JPS63227710A - Method for heating raw material in arc furnace - Google Patents

Abstract

PURPOSE:To efficiently heat raw material and to effectively reduce the power cost by injecting liquid fuel from a fuel injecting hole arranging at lower position than the molten metal surface in an arc furnace and burning by oxygen supplying in the furnace. CONSTITUTION:In the arc furnace 22 charging the raw material 14 of scrap, etc., the liquid fuel is injected from the injecting hole 10 arranging at the furnace bottom part 12. Together with this, the oxygen is supplied from a supply tube 15 and the above fuel is burnt. Then, preceded the above combustion, it is desirable that ignition of the liquid fuel is made to facilitate by supplying coke 16 in the furnace bottom part 12. By the combustion of the liquid fuel, the raw material 14 is efficiency heated from the inside without any oxidation thereof. This heating is executed as preceding with arc heating or as paralleling with it. Further, it is desirable that the raw material heating from upper side is used by arranging burner 15 at the position of above the molten metal surface together with the above heating. The heating of the row material 14 is changed to the arc heating at the time of reaching the prescribed temp. with <=1,000 deg.C average temp. of the raw material 14, and it is desirable to promote the refining by blowing N2 gas, etc., from the fuel injecting hole 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for heating raw materials in an arc furnace, and more particularly to technical means for reducing power costs.

(Conventional Technique #i) An arc furnace as an electric melting furnace generates an arc between raw materials such as scrap charged into the furnace and an electrode, and melts the raw materials with the arc heat. Electricity costs account for approximately 40% of operating costs.

Incidentally, the cost of electricity in Japan is extremely high compared to other countries, and therefore reducing electricity costs has become an important issue in order to win international competition.

Under these demands, various attempts have been made to reduce the electric power cost in the operation of such arc furnaces. As part of this process, auxiliary heating of the raw material charged into the furnace is carried out using a burner, and this method has been established to some extent industrially. Specifically, as shown in FIG. 6, a burner 100 is inserted into the arc furnace, and the raw material 102 charged into the furnace is pre-ripened by the combustion heat of the burner 100.
This saves the electrical energy required for melting raw materials.

(Problems to be Solved by the Invention) However, when the raw material is preheated using this method, only the surface portion of the raw material is heated locally, which may promote oxidation of the raw material surface. This causes problems such as shelf temperature phenomenon of raw materials.

In addition, the powder method only heats the surface of the raw material, and moreover, the high-temperature combustion gas from the burner escapes upwards and is exhausted without sufficient heat exchange with the raw material. Therefore, there is a problem in that the heating efficiency deteriorates and the heating efficiency does not sufficiently contribute to the reduction of energy costs.

(Means for Solving the Problems) The present invention has been made to solve these problems, and its gist is that the surface of the molten metal when the raw material charged into the arc furnace is melted. A fuel spout opening into the furnace is provided in the lower part of the fuel jet, and liquid fuel is spouted from the fuel spout, and oxygen is supplied into the furnace to burn the spouted liquid fuel, and the fuel heat is used to burn the jetted liquid fuel. The purpose is to heat the raw materials in the interior prior to or in parallel with arc heating.

According to the present invention, raw materials such as scrap charged into an arc furnace can be efficiently heated.

In the present invention, a fuel spout is formed below the molten metal surface (strictly speaking, the slab surface, hereinafter referred to as sill level) when the raw materials in the furnace are melted, and liquid fuel is spouted and burned from there. This is because the raw material inside the furnace is heated from the inside rather than from the surface side.

In the present invention, the fuel nozzle may be formed anywhere below the sill level, especially when the fuel nozzle 10 is formed at the bottom of the furnace 12 as shown in a specific example in FIG. 1(A). That is, when the liquid fuel is blown up from the furnace bottom 12 and combusted while supplying oxygen from the supply pipe 15, the raw material 14 in the furnace will be heated from the bottom, where heat conventionally cannot reach. Moreover, the combustion gas rises to the upper part of the furnace while fully contacting the raw material 14, and sufficient heat exchange occurs, so that the raw material 14 can be heated efficiently. In addition, if the liquid fuel is ejected from a plurality of locations and combusted, the raw material 14 in the furnace will be heated at a plurality of locations, and the heating efficiency will be further improved.

In the early stage of combustion immediately after the raw material 14, such as scrap (cold material), is inserted, the raw material 14 is still cold, and furthermore, the combustion condition may be poor because the liquid fuel is jetted straight upward. In this case, if coke 16, which is added as a recarburizer during steel manufacturing, is placed so as to cover the spout 10, as shown in FIG. 1(A), combustion can be carried out smoothly. . The liquid fuel ejected from the spout 10 hits the coke 16 and is evenly dispersed in the furnace, and the coke 1 is released in the arc furnace immediately after tapping.
6 quickly becomes red hot, so the liquid fuel that is spouted out burns quickly.

In the present invention, when there is only one arc furnace, raw material heating by combustion of liquid fuel and original arc heating can be performed in parallel to increase production efficiency. In this case, the raw material in the furnace is heated from both the upper and lower sides, and the raw material can be heated efficiently.

By the way, it is practically advantageous to blow out an inert gas such as N2 or Ar gas from the fuel injection port after stopping the injection and combustion of the liquid fuel from the fuel injection port, thereby causing the raw material molten metal to enter the injection port. Not only can this prevent clogging of the jet nozzle, but also the molten metal stirring effect by the inert gas can equalize the temperature and components of the molten metal and promote the slag-metal reaction. When considering the spouting of inert gas from a jet nozzle, the jet nozzle is formed by a bundle of many thin tubes 18, for example, as shown in FIG. 2, and the inert gas is spouted from these many thin tubes 18. It is desirable that the flow rate of the gas from the n-tube tree is defined by the following equation, according to the gas-fluid theory.

V = 958 x 10-P o (kg/am”)
n-s o (c+s")...(1) Cocote, V: Gas flow rate (Nm'/min), PG: Supply pressure (kg/cm2), S o: Internal cross section of one pipe a (am") ).

On the other hand, the apparent linear velocity of gas at the nozzle is expressed by the following equation.

v = V/(ns o)・104/60= 958
X 10-3・10'/60・Po...(2
) where V: apparent linear velocity (m/sec).

According to experiments conducted by the inventors, it has been confirmed that if the apparent linear velocity at the jet nozzle is not higher than the sound velocity (v > 340 m/sec), the tube will become occluded. If you put it in and find Po, it will be P. >2.13, P
If o is not 2 atmospheres or more, the outlet will be blocked.

On the other hand, the stirring energy based on the gas ejected from the nozzle is expressed by the following formula % formula % (3), and if this value is not less than 120 watts/ton, there will be excessive splash, that is, the molten metal will scatter violently from the molten metal surface. This will cause problems in actual operation.

As a result, the amount of gas ejected from the nozzle and the dimensions of the thin tube are naturally restricted. For example, the weight of molten steel W = 3 tons, the temperature of molten steel T =
When the molten steel depth h = 0.4 m at 1873°, the third equation gives V −0,13ONm37 minutes or less, which is entered into equation (1) to obtain ns.

If we calculate n S o ” 0.0452, here, if nx2, then S. = 0.0221i, and when converted to diameter, D = 1.6 mmφ. That is, the inner diameter is 16
It is necessary to use an amφ tube.

On the other hand, when considering a 90-ton furnace, if h = 1.3 m and the same calculation is performed, D = 1.1 mmφ.

In this way, in order to eject gas while preventing clogging of the ejection port and suppressing excessive splash, it is practical to reduce the diameter of each pipe.

Although the present invention uses liquid fuel such as heavy oil or kerosene as the heating fuel, it is also possible in principle to use gaseous fuel such as propane as such fuel. However, when such gaseous fuel is used, the diameter of the pipe forming the jet nozzle is limited (to be thin) as described above, so the amount of energy supplied is significantly smaller (approximately 1/ In this sense, it is difficult to use gaseous fuel from a practical standpoint.The reason why liquid fuel is used in the present invention is based on these circumstances.

As mentioned above, if there is only one arc furnace, heating based on liquid fuel combustion and arc heating can be performed in parallel to reduce electricity costs without reducing production efficiency. can. However, when considering the thermal efficiency when heating raw materials, it is generally better to first heat the raw materials by burning liquid fuel in a relatively low temperature range, and then switch to arc heating at a certain temperature when the raw materials reach a certain temperature. is advantageous. In this case, in order not to reduce production efficiency, two arc furnaces are used as shown in Figure 1, and one arc furnace 22 is preheated by combustion of liquid fuel as shown in Figure 1 (A). While doing this, Figure 1 (B
), if arc heating is performed by energizing the electrode 20 in the other arc furnace 24, and these preheating and arc heating are performed alternately between the two arc furnaces 22 and 24, the production efficiency can be improved compared to the conventional one. It becomes possible to save heating energy more effectively while maintaining the The specific reason for this is that the temperature of the combustion flame of fuel is about 2000°C, whereas the temperature of arc heating is as high as about 3000°C, and there is a considerable temperature difference between the two. Third
The figure shows the relationship between fuel consumption and reduction in electricity consumption when heating by fuel combustion and arc heating are performed simultaneously, but as shown in the figure, fuel consumption increases. It can be seen that as the heating time by combustion becomes longer, the reduction rate of the electric power consumption rate decreases. This is clearly shown in FIG. 4, which shows the relationship between the average temperature of the raw material and thermal efficiency when the raw material is heated only by combustion of fuel. In the figure, A indicates the raw material temperature when the raw material is heated from above using three pulverized coal burners 26 (Fig. 1 (A)) while liquid fuel is jetted up from the bottom of the furnace to heat the raw material in a 90-ton arc furnace. - This is a thermal efficiency curve, and as can be seen from the fact that this curve A drops sharply near 1ooo'c, heating efficiency decreases significantly when the raw material temperature reaches 1000°C or higher when heating by burning fuel. Put it away. Based on this result, heating by combustion of liquid fuel is performed first, and the temperature of the raw material is 1,000 yen.
It is advantageous to be able to cut off arc heating when the temperature reaches a predetermined temperature below 'C.

In addition, B in the figure is the raw material temperature-thermal efficiency curve when only heating is performed by the burner 26, and by comparing this B with the above-mentioned A, it is found that the thermal efficiency is increased when heating by liquid fuel and burner heating are used together. Understand how you can effectively increase your This becomes clear when comparing the temperature of the upper part of the raw material in the furnace with the temperature of the lower part. Figure 5 shows 90) - three wood pulverized coal burners 26 from the top in the arc furnace (Figure 1 (A)
)) is used to heat the raw material preheated to 350°C (pulverized coal consumption 65 kg/min). As shown in the figure, when heating is performed only by the burner 26, even if the surface temperature of the raw material reaches nearly 1500°C, the lower part only reaches a low temperature of about 300 to 400°C.

Therefore, if part of the heating energy from above is transferred to heating energy from below, the raw material can be heated efficiently.

Although the present invention has been described in detail above, the present invention can be implemented with various modifications based on the knowledge of those skilled in the art without departing from the spirit thereof.

(Effects of the Invention) As described above, the present invention provides a fuel injection port opening into the arc furnace at a portion below the sill level, from which liquid fuel is ejected, and the combustion energy is used to supplementally heat the raw material. It is.

The present invention has excellent effects such as being able to effectively reduce power costs in arc furnace operation while suppressing oxidation and shelving caused by local heating of raw materials, and also having good thermal efficiency during auxiliary heating. play.

[Brief explanation of drawings]

FIG. 1 is an explanatory view for explaining an embodiment of the raw material heating method according to the present invention, and FIG. 2 is a perspective view of essential parts showing one embodiment of the fuel injection port according to the present invention. Figures 3 to 5 are diagrams for explaining the advantages of the present invention or one embodiment thereof, and Figure 3 shows the case where heating by fuel combustion and arc heating are performed simultaneously. Figure 4 is a diagram showing changes in power consumption. Figure 4 is a diagram showing thermal efficiency when raw materials in an arc furnace are heated with liquid fuel and burner heating. Figure 5 is a diagram showing thermal efficiency when only burner heating is performed on the raw material in the arc furnace. It is a figure which shows the temperature of each part of a raw material when carrying out this process. FIG. 6 is a diagram showing an example of a conventional auxiliary combustion method. 10, Fuel spout 12: Furnace bottom 14: Raw material 22.24: Arc furnace 26: Harna fuel Takako C1/1on) S (tough)

Claims (6)

[Claims] (1) Provide a fuel spout that opens into the furnace at a location below the molten metal surface when the raw material charged into the arc furnace is melted, and liquid fuel is spouted from the fuel spout and flows into the furnace. A method for heating raw materials in an arc furnace, characterized in that oxygen is supplied to burn the ejected liquid fuel, and the raw material in the furnace is heated by the heat of the fuel prior to or in parallel with arc heating. (2) The fuel injection port is provided at the bottom of the arc furnace, and the liquid fuel is blown up from the bottom of the furnace to heat the raw material in the furnace from below. The raw material heating method in the described arc furnace. (3) A method for heating raw material in an arc furnace according to claim 1 or 2, characterized in that the fuel injection ports are provided at a plurality of locations, and the raw material in the furnace is heated at the plurality of locations. . (4) After charging the raw material into the arc furnace, preheating by combustion of the liquid fuel is performed prior to or in parallel with arc heating, and the average temperature of the raw material is 1000°C.
4. A method of heating raw material in an arc furnace according to any one of claims 1 to 3, characterized in that normal arc heating is started when the following predetermined temperature is reached. (5) placing a burner above the molten metal surface;
5. A method for heating a raw material in an arc furnace according to any one of claims 1 to 4, characterized in that the raw material is heated from above by the burner in conjunction with heating by combustion of the liquid fuel. (6) After the injection of liquid fuel from the fuel injection port is stopped, inert gas such as N_2 and Ar gas is subsequently ejected from the fuel injection port to stir the molten metal in the furnace, thereby making the temperature and composition of the molten metal uniform. 6. A method for heating raw materials in an arc furnace according to any one of claims 1 to 5, characterized in that the slag-metal reaction is accelerated.