EP0066570B1

EP0066570B1 - High-temperature burner

Info

Publication number: EP0066570B1
Application number: EP81900226A
Authority: EP
Inventors: Lennart T. Eriksson; Olle NYSTRÖM; Ebert Andersson
Original assignee: Volvo Flygmotor AB
Current assignee: GKN Aerospace Sweden AB
Priority date: 1980-12-12
Filing date: 1980-12-12
Publication date: 1984-04-25
Also published as: WO1982002084A1; NO822736L; NO152883C; JPS57501925A; NO152883B; DE3067658D1; EP0066570A1

Abstract

The high-temperature burner can be used for both gas and oil by simple replacement of the flame tube unit. The burner consists of a flame tube (13) preferably of metal, with air intake holes (14), a nozzle (23), inlet ducts (21, 22, 25) for air and fuel, a jacket (1) and an outlet cone (8). The flame tube is fastened into the end piece (10) of the burner and is easily replaceable. A conducting ring for reversing the flow of the inlet air through the inlet holes inwardly and backwardly towards the primary combustion zone is arranged around the Flame tube and at each air intake hole there is arranged at least one slot upstream and/or downstream for cooling the flame tube. Additional conducting rings can be arranged to amplify the cooling, and an extra jacket (50) can be arranged around the jacket (1) for circulation of water or air in the space (6) therebetween The outlet cone (8) can also be cooled by film cooling.

Description

The invention concerns a high-temperature burner with a nozzle for gaseous, liquid and slurried fuel, inlets for air and fuel, flame tube with inlet holes for inlet air, jacket and outlet cone and a method of operating this burner.
To bridge over the period until new forms of energy have hopefully been developed, it will be necessary to use existing energy sources as effectively as possible, both by utilizing each primary fuel to a maximum and by selecting the correct type of technology and energy for each use, solid fuel, oil, gas or electricity.
There is a need for a burner which combines good economy with adaptability to various fuels and which is suitable for various manufacturing processes.
There is also a need for a burner having flue gas which contains very low percentages of non-combusted material, hydrocarbons and carbon monoxide. The burner should also be able to use highly pre-heated combustion air. The efficiency should be high and the gas composition should be virtually similar to inert gas, at the same time as the controllability should be quite good.
Such a burner should also be able to be used both as a high-pressure burner and as a high- velocity burner and produce a gas with high temperature and velocity to produce a high heat transfer against a forged part, for example.
These purposes are fulfilled by the burner according to the invention, HTB (High-Temperature Burner), which is characterized in that the flame tube is fastened in the end piece of the burner and is easily replaceable with other types of flame tubes for conversion to various fuels, that the flame tube is made of metal, that a guiding ring is arranged for reversing the inlet air through air-holes inwards and backwards against the primary combustion zone, and with a number of outlet holes for the fuel in the nozzle, corresponding to the number of inlet holes for inlet air in the flame tube.
Further according to the invention, the method of operating the burner is characterized in that the inlet air is conducted into the primary combustion zone through holes in the flame tube, after having reversed its flow direction in a conducting ring, that the flame tube is cooled downstream and/or upstream from each air intake hole by slots in the flame tube, on the same generatrix as the air intake hole and with the same width as said hole, that the fuel nozzle is provided with just as many outlet holes as the number of air intake holes in the flame tube, that the combustion is adjusted by rotating the nozzle to the optimum position, and that the outlet cone is cooled by blowing in air, that the velocity of the airflow is increased on the reverse side of the flame tube with a conducting ring, and that the jacket is optionally surrounded at a distance by an extra jacket for circulation of air or water in the space between said jackets.
The burner is of the can combustion chamber type, i.e. the fuel is combusted in a volume which is limited by a can, or a pre-combustion chamber with very high load per unit of volume. A typical value is 50 MW/m³ as compared with previous constructions, even smaller ones which usually have values of about 10-15 MW/m³ and which often have poorer efficiencies and greater percentages of residual oxygen. This type of burner is distinct from the so-called free- flame burners, such as is described in FR-A-2 118 276.
It is true that in US-A-4 118 171 an adiabatic flame temperature is reached in the first zone, but the flue gases are mixed with cooling air and burnt further in a catalyst zone, and the gases from this zone have only a temperature of about 900 to 1010°C.
The HTB can be easily converted into a gas burner by replacing the interior hot parts. The external parts with connections etc. are completely identical for the gas and oil burners.
The flame tube is easily removable by virtue of the fact that it is only attached to the end piece and inserted into the burner jacket. The flame surveillance, ignitor and spreader are collected at the end also.
In GB-A-1 423 052 the flame tube is fastened on the side wall of the burner casing, but this flame tube is ceramic, and the fastening is specially designed to even out the different thermal expansions in the tube and the casing. Nothing is anticipated about different flame tubes for different fuels.
The burner is made completely of steel, which makes starting up and shutting down quicker than with masonry constructions. Another advantage is that a steel construction does not result in brick and mortar particles in the gas when hot air or hot gas is produced.
One prejudice against metallic materials has been that the material temperature must be kept low to obtain a satisfactory lifetime for the burner. Therefore it has been necessary to keep the air-fuel ratio high, i.e. low gas temperature, or to force the cooling of the combustion chamber wall. In both cases there is a risk of low efficiency with soot formation as a result for example.
Different methods for the circulation of the gases and the cooling are described in DE-A-1 601 531, 2 617 999 and 2 553 097 but all are different from our construction.
The problem of short life has been solved by, on the one hand, using high quality materials, and on the other hand, allowing them to work in a controlled manner at a high temperature. Our construction uses high quality, metallic materials such such as nickel chromium steel, e.g. Avesta 253 MA, or pure nickel alloys, e.g. Inconel^@ or Nimonic^@ with scaling temperatures of about 1100 or 1200°C, respectively. In continuous operation, the nickel chromium steel can be used up to 900°C and the nickel alloy up to 1000°C.
By controlling the operation, we keep the mean temperature for the flame tube at close to the highest temperature at any point, and the material temperature is maintained by controlling the load or the inlet temperature. The flow velocities at the rear side of the flame tube are therefore kept highest where the load is highest, the area closest to the airhole. The reconnection also produces a double cooling here. The velocities are selected so that the material temperatures rise only moderately with elevated inlet temperature. Thus for example a rise in the inlet temperature from 20 to 600°C produces a rise in the maximum material temperature of about 250°C to 950°C at slightly over stoichiometric combustion.
Compressed air supported nozzles are used, both of a standard type and of a specially developed type which permits greater operational range. This is a so-called Y (ypsilon type or multijet type). By having as many separate holes as the number of airholes in the flame tube, it permits a very good control of the dispersing and combustion characteristics by rotating the nozzle.
The type of energy chosen depends in most cases on economic factors. Even if electric heating could produce a 100% efficiency, the primary input would be about 3-5 times as great as long as the electricity primarily comes from thermal power stations. Direct combustion at the place of use is therefore in most cases economically favourable.
The choice of fuel can give various advantages and a fuel which is excellent for one process can be quite disadvantageous in another. Gas, oil and solid fuel require different combustion technologies and different process requirements can make one or the other fuel advantageous. The correct choice of fuel can result in material savings in the process and therefore the fuel costs are not the only consideration.
Natural gas and gasified petroleum products are considered especially suitable for most heating purposes, but in certain cases the advantages of these fuels can not be completely utilized, and fuel oils can be more advantageous.
If various energy forms are compared, fuel oil, gas and electricity, with regard to their most important characteristics, such as minimal dirtying of the equipment and the environment, noise problems, control possibilities and precision, flexibility, heating speed, automation possibilities, ease of handling, maintenance of equipment, reliable delivery and atmospheric effects, electricity and gas are relatively equivalent and are superior to oil. On top of this, however, electricity is a secondary energy form which at present is produced from primary fuel at relatively poor efficiency. Thus gas has a clear advantage over electricity if they both produce equally good results when used. Oil is, however, poorer on most of these points.
One of the many areas where gas has a great advantage over all other fuels is in large furnaces, where for example the flue gases are purified and the expenses for equipment and operation of environmental protection to prevent emission will be minimal.
For flames in automated glass manufacture, gas is also so superior that other fuels are virtually inconceivable.
For other purposes, however, other fuels can be more suitable. For example oils with high sulphur content are advantageous in cement production.
Between the above-mentioned extreme cases, there are a large number of intermediate areas, where the same technology for the same process, but applied under different conditions, produces different results and one or the other fuel can be most advantageous depending on the case.
Industrial processes which require heat are e.g. drying to remove water or solvent from textiles, food products, ceramic products, paper, timber, paints and enamels, etc. Heating of water is also done on a large scale in many industries for textile processing, preparation of foods, etc. Furthermore, metals are treated with heat, e.g. rolling, pressing, forging, melting, etc. Fuel is also used for firing brick and ceramics, for burning lime etc., as well as a great number of different heating purposes in buildings etc.
The invention will be described in more detail in the accompanying drawings.

Fig. 1 shows a high-temperature burner for gas in section.
Fig. 2 shows the same burner but adapted for oil, also in section.
Fig. 3 shows a section along the line III-III in Fig. 2.
Fig. 4 shows a schematic cross section through an oil bruner according to the invention with arrows showing the various airflows, and
Fig. 5 shows the flow at the air intake in a common, commercial burner.

Common to the embodiments for gas and oil, is a cylindrical jacket 1 ending in a rear flange 2 and a front flange 3. The jacket is provided with a pipe 5 for intake of combustion air and the forward portion of the jacket can be provided with an extra jacket 50 which forms a space 6 between the jackets. The forward flange 3 is provided with bolt holes 7 for adapting the burner and a bowl-shaped outlet cone 8 is attached to the flange, with a central opening 9 for the flame and/or flue gases.
The end piece 10 is fastened to the rear flange 2 with bolts 11. The flame tube insert 13 is fastened in a hole 12 in the centre of the end piece and it extends up to the front flange 3 at the same time as it expands in a funnel to the same diameter as the jacket 1. There are holes 14 and 15 in the flame tube 13 for air intake and the ignitor 16, the flame watcher 17 and the observation tube 18 open into the flame tube and are also fixed in the end piece 10 and are connected with couplings 19, 20 to feeder lines 21, 22. In the centre of the end piece there is the burner 23 with the coupling 24 to the fuel line 25. The burner is fastened in the end piece 10 with bolts 26. The entire flame tube unit can be removed and replaced quite simply by detaching the end piece from the jacket and inserting a new unit, for example when changing fuels or for maintenance.
Fig. 2 shows an HTB for oil. If differs from the gas model only in that the flame tube 33 has a cylindrical form and is shorter than the corresponding gas version 13, and that the airholes 34 are arranged in another manner with a covering ring or guiding tube 35 for controlling the supply of air. The gas burner 13 has also been replaced with an oil burner 36 of course.
In contrast to other can combustion chambers, here a significantly larger portion of the combustion air is forced to enter the primary zone. This is achieved by reversing the flow direction of the combustion air via a tube 35 so that it flows opposite to the main direction of flow. This produces a resulting velocity R_A inwards and backwards against the primary zone as shown in Fig. 4.
The flow in a "normal" can combustion chamber is shown in Fig. 5. The resulting velocity R_. is directed downwards and forwards. with such a construction, a maximum of 30% of the air can be forced to enter the primary zone, and even with the aid of guide vanes and similar arrangements, the flow can be increased to at most 50%, while in the construction according to the invention about 75% of the air enters the primary zone. This creates the possibility of operating the burner at somewhere near stoichiometric ratios without fierce flames being formed outside the burner with a combustion chamber of normal length.
This effect has been amplified by slots 43, equal in number and of the same width as the airholes 34 and placed on the same generatrix. This creates an additional flame holding zone, which makes possible recirculation of flue gas from the primary zone and thus prolonging the staying time.
The film of air 44 from the slot which proceeds along the wall towards the holes also contributes to holding down the temperature of the flame tube wall.
The same technique can also be used on the wall closest to the upstream holes, i.e. the various slots 45. This portion of the flame tube can also be cooled more effectively by increasing the flow velocity on the other side of the flame tube with an extra guide tube 46.
The flame tube wall in the area of the holes is subjected to the highest temperatures either just before or just after the holes depending on which type of nozzle is used. With our own so-called multijet nozzle, the highest temperature is obtained downstream of the holes, but with usual standard nozzles, the temperature maximum is moved and will lie upstream of the holes.
By reversing 47 the flow, a very good cooling effect is achieved in that portion of the burner where the final combustion occurs with a resulting high gas temperature.
By combining the various measures at those points where they produce maximal effect, the temperature of the combustion chamber wall can be kept down to a high but permissible level at stoichiometric combustion and with inlet temperatures of up to about 600°C.
To reduce the stresses on the outlet cone 8, rectangular grooves 49 have been made in such a manner that due to the diffusion angle obtained from the grooves, the inside of the outlet opening is completely covered by a film of fresh air. The flow devoted to cooling is at most 10% of the combustion airflow.
Two different types of nozzles have been mentioned above. The type of nozzle which we ourselves manufacture and market is the co- called multijet type, which has a higher efficiency than the standard type which can also be used. One reason for the higher efficiency is that a smaller drop size is obtained by the oil and support air being distributed through a number of holes, usually 6 or 8, instead of through a single hole as in the standard nozzle. The multijet nozzle also permits a greater range of control due to the flame-holding effect obtained around each stream. Also contributing to the higher efficiency of the HTB is the fact that the nozzle can have as many holes as the holes in the flame tube as in the present invention, and by adjusting the relative position of the nozzle and the flame tube, optimum operating conditions are achieved when a stream from the nozzle is directed somewhat displaced in the rotational direction of the induced swirl in relation to the airhole.
Concerning inlet temperatures and choice of materials, it may be added that for inlet temperatures of up to 300°C, Avesta 253 MA was used and for up to 500-600°C, Inconel® or Nimonic@ were used. Work is in progress on a development of flame tubes of ceramic material for still higher inlet temperatures. There is no differences in the appearance of ceramic tubes and metal tubes with the exception that the ceramic tube must be made thicker, about 4-6 mm.
To reduce the pressure drops in "ceramic temperatures," a larger jacket is selected for ceramic flame tubes than for metal flame tubes.
If there are special cooling requirements, a heat reduction can be obtained by placing an extra jacket 50 around the jacket. In the gap, air or water can then be circulated. This results in a cooler jacket and correspondingly increased cooling by increased heat radiation from the hot, inner portions towards the cooler outer portions.

Claims

1. High-temperature burner with a nozzle (23, 36) for gaseous, liquid or slurried fuel, inlets for air and fuel (21, 22, 25), flame tube (13, 33) with inlet holes (14, 34) for inlet air, jacket (1) and outlet cone (8), characterized in that the flame tube (13, 33) is fastened in the end piece (10) of the burner and is easily replaceable with other types of flame tubes for conversion to various fuels, that the flame tube (13, 33) is made of metal, that a guiding ring (35) is arranged for reversing (47) the inlet air through airholes (34) inwards and backwards against the primary combustion zone, and with a number of outlet holes for the fuel in the nozzle (36), corresponding to the number of inlet holes (34) for inlet air in the flame tube (33).

2. High-temperature burner according to claim 1, characterized by a slot (43) in the flame tube (33) for guiding in air and cooling the wall downstream of each air intake hole (34).

3. High-temperature burner according to claims 1 or 2, characterized by an additional slot (45) for guiding in air upstream of each air intake hole (34).

4. High-temperature burner according to claims 1-3 characterized by an additional conducting ring (46) for increasing the air velocity on the reverse side of the flame tube (33).

5. High-temperature burner according to claims 1-4, characterized by an extra jacket (50) for defining a space (6) for cooling medium between the extra jacket (50) and the jacket (1) of the burner.

6. High-temperature burner according to claims 1-5, characterized by rectangular grooves (49) in the front edge of the jacket (1) for blowing in a film of air over the inside of the outlet cone (8).

7. Method of operating a high-temperature burner according to claim 1, characterized in that the inlet air is conducted into the primary combustion zone through holes in the flame tube, after having reversed its flow direction in a guiding ring, that the flame tube is cooled downstream and/or upstream from each air intake hole by slots in the flame tube, on the same generatrix as the air intake hole and with the same width as said hole, that the fuel nozzle is provided with just as many outlet holes as the number of air intake holes in the flame tube, that the combustion is adjusted by rotating the nozzle to the optimum position, and that the outlet cone is cooled by blowing in air, that the velocity of the airflow is increased on the reverse side of the flame tube with a conducting ring and that the jacket is optionally surrounded at a distance by an extra jacket for circulation of air or water in the space between said jackets.