JP7687928B2 - Asphalt Plant - Google Patents

Description

The present invention relates to an asphalt plant that produces asphalt mixtures for road paving, and to an asphalt plant that produces asphalt mixtures using foamed molten asphalt.

Conventionally, when producing an asphalt mixture, a certain amount of water, steam, etc. is added to the molten asphalt, which is the raw material of the asphalt mixture, to make it foamed (bubbly), and this foamed molten asphalt (hereinafter referred to as "foamed asphalt") is mixed with aggregate, stone powder, etc. in a mixer to produce the asphalt mixture.

As shown in Patent Document 1 (JP Patent Publication No. 2020-94367), the applicant has also filed an application for an asphalt plant that, as an apparatus for foaming molten asphalt, includes an asphalt supply pipe equipped with a supply pump that supplies molten asphalt measured in an asphalt measuring tank to a mixer, and a switching valve downstream of the supply pump that selects either a supply path that sends molten asphalt to the mixer or a circulation path that sends molten asphalt back to the supply pump, and connects a water injection nozzle that injects water supplied from a water supply source into the molten asphalt while circulating the molten asphalt in the circulation path, thereby injecting water from the water injection nozzle to foam the molten asphalt and then supplying it to the mixer.

JP 2020-94367 A

However, although the above-mentioned conventional equipment can produce foamed asphalt almost uniformly by adding water to the molten asphalt and circulating it through a circulation path, the equipment configuration that adds a circulation path to the asphalt supply piping just for foaming is somewhat large-scale, and installation requires a certain amount of space and cost. Furthermore, if a switching valve installed in the asphalt supply piping fails to switch, it can affect the production of the asphalt mixture, and the task of replacing a defective switching valve is very troublesome.

In view of the above, the present invention aims to provide an asphalt plant that can produce an asphalt mixture by foaming molten asphalt in a substantially uniform manner using a simple configuration.

In order to solve the above problems, the asphalt plant according to claim 1 of the present invention is an asphalt plant in which a vibrating screen, an aggregate storage bin, an aggregate measuring tank, an asphalt measuring tank, and a mixer are arranged in layers on an elevated platform, and the asphalt plant is equipped with an asphalt supply pipe and a supply pump that supply molten asphalt measured in the asphalt measuring tank to the mixer, and a water injection nozzle that injects water into the molten asphalt is provided in the asphalt supply pipe downstream of the supply pump, and the asphalt supply pipe downstream of the water injection nozzle is equipped with a water injection nozzle that injects water into the molten asphalt. The mixing section is equipped with a mixing section that mixes water and molten asphalt in a supply pipe, and the mixing section is equipped with a cylinder with a larger diameter than the asphalt supply pipe, and an inlet section and an outlet section are connected to both ends of the cylinder via a funnel-shaped connecting section, and the inlet section and the outlet section are connected to the cylinder with their respective central axes offset, while a column is inserted at the middle position of the flow direction of the cylinder in a direction perpendicular to the flow direction, and turbulence is generated in the molten asphalt to which water has been added flowing down inside the cylinder, which is then mixed and stirred before being supplied to the mixer.

The asphalt plant described in claim 2 is characterized in that the inner wall surface of the connecting portion that connects the cylindrical body to the inlet and outlet portions is provided with an obstruction that prevents the flow of water and molten asphalt flowing down inside the cylindrical body.

According to the asphalt plant of claim 1 of the present invention, a water injection nozzle is provided in the asphalt supply pipe downstream of a supply pump that supplies a measured amount of molten asphalt to a mixer, and a stirring and mixing unit is provided in the asphalt supply pipe downstream of the water injection nozzle to mix the water and the molten asphalt. The stirring and mixing unit has a cylinder with a larger diameter than the asphalt supply pipe, and an inlet part and an outlet part are connected to both ends of the cylinder via funnel-shaped connecting parts, and the inlet part The inlet and outlet are connected to the cylinder with their central axes shifted, while a column penetrates the cylinder in the direction perpendicular to the flow direction at the middle position in the flow direction, and the molten asphalt with added water flowing down inside the cylinder is stirred and mixed by generating turbulence, and then supplied to the mixer. By generating turbulence in the flow of molten asphalt with added water flowing down from the inlet of the cylinder to the outlet, water can be dispersed evenly in the molten asphalt, and molten asphalt that has been foamed approximately uniformly can be supplied when it is discharged to the mixer. In addition, the asphalt supply piping has a simple structure without mechanical parts such as a route switching valve, which reduces costs and prevents the occurrence of problems such as the inability to supply molten asphalt. In addition, the simple structure allows the entire device to be compact, and the reduced installation space makes it easy to install in existing plants.

In addition, according to the asphalt plant described in claim 2, the inner wall surface of the connecting portion that connects the cylinder to the inlet and outlet is provided with an obstruction that impedes the flow of water and molten asphalt flowing down inside the cylinder. This creates turbulence while retaining the molten asphalt to which water has been added flowing down from the inlet to the outlet of the cylinder within the cylinder, dispersing the water more effectively and evenly. This allows approximately uniformly foamed molten asphalt to be supplied to the mixer.

FIG. 1 is a schematic explanatory diagram of an asphalt plant according to the present invention. 1 is an explanatory diagram of a main part of an asphalt measuring and supplying device according to the present invention. FIG. 2 is an enlarged front view in which a part of the stirring and mixing section is omitted. FIG. 2 is an enlarged side view in which a part of the stirring and mixing section is omitted. FIG. 4 is a cross-sectional view taken along line AA in FIG. 3 with a portion thereof omitted. 5 is a cross-sectional view taken along line BB of FIG. 4 with a portion thereof omitted. FIG. 3 is a view corresponding to FIG. 2 and showing another embodiment. FIG. 3 is a view corresponding to FIG. 2 and showing yet another embodiment.

In the asphalt plant of the present invention, in a plant of an existing structure, a water injection nozzle that injects water into the molten asphalt is connected to the asphalt supply pipe downstream of a supply pump, such as a gear pump, that is interposed in the asphalt supply pipe with a circular cross section that supplies molten asphalt from the asphalt metering tank to the mixer, and the asphalt supply pipe downstream of the water injection nozzle is equipped with an agitation mixing section that mixes the water and molten asphalt.

The stirring and mixing section has a cylindrical body with a larger diameter than the asphalt supply pipe with a circular cross section, and both ends of the cylindrical body are connected to the cylindrical body with a circular cross section, the inlet section, and the outlet section by funnel-shaped connecting parts, and the central axes of the cylindrical body, the inlet section, and the outlet section are arranged on the same plane and parallel to each other.

The central axes of the inlet and outlet sections are connected to the cylinder with a slight offset so that they are not aligned in a straight line, creating a meandering flow path for the molten asphalt with added water flowing from the inlet to the outlet section, and a cylinder with a circular cross section, for example, is passed through the cylinder at a midpoint in the flow direction in a direction perpendicular to the flow direction, causing the molten asphalt with added water inside the cylinder to collide with the cylinder. This creates turbulence in the molten asphalt with added water flowing down inside the mixing section, stirring and mixing it, and making it possible to supply the molten asphalt to the mixer in a state where the water is evenly dispersed.

When an asphalt mixture using foamed asphalt is produced in an asphalt plant with the above configuration, the amount of asphalt required is calculated from the blending ratio of the asphalt mixture being produced on the plant operation panel, and one batch of molten asphalt is measured in the asphalt measuring tank.

Meanwhile, aggregates of each particle size are discharged from the aggregate storage bin into an aggregate measuring tank based on the above-mentioned mixing ratio, and cumulatively weighed. The cumulatively weighed aggregates, along with various materials such as stone powder that have been separately weighed, are then poured into a mixer for premixing (dry mixing).

After premixing, the molten asphalt is discharged from the asphalt metering tank and the supply pump is driven, and a preset amount of water, for example about 1 to 3% by weight, preferably about 2% by weight of the measured amount of molten asphalt, is sprayed from the water injection nozzle into the molten asphalt flowing down the asphalt supply pipe to the stirring and mixing section.

The water added to the molten asphalt vaporizes and flows down with the molten asphalt into the mixing section. As it flows from the inlet to the outlet of the mixing section, which has a meandering flow path, it collides with a column that penetrates the cylinder, creating turbulence in the flow and stirring it. The added water is dispersed evenly throughout the molten asphalt and is then discharged from the outlet to the asphalt supply pipe.

By mixing and stirring in the mixing section, the vaporizing water is dispersed evenly throughout the molten asphalt, and foamed asphalt with approximately uniform properties can be poured into the mixer after premixing has been completed. It is then mixed with aggregate and other materials in the mixer to produce an asphalt mixture made from foamed asphalt.

In addition, preferably, the connecting section connecting the inlet section and the cylinder is provided with a baffle that prevents the molten asphalt to which water has been added from diffusing into the cylinder along the inner wall surface of the connecting section that expands in diameter from the inlet section, while the connecting section connecting the cylinder and the outlet section is provided with a baffle plate that prevents the molten asphalt to which water has been added from flowing down from the cylinder along the inner wall surface of the connecting section that contracts in diameter to the outlet section.

In this way, some of the molten asphalt with added water introduced from the inlet section flows down along one of the inner wall surfaces of the cylinder toward the outlet section without colliding with the column due to the obstruction on the inlet section side, and is returned to the cylinder body without being discharged from the outlet section due to the obstruction on the outlet section side, and then flows down from the other inner wall surface of the cylinder toward the inlet section.

Meanwhile, some of the molten asphalt with added water introduced from the inlet diffuses inside the cylinder and collides with the column, but flows down from the other inner wall side of the cylinder toward the outlet, where it collides with the molten asphalt with added water flowing down (returning) toward the inlet, generating strong turbulence inside the cylinder, which stirs and mixes the molten asphalt before it is discharged from the outlet. This allows the molten asphalt to be supplied to the mixer with the water more effectively and evenly dispersed.

In this way, the injected water is dispersed evenly in the molten asphalt fed into the mixer, and foamed asphalt with approximately uniform properties can be produced using a simple equipment configuration that involves inserting a stirring and mixing section into the asphalt supply piping. By using this as a raw material, it is expected that materials such as aggregate and stone powder will be mixed well in the mixer, and it is anticipated that the desired asphalt mixture can be produced even if the production temperature is lowered compared to conventional methods.

In addition, since the molten asphalt with added water is supplied to the mixer simply by passing through the stirring and mixing section, the time required from weighing to discharging into the mixer is comparable to the time required to discharge normal molten asphalt without adding water, and the production efficiency per hour does not decrease even when producing an asphalt mixture using foamed asphalt.

Below, one embodiment of the present invention will be described with reference to the drawings.

In Figure 1, 1 is an asphalt plant that produces asphalt mixture, a road paving material, and is mainly composed of a plant body 2, an asphalt tank 3 that stores molten asphalt at an insulated temperature, and an operation panel 4 for operating and controlling the plant's various devices. The plant body 2 has an elevated platform 5 with multiple floors, and a bucket elevator 6 is installed next to the side of the elevated platform 5 to lift new aggregate that has been heated and dried in a dryer (not shown) to the top of the elevated platform 5.

On the elevated platform 5, there are arranged in a hierarchical fashion a vibrating sieve 7 that sifts the heated aggregate discharged from the bucket elevator 6 by particle size, an aggregate storage bin 8 that stores the aggregate sieved by the vibrating sieve 7 by particle size, an aggregate measuring tank 9 that cumulatively measures the aggregate of each particle size discharged from the aggregate storage bin 8, a mixer 10 that mixes various materials such as aggregate and molten asphalt, and an asphalt measuring and supplying device 11 that measures molten asphalt and supplies it to the mixer 10.

The asphalt measuring device 11 is connected to an asphalt supply pipe 12 that supplies molten asphalt from the asphalt tank 3, and a water supply pipe 14 that supplies water from a water storage tank 13, which is a water supply source. The asphalt supply pipe 12 and the water supply pipe 14 are equipped with supply pumps 15 and 16, respectively.

Figure 2 is a schematic diagram of the asphalt metering supply device 11, which includes an asphalt metering tank 17 that measures the molten asphalt supplied through the asphalt supply pipe 12, and an asphalt supply pipe 19 equipped with a supply pump 18, such as a gear pump, that supplies the measured molten asphalt to the mixer 10.

In addition, a water injection nozzle 20 is connected to the asphalt supply pipe 19 midway, which injects water supplied from the water supply pipe 14 into the molten asphalt, and a stirring and mixing section 21 is interposed in the asphalt supply pipe 19 downstream of the water injection nozzle 20, which stirs and mixes the water and molten asphalt.

As shown in Figures 3 to 6, the stirring and mixing section 21 has a cylindrical body 22 that is, for example, about three times larger in diameter than the asphalt supply pipe 19, and an inlet section 23 and an outlet section 24 that have a circular cross section are connected to both ends of the cylindrical body 22 via a funnel-shaped connecting section 25. The connecting section 25 on the inlet section 23 side has an inner diameter that expands toward the cylindrical body 22, while the connecting section 25 on the outlet section 24 side is formed so that the inner diameter decreases toward the outlet section 24, which has an inner diameter similar to that of the asphalt supply pipe 19.

The central axes of the cylinder 22, inlet section 23, and outlet section 24 are arranged on the same plane and in parallel. When the inlet section 23 is extended in the direction of the central axis α, the inlet section 23 and outlet section 24 are connected to the cylinder 22 in a stepped manner via the connecting section 25 so that the contour of the extended inlet section 23 does not overlap with the contour of the outlet section 24. This allows the molten asphalt with added water introduced into the stirring and mixing section 21 to flow down in a meandering manner.

The connecting section 25 is also provided with an obstacle 26a that prevents the molten asphalt to which water has been added from diffusing from the inlet section 23 into the cylindrical body 22, and an obstacle 26b that prevents the molten asphalt from flowing down all at once along the inner wall surface of the connecting section 25 from inside the cylindrical body 22 to the outlet section 24.

In addition, at the midpoint of the flow direction of the cylinder 22, a column 27 with a circular cross section is provided, which runs perpendicular to a plane passing through the central axes of the cylinder 22, the inlet 23, and the outlet 24, and passes through the vicinity of the central axis of the cylinder 22. In addition, the gap C between the inner wall surface of the cylinder 22 and the outer wall surface of the column 27 is ensured to be approximately equal to the inner diameter of the asphalt supply pipe 19.

When water is injected from the water injection nozzle 20 into the high-temperature (approximately 160°C) molten asphalt flowing down the asphalt supply pipe 19 into the mixer 10, the water vaporizes and is introduced into the stirring and mixing section 21, where it is stirred and mixed with the molten asphalt to form a roughly uniform foam before being discharged from the discharge section 24.

The asphalt metering tank 17 is composed of a metering tank body 29 suspended by a load cell 28 and a surge tank 30 that temporarily receives the molten asphalt discharged from the metering tank body 29.

The upper part of the metering tank body 29 is provided with an inlet 31 through which the discharge end of the asphalt supply pipe 12 is inserted, and the lower part is provided with a discharge outlet 32 for discharging the measured molten asphalt. The tank body 29 is also provided with an opening/closing mechanism consisting of a cylinder 33, a piston rod 34, and a plug 35, and the plug 35 is moved back and forth in the vertical direction in response to the extension and contraction of the piston rod 34, thereby opening and closing the discharge outlet 32.

In the figure, 36 is a discharge gate that discharges aggregates of each particle size stored in each compartment of the aggregate storage bin 8, 37 is a load cell that suspends and weighs the aggregate weighing tank 9, 38 is a discharge gate that discharges the aggregate cumulatively weighed in the aggregate weighing tank 9, 39 is an asphalt injection nozzle that injects and feeds the molten asphalt supplied from the asphalt supply pipe 19 into the mixer 10, and 40 is a mixing blade of the mixer 10.

When producing an asphalt mixture using foamed asphalt as a raw material in the asphalt plant 1 configured as described above, the type of asphalt mixture to be produced and the production volume are first input into the plant operation panel 4.

The control panel 4 starts cumulative weighing by discharging aggregate from each compartment of the aggregate storage bin 8 into the aggregate weighing tank 9 according to the inputted composition of the asphalt mixture to be produced, while one batch of molten asphalt is weighed in the asphalt weighing tank 17.

When the cumulative weighing of the aggregate is complete, it is added to the mixer 10 along with various materials such as stone powder that have been weighed separately, and premixing (dry mixing) is performed. In the asphalt metering tank 17, where the weighing of the molten asphalt has been completed, the discharge port 32 of the metering tank body 29 is opened to discharge the weighed molten asphalt, and the supply pump 18 interposed in the asphalt supply pipe 19 is operated.

A predetermined amount of water is injected from the water injection nozzle 20 into the molten asphalt flowing down the asphalt supply pipe 19 to the mixer 10 according to a preset water addition ratio. According to the results of tests conducted by the inventors, when the water addition ratio to the molten asphalt is less than 1% by weight, the amount of water added is small and suitable foamed asphalt cannot be obtained. On the other hand, it was confirmed that good foamed asphalt can be obtained by adding 2% or more by weight of water. However, no difference in properties could be confirmed when comparing asphalt mixtures using foamed asphalt with more than 3% by weight of water added and foamed asphalt with around 2% by weight of water added. For these reasons, it is recommended to set the water addition ratio to around 2% by weight (for example, 1.5 to 2.5% by weight).

The molten asphalt to which a predetermined amount of water has been added from the water injection nozzle 20 flows down the asphalt supply pipe 19 and is introduced from the inlet 23 of the stirring and mixing section 21. The flow in the stirring and mixing section 21 will be explained with reference to the cross-sectional view of FIG. 6. The molten asphalt to which water has been added and introduced from the inlet 23 flows down along the lower inner wall surface of the cylinder 22 in FIG. 6 toward the outlet 24 without diffusing into the cylinder 22 due to the obstruction 26a provided at the connection 25 on the inlet side, and is temporarily returned toward the upper inner wall surface of the cylinder 22 by the obstruction 26b provided at the connection 25 on the outlet 24 side.

Meanwhile, some of the molten asphalt to which water has been added, introduced from the inlet 23, diffuses within the cylinder 22 and collides with the column 27, while flowing downward toward the upper inner wall surface of the cylinder 22 in FIG. 6. The water is returned from the outlet 24 side along the upper inner wall surface of the cylinder 22 to the inlet 23 side, and collides with the molten asphalt to which water has been added, generating strong turbulence within the cylinder 22, and the water is stirred and mixed so as to be evenly dispersed in the molten asphalt.

In the stirring and mixing section 21, the water in the molten asphalt is vaporized and stirred and mixed with the molten asphalt, and is discharged from the discharge section 24 into the downstream asphalt supply pipe 19 while being foamed to a substantially uniform consistency. The water is then injected into the mixer 10, where premixing has been completed, through the asphalt injection nozzle 39 at the downstream end, and mixed with the aggregate and other materials in the mixer 10 to produce the desired asphalt mixture.

Figure 7 shows another embodiment in which the stirring and mixing section 21 is rotated 90° around the central axis of the cylinder 22 and connected to the asphalt supply pipe 19 so that the inlet 23 and outlet 24 are horizontal. Also, Figure 8 shows another embodiment in which the stirring and mixing section 21 is connected to the asphalt supply pipe 19 so that the outlet 24 is below the inlet 23. Even if the stirring and mixing section 21 is connected to the asphalt supply pipe 19 as shown in Figures 7 and 8, the flow path of the molten asphalt to which water has been added in the stirring and mixing section 21 meanders as described above and collides with the column 27 in the cylinder 22, generating turbulence for stirring and mixing, and the added water can be dispersed evenly in the molten asphalt.

In the above embodiment, an example was described in which the connecting portion 25 of the stirring and mixing portion 21 was provided with the obstructions 26a and 26b. However, even if the obstructions 26a and 26b are not provided at the connecting portion 25, the molten asphalt to which water has been added and introduced into the cylinder 22 from the introduction portion 23 collides with the columnar body 27 penetrating the cylinder 22, generating turbulence, which causes the molten asphalt to be stirred and mixed within the cylinder 22, and the added water can be dispersed evenly within the molten asphalt.

In the above embodiment, a cylinder 27 with a circular cross section is inserted through the cylinder 22. However, if the molten asphalt containing added water flowing from the inlet 23 to the outlet 24 inside the cylinder 22 can be collided with the cylinder 27, the cylinder 27 can be made to have a cross section other than a circular one, such as a square or polygonal cylinder, and can be used to stir and mix the water within the cylinder 22. The added water can be dispersed evenly within the molten asphalt.

In addition, when the asphalt plant 1 produces an asphalt mixture using normal (water-free) molten asphalt as a raw material, the asphalt measuring and supplying device 11 can produce a normal asphalt mixture by supplying the molten asphalt measured in the asphalt measuring tank 17 to the mixer 10 without injecting water from the water injection nozzle 20, allowing for flexible production of asphalt mixtures using both foamed asphalt and normal molten asphalt as raw materials.

In addition, compared to conventional operational control, there are no major changes other than the control of water injection from the water injection nozzle 20, and molten asphalt can be foamed in existing asphalt plants simply by adding the water injection nozzle 20 and the stirring and mixing section 21 to the asphalt supply piping 19. This is relatively simple and inexpensive to install, so it can be suitably adopted even when used in existing asphalt plants.

The water injection nozzles 20 connected to the asphalt supply pipe 19 to inject water into the molten asphalt may be, for example, two water injection nozzles 20 arranged and connected at opposing positions on the asphalt supply pipe 19, or multiple water injection nozzles 20 arranged and connected at a predetermined angle in the circumferential direction of the asphalt supply pipe 19. Various modifications can be made as long as water can be injected into the flowing molten asphalt.

The present invention can be widely used in asphalt plants that produce asphalt mixtures using foamed asphalt as a raw material.

REFERENCE SIGNS LIST 10 mixer 11 asphalt metering supply device 17 asphalt metering tank 18 supply pump 19 asphalt supply piping 20 water injection nozzle 21 agitation mixing section 22 cylinder 23 inlet section 24 outlet section 25 connection section 27 column

Claims (2)

In an asphalt plant equipped with an asphalt supply pipe and a supply pump that supply molten asphalt measured in the asphalt measuring tank to the mixer, a vibrating sieve, an aggregate storage bin, an aggregate measuring tank, an asphalt measuring tank, and a mixer arranged in layers on an elevated platform, the asphalt supply pipe downstream of the supply pump is equipped with a water injection nozzle that injects water into the molten asphalt, and a mixing nozzle that mixes the water and the molten asphalt is installed in the asphalt supply pipe downstream of the water injection nozzle. An asphalt plant comprising a mixing section, the stirring and mixing section having a cylinder with a larger diameter than the asphalt supply pipe, an inlet section and an outlet section connected to both ends of the cylinder via a funnel-shaped connecting section, the inlet section and the outlet section connected to the cylinder with their respective central axes offset, and a columnar body penetrating the cylinder at a midpoint in the flow direction in a direction perpendicular to the flow direction, causing turbulence in the molten asphalt to which water has been added flowing down inside the cylinder, stirring and mixing the molten asphalt before supplying it to the mixer. The asphalt plant according to claim 1, characterized in that the inner wall surfaces of the connecting parts that connect the cylinder to the inlet and outlet are provided with obstacles that impede the flow of water and molten asphalt flowing down inside the cylinder.

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