WO2000016890A1

WO2000016890A1 - Apparatus and method for atomising a liquid and granulating a molten substance

Info

Publication number: WO2000016890A1
Application number: PCT/ZA1999/000101
Authority: WO
Inventors: Kevin Philippe Daniel Perry
Original assignee: Kevin Philippe Daniel Perry
Priority date: 1998-09-23
Filing date: 1999-09-23
Publication date: 2000-03-30
Also published as: AU6300399A

Abstract

A method of atomising a liquid by disintegrating a tapping stream of the liquid with at least two media streams, the media streams consisting of liquid and/or gas, wherein the media streams are supplied at an angle to the tapping stream, the gas stream and the liquid stream arriving substantially parallel to each other at the tapping stream and a method of granulating a molten substance, the method including atomising a tapping stream of the molten substance and solidifying the molten atomised particles while keeping the said particles substantially separate from each other as well as a nozzle (110) for use in carrying out the methods claimed above, the nozzle (110) including a nozzle body defining a chamber having a plurality of media inlets (16, 18) and one or more nozzle body outlets and a dividing wall (22) at least partially inside the nozzle body, dividing the chamber into at least two media chambers, each media chamber having one or more outlet in the form of a nozzle orifice, the nozzle orifices of the media chambers together defining the one or more nozzle body outlet.

Description

APPARATUS AND METHOD FOR ATOMISING A LIQUID AND GRANULATING A

MOLTEN SUBSTANCE Field of the Invention

The present invention relates to a method of atomising a liquid, to a method of granulating a molten substance and to an apparatus for performing the methods.

Background to the Invention

The applicant is aware of prior art methods for atomising a liquid and for granulating a molten metal, which methods include the atomising of a tapping stream of molten metal by passing it onto the line of intersection of two or more fluid media streams directed at an angle to each other. The nozzles of such a prior art method are vertical slots or rows of slots directed at an angle of less than 60° to each other, typically between 5° and 20°.

The prior art methods can be used for atomising metal melts by the use of gas or liquid media streams, such as nitrogen, argon, and water, water atomisation leading to irregular shaped particles. When water is used together with air, oxidisation occurs rapidly in the particle surface, thereby preventing them from becoming spherical and leading to the irregular shapes.

Atomising with water or water and air by the prior art methods, requires very large pumping equipment of considerable size in order to obtain sufficient quantities/pressure i.e. 100 to 200 Bar. It can also be noted that the manufacture of conventional nozzles for water atomisation is also very expensive. With the above prior art methods, the yield of particles under 250μm is only about

40%.

Summary of the Invention

According to a first aspect of the invention there is provided a method of atomising a liquid by disintegrating a tapping stream of the liquid with at least two media streams, the media streams consisting of liquid and/or gas, wherein the media streams are supplied at an angle to the tapping stream, the gas stream and the liquid stream arriving substantially parallel to each other at the tapping stream.

The liquid stream may be at least partially entrained in a portion of the gas stream within a boundary region between the gas stream and the liquid stream, such that the entrained liquid and the remainder of the gas stream arrive substantially parallel at the tapping stream.

The entrained liquid stream may be in the form of an aerosol of entrained liquid particles in the gas.

Typically the angle of the media streams to the tapping stream is about 90°, for example, a vertical tapping stream is atomised with the aid of horizontal media streams formed by slot-shaped nozzle orifices or rows of nozzle orifices, the liquid and gas nozzle orifices being stacked on top of each other in the plane of the tapping stream. The method may use water, oil, fluid gas or a mixture thereof as the liquid medium, and air, water vapour, inert gas, gaseous hydrocarbons or a mixture thereof as the gas for the liquid and gas media streams.

The liquid and gas streams may at least initially be separated by means of a dividing wall to induce the parallelity of the media streams arriving at the tapping stream.

According to a second aspect of the invention there is provided a method of granulating a molten substance, the method including:

atomising a tapping stream of the molten substance substantially as described above;

solidifying the molten atomised particles while keeping the said particles substantially separate from each other.

The method may include the additional step of collecting the solidified particles or granules in collecting means.

The collecting step of the method my be incorporated in to the solidifying step, for example, by collecting the molten atomised particles in a quenching medium, such as water, oil, and the like, whereby the said particles are solidified.

The method may include the step of separating the solidified particles from the quenching medium. Typically the method includes the step of separating or classifying the solidified particles by particle size, for example, by means of sieving to obtain solidified particles having a desired particle size distribution.

The method may be applied to molten substances such as metals and metal alloys. Typically the method is applied to metal alloys containing at least one of iron, chromium, manganese, titanium, cobalt, nickel, zinc, or silicon.

In a specific example EN 19 steel is atomised and granulated in accordance with the methods of the invention.

The method may however be applied to other molten substances such as molten sulphur compounds and compositions which are known as matte.

Typically such matte also contain at least one of copper, nickel, iron, zinc, or cobalt.

The granules obtained by the granulating method of the invention are typically in the order of 85% below 250 μm in diameter.

According to a further aspect of the invention there is provided a nozzle for use in carrying out the methods of the invention, the nozzle including:

a nozzle body defining a chamber having a plurality of media inlets and one or more nozzle body outlet; and a dividing wall at least partially inside the nozzle body, dividing the chamber in to at least two media chambers, each media chamber having one or more outlet in the form of a nozzle orifice, the nozzle orifices of the media chambers together defining the one or more nozzle body outlet.

The nozzle body may be of unitary construction, for example, a cast or machined nozzle body, with the dividing wall being attachable to the nozzle body.

Typically, however, the nozzle body is of multi-component construction with the dividing wall being attachable to the nozzle body components during the assembly of the components to make the nozzle body.

The multi-component nozzle body may consist of two dished portions, each dished portion having one or more media inlet, the two dished portions being assemblable to form the nozzle body and define the chamber thereof.

Typically, each of the dished portions is flanged for attachment to the other dished portion during assembly of the nozzle body from the components.

The dividing wall may be a planar dividing wall in the form of a flat sheet having a flange portion extending peripherally around at least a portion of said sheet. The sheet flange portion being sandwichable between the flanges of the dished portions during assembly of the nozzle. The nozzle body components, including the dividing wall, may be fastenable together in forming the nozzle, by fastening means such as bolts, rivets, bonding agent, welding, braising, or the like.

Spacing shims may be provided for adjusting the volume of the chamber of the nozzle body. The thickness of the spacing shims being selectable to provide a desired degree of spacing.

Typically the spacing shims are inserted between the flanges of the dished portions and the sheet for independent adjustment of the volume of each media chamber and/or the media chamber nozzle orifices.

The shims may be tapered.

In a specific embodiment the shims are in the form of flanges sized and dimensioned complementarily to the flanges of the dished portions and the sheet flanges.

Description of the Drawings

The invention will now be described, by way of non-limiting example only, with reference to the following example and diagrammatic drawings.

In the drawings

Figure 1 graphically shows the particle size distribution of granulated EN19 steel, granulated in accordance with the invention; Figure 2 shows the table of data used to generate the graph of Figure 1 ;

Figure 3 shows, in exploded three dimensional view, a nozzle in accordance with the invention; and

Figure 4 shows, in schematic representation, the operation of an atomising apparatus in accordance with the invention.

In Figure 3, reference numeral 10 generally indicates a nozzle broadly in accordance with the invention. The nozzle 10 including a nozzle body 12 defining a chamber 14 having two media inlets 16, 18 and a nozzle body outlet 20. Media inlet 16 is a water inlet and media inlet 18 is an air inlet.

A planar dividing wall, in the form of a flat sheet 22 located inside the nozzle body 12 divides the chamber 14 in to two media chambers 24, 26, each media chamber 24, 26 having an outlet in the form of a nozzle orifice 28, 30. Media chamber 24 is the water chamber and media chamber 26 is the air chamber. The water and air nozzle orifices 28, 30 together define the nozzle body outlet 20.

The nozzle body 12 is of multi-component construction, consisting of two dished portions 32, 34 together with the dividing flat sheet 22 defining the water and air chambers 24, 26. Each of the dished portions 32, 34 is flanged 36, 38 for attachment to the other dished portion during assembly of the nozzle body 12 from the components. The dividing sheet 22 has a flange portion 40 extending peripherally around three sides of said sheet 22. The sheet flange portion 40 being sandwichable between the flanges 36, 38 of the dished portions 32, 34 during assembly of the nozzle. The nozzle body 12 components, including the dividing sheet 22, are fastened together in forming the nozzle 10 by fastening means ion the form of bolts (not shown).

Spacing shims 42, 44 are provided for adjusting the volume of the chamber 14 of the nozzle body 12. The thickness 46, 48 of the spacing shims 42, 44 being selectable to provide a desired degree of spacing. The spacing shims 42, 44 are inserted between the flanges 36, 38, 40 of the dished portions 32, 34 and the sheet 22 for independent adjustment of the volume of each media chamber 24, 26 and/or the air and water chamber nozzle orifices 28, 30.

The shims 42, 44 are in the form of flanges sized and dimensioned complementarily to the flanges 36, 38 of the dished portions 32, 34 and the sheet flange portion 40.

In Figure 4, the nozzle 10 is used to produce metal particles 12 from a molten metal tapping stream 14. Water 16 and air 18 are introduced into the nozzle 10 via inlets 16 and 18 (Figure 3). The two media streams exit the nozzle 10 at orifices 28, 30 projecting the high velocity streams perpendiclualrly to the tapping stream 14.

EXAMPLE 1

EN 19 steel was atomised and granulated to produce particles having a particle size distribution of 85% below 250μm, as shown in Figure 1 and Figure 2. A nozzle as shown in Figure 3 was positioned horizontally with the air media chamber and air inlet on top and the water media chamber and water inlet underneath. The nozzle orifices for the air and water where thus horizontal.

An A8 clay-graphite crucible was positioned 100 mm above the upper orifice in the nozzle forming a 90° angle between the air and water medium flow and the metal tapping stream.

A 7mm hole was used in the crucible to regulate the metal flow rate.

The metal tapping stream was aimed 50 mm in front of the nozzle in the middle of the flow stream of the atomising medium i.e. the air and water streams.

The air and water streams were directed into a 200 mm diameter, pipe 6 m long, by means of a funnel 400 mm ahead of the nozzle in the direction of the air and water streams flow.

The atomised material was collected in a water filled holding tank at the end of the 200 mm diameter pipe.

The air chamber inlet of the nozzle was connected to a 750 cfm compressor capable of reaching 25 Bar pressure.

The water chamber inlet of the nozzle was connected to a pump delivering a maximum of 3 Bar pressure. The water pump was connected to the holding tank thereby circulating the water in the holding tank back through the nozzle.

The atomisation and granulation then took place under the following operating conditions as set out in Table 1 below:

Table 1: Operating conditions during trial run

Three 25 kg melts of EN 19 steel were melted using an induction furnace and transferred with a preheated ladle to the preheated tundish (crucible).

The compressed air and water were turned on and the pressure and flow allowed to stabilise before the molten metal was tapped into the air and water stream.

Over the three batches the atomisation and granulation of 25 kg of EN 19 took 45 seconds to 1 minute and after completion the air and water flow were maintained for 10 to 15 seconds. The atomised solidified particles or powder was allowed to settle out in the holding tank for 24 hours before the water was drained off and the powder removed in the form of a sludge. The sludge was then dried in a vacuum oven at 110°C for 12 hours.

The powder was sieved and the powder below 250 μm was removed. This was 85% of the total powder produced. A 1 kg sample was drawn using recognised sampling techniques, which sample was analysed for particle size distribution by a sieve analysis. The results of the sieve analysis are set out in Table 2 below.

Table 2: Cumulative Particle Size Distribution

Claims

1. A method of atomising a liquid by disintegrating a tapping stream of the liquid with at least two media streams, the media streams consisting of liquid and/or gas, wherein the media streams are supplied at an angle to the tapping stream, the gas stream and the liquid stream arriving substantially parallel to each other at the tapping stream.

2. A method as claimed in claim 1 wherein the liquid stream is at least partially entrained in a portion of the gas stream within a boundary region between the gas stream and the liquid stream, such that the entrained liquid and the remainder of the gas stream arrive substantially parallel at the tapping stream.

3. A method as claimed in claim 2 wherein the entrained liquid stream is in the form of an aerosol of entrained liquid particles in the gas.

4. A method as claimed in any one of the preceding claims wherein the angle of the media streams to the tapping stream is about 90°.

5. A method as claimed in any one of the preceding claims wherein a vertical tapping stream is atomised with the aid of horizontal media streams formed by slot-shaped nozzle orifices or rows of nozzle orifices, the liquid and gas nozzle orifices being in a stacked on top of each other in the plane of the tapping stream.

6. A method as claimed in any one of the preceding claims wherein any one of the group including water, oil, fluid gas or a mixture thereof is used as the liquid medium, and any one of the group including air, water vapour, inert gas, gaseous hydrocarbons or a mixture thereof is used as the gas for the liquid and gas media streams.

7. A method as claimed in any one of the preceding claims wherein the liquid and gas streams are at least initially separated by means of a dividing wall to induce the parallelity of the media streams arriving at the tapping stream.

8. A method of granulating a molten substance, the method including: atomising a tapping stream of the molten substance substantially as described in any one of the preceding claims; and solidifying the molten atomised particles while keeping the said particles substantially separate from each other.

9. A method as claimed in claim 8 which includes the step of collecting the solidified particles or granules in collecting means.

10. A method as claimed in claim 9 wherein the collecting step is incorporated into the solidifying step.

11. A method as claimed in claim 10 wherein incorporation of the collecting and solidifying steps are provided by collecting the molten atomised particles in a quenching medium, such as water, oil, and the like, whereby the said particles are solidified.

12. A method as claimed in any one of claims 8 to 11 which includes the step of separating the solidified particles from the quenching medium.

13. A method as claimed in any one of claims 8 to 12 which includes the step of separating or classifying the solidified particles by particle size.

14. A method as claimed in claims 13 wherein the separating or classifying step is provided by means of sieving to obtain solidified particles having a desired particle size distribution.

15. A method as claimed in any one of claims 8 to 14 which is capable of being applied to molten substances such as metals and metal alloys.

16. A method as claimed in claims 15 wherein metal alloys contain at least one of iron, chromium, manganese, titanium, cobalt, nickel, zinc, or silicon.

17. A method as claimed in any one of the preceding claims wherein EN 19 steel is atomised and granulated.

18. A method as claimed in any one of the preceding claims which is applicable to other molten substances such as molten sulphur compounds and compositions which are known as matte.

19. A method as claimed in claim 18 wherein the matte also contains at least one of copper, nickel, iron, zinc, or cobalt.

20. A method as claimed in any one of claims 8 to 19 wherein the granules obtained are typically in the order of 85% below 250 μm in diameter.

21. A nozzle for use in carrying out the methods claimed above, the nozzle including: a nozzle body defining a chamber having a plurality of media inlets and one or more nozzle body outlet; and a dividing wall at least partially inside the nozzle body, dividing the chamber in to at least two media chambers, each media chamber having one or more outlet in the form of a nozzle orifice, the nozzle orifices of the media chambers together defining the one or more nozzle body outlet.

22. A nozzle as claimed in claim 21 the body is of unitary construction, for example, a cast or machined nozzle body, with the dividing wall being attachable to the nozzle body.

23. A nozzle as claimed in claim 21 wherein the nozzle body is of multi-component construction with the dividing wall being attachable to the nozzle body components during the assembly of the components to make the nozzle body.

24. A nozzle as claimed in claim 21 wherein the multi-component nozzle body consists of two dished portions, each dished portion having one or more media inlet, the two dished portions being configured to be assembled to form the nozzle body and define the chamber thereof.

25. A nozzle as claimed in claim 24 wherein each of the dished portions is flanged for attachment to the other dished portion during assembly of the nozzle body from the components.

26. A nozzle as claimed in claim 23 wherein the dividing wall is a planar dividing wall in the form of a flat sheet having a flange portion extending peripherally around at least a portion of said sheet.

27. A nozzle as claimed in claim 26 wherein the sheet flange portion is configured to be sandwiched between the flanges of the dished portions during assembly of the nozzle.

28. A nozzle as claimed in claim 21 wherein the nozzle body components, including the dividing wall are configured to be fastened together in forming the nozzle, by fastening means such as bolts, rivets, bonding agent, welding, braising, or the like.

29. A nozzle as claimed in claim 28. Wherein spacing shims are provided for adjusting the volume of the chamber of the nozzle body.

30. A nozzle as claimed in claim 29 wherein the thickness of the spacing shims are selectable to provide a desired degree of spacing.

31. A nozzle as claimed in claim 29 or 30 wherein the spacing shims are inserted between the flanges of the dished portions and the sheet for independent adjustment of the volume of each media chamber and/or the media chamber nozzle orifices.

32. A nozzle as claimed in any one of claims 29 to 31 wherein the shims are of tapered.