JP2946136B2 - Dezincing method of galvanized steel sheet waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dezincing galvanized steel sheet scraps, which is heated before melting to evaporate and remove zinc, and is used as a cast iron source.

[0002]

2. Description of the Related Art In recent years, rust prevention of automobiles has been strengthened, and steel sheets in which most of steel sheets constituting a vehicle body are galvanized have been used. As a result, the amount of scrap of zinc-plated steel sheet is increased, and zinc plating is a major problem in recycling.

[0003] That is, galvanized steel sheet scrap is often used as steel scrap for cast iron because the steel sheet of the original sheet is very high in purity. However, in the melting, a large amount of zinc white is generated particularly in a low-frequency melting furnace, which is a serious problem in occupational health. Further, there is a problem that zinc permeates the low-frequency furnace wall and deposits on the coil to cause a short circuit, thereby causing a coil damage accident and significantly shortening the life of the furnace wall.

[0004] As described above, the original sheet of galvanized steel sheet is a steel of high purity and cleanliness close to pure iron for improving the deep drawability.
It is the highest grade of steel scrap for cast iron. However, because the problem of zinc during melting as described above was not solved, it was evaluated as low-grade steel scrap, and it is often used as steel scrap for electric furnace steelmaking. I have.

[0005] For the above reasons, a technique for removing zinc from galvanized steel sheet scrap prior to melting has been desired not only in the cast iron casting industry but also in terms of recovering useful metal such as zinc.

[0006] As a method for removing zinc from galvanized steel sheet waste, there are an extraction method in which zinc on steel sheet waste is dissolved and removed with an acid such as sulfuric acid, an electrolytic method in which zinc on steel sheet waste is subjected to reverse electrolytic removal in an alkaline solution, An evaporation method is known in which steel scrap is heated and zinc on the steel scrap is removed by evaporation. Although each method has its own advantages and disadvantages, the evaporation method has the advantage of not using water and the advantage of being able to combine the preheating of steel sheet waste.

As a method for heating the galvanized steel sheet waste in a limited space such as a foundry in order to easily carry out the evaporation method, for example, a method disclosed in JP-A-51-126911 is preferable. That is, this is a method in which scrap, scrap and other steel scraps are heated and distilled with a reducing combustion gas of 1090 ° C. or higher using a solid reducing agent and a combustion gas to remove zinc, tin and copper. The use of coke as a solid reducing agent is a readily available material for foundries and a very easy method for foundries with cupola experience.

[0008]

However, as is well known, scrap car scrap or other steel scrap is generated in various forms, and if these scraps are used as they are, the following problems occur. . For example, when the above method is applied to galvanized steel sheet scraps, the steel sheet scraps are various in size and shape, and the handling of charging and discharging is not only complicated, but also high-temperature reduction in a heating reduction furnace. The flow of the reactive gas is hindered by the material to be dezinced and does not turn evenly between these materials, so that the temperature does not rise uniformly, and the evaporation of zinc is insufficient and zinc remains on the steel sheet. In particular, the amount of dezincing between the upper and lower portions of the material-filled layer varies, and the dezincing of the upper material becomes insufficient. For this reason, there are drawbacks that the treatment time becomes longer, the distillation temperature must be increased, and the cost increases.

According to the present invention, as described above, when zinc on the surface of steel sheet scrap is heated, evaporated, and removed in a high-temperature reducing gas stream, the zinc-free material inhibits the flow of the high-temperature reducing gas in the conventional method. In addition, it prevents the uniform temperature rise of the material, and makes it difficult to completely dezincify steel plate scraps. This simplifies the handling of the processing material.

[0010]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a method for dezincing galvanized steel sheet waste by evaporating and removing galvanized steel sheet waste by heating the zinc-coated steel sheet waste with a high-temperature reducing gas. 1/10 to 1 of the cross-sectional diameter of the heat treatment container
/ 20, and the heat treatment vessel containing the steel scrap is placed in a vertical heating reduction furnace, and the furnace atmosphere is sucked from above the heating reduction furnace. This is a method for dezincing galvanized steel sheet scraps, wherein the generated high-temperature reducing gas is introduced from the bottom of a heat treatment container and passed through the container to reduce by heating. It is preferable to process the bulk density of the galvanized steel sheet scrap to 1.5 to 2.5 t / m ³ and to stack heat treatment vessels at intervals in the heat reduction furnace.

[0011]

[Action] To observe the behavior of zinc on a galvanized steel sheet by heating it in a combustion reducing gas in order to heat the galvanized steel sheet waste in a reducing gas and evaporate and remove the zinc. As a result of my research, I was able to clarify the following facts.

(1) The evaporation of zinc on a steel plate is rate-determined by heat transfer.
Once heated to the evaporation temperature, the rate of supply of latent heat of evaporation determines the rate of evaporation.

(2) Therefore, in the evaporative removal of zinc by a high-temperature reducing gas flow, how efficiently and uniformly heat transfer between the gas flow and the steel sheet scraps determines the efficiency of dezincing.

(3) Even if the steel sheet scraps are in close contact with each other, they do not affect the evaporation rate of zinc.

From these findings, external heating using a furnace such as a large electric furnace or a vacuum heating furnace capable of adjusting the atmosphere can be considered, but it is not practical considering the equipment costs or running costs of these furnaces. Also, these furnaces are unsuitable for treating large amounts of steel scrap due to the structure of the furnace.

Accordingly, the present invention provides a method for dezincing galvanized steel sheet scraps by heating galvanized steel sheet scraps with a high-temperature reducing gas to evaporate and remove galvanized zinc. Lump of 1/10 to 1/20 of diameter,
Specifically, the galvanized steel sheet waste is bent, consolidated, and processed into, for example, a ball shape, and the heat treatment container containing the steel plate waste is placed in a vertical heating reduction furnace. While sucking the atmosphere, the high-temperature reducing gas generated in the lower part of the heat-reduction furnace is introduced from the bottom of the heat-treatment vessel and passed through the vessel for heat-reduction. The flow distribution of the reactive gas becomes stable and smooth, the gas use efficiency is improved, and the heat reduction temperature in the upper and lower layer direction and the layer width direction of the steel sheet waste in the heat treatment vessel, for example, 900
C. or higher can be reliably achieved. Further, by adjusting the amount of atmosphere in the furnace sucked from above the heating reduction furnace, the heating reduction rate of the plated zinc can be controlled.

[0017] The bulk density of the zinc-coated steel sheet scrap is 1.5 to
If processed to 2.5 t / m ³ , the individual massive steel plate scraps are bent and compacted with an appropriate opening, and the heating and heating efficiency is increased, so that the reduction distillation of the plated zinc proceeds quickly, It becomes a casting material with good melting efficiency in the post-process.

Further, if the heat treatment vessels are stacked in the heat reduction furnace at intervals, the space between the heat treatment vessels forms a convection zone of the reducing gas, and the gas flow distribution and the temperature distribution are reduced. Eliminate bias. Further, the processing amount can be arbitrarily adjusted by adjusting the number of heat treatment containers.

Hereinafter, the present invention will be described specifically.

FIG. 3 shows an example of the structure of a heating and reducing furnace for carrying out the present invention. The lower part of the heating and reducing furnace 1 is a reducing gas generation zone filled with a coke layer 2, and a tuyere 3 for supplying combustion air is provided in a part of the coke layer 2. A roast 4 is provided directly above the coke layer 2, and a heat treatment container 5 is placed on the rost 4. A shielding member 7 for restricting the flow of the reducing gas from below with the heat treatment container 5 mounted thereon is provided on the furnace wall peripheral portion 6 of the rostre 4. Also,
An interval in which coke for forming the coke layer 2 can be inserted is provided in an intermediate portion of the roast 4.

The heat treatment vessel 5 placed on the roast 4 has an outer diameter slightly smaller than the inner diameter of the heat reduction furnace 1 and is charged into the dezincing chamber 8 of the heat reduction furnace 1 from above or from the side. can do. In this example, it is loaded from above as described later. The bottom of the heat treatment container 5 is provided with a slit or a plurality of openings capable of holding the stored massive steel plate waste and uniformly introducing the reducing gas from below into the container 5.

Above the dezincing chamber 8, a dust-collecting facility 9 that can be hermetically sealed is provided. In this example, a movable hood 10 is provided in the dust collecting facility 9 and has a structure capable of being attached to and detached from the dezincing chamber 8. That is, the movable hood 10 is moved and retracted when the heat treatment container 5 is charged or discharged into the dezincing chamber 8.

FIG. 1 shows the relationship between the size of steel sheet waste and the dezincing rate. As a result of performing a dezincing test of various sizes of steel plate debris using a heating reduction furnace having a furnace inner diameter of 90 cmφ, lump steel plate debris having a diameter of 1/10 to 1/20 of the cross-sectional diameter of the heat treatment vessel is in a preferable filling state, It was optimal without impairing the gas flow permeability.

FIG. 2 shows the relationship between the bulk density of steel sheet waste and the dezincing rate. The bulk density is 1.
In the range of 5 t / m ³ or more and 2.5 t / m ³ or less, the higher the density of the steel scrap, the smaller the heat transfer resistance in the steel scrap, and the temperature rises uniformly, so that zinc does not remain partially. Complete dezincing was performed with favorable results.

[0025]

Example: 0.9 mm thickness, average weight 45 g / m
² (one side) a lump of steel plate was prepared by rolling a steel plate waste plated with zinc to a size of 50 mmφ with a shredder. The bulk density of this steel sheet waste was 2.2 t / m ³ . This steel sheet waste 2t was charged in a heat treatment container, and placed in a vertical heating reduction furnace shown in FIG. 3, a dust collecting hood was set, and air blowing was started. After heating to 1000 ° C. for about 10 minutes, the blowing was stopped, the hood was removed, and the heat treatment container was taken out.

The plated steel scrap was completely dezinced with almost no oxidation. In addition, the dezincified steel scrap is transferred together with the container, and the bottom is opened on a low-frequency furnace and charged into the furnace, so that the raw material preheated to 700 ° C. or higher is charged into the low-frequency furnace. I was able to do it. Table 1 summarizes the operating conditions.

[0027]

[Table 1]

Table 2 shows a comparison between the present invention and the conventional method, that is, the dezincing rate and the processing time when the zinc-plated steel sheet scrap is simply cut to about 5 × 5 cm and dezincified.

[0029]

[Table 2]

As a result, it is clear that the present invention is superior in both the dezincing rate and the processing time as compared with the conventional method.

[0031]

According to the present invention, it is possible to completely and efficiently dezinc galvanized steel sheet waste by an evaporation method. In addition, it can also pre-heat steel scrap, which leads to energy saving and improvement of productivity. In addition, it is possible to use the generated dust as a raw material for zinc refining and to recycle resources. This is the zinc method.

[Brief description of the drawings]

FIG. 1 is a view showing the relationship between the size of steel sheet waste and the dezincing rate.

FIG. 2 is a diagram showing the relationship between the bulk density of steel sheet waste and the dezincing rate.

FIG. 3 is a diagram showing an example of an apparatus used to carry out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating reduction furnace 2 Coke layer 3 Tuyere 4 Rostor 5 Heat treatment container 6 Furnace wall peripheral part 7 Shielding member 8 Dezincing room 9 Dust collection equipment 10 Movable hood

Claims (3)

(57) [Claims] 1. A method for dezincing galvanized steel sheet waste by evaporating and removing galvanized steel sheet waste by heating the zinc-coated steel sheet waste with a high-temperature reducing gas, the method comprising the steps of: Processed into a lump of 10/20, placed the heat treatment vessel containing the steel plate scraps in a vertical heating reduction furnace, and while sucking the furnace atmosphere from above the heating reduction furnace,
A method for dezincing galvanized steel sheet waste, comprising introducing a high-temperature reducing gas generated in a lower part of a heat-reduction furnace from the bottom of a heat treatment vessel and passing the gas through the vessel to reduce by heating. 2. The galvanized steel sheet scrap has a bulk density of 1.5 to 1.5.
2. The method for dezincing galvanized steel sheet waste according to claim 1, wherein the method is processed to 2.5 t / m < ³ >. 3. The method for dezincing galvanized steel sheet waste according to claim 1, wherein heat treatment vessels are stacked in the heat reduction furnace at intervals.