Patent Application
20110129296
The present invention relates to the field of asphalt manufacturing and, in particular, to a portable reclaimed asphalt pavement (RAP) pre-heating system for pre-heating RAP being conveyed into asphalt manufacturing modules during the asphalt manufacturing process.
The creation and maintenance of millions of miles of roads depend on asphalt production. Most asphalt production is performed in asphalt plants or factories from whence the asphalt is transported to the pavement site. In many cases, this involves significant distances, while transporting heavy materials, such as silos to store the asphalt and the asphalt itself. Especially for longer distances or in colder climates, there is also a need to keep the asphalt warm enough, and therefore soft enough, to be compacted into the road during paving. The distances traveled, combined with transporting heavy materials, and the need to heat the asphalt during transport, together require a great deal of fuel, which increases the cost and carbon footprint of the operation. Therefore, there is a need for portable asphalt manufacture. As a part of a portable asphalt plant, there is a need to be able to dry aggregate material outside of a factory. In particular, there is a need to safely dry reclaimed or recycled asphalt pavement (“RAP”).
The raw material for roadway asphalt, known in the industry as Hot Mix Asphalt (“HMA”), is usually prepared at a batch plant. In addition to the asphalt oil itself, HMA includes an aggregate, which is typically a mixture of sand, small rocks, and other filler material, such as shredded rubber tires, or may be RAP that is crushed into small pieces. This aggregate used in the manufacturing process invariably has moisture entrapped therein, which must be removed before the asphalt oil is added.
Conventional HMA plants include a conveyor belt upon which aggregate is conveyed into a rotating drying drum, which may include impellers to lift the aggregate to assist in the drying process. The drum is typically rotated and heated to a very high temperature. Heating is typically accomplished by firing an oil burner and using a fan located adjacent to the drum to direct a flow of hot air into the drum. The aggregate is tumbled in the hot air flow by the rotation of the drum, and by the impellers lifting the aggregate and dropping it into the air stream, essentially drying and heating the aggregate. Once the aggregate is heated to a desired temperature, typically in the range of 120-180° C., the aggregate is sufficiently dried and a flow of hot liquid asphalt is introduced to the aggregate, and mixed therewith, producing the finished HMA.
In today's industry, there is great emphasis on using RAP. It reuses existing materials, rather than requiring the quarrying of new aggregate materials. It also has the advantage of already having some asphalt content, thus lowering the amount of asphalt needed to make a new finished product. In these respects, it is both economical and green. Using RAP presents challenges not present with traditional asphalt production, however. Specifically, although the RAP must be heated to at least 212° F. for the moisture to be released from the aggregate, as RAP contains asphalt, it can only be heated to a certain extent before the asphalt ignites around 375-400° F. As traditional asphalt production generally involves aggregate materials such as rock and sand, before the asphalt is introduced to the mix, there was not such a need for temperature control. Demand for asphalt that is 25-50% RAP is common now, but given the challenges inherent in using RAP, it is difficult to raise the percentage above 15%. As demand for, and interest in, RAP grow, production systems with better heat control are necessary.
The process employed by conventional HMA plants is effective at drying and heating the aggregate and generally produces an acceptable end product. However, this process has three substantial drawbacks.
First, the burners used to heat the aggregate during the drying and pre-heating process use an enormous amount of fuel, which is costly both in terms of purchasing the oil and in terms of controlling the emissions produced thereby. Therefore, the longer these burners are forced to run, the greater the expense of producing the HMA. Unfortunately, even with the use of impellers to mix the aggregate during drying, bulk drying of the entire batch of aggregate at one time is inefficient and results in the burners being fired for a significant period of time to effect drying, resulting in a significant amount of expensive fuel being used.
Second, the longer the drying process takes, the fewer batches of HMA that may be produced. Because the equipment used in HMA production is very expensive, and because the demand for HMA is such that all batches produced by a given plant would be readily sold, increasing the rate at which batches of HMA may be processed will greatly increase the profits for HMA manufacturers.
Third, the amount of aggregate used in each batch produced by the HMA manufacturing process is typically measured by the weight of the aggregate in the drying drum. Therefore, variations in the moisture content of the aggregate can cause the amount of aggregate to be too low. Thus, the manufacturer is forced to either live with these variations, resulting in batch-to-batch inconsistencies of the HMA produced, or to add more wet aggregate to the drum, which further increases the amount of fuel used and drying time.
In addition to HMA, a number of companies have recently developed formulations for Warm Mix Asphalt (WMA) to replace traditional HMA. WMA is manufactured using a process similar to HMA, but uses different formulations of aggregate and asphalt additives that are each mixed at lower temperatures than HMA. Switching from HMA to WMA reduces the amount of fuel used in the manufacturing process, as it is heated to lower temperatures than HMA, and allows the use of certain additives that cannot withstand the temperatures required during the production of HMA. Further, WMA has been found to reduce the curing time of the asphalt, allowing a shorter period of time between laying the asphalt surface and allowing the pavement to be used.
A number of tests on WMA have produced encouraging results. However, a recent report by the National Center for Asphalt Technology cautioned that the moisture content of the mix is an important consideration and cites the potential for moisture damage due to too much water left in close content with the aggregate. Thus, there is a need for a means for pre-drying the aggregate used in WMA production in order to reduce the chance of moisture damage.
At least two systems currently exist for drying particulate matter, such as aggregate, using a heating element over a conveyor belt. The first system is disclosed in U.S. Pat. No. 4,136,964 to Swisher. This is an apparatus for simultaneously mixing and conveying particulate material, the apparatus comprising a housing having an input end and an output end disposed vertically higher than the input end, means for feeding the particulate material into the input end of the housing, a conveyor disposed within the housing and having a plurality of lifting surfaces provided with perforations therethrough so that a portion of the particulate material being lifted by each lifting surface descends through the perforations and is mixed with particulate material being lifted by lifting surfaces disposed therebelow, and, means for discharging the mixed particulate material from the output end of the housing.
The housing of the mixer/conveyor is provided with at least one opening through the upper wall section thereof to facilitate the introduction of heated exhaust gases produced by an associated burner assembly connected thereto. Each burner assembly is comprised of a housing having suitable refractory material lining the inner surfaces thereof, and an oil or gas fired burner of the conventional construction. Hydrocarbon fuel for the burner will be supplied in a conventional manner from a suitable source of fuel, while combustion-supporting air is preferably supplied by a blower assembly via an air duct. An adjustable draft, exhaust damper assembly should also be connected to the output end of the housing to facilitate control of the pressure in the mixer/conveyor as well as to direct the heated exhaust gases exiting from the housing.
Although capable of drying particulate matter, this system, and its burner assembly in particular, is ill suited for portability. First, the mixer/conveyor and burner assembly are bulky because they are completely enclosed so that the heated exhaust gases may flow across the material to be dried. This bulk cannot be diminished to provide better portability without thwarting the burner assembly's heating capabilities. Moreover, doing so, especially in the field, would cause the introduction of the exhaust gases into the atmosphere. Second, in part because of the system's bulk, it is difficult to set up and break down, which is a key aspect of portability. Given the size and weight of the various assemblies that make up the system, a crane is necessary to position the assemblies. A crane is another large vehicle, requiring a skilled operator, which would have to come out to the site, greatly increasing the cost and carbon emissions of using the system.
The second currently existing system for drying particulate matter, such as aggregate, using a heating element over a conveyor belt is disclosed in U.S. Pat. No. 5,557,858 to Macaluso et al. This system is an infrared wood product dryer apparatus including an enclosure structure defining an interior, a conveyor assembly configured for conveying a particulate material along a material flow path through the interior substantially between an inlet and an outlet, an array of infrared radiant energy sources configured for exposing the material to infrared radiant energy while it is conveyed along the path, and a series of agitators configured for agitating the material in order to increase the exposure of the material to the infrared radiant energy. A gas recirculation assembly is provided to direct a heated interior gas onto the material in order to convection-dry the material. An exhaust assembly reduces the moisture content of the interior gas by drawing a quantity of the gas from the dryer so that fresh gas having a lower moisture content may be drawn into the dryer.
This system is also capable of drying particulate matter, but is also ill suited for portability. First, as a practical matter, the inlet to which material to be dried is introduced to the system is at the top of the system, so that material must be lifted up to be dried. This lifting up will likely require an added mechanical element, for the system to be used in the field. The more elements necessary for the system's use, the more costly and difficult it becomes to use in the field. Moreover, portable systems need to be able to be driven around on a truck or other vehicle, and this system is too tall for that type of transportation. Any system that is going to be driven on roads needs to be fairly flat so that trucks can get through tunnels and other low passages while hauling the system. This system has at least three stacked layers of conveyor belts and heaters within the enclosure structure, making it quite tall, and thus unwieldy for road transportation.
Therefore, there is a need for a portable system and method for reducing the amount of fuel consumed to dry and pre-heat the aggregate used in the asphalt manufacturing process, for reducing the amount of time that it takes to dry and pre-heat the aggregate used in the asphalt manufacturing process, to increase the accuracy of the amount of aggregate used in the asphalt manufacturing process in order to increase the batch-to-batch consistency of the asphalt produced thereby without the need to add wet aggregate to the batch during drying and pre-heating, and to reduce the risk of moisture damage due to the presence of excess moisture in aggregate used in the production of WMA.
The present invention is a portable system for heating aggregate material, a portable system for producing asphalt, a portable system for continuously repaving roadways, and a method for continuously repaving roadways. In its most basic form, the system for heating aggregate material includes a trailer sized and dimensioned to hold an assembly including a conveyor belt in communication with a source of the aggregate material, at least one infrared chamber, a source of fuel, and at least one mixer disposed between the infrared chamber and the conveyor belt. The conveyor belt is preferably manufactured of a rubberized material that is adapted to convey the aggregate material at a predetermined rate. The infrared chamber, or chambers, is disposed in substantially parallel relation to the conveyor belt at a distance sufficient to allow infrared heating of the aggregate material. The fuel source is preferably a gaseous fuel, such as propane, that is in communication with the infrared chamber. The mixer is dimensioned and disposed relative to the conveyor belt so as to mix the aggregate material during pre-drying.
This system is particularly well suited for partial repaves. Center line cracks in a paved roadway are common and occur more frequently than cracks in the rest of the road. Outer edges of roads that have been widened similarly usually fail long before the original roadway fails. A partial repave could repave only a center line crack and/or damaged outer edges that need repair more frequently than the entirety of the road needs repaving. Such partial repaves save the time and expense of a full repave when the remainder of the road is in good shape. The system is well suited for repaving of areas only 1-2 feet wide, as would be the situation with the repave of only a center line and/or outer edges of a roadway.
In operation, the conveyor belt conveys the aggregate material from its source and under the infrared chamber at a predetermined rate to a terminal end of the conveyor belt. The aggregate is preferably partially or entirely made up of RAP. The fuel flows to the infrared chamber, which burns the fuel causing the infrared chamber to emit infrared radiation therefrom. The infrared radiation contacts the top surface of the aggregate that is conveyed on the conveyor belt and acts to heat the top portion of the aggregate material proximate to the infrared chamber. The mixer then mixes the aggregate material such that heated and unheated aggregate material are mixed together, allowing the unheated aggregate material proximate to the conveyor belt to rise to the top surface proximate to the infrared chamber. The infrared radiation from the infrared chamber then heats the mixed aggregate material to effectively pre-heat and pre-dry the aggregate material.
The preferred heating system includes at least three, and preferably eight infrared chambers. The preferred infrared chambers include a solid aluminum top cover. Moisture escapes out of the upper end of the infrared chambers in the gaps between the chambers where the mixers are placed, as discussed below. The conveyor belt is preferably inclined so as to act as a chimney. In an alternative embodiment, the top portion of the infrared chamber is manufactured of expanded metal, which allows for the escape of such moisture. In still other embodiments, the chamber includes a plurality of holes formed therethrough to allow such moisture to be vented. Each infrared chamber includes a plurality of infrared converters.
The preferred heating system also includes at least one igniter assembly in communication with the infrared chamber. The igniter assembly is adapted to ignite the fuel within the infrared chamber so that it may be burned and turned into infrared radiation. The preferred embodiment utilizes multiple, individual igniter assemblies, which are each in communication with a single infrared chamber and are independently controlled by the control box. Each igniter assembly is itself in communication with the source of fuel, and includes two igniter rods, two sparker transformers with mounting plates, one flame sensor, a main gas valve, and a pressure switch. The rods are in communication with the infrared converters of the infrared chamber, so that the ignited fuel may travel into the converters. Having individual igniter assemblies for each infrared chamber, rather than a single igniter used to ignite the fuel within each of the chambers, is preferable as it allows individual infrared heaters to be turned off. This provides greater control over the heating of the system, which is particularly important when RAP is being used as the aggregate.
The mixers are placed between the infrared chambers so as to mix the aggregate material as it travels along the conveyor belt. The infrared chambers are preferably disposed in a row over the conveyor belt such that each infrared chamber is disposed relative to an adjacent infrared chamber so as to form a gap therebetween. One mixer is preferably disposed within each gap. One mixer is also preferably disposed at the end of the conveyor belt, after the last infrared chamber.
In the preferred embodiment for use with RAP, the mixer is a rotary mixer assembly. This preferred mixer is a bolted roller with 5″ diameter disposed across the conveyor belt. The roller includes six evenly spaced bolts protruding from cross sections spaced 2″ apart down the length of the pipe, with every other set of bolts being offset from the sets of bolts on either side of it. In the preferred embodiment, the mixers are individually controlled as to how fast they rotate, and thus mix the aggregate.
In another embodiment, the mixer is a series of ramps that are disposed proximate to the conveyor belt. Each ramp has a ramp surface that is disposed at an angle from the plane formed by the conveyor belt and is dimensioned to allow the asphalt aggregate to be pushed up the ramp by aggregate that is in contact with the conveyor belt and to tumble back onto the belt, effectively mixing the aggregate. This embodiment is not preferred because the preferred incline of the conveyor belt leads to damming of the aggregate material at the mixers.
In another embodiment, the mixing is a result of multiple conveyor belts that are spaced to allow the aggregate material to tumble from one conveyor belt to the adjacent conveyor belt. Once tumbled, the aggregate material is further mixed by moving through the tines of a mixer as described below. This embodiment is not preferred as the multiple conveyor belts, each with separate mechanics, drive up the cost of the system.
In some embodiments, the mixers include a plurality of tines forming a plurality of spaces therebetween, and each is dimensioned and disposed within each gap such that each tine of one mixer is aligned with a space of adjacent mixers. In this manner, the aggregate is thoroughly mixed rather than just having the areas adjacent to the tines mixed. This embodiment is not preferred for use with RAP because it has been found that it does not release moisture from the aggregate as well as the mixers mentioned above.
In other embodiments, the mixer includes a channel, and a plurality of tines rotatably attached to the channel. The tines are in communication with at least one spring and are disposed in sufficiently close proximity to the conveyor belt so as to contact the aggregate material conveyed by the conveyor belt. The spring allows the tines to flex while preventing them from becoming entangled with the conveyor belt. In this embodiment, the tines may be joined together into a rake and a single spring is used to maintain the tines in position. However, in other embodiments, each tine is independent from the other tines and is in communication with its own spring. These embodiments are also not preferred for being less efficient at moisture release.
In the preferred embodiment, an area at the end of the conveyor belt includes multiple smaller mixers disposed between the conveyor belt and the infrared chambers. This area is preferably the length of two infrared converters down the conveyor belt, but be less or more area of the conveyor belt. The small mixers are preferably similar to the preferred bolted rollers discussed above, but smaller in diameter and the length of the protruding bolts. These small mixers may be directly adjacent to one another, rather than distanced by the length of an infrared chamber. They may also be periodically spaced between the larger mixers that are spaced between each infrared chamber. The speed at which the small mixers rotate is also preferably controllable, and is preferably faster than the speed of rotation of the large mixers. These mixers protect against ignition of the asphalt within the RAP by ensuring even distribution of heat throughout the aggregate when the aggregate is at its hottest at the end of the conveyor belt.
The preferred embodiment includes further heat control measures to safeguard against asphalt ignition. Specifically, the second to last space above the conveyor belt for an infrared chamber is preferably occupied not by an infrared chamber, but by a heat reflector that will reflect back the heat of the aggregate, but not introduce additional heat. There is also preferably a thermometer or other heat sensor between the heat reflector and the last infrared chamber that indicates the temperature of the aggregate at that point. The last infrared chamber will be activated if the aggregate is not near temperatures at which the asphalt is likely to ignite. Alternatively, it will remain dormant, without adding additional heat to the aggregate if the aggregate is near temperatures at which the asphalt is likely to ignite. Although this is the preferred embodiment, it is understood that all spaces may be filled with infrared chambers, and that heat reflectors may be substituted for one or more heat chambers in any of the positions along the conveyor belt. Finally, at least the last infrared chamber at the end of and above the conveyor belt, but preferably all infrared chambers above the length of the conveyor belt are adapted to move up and down to increase or decrease the distance between the infrared chambers and the conveyor belt. Furthermore, as discussed above, as each infrared chamber includes a designated igniter, it is possible to turn each individual infrared chamber on and off as desired.
Some embodiments of the heating system of the present invention include at least one hygrometer and/or thermometer for determining the moisture content and/or temperature of the aggregate at least at the start of the pre-heating process. In such embodiments, the hygrometers and/or thermometers are preferably in communication with a conveyor control, which slows the conveyor belt or speeds up the conveyor belt based upon the amount of moisture within the aggregate. Thus use of such a control is preferred when the system is used in connection with WMA manufacturing as it allows for careful control of the amount of moisture while maximizing the speed of the process in instances where there are minimal amounts of moisture within the aggregate.
The preferred heating system includes a control box in electrical communication with the infrared chamber and the source of fuel. The control box includes controls for controlling several system functions, including the operation of each individual igniter assembly, the flow of fuel from the source to the infrared chambers, blower motor operation, conveyor belt speed control, large mixer rotation speed controls, small mixer rotation speed controls, and infrared chamber elevation controls.
The preferred heating system also includes at least one blower motor in communication with the control box, the source of fuel, a source of air, and the infrared chamber. The blower motor is controlled by the control box and is adapted to mix fuel and air together and force the mixture of fuel and air into the infrared chamber. The use of a blower motor is preferred as it allows the infrared chamber to consistently produce a greater amount of heat than may be produced by relying upon the pressure from the source of fuel.
The preferred heating system also includes a source of power, preferably a generator disposed on top of the trailer and capable of powering the controls and mechanical elements of the system.
In its most basic form, the portable system for producing asphalt includes the heating system as described above with a portable asphalt producing module disposed on the trailer at the terminal end of the conveyor belt so that the conveyor belt provides heated and dried aggregate material to the asphalt producing module. The asphalt producing module includes a pugmill and an additive receptacle. The pugmill is preferably portable, and may be substituted in some embodiments with a drum mill. The additive receptacle is a receptacle adjacent to the pugmill that introduces additives into the aggregate material supplied to the pugmill. When employing conventional HMA methods, the additive receptacle adds liquid asphalt to the dried aggregate material to produce asphalt that may pave a road. Alternatively, when employing WMA methods, the requisite additives may be introduced to turn the mix into WMA that may pave the road. The addition of either liquid asphalt for HMA, or additives for WMA is automated. Moreover, the asphalt producing module is preferably adapted for either alternative.
In its most basic form, the system for continuously repaving a roadway includes a joint heater, a grinder, a hopper, a drying apparatus, an asphalt producing module, a paver, and a roller. The joint heater is adapted to heat the road to be ripped up before it is ripped up so as to soften the material, and includes a tractor pulling at least one trailer with infrared heaters attached to the trailer's underside so as to heat the ground beneath the trailer. The grinder is adapted to rip up the pavement and grind it into small pieces of aggregate material. The grinder deposits the ground up aggregate material into the hopper. The hopper is adapted to level out the flow and depth of aggregate material from the grinder. In the preferred embodiment, the hopper has sensors so that it can determine if more aggregate material is required than what the grinder provided in order to keep up the desired production rate of the repaving system. The hopper also has storage capabilities for holding aggregate material not provided by the grinder so that if the sensors determine that more aggregate material is needed, the hopper can add more material. These features are particularly useful when RAP is being used in the repaving process, as additional material may be necessary to sufficiently repave the area from which the RAP has just been ripped from the road. The hopper provides an even layer of aggregate material to the drying apparatus.
The drying apparatus is a portable heating system as described above including the conveyor belt, infrared chambers, source of fuel, and mixers. The drying apparatus heats and dries the aggregate material as it travels along the conveyor belt. At the conveyor belt's terminal end, the dried aggregate material is deposited in an asphalt producing module, also described above.
The repaving system also includes a paver, which can be positioned adjacent to the asphalt producing module so that the asphalt producing module can provide the newly made asphalt directly to the paver. The paver can then lay down the asphalt over the area of road that was just ripped up. The roller may then follow the paver and compact the asphalt. In this way, the road is replaced with new, recycled asphalt at the same rate at which it was ripped up, moments after it was ripped up.
In the preferred repaving system, the system also includes a cleaning unit that leads the repaving system by vacuuming up dirt in the roadway to be repaved before it is preheated by the join heater.
The preferred repaving system also includes at least one ground infrared heater attached to the bottom of the trailer such that it emits heat onto the area of road that has been ripped up by the grinder. Heating the ground to be repaved allows for a better thermal bond between the ground and the asphalt to be replaced upon the ground. The ground infrared heaters raise the temperature of the ground by approximately 80-100° F., and prepare the ground for the hot asphalt to be laid down so as to avoid a cold joint.
In the preferred embodiment of the repaving system, the system includes six vehicles lined up so that they can operate together. The vehicles are, in order, the cleaning unit, the joint heater, the grinder, the trailer holding the hopper, drying apparatus and asphalt production module, the paver, and the roller. The joint heater follows the cleaning unit so that it preheats the roadway just vacuumed by the cleaning unit. The grinder follows the joint heater so that it rips up the roadway just preheated and softened by the joint heater. The trailer follows the grinder and is aligned with the grinder so that the grinder can deposit the aggregate material into the hopper on the trailer at the first end of the conveyor belt of the drying apparatus. The ground infrared heaters attached to the bottom of the trailer thus heat the ground that has just had pavement removed from it. The paver follows the trailer and is aligned with the trailer so that the asphalt producing module can provide the paver with freshly made asphalt, and the paver lays down the asphalt over the area of ground that has just had pavement removed from it. The roller follows the paver so that it compacts the asphalt just laid down by the paver. Some embodiments do not include the cleaning unit. In some embodiments, the drying apparatus and asphalt producing module are disposed on separate vehicles. In all embodiments, however, the vehicles and/or trailers are aligned so as to operate the system as described and continuously repave the roadway.
The preferred method for continuously repaving a road includes the steps of vacuuming the roadway to be ripped up; pre-heating the roadway to be ripped up; ripping up the roadway to be repaved; grinding the cleaned, ripped up roadway into aggregate material; depositing the aggregate material from the grinder to a hopper; depositing the aggregate material from the hopper to a conveyor belt; conveying the aggregate material along the conveyor belt under heating elements; mixing the aggregate material as it is conveyed along the conveyor belt; heating the ground to be repaved; depositing the aggregate material into an asphalt producing module; providing the asphalt product to a paver; laying down asphalt over the roadway that was just ripped up with the asphalt product; and compacting the asphalt product with a roller.
The systems and method of the present invention greatly reduce fuel consumption in asphalt production and road paving. The heating system alone provides dry, warm aggregate material to the asphalt producing module. The fact the aggregate material is already warm means that asphalt producing module need not provide as much heat. In other words, the liquid asphalt being added to the aggregate need not be so hot. The fact that the aggregate material is completely dry ensures consistent high quality of the asphalt produced in the asphalt producing module. The portability of the repaving system means that asphalt can be produced in situ, eliminating or greatly reducing transportation fuel needs. Moreover, as the asphalt can be laid down immediately after it is produced, when it is still warm, fuel is saved from maintaining the heat of the asphalt and/or having to reheat the asphalt between its production and its placement on a road. The portable repaving system is particularly useful for small or remote towns that may be far from a conventional asphalt producing factory.
The system and methods are also very well suited for use with RAP. As described above, several heat controlling measures, such as adjustable elevation of the infrared chambers, individual controls for each infrared chamber, temperature sensors, additional mixers, and the strategic substitution of heat reflectors for infrared chambers in certain places make these systems much safer to use with RAP. As temperature is well controlled, the possibility of igniting the asphalt inherent in the RAP is lessened, if not eliminated. Moreover, the preferred mixer for these systems and the preferred positioning of the conveyor belts at an incline allow for optimal moisture release from the RAP, which commonly has high moisture content at the outset.
Therefore, it is an aspect of the invention to provide a portable aggregate heating system, a portable asphalt producing system, a portable system for continuously repaving a roadway, and a method for continuously repaving a roadway.
It is a further aspect of the invention to provide systems capable of controlling the heat during RAP drying so that the asphalt in RAP does not ignite.
It is a further aspect of the invention to reduce the amount of fuel consumed to dry the aggregate used in the HMA manufacturing process.
It is a further aspect of the invention to provide a system and method for reducing the amount of time that it takes to dry the aggregate used in the HMA manufacturing process.
It is a further aspect of the invention to provide a reflector used in connection with heaters in order to focus the heat downward.
It is a further aspect of the invention to provide a system and method to increase the accuracy of the amount of aggregate used in the HMA manufacturing process in order to increase the batch-to-batch consistency of the HMA produced thereby without the need to add wet aggregate to the batch during drying.
It is a further aspect of the invention to provide a system and method to reduce the risk of moisture damage due to the presence of excess moisture in aggregate used in the production of WMA.
It is a further aspect of the invention to reduce the amount of transportation necessary to provide asphalt to a road needing paving.
It is a further aspect of the invention to reduce the amount of fuel used in rewarming asphalt in preparation for its use in paving.
It is a further aspect of the invention to provide a portable asphalt making system that may be quickly and easily assembled and rearranged as necessary.
These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims and accompanying drawings.
Referring to
Trailer 9 is preferably a 50′ trailer, but may be smaller or larger depending on the size of the conveyor belt 12 and number of infrared chambers 14 included in the heating system 10 being utilized. In addition, for heating systems 10 that include many infrared chambers 14, more than one trailer 9 may be utilized and aligned with one another.
Referring now to
The heating system 10 includes a conveyor belt 12 in communication with a source (not shown) of the aggregate material 22. The conveyor belt 12 has a first end 11, where aggregate material 22 is first deposited onto the conveyor belt 12, and a terminal end 13, where the dried and heated aggregate material 22 leaves the conveyor belt 12. The conveyer belt 12 preferably takes the form of conveyor belts currently used to transport aggregate material in conventional HMA and WMA manufacturing processes. The belt may be manufactured of a non-combustible material, such as steel, but is preferably a composition belt manufactured of a rubberized material. Such a material is preferred due its gripping properties and price. The conveyor belt 12 is adapted to convey the aggregate material 22 at a predetermined rate from the source to another location, such as a rotating drying drum (not shown). The conveyor belt 12 is preferably in an inclined position, up to a four to one incline, to facilitate the chimney like aspects of the aluminum top portion 77 (shown in
The heating system 10 also includes at least one infrared chamber 14. In the embodiment of
The infrared chambers 14 are in communication with a source of fuel 16, preferably propane but natural gas may also be used. When natural gas is used, the gas must be introduced to the infrared chambers 14 at a higher pressure than when propane is used, but no modifications to the hardware of the system are necessary to use natural gas instead of propane. In the embodiment of
The preferred blower motor 25 also includes a shut off valve (not shown) to shut off the flow of fuel 16 to the infrared chambers 14. A control box 18, which is in electrical communication with the blower motor 25 and a source of power 50, preferably controls the operation of the blower motor 25. Source of power 50 is preferably a generator as shown in
At least one large mixer 20 is disposed between the infrared chambers 14 and the conveyor belt 12. The large mixer 20 is dimensioned and disposed relative to the conveyor belt 12 so as to mix the aggregate material 22 during pre-drying. The large mixer 20 contacts the aggregate material 22 and mixes the hot top layer with the cool lower layer to form a substantially homogenous mixture. The infrared chambers 14 and heat reflector 93 are disposed so as to form a gap 39 therebetween. A large mixer 20 is preferably disposed within each gap 39. A final large mixer 20 is disposed at the terminal end 13 of conveyor belt 12. The large mixer 20 is described in more detail with reference to
Small mixers 19 are preferably included under the heat reflector 93 and infrared chamber 14 closest to the terminal end 13 of the conveyor belt 13. The small mixers 19 are preferably similar in both shape and function to the large mixers 20 discussed above and in more detail with reference to
In operation, the conveyor belt 12 conveys the aggregate material 22 from its source and under the infrared chambers 14 at a predetermined rate. The fuel 16 flows to the infrared chambers 14, which burn the fuel 16 causing the infrared chambers 14 to emit infrared radiation therefrom. The infrared radiation contacts the top surface of the aggregate material 22 that is conveyed on the conveyor belt 12 and acts to heat the top portion of the aggregate material proximate to the infrared chambers 14. Large mixers 20 then mix the aggregate material 22 such that the heated and unheated layers of aggregate material 22 are mixed together, allowing the unheated aggregate material 22 proximate to the conveyor belt 12 to rise to the top surface proximate to the infrared chamber 14. The infrared radiation from the infrared chamber 14 then heats the mixed aggregate material 22 to effectively pre-heat and pre-dry the aggregate material 22.
Referring now to
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The embodiment of
Referring now to
The present invention also includes an asphalt producing system 300 and a system 100 for continuously repaving a roadway.
Drying apparatus 98 is as described above in the heating system 10, including conveyor belt 12, infrared chambers 14, heat reflector 93, source of fuel 16, source of power 50, and mixers 20, 19 mounted on trailer 9. Asphalt producing module 15 includes pugmill 52 and additive receptacle 58. Pugmill 52 is preferably portable, such as one of the portable pugmills sold by Pugmill Systems, Inc of Columbia, Tenn. In some embodiments, pugmill 52 may be substituted for a drum mill. Additive receptacle 58 may contain heated liquid asphalt for HMA production or the requisite additives for WMA production. Heated and dried aggregate material 22 is introduced to pugmill 52 from the terminal end 13 of conveyor belt 12, as are additives for either HMA or WMA from additive receptacle 54. The additive addition is automated. The same asphalt producing module 15 may be used for either WMA or HMA. Asphalt producing module 15 then produces new asphalt that may immediately be laid down and compacted to form new pavement.
Cleaning unit 82 is preferable in repaving system 100 particularly for partial repaves of center lines and widened roads that often have cracks with dirt in them. Cleaning unit 82 is a vehicle that drives ahead of the rest of the repaving system 100 and vacuums up such dirt.
Joint heater 108 follows cleaning unit 82. Joint heater 108 preheats the pavement to be ripped up. This softens the material so that the grinding and milling process will be accelerated. It also limits fracturing of stone in the material. Joint heater 84 includes a tractor pulling at least one trailer with infrared units attached to its underside so as to heat the ground beneath the trailer. For the sake of space, the joint heater 108 depicted in
Grinder 80 rips up roadway and grinds it into small pieces. After the roadway is sufficiently ground up into aggregate material 22, it is provided to hopper 84. Hopper 84 levels out the flow of aggregate material 22 from grinder 80 so that it provides an even layer of aggregate material 22 to the conveyor belt 12 of drying apparatus 98. In some embodiments, hopper 84 includes a sensor and storage for additional aggregate material to add to the aggregate material 22 provided by grinder 80 when hopper 84 senses that there is not enough material to meet a desired production rate for the repaving system 100.
Aggregate material 22 is heated and dried as it moves through drying apparatus 98 as described above. The dried, heated aggregate material 22 is deposited into asphalt producing module 15 from the terminal end 13 of conveyor belt 12. WMA additives or heated liquid asphalt for HMA is added to the aggregate material 22 in asphalt producing module 15 as described above.
Repaving system 100 also preferably includes at least one ground infrared heater 59. Ground infrared heater 59 is affixed to the bottom of trailer 9 or another trailer used in repaving system 100 such that it emits heat onto the area of road that has been ripped up by grinder 80. Heating the ground to be repaved allows for a better thermal bond between the ground and the asphalt to be replaced upon the ground. The ground infrared heater 59 is dimensioned to cover a substantial portion of the bottom of trailer 9, preferably in dimensions of 8′×3′. Although only two ground heat reflectors 59 are depicted in
The newly made asphalt is deposited into paver 54 by asphalt producing module conveyor belt 56. Paver 54 is any paver commonly used in the art capable of laying down asphalt to form newly paved road that is dimensioned so as to work in repaving system 100. Repaving system 100 also preferably includes roller 78, which follows behind the other vehicles in repaving system 100 and compacts the asphalt just laid down by paver 54.
Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions would be readily apparent to those of ordinary skill in the art. Further, although the heating system was developed for use in connection with aggregates used as paving materials, it is readily adapted for use with aggregates used for other purposes, such as livestock feed, or the like. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.
This application is a continuation in part of co-pending U.S. Non-Provisional patent application Ser. No. 11/805,021, filed on May 22, 2007, and claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 60/802,360, filed on May 22, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60802360 | May 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11805021 | May 2007 | US |
| Child | 12924103 | US |
