JPS5844747B2 - Addition method of hydrogen peroxide in continuous pickling of stainless steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adding hydrogen peroxide in continuous pickling of stainless steel strips, and in particular to a method for efficiently performing oxidation with hydrogen peroxide, and an acid bath using a decomposition reaction of hydrogen peroxide. The present invention relates to a method for adding hydrogen peroxide that suppresses boiling of hydrogen peroxide and enables safe pickling treatment.

Conventionally, a mixed acid of nitric acid and hydrofluoric acid has been widely used in continuous pickling lines for stainless steel, but pickling with this mixed acid has the problem of NOx gas generation.

For this reason, in recent years it has been used as an oxidation method to replace mixed acids of nitric acid and hydrofluoric acid.

■) A mixed solution of sulfuric acid and ferric sulfate 2) A mixed solution of hydrochloric acid and ferric oxide 3) A pickling method using an acid solution containing a ferric salt such as a mixed solution of hydrofluoric acid and ferric sulfate is proposed. has been done.

In these pickling solutions, the ferric salt is consumed during the pickling process, so it is necessary to add hydrogen peroxide as appropriate to oxidize and restore the ferrous salt to the ferric salt during the pickling process.

However, when hydrogen peroxide is added to these pickling baths, ferrous salts are oxidized to ferric salts and at the same time a large amount of oxygen gas etc. is generated, which causes the acid bath to boil. There are problems with dangers such as the acid solution flowing outside the pickling tank and acid mist scattering.

In addition, reactions other than the intended oxidation reaction occur as a side effect, reducing the efficiency of the original oxidation treatment, making it impractical from an economic standpoint.

In order to suppress this boiling phenomenon in the acid bath, it is possible to suppress the boiling to a certain extent by reducing the amount of hydrogen peroxide added, but such a method requires an unrealistic amount of hydrogen peroxide to be added. It becomes smaller and is not an essential solution.

The present invention was made to solve various problems when adding hydrogen peroxide to a pickling bath as described above, and its feature is that hydrogen peroxide is blown into a depth of 200 m7IL or more below the acid liquid level. Therefore, we propose a method of adding hydrogen peroxide that can adjust the amount of hydrogen peroxide blown or the concentration of hydrogen peroxide.

The present invention will be explained below based on embodiments shown in the drawings.

First, FIGS. 1 and 2 are a cross-sectional view and a vertical cross-sectional view of an example of an apparatus for carrying out the method of the present invention, respectively, taken along line A-A. The steel strip 1 is constructed so that it can be passed in a fixed path direction 9 while being completely immersed in a pickling solution 3 filled in a pickling tank 2.

The dimensions of this pickling tank are 2m wide x 9m long x 1m deep.
The acid solution is a mixed aqueous solution of ferrous sulfate, ferric iron, and sulfuric acid.14.
The pickling tank 2 has a hydrogen peroxide blowing pipe 7 and a nozzle 8 on the bottom of the pickling tank 2 for blowing hydrogen peroxide sent from the hydrogen peroxide supply pipe 5 via the header 6 into the pickling liquid 3. It is provided.

In this hydrogen peroxide addition device, a total of 60 hydrogen peroxide blowing pipes 7 are branched from one header 6, six in the width direction of the pickling tank 2 and ten in the path direction. Hydrogen peroxide can be injected uniformly over the entire area.

That is, one hydrogen peroxide blowing tube is provided per 0.2477+'' of acid solution.

Note that the reference numeral 4 in Figure 1 indicates the top cover of the pickling tank.

In such a hydrogen peroxide addition device, it is preferable that the hydrogen peroxide injection nozzle 8 is placed at a depth of 200 mm or more below the acid liquid level, and hydrogen peroxide is blown from this point.

The reason for this is that at shallower depths, the efficiency of oxidizing ferrous salt to ferric salt by hydrogen peroxide becomes lower, which is economically disadvantageous.

Further, it is preferable that the inside diameter of the hydrogen peroxide blowing tube 7 is a thin tube having a diameter of about 5 mm.

This is because if the tube is a thin tube, the hydrogen peroxide in the blowing tube will mix with the acid solution that has entered from the nozzle 8, which will prevent the hydrogen peroxide from violently decomposing and causing the acid bath to boil.
For this reason, the inner diameter of the hydrogen peroxide blowing pipe 7 has a cross-sectional area of 2
It is preferable that it is 0 ma or less.

If the cross-sectional area is larger than that, the hydrogen peroxide will violently decompose inside the tube, causing the bath to boil, resulting in an extremely dangerous situation, and the desired oxidation efficiency will also be lowered.

On the other hand, as a method of adding hydrogen peroxide, the flow rate of hydrogen peroxide (35%) per hydrogen peroxide blowing pipe 7 is 300%.
It is preferable that the flow rate be ml/ml or less, especially if the flow rate of hydrogen peroxide is limited to this level.

The cracked gas is dispersed as much as possible and bubbles are created.
Boiling of the acid bath can be suppressed.

Furthermore, it is preferable to limit the concentration of hydrogen peroxide supplied to less than 20% pure H2O2, thereby completely avoiding dangerous boiling of the acid bath.

In addition, as mentioned above, when hydrogen peroxide is blown into a blowing tube, the number of blowing tubes varies depending on the purpose of pickling, pickling conditions, etc., so it cannot be determined unconditionally, but usually the pickling liquid is 0. It is preferable to use about one blowing pipe per .05 m to 577 I''.

In addition, for each hydrogen peroxide injection pipe, one
Although the nozzles are provided at two locations, the present invention is not limited to this, and the intended purpose of the present invention can be achieved even if multiple nozzle holes are provided in the middle of the blow pipe to add hydrogen peroxide. It is not necessary to attach a filter-like object to the camera.

As described above, in the method of the present invention, hydrogen peroxide is injected from a depth of 200+ u+ or more below the acid liquid level to suppress dangerous boiling phenomena and add hydrogen peroxide efficiently. A more detailed explanation will be given below with reference to FIGS. 4 and 5.

First, Figure 3 shows hydrogen peroxide (35% H2O2) at a flow rate of 1.
00m1/mm This is a graph showing the relationship between the blowing depth, the blowing pipe inner diameter, and the oxidation efficiency from ferrous iron to ferric iron when blowing under constant conditions. Area 7.1 ma), (b) has an inner diameter of 5 mm (cross-sectional area 1
9.6m4), (c) has an inner diameter of 8mm (cross-sectional area 50.2m)
m) and ni) indicate an inner diameter of 10 mm (cross-sectional area: 78.5 m1).

As is clear from Figure 3, the hydrogen peroxide injection depth is 2.
00 or more, and the inner diameter of the blowing pipe is 5 mm (cross-sectional area: 19 mm).
It has been found that the oxidation efficiency is significantly improved when the oxidation efficiency is around 6mff1) or less, and from this point it can be seen that when using a blowing pipe to add hydrogen peroxide, it is preferable to use a blowing pipe with a cross-sectional area of 20ma or less. .

Next, the boiling phenomenon observed in the acid bath when hydrogen peroxide is injected is due to hydrogen peroxide not contributing to the oxidation reaction.

This occurs due to oxygen gas generated by decomposition due to the reaction 2H202→2H20+02↑. Regarding this point, Figure 4 shows the blowing depth and blowing of hydrogen peroxide when it is blown under the same conditions as Figure 3. The relationship between the pipe inner diameter and the height of the liquid level is shown.

However, (e) has an inner diameter of 10 mmφ (cross-sectional area of 79.0 mm)
), (f) has an inner diameter of 8 mmφ (cross-sectional area 50.27 ni),
(G) has an inner diameter of 5m71Lφ (cross-sectional area 19.6mm), (
7) indicates an inner diameter of 3Tt7ILφ (cross-sectional area of 7.1 ma).

From Figure 4, when using the hydrogen peroxide addition method with low oxidation efficiency, that is, when the blowing depth is less than 200 mm and the blowing pipe inner diameter exceeds about 51 x 71 Lφ, the liquid level will rise by 50 mm due to the oxygen gas generated in the reaction. It has been confirmed that the above conditions also swell and become extremely dangerous during pickling work.

Furthermore, Fig. 5 shows a blow pipe with an inner diameter of 3 mm to a depth of 500 mm.
This is a graph showing the relationship between the hydrogen peroxide concentration and the height of the drop in the liquid level when injected from a point of
(1 force is 35% H2O2, (nu) is 20% H2O2, (
/1 indicates 10% H2O2.

), as shown in Figure 5, hydrogen peroxide (35% H2O2
) is added to the pickling bath by restricting the blowing flow rate to 300 ml/miA or less, the boiling of the acid bath is suppressed;
Furthermore, it is confirmed that the effect is even greater when the concentration of hydrogen peroxide added is 20% or less.

As explained above in detail, 1. The present invention has a 200 mm diameter from the surface of the acid bath.
It oxidizes ferrous iron to ferric iron by injecting hydrogen peroxide at a depth of more than mm, and can suppress the dangerous boiling phenomenon that occurs when hydrogen peroxide is added to an acid bath. At the same time, it has the excellent effect of improving the efficiency of oxidation treatment.

In addition, although only the example in which hydrogen peroxide was blown in by the blowing pipe was described above, the blowing pipe does not necessarily have to be used in the present invention.

[Brief explanation of drawings]

Figures 1 and 2 are a cross-sectional view and a vertical cross-sectional view of an example of an apparatus for carrying out the method of the present invention along line A-A, respectively, and Figure 3 shows hydrogen peroxide (35% H2O2) at a flow rate of 100 m.
A graph showing the relationship between the blowing depth and inner diameter of the blowing pipe and the oxidation efficiency from ferrous iron to ferric iron when blowing under constant l/mvt conditions. Figure 4 shows the same conditions as Figure 3. A graph showing the relationship between the injection depth of hydrogen peroxide, the pipe inner diameter, and the height of the liquid level when the hydrogen peroxide is blown into the pipe.
It is a graph showing the relationship between the hydrogen peroxide concentration and the height of the liquid level when the hydrogen peroxide is blown from a depth of 500 mm using a φ blowing pipe. Code, ■...Stainless steel strip, 2...
Pickling tank. 3...Pickling liquid, 4...Top cover of pickling tank, 5...Hydrogen peroxide supply piping, 6...
...Header, 7...Hydrogen peroxide injection pipe, 8.
...Hydrogen peroxide injection nozzle 9...Pass direction.

Claims (1)

[Claims] 1. When adding hydrogen peroxide to an acid bath containing ferrous iron to oxidize ferrous iron to ferric iron,
A method for adding hydrogen peroxide in continuous pickling of stainless steel strip, characterized by blowing hydrogen peroxide from a depth of 0TL7IL or more.