JPH0137448B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an electric furnace steelmaking method that achieves an improvement in electric power consumption and a reduction in steelmaking time when melting and refining ferrous materials using an electric furnace. It is related to.

[Prior art] The electric furnace steelmaking method generates an arc between the ferrous raw material charged in the furnace and an electrode, and uses the high temperature to heat and melt the raw material. It is widely used because it has the following characteristics: it is easy to remove P and S, it contains few harmful impurities, and it is possible to refine all types of steel.

FIG. 2 is a flow explanatory diagram showing an overview of such an electric furnace steelmaking method. When the steelmaking process is divided into steps, it can be divided into a melting period, an oxidation period, and a reduction period. In addition, examples of the composition of molten steel are also shown in each figure. First, in the first melting period, an arc is generated from the electrode 4 against the iron-based raw material charged into the electric furnace 1 to melt it. The melting stage occupies most of the steelmaking process, and arc melting is performed at maximum voltage and current, and when the melting is almost complete, limestone and scale are introduced into the furnace. When the melting period ends, oxidation refining is performed to remove harmful P and nonmetallic inclusions, but since oxidation refining requires a high steel bath temperature, the temperature is first raised using electricity during the oxidation period. Do this. This reduces the steel bath temperature to approx.
When the temperature rises to 1600℃, after pulling up electrode 4,
Insert the O ₂ injection lance 3 into the steel bath to a depth of approximately 100 mm, and perform O ₂ injection (bubbling) to oxidize and remove harmful components such as P and nonmetallic inclusions (during the oxidation period). ). The steel bath becomes boiling due to oxygen enrichment, and H ₂ (contaminated from the raw materials) in the steel is also removed at the same time. Next, when the deP removal etc. are completed, the electrode 4 is immersed in the steel bath again, and while the steel bath is maintained at a predetermined temperature by electricity, a reducing agent and an alloying agent are added into the furnace to deoxidize and desulfurize the molten steel and adjust the composition. (reduction period).

[Problems to be Solved by the Invention] Steel making in an electric furnace is carried out as described above, but in the operation of such an electric furnace, as mentioned above, the charged ferrous raw material is heated by electric power during the melting period. Because the temperature rises and melts at once, the maximum output power is consumed. The power consumption at this time is quite large and constitutes a major part of the production cost, partly because the melting period occupies most of the operating period. However, the power addition efficiency in the process of melting iron-based raw materials cannot be said to be very high, and effective use of power is desired from the viewpoint of energy conservation. Also, during the oxidation period,
During oxygen injection operation (oxidation period), the power is stopped and the electrodes are pulled up, so no temperature increase can be expected due to electric power, and therefore the temperature increase period (oxidation period)
A large amount of electricity is required. As described above, the electric furnace steelmaking method requires a large amount of electric power, but as mentioned above, heating and melting using electric power is not necessarily efficient, so the electric power consumption rate becomes high.

The present invention has been made with attention to these circumstances, and aims to achieve such issues as reducing power consumption and shortening operating time while taking advantage of the features of the electric furnace steelmaking process. .

[Means for Solving the Problems] The method of the present invention, which has achieved the above object, uses an electric furnace to melt and refine iron-based materials, and during the melting period, the ratio of pulverized coal to air The gist is that the operation is carried out by injecting reducing gas obtained by burning pulverized coal at an air ratio of 1.0 to 1.2 during the oxidation period. It is something.

[Operation] In the present invention, in order to reduce power consumption, pulverized coal, which is cheaper than electricity and can be expected to be stably supplied, is partially used as an alternative energy source. When using pulverized coal, if the pulverized coal is directly injected into the furnace, harmful components associated with the pulverized coal will be added to the molten steel. It is combusted in a furnace and blown into the electric furnace as high-temperature combustion gas. The injection position is set approximately 300mm above the slag interface. Combustion gas is injected during the melting and oxidation periods, which consume a large amount of electricity, but during the melting period, electrodes are inserted into the furnace and arc melting of iron-based raw materials is performed in parallel, so the arc melting atmosphere is oxidizing. If the atmosphere is present, the oxidative wear and tear of the electrode will increase due to the following reaction.

C (electrode surface) + 1/2O ₂ →CO C (electrode surface) + CO ₂ →2CO The cost required for electrodes in electric furnace operation is comparable to the cost of thermal energy, and it is important to suppress electrode wear as much as possible. desired. Therefore, in the present invention, it is an essential requirement that pulverized coal be combusted at an air ratio of 0.75 to 1.0 in the pre-combustor in order to make the combustion gas blown in during the melting period reducing. By blowing the reducing combustion gas obtained in this way into the electric power furnace during the melting period, the temperature of the iron-based material in the furnace can be raised and melted without consuming the electrodes. Furthermore, if the air ratio is less than 0.75, the
The CO concentration increases and has a negative impact on electric furnace operation. On the other hand, if the air ratio exceeds 1.0, the loss of thermal energy cost increases due to electrode wear.

On the other hand, the oxidation period following the melting period is divided into the oxidation period (temperature raising period) and the oxidation period (oxidation refining period) as described above, and in the oxidation period, the temperature is raised exclusively in preparation for proceeding with the oxidation refining reaction. In the present invention, pulverized coal combustion gas is blown into the furnace during the oxidation period to raise the temperature of the molten steel, in order to reduce the electrical energy needed to raise the temperature. By the way, the oxidation period is a preliminary stage for the next oxidation period, and during the oxidation period, injection into the molten steel is carried out to perform oxidation refining, so in order to promote oxidation refining, the pulverized coal combustion gas during the oxidation period is oxidizing. Therefore, the pre-combustor burns pulverized coal at an air ratio of 1.0 to 1.2. This makes it possible to make the atmosphere in the furnace oxidizing and to accelerate the temperature rise of the molten steel. If the air ratio is less than 1.0, the combustion gas becomes a reducing gas, which adversely affects the oxidation refining reaction.
On the other hand, if the air ratio exceeds 1.2, the adiabatic flame temperature will be low and the loss in thermal energy cost will be large.
Also, the oxidation period is shorter than the dissolution period,
During the oxidation period, the electrodes are lifted from the molten steel, so even if oxidizing combustion gas is blown into the electrodes, wear and tear on the electrodes during this period is relatively small, and accidents like those during the melting period do not pose a problem. Next, in the oxidation stage, even after the electrode is lifted, pulverized coal combustion gas is continuously blown in to maintain the temperature of the molten steel.At this time, as in the oxidation stage, oxidation refining can be promoted by making the combustion gas oxidizing. It can save time. Then, during the reduction period, the injection of pulverized coal combustion gas is stopped, and the electrode is immersed in the molten steel again to perform deoxidation, desulfurization, and component adjustment in the same manner as before.

[Example] Fig. 1 is a flow explanatory diagram showing an embodiment of the method of the present invention, and the steps are the same as in Fig. 2, including a dissolution period, an oxidation period;
, divided into reduction periods. Below each process diagram, an example of the composition of the molten steel at that time is shown.

After charging raw materials into the electric furnace 1, during the melting period, 110KWH of electricity is sent to the electrode 4 shown in the figure, and in the pre-combustor 2, pulverized coal is heated to an air ratio of 480Kg/H.
Reducing gas was generated by combustion at 0.75-1.0.
In pre-combustor 2, ash was removed in the form of slag, and clean reducing combustion gas (CO) was blown into the furnace, creating a puddle and melting proceeded (melting time: approximately 1 hour). The electricity consumption rate during this period was approximately
Improved by 20%. Next, when melting is completed, the power load is reduced to 55KWH, and 240Kg/H of pulverized coal is combusted at an air ratio of 1 in pre-combustor 2, and the oxidizing combustion gas (CO ₂ + H ₂ O) is injected into the furnace for about 10 minutes. The temperature of blown molten steel was raised to approximately 1600℃. When the temperature was raised, the electrode 4 was pulled out of the molten steel, and oxygen gas, which had been sufficiently dehydrated, was injected into the molten steel from the oxygen injection lance 3 to enrich the molten steel with oxygen. At the same time, in pre-combustor 2, oxidizing combustion gas obtained by burning 240 kg/h of pulverized coal was blown into the furnace (for about 20 minutes).
By injecting oxidizing combustion gas during the oxidation period, the oxidation refining time could be shortened by about 10 minutes.
Furthermore, as shown in Figure 1, the P content could be reduced by approximately 0.02%. Next, in the reduction period after slag removal, the injection of pulverized coal combustion gas was stopped, the electrodes were immersed again, and while 110KWH of electricity was being supplied, 150Kg of reducing agent coke powder and alloying agent were introduced into the furnace. deacidification,
After desulfurization and component adjustment, the resulting molten steel was tapped.

In the above example, electricity was used in conjunction with the oxidation period, but during the oxidation period, no electricity was used at all, and pulverized coal of 480 kg/h or more was combusted at an air ratio of 1, and combustion gas was blown in to raise the temperature.
By maintaining the temperature, it was possible to further reduce electricity costs.

[Effects of the Invention] The present invention is configured as described above, and it is possible to reduce electric power cost and shorten melting time and refining time while taking advantage of the features of the electric furnace steel manufacturing method. In particular, we have succeeded in reducing electricity costs by up to 20%, and there is still room for further improvement. Further, consumption of the electrodes can be suppressed to the minimum possible level, and the cost of the electrodes does not rise.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the method of the present invention,
FIG. 2 is a flow explanatory diagram showing a conventional method. 1... Electric furnace, 2... Pre-combustor, 3... Oxygen injection lance, 4... Electrode.

Claims (1)

[Claims] 1. When melting and refining iron-based materials using an electric furnace, during the melting period, reducing gas obtained by burning pulverized coal at an air ratio (air ratio to pulverized coal) of 0.75 to 1.0 is injected to oxidize the material. During the period, pulverized coal is mixed with air.
An electric furnace steelmaking method characterized by operating by injecting oxidizing gas obtained by combustion at a temperature of 1.0 to 1.2.