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Title:
LANCE FOR USE IN A TOP SUBMERGED LANCE FURNACE
Document Type and Number:
WIPO Patent Application WO/2017/195105
Kind Code:
A1
Abstract:
This invention relates to a Iance for use in a top submerged Iance furnace, and also to a top submerged Iance furnace including a iance incorporating a novel Iance tip. The invention also extends to a method of introducing gas into a top submerged Iance furnace using an improved Iance and Iance tip design. The iance includes a process gas supply conduit and a Iance tip secured to the process gas supply conduit. The process gas supply conduit has a first end that can in use be brought in flow communication with a source of process gas, and a second end which is in flow communication with the lance tip. The Iance is characterised in that the iance tip includes a plurality of discrete flow passages that are ail in flow communication with the process gas supply conduit.

Inventors:
FRANCIS, Brett John (Unit 7, 76 Elizabeth Street Paddingto, Queensland 4064, 4064, AU)
JOUBERT, Hugo (17 Patricia Drive, The GapQueensland, 4061, 4061, AU)
BAKKER, Martin Lluis (24 Edinburgh Close, Upper KedronQueensland, 4055, 4055, AU)
NIKOLIC, Stanko (4 Errogie Place, Fig Tree PocketQueensland, 4069, 4069, AU)
GWYNN-JONES, Stephen (1/19 Buckland Road, NundahQueensland, 4012, 4012, AU)
Application Number:
IB2017/052692
Publication Date:
November 16, 2017
Filing Date:
May 09, 2017
Export Citation:
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Assignee:
TENOVA SOUTH AFRICA (PTY) LTD (96 Loper Avenue, Aeroport Spartan, 1643 Johannesburg, 1643, ZA)
International Classes:
C21C5/46; F27D3/16
Domestic Patent References:
WO2015056143A12015-04-23
Foreign References:
DE2438676A11976-02-26
DE1138409B1962-10-25
JP2003034816A2003-02-07
US5308043A1994-05-03
US20140327194A12014-11-06
Other References:
Y. PAN; D. LANGBERG: "Two-Dimensional Physical and CFD Modelling of Large Gas Bubble Behaviour in Bath Smelting Furnaces", THE JOURNAL OF COMPUTATIONAL MULTIPHASE FLOWS, vol. 2, 2010, pages 151 - 164
R. L. PLAYER: "Copper Isasmelt - Process Investigations", INTERNATIONAL SYMPOSIUM, INJECTION IN PYROMETALLURGY, 1996
Attorney, Agent or Firm:
SPOOR & FISHER et al. (11 Byls Bridge Boulevard, Building No. 14Highveld Ext 73, 0157 Centurion, 0157, ZA)
Download PDF:
Claims:
CLAIMS:

1. A lance for use in a top submerged lance furnace, the lance including:

a process gas supply conduit; and

a lance tip secured to the process gas supply conduit;

the process gas supply conduit having a first end that can in use be brought in flow communication with a source of process gas, and a second end which is in flow communication with the lance tip;

characterized in that the lance tip includes a plurality of discrete flow passages that are all in flow communication with the process gas supply conduit.

2. The lance of claim 1 in which the discrete flow passages are defined by process gas injection conduits.

3. The lance of claim 2 in which the process gas injection conduits are spaced apart.

4. The lance of claim 2 in which the process gas injection conduits are spaced apart at equal distances about a central axis of the lance.

5. The lance of any one of claims 2 to 4 in which the longitudinal axes of the process gas injection conduits are parallel to a longitudinal axis of the process gas supply conduit.

6. The lance of any one of claims 2 to 4 in which the longitudinal axes of the process gas injection conduits are angularly offset relative to a longitudinal axis of the process gas supply conduit.

7. The lance of any one of claims 2 to 4 in which the longitudinal axes of the process gas injection conduits are substantially perpendicular relative to a longitudinal axis of the process gas supply conduit.

8. The lance of claim 1 in which the discrete flow passages are defined by a plurality of apertures located in a common accumulator formation.

9. The lance of claim 8 in which the accumulator formation is hemispherical, and in which the apertures are directed in horizontal, vertical and/or oblique directions.

10. The lance of any one claims 2 to 7 including a fuel supply conduit.

11. The lance of claim 10 in which the lance tip includes a fuel injection conduit which is in flow communication with the fuel supply conduit of the lance.

12. The lance of claim 11 in which the fuel injection conduit is located centrally relative to the surrounding process gas injection conduits.

13. The lance of claim 11 or 12 in which the fuel injection conduit is located inside a central process gas injection conduit.

14. The lance of claim 13 in which is the fuel injection conduit is co-axial with a longitudinal axis of the lance, with the other process gas injection conduits radially spaced apart about the central process gas injection conduit.

15. The lance of any one claims 2 to 7 or 10 to 14 including a tip pressure measurement conduit.

16. The lance of claim 15 in which the lance tip includes a tip pressure measurement conduit which is in flow communication with the tip pressure measurement conduit of the lance.

17. The lance of claim 16 in which the tip pressure measurement conduit is located centrally relative to the surrounding process gas injection conduits, concentric with the fuel injection conduit.

18. The lance of any one of claims 15 to 17 in which the tip pressure measurement conduit Is located inside the process gas supply conduit before the connection point to the lance tip.

19. The lance of any one of claims 15 to 17 in which the tip pressure measurement conduit at least partially extends into the central process gas injection conduit.

20. The lance of claim 19 in which is the tip pressure measurement conduit is co-axial with a longitudinal axis of the lance, with the other process gas injection conduits radially spaced apart about the central process gas injection conduit

21. The lance of any one of claims 13 or 20 in which the central process gas injection conduit has a diameter which is larger than that of the outer process gas injection conduits.

22. A lance tip for a lance for use in a top submerged lance furnace, wherein the lance incudes a process gas supply conduit, the lance tip including:

a process gas supply conduit having a first end that can in use be brought in flow communication with the process gas supply conduit;

characterized in that the process gas supply conduit comprises discrete flow passages that are all in flow communication with the process gas supply conduit.

23. A top submerged lance furnace including:

a crucible suitable for holding a molten material bath;

a roof in use covering an open end of the crucible; and a lance as claimed in any one of claims 1 to 21.

24. A method of introducing process gas into a top submerged lance furnace, the method including the steps of:

- supplying process gas via a lance; and

- dividing the process gas supply into a plurality of discrete injection streams prior to injecting the process gas into a molten bath of the furnace.

25. The method of claim 24 including the step of introducing the process gas using a lance and lance tip as claimed in any one of claims 1 to 21.

Description:
LANCE FOR USE IN A TOP SUBMERGED LANCE FURNACE

BACKGROUND TO THE INVENTION

THIS invention relates to a lance for use in a top submerged lance furnace, and also to a top submerged lance furnace including a lance incorporating a novel lance tip. The invention also extends to a method of introducing gas into a top submerged lance furnace using an improved lance and lance tip design.

A top submerged lance furnace is a type of furnace used in pyrometallurgy, and in particular in the smelting of minerals, metals and metallurgical ore. A top submerged lance furnace comprises a crucible for receiving and containing liquid metal, speiss, matte and/or a slag bath. The crucible is typically in the form of an upright-cylindrical shaped vessel that is lined with a containment lining, i.e. refractory bricks or copper coolers. A freeboard extension is provided above the furnace crucible, and an operatively upper zone of the furnace vessel, and hence an operatively upper zone of the freeboard, usually flares out in one radially outwardly direction towards a gas take-off. A vertically orientated, suspended steel lance extends through the roof of the furnace into the crucible through a hole in the roof of the furnace. An end of the lance is, in use, submerged below the surface of the liquid bath located in the crucible. Any one or more of process air, oxygen-enriched air, nitrogen-enriched air, oxygen, fuel, flux, reductant and feed material are injected into the bath via the lance. The feed material, e.g. mineral concentrates or materials for recycling, reductant, flux and solid fuel can also be dropped into the bath through another hole in the furnace roof. The lance will, however, always introduce at least the process air / oxygen- enriched air / nitrogen-enriched air into the molten bath, resulting in vigorous agitation of the bath. The feed materials also react with either an oxygen deficiency in the bath or an oxygen excess in the bath, delivered by the injected gas and or feed materials, resulting in an intensive reaction in a small volume.

In this specification the term process gas should be interpreted to include process air, oxygen-enriched air, nitrogen-enriched air and/or oxygen. In addition, the term also extends to other process gasses that are known to be used in top submerged lance furnaces.

The lance is configured to be able to move up and down relative to the crucible, and hence the molten bath, and this is typically achieved by the lance being supported by a dispiaceable carriage. The displaceable carriage is located outboard of the crucible or furnace vessel, and can be moved up and down in order to control the penetration depth of the lance into the molten bath.

The tip of the lance is designed so that it can be submerged in the molten bath during operation of the furnace. The gas injected by the lance into the molten bath result in the formation of bubbles. These bubbles rise to the surface of the molten bath where the bubbles burst, which in turn result in splashing of molten slag, matte and/or metal. This splashing can become rather severe, and can cause blockages in the gas exit at the top of the furnace and the opening(s) through which feed is added (the feed port). In addition, splashing also damages equipment located at the top of the furnace, and is a significant safety risk. Accordingly, the furnace height has to be designed with sufficient freeboard in order to prevent splash from contacting the roof and/or exiting the roof ports.

The splashing intensity and height is a direct function of the bubble size and frequency. It has been shown by Pan and Langberg (Y. Pan and D. Langberg, 'Two-Dimensional Physical and CFD Modelling of Large Gas Bubble Behaviour in Bath Smelting Furnaces," The Journal of Computational Multiphase Flows, vol. 2, pp. 151-164, 2010.) that the bubble size can cause the thickness of the bubble wall to change. A larger bubble results in an uneven wall thickness that is more likely to rupture and cause more intense splashing compared to splashing caused by a smaller bubble.

A number of lance tip designs are currently in use, and/or have been proposed in the past. In existing designs, fuel is often introduced into the molten bath via a central bore of the lance tip, whilst process gas is introduced into the molten bath via an annular passage provided about the central bore of the lance tip. Some examples include US5, 308,043 (Floyd), US2104/0327194 (Matusewicz) and WO2015/56143 (Reuter). In some existing designs the lance tip pressure is measured through a second concentric central bore to assist with controlling the lance tip depth in the bath (R. L. Player "Copper Isasmelt - Process Investigations" (1996) International Symposium, Injection in Pyrometallurgy). However, in all these designs the process gas is introduced by way of a single (annular) conduit, or multiple concentric conduits, with a relatively large cross- sectional flow area, and this design is therefore not inherently suited for reducing the bubble size of the gas introduced via the annular process gas conduit.

It is accordingly an object of the invention to provide a lance tip for use in a top submerged lance furnace that will, at least partially, alleviate the above disadvantages.

It is also an object of the invention to provide a lance tip for use in a top submerged lance furnace which will be a useful alternative to existing lance tip designs.

It is also an object of the invention to provide a lance tip for use in a top submerged lance furnace which will result in the formation of gas bubbles of reduced diameter.

It is furthermore the object of this invention to provide a method of introducing gas into a top submerged lance furnace which will result in reduced splash inside the furnace.

It is also an object of the invention to provide a top submerged lance furnace that will, at least partially, alleviate the above disadvantages.

It is a still further object of the invention to provide a top submerged lance furnace which will be a useful alternative to existing top submerged lance furnaces.

SUMMARY OF THE INVENTION

According to the invention there is provided a lance for use in a top submerged lance furnace, the lance including:

a process gas supply conduit; and a lance tip secured to the process gas supply conduit;

the process gas supply conduit having a first end that can in use be brought in flow communication with a source of process gas, and a second end which is in flow communication with the lance tip;

characterized in that the lance tip includes a plurality of discrete flow passages that are all in flow communication with the process gas supply conduit.

The discrete flow passages may be defined by process gas injection conduits, for example pipes or tubes.

The process gas injection conduits may be spaced apart, and in one embodiment may be spaced apart at equal distances about a central axis of the lance.

The spaced apart conduits may define an intermittent circle when viewed in plan.

In one embodiment there is provided for longitudinal axes of the process gas injection conduits to be parallel to a longitudinal axis of the process gas supply conduit.

In another embodiment there is provided for the longitudinal axis of the process gas injection conduits to be angularly offset relative to a longitudinal axis of the process gas supply conduit.

In another embodiment there is provided for the longitudinal axis of the process gas injection conduits to be substantially perpendicular relative to a longitudinal axis of the process gas supply conduit.

There is also provided for the discrete flow passages to be defined by a plurality of apertures located in a common accumulator formation. The accumulator formation may for example be hemispherical, and the apertures may be directed in horizontal, vertical and/or oblique directions.

A further feature of the invention provides for the lance to include a fuel supply conduit.

There is provided for the lance tip to include a fuel injection conduit which is in flow communication with the fuel supply conduit of the lance.

There is provided for the fuel injection conduit to be located centrally relative to the surrounding process gas injection conduits.

In one embodiment the fuel injection conduit may be located inside a central process gas injection conduit.

A further feature of the invention provides for the lance to include a tip pressure measurement conduit.

There is provided for the lance tip to include a tip pressure measurement conduit which is in flow communication with the tip pressure measurement conduit of the lance.

There is provided for the tip pressure measurement conduit to be located centrally relative to the surrounding process gas injection conduits, concentric to the fuel conduit.

In one embodiment the tip pressure measurement conduit and measurement point may be located inside a central process gas injection conduit. ln another embodiment the tip pressure measurement conduit and measurement point may be terminated inside the process gas supply conduit before the connection point to the lance tip.

The central process gas injection conduit may be co-axial with a longitudinal axis of the lance, with the other process gas injection conduits radially spaced apart about the central process gas injection conduit.

In one embodiment there is provided for the central process gas injection conduit to have a diameter which is larger than that of the outer process gas injection conduits.

There is provided for the fuel injection conduit to extend only partly inside and along the length of the central process gas injection conduit

According to a further aspect of the invention there is provided a lance tip for a lance for use in a top submerged lance furnace, wherein the lance incudes a process gas supply conduit, the lance tip including:

a process gas supply conduit having a first end that can in use be brought in flow communication with the process gas supply conduit; characterized in that the process gas supply conduit comprises discrete flow passages that are all in flow communication with the process gas supply conduit.

According to a further aspect of the invention there is provided a top submerged lance furnace including:

a crucible suitable for holding a molten material bath;

a roof in use covering an open end of the crucible; and

a lance as described hereinbefore. According to a still further aspect of the invention there is provided a method of introducing process gas into a top submerged lance furnace, the method including the steps of:

- supplying process gas via a lance; and

- dividing the process gas supply into a plurality of discrete injection streams prior to injecting the process gas into a molten bath of the furnace.

The method may include the step of introducing the process gas using a lance and lance tip as described hereinbefore.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described by way of non-limiting example, and with reference to the accompanying drawings in which:

Figure 1 is a schematic perspective view of a top submerged lance furnace as is known in the art;

Figure 2 is a front view of a lance arrangement of the top submerged lance furnace as is known in the art;

Figure 3 is a side view of the lance arrangement of Figure 2;

Figure 4 is a cross-sectional front view of a lance tip of the lance of the top submerged lance furnace in accordance with a first embodiment of the invention;

Figure 5 is bottom plan view of the lance tip of Figure 4; Figure 6a is a side view of an open pipe lance tip as is known in the art;

Figure 6b is a perspective view of the lance tip of Figure 6a;

Figure 7a is a side view of an open pipe lance tip incorporating a helical vaned swirl generator, as is known in the art;

Figure 7b Is a perspective view of the lance tip of Figure 7a;

Figure 8a is a side view of a second lance tip configuration in accordance with an embodiment of the invention;

Figure 8b is a perspective view of the lance tip of Figure 8a;

Figure 9a is a side view of a third lance tip configuration in accordance with an embodiment of the invention;

Figure 9b is a perspective view of the lance tip of Figure 9a;

Figure 10a is a side view of a fourth lance tip configuration in accordance with an embodiment of the invention;

Figure 10b is a perspective view of the lance tip of Figure 10a;

Figure 11a is a side view of a fifth lance tip configuration in accordance with an embodiment of the invention;

Figure 11 b is a perspective view of the lance tip of Figure 11a; and

Figure 12 is a graph showing the comparative performance of the lance tip designs of Figures 6 to 11. DET AILED DESCRIPTION OF INVENTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings and are thus intended to include direct connections between two members without any other members interposed therebetween and indirect connections between members in which one or more other members are interposed therebetween. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings. Additionally, the words "lower", "upper", "upward", "down" and "downward" designate directions in the drawings to which reference is made. The terminology includes the words specifically mentioned above, derivatives thereof, and words or similar import. It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the," and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term "include" and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

Referring to the drawings, in which like numerals indicate like features, a non-limiting example of a top submerged lance furnace in accordance with the invention is generally indicated by reference numeral 10.

A typical top submerged lance furnace is shown in Figure 1 , and comprises a primary furnace vessel 11 , which is typically in the form of an upright cylindrical structure of which an inner wall is lined with a containment lining, for example refractory bricks 12. A crucible 13 is defined in the bottom of the vessel 11 , and in use holds a molten bath of metal, speiss, matte, ore or slag. The molten product can be removed via a tap hole 14. An operatively upper end of the vessel terminates in an inversely conically flared section 15. A roof 16 covers an open end of the vessel 11, with a gas outlet port 18 allowing off gas to escape from the vessel 11 via the flared section 15.

A lance arrangement 20, shown in Figures 2 and 3, extends into the vessel 11 through a lance opening 17. The lance arrangement includes a tubular lance 21 through which air, nitrogen and oxygen (and sometimes also fuel and feed materia!) are introduced into the molten bath. In order to achieve this, an operatively lower end 22 of the lance in use protrudes into the molten bath, with an outlet tip of the lance therefore being submerged below the surface of the molten bath. An opposing, operatively upper end 23 of the lance is rotatably connected to an outer, stationary lance section 25. The lance 21 of this particular embodiment is rotatable relative to the stationary lance section 25, but the present invention is not limited to use with rotating lances. Both the lance 21 and the stationary lance section 25 can also be vertically displaced as a single unit by way of a carriage (not shown). The lance arrangement 20 is secured to such carriage by way of a connecting plate 24 or other means. The tubular lance 21 includes a process gas supply conduit 26 having a first, operattvely upper end (not shown in Figure 4) which is, in use, in flow communication with a source of process gas, as is known in the art. The gas supply conduit also has a second, operatively lower end which is in flow communication with a lance tip 40, and more particularly with flow passages provided in the lance tip 40 as described in more detail below. In some embodiments the tubular lance 21 may also include a fuel supply conduit 27, and a tip pressure measurement conduit 60.

In existing embodiments where both a process gas supply conduit and a fuel supply conduit are present, the fuel supply conduit is typically located in the center of the tubular lance, with an internal bore of the fuel supply conduit defining a fuel supply passage. In existing embodiments where a tip pressure measurement conduit is present in addition to the process gas supply conduit and a fuel supply conduit, the tip pressure measurement conduit is typically located in the center of the tubular lance, concentric to the fuel supply conduit, such that the tip pressure is measured in the cavity formed between the internal bore of the tip pressure measurement conduit and the external bore of the fuel supply conduit. The process gas supply conduit is then defined by an outer conduit which is concentric with the fuel supply conduit, with a process gas flow passage being defined by the annular space between an outer surface of the fuel supply conduit and an inner surface of the process gas supply conduit. The area of the process gas flow passage is large due to the area being annular, and furthermore being a function of the diameter of the passage. It is therefore difficult to achieve a small bubble size using the existing configurations, in particular where the tip also includes a central fuel supply conduit.

An example of a new and inventive tip design suitable for use in the configuration, including process gas, fuel supply and tip pressure measurement conduits, is shown in Figures 4, 5, 8a and 8b. In these embodiments the lance tip 40 include a plurality of operatively outer process gas injection passages 41, a central fuel injection passage 45. In these embodiments the lance tip also includes a central process gas Injection passage 42, with the fuel injection passage 45 located inside the central process gas injection passage 42. The operatively outer process gas passages 41 may be in the form of conduits such as pipes or tubes having a nominal diameter of between 10 and 350, preferably between 50 and 200 mm, depending on the process gas supply conduit diameter and optimum spacing. The ratio of the outer process gas passage nominal diameter to the process gas supply conduit nominal diameter will typically be between 0.1 and 0.5. The operatively outer process gas injection passages 41 are spaced about the central process gas injection passage 42 in a configuration defining an intermittent circle when viewed in plan. The radial distance between the operatively outer process gas injection passages 41 and the central process gas injection passage 42 may for example be between 10 and 250 mm depending on the process gas supply conduit, outer passage and inner passage diameters. The central process gas injection passage 42 may also be in the form of a pipe or tube having a nominal diameter of between 10 and 400 mm, preferably between 50 and 300 mm. It is foreseen for the central process gas injection passage 42, where present, in some embodiments to have a diameter larger than that of the outer process gas injection passages 41.

The fuel injection passage 45, as shown in Figures 4 and 5, is located at least partially inside the central process gas injection passage 42, and accordingly injects fuel into a process gas stream inside the central process gas injection passage 42. The fuel injection passage 45 only extends partially into the central process gas injection passage 42 in order to prevent contact with the furnace bath 13. The fuel injection passage 45 may be located in the central process gas injection passage 42 using a diffuser or spider (not shown) that ensures coherent downstream gas flow, thus preventing fuel from being dispersed onto the wall of the central process gas injection passage 42. The fuel injection passage 45 in the central process gas injection passage 42 may exit from a normal pipe end, providing a relative coherent fuel stream to prevent fuel impingement on the inside of the tip pipes. The fuel injection passage 45 in the central process gas injection passage 42 may alternatively also exit from a laminar or diffused jet nozzle that ensures a coherent fuel stream to prevent fuel impingement on the inside of the tip gas injection passages.

The tip pressure measurement passage 60 of the embodiment shown in Figure 4 is located in the process gas supply passage 46 above the point where it connects to the lance tip 40, and accordingly measures the pressure inside the process gas supply passage 46. Alternatively, the tip pressure measurement passage 60 may also be located in the central process gas injection passage 42, and accordingly measure the tip pressure inside the central process gas injection passage 42. The tip pressure measurement passage 60 only extends partially into the central process gas injection passage 42 in order to prevent contact with the furnace bath 13. The tip pressure measurement passage 60 may be located in the central process gas injection passage 42 using a d iff user or spider (not shown), and in turn support the fuel injection passage 45 whilst ensuring a coherent downstream gas flow, thus preventing fuel from being dispersed onto the wall of the central process gas injection passage 42. in the embodiment shown in Figures 4, 5, 8a and 8b, the passages (41 and 45) are substantially parallel relative to a longitudinal axis of the lance. However, in other embodiments, for example those shown in Figures 9a, 9b, 10a and 10b, the passages are angularly offset relative to the longitudinal axis of the lance. In the embodiment of Figures 9a and 9b, the conduits are angularly offset between 5 and 45 degrees (referred to as the spread angle) relative to the longitudinal axis of the lance. The presence of this spread angle causes the openings of the passages to be further apart, which in turn prevents bubble coalescence and ensures that smaller bubbles are formed. The spread angle also reduces the vertical momentum of the gas injected into the liquid, which reduces the vertical splash. in the embodiment shown in Figures 10a and 10b, the passages are substantially perpendicular relative to the longitudinal axis of the lance, and are therefore arranged horizontally rather than vertically. It is foreseen that the angle may be anything between 45-90 degrees. This design results in the openings being spaced even further apart compared to the design depicted in Figures 9a and 9b, which further prevents bubble coalescence. The other benefit of this design is that the gas momentum is entirely horizontal, which further minimises vertical splash. In this embodiment the fuel passage (not shown) may coincide with one of the process gas injections passages 41, may be in flow communication with an aperture (not shown) in the bottom 48 of the lance tip 40, or may not be included in the lance design at all, i.e. by instead delivering the fuel into the molten bath by way of a separate fuel supply system. This system may for example deliver fuel through the roof or sidewall of the furnace.

A still further embodiment of a lance tip 40 is shown in Figures 11a and 11b. In this embodiment the lance tip 40 does not include individual process gas injection passages, but the discrete flow passages are rather defined by apertures 44 provided in a suitably shaped flow accumulator 43, for example, but not limited to, a hemispherical receptacle which is in flow communication with the process gas supply conduits 26 of the lance arrangement 20. The apertures are therefore arranged both horizontally and vertically. The bubbles formed using this lance tip 40 are even smaller due to the openings in the accumulator being smaller, and also due to the number of apertures being more.

In all the embodiments described above, the lance tip 40 may include a manifold 46 through which the passages are connected to the tubular lance 21. The manifold may be either cast or fabricated from steel, stainless steel, copper, or any other alloy or metal. Apart from the manifold connection, the multiple pipes may be connected to each other further downstream using gussets or a flange or multiple flanges (not shown) at different heights. A tapping point for measuring the static pressure in the gas flow may be located preferably above the manifold or alternatively below the manifold in one or more of the multiple passages, in which case preferably in the central process gas injection passage 42 above the fuel nozzle.

The embodiments described above, as well as two prior art embodiments as shown in Figure 6 (straight open pipe 48) and Figure 7 (pipe 48 incorporating a helical vaned swirl generator 47 that imparts a swirling flow onto gas exiting a single opening), have been tested using a room temperature model consisting of helium injected into a glycerol bath. The results of this experiment are shown in Figure 12, in which it is clear that all the new embodiments resulted in reduced splash, with the embodiment shown in Figures 10a and 10b in particularly showing a significant reduction in splash.

The inventors are of the view that the reduction in splash can be ascribed to the multiple smaller injection passages or apertures (instead of a single, continuous larger aperture) having the effect of decreasing the size of the area of the process gas injection passages and hence the size of the bubbles, which in turn reduces the amount and height of splash. The spacing between the multiple smaller passages or aperture furthermore improves the separation between adjacent bubbles and reduces splash generation. The sizing of the multiple smaller passages or apertures in addition results in optimized linear gas velocity, which also results in reduced splash, as well as the optimized cooling of the conduits.

The multiple smaller passages or apertures furthermore also retain frozen slag layers better and this reduces the external lance tip surface area exposed to the bath, resulting in a reduced heat load and increased lance tip life.

It will be appreciated that the above are only some embodiments of the invention and that there may be many variations without departing from the spirit and/or the scope of the invention.