GB2236114A

GB2236114A - Gas injection

Info

Publication number: GB2236114A
Application number: GB8917457A
Authority: GB
Inventors: Kenneth William Bates; Nicolas Woolley
Original assignee: Injectall Ltd
Current assignee: Injectall Ltd
Priority date: 1989-07-31
Filing date: 1989-07-31
Publication date: 1991-03-27
Also published as: CZ285070B6; DD296627A5; PL286276A1; GB8917457D0; ZW12390A1; SK280495B6; CN1049187A; GR900100555A; CS376490A3; CN1022695C; PL165359B1; EG19405A; IL95195A0

Abstract

The invention provides a gas injector for a molten metal vessel, comprising: a gas inlet chamber 51 having an inlet port and at least one outlet Port 54, said outlet port having secured gas-tightly thereto by means of a compression gland connector 55, 56, 61 and extruded rod 58 which extends to a gas discharge end of the injector, the extruded rod being formed of a substantially gas-impermeable refractory material and having at least one axially-extending gas passage therealong, the passage communicating with the gas inlet chamber, and being of such small dimensions that in use, melt is substantially unable to intrude into the or each passage, the rod and compression gland connector being embedded in a refractory body of the injector save for the discharge end of the rod. <IMAGE>

Description

"GAS INJECTOR" The present invention relates to an improved gas injector for introducing gases into elevated temperature liquids, more especially - but not exclusively - molten metals.

Gases are often injected into molten metals in vessels such as ladles, for diverse purposes. For instance, a gas may be introduced into the bottom part of a vessel to clear the relatively cool bottom area of solidification products, e.g. to remove them from the vicinity of a bottom pour outlet where the vessel has such an outlet. Again, gas may be introduced for "rinsing", or to homogenise the melt thermally or compositionally, or to assist in dispersing alloying additions throughout the melt. Usually an inert gas is used. Reactive gases may be employed, e.g. reducing or oxidising gases, when the melt composition or components thereof need modifying.

Previous gas injection proposals have included the installation of a solid porous refractory plug or brick in the refractory lining of the vessel. They can be simple, but not without various operational drawbacks. Unless very porous, when they would be unduly weak, they can limit the amount of gas reaching the melt significantly. If excessively high gas pressures are used, in order to compensate for the attenuating effect of the porous refractory, problems of sealing arise. Significant and often costly loss of gas results. In an effort to improve the performance of such solid injector bodies, workers in the art have resorted to directional-porosity techniques. In effect, they have tried making refractory injector bodies with a plurality of straight capillary-size passages extending from the inlet to the discharge ends of the bodies.Such passages have been created by casting or pressing refractory material in a mould about tensioned plastics or metal strands which are subsequently removed by burning or by pulling them from the refractory mass.

Whilst an injector body with directional porosity provided by capillary passages is better than an ordinary porous brick or plug, its efficiency is still less than ideal. When pressurised gas is applied to an inlet end of such a body, not all the gas flow is along the passages.

Some of the gas finds its way into the porous refractory mass and thus is dissipated. Again, partly because the capillary passages are in practice less than perfect, gas can dissipate laterally from them into the surrounding refractory. The pressure of gas exiting the passages into the melt may be reduced to a level whereat the gas bubbles rather than jets into the melt. When the gas issues from a passage as a bubble, melt can instastaneously intrude into the passage and block it.

A further, and very significant problem, is how to join the refractory material of the injector body to the gas supply to provide a gas-tight seal. Known injectors have employed a metal jacket as indicated above wherein the jacket is gas-tightly secured (e.g. by threaded attachment) to the gas supply and the refractory body is cemented into the metal jacket. However, the cement between the refractory body and the metal constitutes a weakness. Although the metal jacket chamber may be distanced from the interior of the molten metal vessel by the refractory body; the jacket is nevertheless subjected to extreme elevated temperatures. Differential thermal expansion of the metal jacket, the cement and the refractory body can cause the jacket to break away from the refractory thereby breaking the gas-tight seal and causing the gas to be dissipated.It has now been found that this problem can be overcome by the use of a refractory rod formed of substantially gas-impermeable material, gas flow through the rod being by way of narrow passages along its length, the rod being gas-tightly secured to a gas inlet chamber by means of a compression gland connector.

In a first aspect, therefore, the present invention provides a gas injector for a molten metal vessel, comprising: a gas inlet chamber having an inlet port and an outlet port, said outlet port having secured gas-tightly thereto by means of a compression gland connector an extruded rod which extends to a gas discharge end of the injector, the extruded rod being formed of a substantially gas-impermeable refractory material and having at least one axially-extending gas passage therealong, the passage communicating with the gas inlet chamber, and being of such small dimensions that in use, melt is substantially unable to intrude into the or each passage, the rod and compression gland connector being embedded in a refractory body of the injector save for the discharge end of the rod.

Whilst it is possible for an injector to contain only one refractory rod, it is more usual for an injector to comprise an array of rods arranged, for example, in a particular configuration such as in a circle.

Whereas it is possible in principle for each such refractory rod to be connected to its own gas pipe, such an arrangement is highly impractical and would unnecessarily complicate the manufacture of the injectors thereby increasing the cost of the injectors. It is therefore preferable to employ a manifold arrangement wherein an inlet chamber is provided with a single inlet port for attachment to a gas supply pipe, but has a plurality of outlet ports.

The gas injector will generally be replaced at fairly regular intervals and thus may be regarded as a consumable item. As such, it is important to minimize the complexity of the injector in order to keep costs to an acceptable level. Thus a manifold arrangement of the type referred to hereinabove should be ideally of a simple construction requiring relatively few operations in its manufacture.

A further requirement for such a manifold is that it should resist distortion by the combination of high pressure and temperature encountered in use.

Even though the manifold in use is shielded from direct contact with the molten metal by the refractory material, it is nevertheless subjected to very high temperatures and, at such temperatures, can become plastic and thereby more easily distorted by higher gas pressures.

The above problems can be overcome by employing as the inlet chamber or manifold a cast and/or welded metal enclosure comprising a back wall having an inlet port, a front wall having one or more outlet ports, and a side wall linking said front and back walls, said front and back walls being further linked by one or more support stays therebetween.

Preferably the support stay forms a gas-conduit having a closed end gas-tightly secured (e.g. welded) to the front wall, and an open end forming the inlet port, the side wall of the conduit having holes therein to permit gas flow between the inlet port and the or each outlet port.

The extruded refractory rod is secured gas-tightly to the neck portion of the outlet port by means of a compression gland connector. The compression gland connector comprises a compressible gland packing, usually in the form of a ring through which the refractory rod can be inserted, and a threaded collar which is placed about the refractory rod. The threaded collar can be screwed into or onto the outlet port, by way of an adaptor if necessary, to compress the gland packing therebetween so as to cause it to be compressed against the refractory rod thereby providing a gas-tight seal.

It will be appreciated from the foregoing disclosure that the gland packing will need to be capable of withstanding extreme temperatures and hence advantageously it is formed from graphite. One form of flexible graphitic material particularly suitable for the purposes of the present invention is a form known as exfoliated graphite flake. Exfoliated graphite flake is commercially available under the trade name "Flexicarb" (TRADE MARK) from Flexicarb Graphite Products Ltd., of Heckmondwike, Yorkshire, England.

The refractory rods are formed of a gas impermeable material, for example they can be formed of mullite, a fired alumino-silicate, or recrystallized alumina. Such rods are available commercially for use as thermocouple sheaths.

Because the refractory is formed of a gas-impermeable material and is gas-tightly connected with the outlet port via the packing gland, and because pressurised gas is thereby delivered directly into the passages of the gas impermeable refractory rod, the gas cannot dissipate into the refractory injector body. Accordingly, an efficient transport of gas into the molten metal can be attained.

Preferably, the refractory rod comprises a plurality of passages in the form of capillary bores or slots. In either case, the passages are individually sufficiently small that intrusion of melt into them substantially cannot occur in practice.

Desirably, the refractory rods are disposed in a predetermined array optimised for efficient injection of gas into a melt. By way of example, the rods may be uniformly spaced about a longitudinal axis of the injector body, i.e. in a circular array or in a plurality of concentric circular arrays.

The injector according to the invention can be installed in a gas injection apparatus as disclosed and claimed in our International Patent Application No.

W088/08041. It will then take the place of the plugs 312 shown in the drawings of WO88/08041.

The invention comprehends a molten metal vessel, e.g.

a ladle, having an insulating lining and an injector according to the invention melt-tightly secured in a receiving opening of the lining.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 shows a prior art gas injection apparatus installed in the bottom wall of a vessel such as a ladle; Fig. 2 is a fragmentary longitudinal sectional view through an injection apparatus incorporating a gas injector according to the present invention; and Fig. 3 is a longitudinal sectional view of a gas supply system which can be used in conjunction with the injector shown in Figure 2.

Fig. 1 of the drawings shows a prior art apparatus for injecting gaseous substances into e.g. molten metal. The apparatus, which is the subject of W088/08041, includes a nozzle block 310 for installing in the wall 10 of a vessel 12. The nozzle block 310 has a passage 311 closed by a plug at its gas discharge end, the plug 312 being pierced by capillary bores 313 and having a feed pipe 316 gas tightly coupled thereto. The feed pipe 316 extends along the passage 311 from the plug 312 and terminates in an inlet member 324 by which the pipe receives gas from an external gas duct system 315 which, in turn, is connected to a supply of gas under pressure.

As shown, the vessel 12 has a metal shell 14 and a refractory lining 16 having, in this case, a bottom opening 18 to accommodate the nozzle block 310. It will be apparent from Fig. 1 that the nozzle block 310 comprises an assembly of three refractory members A, B and C in this instance. However, if preferred, the block 310 can be a single monolithic member.

In accordance with the teaching of WO88/08041, the feed pipe 316 can be surrounded by a cartridge element 340 which contains a particulate refractory filling.

For further details of the injection apparatus described briefly above, and alternative embodiments thereof, reference is directed to W088/08041.

The apparatus disclosed in W088/08041 has an injection plug 312 made of a refractory material pierced by a plurality of capillary bores 313. Moreover, gas under pressure is applied to the whole of the lower end face of the plug 312 by the feed pipe 316. This arrangement is practical, but less than ideal as we have indicated hereinbefore. The gas injector to be described hereinafter is primarily, but not exclusively, meant for use in apparatus of the kinds or similar to the injection apparatuses taught in WO88/08041. In principle, for instance, the present gas injector can be substituted for any of the porous brick or plug arrangements hitherto employed in e.g. the bottom wall of a ladle.

Figure 2 shows an improved gas injector according to the present invention.

The injector 50 comprises a gas-tight inlet chamber 51 having an inlet port to which an inlet fitting 53 is secured, the fitting 53 in use serving to couple the feed pipe 316 and the inlet chamber 51 gas-tightly one to the other. The inlet chamber is in this case an all-metal welded capsule with the inlet port in one face. The opposite face of the chamber 51 has a plurality of outlet ports 54.

Connected to each outlet port 54 by means of interengaging screw threads is an open-ended generally cylindrical tubular member 55 formed of mild steel, referred to hereinafter as an adaptor, which has a screw thread on its inner surface for engaging -a corresponding thread on the outer surface of a collar 56. The collar can also be made from mild steel. The join between the outlet port 54 and the adaptor 55 is gas-tightly sealed by means of an annealed copper washer 57. Received within the collar 56 is a refractory rod 58, the end of which abuts against a stepped region 59 of the inner surface of the adaptor 55. A further stepped region 60 on the inner surface of the adaptor accommodates a gland packing ring 61, formed of compressible exfoliated graphite, which encircles the refractory rod 58.During manufacture of the injector, the threaded collar 56 is screwed tightly into the adaptor 55 thereby to compress the gland packing ring 61 such that it forms a gas-tight seal against the refractory rod 58.

The extruded refractory rods are preferably in a fired state. Each rod is extruded to include at least one, and preferably more than one, axially extending gas passage.

The or each passage is of sufficiently large dimensions that it will convey gas freely to the melt in vessel, but is too small to permit the melt to intrude substantially into the passage.

As stated, each refractory rod preferably has a plurality of gas passages. They can take the form of lengthwise-extending capillary bores, or narrow slots, or a combination of both. Suitable rods are commercially available as plural-passage thermocouple tubes.

Apart from their discharge ends, which are not shown in Figure 2, the refractory rods are embedded in a refractory body of the injector. The inlet chamber 51 and gland seal connector 55,56,61 are also partially embedded in the body 62.

As will be appreciated, gas fed to the injector 50 via inlet chamber 51 can only exit from the injector 50 through the discharge ends of the rods 8. Accordingly, there is no call to use the body 62 per se for transporting gas to the melt, thus solving many of the problems mentioned hereinbefore. The body 62 therefore does not have to be made of high grade refractory materials, and moreover it does not need to be enclosed by a metal jacket. A cementitious castable material can conveniently and costeffectively be employed for the body, which is thus readily castable about the inlet chamber and pipes.

Conceivably, the injector could comprise but a single gas delivery rod, but preferably it has several, e.g. 5 or 10 identical rods. The rods are arranged according to some pre-determined array selected for ease of manufacture of the injector, balanced with the desire to optimise efficient distribution of gas into the melt. By way of example, the rods are disposed equidistant from a longitudinal axis of the injector, equally spaced from one another in a circular array. Depending on the number of rods, they could be disposed around a plurality of concentric circles about the longitudinal axis.

The extruded refractory rods can have any convenient number of gas passages. By way of example, they can each feature say ten passages disposed in a circular array about the longitudinal axis of the respective rod.

The inlet chamber 51 is formed of a first mild steel casting 63 which provides a front wall 64 and a side wall 65. Welded into a peripheral recess in the side wall is a circle of mild steel plate 66 which constitutes the back wall of the inlet chamber. A generally cylindrical hollow member 67, formed of mild steel, extends through the back 66 and front 64 walls, a closed end 68 of the cylindrical member being welded to the front wall 64 and a middle portion of the cylindrical member being welded to the back wall 66 to provide a gas tight seal. The outer and inner surfaces of that portion 69 of the cylindrical member extending outwardly from the back wall 66 are threaded, the inner threaded surface enabling attachment of the gas feed pipe 316.The cylindrical member is provided with holes 70 to enable gas flow through from the open end of the member, which serves as the inlet port, to the outlet ports 54.

In addition to functioning as a gas conduit, the cylindrical member, through being welded to both front and back plates, functions as a support or stay to prevent distortion of the inlet chamber under high pressures and at high temperatures.

Ordinarily, as stated above, the injector body is not encased in a metal jacket. It will be installed in the nozzle block 310 using a relatively weak cement. The injector body 62 complete with its refractory rods and inlet chamber 51 can then be extracted from the nozzle block 310 when it has to be replaced. Conveniently, the injector 50 is extracted by a threaded puller which is connected to the outer threaded surface of the cylindrical member 67 after disengaging the feed pipe therefrom.

The injector 50 has been particularly devised for use in the kinds of injection apparatus disclosed in WO88/08041, but it is of wider application. It could, for instance, simply be mounted in an orifice block let into the refractory lining of a vessel. The inlet fitting 53 could then simply project from the shell of the vessel, for connection directly to a gas supply line.

In a specific example, there are five refractory rods each centred upon a circle of 65 mm diameter, and extending the length of the refractory body 62. The body is 41 cm long and tapers from a diameter, at its inlet chamber end, of 14.2 cm to 11 cm at its discharge end. The refractory rods have diameters of 16 mm and each contains a circular array of ten gas passage bores, each being 0.6 mm diameter.

The outer refractory member C of the nozzle block 312 illustrated in Figure 1 has a central void to accommodate the "pig-tail" loop in the feed pipe 316 and the cartridge element 340. The purpose of the loop in the feed pipe 316 is to absorb any movement of the nozzle block relative to the inlet member 324 of the gas supply thereby preventing or minimising any stress on the joints in the gas supply system so as to ensure that the system remains leak-proof.

As indicated above, the injector of the present invention can be used in conjunction with a nozzle block arrangement and gas supply system as shown in Figure 1. However, the injector can also be employed in combination with the gas supply system illustrated in Figure 3. In this case, a modified nozzle block is used. The outer refractory member C is replaced by a member C' which has a much smaller central void and the "pig-tail" loop and cartridge 340 are eliminated. In Figure 3, the feed pipe 316 extends through an orifice 71 in the outer portion C' of the nozzle block, the end of the feed pipe 316 passing through a gland seal 73,74,75 containing an exfoliated graphite gland packing ring 74.The purpose of the gland seal 73,74,75 is to maintain a gas-tight seal about the end of the feed pipe 316 whilst accommodating any movement of the nozzle block injector and feed pipe which may occur as a result of thermal expansion during use. This arrangement replaces the "pig-tail" loop arrangment illustated in Figure 1. The gas supply system includes a pipe 76 and one-way valve assembly to which gas from a source (not shown) is fed. The valve assembly has a valve chamber 77, a valve cover 78 and a valve liner 79.

Located inside the valve chamber is a copper "float" 80 which has gas passages 81 and 82. In use, gas passes into the valve chamber 77 forcing the copper float 80 towards the outlet filter 83 which is held in place between the valve liner 79 and a valve top plate 84. The gas flows through the gas passages 81 and 82 and out, via the filter 83, through an aperture in the valve top plate 84. When the gas supply is turned off, the float falls back against the bottom wall of the valve chamber.

The valve cover is held against a retaining plate 85, with a valve cover gasket 86 compressed therebetween to form a gas-tight seal. Lining an aperture 87 in the retaining plate 85 is an insert 88, formed of copper. The end of the feed pipe 316 extends into the aperture 87.

Sandwiched between the retaining plate 85 and the outer portion C' of the injector nozzle block is a steel plate 89 to which is welded the body of the gland seal 73,74,75.

When dismantling the injector apparatus, for example in order to replace the injector plug, the one-way valve assembly, retaining plate 85 and steel plate 89 are each removed. When replacing them, it is necessary to ensure a gas-tight seal. In practice, due in part to differential thermal expansion in use, it is very difficult to secure a gas-tight seal between plates 89 and 85 by means of a flat seal gasket. Therefore a seal ring arrangement is employed which comprises a seal ring 13 manufacturered for example from mild steel (steel grade EN3) and a seal ring gasket 21 formed for example of asbestos yarn embodying stainless steel reinforced wire with a maximum service temperature of 8150C.

The gas supply system illustrated in Figure 3 provides a leak-free supply of gas to the injector illustrated in Figure 2. A further advantage of the gas supply system illustrated arises from the use of the copper components 80, 84 and 88. Whereas an advantage of the injectors of this invention is their improved durability, it is just conceivable that the refractory rods and surrounding refractory body might break up under the effect of excessive ladle lining wear. This should be a rare event, but if it happened it could result in molten metal entering the gas feed pipe. If such a situation were to arise, the copper components 80, 84 and 88 will rapidly conduct heat away from the molten metal causing it to freeze thereby sealing the system against leakages of molten metal to the surroundings.

The gas supply apparatus illustrated in Figure 3 is intended in particular for use in a ladle apparatus.

Claims

CLAIMS:

1. A gas injector for a molten metal vessel, comprising: a gas inlet chamber having an inlet port and an outlet port, said outlet port having secured gas-tightly thereto by means of a compression gland connector, an extruded rod which extends to a gas discharge end of the injector, the extruded rod being formed of a substantially gas-impermeable refractory material and having at least one axially-extending gas passage therealong, the passage communicating with the gas inlet chamber, and being of such small dimensions that in use, melt is substantially unable to intrude into the or each passage, the rod and compression gland connector being embedded in a refractory body of the injector save for the discharge end of the rod.

2. A gas injector for a molten metal vessel, comprising: a gas inlet chamber having an inlet port and a plurality of outlet ports, each outlet port having secured gas-tightly thereto by means of a compression gland connector, an extruded rod which extends to a gas discharge end of the injector, the extruded rod being formed of a substantially gas-impermeable refractory material and having at least one axially-extending gas passage therealong, the passage communicating with the gas inlet chamber, and being of such small dimensions that in use, melt is substantially unable to intrude into the or each passage, the rods and compression gland connectors being embedded in a refractory body of the injector save for the discharge ends of the rods.

3. An injector according to claim 1 or claim 2, wherein the inlet chamber is a cast and/or welded metal enclosure comprising a back wall having an inlet port, a front wall having one or more outlet ports, and a side wall linking said front and back walls, said front and back walls being further linked by one or more support stays therebetween.

4. An injector according to claim 3, wherein the support stay is a length of tubing having a closed end gastightly secured to the front wall, and an open end forming the inlet port, the wall of the tubing having holes therein to permit gas flow between the inlet port and the or each outlet port.

5. An injector according to any of claims 1 to 4, wherein the compression gland connector contains a gland packing element which is formed of a cpmpressible graphitic material.

6. An injector according to claim 5, wherein the compressible graphitic material is exfoliated graphite.

7. An injector according to any of claims 1 to 6, wherein the or each extruded rod comprises a plurality of passages in the form of caillary bores or narrow slots.

8. An injector according to any of claims 1 to 7, wherein the injector body is a casting made of a cementitious refractory castable.

9. A gas injector for a molten metal vessel, substantially as herein described with reference to and as shown in-the accompanying drawings.

10. Gas injection apparatus for a molten metal vessel, which incorporates a gas injector according to any of claims 1 to 9.

11. A molten metal vessel such as a ladle having an insulating lining, and a gas injector according to any of claims 1 to 9, melt-tightly secured in a receiving opening in the lining.