EP1385920B1

EP1385920B1 - A wall structure for use in a furnace

Info

Publication number: EP1385920B1
Application number: EP02720681A
Authority: EP
Inventors: Anders Ruud; Hogne Linga; Arnstein Fardal; Arnt Johnny Fluge
Original assignee: Norsk Hydro ASA
Current assignee: Norsk Hydro ASA
Priority date: 2001-04-26
Filing date: 2002-04-24
Publication date: 2005-08-17
Anticipated expiration: 2022-04-24
Also published as: WO2002088276A1; CA2445417A1; NO20012044D0; ATE302251T1; CA2445417C; DE60205607D1; DE60205607T2; NO313897B1; EP1385920A1; NO20012044L

Abstract

The present invention concerns a wall structure and a method for constructing such an anchored wall structure. The wall structure is designed for use in a furnace or the similar, where the structure is exposed to cyclical thermal load. The structure consists of a row of individual elements which are placed in the longitudinal direction of the structure and are arranged in one or more courses, one resting on the other. The individual elements may consist of bricks of refractory material and the wall structure may also be provided with internal flue gas ducts. The wall structure is also designed to be able to compensate for longitudinal changes and any vertical changes as a consequence of cyclical thermal load. The wall structure's longitudinal changes are compensated for in a connection (2) arranged at least one end of the wall structure. The structure's individual elements are fixed to each other in the horizontal direction by means of mutually interacting contact elements. This produces a structure which remains stable after repeated thermal cycles, and costs related to restoration and stoppages can be reduced.

Description

The present invention concerns a wall structure for use in a furnace for calcination of carbon blocks as it is mentioned in the preamble of claim 1. Such a wall structure is known from the WO92/227780 A1.

Furnaces for calcination of carbon blocks to be used in the production of aluminium in accordance with the Hall-Héroult process may be designed with several sections arranged in two parallel rows. Such furnaces have a combustion cycle which is moved in relation to the sections as the carbon material is calcinated. The sections are mutually and successively linked by ducts which conduct hot combustion gas or flue gas through the furnace structure. Each section can be divided into several smaller pits by means of flue walls or cassette walls. These flue walls are provided with several flue gas ducts, through which hot gas is conducted in order to be able to transfer heat efficiently to objects placed in the sections so that the calcination process becomes as homogeneous as possible. One problem with such furnaces, in which the flue walls may extend for several metres both vertically and horizontally, is that the walls lose their parallelism over time as a consequence of heating/cooling cycles with large temperature differences. In the worst cases, bowing and creep can cause problems running the furnace in a satisfactory manner. This is on account of leakage and burn-off or problems inserting/removing objects as a consequence of large geometrical deviations in the pits.

CH 258544 shows a furnace in which a partition wall may comprise flue gas ducts (fig. 3). In this solution, an attempt is made to absorb longitudinal changes in the partition wall as a consequence of thermal heating/cooling in vertical joints between each brick, while the wall ends are fixed in place. One problem which will arise over time when using this principle for expansion/contraction is that particles from material placed in the furnace may be deposited in the joints and prevent the intended expansion fully or partially. If the wall has a certain clearance between where it is fixed and the rest of the structure of the furnace, this clearance will gradually be used up as the partition wall is extended permanently as a consequence of the stated mechanism. Over time, therefore, a structure of this type may bow and lose its parallelism. Further problems which may arise are that bricks may be crushed fully or partially if the necessary expansion is not permitted after a given number of thermal cycles. A subsequent collapse of brick work may thus occur, which will give rise to expensive repair work and put the furnace fully or partially out of operation for a period of time.

It is the object of the present invention to provide a wall structure with which the expansion or contraction of the wall structure in its longitudinal direction as a consequence of thermal cycles will be compensated while bricks are mutually locked to each other, whereby a wall structure is provided which is very stable over repeated temperature cycles and with which the costs related to restoration of brick work and possible stoppages of the furnace can thus be reduced considerably.

This object is obtained by a wall structure as it is defined in claim 1.

Specific embodiments of the wall structure according to the present invention are subject-matter of claims 2 to 7.

The present invention will be described in further detail in the following by means of examples and figures, where:

Fig. 1 show, in sections from above, details concerning the fixing of one end of a partition wall in relation to adjacent brickwork,

Fig. 2 shows, in sections from above, two parallel partition walls fixed at their ends to adjacent brickwork,

Fig. 3 shows a detail of the fixing of the ends of the partition walls,

Fig. 4 shows a detail of the end of the partition wall,

Fig. 5 shows another detail of the end of the partition wall,

Fig. 6 shows a detail of the structure of the partition wall.

Figure 1 shows, in sections from above, brickwork 1, which may be a head wall in a furnace which may be built up from a row of individual bricks. The brickwork shown in the figure is adapted for the fixing of partition walls 3', 3", 3"', 3"" (only four are partially shown in the figure). The connection 2 between the partition wall 3' and the brickwork 1 is shown in an enlarged section in the lower part of the figure. This section shows an end brick 4 in the partition wall 3', a wedge brick 6 and an anchor brick 5 which constitutes part of the brickwork 1 and is permanently fixed to it. The wedge brick 6 may expediently have a rectangular cross-section and have side surfaces 10, 10' which interact with the

respective surfaces

8, 9 and 8', 9' of the end brick and anchor brick. The anchor brick 5 and end brick 4 are mutually movable and expansion of the partition wall of which the end brick is a part is permitted via the expansion joint 7 between the end surface 14 of the wedge brick and the surface 11 of the end brick. Contraction, which may occur in the wall structure, can be compensated for in that the end brick 4 is permitted to move away from the anchor brick 5 while the connection via the wedge brick 6 is maintained. In an alternative embodiment, the connection may consist of only two elements, i.e. without the wedge brick, in that a shape equivalent to the wedge brick is made as an integral part of either the anchor brick or end brick. The size of the expansion joint 7 is adjusted according to experience, depending on the brick material, operating conditions with the application in question or other conditions. The same will apply to the longitudinal contact in the connection 2 with regard to contraction of the wall structure.

It is expedient for the interacting surfaces in the connection 2 to run along the full vertical extent of the partition wall, i.e. all courses of bricks in the partition wall and equivalent courses in the brickwork are designed in the way shown in the figure. One advantage of such a design is that variations in the length of the wall structure, including in its vertical direction, can be absorbed in the connection 2.

In the example shown in the figure, the

adjacent surfaces

13, 12 on the anchor brick 5 and end brick 4 respectively are designed with chamfor so that the surfaces create a V-shape. The aim of such a V-shape is that particle material which may lie against the partition wall and which consequently may be pressed in against the connection can be drained out of this area in connection with an expansion (extension) of the partition wall. It is also advantageous for the surfaces to have a V-shape during emptying/cleaning of the section. The angle between the surfaces may expediently be 30° or more. The size of this angle will, among other things, depend on the material to be drained away and the surface pressure for which the surfaces are designed. Moreover, the connection 2 will comprise surfaces which form a seal to the extent that no problems will arise with the penetration of material into the connection during a contraction-related movement of the end brick 4.

Figure 2 shows, in sections from above, two

parallel partition walls

114, 115 which are fixed at their ends to

adjacent brickwork

101, 102. In this embodiment, the connections are designed so that the

anchor bricks

103, 104, 105, 106 are shaped in such a way that the wedge brick forms an integral part of the anchor brick. The anchor bricks thus interact directly with the

adjacent end bricks

107, 108, 109, 110.

The figure shows that the pattern for bricks in the course in partition wall 114 is different from that in partition wall 115 with regard to the design of the bricks. In the first partition wall, end brick 107 has one flue gas duct 111, while end brick 108 in partition wall 115 has two

flue gas ducts

112, 113. An equivalent arrangement is shown at the other ends of the partition walls. Moreover, brick 116 with

flue gas ducts

118, 119 in partition wall 114 has the same design as brick 117 with

flue gas ducts

120, 121 in partition wall 115, but the horizontal position in the respective walls is different.

By laying alternating courses equivalent to that shown in the section of partition wall 114 and that shown in the section of partition wall 115 over each other when building up the partition walls, the bricks will be anchored to each other via courses of bricks above and below each other by means of interacting contact elements, among other things by means of the design of the flue gas ducts. This will be illustrated in further detail in figures 4-6.

Figure 3 shows details of the fixing of the ends of the partition walls, more precisely an expedient design of an anchor brick. The upper part of the figure shows, in perspective, the lower side of a brick 150, while the lower part of the figure shows, in perspective, the upper side of an equivalent brick 150'. The bricks' external shapes correspond to that shown in earlier figures, but figure 3 also shows interacting elements which are designed to ensure mutual retention between the different courses of anchor bricks. In the example shown, anchor brick 150 is provided with rotationally symmetrical recesses 151 which interact with the rotationally symmetrical bosses 151' in anchor brick 150'. It is expedient for the interacting elements to have a semi-spherical shape or rounded cone shape. However, other geometrical shapes may also be used. As the figure also shows, the bricks' protruding parts 153, 153' (equivalent to the integral wedge brick in 6 in figure 1) are provided with interacting elements 152, 152'. In the embodiment shown, the element 152 consists of a rotationally symmetrical recess, while the equivalent element 152' consists of a rotationally symmetrical protrusion. It is expedient for these elements to have a mainly cylindrical shape. A structure of anchor bricks as shown here will produce stable brickwork in which forces which may arise locally in, for example, one or more bricks, can be distributed partially to bricks in courses above and below. This will be particularly favourable for the protruding parts of the bricks, where, for example, forces which arise on the protruding part 153 on brick 150 can be distributed to the underlying brick 150' via interacting elements 152, 152' and, in equivalent fashion, to any brick above (not shown).

Figure 4 shows a brick equivalent to brick 107 as shown in figure 2. The upper part of the figure shows the brick from above. The lower part of the figure shows the brick in a section from the side. The figure shows the flue gas duct 111, which, at its top, has a raised end 200 and, at its lower part, has a recess 201. The raised end 200 is adapted to an equivalent recess in a brick designed to be placed on brick 107, while the recess 201 is designed to fit on a raised part of an underlying brick (not shown). The raised ends and recesses will contribute to the flue gas duct having a sealed connection between the courses and they will contribute to a good mutual anchoring of the bricks. Moreover, the brick 107 may be provided with transverse tongue 202, 202' at its top and equivalent transverse recesses 203 at its bottom for further stabilisation of the brick.

Figure 5 shows a brick equivalent to brick 108 in figure 2. The upper part of the figure shows the brick from above and the lower part of the figure shows the brick in a section from the side. The figure shows

flue gas ducts

112, 113, which, at their top, have raised ends 250, 251 and, at their lower parts, have

recesses

252, 253. The raised ends 250, 251 are adapted to equivalent recesses in one or two bricks designed to be placed on brick 108, while the

recesses

252, 253 are designed to fit on raised parts of one or two underlying bricks (not shown). The raised ends and recesses will contribute to the flue gas ducts having a sealed connection between the courses and they will contribute to a good mutual anchoring of the bricks. As in the previous figure, the brick 108 may be provided with transverse tongues 254, 254' at its top and equivalent transverse recesses 255 at its bottom for further stabilisation of the brick.

Figure 6 shows a brick equivalent to brick 116 in figure 2. The upper part of the figure shows the brick from above and the lower part of the figure shows the brick in a section from the side. The figure shows

flue gas ducts

118, 119, which, at their top, have raised ends 300, 301 and, at their lower parts, have

recesses

302, 303. The raised ends 300, 301 are adapted to equivalent recesses in one or two bricks designed to be placed on brick 116, while the

recesses

302, 303 are designed to fit on raised parts of one or two underlying bricks (not shown). The raised ends and recesses will contribute to the flue gas ducts having a sealed connection between the courses and they will contribute to a good mutual anchoring of the bricks. However, it may be necessary to use mortar or a sealing compound for further stabilisation of the connections between the bricks.

Although the examples show partition walls with flue gas ducts, equivalent advantages and principles to those in the present invention may also be exploited for wall structures without ducts running through them, where the structure is exposed to large thermal loads in another way. This may, for example, be the case for wall structures installed inside a furnace chamber in order to divide the chamber.

In the embodiments shown, the contact elements are designed so that protrusions are arranged on the top of the bricks, while recesses are arranged on the bottom of the bricks. However, it would also lie within the framework of the present invention if the protrusions were arranged on the bottom and the recesses on the top or possibly if a combination of these were used.

In accordance with the present invention, the movements which arise in the wall structure are mainly absorbed at at least one end, which may be fixed against other brickwork in a furnace. A certain relative movement must also be permitted between the wall structure and its underlying structure, for example a fixed floor structure.

Claims

A wall structure for use in a furnace for calcination of carbon blocks, where the wall structure is exposed to cyclic thermal loads, the wall structure consisting of bricks of refractory material in several courses and comprising internal flue gas ducts, wherein the wall structure is able to compensate for longitudinal changes as a consequence of the cyclic thermal loads, which longitudinal changes are absorbed by a connection (2) at at least one end of the wall structure,
characterised in that
the bricks in adjacent courses are offset in relation to each other and at least two of them (107, 108, 116, 117) comprise contact elements (200, 250, 251, 300, 301) interacting with complementary contact elements (201, 252, 253, 302, 303) of the bricks in the adjacent course, wherein the contact elements (200, 250, 251, 300, 301; 201, 252, 253, 302, 303) being raised ends and recesses of the ends of the flue gas ducts respectively arranged in the bricks (107, 108, 116, 117).
A wall structure in accordance with claim 1,
characterised in that
the connection (2) comprises at least one end brick (4) and one anchor brick (5) arranged for mutual movement in the longitudinal direction of the wall structure.
A wall structure in accordance with claim 2,
characterised in that
the connection (2) is also designed for movement between the end brick (4) and the anchor brick (5) in the vertical direction.
A wall structure in accordance with claim 2 or 3,
characterised in that
the end brick (4) and anchor brick (5) are connected to each other by means of a wedge brick (6).
A wall structure in accordance with claim 4,
characterised in that
the end brick (4), anchor brick (5) and the wedge brick (6) are provided with interacting connecting surfaces which are mainly parallel to the longitudinal direction of the wall structure.
A wall structure in accordance with claim 2,
characterised in that
the anchor brick (5) is permanently connected to brickwork, such as a head wall, and is also provided with contact elements at its top and bottom.
A wall structure in accordance with claim 2,
characterised in that
the anchor brick (5) and end brick (4) are designed with surfaces (13, 12) which mutually form a V-shape for drainage of any material away from the connection (2).