Burner Unit

Abstract

A burner unit for fluid fuels and also for pulverized coal comprising comtion chamber means, prechamber means, means to enable combustion gases to pass from said combustion chamber means into said prechamber means, mixing pipe means in communication with said prechamber means and said combustion chambers means, a fuel supply nozzle for distributing finely divided fuel towards said mixing pipe means into the drawn-in combustion gases, and means for supplying oxygen-containing gas, f.i. air, to the mixture of fuel and combustion gases, wherein said means for supplying oxygen-containing gas comprises a plurality of exit openings arranged symmetrically about the longitudinal axis of said fuel supply nozzle to increase the suction effect of the oxygen-containing gas on the combustion gases drawn into said prechamber means.

Description

BACKGROUND OF THE INVENTION

This invention relates to burner units for fluid fuels such as oil, gas or pulverized coal which are injected into hot combustion gases drawn back from the combustion chamber into a prechamber by the suction effect of the combustion air or other oxygen-containing gas supplied to the unit at relatively high velocities. Such burner unit is f.i. disclosed in U.S. Pat. No. 3,174,526. In this known burner the combustion air is supplied through an annular gap co-axial with the longitudinal axis of the fuel supply nozzle and creates a suction effect in the prechamber whereby combustion gases are drawn back from the combustion chamber. The main advantage of such burners is the fact that the fuel is mixed with the hot combustion gases prior to the admixture of combustion air so that the fuel has good ignition properties when it comes in contact with the combustion air. This improves combustion considerably. However, the known burner suffers from some difficulties one of which is the necessity that the combustion air supply pipe must cross the path of the re-circulated combustion gases which affords complicated parts subjected to high thermal stresses. Furthermore, the supply of combustion air through one nozzle only limits the working range of the burner because if the quantity of air is reduced in order to reduce the rate of combustion the velocity of the air streaming through the annular nozzle is correspondingly reduced and therefore also the suction effect on the recirculated combustion gases. In practice, therefore, the capacity of the burner can be varied only between full load and one third load whereas in many applications a variation down to one tenth load would be desirable.

These difficulties are avoided in the present invention by supplying the oxygen-containing gas f.i. air through a plurality of exit openings arranged symmetrically about the longitudinal axis of the fuel supply nozzle. Compared with a single annular air supply gap the same quantity of air passes through the plurality of exit openings with much high velocity so that a higher reduction of the quantity of air is possible without affecting the recirculation of combustion gases. A very simple and effective means for reducing the air supply is the cutting off of some of the exit openings from the air source. The air passing through the remaining exit openings has a velocity high enough to ensure proper recirculation of combustion gases even at one tenth load of the burner.

Accordingly, it is an object of the present invention to provide a burner of the type mentioned above which enables variation of the burner capacity over a comparatively large range without adversely affecting the combustion qualities.

The exit openings are connected via pipes or passages with pressurized air supply means. These pipes or passages can be parallel to the longitudinal axis of the fuel supply nozzle or they can be inclined thereto with an angle of between 5.degree. and 10.degree., in special cases up to 15.degree.. Preferably the exit openings for the combustion air are located downstream of the fuel supply nozzle in order to obtain a big prechamber within which the combustion gases can react with the fuel before the combustion air is added.

The exit openings can be combined to individual groups with the openings of each group being symmetrically arranged about the fuel nozzle axis, whereby each group can be connected or disconnected to or form the air source in order to vary the capacity of the burner. Furthermore, the exit openings of one group may have a different size of the exit openings of another group. If only two exit openings are provided they are arranged diametrically opposed and may have different sizes, the smaller opening only being supplied with air at low load.

Normally the exit openings will be arranged outside the prechamber and f.i. in the wall of the mixing pipe. Nozzles can be inserted in the exit openings.

The connection and disconnection of individual exit openings or groups of exit openings can take place outside the burner by means of valves in the supply pipes.

Further objects, features and advantages of the present invention will become apparent from the following description in connection with the drawings which show, for purposes of illustration only, some embodiments in accordance with the present invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional elevational view of a first embodiment of a burner unit according to the invention;

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1;

FIG. 3 is a sectional elevational view of a second embodiment of a burner unit according to the invention with the combustion chamber omitted; and

FIG. 4 is a sectional elevational view of a third embodiment of a burner unit according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

Referring now to FIGS. 1 and 2, reference numeral 7 designates a combustion chamber having a refractory lining 11 and an outlet opening 12 for the burnt gases. The combustion chamber 7 is flanged to a burner assembly generally designated 20 comprising an outer shell 21 and an inner shell 5. Centrally within inner shell 5 is arranged a mixing pipe 6 having a flange 22 with openings 23. A fuel supply nozzle 1 is arranged in the inner shell 5 co-axial with the longitudinal axis 24 of the burner unit. The space 4 between outer shell 21 and inner shell 5 is connected by a connector 3 to a blower (not shown) which supplies the combustion air. Pipes 2 extend from the space 4 into the prechamber 25 enclosed by inner shell 5 and extending up to the mixing pipe 6.

In operation the combustion air is supplied through connector 3 to space 4 and through pipes 2 into the prechamber 25. By the injector effect of the air streaming out of pipes 2 combustion gases are sucked back from the combustion chamber 7 through the openings 23 in flange 22, through annular chamber 8 into prechamber 25 where they are mixed with the fuel emerging from fuel nozzle 1. The finely divided fuel reacts with the hot combustion gases and forms reduction products of a precombustion. These products are delivered into the mixing pipe 6 by the air jets and are mixed with the air. The mixture of fuel, recirculated combustion gases, reduction products and air emerges from the exit opening 9 of the mixing pipe 6 and is ignited by the flame vortex 10. Naturally the first ignition is effected by the usual ignition device (not shown). The burning of the mixture takes place in the combustion chamber 7.

It is apparent that the fuel droplets or particles (in the case of pulverized coal) cover a long distance within undiluted combustion gases owing to the arrangement of the exit openings of the air pipes 2 downstream of the fuel nozzle 1, so that the fuel has ample time to react with the combustion gases.

As can be seen from FIG. 2, the recirculated combustion gases can flow through the interstices between the pipes 2 into the space surrounding the fuel nozzle 1. In this embodiment three groups of air pipes are formed namely a, a'; b, b' and c, c'. Each group can be individually connected to or disconnected from the air supply. For full load all groups are supplied with air whereas for partial load one or two groups are disconnected. For this purpose a rotary valve 13 shown diagrammatically in FIG. 1 can be provided.

The embodiment of FIG. 3 differs from the embodiment of FIG. 1 only by a shorter mixing pipe 6' and longer air supply pipes 2'. Again the recirculated combustion gases enter partially the space around fuel nozzle 1 through the interstices between the air pipes 2', and partially they mix directly with the combustion air. As can be seen, the exit openings of pipes 2' are a relatively great distance from the fuel nozzle 1, thus enabling a long reaction of the fuel with the recirculated combustion gases prior to the admixture of the combustion air.

In the embodiment of FIG. 4 the combustion air is supplied to the interior of the mixing pipe 46 through openings 42 and 42' which are connected to annular chambers 48, 49 respectively, which are in turn connected to air supply pipes 43, 43'. The air jets emerging from the openings 42 and 42' into the mixing pipe 46 in direction towards the combustion chamber 7 generate a pressure rise in the downstream portion 46' of the mixture pipe. This pressure rise effects a recirculation of hot combustion gases from the combustion chamber 7 through passages 41 in the wall of the mixing pipe 46 into the prechamber 50 accommodating duel nozzle 1. The fuel which mixes with the hot combustion gases has relatively long time to react therewith until it reaches the air exit openings 42, 42'. In this example the combustion chamber 7, which, owing to the good preparation of the fuel and the intimate mixing with the combustion air can be run with very high performance, is liquid-cooled.

The air exit openings 42 of the one group are of smaller cross-section than the air exit openings 42' of the other group. The openings of each group are equally spaced around the circumference of mixing pipe 46 with one opening of one group always between two openings of the other group. According to the desired performance of the burner the one or the other or both groups are supplied with combustion air. This burner is especially suited for operation with liquid hydrocarbons which are burnt with blue flame without generation of soot and even in substochiometric mixture. However, also all combustible gases, particularly the gaseous hydrocarbons, can be burnt.

The burner of the present invention is also well suited for burning pulverized coal owing to the long reaction time available prior to the mixing with the combustion air. Furthermore, it should be pointed out that the burner can be operated with oxygen instead of air. Finally it should be remarked that the combustion air flowing through space 4 is heated and at the same time forms a heat isolation for the prechamber and the space 8 through which the combustion gases are recirculated.

Thus the several aforenoted objects and advantages are most effectively attained. Although several somewhat preferred embodiments have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.

Claims

What we claim is:

1. A burner unit comprising combustion chamber means, prechamber means, means to enable combustion gases to pass from said combustion chamber means into said prechamber means, mixing pipe means in communication with said prechamber means and said combustion chamber means, a fuel supply nozzle for distributing finely divided fuel towards said mixing pipe means into said recirculated combustion gases, and means for supplying oxygen-containing gas to the mixture of fuel and combustion gases, wherein said means for supplying oxygen-containing gas comprises a plurality of exit openings arranged symmetrically about the longitudinal axis of said fuel supply nozzle, said means for supplying oxygen-containing gas comprises pipes extending into the prechamber and arranged symmetrically about the fuel supply nozzle, the interstices between adjacent pipes forming passageways for the recirculated combustion gases into the space of the prechamber surrounding the fuel supply nozzle.

2. A burner unit according to claim 1, wherein said pipes are substantially parallel to the longitudinal axis of the fuel supply nozzle.

3. A burner unit according to claim 1, wherein said pipes are inclined towards the longitudinal axis of the fuel supply nozzle with an angle up to 15.degree., preferably between 5.degree. and 10.degree..

4. A burner unit comprising combustion chamber means, prechamber means, means to enable combustion gases to pass from said combustion chamber means into said prechamber means, mixing pipe means in communication with said prechamber means and said combustion chamber means, a fuel supply nozzle for distributing finely divided fuel towards said mixing pipe means into said recirculated combustion gases, and means for supplying oxygen-containing gas to the mixture of fuel and combustion gases, wherein said means for supplying oxygen-containing gas comprises a plurality of exit openings arranged symmetrically about the longitudinal axis of said fuel supply nozzle, at least two groups of exit openings being provided with each group being connected or disconnected separately to or from a combustion air supply source.

5. A burner unit comprising combustion chamber means, prechamber means, means to enable combustion gases to pass from said combustion chamber means into said prechamber means, mixing pipe means in communication with said prechamber means and said combustion chamber means, a fuel supply nozzle for distributing finely divided fuel towards said mixing pipe means into said recirculated combustion gases, and means for supplying oxygen-containing gas to the mixture of fuel and combustion gases, wherein said means for supplying oxygen-containing gas comprises a plurality of exit openings arranged symmetrically about the longitudinal axis of said fuel supply nozzle, the exit openings being arranged in the inner surface of the mixing pipe and being connected to a source of oxygen-containing gas via annular spaces in the wall of the mixing pipe.

6. A burner unit according to claim 5, wherein two groups of exit openings are provided with each group being individually connectable to or disconnectable from a source of oxygen-containing gas.

7. A burner unit according to claim 6, wherein the exit openings of the one group have a bigger cross-section than the exit openings of the other group with one exit opening of one group being located between two adjacent exit openings of the other group.