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. A process for injecting particulate material into a liquid metal bath by means of a lance, wherein the liquid metal bath contains species to be oxidized and the lance comprises an axial solids injection pipe, said process comprising; injecting the particulate material into the liquid bath by means of a first gas stream and wherein the first gas stream with the particulate material penetrates into the liquid metal bath, controlling solids injection rate of the particulate material such that the liquid metal bath temperature is maintained within a first pre-defined temperature range and/or evolution of the liquid metal 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 metal bath per time unit, controlling penetration depth of the first gas stream into the liquid metal bath by adjusting the flow of the first gas stream, injecting at least two second gas streams into the liquid metal bath at a diverging angle from the first gas stream, wherein the first gas stream and the second gas streams are in each case an oxidizing gas, and wherein gas flows of the second gas streams are controlled such that the liquid metal bath temperature is maintained within the first pre-defined temperature range and/or the evolution of the liquid metal bath temperature is maintained within the second pre-defined range.

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

3. The process according to claim 1, wherein the first gas stream is provided at a velocity between 340 m/s and 1100 m/s.

4. The process according to claim 1, wherein the second gas streams are provided at a velocity between 340 m/s and 1100 m/s.

5. The process according to claim 1, wherein the penetration depth is less than 75% of the depth of the liquid metal bath.

6. The process according to claim 1, wherein the first gas stream and/or the second gas streams comprise at least 80% by volume oxygen.

7. The process according to claim 1, wherein more than 20 kg/min particulate material is injected into the liquid metal bath.

8. The process according to claim 1, wherein the particulate material contains a metallurgical reagent.

9. The process according to claim 1, wherein the particulate material is injected into a metallurgical converter.

10. The process according to claim 1, wherein the first pre-defined temperature range is from 1000° C. to 2000° C.

11. The process according to claim 1, wherein the evolution of the liquid metal bath temperature is less than +/−20° C./min.

12. The process according to claim 1, wherein the diverging angle between the first gas stream and one of the second gas streams is between 5° and 20°.

13. The process according to claim 1, wherein between 2 and 8 second gas streams are provided.

14. The process according to claim 1, wherein the species to be oxidized is carbon and/or silicon.

15. The process according to claim 1, wherein the lance is provided vertical to the surface of the liquid metal bath.

16. The process according to claim 1, wherein said process is employed in a metallurgical refining process.

17. The process according to claim 1, wherein the first and the second gas streams are at least 90% by volume oxygen.

18. The process according to claim 1, wherein the first gas stream is provided at a velocity between 500 m/s and 900 m/s, and the second gas streams are provided at a velocity between 500 m/s and 900 m/s.

19. The process according to claim 1, wherein the penetration depth is less than 50% of the depth of the liquid metal bath.

20. The process according to claim 1, wherein between 3 and 6 second gas streams are provided.

21. The process according to claim 1, wherein the first gas stream and the second gas streams enter the liquid metal bath at different points distanced from each other.

22. The process according to claim 1, wherein the second gas streams diverge from each other and the angle of divergence between each pair of second gas streams is between 5° and 20° .

23. The process according to claim 1, wherein the lance comprises an annular channel, around said axial solids injection pipe, for introduction of said first gas stream into the liquid metal bath, and a plurality of outer channels, each terminating in an outer nozzle, arranged around the annular channel and said axial solids injection pipe, for introduction of the second gas streams.

24. The process according to claim 1, wherein the diverging angle between the first gas stream and one of the second gas streams is between 7° and 15° .

25. The process according to claim 1, wherein the diverging angle between the first gas stream and each of the second gas streams is between 5° and 20° .

Description

(1) The invention as well as further embodiments and details of the invention shall be described with reference to the attached drawings. Therein,

(2) FIG. 1 shows the top view on a lance head for use with the present invention,

(3) FIG. 2 shows the cross section of the lance according to FIG. 1.

(4) 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.

(5) 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.

(6) 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°.

(7) 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.

(8) 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.

(9) 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).

(10) 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.