WO1990004571A1

WO1990004571A1 - Method and apparatus for enhancing combustion and operational efficiency in a glass melting furnace

Info

Publication number: WO1990004571A1
Application number: PCT/SE1989/000435
Authority: WO
Inventors: Martin Petersson; Mark Payne; Howard Hubert; Robert Strosnider
Original assignee: Aga Ab
Priority date: 1988-10-17
Filing date: 1989-08-17
Publication date: 1990-05-03
Also published as: JPH04502897A; EP0438416A1; BR8907723A; DK162764C; DK162764B; US4911744A; DK69291A; DK69291D0; FI911841A0

Abstract

In a glass melting furnace (10) of the type that has a basin (12) wherein a bath (20) of molten glass is heated by a blanket (30) of flame that extends over the molten bath (20), performance and productivity are enhanced by installing oxygen injection lances (100) through holes (104) that are drilled through walls (14) of the furnace above the top surface (22) of the molten bath of glass in the furnace basin (12). The lances are thin walled tubes that each carry an adjustable flange (150) for preventing unwanted convection and radiation through furnace wall holes (104) that receive the lances (100). By bending the thin walled tubes (50) to carefully direct the discharging flows (102) of oxygen so that the discharge paths properly extend across the top surface (22) of the molten glass in closely spaced, parallel relationship thereto, and by selecting discharge opening size and configuration, the injected flows of oxygen are aimed and defined so as to effectively draw the blanket (30) of flame down to the suface portion (22) of the glass that is being heated, and to achieve complete combustion and maximum flame coverage. The lance discharge opening is preferably designed as a laval nozzle.

Description

Method and apparatus for enhancing combustion and operational efficiency in a glass welting furnace

TECHNICAL FIELD

The present invention relates to a method and apparatus for improving the heating performance and productivity of glass melting furnaces and the like. More par icularly, the present invention relates to the use of oxygen lances that are installed through holes or ports in furnace vails to inject flows of oxygen in directions that extend substantially parallel to the top surface of a bath of molten glass contained within the furnace. The injected flows extend in closely spaced relationship to the top surface of the molten glass to draw a blanket of flame from a location spaced above the glass downwardly into contact with the glass, and to improve combustion and flame coverage in selected areas of the furnace, to concurrently improve flame positioning and character, whereby improvements also result in heat transfer from the combustion zone to the molten glass, and combustion efficiency within the combustion zone. BACKGROUND ART

In a glass melting furnace, a large melting tank typically is defined at least in part by wall structures that are thick and provide only limited access to contents within the melting tank. Constituents used to manufacture glass are introduced into the tank and heated therein to provide a bath of molten glass. As some of the molten glass is withdrawn from the bath for use in manufacturing processes, additional ingredients are added to the bath to replenish the bath and to keep its top surface at a substantial constant level.

Contents of the melting tank or "basin" of the furnace are heated, at least in part, by using an array of burner nozzles that inject natural gas or other fuel transversely across the top surface of the molten glass to form what can be thought of as a blanket of flame that extends over a major portion of the bath of molten glass. To optimize productivity and to minimize fuel waste, it is desirable to obtain a flame coverage over the area of the furnace basin that is as uniform as possible, and to feed fuel and oxygen to the combustion zone in such a way that complete combustion of the fuel is achieved.

However, a problem inherent in operating a furnace of this type is that, depending on a variety of factors that vary from location to location across the top of the furnace basin, the character of the flame blanket that results as combustion is used to heat molten glass is found to differ in a variety of ways including such characteristics as flame character, flame sp-read, uniformity of flame coverage, combustion efficiency, heat transfer rate and efficiency, etc. Factors that cause such variations may include the character of the supply of material gas and/or combustion air to a particular region, whether conduits and/or nozzles are fully operational, partially obstructed, deformed and/or detoriated in character, etc. But, regardless of the reason or reasons for nonuniformi- ty of flame blanket composition and character, it is desirable from the point of view of heating the glass efficiently that some means be provided to improve flame character and heating performance. While the need for an effective means to provide localized improvement extends throughout the combustion zone, it is especially prevalent in areas over the furnace basin where deficiencies in the character of the flame blanket are found to be quite pronounced.

Another problem has to do with the height at which the blanket of flame tends to reside above the upper surface of the bath of molten glass. The tendency of the flame blanket to reside at a distance spaced above the top surface of the molten glass may result from the interaction of a number of factors including the presence of upwardly moving flows of hot gases that emanate from the bath, the paucity of oxygen in the combustion zone layer that resides immediately adjacent the top surface of the bath, etc. But, regardless of the reasons that may explain why the flame blanket tends to reside at a location spaced above the molten glass, there can be no disputing the desirability of providing a suitable method and means for forcing the flame blanket downwardly to enhance flame positioning and coverage, and to thereby improve the efficiency of the flame blanket in heating the molten glass.

Still another problem is that of enhancing and maintaining good combustion efficiency. While this problem has been addressed by a wide variety of proposals including the proposed use of devices of various types for injecting oxygen at discrete burner locations to treat the flame patterns within combustion zone areas that are served by selected burners, the need remains for a relatively simple and inexpensive system that is adequately flexible to address the complex needs of a combustion zone in a glass melting furnace as by providing localized enhancement of combustion as by the controlled injection of oxygen. SUMMARY OF THE INVENTION

The present invention overcomes the foregoing and other drawbacks of prior art by providing a novel and improved method and apparatus for effectively altering the positioning and character of a flame blanket at selected locations atop the basin of a glass melting furnace, and for simultaneously enriching the oxygen content of combustion gases to improve combustion efficiency.

The present invention overcomes drawbacks encountered in glass melting furnaces in prior use without extensive or expensive modification of the furnace structure. Improvement is brought about by providing simple tube-type lances to inject flows of oxygen or oxygen containing gases, such as oxygen enriched air, through holes that are formed in the furnace walls or formed in side walls of ports for supplying combustion air to burners (nozzles that inject fuel, such as natural gas), with the lances being adjustable to permit operators to control the flows of oxygen containing gases that are discharged from the lances, and to control their influence on the flame blanket that tends to reside at a distance spaced upwardly from the bath of molten glass in a glass melting furnace.

The ports for supplying combustion air are provided in the side walls above the melting tank perpendicular to the direction of the overall flow of the molten glass. Nozzles fo injecting fuel may be provided through port side wall at right angles to said port side wall or at an angle, e. g. 45 degrees, directed toward the melting tank. In some glass melting furnaces. fuel nozzles are provided below or above said port. In cases were fuel nozzles are provided through port side walls or above ports lances may be provided in the port side walls directed toward the melting tank.

A feature of the preferred practice of the invention resides in the introduction of oxygen or an oxygen containing gas not necessarily where flames from burners are most predominantly located but rather into a portion of the combustion zone where flames are most desirably located for optimum heating of the molten glass or solid glass-making ingredients floating on the body of molten glass in the basin of the furnace. The approach thus taken is to draw the blanke of flames downwardly to the one place where it will do most good, namely the vicinity of the top surface of the molten glass, and, in the same process, to enrich the flames with supplemented flows of oxygen or gases rich in oxygen for improved combustion efficiency in this important part of the combustion zone.

In one preferred embodiment, holes are drilled through the furnace walls of a glass melting furnace at a level that is below the normal level of the flame blanket, but slightly above the level of the top surface of the bath of molten glass. Lances are inserted into the holes to inject flows of oxygen out across the top surface, i. e., into a layer of the combustion zone that immediately overlies the molten glass. One or several lances may be provided for each fuel nozzle.

In another preferred embodiment, lances are inserted into holes provided in port side walls. One or several lances may be provided in each port side wall.

The lances used to effect oxygen injection are preferably of a thin walled type that enables the lances to be adjusted to provide desired directions and characteristics of flow, which, if done properly, advantageously affects the degree of heating that is provided by the flames above the surface of molten glass. Adjustment of the lances is effected

1) by bending the elongate tube that form the lance to aim the flow of gas that discharges from the lance, and

2) by selecting lance diameter or lance discharge opening size and/or lance discharge opening configuration to provide desired rates of flow for each of the lances and within certain limits gas feed pressure.

A further feature of the invention resides in the use of radially extending flange members that are carried on each of the elongate lances near their discharge ends so that, once a lance has been properly positioned and the propriety of its discharge of oxygen or gas rich in oxygen has been assured, the flange can be releasably thightened in place on its associated lance to closely cover and effectively close open parts of a hole that has been drilled through the furnace wall to install the lance. Thus unwanted loss by radiation and/or convection is prevented, and the inspiration entry of unwanted gas into the furnace through holes is minimized.

A feature of the invention resides in the use of lances of thin walled construction. While the use of a thin walled lance naturally enables the lance to be bent more easily than would be the case if the lances were formed from a wall of thicker cross section of the same material, other advantages are also obtained. One such advantage is the fact that minimizing wall thickness of a lance makes it easier to cool the lance so that it does not overheat during use and suffer from heat-induced detoriation. Thus, by using lances of thin walled construction (typically formed from stainless steel), cooling the lance both by means of internal gas flows of oxygen or other oxygen rich gas (or of a purging gas, such as nitrogen that is used to maintain positive pressure in the lance when oxygen flow is shut off during furnace operation), and by means of external flows of ambient cooling air.

In regenerative type furnaces, supplies of lance-injected oxygen are cycled to correspond with the cycling of the burners, whereby when a burner on one side of the furnace is idle, its supply of injected oxygen is cut off. In preferred practice, however, when oxygen flow through a lance is cut off, a low velocity flow of an alternate gas such as nitrogen is maintained through the lance both to cool the lance and to keep unwanted particles and the like from entering the discharge end of the lance.

A significant aspect of features of the oxygen enrichment system of the present invention is that these features ordinarily may be implemented at relatively low installation costs in existing furnace structures, not only to overcome deficiencies in burner performace, but also to enhance combustion efficiency and overall operating efficiency of the furnace. In tests conducted on existing furnaces, the system of the present invention has demonstrated a capability to enhance furnace production capacity well beyond that for which the furnace was originally designed. BRIEF DESCRIPTION OF THE DRAWING

The foregoing and other features, and a fuller understanding of the invention may be had by referring to the following detailed description and claims, taken in conjunction vith the accompanying drawing, wherein:

Figure 1 is a foreshortened elevational view, which is a lateral section of a portion of a glass meltling furnace showing the construction and mounting of a lance that embodies features of present invention;

Figure 2 is an elevational view, on an enlarged scale, of portions of the apparatus of Figure 1, with the lance being foreshortened;

Figure 3 is an elevational view, on an enlarged scale, of a lance having in its tip end an insert defining a laval nozzle; and

Figure 4 is an elevational view, on an enlarged scale, of the insert shown in Figure 3. DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the preferred practice of the present invention, oxygen is injected through lances at relatively high velocities at spaced furnace wall locations above but in close proximity to the top surface of molten glass in a furnace, and serves to draw the burner generated flame down toward the surface of the molten glass to better impart the heat of the flame to the glass. Special thin-walled lances are provided for effecting oxygen injection, with the thin wall character of the lance rendering the lances adequately flexible to be bent as may be needed to enable the lance concurrently to directly discharge flows of oxygen most effectively to both draw the flame down toward the molten glass to improve the transfer of heat energy from the flame to the glass, and to provide the oxygen flow that is needed to improve the character of the combustion activity itself. Radiation and convection shields provide radially extending flanges that are carried by the lances to cover the holes in the furnace walls that were drilled to install the lances. The shields prevent the escape of heat energy and the unwanted convection of gases through the drilled holes.

According to another preferred embodiment the lances are installed in port side walls. This is often the case when fuel nozzles for heating the glass are introduced in port side walls or above or below ports for introducing combustion air. The lances introduced through holes in port side walls may form an angle of less than 90 degrees with the port side wall and are directed toward the melting tank. Usually said angle is about 20 to about 60 degrees, preferably less than 50 de¬ grees. The holes made in port side walls for introducing lan¬ ces may parallel to the furnace side wall, i. e. perpendicular to the port side wall, or form an angle of less than 90 de¬ grees and being directed toward the furnace melting tank. Referring to Figure 1, portions of a conventional glass melting furnace are indicated generally by the numeral 10. Th furnace 10 has a melting tank or basin 12 that is defined, in part, by a vertical wall 14 and a floor structure 16. A bath of molten glass 20 is contained in the basin 14, with the molten glass having a top surface 22.

While the materials that form a typical furnace are mor complex in character than is the simplified structure that is shown in the drawing, it will be .understood that features of furnace construction are well known and are of a conventional character which is outside the scope of the present invention

Referring to Figure 1, a blanket of flame 30 is formed as fuel from a spaced array of burners 40 is injected into th combustion zone 18. The flame blanket 30 tends to reside at a distance spaced above the top surface 22 of the molten bath 20.

It is quite common for the flame pattern that form various zones of the flame blanket 30 to vary in combustion efficiency, and in the efficiency with which heat energy is transferred to adjacent contents of the melting tank 12. The problem of combustion inefficiency and of improper flame pattern positioning is addressed by the present invention by providing a relatively simple and inexpensive system which ma be utilized as needed to enhance combustion efficiency and to favorably modify flame pattern positioning and configurations In accordance with the preferred practice of the presen invention, lances 100 (one of such lances is shown in Figure 1) which inject flows 102 of oxygen are provided so as to extend through holes 104 that are formed in the furnace walls 14. Typically, a hole 104 is drilled in a tuck stone portion of a furnace wall at a location slightly above the top surfac 22 of the molten glass 20 in the basin 12. A lance 100 is installed in the hole 104 and is aimed so that it will desirably alter the configuration and positioning of the flam patterns in the vicinities of the oxygen flow that it introduces, as by drawing the flames 30 downwardly toward the top surface 22, and by enriching the combustion with oxygen to assure complete combustion of fuel.

In testing various lance positioning as well as various oxygen discharge flow rates for use with each of the lances 100, the objectives that are kept in mind are quite straightforward. First, the supply of oxygen needs to be such that it will properly enhance combustion efficiency to give maximum heat energy from combustion of a given quantity of fuel. Second, the oxygen should be supplied at a lance exit velocity that is sufficient both to minimize dissipation of the oxygen as it travels to its desired location and to effect any desired degree of flame pattern modification. Still further, the direction of orientation of the lance should be such as to cause oxygen to flow along a path that is so directed as to effect a desired type of repositioning and/or alteration of the flame pattern, whereby flames are drawn down toward the top surface 22. Since a flame pattern tends to follow a path of an injected flow of oxygen, by aiming the flow path 102 across the top surface 22, the flame pattern 30 issuing can be directed downwardly toward contents of the melting tank 12.

Referring to Figure 2, the inner diameter 125 of the lance 100, and/or the diameter of its discharge opening 130, is selected through testing to provide an injected flow of oxygen that is suitable for each lance location. Typically, the lances 100 are installed at spaced intervals of a few feet along the length of a furnace wall 14. In the case that the lances are installed in furnace ports one or several lances may be positioned in the ports. Of course, lances may be installed both in drilled holes and in burner ports.

The lance 100 is depicted in the drawing as comprising an enlongate tubular member of thin wall construction which will be understood by those skilled in the art to be formed from stainless steel or other heat resisting material. An end cap 132 preferably is welded over the discharge end 120 of the lance 100 to provide a discharge opening 130 that is smaller in diameter than the internal diameter 125 of the lance tube 100, whereby, if the opening 130 needs to be enlared to provide increased flow, it can be drilled out as need be, and there will be no need to change to the use of a substitute lance. Typically, the lance 100 will have an internal diameter of about 9 mm to about 19 mm. Typically, the discharge opening 130 will be of a size of about 5 mm to about 15 mm. Typically, the rate of flow of oxygen discharged from any one lance during operation of the furnace 10 will be within the range of about 200 to about 700 standard cubic meter per hour (about 700 to about 2400 standard cubic feet per hour), with a relatively high discharge velocity typically exceeding about 70 meters per second.

A radially extending flange member 150 is movably carried on the lance 100. The flange member 150 is a welded stainless steel assembly of an annular member 152 formed from a plate stock, and a tubular member 154 to which the annular member 152 is welded. One or more threaded fasteners 156 extends through the tubular member 154 and provides means of installing the flange member 150 on the lance tube 100 at a location quite near the discharge endregion of the lance 100.

A suitable conventional mounting bracket, indicated generally by the numeral 175 is provided for supporting the lance 100 from suitable existing structure 177 that typically forms part of the furnace 10, as those skilled in the art wil unders and.

The lances with openings 130 were tested on a 6 port side-fired regenerative float glass tank rated at 450 ton per day. After the insertion of the present lances a 7.1 X production increase and a 6.7 X decrease in specific fuel consumption was achieved.

Referring to Figure 3, the lance 100 is provided with a insert 60 having a discharge opening 62 designed as a laval nozzle. The insert 60 is welded to the lance body 50 at the discharge end of the lance 100 or held in place by other suitable means. If the insert 60 is worn-out by the heat generated in the furnace when in operation the lance 100 can be cut in front of the inlet end of the laval nozzle insert, thus shortening the lance a short portion, and a new insert may be positioned in the discharge end of the shortened lance 100. The inserts 60 are made of heat resistant material, such as stainless steel, e. g. 316 stainless steel.

Laval lances (i. e. lances 100 with laval nozzles) were installed in a glass melting furnace to achieve a higher velocity and a less divergent flow of the oxygen. Table I in connection with Figure 4 show the dimension of the nozzle inserts 60. The high velocity of the oxygen when using laval nozzles causes a lower pressure where the oxygen is flowing between the flame and the glass which causes the surrounding gases including the flame to be pulled toward the glass. The oxygen flow diverges more slowly than with a conventional lance, such as the lance 100 of Figure 2 having an discharge opening 130, so the high velocity of the flow is retained further into the glass melting tank. The high velocity over a longer distance causes an increase in mixing which spreads combustion and shortens the flame. This effect is counteracted by using larger diameter burner tips, which slows the mixing again. The resulting effect is that the flame is lengthened again, while remaining closer to the glass than with conventional lances. Table I

Dimensions for four different inserts 60 (see Figure 4).

No. 1 No. 2 No. 3 No. 4

A B C D

The dimensions given in Table I are in millimeters.

As B (Table I) is increased, as with inserts No. 3 and No. 4, the curvature of the constriction was sacrified in order to hold A constant. This caused no adverse effects. Enhanced mixing is also exhibited in flue gas readings. With the original lances, it was necessary to operate with flue oxygen levels between 3 and 4 X to bring combustibles to 0.1 X and below. With the lances with laval nozzles, this combustible level can be achieved with 2 X excess oxygen and below.

The first location that a laval lance was installed in was in a port where the flame was very high. The crown temperature was rising from 1627 degrees Centigrade to 1649 degrees Centigrade (2960 to 3000 degrees Fahrenheit) over a course of a 15 minute reversal. When the opposite side was firing, the temperature remained at 1632 degrees Centigrade (2970 degrees Fahrenheit). For comparision, the flame was optimized by adjusting the burner tips and the conventional lances, i. e. lances 100 with openings 132, that were in place. No improvement was seen in the crown temperature. When the center lance was replaced with a laval lance, the flame became much shorter and closer to the glass. Larger burner tips were installed, lengthening the flame. The final result was a wider flame, giving better flame coverage of the glass, with a flame that was much closer to the glass. Crown temperature was constant at 1632 degrees Centigrade (2970 degrees Fahrenheit) when either side was firing.

With lances equipped with laval nozzles, the flame is just as wide as with the original lances, but only about half as high. The bottom of the flame was still close to the glass but the top of the flame was further away from the crown, causing the decrease in the peak crown temperature, directing more energy to the glass.

Additional laval lances were installed into ports where improvement in flame shape was desired. The rather quickly diverging flow of oxygen from the conventional lances can pus surrounding gases away, leaving a "hole" in the flame. When laval lances are substituted in these locations, the "hole" i no longer present, and the flame moves closer to the glass and away from the crown. After installing laval lances, fuel consumption decreased by 85 cubic meter per hour (3000 cfh) in the above mentioned 6 port side-fired regenerative furnace and by 57 cubic meter per hour (2000 cfh) in a second similar furnace.

Table II shows the location of the laval lances in the above mentioned furnace, exit diameter of the laval lances used, and flow and velocity of the oxygen. Port No 1 is at the charge end of the furnace. Two lances were used at port Nos 1, 4 and 5 and three lances at port Nos 2 and 3. TABLE II

Laval lance configuration

Exit diameter flow, cubic velocity Port mm meter per sec meter per sec

Right side

43.9 268 58.9 251 62.3 266 97.6 332 97.6 332

66.8 285 37.4 229 47.9 293 58.0 248 102.1 347

102.1 347

U = upstream port, C ■ center of port, D - downstream port The flows rates shown for port No 5 were the maximum flows attainable with the 10.2 mm exit diameter nozzles. Presence of combustibles in the flue gases while using these oxygen flows prompted manufacture of larger 12.1 mm exit diameter nozzles. Resulting flows and velocities are shown in Table III. Table III

Changes made to laval lance configuration of Table II

Exit diameter flow, cubic velocity Port mm meter per sec meter per sec

Right side

5U 12.1 141.6 342

5D 12.1 141.6 342

Left side

5U 12.1 107.6 260

5D 12.1 107.6 260

U = upstream port, C = center of port, D ^■= downstream port

As can be seen in Tables II and III, supersonic velocities are attainable using the laval lances of the present invention. The advantageous effects of these laval lances appear to be due to the slowly diverging nature of the oxygen stream within the furnace.

The term "oxygen" as used herein, will be understood to include oxygen-rich gas of reasonable purity. The term "oxygen" is intended to include oxygen of commercial grades of purity (typically about 99 X pure) as well as oxygen which may have been produced by such economical processes as pressure swing absorption (typically about 90 X purity). The term "oxygen" may also include other oxygen rich gas mixtures wherein oxygen is the predominant component (typically being of at least about 75 X oxygen purity with the remainder of the mixture being substantially inert gases).

The term "furnace wall opening" or similar terms used in the appended claims is intended to include "opening in furnace port side wall", "port side wall opening" or similar expressions. The term "furnace wall opening" is not intended to be limited to an opening in the furnace side wall 14.

Claims

1. A method of treating glass in an elongate glass melting furnace (10) having a melting tank (12) containing a body (20) of molten glass, a combustion zone (18) located generally atop the melting tank (12), and having combustion means (40) for burning fuel to provide a blanket of flame (30) atop the melting tank (12), characterized by placing a discharge end region of a thin walled lance (100) having an elongate tubular body (59) through a hole (104) in a wall (14) of the furnace (10) above the body (20) of molten glass or through a hole in a side wall of a port, feeding said lance (100) with an oxygen containing gas to inject a flow (102) of said gas through an opening (130, 62) in the discharge end region along a substantially linear flow path at a velocity sufficient to minimize dissipation of the injected flow (102) of said gas and directing said flow path across the furnace (10) above the body (20) of glass so as to draw flames (30) from the blanket of flames toward a selected portion of the combustion zone that overlies the top surface (22) of the glass.

2. The method according to claim 1, characterized in that the lance (100) is adjusted by bending the thin walled tubular body (50) of the lance spaced (100) from the discharge end region of the lance (100) to aim the discharge end region so as to orient the discharge end region of the lance (100) in a direction that is found to cause the flow of gas emanating therefrom to alter the configuration of the pattern of flames (30) within the furnace (10), whereby the efficiency with which these flames (30) transfer heat energy to the molten glass (20) is enhanced.

3. The method according to claim 1 or 2, characterized in that a radiation shield (150) is positioned against the furnace wall (14) to block unwanted gas flow and radiation heat loss through the furnace wall opening (104), said radiation shield (150) being movably carried on the lance body (50).

4. The method according to one or several of claims 1-3, characterized in that the rate of flow of gas that discharges from the lance (100) into the combustion zone (18) is adjusted by adjusting the size of the discharge opening (130, 62) or by adjusting the pressure of the oxygen containing gas supplied to the lance (100).

5. The method according to one or several of claims 1-3, characterized in that said discharge opening (130, 62) is an opening (62) designed as a laval nozzle.

6. The method according to claim 5, characterized in that said gas being discharged into the furnace (10) has a supersonic velocity when leaving said laval nozzle.

7. The method according to one or several of claims 1-6, characterized in that the oxygen containing gas has an oxygen content of 75 percent by volume or more.

8. The method according to claim 7, characterized in that the oxygen containing gas has an oxygen content of at least 90 per cent, preferably at least 99 per cent by volume.

9. Apparatus for introducing a controlled flow of oxygen containing gas through a furnace wall opening (104) and into a glass melting furnace (10), said (10) furnace having a melting tank (12) containing a body of molten glass (20), a combustion zone (18) located generally atop the melting tank, and combustion means (40) for burning fuel to provide a blanket of flame (30) atop the melting tank (12), characterized in that it comprises a lance (100) having an elongate tubular body (50) with a tip end region having a discharge opening (104, 62) for discharging a flow of gas into said furnace (10), with the direction of said flow of gas from said opening (104, 62) being readily changed as by bending a portion of the tubular body (50) of the lance (100) at a location spaced from the tip end region.

10. Apparatus according to claim 9, characterized in that it further comprises shield means (150) that is movably adjustably positionable on the tubular body (50) of the lance (100) so as to be settable in a location adjacent the furnace wall opening (104) to substantially close the furnace wall opening (104), with the shield means (150) serving to provide a radiation and convection shield limiting leakage through the furnace wall opening (104).

11. Apparatus according to claim 9 or 10, characterized in that the discharge opening (130, 62) is designed as a laval nozzle opening (62).

12. Apparatus according to claim 9 or 10, characterized in that an insert (60) defining a lav.al nozzle opening (62) is provided in the tip end region of said lance body (50).

13. Apparatus according to claim 12, characterized in that the insert (60) is a slip insert welded in place.

14. Insert to be placed in a discharge end region of a lance and having a discharge opening, characterized in that the insert opening 62 is designed as a laval nozzle.