GB1572778A

GB1572778A - Manufacture of mineral wool from metallurgical slag

Info

Publication number: GB1572778A
Application number: GB7464/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-12-16
Filing date: 1978-02-24
Publication date: 1980-08-06
Also published as: DE2807753A1; AU3368778A; ES468411A1; AR213354A1; JPS5488326A; SE7802202L; BR7801549A; NL7802108A

Description

(54) IMPROVEMENTS RELATING TO TIE MANUFACTURE OF MINERAL WOOL FROM METALLURGICAL SLAG (71) I, FRANCIS GAGNERAUD, a French citizen, of Villa Montmorency, 6 Avenue des Tilleuls, 75016 Paris, France, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the use of metallurgical slags and scoria, particularly from blast furnaces and other iron and steel works vessels, for the production of, amongst other things, mineral fibrous elements or wool, sometimes called "slag wool".

The manufacture of mineral wool from natural or synthetic materials, such as blastfurnace slags, has been well-known and practised for several decades. The production of this wool is usually carried out either by dispersing a thread of molten material by very high speed gas jets, the formed fibres being rolled into a revolving drum and/or an endless belt and then collected and, if necessary, classified or sorted, or by centrifuging by passing a thread of molten material onto a revolving disc which is externally cooled by a ring of air, the wool being collected in a suitable receptacle.

In the most commonly used manufacturing technique using blast-furnace slags, the starting material is solidified slag which is then remelted in a furnace at a temperature of about 1,400"C before dispersing the molten product by gaseous jets as described above.

The consumption of fuel, generally coke, for reheating the solidified slag is of the order of 200 to 240 kg per tonne of slag.

In another process, the slag, in a molten state is collected in a casting ladle and is poured into a furnace where it is heated to between 1,400 to 1,4500C, and before the operation of thread production by gaseous jets or centrifuging as described above, various products are added to the bath for the purpose of modifying the chemical composition of the molten material. This material should possess certain quite well defined chemical and physical characteristics (for example viscosity to enable it to be con verted into filaments.

These known processes involve several operating stages and demand considerable capital investment. It is true that, in general, the slag wool obtained is intended for relatively high quality applications, for which it is necessary to have a given distribution of the length of the fibres and of the well determined qualities of these fibres (hence the incorporation of various additives during the operation of reheating the cooled slag).

However, there are now demands, such as for a substitute for asbestos fibres the use of which is severely regulated in many countries for reasons of health and safety, for a raw product which has undergone less transform mation, that is to say a slag wool with a less homogeneous distribution of the lengths of the fibres and of an average quality rather than a relatively high quality.

It has been found that molten slags, immediately they leave a blast furnace, are at a sufficient temperature, of the order of 1,4500C, and at the correct viscosity, generally less than 15 poise, to permit consideration of the use of a dispersing device possessing sufficient kinetic energy to overcome the surface tension of the slag and to shear particles of molten material from the slag. On this basis, a new process for the production of slag wool has been developed, which enables the aforementioned disadvantages to be overcome, notably those of successive heatings of the slag and the use of a series of treatment stages.

According to the invention, a method of forming mineral wool from a metallurgical slag comprises withdrawing a stream of molten slag from a metallurgical refining vessel, such as a blast furnace, in which the slag was formed, subjecting a portion of at least of the surface of the molten slag stream to a sufficiently strong shearing action whereby molten material is dispersed from the surface of the slag stream and solidifies in the form of threads or filaments, and sometimes also beads, and recovering the threads or filaments as mineral wool.

The shearing of molten material from the surface of the slag stream can be achieved in various ways. For example, one way is to use a bladed rotor which is rotated at high speed, i.e. a peripheral speed which is of the order of 50 metres per second, and the blades of which dip into the molten slag to a depth of from one to several millimetres. Another equally advantageous way is to subject the surface of the molten slag to the sweeping action of pressurised fluid jets, such as jets of air at a pressure of from 5 to 10 bars and having a speed of at least 300 metres per second, preferably between 500 and 1,000 metres per second.

It is known for molten slag to leave a blast furnace along a casting channel and to fall from the channel either into a slag pit, or onto granulating or ball-producing devices, or quite simply into a removal pit. In the method in accordance with the invention, it is especially advantageous to arrange for the molten slag to leave the metallurgical vessel along a casting channel which leads into a retaining basin for settling particles of cast metal entrained with the slag and equipped at its upper edge with an overflow rim over which the molten slag flows in the form of a parabolic sheet of predetermined width and of a thickness which varies with the instantaneous flow rate. Such a system enables the slag flow rate leaving the vessel to be regulated and is described in more detail, with various improvements, in my U.K.Patent Specification No. 1514379 and my French Specification No. 2401999.

In practice, the bladed rotor or the nozzles for the pressurised fluid jets are installed substantially adjacent the overflow rim of the retaining basin, and in general act on only a portion of the layer of sheet of slag flowing over or from this rim.

In a variant of the present invention the flow of slag leaving the metallurgical vessel is subdivided into a number of branches, and the treatment according to the invention may be carried out at the aforementioned overflow rim and/or at any one of the branches.

For example, it is possible to provide the slag channel with at least one branch having a calibrated opening and intended to capture a small proportion of the slag flow, and to install in association with this branch, either a bladed rotor device or rows of pressurised fluid nozzles. It is also possible to carry out the method in accordance with this invention solely at the surface of the slag at the aforementioned overflow rim, and to convert into fibres the lesser part of the slag flowing from a branch by any other known technique for manufacturing slag wool, for example by centrifuging or blowing. The major fraction of the slag, which is not converted to mineral wool, may be subjected later to the known treatment of granulating or any other known process.

In the case where a bladed rotor is used in the method in accordance with the invention, it may be advantageous to install, following this first rotor, two further revolving elements for the purpose of perfecting the dispersion effect. In addition, in connection with this rotary process, it is preferable to install at the surface of the molten slag and just upstream of the bladed rotor a deflector or equivalent device for arresting and diverting accumulations of solidified particles on the surface of the molten slag.

The quantities and the characteristics (notably their length and diameter) of the threads or filaments obtained by the method in accordance with the invention depend firstly upon factors related to the means which exerts the shearing action and causes the dispersion of the molten slag particles, and secondly upon the physical and chemical characteristics of the slag treated.

The main factors related to the shearing means are, in the case of the bladed rotor, the peripheral speed of the blades, the number and length of the blades, and the depth of immersion of these blades in the sheet of molten slag. In the case where pressurised fluid jets are used, the main factors are the kinetic energy of the jets of air (or other fluid) put into effect per unit area, and the surface tension of the molten slag, generally of the order of 400 dynes/cm for a temperature of 1,400"C. In order to increase the kinetic energy of these air jets, it may be advantageous to adopt a sweeping action in a direction perpendicular to the direction of flow of the slag sheet.

The factors relating to the slag itself concern its chemical composition and its temperature, which determine the surface tension, the viscosity and the suitability of the slag for vitrification. By introducing additives into the molten slag immediately it leaves the metallurgical refining vessel, the chemical composition of the slag can be changed in order to modify the characteristics of the threads or filaments produced by the shearing action to which the surface of the molten slag is subsequently subjected. In order to produce long fibres of small diameter, it is necessary for the slag to have a basicity index B which is less than 1, this index being defined as the ratio (CaO + MgO)/(SiO2 + Al203).In the case where slags with a too high index B are treated, it is possible to reduce this by adding, upstream of the retention basin or branch (if pro vided), suitable agents such as glass waste having a melting point less than the melting point of the slag. For example, by adding from 1 to 3% by weight of glass to a slag having an index B of the order of 1, a considerable addition of SiO2 and of alkali metal oxides of the types K20 and Na2O is made to the slag without substantially increasing the viscosity of the melt and only a slight fall in temperature, and in this way the basicity index of the slag is reduced and the production of wool having filaments of great length is favoured.

Various examples of the method in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic section through a system involving the sweeping of a flowing sheet of molten slag by jets of pressurised fluid; Figure 2 is a diagrammatic view from above of the system illustrated in Figure 1; Figure 3 is a diagrammatic, perspective view of a flow of molten slag as it leaves an overflow rim and is being treated using pressurised fluid jets; Figure 4 is a diagrammatic section through a system in which fibres of threads are dispersed from the surface of a molten slag flow by a revolving device; Figure 5 is a diagrammatic view from above of a system similar to that of Figure 4;; Figure 6 is a diagrammatic plan view of a system in which the threads are obtained from the slag flowing in a branch from the main casting channel along which the slag flows; Figure 7 is a section through a particular form of rotor which may be used in the sys tems of Figures 4 to 6; and, Figure 8 is a diagrammatic view of a mod ification to the system illustrated in Figure 6.

Reference will first be made to Figures 1 to 3, which illustrate embodiments of the inven tion using a set of pressurised fluid jets.

These embodiments comprise a device which is for regulating the flow of molten slag leaving a blast-furnace or converter and which is of the type described in the aforementioned French Patent Specification No. 2,401,999. The device comprises, basi cally, a diverging casting channel 1 and a retention basin 2, the base of which, at 3, permits the discharge and removal of liquid cast metal. The basin 2 is equipped with an overflow rim 4 which is cooled by water cir culation in a pipe 5 embedded in the refrac tory material of the basin.

In accordance with the present invention, the slag flowing as a sheet or layer 6 from the overflow sill 4 is subjected to the dispersing action of pressurised air jets at a pressure of about 7 to 8 bars, just as it leaves the rim 4.

These jets issue from nozzles 7 aligned along one side of the sheet 6, or from nozzles 7 and 7' aligned along both sides of the sheet 6. The fibres and filaments 8 of slag which are formed in the atmosphere as a result of the action of the air jets on the molten slag sheet 6 are entrained into a hollow receptacle 9, for example a suction hood, and are conducted into a collecting chamber (not shown) where they are compacted and made into various forms according to the intended use of the wool collected. A portion only of the slag, for example from 1 to 10% depending upon the air flow rates utilised, is converted into mineral wool recovered at 9, and the major fraction of the molten slag (arrow 10) is subsequently poured into a trough or is treated to obtain balls or grains of porous slag by any one of a number of known ways.

In the embodiments illustrated in Figures 4 to 8, the essential elements for regulating the flow of slag from the metallurgical vessel are the same as before, comprising a casting channel 1 which widens out into a retention basin 2, the bottom of which, at 3, permits the discharge and removal of liquid metal, the basin being equipped with an overflow rim 4 which is cooled by water circulation in a pipe 5 embedded in the refractory material of the basin.

In the embodiments illustrated in Figures 4 and 5, the surface of the sheet or layer 6 of molten slag flowing from the overflow sill 4 is subjected, over a portion of the width of this sill, to the action of a bladed rotor 11 revolving, for example, at a speed of 50 m/sec.

Upstream from the rotor 11 the surface of the slag moving towards the location of the treatment by the rotor is acted upon by a deflector 12 which removes from the path of the rotor solid agglomerates of particles floating upon the surface of the molten slag.

The fibres and filaments 13 of slag immediately formed in the atmosphere by the portions of slag torn away by the rotor are entrained into a hollow receptacle 14 (Figure 4), for example a suction hood, and are conducted into a chamber (not shown) where they are compacted into various forms, depending upon the intended use. A portion only of the slag, for example from 1 to 10%, is converted into mineral wool, the major fraction of the molten slag (arrow 15) subsequently being poured into a cooling trough or treated in order to obtain balls or granules of porous slag in a known manner.

In practice, it is frequently found to be advantageous to provide, as the receptacle 14, a double suction hood (Figure 5), that is to say a chamber 16 for the recovery of the threads and filaments 13 and a chamber 17 intended for the recovery of slightly heavier particles in the form of beads 18, the applications for use of which may be different.

Figure 7 shows diagrammatically a type of rotor 11, equipped with a series of blades 19 which in operation are intended to dip slightly, i.e. by a few millimetres, into the flow of molten slag.

In the embodiment illustrated in Figure 6, a small branch 20 having a calibrated open ing 21 is provided on the casting channel 1.

This branch leads to a widened out portion 22 of the aforementioned retaining basin type where, if desired, the slag may be heated by means of burners 23. The rotary device for shearing particles of slag from the surface of the molten slag is installed at 24 and may, for example, be constituted, as shown in Fig ure 8, by a bladed rotor 11 as described earilier and two further rotors 24 and 26 which revolve in opposite directions and permit the action of the rotor 11 to be con tinued. The fibrous and filamentary mineral particles so obtained are sucked into a chamber 14 where pneumatic separation of the threads (and if necessary beads) is carried out, followed by the compacting and shaping of the collected wool product.

The slag wool thus produced may be suit able for the same purposes as the mineral wools manufactured by the already known processes. Furthermore, it may with advan tage be used as a substitute for asbestos fibres in the conventional applications of such fibres. Also, as a result of the fact that the product is virtually 100% vitrified and pos sesses a maximum hydraulic capacity, it can replace the conventional granulated slages in the manufacture of slag cements. Finally, the raw slag wool may, with advantage, be used by projecting, flocking or analogous techni ques for the insulation of walls, ceilings or other construction elements.

WHAT I CLAIM IS: 1. A method of forming mineral wool from a metallurgical slag, in which a stream of molten slag is withdrawn from the metal lurgical refining vessel in which the slag was formed, a portion of at least of the surface of the molten slag stream is subjected to a suffi ciently strong shearing action whereby mol ten material is dispersed from the surface of the slag stream and solidified in the form of threads of filaments, and sometimes also beads, and the threadsof filaments are reco vered as mineral wool.

2. A method according to claim 1, in which the molten slag stream is withdrawn from a blast furnace.

3. A method according to claim 1 or claim 2, in which the shearing action to which the surface of the molten slag stream is sub jected to produce the threads or filaments is provided by a bladed rotor which is rotated so that its peripheral speed is of the order of 50 metres per second, the blades of the rotor dipping into the molten slag to a depth of at . Ist one millimetre.

A A method according to claim 3, in * tile molten slag is withdrawn from the * q#rgical refining vessel along a casting channel which leads into a basin having an overflow rim over which the molten slag flows, and the bladed rotor is located adjacent the overflow rim.

5. A method according to claim 3, in which the molten slag is withdrawn from the metallurgical refining vessel along a casting channel which has a branch for carrying a portion of the molten slag flow, and the bladed rotor is located adjacent the surface of the slag issuing from the branch.

6. A method according to claim 5, in which two further bladed rotors are disposed adjacent the first bladed rotor, these further rotors being rotated in opposite directions and being arranged to perfect the dispersing effect of the first rotor.

7. A method according to any one of claims 3 to 6, in which a deflector is provided for arresting and diverting accumulations of solidified particles from the surface of the molten slag just upstream of the bladed rotor.

8. A method according to claim 1, in which the shearing action to which the surface of the molten slag stream is subjected to produce the threads or filaments is provided by pressurised fluid jets.

9. A method according to claim 8, in which the pressurised fluid jets are jets of air at from 5 to 10 bars pressure and having a velocity of at least 300 metres per second.

10. A method according to claim 9, in which the molten slag is withdrawn from the metallurgical refining vessel along a casting channel which leads into a basin having an overflow rim over which the molten slag flows, and the pressurised fluid jets are located substantially adjacent the overflow rim so that they act on one or both edges of the flow of slag flowing from the overflow rim.

11. A method according to claim 8 or claim 9, in which the molten slag is withdrawn from the metallurgical refining vessel along a casting channel and is subdivided into one or more branches, and the molten slag from at least one of these branches is subjected in totality to the shearing action of the pressurised air jets.

12. A method according to any one of the preceding claims, in which only a minor proportion of the molten slag which is withdrawn from the metallurgical refining vessel is treated to form mineral wool, the major proportion of this slag continuing its path and undergoing treatments for the purpose of manufacturing slag balls and/or granules.

13. A method according to any one of the preceding claims, in which additives are added to the molten slag immediately it leaves the metallurgical refining vessel, in order to modify the characteristics of the threads or filaments produced by the shearing action to which the surface of the molten slag is subsequently subjected.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

which in operation are intended to dip slightly, i.e. by a few millimetres, into the flow of molten slag.

In the embodiment illustrated in Figure 6, a small branch 20 having a calibrated open ing 21 is provided on the casting channel 1.

This branch leads to a widened out portion

22 of the aforementioned retaining basin type where, if desired, the slag may be heated by means of burners 23. The rotary device for shearing particles of slag from the surface of the molten slag is installed at 24 and may, for example, be constituted, as shown in Fig ure 8, by a bladed rotor 11 as described earilier and two further rotors 24 and 26 which revolve in opposite directions and permit the action of the rotor 11 to be con tinued. The fibrous and filamentary mineral particles so obtained are sucked into a chamber 14 where pneumatic separation of the threads (and if necessary beads) is carried out, followed by the compacting and shaping of the collected wool product.

The slag wool thus produced may be suit able for the same purposes as the mineral wools manufactured by the already known processes. Furthermore, it may with advan tage be used as a substitute for asbestos fibres in the conventional applications of such fibres. Also, as a result of the fact that the product is virtually 100% vitrified and pos sesses a maximum hydraulic capacity, it can replace the conventional granulated slages in the manufacture of slag cements. Finally, the raw slag wool may, with advantage, be used by projecting, flocking or analogous techni ques for the insulation of walls, ceilings or other construction elements.

WHAT I CLAIM IS: 1. A method of forming mineral wool from a metallurgical slag, in which a stream of molten slag is withdrawn from the metal lurgical refining vessel in which the slag was formed, a portion of at least of the surface of the molten slag stream is subjected to a suffi ciently strong shearing action whereby mol ten material is dispersed from the surface of the slag stream and solidified in the form of threads of filaments, and sometimes also beads, and the threadsof filaments are reco vered as mineral wool.
2. A method according to claim 1, in which the molten slag stream is withdrawn from a blast furnace.
3. A method according to claim 1 or claim 2, in which the shearing action to which the surface of the molten slag stream is sub jected to produce the threads or filaments is provided by a bladed rotor which is rotated so that its peripheral speed is of the order of 50 metres per second, the blades of the rotor dipping into the molten slag to a depth of at . Ist one millimetre.
A A method according to claim 3, in * tile molten slag is withdrawn from the * q#rgical refining vessel along a casting channel which leads into a basin having an overflow rim over which the molten slag flows, and the bladed rotor is located adjacent the overflow rim.
5. A method according to claim 3, in which the molten slag is withdrawn from the metallurgical refining vessel along a casting channel which has a branch for carrying a portion of the molten slag flow, and the bladed rotor is located adjacent the surface of the slag issuing from the branch.
6. A method according to claim 5, in which two further bladed rotors are disposed adjacent the first bladed rotor, these further rotors being rotated in opposite directions and being arranged to perfect the dispersing effect of the first rotor.
7. A method according to any one of claims 3 to 6, in which a deflector is provided for arresting and diverting accumulations of solidified particles from the surface of the molten slag just upstream of the bladed rotor.
8. A method according to claim 1, in which the shearing action to which the surface of the molten slag stream is subjected to produce the threads or filaments is provided by pressurised fluid jets.
9. A method according to claim 8, in which the pressurised fluid jets are jets of air at from 5 to 10 bars pressure and having a velocity of at least 300 metres per second.
10. A method according to claim 9, in which the molten slag is withdrawn from the metallurgical refining vessel along a casting channel which leads into a basin having an overflow rim over which the molten slag flows, and the pressurised fluid jets are located substantially adjacent the overflow rim so that they act on one or both edges of the flow of slag flowing from the overflow rim.
11. A method according to claim 8 or claim 9, in which the molten slag is withdrawn from the metallurgical refining vessel along a casting channel and is subdivided into one or more branches, and the molten slag from at least one of these branches is subjected in totality to the shearing action of the pressurised air jets.
12. A method according to any one of the preceding claims, in which only a minor proportion of the molten slag which is withdrawn from the metallurgical refining vessel is treated to form mineral wool, the major proportion of this slag continuing its path and undergoing treatments for the purpose of manufacturing slag balls and/or granules.
13. A method according to any one of the preceding claims, in which additives are added to the molten slag immediately it leaves the metallurgical refining vessel, in order to modify the characteristics of the threads or filaments produced by the shearing action to which the surface of the molten slag is subsequently subjected.
14. A method according to claim 13, in

which the additives comprise glass waste for reducing the basicity index of the slag and for promoting the production of longer threads or filaments.
15. A method according to claim 1, substantially as described with reference to Figures 1 and 2, or Figure 3, or Figure 4, or Figure 5, or Figure 6 or either Figure 7 or Figure 8 when used as a modification in any one of Figures 4 to 6 of the accompanying drawings.
16. Vitreous mineral wool produced from slag by a method according to any one of the preceding claims, and capable of being used as a substitute product for asbestos fibres, as an additive to cements in the manufacture of slag cements, or as an insulating material in buildings.