The present invention relates to a method and to a device for igniting and monitoring a burner.

The invention is mainly concerned with so called SER-type burners, i.e. burners that include in the extension of the burner head a pipe which is surrounded by an outer pipe that has a closed bottom but the invention can also be of the applied to "straight-through" burners or open burners that lack the provision of a protective pipe.

A burner is typically monitored with the aid of an electrode placed at the periphery of the flame. The electrode is coupled to an electric circuit which is unable to conduct electric current until the circuit is connected between electrode and burner or flame pipe as a result of ionization at the flame periphery. Alternatively, there is used a UV-detector for detecting the ultra violet radiation that occurs in the presence of combustion.

Ionization detection requires the placement of an electrode in the edge of the flame, whereas UV-detection requires the ability to capture said UV-radiation.

A problem occurs with ionizing detection in the case of so-called high speed burners. In the case of high speed burners, a fuel mixture flows from the burner head at a high velocity, meaning that the length and the position of the flame will vary with the velocity of the outflowing fuel mixture. The position of the flame therefore requires an electrode whose length is greater than the electrode of a conventional burner and which hangs freely or, in the best of cases, can be supported with the aid of a ceramic outer pipe. There must be no metallic contact with the burner.

The problem is further accentuated by the desire to use a detection electrode to ignite the flame, by applying a high voltage through the electrode in order to generate a spark between its forward part and the burner upstream of the inrushing fuel/air mixture. The use of a high voltage means that the electrode must be enclosed by a ceramic pipe in order to isolate the electrode from the burner, meaning that the cross-sectional surface area of the electrode will be other than negligible in respect of the fuel-mixture delivery channel of the burner.

A typical ignition electrode that is dimensioned to ensure sufficient shape stability and oxidation length of life will, together with an insulating ceramic, reduce considerably the space available for conducting fuel and combustion air/ premix air.

In addition to a high speed burner producing a variable flame form, the position of the electrode becomes more critical when power is increased. The best ionization is obtained at the edge of the flame. An electrode which is placed along the longitudinal axis of the burner will either function poorly or not at all.

Eccentric positioning of the electrode will result in disturbance of the flame symmetry.

It has been observed that in the case of UV-detection a UV-sensor viewing angle that deviates axially is highly sensitive to the position of the flame.

These problems are resolved by means of the present invention, the object of which is to provide a construction which is less pretentious with regard to the cross-sectional area of the burner than traditional present day solutions, while maintaining mechanical stability and oxidation life length.

The present invention thus relates to a method of igniting and monitoring a high speed burner with which a fuel/oxygen mixture flows from a burner head at high velocity, wherewith the length of the flame is dependent on said velocity, wherein the invention is characterized by placing an electrically conductive pipe in and concentrically with the burner channel intended for said fuel mixture wherein the first end of the pipe is terminated close to the fuel mixture outlet of the burner head, wherein the pipe is provided with an electrical insulation, and wherein light from the group ultraviolet light, visible light and/or infrared light is caused to be detected at the other end of the pipe, and wherein, in the case of ignition, a spark is caused to be generated between the first end of the pipe and the surrounding burner head through the medium of the electric voltage.

The invention also relates to a burner of the kind that has the significant characteristic features set forth in the accompanying claim 5.

The invention will now be described in more detail, partly with reference to an exemplifying embodiment of the present invention illustrated in the accompanying drawing, of which Fig. 1 is a longitudinal sectioned view of an inventive burner.

Fig. 1 illustrates a high speed burner with which a fuel/oxygen mixture is intended to exit at high velocity from a burner head 2, wherewith the length of the flame is dependent on said velocity. Figure 1 shows only the front and the rear part of the burner. The rear part of the burner includes respective fuel and oxygen-containing gas inlets 3, 4. The mixture is transported in a tubular channel 5 whose orifice 6 is surrounded by the burner head 2. The burner head includes a mixture outlet 7 and the mixture is combusted externally of the burner head.

According to the invention, the burner includes an electrically conductive pipe 8 placed in and concentrically with the fuel mixture conveying channel 5 of the burner 1. The first end 9 of the pipe 8 terminates close to the fuel mixture outlet of the burner head.

Moreover, the pipe is provided with an electric insulation 10 which, according to a preferred embodiment of the invention is comprised of a ceramic pipe that encases the electrically conductive pipe.

According to the invention, a light detector 11 is placed at the other end 12 of the pipe 5, said detector being intended to detect light belonging to the group ultraviolet light, visible light and/or infrared light. The detector is designed to emit an electric signal dependent on the light detected, said signal being sent to a detection circuit 13 which is caused to detect whether or not combustion has taken place.

Furthermore a voltage source 14 is connected to said pipe 5 and to the burner 1 by means of electrical conductors 16, 17, so that in the case of ignition a spark 15 is generated between the first end 6 of the pipe and the surrounding burner head 2 through the medium of said voltage.

The present invention relates to a method of igniting and monitoring such a burner. According to this method, the pipe is placed in and concentrical with the burner channel for said fuel mixture, and the first end of the pipe is terminated close to the fuel-mixture exit orifice of the burner head. The pipe is insulated electrically. Light from the group ultraviolet light, visible

light and/or infrared light is caused to be detected at the other end of the pipe so as to detect whether or not combustion occurs. Ignition is effected by causing a spark to be generated between the first end of the pipe and the surrounding burner, through the medium of an electric voltage.

This enables conditions to be achieved that result in sufficiently high UV-radiation from a burner flame to allow detection to be achieved with the aid of a typical UV-detector 11 in respect of an industrial burner, with the possibility of maintaining flux symmetry and minimum influence on the flow conditions.

In order to give the detection a function that is not dependent on burner power, the line of view extends in the central axis of the burner, in other words immediately downstream of the flame.

An eccentrically positioned viewing or sighting channel will be more dependent on the position, of the flame in respect of capturing the light to the detector 11, irrespective of whether said channel is parallel with or at a small angle to the burner axis. Moreover, an eccentrically positioned sighting channel will result in asymmetry or disturbance in the flow pattern of the inflowing fuel mixture.

Furthermore, the pipe 8 constitutes a centrally positioned ignition electrode which, as a result of its tubular configuration, is able to permit a sufficiently large sighting or viewing channel, therewith fulfilling requirements with regard to both detection and ignition. It is also possible to lead some of the fuel mixture through the pipe 8. This increases the available cross- sectional area in the burner channel 5 for the fuel mixture. In such cases inlet openings are provided in the pipe 8 at the downstream part of the burner.

According to one preferred embodiment of the invention, at least one support leg 18 that includes radial wings 19 is placed in the fuel mixture channel and adapted to maintain said coaxial position of the pipe.

By constructing the pipe of a material that is electrical conductive in the temperature range of 50-2500 degrees C, it is possible to utilize the ratio of the moment of surface inertia to stiffness, this ratio being greater to that of a rod. This greater stiffness or rigidity enables the

wall thickness to be reduced. As before-mentioned, the cylindrical cavity can be used for medium transportation and therewith provide more room for the passage of gas and air. This reduces the overpressure required to drive the combustion components as distinct from the case when the cavity is not used.

The coaxial positioning of the pipe 8 is of uttermost importance in respect of combustion technology, since it has been found that the positioning of the pipe has no detrimental effect on the combustion characteristics of the burner.

Tests have shown that a centrally positioned pipe 8 that has an internal cross-sectional area of about 19 mm ² will capture sufficient UV-radiation. This pipe will capture more radiation than an eccentrically positioned pipe that has an internal cross-sectional area of 64 mm ² .

Although the invention has been described above with respect of an ultraviolet light detector, it will be understood that this detector can be replaced with a visible light detector or with an infrared light detector said lights being detected by a suitable known detector connected to said detection circuit.

Although the invention has been described above with reference to a number of exemplifying embodiments thereof, it will be understood that the described embodiments can be varied with respect to the choice of material used and their dimensions.

It will therefore be understood that the invention is not restricted to said embodiments but that variations and modifications can be made within the scope of the accompanying claims.