JP7400759B2 - How to make briquettes - Google Patents

Description

The present invention relates to a method for producing briquettes in which a mixture obtained by heating and mixing raw material powder and a binder used in a steel manufacturing process is pressure-molded.

In the steelmaking process, various powdered raw materials are briquetted and used to reduce raw material costs, improve the quality of intermediate products, and reduce environmental impact by preventing scattering. For example, cheap, low-grade iron ore can be used as a high-grade raw material by crushing and sorting it to remove impurities and then briquetting it, briquetting powdered coal to make briquette coal, or briquetting powdered coal to make briquette coal. Ferrocoke is also produced by briquetting coal and powdered iron ore. In addition, scattering of dust is also prevented by briquetting the dust charged into the converter.

Briquettes are manufactured by mixing raw material powder that has been crushed into powder and a binder (also called ``caking agent''), which is a material that binds the powder together, and then press-molding it with a molding machine. be done.

At that time, the briquettes are required to have a certain level of strength or more in order to prevent powdering during transportation, and in order to improve the strength, for example, Patent Document 1 discloses that the raw material powder and binder are sufficiently mixed together in the mixer. A technology has been proposed in which the temperature of the mixture is raised above the softening point of the binder and molded.

However, in order to produce briquettes with sufficient strength, it is important to thoroughly mix the raw materials and binder in a mixer, then heat the mixture to a temperature above the softening point of the binder and mold the resulting mixture. The factors that affect the briquette strength are not only the temperature of the mixture, but also various factors such as the moisture content and particle size of the mixture, the rotation speed of the mixer blades, and the shape. Even if only the temperature is controlled, there is a problem in that the strength of the briquettes varies. Furthermore, even if the mixing and heating time in the mixer is increased to ensure the strength of the briquettes, some types of binder, such as starch, have a viscosity that decreases above a certain temperature range. Prolonging the heating time poses a problem in that it not only reduces production capacity but also causes a reduction in briquette strength.

JP2015-63581A

As mentioned above, in the conventional briquette manufacturing method of mixing raw material powder and a binder and molding the resulting mixture, even if the heating temperature is controlled, the strength of the briquettes may vary or the strength may not be sufficient. There was a problem that strength could not be obtained.

Therefore, an object of the present invention is to provide a method for efficiently manufacturing briquettes that have sufficient strength and have little variation in strength, in a method for manufacturing briquettes in which raw material powder and a binder are mixed and molded. With the goal.

The present inventors have made extensive studies to solve the above problems, and as a result, they have taken into account the mixing ratio of raw materials and binder, the temperature of the mixture, moisture content, particle size, viscosity, fluidity, etc., to ensure the strength of the briquettes. It has been found that a technique that determines the optimal timing for finishing mixing from the viewpoint of production efficiency, that is, the timing for discharging from the mixer, is effective. In particular, when starch is used as a binder, it has been found that the strength of the briquettes is related to the viscosity and fluidity of the mixture, since the viscosity of starch is largely dependent on temperature. We found an efficient method to indirectly monitor sex.

The present invention was made based on the above findings, and the gist thereof is as follows.
[1] A method for producing briquettes in which a raw material powder and a binder are mixed and molded using a mixer having stirring blades, and during the mixing, the stirring blades are driven to rotate while heating. The time gradient (A/sec) of the load is measured, and when the measured value is below the threshold, the rotational drive is stopped, the mixture is discharged, and the discharged mixture is molded into briquettes. A method for producing briquettes, characterized by:
[2] The method for producing briquettes according to [1], wherein the threshold value is 0.1 A/sec.
[3] The method for producing briquettes according to [1] or [2], characterized in that the raw material powder is coal powder.
[4] The method for producing briquettes according to any one of [1] to [3], wherein the binder is starch.

According to the present invention, when manufacturing briquettes that are molded by mixing raw material powder and starch, by optimizing the timing of discharging the mixture from the mixer, the strength of the briquettes is stabilized and the amount of starch used is It is possible to reduce the amount of utilities (electricity, steam, etc.) used for heating and heating, and is expected to reduce manufacturing costs. Furthermore, devices (sensors, etc.) that detect the moisture content and particle size of the raw material powder, the surface of the mixture, etc. can be minimized, and an increase in equipment costs can be suppressed.

1 is a schematic cross-sectional view showing an example of a Henschel type powder mixer. It is a schematic diagram which shows the load of rotational drive of a mixer, and the transition of the temperature of a mixture.

Embodiments of the present invention will be explained below using as an example a method for producing molded coal briquettes used in the iron manufacturing process using starch as a binder. It can also be applied to methods of manufacturing mixed briquettes of powder and coal powder, or dust briquettes fed into a converter.

In the present invention, various raw material powders can be used depending on the use of the briquettes to be manufactured. When producing briquette coal for coke production, coal may be used as raw material powder. When producing ferro coke, carbonaceous interior pellets, etc. as a blast furnace raw material, iron ore or coal can be used as the raw material powder. Alternatively, when manufacturing briquettes for use as a heat source or iron source in the steelmaking process, coke powder, ironmaking dust, etc. can be used as the raw material powder. Therefore, various materials such as coal, iron ore, iron dust, iron sludge, etc. can be used as the raw material powder depending on the purpose.

[Powder mixing method and mixer]
The method of mixing raw material powders of the present invention will be described using a Henschel type mixer 1 having stirring blades 2 (also referred to as "horizontal rotating blades") as shown in FIG. However, when implementing the present invention, it is not necessary to use a Henschel-type mixer, but a vertical paddle type or other device that rotates and mixes the powder, the axis of rotation is a vertical axis (vertical direction), and heating by steam is used. Any mixer can be used as long as it can do this.

Although FIG. 1 shows a configuration in which the stirring blades 2 are provided in two stages in the vertical direction, they may be provided in one or three or more stages. This stirring blade 2 has two blades attached to positions facing each other with respect to the rotating shaft 3, but the number of blades is not particularly limited and may be one or three or more. Further, in order to maintain the strength of the two blades, an auxiliary member may be attached that connects the two blades in the middle in a circular shape. There is no particular restriction on the shape of the blades, and the blades may have a horizontal plate shape, a paddle shape, a propeller shape, or the like. If the rotation speed of the rotary blade is too low, the entire charge powder cannot be mixed. Furthermore, if the rotational speed is too high, the charged powder may fly out of the powder mixer. Therefore, it is preferable to mix and stir at a peripheral speed of the tip of the stirring blade of about 5 to 40 m/s.

The internal volume of the mixer 1 is not particularly limited, and may be as small as about 75L to as large as 4000L or more.

[powder]
Examples of the raw material powder include coal powder, ore powder, and other powders such as converter dust, but it is preferable to use coal powder in the production of shaped coal briquettes in the steel manufacturing process. The particle size of the coal powder is not particularly limited, but the finer the particle size, the better the strength of the briquettes, so it is preferable, less than 10 mm is preferably 90% by mass or more, and more preferably 95% by mass or more. In addition, when using coal powder with a particle size of less than 10 mm and less than 90% by mass, it may be pulverized or mixed with another finer particle size coal powder to adjust the particle size to the above particle size range. .

[binder]
Although various caking agents can be used as the binder to be mixed with the powder, it is preferable to use starch as the binder used in the method for producing molded carbon briquettes of this embodiment.

The type of starch is not particularly limited, and starches manufactured from raw material plants such as tapioca, potatoes, sweet potatoes, corn, rice, wheat, and beans can be used as appropriate, and starch derivatives and chemical processed starches derived from plants can be used as appropriate. Synthesized starch can also be used. Among these starches, it is preferable to use tapioca-derived starch, which has a relatively low gelatinization temperature and a high viscosity during mixing. Note that starch includes alpha starch that is gelatinized (gelatinized) and beta starch before gelatinization, but as described above, it is preferable to use beta starch in the present invention.

[Mixing ratio]
The blending ratio of the raw material powder and starch can be appropriately determined depending on the properties of the raw material powder, the strength required of the briquettes to be produced, and the like. For example, when producing briquette coal for coke raw material, it is preferable to add 0.5 to 2.0% by mass of starch based on the total mass of raw material powder and starch.

[Relationship between viscosity of mixture and briquette strength]
Next, considering the mixing ratio of the raw material powder and binder, the temperature, moisture content, particle size, fluidity, etc. of the mixture, we determine the optimal timing to finish mixing from the perspective of ensuring the strength of the briquettes, that is, the timing of discharge from the mixer. We considered a method for determining the Particularly when starch is used as a binder, the strength of the briquettes is related to the viscosity of the mixture, as the viscosity of starch is highly dependent on temperature. It was found that the briquettes produced by molding the mixture with the lowest hardness had high strength and were difficult to powder. Therefore, we have found an efficient method for terminating the mixing of the mixture when the viscosity of the mixture is at its maximum, which will be described below.

[How to confirm the completion of mixing]
As mentioned above, in order to increase the strength of briquettes, it was found that it is preferable to mix the raw material powder and binder under heat and make the mixture when the viscosity reaches its maximum to form briquettes. , it is necessary to know the viscosity (viscosity) of the mixture. However, since it is complicated to measure the viscosity of the mixture in the mixer during mixing, a method of checking using another index has conventionally been used. The method is to set a target temperature based on the gelatinization temperature of starch, continuously measure the temperature of the mixture, and stop mixing when the target temperature is reached. be. However, even if the mixture reaches the target temperature, the strength of the obtained briquettes varies, and high-strength briquettes may not be obtained. This may be due to the fact that even though the temperature of the mixture has increased, the viscosity itself may not have increased that much, and it has been found that checking the completion of mixing by temperature is not a sufficient method of checking.

Therefore, we investigated a new method for confirming the completion of mixing as an alternative to measuring the viscosity of the mixture, and found that an efficient method was to measure the load of the rotational drive of the stirring blade that mixes the mixture. In other words, since the load of the rotational drive of the stirring blade appears as a current value (A), the time gradient of the rotational drive load that indicates the state in which the current value changes, that is, the rotational drive load per hour (A/ sec) and confirm the completion of mixing based on the measured value.

This is a method in which the time gradient of the load of the above-mentioned rotary drive is measured, and mixing is terminated when the measured value becomes equal to or less than a threshold value. This threshold value is preferably 0.1 A/sec, according to the results of a study experiment described in Examples described later. (More preferably, it is a value within the range of 0 to 0.08 A/sec.) The threshold value is determined by the scale of the mixer, the amount of raw material powder and binder, the mixing ratio, and other mixing factors. Although it may change depending on different conditions, by using the amount of change per time called time gradient as the measurement item, it can be used as a common index even if the conditions are different.

[Mixture heating method]
If the raw material powder and starch are mixed while heating after starting, the time gradient of the drive load will increase to a greater degree and level off quickly, which will reduce the mixing time and improve briquette production. productivity can be improved.

As a method of heating the mixture, a method of blowing steam into the mixed powder is preferred. A steam pipe is inserted from above the mixer, the discharge port at the tip of the steam pipe is placed in the mixed powder, and steam is blown into the mixer.

The temperature of the mixture after steam injection during mixing and stirring is preferably higher than the gelatinization temperature of the starch used as the binder. Since this gelatinization temperature differs depending on the type of starch, the temperature of the mixture after steam injection may be adjusted depending on the starch used. For example, when starch derived from tapioca is used, its gelatinization temperature is 58.5 to 70.0°C, so the temperature of the mixture after steam injection should be 70.0 to 95.0°C. is preferred. More preferably, the temperature is 70.0 to 80.0°C. Similarly, when starch derived from potatoes is used, its gelatinization temperature is 56.0 to 66.0°C, so the temperature of the mixture after steam injection is 66.0 to 95.0°C. is preferable. More preferably, the temperature is 66.0 to 80.0°C.

Controlling the temperature of the mixture can be achieved by adjusting the temperature of the steam blown into the mixed powder. The temperature of the steam can be adjusted by adjusting the flow rate of the steam or by mixing water at room temperature.

[Steam blowing time (mixing time)]
The mixing and stirring time for steam blowing can be adjusted as appropriate depending on the type of powder and binder, but when starch is used, time is required for it to gelatinize and become uniformly mixed with the powder. For example, the heating time in the above-mentioned briquette process is preferably 60 seconds or more, more preferably 120 seconds or more.

Furthermore, the mixing time in an unheated state before steam blowing mixing may be adjusted appropriately depending on the type of powder and binder. The time for mixing in a heated state may be about 15 seconds or more.

[Molding method]
Molded coal briquettes are obtained by charging the mixture obtained by the above-described mixing method into a briquette molding device and molding it under pressure. This molding method is not particularly limited, and any molding machine of roll compression, rolling, or extrusion type may be used as the briquette molding device. In particular, it is preferable to use a double roll molding machine that has recesses on the roll surface that can uniformly apply pressure to the inside of the briquettes. In addition, in this embodiment, although the molded coal briquette was explained as an example, it can also be applied to other briquettes (ore powder briquettes, converter input dust briquettes, etc.) in the steel manufacturing process.

Hereinafter, as an example, a study experiment will be described in which a change in the load of the rotary drive of the stirring blade was compared with a conventional temperature change, which is the basis for discovering the above-mentioned new method for confirming the completion of mixing. The present invention is not limited to this embodiment.

In this experiment, coal powder (coal blend) in which 95% by mass of the particle size is less than 10 mm and the other 5% by mass is 10 mm or more and less than 20 mm was used as the raw material powder, and the binder was derived from tapioca. A total of 1% by mass of β starch was used. This tapioca-derived beta starch is a starch that exhibits the highest viscosity at about 75°C.

The above raw material powder (coal powder) and binder (β starch) were mixed in an unheated state using a Henschel type mixer shown in FIG. 1, and then heated and mixed while blowing steam. The temperature of the mixture was measured with a thermocouple installed in the mixer, and the current value indicating the load of rotational drive of the stirring blade was also measured.

Briquette strength (%) is determined by applying compressive force to the mixture discharged after mixing using a pressurized roll-forming machine, forming it into a Masek-type molded coal briquette of 46 mm x 46 mm x 38 mm, and leaving it for 2 hours in a natural environment. Ten briquettes after curing were dropped three times from a height of 2 m, and the ratio (%) of the mass of lumps of 15 mm or more to the mass of the dropped briquettes was determined as the falling strength (%) of the briquettes.

The above experimental results are shown in FIG. In this figure, the solid line indicates the current value (vertical axis on the left) of the load on the rotary drive of the mixer that changes with the elapsed mixing time. In this curve, the load of the rotary drive initially increases with time, but the increase in load reaches saturation after 120 seconds have elapsed. Moreover, the dotted line is the change in temperature of the mixture (vertical axis on the right) measured at the same time. Here, when we finished mixing at three points (a), (b), and (c) on the horizontal axis and examined the briquette strength, we found that at the point in time (a) when 80 seconds had elapsed, the current value of the driving load was still rising, and the strength of the obtained briquettes was about 80%, which could not be said to be high. However, at the time of 120 seconds in (b), the current value stopped increasing and leveled off, and the strength of the briquettes was as high as 95%. Further, at the time of 170 seconds in (c), the current value remained unchanged, and the strength of the briquettes was high at 95%, which is the same as in (b).

On the other hand, looking at the temperature change shown by the dotted line, the target temperature of 75° C. was reached at point (c). In other words, even though the mixture is expected to have sufficient strength even before the target temperature is reached (corresponding to point B), steam heating and mixing is still being continued. . From the above, it has been found that the method of terminating the mixing at the point when the current value levels off (b) is effective in shortening the mixing time and reducing the amount of steam used.

A way to know when the leveling off (b) is to find the time gradient of the load on the above curve, which is the load per hour (current value), and to determine the time when the time gradient becomes less than a specific value. was found to be preferable. This value was defined as a threshold value and was set to be 0.1 A/sec.

The shape of the curve varies depending on the size of the mixer, the amount of raw material powder and binder, the mixing ratio, and other mixing conditions, but by specifying the amount of change per time called the time gradient, it is possible to change the shape of the curve. Even if they are different, they can be used as a common index.

Based on the above, compared to the method based on temperature, the method of confirming the completion of mixing using the time gradient of the rotary drive load is a more efficient method of confirming the completion of mixing because it can reduce the mixing time and amount of steam. It was also found that this method has the excellent effect of producing high-strength briquettes with little variation. Furthermore, although the temperature of the mixture is a very important factor from the perspective of developing the viscosity of the binder, it is even more important to control the load on the rotational drive during mixing to control the moisture content and particle size of the mixture, as well as the rotational speed of the mixer. The optimal discharge timing can be determined by considering various disturbances such as the shape of the blades and the shape of the blades.

1 Mixer 2 Stirring blade 3 Rotating shaft 4 Raw material powder charging port 5 Steam pipe 6 Steam pipe discharge port 7 Steam pipe insertion port S Steam

Claims (3)

A method for producing briquettes in which coal powder and starch are mixed and molded using a mixer having stirring blades, wherein during the mixing, the stirring blades are driven to rotate while being heated by steam blowing , and the load of the rotational drive is reduced. When the time gradient (A/ sec ) of A method for producing briquettes, characterized by forming briquettes. The method for producing briquettes according to claim 1 , wherein the temperature of the mixture after steam blowing during the mixing is higher than the gelatinization temperature of the starch . The method for producing briquettes according to claim 1 or 2 , wherein the mixing and stirring time for performing the steam blowing is 60 seconds or more .

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