CA1174132A - Asphalt reclamation system and unit - Google Patents
Asphalt reclamation system and unitInfo
- Publication number
- CA1174132A CA1174132A CA000419169A CA419169A CA1174132A CA 1174132 A CA1174132 A CA 1174132A CA 000419169 A CA000419169 A CA 000419169A CA 419169 A CA419169 A CA 419169A CA 1174132 A CA1174132 A CA 1174132A
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- inner enclosure
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- temperature
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Abstract
Asphalt Reclamation System and Unit Abstract A unit for heating initially solid asphaltic material to provide asphaltic concrete in a condition suitable for application. The unit is operated to heat initially cold-material to a temperature between 275° and 300°F and to maintain it at that temperature until it is used. A ther-mostatic control system produces heated air intermittently in accordance with a predetermined schedule, and the heated air is used to heat the asphaltic material.
Description
Asphalt Reclamation System And Unit Background of the Invention This invention relates to the provision of asphaltic con-crete in a state or condition suitable for paving application or the like, and particularly to the production of asphaltic concrete in such condition for application from initially solid asphaltic material. In a specific sense, the invention is directed to an asphalt reclamation unit for this purpose.
It is known to heat chunks or other pieces of initially solid, cold asphaltic material (i.e. asphaltic material initially at ambient atmospheric temperature) to provide asphaltic concrete for paving or like application, e.g. for patchinq. For example, useful asphaltic concrete can be reclaimed in this way from chunks of used asphaltic concrete paving. Desirably, the produced mater-ial should be a substantially homogeneous, soft or flowable mass capable of being spread easily and evenly to constitute a patch.
Heretofore, procedures for reclaiming used asphaltic material have involved rapid heating. Difficulties associated with such prior practice have included excessive heating of the mater-ial, oxidation of the liquid component thereof, segregation of com-ponents, and/or burning. These disadvantages have led to nonhomo-genous or otherwise defective products.
Applicant's prior U.S. patents No. 3,386,435 and No.
3,577,976 describe units for storing materials such as asphalt at an elevated temperature. In these units, the asphalt is contained within an inner enclosure which is surrounded by an outer enclosure that defines spaces or passages beneath and on all sides of the in-ner enclosure. Air, heated by an infrared energy source beneath the inner enclosure, flows through these spaces and/or passages to minimize the thermal gradient across the wall of the inner enclosure and thereby to retard heat loss from the contained hot asphalt;
the rising heated air is introduced to the top of the inner enclosure through plural horizontally spaced apertures ar-ranged to provide a flow of heated air across the top of the contained asphalt, for further minimizing the heat loss. As will be understood from the cited patents, the purpose of these structures is primarily to maintain the elevated temp-erature of a charge of asphaltic material supplied to the inner enclosure in initially heated condition, and not to heat an initially cold charge to a suitable temperature for application.
U.S. patent No. 2,496,113 describes a heater for melting bituminous material wherein heated gas is passed through an essentially horizontal flue system extending with-in or beneath the charge of material to be heated and is then conducted upwardly at one end of the heater so as to be di-rected across the surface of the molten charge. Neither in applicant's prior patents nor in aforementioned patent No.
It is known to heat chunks or other pieces of initially solid, cold asphaltic material (i.e. asphaltic material initially at ambient atmospheric temperature) to provide asphaltic concrete for paving or like application, e.g. for patchinq. For example, useful asphaltic concrete can be reclaimed in this way from chunks of used asphaltic concrete paving. Desirably, the produced mater-ial should be a substantially homogeneous, soft or flowable mass capable of being spread easily and evenly to constitute a patch.
Heretofore, procedures for reclaiming used asphaltic material have involved rapid heating. Difficulties associated with such prior practice have included excessive heating of the mater-ial, oxidation of the liquid component thereof, segregation of com-ponents, and/or burning. These disadvantages have led to nonhomo-genous or otherwise defective products.
Applicant's prior U.S. patents No. 3,386,435 and No.
3,577,976 describe units for storing materials such as asphalt at an elevated temperature. In these units, the asphalt is contained within an inner enclosure which is surrounded by an outer enclosure that defines spaces or passages beneath and on all sides of the in-ner enclosure. Air, heated by an infrared energy source beneath the inner enclosure, flows through these spaces and/or passages to minimize the thermal gradient across the wall of the inner enclosure and thereby to retard heat loss from the contained hot asphalt;
the rising heated air is introduced to the top of the inner enclosure through plural horizontally spaced apertures ar-ranged to provide a flow of heated air across the top of the contained asphalt, for further minimizing the heat loss. As will be understood from the cited patents, the purpose of these structures is primarily to maintain the elevated temp-erature of a charge of asphaltic material supplied to the inner enclosure in initially heated condition, and not to heat an initially cold charge to a suitable temperature for application.
U.S. patent No. 2,496,113 describes a heater for melting bituminous material wherein heated gas is passed through an essentially horizontal flue system extending with-in or beneath the charge of material to be heated and is then conducted upwardly at one end of the heater so as to be di-rected across the surface of the molten charge. Neither in applicant's prior patents nor in aforementioned patent No.
2,496,113 is there disclosed any provision of passages for conducting heated air or gas upwardly through the body of asphaltic concrete, nor any control means for reclaiming and then maintaining the temperature of the material in a suit-able elevated range.
U.S. patent No. 3,315,659 describes an open truck for keeping a load of asphalt at an elevated temperature during transportation thereof. Pipe sections are disposed horizontally and vertically within the truck bed for con-ducting heat through the asphalt. However, there is no dis-closure of any means for controlling the temperature of the material, which cannot be properly maintained in an open truck.
Summary of the Invention It is now found that asphaltic concrete in suitable condition for paving application or the like can be provided 11'7 ~1~3Z
from initially cold asphaltic material by heating the mater-ial, relatively slowly, to a temperature between about 275 and about 300F, and preferably to about 290F, and maintain-ing it at that temperature until it is used. Such heating operation avoids overheating, segregation, oxidation, or ignition of components of the asphaltic material, and pro-vides a very satisfactory product at significantly lower cost than newly produced material.
The present invention contemplates the provision of an asphalt reclamation system and unit for performing this heating procedure. The unit includes an upwardly open inner enclosure defining a volume for containing asphaltic material to be heated, and having a floor, end walls, and side walls;
and an outer enclosure surrounding the inner enclosure and having a floor, end walls, and side walls respectively dis-posed in adjacent spaced relation to the floor, end walls, and side walls of the inner enclosure to define a gas space between the inner and outer enclosure floors, and end side wall gas passages between the inner enclosure walls and the outer enclosure walls respectively adjacent thereto. The outer enclosure also has door means for closing the top of the unit. The gas space communicates with the outside atmos-phere, the passages communicate with the gas space and with the uppermost portion of the aforementioned volume, and the upper portion of that volume is vented to the outside atmos-phere, for enabling continuous air flow into the gas space and thence through the passages and the upper portion of the volume. Additionally, the unit has at least one source of infrared energy, disposed in the gas space, for heating air entering the gas space from the outside atmosphere. The heat source can be arranged to produce heated air intermittently in accordance with a predetermined schedule.
As a particular feature of the invention, the unit includes at least one heating chamber projecting upwardly from the floor of the inner enclosure into an upper portion of the aforementioned volume at a locality intermediate and spaced from the side walls of the inner enclosure, the heating 11'7413'~
chamber comprising thermally conductive wall portions defining a gas flow region isolated by the wall po tions from the volume and opening into and extending upwardly from the gas space above the one infrared energy source; and flue means for conducting heated air from an upper locality in the gas flow region transversely across the upper portion of the volume to the side wall passages such that air heated by this source flows upwardly through the gas flow region and thence through the flue means to the side wall passages. Preferably, the unit has a plurality (at least two) of such heating chambers, extending from end to end of the inner enclosure in spaced relation to each other, with a separate infra-red energy source disposed beneath each heating chamber. Prefer-ably, also, the flue means comprises at least two transverse flues, extending between the side walls of the inner enclosure in horizontally spaced relation to each other, and each communicating with each of the heating chambers. As an additional particular feature of the invention, heat-shielding means are interposed be-tween each infrared energy source and the inner enclosure, for preventing local overheating of portions of the asphaltic material charge adjacent that source.
As a further feature of the invention, the unit includes a control system for maintaining the asphaltic material at the de-sired elevated temperature for a long period of time. The control system includes repeating timers which control the heat source in accordance with the predetermined schedule.
According to a first broad aspect of the present inven-tion, there is provided an asphalt reclamation unit for heating ~-4-~1'7~
initially solid asphaltic material from ambient atmospheric tem-perature to an elevated temperature between about 270F. and about 300 F. and thereafter maintaining the material at the elevated temperature to provide asphaltic concrete in a condition suitable for paving application or the like, comprising: (a) an upwardly open inner enclosure defining a volume for containing asphaltic material to be heated, and including a floor, end walls, and side walls; (b) an outer enclosure surrounding said inner enclosure and including a floor, end walls, and side walls respectively dis-posed in adjacent spaced relation to the floor, end walls, andside walls of said inner enclosure to define a gas space between the inner and outer enclosure floors and end and side wall gas passages between the inner enclosure walls and the outer enclo-sure walls respectively adjacent thereto, said outer enclosure further including door means for closing the top of the unit, said gas space communicating with the outside atmosphere, said passages communicating with said gas space and with the uppermost portion of said volume, and said upper portion of said volume being vented to the outside atmosphere, for enabling continuous air flow into said gas space and thence through said passages and said upper portion of said volume; (c) at least one source of infrared energy disposed in said gas space for heating air entering said gas space from the outside atmosphere; (d) heating chamber means comprising at least one heating chamber projecting upwardly from the floor of the inner enclosure into an upper portion of said volume at a locally intermediate and spaced from the side walls of said inner enclosure, said one heating chamber extending from end to end of said inner enclosure and comprising thermally con-,~
~ -4a-ductive wall portions of said inner enclosure defining a gas flow region isolated by the wall portions from said volume and opening into and extending upwardly from said gas space above said one infrared energy source; and (e) flue means, comprising at least one flue extending from side to side of said inner enclosure and spaced away from both ends thereof, for conducting heated air from the uppermost portion of said gas flow region transversely across said upper portion of said volume to said side wall passages, such that air heated by said source flows upwardly through said gas flow region and thence through said flue means to the side wall passages; (f) said walls of said inner enclosure, said heating chamber means, and said flue means being mutually disposed to enable delivery of solid pieces of the asphaltic material down-wardly from the top of the unit into the lowermost portion of said volume.
According to a second broad aspect of the present inven-tion, there is provided a method for reclaiming initially solid asphaltic material to provide asphaltic concrete, wherein the material is heated from ambient atmospheric temperature to an elevated temperature within a range of about 275-300F and there-after maintained at the elevated temperature such that the mater-ial is in a condition suitable for paving application or the like, comprising: (a) placing asphaltic material in an inner enclosure having thermally conductive walls and a floor and arranged such as to enable delivery of the initially solid asphaltic material downwardly from the top of the inner enclosure toward the floor of the inner enclosure; (b) intermittently producing a heated gas ~-4b-11'7413Z
in accordance with a predetermined schedule; (c) heating the as-phaltic material from ambient atmospheric temperature by passing a first portion of the heated gas within a gas volume defined by the inner enclosure and an outer enclosure, such that the heated gas passing the walls and floor heats the portions of the as-phaltic material in the inner enclosure adjacent the walls and floor until the material reaches a temperature within a range of about 275-300F; (d) further heating the asphaltic material by passing a second portion of the heated gas through at least one heating chamber communicating with and projecting upwardly from the gas volume into the inner enclosure, such that the heated gas passing through the heating chamber heats the interior portions of the asphaltic material in the inner enclosure adjacent the heating chamber from both the longitudinal and transverse direc-tions until the material reaches a temperature within a range of about 275-300F; (e) passing all the heated gas through a plur-ality of small apertures spaced about the upper portions of the walls of the inner enclosure, such that the heated gas flows from the gas volume uniformly across the upper surface of the asphal-tic material in the inner enclosure and the portions of the as-phaltic material near the upper surface are heated until the mate-rial reaches a temperature within a range of about 275-300 F; (f) venting the heated gas to the outside atmosphere after it has flowed across the upper surface of the asphaltic material; and (g) sensing the temperature of the asphaltic material within the inner enclosure and maintaining the asphaltic material through intermittent heating thereof at a uniform temperature within a range of about 275-300 F for a long period of time ~ -4c-~i'7~13.Z
According to a third broad aspect of the present inven-tion, there is provided an asphaltic material delivery and stor-age unit for heating initially solid asphaltic material to pro-vide asphaltic material in a condition suitable for paving appli-cation or the like, comprising: (a) an inner enclosure defining a volume for containing asphaltic material to be heated, and including a floor and walls; (b) an outer enclosure surrounding the inner enclosure and including a floor and walls disposed in adjacent spaced relation to the floor and walls of the inner en-closure to define a gas region therebetween, the outer enclosurefurther including door means for closing the unit, and the gas region communicating with the outside atmosphere; (c) a source of intermittent heat energy disposed in the gas region for heating air entering the gas region from the outside atmosphere, the source of heat energy comprising a supply of fuel, a burner ada-pted to be fired intermittently and positioned to burn fuel, and at least one infrared energy converter for absorbing heat energy produced by the burner and emitting intermittently infrared radiation in accordance with a predetermined schedule for heating air entering the gas region from the outside atmosphere; (d) at least one heating chamber projecting upwardly from the floor of the inner enclosure into the volume and communicating with the gas region such that heated air can pass through the heating chamber and the gas region; (e) the upper portions of the walls of the inner enclosure having a plurality of spaced apart aper-tures communicating with the gas region to permit a flow of heated air into the volume such that the heated air passes across the ~ 4d-1~7~13'~
upper portion of the volume; (f) the door means having a vent such that the heated air passing across the upper portion of the volume is vented to the outside atmosphere; and (g) means for controlling the source of heat energy such that it intermittently produces heated air in accordance with a predetermined schedule sufficient to heat the asphaltic material to, and to maintain the temperature of the material within, a predetermined temperature range in excess of 275F.
The invention will now be described in greater detail with reference to the accompanying drawings, in which:
Fig. 1 is a side elevational view, partly broken away, of an illustrative embodiment of the apparatus used in the system of the invention;
Fig. 2 is a rear elevational view of the same apparatus;
-4e-- 5 ~ 413~
Fig 3 is a sectional elevational view taken along the line 3-3 of Fig. l; and Fig. 4 is a circuit diagram of the control system for the unit.
Detailed Description Referring to Figs. 1 through 3 of the drawings, there is shown an asphalt reclamation unit 10 embodying the invention in a particular form, supported on wheels 11 and having a forwardly extending frame 12 with a front end (not shown) designed to be coupled to a vehicle such as a truck, tractor, or the like so that the unit can be drawn as a trailer. A conventional device (also not shown) is provided at the front end of the frame for supporting the unit in stationary, level position when unhitched from the towing vehicle.
The unit 10 broadly comprises an upwardly open inner enclosure 14 defining a volume 16 containing a quantity of initially solid asphaltic material (not shown), e.g. lumps or other pieces of used asphalt pavement supplied to the volume 16 at ambient atmospheric temperature; an outer en-closure 18 essentially completely surrounding the inner en-closure in outwardly spaced relation thereto; and means 20 for heating the contained asphaltic material to produce asphaltic concrete in a state suitable for paving applica-tion. A pair of propane tanks 22 (one being shown) are removably secured side by side on the frame 12 ahead of the outer enclosure 18 to supply fuel to the heating means, which, in the illustrated embodiment, includes infrared energy converters constituting horizontally elongated sources of infrared radiation and burners fueled by the propane from the tanks.
The inner enclosure 14 includes a generally flat horizontal bottom wall or floor 24, a pair of opposed flat vertical side walls 26 and 28 joined to (and respectively rising from opposite sides of) the floor 24, a vertical rear end wall 30, and a front end wall 32 which slopes forwardly and upwardly from the floor 24 for most of the height of the 13;~
enclosure 14 and terminates in a short ~ertical upper portion 34. The floor and walls of the enclosure 14 are fabricated of a thermally conductive metal to facilitate heating of the contained asphaltic material (which is in direct contact with the interior surfaces of the floor and walls) by heated gas, i.e. air circulating past the exterior surfaces of the floor and walls as hereinafter further described.
The outer enclosure 18 has a generally flat hori-zontal bottom wall or floor 36 spaced below the inner en-closure floor 24 to define a gas space 38 therebetween, ex-tending beneath the full width of the floor 24 and containing the infrared energy converters 20. In addition, the enclosure 18 includes opposed side walls 42 and 44 rising vertically from the floor 36 in outwardly spaced relation to the inner enclosure side walls 26 and 28 to define therewith side gas passages 46 and 48; a vertical rear end wall 50 extending between the side walls 42 and 44 and spaced outwardly of the wall 30 to define therewith a rear end gas passage 52 com-municating laterally with passages 46 and 48; and a front end wall 54 sloping forwardly and upwardly from the floor 36 in outwardly spaced relation to the wall 32 to define therewith a front end gas passage 56, which at its lower end communi-cates directly with the gas space 38, and also communicates laterally with the passages 46 and 48. As shown, the slope of the wall 54 is steeper than that of the wall 32, so that the passage 56 narrows progressively in an upward direction.
This results in an enhanced flow of heated gases through the gas passage 56, sometimes referred to as a 'IVenturi effect."
The uppermost portion 58 of the wall 54 is vertical, and defines with wall portion 34 the upper extremity of passage 56.
At its top, the outer enclosure 18 is provided with movable lid means comprising a pair of loading doors 60 re-spectively secured by hinges 62 to the top edge portions of the side walls 42 and 44 and cooperatively constituting a peaked roof for the unit 10. The loading doors, when shut, cover and complete the enclosure of the volume 16. They are opened by pivotally mounted, manually operable handle - 7 - 1~ 13'~
structures 64 to enable the volume 16 to be filled with asphaltic material to be heated. Three openings 66, formed in the inner and outer rear end walls 30 and 50 and disposed side by side in the lower portion of the rear of the unit 10, are respectively closed by three doors 68 which slide verti-cally in tracks 70 and are opened by pivotally mounted handle structures 72 for removal of produced asphaltic concrete from the volume 16 through the openings 66. An extension 74 of the inner enclosure floor 24, projecting rearwardly beyond the openings 66, serves as a shoveling platform to facilitate such removal of the asphaltic concrete product.
The floor, walls and loading doors of the outer enclosure 18 are preferably all of double construction, viz.
constituted of spaced plates with thermal insulation 76 fil-ling the gap between the plates, to minimize heat loss from the interior of the unit 10. Although generally spaced from the surrounding enclosure 18 to provide the aforementioned gas space and passages, the inner enclosure 14 is fixedly mounted within and secured to the enclosure 18 by suitable support structure (not shown).
The gas space 38 communicates with the external atmosphere, for example through louvered slits 7~ formed in a portion of the outer rear end wall 50 below the inner en-closure floor 24, for supply of air to the gas space. As hereinafter further explained, air heated within the gas space by the infrared converters 20 rises through the gas passages between the inner and outer enclosure walls, con-tributing to the desired heating of the asphaltic material within the volume 16 as well as minimizing the thermal grad-ient across the walls of the inner enclosure 14 to retard heat loss from the contained material when the latter mater-ial is heated. The gas passages communicate with the volume 16 through horizontally elongated apertures spaced around the uppermost portion of the walls of the inner enclosure;
specifically, each side wall 26 and 28 of the inner enclosure has a plurality of small apertures 80 spaced along its length, while small louvered apertures 82 and 84 are provided in the rear and front end walls respectively, at a level somewhat 1~7413~
higher than that of the apertures 80. Each of the loading doors 60 has a pair of louvered vents 86 spaced along its length adjacent the peak of the roof cooperatively formed by the doors, for dis-charging gas to the atmosphere from the volume 16. The apertures 80, 82 and 84 and the vents 86 are so arranged that heated gas (air) rising through the wall passages 46, 48, 52 and 56 flows therefrom through the apertures into the volume 16 and evenly across the upper surface of the body of asphaltic material con-tained therein, further contributing to the heating of that mate-rial, before exiting from the unit 10 to the atmosphere throughthe vents 86.
The structure of the unit 10 as thus far set forth cor-responds generally to features of construction and arrangement shown in one or more of applicant's aforementioned U.S. patents No. 3,386,435 and No. 3,577,976. Particular features of the pre-sent invention, for effecting the heating of initially solid and "cold" (ambient-temperature) asphaltic material to produce asphal-tic concrete, will now be described.
In accordance with the invention, then, the unit 10 fur-ther includes a plurality of heating chambers 100, projecting up-wardly from the inner enclosure floor 24 to the upper portion of the volume 16 (but terminating below the uppermost portion of the inner enclosure 14) and extending from end to end of the inner enclosure in laterally spaced, parallel relation to each other so as to divide the volume 16 lengthwise into plural parallel sub-volumes opening upwardly into a common space through which the gas flow from the apertures 80, 82 and 84 circulates. Two such heat-~ -8-ing chambers 100 are shown in the illustrated embodiment of the invention, dividing the volume 16 into three relatively narrow subvolumes 16', 16" and 16' " each extending lengthwise of the unit 10 and respectively in register with the three openings 66 at the rear of the unit. As will now be appreciated, the provision of three openings 66 facilitates removal of asphaltic concrete from these three subvolumes.
Each of the heating chambers 100 is formed by two walls 102 and 104 which constitute part of the wall structure -8a-9 11'~13'~
of the inner enclosure 14 and are fabricated (like the re-mainder of the inner enclosure) of a thermally conductive metal. These walls converge upwardly so that the heating chamber they cooperatively constitute has an inverted V shape as seen in transverse section (Fig. 3). The walls 102 and 104 of each heating chamber define, between them, a gas flow region 106 which opens downwardly through the inner enclosure floor 24 into, and cooperatively interconnects with, the gas space 38 from the rear end wall 30 to the front end wall 32 of the inner enclosure; these walls 102 and 104 are joined to the front and rear walls 30 and 32 and to the floor 24 to isolate the region 106 from the volume 16. It will be appre-ciated that asphaltic material within the volume 16 is in contact with the walls 102 and 104 of the two heating chambers 100. The unit 10 has two of the infrared energy converters 20, e.g. mounted on a fixed tray (not shown), and respec-tively disposed in the gas space 38 directly beneath the gas flow regions of the -two heating chambers 100, in alignment with the long dimensions of the heating chambers, so that gas (i.e. air) heated by the converters rises from the gas space 38 directly into the gas flow regions of the heating chambers, as indicated by arrows 108. The heated gas also rises from the gas space 38 directly into the end passage 56 and into the side wall passages 46 and 48.
Further in accordance with the invention, trans-verse flues 110 (also fabricated of a thermally conductive metal) extend across the interior of the inner enclosure 14, at an upper level therein, for interconnecting the uppermost portions of the gas flow regions 106 of the heating chambers 100 with the side wall passages 46 and 48. Two of these flues 110 are provided in the unit 10, at locations spaced along the length of the unit. Heated air rising through the regions 106 is conducted by the flues 110 to the side wall passages (as indicated by arrows 112), where it circulates and finally enters the upper portions of the volume 16 through the apertures 80. In this way, a continuous upward flow of heated air is maintained in the heating chamber regions 106 as well as through the wall passages, and the - 1o ll'~ Z
heated air enters the volume 16 only through the apertures 80, 82 and 84 at the top of the walls.
As a still further feature of the invention, heat-shielding means are interposed between the converters 20 and the portions of the inner enclosure structure (i.e. the por-tions of floor 24 and of heating chamber walls 102 and 104) adjacent the converters, to prevent localized overheating of the material within the volume 16 and thereby to contribute to desired uniformity of heating. In the embodiment illus-trated, this shielding means includes absorber plates 114 and 116 disposed externally of the lower portions of the walls 102 and 104 (i.e. on the side of those walls external to the volume 16) and extending around the adjacent portions of the floor 24. The absorber plates are joined to the inner enclosure structure along their edges but are otherwise spaced therefrom so as to define dead air or dampener spaces 118. Additionally, the shielding means includes layers of thermal insulation 120 mounted within the spaces 118 on those portions of the external surfaces of the inner enclosure wall structure which are closest to the converters 20. The shield-ing means prevents heated air in the immediate vicinity of the converters (i.e. that air which is at the highest temp-erature) from coming into direct contact with the thermally conductive walls of the inner enclosure.
The use of the described unit to prepare asphaltic concrete may now be readily understood. The volume 16 is filled with chunks or other pieces of initially solid asphaltic material at ambient atmospheric temperature; these chunks, for example, may be broken up pieces of asphaltic pavement or other suitable starting material for the produc-tion of asphaltic concrete. The burners of the heating means, fueled by propane gas or liquid from one of the tanks 22, are turned on and operated. Air entering the gas space 38 is heated by the infrared energy produced by the con-verters 20. The heated air rises from the converters through the regions 106 of the heating chambers 100 and through the forward gas passage 56, with a flow velocity enhanced by the upward taper of that passage and of the heating chamber 117~1;}Z
regions. From the upper portions of the heating chamber regions the heated air flows laterally through the flues 110, thence through the side wall passages 46 and 48, rising to the plural, small apertures 80, 82 and 84 in the side and end wall passages, and finally enters the upper portion of the volume 16 where it flows uniformly across the top surface of the asphaltic material being heated before leaving the unit through the constantly open vents 86.
The converters 20 are conveniently under thermo-static control (as described below) and are operated to achieve and maintain a temperature between 275F and 300F
throughout the body of asphaltic material in the volume 16.
This heating is accomplished in the described unit with advantageous effectiveness and uniformity of temperature, since the charge of asphaltic material is subdivided or penetrated by the heating chambers 100 with their regions 106 of upwardly flowing heated air, as well as being surrounded by flows of heated air (in the subjacent gas space 38, the wall passages, and the upper portion of volume 16), and since the heat-shielding means prevents local overheating of the portions of the charge nearest the converters. The slow, uniform heating of the material to a temperature in the 275-300F range, afforded by the present unit, produces (from an initially cold charge) asphaltic concrete in a suitable state or condition for use within a reasonable period of time, and avoids such problems of prior practice as excessive heating, burning, oxidizing, and/or segregating components of the asphaltic concrete. Moreover, the unit readily enables maintenance of the asphaltic concrete within the stated temperature range until the material is used. Thus, for example, a unit of the described construction having a 4-ton capacity and two 50,000 B.T.U. infrared-type converters may be charged with cold material at the end of a working day, and operated overnight (for a period of, say, 12 to 14 hours) to heat the material; by the next morning, the asphaltic ccncrete will be at the desired temperature and ready for use, and will be maintained at that temperature by the unit.
The transverse flues 110, providing paths at the - 12 - il~l3z top of the heating chamber regions 106 for outflow of heated air rising through the latter regions, assure continuous directional flow of heated air upwardly through the regions 106 as weil as constituting, in themselves, additional heated air passages extending through the volume 16, and therefore contribute to the even and efficient heating of the asphaltic concrete charge. In the particular unit described, the pro-vision of two heating chambers 100 and two transverse flues 110 affords effective heating of a full day's supply of asphaltic concrete for patching purposes or the like in a structure conveniently dimensioned for transport as a vehic-ular trailer. The slope of the heated chamber walls 102 and 104 and the front end wall 32 in this unit facilitates with-drawal of asphaltic concrete from the interior of the unit through the openings 66.
It is an important aspect of the invention that the asphaltic concrete be heated to, and then maintained within, the elevated temperature range of about 275 to 300F, and preferably at about 290F, for a long period of time, e.g. 48 hours. This is accomplished by use of a special system for controlling the amount of time that heated air passes adjacent to and contacts the asphaltic material, rather than control-ling the temperature or thermal content of the heated air.
The preferred embodiment of the control system is shown in Fig. 4 of the drawings, although other control systems which carry out the function in a similar manner and which accom-plish an equivalent result could be used.
Referring to Fig. 4, there is shown a control system 200 for controlling the heating means for the asphaltic material. The infrared converters 20 cannot readily be controlled either as to temperature or as to the quantity of heat produced, and should always emit the same amount of radiation. The control system 200, therefore, is adapted to control the time of firing of the heating means, and thereby to produce heated air intermittently at the infrared converters 20. The control system 200 generally comprises a power supply, such as a 12VDC, 90.0 amp battery 202; a switch 204 for connecting the battery 202 to the remainder of the control system; a pair of repeat timers 206, 208; and a pair of gas control valves 210, 212 operatively connected to the propane tanks 22 and opened and closed by the repeat timers 206, 208. The control system further includes a sensor 214 connected to the repeat timers 206, 208 and having one or more thermostatic elements 216 for deter-mining the temperature of the asphaltic concrete and control-ling the cyclic patterns of the repeat timers. It is presently preferred to use a Honeywell-type sensor for the above purpose, having a thermostatic element positioned within the asphaltic material in one of the three subvolumes 16', 16" or 16''' (see Fig. 3). The entire control system 200, other than the thermostatic element 216 of the sensor 214 (and other thermostatic elements to be described), desir-ably is contained within a control box (not shown) located at the exterior of the unit for easy access. It is useful to have one or more lamps 218 mounted on the control box so that the operator of the unit can tell when the control system 200 is "on" or "off".
To prevent a malfunction in the control system from causing overheating of the asphaltic material, it is further desirable to incorporate in the control system one or more thermostatic elements 220. These thermostatic elements are positioned so as to sense the temperature at the surface of the material (see Fig. 3) and to shut down the heating means if the temperature exceeds about 300F. It is presently preferred to use two Klixon-type thermostats for this purpose.
In operation of the thermostatic control system, the switch 204 is manipulated to energize the circuits, the lamp 218 thereupon indicating that the system is "on". If the asphaltic material is cold, the thermostatic element 216 of the sensor 214 signals the first repeat timer 206 to open gas control valves 210, 212 to provide fuel from propane tanks 22 to fire the burner of the heating means. Heat energy from the burner is absorbed by the infrared energy converters 20, which then emit infrared radiation to heat the air entering the gas region from the outside atmosphere.
Repeat timer 206 intermittently turns the gas control valves 11'7413Z
210, 212 "on" and "off" in accordance with a first pre-determined cycle until the material is heated to the desired temperature range. It is presently preferred that the first predetermined cycle is 10 minutes "on" and 5 minutes "off".
For certain applications, a different cycle may be appro-priate, for example, 10 minutes "on" and 10 minutes "off".
Other cycles may also be advantageous.
After the temperature of the material reaches the lower end of the desired temperature range of about 275 to 300F, as determined by the sensor 214, the sensor switches to repeat timer 208 and disconnects repeat timer 206. Repeat timer 208 intermittently turns the gas control valves 210, 212 "on" and "off" in accordance with a second predetermined cycle to hold the temperature of the asphaltic material within the desired temperature range. It is presently pre-ferred that the second predetermined cycle is 3 minutes "on"
and 5 minutes "off". However, for certain applications, a different cycle may be appropriate, for example, 5 minutes "on" and 10 minutes "off". The invention contemplates cyclic patterns of sufficient duration to maintain the asphaltic composition within the desired temperature range for a long period of time.
If the temperature of the asphaltic material falls below the lower end of the desired temperature range, as determined by the sensor 214, the sensor switches back to repeat timer 206 and disconnects repeat timer 208. It will be appreciated that use of repeat timer 206 results in greater "on" time than use of repeat timer 208 and thereby results in more heated air being supplied to the operation of the unit. When the temperature of the material again returns to the proper range, the repeat timer 208 again is connected, and the repeat timer 206 again is disconnected.
If the temperature of the a~phaltic material exceeds the upper end of the desired temperature range, as determined by the thermostatic elements 220 positioned adjacent with the asphaltic material, the gas control valves 210, 212 are closed and the heating means is shut down until the temp-erature of the material returns to the proper range. The repeat timer 208 then may continue the cycle.
~1'7413Z
It is also contemplated to provide an override circuit for the control system in certain applications. This provides a mode of operation whereby more heated air is supplied to the unit, for example, under extremely cold operating conditions. It further is contemplated to use a variable sensor, so that as the material is used during the course of a day, less heated air is supplied to the unit to maintain the temperature of the material.
It is to be understood that the invention is not limited to the features and embodiments hereinabove speci-fically set forth, but may be carried out in other ways without departure from its spirit.
U.S. patent No. 3,315,659 describes an open truck for keeping a load of asphalt at an elevated temperature during transportation thereof. Pipe sections are disposed horizontally and vertically within the truck bed for con-ducting heat through the asphalt. However, there is no dis-closure of any means for controlling the temperature of the material, which cannot be properly maintained in an open truck.
Summary of the Invention It is now found that asphaltic concrete in suitable condition for paving application or the like can be provided 11'7 ~1~3Z
from initially cold asphaltic material by heating the mater-ial, relatively slowly, to a temperature between about 275 and about 300F, and preferably to about 290F, and maintain-ing it at that temperature until it is used. Such heating operation avoids overheating, segregation, oxidation, or ignition of components of the asphaltic material, and pro-vides a very satisfactory product at significantly lower cost than newly produced material.
The present invention contemplates the provision of an asphalt reclamation system and unit for performing this heating procedure. The unit includes an upwardly open inner enclosure defining a volume for containing asphaltic material to be heated, and having a floor, end walls, and side walls;
and an outer enclosure surrounding the inner enclosure and having a floor, end walls, and side walls respectively dis-posed in adjacent spaced relation to the floor, end walls, and side walls of the inner enclosure to define a gas space between the inner and outer enclosure floors, and end side wall gas passages between the inner enclosure walls and the outer enclosure walls respectively adjacent thereto. The outer enclosure also has door means for closing the top of the unit. The gas space communicates with the outside atmos-phere, the passages communicate with the gas space and with the uppermost portion of the aforementioned volume, and the upper portion of that volume is vented to the outside atmos-phere, for enabling continuous air flow into the gas space and thence through the passages and the upper portion of the volume. Additionally, the unit has at least one source of infrared energy, disposed in the gas space, for heating air entering the gas space from the outside atmosphere. The heat source can be arranged to produce heated air intermittently in accordance with a predetermined schedule.
As a particular feature of the invention, the unit includes at least one heating chamber projecting upwardly from the floor of the inner enclosure into an upper portion of the aforementioned volume at a locality intermediate and spaced from the side walls of the inner enclosure, the heating 11'7413'~
chamber comprising thermally conductive wall portions defining a gas flow region isolated by the wall po tions from the volume and opening into and extending upwardly from the gas space above the one infrared energy source; and flue means for conducting heated air from an upper locality in the gas flow region transversely across the upper portion of the volume to the side wall passages such that air heated by this source flows upwardly through the gas flow region and thence through the flue means to the side wall passages. Preferably, the unit has a plurality (at least two) of such heating chambers, extending from end to end of the inner enclosure in spaced relation to each other, with a separate infra-red energy source disposed beneath each heating chamber. Prefer-ably, also, the flue means comprises at least two transverse flues, extending between the side walls of the inner enclosure in horizontally spaced relation to each other, and each communicating with each of the heating chambers. As an additional particular feature of the invention, heat-shielding means are interposed be-tween each infrared energy source and the inner enclosure, for preventing local overheating of portions of the asphaltic material charge adjacent that source.
As a further feature of the invention, the unit includes a control system for maintaining the asphaltic material at the de-sired elevated temperature for a long period of time. The control system includes repeating timers which control the heat source in accordance with the predetermined schedule.
According to a first broad aspect of the present inven-tion, there is provided an asphalt reclamation unit for heating ~-4-~1'7~
initially solid asphaltic material from ambient atmospheric tem-perature to an elevated temperature between about 270F. and about 300 F. and thereafter maintaining the material at the elevated temperature to provide asphaltic concrete in a condition suitable for paving application or the like, comprising: (a) an upwardly open inner enclosure defining a volume for containing asphaltic material to be heated, and including a floor, end walls, and side walls; (b) an outer enclosure surrounding said inner enclosure and including a floor, end walls, and side walls respectively dis-posed in adjacent spaced relation to the floor, end walls, andside walls of said inner enclosure to define a gas space between the inner and outer enclosure floors and end and side wall gas passages between the inner enclosure walls and the outer enclo-sure walls respectively adjacent thereto, said outer enclosure further including door means for closing the top of the unit, said gas space communicating with the outside atmosphere, said passages communicating with said gas space and with the uppermost portion of said volume, and said upper portion of said volume being vented to the outside atmosphere, for enabling continuous air flow into said gas space and thence through said passages and said upper portion of said volume; (c) at least one source of infrared energy disposed in said gas space for heating air entering said gas space from the outside atmosphere; (d) heating chamber means comprising at least one heating chamber projecting upwardly from the floor of the inner enclosure into an upper portion of said volume at a locally intermediate and spaced from the side walls of said inner enclosure, said one heating chamber extending from end to end of said inner enclosure and comprising thermally con-,~
~ -4a-ductive wall portions of said inner enclosure defining a gas flow region isolated by the wall portions from said volume and opening into and extending upwardly from said gas space above said one infrared energy source; and (e) flue means, comprising at least one flue extending from side to side of said inner enclosure and spaced away from both ends thereof, for conducting heated air from the uppermost portion of said gas flow region transversely across said upper portion of said volume to said side wall passages, such that air heated by said source flows upwardly through said gas flow region and thence through said flue means to the side wall passages; (f) said walls of said inner enclosure, said heating chamber means, and said flue means being mutually disposed to enable delivery of solid pieces of the asphaltic material down-wardly from the top of the unit into the lowermost portion of said volume.
According to a second broad aspect of the present inven-tion, there is provided a method for reclaiming initially solid asphaltic material to provide asphaltic concrete, wherein the material is heated from ambient atmospheric temperature to an elevated temperature within a range of about 275-300F and there-after maintained at the elevated temperature such that the mater-ial is in a condition suitable for paving application or the like, comprising: (a) placing asphaltic material in an inner enclosure having thermally conductive walls and a floor and arranged such as to enable delivery of the initially solid asphaltic material downwardly from the top of the inner enclosure toward the floor of the inner enclosure; (b) intermittently producing a heated gas ~-4b-11'7413Z
in accordance with a predetermined schedule; (c) heating the as-phaltic material from ambient atmospheric temperature by passing a first portion of the heated gas within a gas volume defined by the inner enclosure and an outer enclosure, such that the heated gas passing the walls and floor heats the portions of the as-phaltic material in the inner enclosure adjacent the walls and floor until the material reaches a temperature within a range of about 275-300F; (d) further heating the asphaltic material by passing a second portion of the heated gas through at least one heating chamber communicating with and projecting upwardly from the gas volume into the inner enclosure, such that the heated gas passing through the heating chamber heats the interior portions of the asphaltic material in the inner enclosure adjacent the heating chamber from both the longitudinal and transverse direc-tions until the material reaches a temperature within a range of about 275-300F; (e) passing all the heated gas through a plur-ality of small apertures spaced about the upper portions of the walls of the inner enclosure, such that the heated gas flows from the gas volume uniformly across the upper surface of the asphal-tic material in the inner enclosure and the portions of the as-phaltic material near the upper surface are heated until the mate-rial reaches a temperature within a range of about 275-300 F; (f) venting the heated gas to the outside atmosphere after it has flowed across the upper surface of the asphaltic material; and (g) sensing the temperature of the asphaltic material within the inner enclosure and maintaining the asphaltic material through intermittent heating thereof at a uniform temperature within a range of about 275-300 F for a long period of time ~ -4c-~i'7~13.Z
According to a third broad aspect of the present inven-tion, there is provided an asphaltic material delivery and stor-age unit for heating initially solid asphaltic material to pro-vide asphaltic material in a condition suitable for paving appli-cation or the like, comprising: (a) an inner enclosure defining a volume for containing asphaltic material to be heated, and including a floor and walls; (b) an outer enclosure surrounding the inner enclosure and including a floor and walls disposed in adjacent spaced relation to the floor and walls of the inner en-closure to define a gas region therebetween, the outer enclosurefurther including door means for closing the unit, and the gas region communicating with the outside atmosphere; (c) a source of intermittent heat energy disposed in the gas region for heating air entering the gas region from the outside atmosphere, the source of heat energy comprising a supply of fuel, a burner ada-pted to be fired intermittently and positioned to burn fuel, and at least one infrared energy converter for absorbing heat energy produced by the burner and emitting intermittently infrared radiation in accordance with a predetermined schedule for heating air entering the gas region from the outside atmosphere; (d) at least one heating chamber projecting upwardly from the floor of the inner enclosure into the volume and communicating with the gas region such that heated air can pass through the heating chamber and the gas region; (e) the upper portions of the walls of the inner enclosure having a plurality of spaced apart aper-tures communicating with the gas region to permit a flow of heated air into the volume such that the heated air passes across the ~ 4d-1~7~13'~
upper portion of the volume; (f) the door means having a vent such that the heated air passing across the upper portion of the volume is vented to the outside atmosphere; and (g) means for controlling the source of heat energy such that it intermittently produces heated air in accordance with a predetermined schedule sufficient to heat the asphaltic material to, and to maintain the temperature of the material within, a predetermined temperature range in excess of 275F.
The invention will now be described in greater detail with reference to the accompanying drawings, in which:
Fig. 1 is a side elevational view, partly broken away, of an illustrative embodiment of the apparatus used in the system of the invention;
Fig. 2 is a rear elevational view of the same apparatus;
-4e-- 5 ~ 413~
Fig 3 is a sectional elevational view taken along the line 3-3 of Fig. l; and Fig. 4 is a circuit diagram of the control system for the unit.
Detailed Description Referring to Figs. 1 through 3 of the drawings, there is shown an asphalt reclamation unit 10 embodying the invention in a particular form, supported on wheels 11 and having a forwardly extending frame 12 with a front end (not shown) designed to be coupled to a vehicle such as a truck, tractor, or the like so that the unit can be drawn as a trailer. A conventional device (also not shown) is provided at the front end of the frame for supporting the unit in stationary, level position when unhitched from the towing vehicle.
The unit 10 broadly comprises an upwardly open inner enclosure 14 defining a volume 16 containing a quantity of initially solid asphaltic material (not shown), e.g. lumps or other pieces of used asphalt pavement supplied to the volume 16 at ambient atmospheric temperature; an outer en-closure 18 essentially completely surrounding the inner en-closure in outwardly spaced relation thereto; and means 20 for heating the contained asphaltic material to produce asphaltic concrete in a state suitable for paving applica-tion. A pair of propane tanks 22 (one being shown) are removably secured side by side on the frame 12 ahead of the outer enclosure 18 to supply fuel to the heating means, which, in the illustrated embodiment, includes infrared energy converters constituting horizontally elongated sources of infrared radiation and burners fueled by the propane from the tanks.
The inner enclosure 14 includes a generally flat horizontal bottom wall or floor 24, a pair of opposed flat vertical side walls 26 and 28 joined to (and respectively rising from opposite sides of) the floor 24, a vertical rear end wall 30, and a front end wall 32 which slopes forwardly and upwardly from the floor 24 for most of the height of the 13;~
enclosure 14 and terminates in a short ~ertical upper portion 34. The floor and walls of the enclosure 14 are fabricated of a thermally conductive metal to facilitate heating of the contained asphaltic material (which is in direct contact with the interior surfaces of the floor and walls) by heated gas, i.e. air circulating past the exterior surfaces of the floor and walls as hereinafter further described.
The outer enclosure 18 has a generally flat hori-zontal bottom wall or floor 36 spaced below the inner en-closure floor 24 to define a gas space 38 therebetween, ex-tending beneath the full width of the floor 24 and containing the infrared energy converters 20. In addition, the enclosure 18 includes opposed side walls 42 and 44 rising vertically from the floor 36 in outwardly spaced relation to the inner enclosure side walls 26 and 28 to define therewith side gas passages 46 and 48; a vertical rear end wall 50 extending between the side walls 42 and 44 and spaced outwardly of the wall 30 to define therewith a rear end gas passage 52 com-municating laterally with passages 46 and 48; and a front end wall 54 sloping forwardly and upwardly from the floor 36 in outwardly spaced relation to the wall 32 to define therewith a front end gas passage 56, which at its lower end communi-cates directly with the gas space 38, and also communicates laterally with the passages 46 and 48. As shown, the slope of the wall 54 is steeper than that of the wall 32, so that the passage 56 narrows progressively in an upward direction.
This results in an enhanced flow of heated gases through the gas passage 56, sometimes referred to as a 'IVenturi effect."
The uppermost portion 58 of the wall 54 is vertical, and defines with wall portion 34 the upper extremity of passage 56.
At its top, the outer enclosure 18 is provided with movable lid means comprising a pair of loading doors 60 re-spectively secured by hinges 62 to the top edge portions of the side walls 42 and 44 and cooperatively constituting a peaked roof for the unit 10. The loading doors, when shut, cover and complete the enclosure of the volume 16. They are opened by pivotally mounted, manually operable handle - 7 - 1~ 13'~
structures 64 to enable the volume 16 to be filled with asphaltic material to be heated. Three openings 66, formed in the inner and outer rear end walls 30 and 50 and disposed side by side in the lower portion of the rear of the unit 10, are respectively closed by three doors 68 which slide verti-cally in tracks 70 and are opened by pivotally mounted handle structures 72 for removal of produced asphaltic concrete from the volume 16 through the openings 66. An extension 74 of the inner enclosure floor 24, projecting rearwardly beyond the openings 66, serves as a shoveling platform to facilitate such removal of the asphaltic concrete product.
The floor, walls and loading doors of the outer enclosure 18 are preferably all of double construction, viz.
constituted of spaced plates with thermal insulation 76 fil-ling the gap between the plates, to minimize heat loss from the interior of the unit 10. Although generally spaced from the surrounding enclosure 18 to provide the aforementioned gas space and passages, the inner enclosure 14 is fixedly mounted within and secured to the enclosure 18 by suitable support structure (not shown).
The gas space 38 communicates with the external atmosphere, for example through louvered slits 7~ formed in a portion of the outer rear end wall 50 below the inner en-closure floor 24, for supply of air to the gas space. As hereinafter further explained, air heated within the gas space by the infrared converters 20 rises through the gas passages between the inner and outer enclosure walls, con-tributing to the desired heating of the asphaltic material within the volume 16 as well as minimizing the thermal grad-ient across the walls of the inner enclosure 14 to retard heat loss from the contained material when the latter mater-ial is heated. The gas passages communicate with the volume 16 through horizontally elongated apertures spaced around the uppermost portion of the walls of the inner enclosure;
specifically, each side wall 26 and 28 of the inner enclosure has a plurality of small apertures 80 spaced along its length, while small louvered apertures 82 and 84 are provided in the rear and front end walls respectively, at a level somewhat 1~7413~
higher than that of the apertures 80. Each of the loading doors 60 has a pair of louvered vents 86 spaced along its length adjacent the peak of the roof cooperatively formed by the doors, for dis-charging gas to the atmosphere from the volume 16. The apertures 80, 82 and 84 and the vents 86 are so arranged that heated gas (air) rising through the wall passages 46, 48, 52 and 56 flows therefrom through the apertures into the volume 16 and evenly across the upper surface of the body of asphaltic material con-tained therein, further contributing to the heating of that mate-rial, before exiting from the unit 10 to the atmosphere throughthe vents 86.
The structure of the unit 10 as thus far set forth cor-responds generally to features of construction and arrangement shown in one or more of applicant's aforementioned U.S. patents No. 3,386,435 and No. 3,577,976. Particular features of the pre-sent invention, for effecting the heating of initially solid and "cold" (ambient-temperature) asphaltic material to produce asphal-tic concrete, will now be described.
In accordance with the invention, then, the unit 10 fur-ther includes a plurality of heating chambers 100, projecting up-wardly from the inner enclosure floor 24 to the upper portion of the volume 16 (but terminating below the uppermost portion of the inner enclosure 14) and extending from end to end of the inner enclosure in laterally spaced, parallel relation to each other so as to divide the volume 16 lengthwise into plural parallel sub-volumes opening upwardly into a common space through which the gas flow from the apertures 80, 82 and 84 circulates. Two such heat-~ -8-ing chambers 100 are shown in the illustrated embodiment of the invention, dividing the volume 16 into three relatively narrow subvolumes 16', 16" and 16' " each extending lengthwise of the unit 10 and respectively in register with the three openings 66 at the rear of the unit. As will now be appreciated, the provision of three openings 66 facilitates removal of asphaltic concrete from these three subvolumes.
Each of the heating chambers 100 is formed by two walls 102 and 104 which constitute part of the wall structure -8a-9 11'~13'~
of the inner enclosure 14 and are fabricated (like the re-mainder of the inner enclosure) of a thermally conductive metal. These walls converge upwardly so that the heating chamber they cooperatively constitute has an inverted V shape as seen in transverse section (Fig. 3). The walls 102 and 104 of each heating chamber define, between them, a gas flow region 106 which opens downwardly through the inner enclosure floor 24 into, and cooperatively interconnects with, the gas space 38 from the rear end wall 30 to the front end wall 32 of the inner enclosure; these walls 102 and 104 are joined to the front and rear walls 30 and 32 and to the floor 24 to isolate the region 106 from the volume 16. It will be appre-ciated that asphaltic material within the volume 16 is in contact with the walls 102 and 104 of the two heating chambers 100. The unit 10 has two of the infrared energy converters 20, e.g. mounted on a fixed tray (not shown), and respec-tively disposed in the gas space 38 directly beneath the gas flow regions of the -two heating chambers 100, in alignment with the long dimensions of the heating chambers, so that gas (i.e. air) heated by the converters rises from the gas space 38 directly into the gas flow regions of the heating chambers, as indicated by arrows 108. The heated gas also rises from the gas space 38 directly into the end passage 56 and into the side wall passages 46 and 48.
Further in accordance with the invention, trans-verse flues 110 (also fabricated of a thermally conductive metal) extend across the interior of the inner enclosure 14, at an upper level therein, for interconnecting the uppermost portions of the gas flow regions 106 of the heating chambers 100 with the side wall passages 46 and 48. Two of these flues 110 are provided in the unit 10, at locations spaced along the length of the unit. Heated air rising through the regions 106 is conducted by the flues 110 to the side wall passages (as indicated by arrows 112), where it circulates and finally enters the upper portions of the volume 16 through the apertures 80. In this way, a continuous upward flow of heated air is maintained in the heating chamber regions 106 as well as through the wall passages, and the - 1o ll'~ Z
heated air enters the volume 16 only through the apertures 80, 82 and 84 at the top of the walls.
As a still further feature of the invention, heat-shielding means are interposed between the converters 20 and the portions of the inner enclosure structure (i.e. the por-tions of floor 24 and of heating chamber walls 102 and 104) adjacent the converters, to prevent localized overheating of the material within the volume 16 and thereby to contribute to desired uniformity of heating. In the embodiment illus-trated, this shielding means includes absorber plates 114 and 116 disposed externally of the lower portions of the walls 102 and 104 (i.e. on the side of those walls external to the volume 16) and extending around the adjacent portions of the floor 24. The absorber plates are joined to the inner enclosure structure along their edges but are otherwise spaced therefrom so as to define dead air or dampener spaces 118. Additionally, the shielding means includes layers of thermal insulation 120 mounted within the spaces 118 on those portions of the external surfaces of the inner enclosure wall structure which are closest to the converters 20. The shield-ing means prevents heated air in the immediate vicinity of the converters (i.e. that air which is at the highest temp-erature) from coming into direct contact with the thermally conductive walls of the inner enclosure.
The use of the described unit to prepare asphaltic concrete may now be readily understood. The volume 16 is filled with chunks or other pieces of initially solid asphaltic material at ambient atmospheric temperature; these chunks, for example, may be broken up pieces of asphaltic pavement or other suitable starting material for the produc-tion of asphaltic concrete. The burners of the heating means, fueled by propane gas or liquid from one of the tanks 22, are turned on and operated. Air entering the gas space 38 is heated by the infrared energy produced by the con-verters 20. The heated air rises from the converters through the regions 106 of the heating chambers 100 and through the forward gas passage 56, with a flow velocity enhanced by the upward taper of that passage and of the heating chamber 117~1;}Z
regions. From the upper portions of the heating chamber regions the heated air flows laterally through the flues 110, thence through the side wall passages 46 and 48, rising to the plural, small apertures 80, 82 and 84 in the side and end wall passages, and finally enters the upper portion of the volume 16 where it flows uniformly across the top surface of the asphaltic material being heated before leaving the unit through the constantly open vents 86.
The converters 20 are conveniently under thermo-static control (as described below) and are operated to achieve and maintain a temperature between 275F and 300F
throughout the body of asphaltic material in the volume 16.
This heating is accomplished in the described unit with advantageous effectiveness and uniformity of temperature, since the charge of asphaltic material is subdivided or penetrated by the heating chambers 100 with their regions 106 of upwardly flowing heated air, as well as being surrounded by flows of heated air (in the subjacent gas space 38, the wall passages, and the upper portion of volume 16), and since the heat-shielding means prevents local overheating of the portions of the charge nearest the converters. The slow, uniform heating of the material to a temperature in the 275-300F range, afforded by the present unit, produces (from an initially cold charge) asphaltic concrete in a suitable state or condition for use within a reasonable period of time, and avoids such problems of prior practice as excessive heating, burning, oxidizing, and/or segregating components of the asphaltic concrete. Moreover, the unit readily enables maintenance of the asphaltic concrete within the stated temperature range until the material is used. Thus, for example, a unit of the described construction having a 4-ton capacity and two 50,000 B.T.U. infrared-type converters may be charged with cold material at the end of a working day, and operated overnight (for a period of, say, 12 to 14 hours) to heat the material; by the next morning, the asphaltic ccncrete will be at the desired temperature and ready for use, and will be maintained at that temperature by the unit.
The transverse flues 110, providing paths at the - 12 - il~l3z top of the heating chamber regions 106 for outflow of heated air rising through the latter regions, assure continuous directional flow of heated air upwardly through the regions 106 as weil as constituting, in themselves, additional heated air passages extending through the volume 16, and therefore contribute to the even and efficient heating of the asphaltic concrete charge. In the particular unit described, the pro-vision of two heating chambers 100 and two transverse flues 110 affords effective heating of a full day's supply of asphaltic concrete for patching purposes or the like in a structure conveniently dimensioned for transport as a vehic-ular trailer. The slope of the heated chamber walls 102 and 104 and the front end wall 32 in this unit facilitates with-drawal of asphaltic concrete from the interior of the unit through the openings 66.
It is an important aspect of the invention that the asphaltic concrete be heated to, and then maintained within, the elevated temperature range of about 275 to 300F, and preferably at about 290F, for a long period of time, e.g. 48 hours. This is accomplished by use of a special system for controlling the amount of time that heated air passes adjacent to and contacts the asphaltic material, rather than control-ling the temperature or thermal content of the heated air.
The preferred embodiment of the control system is shown in Fig. 4 of the drawings, although other control systems which carry out the function in a similar manner and which accom-plish an equivalent result could be used.
Referring to Fig. 4, there is shown a control system 200 for controlling the heating means for the asphaltic material. The infrared converters 20 cannot readily be controlled either as to temperature or as to the quantity of heat produced, and should always emit the same amount of radiation. The control system 200, therefore, is adapted to control the time of firing of the heating means, and thereby to produce heated air intermittently at the infrared converters 20. The control system 200 generally comprises a power supply, such as a 12VDC, 90.0 amp battery 202; a switch 204 for connecting the battery 202 to the remainder of the control system; a pair of repeat timers 206, 208; and a pair of gas control valves 210, 212 operatively connected to the propane tanks 22 and opened and closed by the repeat timers 206, 208. The control system further includes a sensor 214 connected to the repeat timers 206, 208 and having one or more thermostatic elements 216 for deter-mining the temperature of the asphaltic concrete and control-ling the cyclic patterns of the repeat timers. It is presently preferred to use a Honeywell-type sensor for the above purpose, having a thermostatic element positioned within the asphaltic material in one of the three subvolumes 16', 16" or 16''' (see Fig. 3). The entire control system 200, other than the thermostatic element 216 of the sensor 214 (and other thermostatic elements to be described), desir-ably is contained within a control box (not shown) located at the exterior of the unit for easy access. It is useful to have one or more lamps 218 mounted on the control box so that the operator of the unit can tell when the control system 200 is "on" or "off".
To prevent a malfunction in the control system from causing overheating of the asphaltic material, it is further desirable to incorporate in the control system one or more thermostatic elements 220. These thermostatic elements are positioned so as to sense the temperature at the surface of the material (see Fig. 3) and to shut down the heating means if the temperature exceeds about 300F. It is presently preferred to use two Klixon-type thermostats for this purpose.
In operation of the thermostatic control system, the switch 204 is manipulated to energize the circuits, the lamp 218 thereupon indicating that the system is "on". If the asphaltic material is cold, the thermostatic element 216 of the sensor 214 signals the first repeat timer 206 to open gas control valves 210, 212 to provide fuel from propane tanks 22 to fire the burner of the heating means. Heat energy from the burner is absorbed by the infrared energy converters 20, which then emit infrared radiation to heat the air entering the gas region from the outside atmosphere.
Repeat timer 206 intermittently turns the gas control valves 11'7413Z
210, 212 "on" and "off" in accordance with a first pre-determined cycle until the material is heated to the desired temperature range. It is presently preferred that the first predetermined cycle is 10 minutes "on" and 5 minutes "off".
For certain applications, a different cycle may be appro-priate, for example, 10 minutes "on" and 10 minutes "off".
Other cycles may also be advantageous.
After the temperature of the material reaches the lower end of the desired temperature range of about 275 to 300F, as determined by the sensor 214, the sensor switches to repeat timer 208 and disconnects repeat timer 206. Repeat timer 208 intermittently turns the gas control valves 210, 212 "on" and "off" in accordance with a second predetermined cycle to hold the temperature of the asphaltic material within the desired temperature range. It is presently pre-ferred that the second predetermined cycle is 3 minutes "on"
and 5 minutes "off". However, for certain applications, a different cycle may be appropriate, for example, 5 minutes "on" and 10 minutes "off". The invention contemplates cyclic patterns of sufficient duration to maintain the asphaltic composition within the desired temperature range for a long period of time.
If the temperature of the asphaltic material falls below the lower end of the desired temperature range, as determined by the sensor 214, the sensor switches back to repeat timer 206 and disconnects repeat timer 208. It will be appreciated that use of repeat timer 206 results in greater "on" time than use of repeat timer 208 and thereby results in more heated air being supplied to the operation of the unit. When the temperature of the material again returns to the proper range, the repeat timer 208 again is connected, and the repeat timer 206 again is disconnected.
If the temperature of the a~phaltic material exceeds the upper end of the desired temperature range, as determined by the thermostatic elements 220 positioned adjacent with the asphaltic material, the gas control valves 210, 212 are closed and the heating means is shut down until the temp-erature of the material returns to the proper range. The repeat timer 208 then may continue the cycle.
~1'7413Z
It is also contemplated to provide an override circuit for the control system in certain applications. This provides a mode of operation whereby more heated air is supplied to the unit, for example, under extremely cold operating conditions. It further is contemplated to use a variable sensor, so that as the material is used during the course of a day, less heated air is supplied to the unit to maintain the temperature of the material.
It is to be understood that the invention is not limited to the features and embodiments hereinabove speci-fically set forth, but may be carried out in other ways without departure from its spirit.
Claims (18)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An asphalt reclamation unit for heating initially solid asphaltic material from ambient atmospheric temperature to an elevated temperature between about 270°F. and about 300°F. and thereafter maintaining the material at the elevated temperature to provide asphaltic concrete in a condition suitable for paving application or the like, comprising: (a) an upwardly open inner enclosure defining a volume for containing asphaltic material to be heated, and including a floor, end walls, and side walls; (b) an outer enclosure surrounding said inner enclosure and including a floor, end walls, and side walls respectively disposed in adjacent spaced relation to the floor, end walls, and side walls of said inner enclosure to define a gas space between the inner and outer enclosure floors and end and side wall gas passages between the inner enclosure walls and the outer enclosure walls respectively adjacent thereto, said outer enclosure further including door means for closing the top of the unit, said gas space communica-ting with the outside atmosphere, said passages communicating with said gas space and with the uppermost portion of said volume, and said upper portion of said volume being vented to the outside atmosphere, for enabling continuous air flow into said gas space and thence through said passages and said upper portion of said volume; (c) at least one source of infrared energy disposed in said gas space for heating air entering said gas space from the outside atmosphere; (d) heating chamber means comprising at least one heating chamber projecting upwardly from the floor of the in-ner enclosure into an upper portion of said volume at a locality intermediate and spaced from the side walls of said inner enclo-sure, said one heating chamber extending from end to end of said inner enclosure and comprising thermally conductive wall portions of said inner enclosure defining a gas flow region isolated by the wall portions from said volume and opening into and extending upwardly from said gas space above said one infrared energy source;
and (e) flue means, comprising at least one flue extending from side to side of said inner enclosure and spaced away from both ends thereof, for conducting heated air from the uppermost portion of said gas flow region transversely across said upper portion of said volume to said side wall passages, such that air heated by said source flows upwardly through said gas flow region and thence through said flue means to the side wall passages; (f) said walls of said inner enclosure, said heating chamber means, and said flue means being mutually disposed to enable delivery of solid pieces of the asphaltic material downwardly from the top of the unit into the lowermost portion of said volume.
and (e) flue means, comprising at least one flue extending from side to side of said inner enclosure and spaced away from both ends thereof, for conducting heated air from the uppermost portion of said gas flow region transversely across said upper portion of said volume to said side wall passages, such that air heated by said source flows upwardly through said gas flow region and thence through said flue means to the side wall passages; (f) said walls of said inner enclosure, said heating chamber means, and said flue means being mutually disposed to enable delivery of solid pieces of the asphaltic material downwardly from the top of the unit into the lowermost portion of said volume.
2. A unit as defined in claim 1, wherein said heating cham-ber means comprises a plurality of heating chambers projecting upwardly from the inner enclosure floor into said volume in spaced relation to each other, each of said heating chambers extending from end to end of said inner enclosure and comprising thermally conductive wall portions of said inner enclosure defining a gas flow region as aforesaid, and including a corresponding plurality of sources of infrared energy respectively disposed beneath the gas flow regions of the heating chambers, said flue means compri-sing means for conducting heated air from the uppermost portion of each of the gas flow regions to the side wall passages as aforesaid.
3. A unit as defined in claim 2, wherein said flue means comprises a plurality of flues extending from side wall to side wall of said inner enclosure in horizontally spaced relation to each other, each of said flues communicating with each said gas flow region.
4. A unit as defined in claim 3, wherein there are two heating chambers and two flues.
5. A unit as defined in claim 1 or 2, further including heat-shielding means interposed between said inner enclosure and each said infrared energy source for preventing local overheating of asphaltic material contained in portions of said volume adjacent each said source.
6. A unit as defined in claim 5, wherein said shielding means comprises plates joined at their edges to external surfaces of said wall portions and said inner enclosure floor for defining therewith air spaces adjacent each said source.
7. A unit as defined in claim 6, wherein said shielding means further includes bodies of thermally insulated material mounted on said last-mentioned external surfaces within said last-mentioned air spaces.
8. A unit as defined in claim 3, wherein the thermally conductive wall portions of said heating chambers converge up-wardly.
9. A method for reclaiming initially solid asphaltic material to provide asphaltic concrete, wherein the material is heated from ambient atmospheric temperature to an elevated temperature within a range of about 275-300°F and thereafter maintained at the elevated temperature such that the material is in a condition suitable for paving application or the like, comprising: (a) pla-cing asphaltic material in an inner enclosure having thermally conductive walls and a floor and arranged such as to enable delivery of the initially solid asphaltic material downwardly from the top of the inner enclosure toward the floor of the inner enclosure; (b) intermittently producing a heated gas in accor-dance with a predetermined schedule; (c) heating the asphaltic material from ambient atmospheric temperature by passing a first portion of the heated gas within a gas volume defined by the in-ner enclosure and an outer enclosure, such that the heated gas passing the walls and floor heats the portions of the asphaltic material in the inner enclosure adjacent the walls and floor until the material reaches a temperature within a range of about 275-300°F; (d) further heating the asphaltic material by passing a second portion of the heated gas through at least one heating chamber communicating with and projecting upwardly from the gas volume into the inner enclosure, such that the heated gas passing through the heating chamber heats the interior portions of the asphaltic material in the inner enclosure adjacent the heating chamber from both the longitudinal and transverse directions until the material reaches a temperature within a range of about 275-300°F; (e) passing all the heated gas through a plurality of small apertures spaced about the upper portions of the walls of the inner enclosure, such that the heated gas flows from the gas volume uniformly across the upper surface of the asphaltic mate-rial in the inner enclosure and the portions of the asphaltic material near the upper surface are heated until the material reaches a temperature within a range of about 275-300°F; (f) ven-ting the heated gas to the outside atmosphere after it has flowed across the upper surface of the asphaltic material and (g) sen-sing the temperature of the asphaltic material within the inner enclosure and maintaining the asphaltic material through inter-mittent heating thereof at a uniform temperature within a range of about 275-300°F for a long period of time.
10. A method as defined in claim 9, wherein the heated gas is produced intermittently in accordance with a first predeter-mined cycle of about 10 minutes "on" and 5 minutes "off" until the material reaches a temperature range of about 275-300°F.
11. A method as defined in claim 9 or claim 10, wherein the heated gas is produced intermittently in accordance with a second predetermined cycle of about 3 minutes "on" and 5 minutes "off" to maintain the material within the temperature range of about 275-300 F.
12. A method as defined in claim 10 wherein the heated gas is produced intermittently in accordance with a first predeter-mined schedule when the temperature of the material is sensed to be below the temperature range.
13. A method as defined in claim 9, wherein the heated gas is produced by an infrared energy source which is fired inter-mittently in accordance with a predetermined schedule.
140 An asphaltic material delivery and storage unit for heating initially solid asphaltic material to provide asphaltic material in a condition suitable for paving application or the like, comprising: (a) an inner enclosure defining a volume for containing asphaltic material to be heated, and including a floor and walls; (b) an outer enclosure surrounding the inner enclosure and including a floor and walls disposed in adjacent spaced relation to the floor and walls of the inner enclosure to define a gas region therebetween, the outer enclosure further including door means for closing the unit, and the gas region communicating with the outside atmosphere; (c) a source of inter-mittent heat energy disposed in the gas region for heating air entering the gas region from the outside atmosphere, the source of heat energy comprising a supply of fuel, a burner adapted to be fired intermittently and positioned to burn fuel, and at least one infrared energy converter for absorbing heat energy produced by the burner and emitting intermittently infrared radiation in accordance with a predetermined schedule for heating air entering the gas region from the outside atmosphere; (d) at least one heating chamber projecting upwardly from the floor of the inner enclosure into the volume and communicating with the gas region such that heated air can pass through the heating chamber and the gas region; (e) the upper portions of the walls of the inner enclosure having a plurality of spaced apart apertures communi-cating with the gas region to permit a flow of heated air into the volume such that the heated air passes across the upper por-tion of the volume; (f) the door means having a vent such that the heated air passing across the upper portion of the volume is vented to the outside atmosphere; and (g) means for controlling the source of heat energy such that it intermittently produces heated air in accordance with a predetermined schedule sufficient to heat the asphaltic material to, and to maintain the temperature of the material within, a predetermined temperature range in excess of 275°F.
15. A unit as defined in claim 14, wherein the controlling means comprises: (i) a first repeating timer for controlling the source of heat energy in accordance with a first predetermined schedule until the material reaches the temperature range of about 275-300°F; and (ii) a second repeating timer for controlling the source of heat energy in accordance with a second predeter-mined schedule to maintain the material within the temperature range of about 275-300°F.
16. A unit as defined in claim 15, further comprising a sen-sor adapted to be positioned in contact with the material for determining the temperature of the material, the sensor being arranged to signal the first repeating timer when the temperature of the material is below the temperature range, and to signal the second repeating timer when the temperature of the material is within the temperature range.
17. A unit as defined in claim 15, wherein the first repeating timer is arranged to carry out a first predetermined schedule of about 10 minutes "on" and 5 minutes "off" and the second repeating timer is arranged to carry out a second predetermined schedule of about 3 minutes "on" and 5 minutes "off".
18. A unit as defined in claim 14, further comprising means for disconnecting the source of heat energy when the temperature of the material exceeds about 300°F.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/416,629 US4445848A (en) | 1981-06-01 | 1982-09-10 | Asphalt reclamation system and unit |
| US416,629 | 1982-09-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1174132A true CA1174132A (en) | 1984-09-11 |
Family
ID=23650703
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000419169A Expired CA1174132A (en) | 1982-09-10 | 1983-01-10 | Asphalt reclamation system and unit |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1174132A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108760795A (en) * | 2018-08-22 | 2018-11-06 | 沈阳建筑大学 | A kind of device measuring asphalt softening point using air mode of heating |
-
1983
- 1983-01-10 CA CA000419169A patent/CA1174132A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108760795A (en) * | 2018-08-22 | 2018-11-06 | 沈阳建筑大学 | A kind of device measuring asphalt softening point using air mode of heating |
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