JPH01176001A - Method and device for reforming recovered iron powder - Google Patents

Abstract

PURPOSE:To uniformly treat recovered iron powder, to stably form porous surface layer on the iron powder particle and to uniformize product quality by continuously treating the recovered iron powder with the apparatus directly connecting a fluidized bed type oxidizing vessel and reducing vessel. CONSTITUTION:The iron powder 1 recovered from a converter dust, etc., is continuously carried from a hopper 2 to the oxidizing vessel 3. Oxidizing gas 5 is blown from a blowing nozzle 4 at the bottom part of the oxidizing vessel 3 and the iron powder 1 is held in the fluidized condition at high temp. The surface-oxidized iron powder 1 in the oxidizing vessel 3 is carried into the reducing vessel 7 through piping 6 at >=200 deg.C. The reducing gas 9 is blown from a blowing nozzle 8 at the bottom part in the reducing vessel 7, and the iron ore 1 is made to the fluidized condition and high temp. The iron powder 1 treated in the reducing vessel 7 is discharged into a cooling vessel 11 held to non-oxidizing condition through a discharging pipe 10 and cooled to the room temp. By this method, the ion powder is supplied into the vessel 7 without any detaching the surface-oxidized layer formed in the vessel 3 from the base iron.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for modifying the surface of iron powder recovered from dust generated in a molten metal processing vessel such as a converter in order to increase its usefulness. and related to equipment.

[Conventional technology]

Dust generated in a molten metal processing vessel such as a converter is separated from exhaust gas by a wet dust collector such as a bench scrubber. Then, the iron contained in the dust is separated from non-metallic substances such as slag by a magnetic separator, and further separated from oxides, scales, etc. attached to the surface by grinding ore. The recovered iron powder obtained in this way is dense and of extremely high quality with a purity of about 97%, and is suitable for powder metallurgy.
It is used for various purposes such as shot blasting, magnetic particle inspection, welding rods, and iron powder for cutting (Japanese Patent Application Laid-Open No. 54-127810).
(See Japanese Patent Application Laid-open No. 14825/1984, etc.).

However, during the polishing process to separate oxides, scale, etc. adhering to the surface, the iron powder particles become spherical or nearly spherical in shape with a smooth surface and few protrusions. Therefore, the surface activity of this iron powder is low, and when used, for example, as a raw material for powder metallurgy, the bonding between iron powder particles does not proceed smoothly, resulting in poor sinterability. Furthermore, when used as iron powder for fusing, there are problems such as slow ignition and reduced fusing speed.

[Problem that the invention seeks to solve]

One possible means of improving the surface activity of recovered iron powder is to make the surface layer porous with high activity through oxidation and reduction. However, it is difficult to uniformly treat the surface of iron powder particles using, for example, an oxidation furnace or a reduction furnace configured with an ordinary heat-resistant container. Furthermore, if the iron powder is simply oxidized and then reduced, the surface oxide layer formed in the oxidation process will easily peel off from the base iron during the process of transferring the iron powder from the oxidation process to the reduction process, and Variations occur in the porous surface layer formed. As a result, the properties of the product, the modified iron powder, become unstable.

Therefore, by continuously processing the recovered iron powder in a device that directly connects a fluidized bed type oxidation tank and reduction tank, it is possible to treat the recovered iron powder uniformly, and to prevent the formation of particles on the surface of the iron powder particles. The purpose is to stabilize the conditions for forming a porous surface layer and obtain modified iron powder of consistent quality.

[Means for solving problems]

In order to achieve the objective, the reforming method of the present invention surface-oxidizes the iron powder recovered from the dust generated in the molten metal processing container in a fluidized bed oxidation tank, and the iron powder is heated to a high temperature of 200°C or higher. The iron powder is introduced directly from the fluidized bed oxidation tank to the fluidized bed reduction tank, and then the surface oxidation layer formed on the surface of the iron powder is reduced to form a porous surface layer.

In addition, the reforming equipment used in this method consists of a fluidized bed oxidation tank that oxidizes the surface of iron powder recovered from the dust generated in the molten metal processing container, and a fluidized bed reduction tank that reduces the surface oxidation layer formed. In between, a pipe is provided to supply the surface-oxidized iron powder to the fluidized bed reduction tank in a high-temperature state.

[Effect]

In the present invention, a fluidized bed type treatment tank is used to oxidize and reduce iron powder. As a result, the surface of each iron powder particle is uniformly treated. For example, under normal conditions, iron powder particles coagulate with each other due to the temperature increase during the oxidation process, making it easy for only a portion of the surface to be oxidized, but by performing this oxidation process in a fluid state, aggregation can be prevented. However, the entire surface can be treated uniformly. Furthermore, since the atmosphere inside the oxidation tank and the reduction tank can be easily controlled, the degree of surface oxidation and reduction can also be freely controlled.

In addition, since the thermal contraction rate is different between the surface oxidized layer and the steel base, when the iron powder with the surface oxidized layer is cooled, stress corresponding to the difference in thermal contraction rate is generated at the boundary between the surface oxide layer and the base steel. This causes the surface oxide layer to peel off. However, in the present invention, since the surface-oxidized iron powder is sent to the reduction tank in a high temperature state, the thermal contraction caused by cooling is small.
No peeling occurs between the surface oxidized layer and the base iron. the result,
The surface oxidized layer formed in the oxidation step is subjected to treatment in the reduction step. Therefore, the iron powder sent into the reduction tank has a predetermined surface oxidation layer, and the iron powder after reduction has a uniform porous surface layer.

The temperature of the iron powder sent from this oxidation tank to the reduction tank is 2
It is necessary to maintain the temperature above 00°C.

In the continuous process from oxidation to reduction, a certain amount of iron powder that has been reduced for a predetermined period of time is sampled at random, and the cross section is observed under a microscope to determine whether or not the oxidized-reduced porous layer on the surface of the iron powder has peeled off. Figure 3 shows the results of the investigation. Taking the iron powder temperature between the oxidation tank and the reducing species as the horizontal axis, no peeling was observed at temperatures above 208°C, but peeling was observed at temperatures below 208°C.

Furthermore, since hot iron powder is fed to the reduction tank, the temperature required for the reaction in the reduction tank is replenished by the iron powder. Therefore, the amount of heat supplied to the reduction tank is also reduced.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained using examples with reference to the drawings.

FIG. 1 schematically shows the apparatus used in the embodiment of the present invention.

Iron powder 1 recovered from converter dust and the like is stored in a hopper 2, and is continuously fed into an oxidation tank 3 from this hopper 2. Oxidizing gas 5 is blown into the oxidizing tank 3 from a gas blowing nozzle 4 provided at the bottom, and the iron powder 1 is maintained in a fluid state within the oxidizing tank 3 by the oxidizing gas 5. In this example, a mixed gas having a composition of nitrogen, air, and water vapor was used as the oxidizing gas 5, and the temperature inside the oxidizing tank 3 was maintained in a temperature range of 600 to 900°C.

The iron powder 1 whose surface has been oxidized in this oxidation tank 3 has a temperature of 200
It is sent to the reduction tank 7 via the piping 6 in a high temperature state of ℃ or more. In the reducing tank 7, the iron powder 1 sent from the oxidizing tank 3 is brought into a fluid state by blowing reducing gas 9 through a gas blowing nozzle 8 provided at the bottom. In this embodiment, the reducing gas 9 is N2. Using a mixed gas of Co or C0G (coke oven gas) and N2, reducing tank 7
500-800℃, preferably 550-580℃
The temperature range was maintained at ℃.

The iron powder l treated in the reduction tank 7 is discharged through the discharge pipe 10 to the cooling tank 11 maintained in a non-oxidized state.
is cooled to room temperature.

FIG. 2 shows the oxidation tank 3 with a heat supply system and a control system added thereto.

In this embodiment, the oxidation tank 3 is surrounded by a heating tank 20. Inside the heating tank 20, hot air generated by burning air 21 and fuel gas 22 in a hot air generating furnace 23 is sent through a hot air pipe 24 to maintain ceramic particles 25 as a heat carrier in a fluid state. ing. The heat of the ceramic particles 25 is transmitted to the oxidation tank 3 via the tank wall between the heating tank 20 and the oxidation tank 3, and maintains the inside of the oxidation tank 3 at a predetermined temperature. The hot air after receiving heat from the ceramic particles 25 is discharged from the system through the exhaust pipe 26. Note that instead of arranging the heating tanks 20 so as to surround the oxidation tank 3, a plurality of oxidation tanks 3 and heating tanks 20 may be arranged alternately in a sandwich shape. Alternatively, the iron powder 1 in the oxidation tank 3 can also be heated by blowing hot air directly into the oxidation tank 3. This heating means can be applied to the reduction tank 7 as well.

On the other hand, the oxidizing gas 5 sent into the oxidizing tank 3 was adjusted as follows. First, nitrogen 45 and air 27 are mixed and the pressure is increased by a pressure booster blower 28 , and then the mixture is fed into a heat exchanger 31 via a flow rate adjustment valve 29 while measuring the flow rate with a gas flow meter 30 . In the heat exchanger 31, the combustion heat generated by burning the C0G32 with the air 33 is used to blow up the pressure in the booster blower 28.
Heating the gas mixture from Next, water 34 is added to this heated mixed gas as necessary. Also, water 3
The addition of 4 serves to adjust the temperature of the oxidizing gas 5 blown into the oxidizing tank 3. Alternatively, water may be added directly into the layer.

The oxidizing gas 5 thus adjusted is made to flow with a uniform flow rate distribution in the radial direction of the oxidizing tank 3 via the rectifier 36 provided at the bottom of the oxidizing tank 3, and then
The iron powder 1 inside the oxidation tank 3 is fluidized by passing through the perforated plate 37.

At this time, the composition of the oxidizing gas 5 blown into the oxidizing tank 3 is analyzed by the analyzer 35, and based on the analysis results, the composition of the oxidizing gas 5 is blown into the oxidizing tank 3.
5. Air 27. The flow rate of water 34 is adjusted.

As a result, the oxidizing ability of the atmospheric gas in the oxidizing tank 3 is controlled. In addition, the inlet temperature of the oxidizing gas 5 is measured with a thermometer 38, and the temperature of the fluidized bed in the oxidizing tank 3 is measured with a thermometer 39.
The temperature of the fluidized bed of ceramic particles 25 in the heating tank 20 is measured with a thermometer 40. Then, the heating conditions by the heat exchanger 31 and the temperature of the hot air generated in the hot air generating furnace 23 are controlled so as to maintain the temperature of the fluidized bed in the oxidation tank 3 at a set value. Furthermore, in order to maintain the pressure inside the oxidation tank 3 constant, an inlet pressure gauge 41 and an outlet pressure gauge 42 are provided, and the pressure values detected by these pressure gauges 41 and 42 are fed back to the boost blower 28. Then, oxidation tank 3
The pressure of the oxidizing gas 5 sent is controlled. Also,
In order to grasp the oxidation situation in the oxidation tank 3, a sampling pipe 44 extending from a sampling meter 43 is placed facing the fluidized bed inside the oxidation tank 3.

This heat supply system and control system can be similarly provided to the reduction tank 7 except for the blowing of the air 27.

Next, the operating conditions and treatment results when using this apparatus to oxidize and reduce recovered iron powder having the composition and particle size distribution shown in the following table will be explained.

Composition of iron powder C metallic iron FeOFe20s content (wt%) 0.50 95.8 1.72 0.
Particle size distribution of 67 iron powder Particle size (skin) Content (weight%)>250
2.1 250~149 16.0149~105
26.9105~74 1
5.2 74-63 12.7 63-44 16.1 <44 11.1 (Average particle size 94.6AO1+) This iron powder is made of nitrogen as a base and air is 5% by volume.

The sample was treated with oxidizing gas 5 having a composition of 5% by volume of water vapor and a temperature of 750° C. for an average residence time of 1 hour.

At this time, the flow rate of the oxidizing gas 5 blown into the oxidizing tank 3 was maintained at 0.2 N m''/min. By the oxidation treatment of q, the surface of the iron powder particles was oxidized to an average thickness of 15 to 20 p. A layer was formed.Furthermore, since the iron powder contains carbon, decarburization progressed at the same time.

Next, the surface-oxidized iron powder was fed into the reduction tank 7 via the pipe 6 at a high temperature of 200° C. or more. This reducing tank 7 is supplied with a reducing gas 9 based on nitrogen, having a composition of 40% by volume of hydrogen, and having a temperature of 550° C. at a flow rate of 0.2 N.
After reducing the iron powder in the reduction tank 7 for an average residence time of 2 hours, the iron powder was discharged to the cooling tank 11 via the discharge pipe 10, where it was cooled to room temperature.

The surface of the iron powder oxidized and reduced in this way has an average thickness of 2
A porous surface layer of 0p was formed. The state of this porous surface layer is greatly influenced by the temperature of the iron powder flowing through the pipe 6 that connects the oxidation tank 3 and the reduction tank 7. FIG. 3 shows the influence of the temperature of the iron powder flowing through the pipe 6 on the surface condition of the treated iron powder stored in the cooling tank 11.

As is clear from FIG. 3, when the temperature of the iron powder becomes 200° C. or lower, the porous surface layer formed on the iron powder after reduction treatment peels off. This indicates that a part of the surface oxidation layer formed by the treatment in the oxidation tank 3 was peeled off while being sent from the oxidation tank 3 to the reduction tank 7.

On the other hand, when iron powder is supplied from the oxidation tank 3 to the reduction tank 7 at a high temperature of 200°C or higher, the thermal stress generated at the boundary between the surface oxidation layer and the steel base is small, so that the surface oxidation layer is Peeling is suppressed. As a result, the surface oxidized layer generated in the oxidation tank 3 is efficiently processed in the reduction tank 7. This is reflected in the fact that, in FIG. 3, no peeling of the porous surface layer was observed when the iron powder temperature was set to 200° C. or higher. Further, since there is no peeling of the surface oxidized layer, the thickness of the porous surface layer formed in the reduction tank 7 also has small variations.

Further, by feeding the iron powder to the reduction tank 7 in a high temperature state, the heat retained in the iron powder was utilized for the reduction reaction, and the amount of heat required to heat the reduction tank 7 could be reduced. For example, when sending iron powder at a temperature of about 100 °C to the reduction tank 7, 19 xi
o" kcal It was necessary to replenish heat at 7 o'clock. On the other hand, when sending high-temperature iron powder at a temperature of 300 °C from the oxidation tank 3 to the reduction tank 7, the amount of heat required to heat the inside of the reduction tank 7 was The amount of heat was 15 XIO' kcalZ hours.

〔Effect of the invention〕

As explained above, in the present invention, by maintaining the temperature of the iron powder sent from the oxidation tank to the reduction tank at 200 °C or higher, the surface oxidation layer formed in the oxidation tank can be peeled off from the base iron. It is possible to feed iron powder to the reduction tank. As a result, it becomes possible to stably form a porous surface layer with a predetermined thickness in the reduction tank, and a product of constant quality can be obtained. In addition, since the iron powder is sent from the oxidation tank to the reduction tank in a high temperature state, continuous processing is possible and productivity is improved. The iron powder produced in this manner has a porous surface layer with excellent surface activity and a highly dense inner layer. Therefore, when used as a sintering raw material, for example, it exhibits excellent sinterability and the strength of the obtained sintered body is high.

[Brief explanation of the drawing]

Fig. 1 shows an outline of the apparatus used in the embodiment of the present invention, Fig. 2 shows an oxidation tank equipped with a heat supply system and a control system, and Fig. 3 is a graph specifically expressing the effects of the present invention. It is. Patent applicant Nippon Steel Corporation Representative
Masu Kobori (and 2 others) Figure 1

Claims (1)

[Claims] 1. Surface oxidation of iron powder recovered from dust generated in a molten metal processing container is carried out in a fluidized bed oxidation tank, and the iron powder is heated at 200°C.
The recovered iron is led directly from the fluidized bed oxidation tank to the fluidized bed reduction tank in the above high temperature state, and then the surface oxidation layer formed on the surface of the iron powder is reduced to form a porous surface layer. Method for modifying powder. 2. Surface-oxidized iron powder is placed between a fluidized bed oxidation tank that oxidizes the surface of iron powder recovered from the dust generated in the molten metal processing container and a fluidized bed reduction tank that reduces the formed surface oxidation layer. A reforming apparatus for recovered iron powder, characterized in that a pipe is provided to supply the fluidized bed reduction tank in a high temperature state.