Patent Application
20180087121
The present invention concerns a lance for injecting a fluid or solid particulate material into a metallurgical vessel suitable for the refining process of metals production such as pig iron, steel, or ferronickel. In particular, it concerns a lance having a specific design yielding a higher resistance to cracks formation caused by thermal gradients. The present invention also concerns a process for producing such lance.
Metal production often requires injection of a fluid, generally a gas with or without solid particulate material, for example for refining process of pig iron and steel production. As illustrated in
As illustrated in
The coefficient of thermal expansion of steel can be about two orders of magnitude higher than the thermal expansion coefficient of refractory materials usually used for manufacturing such lances. The difference in coefficients of thermal expansion and the variation of strong temperature gradients generate substantial differences in thermal expansions between the steel inner tube and the refractory sheath material. Since no relative movement between the inner tube and outer refractory sheath is possible at the level of the anchoring elements, substantial shear stresses between the inner tube and the refractory sheath material are created during use. As a consequence, cracks are formed in the refractory material as illustrated in
In order to decrease the cracks in the refractory sheath, DE-U1-29705901 proposes a lance made of a thin inner metal tube in close contact with the refractory sheath reinforced by anchor nodes and a metal rod of a smaller diameter than the inner tube, the rod being centered inside the interior space of the inner metal tube and is welded to the inner metal tube through four protrusions close to the lower end of the metal tube. The rigidity of the lance is conferred by the metal rod. Argon is flushed in the cavity created between the inner tube and the metal rod. As the thickness of the inner tube wall is small, the flushing of the gas cools down the wall and prevents to a certain extent the inner tube from expanding axially. The results are however unsatisfactory because the inner tube is still in close contact with the refractory sheath.
An alternative coupling of the inner tube to the refractory sheath is proposed in GB-A-2107034 allowing a reduction of crack formation compared with traditional lances, such as disclosed in EP-A1-2712938 cited supra. An outlet end of the inner tube is provided with anchoring hooks welded around the circumference of the inner tube. The anchoring hooks are embedded in the refractory sheath and prevent the refractory sheath from sliding out of the inner tube. A number of individual (single) coil steel springs are distributed along the rest of the embedded portion of the inner tube to stabilize the inner tube inside the refractory sheath. Whilst the anchoring hooks are fixedly attached to the tube, the coil steel springs afford axial movement of the tube relative to the coil springs. The coils of the springs are a close fit on the inner tube so that they grip the tube which is thus maintained in its axial position. Radially extending members are provided by the free ends of each spring coil and are embedded in the refractory material of the sheath. They can act as levers to assist in splaying the turns of a coil and thus enable a spring to be moved freely into position along the length of the tube and, upon release, the coil is retracted and the spring firmly grips the inner tube.
In a preferred embodiment of the lance disclosed in GB-A-2107034, a sleeve of insulating material, such as ceramic fibers in a bonding matrix, is provided between the tube and the refractory sleeve, either as a sleeve of material extending continuously along the length of the tube or as a series of shorter sleeves extending between the anchoring means. Alternatively, cardboard or other combustible material sleeves can be provided between the refractory sleeve and the tube. During use of the lance, the cardboard or other material will burn away to form an air gap between the refractory sleeve and the tube.
The concept proposed in GB-A-2107034 of providing an inner tube with fixed anchors located solely at the outlet end of the inner tube, and a series of sliding anchors distributed over the remaining length of the inner tube is theoretically interesting as it allows the steel of the inner tube and the refractory material of the sheath to expand relatively freely from one another in response to temperature gradient variations, without building up any substantial shear stresses. The reduction to practice of said concept as disclosed in GB-A-2107034, however, is far from satisfactory for the following reasons. The coils of the springs are already close fit on the inner tube before casting the refractory material of the sheath. When the refractory sheath is formed and set, the coil springs are embedded in said refractory material and the extending members thereof cannot move anymore to splay the coil of the spring. Upon use, the temperature, T1, of the inner tube and coil springs will raise and will thus expand radially. The coil springs, on the other hand cannot expand more than allowed by their being embedded in the refractory material. It follows that the grip of the coil springs on the inner tube becomes so tight that in practice no movement of the inner tube is possible anymore with respect to the refractory sheath. Consequently substantial shear stresses build up as in traditional lances, leading to early crack formation.
There therefore remains a need for a lance for injecting a fluid into a metallurgical vessel which is more resistant to crack formation than henceforth achieved. The present invention proposes a solution to this problem with a novel and original concept of lance design. These and other advantages of the present invention are described with more details in the following.
The present invention is defined in the attached independent claims. Preferred embodiments are defined in the dependent claims. In particular, the present invention concerns a lance for top injection of a fluid or particulate material in metallurgical vessels, wherein the lance comprises:
In some cases, a thermally degradable material, mechanically removable material, and/or thermally removable material can be present in the annular gap. In some cases, a material selected from any of thermally degradable material, mechanically removable material, thermally removable material, and a combination of any of these materials can be present in the annular gap. This is the case if the lance has not been exposed to high temperatures or mechanical stresses sufficient to remove all such materials from around the inner tube. For example if a lance has not been fired and has not been used in a metallurgical vessel, the whole volume of the annular gap will be filled with such material. Alternatively, after use of a lance, temperature conditions may not have been sufficient to remove the whole of said materials, leaving some fragments in the annular gap. The same may apply to the outer surface of the annular portion and/or some portions of the anchor protrusions which may be at least partially covered with a layer of thermally degradable or thermally removable sheet material.
The maximum width of the annular gap may be from and including 0.5 mm to and including 15 mm, from and including 1 mm to and including 10 mm, or from and including 2 mm to and including 5 mm. The annular gap may be homogeneous over the whole circumference of the inner tube, and such result is generally achieved with production methods as described below. But since the inner tube may move in the radial direction within the space defining the annular gap, it cannot be assured that the inner tube will always remain co-axial with the annular gap. In order to restrict the freedom of movement of the inner tube within the annular gap, annular guides can be used. To fulfil this function, the guide gap defined between the inner surface of the annular portion of an annular guide and the outer surface of the inner tube may be smaller than or equal to the annular gap. The maximum width of the guide gap may be smaller than the maximum width of the annular gap and may have a value from and including 0.5 mm to and including 10 mm, or from and including 1 mm to and including 5 mm.
The annular portion of the annular guide may form a closed loop Alternatively, the annular portion of the annular guide forms an open loop with a slit of width of not more than 40% of an inner perimeter of the annular portion. The latter configuration can be advantageous in that it requires less material, and in that the inner diameter of the annular portion can be resiliently varied by increasing or decreasing the width of the slit.
In many lances, an outlet portion of the inner tube adjacent to and including the tube end is coupled to one or more outlet tubes extending from the inner tube, through the refractory sheath to the gas outlet(s) bringing an inner bore of the inner tube in fluid communication with the exterior of the lance. This design allows to orient the flow(s) of gas and/or particles in different directions, and reduces exposure of the inner tube to the high temperatures of the metallurgical vessel.
A single anchoring point may be coupled to said inner tube, to give freedom to most of the embedded length of the inner tube to move longitudinally with respect to the refractory sheath when exposed to temperature gradients. In case several anchoring points are distributed along the length of the inner tube surrounded by the refractory sheath, it is necessary that the coupling locations to the inner tube of the two anchoring points most remote from one another in the longitudinal direction, X1, are separated by a distance, L0, wherein L0≦5.5 10−6/α [m], wherein α is the coefficient of thermal expansion of the inner tube. In all cases it is necessary that the distance, L0, is in any case not greater than 50 cm.
The single anchoring point or the one of several anchoring points located furthest from the inlet end may be coupled to the inner tube at a location at or adjacent to the tube end. This configuration is advantageous for the following reasons. It is well known that refractory materials have better resistance in compression than in tensile mode. Since the lance is generally held in working position by clamping a top portion of the inner tube jutting out of the refractory sheath, in use the weight of the refractory sheath located upstream from the anchor point rests on the anchoring point and is being compressed. The portion of refractory exposed to tensile stresses is the portion extending downstream from the anchoring point. By locating the anchoring point near the tube end of the inner tube, most of the refractory material is located upstream from the anchoring point and is compressed, whilst the portion of refractory material located downstream of the anchoring point, exposed to tensile stresses generated by its own weight is substantially smaller (and lighter).
The anchor protrusions may comprise two portions transverse to each other. For example they can define a T-shape, V-shape, X-shape, or Y-shape in order to create a strong anchor in the refractory sheath.
The present invention also concerns a process for manufacturing a lance as defined above, comprising the following steps:
A lance as defined above can also be produced by an alternative process comprising the following steps:
The thermally degradable material or thermally removable material of the tubular spacers or of the sheet material can be thermally degraded or removed and at least partially disappears from the outer surface of the inner tube during either firing of the lance or upon dipping the lance into a metallurgical vessel, such that:
Either of the two processes defined above may further comprise a step of applying thermally degradable or thermally removable sheet material onto at least a portion of said at least two anchor protrusions and/or of the outer surface of said annular portion of the annular guides. Removal of this material forms a gap allowing for some radial expansion of the annular portion of the annular guides.
In addition to the cracks due to thermal cycles and different expansion coefficients of the refractory sheath and of the inner tube, small cracks resulting from clumsy handling during transportation can occur. Cracks can also be created in the area of the bath level of the molten metal: as the gas flushes in the molten metal bath, the bubbles rise along the lance and burst at the surface of the molten metal bath creating a turbulence. High mechanical forces are generated due to the splashing molten metal, creating new cracks or increasing the size of the existing cracks by the infiltration of molten metal. Sometimes, the radial cracks are very deep and result in the splitting of the refractory sheath into two parts. As the density of the refractory sheath is lower than the density of molten metal, the detached upper part of the sheath floats up as there is no more connection with the inner tube. The inner tube is then no longer protected and enters in contact with the molten metal and eventually melts down. The lower part of the lance is lost in the bath.
In order to prevent any split of the lance in such a case, an advantageous embodiment of the invention comprises a pusher and a blocking element. The blocking element is rigidly coupled to the inner tube in a portion of said inner tube at a distance from the anchor level greater than L1 and the pusher is elastically attached to the blocking element, the pusher being adapted to push the refractory sheath along the direction of the longitudinal axis X1. In another embodiment, the pusher comprises a contact element adapted to contact the surface of the refractory sheath opposite to the anchor level and is attached to the blocking element by one or more resilient elements.
The inner tube (1) is partially embedded in a refractory sheath (2) made of a refractory material surrounding the inner tube (1) from the tube end (1d) over a length, L1≦L, of the inner tube. In use, the refractory sheath (2) protects the inner tube (1) from any contact with molten metal which would inevitably degrade the inner tube due to the high temperature of the molten metal. It acts as an insulating sleeve. Crack formation in the refractory sheath must be prevented as the formation of cracks is detrimental to the insulating function of the sheath. If a crack propagates as far as the inner tube, molten metal may penetrate and contact the inner tube, thus forming a thermal bridge and corresponding high temperature region in the inner tube, which would rapidly degrade the inner tube.
A lance is usually held in substantially vertical operating position with holding means (22) (visible in
Often, the outlet (1t) does not correspond to the tube end (1d). The outlet (1t) is then provided at an end of one or more outlet tubes (6) coupled to and extending from the inner tube, through the refractory sheath to an outer surface of the refractory sheath and forming the gas outlet(s) (1t) bringing the inner bore of the inner tube in fluid communication with the exterior of the lance. The outlet tube(s) (6) are located at or adjacent to the tube end (1d). The expression “adjacent to the tube end” is meant here to mean within 10% of L1 from the tube end, not further than 50 cm, or not further than 30 cm from the tube end (1d). If more than one outlet tubes (6) are transverse to the longitudinal axis, X1, and if they are mechanically strong enough, the outlet tubes can act as anchoring points (4) as illustrated in
A single anchoring point (4) is preferred. Several anchoring points (4) can be used, as illustrated in L0≦5.5 10−6 m K−1/(1 to 1.3 10−5 K−1)=0.42−0.5 m. The distance, L0, between the two anchoring points most remote from one another measured in the direction of the longitudinal axis, X1, may have a value not greater than 0.5 m (L0≦0.5 m). With such constraint on the length, L0, of the anchoring level, the refractory sheath can be safely secured to the inner tube and, at the same time, the thermally induced length variations of the anchoring level are negligible in comparison with the thermally induced length variations over the rest of the inner tube.
The single anchoring point (4) or the one of several anchoring points located furthest from the inlet end (1u) may be coupled to the inner tube at a location at or adjacent to the tube end (1d). The case wherein outlet tubes (6) act as anchoring points (4) discussed supra and illustrated in
The refractory sheath (2) is separated from the inner tube (1) by an annular gap (1g) extending over a length, Lg, which is at least 50% of L1. The maximum width of the annular gap (1g) may be from and including 0.5 mm to and including 15 mm, from and including 1 mm to and including 10 mm or from and including 2 mm to and including 5 mm. The annular gap defined by an outer surface of the inner tube and an opposite inner surface of the refractory sheath, allows said outer surface of the inner tube to move relative to said inner surface of the refractory sheath without generating substantial shear stresses. It follows that it is advantageous to have a gap length, Lg, as long as possible, to reduce the portion of contact between the inner tube and refractory sheath forming an interface in portions of the lance exposed to high thermal gradients. For example, it is advantageous that Lg is at least 60% of the length, L1, of inner tube embedded in (or surrounded by) the refractory sheath (Lg≧0.6 L1), or at least 75% of L1 (Lg≧¾ L1). It should be noted that the term “embedded” is used herein to encompass both the case wherein the inner tube and refractory sheath contact each other forming an interface, and the case wherein they are separated by a gap (1g).
Before firing of the refractory sheath, the annular gap may be filled by a thermally degradable material or thermally removable material. This thermally degradable material or thermally removable material will be discussed more in detail below with respect to the process for producing a lance according to the present invention. In brief, the thermally degradable material or thermally removable material is removed from the annular gap by degradation, melting, vaporization, combustion or dissolution during firing of the refractory sheath, if it applies, or during use in a metallurgical installation (in some cases the refractory sheath is not fired). Even after firing or use, some scraps of said thermally degradable material or thermally removable material may still remain in the annular gap, but at least 80% of the volume of the annular gap should be free of such material during use, in order for a lance according to the present invention to reach its full potential.
The annular gap (1g) together with anchoring points concentrated solely at a single anchor level of length, L0, as discussed above, along the length of the inner tube, allows a movement of the inner tube relative to the refractory sheath over the whole length thereof excluding the anchor level. This geometry as such would, however, be unstable because in use the long portion of tube un-coupled to the refractory sheath (i.e., excluding the anchor level) would vibrate and hit the refractory wall defining the annular gap (1g), thus causing cracks in the refractory material.
In order to stabilize the lance, it must comprise at least one annular guide (5) surrounding the inner tube and located within the length, Lg, of the annular gap (1g).
As shown in
The anchor protrusions can have different geometries, as long as they protrude out of the outer surface of the annular portion (5A) of the annular guide, and can thus be embedded in the refractory material of the sheath. In particular, the anchor protrusions (5P) generally comprise two portions transverse to each other, advantageously defining a T-shape (cf.
In one embodiment the annular guide is provided with two anchor protrusions (5P) separated from one another by an angle comprised between 90 and 270° (cf.
By contrast with the lance disclosed in GB-A-2107034, wherein the coil springs are a close fit on the inner tube, in a lance according to the present invention a guide gap (5g) is provided between the inner tube and the annular portion (5A) of the annular guides (5). The guide gap (5g) must be present between at least 50% of the inner surface of the annular portion and an outer surface of the inner tube. Ideally, the guide gap (5g) extends over the whole perimeter of the annular portion (5A) and inner tube (1). The guide gap (5g) ensures that the inner tube can move freely with respect to the annular guide along the longitudinal direction, X1, without generating substantial shear stresses in the refractory material. The maximum width of the guide gap (5g) is preferably smaller than the maximum width of the annular gap (1g). The maximum width of the guide gap (5g) may be comprised from and including 0.5 mm to and including 10 mm, or from and including 1 mm to and including 5 mm.
As illustrated in
The inner surface of the annular portion (5A) can be provided with at least two, or three (or more) centering elements (5C) illustrated in
There can be as few as a single annular guide (5) located at a distance, such as at least L1/2, from the anchoring level, as illustrated in
A lance according to the present invention can be produced by a process comprising the following steps, illustrated in
As shown in
This process has the advantage that the width of the guide gap (5g) can be controlled independently of the width of the annular gap (1g). It is preferred that the guide gap (5g) be smaller than the annular gap (1g); so that the annular guides (5) restrict the radial movements of the inner tube but not the longitudinal movements. Another advantage of this process is that by resting on the upper edge of a tubular spacer, an annular guide (5) is maintained in good alignment with the longitudinal axis, X1, although the production process of the lance.
The thermally degradable or thermally removable sheet material can be any material that is combusted at temperatures of the order of 600-1000° C. It may consist of paper or cardboard, a polymer sheet, and the like. The sheet material can also be melted or vaporized at such temperatures. For example a wax or low melting temperature thermoplastic material can be used, such as a polyolefin.
The mechanically degradable material can be any brittle material that will lose mechanical coherence upon application of a shear stress, in particular provoked by the differing thermal variations between the inner tube (1) and the refractory sheath (2) upon exposure to temperature variations during use of the lance.
In an alternative process illustrated in
The thermally degradable or thermally removable sheet material (11W) is preferably compressible in thickness, For example, a corrugated cardboard sheet material can be used or, alternatively a synthetic foam material. In this embodiment, it is preferred to use annular guides (5) with an open loop shaped annular portion, such that the slit (5S) can be increased by application of a circumferential stress when inserting the annular portion through the inner tube wrapped with the compressible sheet material (11W) to increase the breadth of the opening of the annular portion. Upon releasing the stress, the annular portion returns to its nominal diameter which is smaller than the diameter of the inner tube wrapped with the sheet material (11W), such that the compressible sheet material is compressed by the annular portion (5A). After degradation or removal of the sheet material (11W) a guide gap (5g) of width smaller than the width of the annular gap (1g) can thus be obtained.
Regardless of which of the two processes described above and illustrated in
In case the refractory material does not require firing, the degradation or disappearance of the sheet materials discussed supra may happen during use of the lance for the first time dipped in a bath of molten metal.
The refractory cement is shown in
With the present invention a lance for injecting a fluid with or without a solid particulate material into a metallurgical vessel filled with molten metal has a substantially longer service life than henceforth achievable. In spite of the severe thermal cycles a lance undergoes during its use, the shear stresses mainly due to thermal dilatation mismatches between the metal inner tube and refractory sheath are avoided, thus maintaining the refractory material integrity for a longer time, which can thus protect the inner tube.
Numerous modifications and variations of the present invention are possible. It is, therefore, to be understood that within the scope of the following claims, the invention may be practiced otherwise than as specifically described.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15163822.8 | Apr 2015 | EP | regional |
| 15202638.1 | Dec 2015 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP16/58179 | 4/14/2016 | WO | 00 |
