US3846068A - Refractory structure,particularly for a metallurgical shaft furnace - Google Patents

Abstract

TEMPERATURE RANGE UP TO ABOUT 50* TO 200*C. BELOW THE OPERATING TEMPERATURE OF SAID ELEMENTS.

1. A REFRACTORY BOTTOM STRUCTURE FOR A METALLURGICAL SHAFT FURNACE COMPRISING A PLURALITY OF HORIZONTAL LAYERS OF SEPARATE REFRACTORY BLOCK ELEMENTS, WHEREIN AT LEAST THE UPPER LAYERS THEREOF HAVE AT LEAST PART OF THE REFRACTORY BLOCK ELEMENTS ARRANGED ONE TO THE SIDE OF THE OTHER WITH OPEN EXPANSION JOINTS HORIZONTALLY SPACED BETWEEN THEM, THE WIDTH OF SAID JOINTS WHEN THE BLOCK ELEMENTS ARE IN COLD CONDITION CORRESPONDING TO THE THERMAL EXPANSION OF THE BORDERING REFRACTORY BLOCK ELEMENTS IN THE DIRECTION TOWARDS SAID JOINTS OVER A

Description

United States Patent [191 Van Laar 1 REFRACTORY STRUCTURE,

PARTICULARLY FOR A METALLURGICAL SHAFT FURNACE [75] inventor: Jacobus Van Laar, Santpoort, Netherlands [73] Assignee: Koninklijke Nederlandsche Hoogouens En Staalfabrieken NV.

[22] Filed: Mar. 13, 1972 [21] Appl. No.: 234,138

[30] Foreign Application Priority Data I Mar. 15, 1971 Netherlands 7103442 [52] US. Cl. 432/251, 266/43 [51] Int. Cl. F27d 1/00 [58 1 Field of Search...26 3/46; 266/43; 432051 252 [56] References Cited UNITED STATES PATENTS 1,896,669 2/1933 Frisch et al. 263/46 2,211,127 8/1940 Keydel 263/46 X 7/1966 Freygang 263/46 X 10/1933 MacDonald 263/46 X Primary ExaminerJohn .1. Camby Attorney, Agent, or Firm-Hall & Houghton [57 r1 HACT A refractory bottom structure for a metallurgical shaft furnace is provided which is characterized by having a plurality of horizontal layers of separate refractory block elements in which at least the upper layers thereof have at least part of the refractory block elements arranged one to the side of the other with open expansion joints horizontally spaced between them, with the width of the expansion joints, when the block elements are in a cold condition, corresponding to the thermal expansion of the bordering refractory block elements in the direction toward the joints over a temperature range up to about 50 to 200C below the operating temperature of the elements.

5 Claims, 4 Drawing Figures PATENTEDNUV 5:914 3.8461368 summer 2 Pmmwmw 51914 3846l068 sum 2@ 2 REFRACTORY STRUCTURE, PARTICULY FOR A NETALLURGICAL SHAFT FURNACE This invention relates to a refractory structure, in particular for a metallurgical shaft furnace, including a bottom built up of several layers of separate refractory elements.

The invention will be described below with particular reference to a refractory structure of the bottom of a blast furnace, although it is not restricted thereto. In particular the invention is also applicable to advantage to the refractory structure of the bottom of several other types of metallurgical furnaces such as cupolas and the like.

In designing and manufacturing bottoms of shaft furnaces a known problem consists in that this bottom during heating up of the furnace shows the tendency to expand thermally. Several attempts have been made to take up this thermal dilatation in order to avoid cracking and spalling of the bottom. A usual method in this respect consists in that between the bottom layers and a steel jacket surrounding the bottom a joint to be filled out with compressed granular filling material is provided. Such a joint consists of an open joint in which such a filling mass is introduced. it is assumed therewith that the expanding layers of the bottom can expand thermally by compressing the mass filling the joint.

However, experiences with modern blast furnaces of very large diameters have raised doubt about the correctness of this assumption. It has particularly appeared that in a new blast furnace after some time of operation the heat flow as measured through the bottom to the lower surface deviates from the heat flow calculated, to such an extent as cannot be explained. Moreover, after cooling down of such a blast furnace it has often appeared that the wear of the bottom of the blast furnace is more serious and has a wear profile differing from what could be expected on the basis of such calculations.

In view of the above the present invention is based upon the idea that the said deviations from the theoretical behaviour are due to a mechanical damaging of part of the bottom layers as a result of too high forces occurring in said bottom.

Such high forces have to be ascribed to a tendency of thermal expansion of the bottom layers, which cannot work out sufficiently. In particular it is assumed that the friction between the several bottom layers restricts such expansion. and that moreover the filling mass for the joint is insufficiently compressible. Finally it has to be assumed that the bottom layers in the center show a higher tendency to expansion than near their outer edges.

It has appeared that the said disadvantages can be removed by applying the structure according to the present invention, which consists in that, at least in the upper layer, part of the refractory elements is arranged one to the side of the other with open expansion joints between them, the width of said joints in cold condition corresponding to the thermal expansion of the mutually bordering refractory elements in the direction of said joints over a temperature range up to about 50 to 200C below the operating temperature of said elements. Due to this structure it is obtainable that the entire thermal expansion can be taken up in the expan-.

tween said operating temperature. When reaching such a temperature the expansion joints should be fully closed in order to be certain that under operating conditions the bottom is absolutely closed.

As the expansion can now be taken up in the areas where it originates, no frictional forces occur between the several layers constituting the bottom, so that also for this reason a building up of too high forces within the bottom is avoided. Another advantage consists in that the filled joint around the bottom layer has no more to be calculated on the basis of the expansion of the entire bottom, which would, particularly for very large blast furnaces, lead to an extremely wide filled joint. It is remarked in this respect that a filled joint has to suffice two contradictory requirements, first that it should be sufficiently porous for taking up expansion and secondly that it should be sufficiently sealing and closing to ensure a sufficient heat conduction.

In the new structure now proposed according to the invention it is possible to make the filled joint very much smaller because it does not have to take up expansions. Moreover it is possible to compress the material in the joint to a greater extent, so that this material will obtain a higher coefficient of heat conduction. Both measures cooperate in giving a better heat discharge to the jacket of the furnace around the bottom.

It is remarked that up to now it was always aimed at obtaining a bottom structure in which the refractory elements fitted one against and in contact with the other as closely and accurately as possible. This was so because it was feared that liquid metal would enter the joints between the several refractory elements, giving firstof all the risk of floating of the bricks as the liquid metal has a higher specific gravity, and secondly the penetrating of the metal through the entire refractory structure. In particular for modern large furnaces operated at high pressure the sum of the ferrostatic pressure and the gas pressure in the furnace are so considerable, that it was generally feared that liquid metal would penetrate between the joints of the bottom elements. This was particularly feared in those cases in which the bottom structure was not made fully gas-tight, so that there is a pressure gradient over the height of the bottom. It has surprisingly appeared that even under such circumstances the refractory structure as proposed according to the present invention closes fully, in conformity with the calculations, before liquid metal is able to penetrate into the joint between the elements. It has moreover appeared therewith that the wearing out of the bottom after a certain period of operation is less and that such wear takes place to give the bottom a shape which corresponds to the shape which was expected on the basis of theoretical considerations.

It is remarked moreover, that a structure is known, in which the refractory elements of a bottom of a furnace are positioned at some distance from one another, the joint thus obtained being filled by a granular filling material to be compressed. Such structure is usually applied if the dimensions of the refractory elements to be used are not sufficiently accurate, so that a full contact over the bordering surfaces between the bricks cannot be expected. In such a case the joints are filled with a filling granular mass which is compressed intimately so as to aim at a very dense filling mass which in all circumstances gives a good sealing against the possible intrusion of liquid metal, and a very good heat conduction through the joints and through the mass filling them. It has, however, appeared that when heating up a furnace with such filled joints the mass in the joints will harden already at rather low temperatures (300 to 400C) to such an extent that in practice they can no more act as dilatation joints. It has therefore appeared that only a very good dilatation is obtainable when using open joints. It is preferable to design the layers of the bottom according to such a pattern that the joints extend approximately in parallel with the heat flow through the bottom. Thereby such open joints do not form a bar to this heat flow, the more so because in the final operating condition they are closed.

It has also appeared that the structure according to the invention is sufficiently closed to avoid that the refractory elements can float in the metal as a result of the penetration of liquid metal between and below the bricks. Moreover an additional measure to avoid this with more certainty is obtainable if the refractory elements are provided in part with inclined surfaces, so that the entire structure is interlocking, which is known as such in other structures of refractory bricks.

An additional degree of safety against the penetration into the entire bottom of liquid metal is according to the invention obtainable if in a manner known as such, when applying the invention, the upper layers are positioned according to patterns which are mutually at different angles horizontally. Often the patterns of subsequent layers are turned about an angle of about 30 with respect to each other. According to the invention in such a case at each intersection of two superposed expansion joints in adjacent layers it is necessary to interrupt the dilatation joint in at least one of these layers by the presence of a filling block in a recess in the refractory elements of this layer at this intersection. In an emergency case, if the metal will penetrate a layer, it will be able to penetrate at most along the depth of one layer into the bottom and not deeper.

Depending on the kinds of refractory materials used for the bottom it is possible for a designer of a furnace bottom to calculate how the course of the temperature through the bottom will be in operation. Therefrom he will be able to calculate what will be the thermal expansion from zone to zone and how wide the joints should be chosen when applying the invention. In particular good results were obtained with a bottom structure in which the upper four layers are made of carbon blocks having a thickness of about 60 cm, and in which the dilatation joints in said layers, as seen from above, are

about 0.4%, 0.3%, 0.2% and 0.1% respectively as a total for each subsequent layer from top to bottom, such percents being percents of the horizontal dimension of a layer as seen transversely to the joints.

According to similar considerations, on which the bottom layers are designed, it is also possible to apply annular layers of bricks, which, bordering said bottom layers, form for instance the wall of the hearth of a blast furnace. If this is realized it is necessary according to the invention at least in the inner annular layer, to position the refractory bricks also one to the side of the other with open expansion joints, the width of which in cold condition corresponds to the thermal dilatation of the elements in a tangential or annular direction over the temperature range from cold condition up to about 50 to 200C below the operating temperature of said elements.

Good results were in this respect obtained with a structure in which the lower annular layers were made of carbon bricks and in which the total space for expansion in peripheral direction was about 0.2 percent of the periphery of such an annular of bricks.

The invention will now be explained in more detail with reference to the enclosed drawings giving diagrammatically the bottom and the wall of the hearth of a blast furnace.

FIG. 1 gives these parts in vertical section.

FIG. 2 is a transverse section along the line IIIl in FIG. 1.

FIG. 3 is a transverse section along .Ihe line III--III in FIG. 1.

FIG. 4 shows the detail at reference IV in FIG. 1 enclosed by a dotted circle, in view from above and in horizontal section.

In FIG. 1 reference numerals 1 to 5 inclusive diagrammatically show several bottom layers of the bottom of a blast furnace. Layer 1 itself is composed of several layers, of which the composition and embodiment are not of importance for the present invention and may be of a type known and usual to the expert. Layers 2 to 5 inclusive are in this case built up of carbon bricks, although the choice of this material is neither essential for the invention. These layers have a thickness of about cm.

In FIG. 2, which shows a view from above of layer 5,

the pattern has been given, according to which the bricks are positioned in said layer. In the case as shown the bottom diameter was about 10 m. The lower layers 2, 3 and 4 have essentially the same pattern, but extending at angles of about 30 to each'adjacent higher layer.

The carbon bricks 8 to 12 inclusive of the central row in layer 5 are shown in FIG. 1 and 2. Several end faces of the blocks are inclined, as for instance shown at the joint 13. It is obtained thereby that the blocks of the same layer wedge together or interlock more or less against the danger of floating in the metal. As already remarked above this danger may occur if the liquid iron of high specific gravity (about 7.8) could penetrate between and below the blocks of a layer of refractory blocks which in general will have a specific gravity of about 1.5.

Crosslets in FIG. 2 indicate the joints which are open in cold condition of the bottom.

At the cross-section 1-1 in FIG. 2 the four joints in the same row have a width of for instance 8, l2, l2 and 8 mm respectively. Over the entire surface in this layer the total possibility of expansion transverse to a series of joints is about 0.4 percent of the length of the layer in the same direction. In the lower layers 4,3 and 2 this percentage decreases to about 0.3, 0.2 and 0.1 percent respectively. The long horizontal joints between the rows are of a width of preferably about 5 mm as an average with no or only slight mutual deviations of said width in the several joints.

During assembly of the bottom structure the joints are filled by sheets or plates of a plastic material to facilitate an accurate positioning. Already at a very low temperature the plastic material will burn away, so that in fact the joints act as open joints.

Along the outer jacket wall of the furnace a layer 6 has been provided which in part consists of a granular material which is compressed into said space. Above layer 5 there is a brick work structure 7 in the form of annular layers of bricks. FIG. 3 shows part of such an annular layer according to the section III-III in FIG. 1. The carbon bricks of this annular layer, three of these bricks being indicated by 14, 15, 16 in FIG. 3, are mutually separated by expansion or dilatation joints of a width of 2 mm.

FIG. 4 shows, on an enlarged scale, detail IV of FIG. 1 in a view from above and horizontal section through layer 4. Two blocks 22 and 23 of layer 4 are positioned so as to have a joint 17 therebetween with some clearance. Dotted lines 18 show the joint between two blocks of the subsequent higher layer 5, which joint intersects the joint 17. In order to avoid a direct communication between joints 17 and 18 joint 17 is interrupted by a small block 19, which fits into recesses in blocks 22 and 23.

The small block 19 leaves joints 20 and 21 with some clearance and which in this area take over the function of joint 17. In the side faces of this small block parallel to the plane of the drawing this block has no open joint, but fits also in cold condition exactly between the bricks of adjacent layers above and below it. It is possible to manufacture this small block 19 from the same material as the adjacent bricks in the same layer.

The means of FIG. 4 are to be seen as an additional security measure against the penetration of metal. As already remarked above this measure will as a rule not be necessary as penetration of liquid metal into the bottom will, even without such a measure, usually be avoided sufficiently. ,ll

I claim:

I. A refractory bottom structure for a metallurgical shaft furnace comprising a plurality of horizontal layers of separate refractory block elements, wherein at least the upper layers thereof have at least part of the refractory block elements arranged one to the side of the other with open expansion joints horizontally spaced between them, the width of said joints when the block elements are in cold condition corresponding to the thermal expansion of the bordering refractory block elements in the direction towards said joints over a temperature range up to about 50 to 200C below the operating temperature of said elements.

2. A structure in accordance with claim 1 wherein the layers of separate refractory block elements are four in number and said block elements are carbon blocks having a thickness of about 60 cm and the expansion joints in said layers in total take up length dimension as measured transversely to the joints being about 0.4 percent for the top one of said layers, 0.3 percent for the next lower layer, 0.2 percent for the next lower layer and 0.1 percent for the bottom layer of said four layers.

3. A structure in accordance with claim 1 wherein annular layers of refractory block elements adjacent to said bottom layer are built up forming a wall for a hearth for the furnace and further characterized in that at least in the inner annular layer of the refractory block elements are alsO arranged one to the side of the other with open expansion joints therebetween having a width corresponding to the width of the joints in said bottom layer.

4. A structure in accordance with claim 3 wherein the lower annular layers thereof are built up of carbon blocks with the expansion joint therebetween in a peripheral direction being about 0.2 percent of the annular periphery.

5. A refractory bottom structure for a metallurgical shaft furnace comprising a plurality of horizontal layers of separate refractory block elements, wherein at least the upper layers thereof have at least part of the refractory block elements arranged one to the side of the other with open expansion joints horizontally spaced between them, the width of said joints when the block elements are in cold condition corresponding to the thermal expansion of the bordering refractory block elements in the direction towards said joints over a temperature range up to about 50 to 200C below the operating temperature of said elements, and wherein further at least the upper layers of said block elements are positioned according to a pattern, which are mutually at a different angle to one another and said block elements being further characterized in that at each intersection of two expansion joints in vertically adjacent layers the expansion joint in at least one of said layers is provided with a recess area and a small filling block positioned within said recess area to prevent direct vertical communication between the two expansion joints through said intersection.

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