DRYER FOR AN INDUSTRIAL PLANT FOR THE PRODUCTION OF BITUMINOUS MACADAMS

Abstract

 Described is a drier of recycled bituminous material comprising a drying drum (10) comprising a combustion chamber (11); a channel (12) for loading the recycled bituminous material into the drying drum (10); an opening (13) for unloading the recycled bituminous material from the drying drum (10) positioned on the opposite side to the loading channel (12) along the drying drum (10); a system for feeding the recycled bituminous material in a feed direction (V) from said loading channel (12) to said unloading opening (13); a burner (14) for introducing in the drying drum a flow (F1) of combustion gas co-current to a flow (F2) of the recycled bituminous material movable between the loading channel (12) and the unloading opening (13); an outlet chamber (15) at least of the flow (F1) of combustion gas located at the unloading opening (13) of the recycled bituminous material; the drier being comprises a recirculation duct (16) extending between the outlet chamber (15) and the combustion chamber (11) and a suction system for sucking a flow (F3) of recirculation air along the recirculation duct (16) and injecting it into the drying drum (10); the recirculation duct (16) and the drying drum (10) are configured in such a way that the flow (F3) of recirculation air is co-current with the flow (F2) of recycled bituminous material.

Description

[0001] This invention relates to a drier and an industrial plant and in particular an industrial plant for the production of mixtures in the form of macadams with bituminous and non-bituminous binders, briefly also bituminous macadams intended in particular for making road surfaces.

[0002] In the sector of industrial plants for the production of bituminous macadams there are widespread plants which allow the use, in the mixtures, of virgin inert lithic materials, such as, for example, gravel, and recycled or regenerated material (Recycled Asphalt Pavement RAP) derived, for example, from milling existing road pavements.

[0003] Both virgin materials and recycled materials must be in predetermined physical conditions in order to be mixed (for example, with high temperature and dried), so they are also processed thermodynamically in the plants of interest.

[0004] All the materials are then processed in suitable driers, for example to condition the humidity, and inserted in hoppers from which they are picked up to make up the desired final mixture.

[0005] Patent document EP3551801, in the name of the same Applicant as this invention, illustrates a plant for the production and distribution of bituminous macadams comprising a counter-current drier (the material to be dried moves inside the drum in the direction opposite to the flow of hot drying air) equipped with a single burner for the drying of the materials to be processed. The drier consists, schematically, of a first and a second drum, positioned one after the other, wherein in the first drum, closest to the burner, virgin materials are dried whilst in the second drum the materials are dried containing bitumen, bituminous macadams or bituminous recycled material or mixed materials which contain at least a part of materials containing bitumen.

[0006] The plant described in patent document EP3551801 is not very versatile since, from the initial design, there must be a drier with a double drum and a single burner which cannot then be replaced, in existing plants, if the requirements of the user have changed.

[0007] Another type of plant, comprising a counter-current drier, is described in patent document EP3221517, in the name of the same Applicant, wherein at least a part of the pollutant compounds are recirculated to the burner to reduce them.

[0008] One drawback of the above-mentioned solution lies in the fact that it is possible to obtain macadams comprising only up to 35-40% of recycled material whilst the main need in the sector is to use increasingly greater percentages of recycled material and reduce the emissions of pollutant compounds produced during the production of macadams.

[0009] In this context, the aim is to propose a drier and industrial plant for the production of bituminous macadams that is capable of overcoming at least some of the drawbacks of the prior art and of meeting the above mentioned need.

[0010] In particular, the aim of this invention is to provide a drier and an industrial plant for the production of bituminous macadams which allow an increase in the percentage of recycled material in the macadams containing the pollutant emissions.

[0011] This aim is achieved by a drier and an industrial plant comprising the technical features described in one or more of the accompanying claims. The dependent claims correspond to possible different embodiments of the invention.

[0012] In accordance with a first aspect, the invention relates to a drier of recycled bituminous material.

[0013] The drier, described only insofar as necessary for understanding this invention, comprises a drying drum in which there is a combustion chamber. The drier comprises a channel for loading the recycled bituminous material into the drying drum.

[0014] The loading channel is shaped for introducing the recycled bituminous material into a lower or bottom zone of the drying drum, inside the combustion chamber, substantially delimited by an inner lateral surface of the drying drum.

[0015] For example, the loading channel has an outlet close to the bottom of the drying drum.

[0016] The drier comprises an opening for unloading the recycled bituminous material from the drying drum located on the opposite side of the loading channel along the drying drum.

[0017] The drier comprises a system for feeding the recycled bituminous material according to a feed direction from the outlet of the loading channel to the unloading opening.

[0018] Preferably, the feed system comprises a plurality of tiles fixed to an inner surface of the drying drum at the combustion chamber. The tiles are configured to prevent the lifting of the recycled bituminous material which therefore advances sliding on the bottom of the drum.

[0019] The drier comprises at least one burner for introducing in the drying drum a flow of combustion gas co-current to a flow of recycled bituminous material which is movable, by means of said feed system, between the outlet of the loading channel and the unloading opening.

[0020] The burner maintains a flame which generates heat for drying the recycled bituminous material and a corresponding flow of hot air.

[0021] The burner is preferably coaxial with the drying drum.

[0022] The above-mentioned tiles, preventing the lifting of the recycled bituminous material, means that it is not affected by the flame and does not release pollutant emissions due to the combustion of bitumen.

[0023] Preferably, the feed system comprises a comb-type blading, fixed to the inner surface of the drying drum downstream of the flame of the burner and the tiles.

[0024] The blading determines a rain of the material through the flow of hot air in a drying zone in the drying drum.

[0025] The drier comprises an outlet chamber at least of the flow of combustion gas located at the unloading opening of the recycled bituminous material.

[0026] The drier comprises a recirculation duct extending between the outlet chamber and the combustion chamber and a suction system for sucking a flow of recirculation air along the recirculation duct and injecting it into the drying drum.

[0027] In this way, the recycled bituminous material, the flame of the burner and the recirculation air are found together in the combustion chamber.

[0028] The recirculation duct and the drying drum are configured in such a way that the flow of recirculation air inside the drying drum is co-current with the flow of recycled bituminous material; the flow of combustion gas and the flow of recirculation air form an overall flow of air in the drying drum.

[0029] Preferably, the recirculation duct and the drying drum are configured in such a way that the maximum speed of the total flow is between 2 and 5 m/s.

[0030] Advantageously, reintroducing into the drying drum part of the flow of combustion gas coming out from the drying drum allows at least part of the unburnt parts which are necessarily present in the flow of combustion gas to be burnt. The recirculation also allows the speed of the gases to be increased at a lower temperature (approximately 650°C) contributing to bringing the recycled bituminous material to a temperature of around 150-160°C.

[0031] This overcomes a limitation of the prior art solutions which have the gas at too high a temperature, since it is not mixed, even after the combustion chamber, in the drying zone. The recirculation in fact mixes, preferably, hot air generated by the burner and air at the outlet of the drier at a lower temperature, in a quantity such as to generate a flow with a maximum temperature of approximately 650°C in the drying zone.

[0032] Heating the RAP material to a temperature of 150-160°C, in accordance with the emissions, makes it possible to increase the percentage of use of the RAP, since the final mixture is also at 160°C. According to prior art solutions of co-current driers a temperature of approximately 130°C is reached.

[0033] Preferably, the recirculation duct leads to the burner in such a way that the flow of recirculation air leads to the flame of the burner.

[0034] Preferably, the recirculation duct has an outlet configured in such a way that the flow of recirculation air leads in the drying drum in a circumferential manner relative to the flame.

[0035] The outlet of the recirculation duct is configured in such a way that the flow of recirculation air adopts a circular arc configuration, preferably coaxial with the flame, surrounding it partly.

[0036] The flow of recirculation air being fed into the drying drum does not affect the recycled bituminous material flowing in the lower zone of the drying drum.

[0037] In other words, the outlet of the recirculation duct is configured in such a way that the flow of recirculation air adopts a circular crown configuration, preferably coaxial with the flame, interrupted at the bottom of the drying drum where the recycled bituminous material flows.

[0038] Advantageously, in this way, preventing the flow of recirculation air striking the recycled bituminous material avoids the lifting and/or generation of dust. Any powder inside the combustion chamber could in fact disturb the combustion, making it worse, increasing the polluting substances produced in the drier.

[0039] For example, the outlet of the recirculation duct is configured in such a way that the flow of recirculation air affects 2/3 of the circumference around the flame without affecting the bottom of the drying drum.

[0040] Preferably, the drying drum comprises a chamber for mixing air or a pre-chamber upstream of the combustion chamber according to the feed direction of the feed system and the recirculation duct leads into the mixing chamber.

[0041] Advantageously, the flow of recirculation air is slowed down in the pre-chamber.

[0042] Preferably, a ratio between a length of the combustion chamber and a length of the pre-chamber is between 1.5 and 8.

[0043] Preferably, the flow of recirculation air is between 20% and 80% of the total air flow in the drying drum and even more preferably between 30% and 40%. Preferably, the drier comprises a system for protecting the flame of the burner from the flow of recirculation air.

[0044] Preferably, the drier comprises at least one baffle in the drying drum configured for mixing and homogenizing the flow of combustion gas and the flow of recirculation air.

[0045] Advantageously, the mixing of the two flows of gas allows the temperature of the overall flow to be adjusted before it enters the drying zone downstream of the baffle.

[0046] Preferably, the baffle is positioned at an end of the combustion chamber on the opposite side relative to the burner.

[0047] Preferably, the burner has a power of between 6 and 15 MW and the drying drum has a ratio between length and diameter d10 of between 3 and 8.5.

[0048] Advantageously, the main dimensions of the drying drum, diameter and length, are greater than those of the prior art driers with the same power of the burner in such a way that the drier has a greater volume for the processing of the gas flows.

[0049] Preferably, a ratio between a length of the combustion chamber and a length of the drying drum is between 0.15 and 0.5.

[0050] According to an aspect, this invention relates to an industrial plant for the production of bituminous macadams.

[0051] The system comprises a first drier at least for inert lithic materials for preparing a dried inert lithic material, a second drier of recycled bituminous material for preparing a dried recycled bituminous material and a system for reducing polluting compounds in communication with the first and the second driers for reducing at least their harmful emissions.

[0052] The plant may comprise at least a first buffer storage system for the dried inert lithic material positioned downstream of the first drier and at least a second buffer storage system for the dried recycled bituminous material positioned downstream of the second drier.

[0053] The plant comprises a section for mixing the dried inert lithic material and the dried recycled bituminous material with a bituminous binder positioned downstream of the first drier and the second drier.

[0054] Preferably, the mixing section is positioned downstream of the first and the second buffer storage systems from which it can receive the dried inert lithic material and the dried recycled bituminous material.

[0055] The second drier is according to the previous aspect and the system for reducing pollutant compounds comprises the outlet chamber at least of the flow of combustion gas of the second drier.

[0056] In practice, a system according to this aspect can be obtained by combining a drier according to the previous aspect with a traditional system, for example that described in patent document EP3221517.

[0057] The system for reducing pollutant compounds comprises, in the outlet chamber, a device for separating bituminous particles from the flow of combustion gas.

[0058] Advantageously, the flow of recirculation air to the drier of the recycled bituminous material may contain fine polluting particles which are subjected again to the flow of combustion gas.

[0059] Preferably, the second drier is positioned at a height greater than the first drier.

[0060] According to an aspect, the invention relates to a method for the processing of recycled bituminous material.

[0061] The method comprises feeding a flow of recycled bituminous material on the bottom of a drying drum and striking, in the drying drum, the flow of recycled bituminous material with a flow of combustion gas co-current with the flow of recycled bituminous material.

[0062] The method comprises sucking a flow of recirculation air from the flow of combustion gas and injecting it into the drying drum in such a way that it is co-current to the flow of recycled bituminous material inside the drying drum.

[0063] Preferably, the flow of recirculation air is introduced, in the drying drum, at a flame of a burner generating the flow of combustion gas.

[0064] Preferably, the flow of recirculation air is introduced, in the drying drum, in such a way as to surround the flame apart from a lower portion at the bottom of the drying drum where the recycled bituminous material passes.

[0065] Preferably, the processing method comprises slowing down the flow of recirculation air in the drying drum, in particular at the moment of an infeed into the drying drum.

[0066] Preferably, the slowing down of the flow of recirculation air occurs upstream of a combustion chamber in the feed direction of the flow of recycled bituminous material.

[0067] Preferably, the method comprises protecting a flame for generating the flow of combustion gas, fed by the burner, from the flow of recirculation air.

[0068] Preferably, the method comprises mixing and homogenizing the flow of combustion gas and the flow of recirculation air.

[0069] The drier according to the invention is preferably designed for processing recycled bituminous material which is heated at least in such a way that its temperature reaches approximately 150-160°C.

[0070] It is also possible to introduce into the drier a percentage of inert material, preferably between 0 and 45% based also on the geometry of the plant.

[0071] The dried recycled bituminous material is unloaded and stored ready to be mixed at least with the dried inert lithic materials and the bituminous binder. Since a dosing mix of any bituminous macadam may comprise a percentage of RAP, a plant according to the above-mentioned aspect is particularly versatile.

[0072] In the case of a "direct" mix (schematically without using a sieve) the inert lithic material and the recycled bituminous material can both be introduced in the first drier, for example if of the type described in EP3221517B1, to obtain a first mixture to which at least the bituminous binder and a filler will be added.

[0073] In the case of an "indirect" mix, the first drier may be used to process the virgin inert lithic material which is then stored whilst the second drier may be used to process the recycled bituminous material which is then stored.

[0074] The materials are then taken from the respective storage systems and transferred to the mixing section where any other ingredients are added in the quantities set out in the mix.

[0075] The use of a second drier for the recycled bituminous material, preferably located at the top, allows the use, in theory, of up to 90-100% of RAP in the mixture.

[0076] The second drier allows, in effect, the RAP to be processed and brought to a high temperature of use (150-160°C) which does not reduce the temperature of the inert lithic material when mixed.

[0077] The second drier allows a high production of processed RAP which is stored and then dosed, in the desired quantity, into the bituminous conglomerate.

[0078] The preferred sizing of the drum, which is greater than that of the prior art driers with the same power of the burner, allows the RAP to be kept further from the flame (compared with the prior art driers) limiting or preventing the deterioration of the bitumen.

[0079] The preferred sizing of the drum, greater than that of the prior art driers with the same power of the burner, allows an increase in the quantity of air inside the drier.

[0080] The passage, in the drying drum, in particular in the combustion chamber, of the flow of recirculation air eliminates, at least partly, polluting substances present in it and contributes to having the bituminous material recycled at 150-160°C at the outlet from the drum.

[0081] The adoption of a second drier of the above-mentioned type may also be implemented in existing plants as "retrofitting" to increase the quantity of recycled bituminous material which can be adopted in the mixes with a low impact on the existing plant.

[0082] In particular, the second drier may be added to an existing system also in place of the drier for RAP that may already be present.

[0083] The recirculation makes it possible to keep the filter already present in the plant since there is no significant increase in the pollutants and the overall flow of air such as to require a larger filter. In this way, it is possible to comply with the limits imposed by the anti-pollution regulations, limiting the implementation costs of the plant.

[0084] On the other hand, solutions are known which require at least an increase in the filter if a drier dedicated to the recycled bituminous material is adopted.

[0085] A part of the flow of recirculation air sucked into the drier of the recycled bituminous material can be sent to the drier of the virgin material for reducing the emissions of the plant.

[0086] Advantageously, the greater the reduction in the pollutant emissions the greater the temperature which can be adopted in the process and the greater is the quantity of RAP which can be processed and used.

[0087] Further features and advantages of the above-mentioned aspects are more apparent in the non-limiting description which follows of a preferred, non-limiting embodiment of an industrial plant for the production of bituminous macadams and a drier of recycled bituminous material.

[0088] The description is set out below with reference to the accompanying drawings which are provided solely for purposes of illustration without restricting the scope of the invention and in which:

• Figure 1 illustrates a schematic front view, with some parts cut away for greater clarity, of an industrial plant for the production of bituminous macadams according to the invention;
• Figure 2 illustrates a schematic rear view, with some parts cut away for greater clarity, of a portion of the plant of Figure 1;
• Figure 3 illustrates a side view diagram, partly in blocks, of a drier for recycled bituminous material;
• Figure 4 illustrates a diagram, partly in blocks, of the plant of Figures 1 and 2;
• Figure 5 illustrates a schematic perspective view of a detail of the drier of Figure 3.

[0089] With reference to Figure 1, the numeral 1 denotes in its entirety an industrial plant for making bituminous macadams.

[0090] The plant 1 is described below limited to the parts necessary for understanding this invention.

[0091] Schematically, the plant 1 comprises a first drier 2, comprising a burner 2a, at least for inert lithic materials for preparing a dried inert lithic material, that is to say, substantially without moisture, in a substantially known manner.

[0092] According to the embodiment illustrated, the first drier 2 is, for example, like the drier described in EP3221517 which is incorporated herein by reference for completeness of description.

[0093] The plant 1 comprises a system for reducing pollutant compounds, for example the gases produced by the combustion in the plant 1.

[0094] The reduction system comprises a filter 3 for reducing at least the fine powders equipped with a respective extractor 3a.

[0095] The fine powders are, for example, collected in a hopper 6 positioned below the filter 3.

[0096] The system 1 comprises a flue 7, downstream of the filter 3, from which is released the air filtered by the filter 3.

[0097] According to the example embodiment illustrated, the plant 1 comprises at least one storage system 8 for the dried inert lithic material positioned downstream of the first drier 2.

[0098] The plant 1 comprises a second drier 9 for recycled bituminous material for preparing a dried recycled bituminous material.

[0099] In general, the term "dried" means a material (virgin or recycled) which is processed at least thermally in such a way as to give it predetermined qualities such as, for example, a substantial absence of moisture.

[0100] As illustrated, the second drier 9 is preferably positioned higher than the first drier 2.

[0101] The second drier 9 comprises a drying drum 10 inside of which a combustion chamber 11 can be identified.

[0102] The drier 9 comprises a channel 12 for loading, in the drying drum 10, the recycled bituminous material and an opening 13 for unloading from the drying drum 10 the recycled bituminous material, positioned on the opposite side of the loading channel 12 along the drying drum 10.

[0103] The loading channel 12 is shaped for directing the recycled bituminous material into a lower zone or bottom 10a of the drying drum 10 inside the combustion chamber 11.

[0104] For example, the loading channel 12 has an outlet 12a close to the bottom 10a of the drying drum 10.

[0105] The drier 9 comprises a system for feeding the recycled bituminous material according to a feed direction V from the channel 12 to the opening 13. For example, the drying drum 10 is inclined towards the opening 13 and rotates to favour the feeding of the recycled bituminous material.

[0106] The feed system is configured in such a way that the recycled bituminous material remains on the bottom 10a of the drum at least in the combustion chamber 11.

[0107] The drier 9 comprises a burner 14 which keeps a flame 14a in the combustion chamber 11 for introducing in the drying drum a flow F1 of combustion gas co-current to a flow F2 of the recycled bituminous material movable between the channel 12 and the opening 13.

[0108] The burner 14 is preferably coaxial with the drying drum 10.

[0109] The above-mentioned system for feeding the recycled bituminous material comprises a plurality of tiles 24, schematically illustrated in Figure 3, associated with an inner surface of the drying drum 10 at the combustion chamber 11.

[0110] The tiles 24 are configured to prevent the lifting of the material which is therefore advances sliding on the bottom 10a of the drying drum 10.

[0111] The feed system comprises a comb-type blading 25, of substantially known type, fixed to the inner surface of the drying drum 10 downstream of the flame 14a of the burner and tiles 24, which, lifting recycled bituminous material, causes a rain in a drying zone 26 in the drying drum 10.

[0112] The drier 9 comprises an outlet chamber 15 located at the unloading opening 13 of the recycled bituminous material.

[0113] The drier 9 comprises a device, of substantially known type, for separating bituminous particles from the flow of combustion gas in the outlet chamber 15.

[0114] Schematically, in the separating device, the larger particles of recycled bituminous material, processed in the drying drum 10, fall to the base of the chamber 15 and are reintroduced into the production cycle through a reintroduction device such as, for example, one or more screw devices.

[0115] The second drier 9 comprises a recirculation duct 16 extending between the outlet chamber 15 and the combustion chamber 11 and a suction system 17 for sucking a flow F3 of recirculation air along the recirculation duct 16 and injecting it into the drying drum 10.

[0116] Preferably, the operating specifications of the recirculation suction system 17 depend on the desired outlet temperature of the dried recycled bituminous material.

[0117] The recirculation duct 16 and the drying drum 10 are configured in such a way that the flow F3 of recirculation air is co-current with the flow F2 of recycled bituminous material.

[0118] The flow F1 of combustion gas and the flow F3 of recirculation air form a total flow F1 +F3 of air in the drying drum 10, in particular in the drying zone 26.

[0119] The recirculation duct 16 leads, in the drying drum 10, at the burner 14 in such a way that the flow F3 of recirculation air leads to the flame 14a of the burner 14.

[0120] The recirculation duct 16 has an outlet 16a configured in such a way that the flow F3 of recirculation air leads in the drying drum 10 in a circumferential manner with respect to the flame 14a.

[0121] The outlet 16a is configured in such a way that the flow F3 of recirculation air adopts a circular arc configuration, without touching the lower zone 10a of the drum 10 and the recycled bituminous material which flows on the bottom 10a.

[0122] In other words, the outlet 16a is configured in such a way that the flow F3 adopts a circular crown configuration, coaxial with the flame, interrupted at the bottom 10a of the drying drum.

[0123] For example, the outlet 16a is in the form of a circular crown interrupted at the bottom 10a of the drying drum 10.

[0124] In a preferred embodiment, the outlet 16a is configured in such a way that the flow F3 of recirculation air affects the 2/3 of the circumference around the flame 14a.

[0125] According to the embodiment illustrated, the drier 9 comprises a head 27 to which the drying drum 10 is coupled in a rotatable fashion.

[0126] The head 27 preferably comprises the outlet 16a of the recirculation duct 16 facing the inside of the drying drum 10. The drier 9 comprises a system 18 for protecting the flame 14a from the flow F3 of recirculation air.

[0127] The drying drum 10 comprises a pre-chamber or chamber 19 for mixing air upstream of the combustion chamber 11 according to the feed direction V of the recycled bituminous material into which the recirculation duct 16 leads.

[0128] The drier 1 comprises at least one baffle 20 in the drying drum 10 configured for mixing and homogenizing the flow F1 of combustion gas and the flow F3 of recirculation air.

[0129] In particular, the baffle 20 is preferably positioned at an end of the combustion chamber 11 on the opposite side relative to the burner 14.

[0130] The baffle 20 is preferably configured to prevent a hot gas from reaching the drying zone 26.

[0131] According to a preferred embodiment, the flow F3 of recirculation air is between 20% and 80% of the total flow F1 +F3 of air in the drying drum 10. Still more preferably, the flow F3 of recirculation air is between 30% and 40% of the total flow F1+F3 of air in the drying drum 10.

[0132] The suction system 17 and the duct 16 are configured in such a way that the flow F3 of recirculation air is between 20% and 80% of the total flow F1+F3 of air in the drying drum 10.

[0133] The suction system 17 and the duct 16 are preferably configured in such a way that the flow F3 of recirculation air is between 30% and 40% of the total flow F1+F3 of air in the drying drum 10.

[0134] According to a preferred embodiment, the burner 14 has a power of between 6 and 15 MW and the drying drum 10 has a ratio between length "L10" and diameter "d10" of between 3 and 8.5.

[0135] According to a preferred embodiment, a ratio between a length "L11" of the combustion chamber 11 and the length "L10" of the drying drum 10 is between 0.15 and 0.5.

[0136] According to a preferred embodiment, a ratio between a length "L11" of the combustion chamber 11 and a length "L19" of the pre-chamber 19 is between 1.5 and 8.

[0137] According to an embodiment, the drier comprises a burner 14 having a power of 9MW, a drying drum 10 with a length 15 m and diameter of 2.5 m, a ratio between the length "L10" and the diameter "d10" equal to 6, a ratio between a length "L11" of the combustion chamber 11 and the length "L10" of the drying drum 10 of 0.37, a ratio between a length "L11" of the combustion chamber 11 and a length "L19" of the pre-chamber 19 equal to 5.5.

[0138] The plant 1 comprises at least a second storage system 21 for the dried recycled bituminous material positioned downstream of the second drier 9. The plant 1 comprises a section 22 for mixing the dried inert lithic material and the dried recycled bituminous material with a bituminous binder positioned downstream of the first drier 2 and of the second drier 9 and in particular positioned downstream of the first buffer storage system 8 and of the second buffer storage system 21 from which it receives, respectively, the dried virgin lithic material and the dried recycled bituminous material.

[0139] The above-mentioned system for reducing pollutant compounds of the plant 1 is in communication with the second drier 9 as well as with the first drier 2.

[0140] In particular, a duct 23 places the outlet chamber 15 in fluid communication with the filter 3 in such a way that at least part of the fine powders and/or the combustion gas produced in the second drier 9 are sent to the filter 3.

[0141] The extractor 3a of the filter 3 may suck a flow F4 from the second drier 9, in particular from the outlet chamber 15, for sending it to the filter 3.

[0142] The extractor 3a of the filter 3 may suck a flow F6 from the first drier 2 for sending it to the filter 3.

[0143] Advantageously, the pollutant compounds produced in the second drier 9 are also sucked by the suction system 17 preventing the release into the environment.

[0144] The reduction system comprises a suction device 4 in communication at least with the first drier 2 and the duct 23 by means of at least one duct 5.

[0145] Preferably, the operating specifications of the suction device 4 depend on the instantaneous power of the burner 2a in the first drier 2.

[0146] Preferably, the extractor 4 can extract, by means of the duct 5, at least a portion F5 of the flow F4 from the duct 23 for sending it to the first drier 2.

[0147] In general, the pollutant compounds are suitably suppressed and eliminated; In particular, the pollutant compounds are burned through exposure to the flame of the burner reaching temperatures higher than 600°C, preferably higher than 800°C.

[0148] In fact, the Applicant has observed that, at the temperatures indicated, the pollutant compounds are easily combustible by thermal oxidation if exposed to these temperatures for a sufficient period of time, in the order of several seconds, preferably in a range of between 0.5 and 5 seconds, even more preferably in a range of between 1 and 2 seconds.

[0149] Preferably, the power of the burners 2a, 14 is modulated on the basis of the desired outlet temperature, respectively, of the inert lithic materials and of the recycled bituminous materials, by the percentage of moisture contained therein and by the flow of the material.

[0150] The flow F4 in the duct 23, coming from the second drier 9, is preferably defined by a modulating baffle, not illustrated, controlled as a function of a negative pressure measured in the combustion chamber 11 of the second drier 9.

[0151] Preferably, operating specifications of the extractor 3a installed in the filter 3 are defined by a modulating baffle, not illustrated, controlled as a function of a negative pressure measured in an inlet zone of all the flows in the filter 3.

[0152] The invention also relates to a method for processing recycled bituminous material.

[0153] The method may be implemented in a system 1 as described above and/or by means of a drier 9 as described above.

[0154] According to an example described below, reference is made to the accompanying drawings without thereby limiting the scope of the invention. The method comprises feeding a flow F2 of recycled bituminous material to a drying drum 10.

[0155] The flow F2 of recycled bituminous material is fed on the bottom 10a of the drying drum 10, for example by means of a loading channel 12 which has an outlet 12a at the bottom 10a.

[0156] The method comprises striking, in the drying drum 10, the flow F2 of recycled bituminous material with a flow F1 of co-current combustion gas with the flow F2 of the recycled bituminous material.

[0157] The method comprises sucking a flow F3 of recirculation air from the flow F1 of combustion gas and injecting it into the drying drum 10 in such a way that it is co-current to the flow F2 of bituminous material.

[0158] The flow F3 of recirculation air is introduced, in the drying drum, at a flame 14a of a burner generating the flow F1 of combustion gas.

[0159] The flow F3 is introduced in the drying drum 10 in a circumferential manner relative to the flame 14a in such a way as to partly surround it.

[0160] The flow F3 of recirculation air adopts a circular arc configuration at the infeed of the drying drum 10 without touching the bottom 10a of the drum 10 and the recycled bituminous material which flows on the bottom 10a.

[0161] In other words, the flow F3 adopts a circular crown configuration, coaxial with the flame, interrupted at the bottom 10a of the drying drum.

[0162] According to a preferred example, the outlet 16a is configured in such a way that the flow F3 of recirculation air affects the 2/3 of the circumference around the flame 14a.

[0163] Preferably, the method comprises slowing down the flow F3 of recirculation air in the drying drum 10, in particular at the inlet of the drying drum 10.

[0164] Preferably, the slowing down of the flow F3 of recirculation air occurs upstream of a combustion chamber 11 in the feed direction V of the flow F2 of recycled bituminous material.

[0165] The method comprises advancing the recycled bituminous material keeping it on the bottom 10a of the drying drum at least in the combustion chamber 11 and/or at the flame 14a.

[0166] Preferably, the flow F3 of recirculation air is between 20% and 80% of the total flow F1+F3 of air in the drying drum 10.

[0167] Preferably, the flow F3 of recirculation air is between 30% and 40% of the total flow F1+F3 of air in the drying drum 10.

[0168] Preferably, the method comprises protecting a flame 14a for generating the flow F1 of combustion gas from the flow F3 of recirculation air.

[0169] Preferably, the method comprises mixing and homogenizing the flow F1 of combustion gas and the flow F3 of recirculation air.

[0170] Advantageously, whilst the bituminous material moves on the bottom of the drying drum it is in the combustion chamber simultaneously with the flame of the burner which participates in the drying of the recycled material.

[0171] The Applicant has observed that in this way, in the combustion chamber, the recycled bituminous material remains protected also from its moisture which is dried by the heat of the flame; The heat from the flame does not affect the inert but only the water.

[0172] At the outlet of the combustion chamber the recycled bituminous material has lost moisture and can be further dried by the flow of recirculation air and by the flow of combustion gas which have mixed until reaching approximately 600°/650°.

Claims

1. A drier of recycled bituminous material, comprising a drying drum (10) comprising a combustion chamber (11);

a channel (12) for loading the recycled bituminous material shaped in such a way that the recycled bituminous material is positioned on a bottom (10a) of the drying drum (10);

an opening (13) for unloading the recycled bituminous material from the drying drum (10) positioned on the opposite side to the loading channel (12) along the drying drum (10);

a burner (14) coaxial with the drying drum (10) for keeping a flame (14a) in the combustion chamber (11) and introducing in the drying drum a flow (F1) of combustion gas co-current to a flow (F2) of the recycled bituminous material movable between the loading channel (12) and the unloading opening (13);

a system for feeding the recycled bituminous material in a feed direction (V) from said loading channel (12) to said unloading opening (13) configured to keep the recycled bituminous material on a bottom (10a) of the drying drum at said flame (14a);

an outlet chamber (15) at least of the flow (F1) of combustion gas located at the unloading opening (13) of the recycled bituminous material;

said drier being characterised in that it comprises a recirculation duct (16) extending between said outlet chamber (15) and said combustion chamber (11) and a suction system for sucking a flow (F3) of recirculation air along the recirculation duct (16) and injecting it into the drying drum (10), the recirculation duct (16) and the drying drum (10) being configured in such a way that the flow (F3) of recirculation air is co-current with the flow (F2) of recycled bituminous material, said flow (F1) of combustion gas and said flow (F3) of recirculation air forming a total flow (F1+F3) of air in the drying drum (10).

2. The drier according to claim 1, wherein the recirculation duct (16) leads to the burner (14) in such a way that the flow (F3) of the recirculation air leads in the drying drum (10) in a circumferential manner relative to said flame (14a), an outlet (16a) of the recirculation duct (16) being configured in such a way that the flow (F3) of recirculation air adopts a circular arc configuration.

3. The drier according to claim 1 or 2, wherein an outlet (16a) of the recirculation duct (16) is configured in such a way that the flow (F3) of recirculation air, entering the drying drum (10), adopts a circular arc configuration, without touching the bottom (10a) of the drying drum (10) and the recycled bituminous material on the bottom (10a).

4. The drier according to any one of the preceding claims, wherein said drying drum (10) comprises a chamber (19) for mixing air upstream of the combustion chamber (11) according to the feed direction (V), said recirculation duct (16) leading into said mixing chamber (19).

5. The drier according to any one of the preceding claims, wherein the flow (F3) of recirculation air is between 20% and 80% of the total flow (F1+F3) of air in the drying drum (10) and is preferably between 30% and 40% of the total flow (F1+F3) of air in the drying drum (10).

6. The drier according to any one of the preceding claims, comprising a system (18) for protecting a flame (14a) of the burner (14) from the flow (F3) of recirculation air.

7. The drier according to any one of the preceding claims, comprising at least one baffle (20) in said drying drum (10) configured for mixing and homogenizing the flow (F1) of combustion gas and the flow (F3) of recirculation air.

8. The drier according to claim 7, wherein the baffle (20) is positioned at an end of the combustion chamber (11) on the opposite side relative to the burner (14).

9. The drier according to any one of the preceding claims, wherein the burner has a power of between 6 and 15 MW and the drying drum (10) has a ratio between length (L10) and diameter (d10) of between 3 and 8.5.

10. The drier according to any one of the preceding claims, wherein a ratio between a length (L11) of the combustion chamber (11) and a length (L10) of the drying drum (10) is between 0.15 and 0.5.

11. The drier according to any one of the preceding claims, wherein said drying drum (10) comprises an air mixing chamber or pre-chamber (19) upstream of the combustion chamber (11) according to the feed direction (V), a ratio between a length (L11) of the combustion chamber (11) and a length (L19) of the mixing chamber (19) being between 1.5 and 8.

12. The drier according to any one of the preceding claims, comprising, in said outlet chamber (15), a device for separating bituminous particles from the flow (F1) of combustion gas.

13. An industrial plant for making bituminous macadams comprising a first drier (2) at least for inert lithic materials for preparing a dried inert lithic material;

a second drier (9) of recycled bituminous material for preparing a dried recycled bituminous material;

a system (3, 3a, 4, 5, 16, 17, 23) for reducing pollutant compounds in communication with the first and the second drier (2, 9);

at least one buffer storage system (21) for the dried recycled bituminous material positioned downstream of the second drier (9);

a section (22) for mixing the dried inert lithic material and the dried recycled bituminous material with a bituminous binder positioned downstream of the first drier (2) and the second drier (9);

said industrial plant being characterised in that the second drier (9) is according to any one of claims 1 to 11 and is in communication with said system (3, 3a, 4, 5, 16, 17, 23) for reducing pollutant compounds.

14. The industrial plant according to claim 13, wherein the second drier (9) is positioned at a height greater than the first drier (2).

15. The industrial plant according to claim 14, comprising at least one storage system (8) for the dried inert lithic material positioned downstream of the first drier (2).

16. The system according to any one of claims 13 to 15, wherein said system for reducing pollutant compounds comprises said device for separating bituminous particles from the flow (F1) of combustion gas.

17. A method for processing recycled bituminous material, said method comprising:

feeding a flow (F2) of recycled bituminous material to a drying drum (10);

striking, in the drying drum (10), the flow (F2) of recycled bituminous material with a flow (F1) of co-current combustion gas with the flow (F2) of the recycled bituminous material;

sucking a flow (F3) of recirculation air from the flow (F1) of combustion gas and injecting it in the drying drum (10) in such a way that it is co-current with the flow (F2) of bituminous material, said processing method being characterised in that said recycled bituminous material is fed on a bottom (10a) of the drying drum (10) and is advanced on the bottom (10a) of the drying drum (10) at a flame (14a) generating said flow (F1) of combustion gas.

18. The processing method according to claim 17, wherein the flow (F3) of recirculation air is introduced, in the drying drum (10), at said flame (14a) in a circumferential manner relative to said flame (14a), the flow (F3) of recirculation air adopting a circular arc configuration which does not affect the bottom (10a) of the drying drum (10) and the recycled bituminous material which flows on said bottom (10a).

19. The processing method according to claim 17 or 18, comprising slowing down the flow (F3) of recirculation air in the drying drum (10), in particular at the inlet of the drying drum (10).

20. The processing method according to claim 19, wherein the slowing down of the flow (F3) of recirculation air occurs upstream of a combustion chamber (11) in the feed direction (V) of the flow (F2) of recycled bituminous material.

21. The processing method according to any one of claims 17 to 20, wherein the flow (F3) of recirculation air is between 20% and 80% of the total flow (F1+F3) of air in the drying drum (10) and preferably between 30% and 40% of the total flow (F1+F3) of air in the drying drum (10).

22. The processing method according to any one of claims 17 to 21, comprising protecting a flame (14a) for generating the flow (F1) of combustion gas from the flow (F3) of recirculation air.

23. The processing method according to claim 17 or 22, comprising mixing and homogenizing the flow (F1) of combustion gas and the flow (F3) of recirculation air.

24. The processing method according to any one of claims 17 to 23, wherein said drying drum (10) is of a drier (9) according to any one of claims 1 to 12.

Drawing