JP7415964B2 - How to make briquettes - Google Patents

Description

The present invention relates to a method for manufacturing briquettes used in iron manufacturing processes.

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. Specifically, for example, cheap, low-grade ore can be crushed, sorted, and briquetted to be used as a high-grade raw material, or coal or iron ore powder can be briquetted to improve bulk density and air permeability. Examples include cases in which the dust fed into the converter is made into briquettes to prevent scattering.

Generally, briquettes are manufactured by crushing raw materials into powder, mixing them with a binder, and then press-molding them in a molding machine. Briquettes also have a certain level of strength to prevent pulverization during transportation. is required. However, when relatively inexpensive starch is used as a binder material, beta starch, which is often found in cheap starches, is water-insoluble, so the strength of the briquettes is very low because the strength of the adhesion between particles in the powder is weak. .

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

Non-Patent Document 1 discloses a method in which β starch is gelatinized by mixing caustic soda with starch to improve adhesive strength and briquette strength. However, caustic soda is harmful to the human body and there are health and safety risks when handling it. Furthermore, since sodium, which acts as a catalyst for the reaction between coke and gas in the blast furnace, is mixed into the briquettes, there is also the problem that the reactivity of the coke produced from the briquettes increases excessively.

Furthermore, Patent Document 1 discloses that starch powder (which is thought to contain a large amount of β starch), powdered charcoal, and water are mixed, and the resulting mixture is heated to gelatinize (gelatize) the starch powder. A technique for obtaining a molded body with improved adhesive strength has been disclosed. However, since no kneading is performed after heating, the mixing state of powdered coal and gelatinized starch (also referred to as pregelatinized starch or α-starch) becomes uneven, resulting in insufficient strength of the compact and a large variation in strength. The problem is that it's big. In the first place, Patent Document 1 is a technology that aims to make the charcoal have a flexible structure while retaining its functions, and does not take into account the prevention of pulverization. This is a technology that cannot be adopted industrially in situations where it is necessary to suppress

Furthermore, Patent Document 2 discloses a method in which a binder is added to the raw material, mixed, and heated in one step in the production of a recarburized material for raw material for iron manufacturing. However, in Patent Document 2, starch is only disclosed as an example of a binder, and the effect of gelatinization of β starch is not considered. When β starch is used as a binder material, gelatinization by heating and dispersion by stirring are performed at the same time. Conditions are unknown.

JP2008-308476A JP 62-158812 Publication

Reiji Takahashi, Masaki Yamamoto, "Behavior of starch in caustic soda", Journal of the Starch Industry Association, Vol. 17, No. 3, pp. 289-293, 1969

As described above, in the conventional method of manufacturing briquettes using starch as a binder in the steel manufacturing process, there is a problem in that it is difficult to obtain briquettes with sufficient strength.

Therefore, the present invention provides a method for producing briquettes in which powder is mixed with a binder and molded, using starch as the binder and without adding caustic soda, to produce briquettes that have high strength and are difficult to powder, suitable for the steel manufacturing process. The purpose is to provide a manufacturing method.

The present inventors have made extensive studies to solve the above problems, and have found that high-strength briquettes can be produced by first mixing powder and binder in an unheated state and then in a heated state. I found out what I can get.

The present invention was made based on the above findings, and the gist thereof is as follows.
[1] In the method for producing briquettes, 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. Characteristic briquette manufacturing method.
[2] The method for producing briquettes according to [1], wherein the powder is coal powder.
[3] The method for producing briquettes according to [1] or [2], wherein the binder is starch.
[4] The method for producing briquettes according to [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], characterized in that the heating temperature in the heating 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 it is also possible to produce briquettes that have small variations in strength and are difficult to powder.

It is a figure showing the relationship between briquette falling strength and total mixing time. It is a figure showing the relationship between briquette falling strength and heating mixing time. It is a schematic diagram showing an example of a mixing device.

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

[Manufacturing process]
First, in this embodiment, coal powder is used as a 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 beta starch in the starch was mixed uniformly in the powder without viscosity. A mixture (hereinafter also referred to as "unheated mixture") is obtained.

Here, the "unheated state" refers to a state without heating, and usually refers to a state at room temperature. 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 it is equivalent to a state in which it is not heated.

After the unheated mixing, the unheated mixture is mixed in a heated state (hereinafter also referred to as "heated mixing") to obtain a mixture (hereinafter also referred to as "heated mixture"). This heated mixing is performed, for example, by blowing steam into a mixer and heating the unheated mixture, thereby gelatinizing the starch (hereinafter also referred to as "gelatinization") while mixing to obtain a viscous mixture. It's a method. In other words, this method allows gelatinized (gelatinized) starch with high adhesive strength to be mixed sufficiently uniformly with the powder, thereby improving the strength of the briquettes and reducing variations in strength.

As described above, the present invention is characterized in that the step of mixing powder and starch is performed by two steps: unheated mixing and heated mixing. In conventional methods, it was considered sufficient to mix the powder and starch and heat them 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 conventional techniques, the present invention has found that the strength of the molded product can be improved by first performing mixing without heating and then also performing mixing during subsequent heating. This is a mixture of powder and pre-gelatinized starch (i.e. β-starch) before heating (unheated mixture), and mixing of powder and paste-like starch after gelatinization (i.e. α-starch) during heating. This is thought to be due to the fact that in (heat mixing), since the mixing forms were different, a higher degree of starch dispersion was achieved by mixing both states than by mixing either one state.

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

[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, and the particle size of 3 mm or less is preferably 80% by mass or more, and more preferably 90% by mass or more. In addition, when using coal powder having a particle size of 3 mm or less and less than 80% 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.

[Starch as a binder]
Although various binders 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 shaped charcoal 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, and wheat can be used as appropriate, and starch derivatives processed from plant-derived starches and chemically synthesized starches can also be used. Starch and the like can also be used.

Note that starch includes gelatinized (gelatinized) pasty α starch and pre-gelatinized β starch, but as mentioned above, in the present invention, β starch or β starch is used at 70% by mass. It is preferable to use starch containing the above.

[Mixing ratio]
The proportion of starch as a binder mixed into coal powder is preferably 0.1 to 5.0% by mass based on the total of coal powder and starch. Further, 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 a powder mixing device, there are no restrictions on the capacity or throughput of the mixer, but any mixer that can sufficiently mix the contents and ensure heating time may be used. A specific example of a suitable mixer is a Henschel mixer, but any mixer that can heat, such as a horizontal paddle type or a vertical paddle type, may be used. For example, it is possible to first perform unheated mixing using a batch type mixer, and then to mix while heating by blowing steam into the mixer.

The heating method is not limited to steam injection, but other heating methods such as microwave irradiation or the installation of a heating medium around or inside the mixer (for example, an electric heater or a gas combustion device) may be used. .

In addition, as a continuous type mixing device that performs unheated mixing and heated mixing, a heated mixing device is installed at the rear stage of the mixer equipped with paddle blades 2 that have a mixing power suitable for unheated mixing as shown in Figure 3. It is preferable to use a device in which a mixer in which a plurality of steam jet ports 4 are provided on a rotary shaft 1 and screw blades 3 having excellent kneading properties are arranged is connected by a connecting means 8.

[Heating temperature]
The heating temperature during heating and mixing is desirably higher than the gelatinization start temperature of the starch used as the binder. Since this gelatinization start temperature differs depending on the type of starch, the heating temperature may be adjusted depending on the starch used. Generally, the gelatinization initiation temperature of starch is 60°C or higher. For example, the gelatinization start temperature in the case of tapioca-derived starch is 65.4°C, and in the case of potato-derived starch, the gelatinization start temperature 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 mixture is usually at room temperature, but as described above, gelatinization will 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, in the case of beta starch derived from tapioca, if the mixture is carried out at 50.0°C or lower, it can be said to be mixed in an unheated state.

[Heating time]
The heating and mixing time may be adjusted as appropriate depending on the type of powder and binder, but as explained in the examples below, when starch is used, it is gelatinized and uniformly mixed with the powder. For example, in the case of the above-mentioned briquette process, the heating time is preferably 150 seconds or more.

Furthermore, the time for performing unheated mixing may be similarly adjusted as appropriate depending on the type of powder and binder, but as explained in the examples below, when starch is used, the starch of the powder and binder For example, when used in the above-mentioned briquette process, the time for unheated mixing is preferably 15 seconds or more.

[Molding process, molding equipment]
Molded coal briquettes are obtained by press-molding the mixture (heated mixture) obtained by the above-mentioned mixing step. 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, which has a relatively simple device and high versatility, and which makes it easy to apply compressive force to the powder, making it easy to obtain high-strength 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.

[Bricket strength]
The strength of the briquettes was determined by applying compressive force to the obtained heated mixture using a pressure roll molding machine, forming it into Masek-type molded charcoal briquettes of 46 mm x 46 mm x 38 mm, and naturally curing the above-mentioned molded charcoal briquettes for 2 hours. The 10 briquettes were dropped three times from a height of 2 m, and the ratio of the weight of the lumps of 15 mm or more to the weight of the dropped briquettes was measured as the drop strength (%).

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 is used as a binder, β starch is added to coal powder, mixed (unheated mixing), further heated and mixed, and then molded to produce briquettes used as a coke raw material. The strength of the briquettes was measured to investigate the effect of the heating method of β starch on the strength of the briquettes.

The coal powder used was powdered coal in which the mass of particles with a particle size of less than 10 mm was 95% by mass of the entire coal. As the binder, beta starch derived from tapioca was used, and the amount added to the coal powder was adjusted to be 1% by weight based on the total weight of the binder and the coal powder.

The above raw materials (coal powder and β starch) were first mixed unheated in a Henschel type mixer 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 was higher than 65.4°C, which is the gelatinization start temperature of β starch derived from tapioca.

The strength of the briquettes was measured by the briquette drop strength test described above. Regarding the falling strength of this briquette, the case (a) where only heated mixing is performed, that is, no unheated mixing is performed, and the case where unheated mixing + heated mixing is performed, and the unheated mixing time is 15 seconds. A comparison was made between the case where the test was carried out for 45 seconds (b) and the case where the test was carried out for 45 seconds (c).

Figure 1 shows the relationship between the falling strength of briquettes and the total mixing time. The total mixing time (seconds) on the horizontal axis in FIG. 1 indicates the total time of the unheated mixing time and the subsequent heated mixing time. Further, the vertical axis indicates the drop strength (%) of the briquettes. Here, in case (a) (circle mark, solid line in Figure 1) without unheated mixing, the time when the drop strength starts to increase is early, but the drop strength is about 70% at the time of heating for 150 seconds, and after 230 seconds Even after heating, the drop strength was about 80%. On the other hand, when unheated mixing is performed for 15 seconds (b) (△ mark and broken line in Figure 1), although the drop strength starts to increase later, the total mixing time is 165 seconds (15 seconds of unheated mixing + The drop strength reached approximately 80% at the time of heating and mixing (150 seconds). In addition, when unheated mixing is performed for 45 seconds (c) (□ mark and dotted line in Figure 1), although the drop strength starts to increase later, the total mixing time is 195 seconds (45 seconds of unheated mixing + heated mixing). The drop strength was approximately 83% at the time of 150 seconds), and the strength was improved by performing unheated mixing before heating, compared to the treatment using only heated mixing without unheated mixing. It can be seen that the longer the mixing time, the higher the strength.

Further, FIG. 2 shows a graph in which the above results are organized in terms of the relationship between the falling strength of the briquettes and the heating and mixing time. The horizontal axis is the heating mixing time (seconds), and the vertical axis is the falling strength (%) of the briquettes. Here, in case (a) without unheated mixing (○ mark and solid line in Figure 2), the falling strength starts to increase after about 40 seconds of heating and mixing time, and the falling strength reaches about 70% after heating for 150 seconds. Even after heating for 230 seconds, the drop strength was about 80%. On the other hand, when unheated mixing is performed for 15 seconds (b) (△ mark and broken line in Figure 2), the falling strength begins to increase after about 40 seconds, and the falling strength begins to rise after 150 seconds of heating and mixing. The strength was approximately 80%. In addition, when unheated mixing was performed for 45 seconds (c) (□ mark, dotted line in Figure 2), the drop strength started to increase at about 40 seconds, but the drop occurred when the heated mixing time was 150 seconds. The strength is approximately 83%, and compared to the treatment of only heated mixing without unheated mixing, the treatment of performing unheated mixing before heating improves the strength, and the longer the unheated mixing time, the stronger the strength. It can be seen that the results are improved. In particular, in FIG. 2, it is clearly seen that even if the heating and mixing time is further increased, the strength improvement tends to be saturated. If we extrapolate from the respective strength increasing trends to estimate the saturated strength value when heated and mixed for a longer time, the saturated strength in case of unheated mixing (a) is over 80%, while When heated and mixed, the saturation strength of (b) and (c) is estimated to be over 90%. The above estimation is shown in FIG. 2 by extrapolation lines drawn as dotted lines on the right side of each graph line. A 10% difference in the strength value means that the powder generation rate is 20% and 10% if you look at the powder generation rate from the strength test (= 100 - strength (%)), and the powder generation rate is 2%. A two-fold difference was observed, and this difference has important industrial significance. From the results shown in FIGS. 1 and 2, it can be seen that briquettes with higher strength can be produced by heating and mixing after unheated mixing than by heating and mixing without performing unheated mixing.

This result also shows that the strength of briquettes is affected not only by the heated mixing time but also by the unheated mixing time. It can be seen that the briquette strength is significantly improved.

(Example 2)
Next, we conducted a molding test 10 times with the same heating time to investigate the variation in briquette strength. In the case of unheated mixing (a), the range of measured strength (maximum strength - minimum strength) was 30 %, whereas in the case of unheated mixing (b) for 15 seconds, the strength range was 10%, and in the case of unheated mixing for 45 seconds (c), the strength range was 5%. It was found that by performing heating and mixing for a long time, variations in strength were also reduced.

For these reasons, the time for performing unheated mixing is preferably 15 seconds or more. Moreover, the time for performing heated mixing after unheated mixing is preferably 130 seconds or more, more preferably 150 seconds or more.

The reason why the above-mentioned difference in briquette strength occurs depending on the presence or absence of unheated mixing is that if unheated mixing is not performed, the β starch temperature rises before the raw material powder and β starch are sufficiently homogeneously mixed. As a result, clumps are formed and the starch is not distributed throughout the raw material after molding, resulting in a decrease in the falling strength of the briquettes 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 performed continuously. In the apparatus shown in Fig. 3, paddle blades 2 with a strong mixing force are placed in the front stage, screw blades 3 with a relatively weak mixing power are installed in the rear stage, and steam is blown from the latter stage (Case 1) and the former stage. The strength of the briquettes obtained by mixing coal powder and β starch and molding the mixture was measured in the case where screw blades 3 were installed in both the rear stage and the rear stage (Case 2). 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 strengthening the mixing in the previous stage.

(Example 4)
In addition, when β starch and coal powder were mixed unheated and then heated to produce briquettes, and the briquettes were carbonized to produce coke, it was confirmed that coke with sufficient strength could be obtained. 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, by using the manufacturing method of the present invention, the strength of briquettes can be improved without adding caustic soda during mixing, so there is no need to handle caustic soda, which is a deleterious substance, and the There is no increase in sodium concentration. Furthermore, in the present invention, heating and mixing are performed after mixing, so that the pregelatinized starch is mixed and kneaded after gelatinization, so that the variation in strength of the briquettes is extremely small, which is a special effect.

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

Claims (2)

In the method for producing briquettes, when coal powder and β starch are mixed, the proportion of the coal powder with a particle size of 3 mm or less is 80% by mass or more, and the ratio of the β starch mixed into the coal powder is the same as that of the coal powder. The mixing ratio is 0.1 to 5.0% by mass with respect to the total amount with the β starch, the coal powder and the β starch are mixed in an unheated state, and the mixing time in the unheated state is 15 seconds or more and 45 seconds or less, and then mixing in a heated state by blowing steam , the heating temperature in the heated state is equal to or higher than the gelatinization start temperature of the β starch, and the mixing time in the heated state is 130 seconds. A method for producing briquettes , which is the above and is characterized by molding the obtained mixture. The method for producing briquettes according to claim 1 , wherein the heating temperature in the heating state is 60.0 to 90.0°C.

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