Patent Publication Number: US-8993931-B2

Title: Rotary drier for plants for the production of bituminous macadams with the use of recycled materials

Description:
FIELD OF THE INVENTION 
     The present invention relates to a rotary drier for plants for the production of bituminous macadams with the use of recycled materials. 
     BACKGROUND OF THE INVENTION 
     It is a type of drier which comprises a hollow rotary cylinder which at least in operation is angled so that its ends are at different heights relative to the ground. In general, the angle of the axis is approximately several degrees relative to the horizontal. 
     Connected to one end of the cylinder there are heating means normally consisting of a burner which generates a flame that extends inside the cylinder. 
     The combustion fumes then pass through the rest of the cylinder and reach a chimney, usually connected to the end of the cylinder opposite the end connected to the burner. 
     Also connected to the two ends of the cylinder there is an infeed section through which the aggregates to be dried are inserted, and an outfeed section through which the treated materials are extracted from the cylinder. 
     Depending whether the infeed section is connected to the end to which the burner is connected or to the other end, the drier is referred to as cocurrent (since the direction of feed of the fumes and of the material is the same) or counter-current (since the direction of feed of the materials is opposite to that of the fumes). 
     However, irrespective of the type of drier, the infeed section is always connected to the cylinder at the end which in operation is higher above the ground, so that the combined effect of cylinder rotation and angling causes the material to be fed through the cylinder. 
     Inside the cylinder there are usually many series of blades designed to mix and feed the material being processed as well as to facilitate heat exchange. 
     In particular, the blades intended only for feed can adopt a very spiral shape relative to the axis of rotation, whilst those also intended for mixing and/or heat exchange normally extend at least mainly parallel with the axis of rotation. 
     Depending on their structure, the blades for mixing and/or heat exchange may generally be divided into tipping blades and containment blades. The former are blades minimized in that they have a mouth for the material whose width is significantly greater than the depth of the blade (understood to be the distance between the edge of the blade and its innermost point) as well as a profile which prevents the formation of undercuts. Said blades are designed to collect the material as they pass in the lower rotation zone and to pour it out so that it showers down through the combustion fumes passing through the central part of the cylinder. 
     With a suitable construction it is possible to unload more than 80% of the material contained in the tipping blades practically just after they have reached the highest point of the rotation (only at that moment is their mouth facing downwards). In contrast, the containment blades are blades in which the width of the mouth is generally comparable (the same as or slightly less than/greater than) to the depth and they have a rounded profile forming an undercut able to retain the material. These blades are designed to minimize the quantity of material unloaded to shower down through the combustion fumes. With the shape described above it is possible to ensure that during rotation they pass the highest point having unloaded even less than 20% of the material initially loaded. 
     The inside of the cylinder is axially divided, starting at the first end, into a first heat exchange zone, in which heat exchange occurs mainly by convection, and a second heat exchange zone, in which heat exchange occurs mainly by radiation and conduction. The different heat exchange is achieved by using tipping blades in the first heat exchange zone where the temperature of the fumes is lower, and containment blades in the second heat exchange zone where the temperature is significantly higher due to the presence of the flame. 
     As regards recycled materials, plants for the production of bituminous macadams usually use materials obtained from cutting existing road surfaces, which are normally mixed with new aggregates in predetermined proportions. 
     For that reason, the driers for which the present invention is intended comprise an insertion section for inserting recycled material into the cylinder, the insertion section being connected to an intermediate portion of the cylinder. In particular, the insertion section may or may not be connected to the cylinder at a change in its diameter. 
     According to the prior art, the insertion section is positioned between the first and second heat exchange zones, so that the recycled materials are subjected to heating mainly by conduction and radiation. 
     Also according to the prior art, the insertion section comprises one or more radial openings made in the wall of the cylinder and a feeder for directing the recycled material to the openings from the outside. Inside the cylinder, there may be a tubular structure coaxial with the cylinder and designed to prevent the entering recycled material from passing directly through the combustion fumes, diverting it at a tangent along the lateral wall of the cylinder (see for example patent EP 1 624 109). 
     However, all types of prior art driers (whether of the counter-current or co-current type) have disadvantages. 
     In particular, all prior art plants have limits regarding the possibility of using recycled material. Above predetermined limits of approximately 15-20%, the bitumen contained in the recycled material usually causes the material to become packed together, attaching to the blades and the cylinder. 
     A second disadvantage of prior art plants is the fact that they cannot guarantee good mixing of the hot aggregates and the cold cut material which is added, meaning that the temperature distribution is very uneven in the cut material, causing the formation of emissions which are harmful to the environment. 
     SUMMARY OF THE INVENTION 
     In this situation the technical purpose which forms the basis of the present invention is to provide a rotary drier for plants for the production of bituminous macadams with the use of recycled materials which overcomes the above-mentioned disadvantages. 
     In particular, the technical purpose of the present invention is to provide a rotary drier for plants for the production of bituminous macadams which allows the use of a greater quantity of recycled material than prior art plants. 
     The present invention also has for a technical purpose to provide a rotary drier for plants for the production of bituminous macadams which guarantees mixing of the hot aggregates and cold recycled materials that is better than the mixing in prior art plants. 
     Yet another technical purpose of the present invention is to provide a rotary drier for plants for the production of bituminous macadams which guarantees compliance with environmental impact regulations, that is to say, which minimizes the formation of harmful emissions. 
     The present invention also has for an aim to be able to be applied to any type of rotary drier (counter-current, co-current). 
     The technical purpose specified and the aims indicated are substantially achieved by a rotary drier for plants for the production of bituminous macadams with the use of recycled materials as described in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and the advantages of the present invention are more apparent in the detailed description a preferred, non-limiting embodiment of a rotary drier for plants for the production of bituminous macadams with the use of recycled materials illustrated in the accompanying drawings, in which: 
         FIG. 1  is a side view of a drier made in accordance with the present invention; 
         FIG. 2  is a longitudinal axial section of the drier of  FIG. 1 ; 
         FIG. 3  is an axonometric view of the sectioned drier of  FIG. 2 ; 
         FIG. 4  shows a detail of the drier of  FIG. 3  with some parts cut away to better illustrate others; 
         FIG. 5  shows another detail of the drier of  FIG. 3 ; 
         FIG. 6  is a cross-section of the drier of  FIG. 1  according to the line VI-VI, with some background details cut away for clarity; 
         FIG. 7  is an axonometric view from the outside and from the top of an intermediate piece of the drier of  FIG. 1  with some parts cut away to better illustrate others (the cylinder is seen from the opposite side to that in  FIG. 1 ); and 
         FIG. 8  illustrates the drier of  FIG. 2 , showing the heating means  9 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     With reference to the accompanying drawings the numeral  1  denotes as a whole a rotary drier for plants for the production of bituminous macadams with the use of recycled materials, made according to the present invention. 
     In the known way, the drier  1  comprises first a hollow rotary cylinder  2  which has a first end  3 , a second end  4  and an axis of rotation  5  extending from the first end  3  to the second end  4 . Although not illustrated in the accompanying drawings, at least in operation the axis of rotation  5  is angled so that the first end  3  and the second end  4  are at different heights above the ground. Advantageously, the angle of the axis is approximately several degrees (usually between 2° and) 6° relative to the horizontal, so that the cylinder  2  is practically reclined. 
     Moreover, the cylinder  2  has a predetermined direction of rotation which in the embodiment illustrated is anti-clockwise with reference to  FIG. 6 . Cylinder  2  rotation is made possible by two supporting rings  6  which have bearings inside them, rings  6  which in practice are supported by a plant frame. Cylinder  2  rotation is driven by suitable motor-driven means of the known type (not illustrated). 
     Depending on the embodiments, the cylinder  2  may comprise a single body with a constant diameter along the entire length (as illustrated in the accompanying drawings) or two or more bodies which are axially aligned and have the same or different diameters. 
     The cylinder  2  also has an aggregates infeed section  7  connected to the cylinder  2  at the end  3 ,  4  which in operation is highest above the ground, and a dried material outfeed section  8  connected to the cylinder  2  at the other end  3 ,  4 . 
     In the accompanying drawings, in which the drier  1  is of the counter-current type, the infeed section  7  is connected to the first end  3 , whilst the outfeed section  8  is connected to the second end  4 . 
     Consequently, the embodiment illustrated in operation has the first end  3  higher than the second end  4 . However, in other embodiments, the present invention may be applied to a co-current drier  1  in which the cylinder  2  infeed section  7  is connected to the second end  4  and the outfeed section  8  to the first end  3 . 
     In general, in the cylinder  2  a material feed direction is always identified, going from the infeed section  7  to the outfeed section  8 . 
     In the accompanying drawings, the infeed section  7  and the outfeed section  8  are not shown in detail since they generally comprise in the known way inlets and outlets at or close to the two ends of the cylinder  2 . 
     Connected to the second end  4  of the cylinder  2  there are heating means  9  (only visible in  FIG. 8 ) preferably consisting of a burner.  FIG. 8  schematically illustrates both the flame  10  produced by the burner and the direction  11  of flow of the fumes. The latter move from the burner towards a chimney (not illustrated) connected to the first end  3  of the cylinder  2 . 
     The inside of the cylinder  2  is axially divided, starting at the first end  3 , into a first heat exchange zone  12 , in which heat exchange occurs mainly by convection, and a second heat exchange zone  13 , in which heat exchange occurs mainly by radiation and conduction. In particular, the first heat exchange zone  12  is advantageously made in such a way that it creates a shower of material through the combustion fumes, whilst the second heat exchange zone  13  is made in such a way that it prevents, or at least minimizes, interference between the material and the flame  10  (and therefore material showering down). 
     The first heat exchange zone  12  is equipped with a plurality of material tipping blades  14 , whilst in the embodiment illustrated the second heat exchange zone  13  is equipped with a plurality of material containment blades  15 . The terms tipping blades  14  and containment blades  15  refer to blades of the known type able to respectively minimize and minimize the showering of material inside the cylinder  2 . Advantageously, in general they may adopt the known shape indicated at the start of this description. 
     In particular, the tipping blades  14  preferably mainly consist of at least one shaped element  16  (advantageously metal) extending along the cylinder  2  inner surface  18  and having a first longitudinal edge  17  (the term longitudinal being understood with reference to the direction of extension of the axis of rotation  5 ) abutted to the cylinder  2  inner surface  18  and a second longitudinal edge  19  distanced from the cylinder  2  inner surface  18 , forming the blade mouth. The shaped element  16  also has two lateral edges  20  (transversal to the longitudinal direction) respectively facing towards the first end  3  and towards the second end  4  (depending on the material feed direction, the lateral edges  20  may also be defined as the front edge and the rear edge). 
     A more detailed description of the various blades used in the embodiment illustrated is provided below. 
     Moreover, as shown in the accompanying drawings, the first heat exchange zone  12 , close to the first end  3 , is also equipped with spiral blades  21 , close together and shaped, which guarantee correct insertion of the aggregates in the cylinder  2 , whilst the second heat exchange zone  13  is also equipped, in the zone which in practice surrounds the flame  10 , with a tubular protective structure  22  coaxial with the cylinder  2 , also shaped, but which is not part of the present invention. 
     Although not visible, there are blades on the inner surface  18  of the cylinder  2  even at the tubular protective structure  22 . Finally, at the burner, the second heat exchange zone  13  is equipped with other shaped blades  23  mainly radial and longitudinal for unloading material to the outfeed section  8 . 
     The type of drier  1  for which the present invention is intended also comprises an insertion section  24  for inserting cut recycled material in the cylinder  2 , the insertion section being connected to an intermediate portion of the cylinder  2 . 
     The cut material insertion section  24  comprises a plurality of radial openings  31  made through the cylinder  2  lateral wall and distributed circumferentially on the cylinder  2  inner surface  18 , as well as, on the outside of the cylinder  2 , means  32  for feeding the cut material to the openings  31 . Advantageously, the insertion section  24  also comprises at least one structure  33  covering the openings  31 , fastened to the cylinder  2  inner surface  18  upstream of the openings  31  relative to the material feed direction, extending in the feed direction and distanced from the cylinder  2  inner surface  18  downstream of the openings  31  (again relative to the feed direction). In this way, the openings  31  are put in communication with the inside of the cylinder  2  but at the same time the covering structure  33  protects the openings  31  from the aggregates arriving. Consequently, mixing of the aggregates with the recycled material only takes place downstream of the covering structure  33 . 
     Whilst in  FIG. 7  the openings  31  are made independent of each other, in other embodiments they may be obtained by making a single annular opening, extending around the entire circumference of the cylinder  2 , and partly covering it (for example from the inside of the cylinder  2  as also indicated below) to form the individual openings  31 . 
     Also according to the present invention, the covering structure  33  comprises a plurality of separator plates  34  distributed circumferentially along the cylinder  2  inner surface  18  so that between each pair of adjacent separator plates  34  there is at least one radial opening  31 . 
     Advantageously, the separator plates  34  are made in such a way that they form a plurality of first channels  35  for guided insertion of the cut material into the cylinder  2 . It should be noticed that the separator plates  34  may also be used to divide from the inside a single annular opening into a plurality of openings  31  as indicated above. 
     As shown in  FIG. 5 , in the preferred embodiment, the separator plates  34  extend radially relative to the axis of rotation  5  along spiral trajectories centred on the axis of rotation  5 . They also have a first end side  36  towards the outfeed section  8  and a second end side  37  towards the infeed section  7 , and they are advantageously positioned so that during cylinder  2  rotation the second end side  37  of each separator plate  34  angularly precedes the first end side  36  of the same separator plate  34  (in other words, they are positioned so that the first channels  35  which they form are angled towards the outfeed section  8  during the ascending part of the rotation). 
     Moreover, in the embodiment illustrated, the covering structure  33  comprises covering partitions  38  mounted over the openings  31 , distanced from them, and connected to the separator panels  34 . 
     Advantageously, the covering structure  33  is also equipped with guide and feed elements  39  for the material arriving from the infeed section  7  which form second channels  40  designed to guide the material arriving from the infeed section  7  until it is mixed with the recycled material. In the embodiment illustrated the guide and feed elements  39  for the aggregates are formed by the separator plates  34  projecting upwards relative to the covering partitions  38 . 
     The cut material feed means  32 , in the embodiment illustrated ( FIGS. 5 and 6 ) comprise first an annular chamber  41  made around the outside of the cylinder  2  at the insertion section  24 . A plurality of scoops  42  extends inside the annular chamber  41  from the outside of the cylinder  2  and is circumferentially distributed along the cylinder  2  outer surface so that between each pair of adjacent scoops  42  there is an opening  31  (in  FIG. 7  the scoops  42  are cut away for clarity). A duct  43  for feeding the cut material to the annular chamber  41  opens into the annular chamber  41  to feed the material at a side of the cylinder  2  which during rotation moves upwards (in  FIG. 6 , to a first approximation, the feed duct  43  outlet into the annular chamber  41  is substantially aligned with the vertical tangent to the outer side of the cylinder  2  which moves upwards during rotation). 
     Moreover, advantageously, the scoops  42  are angled relative to the cylinder  2  outer surface in the direction of the movement (or, in other words, forwards relative to their movement trajectory). 
     The feed duct  43  is also equipped with a mobile partition  44  designed to divert the flow of recycled material either into the annular chamber  41  (position shown with a continuous line in  FIG. 6 ) or towards a secondary outlet  45  (position illustrated with a dashed line in  FIG. 6  and visible in  FIG. 4 ). In the embodiment illustrated the passage between the two positions takes place by rotation about a hinge  46  fastened to the feed duct  43 . 
     It should also be noticed that  FIG. 7  shows the part of the cylinder  2  to which the insertion section  24  is connected from a viewpoint close to the position of the feed duct  43  and that in said figure the feed means  32  are completely removed. 
     Depending on requirements, the insertion section  24  may be placed in any position along the extension of the cylinder  2 . In particular, it may be placed between the first heat exchange zone  12  and the second heat exchange zone  13 . Or, as in the embodiment illustrated, inside the first heat exchange zone  12  ( FIGS. 2 and 3 ). Therefore, in this latter case at least a first group  25  of material tipping blades  14  is mounted circumferentially inside the cylinder  2  between the insertion section  24  and the second heat exchange zone  13 . 
     In the accompanying drawings the tipping blades  14  of the first group  25  are all identical, are mounted inside the cylinder  2  in such a way that they are all in the same position relative to the cylinder  2  axial extension (in other words, the tipping blades  14  of the first group  25  form a single ring of blades around the axis of rotation  5 ), and they are evenly distributed along the circumference of the cylinder  2 . In any case, in other embodiments the tipping blades  14  of the first group  25  may be made or arranged differently, for example they may have different shapes and/or dimensions, or they may be divided into two or more rings of blades, or they may be positioned so that they are axially offset, etc. 
     In the case of a counter-current drier  1 , the presence of the tipping blades  14  downstream of the insertion section  24  allows both improved heating of the recycled cut material compared with prior art plants, and above all improved mixing of the hot aggregates and cold cut material, reducing the temperature gradients within the material being processed compared with prior art driers. 
     In contrast, in co-current driers  1 , the tipping blades  14  of the first group  25  are upstream of the insertion section  24 . In said case, the advantage of using them is the fact that after an initial heating stretch exclusively using radiation and conduction, a first step of convention heating allows improved evenness of temperature in the aggregates before the recycled material is mixed with them. 
     In the embodiment illustrated, the tipping blades  14  of the first group  25  comprise a shaped element  16 , bolted to suitable L-shaped elements  26  welded to the cylinder  2  inner surface  18  (FIG.  5 —notice that in all of the accompanying drawings the welded connections between the various parts are not illustrated), and whose lateral edges  20  are open. 
     Moreover, advantageously, the tipping blades  14  of the first group  25  are provided with a plurality of through-holes  27  designed to allow part of the material being processed to pass, in the embodiment illustrated having the shape of a rhombus. Thanks to the through-holes  27 , during the first step of the rotation (ascending step) part of the material gathered by each tipping blade  14  falls downwards, mixing and being collected by the next tipping blade  14 . In this way, in some applications it is possible to further improve mixing of the aggregates and the recycled materials. 
     However, depending on requirements, some or all of the tipping blades  14  of the first group  25  may even be made without through-holes  27 , having a solid shaped element  16 . In said case, the disadvantage of reduced mixing than occurs with pierced tipping blades  14  may be compensated for by the advantage of an increase in the thermal yield of the plant thanks to heating of all of the material by convection. 
     In other words, the tipping blades  14  of the first group  25  may also be made with a structure like that of the tipping blades  14  located on the other side of the insertion section  24 . 
     As  FIGS. 2 and 3  reveal, in the embodiment illustrated the tipping blades  14  located between the first end  3  and the insertion section  24  are grouped in three successive rings  28  of blades radially offset from each other. Moreover, all of the blades are made with shaped elements having a practically identical profile but different length, bolted on suitable L-shaped elements  26  which are welded to the cylinder  2 . 
     Each tipping blade  14  of the two rings  28  of blades closest to the infeed section  7  has, welded to the shaped element  16  at the second longitudinal edge  19 , a plurality of other L-shaped elements  26  designed to support sections  29 , also L-shaped, which locally increase the capacity of the tipping blade  14 . 
     As  FIGS. 3 and 5  show, the length of the L-shaped sections  29  is approximately half the length of the respective tipping blade  14  and they are alternately fastened to the portion of the blade  14  towards the first end  3  and to the portion of the blade  14  towards the second end  4 . 
     In other embodiments, not illustrated, the drier  1  may comprise a second group of tipping blades  14  mounted circumferentially inside the cylinder  2  close to the insertion section  24  and on one side of it towards the first end  3 . At least some of the tipping blades  14  of the second group are provided with a plurality of through-holes  27  designed to allow part of the material being processed to pass through, like those described above for the tipping blades  14  of the first group  25 . With this solution in counter-current driers it is possible to achieve the same advantages that the pierced blades of the first group  25  give to co-current driers, and in co-current driers the same advantages that the pierced blades of the first group  25  give to counter-current driers. 
     Depending on requirements, the drier  1  may also comprise means  30  for slowing material feed from the infeed section  7  towards the outfeed section  8 . 
     In the embodiment illustrated, said slowing means  30  comprise a plurality of closing partitions fastened to the lateral edge  20 , facing towards the outfeed section  8 , of the shaped element  16  of a plurality of both tipping  14  and containment  15  blades. The closing partitions may close the lateral edge  10  of the shaped element  16  either completely (like those connected to the containment blades  14  of the intermediate ring  28 — FIG. 3 ), or only partly (like those connected to the lateral edge  20  of the ring  28  of tipping blades upstream of the insertion section  24  in the accompanying drawings— FIG. 5 ). In contrast, in other embodiments not illustrated, the slowing means  30  may comprise one or more annular partitions extending transversally relative to the axis of rotation  5 , mounted on the cylinder  2  inner surface  18 . 
     Drier  1  operation derives directly from what is described above, and is minimized below with reference to the counter-current drier  1  shown in the accompanying drawings. For other types of driers  1  operation is similar with the relevant modifications. 
     The cylinder  2  is made to rotate with a speed generally variable between 6 and 11 revolutions per minute, and the aggregates are inserted through the infeed section  7 . At the same time the burner is supplied with the air—fuel mixture and generates the flame  10  as illustrated in  FIG. 8 . The fumes generated by combustion then flow along the entire cylinder  2  and are evacuated through the chimney. 
     The flame  10  temperature usually varies between 1600 and 1300° C. whilst the temperature of the fumes, running regularly, varies approximately between 900 and 150° C. (respectively in the zone close to the flame  10  and at the chimney entrance). 
     In the accompanying drawings, the spiral blades  21  feed the aggregates from the first end  3  to the tipping blades  14  which collect them and allow them to fall, showering through the combustion fumes, at the same time guaranteeing correct mixing. 
     Running regularly, the recycled material is inserted in the feed duct  43  and falls onto the scoops  42  of the annular chamber  41 , which collect it, during their upward rotation. The combined action of the shape of the scoops  42  and the cylinder  2  rotation causes practically all of the recycled material to penetrate the radial openings  31 . Any material which does not enter can in any case be collected by a drain  47  located at the bottom of the annular chamber  41 , then be sent back to the feed duct  43 . 
     The recycled material which enters the openings  31  then flows along the first feed channels  35  formed by the separator plates  34 . When it comes out of the first channels  35  it mixes with the aggregates which arrive from above through the respective second guide channels  40  also formed by the separator plates  34 . 
     At this point the mixture of aggregates and recycled materials reaches the tipping blades  14  of the first group  25  which, in the embodiment illustrated, allow part of it fall, showering through the combustion fumes and release part of it through their through-holes  27 . 
     The mixture is then collected by the containment blades  15 , then made to pass outside the tubular structure  22  until it reaches the outfeed section  8  where it usually arrives at a temperature of approximately 200° C. 
     The present invention brings important advantages. 
     Thanks to the present invention, a rotary drier was provided which allows the use of a greater quantity of recycled material than in prior art plants, since it guarantees improved mixing of the hot aggregates and the cold recycled materials, preventing the bitumen present in the recycled material from becoming packed together and blocking the drier. 
     This is also possible because the recycled material is better distributed in the aggregates with the additional consequence that the temperature gradient in the material is also limited. 
     Moreover, consequently, thanks to the present invention it is possible at the same time to minimize if not eliminate the formation of emissions which are harmful to the environment. 
     It should also be noticed that the present invention is relatively easy to produce and that even the cost linked to implementing the invention is not very high. 
     The invention described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept. 
     Moreover, all details of the invention may be substituted with other technical equivalent elements and in practice all of the materials used, as well as the shapes and dimensions of the various components, may vary according to requirements.