Patent Publication Number: US-4483620-A

Title: Regenerative heating and melting device for recovered asphalt concrete rubble

Description:
The application is a continuation of our copending application Ser. No. 374,589 filed May 3, 1982 now abandoned, the entire disclosure of which is relied on and incorporated herein. 
    
    
     This invention relates to a device for heating and melting the broken asphaltic concrete that occurs in redoing the asphalt concrete pavement of the road, in order to render the crushed concrete re-usable. 
     Such broken asphaltic concrete in the form of rubble results from stripping the existing asphalt concrete pavement. The rubble can be made use of as a back-filling material or a roadbed material but cannot be re-used as a pavement material in its as-stripped form. Many techniques of restoring it to its original mixture of asphalt cement and aggregates have been proposed. 
     According to the currently practice restorative technique, the asphaltic rubble is mechanically broken into smaller lumps or, by using hot water or steam, heated and melted into a proper range of lump sizes, or is finely crushed to the sizes of the original aggregate and then heated in such as a drum drier to make it free of water. 
     The drawback of these known techniques is that the equipment for implementing them is necessarily large in size and complex in construction because the rubble must be crushed to the original aggregate size and heated with hot water or steam, and that, in the case of melting by heating, a large amount of energy has to be expended in removing the water by evaporation. 
     The object of the present invention is to provide a simple and compact means of heating the broken asphalt concrete rubble and melting the asphalt to thereby obtain a re-usable form of aggregate coated with asphalt without involving expenditure of a large amount of energy. 
     The invention also provides a method for the regenerative heating and melting of crushed recovered asphalt concrete rubble. 
     According to this invention, the mechanical and thermal actions are effected concurrently on the rubble inside the device of this invention in such a manner as to minimize the deterioration of asphalt cement in the rubble and to heat it to the temperature desired for its re-use as a pavement material. 
    
    
     How the present invention accomplishes its object will be seen in the following description of examples of the device of this invention illustrated in FIGS. 1 through 7 given in the accompanying drawings: 
     FIG. 1 is an isometric view of the apparatus of the invention; 
     FIG. 2 is a sectional elevation view of another embodiment of the apparatus of the invention; 
     FIG. 3 is a sectional schematic view of the apparatus shown in FIG. 2 and illustrates its operation; 
     FIGS. 4 to 7 are plan views of the tier constructions inside the apparatus of the invention, as follows: 
     FIG. 4 is a cross-section taken at line IV--IV of FIG. 3; 
     FIG. 5 is a cross-section taken at line V--V; and 
     FIGS. 6 and 7 show the configuration of mixing blades in plan view. 
    
    
     The method of the invention is for the regenerative heating and melting of recovered asphalt concrete rubble, wherein crushed asphalt concrete rubble is conveyed to a housing; i.e. the cylindrical casing, where it is subjected to hot gas with agitation. The heated rubble moves downwardly in the housing during the heating step. The hot gas may move in the same direction as the rubble; i.e. concurrent, or it may be countercurrent. In the course of this movement, the old asphalt is melted and the aggregate becomes coated with soft asphalt. The result is a soft state regenerated hot paving material which is ready for deposition to the road surface. 
     Referring to FIG. 1 showing one of the examples, support frame 2 is solidly set on ground surface 1. On the frame is rigidly mounted cylindrical casing 3, whose top plate 4 is complete with an opening serving as rubble inlet 5 and whose bottom plate 6 is complete with an opening serving as regenerated material outlet 7. In the cylindrical wall of casing 3, near top plate 4, has an opening serving as hot-gas inlet 8 for connection with a hot-gas supply duct. Near bottom plate 6, the cylindrical wall has an opening to which exhaust gas outlet duct 9 is connected. 
     Rotary shaft 10, whose axis coincides with that of cylindrical casing 3, is provided inside the casing and is supported by bearings 11, one being fitted to top plate 4 and the other to bottom plage 6. (See FIG. 2). 
     The space inside cylindrical casing 3 is divided into a plurality of tier sections 13a, 13b, 13c, 13d, 13e and so on, by means of partition plates 12a, 12b, 12c, 12d, 12e and so on. (Except when a specific partition plate is indicated, all plates will be referred to by number 12.) (Similarly, all tier sections will be referred to by number 13.) Two adjacent tier sections 12 are communicated to each other through communicating hole or opening 14 formed in partition plate 12 between the two sections. Guide plate 14a is attached to the underside of all plates and serves to guide the filling rubble onto the next plate below. The guide plate is arranged to deposit the filling rubble away from the hole 14 in that plate. The hole 14 in each position in FIG. 1 is located in line with the corresponding hole in adjacent plates, as shown. However, the holes may also be offset. The holes are generally of the same size. In each tier section, a plurality of mixing blades 15 extend radially from rotary shaft 10, the blades being integral with the shaft and being so shaped that, as shaft 10 rotates, blades 15 revolve in sliding contact with partition plate 12. As is shown in FIG. 1, the mixing blade 15 has a diameter slightly less than the inside diameter of the casing to permit rotation inside the casing with sufficient clearance to permit movement without any impediment. 
     The materials which are dropped on the partition plate are moved by mixing blade 15 in a circular pass approximately slightly less than 360 degrees whereupon the materials then drop to the underside plate through the hole. 
     FIG. 2 shows that the bottom end of rotary shaft 10 is secured to gear 16, which is in mesh with gear 17 mounted on the output shaft of speed reducer 18. Reducer 18 is coupled to electric motor 19 to continuously drive shaft 10 through gears 17 and 16. Instead of this arrangement, any other known means of drive may be used. 
     The external surface of cylindrical casing 3 is preferably covered with insulation material 20 to minimize heat loss. To said rubble inlet 5 and regenerated material outlet 7 are connected rubble feeding means 21 and regenerated material conveying means 22, respectively, in that order and as shown in FIG. 1. 
     The device arranged and constructed as above is started up for operation by starting up the blower, not shown, connected to exhaust gas outlet duct 9 and then starting up the hot-gas supply source, now shown, or, for example, a hot-gas furnace. The chemical composition of the gas is not critical and will be known to persons skilled in the art. The temperature of the hot gas at inlet 8 should be anywhere between about 500° C. and 600° C. With hot gas being supplied and exhaust gas being drawn out, motor 19 is to be started up to drive rotary shaft 10 through reducer 19 and gears 17 and 16, thereby setting mixing blades 15 in revolving motion. When the temperature of exhaust gas has risen to about 200° C., rubble feeder 21 is to be started to feed rubble 23 through inlet 5. The desired average lump size of rubble 23 is about 80 mm but any lump size will do as long as the rubble is suitable for being handled by feeder 21. The rubble need not be broken into lumps and sifted for sizing prior to feeding; broken asphalt concrete in melted form consisting of aggregates not bound by asphalt cement may be fed into the casing. The crushed rubble is about 80 mm or less, and preferably 40 mm or less and not preferably less than 20 mm in diameter. 
     Rubble 23 fed into the top tier section falls onto partition plate 12a and is then pushed around by mixing blades 15 to enter by gravity into the next section through communicating hole 14. This process is repeated to forward rubble 23 downward through successive tier sections 13b, 13c, 13d, 13e and so on. During this process, rubble 23 is exposed to the hot gas, which melts the asphalt cement, and the agitating action of mixing blades 15 separates the pieces of aggregates, so that the rubble becomes transformed into regenerated paving material 24, which comes out of outlet 7 with a temperature between 150° C. and 170° C. Since the rotating speed of shaft 10 can be adjusted as desired by means of speed reducer 18, the temperature with which regenerated paving material 24 comes out can be controlled by varying the speed of shaft 10 to control the duration of each portion of the rubble remaining inside the cylindrical casing. Generally, the speed of the shaft is from 2 to 5 rpm. 
     Referring to FIG. 2 showing the other example, blades 15 differ from those of FIG. 1 and, accordingly, the location of communicating hole 14, too, differs, as will be explained later. With respect to all other features, the device shown in FIG. 2 is substantially the same as that shown in FIG. 1. 
     FIGS. 3, 4 and 5 serve to describe the example illustrated in FIG. 2. Note that communicating hole 14a is formed of partition plates 12a and 12c and is located around rotary shaft 10 (not shown), the hole being concentric with cylindrical casing 3. On the other hand, communicating hole 14b is formed of partition plates 12b and 12d, the hole being located alongside of the cylindrical wall of the casing. 
     From top to bottom, communicating holes 14a and 14b alternate: if partition plate 12a forming uppermost tier section 13a is given hole 14a, as shown, then partition plate 12b forming the next tier section 13b has hole 14b. How these concentrically located communicating holes are to be formed of partition plates is shown in FIGS. 4 and 5, in which (as seen from top side) the communicating hole of the plate immediately below is indicated in dot lines. In FIGS. 3, 4 and 5, arrows A in real lines indicate the direction of rubble flow and arrows B in broken lines indicate the direction of hot-gas flow. In the illustrated example, rubble and hot gas flow in the same direction, that is, parallel directions. In the case of counter-flow arrangement with the hot gas supplied into the bottom part of cylindrical casing 3, broken-line arrows B reverse the direction and point upward. 
     Mixing blades 15 may be shaped and designed as desired to suit the purpose, and their configuration too may be determined as desired. FIGS. 6 and 7 shows the configurations of blades 15 that are applicable to the example of FIG. 2. In the configuration of FIG. 6, the rubble flows radially outward from the center area, as indicated by arrow A; in the configuration of FIG. 7, the rubble flows radially inward as indicated by arrow A. Thus, the path of rubble flow indicated by arrows A in FIGS. 3, 4 and 5 can be set by selectively determining the installed position of mixing blades 15 to suit the positions of communicating holes 14 (14a and 14b). 
     It will be seen from the foregoing description that this invention provides a simple device in which the regenerated paving material of a desired temperature can be obtained through a single process and, at the same time, the deterioration of asphalt cement resulting from the melting of the rubble can be minimized. Specifically, the mechanical and thermal actions on the recovered asphalt concrete rubble can be concurrently and effectively effected so that, even when the as-fed rubble is in large lump sizes (of about 80 mm), the single-process heating and melting in the device of this invention transforms the rubble into the regenerated paving material in which the aggregates are in original sizes. 
     It should be noted that the product discharged from the apparatus of the invention is discharged in the hot state and therefore is ready to use on the road building site. The device of the invention is therefore a portable apparatus which can be moved from site to site as needed. Fresh asphalt can be added in the lowest mixing chamber if desired.