JPS5848834B2 - Arc furnace for melting reduced iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an arc furnace for melting reduced iron in which reduced iron is continuously charged and melted.

In the method of making reduced iron steel using an arc furnace, 10 to 30% of the total amount of scrap is first charged into the furnace, and after melting it in the arc, reduced iron is continuously charged. Since melting is carried out, it is best to operate the process so that the specified composition is achieved when the continuous charging of reduced iron is completed.

However, reduced iron contains a large amount of oxygen as iron oxide, and this is reduced by the carbon in the molten steel during melting, so it is necessary to add an appropriate amount of extra carbon when charging the scrap, and the amount of carburization increases. If this is not appropriate, the time required for carburization and decarburization will be long, and sulfur content will enter the molten steel from the excess carburizer, which is undesirable.

Since reduced iron contains acidic gangue, acidic slag is produced and the furnace wall, which is made of basicity ratio refractories, is severely eroded. 4) It is necessary to maintain K.

Further, continuous charging of reduced iron is carried out at a rate of 4% when the electrode is energized, but in order to perform efficient melting, it is necessary to maintain the molten steel mixture within a certain range (usually 1575°C to 1585°C) so as not to decrease.

The present invention has been made in view of the above points, and aims to automatically control all of the carbon content in molten steel, the basicity of slag, and the molten steel content to efficiently obtain molten steel with a predetermined composition at the maximum melting rate. The purpose of this invention is to provide an arc furnace for melting reduced iron that can be used to melt reduced iron.

An embodiment of the present invention will be described below with reference to FIG.

In the figure, 1 is the furnace shell of the arc furnace, 2 is the furnace lid, 3 is the electrode, 4 is the molten steel, 5 is the molten slag, 11 is a sample collector whose tip is immersed in the molten steel and operates at predetermined short time intervals, 12 13 is a chute for transferring the sample, 13 is a carbon content measuring device that uses spectroscopic analysis, etc., and 14 is an on/off controller that compares the output signal of the carbon content measuring device with the internal carbon content upper limit setting value to ensure that the deviation is sufficient. 15 is an on-off controller that compares the output signal of the carbon content measuring device with the internal carbon content lower limit set value and continuously issues an on signal when the difference is one. , 16.17 is an electromagnetic on-off valve that opens when energized, 18 is an oxygen blowing pipe communicating with the inside of the furnace, 19 is a pipe leading to an oxygen supply source, 20 is a carbon powder blowing pipe communicating with the inside of the furnace, 2
1 is a pipe leading to a carbon powder supply source.

31 is a sample collector whose tip is immersed in molten slag and operates at predetermined short time intervals, 32 is a chute for sample transfer, 33 is a slag basicity measuring device, and 34 is an on/off controller that operates from the basicity measuring device. A device that compares the output signal with the internal basicity setting value and continuously emits an on signal when the difference is 1, 35 is an electromagnetic on-off valve that opens when energized, and 36 is a lime charge that communicates with the inside of the furnace. 37 is a hopper for lime, 37a is a nozzle chamber at its lower end, 38 is a lime powder chute,
An air blowing pipe 240 having a nozzle at its tip is a pipe leading to an air supply source.

1, 51 is a thermocouple-type humidity detector whose tip is immersed in molten steel and measures the depth of molten steel at predetermined short intervals; 52 is a temperature converter; and 53 is a controller that internally receives the output signal of the mixture converter. 54 is a furnace transformer; 55 is a furnace transformer;
is a tap changer built into this transformer, 56 is a pulse motor for driving the tap changer, 57 is a tap position detector connected to this pulse motor and emits a signal when the highest voltage tap is changed, and 58 is a tap position detector. A selector switch 59 is a controller that closes the circuit according to the output signal of the temperature converter 52.
Compares the output signal with the internal mixture setting value, and when the deviation is one, continuously emits an output signal proportional to the amount of deviation,
60 is a setting device that emits a signal corresponding to the maximum reduced iron charging speed, and 61 is an arithmetic unit that uses the output signal of the setting device 60 to output a signal to the controller 5.
What subtracts the output signal of 9, 62 is a DC amplifier, 63
65 is a direct current motor that drives the rotary feeder 64 for charging reduced iron, and 65 is a chute for charging reduced iron that communicates with the inside of the furnace.
A hopper 66 for reduced iron 67 is a pellet-shaped reduced iron hopper.

That is, when the melting of the scrap is now completed and the continuous charging of reduced iron is started at the maximum charging speed, the sample collector 11 is operated at predetermined short intervals, and the collected sample is transferred to the carbon from the chute 12Vc. The carbon content is transferred to the quantity measuring device 13, where the carbon content is automatically analyzed and a signal proportional to the carbon content is given to the on/off controller 1415.

If the carbon content exceeds the specified upper limit, turn on/off controller 1.
4, an on-signal is issued, the electromagnetic on-off valve 16 is opened, and oxygen is supplied into the furnace through the oxygen blowing pipe 18, and this supply is continued by a trench that detects that the amount of carbon has fallen below the upper limit.

When the amount of carbon is below the predetermined lower limit, an on-off signal is output from the on-off controller 15 in the same way as above, the electromagnetic on-off valve 11 is opened, and carbon powder is blown into the furnace from the carbon powder injection pipe 20. 1.

On the other hand, with the start of continuous charging of reduced iron, the sample collector 31 is activated at predetermined short intervals, and the sampled slag is transferred to the basicity measuring device 33 via the chute 32 and analyzed, and a signal proportional to the basicity of the slag is turned on and off. The controller 34K is applied, and when the basicity falls below a predetermined value, the on-off controller 34 issues an on signal, the electromagnetic shut-off valve 35 opens, and the air blowing tube 39 is opened.
Lime 38 is charged into the furnace through the chute 36 by the ejected air, and lime charging is stopped by an off signal from the on/off controller 34 when the basicity reaches a predetermined value or more.

Encased depth detector 51 and temperature converter 5 connected to it
The molten steel content detected by the 2K is given as an input signal to the controller 53 at predetermined intervals, and when the molten steel temperature is lower than the predetermined value, the controller 53 emits a pulse signal, and the pulse motor 56 operates to change the tap. 55 is switched to the high voltage side.

When the tap changer 55 is switched to the highest voltage position, the tap changer is mechanically and electrically locked, while the tap position detector 57 provides an output to switch the transfer switch 58 into a conductive state.

When the depth of molten steel is still below the set value, the controller 59 emits an output signal proportional to the deviation between the signal from the temperature converter 52 and the set value, and this signal is converted to the output signal of the setting device 60 in the calculator 61. Since the input signal to the DC amplifier 62 decreases, the armature voltage of the DC motor 63 decreases, the rotation speed of the rotary leaf feeder 64 decreases, and the amount of charged reduced iron decreases, so the molten steel depth decreases. Controlled in the upward direction.

As the molten steel temperature rises, the deviation from the set value decreases, the subtraction signal from the controller 59 decreases, and the rotational speed of the DC motor increases, and when the molten steel content exceeds the set value, the subtraction signal becomes O. The reduced iron is continuously charged at a predetermined maximum speed according to the setting value of the setting device 60.

Next, FIG. 2 shows another embodiment of the present invention, showing only the parts related to molten steel depth control and omitting the illustration of other parts.
Same as the figure.

This embodiment differs from the controller 53 in the embodiment shown in FIG.
The tap position detector 5γ, the changeover switch 58, and the connection between them are omitted so that the output signal of the mixture converter 52 is directly given only to the controller 59, and the tap changer 55 is used for other operations. For example, melting is performed with the switch Σ maintained at the highest voltage position.

In this case, the molten steel humidity is controlled only by controlling the rotation speed of the rotary feeder 64, which simplifies the apparatus.

In each of the above embodiments, the amount of carbon in molten steel, the basicity of slag, and the temperature of molten steel are detected at predetermined short intervals. Each operating section may be continuously controlled by continuous signals from the controller.

The recessed electromagnetic on-off valves 16, 17, and 35 may be configured to have their opening degrees adjusted in accordance with deviations in addition to on/off control.

Furthermore, in addition to using carbon powder as a carbon supply source, molten steel containing a large amount of carbon may be injected into the furnace.

As explained above, the present invention detects the amount of carbon in molten steel, the basicity of slag, and the humidity of molten steel at predetermined time intervals or continuously during continuous charging of reduced iron, and compares them with each predetermined set value. Oxygen supply device according to the deviation,
The operation of the carbon supply device and lime charging device, the adjustment of the reduced iron charging speed, the tap switching of the transformer, and the adjustment of the reduced iron charging speed are all automatically controlled by the K button. During continuous charging of reduced iron, the amount of carbon in the molten steel, the basicity of the slag, and the molten steel temperature are accurately and easily maintained within specified ranges, eliminating the need for large-scale carburization or decarburization during or after melting. , Furnace wall damage due to base ratio slag is eliminated, furnace wall repair time is reduced, and high-efficiency melting work can be performed with the highest melting speed of the equipment, resulting in improved production efficiency and labor savings. .

[Brief explanation of drawings]

FIG. 1 is a system diagram showing one embodiment of this invention, and FIG. 2 is a system diagram of main parts showing another embodiment of this invention. DESCRIPTION OF SYMBOLS 1... Furnace shell, 11... Sample collector, 12... Shooter, 13... Carbon content measuring device, 14.15... On/off controller, 16.17... Solenoid shut-off valve, 18...
Oxygen blowing pipe, 20... Carbon powder blowing pipe, 31... Sample collector, 32... Shooter, 33... Slag basicity measuring device, 34... On/off controller, 35... Electromagnetic Opening/closing valve, 36... Chute for lime charging, 39... Air blowing pipe, 51... Temperature detector, 52... Temperature converter, 53... Controller, 54... For furnace Transformer, 55...
・Tap changer, 56...Pulse motor, 57...
Tap position detector, 58... changeover switch, 59...
・Controller, 60... Setting device, 61... Arithmetic unit, 62
...DC amplifier, 63...DC motor, 64...
Rotary feeder, 65...Chute for charging reduced iron.

Claims (1)

[Scope of Claims] 1. An oxygen supply device and a carbon supply device that supply oxygen and carbon into the furnace, and a lime charging device and a continuous reduced iron charging device that charge lime and reduced iron into the furnace. A carbon detector is used to detect the amount of carbon in molten steel, the basicity of slag, and the mixture of molten steel continuously or at predetermined time intervals during continuous charging of reduced iron by pressing a button on the arc furnace equipped for melting reduced iron. A quantity detector, a basicity detector, a molten steel temperature detector, and a detection signal of the carbon quantity detector are compared with a set value, and when the carbon quantity is above a predetermined upper limit value, a signal is issued to operate the oxygen supply device. , a carbon amount control device that emits a signal to operate the carbon supply device when the carbon amount is below a predetermined lower limit value, and a detection signal of the basicity detector and a set value are compared, and when the basicity is below a predetermined value; A basicity control device that issues a signal to operate the lime charging device and a detection signal of the molten steel temperature detector are compared with a set value, and when the molten steel content is below a predetermined value, the unit of the continuous reduced iron charging device is An arc furnace for melting reduced iron, characterized in that it is equipped with a molten steel saturation control device that issues a signal to reduce the charging amount per hour. 2. Equipped with an oxygen supply device and a carbon supply device that supply oxygen and carbon into the furnace, and a lime charging device and a continuous reduced iron charging device that charge lime and reduced iron into the furnace,
In an arc furnace for melting reduced iron connected to a furnace transformer with a tap changer, carbon content in molten steel, basicity of slag, and molten steel are measured continuously or at predetermined time intervals during continuous charging of reduced iron. The carbon content detector, basicity detector, and molten steel humidity detector each detect a mixture of Compare the detection signal of the basicity detector and the set value with a carbon amount control device that emits a signal to activate the feeding device and when the carbon amount is below a predetermined lower limit value, a signal to activate the carbon feeding device. A basicity control device that issues a signal to operate the lime charging device when the basicity is below a predetermined value, and a basicity control device that compares the detection signal of the molten steel temperature detector with a set value and operates the tap when the molten steel temperature is below a predetermined value. It is characterized by being equipped with a molten steel temperature control device that issues a signal to switch the switching device to the high voltage side, and after switching to the highest voltage, issues a signal to reduce the charging amount per unit time of the continuous reduced iron charging device. Arc furnace for melting reduced iron.