CARLOTTO, Mario (Ammann Italy S.p.A, Via dell'Industria 1 Bussolengo, Verona, I-37012, IT)
| CLAIMS 1 . A burner for drying cylinders comprising: a central unit (4) having a flame emission outlet (5) and which can be fed with at least one fuel and at least a first primary air flow for combustion ; at least one auxiliary pipe (6) mounted around the central unit (4) and comprising an outlet (7) positioned around the flame emission outlet (5) and at least a first inlet section (8) which can be fed with a secondary air flow for combustion; air feed means (9) connected to the central unit (4) and to the first inlet section (8) of the auxiliary pipe (6); characterised in that the air feed means (9) comprise first adjusting means (10) for the primary air flow fed to the central unit (4) and second adjusting means (11 ) for the secondary air flow fed to the auxiliary pipe (6), and also being characterised in that the first adjusting means (10) and the second adjusting means (11 ) can be adjusted independently of each other. 2. The burner according to claim 1 , characterised in that the first adjusting means and the second adjusting means (11 ) each comprise at least one panel (12) able to move so as to vary the working cross-section for the passage of the air. 3. The burner according to claim 1 or 2, characterised in that the air feed means (9) are integral with the central unit (4) and with the auxiliary pipe (6) with which they form a single rigid body. 4. The burner according to claim 3, characterised in that the fan (15) has a delivery direction M set at an angle of between 40° and 80° and preferably between 50° and 70 ° relative to an axial direction F of flame emission. 5. The burner according to any of the foregoing claims, characterised in that the feed means (9) also comprise a shaped hood (17) mounted on a fan (15) intake inlet. 6. The burner according to the foregoing claim, characterised in that the shaped hood (17) is at least partly internally covered with sound-insulating material (18). 7. The burner according to any of the foregoing claims, characterised in that the auxiliary pipe (6) also comprises Venturi effect intake means (42) in an intermediate position between its first inlet section (8) and the outlet (7), said intake means in turn comprising at least a second inlet section (43) which puts into communication the outside and the inside of the auxiliary pipe (6). 8. The burner according claim 7, characterised in that the second inlet section (43) is at least partly internally covered with sound-insulating material (18). 9. The burner according to any of the foregoing claims, characterised in that the central unit (4) comprises at least one device (20) which in practice supplies an air/fuel mixture, and an outer duct (21 ) mounted coaxially with and around the device (20) and fed by the feed means (9) with air which in practice is intended for mixing with the mixture that comes out of the device (20). 10. The burner according to claim 9, characterised in that the device (20) comprises a central tube (22) for supplying a liquid fuel surrounded by an inner duct (23) fed with air by the feed means (9) and means (24) for nebulising the fuel fed out of the central tube (22) by means of the air fed out of the inner duct (23). 11 . The burner according to claim 9 or 10, characterised in that the device (20) comprises an outer tube (35) for supplying a gaseous fuel mounted coaxially with and around an inner duct (23) fed by the feed means (9). 12. The burner according to claim 10 or 11 , characterised in that the central unit (4) also comprises first means (30) for making the air rotate, said means being mounted in the inner duct (23). 13. The burner according to any of the claims from 9 to 12, characterised in that the central unit (4) also comprises second means (34) for making the air rotate, said means being mounted in the outer duct (21 ). 14. The burner according to any of the foregoing claims, characterised in that the air feed means (9) comprise a single fan (15) for feeding air both to the central unit (4) and to the auxiliary pipe (6). 15. A drying cylinder characterised in that it comprises a burner (1 ) made according to any of the foregoing claims. 16. A method for using a burner for drying cylinders comprising a central unit (4) having a flame emission outlet (5) and which can be fed with at least one fuel and with at least a first primary air flow for combustion, and at least one auxiliary pipe (6) mounted around the central unit (4) and comprising an outlet (7) positioned around the flame emission outlet (5) and at least a first inlet section (8) which can be fed with a secondary air flow for combustion, characterised in that it comprises the operating step of independently adjusting the quantity of air fed to the central unit (4) and that supplied to the auxiliary pipe (6) for adjusting the shape and size of the flame produced. 17. The method according to claim 16, characterised in that it comprises the operating steps of: reducing the quantity of air fed to the central unit (4) and increasing that fed to the auxiliary pipe (6) so as to obtain a longer, narrower flame; and increasing the quantity of air fed to the central unit (4) and reducing that fed to the auxiliary pipe (6) so as to obtain a shorter, wider flame. |
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DESCRIPTION
This invention relates to a burner for drying cylinders of the type normally used for example in plants for the production of bituminous macadams. Drying cylinders are devices in which aggregate materials to be dried are inserted. In particular, the cylinders are hollow, rotate about their own axis and house a plurality of paddles which guarantee continuous mixing of the materials being dried.
Mounted at one end of the cylinder there is a burner which generates the heat necessary for drying. Both the flame generated by the burner and the combustion fumes extend inside the cylinder to guarantee the best possible heating of the materials being dried.
As indicated, this invention relates in particular to the burner which is used in such plants.
Prior art burners may be fed either with a liquid fuel, or with a gaseous fuel, or with both.
As regards the use of liquid fuel, there are currently two known types of burners, high pressure burners in which the fuel is nebulised by a pressurised spraying nozzle, and low pressure burners in which the fuel is supplied in liquid form then nebulised by means of a jet of air.
This invention may be used with any type of burners, however, it is preferably intended for low pressure burners. Therefore, that type is mainly referred to below, although the same evaluations, where compatible, may also apply to other types of burners.
As indicated, in low pressure burners the fuel is nebulised by the action of one or more air currents on the fuel which comes out in liquid form. It should be noticed that the greater the nebulisation which can be achieved, the better the combustion is and therefore the more efficient the burner is overall. To achieve this, in most cases the fuel is released in liquid form from a suitable pipe and is struck by one or more air currents directed in such a way as to create a predetermined turbulence. However, the air supplied in this way normally represents only most of the stoichiometric air necessary for combustion. However, in the known way, for more efficient combustion, as well as a greater flow of hot air for the subsequent drying, it is essential that combustion takes place in conditions with an excess of air. In the prior art burners this is achieved by supplying the excess of air through an auxiliary pipe mounted coaxially around one or more central pipes which supply the air for nebulising. Advantageously, a Venturi effect air intake device is also mounted on the auxiliary pipe.
However, all of the various pipes are generally fed upstream by one or more fans by means of suitable piping. In particular, in a very widespread embodiment, all of the pipes are fed by means of a flexible pipe by a single fan mounted close to the drying cylinder. Between the fan and the pipes there is normally a valve which allows adjustment of the overall air flow supplied to the assembly of various pipes.
However, this prior art technology has several disadvantages.
In particular, studies by this Applicant revealed that, depending on the drying cylinder operating conditions it would be necessary to be able to adjust the shape and size of the flame in order to optimise heat exchange and therefore increase system efficiency.
However, prior art burners proved unable to achieve that aim. In prior art burners, adjustment of the quantity of fuel and of the valve located downstream of the fan only allow a variation of the flame size, not of its shape.
Secondly, prior art burners have limited combustion efficiency and quality which is not always optimum in the whole operating range.
In this situation the technical purpose which forms the basis of this invention is to provide a burner for drying cylinders which overcomes the above- mentioned disadvantages.
In particular, the technical purpose of this invention is to provide a burner for drying cylinders which allows the shape of the flame to be adjusted.
The technical purpose of this invention is also to provide a burner for drying cylinders which has high efficiency and a low level of emissions.
The technical purpose specified and the aims indicated are substantially achieved by a burner for drying cylinders as described in the appended claims.
Further features and the advantages of this invention are more apparent in the detailed description of a preferred, non-limiting embodiment of a burner for drying cylinders illustrated in the accompanying drawings, in which :
- Figure 1 is a schematic side view of a drying cylinder equipped with a burner made in accordance with this invention ;
- Figure 2 is a side view of only the burner of the cylinder of Figure 1 ;
- Figure 3 shows the burner of Figure 2 from the opposite side;
- Figure 4 is an axonometric three-quarter view of the burner of Figure 3;
- Figure 5 shows the detail V of Figure 4 enlarged and with some parts cut away to better illustrate others;
- Figure 6 shows the detail VI of Figure 5 enlarged and with some parts cut away to better illustrate others which are more internal ;
- Figure 7 is a front view of the burner of Figure 2;
- Figure 8 is an axonometric cross-section of the burner of Figure 7 according to the line IX - IX;
- Figure 9 is a cross-section of the burner of Figure 7 according to the line IX - IX;
- Figure 1 0 is an enlarged view of the detail X of Figure 9;
- Figure 1 1 is an enlarged view of the detail XI of Figure 9;
- Figure 1 2 shows the detail VI I of Figure 9 enlarged and with some parts cut away to better illustrate others; and
- Figure 1 3 is a cross-section of the burner of Figure 2 according to the line XI I I - XI I I.
With reference to the accompanying drawings the numeral 1 denotes as a whole a burner for drying cylinders made in accordance with this invention. In Figure 1 the burner 1 is shown mounted at one end of a drying cylinder 2 (only schematically illustrated) by means of its connecting flange 3.
In accordance with this invention, the burner 1 in general comprises a central unit 4 for emitting the air/fuel mixture, having a flame emission outlet 5 and which can be fed with at least one fuel and with at least a first primary air flow for combustion (usually equal at least to most of the stoichiometric air for combustion). Mounted around the central unit 4 there is at least one auxiliary pipe 6 which in turn comprises an outlet 7 positioned substantially around the flame emission outlet 5 and at least a first inlet section 8 which can be fed with a secondary air flow for combustion. In the embodiments illustrated the position of the central unit 4 and of the auxiliary pipe 6 is concentric so that the outlet 7 has a circular ring-shaped cross-section. The structure of the central unit 4 and the auxiliary pipe 6 is described in more detail below.
The burner 1 also comprises air feed means 9 connected to the central unit 4 and to the first inlet section 8 of the auxiliary pipe 6. In accordance with this invention, the air feed means 9 comprise first adjusting means 1 0 for the primary air flow fed to the central unit 4 and second adjusting means 11 for the secondary air flow fed to the auxiliary pipe 6. In order to be able to achieve the preset aims of this invention, the first adjusting means 1 0 and the second adjusting means 1 1 can be adjusted independently of each other. Advantageously, the first adjusting means and the second adjusting means 11 may each comprise at least one panel 1 2, able to move so as to vary the working cross-section for the passage of the air. In the accompanying drawings the first adjusting means instead comprise two mobile (rotating) panels 1 2 positioned side by side and moved in a synchronised way by means of an outer mechanical connection 1 3 of the respective supporting shafts. The movement (rotation) of the various panels 1 2 is guaranteed by two servomotors 14 which are controlled independently (Figure 2).
In the preferred embodiment, the air coming out of the first adjusting means 1 0 is completely separate from the air coming out of the second adjusting means 11 , since the first adjusting means 1 0 and the second adjusting means 1 1 are mounted in two stretches of the air path which, downstream of the means, are mechanically completely separate and independent. However, that may not always be necessary, provided that most of the air coming out of the first adjusting means 1 0 is in any case fed to the central unit 4 and most of the air coming out of the second adjusting means 1 1 is in any case fed to the auxiliary pipe 6.
As shown in the accompanying drawings, in the preferred embodiment the air feed means 9 comprise a single fan 1 5 for feeding both the central unit 4 and the auxiliary pipe 6. Advantageously, the fan 1 5 has a delivery direction M (substantially corresponding to the direction of the air at the delivery outlet) which is set at an angle of between 40 ° and 80 °, and preferably between 50 ° and 70 °, relative to an axial direction F of flame emission.
In the preferred embodiment, the air feed means 9 are integral with the central unit 4 and with the auxiliary pipe 6 with which they form a single rigid body. Preferably, to reduce the overall dimensions, the fan 1 5 is positioned in such a way that the centrifugal impeller 1 6 is positioned above the straight lines identifying the delivery direction M and the flame emission direction F.
Moreover, preferably, to reduce the noise emitted by the fan 1 5, the air feed means 9 may comprise a shaped hood 1 7 mounted on a fan 1 5 intake inlet, and at least partly internally covered with sound-insulating material 1 8 (Figure 1 2).
With reference to the assembly comprising the central unit 4 and the auxiliary pipe 6, as Figures 8 to 1 1 show, in the preferred embodiment it is obtained from a plurality of concentrically mounted, substantially cylindrical tubular elements 1 9, with a predetermined fluid, whether fuel or air, flowing between most of them.
The central unit 4 comprises at least one device 20 which in practice is intended to supply an air/fuel mixture, and at least one outer duct 21 mounted coaxially with and around the device 20. The outer duct 21 is fed by the feed means 9 with air which in practice is intended for mixing with the mixture that comes out of the device 20.
In more detail, the device 20 for supplying the mixture comprises a central tube 22 for supplying a liquid fuel surrounded by an inner duct 23 fed with air by the feed means 9, and means 24 for nebulising the fuel fed out of the central tube 22 by means of the air arriving from the inner duct 23. As shown in Figure 11 , the nebulising means 24 comprise a fuel supply head 25 mounted at the end of the central tube 22 and equipped with a plurality of radial fuel outfeed holes 26 (radial relative to the axial direction F of flame emission which corresponds to the main direction of extension of the central unit 4 and of the auxiliary pipe 6). The outside of the head 25 substantially has the shape of two cones/truncated cones with opposite respective bases, the radial holes 26 giving onto an annular groove 27 positioned at said bases. The nebulising means 24 comprise a hollow shaped element 28 positioned at the end of the inner duct 23 at the supply head 25. The hollow part of the shaped element 28 has the shape of two truncated cones with the lower bases together and positioned close to the radial supply holes 26 (that is to say, the supply head 25 maximum width point). In this way, the inner duct 23 has a minimal cross-section 29 for passage substantially at the outfeed of the supply holes 26 (precisely, just upstream of them). The central unit 4 comprises first means for making the air rotate which are mounted in the inner duct 23, advantageously comprising first fixed blading 30.
Consequently, the fuel which comes out of the radial holes 26 is struck by an air flow which advances at high speed with a predetermined rotational component. The drop of fuel is therefore nebulised and distributed on the inner surface 31 of the diverting part 32 of the shaped element 28, on which a film of fuel is formed which gradually advances towards the flame emission outlet 5 where it is intercepted by the air arriving from the outer duct 21 .
To optimise this mixing, the outer duct 21 has a tapered final section 33 as well as second means for making the air rotate (also advantageously comprising fixed blading 34) which are mounted inside it (Figure 6). Advantageously, the first and second means for making the air rotate are made in such a way that they impart to the air a rotation in the opposite direction.
In the preferred embodiment, the central unit 4 is designed to also be able to operate with a gaseous fuel. For that purpose, the air/fuel mixture supply device 20 comprises an outer tube 35 for supplying a gaseous fuel mounted coaxially with and around the inner duct 23. In particular, the fuel supply outer tube 35 is mounted coaxially between the inner duct 23 and the outer duct 21 and is fed with the fuel by means of a radial pipe 36. The outer tube 35 comprises, at the flame emission outlet 5, a supply element 37 which plugs it and which is equipped with a plurality of outfeed holes 38 angled in such a way that they supply the fuel with a rotational movement component. In other embodiments, not illustrated, the burner 1 may be fed only with a liquid fuel or only with a gaseous fuel.
In all of the fluid paths of the central unit 4 there may be axially angled blades 39 of the type shown in Figure 6 with reference to the outer duct 21 . The auxiliary pipe 6 is mounted coaxially with and around the central unit 4 and is internally divided into a plurality of axial compartments 40 by one or more sets of fixed blades 41 .
Advantageously, the auxiliary pipe 6 comprises Venturi effect intake means 42 in an intermediate position between its first inlet section 8 and the outlet 7 and in turn comprising at least a second inlet section 43 which puts into communication the outside and the inside of the auxiliary pipe 6 (Figure 12). In the embodiment illustrated, the second inlet section 43 comprises a circular opening 44 made along the entire outer wall of the auxiliary pipe 6 at a stretch where the auxiliary pipe 6 has a narrowing in its working cross- section and therefore an increase in the speed of the air in transit. Said narrowing is obtained by means of a separator 45 transversal to the auxiliary pipe 6 through which a plurality of cylindrical sleeves 46 extend, evenly distributed along the entire cross-section of the auxiliary pipe 6, through which the air passes.
Advantageously, the second inlet section 43 also comprises an annular covering element 47 positioned at a predetermined distance from the circular opening 44 and is at least partly internally covered with sound- insulating material.
Finally, in the known way, the burner 1 is equipped with an igniter 48 and a flame detector 49 (whose inspection hole 50 is visible in Figure 11 ).
Finally, this invention relates to a method for using a burner 1 for drying cylinders of the type comprising a central unit 4 having a flame emission outlet 5 and which can be fed with at least one fuel and at least a first primary air flow for combustion, and also having at least one auxiliary pipe 6 mounted around the central unit 4 and comprising an outlet 7 positioned around the flame emission outlet 5 and at least a first inlet section 8 which can be fed with a secondary air flow for combustion.
The method comprises the operating step of independently adjusting the quantity of air fed to the central unit 4 and that supplied to the auxiliary pipe 6 so as to adjust the shape and size of the flame produced. In particular, the method comprises reducing the quantity of air fed to the central unit 4 and increasing that fed to the auxiliary pipe 6 so as to obtain a longer, narrower flame (also thanks to the reduced rotation imparted to the primary air) and increasing the quantity of air fed to the central unit 4 and reducing that fed to the auxiliary pipe 6 so as to obtain a shorter, wider flame (also thanks to the greater rotation of the primary air obtained in this case).
The method just described can be used for adjusting the shape and size of the flame even in the burner 1 described above.
It should also be noticed that, thanks to the significant flow resistance caused by the structure of the inner duct 23, the air flow through it varies very little for a primary air adjustment range between 30% and 1 00% opening of the first adjusting means 1 0. In the embodiment illustrated, primary air adjustment therefore mainly affects the quantity of air flowing through the outer duct 21 .
Another adjustment possibility is provided by the use of an inverter for controlling the fan 1 5 speed of rotation.
The rest of its operation is the same as that of prior art burners.
This invention brings important advantages.
First, thanks to this invention it was possible to make a burner for drying cylinders which allows adjustment of the shape of the flame according to operating requirements.
Second, thanks both to the method for mixing the air with the fuel, and in particular the structure and position of the air feed means 9, it was possible to make a burner for drying cylinders which has high efficiency and a low level of emissions.
Finally, it should be noticed that this invention is relatively easy to produce and that even the cost linked to implementing the invention is not very high. The invention described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept. Moreover, all details of the invention may be substituted with other technically equivalent elements and the materials used, as well as the shapes and dimensions of the various components, may vary according to requirements.
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