ITMI20111354A1 - ROTARY CYLINDER DRYER FOR MIXTURES OF VIRGIN INERTES AND RECOVERY MATERIALS FOR THE PREPARATION OF BITUMINOUS CONGLOMERATES - Google Patents

Description

DRYER WITH ROTATING CYLINDER FOR BLENDS OF VIRGIN INERT AND RECOVERY MATERIALS FOR THE PREPARATION OF BITUMINOUS CONGLOMERATES.

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The present invention refers to a rotary cylinder dryer for mixtures of virgin aggregates and recovery materials (RAP) for the preparation of bituminous conglomerates.

In the packaging of bituminous conglomerates, as known, mixtures of virgin aggregates have been used for some time, which are made up, for example, of gravel, sand and rock grit, and recycled materials, which are made up, in particular, of materials deriving from the dismantling of old asphalt pavements and commonly referred to with the acronym RAP (Reclaimed Asphalt Pavment).

Before amalgamating these mixtures with a bituminous binder, the humidity present in them must be eliminated by means of a drying process.

To this end, dryers generally of the rotary cylinder type are used.

A dryer of this type is, for example, described in patent application no. MI2008A02312 (EP2202473) in the name of the same applicant and includes a cylinder with an axis inclined with respect to the horizontal, placed in rotation around its own axis by motor means and provided, in correspondence with one of its two opposite heads, with a mouth of Inlet of virgin and recovered materials to be dried already mixed together and, in correspondence with the opposite head, of an outlet of the dried materials.

The heat necessary for drying is generated by a burner which is placed in correspondence with the head where the outlet of the dried materials is defined and which is coaxial to the cylinder.

The combustion and drying fumes, on the other hand, are evacuated through an opening which is obtained in correspondence with the head where the inlet of the materials to be dried is defined and which flows into a chamber which is A suction group is associated with the interposition of a filter group, generally of the bag type.

Thanks to the inclination of the cylinder and the presence inside it of suitable means of handling, the materials introduced into it advance from one head to the other, counter-current with respect to the combustion and drying fumes, drying and heating.

A tubular body open at opposite ends is fixed inside the cylinder. One of the two open ends of the tubular body faces the burner and placed at a defined distance from it, so that the flame and combustion fumes are directed inside the tubular body, while the opposite open end of the body tubular is turned inside the cylinder.

The burner and tubular body together define a combustor or post-combustor crossed by both the combustion fumes of the burner and the drying fumes which are sucked into it by a dynamic effect. The drying fumes derive, in particular, from the drying of recycled materials containing aged bitumen (RAP) which, together with the virgin materials, advance on the bottom of the gap defined between the cylinder and the tubular body.

The tubular body, in fact, forms a hot combustion and / or post-combustion chamber.

This known type drier has proved to be particularly advantageous, allowing, in particular, to dry and amalgamate mixtures containing recycled materials (RAP) in percentages up to 40% by weight.

However, it has some drawbacks which make it susceptible to further improvements.

The suction group that sucks the combustion and drying fumes from the inside of the cylinder, where they are formed, and which forces them to cross the filter group and then convey them to the chimney, is able to put the entire cylinder, filter and connecting pipes.

Given the high volumetric flow rates of the aspirated fumes, of the order of 20,000-30,000 m <3> / h, and the high suction power used frequently, together with the fumes, important quantities of fine dust from the treated materials are aspirated. .

Generally, the filter group consists of a bag filter and the fine powders that reach it are retained in them.

This causes premature clogging of the filter bags, whose filtering capacity is considerably reduced with a consequent increase in the concentrations of fine dust in the fumes released into the atmosphere and the need for costly maintenance and replacement of the filter bags.

This effect is particularly problematic if recovery material (RAP) is present in the mixture treated in the dryer.

In fact, the fine powders of this material (RAP) which are retained in the filter sleeves tend, over time, to release the humidity contained in them due to the progressive heating of the filter itself which, when fully operational, reaches temperatures of the ™ order of 130-140 ° C.

This humidity condenses into dew which, on the one hand, packs the fine dust in the filter bags and which, on the other hand, causes a reduction in the temperature of the filter itself, considerably reducing its filtering capacity and favoring the formation of further condensation.

The purpose 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 aggregates and recycled materials (RAP) for the preparation of bituminous conglomerates which allows to reduce the clogging of the filter group bags by the fine dust of the treated material, in particular, recovered material (RAP) and, therefore, to limit the maintenance and replacement of the filter group bags and to guarantee efficient filtration of the fumes before their release into the atmosphere.

These purposes according to the present invention are achieved by making a rotary cylinder dryer for mixtures of virgin aggregates and recovery materials (RAP) for the preparation of bituminous conglomerates as set forth in claim 1.

Further characteristics are provided in the dependent claims.

The characteristics and advantages of a rotary cylinder dryer for mixtures of virgin aggregates and recycled materials (RAP) for the preparation of bituminous conglomerates according to the present invention will become more evident from the following description, which is exemplary and not limiting, referring to the schematic drawings attachments in which:

Figure 1 is a schematic side elevation view of the dryer according to the present invention;

figure 2 is a schematic, longitudinal and partial section of the dryer according to figure 1;

figure 3 is a front axonometric view of the flue gas intake chamber only, seen from the cylinder side;

figure 4 is a top plan view of figure 3;

figure 5 is a side view of figure 3.

With reference to the attached figures, the number 10 generally indicates a rotary cylinder dryer for mixtures of virgin aggregates and recycled materials (RAP) for the preparation of bituminous conglomerates.

The dryer 10 comprises a cylinder 11 which is supported rotatably about its own longitudinal axis A by supports 12 mounted on a frame 13 resting on the ground.

On the frame 13 there are mounted motor means 14 which, by means of transmission means 15, for example of the gear type, cause the cylinder 11 to rotate around its own longitudinal axis A.

As is evident from Figures 1 and 2, the longitudinal axis A of the cylinder 11 is inclined with respect to the horizontal plane or the support plane of the frame 13 by an angle Î ± of the order of a few degrees, typically 3 °.

The cylinder 11 is delimited at its opposite ends by two heads, respectively a first head 16 at a higher level and a second head 17 at a lower level.

An inlet 18 of a mixture of virgin aggregates and recycled materials (RAP, Reclaimed Asphalt Pavment) to be dried is defined in correspondence with the first head 16, while in correspondence with the second head 17 an outlet 19 is defined of the dried mixture.

The heat necessary for drying is generated by a corresponding group consisting of at least one burner 20 associated with the second head 17 and arranged coaxially to the longitudinal axis A of the cylinder 11 inside which it directs the flame.

In correspondence with the first head 16, on the other hand, there is an outlet opening 21 for the exhaust fumes of the dryer 10 which communicates with an aspiration chamber 22 which in turn can be associated with a fumes aspiration and treatment unit discharge of the dryer 10 and not shown in detail, being known to those skilled in the art.

On the internal lateral surface of the cylinder 11 are mounted means for mixing and handling the aggregates and the treated recovered material (RAP) which mix them and accompany them in their forward motion along the entire cylinder 11, from the inlet 18 to the inlet. exit 19.

As can be seen from figures 1 and 2, the inlet 18 and the outlet 19 of the mixture are obtained at the opposite ends (heads) of the cylinder 11, as well as the burner 20 and the outlet 21 for the fumes exhaust pipes are arranged at the opposite ends (heads) of the cylinder 11; this makes it possible to exploit the entire length of the cylinder 11 for the heat exchange between the heat generated by the burner 20 and the treated mixture.

Fixed inside the cylinder 11 is a tubular body 23 open at the opposite ends 23a, 23b and arranged coaxially to the longitudinal axis A of the cylinder 11 with one of its open ends 23a facing the burner 20 and at a defined distance from it and with the opposite open end 23b facing the first head 16.

The tubular body 23 has a maximum diameter smaller than the internal diameter of the cylinder 11 so as to form with it an annular interspace crossed on the bottom by the mixture being dried.

The combustion fumes and the flame generated by the burner 20 are axially directed inside the tubular body 23, inside which, moreover, the drying fumes of the drying mixture which advances on the bottom of the interspace defined between the cylinder 11 and the tubular body 23, without, however, impacting the latter.

In succession to the tubular body 23 and downstream of it with respect to the direction of the flow of combustion and drying fumes, there is an auxiliary tubular body 24, also open at the opposite ends 24a, 24b, fixed inside the cylinder 11 and arranged coaxially to the longitudinal axis A of the cylinder 11 itself.

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 the burner 20 and at a defined distance from it and the opposite open end 24b directed towards the inside of the cylinder 11 and towards the first head 16.

The auxiliary tubular body 24 has a maximum diameter smaller than the internal diameter of the cylinder 11 and with it defines an interspace crossed by the mixture being dried.

The combustion and drying fumes that come out of the tubular body 23 are directed inside the tubular body 24, inside which, moreover, the fumes external to it are aspirated by a dynamic effect. The tubular body 23 and the auxiliary tubular body 24 each define a respective hot chamber for combustion and / or post-combustion of the combustion fumes and drying fumes, where the latter are generated by the fraction of recovery material (RAP) present in the mixture being dried and, in particular, from the aged bitumen present in them.

Both the tubular body 23 and the auxiliary tubular body 24 are made of heat-resistant steel, even of a different type, since the second must withstand lower temperatures than the first. In a preferred embodiment, the tubular body 23 is made of AISI 310 S steel, while the auxiliary tubular body 24 is made of 304-306 steel.

The assembly consisting of the burner 20, the tubular body 23 and the auxiliary tubular body 24 forms a combustor or post-combustor group; in particular, the tubular body 23 and the auxiliary tubular body 24 form two hot chambers inside which the flame and combustion fumes are directed and the drying fumes generated by the recovery materials (RAP) are aspirated by a dynamic effect or in any case the fumes present in the cylinder 11, allowing the completion of the combustion (oxidation) of the organic substances contained therein.

The distance between the tubular body 23, or rather 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 rather between their open ends facing each other , respectively 23b and 24a, is determined in such a way as to ensure the desired suction effect of the fumes, in particular of the drying fumes, inside them.

The whole of the tubular body 23 and of the auxiliary tubular body 24 and the structure of these bodies is the subject of a co-pending application from the same Applicant.

Inside the cylinder 11 and along its longitudinal development there is a sequence of different zones for treating the mixture at different temperatures progressively increasing as the mixture introduced through the inlet 18 advances towards the outlet 19.

In particular, starting from the first head 16 in correspondence with which the inlet 18 of the mixture of aggregates and recycled materials (RAP) to be dried is defined, continuing towards the second head 17 in correspondence with which it is defined the outlet mouth 19 of the dried mixture is followed by: a first zone 25 for the inlet of the mixture and in correspondence with which a plurality of helical blades 26 is distributed on the internal surface of the cylinder 11, a second zone 27 for evaporation of humidity present in the mixture and in correspondence with which on the internal surface of the cylinder 11 there is distributed a plurality of lifting cups 28 of the aggregates and of the recovery material (RAP) which fall like rain, a third zone 29 for mixing the aggregates and the recovery material (RAP) and in correspondence with which a plurality of mixing blades 30 and a fourth zone 31 of final heating of the mixture and in correspondence with which a plurality of helical blades 32 are distributed on the internal surface of the cylinder 11.

As is evident from Figures 1 and 2, in a preferred embodiment, the tubular body 23 extends along at least a portion of the fourth heating zone 31 and the auxiliary tubular body 24 extends along at least a portion of the third mixing zone 29 .

The dryer 10 also comprises a heating unit for the combustion air fed to the burner 20. This heating unit comprises a pre-heating chamber 33 which extends behind the second head 17 and inside which The burner body 20 is housed.

Around the cylinder 11, for at least a portion of the length of the fourth zone 31, the one with the highest temperature, a skirt 34 is mounted which forms, around the cylinder 11, an interspace 35 which communicates, at one end, with the pre-heating chamber 33 and, at the opposite end, with one or more inlet openings 36 for 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 the ambient air inside it through the cavity 35.

In addition, sensor means for the temperature of the sucked air are provided, such as, for example, a thermal probe, and means for measuring the flow rate of the sucked air, such as, for example, a Pitot tube, so as to control and regulate operation of the burner 20.

The air sucked in from the external environment first passes through the cavity 35 from which it then enters the pre-heating chamber 33 to be then fed inside the cylinder 11 to support the combustion of the fuel injected with the burner 20 .

The heat of the walls of the cylinder 11, which when fully operational reach temperatures of about 500-550 ° C, is transferred by convection to the sucked air whose temperature is on average increased by about 45-50 ° C before being injected into the cylinder 11, with obvious advantages in terms of combustion efficiency.

A peculiar characteristic of the present invention is the provision of at least one baffle plate 38 at the flue outlet 21.

The baffle plate 38 extends along at least a portion of the perimeter that delimits the outlet opening 21 and extends inside the cylinder 11; whereas the outlet opening 21 advantageously has a circular shape.

In a preferred embodiment, the baffle plate 38 has conical or frusto-conical surface walls with conicity diverging towards the outlet 21 of the fumes and converging towards the inside of the cylinder 11, or better towards the inside of the cylinder 11. longitudinal axis A of it.

Furthermore, below the outlet opening 21 there is a wall 39 which extends towards the inside of the cylinder 11.

The wall 39 extends along at least a portion of the perimeter that delimits the outlet opening 21 and extends inside the cylinder 11.

In a preferred embodiment, the wall 39 has the shape of a sector of a cylindrical surface and extends parallel to the internal lateral surface of the cylinder 11 at a defined distance therefrom.

In particular, as shown in figure 3, the wall 39 extends below the channel which defines the inlet 18 of the mixture and which is equipped with a door 40 that can be opened for maintenance purposes and from which the mixture falls to the ™ inside the cylinder through openings defined in the wall 39.

Wall 39 is connected along one side to the deflector partition 38.

As can be seen from Figure 2, the deflector partition 38 and the wall 39 extend into the first zone 25, downstream of which the `` rain '' of the material raised by the lifting cups 28 forms.

The arrangement of the baffle plate 38 depends on the direction of rotation of the cylinder 11.

Considering a front view of the flue gas outlet opening 21 from the cylinder 11 side, that is a view according to the arrow F indicated in figure 2, and considering a Cartesian coordinate system centered in the outlet opening 21 itself, if the cylinder 11 is rotated clockwise, as indicated by the arrow W, the deflector partition 38 extends along at least a portion of the perimeter of the outlet opening 21 included in the second and third quadrant defined by the Cartesian coordinate system.

If, on the other hand, the cylinder 11 is rotated in the true opposite direction, the deflector partition will extend along at least a portion of the perimeter of the outlet opening 21 included in the first and fourth quadrant of the Cartesian coordinate system as defined above. .

This is because, the arrangement of the deflector part 38 must be in agreement with the formation of the rain of material that forms in the second zone 27.

With reference to the attached 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 18.

The materials thus fed cross the first zone 25 and are mixed and amalgamated by the helical blades 26.

The average temperature inside the cylinder 11 in correspondence with the first zone 25 is generally of the order of 120-150 ° C.

The mixture then advances along the second zone 27, inside which there is an average temperature of the order of 280-300 ° C, where the evaporation of the humidity contained in the materials and, in particular, in the materials takes place. recovery (RAP).

The lifting cups 28, or similar lifting means, for example with shovels or cups, lift the materials, which fall down â € œa rainâ €; the mixing and amalgamation of virgin inert materials with recycled materials are thus favored. In particular, the bitumen fraction present in the recovery materials (RAP) softens, favoring the bond with virgin aggregates; in this way, aggregates of virgin inert materials and recycled materials (RAP) are formed.

Along the third zone 29 there is a further mixing of the materials by the mixing blades 30 which, thanks to their particular arrangement and conformation, which is the subject of a co-pending request in the name of the same Applicant, give the materials a controlled advancement motion. such as to favor the formation of a substantially homogeneous mixture.

Along this third zone 29, the mixture advances in the interspace defined between the cylinder 11 and the auxiliary tubular body 24, without contacting the latter.

Inside this cavity there is an average maximum temperature of the order of 450 ° C, while inside the auxiliary tubular body 24 there is an average maximum temperature of the order of 550 ° C.

Finally, the dried and amalgamated mixture advances in the fourth final heating zone 31 to leave the outlet 19 at an average temperature of about 180-200 ° C.

The flame of the burner 20 flows into this fourth zone 31, the average temperature of which is in the order of 1000-1400 ° C.

In particular, it is noted that the mixture advances without coming into contact with the flame, nor with the external wall of the tubular body 23.

The efficiency of the burner 20 is improved thanks to the pre-heating of the combustion air.

The flame and combustion fumes are directed into the tubular body 23 (inside which there is an average maximum temperature of the order of 800-900 ° C) and from this into the auxiliary tubular body 24.

Furthermore, the drying fumes, ie the fumes generated by the recovery material, are aspirated inside the tubular body 23 and the auxiliary tubular body 24.

The two hot chambers in succession, formed respectively by the tubular body 23 and by the auxiliary tubular body 24, are crossed by the combustion and drying fumes and the volatile organic substances present in them oxidize thanks to the heat present inside these two hot chambers and their walls.

The fumes are then evacuated through the outlet opening 21 and the chamber 22 and conveyed to a treatment and abatement unit.

The baffle plate 38 allows the dust of material, in particular of recovery material (RAP), to be retained throughout the cylinder 11, which fall to the bottom of the cylinder 11 where, due to the effect of heat, they oxidize or are reduced, without reaching the filter unit located downstream of the cylinder 11.

The conical shape of the baffle plate 38 favors the fall on the bottom of the cylinder 11 of the material powders which are deposited thereon.

The wall 39 helps to retain the dust of materials inside the cylinder 11 preventing them from reaching the filter unit located downstream of the cylinder 11 and, moreover, limits the dissipation of the fumes towards the suction unit if the latter is non-operational, thus preventing the dust of materials carried by the fumes from reaching the filter unit.

The dryer object of the present invention has the advantage, thanks to the provision of at least one baffle plate 38 and the lower wall 39 associated with the smoke outlet 21, it allows the dust to be retained inside the drying cylinder of inert and recovery materials that are formed during the drying treatment, avoiding, in particular, that they can reach the filter unit located downstream of the drying cylinder.

In this way, the filtration efficiency of the filter group is preserved, thus reducing maintenance and replacement of the filter bags and limiting the emission of fine dust into the atmosphere.

The presence of the auxiliary tubular body 24 in succession to the tubular choir 23, moreover, allows to further reduce, compared to known dryers, the percentages of volatile organic substances (VOC, COT) present in the exhaust fumes in compliance with the regulations in force, regardless of the nature of virgin aggregates and recycled materials (RAP) and also for percentages of recycled materials (RAP) higher than 25% and even in the order of 40%.

The pre-heating of the combustion air improves the combustion efficiency in terms of fuel savings of the order of 10% -20%.

Finally, the particular conformation and arrangement of the mixing blades 30 allows to obtain homogeneous mixtures.

It should be noted that the temperatures shown in this description are purely indicative, depending on the flow rate and type of both the virgin inert material and the recovery material (RAP), the fuel used, the ambient air temperature and the temperature at which it is It is necessary to heat the material.

The dryer thus conceived is susceptible of numerous modifications and variations, all falling within the scope of the invention; furthermore, all the details can be replaced by technically equivalent elements. In practice, the materials used, as well as the dimensions, can be any according to the technical requirements.

Claims (8)

CLAIMS 1) Dryer (10) with rotating cylinder for mixtures of virgin aggregates and recycled materials (RAP) for the preparation of bituminous conglomerates, comprising a cylinder (11) which can be associated with motor means (14) able to rotate it around to its longitudinal axis (A) and which is equipped with two opposite heads (16, 17), an inlet (18) for a mixture of virgin aggregates and recovery materials (RAP) to be dried and which is defined in correspondence of one of said two heads (16), an outlet (19) of the dried mixture and which is defined in correspondence of the other of said two heads (17), at least one burner (20) for the generation of the drying heat of said mixture and which is associated with said head (17) in correspondence of which is defined the outlet (19) and an outlet (21) of the combustion and drying fumes which they are generated inside said cylinder (11) which is defined in correspondence dence of said head (16) in correspondence with which said inlet mouth (18) is defined, characterized in that it comprises at least one deflector partition (38) associated with said outlet opening (21) for the fumes. 2) Dryer (10) according to claim 1, characterized in that said at least one deflector partition (38) extends along at least a portion of the perimeter that delimits said smoke outlet (21) and extends inside said cylinder (11). 3) Dryer (10) according to claim 2, characterized by the fact that said at least one deflector partition (38) has walls with a conical or frusto-conical surface with conicity diverging towards said outlet opening (21) of the fumes and converging towards the ™ inside of said cylinder (11). 4) Dryer (10) according to claim 3, characterized in that, in a front view of said outlet opening (21) of the fumes from the cylinder side and considering a Cartesian coordinate system centered in said outlet opening (21) of the fumes, said at least one deflector partition (38) extends along at least a portion of the perimeter of said smoke outlet (21) included in the second and third quadrant, if the direction of rotation of said cylinder (11) is clockwise, or along at least a portion of the perimeter of said smoke outlet (21) included in the first and fourth quadrant, if the direction of rotation of said cylinder (11) is counterclockwise. 5) Dryer (10) according to one or more of the preceding claims, characterized in that it also comprises a wall (39) which extends below said outlet opening (21) of the fumes towards the inside of said cylinder (11). 6) Dryer (10) according to claim 5, characterized in that said wall (39) extends along a portion of the perimeter that delimits the outlet opening (21) of the fumes. 7) 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 internal lateral surface of said cylinder (11) at a defined distance from it. 8) Dryer (10) according to one or more of claims 5 to 7, characterized in that said wall (39) is connected to said at least one deflector partition (38).