JP2022112263A - Method for manufacturing briquette - Google Patents

Abstract

To provide a method for producing briquette by mixing and molding powders with a binder, using starch as the binder, and without adding caustic soda during mixing, and thereby to provide a method for manufacturing a briquette which is suitable for an ironmaking process and has high strength and is hardly pulverized.SOLUTION: The inventive method for producing the briquette comprises mixing the powder and the binder in an unheated state, then mixing the powder and the binder in a heated state, and molding the obtained mixture, wherein the binder is preferably starch.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing briquettes used in ironmaking processes.

In the steelmaking process, various powdered raw materials are briquetteized and used for the purpose of reducing raw material costs, improving the quality of intermediate products, and reducing environmental impact by preventing scattering. Specifically, for example, when cheap low-grade ore is crushed, sorted and made into briquettes for use as high-grade raw materials, and coal and iron ore powder are made into briquettes to improve bulk density and air permeability. and to prevent scattering by briquetting the dust introduced into the converter.

In general, briquettes are produced by crushing raw materials into powder, mixing them with a binder, and then pressing and molding them with a molding machine. is required. However, when relatively inexpensive starch is used as a binder material, β-starch, which is abundantly contained in inexpensive starch, is water-insoluble, so the adhesion between particles in the powder is weak and the strength of the briquette is very weak. .

Therefore, conventionally, the following methods have been proposed in order to improve the strength of briquettes when starch is used as a binder.

Non-Patent Literature 1 discloses a method of mixing caustic soda with starch to gelatinize β-starch to improve adhesion and briquette strength. However, caustic soda is harmful to the human body and poses safety and health risks when handled. In addition, since sodium, which acts as a catalyst for the reaction between coke and gas in the blast furnace, is mixed in the briquettes, there is also the problem that the reactivity of the coke produced from the briquettes is excessively increased.

Further, in Patent Document 1, starch powder (considered to contain a lot of β-starch), powdered charcoal and water are mixed, and the resulting mixture is heated to gelatinize the starch powder. Techniques for obtaining molded articles with improved adhesive strength have been disclosed. However, since kneading is not performed after heating, the mixed state of the powdered charcoal and gelatinized starch (also called pregelatinized starch or alpha starch) becomes uneven, and the strength of the molded product is insufficient and the strength varies greatly. There is the problem of being big. In the first place, Patent Document 1 is a technology for the purpose of making a flexible structure while maintaining the function of charcoal, and since it does not consider suppression of pulverization, pulverization in the transportation process, such as when using a molded product in the iron manufacturing process. It is a technology that cannot be industrially adopted in situations where it is necessary to suppress

Furthermore, Patent Document 2 discloses a method of adding a binder to a raw material, mixing it, and heating it in one step in the production of a recarburizing material for use as a raw material for ironmaking. However, in Patent Document 2, starch is disclosed only as an example of a binder, and no consideration is given to the effect of gelatinization of β-starch. There, when β-starch is used as a raw material for the binder, β-starch is heated to be gelatinized and dispersed by stirring at the same time. Conditions are unknown.

JP 2008-308476 A JP-A-62-158812

Reiji Takahashi, Masaki Yamamoto, "Behavior of Starch in Caustic Soda", Journal of Starch Industry, Vol. 17, No. 3, pp. 289-293, 1969

As described above, the conventional method of producing briquettes using starch as a binder in the ironmaking process has the problem that it is difficult to obtain briquettes having sufficient strength.

Therefore, the present invention provides a method for producing briquettes by mixing powders with a binder and forming them, using starch as a binder and without adding caustic soda, to produce briquettes having high strength and resistance to pulverization suitable for the iron-making process. The object is to provide a manufacturing method.

The inventors of the present invention have made intensive studies to solve the above problems, and as a result, by first mixing the powder and the binder in an unheated state and then mixing them in a heated state, a high-strength briquette can be obtained. I found what I got.

The present invention was made based on the above findings, and the gist thereof is as follows.
[1] In the briquette manufacturing method, when mixing the powder and the binder, the powder and the binder are mixed in an unheated state, then mixed in a heated state, and the resulting mixture is molded. A method for producing a briquette, characterized in that:
[2] The method for producing briquettes in [1], wherein the powder is coal powder.
[3] The method for producing briquettes in [1] or [2], wherein the binder is starch.
[4] The method for producing briquettes in [3], wherein the heating temperature in the heating state is equal to or higher than the gelatinization start temperature of the starch.
[5] The method for producing briquettes according to any one of [1] to [4], wherein the heating temperature in the heated state is 60.0 to 90.0°C.

According to the present invention, it is possible to improve the strength of briquettes without adding caustic soda, and to produce briquettes with less variation in strength and less pulverization.

FIG. 4 is a diagram showing the relationship between briquette drop strength and total mixing time. FIG. 3 is a diagram showing the relationship between briquette drop strength and heating and mixing time. It is a schematic diagram showing an example of a mixing device.

Hereinafter, embodiments of the present invention will be described with an example of a method for producing briquette charcoal briquettes used in an iron-making process using starch as a binder. It can also be applied to a method for producing mixed briquettes or dust briquettes fed into a converter.

[Manufacturing process]
First, in this embodiment, coal powder is used as the raw material powder, starch is added to the powder, mixed and kneaded, and the mixed and kneaded product is compressed and granulated. Next, the powder and starch were first mixed in an unheated state (hereinafter also referred to as "unheated mixing"), and the β-starch in the starch was uniformly mixed in the powder in a non-viscous state. A mixture (hereinafter also referred to as "unheated mixture") dispersed in a state is obtained.

Here, the "unheated state" means a state in which no heat is applied, and usually refers to a normal temperature state. However, even in a heated state, if the temperature is lower than the gelatinization start temperature of starch, which will be described later, the starch will not gelatinize, so the state is equivalent to the state without heating.

After the unheated mixing, the unheated mixture is mixed in a heated state (hereinafter also referred to as "heated mixture") to obtain a mixture (hereinafter also referred to as "heated mixture"). In this heating and mixing, for example, by blowing steam into the mixer and heating the unheated mixture, the starch is gelatinized (hereinafter also referred to as "gelatinization") while mixing to obtain a viscous mixture. The method. That is, according to this method, the gelatinized (pregelatinized) starch having high adhesive strength can be sufficiently uniformly mixed with the powder, so that the strength of the briquette is improved and the variation in strength is reduced.

As described above, the present invention is characterized in that the step of mixing powder and starch is carried out by two steps of unheated mixing and heated mixing. In conventional methods, it was considered sufficient to mix and heat the powder and starch in a single step. Incidentally, in Patent Document 1, only heating is performed after mixing, and in Patent Document 2, there is no unheated mixing, and mixing and heating are performed simultaneously.

In contrast to these prior arts, the inventors of the present invention have found that the strength of the molded product is improved by first performing the mixing without heating and then performing the mixing while heating. This is a mixture of powder and starch before pre-gelatinization (i.e., β-starch) before heating (unheated mixture), and a mixture of powder and pasty starch after pre-gelatinization (i.e., α-starch) during heating. In (heated mixing), since the mixing mode is different, it is considered that a higher degree of starch dispersion was achieved by mixing in both states than by mixing in either state.

Therefore, in the present invention, since the briquette strength can be improved without adding caustic soda during mixing, there is no need to handle caustic soda, which is a deleterious substance, and the sodium concentration in the briquette does not increase. Furthermore, in the present invention, since the powder and starch are mixed in an unheated state and the resulting mixture is further mixed in a heated state, the gelatinized gelatinized starch and the powder are mixed and kneaded. Therefore, the variation in briquette strength is very small.

[powder]
Powders used as raw materials include powders such as coal powder, ore powder, and converter dust, but coal powder is preferably used in the production of briquette coal briquettes in the ironmaking process. The particle size of the coal powder is not particularly limited, but the finer the powder, the better the strength of the briquette. When coal powder having a particle size of 3 mm or less and less than 80% by mass is used, it may be pulverized or mixed with another fine coal powder to adjust the particle size within the above range.

[Starch as binder]
Various binders can be used as the binder to be mixed with the powder, but it is preferable to use starch as the binder used in the method for producing the molded coal briquette of the present embodiment.

The type of starch is not particularly limited, and starch produced from raw material plants such as tapioca, potato, sweet potato, corn, rice, and wheat can be used as appropriate. Starches and the like can also be used.

Starch includes gelatinized (pregelatinized) pasty α-starch and pre-gelatinized β-starch. It is preferred to use a starch containing the above.

[Mixing ratio]
The ratio of starch as a binder to coal powder is preferably added so as to be 0.1 to 5.0% by mass with respect to the total of coal powder and starch. Also, 0.5 to 3.0% is more preferable. This is because if the amount of starch is too small, the effect as a binder will be weakened, and if it is too large, the cost of the raw material will increase.

[Mixing process, mixing device]
As for the powder mixing device, there are no restrictions on the capacity of the mixer and the processing amount, but any mixer that can sufficiently mix the contents and secure the heating time may be used. A specific example of a suitable mixer is a Henschel mixer, but any mixer such as a horizontal paddle type or a vertical paddle type may be used as long as it can be heated. For example, a batch-type mixer can be used to first perform unheated mixing and then to mix while heating by blowing steam into the mixer.

The heating method is not limited to steam blowing, and other heating methods such as microwave irradiation or installation of a heat medium around or inside the mixer (such as an electric heater or gas combustion device) may be adopted. .

In addition, as a device for performing unheated mixing and heated mixing in a continuous type mixing device, as shown in FIG. It is preferable to use a device such as a mixer in which a plurality of steam ejection ports 4 are provided on a rotating shaft 1 for use and screw blades 3 having excellent kneading properties are arranged and connected by a connecting means 8 .

[Heating temperature]
The heating temperature during heating and mixing is desirably equal to or higher than the gelatinization starting temperature of the starch used as the binder. Since this gelatinization initiation temperature varies depending on the type of starch, the heating temperature may be adjusted according to the starch used. Generally, starch gelatinization initiation temperature is 60° C. or higher. For example, the gelatinization initiation temperature of tapioca-derived starch is 65.4°C, and the gelatinization initiation temperature of potato-derived starch is 61.0°C. Therefore, the heating temperature during heating and mixing is preferably 60.0 to 90.0°C.

In the case of unheated mixing, the state is usually room temperature, but as described above, gelatinization does not occur if the temperature is lower than the gelatinization start temperature of starch, so it is the same as the unheated state. For example, β-starch derived from tapioca can be said to be mixed in an unheated state if performed at 50.0° C. or lower.

[Heating time]
The time for heating and mixing may be appropriately adjusted depending on the type of powder and binder. As will be described later in Examples, when starch is used, starch is gelatinized and uniformly mixed with powder. For example, the heating time in the case of the coal briquetting process described above is preferably 150 seconds or more.

Furthermore, the time for unheated mixing may be similarly adjusted according to the type of powder and binder. is required to be uniformly mixed as an unheated mixture. For example, when used in the above-described coal briquette process, the unheated mixture is preferably performed for 15 seconds or more.

[Molding process, molding equipment]
A briquette of coal briquette is obtained by pressure-molding the mixture (heated mixture) obtained by the above-described mixing step. The molding method is not particularly limited, and as the briquette molding apparatus, any molding machine of roll compression, tumbling, and extrusion may be used. In particular, it is preferable to use a double roll molding machine, which is relatively simple and highly versatile, and can easily apply a compressive force to the powder, thereby easily obtaining a briquette with high strength. In this embodiment, the briquette coal briquette was explained as an example, but it can also be applied to other briquettes (ore powder briquettes, converter dust briquettes, etc.) in the ironmaking process.

[Briquette strength]
The briquette strength was determined by subjecting the obtained heated mixture to a compression force with a pressure roll type molding machine to form a Macek type charcoal briquette briquette of 46 mm × 46 mm × 38 mm, and subjecting the briquette briquette to natural curing for 2 hours. The 10 briquettes after being dropped were dropped from a height of 2 m three times, and the ratio of the weight of lumps of 15 mm or more to the weight of the dropped briquettes was measured as drop strength (%).

EXAMPLES Hereinafter, embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
First, in this example, β-starch was used as a binder, β-starch was added to coal powder, mixed (unheated and mixed), further heated and mixed, and then formed into briquettes to be used as coke raw materials. The strength of the briquettes was measured to investigate the effect of the heating method of β-starch on the strength of the briquettes.

As the coal powder, pulverized coal was used in which the mass of particles having a particle size of less than 10 mm accounted for 95% by mass of the entire coal. Tapioca-derived β-starch was used as the binder, and was added to the coal powder so as to have a weight ratio of 1% by weight with respect to the total with the coal powder.

The above raw materials (coal powder and β-starch) were mixed in a Henschel mixer without heating to obtain an unheated mixture, and then heated and mixed while blowing steam to obtain a heated mixture. The heating temperature at this time was adjusted to about 70.0° C., which is higher than 65.4° C., which is the gelatinization start temperature of β-starch derived from tapioca.

The briquette strength was measured by the briquette drop strength test described above. Regarding the falling strength of this briquette, when only heating mixing is performed, that is, when unheated mixing is not performed (a), and when unheated mixing + heating mixing is performed, the unheated mixing time is 15 seconds (b) and 45 seconds (c) were compared.

Fig. 1 shows the relationship between the falling strength of briquettes and the total mixing time. The total mixing time (seconds) on the horizontal axis of FIG. 1 indicates the total time of non-heated mixing and subsequent heated mixing. The vertical axis indicates the drop strength (%) of the briquette. Here, in the case of no unheated mixing (a) (○ mark in FIG. 1, solid line), the drop strength starts to rise early, but the drop strength is about 70% when heated for 150 seconds, and the drop strength is about 70% after 230 seconds. Even after heating, the drop strength was about 80%. On the other hand, when the unheated mixing was performed for 15 seconds (b) (marked Δ in FIG. 1, dashed line), although the drop strength started to rise later, the total mixing time was 165 seconds (unheated mixing 15 seconds + After 150 seconds of heating and mixing, the drop strength reached about 80%. In addition, when unheated mixing was performed for 45 seconds (c) (marked with □ in FIG. 1, dotted line), although the drop strength began to rise later, the total mixing time was 195 seconds (unheated mixing 45 seconds + heated mixing 150 seconds), the drop strength is about 83%, and the strength is improved by performing unheated mixing before heating and mixing, compared to the heat mixing alone without unheated mixing. It can be seen that the longer the mixing time, the higher the strength.

Furthermore, FIG. 2 shows a graph in which the above results are arranged in relation to the falling strength of the briquette and the heating and mixing time. The horizontal axis is the heating and mixing time (seconds), and the vertical axis is the drop strength (%) of the briquette. Here, in the case of no unheated mixing (a) (○ mark in FIG. 2, solid line), the drop strength starts to increase after about 40 seconds of heating and mixing time, and when heated for 150 seconds, the drop strength is about 70%. The drop strength was about 80% even after heating for 230 seconds. On the other hand, when the unheated mixing was performed for 15 seconds (b) (marked Δ in FIG. 2, dashed line), the drop strength began to increase in about 40 seconds, and the drop strength started at about 40 seconds. The strength became about 80%. In addition, when unheated mixing was performed for 45 seconds (c) (marked with □ in FIG. 2, dotted line), the drop strength began to increase at about 40 seconds, but the drop strength started at about 150 seconds. The strength is about 83%, and the strength is improved by the process of performing unheated mixing before heating and mixing, compared to the treatment of only heating and mixing without unheated mixing, and the longer the unheated mixing time, the stronger the strength. It can be seen that the In particular, in FIG. 2, it is clearly observed that even if the heating and mixing time is further increased, the improvement in strength tends to be saturated. When estimating the saturation strength value when heating and mixing for a longer time is performed by extrapolation from the tendency of each strength increase, the saturation strength in the case of no unheated mixing (a) is a little over 80%, whereas the unheated It is estimated that the saturation strength of (b) and (c) is a little over 90% when heat mixing is performed. The above estimation is indicated by the extrapolation line indicated by the dotted line on the right side of each graph line in FIG. A difference of 10% in the strength value means that the powder generation rate is 20% and 10% in terms of the powder generation rate (= 100 - strength (%)) in the strength test, and the powder generation rate is 2. A two-fold difference is recognized, and this difference has an important meaning industrially. From the results of FIGS. 1 and 2, it can be seen that briquettes with higher strength can be produced by heat-mixing after unheated mixing than by heat-mixing without unheated mixing.

From this result, the strength of the briquette is affected not only by the heating and mixing time but also by the unheated and mixed time. It can be seen that the briquette strength is greatly improved.

(Example 2)
Next, the molding test was conducted 10 times with the same heating time, and the variation in briquette strength was investigated. %, in the case of unheated mixing 15 seconds (b), the strength range is 10%, and in the case of unheated mixing 45 seconds (c), the strength range is 5%. It was found that longer heating and mixing also reduces variations in strength.

For these reasons, it is preferable that the non-heated mixing time is 15 seconds or longer. The time for heating and mixing after unheated mixing is preferably 130 seconds or longer, more preferably 150 seconds or longer.

The reason why the above-mentioned difference in briquette strength occurs depending on the presence or absence of unheated mixing is that when unheated mixing is not performed, the temperature of the β-starch rises before the raw material powder and β-starch are sufficiently homogeneously mixed. As a result, it is conceivable that lumps are generated and the starch is not distributed throughout the raw material after molding, resulting in a decrease in drop strength of the briquette and variations in strength.

(Example 3)
Furthermore, using the apparatus shown in FIG. 3, a test was also conducted in which unheated mixing and heated mixing were continuously performed. In the apparatus of FIG. 3, the paddle blades 2 with strong mixing power are arranged in the front stage, the screw blades 3 with relatively weak mixing power are installed in the rear stage, and steam is blown in from the rear stage (Case 1), and the front stage Coal powder and β-starch were mixed in the case (Case 2) in which the screw blades 3 were installed in both the second stage and the latter stage, and the strength of the briquette obtained by molding the mixture was measured. As a result, the strength in case 1 was 93.8%, and the strength in case 2 was 62.6%, confirming that the strength of the briquettes was increased by increasing the mixing in the previous stage.

(Example 4)
In addition, it was confirmed that β-starch and coal powder were mixed without heating, then heated and mixed to produce briquettes, and the briquettes were carbonized to produce coke, resulting in sufficiently strong coke. Briquettes obtained by molding coal powder by the method of the present invention can also be suitably used as a raw material for coke production.

As described above, according to the production method of the present invention, the strength of the briquette can be improved without adding caustic soda at the time of mixing. No increase in sodium concentration. Furthermore, since the present invention heats and mixes after mixing, the pregelatinized starch is mixed and kneaded after gelatinization, so that there is an exceptional effect that the variation in strength of the briquettes is very small.

1 Rotating shaft 2 Paddle blade 3 Screw blade 4 Steam injection port 5 Container 6 Bearing 7 Device frame 8 Connection means

Claims (5)

In the method for producing briquettes, in mixing the powder and the binder, the powder and the binder are mixed in an unheated state, then mixed in a heated state, and the resulting mixture is molded. A method of making briquettes. 2. The method for producing briquettes according to claim 1, wherein the powder is coal powder. 3. The method for producing briquettes according to claim 1, wherein the binder is starch. 4. The method for producing briquettes according to claim 3, wherein the heating temperature in the heated state is equal to or higher than the gelatinization start temperature of the starch. The method for producing briquettes according to any one of claims 1 to 4, wherein the heating temperature in the heated state is 60.0 to 90.0°C.

Images