EP0867658B1 - Process and device for combustion of liquid fuel - Google Patents

Abstract

Liquid fuel is sprayed into the flame tube (15) of an oil burner in front of the flame root (77), entering returning flue gas and evaporating there. Flue gas enriched with the fuel is mixed in a turbulent manner with air (71). The air is preferably injected into the flame tube through a central orifice (29) in a baffle disc (13) and the flue gas enters at the disc end of the flame tube so that it sheathes (67) the central air stream (69). Also claimed is an oil burner with flue gas recirculation in which the spray orifice (21) of the fuel nozzle (23) is in the plane of the baffle disc producing low pressure and the disc has a ring-shaped air inlet around the fuel nozzle.

Description

The present invention relates to a method for Combustion of liquid fuel by means of a Oil burner in which the fuel is in a flame tube sprayed, air blown into the flame tube and exhaust gas through Suction effect of the air is returned to the flame tube and a device for implementing this method.

EPA 0 655 580 describes an oil burner, at which is a nozzle in a cone-like nozzle chamber is arranged. The nozzle chamber has a cylindrical one Section on that on one side of an end wall and on the other side of a truncated cone Area is limited. Two protrude through the end wall Ignition electrodes. The nozzle chamber is one with radial Slotted baffle plate connected to the by the side facing away from the nozzle is connected to a tube, which has slot-shaped openings. That the Breakthrough tube is coaxial in one arranged another tube. The two pipes are over one conical section joined together. The whole is from surround a jacket called a mixing tube, which on End has a flange so that between the flange and an annular gap in the perforated tube is formed. Is on the flame side of the mixing tube an outer recirculation pipe and an inner flame pipe. Around The recirculation pipe is to facilitate the cold start an electrical resistance heater. If air is out flows into the above-mentioned annular gap, it comes to a negative pressure, which is used for the recirculation of exhaust gases the inner flame tube provides.

The measures described arise shortly after Nozzle a core flame zone with a yellow core flame that is about 10 up to 30% of the fuel with lack of air with increased Exhaust emissions burns. This yellow core flame becomes Blue flame stabilization needed. To the core flame around and further downstream there is a blue flame that 70 to 90% of the fuel burns. Because the nozzle Spraying fuel into the core flame, gasification and Combustion both in the core flame and in the Main flame.

The burner described has the disadvantage of a very complicated and expensive construction. Another disadvantage is that he had an electric one for a good cold start Resistance heating is required, which is also considerable Cost factor in the manufacture and operation of the burner represents. The disadvantage for the stable Burning required yellow core flame, which made it difficult power, the limits for carbon monoxide and unburned Comply with hydrocarbons and also because of Soot formation the operational safety of the burner impaired.

From EP-A-0410 135 is a burner for liquid or known gaseous fuel, in which one of the Fuel atomizing atomizer nozzle from one Air supply line is surrounded. One in a boiler room protruding burner tube is equipped with an orifice and forms a combustion chamber. There are savings in the burner tube provided with certain dimensions and proportions to Introduce exhaust gas from the boiler room into the combustion chamber. These cutouts are in the area facing the aperture provided the burner tube. The atomizer nozzle comes with a fan or the like over the Air supply line is supplied with combustion air. The Atomizer nozzle atomizes the fuel in a full cone shape the combustion air. Exhaust gas is created by the injection effect of combustion air and fuel through the cuts sucked into the burner tube and the flame in the Flame root added to cool the flame.

It is therefore an object of the invention, a method and to create a device which the combustion of liquid fuel with low pollutant emissions enables. The burner should continue without feeding External energy have a very good starting behavior and practically quiet regardless of the shape of the furnace and burn stably. The burner should continue easy to maintain and inexpensive to manufacture. The essential components of the burner are intended for both the combustion of gas as well as oil. This is supposed to the burner by small changes from gas to oil or from Oil to gas can be switched.

According to the invention, this is achieved by a method where practically all of the fuel in front of the flame root goes into that recirculated exhaust gas is sprayed and evaporated in the exhaust gas, and the exhaust gas enriched with vaporized fuel with the Air is swirled.

By spraying practically all of the fuel into the exhaust gas in front of the flame root, it reaches a low-oxygen and hot environment without flame formation in a first phase and vaporizes very quickly and completely. The mixture of exhaust gas and fuel vapor is only swirled with the air in a second phase and then burns blue at a relatively low temperature at which hardly any nitrogen oxides are formed. By separating the gasification phase from the combustion phase, the fuel is only burned in the fully gasified state, which also has a positive effect on the other exhaust gas values. With this process, exhaust gas values for NO _x of less than 60 mg / kW and for CO of less than 16 mg / kW are achieved. No unburned hydrocarbons can be detected practically immediately after starting.

The air is advantageous through a central opening in a baffle plate is blown into the flame tube and the exhaust gas at the baffle plate end of the flame tube let in that it encases the central airflow. As Alternatively, the reverse is also possible namely that the air flow encases the exhaust gas flow. This brings the advantage that the fuel is central in the exhaust gas flow is atomized and the flame expand and thereby cool can burn. For constructional reasons, however, it does especially a method with a central air flow. The Flame tube is in operation of the burner in a combustion chamber arranged and is therefore surrounded by exhaust gas. On the Exhaust gas is thus everywhere available on the outside of the flame tube Disposal and air can be very easily in a central Beam are fed.

The fuel can be injected directly into the low-oxygen and hot vacuum area sprayed become. But since a single nozzle is less prone to failure and is structurally less expensive, the fuel advantageous with a cone-shaped nozzle from the center of the air flow out of the air flow into the hot and low-oxygen exhaust jacket sprayed. It becomes the kinetic Energy from the fuel droplets used to the central Air flow to penetrate and to the periphery in the interior of the flame tube.

For this purpose, the fuel is advantageously at an angle of 30 to 45 degrees to the flame tube axis towards the inner one Wall of the flame tube sprayed. The speed of the Air flow and the axial velocity component of the Fuel droplets are advantageously similar, so the kinetic energy of the fuel droplets mainly to do so can be used to cross the air flow. A preferred cone jacket characteristic of a fuel nozzle has 80 °.

The air flow is advantageous in rotation around the Flame tube axis offset. This creates a stable Swirling the air flow with the fuel vapor / exhaust jacket.

This is advantageous on the inner wall of the Flame tube of fuel vapor / exhaust gas mixture flowing downstream by narrowing the flame outlet opening on Flowing out of the flame tube prevented and with the air swirled. This will make the fuel / exhaust jacket forced to mix with the airflow. Through the The flame is also held narrowing on the flame tube.

The invention also relates to an oil burner Exhaust gas recirculation, with a centrally located Fuel nozzle with a cone jacket characteristic, one Baffle plate with air opening and in the direction of flow to the Baffle plate then a flame tube, which in Openings near the baffle plate for the admission of exhaust gas into Vacuum area in the flow direction behind the baffle plate having.

The fuel in the invention Burner arrangement according to the procedure outlined above evaporates in a jacket area in the exhaust gas by the Spray opening of the fuel nozzle approximately in the plane of the Vacuum-producing baffle plate lies and the baffle plate has only one opening, which has an annular, Air inlet arranged concentrically around the fuel nozzle forms. As a result, the nozzle preferably sprays at an angle from 40 degrees to the flame tube axis through the fuel Airflow in the exhaust jacket. This with fuel vapor Enriched coat layer is then with the swirled central airflow. The flame is hollow at the root with a circular cross section, and burns from the evaporation zone near the flame tube wall the center with the air flow. During the evaporation zone is hot and low in oxygen because it has hot exhaust gas is fed and hot in the immediate vicinity Flame tube is the fire zone by the air flow cooled and oxygenated. The surface of the Flame is due to its hollow shape in relation to its volume larger and therefore the flame is easier to cool than with a full one Flame bodies and the burning happens in the neighborhood to the cooling air flow and not to the hot exhaust gas. Thereby that the gasification zone through exhaust gas and flame tube wall heated up and the fire zone cooled by the air, there is a smaller temperature gradient between Flame root and flame tip, i.e. the flame has one balanced temperature at a low level.

The gasification in the hot exhaust gas and away from the cold air flow during a cold start out. As soon as the oxygen in the combustion chamber burns, i.e. immediately after the cold start, is the Gasification zone in the hot, recirculated exhaust gas. The Fuel turns into fractions within a fraction of a cold start Second completely gassed. After about a half Second the flame is already burning blue.

We are made aware of a preheating of the fuel waived. This can be done thanks to the excellent Cold start behavior can also be done with ease not only cheap on the manufacturing costs and the Affects electricity consumption. By foregoing one Preheating the fuel is a risk of coking Nozzle banned at low outputs. The burner can even without accompanying measures up to a minimum performance from about 8.5 to 9 kW. With a Frequency pump, i.e. a pump that has a pulsating Generates the minimum power lower further down to approx. 6 kW.

The burner according to the invention thus not only enables combustion according to the above Process, but is essential in manufacturing easier and therefore less expensive since it consists of less and easier to assemble parts. In addition is maintenance completely unproblematic. The are also suitable most parts also for the production of a gas burner.

The air opening of the baffle plate is also advantageous swirl-generating guide surfaces to provide the desired To cause rotation of the air flow.

Is advantageous between the flame tube and baffle plate essentially circulating recirculation slot with a Opening width of at least 0.2 mm for self-cleaning of the Baffle plate arranged. This slot causes one reliable cleaning of the surface of the baffle plate by recirculated exhaust gas sweeps along this. This will a soot deposit on the baffle plate is prevented. The Recirculation slot is different depending on whether additional Recirculation openings are provided or not to dimension differently. To a soot deposit Preventing the baffle plate is one Appropriate minimum opening width of 0.2 mm.

The flame tube with spacers is advantageous Fasteners attached to the baffle plate. The assembly the flame tube on the baffle plate is very easy. The Opening width is thanks to the integrated spacers given. There are preferably three of them Links, because at least three attachment points needed for a stable connection, a larger one Number but no advantages.

Are advantageous in the flame tube wall in A large number of baffle plates near the baffle plate arranged from recirculation openings. This Recirculation openings can be designed such that the sucked-in exhaust gases form vortices so that the injected and vaporized fuel with the exhaust gas is thoroughly mixed.

The flame tube at its outlet opening is advantageous narrowed. The constriction holds the exhaust gas / fuel vapor jacket back in the flame tube, thereby promoting its swirling with the central airflow. The narrowing also prevents detachment of the flame from the flame tube. A practical one Constriction makes up about 1/13 of the flame tube diameter.

The length of the flame tube advantageously corresponds approximately its double diameter. These proportions allow that Form a stable flame.

The air opening in the baffle plate is advantageous an aperture insert narrowing the baffle plate opening certainly. This can result in the air opening in the panel insert different dimensions and any swirl generating Guiding surfaces can be designed differently. The baffle plate does not need to be changed to change the air opening become. The aperture insert can also be used with a smaller one Material thickness can be made as the baffle plate what for setting up air guiding surfaces is advantageous because this by twisting one piece with the Aperture insert punched slats can be achieved. Changing the aperture insert can also be related with changing the nozzle may be necessary because the baffles Advantageously connect to the nozzle to achieve an optimal To have an effect on the air.

The parameters of air flow velocity and Air volume and cross section of the air flow in relation to the Flame tube cross-section have an impact on the functioning of the Brenners. Through the cross-sectional area of the air opening and the Blower output, these parameters are adjustable. The air opening expediently has one Cross-sectional area of 4 to 13%, preferably 8 ± 2% of the Cross-sectional area of the flame tube.

Because the fuel first starts with the Combustion chamber existing oxygen-containing exhaust gas and the air must be mixed, especially along the Flame tube wall, where the fuel hits on cold start, happens, the ignition point of the ignition electrodes is advantageous arranged in the middle third of the flame tube. The proximity to Flame tube wall is also useful because of the distance to the central, cool airflow that has practically no fuel contains. On the other hand, the flame tube wall develops very quickly a great heat, so the fuel already Fractions of a second, approx. 1/2 second, after the cold start completely gasified and burning blue.

The ignition point of the ignition electrodes in the is advantageous upstream half at about 2/5 the length of the flame tube arranged, because there the mixture is already easily ignitable and further downstream the electrodes would Flame root area unnecessarily disruptive.

The oil burner according to the invention works practically regardless of the shape of the furnace. He is especially suitable for compact combustion plants with short Furnace rooms. The burner according to the invention is suitable especially for the combustion of heating oil extra light, eco oil or kerosene. Another advantage is that the Burner according to the invention also for the combustion of gas fuel is suitable. By adding gas in the air in front of the baffle plate and blow in the The burner can mix gas / air without changing the oil nozzle would have to be removed, converted into a gas burner.

Fig. 1

den Brennerkopf im Längsschnitt,

Fig. 2

schematisch das Verbrennungsverfahren,

Fig. 3

Aufsicht auf einen Blendeneinsatz mit ausgeschnittenen, jedoch noch nicht verdrehten Führungsflächen,

Fig. 4

Schnitt durch den Blendeneinsatz nach Fig. 3, wobei die Führungsflächen zur Drallerzeugung verdreht sind.

To better understand the invention, exemplary embodiments of the invention are described below with reference to the figures. It shows:

Fig. 1

the burner head in longitudinal section,

Fig. 2

schematically the combustion process,

Fig. 3

Supervision of an aperture insert with cut out but not yet twisted guide surfaces,

Fig. 4

Section through the panel insert according to Fig. 3, wherein the guide surfaces are twisted to generate swirl.

FIG. 1 shows a burner head 11 with a baffle plate 13, which in a wall, not shown Combustion chamber 12 is mountable. On the baffle plate 13 is in Flow direction, which is indicated by arrow 14, a flame tube 15 with a ratio of diameter to Length of about 1 to 2 arranged. Next is central to the Flame tube axis 17 a lance or nozzle 19 is arranged. The Fastening means for the nozzle 19 and the baffle plate 13 together form e.g. an aperture unit like her is described for example in EPA 0 650 014. The Nozzle head 23 sits centrally in an aperture insert 25 Spray opening 21 of the nozzle 19 lies in the plane of the Baffle plate 13 and the aperture insert 25. Der Aperture insert 25 is attached to the baffle plate 13 and covers up to an annular air opening 29 around the Nozzle head 23 around opening 27 in baffle plate 13. The annular air opening 29 takes up an area of approximately 8 the cross-sectional area of the flame tube 15.

The air opening 29 is also swirling Guide surfaces 31 equipped. These guide surfaces 31 are radial aligned and are opposite the flame tube axis 17 and Flow direction 14 inclined so that through the air opening 29 flowing air is set in rotation about the axis 17. The slats or guide surfaces 31 are made in one piece with the Aperture insert 25 made (Fig. 3 and 4). At her They are manufactured and aligned except for approximately one Compound 32 corresponding to twice the material thickness the aperture insert plate 34 cut out or punched and then by 60 to 88 compared to the aperture insert level Degrees twisted. Here are the by the twist on most of the joints to be deformed the lengths the deformed sheet edges through round cutouts (36) enlarged to prevent cracking.

The flame tube 15 is with links 33 on the Baffle plate 13 attached. The links 33 are formed integrally with the wall of the flame tube 15, protrude over the baffle plate end of the flame tube 15 out and are through slots in the baffle plate 13th put through. Upstream of the baffle plate 13 are the Links 33 twisted after plugging together, so that a firm connection between baffle plate 13 and Flame tube 15 is formed.

The connecting links 33 have a stepped, themselves tapered silhouette on. Paragraphs 37 in the stairs are on the flame tube side of the baffle plate 13 and thus define the opening width of the recirculation slot 35. Exhaust gas is passed along through this recirculation slot 35 the baffle plate 13 and the aperture insert 25 in the flame tube 15 sucked to prevent sooting of this area. A favorable opening width is around 1 mm.

In the vicinity of the baffle plate, the flame tube has 15 recirculation openings 39 through which the exhaust gas through the Vacuum, which is downstream of the baffle plate 13 due to Air flow is created, is sucked in. In the case shown there are 18 circular recirculation openings 39 with one respective diameter of approx. 6 mm. The openings 39 can but also in a different number and / or other form.

The flame tube 15 has an inner diameter of about 80 mm and a length of about 160 mm. At the Combustion chamber 12 facing end of the flame tube 15 is this constricted. The constriction 41 narrows the Flame outlet opening 43 with respect to the flame tube cross section. The edge region 45 of the flame tube 15 is to form the Constriction 41 turned round inwards.

The ignition electrodes 47 are near the periphery of the Flame tube 15 with ceramic insulation pieces 49 through the Thrust plate 13 passed through and protrude with their ends 51 into the flame tube 15. The ignition point 53 is in one Distance from the baffle plate 13 of about 2/5 the length of the Flame tube 15.

In Figure 2, the different zones during the Combustion is shown schematically. By making the air is blown through the air opening 29 downstream the baffle plate 13 has a negative pressure in the area 61 Exhaust gas is drawn in under vacuum, represented by the arrows 63 and 65. This exhaust gas forms a jacket 67 around the Core flow 69. The exhaust gas flowing in along arrow 65 strokes the surface of the baffle plate and protects them from depositing soot. Between the core flow 69 and the Sheath 67 creates vortices 71 in which the two media Air and exhaust gas are mixed.

The fuel is the shortest route through the Air flow sprayed through, shown with broken lines 72. The cone shell of the sprayed Fuel has an angle between 60 and 90 degrees. The nozzle preferably has a conical jacket characteristic 80 degrees. In a region 73 of the exhaust jacket 67 the gasified Fuel and is by vortex 75 in the exhaust jacket 67 with the Exhaust gas mixed. Since upstream of the gasification zone 73 none gasified fuel is present that could burn, and on the short path of penetration that the fuel takes through the Airflow 69 must travel through, the fuel does not starts to burn, practically all fuel in the Gas jacket 67 gasifies and only arrives in gasified form the air into a contact that triggers a reaction.

Gasified fuel is thus in the vortex 71 with the Exhaust gas swirls with the air and only burns in the Area of this vortex 71 cool and low in pollutants.

The flame begins in its root area 77 at the end of the first third of the flame tube 15. The flame root is annular between exhaust jacket 67 and air flow 69 embedded. The ends in the last third of the flame tube central air flow 71 in the center of the flame and cools it. The thickness of the jacket 67 is decreasing downstream because the exhaust gas / fuel vapor mixture is on this route mixed with the air. The fuel vapor is about two thirds of the flame tube length fed to the flame. The Flame thus has an annular and elongated Root area and is out of the cladding area 67 nourished.

The jacket zone 67 becomes through the constriction 41 limited downstream. The gas in the jacket area 67 is at Flowing out of the flame tube 15 hindered. A swirl this favors the two media. The exiting Flame sticks to the flame tube.

Claims (16)

1. Process for burning liquid fuel by means of an oil burner, in which the fuel is sprayed into a flame tube (15), air is blown into the said flame tube (15) and waste gas is fed back into the said flame tube (15) as a result of the suction effect of the air, characterised in that virtually all the fuel is sprayed (72) into the fed-back waste gas in front of the root of the flame (77) and is vaporised in the said waste gas, and the waste gas enriched with the vaporised fuel is swirled (71) with the air.
2. Process according to claim 1, characterised in that the air is blown into the flame tube (15) through a central aperture (29) in a baffle plate (13) and the waste gas is admitted (63, 65) at the baffle plate end of the flame tube (15) in such a way that it envelopes (67) the central air flow (69).
3. Process according to claim 2, characterised in that the fuel is squirted, with the aid of one nozzle (23), out of the air flow and into the hot, low-oxygen waste-gas envelope (67), from the centre of the air flow (69) in the form of a conical-envelope.
4. Process according to claim 3, characterised in that the fuel is sprayed, at an angle of 30 to 45 degrees to the axis (17) of the flame tube, in the direction of the inner wall of the said flame tube (15).
5. Process according to one of claims 2 to 4, characterised in that the air flow (69) is set in rotation about the axis (17) of the flame tube.
6. Process according to one of claims 2 to 5, characterised in that the fuel-vapour/waste-gas mixture flowing downstream at the inner wall of the flame tube (15) is prevented, by a narrowed portion (41) of the flame exit aperture (43), from flowing out of the flame tube (15), and is swirled with the air, and the emerging flame is thereby held on the flame tube (15).
7. Oil burner with waste-gas recirculation, a centrally disposed fuel nozzle (19), a baffle plate (13) with an air aperture (29) and, adjoining the baffle plate (13) in the direction of flow, a flame tube (15) which has, in the vicinity of the baffle plate, apertures (35, 39) for admitting waste gas into a negative-pressure area (61) behind the baffle plate (13) in the direction of flow, the spraying aperture (21) of the fuel nozzle (23) lying approximately in the same plane as the baffle plate (13) which produces negative pressure, and the said baffle plate (13) having only one aperture which forms an air inlet (29) disposed concentrically round the fuel nozzle (23) in an annular manner, characterised in that the fuel nozzle (19) has a conical-envelope characteristic.
8. Oil burner according to claim 7, characterised in that the air aperture (29) in the baffle plate (13) is provided with spin-producing deflecting faces (31).
9. Oil burner according to claim 7 or 8, characterised in that recirculation slots (35) with an aperture width of at least 0.2 mm are disposed between the flame tube (15) and the baffle plate (13) for the self-cleaning of the said baffle plate (13).
10. Oil burner according to claim 9, characterised in that the flame tube (15) is fastened to the baffle plate (13) with the aid of, preferably, three spacing connecting members (33).
11. Oil burner according to one of claims 7 to 10, characterised in that a multitude of recirculation apertures (39) are disposed in the wall of the flame tube in the vicinity of the baffle plate (13) but at a distance from the latter.
12. Oil burner according to one of claims 7 to 11, characterised in that the flame tube (15) is narrowed at its exit aperture (43).
13. Oil burner according to one of claims 7 to 12, characterised in that the length of the flame tube (15) corresponds to approximately twice the diameter.
14. Oil burner according to one of claims 7 to 13, characterised in that the air aperture (29) in the baffle plate (13) is determined by a screen insert (25) which narrows the aperture (27) in the baffle plate.
15. Oil burner according to one of claims 7 to 14, characterised in that the air aperture (29) has a cross-sectional area of 4 to 13%, and preferably 8 ± 2%, of the cross-sectional area of the flame tube (15).
16. Oil burner according to one of claims 7 to 15, characterised in that the ignition point (53) of the ignition electrodes (47) is disposed in the middle third of the flame tube (15) in proximity to the wall of the said flame tube.

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