A burner for liquid fuels

Abstract

 A burner for liquid fuels, in particular fuel oil, operable to encourage an intimate mixing of the fuel with a combustion agent has a plurality of injector ducts (8) from which the fuel is injected into a combustion chamber, the axes of the injector ducts (8) being disposed along generatrices of a hyperboloid of rotation having an axis directed towards the combustion chamber.

Description

[0001] The present invention relates to a burner for liquid fuels, provided with injector nozzles having a particular spatial disposition.

[0002] It is known that to obtain good combustion of liquid fuels it is necessary to obtain an intimate mixing of the fuel with the combustion agent (normally pre-heated air) in a ratio preferably slightly greater than the stoichiometric ratio. This intimate mixing usually involves a preliminary atomisation of the liquid fuel to break it down to very small droplets, of the order of a few microns in diameter and its subsequent turbulent mixing with the combustion agent, for example by means of copenetration of two fluid streams, one composed of the jet of fuel and the other the combustion agent. The turbulence is often obtained by means of suitable differences between the vector velocities of the streams of the two fluids.

[0003] Various different means are used to obtain atomisation. Indeed atomisers in industrial use can be sub-divided into two main groups, namely a first, purely mechanical group of atomisers, in which the fuel, suitably pre-heated and compressed, is atomised at the output of the atomiser by the combined effect of the high velocity reached in atomisation nozzles, for transformation of the pressure energy into kinetic energy, and subsequent turbulent "impact" at the output of the nozzles in the environment of the combustion chambers. The orientation of the axes of the nozzles can be utilised to optimise the relative velocities for the purpose of improving the atomisation and mixing. The second group of atomisers comprises the so-called assisted atomisation devices. In these latter atomisers the energy for acceleration of the liquid fuel in the nozzles is provided predominantly by steam or other vapour under pressure, or by other gas, whether it is a combustion agent or not. In these latter burners (for the most part belonging to the sub group called in the international field the "jet" type) the fuel and the atomisation fluid are made to flow together in a suitable quantitative ratio and with suitable angles of incidence into the initial part of the burner nozzle or nozzles, and upon expansion of the atomisation fluid flowing along the nozzles towards the combustion chamber the fuel acquires the necessary kinetic energy, required for subsequent atomisation as it enters the combustion chamber from the burner's atomisation nozzle or nozzles.

[0004] The present invention seeks to provide a burner for liquid fuels which is able to provide significant improvements in the mixing process between the fuel and the combustion agent.

[0005] According to the present invention there is provided a burner for liquid fuels, characterised by the fact that it comprises a duct for the delivery of the liquid fuel and a plurality of ducts in a nozzle body, the axes of the injector ducts being disposed along generatrices of a hyperboloid of rotation, the axis of which is directed along the axis of the burner.

[0006] A particular advantage of the present invention is that of providing a burner for liquid fuels, which can be utilised both for purely mechanical atomisation as well as for assisted atomisation by means of an auxiliary fluid.

[0007] Another advantage of the present invention is that it provides a burner for liquid fuels, which is of simple construction and high reliability.

[0008] Three embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal section of a first embodiment of a burner formed, in accordance with the principles of the present invention, as an auxiliary fluid atomising burner;

Figure 2 is a schematic view from above of the atomisation unit of the burner, illustrated in Figure 1 ,

Figure 3 is a longitudinal section of an alternative embodiment similar to the burner illustrated in Figure 1 but provided with conveyor ducts for liquid fuel and vapour which are reversed with respect to the corresponding ducts in the embodiment of Figure 1;

Figure 4 is a schematic view from above of the atomisation unit shown in Figure 3; and

Figures 5 and 6 are schematic sectional views of a further embodiment of the invention functioning with direct thrust, that is to say, provided with a single fuel induction duct.

[0009] Referring now to Figures 1 and 2 of the attached drawings, the burner for liquid fuels shown therein comprises a first cylindrical tubular body 1 for the inlet of steam or other suitable auxiliary fluid under pressure, surrounded by a second cylindrical tubular body 2 coaxial therewith and delimiting an annular chamber 3 along which the liquid fuel is supplied.

[0010] A suitably shaped head 5 is fixed to the adjacent ends of the said two tubular bodies 1, 2 by means of a ring nut 4. More precisely, this head 5 has a central portion 6 communicating with the first tubular body 1 for inlet of the steam, and is shaped with a tubular skirt portion 10 which is sealed against a peripheral flange 12 of the first tubular body 1 by a sealing ring 11. The head 5 also has a perimetral portion 7 communicating with the annular chamber 3 along which the liquid fuel arrives and sealed to the end of the second tubular body 2 by a sealing ring 13.

[0011] In the head 5 there are formed two sets of calibrated ducts, namely a first set of injector ducts 8 which put the interior of the said first tubular body into communication with the surrounding regions outside the nozzle (this will usually be the combustion chamber), and a second set of transverse ducts 9 which communicate at one end with the annular chamber 3 and at the other end with a mid part of a respective injector duct 8 from the first set. The axes of the injector ducts 8 are disposed according to the generatrices of a hyperboloid of rotation. This disposition of the axes of the said injector ducts 8, in practice, permits a relative rotation of the fuel exiting from the ducts to be obtained with respect to the combustion-supporting air the flow of which is introduced parallel to the axis of the tubular bodies 1 and 2 of the burner, thus allowing the adoption of a flame cone over a wide range of choice. This rotational component of the fuel's motion is exploited to improve, in a determined manner, the mixture of the fuel with the combustion agent.

[0012] The burner of the present invention is of extremely practical realisation; in fact as shown, the head 5 can be constituted simply by a single piece formed with two sets of circular holes having rectilinear axes, which axes are arranged to lie according to the generatrices of a hyperboloid. Moreover, it is not necessary for this hyperboloid to be formed with great accuracy although adherence to the pure geometric figure improves the results.

[0013] In large steam generaters the combustion air is sometimes introduced in to the combustion chamber along a duct concentric with the axis of the burner, which duct is provided with means for imparting to the combustion air a rotational component. In such constructional arrangements also, the positive practical effect of the burner according to the invention can be obtained in its entirety, it being sufficient to choose, for the axes of the ducts of the burner, a set of generatrices of a hyperboloid with a suitable axial and circumferential inclination.

[0014] The burner of the invention has, moreover, exceptional robustness and simplicity of maintenance, both of which are very important aspects in industrial installations operating continuously.

[0015] In the alternative embodiment illustrated in Figures 3 and 4 the same reference numerals have been used to identify components fulfilling the same or similar purposes: In this embodiment the inner duct 1 is intended to convey the fuel oil and the annular chamber 3 between the outer duct 2 and the inner duct 1 is intended to convey steam or other compressible fluid. Thus the ducts 8 in the head 5 lead from an inner end in communication with the annular duct 3 to an outer end which communicates with the environment surrounding the burner nozzle itself. Whilst the fuel ducts 9 lead from an end in communication with the interior of the inner duct 1 to an end communicating with a mid portion of the injector ducts 8.

[0016] In the alternative embodiment shown in Figures 5 and 6 there is a single internal duct 1A which conveys the liquid fuel to a nozzle head 7 in which there are formed a single set of ducts 8 the axes of which, as in the embodiments of Figures 1 to 4 lie in accordance with generatrices of a hyperboloid.

[0017] Tests performed on industrial boilers with a capacity up to 1000 t/h of steam production have shown significant improvements, with respect to the use of burners of other type, even with the use of very poor quality heavy liquid fuel oils, which, following conspicuous increases in cost of crude oils, are ever more widely being substituted on the international market for products of this general class available up to the end of the 1970s, because the refineries now exploit the crude oil more greatly to the detriment of the heavy products. The results obtained in the course of tests have been such as to allow, in all cases, the regular functioning of flame protection systems sensitive to ultra violet rays which systems, with burners of other type, had often to be disconnected as soon as the asphaltene content of the oil rose to medium values (8 - 25%). This latter aspect is of particular importance in view of the safety aspect and for security of operation.

[0018] The burner described lends itself, moreover, particularly in the "jet" type arrangement to the adoption of multiple injectors which cause the fuel and/or the atomisation fluid to flow into many distinct points along the axis of the nozzle.

Claims

1. A burner for liquid fuels, characterised by the fact that it comprises a duct (1,3) for the delivery of the liquid fuel and a plurality of injector ducts (8) in a nozzle body (5,7), the axes of the injector ducts (8) being disposed along generatrices of a hyperboloid of rotation the axis of which is directed along the axis of the burner.

2. A burner-for liquid fuels according to Claim 1 , characterised by the fact that it includes a first cylindrical tubular body (1) for delivery of either liquid fuel or an auxiliary fluid under pressure, the first tubular body (1) being coaxially surrounded by a second cylindrical tubular body (2) and delimiting an annular duct (3) for delivery of either auxiliary fluid under pressure or liquid fuel respectively.

3. A burner for liquid fuels, according to Claim 2, characterised by the fact that the nozzle body (5,7) comprises a head (5) fixed to the end of the outer tubular body (2) by means of a ring nut (4), the head (5) having a central portion (6) communicating with the first inner tubular body (1) and a perimetral portion (7) communicating with the said annular duct (3).

4. A burner for liquid fuels, according to Claim 3, characterised by the fact that in the said head (5) there are formed calibrated injector ducts (8) able to put the interior of the said first tubular body (1) into communication with the environment outside the burner, each of the said calibrated injector ducts (8) communicating at an intermediate point therealong with a transverse duct (9) communicating with the said annular duct (3) between the said first and second tubular bodies (1,2).

5. A burner for liquid fuels as in one or more preceding Claims, characterised by the fact that the axes of the injector ducts (8) therein are skew and do not lie in pairs on the same plane.

6. A burner for liquid fuels according to Claim 3, characterised by the fact that in the said head (5) there are formed calibrated injector ducts (8) leading from th= annular duct (3) between the first and second tubular bodies (1,2) to the environment around the burner, and a plurality of transverse ducts (9) each leading from an end communicating with the interior of the said inner tubular body (1) to an end communicating with a respective injector duct (8).

7. A burner system for liquid fuels, comprising a burner according to any preceding Claims and an air supply means, characterised by the fact that the air supply means directs air parallel to the axis of the burner and the arrangement of the said injector ducts (8) is such that the outflowing fuel rotates with respect to the combustion air flowing parallel to the axis of the burner itself.

Drawing