JP5984139B2 - Briquette manufacturing method - Google Patents

Description

  The present invention relates to a briquette manufacturing method for manufacturing briquettes from dust discharged and collected from a rotary kiln that performs calcination of nickel oxide ore in ferronickel smelting.

  Conventionally, as a general manufacturing method of ferronickel, which is an alloy of iron and nickel, a dry product having a drying step, a firing step, a reduction melting step, and a purification step using a laterite ore such as a saporolite ore containing nickel as a raw material. A smelting method is adopted. In this method, usually, ore is dried with a rotary dryer so that the adhering moisture of the ore is 15 to 25% (preliminary drying), and then a firing process (firing step) using a rotary kiln is performed.

  In this firing step, pre-dried ore and coal such as anthracite are charged into a rotary kiln and heated to about 800 to 1000 ° C. to remove adhering water (dry) and decompose crystal water (fire), Furthermore, preliminary reduction is performed to obtain a calcined ore. Thereafter, in the smelting reduction process, the obtained sinter is melted and reduced in an electric furnace to form a metal and slag containing nickel and iron.

  At this time, dust is generated in the rotary dryer and the rotary kiln as the ore is dried or fired. Therefore, the dust generated in the exhaust gas treatment facility is collected. Since the recovered dust contains nickel of the same grade as ore, the rotary dryer or rotary kiln is usually used to recycle the dust as it is or after granulating the pellet into pellets with a pelletizer or the like. The method of repeatedly charging is used (repeated dust treatment).

  When the dust is repeated as it is, if the ore is clayey and self-granulating ore, the charged dust is granulated together with the ore in the rotary dryer, and the rate of scattering as dust again is small. Become. However, ores used in recent years have few self-granulating properties, and repeated dust is scattered again as dust as it is.

  Therefore, granulation of dust for repeated charging is performed. However, since kiln dust contains coal charged in the kiln as a reducing agent, there is a problem that wettability is low and the strength of the resulting pellets is low.

  In general dust granulation, processing using a pelletizer is performed, but since a solvent is used as a binder for the purpose of obtaining the strength of the pellets, the disadvantage is that the cost is very high. There is. For example, Patent Document 1 discloses a method of producing pellets using an alkaline aqueous solution, which is a water-soluble inorganic salt containing an alkali metal and having a pH of 8.5 or more, as granulated water (solvent). There is a problem in that the production cost of dust pellets is high because it takes cost to produce granulated water.

  For example, Patent Document 2 discloses a method of manufacturing briquettes having a predetermined strength without using a binder with respect to steelmaking dust. However, the technique described in Patent Document 2 is a technique in steel smelting, and this technique cannot be applied to dust treatment in ferronickel smelting with different dust properties.

  Thus, in a method for obtaining a molded product such as pellets or briquettes from dust generated in a rotary kiln or the like in ferronickel smelting, the molded product has strength, and the molded product can be manufactured at a low manufacturing cost. It has been demanded.

JP 2006-291320 A JP 2006-137976 A

The present invention has been proposed in view of such circumstances, the dust recovered from the rotary kiln exhaust gas to perform b over tally dryer firing to dry the nickel oxide ore, briquettes having a high strength Another object of the present invention is to provide a method that can be manufactured at low cost.

  The inventors of the present invention have made extensive studies to achieve the above-described object. As a result, after the collected dust and ore are mixed in advance, a high-strength briquette is formed by molding based on a kneaded product obtained by adding a predetermined amount of water to the mixture and kneading. As a result, the present invention has been completed.

That is, the manufacturing method of the briquette according to the present invention is a method of manufacturing briquette from dust generated from a rotary kiln in ferronickel smelting, the mixing step of mixing the dust and ore in advance, and the mixing step A kneading step of adding water to the resulting mixture so that the moisture value of the briquette is 17 to 19% and kneading, and a molding step of molding the kneaded product obtained through the kneading step It is characterized by.

  According to the present invention, a briquette having high strength can be produced at a low cost without using a solvent or the like as a binder, and can be repeatedly charged into a rotary kiln effectively without being pulverized.

It is process drawing of the manufacturing method of a briquette. It is a figure for demonstrating the flow of the manufacturing method of a briquette. It is a figure for demonstrating the intensity | strength of the molded article obtained by shape | molding a kneaded material with a briquette machine.

  Hereinafter, a specific embodiment of a briquette manufacturing method according to the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment, In the range which does not deviate from the summary of this invention, a change is possible.

  The manufacturing method of the briquette according to the present embodiment includes a rotary dryer that performs preliminary drying on nickel oxide ore in ferronickel smelting and dust generated from a rotary kiln that performs firing and preliminary reduction on dry ore obtained by preliminary drying. A method of manufacturing briquettes. Hereinafter, the rotary dryer used for preliminary drying and the rotary kiln used for preliminary reduction and firing may be generally referred to as “rotary kiln”.

  The nickel oxide ore used in ferronickel smelting (hereinafter, also simply referred to as “ore”) is not particularly limited, but generally, a mixture prepared by blending several kinds of laterite ores is used. In ferronickel smelting, the ore is first pre-dried with a rotary dryer to reduce the adhering moisture to about 20%, and then the resulting dried ore and coal such as anthracite as a reducing agent are rotary kiln. Calcination and preliminary reduction are carried out. The ore that has been baked and discharged is called calcined ore, and the temperature of this calcined ore is maintained at 800 ° C. or higher in order to avoid troubles caused by reductive melting in an electric furnace in a subsequent process.

  In the rotary dryer and rotary kiln, dust is generated as the ore is dried and fired. The generated dust contains nickel of the same grade as the ore. For this reason, in order to reuse the raw material as a raw material, a method of repeatedly charging the collected dust into a briquette and then repeatedly charging it into a rotary kiln or the like is employed.

  As shown in the process diagram of FIG. 1, the briquette manufacturing method according to the present embodiment includes a mixing step S1 in which generated dust and ore are mixed in advance, and a predetermined amount of water is added to the mixture obtained by mixing. Kneading step S2 for adding and kneading, and molding step S3 for molding the kneaded material obtained by kneading using a briquette machine or the like. FIG. 2 is a diagram for explaining the flow of the manufacturing method. According to such a manufacturing method, a briquette having high strength can be manufactured at a low cost, and can be effectively subjected to repeated treatment without being pulverized. Hereinafter, each process is demonstrated in order.

  In addition, the “briquette” in this specification is used as a concept including pellets.

(Mixing process)
In mixing process S1, the dust and ore which generate | occur | produced and collect | recovered from the rotary kiln are mixed previously, and a mixture is obtained.

  Dust is mainly generated in a rotary kiln. The dust used in the manufacturing method of the briquette according to the present embodiment is dust recovered from the exhaust gas of the rotary kiln that performs the preliminary drying of the ore and the rotary kiln described above, and mainly the adhering water from the ore. It consists of dry ore that has been removed, calcined ore from which crystal water has been partially removed, and coal as a reducing agent. Such dust has poor granulation properties. This is considered to be due to the deterioration of wettability due to the fact that coal is contained in the dust and the baked ore is included.

  In general, the strength of a molded product such as a briquette formed from dust is considered to depend on the capillary force of water adhering between particles in a wet state immediately after granulation. Therefore, in the molded product, it is considered that the strength is increased by ore particles being sucked by moisture movement due to capillary action and a vacuum (low atmospheric pressure) space is developed.

  For this reason, in the briquette manufacturing method according to the present embodiment, the ore is mixed with the collected dust. Dust and ore have different particle sizes. Therefore, by mixing and granulating dust and ore in this way, the energy required when the grains move can be increased, that is, the grains constituting the molded product can be made difficult to move. The strength of the molded product obtained can be increased. That is, by mixing the ore with the dust in this way, the ore acts as a so-called binder.

  At this time, it is important to mix and granulate dust and ore, and to eliminate the uneven distribution of ores with a large particle size and dust with a small particle size and to lower the porosity, that is, , Mixing dust and ore well enough.

  Therefore, the briquette manufacturing method according to the present embodiment is characterized in that a mixing step S1 for mixing dust and ore is provided in advance. Thus, prior to producing a kneaded product of dust and ore, by providing a mixing step of mixing dust and ore, mixing becomes sufficiently effective, and the particle size is large. It is possible to eliminate the uneven distribution of the ore and dust having a small particle diameter, and to reduce the porosity. And thereby, the intensity | strength of the briquette obtained can be raised effectively.

  As described above, the dust is dust collected from the exhaust gas of the rotary kiln, and is not particularly limited. However, it is preferable to use dust whose water content is adjusted to a predetermined ratio. Specifically, for example, it is preferable to use dust adjusted to have a moisture content of 16 to 20 wt%. The method for adjusting the moisture content of the collected dust is not particularly limited as long as the moisture content can be set to a desired value. For example, a drying process using a dryer or natural drying may be used.

  As the ore, a dried ore whose attached moisture is reduced to about 20 wt% or less (for example, about 16 to 20 wt%) through a rotary dryer is used. The particle size of the ore is not particularly limited, but it is preferable to use an ore (powder ore) of about 10 mm or less. In this way, by mixing powder ore with a particle size of about 10 mm or less with dust, the porosity of the dust and ore can be reduced in the kneading step S2 to be described later, and an even stronger briquette is produced. can do.

  The ore used for mixing is not particularly limited. As shown in FIG. 2, after being discharged from the rotary dryer, the ore under the sieve obtained by sieving using a 10 mm sieve or the like is recovered. Can be used.

(Kneading process)
In the kneading step S2, a predetermined amount of water is added to the mixture of dust and ore obtained by mixing in the mixing step S1 and kneaded to obtain a kneaded product. In the kneading step S2, a raw material (kneaded material) to be formed into a briquette is prepared by kneading the mixture with final moisture adjustment using, for example, a water adjusting device.

  Here, the moisture value finally adjusted in the kneading step S2 is important from the viewpoint of the strength and productivity of the briquette as a molded product. The molding method will be described in detail later, but in the case of filling the mixture into a roller cup such as a briquette machine, if the moisture value is too high, the strength of the molded product will be extremely lowered and the shape of the molded product can be maintained. Disappear. Furthermore, there is a possibility that the amount of deposits in the cup increases and proper operation cannot be maintained. On the other hand, if the moisture value is too low, the capillary force is not expressed, and thus the strength of the briquette as a molded product is extremely deteriorated. From this, in the kneading step S2, a predetermined amount of water is added so that the ratio of water adhering to the kneaded product obtained is preferably in the range of 18 ± 3%, more preferably in the range of 18 ± 2%. Add and knead. By kneading in this way, a briquette with high strength can be obtained.

  In the kneading step S2, it is preferable to lower the porosity by kneading sufficiently firmly. Although it does not specifically limit as a concrete kneading method, For example, when processing the quantity of about 50 (kg / min), it knead | mixes using the mixer which has an effective volume of about 80L. Moreover, it does not specifically limit about the mixer to be used, For example, a pug mill mixer etc. can be used. In addition, the effective volume of a mixer here means the accommodation volume of the mixture which can be knead | mixed effectively with the mixer.

(Molding process)
In the molding step S3, the kneaded product obtained through the kneading step S2 described above is molded using, for example, a compression-type continuous molding machine (briquette machine) to obtain a briquette that is a molded product. Specific molding conditions and the like are not particularly limited, and molding can be performed under general conditions.

  Here, the strength mechanism of the molded product molded by the briquette machine or the like in the molding step S3 can be described by a model diagram as shown in FIG.

  That is, as shown in FIG. 3, when the powder is inserted into the roll gap, the flow of the powder becomes a flow related to the roll rotation below the “break-in point”. That is, as the roll rotates, the powder is compressed, the gap gradually decreases, and the individual particles are brought into close contact with each other to be molded. Therefore, the decreasing rate of the roll gap below the biting point determines the molding pressure and determines the specific gravity and strength of the molded product. This relationship can be expressed by a simple expression as follows.

  In the above formula, “θ” represents the biting angle, “Vf” represents the porosity of the raw material powder, “Vp” represents the porosity of the molded product, “S” represents the roll gap, and “d” represents the roll diameter. .

  If “d”, “S”, and “Vf” are determined in such a relational expression, the porosity of the molded product is determined. That is, the specific gravity of the molded product is determined by the biting angle. The biting angle is determined by the raw material powder form if the roll is constant. That is, since the biting angle is the same even if the roll diameter is changed, a molded product having a larger specific gravity can be obtained as the roll diameter is larger. Further, the higher the porosity of the raw material powder, the lower the porosity of the molded product, and as a result, the strength of the molded product (briquette) increases.

  In the molding process using a briquette machine or the like in the molding step S3, the moisture content is generally reduced by about 1 to 2%. For this reason, in the above-described kneading step S2, it is preferable to determine the amount of water to be added in consideration of a decrease in the water content in the molding process.

  As described above in detail, the briquette manufacturing method according to the present embodiment is obtained by mixing the collected dust and ore in advance and then adding and kneading a predetermined amount of water to the mixture. Based on the kneaded material, a briquette as a molded product is formed. The briquette thus obtained has a very high strength, for example, a crushing strength of about 5 to 10 (kgf / piece (p)).

  Further, in the briquette manufacturing method according to the present embodiment, it is possible to manufacture a briquette with high strength without using a solvent as a binder as in the prior art, so that the manufacturing cost can be reduced extremely effectively. It is possible to manufacture briquettes efficiently.

  In addition to the above-mentioned crushing strength, generally, the index as the strength of the molded product includes yield, drum strength, drop strength, etc. In any case, the conveyance system and kiln are fundamentally used. It must be strong enough to withstand rolling. For example, a briquette obtained by this briquette manufacturing method has a yield of +10 mm of 80% or more.

  Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.

≪Manufacture of briquettes≫
Briquettes were produced from dust generated from a rotary kiln as follows.

(Mixing process)
First, the dust recovered from the rotary kiln and the sieving ore obtained by sieving the dried ore obtained by pre-drying the nickel oxide ore to 10 mm or less are premixed for 2 to 7 minutes. (Preliminary mixing).

Here, as dust, the dust collected from the exhaust gas of the rotary dryer which performs preliminary drying of nickel oxide ore and the rotary kiln which performs baking was used. This dust contains dry ore from which the adhering water has been removed from the ore, burned ore from which crystal water has been partially removed, and reducing agent coal. As the raw material ore, a Ni-grade of about 2%, an Fe-quality about 22%, an MgO grade about 16%, by several blending laterite ore SiO ₂ grade is about 35% What was prepared was used. Ore grade after preparation is, Ni grade of about 1.9 to 2.4% Fe grade of about 10 to 16% MgO grade of about 22 to 27% SiO ₂ grade of about 37 to 41%, water attached Was about 25 to 30%.

  Table 1 below shows an example of the particle size distribution of dust and ore, which are raw materials used for mixing. As shown in Table 1, it can be seen that dust has a relatively small particle size, powder ore has a relatively large particle size, and dust and powder ore have different particle sizes.

(Kneading process)
Next, a mixture obtained by mixing dust and fine ore using a pug mill mixer equipped with a water conditioning device and having an effective volume of about 0.08 m ³ per 50 kg / min. A kneaded product was prepared by adding a predetermined amount of water and kneading. Industrial water was used as water for conditioning. Moreover, as the ratio of the water conditioning, water was prepared so that the moisture value of the molded product was as shown in Table 3 below.

(Molding process)
Next, the obtained kneaded material was charged into a briquette machine and molded to produce a briquette.

≪Evaluation≫
<Effect of premixing>
Prior to the kneading of the dust and the ore, the strength of the obtained briquettes was compared when the mixing (preliminary mixing) was performed in advance and when the premixing was not performed as described above. Table 2 below shows the results when using the compressive strength as an index of briquette strength. In Table 2 below, “(+) 3 minutes” means the mixing time associated with kneading at the time of kneading, and “preliminary mixing + 3 minutes” indicates a test example in which premixing was performed prior to kneading. “3 minutes” indicates a test example in which only mixing during kneading was performed without performing preliminary mixing. Further, the raw compressive strength refers to the compressive strength measured with respect to the obtained raw briquette.

  As shown in Table 2, prior to kneading, the strength of the briquette obtained can be increased by a factor of 2 by pre-mixing dust and ore (preliminary mixing), and the strength can be effectively increased. I understood. This is because by performing premixing, the ore having a large particle size and the dust having a small particle size are mixed evenly without being unevenly distributed, whereby the porosity of the kneaded material obtained by kneading becomes very small. This is probably because

<Percentage of moisture adjustment>
Based on the ratio of moisture adjustment (conditioning) in the kneading step, the strength of the obtained briquettes was compared. As a test example, the moisture values (moisture ratio) in raw briquettes (molded products) were 20%, 19%, 18%, 17%, and 15%, respectively, and the water content adjusted during kneading was compared. . The moisture value was calculated based on the weight before and after drying when the sample was dried at 100 ° C. for 24 hours.

  Table 3 below shows the strength of briquettes having respective moisture contents. As strength indicators, yield (+10 mm), green pressure strength (kgf / piece (p)), and ID strength (drum strength, +10 mm) were used. In addition, “-” in Table 3 indicates that measurement was not performed.

  As shown in Table 3, by adding water in the kneading step so that the moisture value of the briquette as a molded product is 17 to 19%, the yield of the briquette is 80% or more and the crushing strength is 5 It turned out that it becomes more than (kgf / piece (p)).

Claims (3)

A method for producing briquettes from dust generated from a rotary kiln in ferronickel smelting,
A mixing step of previously mixing the dust and the ore;
A kneading step of adding water to the mixture obtained through the mixing step so that the briquette has a moisture value of 17 to 19% and kneading; and
And a molding step of molding the kneaded material obtained through the kneading step.   The briquette manufacturing method according to claim 1, wherein the ore is a dried ore obtained by pre-drying nickel oxide ore with a rotary dryer.   The briquette manufacturing method according to claim 1, wherein the ore is an ore having a particle size of 10 mm or less.

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