DESCRIPTION

METHOD OF INJECTING AN AGGREGATE INTO A SMALL GAP FORMED IN

THE BOTTOM PORTION OF A BLAST FURNACE - AND AGGREGATE USED THEREFOR

[0001] This application claims priority to Japanese Application 2005-277548, filed in Japan on September 26, 2005, the entire contents of which are herein incorporated by reference.

Field of Technology

[0002] The present invention relates to a method of injecting an aggregate into small gaps formed in a bottom portion of a blast furnace. The, present method is able to repair a small gap having a width of about lmm or less.

[0003] As shown m FIG. IA, a bottom portion of a blast furnace is composed of carbon brick 1, a (ramming) stamp 2, a stave 3 and a shell 4 in order from the innermost side. The main components of the stamp 2 are graphite and resin, and the stave is made of a metallic material. Cooling the outside of the shell 4 cools the bottom portion of the blast furnace. This lowers the temperature of the carbon brick 1 so as to avoid fusing damage. FIG. IB is a sectional view of a bottom portion of a blast furnace and illustrates temperature distributions before and after filler injection.

[0004] _^ However, when the blast furnace is operated long term, a very small gap 5 having a width of about lmm or less may be formed at the interface area between the carbon brick 1 and the stamp 2 and/or between the stamp 2 and the stave 3. Once the gap 5 is formed, thermal conduction from the carbon brick 1 to the shell 4 is restricted. This cases the temperature of the carbon brick 1 having the gap to abnormally increase and thus shorten the life of the brick.

[0005] A high heat conductivity castable refractory containing metal aggregate has been -developed. This is disclosed in JP2004-315348 , the entire contents of which are herein incorporated by reference. It was previously attempted to inject the above castable refractory into a small gap formed in the bottom portion of a blast furnace. This was attempted in order to restore the thermal conductivity of the inside of a furnace wall. However, it was difficult to fill in a small gap having a width of about lmm or less while maintaining the fluidity of the castable refractory at a high temperature such as 200-250 ⁰ C. Thus, the castable refractory was not satisfactory as a material for repairing a small gap formed in the bottom of a blast furnace.

Summary of the Invention

[0006] An object of the present invention is to provide a method capable of solving the above-described problem. Thus, one object of the present invention relates to injecting an aggregate into a small gap formed in the bottom portion of a blast furnace. This is performed so that the restoration of the - thermal conductivity of the inside of a furnace wall is successfully achieved.

[0007] The method of the present invention _^ involves injecting an aggregate into a small gap formed in the bottom portion of a blast furnace, wherein the aggregate is a paste comprising: a metal aggregate having a grain size of about 500μm or less; a refractory aggregate having a grain size of about 500μm or less; and a bed material, wherein the metal aggregate and the refractory aggregate are dispersed in the bed material so as to form the paste.

[0008] In another aspect of the present invention, a roundness of the metal aggregate is about 30% or less, wherein the roundness is defined as (maximum diameter of metal aggregate - minimum diameter of metal aggregate) / (maximum diameter of metal aggregate) x 100%.

[0009] In yet another aspect of the present invention, both grain sizes of the metal aggregate and the refractory aggregate range from about 75μm to about 300μm.

[0010] In another aspect of the present invention, the bed material includes a furan resin or an ethylene glycol.

[0011] In another aspect of the present invention, the metal aggregate includes copper grains.

[0012] In another aspect of the present invention, the refractory aggregate is at least one of spherical silica, spherical zirconia and spherical mullite.

[0013] According to the present invention, it is possible to fill m the small gap 5 having a width of about lmm or less with a filler containing a metal aggregate, and a refractory aggregate while maintaining the fluidity of the filler at a high temperature such as 200-250 ⁰ C. Consequently, the thermal conductivity and the. strength of the bottom portion of the blast furnace can be quickly restored to thus avoid shortening the life of the brick.

Brief Description of the Drawings

[0014] _% FIG. IA is a schematic diagram of a bottom portion of a blast furnace with an injector.

[0015] FIG. IB is a sectional view of a bottom portion of a blast furnace and illustrates temperature distributions before and after filler injection.

[0016] FIG.2 is a graph showing a relation between the injection success (%) and the maximum grain size of the aggregate.

[0017] FIG.3 is a graph showing a -relation between the internal friction coefficient and the percentage roundness of copper grain.

[0018] FIG.4 is a graph showing a relation between the ratio of the bed material and the total amount of the metal aggregate and the refractory aggregate (horizontal axis) and the viscosity of a filler of the mixture of the bed material and the aggregate (vertical axis).

[0019] FIG.5 is a conceptual diagram illustrating injection in the case of narrow grain size distribution where injection flow is smooth.

[0020] _s FIG.6 is a conceptual diagram illustrating infection in the case of broad grain size distribution where a sudden blockage xs caused thus making injection of filler impossible.

[0021] FIG.7 is a graph showing a summary of results regarding the study of the grain size wherein injectable grain size range of aggregate is shown.

[0022] FIG.8 is a conceptual diagram of the status of the filler mixture used in the present Example.

Detailed Description of the Invention [0023] In the present invention, a paste filler is formed by dispersing a metal aggregate and a refractory aggregate in a bed material. This paste material is then injected into a small gap formed in the bottom portion of a blast furnace. The present metal aggregate preferably functions to restore the thermal conductivity of the bottom portion of the blast furnace after injection. As a metal aggregate, any metal aggregate may be used. However, a metal aggregate of copper grains is preferable in terms of heat resistance, thermal conductivity and cost. The present metal aggregate is preferably a spherical grain rather than

a flaky grain or an amorphous grain so as to maintain fluidity during injection into the small gap. The most preferable spherical grain is an atomized copper powder

(AtCu) which is formed by spraying molten copper in the air and allowing the sprayed copper to solidify into a spherical shape due to its surface tension.

[0024] The material for the refractory aggregate is not specifically limited. Any material can be used as long as the material has a sufficient heat resistance against the heat of the bottom portion of the blast furnace after injection. As for a shape of the refractory aggregate, similar to the metal aggregate, a spherical grain is preferable so as to maintain fluidity. Illustrative, but non-limiting examples of suitable refractory aggregate include spherical silica, spherical zirconia and spherical mullite .

[0025] The present bed material is preferably a substantially liquid material for fluidizing the metal aggregate and refractory aggregate. The present bed material is also preferably capable of maintaining fluidity at temperatures such as 200-250 ⁰ C and to have an appropriate viscosity suitable for transporting the metal aggregate and the refractory aggregate. Illustrative, but

non-limiting preferable examples of suitable bed materials include low viscosity resins such as furan resin or low viscosity liquids such as ethylene glycol. The present bed material is preferably thermally decomposed after injection, leaving only the metal aggregate and the refractory aggregate behind. According to one aspect of the present invention, it is also possible to add a surface active surfactant to the bed material to increase slipping properties .

[0026] Preferable conditions to inject the above- described filler into a small gap have been experimentally investigated by the present inventors-. As a result, it is found that the filling (injection) is largely influenced by factors such as the maximum diameter of the grains of the metal aggregate and the refractory aggregate, the roundness of the metal aggregate, the blend ratio of aggregate and bed material and/or the grain size difference between the metal aggregate and the refractory aggregate. Each factor is described below.

[0027] FIG.2 is a graph showing the relation between the maximum diameter of aggregate and the injection success (%). It is impossible to visually confirm the filling status of aggregate in a small gap on a real bottom portion of a

blast furnace. Instead, an experimental device is ^' prepared. The experimental device includes a pair of transparent resin panels facing to each other with a gap of about lmm separating the panels. The filling status is visually checked while injecting a variety of paste aggregates using a pressure feed pump with a maximum discharging pressure of 3MPa. The injection success (%) is defined as M/N xlOO%, where N is the number of injections attempted at N locations of the bottom portion of the blast furnace and M is the number of smooth injections (N-M means the number of failed injections because the feeding pump pressure reaches an abnormally high pressure) . As shown in the graph, it is preferable to use a metal aggregate and a refractory aggregate both of which have a maximum diameter of about 500μm or less in order to accomplish the injection filling of the aggregate into the gap of about lmm or less. If the maximum diameter exceeds 500μm, the injection success (%) quickly decreases. In view of this, each grain of metal aggregate and refractory aggregate preferably has a size of about 500μm or less. More preferably, each grain -of metal aggregate and refractory aggregate preferably has a size of about 300μm or less.

[0028] The roundness of the metal aggregate is also a factor to be defined. FIG.3 is a graph showing the relation

between the roundness of copper grain and the internal friction coefficient of the paste. The roundness is defined as (maximum diameter of metal aggregate - minimum diameter of metal aggregate) / (maximum diameter of metal aggregate) x 100%. If the roundness exceeds 30%, the internal friction coefficient increases. This makes pressure feeding difficult. In view of this, the roundness of ^' the metal aggregate is preferably about 30% or less. More preferably, the roundness of the metal aggregate is about 20% or less.

[0029] When the metal aggregate and the refractory aggregate are injected in the form of a mixture with the bed material, it is preferable to maintain the viscosity of the mixture suitable to flow. This may be accomplished by adjusting the ratio of the bed material to the total amount of the metal aggregate and the refractory aggregate.

[0030] FIG.4 is a graph showing the relation between the ratio of the bed material to the total amount of the metal aggregate and the refractory aggregate (horizontal axis) and the viscosity of a filler of the mixture of the bed material and the aggregate (vertical axis). At the left end of the graph, copper grains with high specific gravity are easily precipitated because of very low viscosity. At

the right end of the graph, injection becomes very difficult because of very high viscosity. For a smooth injection without separating the metal aggregate and the refractory aggregate from each other, it is preferable to maintain the viscosity of the filler in the range of about

2000-2000OmPa ^• sec and to maintain the ratio of bed

material and aggregate in mass ranging from about 8:2 to about 3:7.

[0031] The ratio of grain size between the metal aggregate and the refractory aggregate is another factor to determine the smoothness of injection of the filler into a small gap. FIG.5 is a conceptual diagram illustrating injection in the case of a narrow grain size distribution of both the metal aggregate and the refractory aggregate. FIG.6 is a conceptual diagram illustrating injection in the case of a broad grain size distribution. In the case of a broad grain size distribution, as shown in FIG.6 where a variety of size of grains are contained, spaces between the aggregate grains are extremely reduced. This may lead to a sudden blockage to thus make it impossible to further inject filler. On the contrary in the case of a narrow grain size distribution, as illustrated in FIG.5, the spaces between the aggregate grains are kept in moderation.

This prevents sudden blockages and thus allows maintenance of smoo.th injection of the aggregate.

[0032] FIG.7 is a graph showing a summary of results regarding the study of the grain size described above. If the grain size contained in ^' metal aggregate and/or refractory aggregate exceeds 300μm, injection to a gap having a width of about lmm or less becomes difficult. If the grain size contained in the metal aggregate and/or the refractory aggregate becomes 75μm or smaller, the fluidity may be reduced as the spaces between grains tend to be reduced. 'It is thus preferable to prevent the grain size difference between the metal aggregate and the refractory aggregate from becoming large. Therefore, the grain sizes of both the metal aggregate and the refractory aggregate are preferably in the range of from about 75μm to about 300μm, more preferably in the range of from about lOOμm to about 200μm.

Example

[0033] The following three materials are stirred to form a uniform mixture of filler: (1) atomized copper powder (AtCu) of 50% by mass with a grain size ranging from lOOμm to 200μm, (2) mullite beads of 30% by mass with a grain size ranging from lOOμm to 200μm, and (3) a bed material of

ethylene glycol of 20% by mass. The apparent specific gravity and the thermal conductivity of the atomized copper powder (AtCu) is 4.86 and 391.7W/m-K, respectively, and the upper temperature limxt of the mullite beads is 1500 °C. The status of the above three-component mixture is illustrated in FIG.8.

[0034] The above_ filler can be easily injected into a small gap of the bottom portion of a blast furnace under a feeding pressure of around 0.3MPa. This can improve the heat conductivity of the bottom portion of blast ₍ furnace and lower the temperature of the carbon brick by about 130 "C compared to the status before injection. Thus, the present invention can recover deteriorated thermal conductivity of the inside of the furnace wall due to the formation of a small gap in the bottom portion of the blast furnace .

[0035] All cited patents, publications, copending applications, and provisional applications referred to in this application are herein incorporated by reference.

[0036] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the

spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are - intended to be included within the scope of the following claims.