EP0346284B1 - Burner for the combustion of liquid fuel in the gaseous phase - Google Patents

Abstract

A stationary gasifier (17) is located at a distance (49) from an air aperture plate (35). At the outlet (42) of the gasifier there is a stationary mixing head (29) having a deflector section (31) and lateral outlets (33). Fuel is supplied coaxially through an opening (55) of the air aperture plate. A flame tube (21) surrounds the gasifier (17) and an electric heater (39) leaving an annular space (40). When the burner is started up, the electric heater (39) is switched on until the gasifier has the necessary operating temperature. Fuel is then supplied. The fuel/air mixture is ignited by an electrode (65). The flame tube (21) extends to the end of the mixing head (29), or only a little therebeyond. A flame is formed at the outlets (33) that touches the flame tube after a short travel, then emerges from it and expands. Because the flame can immediately expand, only little NOx is formed. A portion of the hot combustion gases is recirculated through the annular space (40) and sucked into the gasifier to heat the gasifier (17) after the shutoff of the electric heater (39).

Description

The invention relates to a burner for the combustion of liquid fuels in the gaseous state, with a stationary carburetor which has an inlet proximally and an outlet distally, a flame tube which surrounds the carburetor, the space between the carburetor and the flame tube as a recirculation path for hot Combustion gases serve to the inlet of the carburetor, and a fuel supply to the carburetor. Such a burner is described in EP-A-232 677.

A burner with a burner chamber is known from DE-A 26 49 669, in the front area of which a rotating evaporator pot consisting of a base and a jacket is arranged. The outlet opening of the evaporator pot is arranged at an axial distance from the end wall of the combustion chamber. The jacket of the evaporator pot is surrounded by an annular deflection chamber at a radial distance, forming an injector channel through which air flows. As described in DE-A 33 46 431 for the burner described, it provides a good mixture of fuel and combustion air with a sufficient excess of air, which is shown in a blue flame. However, a high excess of air is not permissible for continuous operation, since the CO2 value and thus the combustion efficiency do not meet the requirements. The excess air even disturbs the thermal balance in such a way that condensation occurs on the rear wall. When operating in the near-stoichiometric range, there is a deterioration in the mixing of the oil vapor with the fresh air and the combustion gases. If, in order to improve the mixing, stumbling edges, bypasses or a change in the injector geometry were carried out, this reduced the injector effect. This in turn resulted in less combustion gas being recirculated. Then there was a disturbance in the temperature equilibrium, signs of condensation and an inadmissibly high increase in NOX and CO values.

DE-A 33 46 431 therefore set itself the task of improving the burner according to DE-A 26 49 669 in such a way that the oil vapor is mixed well with the fresh air and the combustion gas without influencing the injector effect. The improved burner also has a rotating evaporator pot. This is closed on the flame side and only has an outlet for the vaporized fuel on the engine side. The evaporator pot is provided with several rows of recesses distributed over the circumference and surrounded by an annular deflection chamber for the air supply. Gasified fuel and air then flow between the evaporator pot and the flame tube in two concentric streams of annular cross-section, meet a baffle ring, mix and then form a flame. However, it is disadvantageous that the evaporator chamber is not exposed to a strong flow of hot gases, so that deposits form there, which soon impair the function of the burner. In particular when the burner is switched off, there is a strong release of unburned hydrocarbons.

FR-A 2 269 029 also shows a burner which has a rotating evaporator pot which is distal, i.e. flame side, is closed. The inside of the evaporator pot is lined with a wire mesh, which serves to prevent the fuel from escaping. This burner requires a powerful fan with a relatively high energy consumption because both the fresh air and the air / gas mixture are deflected several times. Another disadvantage is that after the burner has been switched off, a lot of fuel still evaporates from the wire network which has previously been coated with air and therefore has remained relatively cool, so that there is a strong release of unburned hydrocarbons.

In the burner according to CH-A 628 724, a so-called mixing tube and a flame tube are provided coaxially with a nozzle.

In operation, the oil is injected through the nozzle into the mixing tube, into which the air necessary for combustion is also blown. A flame then forms at the distal end of the mixing tube. Part of the hot combustion gases is then recirculated to the beginning of the mixing tube by the action of an injector and mixed there with the oil / air mixture for the purpose of heat exchange. Thanks to the recirculation of some of the combustion gases, this burner enables the oil droplets in the mixing tube to be largely gasified and thus relatively good combustion with relatively little soot formation. However, this advantage is paid for by the increased formation of nitrogen oxides (NOX). The burner requires a long flame tube. Since the flame relaxes only after it has emerged from the flame tube, there is a relatively large flame zone with high temperatures, which favors the formation of nitrogen oxides. Another disadvantage of the burner is that the mixing tube is cold at the start and therefore has no vaporizing effect. The flame is therefore sooty until the mixing tube reaches a high temperature and is able to effectively evaporate the oil that hits it.

In Patent Abstracts of Japan, Volume 12, No. 31 (M663) 2878, January 29, 1988; JP-A-62 186 114 describes a kerosene burner which has an electrically heatable evaporator pot, into which fuel and air are introduced laterally in order to produce an air / fuel premix. A mixing plate with a central opening is arranged above the evaporator pot, through which the premix can rise into a cylinder closed with a cover and can exit the cylinder through a large number of pores and through the mesh of a wire mesh, where it is ignited. A number of hollow heat radiators, which have air holes, are arranged around the cylinder surrounded by the wire mesh. Secondary air flows through these air holes to form a secondary flame in addition to the primary flame on the wire mesh, at the end of which a practically complete combustion takes place. The flame is surrounded all around by a combustion cylinder, which expands it radially prevents. Because of this and because of the lack of recirculation of combustion gases, the flame is relatively hot, so that a relatively large amount of NOX is formed.

It is an object of the present invention to provide a burner of the type mentioned at the outset which at least partially avoids the disadvantages mentioned. It should be reliable and require little maintenance work. It should also meet high environmental protection requirements and ensure clean combustion, generate little nitrogen oxides and, when switched on and off, should not cause any emissions of unburned hydrocarbons.

According to the invention, this is achieved in a burner of the type mentioned at the outset in that a stationary mixing head with outlet openings for a combustible gas mixture is arranged at the outlet of the gasifier, that a deflection section is provided on the mixing head for deflecting the escaping gas mixture in a practically radial direction and that the flame tube extends to the end of the mixing head or only slightly beyond. There is thus a combination, with a stationary carburetor which has an inlet proximally and an outlet distally, a flame tube which surrounds the carburetor, the space between the carburetor and flame tube serving as a recirculation path for hot combustion gases for the carburetor inlet, a fuel supply to the carburetor and a stationary mixing head at the outlet of the carburetor, the stationary mixing head having a deflection section for deflecting the emerging gas mixture in a practically radial direction and the flame tube extending to the end of the mixing head or only a little beyond. This combination contains no moving elements and is therefore very reliable. Due to the recirculation of hot gases, the gasifier is heated up, which practically prevents the formation of coking. The high temperature of the carburetor also causes the fuel to evaporate reliably when the burner is switched off, so that it burns Stage there are no inadmissible emissions of unburned hydrocarbons. Of particular importance is the fact that the flame tube can be dimensioned relatively short without impairing the injection effect and thus the return of the hot combustion gases to the gasifier inlet. According to the invention, the flame tube extends only to the end of the mixing head or only a little beyond, the mixing head at the end of the gasifier causing the flame to be in contact with the flame tube after a short distance and to come out of it and relax. This reduces the flame temperature. A low flame temperature has the major advantage from the point of view of environmental protection that only little nitrogen oxides are formed.

Carburetor and mixing head can form a single unit. For example, the carburetor and the mixing head can be tubular. The unit can then be made from a piece of pipe or from one consist of a piece of pipe shaped sheet metal. This considerably simplifies and reduces manufacturing costs. In order to prevent fuel from leaking at the ends of the pipe section, an annular, radially inwardly directed section, for example a constriction, is expediently provided at the outlet end of the carburetor. It is also possible to provide a radially inward extension at the inlet of the carburetor. This can be produced, for example, by flanging.

In order to be able to heat the carburetor when the burner is switched on, an electric heater is expediently arranged on the carburetor. The carburetor is then heated up before the fuel supply is switched on. This avoids that unburned hydrocarbons are released to an unacceptable extent at the start of the heating process. The carburetor, mixing head, deflection part, air panel and electric heater advantageously form a single structural unit. Such a unit can be easily replaced during service work.

The flame tube is advantageously arranged coaxially with the carburetor and with the electric heater. This results in a particularly expedient construction in which the recirculated hot combustion gases heat the carburetor evenly.

The combination of the electrical heating and the recirculation path has the advantage that the electrical heating can be switched off shortly after the start, because the carburetor is kept at the desired high operating temperature by the recirculated hot gases.

Different types of fuel supply to the carburettor are possible. For example, a spray rotor can be provided at the inlet, which causes a uniform distribution of the fuel in the carburetor. Especially for burners For greater performance, it is advisable to provide an atomizer nozzle at the inlet. This can preferably be arranged coaxially with the carburetor. The fuel can be finely distributed over the carburetor walls using an atomizing nozzle. A hollow cone nozzle is particularly expediently used as the atomizing nozzle. The atomizer nozzle can also be designed such that at least one spray jet with a limited scattering angle is directed against the carburetor wall. In this case, it is expedient if the air diaphragm has a shielding section in the area of the respective spray jet. Through this section, the spray jet is then shielded from the incoming air in such a way that it safely reaches the carburetor wall. Then no oil droplets are entrained with the air flow and shipped to the mixing head.

The air screen is advantageously arranged at a distance from the carburetor, the gap between the air screen and the carburetor forming a recirculation inlet. Thanks to this arrangement, it is primarily the hot recirculating gases that run along the inner wall of the carburetor, while the cold air flows more inside the carburetor. Good evaporation of the fuel is thereby achieved and re-vaporization of the fuel is avoided after the burner has come to a standstill. When the burner is switched off, the carburetor is still so hot that the remaining fuel will evaporate shortly and be burned with the air that is still being pumped until the burner comes to a standstill.

The carburetor advantageously has a surface-enlarging center, for example a metal mesh. This increases the effective surface area of the fuel film and accelerates gasification. When using a metal mesh or a porous sintered mass, capillary forces also become effective, which facilitate the distribution of the fuel over the entire wall of the carburetor. Expediently, the surface enlarging Means formed by an insert which occupies the inner wall of the hollow body. Such an insert can easily be replaced when necessary for revision work. Because the liquid fuel comes into contact with the surface-enlarging metal mesh as it emerges, capillary forces are immediately effective, which endeavor to distribute it over the entire inner surface of the carburetor. The insert advantageously has a practically radially inwardly projecting flange. This causes any oil droplets to be trapped and evaporated on the hot surface of the insert. For this reason, the flange of the insert is expediently arranged at the distal end of the gasification chamber.

A Volustat can be provided to control the fuel supply. A volustat is understood to mean a device which, according to an input signal, delivers a corresponding delivery volume per unit of time, which is practically not influenced by resistances in the delivery line. The delivery volume is hardly influenced by the viscosity of the fuel.

An air screen with an opening for air supply to the inlet of the carburetor is advantageously provided. This opening for the air supply is expediently arranged centrally and also serves as a passage for the drive shaft of a spray rotor or as a passage for an atomizer nozzle.

It is possible to arrange the burner in a vertical position instead of the usual horizontal position. This increases the possible uses of the burner.

Fig. 1

eine Ansicht eines Brenners gemäss der Erfindung,

Fig. 2

einen Schnitt durch eine erstes Ausführungsbeispiel des Brenners mit einer Zerstäuberdüse,

Fig. 3

einen Schnitt entlang der Linie III-III von Fig. 2,

Fig. 4

einen Schnitt durch eine zweites Ausführungsbeispiel des Brenners mit einem Sprührotor,

Embodiments of the invention will now be described with reference to the drawing. It shows:

Fig. 1

2 shows a view of a burner according to the invention,

Fig. 2

2 shows a section through a first exemplary embodiment of the burner with an atomizing nozzle,

Fig. 3

2 shows a section along the line III-III of FIG. 2,

Fig. 4

3 shows a section through a second exemplary embodiment of the burner with a spray rotor,

The burner shown in Fig. 1 has a motor 11 which serves to drive the fuel pump 13, the fan 15 and optionally a spray rotor 18 (Fig. 4). A fuel line 19 leads from the fuel pump 13 to the carburetor 17 (FIG. 3), which is enclosed by a flame tube 21. The flame tube can be easily removed by loosening the screws 23. A Volustat, a solenoid valve or another suitable device 25 serves to control the fuel supply in accordance with the control commands of the heating control 26. Volustaten are supplied, for example, by the company SATRONIK, Regensdorf, Switzerland.

Fig. 2 now shows an easily replaceable assembly 27, which consists essentially of the carburetor 17, the mixing head 29 forming a unit with the carburetor 17 and having a deflection section 31, the air screen 35, the electric heater 39 and possibly other parts. The assembly 27 is enclosed by the flame tube 21. This is relatively short. It therefore only extends to the end of the mixing head 29 or only slightly beyond. The space 40 between the carburetor 17 and the flame tube 21 form a recirculation path for hot combustion gases to the inlet 41.

Carburetor 17 and mixing head 29 are designed as hollow rotating bodies. In the embodiment shown, the carburetor 17 and mixing head 29 consist of a single piece of pipe 30 which is closed at the front by a disk 31. The disk 31 serves as a deflection section for the gas mixture. The gas mixture generated in the mixing head can exit through a large number of outlet openings 33. In the exemplary embodiment shown, the outlet openings 33 are slot-shaped. However, a different shape is also possible. Since the outlet openings 33 are located in the cylindrical lateral surface 36 of the mixing head, the gases emerge on the mixing head 29 in a practically radial direction. The boundary between the carburetor 17 and the mixing head 29 is formed by a constriction 37 in the exemplary embodiment shown. This constriction 37 forms an annular, radially inwardly directed section 37 'at the distal outlet 42 of the carburetor 17, which prevents liquid fuel from flowing out of the carburetor 17 into the mixing head 29. At the proximal end 41, i.e. at the inlet of the carburetor 17, an inwardly directed extension 43 prevents liquid fuel from flowing out.

The unit 45 consisting of the carburetor 17 and the mixing head 29 is fastened, for example, to the air shield 35 by spot welding, rivets or the like with three feet 47, which can represent extensions of the tube 30. Through the Gaps between the feet 47 create recirculation inlets 49.

The assembly 27 is attached to an extension ring 51 of the flame tube 21, for example with screws (not shown). A sealing ring 53 made of a heat-resistant material ensures a practically airtight seal. This ensures that the air necessary for combustion can only flow through the central opening 55 of the air screen 35.

The carburetor 17 is enclosed by the electric heater 39. In the exemplary embodiment shown, the electrical heater 39 is arranged concentrically to the carburetor 17 at a short distance. In this case, the carburetor 17 is heated only by radiant heat. A better heat transfer is achieved if the winding of the electric heater 39 is in direct contact with the wall of the carburetor 17.

It has proven to be advantageous to provide surface-enlarging means 57 in the carburetor 17. These can consist, for example, of an insert 57 made of a metal mesh. Such a metal mesh creates a capillary effect through which the fuel is finely distributed over the inner wall of the carburetor. However, it would also be possible to provide a coating of porous ceramic material on the inner wall of the carburetor 17. The insert 57 has a practically radially inwardly directed flange 58, which serves to catch any oil droplets so that they do not get into the mixing head 29. An atomizer nozzle 59 is provided at the inlet 41 of the carburetor 17. It is a hollow cone nozzle. In the exemplary embodiment according to FIG. 3, the nozzle 59 has four different spray jets 61 with a limited scattering angle. To spray these against a To protect deflection by the inflowing air, the air screen 35 has a shielding section 63 in the area of the respective spray jet 61.

In the embodiment of FIG. 4, a spray rotor 18 is provided instead of an atomizing nozzle 54, which is driven by the motor 11 (FIG. 1) via the shaft 20. The fuel line 19 leads in the immediate vicinity of the spray rotor 18. The ignition electrode 65 projects into the carburetor chamber. The ignition in the carburetor chamber has the advantage that a pressure surge during ignition is largely avoided. So there is a soft start. The ignition also takes place quite quickly because at the start in the carburetor 17 there are higher temperatures than at the outlet openings 33 of the mixing head 29.

Claims (22)

1. A burner for the combustion of liquid fuel in the gaseous state, comprising a stationary gasifier (17) having a proximal inlet (41) and a distal outlet (42), a flame tube (21) enclosing the gasifier (17) with a space located in between, said space (40) between the gasifier (17) and the flame tube (21) serving as recirculation path for hot combustion gases to the inlet (41) of the gasifier (17), and fuel supply means (19, 59) to the gasifier (17), characterised in that at the outlet of the gasifier (17) a stationary mixing head (29) with outlet openings (33) for a combustible gas mixture is located, in that at the mixing head (29) a deflector section (31) is provided for deflection of the outflowing gas mixture in practically radial direction and in that the flame tube (21) extends to the end of the mixing head (29) or little beyond.
2. A burner as claimed in claim 1, characterised in that the gasifier (17) and the mixing head (29) form a single unit.
3. A burner as claimed in claim 1 or 2, characterised in that the gasifier (17) and the mixing head (29) are of tubular form.
4. A burner as claimed in one of the claims 1 to 3, characterised in that at the outlet (42) of the gasifier (17) an annular, radially inwardly oriented extension (37′), for example formed by a necked-down portion, is provided.
5. A burner as claimed in one of the claims 1 to 4, characterised in that at the inlet (41) of the gasifier (17) an inwardly extending flange (43) is provided.
6. A burner as claimed in one of the claims 1 to 5, characterised in that an air aperture plate (35) with an opening (55) for the supply of air to the inlet (41) of the gasifier (17) is provided.
7. A burner as claimed in one of the claims 1 to 6, characterised in that at the gasifier (17) an electric heater (39) is provided.
8. A burner as claimed in claim 7, characterised in that the gasifier (17), the mixing head (29), the deflector section (31), the air aperture plate (35), and the electric heater form a component unit.
9. A burner as claimed in claim 7 or 8, characterised in that the flame tube (21) is arranged coaxially to and spaced apart from the gasifier (17) and the electric heater (39).
10. A burner as claimed in one of the claims 1 to 9, characterised in that at the inlet (41) a rotating spraying device (18) is provided.
11. A burner as claimed in one of the claims 1 to 9, characterised in that at the inlet (41) an atomizer nozzle (59) is located preferably coaxially to the gasifier (17).
12. A burner as claimed in claim 11, characterised in that the atomizing nozzle is a hollow cone nozzle.
13. A burner as claimed in claim 11 or 12, characterised in that the atomizing nozzle is designed to direct at least one atomized fuel beam (61) of limited divergence angle against the wall of the gasifier.
14. A burner as claimed in claim 13, characterised in that the region of the respective atomized fuel beam (61) the aperture plate (35) is provided with a shield section.
15. A burner as claimed in one of the claims 6 to 14, characterised in that the air aperture plate (35) is located at a distance from the gasifier (17), with the gap between the aperture plate and the gasifier (17) providing a recirculation inlet (49).
16. A burner as claimed in one of the claims 1 to 15, characterised in that the gasifier has means (57), such as metal cloth, for increasing its surface area.
17. A burner as claimed in one of the claims 1 to 14, characterised in that the means for increasing the surface area are formed by an insert (65) which at least partially covers the inner wall of the gasifier (17).
18. A burner as claimed in one of the claims 1 to 17, characterised in that the insert has a flange (66) protruding practically radially inward.
19. A burner as claimed in claim 18, characterised in that the flange (58) of the insert (57) is located at the distal end of the gasifier (17).
20. A burner as claimed in one of the claims 1 to 19, characterised in that a ignition electrode (65) is located at the inlet (41) to the gasifier (17).
21. A burner as claimed in one of the claims 1 to 20, characterised in that a volustat (25) is provided for the control of the fuel supply.
22. A burner as claimed in one of the claims 1 to 21, characterised in that the burner is arranged vertically.

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