US3788622A

US3788622A - Furnace

Info

Publication number: US3788622A
Application number: US00310719A
Authority: US
Inventors: Laar J Van; J Felthuis
Original assignee: Hoogovens Ijmuiden BV
Current assignee: Hoogovens Ijmuiden BV
Priority date: 1971-12-01
Filing date: 1972-11-30
Publication date: 1974-01-29
Anticipated expiration: 1991-01-29
Also published as: DE2159667A1; GB1407066A; BE792108A; LU66566A1; DE2159667C3; DE2159667B2; FR2164218A5; IT1053711B

Abstract

A furnace provided with a wall and a refractory inner masonry structure, between which there is a space, there being compressible elements from a material of high heat conductivity arranged in contact with the walls of said space, for improving heat discharge from the interior of the furnace. The said space may be filled with a ramming mix or tamping mixture. The elements are preferably copper pipes. For many furnaces and applications said space will be annular around the furnace and the elements are provided at regular intervals and compressible in a radial direction with respect to the furnace.

Description

United States Patent [19] van Laar et al.

[ Jan. 29, 1974 FURNACE Netherlands [73] Assignee: Hoogovons Ijmuiden lB.V., Ijmuiden,

Netherlands [22] Filed: Nov. 30, 1972 [21] Appl. No.: 310,719

8/1971 Maloney 266/32 Primary Examiner-Gerald A. Dost Attorney, Agent, or FirmHall & Houghton [57] ABSTRACT A furnace provided with a wall and a refractory inner masonry structure, between which there is a space, there being compressible elements from a material of high heat conductivity arranged in contact with the walls of said space, for improving heat discharge from the interior of the furnace. The said space may be filled with a ramming mix or tamping mixture. The elements are preferably copper pipes. For many furnaces and applications said space will be annular around the furnace and the elements are provided at regular intervals and compressible in a radial direction with respect to the furnace.

8 Claims, 2 Drawing Figures llTv Q \V G FURNACE This invention relates to a furnace provided with a wall and a refractory inner lining of bricks, between which wall and lining there is a narrow space.

Furnaces, in particular blast furnaces, are often provided with exterior cooling means for discharging heat flow from the refractory brick work, which heat flow particularly for a large furnace will be considerable.

Between the masonry and the outer wall a small space is left open intentionally when making the masonry, in order to be able to take up thermal expansions of the masonry. This space is usually filled with a socalled ramming mix or tamping mixture, usually consisting of a mixture of granular graphite or carbon and tar. Such a ramming mix is more or less porous and thus compressible. The disadvantage of such a mix is, however, the low heat conductivity thereof, which in several cases is even lower than the conductivity of the masonry. This results in a loss of heat discharge to the exterior, which in the long run is not favourable for the masonry. If the ramming mix has to take up the fullthermal expansion of the masonry, the necessary thickness of the layer of ramming mix increases with the diameter of the furnace, and this will result in an increase of the heat insulating capacity of the layer.

According to an earlier proposal it is possible to decrease the required thickness of the layer or ramming mix between the masonry of the bottom and the outer wall (mantle) to a thickness of about -35 mm if in the bottom of such a large blast furnace expansion or dilatation joints are provided. It has, moreover, been previously proposed to replace such ramming mixes by a quantity of metal cast into the concerning space with a heat conductivity, which is substantially the same as the conductivity of the neighbouring masonry. This allows for an unhampered and continuous heat discharge from the masonry to the exterior cooled wall (mantle), but the expansion possibility in this area is thereby fully eliminated.

Another proposal is known to mix such ramming mixes with metals, but this has the disadvantage that the heat contact between the graphite layers and the steel outer wall hardly increases.

It is an object of the invention to avoid the said disadvantages and to offer a structure, which allows for a sufficient heat flow from the masonry to the cooled wall while maintaining the possibility of thermal expansion.

To this end compressible elements from thermally good conductive material are provided between the wall (mantle) and the refractory lining or masonry.

In particular for a shaft furnace, where the said space is annular, the refractory inner masonry and the wall are according to the invention brought in heat conducting contact by the presence of compressible elements from thermally good conductive material provided at regular intervals and compressible in a radial direction.

Such elements may have different possible shapes. However, the most simple and least expensive possibility is the use of copper pipes as such elements. If the faces bordering the said space have a mutually somewhat converging shape and if the largest distance between these surfaces is at most equal to the outer diameter of the pipes there will with certainty be obtained a good heat conductive contact between both surfaces after arranging the pipes.

The wall as indicated willbe an outer wall or mantle of the furnace, but need not be the outermost wall, as it may be the inner wall of a double walled cooling space, through which a cooling liquid is passed.

The invention will now be explained in more detail with reference to the enclosed drawing showing the application of the invention to the bottom of a blast furnace for making iron. It will be clear that this is only an example and that the invention may well be applied in other areas of different types of furnaces and, for a blast furnace, it may also be applied to the bosh thereof, and in general in all those cases where in furnaces a good heat transfer in combination with compressibility in view of thermal expansion are required. In the drawing:

FIG. 1 shows an axial, vertical section through a blast furnace bottom with part of the upstanding walls, in which the invention is applied.

FIG. 2 shows a horizontal section through part of the bottom along the line IIII in FIG. 1 on an enlarged scale.

In FIG. 1 reference numeral 1 indicates a steel mantle or outer wall around a refractory bottom structure for the furnace. This mantle or outer wall is connected to a steel bottom plate 2 supported on a structure of steel beams not shown in the drawings. As stated, the outer wall 1 may be the inner wall of a double-walled space for a cooling liquid.

In a blast furnace the bottom is subjected to continuous heavy thermal loads as a result of the quantity of liquid iron above the bottom, the temperatures in the vicinity of the tap hole 8 being about 1,400C 1,500C. The bottom should be resistant to such high temperatures, but also it has the function to support a large part of the blast furnace structure and the contents thereof. In order to be able to fulfil the requirements for the supporting function it is necessary that those parts of the bottom which substantially support the structure have rather low temperatures.

A complication in blast furnace bottoms consists in that they are gradually attacked by the liquid iron. This liquid iron has the tendency for most of the refractory materials in use to penetrate into the bottom to a depth where the temperature of the bottom is about equal to the solidification temperature of iron, which is about 1,130C. The zone above this temperature limit will gradually be attacked and worn out, whereby the said temperature limit is displaced downwardly, until an equilibirum condition has been attained. In the space thus generated, the so-called salamander, thereis a temperature gradient in the vertical direction. The salamander will be filled from top to bottom with liquid iron and possibly in part with solid iron, and often in part also with a coke matrix or skeleton.

By covering the graphite layer with a layer of material which gives a higher thermal heat insulation the temperature of the graphite layer will be decreased to below the solidification temperature of the iron, which avoids that the salamander can penetrate downwardly into the graphite layer. The lower layer, consisting of less conductive material, restricts the heat flow to and through the steel bottom plate. The remainder of the heat will thereby be transferred to the periphery of the graphite layer and will thus be discharged through the steel mantle or outer wall. With the aid of the liquid cooling above indicated by means not shown, the temperature thereof is kept sufficiently low.

The bottom proper is built up of four layers indicated by 4, 5, 6 and 7 in the drawing. The upper layer 4 with a thickness of about 60 cm consists of semi-graphite. The heat conduction coefficient A of such semigraphite is about 20 kcal/m/h/C. Layer 5 has a thickness of about 60 cm and consists of blocks of graphite with a coefficient of about 90 kcal/m/h/C, which have been carefully finished as to the shape and accuracy of their outer walls. Layer 6 also consists of blocks of graphite laid in directions perpendicular to the direction in which the blocks in layer 5 are oriented. Both layers are provided with dilatation joints in order to be able to take up the thermal expansions of the graphite in operating conditions. Layer 7 has a thickness of about 60 cm and consists of carbon bricks with a coefficient A of about 4 kcal/m/h/C. The said coefficient values are given for operating conditions and not for normal temperatures. The furnace diameter in the hearth may be about 13 in. By means of spray cooling or liquid flow cooling not shown in detail but known as such, the outer mantle or wall 1 is cooled down to about 60C. A fan shown of e.g., a power of 100 horse powers is used to blow air along the steel bottom plate 2 to keep it cooled to a temperature below 100C. The total quantity of heat Q discharged through the

layers

5 and 6 is divided into two components, i.e. heat flow Q, through bottom plate 2 and Q which is discharged through the outer mantle or steel wall 1. As an example, Q may be about 200.000 kcal/h and Q may be about 240.000 kcal/h. In the area of the tap hole 8 the temperature within the blast furnace is about l,400 to l,500C. In the centre of the bottom the isotherm for l,lC does not reach the top face of layer 4, which shows that no salamander will form and the bottom will not be attacked.

In FIG. 2 reference numeral 1 again indicates the steel mantle or outer wall of the furnace. The layers of carbon graphite are also indicated by and 6. In existing structures there is an annular space between the mantle l and the

bottom

5, 6, which is filled with a ramming mix, indicated in FIG. 2 with reference numeral 10. This ramming mix usually has a porosity of about 30 percent to 50 percent and is compressed when the furnace reaches operating temperature, by expansion of the bricks of the

bottom layers

5, 6.

In order to maintain a good heat conduction between the

layers

5 and 6 on the one hand and the steel mantle l on the other hand when the furnace is heated, there are, according to the invention, arranged in this annular space bodies such as copper pipes 9 being in permanent contact between the steel outer mantle 1 on the one hand and the

graphite layers

5 and 6 on the other side.

After building up the

bottom layers

7, 6 and 5 in this sequence these copper pipes 9 are hammered in all around between

layers

5 and 6 on the one hand and the steel mantle l on the other hand. In order to warrant good heat conductive contact, the outer surfaces of the

layers

5 and 6 and the inner surface of the steel mantle l0, bordering said annular space, have a somewhat converging configuration downwardly, so that the largest distance between said surfaces is at most equal to the outer diameter of pipes 9. The distance is somewhat smaller at the bottom.

The heat conduction coefficient of copper is about 320 kcal/m/h/C. If e.g. at mutual distances of 25 cm a copper pipe is hammered in, having an outer diameter of 36 mm and an inner diameter of 32 mm, a double value of the total heat conductivity through the annular space is obtained as compared with the ramming mix alone about 5-l0). By applying the features of the invention it is obtainable that in all circumstances the temperature at the periphery of the graphite bottom having a rather high conductivity does not increase too much. Thus there is no possibility for the pig iron to penetrate into the bottom and to form the so-called salamander.

The measure of the invention is not restricted to the said embodiment, but may as well be applied in other areas, such as near the wind holes, the bosh, the belly or cylinder and the lower part of the shaft or stack of a blast furnace, or for other furnaces.

We claim:

1. A furnace provided with a wall and a refractory inner masonry structure, between which there is a space, characterized in that in this space compressible elements from a material with high heat conductivity are arranged in contact with the walls of said space.

2. A furnace provided with a wall and a refractory inner masonry structure, between which there is an annular space, characterized in that the refractory inner masonry structure and the wall are in heat conductive contact by the presence of elements of thermally good conductive material provided at regular intervals and compressible in a radial direction.

3. A furnace according to claim 1, characterized in that the compressible elements consist of copper pipes.

4. A furnace according to claim 3, characterized in that the surfaces bordering the said space have a somewhat converging configuration mutually, the largest distance between said surfaces being at most equal to the outer diameter of said pipes.

5. A furnace, in particular a blast furnace for making pig iron, having liquid cooling along the outer periphery of the wall and air cooling of the bottom, said bottom having a horizontal layer of refractory material with a heat conduction coefficient A higher than 20 kcal/m/h/C under operating conditions, characterized in that this layer at the outer periphery is in heat conductive contact with the wall by the presence of elements of high thermal heat conductivity, compressible in a radial direction and arranged at regular intervals.

6. A furnace according to claim 5, characterized in that said layer consists of graphite with a heat conduction coefficient A of 60-100 kcal/m/h/C and that said elements consist of copper pipes.

7. A furnace, in particular a blast furnace for making pig iron, in which the part of the bosh between the inner masonry structure and the wall is provided with a ramming mix or tamping mixture, characterized in that the radial heat conduction of the inner masonry structure to the wall is increased by providing elements of high thermal conduction in the ramming mix space, said elements being compressible in a radial direction.

8. A furnace according to claim 1, characterized in that the said wall of the furnace is embodied as the wall of a cooling space through which a cooling liquid can be passed.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,786,622 DATED Jan. 29, 197k lNVENTORiS) Jacobus Van Leer et a1 it is certified that error appears in the above-identified patent and that said Letters Paient are hereby corrected as shown below:

In fine Caption, "Item 73 for 'Hoogovans read Hoogovans Signed and sealed this 24th day of June 1975.

( EJAXL) Attest:

C. E- ARSHALL DANN TH C. MASON Commissioner of Patents A t esting Officer and Trademarks

Claims

5. A furnace, in particular a blast furnace for making pig iron, having liquid cooling along the outer periphery of the wall and air cooling of the bottom, said bottom having a horizontal layer of refractory material with a heat conduction coefficient lambda higher than 20 kcal/m/h/*C under operating conditions, characterized in that this layer at the outer periphery is in heat conductive contact with the wall by the presence of elements of high thermal heat conductivity, compressible in a radial direction and arranged at regular intervals.

6. A furnace according to claim 5, characterized in that said layer consists of graphite with a heat conduction coefficient lambda of 60-100 kcal/m/h/*C and that said elements consist of copper pipes.