GB2025390A

GB2025390A - Recovering Blast-Furnace Slag

Info

Publication number: GB2025390A
Application number: GB7925005A
Authority: GB
Original assignee: Centre de Recherches Metallurgiques CRM ASBL
Current assignee: Centre de Recherches Metallurgiques CRM ASBL
Priority date: 1964-04-14
Filing date: 1979-07-18
Publication date: 1980-01-23
Also published as: GB2025390B

Abstract

Finely divided lime or lime- containing material is added to liquid blast-furnace slag in a rotary furnace to give the product the properties of a Portland cement. If necessary, an iron- bearing additive is introduced to bring the iron content to 2 to 5%. The finely divided material may be introduced by suspending it in a gas supplied to a burner.

Description

SPECIFICATION Recovering Blast-furnace Slag The present invention relates to a process for recovering blast-furnace slag and to apparatus for performing the process.

The metallurgical slags produced in the course of blast-furnace iron manufacture are commonly used in the preparation of the so-called "slag cement", and as a component in certain types of road beds. However, it now appears that these outlets are becoming unable to absorb the quantities of slag being offered. In this case, the considerable amount of unused slag is generally dumped on tips, a practice which has the disadvantage, among others, of total financial loss, because the material is considered as being non-recoverable.

With this in view, and this constitutes the purpose of the present invention, it is proposed to modify, by judicious additions, the composition of the slag so as to transform it into a material closely approximating the Portland cements and being suitable for use as such. Thanks to this process, it becomes possible to recover and make use of such slag, previously unused and dumped on tips.

The present invention provides a process in which finely divided lime is introduced into liquid blast-furnace slag, and the composition of the product thus formed is so controlled as to impart to it the properties of a Portland cement.

This addition of lime is effected on the liquid or molten slag, taken either at the outlet of the blastfurnace after an optional cooling, or after appropriate reheating.

This lime can be introduced into the slag by the intermediary of lime carriers, for example sulphatic slag with lime or calcium carbide; the advantage of using such lime carriers consists in the recovery of the metallic iron contained in the sulphatic slag, by way of crushing and magnetic separation of the components of this slag. It is to be noted furthermore that this source of lime is particularly cheap.

Since a final iron content of 2 to 5% is desirable in the Portland cement, in the case where this value would not otherwise be reached it is possible to effect an adjustment by adding, in appropriate proportions, at least one iron-bearing additive (iron-containing dusts or red fumes), for example) simultaneously with the addition of at least one lime-bearing additive.

From the practical point of view, the slag mixture can be realized at the blast furnace. The slag leaving the furnace is channeled to a mouth allowing the discharge of the slag into a rotary furnace disposed facing the lower end of the mouth. This rotary furnace is provided for example with an inlet aperture and an outlet aperture, its axis of rotation being substantially horizontal and slightly inclined in the direction of its outlet aperture. The furnace further comprises means for being heated to a temperature allowing the reaction between the lime and the slag to take place, so that a Portland cement clinker is formed in the interior of this furnace.

The addition of lime to the slag bath is preferably effected by means of a burner, comprising, for example, two coaxial conduits for this purpose: the central conduit serves for injecting into the slag an oxygen-rich gas or pure oxygen, the external conduit serving for the supply of a fuel (e.g. natural gas). The limebearing additive (e.g. powdered lime) is suspended preferably in the injected fuel, and is thus brought into contact with the liquid slag. In the case where the oxygen-rich gas is air, the air is preferably preheated, as can be the limebearing additive. Moreover, it is advantageous, in order to promote the reactions of the fuel, to provide a small chamber at the outlet extremity of the burner. With this end in view, the inner tube of the burner terminates slightly (less than 8 mm) short of the end of the outer tube.

The outer tube of the burner is advantageously internally protected against abrasion over a length of less than 20 mm measured from its outlet end, by lining it with or making it of a refractory material, for example electrically fused and, in the present case, preferably of CaO. This protection is particularly advantageous when the additives to be injected into the slag are suspended in the fuel gas passing through the burner in the space between the inner tube and the outer tube.

A burner serving for lime feed can be located at the extremity of a lance (preferably cooled by water and disposed in proximity to the slag discharge mouth) so as to project the lime at the outlet of the mouth into the jet of slag leaving the blast-furnace.

Example At the outlet of a blast-furnace the starting slag had the following composition, calculated for 1000 kg of slag: SiO2 35% 350 kg Al203 14% 140 kg CaO 45% 450kg MgO 3% 30 kg FeO 1.5% 15 kg MnO 1% 10 kg S 0.5% 5 kg 100% 1000 kg To this slag there were added, as described above: a) 850 kg of finely divided lime, containing.

92% of CaO, that is 780 kg 1.5% of SiO2, that is 13 kg remainder=ignition loss 0 kg b) 40 kg of red fumes, that is, 100% Foe203 40 kg a total of 833 kg There were obtained in this manner 1833 kg of a product which had the following composition: SiO2 20% At203 7 6% CaO 67% MgO 1.6% Fe2O3 3% MnO 0.5% S 0.3% which can be considered- as being comparable to that of Portland cements, which is as follows: SiO2 19 to 25% Awl203 3 to 8% CaO 62 to 67% MgO 0.5 to 2% Fe203 2 to 5%

Claims

1. A process for recovering blast-furnace slag, in which at least one finely divided lime-bearing additive comprising or consisting of lime is introduced into liquid or molten blast-furnace slag and the composition of the product thus formed is so controlled as to impart to it the properties of a Portland cement.

2. A process as claimed in claim 1, in which at least one said additive is a slag which has been used in desulphurisation by lime or calcium carbide.

3. A process as claimed in claim 1 or 2, in which at least one iron-bearing additive is introduced into the blast-furnace slag simultaneously with the lime-bearing additive(s) in such a proportion that the final iron content of the product thus obtained is 2 to 5 wt.%.

4. A process as claimed in any of claims 1 to 3, in which at least one said additive is introduced into the blast-furnace slag after being suspended in a gas.

5. A process as claimed in claim 4, in which the introduction is effected by means of a burner fed with a combustion-supporter constituted by oxygen or an oxygen-rich gas and with a fuel gas, the supply of the burner with the combustionsupporter being effected through a central part and its supply with fuel gas being effected peripherally around the combustion supporter.

6. A process as claimed in claim 5, in which at least one said additive is suspended in the fuel gas.

7. A process as claimed in claim 5 or 6, in which partial mixing of the combustion-supporter and the fuel gas is effected upstream of the burner outlet.

8. A process as claimed in any of claims 5 to 7, in which the combustion-supporter is preheated air.

9. A process as claimed in any of claims 1 to 8, in which the introduction of at least one said additive is effected into the slag stream at the blast-furnace outlet.

1 0. Apparatus for recovering blast-furnace slag, comprising: (a) a rotary furnace designed for location below a discharge mouth connected to the slag spout of a blast furnace, the rotary furnace having its rotational axis inclined in the direction of an outlet; (b) optionally, slag-heating means for heating the slag prior to entering the rotary furnace; (c) supply means for supplying at least one finely divided lime-bearing additive to the rotary furnace; (d) supply means for supplying at least one iron-bearing additive to the rotary furnace; and (e) means for heating the rotary furnace to a temperature allowing reaction between the lime and the blast-furnace slag in such a manner that a Portland cement clinker is formed in the rotary furnace.

11. Apparatus as claimed in claim 10, in which the furnace heating means comprises at least one burner comprising two tubes, one inside the other, in which the inner tube serves for carrying a combustion-supporter whilst the space between the tube serves for carrying fuel gas.

12. Apparatus as claimed in claim 11, in which at least one said supply means is connected to at least one said burner.

13. Apparatus as claimed in claim 12, in which the connection is via a fuel-gas conveying conduit.

14. Apparatus as claimed in claim 13, in which the internal surface of the outer burner tube, over a length of less than 20 mm measured from its outlet end, is of refractory material.

15. Apparatus as claimed in any of claims 11 to 14, in which the inner tube of the burner terminates at its outlet end less than 8 mm short of the corresponding end of the outer tube.

16. A process as claimed in claim 1, substantially as described in the Example given.

17. Apparatus as claimed in claim 10, substantially as described above.