DEVICE AND METHOD FOR CONTINUOUS DESULPHURISATION OF LIQUID HOT METAL

Abstract

A device and a method for continuous desulphurisation of liquid iron provided by a blast furnace process or a direct reduction process.

Claims

1. A device for continuous desulphurisation of liquid iron comprising a desulphurisation reactor or a plurality of consecutive desulphurisation reactors, wherein the desulphurisation reactor or reactors each comprise an entry section for receiving liquid iron from liquid iron production means or from the desulphurisation reactor immediately preceding the subsequent desulphurisation reactor, and a reaction section for removing the sulphur from the liquid iron, wherein the entry section and the reaction section in the desulphurisation reactors act as communicating vessels, wherein a passage is provided between the entry section and the reaction section to allow, in use, the liquid iron to flow from the entry section to the reaction section, wherein supply means for the liquid iron into the first or only desulphurisation reactor are provided in the entry section, and wherein means for introducing reagents into the liquid iron in the reaction section or in the entry section are provided and wherein the means for introducing reagents into the liquid iron comprise a submerged lance, and wherein an outlet is provided in the reaction section, to allow desulphurised liquid iron to exit the reaction section, and wherein (i) a return passage is provided between the reaction section of desulphurisation reactor and the entry section of said desulphurisation reactor, and/or (ii) wherein a return passage is provided between the first and the second desulphurisation reactor, wherein the return passage connects the entry section of the second reactor to the reaction section of the first desulphurisation reactor, to increase, in use, the residence time of the liquid iron in the device.

2. The device according to claim 1, wherein slag removal means are provided for separating the slag that, in use, is floating on top of the liquid iron, from the liquid desulphurised iron.

3. The device according to claim 1, wherein a plurality of desulphurisation reactors is provided, and wherein the outlet of a first desulphurisation reactor is connected to the inlet of a second desulphurisation reactor to allow the already desulphurised liquid iron to pass from the reaction section of the first desulphurisation reactor to the entry section of the second desulphurisation reactor.

4. The device according to claim 1, wherein the entry section and the reaction section are separated from each other by a separation wall, wherein the passage consists of an opening in the separation wall.

5. The device according to claim 1, wherein the return passage or passages is or are provided with opening-and-closing means for adjusting, in use, the return flow of desulphurised liquid iron from the entry section of the second desulphurisation reactor to the reaction section of the first desulphurisation reactor.

6. The device according to claim 1, wherein the return passage or passages is provided with opening-and-closing means for adjusting, in use, the return flow of desulphurised liquid iron from the entry section of the second desulphurisation reactor to the reaction section of the first desulphurisation reactor.

7. The device according to claim 1, wherein the entry section of the second desulphurisation reactor and the reaction section of the first desulphurisation reactor are separated by a separation wall, wherein the return passage consists of an opening in the separation wall.

8. The device according to claim 1, wherein the liquid iron production means comprise a direct reduction ironmaking process.

9. The device according to claim 1, wherein a slag flotation section is provided behind the one or more reactors, to allow, in use, the slag and any inclusions in the slag to float to the surface of the liquid iron and remove the slag from the liquid iron.

10. The device according to claim 1, wherein the aspect ratio (height of the reaction section/the largest diameter or diagonal of the cross-section of the respective reaction section) is at least 3.

11. A method of continuous desulphurisation of liquid iron in a device comprising one desulphurisation reactor or a plurality of consecutive desulphurisation reactors, wherein liquid iron produced by liquid iron production means enters the entry section of a desulphurisation reactor and subsequently flows to the reaction section of the desulphurisation reactor through the passage between the entry section and the reaction section, wherein the entry section and the reaction section (4) act as communicating vessels, and wherein reagents are introduced into the liquid iron in the reaction vessel by means for introducing reagents into the liquid iron wherein the means for introducing reagents into the liquid iron comprise a submerged lance, vaporising, dissociating or reacting at least part of the reagents to form bubbles after introduction into the liquid iron, wherein the bubbles reduce the specific weight of the liquid iron in the reaction section, while simultaneously desulphurising the liquid iron by reacting with the sulphur in the liquid iron, and wherein, because of the difference in specific weight of the liquid iron entering the entry section and the specific weight of the liquid iron in the reaction section, the liquid iron causes an overall flow of the liquid iron from the entry section to the reaction section and subsequently to and through the outlet of the reaction section, and wherein (i) a return passage is provided between the reaction section of a desulphurisation reactor and the entry section of that desulphurisation reactor, and/or (ii) wherein a return passage is provided between the first and the second desulphurisation reactor, wherein the return passage connects the entry section of the second reactor to the reaction section of the first desulphurisation reactor, to increase the residence time of the liquid iron in the device.

12. The method according to claim 11, wherein the reagents are injected through the submerged lance into the liquid iron in the reaction vessel.

13. The method according to claim 11, wherein a plurality of subsequent desulphurisation reactors is connected in series, wherein the outlet of a first desulphurisation reactor is connected to the inlet of a second desulphurisation reactor to allow the desulphurised liquid iron to pass from the reaction section of the first desulphurisation reactor to the entry section of the second desulphurisation reactor for continued desulphurisation of the liquid iron.

14. The method according to claim 11, wherein the reagents are below 0.33 times the liquid iron level (h.sub.iron).

15. The method according to claim 11, wherein the return passage is provided with opening-and-closing means to enable adjusting the return flow.

16. The method according to claim 11, wherein liquid iron is continuously provided to the device, and wherein the liquid iron is continuously desulphurised in the device, and wherein desulphurised liquid iron continuously exits the device.

17. The method according to claim 11, wherein the liquid iron production means comprise a direct reduction ironmaking process.

18. The method according to claim 11, wherein the reagent introduced into the liquid iron by means of the submerged lance comprises magnesium.

19. The method according to claim 9, wherein slag forming compounds, such as SiO.sub.2, Al.sub.2O.sub.3, N.sub.2O, K.sub.2O, CaF.sub.2, KAlF.sub.4, Na.sub.3AlF.sub.6 or CaCl.sub.2, MnO or TiO.sub.2 are added to the liquid iron together with the reagents or added separately, to produce a liquid slag that floats on the liquid iron.

20. The device according claim 1, wherein the outlet is provided at or near the top of the reaction section, to allow desulphurised liquid iron to exit the reaction section.

21. The device according to claim 1, wherein a slag flotation section is provided at least behind the last or only reactor, to allow, in use, the slag and any inclusions in the slag to float to the surface of the liquid iron and remove the slag from the liquid iron.

22. The method according to claim 11, wherein the injection depth (di) is below 0.50 times the liquid iron level (h.sub.iron).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] The invention will now be explained by means of the following, non-limiting figures.

[0082] FIG. 1—schematic representation of the steelmaking process.

[0083] FIG. 2—schematic representation of an embodiment of the device according to the invention consisting of one desulphurisation reactor.

[0084] FIG. 3—schematic representation of another embodiment of the device according to the invention consisting of one desulphurisation reactor.

[0085] FIG. 4—as FIG. 2 with return passage 13.

[0086] FIG. 5—as FIG. 3 with return passage 13.

[0087] FIG. 6—schematic representation of another embodiment of the device according to the invention consisting of three desulphurisation reactors A, B and C connected in series.

[0088] FIG. 7—as FIG. 6 with return passages 13 in separation wall(s) 12.

[0089] FIG. 8—as FIG. 6 with return passages 13.

[0090] FIG. 9—definitions of injection depth and liquid iron level.

[0091] FIG. 10—schematic representation of cross sections of one desulphurisation reactor.

[0092] FIG. 11—schematic representation of a movable unit such as a ladle comprising a plurality of entry and reaction sections.

[0093] FIG. 12—schematic representation of slag removal means.

[0094] FIG. 13—Steady state sulphur content vs reactor aspect ratio for 100 m.sup.3 reactor.

DETAILED DESCRIPTION OF THE DRAWINGS

[0095] In FIG. 1 a simple schematic diagram of the steelmaking process is shown. Ore and coal and cokes are the main raw materials which are used to produce iron in an ironmaking process such as a blast furnace process or a direct-reduction ironmaking process. The liquid iron which is the product of this process needs to be desulphurised to remove the excess sulphur in the iron. After desulphurisation the iron is further refined (de-phosphorised, de carburised, etc.) in the steelmaking process, usually in a basic oxygen furnace (BOF). The resulting steel is further cleaned and compositionally fine-tuned in the secondary steelmaking (SM) and subsequently cast into slabs or strips.

[0096] FIG. 2 shows an embodiment of the device according to the invention consisting of one desulphurisation reactor A. The liquid iron production means 1 provide liquid iron to the device through inlet 2 into the entry section 3 of the reactor. The entry section and the reaction section 4 are communicating vessels due to the presence of passage or conduit 5 and the liquid iron is pushed through the device as a result. Slag, floating on the liquid iron in the reaction section is skimmed off (e.g. see FIG. 9) and separated from the liquid iron that exits the reaction section through outlet 8. Reagents are introduced in the liquid iron in the reaction section by a submerged lance 11 (and/or through bottom plugs or the like (not shown) and these reagents are chosen such that they form bubbles in the liquid iron and act as desulphurising compounds. The bubbles ensure that the specific weight of the iron decreases, which aids the flow of iron from the entry section to the reaction section because the specific weight of the iron in the entry section is higher than the iron+bubbles in the reaction section. The sulphur is moved from dissolved sulphur in the liquid iron to the slag in the form of (e.g.) CaS or MgS, after which the slag layer is separated from the metal (see Schrama et al.). The liquid iron production means is not particularly restrictive and may be a conventional blast furnace, a scrap melting facility or a direct reduced iron making facility.

[0097] FIG. 3 shows a more compact version of the device A of FIG. 2. The passage 5 is now an opening in the common wall separating the entry section from the reaction section.

[0098] FIG. 4 shows the same device A as FIG. 2 with a return passage between the reaction section 4 and the entry section 3.

[0099] FIG. 5 shows the same device A as FIG. 3 with a return passage between the reaction section 4 and the entry section 3.

[0100] FIG. 6 shows a device comprising a plurality (i.c. 3) devices as depicted schematically in FIG. 3. This allows the desulphurisation to be performed in steps. In the figure the liquid iron is desulphurised in the reaction section of the first desulphurisation reactor A, and is led to the entry section of the second reactor B, and the process of reactor A is repeated, and again in reactor C. The individual reactors A, B and C are indicated with the brackets.

[0101] FIG. 7 shows a device comprising a plurality (i.c. 3) devices as depicted schematically in FIG. 3. The difference between this device and the one in FIG. 6 is the presence of a return passage 13 in the separation wall 12 which allows (part of) the liquid iron in the entry section of the second reactor B to flow back to the reaction section of reactor A. This increases the residence time of (part of) the liquid iron in the reaction section of reactor A. Preferably the return passage 13 is provided with opening-and-closing means to regulate the return flow of liquid iron. In FIG. 7 a return passage is also provided between reactor B and C. The individual reactors A, B and C are indicated with the brackets.

[0102] FIG. 8 follows the same principle as in FIG. 7, but here the return passages 13 are present in the individual reactors in the separation wall 12 between the entry section from the reaction section in a reactor and not, as in FIG. 7, in the wall separating two subsequent reactors. The individual reactors A, B and C are indicated with the brackets.

[0103] FIG. 9 intends to define the feature of injection depth in case a submerged lance is used to introduce the reagents into the liquid iron.

[0104] FIG. 10 depicts schematic shapes of the reactor as seen from above, and intends to explain the feature of the “largest diameter or diagonal of the cross-section of the respective reaction section” as used herein above in the aspect ratio. Many other shapes are conceivable in which case the largest diameter or diagonal is determined in a similar way as in FIG. 10.

[0105] FIG. 11 shows an alternative layout of FIG. 6, 7 or 8 as seen from above with consecutive entry sections and reaction sections effectively comprising 3 separate desulphurisation reactors. The liquid enters the device in reaction section 3 through entry 2 and moves in a clockwise direction continuously to the outlet 8.

[0106] FIG. 12 shows one example of slag removal means 9 which assists in separating the slag that contains the sulphur that was removed from the liquid iron, from the desulphurised liquid iron by skimming off the slag that floats on top of the liquid iron.

[0107] FIG. 13 shows the effect of an increased aspect ratio on the sulphur content for a reactor of a certain size (100 m.sup.3).