WO2005052480A1

WO2005052480A1 - Method of providing a silica refractory structure and use thereof

Info

Publication number: WO2005052480A1
Application number: PCT/GB2004/004533
Authority: WO
Inventors: Reiner Linden
Original assignee: Fosbel Intellectual Limited
Priority date: 2003-10-30
Filing date: 2004-10-28
Publication date: 2005-06-09
Also published as: GB0325319D0

Abstract

A method of providing a silica refractory structure in a working environment at a temperature in excess of substantially 873 K, which comprises providing a assembly of at least two vitreous silica bricks (5,6’,7’,8,’) connected into adjacent position by at least one complementary interlocking formation (9,11,12,13) and projecting on this assembly a powdery mixture comprising finely divided particles of exothermically oxidisable material and particles of silica incombustible refractory material and burning said powdery mixture during its projection.

Description

Method of providing a silica refractory structure and use thereof .

FIELD OF THE INVENTION The present invention relates to a method of providing a silica refractory structure in a working environment at a temperature in excess of 873 K (600°C) .

BACKGROUND OF THE INVENTION Principal uses of silica refractories are in steel furnaces, coke ovens, gas retorts, glass tank •furnaces and pottery or enamel furnaces . In the course of time, silica refractory structures in ovens or furnaces deteriorate for one reason or another, and they consequently require repair. Large furnaces take several days to cool to ambient from their working temperature, and they require a similar reheating time because the silicon dioxide in their structure, present in cristobalite and tridymite form is extremely sensitive to thermal shock at temperatures between 20°C and 600°C. In particular, cristobalite is characterised by a crystalline inversion, generally between 200°C and 250°C, which is accompanied by a change in length of about 1%. It is accordingly desirable to effect any necessary repair while the silica refractory structure is hot. Unfortunately, the sensitivity of conventional refractory silica bricks to thermal shock effectively prevents their use in hot repair work unless they have been preheated. It will be appreciated that such preheating is also time-consuming. It will be understood that it is necessary that a silica refractory wall should be repaired with silica refractory and not some other material in order to achieve compatibility, inter alia, of rates of expansion and thermal conductivity as between the repair and the original brickwork. Hot repairs have in the past been carried out according to a method using vitreous silica bricks. Vitreous silica has indeed a very small coefficient of thermal expansion so that bricks at ambient temperature can be transferred immediately to the hot repair site without any substantial risk that they will crack due to thermal shock. The bricks are laid and their interstices are packed with granular refractory material to hold them in position. Such thermal expansion of the bricks as does take place further compresses the packing granules. Unfortunately, operating according to this system does not result in a very high quality repair, since the interstices between the vitreous silica bricks are not airtight. This is of very considerable importance in the case of coke ovens because of the different gas compositions inside and outside such ovens and is also important for example when repairing the roof of a glass melting tank furnace. Any flame which penetrates an interstice in the roof of such a furnace will rapidly erode the surrounding material so that further repair is soon required. To obviate disadvantages of this known method it has been proposed in GB-A 2 138 927 (Glaverbel) to bond the vitreous silica bricks into position by projecting a powdery mixture comprising finely divided particles of exothermically oxidisable material and particles of silica incombustible refractory material and burning the powdery mixture during its projection to form a coherent refractory mass which effects such bonding.

SUMMARY OF THE INVENTION This invention aims to improve the repairing method of GB-A 2 138 927 to make it more efficient, less time-consuming and less material-consuming and to allow repairs of better quality. More generally it is an object of this invention to provide an improved method of providing a silica refractory structure in a working environment at a temperature in excess of 873 K (or 600°C) which overcomes ^' the disadvantages of the known method explained hereabove . A particular object of this invention is to furnish an improved method of providing a silica refractory structure in an industrial furnace or oven while maintaining this furnace or oven at substantially working temperature . A further object of this invention is to furnish an improved repairing method of furnaces or ovens, which allows maintaining these furnaces or oven at substantially working temperature. Accordingly the present invention relates to a method of providing a silica refractory structure in a working environment at a temperature in excess of substantially 873 K, which comprises bonding a assembly of at least two vitreous silica bricks, having at least one complementary interlocking formation, into adjacent position by projecting on this assembly a powdery mixture comprising finely divided particles of exothermically oxidisable material and particles of silica incombustible refractory material and burning said powdery mixture during its projection to form -a^' coherent refractory mass which effects such bonding. In this specification the expression "silica refractory" is used herein in the sense used in British Standard 3446 to define "silica refractory" as a refractory material which, in the fired state, contains not less than 92% Si0₂ by weight. In the meaning of this invention a silica refractory structure may concern any structure of an industrial apparatus, such as an outer or inner wall of a furnace or oven, a chimney, a funnel, a liquid- or gaseous-fuel burner or any other duct or chamber adapted to contain or to be in contact with hot gas, liquid or solid material. Outer and inner walls of a furnace or oven may comprise lateral walls (either vertically or obliquely directed) , a roof or a hearth of this furnace or oven . The working environment may be as well a liquid environment as a gaseous environment. This environment is at a temperature in excess of substantially 873 K. A temperature in excess of substantially 873 K means a temperature above which the silicon dioxide in its cristobalite and/or tridymite form is substantially not sensitive to thermal shock when heated or cooled. The optimum temperature in excess of substantially 873 K will thus depend on the silica refractory, notably its content in silicium dioxide and it may be determined in each particular case by one skilled in the art. In the method according to the invention the shape and dimensions of the bricks is not critical and depend on the apparatus, furnace, oven or any other application of the invention. The bricks are made of vitreous silica. Vitreous silica (sometimes called fused silica) is well known in the art . In the method according to the invention, two (or more) bricks made of vitreous silica are positioned adjacently and bonded together by a coherent silica refractory mass formed in situ on at least a portion of the assembly of bricks. Vitreous silica has a small coefficient of thermal expansion and is accordingly not susceptible to degradation by a thermal shock when heated. The bricks of vitreous silica may thus simply be positioned at ambient temperature, in contact with an environment at elevated temperature (in excess of 873 K (or 600°C) such as the atmosphere inside an industrial furnace while in operation. To have these bricks bonded together, a powdery mixture including finely divided silica and a finely divided exothermically oxidisable material is projected against the brick assembly and burnt during projection so that under the heat of combustion of the exothermically oxidisable material a coherent refractory mass is formed in situ on the brick assembly. Burning of the powdery mixture is obtained by oxidation of said exothermically oxidisable material at high temperature in the presence of oxygen. Exothermically oxidisable materials are well known in the art and may include inorganic materials as well as organic materials. In the method according to the invention inorganic materials are preferred. Inorganic materials containing metallic compounds are more preferred, metals and metal alloys being still more preferred. Aluminium and silicon are particularly preferred, silicon being the most preferred. The necessary oxygen for burning said exothermically oxidisable material may be provided by atmospheric air which is normally present in the vicinity of the brick assembly or by air or oxygen which is used as propellant ^• of the powdery mixture toward the brick assembly or by any other adequate means. Within a few days of continued exposure to high temperature, the vitreous silica bricks progressively crystallise to silica in its tridy ite and/or cristobalite form. The silica refractory mass formed in situ on the brick assembly will form an effective bond with the vitreous silica brickwork and also with original adjacent silica refractory structure if any and this bond to the vitreous silica brick assembly will remain effective during and after the transformation of said silica brick assembly from its , vitreous to its crystalline form. Details of this method of bonding brick assembly are available in GB-2 138 927 (Glaverbel) and in article "Hot Repair of Glass Furnace" by E.R. Plumat published in "The glass industry", August • 1982, pages 16-20 and 39. According to the invention bricks are selected for said assembly of bricks, which comprise at least one complementary interlocking formation. In this specification the expression "complementary interlocking formation" means that adjacent bricks of the assembly are physically or mechanically interlocked together to prevent a relative displacement of said bricks in one or more directions. Mechanical complementary interlocking formations are well known in the art and normally include two separate elements which are so complementary shaped that they may interlock. Example of mechanical complementary interlocking formations in the meaning of this invention include the assembly of a rib provided on the surface of a brick into a corresponding groove of another brick, or the assembly of a corrugated surface of a brick against a similar corrugated surface of another brick, or the assembly of a series of rods or similar provided on the surface of a brick into corresponding slots provided through the surface of another brick, or a dovetail joint, or an assembly of two or more of these examples of mechanical complementary interlocking formations. The complementary ^' interlocking formation is said an unidirectional complementary interlocking formation or a bi-directional complementary interlocking formation or a tri- (or multi-) directional complementary interlocking formation depending on whether said complementary interlocking formation prevents .a relative displacement of two adjacent bricks in only one direction or in two directions of a plane or in the three directions of the space. Examples of complementary interlocking formations which are convenient for the bricks used in the method according to the invention are available in WO-97/05215. In the method according to the invention said complementary interlocking formation makes easier having the vitreous silica bricks positioned adjacently. In addition, this complementary interlocking formation retains said brick assembly in place and avoids a displacement of said bricks during the projection of the powdery mixture of silica and oxidisable material and the burning (ceramic welding) thereof. An additional and important advantage of said complementary interlocking formation is that this complementary interlocking formation forms cavities within the brick assembly, which receives and retains at least part of said coherent refractory mass and this coherent refractory mass in said cavities acts to improve the solidity of the brick assembly and its i perviousness to liquids and/or gas. The method according to the invention may be used to provide a structure of two or more bricks bonded together by a coherent refractory mass. In the method according to the invention the relative position of adjacent bricks is not critical. In a particular embodiment, the method of this invention is directed to an assembly of at least two adjacent ranges of bricks. In this embodiment of this invention said at least two adjacent ranges of bricks may comprise two adjacent upwardly extending ranges of bricks or two superposed ranges of bricks. In this specification "upwardly extending" means either "vertically extending" or "obliquely extending with an angle less than 45 degrees with the vertical direction" . In another embodiment of this invention specifically directed to an assembly of at least two superposed ranges of bricks said at least one complementary interlocking formation includes an upwardly directed interlocking formation joining each pair of adjacent bricks of each range of bricks. In an alternative embodiment said at least one complementary interlocking formation comprises a longitudinally directed interlocking formation which joins each pair of superposed adjacent bricks. In a preferred embodiment said bricks are provided with at least one upwardly directed complementary interlocking formation and at least one longitudinally directed complementary interlocking formation. In this preferred embodiment said at least one upwardly directed complementary interlocking formation joins each pair of adjacent bricks of each range of bricks and said at least one longitudinally directed interlocking formation joins each pair of superposed adjacent bricks. In the aforesaid another, alternative and preferred embodiments, "upwardly extending" means either "vertically extending" or "obliquely extending with an angle less than 45 degrees with the vertical direction" as explained above and "longitudinally extending" means either "horizontally extending" or "obliquely extending with an angle of at most 45 degrees with the horizontal direction". In an advantageous embodiment of this invention the aforesaid assembly of bricks includes at least two superposed ranges of bricks and said complementary interlocking formation comprises upwardly directed complementary ribs and grooves on adjacent upwardly directed lateral faces of each range of bricks and longitudinally directed complementary ribs and grooves on adjacent superposed faces of said at least two superposed ranges of bricks. In this advantageous embodiments, said superposed ranges of bricks may include two or preferably more than two superposed ranges of bricks . The number of superposed ranges of bricks is not critical to fulfil the invention but depends on the shape and dimensions of the bricks, as well as of the dimensions of the oven, furnace or any other apparatus or device in which this invention is used. In a preferred alternative of this advantageous embodiment of this invention, each of said at least two superposed ranges of bricks comprises two lines of bricks connected by an angle-shaped brick. In this alternative embodiment said angle-shaped brick acts to connect said two ranges of bricks which are extending respectively in two different directions. Said two different directions of both ranges of bricks may be two different upwardly directed directions or two different longitudinally directed directions or an upwardly directed direction and a longitudinally directed direction. "Upwardly" and "longitudinally" have been defined above. A particular application of this preferred alternative of this invention relates to an embodiment which comprises a first set of two superposed ranges of bricks, a second set of two superposed ranges of bricks, a set of two superposed angle-shaped bricks which respectively connect said first set and said second set of superposed ranges of bricks, a first line of longitudinally directed complementary ribs and grooves on adjacent faces of said first set of superposed ranges of bricks, a second line of longitudinally directed complementary ribs and grooves on adjacent faces of said second set of superposed ranges of bricks, and an angle shaped complementary rib and groove on adjacent faces of said set of two superposed angle-shaped bricks. In another preferred embodiment of this invention said at least two adjacent bricks have chamfered edges along their adjacent faces thus forming a gap along said adjacent faces and at least a portion of said powdery mixture comprising exothermically oxidisable material and silica refractory material is projected in said gap. When said assembly of bricks includes at least two superposed ranges of bricks, said chamfered edges and said gap are longitudinally provided along longitudinal adjacent faces of said two ranges of bricks and are so arranged that said gap extends up to but excluding an end limit of said two superposed ranges of bricks.

Alternatively, bricks which are adjacent in each range of bricks may have upwardly directed chamfered edges along adjacent faces thereof thus forming additional upwardly directed gaps in which a portion of said powdery mixture may be projected. A more preferred embodiment of this invention concerns the case where said brick assembly includes at least two adjacent ranges of bricks. In this more preferred embodiment said at least two adjacent ranges of bricks have chamfered edges which are so arranged as to provide a network of transversal gaps on a face of said assembly of bricks and said projecting a powdery mixture on the assembly comprises projecting at least a portion of said powdery mixture in said network of gaps . The method according to the inventions finds use in repairing any industrial or domestic refractory structure, such as an outer or an inner wall of a furnace or oven, a chimney, a funnel, a liquid- or gaseous-fuel burner or any other duct or chamber adapted to contain or to be in contact with hot gas, liquid or solid material. It finds use in repairing or erecting new walls in industrial structures, such as roofs or hearths or upwardly directed walls of ovens or furnaces, such as glass furnaces, coke ovens, blast furnaces, lime kilns, pottery or enamel kilns, as well as furnaces and kilns used in the steel making industry (non exhaustive list) . The invention finds a preferred use in repairing walls in coke ovens or erecting new walls in coke ovens, such as lateral vertical walls and cross-binder walls, and also in replacing defective bricks in fuel burners of coke ovens .

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a 3D view of a portion of an oven incorporating a brick assembly in accordance with a preferred embodiment of the invention; Figure 2 is an exploded view of a detailed portion of the brick assembly of figure 1; Figure 3 is a front view of a wall of the oven of figure 1; Figure 4 is an enlarged view of part of the wall of Figure 3; and Figure 5 is a view of the exterior of an end of the wall of Figure 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The oven of Figure 1 comprise a series of superposed ranges of bricks denoted respectively by the reference numerals 1, 1', 1", 1 " ' and 1 " " . Each range of bricks comprises five lines of bricks, denoted 2, 3 et 4 (range 1); 2', 3'and 4' (range 1'); 2", 3" and 4" (range 1"); 2"', 3"' and 4"' (range 1"'); 2"", 3"" and 4"" (range 1""). Part of range 1' is shown in Figure 2, comprising a series of bricks denoted 5', 6', 7' and 8' respectively. Brick 5' is a brick of line 2' and brick 7' is a brick of line 3'. Bricks 6' and 8' are angle-shaped bricks. Angle-shaped brick 6' connects brick 5' of range line 2' to brick 7' of range line 3' and angle-shaped brick 8 ' connects brick 7 ' of range line 2 ' to a brick (not shown) of range line 4'. Each brick 5 ' , 7 ' of the lines 2 ' , 3 ' has a longitudinal rib 9 on its upper face 10. Each angle- shaped brick 6', 8' has a circular rib 11 on its upper face 10. The circular rib 11 of the angle-shaped brick 6' connects the longitudinal rib 9 of brick 5' with the longitudinal rib 9 of brick 7 ' . Similarly the circular rib 11 of the angle-shaped brick 8' connects the longitudinal rib 9 of brick 7' to the longitudinal rib of a brick (not shown in Figure 2) of line 4' of bricks. The ribs 9 and 11 are engaged in corresponding grooves (not shown in Figure 2) on the respective lower faces of the range 1" of bricks. Similarly said bricks 5', 6', 7', 8' are provided with grooves on their respective lower faces, which are engaged by corresponding ribs provided on the upper face of the respective bricks ^'of the range 1 of bricks . Bricks 5', 6', 7', 8' are further provided with vertical grooves 12 and vertical ribs 13, which are so disposed that ribs 13 of each brick engage corresponding grooves 12 of an adjacent brick. Preferably the vertical rib 13 of each brick is a prolongation of the longitudinal rib 9 or circular rib 11 of the same brick. Similarly the vertical groove 12 of each brick is preferably a prolongation of the longitudinal or circular groove (not shown) of the same brick. Figure 4 shows rib 9 of a brick of line 4"' of bricks received in a groove 17 in the lower face of a brick of line 4"' of bricks, with its vertical groove 12 also being shown. Figures 1 and 3 show the bricks assembled into the superposed ranges 1, 1', 1", 1"', 1"". In this assembly the ribs and grooves 9, 11, 12, 13 interlock and so retain the assembly of bricks in position forming a wall of a cavity (for example a chamber of a coke oven) . In this assembly the outer face of the bricks (i.e. the face which are outside the cavity) is chamfered along adjacent faces forming a network of longitudinal gaps 14 and vertical gaps 15. The longitudinal gaps 14 extend along the entire length of the wall, except at the end 16 thereof as shown in Figure 3. Figure 5 shows that there are no gaps 14, 15 at the exterior of an end wall of the oven. According to the invention a flow of a powdery mixture comprising finely divided particles of silicon and finely divided particles of silica is projected with against the assembly of bricks . Oxygen is used as a propellant. During the projection the particles of silicon burn in contact with the oxygen and the heat of combustion causes silica to fuse. The projection of the mixture is so arranged that by virtue of this ceramic welding a coherent refractory mass of silica is formed on the outer face of the brick assembly and inside the network of gaps 14 and 15.

Claims

1. In a method of providing a silica refractory structure in a working environment at a temperature in excess of substantially 873 K, which comprises bonding a assembly of at least two vitreous silica bricks, having at least one complementary interlocking formation, into adjacent position by projecting on this assembly a powdery mixture comprising finely divided particles of exothermically oxidisable material and particles of silica incombustible refractory material and burning said powdery mixture during its projection to form a coherent refractory mass which effects such bonding.

2. Method according to claim 1, characterized in that said assembly of bricks includes at least two adjacent ranges of bricks.

3. Method according to claim 2, characterized in that said at least two adjacent ranges of bricks include two superposed ranges of bricks.

4. Method according to claim 3, characterized in that said at least one complementary interlocking formation comprises an upwardly directed interlocking formation.

5. Method according to claim 3, characterized in that said at least one complementary interlocking formation comprises a longitudinally directed interlocking formation.

6. Method according to any one of claims 2 to 5 , characterized in that said bricks are provided with at least one upwardly directed complementary interlocking formation and at least one longitudinally directed complementary interlocking formation.

7. Method according to any one of claims 1 to 6, characterized in that said at least one complementary interlocking formation includes complementary ribs and grooves of said bricks .

8. Method according to claim 7, characterized in that said assembly of bricks includes at least two superposed ranges of bricks and in that said complementary ribs and grooves comprise upwardly directed complementary ribs and grooves on adjacent upwardly directed faces of said bricks and longitudinally directed complementary ribs and grooves on adjacent superposed faces of said at least two superposed ranges of bricks.

9.- Method according to claim 8, characterized in that each of said at least two superposed ranges of bricks comprises two lines of bricks connected by an angle-shaped brick.

10. Method according to claim 9, characterized in that said longitudinally directed complementary ribs and grooves comprise a first line of longitudinally directed complementary ribs and grooves on a first set of two superposed ranges of bricks, a second line of longitudinally directed complementary ribs and grooves on a second set of two superposed ranges of bricks and an angle shaped complementary rib and groove on adjacent faces of a set of two superposed angle-shaped bricks connecting said first set and said second set of ranges of bricks .

11. Method according to any one of claims 1 to 10, characterized in that said at least two adjacent bricks have chamfered edges along their adjacent faces thus forming a gap along said adjacent faces and at least a portion of said powdery mixture is projected in said gap.

12. Method according to claim 11, characterized in that in case of said assembly of bricks includes at least two superposed ranges of bricks, said chamfered edges and said gap are longitudinally provided along longitudinal adjacent faces of said two ranges of bricks and are so arranged that said gap extends up to but excluding an end limit of said two superposed ranges of bricks .

13. Method according to claim 12 , characterized in that adjacent bricks in each of said at least two superposed ranges of bricks have chamfered edges along upwardly directed adjacent faces thereof, thus forming additional upwardly directed gaps and in that said projecting a powdery mixture on the assembly comprises projecting a portion of said powdery mixture in said additional upwardly directed gaps .

14. Method according to claim 13, characterized in that said at least two superposed ranges of bricks have chamfered edges which are so arranged as to provide a network of transversal gaps on a face of said assembly of bricks and in that said projecting a powdery mixture on the assembly comprises projecting at least a portion of said powdery mixture in said network of gaps.

15. Method according to any one of claims 1 to 14, characterized in that said finely divided particles of oxidisable material comprises silicon particles.

16. Method according to any one of claims 1 to 15, characterized in that it is used to effect a repair to a wall of a furnace.

17. Method according to claim 16, wherein said furnace is a coke oven.