JP2659596B2 - Preservation method of metal-containing iron dust powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial application field> The present invention relates to a method for suppressing oxidation of metal-containing iron dust powder such as collected dust powder of a steelmaking converter provided with an unburned exhaust gas recovery device.

<Prior art> With the introduction of an unburned exhaust gas recovery system in the steel refining process, especially in the converter refining process in recent years, dust generated during oxygen blowing in the converter is cooled without contact with atmospheric oxygen at high temperatures. 10 to 40% by weight in dust to be removed and collected
(Hereinafter abbreviated as%). This metal-containing iron dust (hereinafter abbreviated as dust) contains a large amount of valuable metals such as Cr and Ni or metal oxide components depending on the type of steel to be blown, mainly iron, and is highly valuable for reuse.

As a reuse form, a method of dewatering and drying dust and adding it to a converter from the furnace top is common. As disclosed in Japanese Patent Application Laid-Open No. 49-109212, the heating gas temperature for drying the unburned dust collected by sprinkling with a dryer as disclosed in JP-A-49-109212 is 900. ℃ while less dust after drying to regulate the water content at the time of dryer exhaust in 5-10%, most oxidation converter unburned dust, characterized in that changing the Fe ₃ O ₄ of dust in Fe There is a processing method.

However, in this method, (a) Fe ₃ O
Extra heat energy is required for the reduction of ₄ . (B) Extra heat energy is required for the oxidation treatment. (C) When added to an iron bath of a converter or the like, local heat absorption due to reduction of Fe ₃ O ₄ does not prevent defects such as unnecessarily increasing the iron oxide content in slag.

Further, there is disclosed a means for improving the iron yield by complete drying as in the technique disclosed in Japanese Patent Application Laid-Open No. 62-136534. However, when storage is required, moisture is reduced by moisture absorption after drying. % And oxidation occurs.

In addition, there is a technique of adding an alkali salt to form a bulk as in the technique disclosed in Japanese Patent Application Laid-Open No. 63-129920.

<Problems to be Solved by the Invention> The present invention has been made to solve the above-mentioned problems of the prior art and to provide a technique for preserving metal-containing dust powder in powder form without oxidizing it. .

<Means for Solving the Problems> The present invention relates to a method for preserving metal-containing iron dust by reducing the water content of the metal-containing iron dust to 0.8% by weight or less and suppressing the oxidation of metal components. A method for preserving metal-containing iron dust powder that suppresses oxidation of metal components by adding an alkali in the dust and setting the pH of the suspension of 1 g of the dust to 100 or more in 100 cc of water to suppress the oxidation of metal components. A method for storing metal-containing iron dust powder that suppresses oxidation of metal components by reducing the atmosphere oxygen concentration of the storage location to 8% by volume or less, and directly contacting the metal-containing dust dust with a cooling medium such as water. A method for storing metal-containing iron dust powder that suppresses the oxidation of metal components by cooling the dust by flowing a cooling medium through the means, and using the method described in the preceding section and the method. Metallic iron dust powder that suppresses oxidation of components In storage method, a further storage method for suppressing metallized iron dust powder oxidation of the metal components using the methods set forth in the preceding paragraph and wherein.

<Procedures and Functions Leading to the Invention> The present inventors have found the following findings as a result of studying and examining important factors in storing metal-containing iron dust powder while suppressing oxidation.

That is, the oxidation reaction of the metal-containing iron dust is determined by water (%), hydrogen ion concentration [H ⁺ ], or pH = log10 1 /
[H ⁺ ], the atmospheric oxygen concentration (vol%) is high, and the temperature rapidly rises due to the high temperature of the dust layer.

Then, regarding each factor, the influence on the oxidation reaction was quantitatively investigated using the same converter dust, and as a result, the following was found.

First, regarding the effect of moisture, 1 kg of converter dust was placed in an insulated environment, and the moisture content was changed to reduce the dust temperature.
FIG. 1 shows the results of measuring the change over time during the time and investigating the temperature attained during this time. From FIG. 1, it was found that when the water content exceeded 0.8%, the oxidation proceeded rapidly, and the temperature rose to about 200 ° C. due to the heat generated by the oxidation.

Next, regarding the effect of pH, 100 g of dust with 0.05% moisture
Into a beaker and 0-10 g of NaO for pH control.
After the H powder was mixed in, the temperature reached 10 minutes after the start of the test was examined by a method of measuring the change in dust temperature by dropping about 10 cc of water, and the results are shown in FIG. As is clear from FIG. 2, an oxidation reaction occurs when the pH falls below 11. If heat is generated by oxidation, the temperature will be 75 ° C. or higher. Here, the pH was measured with a hydrogen ion concentration meter after suspending 1 g of pH-controlled dust in 100 cc of water.

Further dust 1kg was 2% moisture from the ambient environment heat insulation, and placed under the outside air cutoff state, the atmosphere feed gas and O ₂
As a mixed gas with N ₂ gas, the O ₂ volume% in the gas was changed, and the saturation attainment temperature during 24 hours was examined in the same manner as described above.
The result is shown in FIG. As is clear from FIG. 3, when the O ₂ volume% in the atmosphere exceeds 8%, the oxidation rapidly proceeds, and the temperature rises up to 220 ° C. due to heat generation.

In each case during the test, when a water-cooled tube was inserted into the dust and the cooling water was allowed to pass through the tube, all rises in the dust temperature were suppressed.

From the above, the operation of the constituent elements of the present invention can be summarized as follows.

First, if the amount of water is 0.8% or less, the oxidation reaction becomes extremely slow and is substantially suppressed.

Next, the pH can be controlled by setting the pH to 11 or more, whereby H ⁺ ions as an oxidizing agent are reduced, so that oxidation can be suppressed.

Furthermore, although the progress of oxidation is required O ₂ in the atmosphere, in an atmosphere O ₂ concentration of 8 vol% or less oxidation reaction is suppressed.

In any case, the heat generated by the oxidation reaction is indirectly removed by the cooling fluid, so that the reaction rate can be kept low. Therefore, the oxidation is suppressed.

The substance to be oxidized in the dust is an oxide having a low metal content and a low oxidation number, specifically, Fe, FeO, Cr, CrO and the like. In the safest case where all of these are considered Fe, 70% Fe in dust
Degree exists. It is safest to consider this as 100% Fe dust.

When considering complete oxidation of Fe + O ₂ → Fe ₂ O ₃ , the calorific value is 175
It is 5 kcal / kg-Fe. Assuming that the water temperature rise is 20 ° C when removing the heat generated by water cooling, χkg ・ water / kg ・ Fe = 1755 / 1000kcal / kg ・ ℃ × 20 ℃ ＝ 0.09k
g ・ water / kg ・ Fe Therefore, the water cooling only needs to substantially exist and flow. In air cooling, if the temperature rise is 50 ° C, 100Nm ³
/ kg · Fe. The reaction takes 10hrs or more, so 10Nm ³ / hr
・ Kg / Fe is required. The arrangement of the cooling pipes is preferably denser from the viewpoint of heat removal, but a pitch of 100 mm or more is desirable in order to prevent dust clogging (shelf hanging).

In addition, although these methods are effective alone,
Needless to say, by combining some of the four methods depending on the place and period of storing the dust, it is more preferable in terms of more reliably suppressing the oxidation reaction and maintaining the effect and backing up between the mutual methods. .

<Example> Dust generated in the 83TON top-bottom blower is washed and collected by a venturi scrubber in an exhaust gas collection device, collected as dust collection water, and part of the water is separated by a thickener. After making the slurry into a high-concentration slurry, the slurry is made into a cake having a water content of 13% by a filter press type dehydrator. After that, the moisture content in the dust is controlled to be in the range of 0.2 to 1.5% by a drying dryer, and after drying, it is stored in a storage hopper for injection into hot metal and molten steel. The antioxidant effects of the method of sealing in air and the method of the present invention were compared.

In order to compare the antioxidant effect, the dust temperature in the hopper and the change of the cut-out amount were investigated.

The storage period was a maximum of three days during regular maintenance and suspension of work.

The moisture content in the dust was controlled by passing the dust several times by changing the operating conditions of the drying dryer. CaO powder was used for pH control, kneaded with the dust, and in the case of dust having a high moisture content, after mixing, the powder was further passed through a pulverizing step to keep the dust in a powder state. The oxygen concentration in the storage hopper is controlled by improving the hopper to an airtight structure and supplying piping to control the oxygen concentration.
It was controlled by the O ₂ gas flow rate and the N ₂ gas flow rate. That is, the oxygen concentration was controlled by controlling the O ₂ gas flow rate and the N ₂ gas flow rate while analyzing using a commercially available O ₂ continuous analyzer. For water cooling, 10 water cooling tubes were passed through the hopper in the radial direction so that cooling water could be circulated.

Each level was tested twice and the worse results are shown in Table 1.

As is clear from Table 1, according to the method for preserving metal-containing iron dust powder according to the present invention, there was no oxidation of the metal component, the dust temperature in the hopper did not rise so much, and the dust cutting out after 3 days was successfully performed. .

For dust that cannot be cut out, the upper lid of the hopper was opened and the dust was removed manually using a shovel, which required a great deal of time (5 HR). In addition, 2 to 10% of hydrogen was generated due to heat generated by oxidation, which was a very dangerous state.

<Effect of the Invention> According to the method of the present invention, it is possible to store the metal-containing iron dust powder while suppressing the oxidation of the metal iron component.

Therefore, heat of reduction is unnecessary at the reuse destination, and fluid handling such as injection with a carrier gas can be performed, which is economical.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the relationship between the moisture in the dust and the attained temperature, FIG. 2 is a characteristic diagram showing the relationship between the pH of the dust and the attained temperature 10 minutes after the start of the test, and FIG. FIG. 4 is a characteristic diagram illustrating a relationship between a middle oxygen concentration and a saturation reaching concentration.

Claims (7)

(57) [Claims] 1. A method for preserving metal-containing iron dust powder in which the moisture content of the metal-containing iron dust powder is reduced to 0.8% by weight or less to suppress oxidation of metal components. 2. An alkali added to said metal-containing iron dust powder, and 1 g of said dust is suspended in 100 cc of water.
A method for storing metal-containing iron dust powder in which H is set to 11 or more to suppress oxidation of metal components. 3. A method for storing metal-containing iron dust powder, wherein the oxygen concentration in the atmosphere at the storage location of the metal-containing iron dust powder is 8% by volume or less to suppress oxidation of metal components. 4. Means are provided for passing a cooling medium such as water through the metal-containing iron dust powder without directly contacting the dust, and flowing the cooling medium through the means to cool the dust and oxidize metal components. Method of preserving metal-containing dust dust. 5. A method for preserving metal-containing iron dust powder using the method according to claim 1 and 2, wherein the oxidation of metal components is suppressed. 6. A method for preserving metal-containing iron dust powder using the method according to claim 1 and 3, wherein the oxidation of metal components is suppressed. 7. The method according to claim 4 and claims 1, 2, 3, 5
Or a method for preserving a metal-containing iron dust powder which suppresses oxidation of a metal component using the method according to 6.