JPH0645814B2 - How to dissolve scrap - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for melting iron scrap using an upper-bottom blowing converter, a converter equipped with side blowing tuyeres, and the like. Hereinafter, iron scrap is simply referred to as scrap in the present invention.

(Prior Art) Conventionally, scrap as an iron source has also been used as a cold material during steelmaking in a converter, but most of it has been melted and refined in an electric furnace. However, in Japan, where electricity prices are high,
The power consumption increases remarkably as the usage amount increases, and the advantage of using scrap is being lost.

Therefore, various converter scrap melting methods have been proposed in which carbonaceous materials such as coke, which are cheaper than electric power, are used as a heat source for melting and the scrap is melted in the converter. For example, the method disclosed in JP-A-62-47417 proposed by the present applicant is one of them. This is to put a large amount of bedding coke into the top-bottom blowing converter, blow oxygen gas from the top-blowing lance and bottom blowing tuyere to ignite the coke, and then create a spark, then charge the scrap and coal. This is a method in which oxygen gas is blown into the material while it is being charged to dissolve scrap.

Further, the present applicant has proposed a method of melting scrap by using a converter having a side blowing tuyere on the bellows of an upper-bottom blowing converter (Japanese Patent Application No. 61-303365).

(Problems to be Solved by the Invention) However, the conventional method for melting scrap using a converter has the following problems because a large amount of coke is used.

(1) When coke is put into the preheated converter, the coke near the furnace bottom and the furnace wall easily ignites and reacts well with oxygen blown from the tuyere, but inside and above the coke layer. The ignition is slow and does not react well with oxygen. For this reason,
As shown in Fig. 1 (total melting time is 1.0 and changes in exhaust gas composition during that period), oxygen is discharged together with exhaust gas and is not effectively used in the first half of the period during scrap melting. This phenomenon is particularly remarkable when the preheating of the refractory in the furnace is not sufficient.

(2) Although coke is cheaper than electricity, it is still expensive at about 15,000 yen per ton.

(3) Sulfur content in coke is high. Therefore, it is necessary to desulfurize because the sulfur concentration in the hot metal becomes high. Therefore, an object of the present invention is to solve the problems of the conventional scrap method using a large amount of coke, and to provide a scrap melting method for a converter, which is capable of producing molten pig iron containing less impurities at low cost.

(Means for Solving the Problem) The present inventors have conducted various studies on a method of melting scrap, which can produce molten iron with a low amount of impurities at a low cost, and as a result, has good ignitability, is inexpensive, and has no impurity component I have found that it is most important to use fuel that does not contain much.

As a result of further studies on the fuel having the above properties, it was found that a waste plastic having the following properties (hereinafter, referred to as plastic since it is not necessarily limited to the waste plastic) has all of them. did. That is, (a) the ignition temperature of plastic is 300 to 500 ° C, which is about 400 ° C lower than that of coke.

(b) For example, even if waste plastic is dried and subjected to volume reduction treatment, the unit price is about 1,500 yen / ton, which is about one-tenth of the unit cost of coke.

(c) As shown in Table 1 in comparison with the components of coke, the components of general waste plastics contain almost no sulfur and phosphorus that are impurities contained in the hot metal. Therefore, the sulfur content in the hot metal is reduced, and the burden of desulfurization treatment can be reduced.

(d) Although some plastics contain chlorine, chlorine can be removed by absorbing it in dust collection water, so it will not be emitted into the atmosphere and pollute the environment.

The present invention was made on the basis of the above findings, and the gist thereof is "when melting scrap by using a converter, a floor coke is charged before charging the scrap, and a floor coke layer is used. The method for melting scrap is characterized in that the plastic is mixed in the upper part and the upper part in a range of more than 0 kg and 100 kg or less per ton of scrap and melted.

The plastic used here is, for example, JP-A-61-2739.
Waste plastics that have been volume-reduced by the method of JP-A-13 are desirable.

(Operation) Hereinafter, the scrap melting method of the present invention will be described with reference to FIG. In FIG. 2, 1 is an upper-bottom blowing converter equipped with a side-blowing tuyere 4, 2 is an upper-blowing lance, and 3 is a bottom-blowing tuyere.

To melt scrap using a converter like this,
First, the bedding coke 5 is loaded into the converter 1 in which the refractory material in the furnace has been preheated to a high temperature. At this time, the plastic 6 having a low ignition temperature is charged in the inside and the upper part of the floor coke 5 so that a large amount of the plastic 6 is mixed. The bedding coke 5 charged near the furnace wall and the furnace bottom is easily ignited by furnace heat.
Even at a position away from the furnace wall and the bottom of the furnace, the entire interior of the furnace is ignited almost at the same time because a large amount of the plastic 6 having a low ignition temperature is mixed inside and above the floor coke. After this, scrap 7 is charged, and at the same time, oxygen is blown from the top blowing lance 2, the bottom blowing tuyere 3, and the side blowing tuyere 4 to scrap 7
Is dissolved.

FIG. 3 shows the change in the exhaust gas composition when the above scrap melting is performed. It can be seen from FIG. 3 that in the case of the method of the present invention, the oxygen concentration decreases immediately after the start of dissolution, and the oxygen blown from the tuyere is effectively used. In this figure, the amount of plastic used is 60 kg per ton of scrap, and the horizontal axis of the figure is the total melting time of 1.0.

Conventionally, according to the method of the present invention, it is possible to ignite the inside and the top of a bedding coke, which has been delayed in ignition, almost simultaneously, so that the reaction with oxygen is smoothly performed, and oxygen is not reacted. It will not be emitted into the exhaust gas as it is.

By the way, in the present invention, the amount of plastic used is more than 0 kg per ton of scrap and 100 kg or less (hereinafter referred to as kg / T, which means the same as the basic unit).
More preferably, it is 30 to 60 kg / T. The reason will be described below.

Figure 4 shows the amount of plastic used as 0, 20, 30, 60, 100, 1
Coke when melted with various changes of 20 kg / T (○ in the figure
(Mark) and oxygen (mark □ in the figure). If the amount of plastic used is 20 kg / T, the effect is small because the amount is small. That is, the improvement in the usage amount of both coke and oxygen is small as compared with the case where no plastic is added. When the amount of plastic used is 30, 60 kg / T, the rapid ignition property works effectively, and the amount of coke and oxygen used is greatly reduced.
However, when the amount of plastic is 12 kg / T, the amount of oxygen increases because the plastic burns rapidly. In addition, the coke burns rapidly due to the rapid combustion of plastic, and the utilization efficiency of the heat of combustion for melting is reduced, but the amount of coke used is saved. Therefore, the sulfur and phosphorus contents of the hot metal are reduced.

As shown in Fig. 4, if the amount of plastic used is in the range of more than 0 kg / T and less than 100 kg / T, the amount of coke used and the amount of oxygen used may be less than those when not using plastic. it is obvious.

(Example) A furnace belly provided with four side blowing tuyeres as shown in FIG.
The melting heat source materials (coke, plastic, oxygen) shown in Table 2 were used for scrap melting in a ton top-bottom blowing converter, and the components of hot metal in each case, production cost, etc. were investigated. The results are shown in Table 2. In Table 2, the conventional method is a case where no plastic is used.

From the results shown in Table 2 above, in the method of the present invention, the impurities (sulfur, phosphorus) contained in the molten pig iron after dissolution are also improved as compared with the case of being dissolved by the conventional method. Especially 60 plastic consumption
The improvement effect of the method 3 of the present invention of kg / T is remarkable. In the comparison of the melting costs, when the index of the case of the conventional method is 1, and the case of the method of the present invention is 1 or less, the scrap melting can be performed cheaper than the conventional method.

(Effect of the invention) In recent years, a large amount of waste was generated and was found to have good ignitability and a small amount of impurity components from waste plastic that had no suitable treatment method, and this was used as a heat source material for scrap melting. However, the effect of the method of the present invention, which is capable of producing hot metal containing few impurities at low cost, is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing an exhaust gas composition when scrap is melted by a conventional method, FIG. 2 is a diagram showing a state where scrap is melted by the method of the present invention, and FIG. 3 is a scrap by the method of the present invention. FIG. 4 is a diagram showing an exhaust gas composition in the case of dissolving the above, and FIG. 4 is a diagram showing a relationship between the amount of plastic used and the amounts of coke and oxygen used. 1 is a top-bottom blowing converter, 2 is a top-blowing lance, 3 is a bottom-blowing tuyere, 4 is a horizontal blowing tuyere, 5 is bedding coke, 6 is plastic, and 7 is scrap.

Claims (1)

[Claims] 1. A method for melting iron scrap by using a converter, in which bedding coke is charged before charging iron scrap, and a plastic scrap ton is provided inside and above the bedding coke layer. A method for melting iron scrap, characterized by mixing and melting in a range of more than 0 kg and 100 kg or less per unit.