JP7589727B2 - Sintered ore manufacturing method and manufacturing device - Google Patents

Description

The present invention relates to a method and apparatus for producing sintered ore that can obtain higher quality sintered ore by reflecting the temperature distribution in the sintered layer in the operation of the sintering machine.

In the production of sintered ore, the main raw material for blast furnaces, iron ore powder, limestone, fine coke and return ore mixed in the yard are granulated in a drum mixer and then charged into a sintering machine. In the sintering machine, the upper layer of the sintering bed is ignited in an ignition furnace, and the sintering reaction proceeds due to the heat of combustion of the fine coke. Sintering productivity is determined by the firing speed and product yield; the firing speed is greatly influenced by the gas permeability in the sintering bed, while the product yield is greatly influenced by the firing condition of the entire bed and the strength of the individual sintered ores.

In the ironmaking process, the important issues are stable production of molten iron in the blast furnace and reduction of _CO2 emissions by reducing the amount of lump coke used as a reducing agent. While sintered ore with high reducibility is necessary to reduce the lump coke ratio, sintered ore with a particle size of 5 mm or less deteriorates the gas permeability in the blast furnace and reduces productivity, so it is necessary to produce high-strength sintered ore that is less likely to disintegrate.

To measure the quality of sintered ore, the strength is measured using the tumbler strength test specified in JIS M 8712 and the shutter strength test specified in JIS M 8711. In addition, the reducibility of sintered ore is evaluated using the RI test specified in JIS M 8713.

The produced sintered ore is sampled at regular intervals during daily operation using a sampling device, and the quality is monitored using an offline analyzer. The operator usually takes necessary actions such as changing and adjusting the operating conditions while checking the results. The measured value of sintered ore strength is sometimes compared with the FeO analysis value in the sintered ore (the content of _Fe3O4 in the sintered ore converted into FeO ₎ . The magnetite structure in sintered ore is a structure that is formed in a reducing atmosphere in the combustion melting zone and remains without being reoxidized under the rapid cooling conditions of the sintering machine. When the heat input is large, the FeO concentration in the sintered ore tends to be high, so it is used as an index of the heat input.

In this situation, in order to improve the quality of sintered ore, it is necessary to control the heat input based on the sintered ore structure, which is closely related to quality. Regarding the strength of sintered ore, Non-Patent Document 1 discloses an estimation formula for sintered ore yield. According to this, it is possible to estimate the yield using the matrix strength and porosity of sintered ore obtained by tablet testing. In addition, Non-Patent Document 2 reports examples of measurements of reducibility and strength for each matrix. According to these, hematite and calcium ferrite, which are the main mineral structures of sintered ore, have higher strength and reducibility than slag structures. In addition, Non-Patent Document 3 reports that a structure called acicular calcium ferrite, in which the width of calcium ferrite is 10 μm or less, improves reducibility.

However, these reports on the relationship between sinter ore quality and structure are all evaluations made after sinter ore production, and sampling and measurement take time, making it difficult to take prompt action. This poses the problem of not being able to reflect the results in actual plant operations.

On the other hand, as a method for understanding the quality of sintered ore in advance and proposing rapid action, Patent Document 1 discloses a method in which the raw material before sintering is solidified with resin, the cross section is observed, and the strength is estimated from the area ratio of the solid part to the pore part.

It is also known that the quality of sintered ore is closely related to the firing temperature. In Patent Document 2, in a sintering pot test in which the oxygen concentration in the suction gas was increased, the temperature was measured using a thermocouple, and according to this document, the retention time of temperatures above 1100°C in the layer increased, and the strength increased.

On the other hand, Non-Patent Document 3 discloses a method of calculating the temperature history in the layer in advance using a heat transfer model instead of thermocouples, and taking operational actions to always maintain the same temperature history, i.e., quality.

Japanese Patent Application Publication No. 5-295455 Japanese Patent Application Publication No. 11-131152 Japanese Unexamined Patent Publication No. 58-144433

Oyama et al.: Tetsu-to-Haganen, 82 (1996), p719. D.A.Kissin:STAL’, 5(1960), p318. Sasaki et al.: Tetsu-to-Haganen, 68(1982), p563.

The method described in Patent Document 1 above makes it possible to determine the blending conditions in advance by predicting the strength of the sintered body for each raw material. However, in addition to not taking into account the effects of the sintered ore structure after firing, the method does not include information on the coagulant ratio, moisture, particle size distribution, height and void ratio of the granulated particles charged to the pallet, flow rate during firing, and the concentration and time of city gas and oxygen injection. As a result, there was an issue that it could not be adapted to actual operations where operating conditions change rapidly.

To introduce the temperature control method of Patent Document 2 into an actual sintering machine, thermocouples are required, which poses many issues, such as large-scale capital investment, maintenance of the thermocouples, which are consumables, as well as disturbance of the charged materials and variations in the temperature measurement position. According to Patent Document 3, it is possible to improve quality variations through high-precision temperature control based on fundamental principles, but it is not possible to estimate or improve quality because it is unclear what type of temperature history is optimal.

The present invention was made in consideration of these circumstances, and its purpose is to provide a manufacturing method and manufacturing apparatus for sintered ore that can estimate the quality of sintered ore after firing in advance from the raw material blending conditions and operating conditions at the sintering plant, thereby obtaining sintered ore of higher quality. The differences between the prior art and the present invention are shown in Figure 1.

In order to estimate the quality of sintered ore after firing in advance from the raw material blending conditions and operating conditions at the sintering plant, the inventors came up with a method to maximize quality by controlling the amount of sintered ore structure produced, which is the controlling factor for quality, through temperature management in the sintering layer.

The present invention is a method for producing sintered ore by adding moisture to a sintering raw material, which is a mixture of powdered materials containing iron ore, auxiliary raw materials, miscellaneous raw materials, and solid fuel, mixing and granulating the resulting granulated pseudo-particles in a sintering machine, comprising a thermal index calculation step for calculating a thermal index based on the temperature distribution in the sintering layer of the sintering machine, and an operating condition setting step for setting the operating conditions of the sintering machine so that the calculated thermal index satisfies a target value.

In the method for producing sintered ore according to the present invention configured as described above,
(1) The temperature distribution is calculated from a heat transfer model to which the blending conditions of the sintering raw materials and the preset operating conditions of the sintering machine are input;
(2) The thermal index is calculated based on a retention time of a formation temperature range of the sintered ore structure to be estimated in the temperature distribution;
(3) the sintered ore structure to be estimated is calcium ferrite, and the thermal index is calculated based on a retention time at a temperature range of 1200°C or more and less than 1350°C, which is a temperature range for generating calcium ferrite;
(4) Using a thermal index ΔT defined by the following formula (1) as the thermal index;
ΔT=aΔt ₁ −bΔt ₂ (1)
Here, _Δt1 is the holding time (min) at 1200° C. or higher,
_Δt2 is the holding time (min) at 1350°C or higher,
ΔT is the holding time (min) between 1200° C. and 1350° C.
a and b are coefficients.
(5) As the operating conditions, at least one of the mixing ratio of the coagulating agent and the concentration and time of the oxygen and city gas blown into the sintering machine is controlled;
This is believed to be a more preferable solution.

The present invention also provides a sintered ore manufacturing apparatus that includes at least a mixer/granulator for adding moisture to a sintering raw material, which is a blend of powdered materials containing iron ore, auxiliary raw materials, miscellaneous raw materials, and solid fuel, and mixing and granulating the mixture to obtain a granulated material, a sintering machine for sintering the pseudo-particles that are the obtained granulated material to produce sintered ore, and a control device for controlling the mixer/granulator and the sintering machine, in which the control device calculates a thermal index based on the temperature distribution in the sintering layer of the sintering machine and sets the operating conditions of the sintering machine so that the calculated thermal index satisfies a target value.

Conventionally, it was not possible to quickly and thoroughly identify the cause of variations or declines in the strength and reducibility of sintered ore, and so actions had to be taken to improve strength and quality as a symptomatic treatment. As a result, over-specification of sintered ore strength led to increased costs for agglomeration materials and increased strength fluctuations. However, with the present invention, from the perspective of sintered ore structure, it is possible to propose actions in advance to optimize strength and reducibility by controlling the structure generation that contributes to quality through temperature management. As a result, it is possible to reduce variations in strength and reducibility, reduce manufacturing costs, and improve productivity.

FIG. 1 is a diagram for explaining the difference between the prior art and the present invention. 1 is a graph showing an example of a temperature distribution in a sintered layer calculated using a heat transfer model, for explaining an example of calculating a thermal index in the sintered ore manufacturing method of the present invention. 1 is a graph showing the relationship between thermal index and strength in the method for producing sintered ore of the present invention. FIG. 1 is a diagram showing a configuration of an example of an apparatus for producing sintered ore according to the present invention. 1 is a graph showing a comparison of rotational strength indexes for a conventional example, a comparative example, and an embodiment of the present invention. 1 is a graph showing a comparison of reducibility among a conventional example, a comparative example, and an embodiment of the present invention.

The following is a detailed description of the embodiments of the present invention. Note that the following embodiments are intended to exemplify devices and methods for embodying the technical ideas of the present invention, and are not intended to specify the configurations described below. In other words, the technical ideas of the present invention can be modified in various ways within the technical scope described in the claims.

<Regarding the method for producing sintered ore of the present invention>
The inventors have come up with a method for maximizing quality by controlling the amount of sintered ore texture, which is a controlling factor for quality, through temperature management in the sintering layer. This method will be described below.

There are various reports on the formation of sintered ore structure (for example, Tetsu to Hagane, 50 (1964), 1563. and Tetsu to Hagane, 73 (1987), 804.). Sintered ore structure is composed of hematite, magnetite, multi-element calcium ferrite (hereinafter, also referred to as CF: calcium ferrite), amorphous slag structure and pores. Calcium ferrite, which has high strength and high reducibility, is formed when _CaO.Fe2O3 formed by the solid-phase reaction of hematite and _CaO melts at 1200°C or higher and dissolves the surrounding _SiO2 and _Al2O3 . When the temperature exceeds 1350°C, CF decomposes into hematite, and the remaining _components crystallize as slag during cooling. In addition to the pores that iron ore originally has, pores are generated during the heating process by the dehydration of moisture and bound water and the vaporization of _CO2 in fine coke and limestone, and at high temperatures when the molten liquid is generated, the pores become smaller as the molten liquid fills the interparticle gaps. Therefore, the temperature distribution (heat pattern) in the sintered layer has a significant effect on the mineral structure and pores of the sintered ore, i.e., its quality.

According to academic literature: Tetsu to Hagane, 56 (1970), 371., Tetsu to Hagane, 56 (1970), 661., Tetsu to Hagane, 58 (1972), 1567., Tetsu to Hagane, 60 (1974), 465., and Tetsu to Hagane, 62 (1976), 1567., many attempts have already been made to evaluate the temperature distribution (heat pattern) in the sintering layer using a heat transfer model in the sintering process. According to the methods disclosed in these academic literature, it is possible to estimate the temperature distribution by inputting various operational factors such as the coagulant ratio, layer thickness, and added moisture. However, there have been no examples of estimating the quality of sintered ore from the estimated temperature distribution in the sintering layer.

The inventors therefore constructed a model that inputs the raw material blending conditions and operating conditions into a heat transfer model (ISIJ Int., 51(2011), 913.) and can estimate the quality of sintered ore from the calculated temperature distribution. They found that by using this model, it is possible to propose in advance operating conditions that can ensure the amount of structure generated that satisfies the target quality set by each plant.

That is, according to the method for producing sintered ore of the present invention, the sintering raw material is a mixture of iron ore, auxiliary raw materials, miscellaneous raw materials, and powdered materials containing solid fuel, and the mixture is granulated by adding moisture to the sintering raw material, and the resulting granulated pseudo-particles are sintered in a sintering machine to produce sintered ore. The method includes a thermal index calculation step for calculating a thermal index based on the temperature distribution in the sintering layer of the sintering machine, and an operating condition setting step for setting the operating conditions of the sintering machine so that the calculated thermal index satisfies a target value.

Below, we will specifically explain the thermal index calculated based on a heat transfer model in the sintered ore manufacturing method of the present invention, and the method for setting the operating conditions based on the calculated thermal index.

Figure 2 is a graph showing an example of the temperature distribution in the sintered layer calculated using a heat transfer model to explain an example of the calculation of the thermal index in the sintered ore manufacturing method of the present invention. The sintered layer here refers to a layer in which pseudo-particles, which are granulated products obtained by adding moisture to the sintering raw materials and mixing them, are packed to a specified thickness on, for example, the pallet of a Dwight Lloyd sintering machine. The temperature distribution in the sintered layer is calculated using a heat transfer model to calculate the change in temperature over sintering time in the center part of the sintered layer in the height direction as the sintered layer is transported on the pallet after ignition of the surface layer of the sintered layer.

The temperature distribution in the sintered layer was calculated using a heat transfer model as shown in Fig. 2, and the sintered ore structure to be estimated here was calcium ferrite. The inventors defined a new thermal index ΔT as the high-temperature holding time in the formation temperature range of calcium ferrite, which is a high-strength and highly reducible structure, from 1200°C to 1350°C, as shown in the following formula (1).
ΔT=aΔt ₁ −bΔt ₂ (1)
Here, _Δt1 is the holding time (min) at 1200° C. or higher,
_Δt2 is the holding time (min) at 1350°C or higher,
ΔT is the holding time (min) between 1200° C. and 1350° C.
a and b are coefficients.

In this case, the thermal index ΔT defined in equation (1) must be changed in the temperature range based on the mineral structure to be estimated. For example, to estimate pores, a holding time of 1200°C or more must be used, and to generate magnetite, a holding time of 1350°C or more, which is the thermal dissociation temperature from hematite, must be used.

ここで、（２）式で定義する熱指標ΔＱは１２００℃～１３５０℃の積分値(℃・ｍｉｎ)だが、計算時は左辺及び右辺にそれぞれ係数ａ、ｂなどをかけて補正しても良い。また、昇温側（温度が極大値を示すまで）に要する保持時間、冷却時間の影響を組み込む等、目的とする品質の特徴量を捉えている指標を用いても良い。 Furthermore, in order to strictly evaluate the influence of city gas injection, it is necessary to use a thermal index ΔQ consisting of an integral value, for example, as shown in the following equation (2), instead of the thermal index ΔT defined in the above equation (1).

Here, the thermal index ΔQ defined in formula (2) is the integral value (°C·min) from 1200°C to 1350°C, but during calculation, corrections may be made by multiplying the left and right sides by coefficients a and b, respectively. In addition, an index that captures the characteristic quantities of the target quality may be used, such as by incorporating the effects of the holding time required on the heating side (until the temperature reaches its maximum value) and the cooling time.

Figure 3 is a graph showing the relationship between the thermal index and strength in the sintered ore manufacturing method of the present invention. Here, the thermal index ΔT was calculated using the simplest and most quickly applicable formula (1) with coefficients a = 1 and b = 1.5, and the applicability to an actual machine was examined. For strength, the rotational strength index TI measured based on JIS M 8712 was used. From this Figure 3, it can be seen that a model can be constructed that can estimate sintered ore strength using ΔT, which promotes the formation of high-strength calcium ferrite. That is, for example, sintered ore with a rotational strength index TI of 66% or more is considered to be of high quality, and a thermal index ΔT that satisfies the quality (here, around 3.2 min) is defined in advance based on Figure 2, and the operating conditions of the sintering machine, such as the coagulant ratio and the conditions for blowing in city gas and oxygen (concentration and time), are controlled to form a temperature distribution that satisfies the thermal index ΔT according to the raw material blending conditions, thereby improving sintered ore quality and reducing variation.

In addition, in the present invention, the operational actions (operational conditions to be controlled) include not only the above-mentioned coagulant ratio and oxygen/city gas injection conditions (concentration and time), but also various operational conditions related to the temperature in the sintered layer, such as the thickness of the sintered layer, carbon segregation, the air ratio and gas volume of the ignition furnace, and air volume.

<Regarding the sintered ore manufacturing apparatus of the present invention>
Fig. 4 is a diagram showing the configuration of an example of the sintered ore manufacturing apparatus of the present invention. In the example shown in Fig. 4, the sintered ore manufacturing apparatus includes at least a mixer granulator 1 for adding moisture to the sintered raw material, which is a mixture of powdery materials containing iron ore, auxiliary raw materials, miscellaneous raw materials, and solid fuel, and mixing and granulating the mixture to obtain a granulated material, a sintering machine 2 for sintering the pseudo-particles, which are the granulated material obtained, to produce sintered ore, and a control device 3 for controlling the mixer granulator 1 and the sintering machine 2. The control device 3 calculates a thermal index based on the temperature distribution in the sintered layer of the sintering machine 2, and sets the operating conditions of the sintering machine 2 so that the calculated thermal index satisfies a target value. Note that a drum mixer or the like can be used as the mixer granulator 1, and a Dwight Lloyd type sintering machine or the like can be used as the sintering machine 2.

Below, we will explain in detail the examples of the invention. Here, we will compare the strength and reducibility of sintered ore in an actual sintering machine with a conventional example, a comparative example, and an example of the invention.

In the conventional example, the operator judged the heat level based on the rotational strength index TI value of the sintered ore sampled by a sampler (extraction device) every hour, and took action to adjust the coke fine blend ratio. When the rotational strength index TI (hereinafter referred to as the measured value) of the sampled sintered ore was lower than the target rotational strength index TI (hereinafter referred to as the target value), the coke fine blend ratio was increased as heat input control, and when the strength of the sampled sintered ore was higher than the target, the coke fine blend ratio was decreased. In addition, for reducibility, sampling was performed at the same time three times a week, and the RI test specified in JIS M 8713 was performed to investigate whether the target value was reached, but the heat input index prioritized strength and took action. In the comparative example, referring to the method of Patent Document 2, an action was taken to adjust the coke fine blend ratio based on a heat transfer model so that the temperature history was always the same.

In the invention example, the heat index ΔT was calculated in advance by a heat transfer model, and two levels were investigated: one in which only the coagulant ratio (coke powder blending ratio) was controlled to control the calculated ΔT to a target value (Example 1), and one in which both the coagulant ratio (coke powder blending ratio) and the amount of city gas (LNG) and oxygen (O ₂ ) blown in were controlled to study the case where the coagulant ratio was set to a value higher than the target value (Example 2). The results are shown in Table 1 below.

In Table 1, the thermal index ΔT was 2.30 in the conventional example and comparative example, but by taking action according to the sintered ore manufacturing method of the present invention, the thermal index ΔT was controlled to 3.20 in the inventive example (Example 1), and to 3.30 in the inventive example (Example 2). Then, for the obtained sintered ore, the rotational strength index TI was obtained by the tumbler strength test specified in JIS M 8712, and the reducibility was obtained by the RI test specified in JIS M 8713. Figure 5 shows a comparison of the rotational strength index TI for the conventional example, comparative example, and Examples 1 and 2, and Figure 6 shows a comparison of the reducibility for the conventional example, comparative example, and Examples 1 and 2.

From the results of FIG. 5, it was found that the average value of the rotational strength index TI was 65.6% in the conventional example, 65.5% in the comparative example, 66.4% in the inventive example (Example 1), and 67.5% in the inventive example (Example 2). In addition, it was found that the standard deviation σ of the rotational strength index TI was 1.5% in the conventional example, 1.3% in the comparative example, 1.1% in the inventive example (Example 1), and 0.89% in the inventive example (Example 2). Furthermore, from the results of FIG. 6, it was found that the average value of the reducibility was 66.8% in the conventional example, 66.9% in the comparative example, 69.4% in the inventive example (Example 1), and 72.6% in the inventive example (Example 2). Furthermore, it was found that the standard deviation of the reducibility was 2.33% in the conventional example, 2.0% in the comparative example, 1.95% in the inventive example (Example 1), and 1.10% in the inventive example (Example 2).

From the above, when comparing the conventional example with the inventive examples (Examples 1 and 2), it was found that in the inventive examples, the rotational strength index TI and reducibility were improved and the variation in both was reduced by controlling based on the thermal index ΔT. Furthermore, with regard to the operational action (operating conditions to be controlled) of the inventive examples, it was found that the variation in the rotational strength index TI and reducibility could be reduced by adjusting both the coagulating agent and the amount of city gas and oxygen blown in as in Example 2, rather than adjusting only the coagulating agent as in Example 1. This is presumably because the temperature in the sintered layer was raised by adjusting the coagulating agent, and the high temperature retention time was extended by adjusting the amount of oxygen and city gas blown in (concentration and time).

In addition, while in this study operational actions were controlled for strength and reducibility, it is also possible to use a similar approach for other qualities (grain size, reduction disintegration, etc.) by constructing a thermal index that focuses on the structure formation that governs the target quality.

The sintered ore manufacturing method and manufacturing device of the present invention make it possible to propose actions in advance to optimize strength and reducibility, reducing the variation in strength and reducibility of the sintered ore produced, and reducing sintered ore manufacturing costs and improving productivity, making it industrially useful.

1 Mixing and granulating machine 2 Sintering machine 3 Control device

Claims (4)

A method for producing sintered ore by adding moisture to a sintering raw material, which is a blend of powdery materials including iron ore, auxiliary raw materials, miscellaneous raw materials, and solid fuel, mixing and granulating the resulting granulated pseudo-particles in a sintering machine, comprising:
a thermal index calculation step of calculating a thermal index from a thermal index ΔT defined by the following formula (1) based on a retention time of 1200°C or more and less than 1350°C, which is a generation temperature range of calcium ferrite to be estimated in a temperature distribution in the sintered layer of the sintering machine;
ΔT=aΔt ₁ −bΔt ₂ (1)
Here, Δt1 _is the holding time (min) at 1200° C. or higher,
Δt2 is the holding time (min) at 1350° C. or higher _,
ΔT is the holding time (min) from 1200° C. to less than 1350° C.
a and b are coefficients.
an operation condition setting step of setting operation conditions of the sintering machine so that the calculated thermal index satisfies a target value;
A method for producing sintered ore comprising the steps of: The method for producing sintered ore according to claim 1, wherein the temperature distribution is calculated from a heat transfer model into which the blending conditions of the sintering raw materials and the preset operating conditions of the sintering machine are input. 3. The method for producing sintered ore according to claim 1, wherein at least one of a mixing ratio of a coagulant and a blowing concentration and time of oxygen and city gas blown into the sintering machine is controlled as the operating conditions. A sintered ore manufacturing apparatus including at least a mixer/granulator for adding moisture to a sintering raw material, the raw material being a mixture of iron ore, auxiliary raw materials, miscellaneous raw materials, and powdered materials containing a solid fuel, and mixing and granulating the mixture to obtain a granulated material, a sintering machine for sintering pseudo-particles, which are the granulated material, to produce sintered ore, and a control device for controlling the mixer/granulator and the sintering machine,
The control device calculates a thermal index from a thermal index ΔT defined by the following formula (1) based on a retention time of 1200°C or more and less than 1350°C, which is a generation temperature range of calcium ferrite to be estimated in a temperature distribution in a sintered layer of the sintering machine ,
ΔT=aΔt ₁ −bΔt ₂ (1)
Here, Δt1 _is the holding time (min) at 1200° C. or higher,
Δt2 is the holding time (min) at 1350° C. or higher _,
ΔT is the holding time (min) from 1200° C. to less than 1350° C.
a and b are coefficients.
and setting operating conditions of the sintering machine so that the calculated thermal index satisfies a target value.

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