GRANULATION METHOD

Abstract: A method of producing a granular metal, matte or like material is provided. The method includes the steps of providing a source of material in molten form in a vessel, providing a distribution plate (26) having at least one edge (32) and located above a body of cooling liquid (12) and causing the molten metal to leave the vessel, pass on to the distribution plate, flow over the edge and into the body of cooling liquid. Preferably, a region of flowing liquid within the body of cooling liquid is created. This region has a first zone of predetermined velocity and at least one other zone of higher velocity. The flow of molten material is caused to enter the region and into the first zone before the other zone.

Description: GRANULATION METHOD BACKGROUND OF THE INVENTION This invention relates to a granulation method. The production of alloys such as ferrosilicon and ferrochrome in granular form is known. One such granulation method involves pouring molten alloy from a ladle into a tundish from which it passes through a nozzle. The stream of liquid metal emerging from the nozzle strikes a circular refractory spray head, splits up and forms droplets which fall into a body of circulating cooling water underneath. After rapid solidification in the water, the granules are discharged and collected. Another granulation method is one which involves directing the alloy, which passes out of the nozzle, through a jet of water and then into the water. This method is known as the Showa Denko method. United States Patent 5,258,053 describes a method of granulating molten metals in which at least one continuous stream of molten metal is caused to fall from a launder down into a cooling liquid bath contained in a tank wherein the metal stream is divided into granules which solidify. A substantially even flow of cooling liquid is caused to flow across the tank in a direction substantially peφendicular to the falling metal stream, the flow of the cooling liquid having an average velocity of less than 0, 1 m/sec. One of the problems with these prior art methods is the consistency of the product obtained. There is generally a large amount of fines in the granular product which is undesirable. SUMMARY OF THE INVENTION According to the present invention, a method of producing a granular metal, matte or like material, includes the steps of providing a source of the material in molten form in a vessel, providing a distribution plate having at least one edge and located above a body of cooling liquid, and causing the molten metal to leave the vessel, pass on to the distribution plate, flow over the edge and into the body of cooling liquid. Further according to the invention, the molten metal which passes on to the distribution plate is split into two or more streams which flow over at least one edge of the distribution plate. In one form of the invention, the plate has an upper surface defining at its periphery the edge over which the molten material flows, and an obstruction is provided on the upper surface to split the molten material which passes on to the plate into two or more streams. Still further according to the invention, a region of flowing liquid within the body of cooling liquid is created, the region having a first zone of predetermined velocity and at least one other zone of higher velocity, and the flow of molten material is caused to enter the region and into the first zone before the other zone. Preferably, the region has a plurality of zones, a first zone having a predetermined velocity and each successive zone having a higher velocity than its immediate preceding neighbour. DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a diagrammatic sectional side view of an embodiment of the invention, Figure 2 is a plan view of the distribution plate of Figure 1 , and Figure 3 is a graph illustrating a water velocity profile for the region of flowing liquid. DESCRIPTION OF EMBODIMENTS The method of the invention is suitable for producing granular metal, matte or like material. The metal may be any known in the art, but will typically be an alloy such as ferrosilicon or ferrochrome. The production of ferrosilicon, for example, usually involves rough handling and environmental problems caused by dust and heat. The efficient production of ferrosilicon granules by the method of the invention minimises these problems. The invention also has application to mattes of any type. An example of a matte which can be granulated by the method of the invention is a sulphide matte. The material to be granulated must be rendered molten prior to granulation. The material will generally be rendered molten in a furnace from whence it will be introduced into a vessel such as a tundish, ladle or launder. It is from such a vessel that the molten material is delivered to the distribution plate. The size and shape of the distribution plate will vary according to the nature of the material which is being granulated. Generally, the plate will have at least one edge, and generally several edges, over which a flow of the molten material will be caused to pass. Preferably, the flow of molten material leaving the edge or edges of the plate is a continuous curtain-type flow. Typically the plate will have a square, rectangular or triangular shape. The plate may be provided with an obstruction to cause the molten material flow to take place over some of the edges only of the plate or over more than one edge of the plate. The stream of molten material may be split into two or more streams which may flow over one or more of the edges of the plate. Each such stream preferably has a continuous curtain-type flow. In a preferred form of the invention, and one which results in particularly effective granulation being achieved, the molten material which enters the cooling liquid is caused to flow transverse to and through a region of flowing cooling liquid. The region, as mentioned above, has a first zone of predetermined velocity and at least one other zone of higher velocity. The flow of molten metal is caused to enter the region and into the first zone before the other zone. The region of flowing liquid may be created by means of a uniform flow of liquid passing into the liquid body through an inlet. Typically, this inlet will be a nozzle. The various zones of differing velocity may be created by deflecting the flow liquid, the deflection causing the flow to accelerate. One or more μ tes may be located in the flow of liquid to cause this deflection. In one particular form of the invention a bank of vertically disposed spaced deflector plates is provided. The cooling liquid will generally be water, although other cooling liquids or mixture of cooling liquids may be used. An embodiment of the invention will now be described with reference to the accompanying drawings. Referring first to Figures 1 and 2, there is shown apparatus suitable for producing granules of a molten material such as molten ferrochrome or ferrosilicon. The apparatus comprises a container 10 holding a body of water 12 which has a level or exposed surface 14. Water is introduced horizontally into the container through nozzle 16. The water leaves the nozzle 16 and comes into contact with a bank of vertically disposed spaced deflector plates 18. Downstream of these deflector plates a region of liquid flow, generally indicated by 20, is created. The deflector plates 18 have the effect of accelerating the flow of liquid which comes into contact with them, the extent of acceleration depending on the shape, size and disposition of the particular plate. Thus, the region 20 is made up of a number of zones 22 differing from each other in the velocity of the liquid flow. The zone of slowest velocity is at the top of the region and that of the fastest velocity is at the lower end of the region. Preferably, the velocity of each zone is higher than its immediately preceding neighbour as one progresses from the zone of slowest velocity to that of fastest velocity. An example of a velocity profile is illustrated graphically by Figure 3. The height from the top (or depth from the surface of the liquid body) is given on the vertical axis. It will also be noted the slowest velocity is 0, 1 m/s. Located above the container and above the water level 14 is a launder 24 and a metal distribution plate 26. The plate 26 has an obstruction 28 located close to the front edge 30. The obstruction 28 is an optional feature. In use, molten material from a furnace is introduced into the launder 24 from whence it overflows on to distribution plate 26 as is shown by the arrows in Figures 1 and 2. The molten metal which passes on to the distribution plate 26 is split by the obstruction and flows over the outer side edges 32 as two continuous curtain-like streams and into the water. The obstruction 28 substantially prevents flow of molten metal over the front edge 30. When the streams of molten material hit the water, they pass into the region 20, which is transverse to the streams. The metal streams pass into the zone of slowest velocity first and then progressively through the other zones. As the molten material does so, it disintegrates forming granules which are cooled. The formed granules pass on to conveyor 34 and are removed for collection in the direction of the arrow 36. The cooling liquid will generally be water, although other cooling liquids or a mixture of cooling liquids may be used. When the hot material streams pass into the water initially only a thin solidified skin, surrounded by a vapour film of the liquid, is formed on the globules or granules of molten material. In order to avoid distortion of the granule form, a smooth flow of water is introduced through the nozzle 16 and thereby a more solid and regular form is obtained. In order to obtain sufficient cooling of the granules the water flow velocities underneath are gradually increased by use of the deflector plates described above. In doing so, more heat can be removed from the granules as they fall further downwards to the bottom of the tank. As this results in an increase of heat transfer, higher hot metal flow rates (up to 5 ton/min) can be achieved, without a risk of explosions. The metal distribution plate 26 illustrated is substantially square in shape. Other shapes may also be used. The shape of the plate and size thereof will generally vary according to the nature of the material being granulated and the size of granules required. Further, plate 26 is illustrated as being horizontal and substantially parallel to the level 14. The plate may be located at an angle to the horizontal. The embodiment described above can also be used in the granulation of a metal, matte or like material. The method and apparatus as described above was used for granulating ferrosilicon. Excellent results were achieved with more consistent, solid and round granule sizes, most exceeding 4mm in size and a substantial fraction exceeding 12,5mm in size, when compared with the conventional Showa Denka method. Further, compared with this conventional granulation method, ten times less fines were produced.

Claims: CLAIMS 1. A method of producing a granular metal, matte or like material includes the steps of providing a source of the material in molten form in a vessel, providing a distribution plate having at least one edge and located above a body of cooling liquid and causing the molten material to leave the vessel, pass on to the distribution plate, flow over the edge and into the body of cooling liquid. 2. A method according to claim 1 wherein the molten material which passes on to the distribution plate is split into two or more streams which flow over at least one edge of the distribution plate. 3. A method according to any one of the preceding claims wherein the plate has an upper surface defining at its periphery the edge over which the molten material flows, and an obstruction is provided on the upper surface to split the molten material which passes on to the plate into two or more streams. 4. A method according to claim 2 or claim 3 wherein the distribution plate has more than one edge and the streams are caused to pass over more than one of the edges. 5. A method according to any one of the preceding claims wherein the plate has a square, rectangular or triangular shape. 6. A method according to any one of the preceding claims wherein the flow of molten material over the edge of the plate and into the body of cooling liquid is a continuous curtain-type flow. 7. A method according to any one of the preceding claims wherein a region of flowing liquid within the body of cooling liquid is created, the region having a first zone of predetermined velocity and at least one other zone of a higher velocity, and the flow of molten material is caused to enter the region and into the first zone before the other zone. 8. A method according to claim 7 wherein the region has a plurality of zones, a first zone having a predetermined velocity and each successive zone having a higher velocity than its immediate preceding neighbour. 9. A method according to any one of the preceding claims wherein the region of flowing liquid is created by means of a uniform flow of liquid passing into the liquid body through an inlet. 10. A method according to claim 9 wherein the inlet is a nozzle. 11. A method according to claim 9 or claim 10 wherein the uniform flow of liquid passing into the liquid body is deflected by one or more plates. 12. A method according to any one of claims 7 to 11 wherein the liquid flow in the first zone has a velocity of at least 0, 1 m/s. 13. A method according to any one of the preceding claims wherein the vessel containing the source of molten material is a ladle, launder, tundish or the like.

Inventors: BOTHMA JOHANNES HENDRIK, KESTENS PAUL HIPPOLIET ISIDOOR, LABUSCHAGNE JAN HENDRIK, VENTER STEPHANUS ALBERTUS, BOTHMA, JOHANNES, HENDRIK, KESTENS, PAUL, HIPPOLIET, ISIDOOR, LABUSCHAGNE, JAN, HENDRIK, VENTER, STEPHANUS, ALBERTUS
Applicants: BOTHMA JOHANNES HENDRIK, CONSOLIDATED METALLURG IND LIM, KESTENS PAUL HIPPOLIET ISIDOOR, LABUSCHAGNE JAN HENDRIK, VENTER STEPHANUS ALBERTUS, BOTHMA, JOHANNES, HENDRIK, CONSOLIDATED METALLURGICAL INDUSTRIES LIMITED, KESTENS, PAUL, HIPPOLIET, ISIDOOR, LABUSCHAGNE, JAN, HENDRIK, VENTER, STEPHANUS, ALBERTUS
Application year: 1997
Main classification: B22F9
IPC codes: B22F9