JPH09143525A - Operation of iron bath type smelting reduction furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eable the efficient operation of an iron bath type smelting reduction furnace in low cost by storing coal classified with a specific mesh and charging the coal into the iron bath type smelting reduction furnace. SOLUTION: As the grain diameter of a carbonaceous material is smaller, the dropping end speed of the carbonaceous material becomes lower, and the carbonaceous material is scattered in the atmosphere on the furnace and does not come to the steel bath. Since the rising flow speed of the generated gas in the furnace is about 8-10m/sec, it is considered that the carbonaceous material passing through sieve of 6 mesh and <3mm sizes does not come to the steel bath. In the iron bath type smelting reduction furnace, molten iron, scrap and ore as main raw materials and the coal as a solid reducing material are used to produce the crude molten steel. At this time, the coal remained after classified with 3.5 mesh is stored in the outdoor yard and charged into the iron bath type smelting reduction furnace. The coal is again classified with 3.5 mesh and the remained coal is charged. By this method, the yard, etc., for drying device, remixing device, storing vessel, can be unnecessitated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for operating an iron bath type smelting reduction furnace, and more particularly to a method for using coal as a solid reducing agent.

[0002]

2. Description of the Related Art In order to produce stainless steel in a converter, molten iron, chrome ore, iron ore and a carbon-based solid reducing agent are placed in a furnace having the same or similar shape to the converter called an iron bath smelting reduction furnace. In some cases, charging is performed and oxygen blowing is performed to previously produce so-called crude molten steel, and then the crude molten steel is subjected to finish refining such as decarburization in a converter. At that time, carbonaceous materials such as coke and coal are generally used as the carbon-based solid reducing agent.

By the way, when coal is charged into the iron bath type smelting reduction furnace (hereinafter referred to simply as "reduction furnace"), all of the charged coal does not reach the steel bath surface, and some coal is always in the middle. Is scattered in the atmosphere, and there is a problem that the efficiency of coal charging is low. This is because the gas generated by the reaction in the reduction furnace becomes an upflow in the vicinity of the furnace opening, and the small-sized coal rides on the flow and goes out of the furnace. Further, when using coal in the reduction furnace, the water content is endothermically decomposed in a steel bath or a slag bath, the amount of heat input to the furnace, that is, the reduction heat amount becomes a loss by the amount of the water supply, This was a cause of a decrease in the productivity of crude molten steel.

[0004] On the other hand, there have been various studies on treatments such as storage before use and drying of coal for iron making, and many technologies have been disclosed. For example, Japanese Patent Laid-Open No. 56-115670 discloses a technique of classifying coal for ironmaking raw material before loading it into a storage tank and performing storage suitable for each particle size. Further, JP-A-57-100185 discloses a coke oven in which a raw coal is classified into a fine-grained coal and a coarse-grained coal by a classifier, only the fine-grained coal is dried and then mixed with an undried coarse-grained coal. Is disclosed as a raw coal. Further, Japanese Patent Application Laid-Open
-62408 is a so-called vertical smelting reduction furnace (ore powder or flux powder is blown together with hot air from a multi-stage tuyere into a packed bed of solid carbonaceous material to reduce and produce molten iron or alloy). We propose a technology in which a classifying means is installed in the equipment, the carbonaceous material is divided into about 3 mm, and +3 mm is supplied from the furnace top and -3 mm is supplied from the tuyere arranged above and below.

However, JP-A-56-115670
The technique described in Japanese Patent Publication changes the storage method for each particle size, and thus requires a dedicated storage means according to each particle size.
A vast storage means installation site is required, and the installation cost of the storage equipment is excessive. Also, Japanese Patent Application Laid-Open No.
Since the technology described in Japanese Patent No. 00185 is intended to be used only as a raw coal for coke production, it is a method of using the entire amount of coal carried into a storage tank. A mixing facility for fine-grained coal and coarse-grained coal was required, which was effective only for the use of coking coal in a coke oven and the facility cost was excessive. Further, JP-A 64-06240
The technique described in Japanese Patent Publication No. 8 is also a method of using the entire amount of coal carried into a storage tank, and in order to supply -3 mm from the tuyere to the vertical smelting reduction furnace, a fine coal drying facility is required. Moreover, a plurality of storage means were required, and the equipment cost was excessive.

That is, as described above, the raw material coal for iron making requires a vast storage tank and a drying facility before it is used, and thus it has been processed at a high cost.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and provides an iron bath type smelting reduction process for efficiently producing crude molten steel without incurring a large amount of cost for pre-use treatment of coal. The purpose is to provide a method of operation.

[0008]

In order to achieve the above-mentioned object, the inventor diligently studied the relationship between the size of coal and the scattering, or the relationship between the coal size and the water content stored in an outdoor yard, and the results thereof. Was embodied as the present invention. That is,
The present invention uses an iron bath smelting reduction furnace to produce crude molten steel by using hot metal, scrap, various ores as main raw materials, and coal as a solid reducing material. Is stored in an outdoor yard and put into an iron bath type smelting reduction furnace, which is an operating method of the iron bath type smelting reduction furnace. Further, the present invention is characterized in that, at the time of the charging, the sieve stored in an outdoor yard is classified again with 3.5 mesh and the sieve is charged, or a drying step is performed on the sieve. It is a method for operating an iron bath type smelting reduction furnace, which is characterized in that it is charged without being passed through.

When these inventions are carried out, the coal in the outdoor yard can be used in the iron bath type smelting reduction furnace only by classifying, so that a large amount of cost is not required for the pretreatment of the coal and the heat quantity is insufficient. Therefore, the crude molten steel can be efficiently manufactured.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Since the embodiments of the present invention are as described above, the background of the present invention will be described here with reference to FIGS. In the present invention, the gas generated by the reaction in the furnace is introduced into a gas recovery device installed near the furnace opening to recover the gas, or the entire amount of the gas is burned at the furnace opening and the exhaust gas is installed near the furnace opening. A general iron bath type smelting reduction furnace to be introduced into the collected flue is used. And
FIG. 1 shows the particle size of coal charged from the furnace port and whether or not the coal reaches the steel bath. As is clear from FIG.
As the particle size of the carbonaceous material becomes smaller, the falling terminal velocity of the carbonaceous material due to charging decreases, it becomes impossible to counter the upward flow of the gas generated in the furnace, and it scatters in the atmosphere above the furnace and does not reach the steel bath. Since the rising velocity of the gas generated in the furnace in an actual iron bath type smelting reduction furnace is about 8 to 10 m / sec, the carbonaceous material under the 6 mesh sieve, specifically 3 mm or less, reaches the steel bath. Not considered.

On the other hand, FIG. 2 shows the allowable water content with respect to the average particle size of coal measured by the inventor, that is, the weight% of the maximum moisture that can be absorbed. When coal is stored in piles in an outdoor yard, fluctuations in coal moisture depend almost entirely on weather conditions. Therefore, in case of rain, coal will be supplied with sufficient water. When coal is used as the solid reducing material in the iron bath smelting reduction furnace, the water causes endothermic decomposition reaction in the steel bath or the slag bath as described above. Therefore, the amount of heat input into the furnace, that is, the amount of reduction heat, is lost by the amount of the supplied water, which ultimately results in a decrease in productivity.

In FIG. 2, it is clear that coal having a size of 3.5 mesh or below is significantly increased in its water content and becomes a problem when it is used after rainy weather. Further, wet coal may adhere to and grow on the inner surface of a raw material bunker or hopper attached to an iron bath type smelting reduction furnace, and may block the raw material cutout holes. Therefore, the inventor has set the coal grain size to 3.
It was considered that the water level of the coal could be stably maintained at a low level even if it was placed on a 5-mesh sieve and the inexpensive outdoor storage was continued without any change. Then, it was expected that the coal could be used with high efficiency when used for iron bath type smelting reduction, and the present invention was completed.

[0013]

Example An upper or bottom blowing converter having a capacity of 160 tons was used as an iron bath type smelting reduction furnace, and a smelting reduction operation of iron ore was carried out in combination with scrap melting. The amount of coal used was 45 tons / charge (40 tons / hour), and the batch processing of 15 charges / day was continued for 10 days. The average water content of the coal used was measured twice a day by sampling samples at 8 am and 8 pm. For the coal scattered from the furnace mouth, the operating results were evaluated by calculating from the amount of dust obtained by wet dust collection of the furnace exhaust gas and the carbon content.

Application conditions of the present invention The particle size of the coal used was classified with 3.5 mesh, and the sieve was stored in an outdoor yard without a roof and used for the above smelting reduction operation. Specifically, coal having a particle size distribution of -5 mm containing 2% by weight or less was used. During the period of use, the average amount of rainfall was 20 mm / day for three consecutive days.

Application Conditions of Comparative Example The particle size of coal used was not regulated, and the entire amount was stored in an outdoor yard without a roof and used. Specifically, coal having a particle size distribution in which -5 mm was present at 20% by weight was used. During the period of use of this coal, average rainfall of 15 mm / day continued for two consecutive days. In the smelting reduction operation, the steel bath temperature is 15
The input amount of iron ore was adjusted so as to be 50 ° C.

The above-mentioned results of performance are shown in FIG. 3 as changes in the yield of coal in the steel bath, which is calculated from the daily water content of the coal, the consumption of iron ore, and the amount of scattered coal. In addition, Table 1 shows the average values for 10 days.

[0017]

[Table 1] ──────────────────────────────────── Present Invention Comparative Example Coal Moisture 2.8 ± 0.3% 4.9 ± 3.0% Ore consumption 960 tons / day 655 tons / day Steel bath carburizing retention 95% 72% ───────────────── ─────────────────── According to Table 1 and FIG. 3, although the present invention example using coal containing not more than 2% by weight of -5 mm had rainy weather, Very stable and highly efficient smelting reduction could be realized with very little fluctuation of water content and small amount of scattered coal. On the other hand, in the comparative example, the water content increased to about 10% in rainy weather, the water content remained at 6 to 7% after rainy weather, and the carburization yield was -5 mm.
Of 20% by weight indicates the result of scattering of coal, which is almost in balance. The amount of iron ore consumed was less than 70% of that of the examples of the present invention due to insufficient reduction heat due to reduction in carburization yield and insufficient reduction heat due to endothermic decomposition of water. In other words, the application of the present invention suggests that a productivity improvement of over 45% can be achieved as compared with the comparative example.

After the operation of the comparative example, the coal bunker on the furnace of the smelting reduction furnace was found to have adhered moist pulverized coal which was not seen after the operation to which the present invention was applied, and the operation was stopped for 2 days and cleaned. A situation has occurred.

[0019]

As described above, according to the present invention, it is possible to operate an iron bath type smelting reduction furnace at a low cost and with high efficiency without requiring a drying device, a remixing device, a site for a storage tank and the like. I can do it now.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the particle size of coal charged into a furnace and the amount of scattering at the furnace mouth.

FIG. 2 is a diagram showing the relationship between coal particle size and its maximum water content.

FIG. 3 is a diagram showing application results of the present invention and a comparative example.

Claims (3)

[Claims] 1. A sieve of coal classified with 3.5 mesh in producing crude molten steel using an iron bath type smelting reduction furnace and using hot metal, scrap, various ores as main raw materials and coal as a solid reducing material. A method for operating an iron-bath type smelting reduction furnace, characterized in that the upper part is stored in an outdoor yard and put into an iron-bath type smelting reduction furnace. 2. The iron-bath type smelting reduction according to claim 1, wherein, at the time of the feeding, the sieve stored in an outdoor yard is classified again with 3.5 mesh and the sieve is fed. How to operate the furnace. 3. The method for operating an iron bath type smelting reduction furnace according to claim 1, wherein the sieve is charged without a drying step.