GB2274510A

GB2274510A - Gas burner for furnaces or kilns

Info

Publication number: GB2274510A
Application number: GB9401197A
Authority: GB
Inventors: Alfred Moser
Original assignee: Riedhammer GmbH and Co KG
Current assignee: Riedhammer GmbH and Co KG
Priority date: 1993-01-23
Filing date: 1994-01-21
Publication date: 1994-07-27
Anticipated expiration: 2014-01-21
Also published as: FR2700830A1; GB9401197D0; ITMI940081A1; GB2274510B; IT1269447B; ITMI940081A0; DE4301840C2; DE4301840A1; PT101442A

Description

2274510 Gas burner The invention relates to a gas burner for furnaces and

kilns. Such gas burners, which are fired with natural gas, liquid gas or lean gas for example, can be used inter alia in furnaces of the ceramic industry (e.g. in shuttle kilns, batch furnaces and tunnel kilns), in furnaces of the iron and steel industry (e.g. smelting furnaces and shaft furnaces), but also in dryers.

Gas burners of this type are known in the art, having the following features:

- a central gas feed pipe, - a burner pipe concentric with, but with clearance from, the gas feed pipe, - wherein the burner pipe projects over the gas feed pipe in the direction of flow of the gas, - a disc extending radial to the gas feed pipe is disposed in the annular gap formed between the gas feed pipe and the burner pipe in order to supply combustion air, the disc has a plurality of cut-outs through which the combustion air flows, - radial apertures, from which the gas flows more or less perpendicular to the direction of flow of the combustion air, are provided at the front end (in the direction of flow) of the gas feed pipe.

These burners have the following problems: if the burner is started up in the cold state, only relatively little combustion air is required, and this flows through the cutouts in the disc in the annular channel in a more or less laminar fashion. In spite of the perpendicular discharge of the gas stream relative to the combustion air, in many cases it is not possible to achieve intensive mixing of the combustion gas with the combustion air. Consequently, heavy 2 carbonization occurs in the region of the gas outlet apertures, which may put the burners out of action.

Although a certain degree of spin is exerted on the combustion air by cutouts in the disc oblique to the direction of flow of the combustion air, mixing with the combustion gas is still unsatisfactory in the cold state. An increase in the flow speed of the combustion air or an increased supply of combustion air is therefore out of the question, as it brings excess air, and hence unburned oxygen, into the furnace. For example, in order to fire ceramic parts, it is necessary to retain a specified furnace temperature and therefore a specified A.value.

After a certain starting-up period of the burner, instead of cold combustion air, preheated combustion air is supplied. Although the increased volume of combustion air due to preheating (at 5000C the volume of the combustion air has already risen by a factor of 2.6) leads to improved mixing of the combustion air with the gas, the increased quantity of air and increased flow speed create a considerable noise nuisance when the combustion air is flowing through the apertures in the disc, particularly if the cut-outs are positioned obliquely to the inflow direction of the combustion gases.

The object of the invention is to make available a gas burner of the above-mentioned type - in particular with periodic operation - which creates as thorough a mixture of the combustion air with the combustion gas as possible, even during starting up of the burner, without having to increase the flow speed of the cold combustion air or its quantity. The invention at the same time aims to prevent the carbonization in the region of the burner tip mentioned at the outset.

Based on the principle that optimum mixing of the combustion 3 air and combustion gas leads to optimum combustion, the invention is based on the knowledge that this object can be achieved if first of all an adequate flow cross-section for the combustion air is provided in the disc, and secondly if the gas discharged from the gas outlet apertures of the gas feed pipe is fed direct into the combustion air stream.

It has been unexpectedly discovered that by these two structurally relatively simple measures a substantial optimisation of the efficiency of the burner and significantly improved reliability are achievable, even during starting up of the burner.

Accordingly, the invention proposes in its general embodiment a gas burner, for furnaces and kilns, having the following features:

- a central gas feed pipe, - a burner pipe extends around the gas feed pipe with clearance therefrom, - a disc extending radial to the gas feed pipe is disposed in the annular gap formed between the gas feed pipe and the burner pipe in order to supply combustion air, - the disc has a plurality of through-ways in the flow direction of the combustion air, the cross-sectional area of the through-ways is at least 50% of the cross-sectional area of the disc, - the gas outlet end of the gas feed pipe is so formed that the gas discharged via a plurality of gas outlet apertures is fed direct into the combustion air stream.

According to one embodiment, the gas outlet apertures (at the front end of the gas feed pipe in the direction of flow; i.e. behind the disc in the direction of flow of the gas) are arranged in a hypothetical circle. In this way an even radial stream of the combustion gas is ensured. This is important because the through-ways in the disc are 4 distributed statistically over its whole cross-sectional area. Thus not only is an even flow of combustion air achieved, viewed in the radial direction, but also even contact with the combustion gas is ensured.

In order to guide the gas direct into the combustion air stream, one embodiment of the invention proposes to form the gas outlet apertures as nozzles projecting radially outwards from the gas feed pipe. Thus the gas is introduced centrally into the combustion air stream flowing axially to the burner pipe, so that optimum mixing is achievable.

In other words, the nozzles (or their gas outlet ends) project into the annular gap between the gas feed pipe ana the burner pipe.

It is particularly advantageous if the nozzles - viewed in the flow direction of the gas - extend at an angle of between > 20 and < 90'. In this way, the gas is passed, not perpendicular to the flow direction of the combustion air, but - at a specified angle - in the flow direction of the combustion air. Thus mixing is further improved, and the flow direction is not interrupted, promoting the formation of an optimum burner flame.

Obviously - and for this reason the matter will be discussed no further here - an appropriate igniter is provided in the region of the gas outlet apertures in order to start up the burner. In addition, probes may be provided in this region to test the quality and quantity of combustion air.

The through-ways in the disc may be formed as holes and/or as slots open to the exterior and covered at the circumference by the burner pipe.

In the latter configuration, it is advantageous to extend the nozzles as far as the cross-sectional region of the slots in order to guide the gas again direct into the combustion air stream.

An essential feature of the burner according to the invention is also that the cross-sectional area of the through-ways is at least 50% of the cross-sectional area of the disc. Thus the supply of a sufficient quantity of combustion air at a reduced flow speed is ensured.

But it is also within the scope of the invention to arrange the throughways in the disc at an angle to the flow direction of the combustion air in front of the disc (inflow direction of the combustion air). Contrary to the prior art however, this angle may be limited to values between 1 and 300.

Homogeneous mixing of the combustion air with the combustion gas is promoted if the geometric shape of the disc, the gas outlet-side (front) end of the gas feed pipe and/or of the burner pipe are rotationally symmetrical. In this way, uniform conditions are set for the total crosssection of the annular gap.

In order to operate the burner it is also important that the flow speed of the combustion gas is higher than that of the combustion air.

According to its application, the invention offers the further advantage in one embodiment that the distance between the outlet point of the gas from the gas feed pipe and the disc upstream thereof (in the flow direction of the gas) is adjustable. In real terms, this is achieved in one embodiment by the possibility of mounting the disc axially displaceably on the gas feed pipe. To this end, suitable catches may be provided on the gas feed pipe. In the simplest case, the disc or its interior edge is screwed tightly to the gas feed pipe. The distance between the 6 outlet point of the gas (from the nozzles) and the disc is in this case conventionally between 2 and 10 cm.

Finally, the invention proposes an embodiment of the gas burner in which the burner pipe has, behind the nozzles (the outlet point of the gas) again viewed in the flow direction of the gas - a tapered cross-section, to which a section of the burner pipe having a larger cross-section follows. In this manner the mixture of combustion air and combustion gas is guided radially inwards, and further mixing is achieved. At the same time, the burner itself is protected from the furnace interior by the tapering burner pipe. This is particularly important in applications where particularly high temperatures, e. g. of more than 2 0OWC, are reached in the furnace or kiln chamber, as the individual burner parts, such as the gas feed pipe, the disc or the nozzles are made of metallic, and therefore heat-sensitive, materials. Although previously a burner pipe has been discussed, this may also be partly replaced by a nozzle brick.

If desired, the section of the gas feed pipe on the gas outlet side and optionally the disc or the front section of the burner pipe may be made of ceramic, particularly heat-resistant materials such a silicon nitride. One option is to form the tip of the gas feed pipe on the gas outlet side and the disc as an integral component.

Further features of the invention will appear from the features of the subclaims and from the remaining application documents.

The invention will be explained, by way of example, in more detail below with the aid of an embodiment.

Figure 1 shows a vertical longitudinal section through the front section, in the flow direction, of a gas 7 burner according to the invention, and Figure 2 shows a plan view of the burner according to Figure 1 in the region of the section line 2 - 2 according to Figure 1.

It is to be understood that insofar as alternative constructions described above are not again described hereinafter, such constructions can nevertheless be incorporated into the embodiment now to be described.

Referring to the Figures, a central gas feed pipe 10 can be seen. The gas feed pipe 10 is bent at the front end in the flow direction of the gas (arrow S) and has in this region six apertures 12 in all, into which radially outward-facing nozzles 14 are inserted.

The individual nozzles 14 are arranged with equal spacing in a ring, as can be seen in Figure 2.

The nozzles 14 protrude beyond the circumference face of the gas f eed pipe 10 in the radial direction. The purpose of this geometric arrangement will be described in more detail below.

Figure 1 further shows that, in front of the nozzle ring 14, with respect to the direction of the arrow S, an annular disc 16 rests on the gas feed pipe 10 and is bounded at the circumference by a burner pipe 18, which extends concentrically with the gas feed pipe 10.

In this manner an annular gap 20 is formed between the gas feed pipe 10 and the burner pipe 18, through which gap the combustion air is fed concentrically to the combustion gas in the direction of the arrow S.

From Figures 1 and 2 together, it can be further seen that 8 the disc 16 has a plurality (in this case 20) of throughways in the form of slots or cut-outs 22, which are also f ormed in a circle and arranged rotationally symmetrically on the disc 16 with equal spacing. The cut- outs 20 are open towards the outside and are covered there by the burner pipe 18.

In addition, (in this case 8 in all) further through-ways in the form of axial through-bores 24 are provided in the disc 16.

Concentrically with the burner pipe 18 extends a nozzle brick 181, which is considered structurally part of the burner pipe 18.

The nozzle brick 18' extends inwards in a conically tapering manner from the free end of the burner pipe 18 and then follows a cylindrical section. Thereafter the open cross-section of the nozzle brick 18' widens conically again, before being followed by a further cylindrical end section.

The modus operandi of the burner is as follows:

When starting from cold, combustion gas is supplied through the gas feed pipe in the direction of the arrow S and then flows out through the circularly arranged nozzles 14, which are in this case arranged at an angle a of approximately 45' to the central longitudinal axis M. Simultaneously, combustion air is fed through the annular gap 20 concentrically to the gas stream in the direction of the arrow S. The combustion air, as can be deduced from Figure 2, flows through the cutouts 22 and through-bores 24 positioned slightly obliquely to the inflow direction of the combustion air and is then deflected inwards, due to the conically tapering section of the nozzle brick 181, where it comes into direct contact with and mixes with the combustion 9 gas flowing out through the nozzles 14.

Due to the fact that the nozzles 14 project into the stream of combustion air, optimum mixing of the combustion gas with the combustion air is achieved according to the invention, together with complete combustion without any carbonization, even in this starting-up phase of the burner.

For the initial ignition of the gas/combustion air mixture, as can be deduced from Figure 2, an igniter 26 is disposed in the region of the first conical section of the nozzle brick 18'.

Thus a combustion flame is produced which forms along the nozzle brick 18' in the direction of the arrow S.

In the left-hand section of Figure 2, an electrode 28 can also be seen, via which the burner flame is monitored. Both the electrode and the igniter are known in the prior art, and therefore neither are discussed further.

As the burner continues in operation, instead of the originally used cold combustion air, hot combustion air is supplied, and in the same way as described above, optimum mixing of the combustion air with the combustion gas takes place. Due to the relatively large cut-outs 22 in the disc 16, the flow speed of the combustion air, and therefore the noise, is relatively low.

Thus the burner operates under the same conditions throughout the burning period, so that the burner can also be used in periodic operation without any problem.

A further feature of the invention is that the disc 16 is mounted displaceably in the direction of the arrow S, so that the distance between the disc 16 and the circle of nozzles 14 can be adjusted according to the particular application.

Claims

1. Gas burner, for furnaces and kilns, having the following features: 1.1 a central gas feed pipe, 1.2 a burner pipe extending around the gas feed pipe with clearance therefrom, 1.3 a disc, extending radial to the gas feed pipe, disposed in the annular gap formed between the gas feed pipe and the burner pipe in order to supply combustion air, 1.4 the disc has a plurality of through-ways in the flow direction of the combustion air, 1. 5 the cross-sectional area of the through-ways is at least 50% of the cross-sectional area of the disc, 1.6 the gas outlet end of the gas feed pipe is so formed that the gas discharged via a plurality of gas outlet apertures is fed direct into the combustion air stream.

2. Gas burner according to claim 1, in which the gas outlet apertures are arranged in a hypothetical circle.

3. Gas burner according to claim 1 or 2, in which the gas outlet apertures are formed as nozzles projecting radially outwards from the gas feed pipe.

4. Gas burner according to claim 3, in which the nozzles viewed in the flow direction of the gas - are arranged at an angle of between > 20 and < 9T.

5. Gas burner according to claim 3 or 4, in which the nozzles extend into the cross-sectional region of the through-ways in the disc.

6. Gas burner according to claim 3, 4 or 5, in which the outlet point of the gas from the nozzles is between 2 and 10 cm behind the disc viewed in the flow direction of the gas.

7. Gas burner according to any one of claims 1 to 6, in which throughways in the disc are arranged at an angle to the flow direction of the combustion air upstream of the disc.

8. Gas burner according to claim 7, in which the lastmentioned angle is 1 to 30 degrees.

9. Gas burner according to any one of claims 1 to 8, in which the burner pipe (the nozzle brick) projects beyond the gas feed pipe in the flow direction of the gas.

10. Gas burner according to claim 3 or any one of claims 4 to 9 as appendant directly or indirectly to claim 3, in which the burner pipe (the nozzle brick) has a tapered cross-section behind the nozzles - viewed in the flow direction of the gas -, which is followed by a section of the burner pipe (the nozzle brick) with a larger cross-section.

11. Gas burner according to any one of claims 1 to 10, in which the geometric shape of the disc, of the gas outlet-side (front) end of the gas feed pipe and/or of the burner pipe (the nozzle brick) is rotationally symmetrical.

12. Gas burner according to any one of claims 1 to 11, in which the disc is axially displaceably mounted on the gas feed pipe.

13. Gas burner according to any one of claims 1 to 12, in which the end of the gas feed pipe on the outlet side and/or the disc consist(s) Of a ceramic material, such as silicon 12 nitride, that is resistant to high temperatures.

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14. Gas burner, for furnaces and kilns, substantially as v hereinbefore described with reference to the accompanying drawings.

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