Flat-flame Burner Utilizing Heavy Liquid Fuels

Abstract

The invention relates to a flat-flame burner in which the special geometrical configuration of the burner components for introducing the fuel and the combustion air ensure proper mixing thereof and the required geometrical shape of the flames over a wide range of operating conditions.

Description

The present invention relates to a flat-flame burner utilizing liquid fuels and has more particularly for its object to provide a structure for such a burner enabling the same to utilize heavy fuels.

In certain steelmaking applications such as for annealing certain substances in heating furnaces, it is often the practice to use the so-called radiant arch technique, which is based on the utilization of "wall flame" burners in which the flame develops along a divergent tunnel, in a plane perpendicular to the axis thereof, so as to lick the wall of the furnace formed by an arch or a wall. Thus the heat transmitted by the flame to the furnace wall by convection is restored by this wall by radiation and is transmitted to the items to be annealed in the furnace.

Prior art "wall flame" burners can operate only on gas or domestic fuel, and it would obviously be most useful for users to have burners capable likewise of operating on fuel-oil and especially heavy fuel-oil.

It is an object of the present invention to provide a structure for a liquid fuel burner of the above-mentioned kind capable of utilizing heavy liquid fuels.

Generally speaking, operation of the aforementioned kind of burner with a flat-flame requires a special geometrical configuration of the fuel and combustion-air-admitting components. Such configuration must ensure not only proper mixing of the fuel and the oxidant but also the required geometrical shape of the flame over a wide range of operating conditions.

In the paticular case of liquid fuel burners, the above requirements are particularly stringent since the geometry of fuel injection into the divergent burner tunnel must be continuously ensured. Hence protracted fouling (due to coking for instance) of the burner tip must be avoided at all costs since this could modify the angle of fuel injection into the tunnel and thereby cause a change in the geometrical shape of the flame.

Further, the position of the injector must be so chosen as to ensure absolute cleanness of the burner tunnel in operation.

A flat-flame burner according to this invention for heavy liquid fuels, comprising a cylindrical body coaxially surrounding a fuel and primary air feeding stick terminating in an injector, a divergent tunnel downstream of the injector, said body being further provided with a secondary air inlet opening in the annular compartment bounded by said body and said stick, and further means being provided for rotating said secondary air before releasing it through an annular slit surrounding the burner tip, is characterized in that said injector includes a needle-valve along which the liquid fuel flows and at the end of which it turns into droplets, said needle-valve being surrounded by a diffuser having helicoid primary air inlet passages for atomizing said droplets, the air/fuel suspension being thereafter directed towards an orifice which is formed in a disc and which is shaped as a convergent nozzle terminating in a rounded edge which joins the convergent portion of the nozzle to that face which lies in a plane perpendicular to the burner axis or very slightly inclined relative to said plane.

The description which follows with reference to the accompanying non-limitative exemplary drawing will give a clear understanding of how the invention can be carried into practice.

In the drawing:

FIG. 1 is a longitudinal sectional view of a flat-flame burner; and

FIG. 2 is a longitudinal sectional view of the injector built into the burner of FIG. 1.

Referring first to FIG. 1, there is shown thereon a flat-flame burner which includes a burner body 1. Inside this body, coaxially therewith, is a fuel input stick 2 which is formed with primary air channelling means (not shown in FIG. 1). Stick 2 terminates in an injector 3 which will be described in greater detail hereinafter. The body 1 is formed with a secondary air opening 4 provided with a diaphragm 5 for swirling the secondary air. This secondary air is discharged through an annular slit 6 surrounding the burner tip. The compound consisting of the burner body, the fuel stick, the injector and the secondary air distributor is fixed to a gun 7 which extends said compound and is itself fixed to the burner unit 8 which is formed with a divergent tunnel 9 therein.

The injector will now be described in detail with reference to FIG. 2. Screwed into the end of fuel stick 2 is a burner tip 10 onto which is screwed a tip nut 11. Into the front face of nut 11 is set a disc 12 made of a material having refractory properties (e.g. steel or ceramics) and having moderate heat conducting properties whereby to obtain a high temperature on the flame side. The fuel stick includes a central fuel-feed duct 13 which is surrounded by a primary air-feed duct 14. Secured by ribs 15 at the end of duct 13, positioned coaxially with the latter, is a needle-valve 16. The walls of duct 13 surrounding said needle-valve form a diffuser having helicoid passages 17 formed therethrough. The disc 12 has a central hole therein to form a convergent 18 terminating in a flared portion which blends the convergent portion with the front face of the disc. This face is shown as being flat and perpendicular to the burner axis in FIG. 2 but could alternatively by formed by a concave or convex cone having a very large apex angle. Alternatively again, the hole 18 could be made very short and consist merely of a profiled hole with flared upstream and downstream portions.

The theory of operation of a burner as hereinbefore described is as follows:

The liquid fuel flowing along needle-valve 16 forms droplets at the end thereof and these droplets are atomized by the jet of primary air swirling about the needle-valve and delivered through helicoid passages 17. The air/fuel suspension formed thus is thereafter directed towards convergent 18, and upon issuing therefrom is mixed with the eddying secondary air escaping through slit 6. The position of the injector in the burner tunnel is so chosen that the external envelope of the jet of atomized liquid fuel lies close to the tangent to the divergent and flared portion 9 of the tunnel, the jet forming an aperture angle of close upon 40.degree..

Claims

1. A flat-flame burner for heavy liquid fuels, comprising a cylindrical body coaxially surrounding a primary air and fuel feeding stick terminating in an injector, a divergent tunnel downstream of the injector, said body being furthermore provided with a secondary air feeding opening in the annular compartment bounded by said body and said stick, and means being further provided for rotating said secondary air before it is released through an annular slit surrounding the injector, characterized in that said injector includes a needle-valve along which the liquid fuel runs and at the end of which it is transformed into droplets, said needle-valve being surrounded by a diffuser formed with helicoid primary-air-feeding passages that atomizes said droplets, the air/fuel suspension being thereafter directed towards an orifice provided in a disc which has formed therein a convergent nozzle terminating in a flared portion which blends the convergent nozzle portion with the disc face, which face lies in a plane perpendicular to the burner axis or very

2. A burner according to claim 1, characterized in that said orifice in said disc forming the burner tip is a very short profiled hole which is

3. A burner according to either preceding claim, characterized in that said

4. A burner according to claim 1, characterized in that said injector is disposed in the burner tunnel so that the external envelope of the jet of atomized liquid fuel lies close to the tangent to the divergent and flared portion of the tunnel, the jet forming an aperture angle of close on 40.degree..