EP2549017A1

EP2549017A1 - Rotary cylinder dryer for mixtures of virgin inerts and recovery materials for preparing bituminous conglomerates

Info

Publication number: EP2549017A1
Application number: EP12177187A
Authority: EP
Inventors: Stefano Belloli
Original assignee: Bernardi Impianti International SpA
Current assignee: Bernardi Impianti International SpA
Priority date: 2011-07-20
Filing date: 2012-07-19
Publication date: 2013-01-23
Also published as: CN102889761A; ITMI20111354A1; RU2012130865A

Abstract

The present invention relates to a rotary cylinder dryer (10) for mixtures of virgin inerts and recovery materials (RAP) for preparing bituminous conglomerates, which comprises a cylinder (11) which is associable with motor means (14) suitable for putting it in rotation around its own longitudinal axis (A) and which is provided with two opposite heads (16, 17), an inlet mouth (18) of a mixture of virgin inerts and of recovery material (RAP) to be dried and which is defined at one of the two heads (16), an outlet mouth (19) of the dried mixture and which is defined at the other one of the two heads (17), at least a burner (20) for generating drying heat of the mixture and which is associated to the head (17), at which the outlet mouth (19) is defined, and an outlet opening (21) of the combustion and drying smokes which generate inside the cylinder (11), outlet opening (21) which is defined at the head (16) at which the inlet mouth (18) is defined, characterized in that it comprises at least one deflecting baffle (38) associated with the outlet opening (21) of the smokes.

Description

The present invention relates to a rotary cylinder dryer for mixtures of virgin inerts and recovery materials (RAP) for preparing bituminous conglomerates. As known, in order to make bituminous conglomerates, mixtures of virgin inerts, which consist for example of pebble gravel, sand and rock shots, and recovery materials, which in particular consist of material resulting from the dismantling of old bituminous conglomerate flooring and commonly referred to as RAP (Reclaimed Asphalt Pavement), have long been used. Before mixing such mixtures with a bituminous binder it is necessary to eliminate the humidity present therein through a drying process.
Dryers, generally of the rotary cylinder type, are generally used to this end.
A dryer of this type is described, for example, in patent application no. MI2008A02312 ( EP2202473 ) in the name of the same Applicant and it comprises a cylinder with axis inclined with respect to the horizontal placed in rotation about its own axis by motor means and provided, at one of its two opposite heads, with an inlet mouth for the virgin and recovery materials to be dried, already mutually mixed, and at the opposite head, with an outlet mouth for the dried materials.
The heat required for drying is generated by a burner placed at the head where the outlet mouth of the dried materials is defined and which is coaxial to the cylinder.
The combustion and drying smokes, on the other hand, are vented through an opening obtained at the head where the inlet mouth of the materials to be dried is defined and which leads into a chamber that is associated with a suction assembly with the interposition of a filter assembly, generally of the bag type.
Thanks to the inclination of the cylinder and to the presence of suitable moving means inside it, the materials introduced thereinto advance from one head to the other, in countercurrent with respect to the combustion and drying smokes, drying and heating.
A tubular body open at the opposite ends is fixed inside the cylinder. One of the two open ends of the tubular body faces the burner and is placed at a definite distance therefrom, so that the flame and the combustion smokes are directed into the tubular body, whereas the opposite open end of the tubular body faces the inside of the cylinder.
The burner and tubular body assembly define a combustor or post-combustor crossed by both the combustion smokes of the burner and by the drying smokes, which are sucked thereinto by dynamic effect. In particular, the drying smokes result from the drying of recovery material containing aged bitumen (RAP) which, together with virgin materials, advance on the bottom of the interspace defined between the cylinder and the tubular body.
In fact, the tubular body forms a hot combustion and/or post-combustion chamber.
This known dryer has proved to be particularly advantageous, in particular allowing mixtures containing recovery materials (RAP) in percentages up to 40% by weight to be dried and mixed.
However, it has some drawbacks that make it capable of being further improved.
The suction unit that sucks the combustion and drying smokes from the inside of the cylinder, where they are formed, and which forces them to cross the filter assembly to then convey them to the stack, is capable of placing the entire cylinder, the filter and the connecting piping to vacuum.
Given the high volumetric flow rates of the sucked smokes, in the order of 20,000-30,000 m³/h, and the high suction power used, significant quantities of fine powders of the treated materials are frequently sucked along with the smokes.
Generally, the filter assembly consists of a bag filter and the fine powders that reach it are retained therein.
This is due to an early clogging of the filter bags, the filtering capacity of which is considerably reduced with consequent increase in the concentrations of fine powders in the smokes released to the atmosphere, and need for expensive maintenance and replacement work on the bags of the same filter.
Such an effect is particularly a problem if recovery material (RAP) is present in the mixture treated in the dryer.
In fact, the fine powders of such material (RAP) which are retained in the filter bags tend to release the humidity contained therein over time, by the effect of the progressive heating of the same filter which, at full operation, reaches temperatures in the order of 130-140°C.
Such humidity condensates into dew which on the one hand packs the fine powders in the filter bags and on the other hand causes a reduction in the temperature of the same filter, greatly reducing the filtering capacity thereof and favoring the forming of further condensation.
The object of the present invention is to obviate the drawbacks of known dryers and in particular to propose a rotary cylinder dryer for mixtures of virgin inerts and recovery materials (RAP) for preparing bituminous conglomerates which allows the reduction of the clogging of the filter assembly bags by the fine powders of the treated material, in particular of recovery material (RAP) and thereby allows the maintenance and replacement works on the bags of the filter assembly to be limited and an efficient filtering of the smokes to be ensured prior to their release to the atmosphere.
These objects according to the present invention are achieved by providing a rotary cylinder dryer for mixtures of virgin inerts and recovery materials (RAP) for preparing bituminous conglomerates according to claim 1.
Further features are provided in the dependent claims. The features and the advantages of a rotary cylinder dryer for mixtures of virgin inerts and recovery materials (RAP) for preparing bituminous conglomerates according to the present invention will appear more clearly from the following description, made by way of an indicative non-limiting example with reference to the annexed schematic drawings, wherein:

figure 1 shows a schematic side elevation view of the dryer according to the present invention;
figure 2 shows a schematic, longitudinal and partial section view of the dryer according to figure 1;
figure 3 shows a front axonometric view of the sole smoke suction chamber seen from the cylinder side;
figure 4 shows a top plan view of figure 3;
figure 5 shows a side view of figure 3.

With reference to the annexed figures, reference numeral 10 globally denotes a rotary cylinder dryer for mixtures of virgin inerts and recovery materials (RAP) for preparing bituminous conglomerates.
Dryer 10 comprises a cylinder 11 rotatably supported about its longitudinal axis A by supports 12 mounted on a frame 13 resting on the ground.
Motor means 14 are mounted on frame 13 which, through driving means 15, for example of the gear type, place cylinder 11 in rotation about its longitudinal axis A.
As it is clear from figures 1 and 2, the longitudinal axis A of cylinder 11 is inclined with respect to the horizontal plane or the support plane of frame 13 by an angle α in the order of a few degrees, typically 3°. Cylinder 11 is delimited at its opposite ends by two heads, respectively a first head 16 at higher height and a second head 17 at smaller height.
An inlet mouth 18 of a mixture of virgin inerts and recovery materials (RAP, Reclaimed Asphalt Pavement) to be dried is defined at the first head 16, whereas an outlet mouth 19 of the dried mixture is defined at the second head 17.
The heat required for drying is generated by a corresponding assembly consisting of at least one burner 20 associated with the second head 17 and placed coaxially to the longitudinal axis A of cylinder 11 into which it directs the flame.
On the other hand, an outlet opening 21 of the discharge smokes of the dryer 10 is defined at the first head 16, the outlet opening 21 communicates with a suction chamber 22 in turn associable with a unit for sucking and treating the discharge smokes of the dryer 10 and not shown in detail as it is known by the man skilled in the art.
Means for mixing and moving the inerts and the recovery material (RAP) treated are mounted on the inner side surface of the cylinder 11 which mix and accompany them in their advance motion along the entire cylinder 11, from the inlet mouth 18 to the outlet mouth 19.
As it is seen in figures 1 and 2, the inlet mouth 18 and the outlet mouth 19 of the mixture are obtained at the opposite ends (heads) of the cylinder 11, as the burner 20 and the outlet opening 21 of the discharge smokes are placed at the opposite ends (heads) of the cylinder 11; this allows the entire length of the cylinder 11 to be used for the thermal exchange between the heat generated by burner 20 and the mixture treated.
A tubular body 23 open at the opposite ends 23a, 23b is fixed inside the cylinder 11 and placed coaxially to the longitudinal axis A of the cylinder 11 with one of its open ends 23a facing the burner 20 and at a definite distance therefrom and with the opposite open end 23b facing the first head 16.
The tubular body 23 has a maximum diameter smaller than the inner diameter of the cylinder 11 so as to form an annular interspace therewith crossed by the drying mixture on the bottom.
The combustion smokes and the flame generated by the burner 20 are axially directed into the tubular body 23, inside which the drying smokes of the drying mixture, which advances on the bottom of the interspace defined between cylinder 11 and the tubular body 23, also without impacting the latter, are sucked by dynamic effect.
In succession to the tubular body 23 and downstream of it with respect to the flow direction of the combustion and drying smokes an auxiliary tubular body 24 is placed, which is also open at the opposite ends 24a, 24b, fixed inside the cylinder 11 and placed coaxially to the longitudinal axis A of the same cylinder 11.
The auxiliary tubular body 24 is arranged with one of its two opposite open ends 24a facing the open end 23b of the tubular body 23 opposite to that 23a facing burner 20 and at a definite distance from it, and the opposed open end 24b directed towards the inside of cylinder 11 and facing the first head 16.
The auxiliary tubular body 24 has a maximum diameter smaller than the inner diameter of the cylinder 11 and defines an interspace with it crossed by the drying mixture.
The combustion and drying smokes coming out of the tubular body 23 are directed into the tubular body 24, into which the smokes external thereto are also sucked by dynamic effect.
The tubular body 23 and the auxiliary tubular body 24 define each a respective hot combustion and/or post-combustion chamber of the combustion smokes and of the drying smokes, where the latter are generated by the fraction of recovery material (RAP) present in the drying mixture and in particular, by the aged bitumen present therein.
Both the tubular body 23 and the auxiliary tubular body 24 are made of heat resistant steel, also of different type, the second one having to withstand lower temperatures than the first one.
In a preferred embodiment, the tubular body 23 is made of AISI 310 S steel, whereas the auxiliary tubular body 24 is made of 304-306 steel.
The assembly consisting of the burner 20, of the tubular body 23 and of the auxiliary tubular body 24 forms a combustor or post-combustor assembly; in particular, the tubular body 23 and the auxiliary tubular body 24 form two hot chambers into which the flame and the combustion smokes are directed and the drying smokes, generated by the recovery material (RAP) or in any case the smokes present inside cylinder 11, are sucked by dynamic effect, allowing the combustion (oxidation) of the organic substances contained therein to be completed.
The distance between the tubular body 23, or better between its open end 23a, and the burner 20, as well as the distance between the tubular body 23 and the auxiliary tubular body 24, or better between their open and mutually facing ends, respectively 23b and 24a, is determined so as to ensure the desired smokes suction effect, in particular of the drying smokes, into them. The assembly of the tubular body 23 and of the auxiliary tubular body 24 and the structure of such bodies are the object of a co-pending application to the same Applicant.
Different mixture treatment zones follow to each other inside the cylinder 11 and along its longitudinal development at different temperatures, which are progressively increasing as the mixture introduced through the inlet mouth 18 advances towards the outlet mouth 19.
In particular, starting from the first head 16 at which the inlet mouth 18 of the inert and recovery materials (RAP) mixture to be dried is defined, continuing towards the second head 17 at which the outlet mouth 19 of the dried mixture is defined, follow to each other:

a first inlet area 25 of the mixture at which a plurality of helical blades 26 is distributed on the inner surface of the cylinder 11;
a second evaporating area 27 of the moisture present in the mixture at which a plurality of rising cups 28 of the inerts and of the recovery material (RAP) falling rain-wise is distributed on the inner surface of the cylinder 11;
a third area 29 for mixing the inerts and the recovery materials (RAP) at which a plurality of mixing blades 30 is distributed on the inner surface of the cylinder 11; and
a fourth area 31 for the final heating of the mixture at which a plurality of helical blades 32 is distributed on the inner surface of the cylinder 11.

As it is clear from figures 1 and 2, in a preferred embodiment, the tubular body 23 extends along at least one tract of the fourth heating area 31 and the auxiliary tubular wall 24 extends along at least one tract of the third mixing area 29.
Dryer 10 further comprises an assembly for heating the comburent air fed to the burner 20. Such heating assembly comprises a pre-heating chamber 33 which extends behind the second head 17 and inside which the body of the burner 20 is housed.
Around the cylinder 11, by at least one tract of the length of the fourth area 31, the one at higher temperature, a shell 34 is mounted which forms around the cylinder 11 an interspace 35 which at one end communicates with the pre-heating chamber 33 and at the opposite end with one or more inlet openings 36 of the ambient air.
A suction fan 37 is mounted below the frame 13 and communicates with the pre-heating chamber 33 so as to suck ambient air into it through the interspace 35. Moreover, sensing means of the sucked air temperature are provided, such as for example a thermal probe, and means for measuring the sucked air flow rate, such as for example a Pitot tube, so as to control and adjust the operation of the burner 20.
The air sucked from the external environment first crosses the interspace 35 wherefrom it then enters the pre-heating chamber 33 to then be fed into the cylinder 11 for supporting the combustion of the fuel injected by the burner 20.
The heat of the walls of the cylinder 11, which at full operation reach temperatures of about 500-550°C, is yield by convection to the sucked air the temperature of which is on the average increased by about 45-50°C before being injected into the cylinder 11, with clear advantages in terms of combustion efficiency.
A peculiar feature of the present invention is the provision of at least one deflecting baffle 38 at the outlet opening 21 of the smokes.
The deflecting baffle 38 extends along at least one tract of the perimeter which delimits the outlet opening 21 and extends inside cylinder 11; where the outlet opening 21 advantageously has a circular shape. In a preferred embodiment, the deflecting baffle 38 has walls with a conical or frusto-conical surface, with a diverging taper towards the outlet opening 21 of the smokes and converging towards the inside of the cylinder 11, or better towards its longitudinal axis A. Moreover, below the outlet opening 21 a wall 39 which extends towards the inside of cylinder 11 is provided. Wall 39 extends along at least one tract of the perimeter which delimits the outlet opening 21 and extends inside cylinder 11.
In a preferred embodiment, the wall 39 has the shape of a sector of a cylindrical surface and extends parallel to the lateral internal surface of the cylinder 11 at a definite distance from it.
In particular, as it is seen in figure 3, the wall 39 extends below the channel that defines the inlet mouth 18 of the mixture and which is provided with a door 40, which can be opened, for maintenance and from which the mixture falls into the cylinder through openings defined in the wall 39.
The wall 39 is jointed along one side to the deflecting baffle 38.
As it is seen in figure 2, the deflecting baffle 38 and the wall 39 extend in the first area 25, downstream of which the "rain" of the material lifted by the rising cups 28 is formed.
The arrangement of the deflecting baffle 38 depends on the sense of rotation of the cylinder 11.
Considering a front view of the outlet opening 21 of the smokes on the side of the cylinder 11, i.e. a view according to the arrow F indicated in figure 2, and considering a system of Cartesian coordinates centered in the same outlet opening 21, if cylinder 11 is placed in clockwise rotation, as indicated by the arrow W, the deflecting baffle 38 extends along at least one tract of the perimeter of the outlet opening 21 comprised in the second and third face defined by the system of Cartesian coordinates.
On the contrary, if cylinder 11 is placed in rotation in the opposite sense, the deflecting baffle will extend along at least one tract of the perimeter of the outlet opening 21 comprised in the first and fourth face of the system of Cartesian coordinates as defined above.
This is because the arrangement of the deflecting baffle 38 must agree with the forming of the rain of the material that forms in the second area 27.
With reference to the annexed figures, the operation of the dryer is as follows.
The virgin inert material and the recovery material (RAP) are fed into the cylinder 11 through the inlet mouth 18.
The materials thus fed cross the first area 25 being mixed and blended by the helical blades 26.
The average temperature inside the cylinder 11 at the first area 25 is generally in the order of 120-150°C. The mixture then advances along the second zone 27, wherein there is an average temperature in the order of 280-300°C, where the humidity contained in the materials and in particular in the recovery materials (RAP) evaporates.
The rising cups 28, or similar lifting means, for example blade or cup means, lift the materials, which fall "rain-wise"; the mixing and blending of the virgin inert materials with the recovery materials are thus favored. In particular, the bitumen fraction present in the recovery materials (RAP) softens, favoring the bond with virgin inert materials; aggregates of virgin inert materials and of recovery materials (RAP) are thus formed.
A further mixing of the materials occurs along the third area 29 by the mixing blades 30 which, thanks to their particular arrangement and shape, object of a co-pending application to the same Applicant, impart a controlled advance motion to the materials such as to favor the forming of a substantially homogeneous mixture.
Along such third area 29, the mixture advances into the interspace defined between the cylinder 11 and the auxiliary tubular body 24, without contacting the latter.
Inside such interspace there is a maximum average temperature in the order of 450°C, whereas inside the auxiliary tubular body 24 there is a maximum average temperature in the order of 550°C.
Finally, the dried and blended mixture advances into the fourth final heating area 31 to exit from the outlet mouth 19 at an average temperature of about 180-200°C.
The flame of the burner 20, the average temperature of which is in the order of 1000-1400°C, flows into such fourth area 31.
It is noted, in particular, that the mixture advances without contacting the flame or the outer wall of the tubular body 23.
The efficiency of the burner 20 is improved thanks to the pre-heating of the comburent air.
The flame and the combustion smokes are directed into the tubular body 23 (inside which there is a maximum average temperature in the order of 800-900°C) and therefrom into the auxiliary tubular body 24.
Moreover, the drying smokes, i.e. the smokes generated by the recovery material, are sucked by dynamic effect into the tubular body 23 and the auxiliary tubular body 24.
The two hot chambers in a sequence, respectively formed by the tubular body 23 and by the auxiliary tubular body 24, are crossed by the combustion and drying smokes and the volatile organic substances present therein oxidize thanks to the heat present inside such two hot chambers and their walls.
The smokes are then vented through the outlet opening 21 and the chamber 22 and conveyed in a treatment and removal assembly.
The deflecting baffle 38 allows the powders of material, in particular of the recovery material (RAP), which fall onto the bottom of the cylinder 11 where by the effect of the heat oxidize or are reduced, to be retained inside the cylinder 11 without reaching the filter assembly placed downstream of the cylinder 11.
The conical shape of the deflecting baffle 38 favors the fall back onto the bottom of the cylinder 11 of the powders of material deposited thereon.
The wall 39 contributes to retaining the powders of material inside cylinder 11 preventing them from reaching the filter assembly placed downstream of the cylinder 11 and moreover it limits the dissipation of the smokes towards the suction assembly if the latter is non operative, thus preventing the material powders pulled by the smokes from reaching the filter assembly. Thanks to the provision of at least one deflecting baffle 38 and of the lower wall 39 associated with the outlet opening 21 of the smokes, the dryer object of the present invention has the advantage that it allows the powders of inert and recovery materials formed during the drying treatment to be retained inside the drying cylinder, in particular preventing them from reaching the filter assembly placed downstream of the drying cylinder.
The filtering efficiency of the filter assembly is thus preserved, thereby reducing the maintenance and replacement works on the bags of the same filter and limiting the release of fine powders to the atmosphere. Moreover, the presence of the auxiliary tubular body 24 in a succession to the tubular body 23 allows to further reduce, compared to the known dryers, the percentages of volatile organic substances (VOC, TOC) present in the discharge smokes in compliance with the regulations in force, irrespective of the nature of the virgin inert materials and of the recovery materials (RAP) and also for percentages of recovery materials (RAP) higher than 25% and even in the order of 40%.
The pre-heating of the comburent air improves the combustion efficiency in terms of fuel saving in the order of 10%-20%.
Finally, the particular shape and arrangement of the mixing blades 30 allows homogeneous mixtures to be obtained.
It is noted that the temperatures indicated in the present description are purely indicative, depend on the flow rate and type of both the virgin inert material and the recovery material (RAP), on the fuel used, on the ambient air temperature and on the temperature the material must be heated to.
Several changes and variations can be made to the dryer thus conceived, all falling within the invention; moreover, all details can be replaced with technically equivalent elements. In the practice, the materials used as well as the sizes, can be whatever, according to the technical requirements.

Claims

Rotary cylinder dryer (10) for mixtures of virgin inerts and recovery materials (RAP) for preparing bituminous conglomerates, comprising a cylinder (11) which is associable with motor means (14) suitable for putting it in rotation around its own longitudinal axis (A) and which is provided with two opposite heads (16, 17), an inlet mouth (18) of a mixture of virgin inerts and of recovery material (RAP) to be dried and which is defined at one of said two heads (16), an outlet mouth (19) of the dried mixture and which is defined at the other one of said two heads (17), at least one burner (20) for generating drying heat of said mixture and which is associated with said head (17), at which said outlet mouth (19) is defined, and an outlet opening (21) of the combustion and drying smokes which generate inside said cylinder (11), outlet opening (21) which is defined at said head (16) at which said inlet mouth (18) is defined, characterized in that it comprises at least one deflecting baffle (38) associated with said outlet opening (21) of the smokes.
Dryer (10) according to claim 1, characterized in that said at least one deflecting baffle (38) extends along at least one tract of the perimeter delimiting said outlet opening (21) of the smokes and which extends inside said cylinder (11).
Dryer (10) according to claim 2, characterized in that said at least one deflecting baffle (38) has walls with a conical or frusto-conical surface, with a diverging taper towards said outlet opening (21) of the smokes and converging towards the inside of said cylinder (11).
Dryer (10) according to claim 3, characterized in that in a front view of said outlet opening (21) of the smokes from the cylinder side, and considering a system of Cartesian coordinates centered in said outlet opening (21) of the smokes, said at least one deflecting baffle (38) extends along at least one tract of the perimeter of said outlet opening (21) of the smokes, comprised in the second and third face, if the rotary direction of said cylinder (11) is clockwise, or along at least one tract of the perimeter of said outlet opening (21) of the smokes comprised in the first and fourth face, if the rotary direction of said cylinder (11) is counter-clockwise.
Dryer (10) according to one or more of the preceding claims, characterized in that it also comprises a wall (39) extending below said outlet opening (21) of the smokes towards the inside of said cylinder (11).
Dryer (10) according to claim 5, characterized in that said wall (39) extends along a tract of the perimeter delimiting said outlet opening (21) of the smokes.
Dryer (10) according to claim 5 or 6, characterized in that said wall (39) has the shape of a sector of a cylindrical surface and extends parallel to the lateral internal surface of said cylinder (11) at a definite distance from it.
Dryer (10) according to one or more of the claims from 5 to 7, characterized in that said wall (39) is connected with said at least one deflecting baffle (38).