature above a predetermined temperature, it may be considered that sparks from the combustion state have passed through the kiln body 4, and the injection of rice husks from the burner 2 may be stopped in the same manner as described above.
[0062] In this embodiment, the amount of aggregate supplied into the kiln body 4 was measured using the conveyor scale 37 of the aggregate input conveyor 38. However, this is not the only method. For example, the amount of each type of aggregate cut from an aggregate hopper (not shown) installed upstream of the aggregate input conveyor 38 may be used. Any method that allows for the determination of the amount of aggregate supplied into the kiln body 4 can be employed.
[0063] Furthermore, the arrangement of each scraping blade 28 is not limited to the configuration of this embodiment. As shown in Figures 7 and 8, each scraping blade 28, located before and after the aggregate flow direction with respect to each damming body 42, may be arranged at a predetermined angle in the circumferential direction of the kiln body 29, creating a stepped arrangement.
[0064] By arranging the components as described above, the starting positions of the aggregate falling from each scraping blade 28, which are located before and after each damming body 42, are shifted by a predetermined angle. As a result, large gaps are less likely to form in the bale of aggregate formed inside the kiln body 4, further suppressing the scattering of sparks to the downstream bag filter 5. It is also expected that the amount of rice husks (solid fuel) used (co-firing ratio) in the co-firing burner 2 can be increased.
[0065] Furthermore, the mixed-combustion burner 2 is not limited to the form of this embodiment; various types of mixed-combustion burners can be used as long as they are capable of co-combusting powdered solid fuel and liquid (gaseous) fuel. [Explanation of Symbols]
[0066] 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…Cleaning blade 33... Exhaust flue 37... Conveyor scale 38...Aggregate input conveyor 42...Damming structure 43…Controller
Claims
1. A dryer for an asphalt plant, comprising: a mixed-combustion burner equipped with a liquid or gaseous fuel injection nozzle for flame formation and a powdered solid fuel injection nozzle; a combustion chamber positioned in front of the burner; a cylindrical kiln body rotatably tilted and supported in front of the combustion chamber, with a variable rotational speed; and a controller for controlling the combustion amount of the burner, which is the amount of liquid or gaseous fuel and solid fuel injected by the burner, and the rotational speed of the kiln body; wherein the inner circumferential wall of the kiln body is provided with a plurality of scraping blades for scraping aggregate and a damming body that blocks and retains a portion of the flow of aggregate within the kiln body; and the controller is configured to increase the rotational speed of the kiln body as the amount of solid fuel injected by the burner increases.
2. The dryer for an asphalt plant according to claim 1, characterized in that the controller stops injecting solid fuel from the burner when the amount of aggregate supplied to the kiln body falls below a predetermined amount.