WO2008070089A1

WO2008070089A1 - Apparatus for injecting gas into a vessel

Info

Publication number: WO2008070089A1
Application number: PCT/US2007/024857
Authority: WO
Inventors: George Cingle; Todd G. Smith; Derek S. Dengel
Original assignee: Berry Metal Company
Priority date: 2006-12-05
Filing date: 2007-12-05
Publication date: 2008-06-12
Also published as: US20080128963A1

Abstract

A lance for injecting gas into a furnace vessel. The lance imparts a spiral or swirling flow to gas discharged by the lance. The lance includes a plurality of internally water-cooled flow vanes in fluid communication with a fluid- cooled structure that is discrete from the fluid-cooled outer wall of the lance. The result is a lance that effectively discharges gas with a desired swirling motion, that is comparatively simple in design and construction, and whose flow vanes are capable of withstanding the extreme thermal stresses encountered in a metallurgical or other high temperature furnace vessel.

Description

APPARATUS FOR INJECTING GAS INTO A VESSEL

FIELD OF THE INVENTION

The present invention provides an apparatus for injecting gas into a vessel. It has particular, but not exclusive, application to apparatus for injecting a flow of gas into a metallurgical vessel under high temperature conditions. Such metallurgical vessel may, for example, be a smelting vessel in which molten metal is produced by a direct smelting process.

BACKGROUND QF THE INVENTION

The term "smelting" is herein understood to mean thermal processing wherein chemical reactions take place that reduce metal oxides to produce liquid metal.

A known direct smelting process, which relies on a molten metal layer as a reaction medium, and is generally referred to as the HIsmelt process, is described in U. S Patent Nos . 6,398,842; 6,440,356; 6,773,659 and 6,939,391 and published U.S. Patent Application No. 2006/0108722, the disclosures of which are incorporated herein in their entireties by reference thereto.

The HIsmelt process generally comprises: (a) forming a bath of molten iron and slag in a vessel; (b) injecting into the bath: (i) a metalliferous feed material, typically metal oxides; and (ii) a solid carbonaceous material, typically coal, which acts as a reductant of the metal oxides and a source of energy; and (c) smelting metalliferous feed material to metal in the metal layer. The HIsmelt process also comprises post -combusting reaction gases released from the bath, such as CO and H₂, in the space above the bath with oxygen-containing gas, and transferring the heat generated by the post -combustion to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials.

The HIsmelt process also comprises forming a transition zone above the nominal quiescent surface of the bath in which there is a favorable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.

In the HIsmelt process the metalliferous feed material and solid carbonaceous material are injected into the metal layer through a number of lances/tuyeres which are inclined to the vertical so as to extend downwardly and inwardly through the side wall of the smelting vessel and into the lower region of the vessel so as to deliver the solids material into the metal layer in the bottom of the vessel . To promote post -combustion of reaction gases in the upper part of the vessel, a blast of hot air, which may be oxygen enriched, is injected into the upper region of the vessel through a downwardly extending hot air injection lance. To promote effective post -combustion of the gases in the upper part of the vessel, it is desirable that the incoming hot air blast exit the lance with a swirling motion. To achieve this, the outlet end of the lance may be fitted with internal flow guides to impart an appropriate swirling motion. The upper regions of the vessel may reach temperatures of the order of 2000⁰C and the hot air may be delivered into the lance at temperatures of the order of 1100-1400⁰C. The lance must therefore be capable of withstanding extremely high temperatures both internally and on the external walls, particularly at the delivery end of the lance which projects into the combustion zone of the vessel .

U.S. Pat. No. 6,673,305 and published U.S. Patent Application No. 2006/0108722 disclose gas injection lance constructions for use in a direct smelting process such as the HIsmelt process. In those constructions, spiral flow guide vanes are mounted on a central tubular structure extending throughout the length of the gas flow duct. The central structure includes water flow passages which provide for the flow of cooling water to the front part of the central structure which is located generally within the tip of the gas flow duct. The flow guide vanes are disposed near the tip of the duct within a refractory lined wall section of the duct. Although the central structure on which they are carried is water-cooled, the vanes themselves are not. Consequently, they are exposed, essentially uncooled, to the extreme thermal stresses caused by the high temperature conditions within the furnace vessel which may cause warping, erosion or other thermally-related damage to the vanes .

U.S. Pat. Nos. 6,440,356; 6,773,659 and 6,939,391 disclose alternative lance constructions in which the flow guides are in the form of spiral vanes mounted on a central body at the forward end of a gas flow duct. The vanes are physically connected to the wall of the gas flow duct and are internally water cooled by cooling water which flows through supply and return passages within the wall of the duct. While the gas flow vanes of these lances are water- cooled to enhance their resistance to thermal damage, their direct physical connection with the coolant flow passages of the lance results in a construction which is highly complex in design and manufacture. First, the direct fluid connection between the vanes and the wall of the duct requires considerable modification to the simple lance coolant flow passageway system employed in conventional water-cooled lances. Second, the designs of the vanes' own internal coolant flow passages as well as those of the central body, with which they are also in fluid communication, are quite complicated.

An advantage exists, therefore, for a lance for injecting a flow of gas into a metallurgical vessel under high temperature conditions, which lance has internally- cooled gas flow directing vanes of simple design and construction that impart a spiral flow to gas discharged from the lance.

SUMMARY OF THE INVENTION

The present invention provides a lance for injecting gas into a furnace vessel . The lance imparts a spiral or swirling flow to gas discharged by the lance. In this regard, the lance includes a plurality of internally water- cooled flow vanes in fluid communication with a coolant fluid-cooled structure that is discrete from the water cooled outer wall of the lance. The result is a lance that effectively discharges gas with a desired swirling motion, that is comparatively simple in design and construction, and whose flow vanes are capable of withstanding the extreme thermal stresses encountered in a metallurgical or other high temperature furnace vessel . Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently- preferred methods of practicing the invention proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more readily apparent from the following description of preferred embodiments thereof shown, by way of example only, in the accompanying drawings wherein:

FIG. 1 is a vertical section through a direct smelting vessel incorporating a pair of solids injection lances and a hot air blast injection lance constructed in accordance with the present invention;

FIG. 2 is a longitudinal cross-section through a hot air injection lance according to the present invention;

FIG. 3 is a top plan view of a water-cooled gas flow guide assembly according to the present invention that may be attached to a central structure of a hot air injection lance;

FIG. 4 is a cross section of the water-cooled gas flow guide assembly taken along line IV-IV of FIG. 3; and

FIG. 5 is enlarged view of encircled portion V of FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein like or similar references indicate like or similar elements throughout the several views, there is shown in FIG. 1 a direct smelting vessel suitable for operation by the HIsmelt process as described above. A metallurgical vessel is denoted generally as 11 and has a hearth that includes a base 12 and sides 13 formed from refractory bricks. Side walls 14 form a generally cylindrical barrel extending upwardly from the sides 13 of the hearth. Vessel 11 further includes an upper barrel section 15, a lower barrel section 16, a roof 17, an outlet 18 for off-gases, a forehearth 19 for discharging molten metal continuously, and a tap-hole 21 for discharging molten slag. It will be understood that vessel 11 is an example of but one of many possible furnace vessels with which the hot air injection lance of the present invention, described below, may find beneficial application.

In use, vessel 11 contains a molten bath of iron and slag which includes a layer 22 of molten metal and a layer 23 of molten slag above the metal layer 22. The arrow marked by the numeral 24 indicates the position of the nominal quiescent surface of the metal layer 22 and the arrow marked by the numeral 25 indicates the position of the nominal quiescent surface of the slag layer 23. The term "quiescent surface" is understood herein to mean the surface when there is no injection of gas and solids into the vessel.

Vessel 11 is fitted with a downwardly extending hot air injection lance 26 for delivering a hot air blast into an upper region of the vessel and two solids injection lances 27 extending downwardly and inwardly through the side walls 14 and into the slag layer 23 for injecting iron ore, solid carbonaceous material, and fluxes entrained in an oxygen- deficient carrier gas into the metal layer 22. The position of the lances 27 is preferably selected so that their outlet ends 28 are above the surface of the metal layer 22 during operation of the process. This position of the lances reduces the risk of damage through contact with molten metal and also makes it possible to cool the lances by forced internal water cooling without significant risk of water coming into contact with the molten metal in the vessel .

A representative, although not limitative, construction of hot air injection lance 26 according to the present invention is illustrated in FIGS. 2-5. As shown in these figures, lance 26 comprises an elongate duct 31 which receives hot gas through a gas inlet structure 32 and injects it into the upper region of vessel 11. Lance 26 includes an elongate tubular central structure 33 which extends within the gas flow duct 31 from its rear end to its forward or distal end. Adjacent the forward end of the duct, central structure 33 carries a plurality of helical vanes 34 for imparting swirl to the gas flow exiting the duct. In the exemplary construction, four gas flow vanes 34 are shown although it is contemplated that a greater or fewer number of vanes may be provided depending on the requirements of the materials processing operation in which lance 26 is utilized. The forward end of central structure 33 has a domed nose 35 which may project forwardly beyond the tip 36 of duct 31. The forward end of central structure 33 and the duct tip 36 cooperate to form an annular nozzle for divergent flow of gas from the duct with swirl being imparted to the gas flow by vanes 34. Vanes 34 are desirably slidably received within the forward end of duct 31.

Downstream from the gas inlet 32 duct 31 is internally water cooled. This section of the duct is desirably comprised of a series of three concentric steel tubes 37, 38 and 39 extending to the forward end of the duct where they are connected to the duct tip 36. The duct tip 36 is of hollow annular formation and it is internally water cooled by cooling water supplied and returned through passages in the wall of duct 31 defined by tubes 37, 38 and 39. Specifically, cooling water is supplied through an inlet 41 and annular inlet manifold 42 into an inner annular water flow passage 43 defined between the tubes 38 and 39 of the duct through to the hollow interior of the duct tip 36 through circumferentially spaced openings in the tip. Water is returned from the tip through circumferentially spaced openings into an outer annular water return flow passage 44 defined between the tubes 37 and 38 and upwardly to a water outlet 45 at the rear or upper end of the water cooled section of duct 31.

The water cooled section of duct 31 is preferably internally lined with a refractory lining 46 that fits within the innermost metal tube 39 of the duct and extends through to the water cooled tip 36 of the duct. The inner periphery of duct tip 36 is preferably generally flush with the inner surface of the refractory lining which defines the effective flow passage for gas through the duct . The forward end of the refractory lining desirably has a slightly reduced diameter section 47 which receives the swirl vanes 34 with a snug sliding fit. Rearwardly from section 47 the refractory lining is of slightly greater diameter to enable the central structure 33 to be inserted downwardly through the duct on assembly of the lance until the swirl vanes 34 reach the forward end of the duct where they are guided into snug engagement with refractory section 47 by a tapered refractory land 48 which locates and guides the vanes into the refractory section 47. Reduced diameter refractory section 47 is not necessary, however it does provide radial stability to central structure 33 during lance operation.

The front end of central structure 33 which carries swirl vanes 34 is internally water cooled by cooling water supplied forwardly through the central structure from the rear end to the forward end of the lance and then returned back along the central structure to the rear end of the lance. This enables a very strong flow of cooling water directly to the forward end of the central structure and to the domed nose 35 in particular which is subjected to very high heat flux in operation of the lance.

Central structure 33 preferably comprises inner and outer concentric steel tubes 50 and 51 formed by tube segments disposed end-to-end and welded together. Inner tube 50 defines a central water supply passage 52 through which water flows forwardly through the central structure from a water inlet 53 at the rear end of lance 26 to the front end or nose 35 of the central structure and an annular water return passage 54 defined between tubes 50 and 51 through which the cooling water returns from nose 35 back through the central structure to a water outlet 55 at the rear end of the lance.

The nose end 35 of central structure 33 comprises an inner copper body 61 fitted within an outer domed nose shell 62 also formed of copper. The inner copper body 61 is formed with a central water flow passage 63 to receive water from the central passage 52 of structure 33 and direct it to the tip of the nose. Nose end 35 is preferably formed with projecting ribs (not illustrated) which fit snugly within the nose shell 62 to define and maintain a continuous cooling water flow passage 65 between the inner section 61 and the outer nose shell 62. The forced flow of cooling water in a single coherent stream through passage 65 extending around and back along the nose end 35 of central structure 33 ensures efficient heat extraction and avoids the development of "hot spots" on the nose which could occur if the cooling water is allowed to divide into separate streams at the nose. The specific structure which defines the manner by which water flows through the forward end of central structure 33, including vanes 34 is described in greater detail hereinafter.

Central structure 33 is preferably surrounded by an external heat shield 69 to shield against heat transfer from the incoming hot gas flow in the duct 31 into the cooling water flowing within the central structure 33. If subjected to the very high temperatures and high gas flows required in a large scale smelting installation, a solid refractory shield may provide only short service. In the illustrated construction, the shield 69 is formed of tubular sleeves of ceramic material marketed under the name UMCO. The sleeves are arranged end-to-end to form an essentially continuous ceramic shield surrounding an air gap 70 between the shield and the outermost tube 51 of the central structure. In particular, the shield may be made of tubular segments of UMCO 50 which contains by weight 0.05 to 0.12% carbon, 0.5 to 1% silicon, a maximum of 0.5 to 1% manganese, 0.02% phosphorous, 0.02% sulfur, 27 to 29% chromium, 48 to 52% cobalt and the balance essentially of iron. This material provides excellent heat shielding but it undergoes significant thermal expansion at high temperatures. To deal with this problem the individual tubular segments of the heat shield are formed and mounted to enable them to expand longitudinally independently of one another while maintaining a substantially continuous shield at all times. It will be understood, however, that any suitable refractory or ceramic material that is capable of thermally shielding tube 51 would be acceptable for use as shield 69.

Hot gas is delivered to duct 31 through the gas inlet section 32. The hot gas may be oxygen enriched air provided through heating stoves at a temperature of the order of 1200⁰C. This air must be delivered through refractory lined ducting and it will pick up refractory grit which can cause severe erosion problems if delivered at high speed directly into the main water cooled section of duct 31. Gas inlet 32 is designed to enable the duct to receive high volume hot air delivery with refractory particles while minimizing damage of the water cooled section of the duct. In this regard, the duct gas inlet 32 preferably comprises a T- shaped body 81 molded as a unit of hard wearing refractory material and located within a thin walled outer metal shell 82. Body 81 defines a first tubular passage 83 aligned with the central passage of duct 31 and a second tubular passage 84 normal to passage 83 to receive the hot airflow delivered from stoves (not shown) . Passage 83 is aligned with the gas flow passage of duct 31 and is connected to it through a central passage 85 in a refractory connecting piece 86 of inlet 32.

The hot air delivered to inlet 32 passes through tubular passage 84 of body 81 and impinges on the hard wearing refractory wall of the thick refractory body 82 which is resistant to erosion. The gas flow then changes direction to flow at right angles down through passage 83 of the T-shaped body 81 and the central passage 85 of transition piece 86 and into the main part of the duct. The wall of passage 83 may be tapered in the forward flow direction so as to accelerate the flow into the duct. It may for example be tapered to an included angle of the order of 7°. The transition refractory body 86 is tapered in thickness to match the thick wall of refractory body 81 at one end and the much thinner refractory lining 48 of the main section of duct 31. It is accordingly also preferably water cooled through an annular cooling water jacket 87 through which cooling water is circulated through an inlet 88 and an outlet 89. The rear end of central structure 33 extends through the tubular passage 83 of gas inlet 32. It is located within a refractory liner plug 91 which closes the rear end of passage 83, the rear end of central structure 33 extending back from gas inlet 32 to the water flow inlet 53 and outlet 55.

The nose end 35 of central structure 33 comprises an inner copper body 61 fitted within an outer domed nose shell 62 also formed of copper. The inner copper piece 61 is formed with a central water flow passage 63 to receive water from the central passage 52 of structure 33 and direct it to the tip of the nose. Nose end is preferably formed with projecting ribs (not shown) which fit snugly within the nose shell 62 to define a continuous cooling water flow passage 65 between the inner section 61 and the outer nose shell 62. If present, -the ribs are desirably generally helical such that passage 65 extends from the tip of the nose in a spiral whereby the forced flow of cooling water in a single coherent stream through spiral passage 65 extending around and back along the nose end 35 of central structure ensures efficient heat extraction and avoids the development of "hot spots" on the nose which could occur if the cooling water is allowed to divide into separate streams at the nose.

As most clearly shown in FIG. 4, prior to passing from central passage 52 of central structure 33 into central water flow passage 63 of nose end 35, a substantial portion of coolant water from the central passage 52 is diverted into coolant fluid passage means that internally cool the helical gas flow guide vanes 34. The coolant fluid passage means comprise one or more coolant passageways 100 that lie within vanes 34 and follow the helical contours thereof. Each coolant passageway 100 includes an inlet 102 provided in an upper region of its associated vane and an outlet 104 provided in a lower region its associated vane. According to a presently preferred embodiment, each of vanes 34 includes a plurality of coolant passageways 100 that are arranged in an axially and radially nested array within the vanes to provide consistent cooling throughout the vanes. Alternatively, however, it will be understood that a single slot-like passageway spanning a substantial portion of the axial and radial dimensions of the vanes could be used to achieve the desired cooling effect. Regardless of their number, coolant passageway (s) 100 are preferably formed by copper or steel conduit 106 that is bendable to assume the desired ultimate helical shape of vanes 34. A casting block assembly having the appropriate number and shape of vane cavities is then enclosed around the conduit and molten copper is poured in the casting block assembly. As seen in FIG. 4, the resultant casting is a monolithic gas flow guide member 108 including masses of cast copper 110 with conduit 106 embedded therein to define vanes 34 and a cast copper central sleeve 110 which is adapted to closely surround the outer wall of tube 51. So constructed, the mass of the vanes renders gas flow guide member 108 highly structurally rigid as well providing the vanes with excellent thermal conductivity characteristics that enhance their effective cooling by the internal water flow through coolant passageway (s) 100 during operation of lance 26.

Water restriction means, exemplified in the form of a plate 114, is affixed such as by welding or the like to the inner wall of a distal segment of inner tube 50 at a location between the coolant passageway inlet (s) 102 and outlet (s) 104. Plate 114 preferably has one or more appropriately sized apertures 116 to assure a high water flow rate through central structure 33 so that the entire central structure and the gas flow vanes 34 carried thereby are effectively cooled, as described in greater detail below.

As previously noted, during operation of the lance 26 water is supplied to lance in order to cool its outer wall. According to the present invention, a separate flow of water is directed downwardly through central passage 52 of central structure 33. When water passing through central passage strikes 52 strikes plate 114, back pressure is generated which forces a substantial portion of the water flow to enter the vane coolant passageway inlet (s) 102, pass through coolant passageway (s) 100 and exit vane coolant passageway outlet (s) 104 to thereby cool vanes 34. As mentioned above, it is preferred that plate 114 include one or apertures 116 Such aperture (s) are provided to permit passage of the balance of the water that flows through central passage 52 but that does not enter the vane coolant passageway (s) to pass directly to the central water flow passage 63 of inner copper body 61. It is conceivable that in certain situations the absence of aperture (s) 116 in plate 114 could constrict water flow through central structure 33 to an extent that thermally related damage could result in the central structure and/or vanes 34. A further advantage of apertures (s) 116 is that it/they produce one or more downwardly flowing columns of water beneath plate 114 that intersect and mix with the water discharged from outlet (s) 104. Consequently, the kinetic energy and potentially erosive effects of high-velocity water exiting the outlet (s) 104 and aperture (s) 116 are substantially reduced. Assembly of the lower portion of the central structure 33 of the present invention, hereinafter generally referred to as gas flow guide assembly 118, may be as follows, although variations in the manufacturing steps are possible. Plate 114 is initially affixed to a distal segment of pipe 50 between inlets 102 and outlets 104. A weld sleeve 51a is welded to the upper end of the distal segment of pipe 51. The distal segment of pipe 51 is then inserted into and welded to gas flow guide member 108 at upper and lower continuous fluid-tight welds.

Referring to FIG. 5, there is shown an enlarged view of threaded orifices 120 that form the openings for inlets 102 Orifices 120 are adapted for threaded engagement with pipe

50. During assembly, the orifices 120 are first partially threaded into pipe 50 and then pipe 50 is inserted in pipe

51. The orifices are then brought into alignment with the openings of conduits 106. Thereafter, the orifices are threaded into pipe 50 causing reduced diameter portions 122 of the orifices to be received in the openings of conduits 106. Threading of the orifices is continued until leading ends of tapered surfaces 124 of the orifices come into firm contact with the openings of conduits 106 whereby a metal- to-metal fluid seal is created between central passage 52 and return water flow passage 54. In the alternative, the fluid seal between orifices 120 and the openings of conduits 106 may be achieved by O-rings or similar sealing means. To facilitate threading of orifices 120 into pipe 50 the orifices may be provided with tool-engageable internal or, as shown, external surfaces 130 that are configured to receive a suitable tool such as a wrench or the like. Optionally, but preferably, the outer surface of pipe 50 is provided with spacers 132 to maintain substantially uniform spacing between pipes 50 and 51 to define a substantially uniform return water flow passage 54 in gas flow guide assembly 118.

Upon installation of orifices 120, an annular sleeve 126 is then welded by a continuous fluid-tight weld to the bottoms of both of pipe 51 and gas flow guide member 108. An 0-ring 134 is placed in a corresponding groove in an upper neck portion of inner copper body 61 and the upper neck portion of the inner copper body is inserted into the lower end of the distal pipe section of pipe 50. The frictional yet sealing fit thus produced between inner copper body 61 and pipe 50 provides a fluid seal between central water flow passage 63 of the inner copper body and return water flow passage 54. It also permits limited movement of the inner copper body 61 that may be useful to avoid possible hydraulic and/or thermal shock that could damage a rigid connection between pipe 50 and the inner copper body when the lance 26 is in operation. Lastly, the outer domed nose shell 62 is welded by a continuous fluid-tight weld to annular sleeve 126. The resultant gas flow guide assembly 118 may then be connected to the reminder of central structure 30 by welding the upper ends of pipe 50 and weld sleeve 51a of FIG. 4 to the next corresponding segments of pipes 50 and 51 in the central structure.

As noted above, the water supply used for cooling the gas flow guide assembly 118 is separate from the coolant supply for the outer wall of lance 26. And, gas flow guide assembly 118 also lacks many of the internal components and flow channels that reside in the water-cooled central body parts of the lances disclosed in U.S. Pat. Nos . 6,440,356; 6,773,659 and 6,939,391. As a result, a gas flow guide assembly constructed in accordance with the present invention simplifies construction and maintenance of a hot air injection lance to which it is connected in comparison to the lances described in those patents.

Although the invention has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention as claimed herein.

Claims

CLAIMS What is claimed is:

1. A gas flow guide assembly for use in a lance for injecting gas into a vessel, the lance having a water-cooled enclosed duct in fluid communication with a first water supply, a water-cooled central structure disposed within the duct and in fluid communication with a second water supply separate from the first water supply, and a gas flow passageway between the duct and central structure in communication with a supply of gas for injecting the gas into a vessel, said gas flow guide assembly comprising: an enclosed end; pipe sections adapted for connection to the central structure and connected to said enclosed end, said pipe sections defining a water supply passage and a water return passage for circulating water from an inlet of the second water supply to an outlet of the second water supply; helical gas flow guide vane means for imparting a swirling motion to gas discharged by the gas flow passageway; and at least one coolant passageway in communication with said water supply passage for internally cooling said gas flow guide vane means with water supplied by the second coolant supply.

2. The gas flow guide assembly of claim 1 wherein said at least one coolant passageway comprises a plurality of coolant passageways .

3. The gas flow guide assembly of claim 2 wherein said plurality of coolant passageways are arranged in an axially and radially nested array.

4. The gas flow guide assembly of claim 1 wherein said at least one coolant passageway includes an inlet and an outlet in communication with said water supply passage.

5. The gas flow guide assembly of claim 4 further comprising water restriction means disposed in said water supply passage between said inlet and said outlet of said at least one coolant passageway for creating back pressure in said water supply passage for forcing water into said at least said inlet of said at least one coolant passageway.

6. The gas flow guide assembly of claim 5 wherein said water restriction means includes at least one aperture for permitting water not directed into said at least said inlet of said at least one coolant passageway to pass through said water restriction means.

7. A lance for injecting gas into a vessel, said lance comprising : a water-cooled enclosed duct in fluid communication with a first water supply; a water-cooled central structure disposed within said duct and in fluid communication with a second water supply separate from said first water supply; a gas flow passageway between the duct and central structure in communication with a supply of gas for injecting the gas into a vessel; and a gas flow guide assembly comprising: an enclosed end; pipe sections connected to said central structure and said enclosed end, said pipe sections defining a water supply passage and a water return passage for circulating water from an inlet of said second water supply to an outlet of said second water supply; helical gas flow guide vane means for imparting a swirling motion to gas discharged by the gas flow passageway; and at least one coolant passageway in communication with said water supply passage for internally cooling said gas flow guide vane means with water supplied by the second coolant supply.

8. The lance of claim 7 wherein said at least one coolant passageway comprises a plurality of coolant passageways.

9. The lance of claim 8 wherein said plurality of coolant passageways are arranged in an axially and radially nested array.

10. The lance of claim 7 wherein said at least one coolant passageway includes an inlet and an outlet in communication with said water supply passage.

11. The lance of claim 10 further comprising water restriction means disposed in said water supply passage between said inlet and said outlet of said at least one coolant passageway for creating back pressure in said water supply passage for forcing water into said at least said inlet of said at least one coolant passageway.

12. The lance of claim 11 wherein said water restriction means includes at least one aperture for permitting water not directed into said at least said inlet of said at least one coolant passageway to pass through said water restriction means.

13. A lance for injecting gas into a vessel, the lance including gas flow guide vane means for imparting a swirling motion to gas discharged by the lance, said gas flow guide means comprising at least one helically-shaped metal conduit embedded in cast copper and operable to convey coolant through said gas flow guide means.