GB1591318A - Injection of combustibles into a blast furnace - Google Patents

Description

(54) INJECTION OF COMBUSTIBLES INTO A BLAST FURNACE (71) We, ACIERIES REUNIES DE BUR BAcH-EicH-DUDELANGE S.A. ARBED, of Avenue- de la Liberty, Luxembourg, a society' anonyme organised under the laws of Luxem burg, do hereby- declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention concerns a method and apparatus for introducing combustibles into the air stream injected into a blast furnace.

Conventional smelting in the blast furnace consists essentially in reduction of iron oxides of the charge by means of a reducing agent constituted by coke. Because coke is expensive and bulky it has been the practice for many years to replace some of this solid combustible by liquid or gaseous combustibles; notably hydrocarbons, with the double- objective of reducing cost and improving the productivity of the blast furnace.

Heretofore the addition of liquid combustibles to replace part of the coke has been effected by injection or atomisation into the hot air stream at the entrance to or within the tuyères. Generally the droplets were too large, or their mixture with the air too- imperfect, so that the rate of combustion diminishes in proportion to the increase in the quantity of combustible injected.

To obtain, with the injection of substantial quantities of auxiliary- combustible, a good rate of coke replacement, which is defined as being the ratio between the auxiliary combustible added to the air and the quantity of the coke effectively replaced by the combustible; a series of measures have already been- proposed. Apart from: measures- consisting in improving pulverisation, for example by emulsifying the liquid combustible or improving the pulverising equipment, many proposals are known which seek to modify the flow characteristics of the hot air through special tuyères to give better mixing of the combustible with the air and the combustion of substantial' quantities of liquid combustible- without the formation of soot.

Certain of these proposals provided tuybres formed with converging, neck and diverging portions specially designed to improve the dispersal of the combustible injected (usually at the convergence or at the neck) into the air travelling along at subsonic speed; to avoid eddy currents and delay ignition of the combustant-combustible mixture, after its arrival at the nozzle of the tuyère, the divergent portion may haye a curvilinear profile.

Another proposal aims at a tune'rye provided with a convergent portion, a sonic neck, and a divergent portion, to accelerate the air momentarily to supersonic speed and cause a shock wave in the divergent portion.

Under the effect of the variation in pressure and the turbulence due to the shock wave, the liquid combustible injected upstream of the shock wave is atomised and mixed with the air.

Because of the special configuration of the internal walls, the making of these tuyères is considerably more difficult and delicate than that of conventional simple tuyères.

Further the combustible injection system generally passes through the tuyère wall or is mounted within it, this evidently not simplifying the construction. It follows that most of these special tuyères cost between 50% or 100% more than normal tuyères. The extra costs occurring on installation and on replacement of used or damaged tuyCres- certain special tuyères are particularly liable to damage by melt flow-back--are consequently not negligible.

The present invention provides a method of injecting combustible into a blast furnace in partial replacement of reductant coke, in which air is fed to a tuytre of the furnace through an air pipe having a constriction of its- internal wall capable of accelerating air flow therethrough and an expansion zone downstream of the constriction; and the combustible is injected into the air in this expansion zone. It also provides apparatus for the injection of combustible into a blast furnace, the apparatus comprising an air pipe connected to a tuyère, the pipe having a construction of its internal wall capable of accelerating air flow therethrough, an air expansion zone downstream of the constriction and means for injecting a combustible into the air in the expansion zone.

The method according to the invention is different from the operation of the prior special tuyeres, and allows good mixing of the combustible with the combustant and complete combustion of substantial quantities of the combustible, resulting in a high rate of replacement of coke by the auxiliary combustible. Thus results equivalent to those of known procedures may be obtained without use of special tuybres and hence with simpler equipment and at less expense.

Embodiments of the invention are described below, by way of example only, with reference to the accompanying drawing. In this drawing Figure 1 is a longitudinal sectional view of apparatus according to the invention comprising an air pipe mounted on a conventional tuyère, and Figure 2 shows, likewise in longitudinal section, another embodiment of the air pipe.

It is seen from Figure 1 that the tuybre 1 is of wholly conventional construction. It is constituted essentially by an annular chamber 11 cooled by circulation of water.

The inner wall 12 defines a standard slightly tapering passage which opens into the blast furnace at the nozzle of the tuyère.

The air pipe 2 is provided with an inner profile in which the cross-section of the passage 21 (Figure 1), 211 (Figure 2) is adapted to the required speed of the air.

This speed may be subsonic or supersonic, but it will usually be at least Mach 0 35.

In the example illustrated by Figure 1 the profile is formed by frusto-conical convergent and divergent portions 22 and 23. The convergent portion 22 starts at the junction of the air pipe 2 with the outlet of main piping sypplying the air, oxygenated or not, to the various tuyères 1 of the blast furnace.

The divergent portion 23 extends from the neck 21 to the mouth of the air pipe.

Figure 2 shows a second embodiment of an internal profile for the air pipe of the apparatus. This profile comprises a convergent portion 221, a cylindrical neck 211 and divergent portion 231.

It will be understood that different configurations of this profile are possible according to the air flow characteristics required and according to the parameters imposed by the operation of the blast furnace.

The air pipes illustrated are constituted by conventional metallic casings 24, 24' which are lined internally with a refractory facing 25, 251 preformed or cast according to the profile required.

The conduit 3, 31 for supplying the combustible into the air flow opens into the divergent portion 23, 23' of the air pipe.

Embodiments different from the illustrated arrangement in which a supply conduit passes obliquely through the wall of the air pipe are possible. Likewise one may use pipes or injectors of different design, provided that they deliver the combustible into the air expansion zone. By the same method and apparatus one can introduce liquid, gaseous or solid combustibles into the blast furnace with the same favourable results; WHAT WE CLAIM IS:- 1. A method of injecting combustible into a blast furnace in partial replacement of reductant coke, in which air is fed to a tuybre of the furnace through an air pipe having a constriction of its internal wall capable of accelerating air flow therethrough and an expansion zone downstream of the constriction, and the combustible is injected into the air in this expansion zone.

2. A method according to claim 1 wherein the combustible is liquid.

3. Apparatus for the injection of combustible into a blast furnace, the apparatus comprising an air pipe connected to a tuyère, the pipe having a constriction of its internal wall capable of accelerating air flow therethrough, an air expansion zone downstream of the constriction, and means for injecting a combustible into the air in the expansion zone.

4. Apparatus according to claim 1 wherein the air pipe interior comprises a portion converging away from the pipe inlet and a portion diverging towards the pipe outlet.

5. Apparatus according to claim 4 having a cylindrical neck between the said portions.

6. Apparatus according to any of claims 3 to 5 in which the air pipe has an internal refractory lining.

7. A method of injecting combustible into a blast furnace, the method being substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawing.

8. A method of injecting combustible into a blast furnace, the method being substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawing.

9. Apparatus for injecting combustible into a blast furance the apparatus being substantially as hereinbefore described with reference to Figure 1 of the accompanying 'drawing.

10. Apparatus for injecting combustible

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. this expansion zone. It also provides apparatus for the injection of combustible into a blast furnace, the apparatus comprising an air pipe connected to a tuyère, the pipe having a construction of its internal wall capable of accelerating air flow therethrough, an air expansion zone downstream of the constriction and means for injecting a combustible into the air in the expansion zone. The method according to the invention is different from the operation of the prior special tuyeres, and allows good mixing of the combustible with the combustant and complete combustion of substantial quantities of the combustible, resulting in a high rate of replacement of coke by the auxiliary combustible. Thus results equivalent to those of known procedures may be obtained without use of special tuybres and hence with simpler equipment and at less expense. Embodiments of the invention are described below, by way of example only, with reference to the accompanying drawing. In this drawing Figure 1 is a longitudinal sectional view of apparatus according to the invention comprising an air pipe mounted on a conventional tuyère, and Figure 2 shows, likewise in longitudinal section, another embodiment of the air pipe. It is seen from Figure 1 that the tuybre 1 is of wholly conventional construction. It is constituted essentially by an annular chamber 11 cooled by circulation of water. The inner wall 12 defines a standard slightly tapering passage which opens into the blast furnace at the nozzle of the tuyère. The air pipe 2 is provided with an inner profile in which the cross-section of the passage 21 (Figure 1), 211 (Figure 2) is adapted to the required speed of the air. This speed may be subsonic or supersonic, but it will usually be at least Mach 0 35. In the example illustrated by Figure 1 the profile is formed by frusto-conical convergent and divergent portions 22 and 23. The convergent portion 22 starts at the junction of the air pipe 2 with the outlet of main piping sypplying the air, oxygenated or not, to the various tuyères 1 of the blast furnace. The divergent portion 23 extends from the neck 21 to the mouth of the air pipe. Figure 2 shows a second embodiment of an internal profile for the air pipe of the apparatus. This profile comprises a convergent portion 221, a cylindrical neck 211 and divergent portion 231. It will be understood that different configurations of this profile are possible according to the air flow characteristics required and according to the parameters imposed by the operation of the blast furnace. The air pipes illustrated are constituted by conventional metallic casings 24, 24' which are lined internally with a refractory facing 25, 251 preformed or cast according to the profile required. The conduit 3, 31 for supplying the combustible into the air flow opens into the divergent portion 23, 23' of the air pipe. Embodiments different from the illustrated arrangement in which a supply conduit passes obliquely through the wall of the air pipe are possible. Likewise one may use pipes or injectors of different design, provided that they deliver the combustible into the air expansion zone. By the same method and apparatus one can introduce liquid, gaseous or solid combustibles into the blast furnace with the same favourable results; WHAT WE CLAIM IS:-

1. A method of injecting combustible into a blast furnace in partial replacement of reductant coke, in which air is fed to a tuybre of the furnace through an air pipe having a constriction of its internal wall capable of accelerating air flow therethrough and an expansion zone downstream of the constriction, and the combustible is injected into the air in this expansion zone.

2. A method according to claim 1 wherein the combustible is liquid.

3. Apparatus for the injection of combustible into a blast furnace, the apparatus comprising an air pipe connected to a tuyère, the pipe having a constriction of its internal wall capable of accelerating air flow therethrough, an air expansion zone downstream of the constriction, and means for injecting a combustible into the air in the expansion zone.

4. Apparatus according to claim 1 wherein the air pipe interior comprises a portion converging away from the pipe inlet and a portion diverging towards the pipe outlet.

5. Apparatus according to claim 4 having a cylindrical neck between the said portions.

6. Apparatus according to any of claims 3 to 5 in which the air pipe has an internal refractory lining.

7. A method of injecting combustible into a blast furnace, the method being substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawing.

8. A method of injecting combustible into a blast furnace, the method being substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawing.

9. Apparatus for injecting combustible into a blast furance the apparatus being substantially as hereinbefore described with reference to Figure 1 of the accompanying 'drawing.

10. Apparatus for injecting combustible

into a blast furnace the apparatus being substantially as hereinbefore described with reference to Figure 2 of the accompanying drawing.