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(11) | EP 0 024 755 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method and device for heating asphalt-containing materials |
| (57) A method of heating asphalt-containing materials in a device with the aid of combustion
gases or heated air respectively, whereby the asphalt-containing materials are indirectly
heated with the aid of combustion gases, the combustion gases being passed in the
same direction through the device as the asphalt-containing materials, whilst the
asphalt-containing materials are simultaneously brought into direct contact with combustion
gases which have cooled in the meantime as a result of the indirect heating to below
about 450°C and which are passed also in the same direction as the asphalt-containing
materials through the device. |
[0001] The invention relates to a method of heating asphalt-containing materials in a device with the aid of combustion gases or heated air respectively.
[0002] In order to be able to re-use asphalt-containing materials obtained, for example, by breaking up road covers and the like it is necessary to heat these asphalt mixtures. Since such asphalt mixtures contain binders such as bitumen, these binders should be prevented from evaporating or burning duL ring the heating process. Therefore, it is common practice to heat such asphalt-cotaining materials in rotating drums, in which fire tubes are arranged in a manner such that combustion gases can be passed through said fire tubes in a direction corresponding to the direction of movement of the asphalt-containing materials across the drum. In order to obtain reasonable effect a great number of fire tubes and a drum of large size are required. A disadvantage thereof is that the tubes must have a comparatively high temperature, which results in sticking material on the tubes so that the passage of the materials to be heated between the tubes is soon blocked. Cleaning the interior of the drum with the tubes arranged therein, which is then unavoidable, is particularly onerous and costly, whilst in addition the device has to be put out of operation.
[0003] The invention has for its object to provide a method of the kind set forth in which such asphalt-containing materials can be more effectively heated.
[0004] According to the invention this can be achieved in that the asphalt-containing materials are indirectly heated with the aid of combustion gases, whilst the asphalt-containing materials are simultaneously brought into direct contact with combustion gases, which have already cooled down by giving off heat as a result of the indirect heating below 450°C and which are padsed in the same direction as the asphalt-containing materials through the device, whilst the combustion gases are passed in the same direction through the device as the asphalt-containing materials during the first period. Owing to the direct contact between the combustion gases and the asphalt-containing material an effective, uniform heating of this material is obtained, and because the temperature of the combustion gases coming into direct contact with the material is maintained below about 450°C an adverse effect on the properties of the asphalt-containing materials by heating is avoided. Apart therefrom, the gases used for the indirect heating may have a higher temperature so that optimum heating is obtainable.
[0005] According to the invention an effective device for heating asphalt-containing materials can be obtained by providing it with a rotatable drum comprising channels,extending in the direction of the lenght of the drum, through which the flue gases are passed from one end of the drum towards the other end thereof, there being provided means for guiding the flue gases emanating from the channels towards the interior of the drum. With the aid of the flue gases having a comparatively high temperature the material can be indirectly heated, whilst the flue gases cooled down in the channels can be utilised for directly heating the material.
[0006] The invention will be described more fully hereinbelow with reference to a few embodiments of devices according to the invention shown schema- titally in the accompanying figures.
Fig. 1 shows schematically a first embodiment of a device in accordance with the invention.
Fig. 2 shows schematically a second embodiment of a device in accordance with the invention.
Fig. 3 is an enlarged sectional view of part of the drum used in the device shown in fig. 2, taken on the line III-III in fig. 2.
Fig. 4 shows schematically a third embodiment of a device in accordance with the invention.
[0007] The device shown schematically in fig. 1 comprises-a drum adapted to rotate about its longitudinal axis, which is at a small angle to the horizon. With the topmost left-hand end of the drum 1, viewed in fig. 1, communicates a burner chamber 2, in which a burner 3 is arranged. Inside the drum 1 is arranged a drum 4 concentrically with the drum 1 and connected in a manner not shown in detail with the drum 1 so that the two drums 1 and 4 together are rotatable about the centre line of the drum 1.
[0008] The left-hand end of the drum 4 is closed by a head wall 5 having holes for connecting a plurality of tubes 6 extending in the direction of lenght of the drum.
[0009] ) The right-hand ends of the inner drum 4 and of the tubes 6 are located at a given distance from the right-'hand head wall 7 of drum 1.
[0010] Near the left-hand end of the drum 1 is arranged a feeding member (not shown in detail) for feeding asphalt-containing materials into the interior of the drum 4 in the direction of the arrow A, whereas near the right-hand end of the drum 1 a delivery memE . (not shown in detail) is arranged for the delivery of the heated material in the direction of the arrow B. Since during operation the drums 1 and 4 are rotating, the material carried along also by the tubes 6 in the drums will move across the drum more or less along a helical path as is indicated by the line of connection between the arrows A and B.
[0011] The heated air of the oombustion chamber or the combustion gases produced therein will flow out of the combustion chamber 2 partly through the the space between the drums 1 and 4 and partly through the tubes 6 as is indicated by the arrows C and D.
[0012] Near the right-hand end of the drum 1 these combustion gases flow freely into the interior of the drum 1 and will subsequently flow back in direct contact with the asphalt-containing material in the drum in the direction of the arrow E towards an outlet (not shown in detail), from which the combustion gases are conducted away in the direction of the arrow F. If desir desired, at least part of this heated air or combustion gases can be recycled to the combustion chamber 2.
[0013] Preferably, the asphalt-containing material obtained, for example, by breaking up a road cover is preheated at about 85°C by direct injection of steam into this material, after which the moisture content of the material is reduced to about 4% by forced or natural leakage.
[0014] Owing to the direct injection of steam into this material the lumps of asphalt disintegrate so that also owing to the inserted moisture a starting material for the further process is obtained, which can be satisfactorily worked at said temperature.
[0015] The material thus preheated at 850 C is fed as described above in the direction of the arrow A into the device and will gradually flow through the drum and be conducted away in the direction of the arrow B. The hot gases flowing out of the combustion chamber, which gases may have a temperature of about 600°C, will initially give off heat indirectly across the wall of the drum 4 and the walls of the tubes 6 to the asphalt-containing material and by this indirect heat transfer overheating of the combustion gases of high temperature is avoided. When the combustion gases freely flow out into the drum 1 at the right-hand end thereof, the temperature of the combustion gases will have dropped below 450°C, preferably below about 400 C, so that the combustion gases then coming into direct contact with the material will not cause undesirable conversions in the material but will bring about an effective, uniform heating of this material.
[0016] Preheating of the material at about 85°C prevents to a great extent sticking material in the interior of the device. Moreover, the moisture still contained in the material will counteract adhesion of material in the interior of the device. Moreover, the mode of heating described is found to counteract sticking of material so that by applying the method according to the invention, the device can be maintained in operation undisturbed for a long time, whilst a particularly effective and uniform heating of the material is produced.
[0017] Since in the areas of direct contact with the material the combustion gases still have a comparatively high temperature and the material is exposed to the influence of the combustion gases only for a short time before the material leaves the device, a slightly higher temperature, if ocur- ring, will practically no adversely affect the properties of the material whereas it even contributes to the expulsion of residual moisture, if any.
[0018] The system shown in fig. 2 comprises a rotatable drum 8, the interior of which comprises more or less triangular channels 9 (fig. 3), to which inwardly projecting blades 10 are fastened. This drum 8 is also rotatable about its longitudinal axis and arranged at a small angle to the horizontal. A burner chamber 11 disposed near the drum communicates through a conduit 12 with an annular conduit 13 surrounding the right-hand end of the drum, viewed in fig. 2, with which the channels 9 are in open communication. The left-hand ends of the channels 9 open out in an annular conduit 14 also surrounding the drum 8, which is connected through a bypass conduit 5 with a burner chamber 16 disposed near the right-hand top end of the drum 8. The material can be fed in the conventional manner at the right-hand top end of the drum 8, as is illustrated schematically by the conveyor belt 17.
[0019] The end of the drum 8 projecting beyond the annular conduit 14 communicates with an outlet conduit 18 for the flue gases, in which conduit, if desired, a heat exchanger 19 may be arranged, for example, for heating boiler water or the like. The conduit 18 includes furthermore a blower 20 for sucking away the exhaust gases. The exhaust gases are passed through a washing device 21 for removing dust, after which the combustion gases can flow away through a chimney 22. As the case may be, part of the used combustion gases may be fed back to the burner chamber, as is indicated by broken lines, so that these hotter gases can again be utilized in the process, which will have an energy saving' effect.During operation the comparatively hot combustion gases flowing out of the burner chamber 11 will first be passed through the channels 9 and thus indirectly heat the asphalt-containing materials in the drum. Subsequently, these combustion gases are fed to the burner chamber 16, where the temperature of the combustion gases can be raised, if necessary, to a value such that these combustion gases subsequently introduced into the drum 8 and thus being in direct contact with the material will not adversely affect the properties of the material to be heated. For controlling the temperature of the combustion gases conventional control-devices 24 may be provided. The combustion gases flowing out of the burner chamber 16 through the drum 8 have the same direction of flow as the combustion gases through the channels 9. The gases passing through the interior of the drum will, in addition, be indirectly heated by the gases passing through the channels,-which contributes to an effective, uniform heating of the material, which is effectively kept moving by the blades 10, to which the material is not likely to stick.
[0020] The system shown in fig. 4 corresponds at least partly with the system shown in figs. 2 and 3 and parts corresponding with those shown in figs. 2 and 3 are designated by the same reference numerals. In this embodiment the annular conduit 14 is connected with a conduit 25 communicating with with a blower 26.
[0021] The outlet of the blower 26 is branched into two conduits 27 and 28. The conduit 27 opens out in the burner chamber 11 and the conduit 27 includes a control-valve 29 actuated by a control-device 24 in a manner similar to the preceding embodiment.
[0022] The conduit 28 including a valve 30 for controlling the subatmospheric pressure opens out in a mixing chamber 31 arranged in front of the drum 8. On the side of the mixing chamber 31 remote from the drum 8 a burner chamber 32 communicates with said mixing chamber.
[0023] The outlet conduit 18 communicates with a conduit 33, which connects the outlet conduit 18 with a blower 34. With the blower 34 communicates a conduit 35 opening out in the burner chamber 32. The end of the conduit 35 has a control-valve 36, which is adjustable in dependence upon the temperature. If desired, as is shown in fig. 4, the conduit 35 may include a device 37 for washing the gases flowing through the conduit 35 in order to remove dust from the combustion gases.
[0024] With the outlet conduit 18 furthermore communicates a moisture cyclone 38 through an intermediate conduit 39. The intermediate conduit 39 comprises a control-valve 40 for controlling the subatmospheric pressure. Through a conduit 41 a blower 43 communicates with the cyclone 38 for sucking away the combustion gases and conducting them into the chimney 22.
[0025] During operation the gases emanating from the burner chamber 11 are used for indirect heating in a manner similar-to-that described with reference to the preceding embodiment. In contrast to the preceding embodiment the combustion gases are partly fed back to the burner chamber 11 and partly to a mixing chamber 31, where these combustion gases from the burner chamber 11, which have already given off part of their heat, are mixed with combustion gases emanating from the burner chamber 32. The mixture of combustion gases thus formed in the mixing chamber 31 is passed through the drum 8 in direct contact with the asphalt-containing materials, which are thus directly heated. The gases flowing out of the drum are partly sucked off by the blower 34 and fed back to the burner chamber 32. The remaining portion of the combustion gases is passed through the cyclone 38, where dust is removed from the combustion gases, the clean combustion gases being subsequently conducted away through the chimney 22.
1. A method of heating aspahlt-containing materials in a device with the aid of combustion
gases or heated air respectively characterized in that the asphalt-containing materials
are indirectly heated with the aid of combustion gases, the combustion gases being
passed in the same direction through the device as the asphalt-containing materials,
whilst the asphalt-containing materials are simultaneoulsy brought into direct contact
with combustion gases which have cooled in the meantime as a result of the indirect
heating to ; below about 450°C and which are passed also in the same direction as
the asphalt-containing materials through the device.
2. A method as claimed in Claim 1 characterized in that combustion gases originating
from a first burner are first used for indirect heating and are subsequently mixed
at least partly with the combustion gases originating from a second burner, the resultant
mixture being used for direct heating.
3. A method as claimed in Claim 1 or 2 characterized in that prior to supply to the
device the material is preheated at about 80 to 85 C.
4. A method as claimed in Claim 3 characterized in that the material is preheated
and comminuted by passing steam across the material, after which he moisture content
of the material is reduced to about 4%.
5. A device for heating asphalt-containing materials characterized in that the device
comprises a rotatable drum having channels extending in the direction of length, through
which the flue gases are passed from one end of the drum to the other end thereof,
whilst means are provided for guiding the the flue gases emanating from the channels
towards the interior of the drum.
6. A device as claimed in Claim 5 characterized in that near one end of the drum a
combustion chamber is arranged and is in open communication with tubes extending through
the drum and having their ends remote from the combustion chamber in open communication
with the interior of the drum, whilst with the interior of the drum at the end of
the drum located near the combustion chamber communicates an outlet for the combustion
gases.
7. A device as claimed in Claim 5 or 6 characterized in that the drum has a double-walled
structure and the space between the two walls of the drum directly communicates at
one end of the drum with a combustion chamber and at the other end of the drum directly
with the interior of the drum, whilst near the combustion chamber the drum is provided
with an outlet for the combustion gases.
8. A device as claimed in Claim 7 characterized in that the channels extend along
the circumference of the drum and are constructed so that the inner wall of the drum
has an irregular shape.
9. A device as claimed in Claim 8 characterized in that the channels have a more or
less triangular section.
10. A device as claimed in Claim 8 or 9 characterized in that blades extending towards the centre of the drum are fastened
to the channels.
11. A device as claimed in anyone of Claim 8 to 10 characterized in that near one
end of the drum the channels communicate with a combustion chamber and near the other
end of the drum with a bypass conduit which guides the combustion gases near the first-mentioned
end of the drum into the interior of the drum.
12. A device as claimed in Claim 11 characterized in that the bypass , conduit is
connected with a further combustion chamber, in which the combustion gases can be
reheated before being introduced into the interior of the drum.
13. A device as claimed in anyone of Claim 8 to 10 characterized in that near a first
end of the drum the channels communicate with a combustion chamber and near the other
end of the drum with a bypass conduit connected both with the combustion chamber concerned
and with the inlet side of the drum.
14. A device as claimed in Claim 13 characterized in that the bypass conduit is connected
with a mixing chamber arranged near the inlet side of of the drum and receiving combustion
gases of a further combustion chamber.
15.. A device as claimed in anyone of Claims 13 or 14 characterized in that with the
end of the drum is connected an outlet for the combustion gases, which communicates
both with a chimney and with the further combustion chamber.
16. A device as claimed in anyone of the preceding Claims 5 to -15 characterized in
that the combustion gases emanating from a combustion chamber for indirect heating
are passed in the same direction through the device as the materials to be heated.