JP2012211363A - Method for producing carbon containing nonfired agglomerated ore for blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing carbon containing nonfired agglomerated ore for a blast furnace having a high content of interior carbon and high cold crushing strength and hot crushing strength by using a small amount of a hydraulic binder.SOLUTION: In the method for producing the carbon containing nonfired agglomerated ore for a blast furnace, the carbon containing nonfired agglomerated ore for a blast furnace is produced by adding water to a raw material including finely-powdered iron oxide, a finely-powdered carbonaceous material, and a hydraulic binder and performing mixing and pelletization, wherein the finely-powdered iron oxide having a particle diameter of 1,000 μm or more is less than 5 mass% and the content ratio of the finely-powdered iron oxide having a particle diameter of 125 μm or less is 40 mass% or less.

Description

  The present invention relates to a method for producing an unfired carbon-containing agglomerated ore for a blast furnace.

  Conventionally, steel mills mix various types of iron-containing and carbon-containing dust collected from various dust collectors, add cement-based aging binders, knead and mold to produce non-fired pellets and briquettes It has been used as a blast furnace raw material.

  These unfired carbon-containing agglomerated ores for blast furnaces must have a certain cold crushing strength to withstand transportation to the blast furnace and pulverization during blast furnace charging. Therefore, when granulating iron dust etc. with a granulator, adjust the dust particle size distribution to an appropriate range, add moisture to binders such as limestone and cement, granulate, and then cure and harden The strength has been secured.

  In addition, these unfired carbon-containing agglomerated ores for blast furnaces deteriorate in response to the reaction under the gas and temperature conditions in the thermal preservation zone and reduction reaction equilibrium zone of the blast furnace shaft, so that smooth blast furnace operation is possible. For this purpose, a certain hot crushing strength is required.

  In addition, these unburned carbon-containing agglomerated ores for blast furnaces cause a reduction reaction in the blast furnace due to the carbon contained in the blast furnace. As a result, the reduction rate is improved. Increases have been made.

  From the above, it is desired that the unfired carbon-containing agglomerated ore for blast furnace has a large amount of interior carbon and high cold crush strength and hot crush strength.

As a method of increasing the cold crushing strength of unfired carbon-containing pellets for blast furnaces, “addition of a hydraulic binder to a finely divided iron-containing raw material and finely divided carbonaceous material, and a carbon content ratio in all raw materials (TC) Is adjusted to a blending ratio of the pulverized carbonaceous material so that it is 15 to 25% by mass, further mixed and granulated while adjusting the moisture, and then subjected to a curing treatment to obtain a cold crushing strength of 85 kg / cm ^2. (8300 kN / m ² ) A method for producing unfired carbon-containing pellets for blast furnaces, wherein the curing treatment is performed after the pellets after granulation are left in the atmosphere for 12 to 48 hours in a primary curing yard. The pellet is charged into a shaft furnace for secondary curing, and steam blowing treatment is performed in the shaft furnace at a temperature of 60 to 90 ° C. and a treatment time of 5 hours or more. And before the steam blowing process The total processing time of the drying process should be within 8 hours "is the invention (Patent document 1).

  According to the present invention, the amount of carbon incorporated in the blast furnace non-fired carbon-containing pellets is large, and a non-fired carbon-containing pellet having a high cold crushing strength can be obtained. In a shaft furnace for steam, steam blowing curing and subsequent drying treatment are required, and there is a problem that equipment costs and treatment costs increase. In this document, there is no mention of the hot crushing strength of the unfired carbon-containing agglomerated blast furnace.

In addition, for the purpose of reducing the ratio of reducing material in blast furnace operation, “in-carbon non-fired agglomerated minerals that are kneaded, molded, and cured by blending iron-containing raw material and carbon-based carbonaceous material and adding a binder. The binder is selected so that it contains 80 to 120% of the theoretical carbon required to reduce the reducible oxygen of stones to metallic iron, and the crushing strength at room temperature is 7850 kN / m ² or more. An invention of a carbon-incorporated non-fired agglomerated blast furnace for a blast furnace characterized by being kneaded, molded and cured is proposed (Patent Document 2).

According to this method, the thermal preservation zone and reduction of the blast furnace shaft part, in which the progress of the reduction reaction of iron oxide is generally restricted from the relationship between the temperature of the reducing gas and the gas composition (ηCO = CO ₂ / (CO + CO ₂ )). Even in the reaction equilibrium zone, in the temperature range of 900 to 1100 ° C., the iron oxide in the uncalcined agglomerate undergoes a reduction reaction due to the carbon incorporated therein, and as a result, the reduction rate is improved, so the ratio of reducing materials during blast furnace operation The reduction effect can be expected.

  However, in this method, the C content contained in the unfired agglomerated mineral is 120% or less in terms of the theoretical carbon amount (hereinafter sometimes referred to as C equivalent) necessary for reducing the oxide ore into metallic iron. The total carbon content (TC) is limited to about 15% by mass or less), and if the C content is further increased, the cold crushing strength and hot crushing strength of the unfired agglomerated minerals are impaired. There is a problem.

  Furthermore, in this method, in order to maintain the cold crushing strength of the unfired agglomerated minerals with the carbonaceous material, a cement-based binder such as early-strength Portland cement is used instead of quick lime. Increasing the amount not only reduces the rate of temperature rise at the shaft in the blast furnace due to the dehydration reaction of cement, which is an endothermic reaction, but also generates a reduction stagnation zone (low temperature thermal preservation zone) at low temperatures, which causes iron for blast furnaces. The problem is that the reduced ore in the blast furnace of the sintered ore charged as a raw material is promoted.

  In addition, for the purpose of reducing the strength after reduction of the unfired briquette containing carbonaceous materials used in the blast furnace method and DR method (direct reduction method), “the porosity after molding and drying is 15 to 25%. There is a proposal of “carbonized material non-fired briquette” (Patent Document 3).

  According to this method, it can be expected to some degree that the carbon material-incorporated non-fired briquette can suppress a reduction in strength during reduction in a blast furnace.

  However, the porosity after molding and drying of the carbonaceous material-incorporated non-fired briquette is affected by the properties and particle size of the raw material and the carbonaceous material, and it is difficult to control the porosity within the range of 15 to 25%. There is a problem of receiving.

In addition, by adjusting the particle size of all iron raw materials, the blending ratio of fine powdered carbon materials, and adjusting the median diameter of fine powdered carbon materials, 50 kg / cm ² (4900 kN / m) required as raw material pellets for blast furnaces. ² ) While maintaining the above cold strength, it has sufficient carbon content to greatly reduce the reducing material ratio during blast furnace operation, and has a crushing strength of 7 (690 kN / m ² ) cm ² or more after reduction. An unfired carbon-containing pellet manufacturing method has been proposed (Patent Document 4).

  According to this method, the blending ratio of the fine carbonaceous material is adjusted so that the particle size in all raw materials is 2 mm or less, and the carbon content ratio (TC) in all raw materials is 15 to 25% by mass. By setting the median diameter of 100 to 150 μm, it is possible to produce a non-fired carbon-containing agglomerated mineral having good cold crushing strength and post-reduction crushing strength and having a high reducing material ratio reducing effect.

  However, in this method, the particle size in all raw materials must be 2 mm or less, the median diameter of the carbonaceous material must be 100 to 150 μm, and there are restrictions from both the raw material and the carbonaceous material. If the amount of non-fired carbon-containing agglomerated mineral used in the blast furnace is increased, the amount of slag charged into the blast furnace also increases. In addition, since the early strong cement undergoes a dehydration reaction (endothermic reaction) at 400 to 500 ° C., excessive use of the carbon-containing agglomerated mineral with 10% added cement lowers the temperature in the blast furnace, There is a problem that a temperature rise delay and a reduction delay occur.

JP 2009-161791 A JP 2003-342646 A JP 62-290833 A JP 2008-95177 A

The unfired carbon-containing agglomerated ore for blast furnace is desired to have a large amount of interior carbon and high cold crushing strength and hot crushing strength.
The cold crushing strength can be increased by adding a hydraulic binder, but the hydraulic binder is decomposed in the blast furnace and does not help maintain the hot strength. Further, the hydraulic binder has a problem that due to the dehydration reaction (endothermic reaction) in the blast furnace, excessive use lowers the temperature in the blast furnace, causing a delay in temperature rise and a reduction in reduction of the blast furnace interior.

  It is an object of the present invention to provide a method for producing a non-fired carbon-containing agglomerated mineral for blast furnaces that uses a small amount of hydraulic binder, has a large amount of interior carbon, and has high cold crushing strength and hot crushing strength. To do.

  The present inventor has found that by controlling the particle size of iron oxide for fine powder, it is possible to produce a non-fired carbon-containing agglomerated ore for blast furnace having high cold crushing strength and hot crushing strength.

  The present invention has been made to solve the above-mentioned problems based on this finding, and the gist thereof is as follows.

(1) It is a method for producing an unfired carbon-containing agglomerated mineral for a blast furnace by adding water to a raw material having a finely divided iron oxide, a finely divided carbonaceous material, and a hydraulic binder, and mixing and granulating it. The pulverized iron oxide has a particle size of 1,000 μm or more and less than 5% by mass, and the content ratio of the particle size of 125 μm or less is 40% by mass or less. Manufacturing method of ore.
(2) The method for producing a non-fired carbon-containing agglomerated mineral for blast furnace according to (1), wherein the fine powdered iron oxide has a particle size of 10% by mass or less with a particle size of 250 μm or more.
(3) The non-fired carbon-containing agglomerated ore for blast furnace is either a non-fired carbon-containing pellet or a non-fired carbon-containing briquette having 10% or more of the finely divided carbonaceous material with respect to the total mass of the raw material. The method for producing an unfired carbon-containing agglomerated mineral for a blast furnace according to any one of (1) and (2).

  INDUSTRIAL APPLICABILITY The present invention can provide a method for producing an unfired carbon-containing agglomerated blast furnace for blast furnaces with a small amount of hydraulic binder, a large amount of carbon incorporated, and a high cold crushing strength and hot crushing strength. .

The figure which shows the measuring apparatus of the crush strength after reaction of the non-baking carbon-containing agglomerated mineral for blast furnaces. The figure which shows the measurement conditions of the crush strength after reaction of the non-baking carbon-containing agglomerated mineral for blast furnaces. The figure which shows the sample cross section after reaction of the non-baking carbon-containing agglomerated mineral for blast furnaces.

  The present invention is a method for producing a non-fired carbon-containing agglomerated blast furnace for blast furnace by adding water to a raw material having a finely divided iron oxide, a finely divided carbonaceous material, and a hydraulic binder, and mixing and granulating it. The method is characterized by reducing the content of finely divided iron oxide having a particle size of 125 μm or less and further increasing it in the range of 125 to 250 μm. Here, both the iron oxide and the carbonaceous material are in a fine powder form, which means a particle size that can be formed by pelletizing or briquetting, for example, 2 mm or less. In particular, in the raw material having iron oxide, the ratio of the particle size of 1 mm or more is less than 5% because the blending ratio is larger than that of the carbonaceous raw material, which has an important influence on the formability. If the content exceeds 5%, the granulation cannot be performed smoothly.

  If these conditions are satisfied, the granulation equipment for adding water to the raw material having finely divided iron-containing raw material, finely divided carbonaceous material, and hydraulic binder, mixing, and granulating is not particularly limited. What is necessary is just to have a function of kneading, hydration, granulation, and a product sieve, and a kneading machine, a granulator, etc. are not specifically limited.

Examples of the non-fired carbon-containing agglomerated blast furnace according to the present invention include non-fired carbon-containing pellets and non-fired carbon-containing briquettes.
Examples of pellets include those formed into a spherical shape by a disk pelletizer, and examples of briquettes include symmetric pillow-type briquettes and almond-type briquettes that have a hollow mold and are formed by a pair of opposed forming rolls. It is not limited.

  The raw non-calcined agglomerated agglomerates immediately after molding must have a certain strength to withstand the subsequent transportation to the blast furnace and pulverization during charging of the blast furnace. Therefore, the raw unfired carbon-containing agglomerated mineral for blast furnace after curing is cured to promote a hydraulic reaction between an inorganic binder such as cement and water. The cold crushing strength after curing is preferably 5000 kN / m 2 or more for non-fired carbon-containing pellets (diameter of about 10 to 15 mm), and 1000 N / sample or more for non-fired carbon-containing briquettes (about 20 to 25 cc). .

  The crushing strength is measured in accordance with JIS M8718 “Iron Ore Pellet Crushing Strength Test Method” by applying a compressive load to one sample at a specified pressure rate to measure the load value when it breaks. .

Unfired carbon-containing agglomerated ore deteriorates in the blast furnace due to the reaction under the gas and temperature conditions in the thermal preservation zone and the reduction reaction equilibrium zone of the blast furnace shaft, but for steady blast furnace operation, it remains constant. It is necessary to maintain the hot crushing strength. The hot crush strength after the reaction is preferably 700 kN / m ² or more for non-fired carbon-containing pellets (diameter of about 10 to 15 mm), and 100 N / sample or more for non-fired carbon-containing briquettes (about 20 to 25 cc). preferable.

The hot crushing strength is measured by using a reduction test apparatus that can simulate the reduction reaction in the blast furnace by applying a load, and the reducing gas composition (CO 36%, CO ₂ ; 14%) in the thermal preservation zone and reduction reaction equilibrium zone of the blast furnace shaft portion. , N2; 50%) and temperature (900 to 1100 ° C.) under almost the same conditions, the reduction test was performed, and the crushing strength after the reaction of the unfired carbon-containing agglomerated ore was measured according to JIS M8718 “Iron ore pellet crushing strength test method”. Follow the same procedure.

  As the finely divided iron-containing raw material, a material obtained by pulverizing iron ore to a predetermined particle size can be used. More realistically, there are iron-containing dust, sludge, scale, and the like that are collected by a dust collector or the like in a pellet feed and a large amount of dust generated in the iron making process. These pulverized iron-containing raw materials are hardly 1 mm or more, and a particle size of 250 μm or less occupies 80% or more of the whole.

  The present invention reduces the content ratio of the particle size of 125 μm or less in the pulverized iron-containing raw material, thereby promoting the networking of iron produced in the reduction process, thereby increasing the heat of the unfired carbon-containing agglomerated ore. It is characterized by improving the interlaminar crushing strength. In addition, by reducing the content ratio of the particle size of 250 μm or more in the finely divided iron-containing raw material, the compacted agglomerated ore at the time of molding is made compact, and the cold crushing strength and heat It is characterized by improving the interlaminar crushing strength. That is, by controlling the particle size of the pulverized iron-containing raw material to 125 μm to 250 μm, an unfired carbon-containing agglomerated mineral for blast furnaces with excellent cold crushing strength and hot crushing strength is produced.

Examples of the finely powdered carbon material include powdered coke pulverized to a predetermined particle size, powdered coal, coke dust, and powdered solid carbon material such as blast furnace primary ash containing powdered coke.
The blending amount of the finely powdered carbon material is preferably 10% or more with respect to the total mass of the raw material, whereby iron oxide in the carbon-containing agglomerated mineral can be generally reduced only by the carbon material inherent in the carbon-containing agglomerated mineral, As a result, it can be reduced quickly. Furthermore, 15% or more is more preferable, and 18% or more is particularly preferable. This promotes the reduction of iron raw materials other than non-fired pellets (for example, sintered ore) in the blast furnace by gasifying excess carbon even if iron oxide in the carbon-containing agglomerated mineral is reduced. Energy saving can be expected to reduce CO ₂ . This is because the remaining carbon content promotes the reduction of the sintered ore in the vicinity thereof.

  Conventionally, the ratio of the carbon content to the theoretical carbon amount required to reduce iron oxide in the pellet is defined as “carbon equivalent”, which is a measure of the degree of reduction of iron oxide by carbon. Conventionally, in order to maintain the cold crushing strength of 4900 kN / m 2 or more required as a blast furnace raw material, the carbon content has to be limited to 15% by mass (corresponding to 1.2 in terms of carbon equivalent). (See Patent Document 2). However, in the present invention, by controlling the particle size of the finely divided iron-containing raw material to 125 μm to 250 μm, 15% or more of finely powdered carbon material can be added to the finely divided iron-containing raw material.

  The hydraulic binder means a binder having a function of increasing the cold crushing strength of the granulated product by being cured by a hydration reaction with moisture contained in the raw material or added moisture. Examples of the hydraulic binder include, but are not limited to, an aging binder composed of fine powder mainly composed of blast furnace granulated slag and an alkali stimulator, Portland cement, alumina cement, blast furnace cement, and the like.

By adding the hydraulic binder, the necessary cold crushing strength of the unfired carbon-containing agglomerated ore for blast furnace can be maintained. For example, in the case of a non-fired carbon-containing pellet for a blast furnace, generally about 10% by mass of a hydraulic binder is added to the total mass of the raw material.
However, the addition of a hydraulic binder increases the amount of slag in the blast furnace, leading to an increase in required energy and an increase in the amount of generated CO ₂ . In addition, since the hydraulic binder undergoes a dehydration reaction with an endothermic reaction at 400 to 500 ° C. in the blast furnace, excessive addition of the binder causes a low temperature in the blast furnace, and the efficiency of the blast furnace decreases.

  In the present invention, by controlling the particle size of the pulverized iron-containing raw material to 125 μm to 250 μm, the blast furnace excellent in cold crushing strength and hot crushing strength with a smaller amount of hydraulic binder added than before. Unfired carbon-containing agglomerated minerals can be produced.

  Next, examples of the present invention will be described, but the present invention is not limited thereto.

The raw material used was a mixture of sintered dust and fine powdered iron ore having various particle size configurations as the finely divided iron-containing raw material, and blast furnace primary ash and coke dust were used as the finely divided carbonaceous material. Portland cement was added to the finely divided iron-containing raw material and finely divided carbonaceous material, and after kneading, pellets (average particle size 13 mm) were granulated by a disk pelletizer. Their blending ratio is shown in Table 1.

The particle size of the finely divided iron-containing raw material was adjusted by mixing fine dusty iron ore, which had been previously adjusted to a particle size of 125 to 250 μm and 250 to 1000 μm, into the sintered dust so as to have a predetermined overall particle size.
Examples 1, 2, and 3 are examples of the present invention, and the particle size of the finely divided iron oxide was adjusted such that the content ratio of the particle size of 125 μm or less was 10, 30 and 40% by mass, respectively.
In the comparative example, the content ratio of the particle size of 125 μm or less is 50%, which exceeds the specified range.

  The raw materials of each Example and Comparative Example were granulated into pellets with a moisture content of 8 to 11% by mass using a disk pelletizer, and the product was naturally cured for 14 days. After curing, a product having a diameter of 10 to 15 mm was sieved, and its cold crushing strength and hot crushing strength were measured.

The cold crushing strength is measured in accordance with JIS M8718 “Iron Ore Pellet Crushing Strength Test Method” by applying a compressive load to a single sample at a specified pressure rate to determine the load value at the time of failure. The strength index was measured and the load value per unit cross-sectional area (kN / m ² ) was used.
The crushing strength after reacting to 1200 ° C. was measured.

  As the hot crushing strength, the post-reaction crushing strength simulating the temperature and gas conditions in the blast furnace was measured. FIG. 1 shows an apparatus for measuring the post-reaction crush strength of a non-fired carbon-containing agglomerated blast furnace. A predetermined reactive gas flows from the inlet 3 between the inner reaction tube 1 (Φ73 mm) and the outer reaction tube 2 and is introduced into the reaction tube from the bottom of the reaction tube. Alumina balls 5 are spread on the lower part of the reaction tube, and a sample 6 comprising 350 g of sintered ore and 150 g of unfired carbon-containing pellets is filled thereon. The sample is heated by the heating device 7, and the sample temperature is measured by the thermocouple 8. The gas after the reaction is discharged from the reaction inner pipe 1 to the outside through the gas outlet 4 after the reaction. FIG. 2 shows the measurement conditions for the post-reaction crush strength of the unfired carbon-containing agglomerated blast furnace. The gas composition and temperature simulate the conditions in the shaft portion of the blast furnace. After completion of the reaction, the sample was taken out after cooling with nitrogen, and the crushing strength was measured. The crushing strength after the reaction was measured according to JIS M8718 “Iron ore pellet crushing strength test method”.

Table 2 shows the measurement results of cold crushing strength and post-reaction crushing strength of Examples and Comparative Examples. As can be seen from Examples 1 to 4, although the cold crushing strength is improved with an increase in the ratio of −125 μm, the post-reaction crushing strength is decreased, and the post-reaction crushing strength is 700 kN / Below m ² . Further, in Examples 4 and 5 in which 250 to 1000 μm was further limited to 10% and 125 to 250 μm was increased, both cold and post-reaction crushing strength were further improved as compared with Examples 2 and 3, respectively. Favorable results have been obtained. Incidentally, as shown in Comparative Example 2, a raw material having a large particle size in which coarse particles exceeding 1000 μm were mixed could not obtain a satisfactory cold and post-reaction crushing strength. As mentioned above, when this invention was implemented, the carbon containing agglomerated mineral which has the intensity | strength excellent in both the cold crushing strength and the crushing strength after reaction was obtained compared with the comparative example.
FIG. 3A shows a cross-sectional photograph of the sample after the reaction in Comparative Example 1. Since the content ratio is 125 μm or less, the reduction to wustite and metallic iron proceeds uniformly, but no metal network in which the metallic iron after the reaction is firmly bonded is observed. FIG. 3B shows a sample cross-sectional photograph after the reaction in Example 1. By containing iron oxide B having a particle size of 125 μm or less and a particle size of 250 μm or less and containing 125 μm to 250 μm of iron oxide B, metal iron after reduction forms a strong metal network, and non-fired carbon-containing pellets This confirms the dramatic improvement in strength after reaction.

  By using a small hydraulic binder, it is possible to provide a method for producing a non-fired carbon-containing agglomerated blast furnace ore for blast furnaces that has a large amount of interior carbon and high cold crush strength and hot crush strength.

  DESCRIPTION OF SYMBOLS 1 ... Inner tube, 2 ... Outer tube, 3 ... Reactive gas inlet, 4 ... Post-reaction gas outlet, 5 ... Alumina ball, 6 ... Sample, 7 Heating device, 8 ... Thermocouple

Claims (3)

  A method for producing an unfired carbon-containing agglomerated mineral for a blast furnace by adding water to a raw material having a finely divided iron oxide, a finely divided carbonaceous material, and a hydraulic binder, and mixing and granulating. The iron oxide has a particle size of 1,000 μm or more and less than 5% by mass, and the content ratio of the particle size of 125 μm or less is 40% by mass or less. Method.   The method for producing an unfired carbon-containing agglomerated mineral for blast furnace according to claim 1, wherein the fine powdered iron oxide has a content ratio of a particle size of 250 µm or more of 10 mass% or less.   The non-fired carbon-containing agglomerated mineral for blast furnace is any one of non-fired carbon-containing pellets and non-fired carbon-containing briquettes having 10% or more of the pulverized carbonaceous material with respect to the total mass of the raw material. The manufacturing method of the non-baking carbon-containing agglomerated mineral for blast furnaces in any one of Claim 1 and Claim 2 to do.