PROCESS FOR INJECTING PARTICULATE MATERIAL INTO A LIQUID METAL BATH

Abstract

The invention relates to a process for injecting particulate material into a liquid metal bath wherein the liquid metal bath contains species to be oxidized, wherein the particulate material is carried to the liquid bath by means of a first gas stream. The solids injection rate is controlled such that the liquid bath temperature and/or the evolution of the liquid bath temperature is maintained within a pre-defined temperature range and the penetration depth of the first gas stream into the liquid bath is controlled by adjusting the flow of the first gas stream. At least one second gas stream is injected into the liquid, wherein the first and the second gas streams are an oxidizing gas, in particular oxygen, and the sum of the gas flows of the first and the second gas streams is determined based on the mass of the species to be oxidized and on the desired time for oxidizing the mass of the species.

Claims

1. Process for injecting particulate material into a liquid metal bath by means of a lance, the lance comprising an axial solids injection pipe, wherein the liquid metal bath contains species to be oxidized, wherein the particulate material is carried to the liquid bath by means of a first gas stream and wherein the first gas stream with the particulate material penetrates into the liquid bath, characterized in that the solids injection rate is controlled such that the liquid bath temperature is maintained within a first pre-defined temperature range and/or the evolution of the liquid bath temperature is maintained within a second pre-defined range, wherein the solids injection rate is defined as the mass of particulate material introduced into the liquid bath per time unit, that the penetration depth of the first gas stream into the liquid bath is controlled by adjusting the flow of the first gas stream, that at least two second gas streams are injected into the liquid at a diverging angle from the first gas stream, that the first and the second gas streams are an oxidizing gas, in particular oxygen, and that the sum of the gas flows of the second gas streams is controlled such that the liquid bath temperature is maintained within the first pre-defined temperature range and/or the evolution of the liquid bath temperature is maintained within the second pre-defined range.

2. Process according to claim 1, characterized in that the lance is provided at a lance height above the liquid bath, the lance height being defined as the distance in axial direction between the outlet of the solids injection pipe and the surface of the liquid bath, and that the penetration depth of the first gas stream is controlled by adjusting the lance height and/or the flow of the first gas stream.

3. Process according to claim 1, characterized in that the first gas stream is provided at a velocity between 340 m/s and 1100 m/s, preferably between 500 m/s and 900 m/s.

4. Process according to claim 1, characterized in that the second gas streams are provided at a velocity between 340 m/s and 1100 m/s, preferably between 500 m/s and 900 m/s.

5. Process according to claim 1, characterized in that the penetration depth is less than 75% of the depth of the liquid bath, preferably less than 50% of the depth of the liquid bath, more preferred less than 25% of the depth of the liquid bath.

6. Process according to claim 1, characterized in that the first gas stream and/or the second gas streams comprise at least 80% by volume oxygen, preferred at least 90% by volume oxygen, more preferred technical pure oxygen.

7. Process according to claim 1, characterized in that more than 20 kg/min particulate material, preferably more than 50 kg/min particulate material, is injected into the liquid bath.

8. Process according to claim 1, characterized in that the particulate material contains a metallurgical reagent, such as iron, chromium, molybdenum and/or alloys of these metals.

9. Process according to claim 1, characterized in that the particulate material is injected into a metallurgical converter, such as a BOS (Basic Oxygen Steel-Making) converter, a AOD (Argon-Oxygen-Decarburization) converter or a CLU (superheated steam) converter.

10. Process according to claim 1, characterized in that the first pre-defined temperature range is from 1000 C. to 2000 C., preferably from 1450 C. to 1850 C., preferably from 1500 C. to 1650 C.

11. Process according to claim 1, characterized in that the evolution of the liquid bath temperature is less than +/20 C./min, preferably less than +/15 C./min.

12. Process according to claim 1, characterized in that the angle between the first gas stream and one of the second gas streams is between 5 and 20.

13. Process according to claim 1, characterized in that between 2 and 8 second gas streams, preferably between 3 and 6 second gas streams, preferably 3 or 4 second gas streams, are provided.

14. Process according to claim 1, characterized in that the species to be oxidized is carbon and/or silicon.

15. Process according to claim 1, characterized in that the lance is provided vertical to the surface of the liquid bath.

16. Process according to claim 1, employed in a metallurgical refining process, in particular in the manufacture of stainless steel and/or other ferroalloys and/or in the processing of copper, lead, zinc or tin.

Description

[0052] The invention as well as further embodiments and details of the invention shall be described with reference to the attached drawings. Therein,

[0053] FIG. 1 shows the top view on a lance head for use with the present invention,

[0054] FIG. 2 shows the cross section of the lance according to FIG. 1.

[0055] FIG. 1 shows a multi-port injection lance with a central solids injection pipe 1 surrounded by an annular channel 2 for the first gas stream. The lance head further comprises four nozzles 3 for second gas streams. The four outer nozzles 3 are evenly distributed on a circle around the central solids injection pipe 1.

[0056] As shown in FIG. 2 the annular channel 2 is provided with a Laval nozzle 4 for accelerating the first gas stream. The solids injection pipe 1 terminates downstream of the throat of the Laval nozzle 4.

[0057] Four outer channels 5 terminating in the outer nozzles 3 are arranged around the central solids injection pipe 1 and the annular channel 2. The outer channels 5 are divergent with respect to the central solids injection pipe 1 and the axis 6 of the lance. The angle between the solids injection pipe 1 and an outer channel 5 is between 5 and 20, preferably between 7 and 15.

[0058] The multi-port lance according to FIGS. 1 and 2 is used for injecting particulate material, such as dusts, scales, granules or powders into a converter for manufacturing stainless steel. The lance is arranged with its axis in a vertical direction. The particulate material is supplied via the central solids injection pipe 1. Technical pure oxygen with a purity of more than 99.3% by volume is supplied to the annular channel 2. In Laval nozzle 4 the oxygen stream is accelerated to a supersonic velocity, for example to Mach 2. The particulate material leaving the central solids injection pipe 1 is entrained into the surrounding supersonic oxygen stream and accelerated. The resulting stream of oxygen and particulate material is perpendicular to the surface of the liquid metal in the converter.

[0059] Technical pure oxygen is also supplied to the outer channels 5. The oxygen streams (second gas streams) leave the outer nozzles 3 divergent to the central first stream of oxygen and particulate material. The second gas streams do not form a continuous coaxial gas envelope with the central first gas stream. Instead there will be four distinct second gas streams and four distinct impact zones for the outer oxygen streams on the surface of the liquid metal bath.

[0060] The total oxygen mass required depends on the mass of species which shall be oxidised. For sake of simplicity it is assumed that the oxygen is uniformly consumed during the blowing time. The total oxygen flow can then be calculated from the total oxygen mass and the duration of the oxygen blow (blowing time).

[0061] For example, the duration of the oxygen blow is pre-set to 20 minutes. Thus all species shall be oxidised within these 20 minutes. The total oxygen flow is distributed to the annular channel 2 and the outer channels 5. The proportion sent to the annular channel 2 is calculated depending on the desired lance height, the lance and nozzle type and the required penetration depth. The remaining oxygen is sent to the outer channels 5.