JPH0580535B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to a method for producing resin-coated reduced iron pellets. Prior Art and Problems Examples of direct reduction iron making methods that directly reduce iron ore using reducing gas include Midrex method, Hill method,
The fior method and the like are widely known. The iron ore raw material for directly reduced iron is powdery or porous depending on the iron manufacturing method. The Midrex method and the Hill method process iron ore in the form of lumps or powder with a diameter of 5 to 20 mm.
In this method, reduced iron is obtained by solidifying the iron into a pellet shape, putting it into a reducing furnace, and introducing reducing gas. These reduced iron pellets typically have a porosity of approximately
It has the disadvantage that it is relatively easy to become fine powder due to friction between pellets, and is easily oxidized by contact with air or water. On the other hand, iron manufacturing methods such as the Feol method use natural lumpy or powdered ores as they are, so they are inexpensive, but the products are powdery and spongy, which makes them more susceptible to oxidation. Therefore, in this method, the produced reduced iron is heated again (e.g. 770
~780℃) and stored or transported as briquettes with a porosity of 20 to 30%. Oxidation and corrosion reactions differ depending on whether the target is air (oxygen) or water, and the product is hematite (Fe ₂ O ₃ ).
There are different types of iron, such as iron and magnetite (Fe ₃ O ₄ ), but most of them generate heat, which can cause a fire depending on the storage format, and reduced iron is difficult to handle because it generates hydrogen gas. be. As a means to prevent oxidation, physically briquetting is performed by compression molding as seen in the Feol method as mentioned above, and chemically, treatment with water glass or carburization is mainly used for pelletized reduced iron. It is. Although briquettes have a uniform iron-like surface appearance, they still have a water absorption rate of 3 to 5%, and the equipment is subject to severe wear and tear.While chemical treatment is effective for air oxidation, it is difficult to absorb water. reoxidation is almost ineffective, and powdering and tearing phenomena are likely to occur due to friction. To prevent water absorption phenomenon, US Patent No. 3573959
The patent describes a method in which the pores of a briquette are impregnated with a resin, and the resin is cured by the heat of the briquette itself, thereby sealing the pores. The resins used here are alicyclic olefins, cyclic olefins, diolefins, triolefins, etc.
It is stated that mixtures containing cyclopolyene oligomers are particularly preferred, and that naphtha decomposition residue partial polymers are particularly suitable. These are generally a type of liquid petroleum resin polymerized from compounds having about 5 to 9 carbon atoms, and are thought to polymerize in the briquette pores due to the heat of the briquette itself, thereby sealing the pores. However, this technique of sealing the pores of briquettes to prevent water absorption is not useful for preventing water absorption and pulverization of reduced iron pellets. The reason for this is that reduced iron pellets have a significantly larger porosity than briquettes, are more brittle than briquettes, and generally the temperature of the pellets themselves after being impregnated with resin is not high enough to polymerize polyenes. This is because there are many. When liquid resins such as those described in US Pat. No. 3,573,959 are used to coat reduced iron pellets, the amount of resin impregnated increases significantly at polymerizable temperatures, making it unprofitable. Moreover, the coating thickness on the pellet surface becomes thinner, and the wear resistance decreases. Also, if the temperature is low,
A separate heating step is required to promote the polymerization of the polyenes, or promoters such as elementally unfavorable metal compounds are required. No technology has been established to prevent reduced iron pellets from absorbing water or being covered by resin. Furthermore, British Patent No. 2129708A discloses a technique in which reduced iron is immersed in molten paraffin at 110 to 120°C to coat the surface of the reduced iron with paraffin in order to prevent reoxidation of the reduced iron. . In this immersion method, the reduced iron rises above the softening point of paraffin, and the paraffin is impregnated into the fine pores of the reduced iron, so a large amount of paraffin is required to achieve complete coverage, making it uneconomical. . The present inventors have solved the above-mentioned problems, namely, that they are easily pulverized and rust due to water absorption, and that when water-absorbed reduced iron pellets are put into an electric furnace or the like, water bumping occurs, which is extremely dangerous. In order to solve this problem, we first proposed a technology to melt and coat the surface of reduced iron pellets with thermoplastic resin (patent application 1986-
No. 122143 and Japanese Patent Application No. 122144). However, in these methods, it is necessary to maintain the processing temperature at a considerably high temperature before the surface of the reduced iron pellets is completely coated with resin, and the processing system must be filled with an inert gas to prevent re-oxidation of the reduced iron. For example, it was necessary to create a nitrogen gas atmosphere. This has the disadvantage that equipment for continuous surface treatment of reduced iron pellets becomes expensive. Means for Solving the Problems The present invention involves spraying a thermoplastic resin onto reduced iron pellets or briquettes held at a temperature lower than the softening temperature of the thermoplastic resin, and bringing the pellets or briquettes into rotational contact to coat the resin on the surface. cover,
Furthermore, if desired, the present invention relates to a method for producing resin-coated reduced iron, which is characterized by heating the reduced iron to a temperature higher than the softening temperature of the resin. The reduced iron pellets used in the present invention are obtained by Midrex method, Hill method, etc., and usually have a porosity of about 50 to 60% by volume and a water absorption of 12 to 15% by weight.
(saturated by immersion in water), apparent specific gravity of about 3 to 4, and substantially spherical pellets with a particle size of about 5 to 20 mm. These are obtained by bringing unreduced iron pellets obtained by pelletizing iron ore into contact with reducing gas in a reducing furnace. The reduced iron briquette used in the present invention is a block of reduced iron having a porosity of about 20 to 30%, which is obtained by hot-compressing sponge-like reduced iron obtained by the Feol method or the like. The present invention is a more effective coating method for pellets with higher porosity. The resin used to coat the reduced iron pellets is a thermoplastic resin, such as polyolefin resin such as polyethylene, polypropylene, polybutylene, methylpentene, ethylene-vinyl acetate copolymer, ethylene-ethyl (methyl) acrylate copolymer, etc. Olefin copolymers; examples include poly-p-xylylene, polyvinyl acetate, polyacrylate, polymethacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl ether, polyacrylonitrile, thermoplastic polyester, polycarbonate, polybutadiene, polyisoprene, etc. be done. Preferred thermoplastic resins include polyolefins, polyolefin copolymer resins, vinyl acetate, etc., and polyolefins, particularly polyethylene, are preferred. In the present invention, the thermoplastic resin is atomized and the mist is sprayed onto reduced iron pellets or briquettes maintained at a temperature below the softening temperature of the resin. The mist may be either a molten resin mist or a powdered mist, but the particle size is preferably
It is less than 100μ. Even if the sprayed mist is molten mist, it solidifies on the surface of the reduced iron. As a result, the resin is not impregnated into the voids of the reduced iron pellets, etc., and is effective in coating the surface with a small amount. Therefore, the surface temperature of reduced iron pellets, etc. is preferably lower than the softening temperature of the resin, and is generally between room temperature and about 80°C. Reduced iron pellets are usually obtained at 50 to 60°C, so they can be used as they are. The amount of thermoplastic resin attached to the reduced iron pellets is suitably 0.1 to 4 parts by weight, particularly 0.5 to 3 parts by weight, per 100 parts by weight of the reduced iron pellets. If it is less than 0.1 parts by weight, the coating thickness will be insufficient, and if it is more than 4 parts by weight, it will only become uneconomical. By employing the method of the present invention, pellets can be uniformly coated with a small amount of resin as described above. Similarly, in the case of reduced iron briquettes, the briquette
0.1 to 4 parts by weight of thermoplastic resin per 100 parts by weight,
Particularly suitable is 0.5 to 3 parts by weight. The reduced iron pellets (briquettes) obtained by the above method have thermoplastic resin mist attached to their surfaces, and many uncoated portions remain on the surfaces. Therefore, resin-coated reduced iron pellets (briquettes) are brought into rotational contact with each other in a suitable rotating body to uniformly adhere the resin to their surfaces.
At this time, the temperature of the processing atmosphere is preferably maintained at a low temperature, particularly at a temperature lower than the softening temperature of the resin.
By doing this, there is no risk that the reduced iron surface not coated with resin will be exposed to high temperatures and oxidized.
In addition, the resin is not consumed by being impregnated into the voids of the pellets (briquettes) more than necessary.
As a result, there is no need to carry out the processing in an inert gas atmosphere, making continuous processing easier and the structure of the processing apparatus simpler. The resin-coated reduced iron pellets (briquettes) obtained by the above method have sufficient oxidation resistance as is, absorb little water, and are difficult to turn into dust, but if necessary, coated pellets (briquettes) can be further coated. may be heated above the softening temperature of the resin. In this case, since the pellets (briquettes) are coated with resin, oxidation due to heating can be prevented. Post-heating is preferred in order to achieve resin adhesion and uniformity. An example of a method for manufacturing reduced iron coated with a thermoplastic resin will be described below with reference to FIGS. 1 to 4. FIG. 1 is a schematic sectional view of the apparatus for producing resin-coated reduced iron of the present invention, FIG. 2 is a left side view of the apparatus of FIG. 1, FIG. 3 is a - sectional view, and FIG. 4 is a right side view. shows. The cylindrical horizontal rotating drum 1 has a motor 2
The drum is rotatably installed on a rotary support 3 which is rotated by the drum, and the left side of the drum is provided with a supply port 5 for supplying reduced iron pellets and a heated spray device, and the right side of the drum is provided with a heating spray device for supplying reduced iron pellets. A discharge port 6 is provided for discharging the iron pellets. In order to use a continuous manufacturing method (overflow method),
The discharge port may be made larger than the supply port, and the height l of the drum wall on the exit side up to the discharge port 6 may be made smaller than the height l' up to the supply port. A blade 4 is provided inside the drum. A fixed amount of reduced iron pellets and a thermoplastic resin for coating the pellets are charged from the supply port by heating spray, and the drum is rotated. The rotation of the pellets is hindered by the blades, so they come into close contact with each other,
Pressure bonding occurs due to the co-rubbing effect, and the resin adheres uniformly. The resin coating of the reduced iron pellets may be carried out in two steps. That is, the surface of the reduced iron pellet coated with the thermoplastic resin in the same manner as above is then heated, if necessary. In this case, since the resin film is formed in the first step, reoxidation due to heating can be suppressed. The surface of the reduced iron pellet coated with thermoplastic resin in the same manner as above may be further coated with thermoplastic resin by repeating the same operation as in the second step. At that time, the resin used in the first step and the resin used in the second step may be different. For example, in the first step, a resin that is difficult to impregnate inside the reduced iron pellet, such as a resin with a molecular weight
A thermoplastic resin having a molecular weight of about 5000 may be used, and a resin having a molecular weight of about 1500 may be used in the second step. Further, a resin with high wear resistance may be used in the second step. This second step does not necessarily need to employ the method described above, and may also employ a dipping method. In this case, since the resin coating is formed in the first step, penetration of resin into the pellets due to immersion can be suppressed. However, even in such a case, conditions should be adopted so that the resin coating formed in the first step does not dissolve again. As described above, according to the present invention, it is possible to uniformly coat the surface of porous reduced iron pellets while minimizing blowing, and it is also possible to supply resin-coated reduced iron pellets that do not cause oxidation, powdering, breakage, etc. This is the result. Incidentally, the present invention can also be applied to briquettes. The present invention will be explained below with reference to Examples. Example 1 Reduced iron pellets (porosity 55%, water absorption rate 15%) were continuously introduced in fixed amounts as shown in Figure 1, and polyethylene resin with a molecular weight of 1400 and a softening point of 83°C was heated and sprayed into powder form. The drum was rotated while continuously supplying the pellets as a mist at a ratio of 2wt% to the pellets. Using the overflow method, changes in the metallization rate of the resulting polyethylene-coated pellets, water absorption during rainfall, and powdering due to strong vibration were observed. The results are shown in Table-1. Metalization rate: Measured by wet analysis based on JIS-M-8202. Water absorption rate: 100 samples during rainfall with an average rainfall of 2 mm/Hr
Calculated by exposing the paper for 5 hours, absorbing the water adhering to the surface, and then immediately weighing it. Powdering rate: 100 samples in an iron container (20cmφ, 5cm height)
g, shake vigorously up and down 15 times with an amplitude width of 30 cm, and -
Calculated by weighing 0.104mm (150mesh). Example 2 As the first step, reduced iron pellets (porosity 55
%, water absorption rate 15%) as shown in Figure 1.
The drum was rotated while continuously supplying polyethylene resin as a powder mist at a ratio of 2 wt % to reduced iron by heated spraying. In the second step, the material obtained by the overflow method was heated to 130°C.
The resulting polyethylene-coated pellets were heated for 8 minutes, and changes in metallization rate, water absorption during rain, and powdering due to strong vibration were observed. The results are shown in Table-1. Comparative example 1 Reduced iron pellets (porosity 55%, water absorption rate 15%)
Put 100Kg into a drum and heat it at 50℃ under nitrogen gas atmosphere.
2 kg of polyethylene resin with a molecular weight of 1400 and a softening point of 83° C. was added to it, the temperature was raised, the viscosity of the polyethylene was maintained at 90 cps, and the drum was rotated for 3 minutes.
The resulting polyethylene-coated pellets were evaluated for changes in metallization rate, water absorption during rainfall, and powdering in the same manner as in the examples. The results are shown in Table-1. Comparative example 2 Reduced iron pellets (porosity 55%, water absorption rate 15%)
Put 100Kg into an open rotating drum and heat it to 50℃.
Add 2 kg of polyethylene resin with a molecular weight of 1400 and a softening point of 83°C to this, and raise the temperature to increase the viscosity of the polyethylene.
The drum was kept at 90 cps and rotated for 3 minutes. Changes in the metallization rate of the obtained polyethylene-coated pellets,
We observed water absorption during rainfall and powdering due to strong vibration. The results are shown in Table-1. Comparative example 3 Reduced iron pellets (porosity 55%, water absorption rate 15%)
100Kg is placed in an open rotating drum, and the molecular weight is
1400, and 2 kg of polyethylene resin with a softening point of 83° C. was added as a powder mist by heating spray (air temperature 200° C.), and the drum was rotated for 5 minutes. The resulting polyethylene-coated pellets were evaluated for changes in metallization rate, water absorption during rainfall, and powdering in the same manner as in the examples. The results are shown in Table-1. Comparative Example 4 In addition to examining the metallization rate of uncoated reduced iron pellets, water absorption during rainfall and pulverization due to strong vibration were also observed. The results are shown in Table-1.

[Table] Example 3 Reduced iron briquette (porosity 35%, water absorption rate 6%)
As shown in Figure 1, a fixed amount of polyethylene resin with a molecular weight of 1400 and a softening point of 83°C was heated and sprayed into a powder mist, which was continuously supplied at a ratio of 2 wt% to the briquette. I rotated the drum. Changes in overflow metallization rate, water absorption rate during rainfall, and powdering due to strong vibration were observed. The results are shown in Table-2. Example 4 As the first step, reduced iron briquettes (porosity 35
%, water absorption rate: 6%) as shown in Figure 1.
The drum was rotated while continuously supplying 2 wt% of polyethylene resin to the reduced iron briquette as a powder mist by heated spraying. In the second step, the material obtained by the overflow method was heated at 130°C for 8 minutes, and changes in the metallization rate of the obtained polyethylene-coated briquettes, water absorption during rain, and powdering due to strong vibration were observed. Table 2 of the results
Shown below. Comparative example 5 Reduced iron briquette (porosity 35%, water absorption rate 6%)
Put 100Kg into a drum and heat it at 50℃ under nitrogen gas atmosphere.
2 kg of polyethylene resin with a molecular weight of 1400 and a softening point of 83° C. was added to it, the temperature was raised, the viscosity of the polyethylene was maintained at 90 cps, and the drum was rotated for 3 minutes.
The resulting polyethylene-coated briquettes were evaluated for changes in metallization rate, water absorption during rainfall, and powdering in the same manner as in the examples. The results are shown in Table-2. Comparative example 6 Reduced iron briquette (porosity 35%, water absorption rate 6%)
Put 100Kg into an open rotating drum and heat it to 50℃.
Add 2 kg of polyethylene resin with a molecular weight of 1400 and a softening point of 83°C to this, raise the temperature, and reduce the viscosity of the polyethylene.
The drum was rotated for 3 minutes at 90 cps. Changes in the metallization rate of the resulting polyethylene-coated briquettes, water absorption during rainfall, and pulverization due to strong vibration were observed. The results are shown in Table-2. Comparative example 7 Reduced iron briquette (porosity 35%, water absorption rate 6%)
100Kg is placed in an open rotating drum, and the molecular weight is
1400, and 2 kg of polyethylene resin with a softening point of 83° C. was added as a powder mist by heating spray (air temperature 200° C.), and the drum was rotated for 5 minutes. The resulting polyethylene-coated briquettes were evaluated for changes in metallization rate, water absorption during rainfall, and powdering in the same manner as in the examples. The results are shown in Table-2. Comparative Example 8 In addition to examining the metallization rate of uncoated reduced iron briquettes, the water absorption rate during rainfall and powdering due to strong vibration were also observed. The results are shown in Table-2.

[Table] Effects of the Invention The method of the present invention makes it possible to continuously produce resin-coated reduced iron pellets (briquettes). Further, the pellet surface can be substantially completely coated with a small amount of resin. The resulting coated pellets are less susceptible to oxidation, have less water absorption, and are less likely to turn into dust. Therefore, the reduced iron pellets can be easily stored and transported.

[Brief explanation of the drawing]

Figure 1 is a schematic sectional view of the apparatus for continuous production of reduced iron pellets according to the present invention, Figure 2 is a left side view of the apparatus shown in Figure 1 (reduced iron pellet supply port), Figure 3 is a cross-sectional view of the apparatus shown in Figure 1, and Figure 4 is a cross-sectional view. shows the right side view (reduced iron pellet discharge port). DESCRIPTION OF SYMBOLS 1... Rotating drum, 2... Motor, 3... Rotating support stand, 4... Vane, 5... Supply port, 6... Discharge port, 7... Reduced iron pellet continuous supply device, 8...
…heated spray equipment.

Claims (1)

[Claims] 1. Spraying a thermoplastic resin onto reduced iron pellets or briquettes held at a temperature lower than the softening temperature of the thermoplastic resin, bringing the pellets or briquettes into rotational contact to coat the surface with the resin, and further A method for producing resin-coated reduced iron, which comprises heating it above the softening temperature of the resin, if desired. 2. The manufacturing method according to item 1, wherein the thermoplastic resin is melted or sprayed as a powder mist. 3. The manufacturing method according to item 1, wherein the rotating contact is continuously performed using a cylindrical horizontal rotating body. 4. The method according to item 1, wherein the thermoplastic resin is a polyolefin resin. 5. The method according to item 1, wherein the thermoplastic resin has a softening temperature of 80 to 120°C. 6. The method according to item 1, wherein the thermoplastic resin is used in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the reduced iron pellets. 7. The method according to item 7, wherein the reduced iron is coated with a thermoplastic resin in two steps. 8. The method according to item 5, in which the thermoplastic resin used for coating in the first step uses a resin having a higher molecular weight than the resin used for coating in the second step.