JP7750694B2 - 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 predetermined amount of water, steam, etc. is added to molten asphalt, the raw material for the asphalt mixture, to foam it (make it foamy), and this foamed molten asphalt (hereinafter referred to as "foamed asphalt") is then mixed in a mixer with aggregate, stone powder, etc. to produce the asphalt mixture.

As for equipment for foaming molten asphalt, the applicant has also filed an application for an asphalt plant as shown in Patent Document 1 (JP 2020-94367 A), which 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 switch valve downstream of the supply pump that selects either a supply path that sends molten asphalt to the mixer or a circulation path that returns the molten asphalt to the supply pump. Water injection nozzles are connected midway along the circulation path, which inject water supplied from a water supply source into the molten asphalt. While the molten asphalt is circulating within the circulation path, water is injected from the water injection nozzles to foam the molten asphalt, which is then supplied to the mixer.

Japanese Patent Application Laid-Open No. 2020-94367

However, while 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, which adds a circulation path to the asphalt supply piping just for foaming, is somewhat large-scale, and installation requires a considerable amount of space and cost. Furthermore, if a switching valve installed in the asphalt supply piping fails to switch, it could affect the production of the asphalt mixture, and replacing a malfunctioning switching valve is extremely 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 has a vibrating screen, aggregate storage bins, aggregate measuring bins, asphalt measuring bins, and mixers arranged in layers on an elevated platform, and is equipped with an asphalt supply pipe and a supply pump that supplies molten asphalt measured in the asphalt measuring bin to the mixer. In this asphalt plant, a water injection nozzle that injects water into the molten asphalt is provided in the asphalt supply pipe downstream of the supply pump, and a nozzle that injects water into the molten asphalt is provided in the asphalt supply pipe downstream of the water injection nozzle. and an asphalt injection nozzle in an asphalt supply pipe downstream of the swirling mixing section. The swirling mixing section is formed in an inverted cone shape with an inner diameter gradually decreasing toward a lower outlet, while an inlet is formed at the top from the side tangent line direction to introduce molten asphalt with added water, and the piping diameters of the inlet and outlet are the same. The molten asphalt with added water introduced from the inlet is mixed while swirling toward the lower outlet, and then supplied to the mixer from the downstream asphalt injection nozzle .

According to the asphalt plant of claim 1 of the present invention, the asphalt supply piping downstream of the supply pump interposed in the asphalt supply piping is equipped with a water injection nozzle, the asphalt supply piping downstream of the water injection nozzle is equipped with a swirling mixing section that mixes water and molten asphalt, and the asphalt supply piping downstream of the swirling mixing section is equipped with an asphalt injection nozzle, and the swirling mixing section is formed in an inverted cone shape whose inner diameter gradually decreases toward the outlet at the bottom, while an inlet is formed at the top for introducing molten asphalt with added water from the side tangent direction , and the piping diameters of the inlet and the outlet are the same, and the molten asphalt with added water introduced from the inlet is mixed while swirling toward the outlet at the bottom and then supplied to the mixer from the downstream asphalt injection nozzle , so that swirling mixing in the swirling mixing section can evenly disperse water in the molten asphalt, and when released into the mixer, a substantially uniformly foamed molten asphalt can be supplied. In addition, the asphalt supply piping has a simple structure that does not involve mechanical parts such as route switching valves, which reduces costs and prevents problems such as an inability to supply molten asphalt.In addition, the simple structure allows the entire device to be made compact, and by reducing installation space, it can be easily installed in existing plants.

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 view in which a part of the swirling mixer is omitted. FIG. 4 is a cross-sectional view taken along line AA in FIG. 3 with a portion thereof omitted.

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 piping downstream of a supply pump, such as a gear pump, that is interposed in the asphalt supply piping that supplies molten asphalt from an asphalt metering tank to a mixer, and the asphalt supply piping downstream of the water injection nozzle is equipped with a swirling mixing section that mixes the water and molten asphalt, and an asphalt injection nozzle .

The swirling mixing section has a circular horizontal cross section, and the outlet at the bottom is positioned on the central axis of the circle. It is formed in an inverted cone shape with the inner diameter gradually decreasing toward the outlet. On the other hand, an inlet is formed at the top from the side tangential direction to introduce molten asphalt with added water. The piping diameters of the inlet and the outlet are the same, and the molten asphalt with added water introduced from the inlet is mixed while swirling along the inner wall surface and discharged from the outlet at the bottom, and the molten asphalt with water evenly dispersed is supplied to the mixer.

When producing an asphalt mixture using foamed asphalt 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 control panel, and one batch of molten asphalt is measured out 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. This cumulatively weighed aggregate, along with various materials such as stone powder that have been separately weighed, are then poured into a mixer for pre-mixing (dry mixing).

After premixing, the molten asphalt is discharged from the asphalt metering tank and the supply pump is driven. A predetermined amount of water, for example, approximately 1 to 3% by weight of the measured amount of molten asphalt, is sprayed from the water injection nozzle onto the molten asphalt flowing down the asphalt supply pipe to the swirling mixer.

Water added to the high-temperature molten asphalt flows down into the swirling mixer along with the molten asphalt, and as it swirls within the swirling mixer and flows down to the outlet at the bottom, it vaporizes and is dispersed evenly throughout the molten asphalt, and is then discharged from the outlet at the bottom into the asphalt supply pipe.

By swirling and mixing in the swirling mixing section, the vaporizing water is dispersed evenly within the molten asphalt, and foamed asphalt with approximately uniform properties can be poured into the mixer after pre-mixing has been completed from the downstream asphalt injection nozzle , where it is mixed with materials such as aggregate in the mixer to produce an asphalt mixture made from the foamed asphalt.

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 swirling mixing section into the asphalt supply pipe. 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 lower than conventional levels.

In addition, because the molten asphalt with added water is supplied to the mixer simply by passing through the swirling mixing section, the time required from metering to discharging into the mixer is comparable to the time required to discharge normal molten asphalt without added water, and hourly production efficiency does not decrease even when producing asphalt mixtures using foamed asphalt.

One embodiment of the present invention will be described below with reference to the drawings.

In Figure 1, reference numeral 1 denotes an asphalt plant that produces asphalt mixtures used in road paving. It mainly comprises a plant body 2, an asphalt tank 3 for storing molten asphalt at an insulated temperature, and a control panel 4 for operating and controlling the plant's various devices. The plant body 2 is supported by an elevated platform 5 with multiple floors, and a bucket elevator 6 is installed alongside 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.

The elevated platform 5 is equipped with 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 supply device 11 that measures molten asphalt and supplies it to the mixer 10, all arranged in layers.

The asphalt metering supply 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 serves as 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 via 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 midway along the asphalt supply pipe 19, which injects water supplied from the water supply pipe 14 into the molten asphalt, and a swirling mixer 21 is located downstream of the water injection nozzle 20 in the asphalt supply pipe 19, which swirls and mixes the water and molten asphalt.

As shown in Figures 3 and 4, the swirling mixer 21 has a circular horizontal cross section, with an outlet 22 located at the bottom on the central axis of the circle. It is formed in an inverted cone shape with an inner diameter that gradually decreases toward the outlet 22. Meanwhile, an inlet 23 is formed at the top tangential direction of the side wall, through which molten asphalt with added water is introduced. The molten asphalt with added water introduced from the inlet 23 is swirled along the inner wall surface and flows downward to the outlet 22 at the bottom, thereby evenly mixing the water into the molten asphalt.

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 swirling mixing section 21, where it is swirled and mixed with the molten asphalt to form a roughly uniform foam, which is then discharged from the outlet 22.

The asphalt metering tank 17 is composed of a metering tank body 25 suspended by a load cell 24 and a surge tank 26 that temporarily receives the molten asphalt discharged from the metering tank body 25.

The upper part of the metering tank body 25 is equipped with an inlet 27 through which the discharge end of the asphalt supply pipe 12 is inserted, and the lower part is equipped with an outlet 28 through which the measured molten asphalt is discharged. It is also equipped with an opening/closing mechanism consisting of a cylinder 29, a piston rod 30, and a stopper 31, and the stopper 31 can be moved back and forth in the vertical direction in response to the extension and retraction of the piston rod 30 to open and close the discharge outlet 28.

In the figure, 32 denotes a discharge gate that discharges aggregate of each particle size stored in each compartment of the aggregate storage bin 8, 33 denotes a load cell that suspends and weighs the aggregate measuring tank 9, 34 denotes a discharge gate that discharges the aggregate cumulatively measured in the aggregate measuring tank 9, 35 denotes an asphalt injection nozzle that injects and pours the molten asphalt supplied from the asphalt supply pipe 19 into the mixer 10, and 36 denotes the mixing blades 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 and production volume of the asphalt mixture to be produced are first input into the plant operation panel 4.

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

Once the cumulative weighing of the aggregate is complete, it is poured into the mixer 10 along with various other materials, such as stone powder, which have been weighed separately, for pre-mixing (dry mixing). In addition, once the weighing of the molten asphalt has been completed, the asphalt metering tank 17 opens the discharge outlet 28 of the metering device main body 25 to discharge the weighed molten asphalt, and activates the supply pump 18 installed in the asphalt supply pipe 19.

A predetermined amount of water is injected from the water injection nozzles 20 into the molten asphalt flowing down the asphalt supply pipe 19 toward the mixer 10, depending on the preset water addition ratio. The water addition ratio to the molten asphalt can be set appropriately by determining through testing, etc., the ratio that produces an appropriate foamed asphalt; for example, it is recommended to set it in the range of approximately 1 to 3% by weight.

The molten asphalt, to which a predetermined amount of water has been added from the water injection nozzle 20, is introduced through the inlet 23 at the top of the swirling mixer 21 and flows downward to the outlet 22 at the bottom, swirling along the inner wall surface. At this time, as the inner diameter of the swirling mixer 21 becomes smaller at the bottom, the molten asphalt and water accelerate, forming a vortex near the bottom discharge, which mixes the molten asphalt and water evenly.

In the swirling mixing section 21, the water in the molten asphalt vaporizes and is swirled and mixed with the molten asphalt, forming a substantially uniform foam that is then discharged from the outlet 22 into the asphalt supply pipe 19. The foam is then injected into the mixer 10, where premixing has been completed, via the downstream asphalt injection nozzle 35, and mixed with the aggregate and other materials in the mixer 10 to produce the desired asphalt mixture.

When producing an asphalt mixture using regular (water-free) molten asphalt in the asphalt plant 1, the asphalt measuring device 11 can produce a regular asphalt mixture by supplying the molten asphalt measured in the asphalt measuring tank 17 to the mixer 10 without spraying water from the water injection nozzle 20, allowing for flexible production of asphalt mixtures using both foamed asphalt and regular molten asphalt.

Furthermore, compared to conventional operational control, there are no major changes other than the control of water injection from the water injection nozzles 20, and molten asphalt can be foamed in existing asphalt plants simply by adding the water injection nozzles 20 and swirling mixer 21 to the asphalt supply piping 19. Because installation is relatively simple and inexpensive, this system can be suitably used in existing asphalt plants.

Furthermore, the water injection nozzles 20 connected to the asphalt supply pipe 19 to inject water into the molten asphalt can 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 around the circumference of the asphalt supply pipe 19.Various modifications can be made as long as water can be injected into the flowing molten asphalt.

This 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... Swirling mixing section 22... Outlet 23... Inlet

Claims (1)

In an asphalt plant having a vibrating screen, aggregate storage bins, aggregate measuring tanks, asphalt measuring tanks, and mixers arranged in layers on an elevated platform, and an asphalt supply pipe and supply pump for supplying molten asphalt measured in the asphalt measuring tank to the mixer, the asphalt supply pipe downstream of the supply pump is equipped with a water injection nozzle for injecting water into the molten asphalt, and the asphalt supply pipe downstream of the water injection nozzle is equipped with a swirling mixer for mixing water and molten asphalt, and The asphalt supply pipe is equipped with an asphalt injection nozzle, the swirling mixing section is formed in an inverted cone shape with the inner diameter gradually decreasing toward the lower outlet, while an inlet is formed at the top from the side tangent line direction for introducing molten asphalt with added water , and the outlet and the inlet have the same pipe diameter, and the molten asphalt with added water introduced from the inlet is mixed while swirling toward the lower outlet, and then supplied to the mixer from the downstream asphalt injection nozzle .