RANGMARK LENNART (SE)
EKMAN TOMAS (SE)
RANGMARK LENNART (SE)
| US4525138A | 1985-06-25 | |||
| US4541798A | 1985-09-17 | |||
| US5503548A | 1996-04-02 | |||
| US4378205A | 1983-03-29 | |||
| US6196831B1 | 2001-03-06 |
| Claims
1. A method during the combustion of a fuel with an oxidant in an industrial furnace, in which the fuel and the oxidant are supplied to a burner head and where the flame is monitored by means of a detector for ultraviolet light, characterised in that at least one channel (3) for the supply of fuel and at least two channels (4, 5) for the supply of oxidant are present and open out into the surface (6) of the burner head
(1) that faces into the furnace, in that the channel (3) for fuel and a first channel (5) for oxidant are located at a distance from each other, in that the channel (3) for fuel and the second channel (4) for oxidant are located more closely to each other, in that the said detector (2) is arranged at the channel (3) for fuel or at the second channel (4) for oxidant, and in that a fraction of the total amount of oxidant supplied is caused to be supplied to the said second channel (4) for oxidant, and in that oxidant is supplied to the said second channel during the complete combustion process.
2. The method according to claim 1, characterised in that between 4 and 40% of the oxidant is caused to be supplied to the said second channel (4) .
3. The method according to claim 1 or 2, characterised in that between 5 and 15% of the oxidant is caused to be supplied to the said second channel (4) .
4. The method according to claim 1, 2 or 3, characterised in that the said second channel (4) and the channel (3) for fuel are caused to be coaxial.
5. The method according to claim 1, 2 or 3, characterised in that the said second channel (4) and the channel (3) for fuel are caused to be separate and parallel.
6. A burner for the combustion of a fuel with an oxidant in an industrial furnace, in which the burner is arranged to supply fuel and oxidant to the burner head of the burner and where a detector for ultraviolet light is present in order to monitor a flame from the burner head, characterised in that at least one channel (3) for the supply of fuel and at least two channels (4, 5) for the supply of oxidant are present and open out into the surface (6) of the burner head (1) that faces into the furnace, in that the channel (3) for fuel and a first channel (5) for oxidant are located at a distance from each other, in that the channel (3) for fuel and the second channel (4) for oxidant are located more closely to each other, in that the said detector (2) is arranged at the channel (3) for fuel or at the second channel (4) for oxidant, and in that the burner is arranged to supply a fraction of the total amount of oxidant to the said second channel (4) for oxidant.
7. The arrangement according to claim 6, characterised in that the burner is arranged to supply between 4 and 40% of the oxidant to the said second channel (4) .
8. The arrangement according to claim 6, characterised in that the burner is arranged to supply between 5 and 15% of the oxidant to the said second channel (4) .
9. The arrangement according to claim 6, 7 or 8, characterised in that the said second channel (4) and the channel (3) for fuel are coaxial.
10. The arrangement according to claim 6, 7 or 8, characterised in that the said second channel (4) and the channel (3) for fuel are separate and parallel. |
Method and Arrangement for Monitoring a Burner
The present invention relates to a method and an arrangement for monitoring a burner, principally burners used in indus- trial furnaces .
One way of solving the problem of the formation of NO x during the combustion of fossil fuels is to inject gases at a high rate of flow into the combustion zone. Gaseous fuel and a gaseous oxidant are injected at a distance from each other into the combustion zone. The gases are injected through lances that are provided with nozzles into a burner head. The injected gases will be diluted with combustion gases since the gases are injected at a distance from each other. This 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 lower rate than that of conventional combustion due to a lower concentration of gases. This combustion ensures that the formation of NO x 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 sensitive to ultra- violet radiation. The sensor is normally mounted in the burner such that the UV-sensor sees a part of a flame that is present .
The flame will become longer and more spread out through the method of combustion described above, and thus less visible. This makes the detection of a flame by means of the sensor considerably more difficult. Furthermore, the method of combustion described above requires that the furnace is first heated to the spontaneous ignition temperature of the gases
before combustion by the method described above can be commenced. The furnace is in this case operated at a temperature that lies under approximately 800 0 C. A burner of the type specified above cannot for reasons of safety be used during the heating phase since a flame of the type described is difficult to detect at a temperature under 800 0 C, while safety regulations at the same time specify that UV- monitoring is to take place at temperatures that lie under 800°C.
The present invention solves this problem.
The present invention thus relates to a method during the combustion of a fuel with an oxidant in an industrial fur- nace, in which the fuel and the oxidant are supplied to a burner head and where the flame is monitored by means of a detector for ultraviolet light, and it is characterised in that at least one channel for the supply of fuel and at least two channels for the supply of oxidant are present and open out into the surface of the burner head that faces into the furnace, in that the channel for fuel and a first channel for oxidant are located at a distance from each other, in that the channel for fuel and the second channel for oxidant are located more closely to each other, in that the said detector is arranged at the channel for fuel or at the second channel for oxidant, and in that a fraction of the total amount of oxidant supplied is caused to be supplied to the said second channel for oxidant, and in that oxidant is supplied to the said second channel during the complete combustion process.
The invention furthermore relates to an arrangement of the type and having the principal characteristics that are specified in claim 6.
The invention is described in more detail below, partially in association with an embodiment of the invention shown on the attached drawings, where
- Figure 1 shows schematically a longitudinal section of a burner head according to the invention, and
- Figures 2a, 2b and 2c show alternative embodiments of a central part of the burner head seen from the right in Figure 1.
Figure 1 shows a burner for the combustion of a fuel with an oxidant in an industrial furnace. The burner is arranged such that fuel and oxidant are supplied to the burner head 1. A detector 2 for the detection of ultraviolet light is present outside of the burner head 1 in order to monitor a flame.
According to 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, opening out in the surface 6 of the burner head that faces the furnace. The channel 3 for fuel and a first channel for oxidant are located at a distance from each other, and the channel 3 for fuel and the second channel 4 for oxidant are located more closely to each other.
Figure 1 shows also a third channel 7 for the supply of oxidant.
The said detector 2 is arranged at the channel 3 for fuel or in the second channel 4 for oxidant. It is appropriate that the detector is arranged at the end of the channel that lies farthest away from the furnace and so arranged that UV-light from the flame that is led into the channel impinges upon the detector. The detector is connected to a detector circuit, not shown in the drawings, by means of which circuit the presence or otherwise of a flame can be assessed. In the case
in which a flame is not detected, supply of fuel and oxidant is interrupted.
When fuel of low value, such as blast furnace gas, is used, it may be advantageous, in the case in which the said detector 2 is arranged at the channel 3 for fuel, to arrange the detector at a special pipe that runs within the channel 3 for fuel .
Furthermore, the burner is arranged to supply a fraction of the total amount of oxidant supplied to the said second channel 4 for oxidant.
The channel 3 for fuel and the second channel 4 for oxidant, which are located more closely to each other, have a distance between them such that a stable flame that begins close to the burner head can be maintained.
The channel 3 for fuel and the first channel 5 for oxidant are located at such a distance from each other that the gases injected are diluted with combustion gases. This 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 in which the formation of NO x is suppressed, as has been described above.
It is most advantageous to use oxidants with the present invention that have an 02~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 space through one or several nozzles designed as straight pipes or through
Laval nozzles or Venturi nozzles. A preferred pressure for the oxidant is an excess pressure of at least 2 bar. The greater this pressure, the greater will be the suppression of the formation of NO x that is achieved. A preferred pressure for normal applications is 4-5 bar. The fuel is injected through normal nozzles at the pressure that is available.
The distance between the channel 3 for fuel and the said first channel should exceed approximately 40 mm in order to achieve the desired effect.
When oxidant is supplied to the first channel 5, supply of oxidant to the second channel 4 for oxidant continues . A stable combustion process is in this way obtained also for fuel and the oxidant that is supplied through the first channel for oxidant.
As has been described above, the detector 2 is arranged in the channel 3 for fuel or in the second channel 4 for oxi- dant . Both of these channels open out close to each other in the side of the burner head that faces the furnace, and for this reason detection of a flame that arises from combustion with oxidant from the second channel 4 for oxidant will be extremely secure. Fuel and oxidant from the first channel 5 for oxidant will be combusted provided that this flame is present .
Thus, an extremely secure indication of combustion is obtained. This means that the present method and arrangement make possible the detection of the flame by a UV-detector under all conceivable operating conditions .
According to one preferred design, between 4 and 40% of the oxidant is caused to be supplied by the said second channel
4. This amount of oxidant gives a stable flame, while at the same time the fraction of oxidant is sufficiently small not to influence the formation of NO x .
According to a further preferred design, between 5 and 15% of the oxidant is caused to be supplied through the said second channel 4.
Figures 2a-2c show different designs of the channel for fuel and the said second channel, seen from the right in Figure 1.
According to one preferred design shown in Figure 2a and Figure 2b, the said second channel 4;4B and the channel 3;3B for fuel are coaxial .
According to an alternative design shown in Figure 2c, the said second channel 4C and the channel 3C for fuel are separated and parallel.
It is clear that the channels may be designed in another way and that there may be other quantities of these without deviating from the innovative concept.
Furthermore, it is clear that one skilled in the arts will have no difficulty in determining dimensions and positions for the channels such that the technical effects described above are obtained.
Thus, the present invention is not to be considered to be limited to the embodiments specified above: it can be varied within the framework specified by the attached patent claims.