Patent Application
20070042302
1. Field of the Invention
The present invention relates to a method and an arrangement for monitoring a burner, principally burners used in industrial furnaces.
2. Description of the Related Art
One way of solving the problem of the formation of NOx during the combustion of fossil fuels is to inject gases into the combustion zone at a high rate of flow. Gaseous fuel and a gaseous oxidant are injected into the combustion zone at a distance from each other. The gases are injected into a burner head through lances that are provided with nozzles. The injected gases will be diluted with combustion products since the gases are injected at a distance from each other. The dilution, together with the fact that the diluted gases are first mixed at a certain distance away from the burner head, means that the gases react with each other in a combustion process that proceeds at a slower rate than that of conventional combustion due to a lower concentration of the gases. Such combustion ensures that the formation of NOx is suppressed.
For reasons of safety, a burner must be monitored for the presence of a flame during operation. Such monitoring usually takes place through a UV sensor, which is a sensor that is sensitive to ultraviolet radiation. The UV sensor is normally mounted in the burner in such a way that the sensor sees a part of a flame that is present.
The flame becomes longer and more spread out through the method of combustion described above, and thus become less visible. That makes the detection of a flame by means of the UV sensor considerably more difficult. Furthermore, the method of combustion described above requires that the furnace first be heated to the spontaneous ignition temperature of the gases before combustion by the method described above can be commenced. In that case the furnace is operated at a temperature below approximately 800° C. For reasons of safety, a burner of the type identified above cannot be used during a heating phase because a flame of the type described is difficult to detect at a temperature below 800° C., whereas at the same time safety regulations specify that UV monitoring is to take place at temperatures below 800° C.
The present invention solves that problem.
The present invention thus relates to a method for monitoring a burner during the combustion of a fuel with an oxidant in an industrial furnace. The fuel and the oxidant are supplied to a burner head and the flame is monitored by means of a detector for ultraviolet light. At least one channel for the supply of fuel and at least two channels for the supply of oxidant are present in the burner and extend to openings at a surface of the burner head that faces into the furnace. The channel for fuel and a first channel for oxidant are spaced from each other, and the channel for fuel and a second channel for oxidant is spaced from the fuel channel at a distance that is smaller than the spacing between the first oxidant channel and the fuel channel. The detector is arranged upstream of the burner outlet at the channel for fuel or at the second channel for oxidant. A fraction of the total amount of oxidant that is supplied to the burner is supplied to the second oxidant channel, and the oxidant is supplied to the second oxidant channel during the entire combustion process.
The invention also relates to a burner for carrying out the method.
The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings in which:
In accordance with the invention, at least one channel 3 is present for the supply of fuel and at least two channels 4, 5 for the supply of oxidant. Channel outlet openings are provided at outlet surface 6 of the burner head that faces the furnace interior (not shown). The fuel channel 3 and a first oxidant channel 5 are spaced from each other at a predetermined distance, and the fuel channel 3 and the second oxidant channel 4 are located closer to each other than the spacing between fuel channel 3 and oxidant channel 5. Fuel is introduced into fuel channel 3 at fuel inlet 3a, and oxidant is introduced into oxidant channel 4 at oxidant inlet 4a.
The UV detector 2 is positioned adjacent an upstream side of the fuel channel 3 or adjacent an upstream side of the second oxidant channel 4. It is appropriate that the UV detector is arranged at the end of a channel that lies farthest away from the furnace, and is so positioned that UV light from the flame passes into the channel and impinges upon the detector. The detector is connected to a detector circuit (not shown), by means of which circuit the presence or absence of a flame can be determined. In the case in which a flame is not detected, the supply of fuel and oxidant is interrupted.
When fuel of a low heating value, such as blast furnace gas, is used, it can be advantageous, when the detector 2 is arranged at fuel channel 3, to arrange the detector at a special pipe that runs within fuel channel 3.
Furthermore, the burner is arranged to supply to the second oxidant channel 4 a fraction of the total amount of oxidant supplied to support the combustion process.
Fuel channel 3 and the second oxidant channel 4, which are located closer to each other than are fuel channel 3 and first oxidant channel 5, are so positioned that a stable flame that begins close to the burner head outlet can be maintained.
Fuel channel 3 and the first oxidant channel 5 are located at such a distance from each other that the gases that are injected are diluted with combustion gases adjacent to the burner head outlet. That dilution, together with the fact that the diluted gases are first mixed at a certain distance away from the burner head outlet, means that the gases react with each other in a combustion process in such a way that the formation of NOx is suppressed, as has been described above.
It is most advantageous to use with the present invention oxidants that have an O2 content that is greater than 85%. The fuel can be natural gas, propane, butane, gasol, heating oil, etc.
The oxidant is injected into the combustion zone through one or several nozzles designed as straight pipes, or as Laval nozzles, or as Venturi nozzles. A preferred pressure for the oxidant is an excess pressure of at least 2 bar above that of the fuel pressure. The greater that oxidant pressure, the greater will be the suppression of the formation of NOx that is achieved. A preferred oxidant pressure for normal applications is 4-5 bar. The fuel is injected through normal nozzles at the pressure that is available.
The distance between fuel channel 3 and the first oxidant channel 5 should exceed approximately 40 mm in order to achieve the desired effect.
When oxidant is supplied to the first oxidant channel 5, the supply of oxidant to the second oxidant channel 4 continues. In that way a stable combustion process also is obtained for fuel and the oxidant that is supplied through the first oxidant channel 5.
As has been described above, the detector 2 is arranged at the fuel channel 3 or at the second oxidant channel 4. Both of those channels open out close to each other at the outlet side of the burner head that faces the furnace, and for that reason detection of a flame that arises from combustion of fuel with oxidant from the second oxidant channel 4 will be extremely secure. Fuel and the oxidant from the first oxidant channel 5 will be combusted, provided that a flame is present.
Thus, an extremely secure indication of combustion is obtained. That means that the present method and arrangement make possible the detection of the flame by a UV detector under all conceivable operating temperature conditions.
In accordance with one preferred design, between 4 and 40% of the oxidant is supplied by the second oxidant channel 4. That amount of oxidant provides a stable flame, while at the same time the fraction of oxidant is sufficiently small not to adversely influence the formation of NOx.
In accordance with a further preferred design, between 5 and 15% of the oxidant is supplied through the second oxidant channel 4.
In accordance with one preferred design shown in
In accordance with an alternative design shown in
It is clear that the channels can be designed in another way and that there can be other channels without deviating from the innovative concept.
Furthermore, it is clear that one skilled in the art will have no difficulty in determining dimensions and positions for the channels such that the technical effects described above are obtained.
Although particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit of the present invention. It is therefore intended to encompass within the appended claims all such changes and modifications that fall within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0501840-3 | Aug 2005 | SE | national |
