Method of continuous manufacturing of solidified steelmaking slag and associated device

Abstract

A method of continuous manufacturing of solidified steelmaking slag including the steps of solidifying molten steelmaking slag comprising at least 2% in weight of free lime so as to produce solidified slag particles having a diameter below 1 mm, the molten steelmaking slag being put in contact with at least a first carbonation gas during such solidification, cooling the solidified slag particles down to a temperature below or equal to 300° C., in a closed chamber, the solidified slag particles being put in contact with at least one second carbonation gas during such cooling. The invention is also related to an associated device.

Claims

1. A method of continuous manufacturing of solidified steelmaking slag comprising the steps of: solidifying molten steelmaking slag including at least 2% in weight of free lime so as to produce solidified slag particles having a diameter below 1 mm, the molten steelmaking slag being put in contact with at least a first carbonation gas during such solidification, the first carbonation gas includes at least 20% in volume of CO.sub.2, between 5 and 30% in volume of CO, between 1 and 55% in volume of H.sub.2, between 1 and 55% in volume of N.sub.2 and between 1 and 5% in volume of O.sub.2; and cooling the solidified slag particles down to a temperature below or equal to 300° C., in a closed chamber, the solidified slag particles being put in contact with at least one second carbonation gas during such cooling.

2. The method as recited in claim 1 wherein the first carbonation gas includes at least 50% in volume of CO.sub.2.

3. The method as recited in claim 1 wherein the first carbonation gas includes steam.

4. The method as recited in claim 3 wherein the first carbonation gas includes at least 20% in volume of steam.

5. The method as recited in claim 1 wherein the second carbonation gas includes at least 25% in volume of CO.sub.2.

6. The method as recited in claim 1 wherein the second carbonation gas is maintained at a temperature comprised between 300 and 500° C. during the cooling step.

7. The method as recited in claim 1 wherein the second carbonation gas includes steam.

8. The method as recited in claim 7 wherein the second carbonation gas includes at least 25% in volume of steam.

9. The method as recited in claim 1 wherein the cooling rate of solidified slag particles is between 1 and 100° C./min during the cooling step.

10. The method as recited in claim 1 wherein the solidified slag particles are kept in motion during the cooling step.

11. The method as recited in claim 10 wherein the solidified slag particles are kept in motion during the cooling step by injection of a third gas into the closed chamber.

12. The method as recited in claim 11 wherein the third gas includes at least 20% in volume of CO.sub.2.

13. The method as recited in claim 1 further comprising exhausting at least a part of the gases inside the closed chamber and collecting the exhausted gases to be recycled as the first carbonation gas, the second carbonation gas or a third gas for keeping the solidified slag particles in motion.

14. The method as recited in claim 1 wherein the first carbonation gas, the second carbonation gas or at least a third gas for keeping the solidified slag particles in motion includes exhausts gases from ironmaking, steelmaking, sintering or coking plant.

15. The method as recited in claim 1 wherein the second carbonation gas includes at least 25% in volume of CO.sub.2, between 5 and 30% in volume of CO, between 1 and 55% in volume of H.sub.2, between 1 and 55% in volume of N.sub.2, and between 1 and 5% in volume of O.sub.2.

16. The method as recited in claim 1 wherein a stay time within the closed chamber is below 30 minutes.

17. The method as recited in claim 1 wherein at least 60% of free lime of the molten steelmaking slag is transformed into calcium carbonates.

18. The method as recited in claim 1, wherein said solidifying and cooling is performed in comprising: a closed chamber, the closed chamber including: a solidification device able to produce solidified slag particles having a diameter inferior or equal to 1 mm; a bottom porous wall; and gas injectors for injecting the at least first carbonation gas and the at least one second carbonation gas.

19. The method as recited in claim 18 further comprising an exhaust gas collector and a gas recirculator.

20. The method as recited in claim 18 wherein the solidification device is an atomizer.

21. The method as recited in claim 18 wherein the solidification device is a granulator.

22. The method as recited in claim 18 wherein at least one of the injectors is connected to an ironmaking, steelmaking, sintering or coking plant.

23. A method of continuous manufacturing of solidified steelmaking slag comprising the steps of: solidifying molten steelmaking slag including at least 2% in weight of free lime so as to produce solidified slag particles having a diameter below 1 mm, the molten steelmaking slag being put in contact with at least a first carbonation gas during such solidification; and cooling the solidified slag particles down to a temperature below or equal to 300° C., in a closed chamber, the solidified slag particles being put in contact with at least one second carbonation gas during such cooling, wherein the second carbonation gas includes at least 25% in volume of CO.sub.2, between 5 and 30% in volume of CO, between 1 and 55% in volume of H.sub.2, between 1 and 55% in volume of N.sub.2, and between 1 and 5% in volume of O.sub.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood upon reading the description which follows, given with reference to the following appended figures:

(2) FIG. 1 illustrates a method according to the invention

(3) FIG. 2 illustrates a first example of an installation to implement a method according to the invention

(4) FIG. 3 illustrates a second example of an installation to implement a method according to the invention

DETAILED DESCRIPTION

(5) In FIG. 1 is represented a continuous manufacturing method of solidified steelmaking slag according to the invention. Molten steelmaking slag 1 coming from the steel making step undergoes a solidification step 21, molten slag temperature depends on the composition of the slag but is generally comprised between 1300 and 1600° C. During this solidification step the slag is solidified in particles 6 and its temperature decreases up to 1000° C. The size of the slag particles 6 is inferior to 1 mm, preferentially inferior to 0.5 mm. The reason for this specific particles size will be explained later. During this solidification step, the molten slag is put in contact with a first carbonation gas 31. This first carbonation gas 31 comprises, for example, at least 20% in volume of CO.sub.2, and preferentially more than 50% in volume. The remaining part of the first carbonation gas 31 may be composed of hydrogen, methane, carbon monoxide, nitrogen, oxygen or steam. This first carbonation gas 31 may be or may contain an exhaust gas from an iron making or a steelmaking plant, such as coke oven, blast furnace or converter gas which may have been firstly subjected to a cleaning step. This first carbonation gas 31 comprises for example at least 20% in volume of CO.sub.2, between 5 and 30% in volume of CO, between 1 and 55% in volume of H.sub.2, between 1 and 55% in volume of N.sub.2, between 1 and 5% in volume of O.sub.2. In another embodiment, the first carbonation gas 31 comprises also steam in addition to CO.sub.2, the volume of steam in the gas being comprised between 20 and 70% in volume. The first carbonation gas 31 contains for example at least 20% in volume of CO.sub.2, between 5 and 30% in volume of CO, between 1 and 55% in volume of H.sub.2, between 1 and 55% in volume of N.sub.2, between 1 and 5% in volume of O.sub.2, the balance being steam. This injection of a first gas 31 allows first carbonation reaction between CO.sub.2 and free lime contained in the slag according to the carbonation reaction (2). In a further embodiment there may be more than one first carbonation gas.

(6) Slag particles 6 are then subjected to a cooling step 22 during which their temperature decreases up to 300° C. The cooling rate is preferentially comprised between 1° C./min and 100° C./min. It has to be upper than 1° C./min to keep a short treatment time but lower than 100° C./min to get a sufficient CO.sub.2 uptake for the carbonation reaction. This cooling step is performed in a closed chamber wherein a second carbonation gas 32 is injected, this second carbonation gas 32 comprising, for example, at least 25% in volume of CO.sub.2, and preferentially more than 50% in volume. The remaining part of the second carbonation gas may be composed of hydrogen, methane, carbon monoxide, nitrogen, oxygen or steam. This second carbonation gas 32 may be or may contain an exhaust gas from an iron making or a steelmaking plant, such as coke oven, blast furnace or converter gas which may have been firstly subjected to a cleaning step. This second carbonation gas 32 comprises for example at least 25% in volume of CO.sub.2, between 5 and 30% in volume of CO, between 1 and 55% in volume of H.sub.2, between 1 and 55% in volume of N.sub.2, between 1 and 5% in volume of O.sub.2. The temperature of this second carbonation gas 32 is chosen so as to achieve the required cooling rate; but it has preferentially a temperature comprised between 300 and 500° C. In another embodiment, the second carbonation gas 32 comprises also steam in addition to CO.sub.2, the volume of steam in the gas being comprised between 20 and 70% in volume. This second carbonation gas 32 contains for example at least 25% in volume of CO.sub.2, between 5 and 30% in volume of CO, between 1 and 55% in volume of H.sub.2, between 1 and 55% in volume of N.sub.2, between 1 and 5% in volume of O.sub.2, the balance being steam. The size of the granulated slag particles inferior to 1 mm and preferentially inferior to 0.5 mm allows having a higher CO.sub.2 uptake of the particles, which increases the kinetics of reaction between CO.sub.2 and lime contained in the slag, according to carbonation reaction (2). In a further embodiment there may be more than one second carbonation gas.

(7) After this cooling step, at least 60% and preferentially more than 75% of the free lime initially contained in molten slag has been transformed into carbonates, according to reaction (2). The production time, between the pouring of the molten slag and the recovery of cooled slag particles 11 is inferior to 30 minutes, preferentially inferior to 15 minutes.

(8) The production method according to the invention is a continuous method, all the steps being performed one after the other without interruption. This allows having a short treatment time.

(9) FIG. 2 illustrates a first embodiment of an installation to perform a continuous manufacturing method according to the invention. In this installation, molten slag 1 from a steelmaking device 2 is poured into a closed chamber 3 on a granulation device 4 so as to form solidified particles of slag 6. This granulation device 4 may be for example a rotating wheel (as illustrated). In the configuration of FIG. 2 the rotating wheel 4 is a horizontal wheel, but in another embodiment, not illustrated, it may be a vertical wheel. At the same time and is the neighboring of the slag pouring, the first carbonation gas 31 is injected through first gas injection means (not illustrated) towards the molten slag. The characteristics of this first carbonation gas 31 are the same as the ones described for the first carbonation gas 31 used in the solidification step 21 of FIG. 1. The closed chamber 3 may be insulated. The solidified slag particles 6 thus formed stay in the closed chamber 3 where they are cooled according to the cooling step 22 previously described. The closed chamber 3 comprises injection means (not illustrated) designed to inject a second carbonation gas 32 towards the solidified slag particles 6. The characteristics of this second carbonation gas 32 are the same as the ones described for the second carbonation gas 32 used in the cooling step 22 of FIG. 1. The closed chamber is also equipped with collection means (not illustrated) to collect exhaust gas 34 from the inside of the closed chamber. These exhaust gas 34 may further be recycled by re-injection in the closed chamber as part of or as first 31 and/or second carbonation 32 gas.

(10) FIG. 3 illustrates a second embodiment of an installation to perform a production method according to the invention. In this installation, molten slag 1 from a steelmaking equipment 2 is put into contact into a closed chamber 3 with a first carbonation gas 31 projected by an atomizer 7 so as to form solidified slag particles 6. The characteristics of this first carbonation gas 31 are the same as the ones described for the first carbonation gas 31 used in the solidification step 21 of FIG. 1. The atomizer 7 can be for example a SAT (Slag Atomizer Technology), developed by company Ecomaister-Hatch. The solidified slag particles 6 thus formed stay in the closed chamber 3 where they are cooled according to the cooling step 22 previously described. The closed chamber 3 comprises injection means (not illustrated) designed to inject a second carbonation gas 32 towards the solidified slag particles 6. The characteristics of this second carbonation gas 32 are the same as the ones described for the second carbonation gas 32 used in the cooling step 22 of FIG. 1. The closed chamber 3 is also equipped with collection means (not illustrated) to collect exhaust gas 34 from the inside of the closed chamber. These exhaust gas 34 may further be re-injected in the closed chamber as part of or as first 31 and/or second carbonation 32 gas.

(11) In both embodiments the closed chamber 3 may further comprises means to keep the slag particles in motion during the cooling step. This allows to enhance contact between CO.sub.2 and solidified slag particles 6 and so to improve CO.sub.2 uptake by the solidified slag particles 6. For example, as illustrated in FIGS. 2 and 3, the bottom wall 5 of the closed chamber 3 may be porous and a third gas 33 may be injected through this porous wall 5, so as to create a fluidized bed. The flow rate of this third gas 33 has to be sufficient to keep the solidified slag particles 6 in motion. The third gas 33 may comprise at least 25% in volume of CO.sub.2, remaining part being air and steam. Those means to keep the slag particles in motion may also be means to rotate the closed chamber 3, by using a rotating drum for example. This third gas may be or may contain an exhaust gas from an iron making or a steelmaking plant, such as coke oven, blast furnace or converter gas which may have been firstly subjected to a cleaning step or it may also be exhaust gas 34 collected from the closed chamber 3.

(12) As illustrated in the embodiments, both solidification and cooling steps are performed in the same device and slag particles are treated in the same closed chamber which allows improving treatment time and yield.