JP7782667B2 - Sinter manufacturing method - Google Patents

Description

The present invention relates to a method for producing sintered ore, which comprises granulating a sintering compound raw material containing carbonaceous material as a solid fuel to produce granulated raw material for sintering, and sintering the granulated raw material for sintering to obtain sintered ore.

In the sintering process, iron ore, flux, and carbonaceous material used as solid fuel are mixed in a sintering machine and then baked using the heat from the combustion of the carbonaceous material to produce sintered ore. Generally, coke breeze is used as the carbonaceous material, but anthracite and other coals are sometimes used to diversify the risk of fluctuations in the price of raw coal and problems with coke production equipment.

Meanwhile, with the recent rise in environmental awareness, diversification of carbonaceous materials is progressing with the intention of reducing the burden on the environment, regardless of risk diversification. As an example, Patent Document 1 proposes a carbonaceous material for sintered ore production, assuming subbituminous coal or lignite. This carbonaceous material has the following properties: a reaction initiation temperature of 550°C or less, a volatile matter (VM) of 1.0% or more, a hydrogen-to-carbon atomic ratio (H/C) of 0.040 or more, and a pore volume of 0.1 to 10 μm in diameter measured by mercury porosimetry of 50 mm ³ /g or more. Patent Document 2 also proposes the use of a sintering raw material containing 10 mass% or more of solid fuel with a combustion initiation temperature of less than 450°C when using 30% or more of high-crystallization-water iron ore containing 4.0 mass% or more of crystallization water.

However, all of these methods set an upper limit on the reaction initiation temperature, and therefore fail to take into account the negative impact on yield in the sinter ore production process. In this regard, Patent Document 3 proposes a two-stage ignition sintering method in which a sintered charge bed is formed in two stages, and sintering is carried out by igniting the surfaces of each stage. This method uses coke or anthracite as the raw material for the lower stage, along with a carbonaceous material with a lower combustion initiation temperature than coke or anthracite, in an amount ranging from 25 to 75% of the total carbon content, and adds at least one of a low combustion initiation temperature carbonaceous material and a high combustion initiation temperature carbonaceous material in the latter half of the granulation process.

Patent No. 4681688 Patent No. 4837799 Japanese Patent Application Laid-Open No. 2020-186436 Japanese Patent Application Laid-Open No. 2022-033594

However, the method disclosed in Patent Document 3 is based on the premise of a two-stage ignition sintering method, and therefore could not be used for general sintering methods. Furthermore, with the method disclosed in Patent Document 4, there are different types of carbonaceous materials with low combustion initiation temperatures, and these combustion initiation temperatures vary, so there was a risk in uniformly sorting by carbon content.

The object of the present invention is to solve the above problems and propose a method for producing sintered ore that can prevent a decrease in yield when using carbonaceous material with a low combustion start temperature in a method for producing sintered ore by granulating a sintering compound raw material containing carbonaceous material as a solid fuel to produce granulated raw material for sintering, and then sintering the granulated raw material for sintering to obtain sintered ore.

The method for producing sintered ore of the present invention involves granulating a sintering blended raw material containing a carbonaceous material as a solid fuel to produce a granulated raw material for sintering, and then sintering the granulated raw material for sintering to obtain sintered ore, characterized in that the carbonaceous material used is a blend of at least two types of carbonaceous material, and the weighted average of the combustion start temperatures is 550°C or higher.

In the method for producing sintered ore according to the present invention configured as described above,
(1) The carbonaceous material to be blended includes one having a combustion start temperature of less than 550°C;
(2) The carbonaceous material having a combustion start temperature of less than 550°C includes an organic resource other than fossil fuel, or a material produced using the organic resource as a raw material;
(3) The carbonaceous material having a combustion start temperature of less than 550°C is a coke made from biomass coal, anthracite, waste plastic coal, lignite, or subbituminous coal;
(4) The entire amount of the blended carbonaceous material is added before the granulation process;
This is considered to be a more preferable solution.

According to the method for producing sintered ore of the present invention, by sintering a carbonaceous material that is a blend of at least two types of carbonaceous material and has a weighted average combustion start temperature of 550°C or higher, it is possible to suppress yield reduction when blended into sintered ore and used.

1 is a schematic diagram showing an embodiment of a sintered ore manufacturing facility used in a sintered ore manufacturing method of the present invention. FIG. 1 is a graph showing the relationship between product yield and weighted average of combustion initiation temperature in Examples. 1 is a graph showing a comparison of product yields between addition before carbonaceous material granulation and addition after carbonaceous material granulation.

The following provides a detailed description of embodiments of the present invention. Note that the following embodiments are intended to exemplify devices and methods that embody the technical concepts of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concepts of the present invention can be modified in various ways within the technical scope described in the claims.

<Regarding the sintered ore manufacturing equipment used in the sintered ore manufacturing method of the present invention>
1 is a schematic diagram showing one embodiment of a sinter ore production facility 1 used in the sinter ore production method of the present invention. The sinter ore production facility 1 has a drum mixer 2, which is a granulating device, a sinter machine 3, a crusher 4, a cooler 5, and a sieving device 6. Sinter raw materials including iron-containing raw materials, auxiliary raw materials, and coagulating agents such as carbonaceous material and coke powder are granulated in the drum mixer 2 after granulation water is added. The granulated raw materials for sintering are transported to the sinter machine 3.

The sintering machine 3 is, for example, a Dwight Lloyd type sintering machine. The sintering machine 3 has a sintering raw material supply device 11, an endless moving pallet cart 12, an ignition furnace 13, and a wind box 14. Granulated sintering raw material is loaded from the sintering raw material supply device 11 onto the pallet cart 12, forming a sintering raw material bed. The ignition furnace 13 ignites the coagulant contained in the surface layer of the sintering bed, and air within the sintering bed is sucked downward through the wind box 14, moving the combustion and melting zone within the sintering bed below the sintering bed. This movement of the combustion and melting zone sinters the sintering bed into a sintered cake.

When the air in the sintering bed is sucked downward through the wind box 14, gaseous fuel and/or oxygen-enriched air may be supplied from above the sintering bed. The gaseous fuel is any combustible gas selected from blast furnace gas, coke oven gas, converter gas, city gas, natural gas, methane gas, ethane gas, propane gas, and mixtures thereof.

The sinter cake is crushed by crusher 4 and cooled in cooler 5. The crushed sinter cake is sieved in sieving device 6 into sinter ore with a particle size of 5 mm or more and return ore with a particle size of less than 5 mm. The return ore is reused as sinter raw material. In this way, sinter ore is produced.

<Regarding the method for producing sintered ore of the present invention>
The method for producing sintered ore according to the present invention is characterized in that the carbonaceous material used as the solid fuel is a blend of at least two types of carbonaceous material, and the weighted average of the combustion start temperatures is 550° C. or higher. The carbonaceous material used in the method for producing sintered ore according to the present invention, which is a characteristic of the present invention, will be described below.

In an effort to diversify carbonaceous materials to reduce environmental impact, biomass-derived carbonaceous materials (hereinafter referred to as biomass charcoal) are attracting attention. Because biomass charcoal absorbs carbon dioxide while the plants that serve as its raw material grow, fuels made from biomass charcoal can be counted as carbon-neutral, meaning that no carbon dioxide is emitted outside the system. As a result, the use of biomass charcoal is being considered even in iron ore sintering processes, which typically use coke breeze. A characteristic of biomass charcoal is that its combustion start temperature is lower than that of coke (600-750°C), generally below 550°C.

In the sintering process in the sintering machine 3 described above, flux and carbonaceous material are added to the iron ore and continuously charged onto the sintering machine 3, forming a sintering bed consisting of a layer of sintering raw materials. After igniting the sintering bed at the top, exhaust gas is drawn in from the bottom, causing the combustion of the carbonaceous material to spread from the top to the bottom of the bed, and the heat is used to cause the iron ore and flux to react and form into agglomerates. Exhaust gas is drawn in from the bottom layer using a blower, and the drawn-in exhaust gas passes through a duct, passes through a dust collector, and desulfurization and denitrification equipment before being discharged from the chimney.

As mentioned above, a distinctive feature of biomass charcoal is its low combustion initiation temperature. This is thought to be because, compared to the fine coke (derived from fossil fuels) commonly used in the sintering process, biomass charcoal is porous and has a very high surface area, allowing for a high combustion rate even at low temperatures. Therefore, although biomass charcoal has a low combustion initiation temperature, it tends to have a high subsequent combustion rate.

The combustion reaction of carbonaceous materials is a gas-solid reaction. Carbonaceous materials burn by reacting with oxygen in the surrounding gas. In gas-solid reactions under flowing gas conditions, such as sintering, a very thin layer called a gas film exists on the solid surface. The gas film maintains a laminar flow unaffected by external turbulence. Oxygen diffuses from the outside of the gas film through the gas film and reaches the surface of the carbonaceous material, where it is used for combustion. However, if the combustion rate of the carbonaceous material is very fast, even when the ambient oxygen concentration is high, the rate of oxygen consumption at the surface due to the burning of the carbonaceous material is greater than the rate of oxygen supply due to oxygen diffusion within the gas film, resulting in a decrease in the oxygen concentration within the gas film. This causes incomplete combustion of the carbonaceous material, resulting in increased carbon monoxide generation. Therefore, if the combustion rate is very fast, some of the combustion heat of the carbonaceous material is emitted outside the system as carbon monoxide, reducing the reaction heat used for sintering and resulting in a decrease in yield. Here, by reducing the combustion rate of the carbonaceous material used and setting the combustion initiation temperature to 550°C or higher, it is possible to eliminate the diffusion rate limitation within the gas boundary film in the oxygen supply during the combustion reaction and to suppress the emission of part of the combustion heat to the outside of the system as carbon monoxide.

The combustion rate of carbonaceous materials is thought to be affected by a decrease in the combustion rate constant per unit area of the carbonaceous material and a decrease in surface area, but the combustion rate constant is a value determined by the properties of the carbonaceous material and is difficult to control. Methods for decreasing surface area include increasing the particle size of the carbonaceous material or coating the surface. However, the particle size needs to be increased to a size that is difficult to use with existing processes, and coating powder is technically difficult, making it difficult to control the surface area to the target level.

For these reasons, it is practical to use a carbonaceous material with a high combustion rate by mixing it with a carbonaceous material with a low combustion rate to comprehensively control the combustion rate. Therefore, in the present invention, when using a carbonaceous material other than fossil fuels, such as biomass charcoal, whose combustion initiation temperature is less than 550°C, a carbonaceous material with a high combustion initiation temperature is added and blended to make the weighted average of the combustion initiation temperatures of the blended carbonaceous materials 550°C or higher. This makes it possible to suppress a decrease in sinter yield while suppressing _CO2 emissions outside the system from the perspective of carbon neutrality.

In a preferred embodiment, the entire amount of the blended carbonaceous material containing at least two or more types of carbonaceous material is added before the granulation process. This suppresses segregation of the blended carbonaceous material and reduces the variation in the combustion start temperature of the carbonaceous material blended in the sintered granulated raw material, thereby suppressing the variation in sintered ore yield.

As carbonaceous materials with a combustion initiation temperature of less than 550°C, organic resources other than fossil fuels, or materials produced using the above organic resources as raw materials, more specifically, coke made from biomass coal, anthracite, waste plastic coal, lignite, or subbituminous coal, can be suitably used.

Example 1
Using a batch-type sintering test apparatus, sintered ore was produced using a blend of at least two or more carbonaceous materials with different combustion initiation temperatures, sintering them under the same input heat. Commonly used carbonaceous materials were coke breeze, anthracite, and other biomass charcoal and lignite with combustion initiation temperatures below 550°C. Reference Examples 1-4 were used as examples using the carbonaceous materials alone. Comparative Examples 1-3 were used as examples using at least two or more of the carbonaceous materials, with a weighted average combustion initiation temperature below 550°C. Examples 1-6 were used as examples using at least two or more of the carbonaceous materials, with a weighted average combustion initiation temperature above 550°C. The blending of raw materials other than the carbonaceous materials was kept constant. The yield of sintered ore produced using each carbonaceous material was calculated as the percentage of particles 5 mm or larger when all sintered samples were dropped four times from a height of 2 m. The results are shown in Table 1, and the relationship between product yield and weighted average combustion initiation temperature is shown in Figure 2.

Here, the combustion initiation temperature was determined using the following method. 10 mg of the target carbonaceous material was weighed out and heated at 10°C/min in an electric furnace equipped with differential thermal analysis functions while air was circulated at 200 ml/min. When the combustion initiation temperature was reached, the carbonaceous material began to burn and rapidly generated heat. At this time, time was plotted on the horizontal axis and the heat change in the differential thermal analysis on the vertical axis, and a line representing the relationship between time and heat change was drawn. The combustion initiation temperature was determined as the intersection of the extension of the line representing the heat change just before the sudden heat generation was detected in the differential thermal analysis and the extension of the line representing the heat change just after the detection.

The results in Table 1 and Figure 2 show that product yield increases as the weighted average of the combustion initiation temperature after blending increases. Furthermore, it was found that in Comparative Example 1-3, where the weighted average of the combustion initiation temperature after blending was less than 550°C, the product yield was low. On the other hand, in Example 1-6, where the weighted average of the combustion initiation temperature after blending at least two types of carbonaceous materials was 550°C or higher, the product yield was higher than in Comparative Example 1-3, and it was found that the increase in product yield saturates around 550°C. Furthermore, when biomass charcoal and lignite, which have combustion initiation temperatures less than 550°C, were used alone (Reference Example 1, Reference Example 2), the product yield was low. However, it was found that by mixing them with other carbonaceous materials and setting the weighted average of the combustion initiation temperature to 550°C or higher (Example 1-6), the product yield increased. From the above, it was found that even carbonaceous materials with a sintering start temperature of less than 550°C, which cannot be used alone due to low product yield, can be used as carbonaceous materials by blending them with other carbonaceous materials to make the weighted average sintering start temperature 550°C or higher.

Example 2
The carbonaceous material blended under the conditions of Example 1 in Table 1 was added multiple times before the granulation process and in the latter half of the granulation process, and the variability in product yield was investigated. The results are shown in Figure 3. As a result, in the level where the carbonaceous material was added before granulation, there was a variability of about 8% in product yield, with an average value of 87%. On the other hand, in the level where the carbonaceous material was added in the latter half of granulation, there was a variability of about 17%, with some levels exceeding 85%, but on average the value was lower than in the level where the carbonaceous material was added before granulation. From the above, it was found that it is a preferable embodiment for the entire amount of carbonaceous material after blending to be added before the granulation process.

According to the sintered ore manufacturing method of the present invention, by using a specified carbonaceous material, it is possible to prevent a decrease in yield when using carbonaceous material with a low combustion start temperature, making it industrially useful.

REFERENCE SIGNS LIST 1 sintered ore manufacturing equipment 2 drum mixer 3 sintering machine 4 crusher 5 cooler 6 sieving device 11 raw material supply device 12 pallet cart 13 ignition furnace 14 wind box

Claims (4)

A method for producing sintered ore, which comprises granulating a blended sintering raw material containing a carbonaceous material as a solid fuel to produce a granulated raw material for sintering, and sintering the granulated raw material for sintering to obtain sintered ore, characterized in that the carbonaceous material is a blend of at least two types of carbonaceous material, the weighted average of whose combustion start temperatures is 550°C or higher , and the entire amount of the blended carbonaceous material is added before the granulation step . The method for producing sintered ore described in claim 1, characterized in that the blended carbonaceous material includes one with a combustion start temperature of less than 550°C. The method for producing sintered ore described in claim 2, characterized in that the carbonaceous material having a combustion initiation temperature of less than 550°C includes organic resources other than fossil fuels, or materials produced using such organic resources as raw materials. The method for producing sintered ore described in claim 3, characterized in that the carbonaceous material having a combustion start temperature of less than 550°C is coke made from biomass coal, anthracite, waste plastic coal, lignite, or subbituminous coal.