MOBILE ASPHALT PLANT

Abstract

A mobile asphalt plant for producing asphalt includes a heating unit, a container unit, a plurality of augers, and an injector. The heating unit includes one or more heaters to generate heated gas, a tank to hold heat transfer oil, and one or more first plenum tubes extending from the heaters to within the tank. The first plenum tubes transport the heated gas to the tank to heat the heat transfer oil. The container unit includes a hopper to receive the aggregate material and one or more second plenum tubes extending from the one or more first plenum tubes and extending within the hopper. The second plenum tubes transport the heated gas from the first plenum tubes to heat the aggregate material. The augers are arranged as a series of augers, with a first one of the augers receiving the aggregate material from the hopper. Each of the augers conveys the aggregate material to a next one of the augers. Each of the augers heats the aggregate material using the heat transfer oil from the tank. The injector is connected to one of the augers and injects asphalt oil into the aggregate material to produce asphalt.

Description

FIELD OF THE INVENTION

The invention relates to an apparatus used to produce asphalt, and in particular, to a mobile asphalt plant.

BACKGROUND OF THE INVENTION

Asphalt is a viscous or semi-solid substance that is commonly used in road construction. The main ingredients for producing asphalt are aggregate material (such as gravel) and asphalt oil. Typically, the production process requires that the gravel and asphalt oil must first be heated to a temperature of greater than 300° F. before being mixed together. An immense amount of heat is required to heat the gravel from ambient temperature to the required mix temperature. The specific heat for basalt rock (one of components of gravel) is 0.2 BTU/lb ° F. For example, at 100% efficiency, it would take approximately 150,000 BTU to heat 1 (cubic) yard of gravel from approximately 50° F. to 300° F.

Conventional asphalt production involves the use of a large, rotating internally fired drum. Gravel is fed into the drum and travels slowly through the drum while being heated by hot flue gases from the flames. Although this may be effective in heating the gravel, the flue gases are able to leave the drum unimpeded, with most of the heat being lost. The escaping flue gases leave as wasted heat, resulting in higher operating costs, increased greenhouse gas emissions, and poor efficiency.

Another challenge facing asphalt plants is that care must be taken when operating in below-freezing temperatures. Conventional asphalt plants cannot accommodate gravel that has been frozen into lumps. As a result, additional steps and/or procedures must be taken to handle frozen gravel.

Furthermore, as asphalt is commonly used for road construction, it would be advantageous to be able to have the asphalt plant as close as possible to the location where the road is being constructed, thereby reducing the time and cost required to transport the asphalt.

Therefore, there is a desire for a mobile asphalt plant that is more energy efficient and more environmentally friendly than conventional asphalt plants. There is also a desire for a mobile asphalt plant that can be operated in below-freezing temperatures.

These and other objects will be better understood by reference to this application as a whole. Not all of the objects are necessarily met by all embodiments of the invention described below.

SUMMARY OF THE INVENTION

In one aspect, the invention comprises a mobile asphalt plant that uses conductive heat transfer to heat aggregate material. In addition, the mobile asphalt plant is able to use the flue gases emanating from burners to transfer heat to a hopper and to augers.

The mobile asphalt plant channels heat energy from combustion and directs it to preheat aggregate material stored in the hopper and further adds heat energy to the process as exhaust gases are introduced to the aggregate material within the augers.

Furthermore, the mobile asphalt plant is able to be used in below-freezing temperatures, even with gravel in the hopper. If the gravel contains frozen lumps, the mobile asphalt plant is able to slow down the overall process to allow the gravel to defrost before it is it further heated to the final mixing temperature.

In accordance with one embodiment, a mobile asphalt plant for producing asphalt from aggregate material and asphalt oil comprises a heating unit, a container unit, a plurality of augers, and an injector. The heating unit comprises one or more heaters configured to generate heated gas, a tank configured to holding heat transfer oil, and one or more first plenum tubes extending from the heaters to within the tank. The first plenum tubes are configured to transport the heated gas to the tank to heat the heat transfer oil. The container unit comprises a hopper configured to receive the aggregate material and one or more second plenum tubes extending from the one or more first plenum tubes and extending within the hopper. The second plenum tubes are configured to transport the heated gas from the one or more first plenum tubes to heat the aggregate material. The augers are arranged as a series of augers, with a first one of the series of augers configured to receive the aggregate material from the hopper. Each of the augers is configured to convey the aggregate material to a next one of the series of augers. Each of the augers is configured to heat the aggregate material using the heat transfer oil from the tank. The injector is connected to one of the augers and is configured to inject the asphalt oil into the aggregate material to produce asphalt.

In another embodiment, the mobile asphalt plant further comprises a conveyor belt for transporting the aggregate material between the hopper and the first one of the series of augers.

In still another embodiment, each of the plurality of augers comprises a rotating shaft, one or more flights attached to the shaft, and an auger motor configured to effect rotation of the shaft. The rotation of the shaft effects movement of the aggregate material along the auger.

In still yet another embodiment, at least one of the flights comprise one or more vent openings.

In yet another embodiment, each of the augers further comprises an interior shell and an exterior shell. The interior shell substantially encloses the shaft and the one or more flights, with the aggregate material moving within the interior shell. The exterior shell substantially encloses the interior shell. The interior shell and the exterior shell define, at least in part, a cavity through which the heat transfer oil flows, thereby heating the aggregate material within the interior shell.

In a further embodiment, movement of the aggregate material through each of the plurality of augers is in an opposite direction to movement of the heat transfer oil through each of the plurality of augers.

In still a further embodiment, the mobile asphalt plant further comprises first tubing configured to transport heat transfer oil from the tank to a last one of the augers in the series of augers.

In still yet a further embodiment, the heat transfer oil moves through each of the augers in order from the last one of the augers to the first one of the augers.

In a further embodiment, the mobile asphalt plant further comprises one or more auger tubing configured to transport heat transfer oil between the augers.

In another embodiment, the mobile asphalt plant further comprises second tubing configured to transport heat transfer oil from the first one of the augers to the tank.

In yet another embodiment, the mobile asphalt plant further comprises a load-out conveyor for transporting the asphalt from the augers off of the mobile asphalt plant.

In still yet another embodiment, the load-out conveyor is a drag slat conveyor.

In a further embodiment, the load-out conveyor is configured to heat the asphalt.

In yet a further embodiment, the load-out conveyor receives heat transfer oil from the tank for heating the asphalt.

In still yet a further embodiment, each of the augers comprise an inlet for receiving the aggregate material and an outlet for expelling the aggregate material.

In still another embodiment, the inlet and the outlet are located proximate to opposite ends of the auger.

In still yet another embodiment, for at least some of the augers, the auger is angled such that the inlet is lower than the outlet.

In still a further embodiment, the plurality of augers is six augers.

In a further embodiment, the mobile asphalt plant further comprises a bed for supporting the heating unit, the container unit, the plurality of augers, and the injector.

In yet a further embodiment, the mobile asphalt plant further comprises a plurality of wheels for supporting the bed.

The foregoing was intended as a summary only and of only some of the aspects of the invention. It was not intended to define the limits or requirements of the invention. Other aspects of the invention will be appreciated by reference to the detailed description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by reference to the drawings thereof, in which:

FIG. 1 shows a side view of the mobile asphalt plant of the present invention in accordance with one embodiment of the invention;

FIG. 2 is a top view of the mobile asphalt plant of FIG. 1;

FIG. 3 is an end view of the mobile asphalt plant of FIG. 1;

FIG. 4 is an end view of the heating unit of the mobile asphalt plant of FIG. 1;

FIG. 5 is a side view of the heating unit of FIG. 4;

FIG. 6 is a longitudinal section view of the heating unit of FIG. 4;

FIG. 7 is an end view of the container unit and the conveyor belt of the mobile asphalt plant of FIG. 1;

FIG. 8 is a side view of FIG. 7;

FIG. 9 is a lateral section view of FIG. 7, taken along line 9-9 of FIG. 8;

FIG. 10 is a side view of one of the augers of the mobile asphalt plant of FIG. 1;

FIG. 11 is a lateral section view of the auger of FIG. 10, taken along line 11-11 of FIG. 10;

FIG. 12 is a longitudinal section view of the auger of FIG. 10;

FIG. 13 is a top view of a load-out conveyor of the mobile asphalt plant of FIG. 1;

FIG. 14 is side view of the load-out conveyor of FIG. 13;

FIG. 15 is a lateral section view of the load-out conveyor of FIG. 13, taken along line 15-15 of FIG. 14;

FIG. 16 is a side view of another embodiment of the mobile asphalt plant;

FIG. 17 is an end view of the mixing unit of the mobile asphalt plant of FIG. 16;

FIG. 18 is a side view of the mixing unit of FIG. 17; and

FIG. 19 is a longitudinal section view of the mixing unit of FIG. 17.

DETAILED DESCRIPTION

Referring to FIGS. 1 to 3, a mobile asphalt plant 10 in accordance with the invention may take the form of a trailer, comprising a bed 11 supported by a plurality of wheels 13. The mobile asphalt plant 10 further comprises a container unit 12 configured to receive aggregate material 2 (for example, crushed gravel or other suitable material) to be used in producing asphalt. The mobile asphalt plant 10 also comprises a heating unit 14 for providing heat for the mobile asphalt plant 10. The container unit 12 and the heating unit 14 are preferably supported on the bed 11.

Referring to FIGS. 4 to 6, in one embodiment, the heating unit 14 comprises a tank 16 and one or more first plenum tubes 18. The tank 16 is configured to hold heat transfer oil 4. The one or more first plenum tubes 18 extend into and within the tank 16. The heating unit 14 further comprises one or more heaters 20 that are connected to the first plenum tubes 18. The heaters 20 are configured to provide heated gas into the first plenum tubes 18. For example, the heaters 20 may be diesel-fired burners, with a capacity of approximately 2 MBTU, that are located proximate to the tank 16.

Heated gas from the heaters 20 is conveyed into the tank 16 through the first plenum tubes 18. Heat is transferred from the heated gas to the heat transfer oil 4 in direction A (as shown in FIG. 6) through the first plenum tubes 18, thereby heating the heat transfer oil 4 within the tank 16. Preferably, at least some of the first plenum tubes 18 comprise a plenum tube surface 68, with one or more fins 64 located on the plenum tube surface 68 to increase the effective surface area of the first plenum tubes 18. In particular, the fins 64 are preferably located on the portions of the first plenum tubes 18 within the tank 16 in order to improve the efficiency of the heat transfer to the heat transfer oil 4. The first plenum tubes 18 may also comprise a number of bends or curves within the tank 16, again to increase the effective surface area of the first plenum tubes 18 within the tank 16, thereby increasing the efficiency of the heat transfer. The tank 16 may be insulated in order to minimize or reduce heat loss to the ambient air.

Preferably, the heaters 20 are configured to activate (or fire) when required in order to maintain the temperature of the heat transfer oil 4 within the tank 16 at approximately 450° F. The first plenum tubes 18 may also extend out of the tank 16 towards the container unit 12, carrying (still) heated gas away from the tank 16 in direction B (as shown in FIG. 6).

Referring to FIGS. 7 to 9, the container unit 12 comprises a hopper 15 with upper and lower hopper openings 22, 24. Preferably, the aggregate material 2 is introduced into the hopper 15 through the upper hopper opening 22 and subsequently leaves the hopper 15 through the lower hopper opening 24. Gates may be provided at one or both of the upper and lower hopper openings 22, 24 to control the ingress and egress of the aggregate material 2 into and out of the hopper 15, respectively.

Heat is provided to the aggregate material 2 located within the hopper 15. The container unit 12 comprises one or more second plenum tubes 26 that are connected to the first plenum tubes 18. The heated gas from the first plenum tubes 18 are conveyed to the second plenum tubes 26 in direction C (as shown in FIG. 8). At least a portion of the second plenum tubes 26 preferably extend within the hopper 15, for example, along a length of the hopper 15, and through the aggregate material 2. In one embodiment, the second plenum tubes 26 may take the form of an array of second plenum tubes 26 that are arranged substantially parallel to each other and extending for substantially an entire length of the hopper 15. As the heated gas is conveyed through the second plenum tubes 26, heat is transferred through the plenum tubes 26 to the aggregate material 2, thereby heating the aggregate material 2.

Preferably, the hopper 15 is insulated by an outer surrounding hopper jacket 70 covering at least a portion of an exterior of the hopper 15 to minimize or reduce heat loss to the ambient air. In one embodiment, one or more of the second plenum tubes 26 may also extend within the hopper jacket 70, as best shown in the section view of FIG. 9.

The heated gas generated by the heating unit 14 is channeled through the first plenum tubes 18 and through the second plenum tubes 26 before exiting through a gas release 72 proximate to a rear of the hopper 15 in direction D (as shown in FIG. 8). The heated gas moves by convection and pressure differential through the second plenum tubes 26 through the hopper 15 and within the hopper jacket 70.

Preferably, the hopper 15 holds approximately three cubic yards of the aggregate material 2. The aggregate material 2 may be held within the hopper 15 for a period of time before exiting the hopper 15. In one embodiment, this period of time is approximately 12 minutes, although other periods of time are also possible. During this time, the aggregate material 2 is subjected to heat from the second plenum tubes 26.

Referring again to FIGS. 7 to 9, the mobile asphalt plant 10 further comprises a conveyor belt 28, at least a portion of which is located preferably under the lower hopper opening 24 and is configured to receive the aggregate material 2 exiting from the hopper 15. The conveyor belt 28 comprises first and second belt ends 76, 78, with the aggregate material 2 preferably being received by the conveyor belt 28 proximate to the first belt end 76. When the aggregate material 2 leaves the hopper 15, it has already been prewarmed, thereby requiring less energy to bring it up to its final mix temperature. The hopper 15 is able to operate in below-freezing temperatures without the danger of the aggregate material 2 freezing up. This is due partly to the container unit 12 providing interior and exterior heating zones.

The mobile asphalt plant 10 further comprises one or more augers 30. The conveyor belt 28 and the augers 30 are also preferably supported by the bed 11. The conveyor belt 28 conveys the (prewarmed) aggregate material 2 from the first belt end 76 to the second belt end 78, towards the one or more augers 30, in direction E (as shown in FIG. 8). Preferably, at least two of the augers 30 are provided. In the embodiment shown in FIGS. 1 to 15, six of the augers 30 (i.e. 30a, 30b, 30c, 30d, 30e, and 30f) are provided. Once the aggregate material 2 reaches the end of the conveyor belt 29, the aggregate material 2 is introduced into the first one of the augers 30 (i.e. auger 30a). The aggregate material 2 will then travel through the first one of the augers 30 before exiting and then entering the next one of the augers 30 (i.e. auger 30b). In this manner, the aggregate material 2 will travel through along each of the augers 30 sequentially until it reaches the end of the last one of the augers 30 (i.e. auger 30f). It is understood that other numbers of the augers 30 may be used.

Referring to FIGS. 10 to 11, each of the augers 30 comprises an inlet 32, where the aggregate material 2 enters the auger 30 in direction F (as shown in FIG. 12), and an outlet 34, where the aggregate material 2 exits the auger 30 in direction G (as shown in FIG. 12). Preferably, the inlet 32 and the outlet 34 are located proximate to opposite ends of the augers 30. The augers 30 are arranged such that the aggregate material 2 will travel along an ascending series of the augers 30. Preferably, at least for some of the augers 30, the outlet 34 is oriented higher than the inlet 32, as shown in FIGS. 10 and 12. For example, in the embodiment shown in FIGS. 1 to 3, for at least the augers 30a, 30b, 30c, 30d, and 30e, this is the case.

Furthermore, the inlet 32 for one of the augers 30 is preferably lower than the inlet 32 for a successive one of the augers 30. For example, the inlet 32a for the auger 30a is preferably lower than the inlet 32b for the auger 30b. Therefore, the inlet 32a for the auger 30a may be at a relative low point (compared to inlets 32b, 32c, 32d, 32e, 32f). However, it is understood that the configuration and orientation of the augers 30 may be varied, such that only a subset of the augers 30 follows certain configurations and orientations.

The augers 30 perform the function of moving the aggregate material 2 from the conveyor belt 28 to where the asphalt oil is introduced. However, the augers 30 also perform the function of heat transfer to the aggregate material 2.

Referring again to FIGS. 10 to 12, each of the augers 30 comprises an interior shell 36, within which the aggregate material 2 moves. The interior shell 36 is preferably made from formed sheet metal, such as hardened wear-resistant steel. This allows the interior shell 36 to resist abrasion as the aggregate material 2 moves within the interior shell 36. Each of the augers 30 further comprises a rotating shaft 38 that is substantially enclosed by the interior shell 36. A plurality of fine pitch flights 40 extends from the rotating shaft 38. The rotation of the shaft 38 and the flights 40 within the interior shell 36 acts to move the aggregate material 2 from the inlet 32 towards the outlet 34. Alternatively, the flights 40 may take the form of a single helical flight 40 extending from the shaft 38 that acts to convey the aggregate material 2 from the inlet 32 towards the outlet 34. Each of the augers 30 may further comprise an auger motor 50 for effecting rotation of the shaft 38

Each of the augers 30 further comprises an exterior shell 42 that is also preferably made from formed sheet metal. The auger motor 50 may be mounted on the exterior shell 42 and is mechanically connected to the shaft 38 to effect rotation of the shaft 38. The exterior shell 42 substantially encloses the interior shell 36, generally defining a cavity 44 between the interior shell 36 and the exterior shell 42. The heated heat transfer oil 4 from the tank 16 is pumped into the cavity 44 through which it flows.

As described above, the heat transfer oil 4 is heated to a temperature of approximately 450° F. in the tank 16. The heat transfer oil 4 is conveyed using first tubing 60 from the tank 16 to the last one of the augers 30 (e.g. auger 30f) in direction H (as shown in FIG. 2), proximate to the outlet 34 (e.g. outlet 34f). For each of the augers 30, the heat transfer oil 4 is pumped into the cavity 44 proximate to the outlet 34 in a direction towards the inlet 34. In other words, the heat transfer oil 4 will flow in a direction opposite to the movement of the aggregate material 2. As the heat transfer oil 4 flows along the cavity 44 of each of the augers 30, some of its heat energy will be transferred to the aggregate material 2 through the interior shell 36.

After the heat transfer oil 4 has flowed through the last one of the augers 30 (e.g. auger 30f) and has flowed proximate to the inlet 32 of the last one of the augers 30, the heat transfer oil 4 may be conveyed to the second last one of the augers 30 (e.g. auger 30e) through auger tubing 74, proximate to the outlet 34 of the second last one of the augers 30. The heat transfer oil 4 will have cooled slightly (from the heat transfer to the aggregate material 2). The heat transfer oil 4 is then conveyed into the cavity 44 of the second last one of the augers 30 (e.g. auger 30e) proximate to the outlet 34, so that the heat transfer oil 4 again flows through the auger 30 in a direction opposite to that of the movement of the aggregate material 2. More heat energy is transferred to the aggregate material 2 before the heat transfer oil 4 flows proximate to the inlet 32 of the second last one of the augers 30.

In a similar manner, the heat transfer oil 4 is then conveyed to the next one of the augers 30 (e.g. to the auger 30d, then to the auger 30c, then to the auger 30b, then to the auger 30a, etc.), using auger tubing 74. As can be appreciated by the above, the heat transfer oil 4 and the aggregate material 2 move through the augers 30 in opposite directions. As the heat transfer oil 4 moves through the augers 30, heat energy is transferred to the aggregate material 2. Eventually, the heat transfer oil 4 will exit the first one of the augers 30, proximate to the inlet 32. At that point, the heat transfer oil 4 has cooled considerably (from the heat transfer to the aggregate material 2) and is returned to the tank 16 through second tubing 62, in direction J (as shown in FIG. 2). Once in the tank 16, the heat transfer oil 4 is heated using the first plenum tubes 18 (as discussed above).

In one embodiment, the flights 40 may comprise one or more vent openings 46 formed thereon, as shown in FIG. 11. The vent openings 46 aid in the mixing process and encourages increased air movement through the auger 30.

An injector 48 introduces asphalt oil into the aggregate material 2. The injector 48 is located on one of the augers 30, preferably closer to the end of the series of augers 30. For example, in one embodiment, where there are six of the augers 30, the injector may be located on the second-to-last one of the augers 30 (i.e. the auger 30e). However, it is understood that the injector 48 may be located at any one of the augers 30. The asphalt oil acts to bind the aggregate material 2 together. The aggregate material 2 and the asphalt oil are preferably mixed within the last ones of the augers 30. For example, in the embodiment shown in FIGS. 1 to 3, the injector 48 is located on the auger 30e. Therefore, much of the mixing of the aggregate material 2 and the asphalt oil would occur within the last of the augers (i.e. the auger 30f). Because of this, the configuration of the last one of the augers 30 may have a different configuration in terms of the orientation and size of the flights 40, in order to promote mixing.

In order to achieve improved efficiency (i.e., lower operating cost, lower environmental impact), in one embodiment, an inlet air shroud 54 may be provided proximate to the inlet 32 of the first one of the augers 30 (i.e. auger 30a). The inlet air shroud 54 may be connected to the gas release 72 and is configured to guide the heated gas into the first one of the augers 30.

Referring to FIGS. 13 to 15, the mobile asphalt plant 10 further comprises a load-out conveyor 80 that receives the mixture of the aggregate material 2 and asphalt oil after it leaves the outlet 34 of the last one of the augers 30. The load-out conveyor 80 may take the form of a drag slat conveyor, comprising first and second conveyor ends 82, 84, with the mixture of the aggregate material 2 and asphalt oil entering the load-out conveyor 80 proximate to the first conveyor end 82. The load-out conveyor 80 comprises one or more chains 81 with conveyor paddles 94 attached to the chains 81. The chains 81 are configured to move along the load-out conveyor 80 from the first conveyor end 82 to the second conveyor end 84. The movement of the chains 81 in turns moves the conveyor paddles 94, thereby moving the mixture along the load-out conveyor 80 towards the second conveyor end 84. Preferably, the load-out conveyor 80 extends away from the bed 11 at an angle (as best shown in FIG. 3) and acts to move the mixture away from and out of the mobile asphalt plant 10. For example, the mixture may be conveyed over the second conveyor end 84 and into waiting trucks for transporting the mixture away, to be used as asphalt. In one embodiment, the load-out conveyor 80 extends from the bed 11 at an angle of approximately 30° from the horizontal.

In one embodiment, the load-out conveyor 80 may further be configured to provide heat to the mixture of the aggregate material 2 and asphalt oil. In this embodiment, the load-out conveyor 80 comprises one or more exterior walls 96 and one or more interior walls 98, with the exterior walls 96 and the interior walls 98 generally defining conveyor cavities 100. A heating fluid, such as the heat transfer oil 4, may be conveyed through the conveyor cavities 100 to provide heat to the mixture as it passes along the load-out conveyor 80. In the case where the heating fluid is the heat transfer oil 4, the heat transfer oil 4 may be transported by the first tubing 60 from the tank 16 to the load-out conveyor 80. Preferably, the heat transfer oil 4 travels along the conveyor cavities 100 in a direction from the second conveyor end 84 to the first conveyor end 82 (i.e. in an opposite direction to the movement of the mixture). After the heat transfer oil 4 reaches the first conveyor end 82, the heat transfer oil 4 may then be transferred to the last one of the augers 30 for movement through the augers 30 (as described above).

Referring to FIG. 16, in another embodiment of the invention, in addition to, or in place of, the augers 30, the mobile asphalt plant 10 may comprise one or more heating conveyors 90 for moving the aggregate material 2 from the conveyor belt 28. The heating conveyors 90 may operate in a manner similar to that of the load-out conveyor 80, moving the aggregate material 2 along while also providing heat to the aggregate material 2 as it moves along the heating conveyors 90. Multiple ones of the heating conveyors 90 may be arranged sequentially (similar to the augers 30) such that the aggregate material 2 is conveyed along each of the heating conveyors 90 sequentially. Heat transfer oil 4 may be used to provide heat to the aggregate material 2.

For example, in one embodiment, the heating conveyors 90 may be located after the last one of the augers 30 such that the aggregate material 2 will exit the outlet 34 of the last one of the augers 30 and enter the first one of the one or more heating conveyors 90. After the aggregate material 2 has moved through all of the heating conveyors 90, the aggregate material 2 is then conveyed to the load-out conveyor 80. The injector 48 may be located on one of the heating conveyors 90 to introduce asphalt oil to the aggregate material 2.

Alternatively, in another embodiment, the augers 30 may be completely replaced by the heating conveyors 90 such that the aggregate material 2 exits the conveyor belt 28 and into the first one of the heating conveyors 90, as shown in FIG. 16. In this embodiment, the injector 48 may also be located on one of the heating conveyors 90 to introduce asphalt oil to the aggregate material 2.

In still another embodiment, the heating conveyors 90 may be located such that the aggregate material 2 exits the conveyor belt 28 and into the first one of the heating conveyors 90. After moving through each of the heating conveyors 90, the aggregate material 2 then enters into the first one of the augers 30 and moves through each of the augers 30 (as discussed above).

Referring back to FIGS. 16 to 19, in one embodiment, instead of the load-out conveyor 80, the mixture of aggregate material 2 and asphalt oil enters into a mixing unit 52 in direction K (as shown in FIG. 19) after passing through the augers 30 and/or the heating conveyors 90. Referring to FIGS. 17 to 19, the mixing unit 52 is preferably in the form of a rotating cylinder that is able to accept the mixture of aggregate material and asphalt oil from the augers 30 and/or the heating conveyors 90. Preferably, the mixing unit 52 comprises internally-welded mixing paddles 56 that are configured to scoop and drop the mixture as it rotates. As the mixture tumbles inside the mixing unit 52, the aggregate material 2 is evenly coated by the asphalt oil. Rotation of the mixing unit 52 may be effected by a mixing motor 66. When the mixture exits the mixing unit 52, in direction L (as shown in FIG. 19), it has become hot mix asphalt and is ready to be spread onto road surface.

The mobile asphalt plant 10 may be transported to different locations, such as by towing. This would allow the mobile asphalt plant 10 to be moved close to locations where asphalt is required, such as a road under construction or the like.

The mobile asphalt plant 10 is able to provide increased energy efficiency in the production of asphalt. Furthermore, by providing a gentle heating process for the aggregate material 2, the resulting mixture is less likely to experience degradation in either the aggregate material 2 or the asphalt oil.

It will be appreciated by those skilled in the art that the preferred embodiment has been described in some detail but that certain modifications may be practiced without departing from the principles of the invention.

Claims

1. A mobile asphalt plant for producing asphalt from aggregate material and asphalt oil, the mobile asphalt plant comprising: a heating unit comprising: one or more heaters configured to generate heated gas;a tank configured to holding heat transfer oil; andone or more first plenum tubes extending from the heaters to within the tank, the one or more first plenum tubes configured to transport the heated gas to the tank to heat the heat transfer oil;a container unit comprising: a hopper configured to receive the aggregate material; andone or more second plenum tubes extending from the one or more first plenum tubes and extending within the hopper, the one or more second plenum tubes configured to transport the heated gas from the one or more first plenum tubes to heat the aggregate material; anda plurality of augers arranged as a series of augers, wherein a first one of the series of augers is configured to receive the aggregate material from the hopper, wherein each of the plurality of augers is configured to convey the aggregate material to a next one of the series of augers, and wherein each of the plurality of augers is configured to heat the aggregate material using the heat transfer oil from the tank; andan injector connected to one of the plurality of augers and configured to inject the asphalt oil into the aggregate material to produce the asphalt.

2. The mobile asphalt plant of claim 1, further comprising a conveyor belt for transporting the aggregate material between the hopper and the first one of the series of augers.

3. The mobile asphalt plant of claim 1, wherein each of the plurality of augers comprises: a rotating shaft;one or more flights attached to the shaft; andan auger motor configured to effect rotation of the shaft;

4. The mobile asphalt plant of claim 3, wherein at least one of the flights comprise one or more vent openings.

5. The mobile asphalt plant of claim 3, wherein each of the plurality of augers further comprises: an interior shell substantially enclosing the shaft and the one or more flights, wherein the aggregate material moves within the interior shell; andan exterior shell substantially enclosing the interior shell;

6. The mobile asphalt plant of claim 5, wherein movement of the aggregate material through each of the plurality of augers is in an opposite direction to movement of the heat transfer oil through each of the plurality of augers.

7. The mobile asphalt plant of claim 6, further comprising first tubing configured to transport heat transfer oil from the tank to a last one of the plurality of augers in the series of augers.

8. The mobile asphalt plant of claim 7, wherein the heat transfer oil moves through each of the plurality of augers in order from the last one of the plurality of augers to the first one of the plurality of augers.

9. The mobile asphalt plant of claim 8, further comprising one or more auger tubing configured to transport heat transfer oil between the plurality of augers.

10. The mobile asphalt plant of claim 9, further comprising second tubing configured to transport heat transfer oil from the first one of the plurality of augers to the tank.

11. The mobile asphalt plant of claim 1, further comprising a load-out conveyor for transporting the asphalt from the plurality of augers off of the mobile asphalt plant.

12. The mobile asphalt plant of claim 11, wherein the load-out conveyor is a drag slat conveyor.

13. The mobile asphalt plant of claim 11, wherein the load-out conveyor is configured to heat the asphalt.

14. The mobile asphalt plant of claim 13, wherein the load-out conveyor receives heat transfer oil from the tank for heating the asphalt.

15. The mobile asphalt plant of claim 1, wherein each of the augers comprise an inlet for receiving the aggregate material and an outlet for expelling the aggregate material.

16. The mobile asphalt plant of claim 15, wherein the inlet and the outlet are located proximate to opposite ends of the auger.

17. The mobile asphalt plant of claim 16, wherein for at least some of the plurality of augers, the auger is angled such that the inlet is lower than the outlet.

18. The mobile asphalt plant of claim 1, wherein the plurality of augers is six augers.

19. The mobile asphalt plant of claim 1, further comprising a bed for supporting the heating unit, the container unit, the plurality of augers, and the injector.

20. The mobile asphalt plant of claim 19, further comprising a plurality of wheels for supporting the bed.