GB2150269A

GB2150269A - Metallurgical lance with flame detector

Info

Publication number: GB2150269A
Application number: GB08331572A
Authority: GB
Inventors: Francis James Simmonds; John Graham Whellock
Original assignee: TOLLTRECK Ltd
Current assignee: TOLLTRECK Ltd
Priority date: 1983-11-25
Filing date: 1983-11-25
Publication date: 1985-06-26
Also published as: GB2150269B; GB8331572D0

Abstract

A metallurgical lance comprises a fibre optic (40) housed within the lance or in a tube mounted thereon, the fibre optic being protected against the heat and arranged to view the flame at the lance tip (50) to provide a signal for flame detection purposes. The fibre optic may as shown be located within a central fuel gas passage (10) of the lance which is surrounded by an oxygen air passage (15) itself enclosed in a cooling jacket (20). The output of the fibre optic may pass through a lens and may be applied to a system to discriminate signals in the range 200-600 Hertz. <IMAGE>

Description

SPECIFICATION Metallurgical processes This invention is concerned with metallurgical processes and, more particularly, with lances for use therein.

In many metallurgical processes, lances or torches or specialised burners are used for providing the highest possible heat flux for the process.

Such lances are usually characterised by the fact that they are water-cooled or gas-cooled, and may be oxy/fuel-fired or oxygen-enriched air fired and have an exceptionally high combustion intensity Unlike conventional burners, their application in the metallurgical process requires them to be used in an extremely flexible manner. For example, lances are used for combustion of oxygen and fuel to provide the heat liberation; they may be used for direct injection of oxygen into a bath without the provision of fuel; or they may be used for providing a reducing atmosphere for example, by the provision of propane or natural gas into the bath to effect a reducing metallurgical reaction.Moreover, lances are frequently retracted from the vessel, or their angle of application altered, and there is frequently much splashing of metal and slag occasioned by the high velocities that this type of equipment requires.

Conventional burners have a sizeable head and usually some form of flame retention using a refractory tile or quarl but, whatever the geometry, it is frequently an easy matter to incorporate a flame sensing device to provide safe-guards in the event the flame may be extinguished. A number of flame sensing devices are available in the market which may be used for this application and consist for example of flame rod detection, infra-red or ultraviolet emission detection systems.

In the case of lances, the application of these conventional flame detection devices and provision of a system for safe flame-failure is not an easy task. Bearing in mind the lance must be retracted, its angle of use could be altered and the high temperature, turbulent and fume laden environment of the furnace in which this type of equipment is used, the conventional methods of sighting the flame would be a severe encumbrance to the satisfactory operation of the lance itself. This is the reason why flame detection to date has not been incorporated on lances, torches or high velocity burners of this nature. The problems have proved insurmountable.

We have investigated the matter and have found that the provision of a flame detection rod is not a viable practice with the use of oxy/fuel-fired systems due to the sheer severity and high temperature of the application. Infra-red detection sources on their own are not a viable solution due to the significant infra-red radiation and re-radiation from refractories and metal/slag charge. The difficulty of sightng the flame for such a moving target is also a major obstacle to flame sensing. Lastly, ultra violet sensing, although it may better discriminate between the flame source and background radiation, likewise suffers the difficulty of being able to sense the lance tip satisfactorily.

However, we have devised a way in which flame detection may be achieved.

In accordance with a feature of the present invention, flame detection is integrated within the lance assembly or in a parallel water-cooled pipe.

For the implementation of this, a fibre-optic line is required to satisfactorily view the combustion at the tip of the lance. The fibre-optic can, for example, be located in the internal gas or oxygen passages of the annular assembly of the lance or in a central core, or be in a separate air cooled passage, so long as it has the benefit of being recessed within the burner head to avoid the intense heat, splashing and possible submergence in slag and metal and also the ability to adequately view the flame. An alternative embodiment would be to have an elliptical lance assembly in which the fibre-optic is located so as effectively not to interfere with the air, oxygen, gas or oil passages. Yet another arrangement involves the incorporation of a separate parallel water or gas-cooled pipe which is moved in conjunction with the main lance so as not to have variable geometry problems.This however, is not a preferred solution since the protection of the viewing head of the fibre-optic is not so easy.

With regard to the actual detection of the flame, the viewing head itself may be a convex type of lens or prism attached to the fibre-optic which may be arranged to view directly or at some acute angle, such that the combustion process may be observed throughout the turn-up/turn-down conditions of the lance.

In recognising the need for a lens and fibre-optic facility, it is important to note that materials of selection for fibre-optics are critical because of losses in transmission of the appropriate ultra-violet or infra-red wave-length. For this reason a preferred solution is the use of an infra-red detection system which suffers much less loss of transmission through conventional fibre-optics and lens assemblies. However, under this circumstance as aforementioned, the viewing head will be seeing spurious signals coming from refractories, molten metal or slag etc. and it is therefore necessary to carry-out signal conditioning to achieve a suitably discriminated source.

A suitable example of a signal discrimination system is one which screens out all signals except those in the band width of 200-600 Hertz frequency which coincides with the flame noise. Under these circumstances, provided a suitable level infra-red wave-length signal is achieved within this band width of frequencies, then flame is satisfactorily detected and conventional circuitry can be used to maintain oil or gas and oxygen valves etc. in their appropriate open positions. Outside this position flame is out and the appropriate valves would be closed accordingly.

Alternatively, ultra-violet sensing may be employed but the fibre-optic materials, lens, couplings etc. require careful selection to avoid transmission loss of the ultra violet so that a suitably strong sig nal may be derived for subsequent signal processing.

A typical application for a lance of the invention would be in a high-speed rotating furnace such as a top blown rotary furnace or converter where the position of the lance must be varied according to the requirements of the process. Often in such furnaces, the lance position adjacent to the molten charge is varied significantly during the course of operation and also the angle of the lance relative to the charge may be varied in both vertical and horizontal planes. In such circumstances it is clear that the incorporation of variable geometry viewing with conventional sensing heads would be a difficult problem and hence the application of the fibre-optic sensing technique.

In order that the invention may be more fully understood, one embodiment of lance of the invention will now be described, by way of illustration only, with reference to the accompanying drawings, in which Figures 1 and 2 are both longitudinal sections of the lance, Figure 1 showing the forward end and Figure 2 the rearward end of the same lance.

Referring to the drawings, the lance comprises an assembly of elongate concentric tubes defining gas and liquid flow passageways. The innermost tube 10, of miid steel or stainless steel, extends from an inlet 11 at the rear end of the lance to the flame plate 12 at the forward end of the lance.

Plate 12 has orifices 13 to allow gas (in this case fuel gas) passing aiong tube 10 to exit to the flame.

Around tube 10 is tube 15 also of mild steel or stainless steel. At the forward end of the lance (Figure 1) plate 12 seats in tube 15 to ciose the end thereof apart from the provision of orifices 16 in plate 12 to allow gas (in this case oxygen) to pass from tube 15 to the flame. At the rearward end of the lance (Figure 2), tube 15 has a lateral gas supply port 17.

Around tube 15 is outer tube 20 (of stainless steel) which, together with the outer surface of tube 15 defines a cooling jacket. A baffle tube 21 is provided in tube 20. At the rearward end of tube 20 (which does not extend to the rear end of the lance) are cooling fluid inlet (22) and outlet (23) ports.

The flame detection means of the invention comprises a fibre optic bundle 40 disposed in tube 10.

The bundle 40 is supported to observe through one end 41 thereof, the lance flame via orifices 13.

The other end 43 of the bundle, at the rearward end of the lance, is mounted to emit light to a lens 42 (from whence it may be transmitted to control apparatus as desired).

In operation, fuel gas is supplied via inlet 11 to tube 10 from when it flows through orifices 13 in plate 16 to ignite in space 50. Oxygen (or air) is supplied from inlet 17 into the annul us between tubes 15 and 10, from whence it flows through orifices 16 to burn in space 50. A cooling fluid, e.g.

water is passed through the annulus between tubes 15 and 20. Observation of the flame in space 50 is made via the fibre optic bundle 40 which views the flame through orifices 13. Means may be provided, if necessary, to mount bundle 40 in the appropriate position for optimum visibility of the flame. The signal output from end 43 of bundle 40 passes through lens 42 and is viewed or automatically monitored in control apparatus (not shown).

Features of the invention include: 1. The principal of incorporation of a fibre-optic or other sensing device within the body of a lance with or without a viewing lens capable of viewing the flame or combustion process from within the body of the lance assembly and protected from the heat flux and metallurgical process by its own water cooling jacket.

2. The processing of the fibre-optic signal such that discrimination can be made between combustion process and the radiation or re-radiation effects within the furnace.

3. The incorporation of a flame sensing system as in (1) above whereby the fibre-optic is incorporated within either the gas, oxygen or air passage within the lance which may be annular or central to the access of the lance.

4. The incorporation of a flame sensing device as in (1) above whereby the sensing system is a parallel water-cooled pipe incorporating appropriate viewing lens to sense the combustion process.

5. The incorporation of a flame sensing device as in (1) above using an elliptical pipe whereby the flame sensing system is outside the main body of the gas or oil or oxygen system, yet within the same water-cooled assembly and capable of viewing the combustion phenomenon through an appropriate lens.

Claims

1. A metallurgical lance which includes a flame detection device comprising at least one optical fibre arranged to view (in use), at the tip of the lance, combustion of one or more combustible fluids supplied through the lance, said optical fibre(s) being at least partly housed within the lance or in a pipe mounted externally on, and movable with, the lance.

2. A lance according to claim 1, wherein the or each optical fibre is within a gas passage internally of the lance.

3. A lance according to claim 1 or 2 wherein the or each optical fibre is so located in the lance as not to interfere with the flow of combustible fluids through the lance.

4. A lance according to claim 1,2 or 3, which further includes a system for receiving signals from the optical fibre(s) and discriminating those required for flame detection.

5. A lance according to claim 4, wherein the said system is arranged to discriminate signals in the band with 200-600 Hertz only for flame detection.

6. A lance substantially as herein described with reference to the accompanying drawings.

7. A method of operating a rotating furnace which includes the step of supplying combustible material thereto through a lance characterised in that the lance is as defined in any of claims 1 to 6 and said method includes monitoring the presence of a flame at the lance tip.