JP2022129696A - Manufacturing method of sintered ore - Google Patents

Abstract

To suppress the increase of NOx content in an exhaust gas from sintering, caused by a change in the blending ratio of raw materials.SOLUTION: A manufacturing method of sintered ore blends whole iron ore with new raw materials at a predetermined ratio, the whole iron ore obtained by blending a plurality of brands of iron ore at a predetermined composition ratio. In changing the composition ratio of two or more brands of iron ore in the whole iron ore, if a crystal water content in the whole iron ore after the change is higher than that before the change, the blending ratio of low nitrogen anthracite is increased according to an increment of the crystal water content so that the NOx content in an exhaust gas may not increase from that before the change of the composition ratio.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing sintered ore.

At present, the main raw material for blast furnace ironmaking is sintered ore. Raw materials for sintered ore include iron ore (multiple brands of iron ore), miscellaneous raw materials (recycled raw materials containing iron such as scale and steelmaking dust), and auxiliary raw materials (limestone, CaO in sintered ore such as peridotite, etc. , raw materials for adjusting the MgO component), carbon materials (also known as coagulants, raw materials that serve as heat sources for sintering reactions such as coke fines and anthracite), and return ores (circulating under the sieves of products used).

Sintered ore is usually manufactured as follows. First, the raw materials are mixed at a predetermined ratio to obtain a blended raw material, and the blended raw material is granulated to obtain raw material granules. Next, the raw material granules are loaded from the hopper onto a pallet of a downward suction type Dwight Lloyd (DL) type sintering machine to form a raw material packed bed. The carbon material in the raw material packed bed is ignited from above (surface layer) of the formed raw material packed bed. Then, while continuously moving the pallet, air is sucked from below the pallet to supply oxygen, and the carbonaceous material in the raw material packed bed is burned from the top to the bottom, so that the combustion heat of the carbonaceous material sequentially Sinter. The obtained sintered part (sinter cake) is pulverized to a predetermined particle size, sieved, or the like to obtain sintered ore, which is a raw material for a blast furnace.

Sintering exhaust gas (hereinafter also simply referred to as exhaust gas) discharged from the sintering machine contains nitrogen oxides NOx (NO and NO ₂ ). Most of the nitrogen oxide NOx in the exhaust gas is fuel NOx generated when the fuel carbonaceous material is burned in the sintered layer. Generated by reaction.

Nitrogen oxide NOx is one of the causative substances of air pollution, and reduction of its emission is important. The NOx concentration in the exhaust gas fluctuates due to changes in the blending ratio of raw materials and other changes in daily operation of the sintering machine. is operating in This control value is set to a value lower than the NOx emission control value (ordinance standard value, etc.) in each operating area for each ironworks.

NOx concentration is generally monitored using the value of "NOx concentration (O ₂ =15% correction value)". The NOx concentration (O ₂ =15% correction value) is the NOx concentration C after the oxygen concentration correction corrected so that the standard oxygen concentration remaining in the exhaust gas is 15%. NOx concentration C (O ₂ =15% correction value) is calculated using the following formula (1) based on the measured NOx concentration (actual measurement value Cs) and oxygen concentration Os. The NOx concentration (actual value) and oxygen concentration (actual value) in the exhaust gas can be measured by, for example, an analyzer (NOx analyzer (chemiluminescence method), zirconia It is measured continuously by a formula analyzer, etc.).
C=(21−On)/(21−Os)×Cs (1)
C: NOx concentration after oxygen concentration correction (ppm)
Os: Oxygen concentration in the exhaust gas (20% if the concentration exceeds 20%)
On: Standard oxygen concentration (%) *15% for sintering machine
Cs: Measured NOx in exhaust gas (ppm)

In the steelworks, the calculated NOx concentration C (O ₂ =15% correction value) is constantly monitored, and if it exceeds the control value, measures are taken to reduce NOx emissions. As a reduction measure, for example, a measure of changing the brand of carbon material is taken. Also, the following techniques have been proposed.

In Patent Document 1, the sintering raw material is granulated with a granulation moisture content of 4.0 to 6.0%, the sintering raw material is supplied to a continuous downward suction sintering machine, and sintering is performed while the coke combustion reaction is in progress. A method for producing sintered ore is disclosed in which 5.0 to 90.0 l/t-raw material moisture is supplied to the bed surface. Further, in Patent Document 2, as sintering raw materials, iron ore containing high crystal water iron ore containing 4.0 mass% or more of water of crystallization, auxiliary raw materials, and a combustion reaction initiation temperature of less than 450 ° C. A method for producing sintered ore is disclosed in which a solid fuel containing 10 mass% or more of a low-temperature combustible solid fuel is blended with the high crystal water iron ore so that the sintering raw material contains 30 mass% or more.

The technique described in Patent Document 1 is to reduce the amount of NOx generated by sprinkling water on the surface of the sintered layer to optimize the distribution of the amount of water in the blended raw material and the amount of sprinkled water. The technology described in 1. combines a high crystal water ore and a solid fuel (char), and reduces the amount of NOx generated by setting the mixing ratio of the solid fuel (char) and the high crystal water ore to a predetermined amount or more. be. The technique described in Patent Document ₂ is based on the premise that H2 is generated in the calcining zone and NO is reduced there, but the reduction of NO occurs in the calcining zone (low temperature). It is known to occur within the coke gas boundary film (combustion zone) rather than within the coke gas boundary film.

JP-A-61-204342 International Publication No. 2010/106756

By repeating sintering experiments using a small pot test apparatus, the present inventors found that even if the blending ratio of the carbonaceous material used as the fuel for sintering was constant, when different brands of iron ore were used, It was found that the amount of NOx generated during sintering was significantly different. The present inventors have found that there is a correlation between the water of crystallization content (average value) of the iron ore in the raw material for sintering and the amount of NOx produced. This finding shows a result opposite to the technique disclosed in Patent Document 2, which reduces the amount of NOx generated by using a ratio of high crystal water ore ore of a predetermined amount or more.

The present invention was created based on such knowledge, and an object of the present invention is to provide a new method for producing sintered ore that can suppress an increase in the amount of NOx contained in sintering exhaust gas.

The gist of the present invention is as follows.
(1) A method for producing sintered ore in which a mixture of multiple brands of iron ore at a predetermined composition ratio is used as total iron ore, and the total iron ore is mixed with a new raw material at a predetermined ratio,
When changing the composition ratio of two or more brands of iron ore in the total iron ore, if the crystal water content of the total iron ore after the change is higher than before the change, the NOx concentration in the exhaust gas will change the composition ratio. A method for producing sintered ore, wherein the blending ratio of low-nitrogen anthracite coal is increased according to the increase in crystal water content so as not to increase the content from before the change.
(2) determining in advance the NOx concentration increase coefficient Ccw (d ₁ NOx/dCW) with respect to the increase in the crystal water content of the total iron ore;
Obtaining in advance the reduction coefficient Cans (d ₂ NOx/dAns) of the NOx concentration with respect to the increase in the blending ratio of the low-nitrogen anthracite,
The sintered ore according to (1), wherein when the increase in the crystal water content of the total iron ore is Δx, the increase in the blending ratio of the low-nitrogen anthracite is set to (Ccw/Cans)×Δx or more. Production method.
(3) The method for producing sintered ore according to (2), wherein the unit of the increment Δx in the water of crystallization content of the total iron ore is % by mass, and Ccw/Cans is 0.5.
Here, the low-nitrogen anthracite is anthracite whose nitrogen content is lower than that of coke fine, which is a general carbonaceous material for sintering.

According to the present invention, when the crystal water content of the total iron ore increases during an operational action that changes the composition ratio of two or more brands of iron ore in the total iron ore, low-nitrogen anthracite is blended according to the increased amount. By increasing the ratio, an increase in the amount of NOx in the exhaust gas from the sintering machine can be suppressed.

FIG. 3 is a diagram showing the relationship between the water of crystallization content of each brand of iron ore and the NOx concentration in the sintering exhaust gas (O ₂ =15% correction value).

As a result of extensive studies to reduce NOx emissions, the present inventors found that even if the blending ratio of iron ore in the new raw material is constant, the amount of NOx generated when iron ore with a high content of water of crystallization is used. A correlation has been found that the amount of NOx generated decreases when iron ore with a large amount of water of crystallization is used. Based on this knowledge, the present inventors, in producing sintered ore, calculated the average amount of water of crystallization contained in all iron ore in the raw material blend (the content of water of crystallization in all iron ore) in the sintering exhaust gas. It was devised to use it as an index for managing NOx emissions. First, an experiment and its results supporting the above findings will be described below.

<Fundamental study leading to the invention>
In order to confirm the NOx emission tendency peculiar to each brand of iron ore, five experiments (experiment 1- Experiment 5) was performed. Experiments 1 to 5 were conducted using a small sintering pot test (100 mm in diameter) simulating the sintering phenomenon in a sintering machine.

(Raw material composition)
Table 1 shows the mixing ratio of each raw material for sintering used in Experiments 1 to 5. As shown in Table 1, the new raw materials (iron ore, limestone, quicklime, and peridotite) excluding the return ore and the carbonaceous material are assumed to be 100% by mass, and the mixing ratio of the return ore and the carbonaceous material is expressed as an external number, 15.0% by mass and 4.5% by mass.

Table 2 shows the amounts (% by mass) of main components of iron ores A to E used in Experiments 1 to 5. In each experiment of Experiments 1 to 5, one type of iron ore (one brand) was used singly as the raw material iron ore shown in Table 1. For example, in Experiment 1, only iron ore A was used as the raw iron ore. As shown in Table 2, iron ore A and iron ore B are pisolite iron ores with a high content of water of crystallization (CW: combined water), and iron ore D and iron ore E have a high content of water of crystallization. It is a hematite ore with little Iron ore C is a Marra Mamba iron ore having a water of crystallization content lower than iron ore A and iron ore B and higher than iron ore D and iron ore E.

Table 3 shows the particle size distribution of iron ore and carbonaceous materials used as raw materials. This particle size distribution was obtained by classifying with sieves having opening sizes of 5.0 mm, 3.0 mm, 1.0 mm, 0.5 mm and 0.25 mm. For example, the particle size division "1 mm-0.5 mm" means above the sieve when sieved with a sieve with a sieve of 0.5 mm, and under sieve when sieving with a sieve with a sieve of 1 mm. In each of Experiments 1 to 5, the particle size conditions were the same, and iron ore and carbonaceous materials having particle size distributions shown in Table 3 were used.

(Experimental conditions)
Each raw material for sintering was mixed at the mixing ratio shown in Table 1, and the mixed raw material was granulated, and the granulated raw material was fired. The main experimental equipment is as shown in Table 4.

In the above sintering experiment, the raw materials were mixed (dry mixed) for 1 minute at 32 rpm in a drum mixer. After mixing, 7.0% by mass of water was added to the blended raw material, and the mixture was granulated for 4 minutes to produce raw material granules. In the sintering pot, first, cao wool was laid on the rostle. Next, the raw material granules were charged into a sintering pot so as to have a layer thickness of 445 mm. After charging, the surface of the raw material was heated and ignited in an ignition furnace for 60 [sec], and fired at an air volume (constant) of 0.08 [Nm ³ /min] in the wind box.

(measurement)
A portable gas analyzer PG-350 manufactured by Horiba, Ltd. was used for gas analysis. The NOx concentration was measured using a chemiluminescence analysis unit, and the oxygen concentration was measured using a zirconia analysis unit.

(Experimental result)
The rightmost column of Table 5 shows the NOx concentration (O ₂ =15% correction value) calculated from the measured NOx concentration and oxygen concentration. FIG. 1 is a graph showing the relationship between the water of crystallization content in Table 5 and the NOx concentration (O ₂ =15% correction value). As shown in FIG. 1, there is a correlation between the water of crystallization content and the NOx concentration (O ₂ =15% correction value). NOx emissions) tended to decrease.

The NOx concentration increase coefficient Ccw, which is derived from FIG. 1 and indicates the correlation between the water of crystallization content and the NOx concentration (O ₂ =15% correction value), is shown in the following equation (2). As shown in the formula (2), it was found that when the crystal water content in the iron ore increases by 1% (mass %), the NOx concentration (O ₂ =15% correction value) increases by about 5 ppm.
NOx concentration increase coefficient Ccw = 5 ppm/increase in crystal water content 1% by mass (2)

<Embodiment>
(The present invention and its features)
The present invention was invented by combining the above findings with a method for reducing the amount of NOx using low-nitrogen anthracite (details will be described later). The present invention provides a method for producing sintered ore in which a mixture of multiple brands of iron ore at a predetermined composition ratio is used as total iron ore, and the total iron ore is mixed with a new raw material at a predetermined ratio. When changing the composition ratio of two or more brands of iron ore, if the crystal water content of all the iron ores after the change is higher than before the change, the NOx amount (NOx concentration) in the exhaust gas will change. The blending ratio of the low-nitrogen anthracite coal is increased according to the increased amount so as not to increase from before.

(Change in composition of iron ore)
The iron ore of the blended raw material is usually blended with a predetermined ratio of multiple brands of iron ore. Since the arrival amount and price of each brand of iron ore are not constant and fluctuate, the mixing ratio of each brand of iron ore is changed as appropriate. Specifically, the composition ratio (mass%) of all iron ore (multiple brands of iron ore mixed in a predetermined ratio) in the new raw material will not be changed, and the composition ratio of each brand of iron ore in all iron ore will be take operational actions that change part or all of This operation action is called an iron ore composition ratio change operation. In the following description, the entire iron ore of multiple brands blended at a predetermined ratio is referred to as all iron ore or uniform ore.

(Crystal water content of uniform ore)
The crystal water content of uniform ore is calculated by the following formula (3). Formula (3) uses the water of crystallization content CW of the graded ore as the average water of crystallization content of all brands of iron ore, and the water of crystallization content CWi for each brand weighted by the composition ratio of each brand in the graded ore. Indicates to be calculated on average.
CW=Σ(Xi×CWi)/100 (3)
CW: Crystal water content of uniform ore (% by mass)
Xi: Composition ratio of iron ore brand i in uniform ore (% by mass)
CWi: Crystal water content of iron ore grade i (% by mass)

(Low nitrogen anthracite)
Next, the low-nitrogen anthracite and the NOx amount reduction method using it will be described in order.
In the present invention, low-nitrogen anthracite is defined as anthracite whose nitrogen content is lower than coke breeze (nitrogen content is about 1% by mass), which is a common carbonaceous material for sintering. Low-nitrogen anthracite has a low nitrogen content, so it produces less NOx than coke breeze when burned. In order to obtain a large NOx reduction effect, it is desirable to use anthracite with a nitrogen content of 0.6% by mass or less. Table 6 shows an example of properties of coke breeze and low-nitrogen anthracite.

When the content of water of crystallization in all iron ores increases due to changes in the composition ratio of iron ores for each brand, the amount of NOx in the sintering exhaust gas also increases. In the present invention, an increase in the amount of NOx in the sintering exhaust gas is suppressed by increasing the blending ratio of the low-nitrogen anthracite according to the amount of increase in the content of water of crystallization.
Preferred embodiments of the present invention are described below.

First, the correlation between the amount of NOx in the sintering exhaust gas (NOx) and the water of crystallization of iron ore (CW) is determined by experiments, regression analysis of operation data, etc., and the increase in water of crystallization of iron ore (dCW) An increase coefficient Ccw (d ₁ NOx/dCW) indicating an increase in NOx (d ₁ NOx) in the sintering exhaust gas relative to the sintering gas is obtained. In addition, the correlation between the amount of NOx in the sintering exhaust gas and the amount of anthracite coal used (Ans) was obtained by experiments, regression analysis of operation data, etc., and the NOx A reduction coefficient Cans (d ₂ NOx/dAns) indicating the reduction amount (d ₂ NOx) of is also obtained.
Then, when the water of crystallization of all iron ores (average water of crystallization of all brands of iron ore) increases (ΔCW) due to the operation to change the composition ratio of iron ore, the amount of NOx in exhaust gas The blending ratio of low nitrogen anthracite coal is increased (ΔAns) according to the amount of increase in water of crystallization so that (NOx concentration) does not increase from before the operation of changing the composition ratio.
That is, the amount of increase (ΔAns) in the blending ratio of the low-nitrogen anthracite should satisfy the following formula (4).
ΔAns≧ΔCW×((d ₁ NOx/dCW)/(d ₂ NOx/dAns))
=ΔCW×(Ccw/Cans) (4)

In the above-described embodiment, a specific example of the increase coefficient Ccw (d ₁ NOx/dCW), which indicates the amount of increase in NOx in the sintering exhaust gas with respect to the amount of increase in water of crystallization of iron ore, has already been shown as formula (2). Specific examples of the reduction coefficient Cans (d ₂ NOx/dAns) indicating the amount of NOx reduction in the sintering exhaust gas with respect to the amount of increase in the amount of anthracite coal used are shown below.

(NOx reduction method using low-nitrogen anthracite)
In the present invention, as a measure to reduce the amount of NOx (NOx concentration) in the sintering exhaust gas, a large amount of the low-nitrogen anthracite coal described above is used instead of coke fine as the carbon material.
The present inventors newly conducted an experiment similar to the small sintering pot test described above, and confirmed the effect of reducing the amount of NOx when using low-nitrogen anthracite coal. Specifically, in the above-mentioned small sintering pot test, after confirming the amount of NOx when using coke fine alone as a carbon material blended with an external number of 4.5% by mass, coke fine is gradually added to low nitrogen The amount of NOx when replacing with anthracite in equal amounts was recorded, and the relationship between the amount of replacement with low-nitrogen anthracite and the reduction in NOx concentration was quantified. As a result, as shown in the following formula (5), the amount of NOx generated was reduced by 10 ppm per 1% by mass of replacement with low-nitrogen anthracite. As the iron ore in Table 1, a mixture of multiple brands of iron ore as shown in Table 7 was used.
NOx concentration reduction coefficient Cans = 10 ppm/Low nitrogen anthracite replacement amount 1% by mass (5)

(Adjustment of NOx amount in exhaust gas based on increase in crystal water content of all iron ores)
From the above formula (2), the NOx concentration increases by 5 ppm when the amount of increase in the crystal water content is 1% by mass. Further, according to the above formulas (4) and (5), in order to suppress an increase in the NOx concentration, the replacement amount of low nitrogen anthracite should be 0.5% by mass. That is, in order not to increase the NOx concentration after the iron ore composition ratio change operation, the amount of low nitrogen anthracite replaced with respect to the increase amount Δx mass% of the water of crystallization is (0.5 × Δx) mass% or more. The suppression effect coefficient for suppressing the increase in NOx concentration is 0.5.

Experiments similar to the above-described small sintering pot test were conducted using the blended raw materials of the blending ratios shown in Table 8 to verify the effects of the above invention.
As shown in Table 8, the NOx concentration in the sintering exhaust gas was measured before and after changing the composition ratio of multiple brands of iron ore. The water of crystallization in the total iron ore increased after the change compared to before the change in the composition ratio of multiple brands of iron ore. Specifically, the crystal water content in the total iron ore increased by 1.5% by mass compared to before the change, so based on the above-mentioned suppression effect coefficient value (0.5), coke fine was added to the new raw material. was replaced with low-nitrogen anthracite at an external number of 0.75% by mass.

As shown in the rightmost column of Table 8, it was confirmed that the NOx concentration in the sintering exhaust gas did not increase even after changing the composition ratio of iron ore.

In this example, the relationship between the amount of low-nitrogen anthracite replaced with low-nitrogen anthracite and the amount of NOx concentration reduction was determined for the low-nitrogen anthracite and coke fine shown in Table 6, but other low-nitrogen anthracite and/or When using other coke fines with different nitrogen contents, a new sintering pot test is performed to determine the relationship between the amount of replacement with low-nitrogen anthracite and the amount of NOx concentration reduction (NOx concentration reduction coefficient Cans). is desirable.

Claims (3)

A method for producing sintered ore in which a mixture of multiple brands of iron ore at a predetermined composition ratio is used as total iron ore, and the total iron ore is mixed with a new raw material at a predetermined ratio,
When changing the composition ratio of two or more brands of iron ore in the total iron ore, if the crystal water content of the total iron ore after the change is higher than before the change, the NOx concentration in the exhaust gas will change the composition ratio. A method for producing sintered ore, wherein the blending ratio of low-nitrogen anthracite coal is increased according to the increase in crystal water content so as not to increase the content from before the change. Obtaining in advance the NOx concentration increase coefficient Ccw (d ₁ NOx/dCW) with respect to the increase in the crystal water content of the total iron ore,
Obtaining in advance the reduction coefficient Cans (d ₂ NOx/dAns) of the NOx concentration with respect to the increase in the blending ratio of the low-nitrogen anthracite,
2. The sintered ore according to claim 1, wherein when the amount of increase in the water of crystallization content of the total iron ore is Δx, the amount of increase in the blending ratio of the low-nitrogen anthracite is set to (Ccw/Cans)×Δx or more. Production method. The method for producing sintered ore according to claim 2, wherein the unit of the increase amount Δx of the water of crystallization content of the total iron ore is % by mass, and Ccw/Cans is 0.5.

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