RU2731711C1 - Method of controlling parameters of arc furnaces - Google Patents

Abstract

FIELD: automation of process parameters control in electrometallurgical technological processes.

SUBSTANCE: invention can be used in adaptive control systems for automatic control of arc furnaces thermal mode. Proposed method comprises control of bath furnace thermal state and electrode working surface temperature. Additionally, initial bath furnace temperature values, lining temperature, temperature under electrodes, metal temperature and current melting time are measured, further evaluating temperature parameters from all measurement points, determining average values of bath temperature of furnace, lining, electrodes, measured temperature values are compared with calculated values, wherein depending on the current melting time, a correction coefficient is introduced, which takes into account abrupt change of thermophysical properties of the lining and electrodes during operation, then control signal is sent to electrodes position change control drive.

EFFECT: invention reduces power consumption and improves ready melt quality, reducing the number of prematurely failing electrodes, bottom and side lining due to increased reliability of assessment of the furnace bath thermal state.

1 cl, 1 ex, 5 dwg

Description

The invention relates to the field of automation of control of technological parameters in electrometallurgical technological processes and can be used in adaptive control systems for automatic regulation of the thermal regime of arc furnaces.

The known method and control system for the process of melting and refining metal (RF patent No. 2571971, publ. 27.12.2015). This method includes the steps of calculating / determining the mass of molten metal and the mass of solid metal at a given point in time. The calculation is based on the initial values of the molten and solid metal masses, the arc power supplied to the electric arc furnace, and the temperatures of the molten and solid metal. The stirring power is determined based on the calculated / determined masses. A certain stirring power is supplied to the electromagnetic stirrer.

The disadvantages of this method are the low accuracy of measuring the mass of the charge and melt; this method cannot be applied to furnaces that do not have magnetodynamic stirring.

A known method of controlling the electric arc mode of smelting ore-thermal furnaces when receiving phosphorus (RF patent No. 2516360, publ. 20.05.2014). The method includes loading and melting a charge in a furnace, measuring in the process of melting the current and voltage of the electrodes, the power consumption, the value of the constant component of the phase voltage of the electrodes and the furnace, and regulating the operating power of the furnace by switching the steps of the furnace transformer, moving the electrodes and / or adjusting the composition of the charged batch. In the process of melting, the value of the arc current fraction in the electrode current is additionally determined, and the operating power of the furnace is regulated depending on the value of the mismatch with the set value of the arc current fraction in the electrode current, equal to 5-10%.

The disadvantage of this method is that when it is implemented, the temperature distribution in the furnace space is not taken into account, and the position of the electrode end is not fixed.

A known method for determining the parameters of heating ore-thermal furnace after downtime (RF patent No. 94039440, publ. 27.06.1996). In accordance with this method, the thermoEMF is measured in the "electrode - ground" circuit at the moment the furnace is turned off and its change is monitored during the idle period, and the thermal state of the bath and the electrode is determined by the nature of the change.

The disadvantage of this method is the indirect determination of the temperature, which is not a reliable and accurate way to control the thermal state of the furnace.

A known method for determining the parameters of heating ore-thermal furnace after downtime (RF patent No. 2305242, published on August 27, 2007), taken as a prototype. The thermal state of the furnace bath is monitored, the nominal electrode current, thermoEMF in the electrode-ground circuit are measured, the initial heating current and further change in electrical parameters are determined according to a given program. In this case, the temperature of the inner wall of the furnace bath, the temperature of the working surface of the electrode at the rated current are measured, and the initial heating current is determined by a mathematical expression.

The disadvantage of this method is the discreteness of temperature measurement, since only the temperature of the inner wall of the furnace bath and the temperature of the working surface of the electrode at rated current are measured, the rest of the time the temperature is not controlled.

The technical result of the proposed method is to reduce energy consumption and improve the quality of the finished melt, reduce the number of prematurely failing electrodes and bottom and side lining by increasing the reliability of assessing the thermal state of the furnace.

The technical result is achieved by additionally measuring the initial values of the furnace bath temperature, the lining temperature, the temperature under the electrodes, the metal temperature and the current melting time, then the temperature parameters are estimated from all measurement points, the average values of the furnace bath temperature, the lining, under the electrodes and metal are determined , the measured temperature values are compared with the calculated ones, while, depending on the current melting time, a correction factor is introduced, which takes into account the abrupt change in the thermophysical properties of the lining and electrodes during operation, then a control signal is sent to the drive for controlling the change in the position of the electrodes.

The method is illustrated by the following figure:

fig. 1 - diagram of the location of thermocouples (side view);

fig. 2 - layout of thermocouples (top view);

fig. 3 - electrode control algorithm;

fig. 4 is a diagram of the experimental setup;

fig. 5 is a graph of temperature changes during melting.

1 - thermocouple;

2 - electrode;

3 - electrode holder;

4 - furnace roof;

5 - furnace lining;

6 - furnace bath;

7 - oven casing;

8 - personal computer;

9 - analog-to-digital converter;

10 - stand;

11 - tripod;

12 - fireclay crucible;

13 - graphite crucible;

14 - melt;

15 - current lead;

16- electric holder;

17 - welding transformer.

The method is carried out as follows. To measure the temperature and control the thermal state of the arc furnace, thermocouples (TPP (S)) are installed at the control points. Control points are assumed on each electrode of a three-electrode plug directly under the electrode holder, between the lining and the furnace casing (at six points along the perimeter of the unit), in the hearth of the furnace (at six points opposite each electrode and between them). The arrangement of the thermocouples is shown in FIG. 1.

The melting time in the ДСП-90 furnace in this case is approximately 52 minutes. After the start of melting, the current melting time (t) is determined and the temperature is measured by the indicated thermocouples, then the data for calculation is transferred to the controller.

The program in the controller works according to the following algorithm (Fig. 3).

The formulas are used to calculate the average temperature of the electrodes (T _E ), the average temperature of the molten metal (T _M ), and the average temperature of the lining (T _F ).

The current value of the melting time is determined.

If the current value of the melting time is less than 10 minutes, then the coefficient of temperature change at the electrode (K _E ) is calculated.

Where

where P is the power used for heating, W;

- средняя удельная теплоемкость металла,

;

- the average specific heat of the metal,

;

- масса металла, кг;

- metal mass, kg;

t - current melting time, s.

The value of K _E is transmitted to the electrode regulator, then the control signal is transmitted to the drive of the electrode holder.

If the melting time is more than 10 minutes, but less than 45 minutes, then the coefficients are calculated: K _E , the coefficient of change in metal temperature (K _M ) and the coefficient of change in lining temperature (K _F ).

K _{E is} calculated by formula (4), K _M and K _F are calculated by formulas (5) and (6), respectively.

Then the total coefficient of temperature change K is calculated:

The K value is transmitted to the electrode regulator, then the control signal is transmitted to the drive of the electrode holder.

If the current value of the melting time is greater than or equal to 45 minutes, then the temperature of the steel is additionally measured when immersed in the bath of the sensor - thermocouple. E.D.S. thermocouple is converted to temperature and issued to the operator. The accuracy of the sensor is ± 3 ° С, and the accuracy of the measuring device is ± 2 ° С. The sensors are usually of the platinum / platinum-10% rhodium type and are suitable for measuring temperatures up to 1760 ° C. To measure higher temperatures (up to 1820 ° C) thermocouples such as platinum-10% rhodium / platinum-13% rhodium should be used).

Temperature should not be measured until flat bath conditions are reached or a certain amount of energy has been applied to melt. The temperature is measured manually by the operator. Then the measured temperature value (T _met1 ) is transferred to the controller. Compare T _M and T _met1 . If T _{M is} greater than T _met1 , then K _{M is} greater than 1, otherwise K _{M is} less than 1. The choice of the K _M value is made from the previously calculated K _M. The K _M value is transmitted to the electrode regulator, then the control signal is transmitted to the drive of the electrode holder.

The method is illustrated by the following example.

Example 1. As you know, the uniformity of heating the furnace and the material directly depends on the quality of the arc length control. Depending on the grade of the steel produced, to stabilize the temperature within the specified limits, it is necessary to maintain a certain electrical mode of the furnace with the specified values of current, voltage and power. It is important to consider that these values should be as consistent as possible with each other. During melting in an electric arc furnace, the length of the electric arc is constantly changing, therefore, the power of this arc and the temperature regime also change. This directly affects the temperature drops that change the thermal state of the furnace shaft and its elements and structures when heating the charge materials to melt. Product quality and the destruction of electrodes and furnace lining are directly affected by sudden heating or insufficient melting temperature.

Depending on the change in arc length, the degree of heating of the charge and melt in the furnace shaft, built-in thermocouples measure the temperature value at the control points. The current (numerical) value is transferred to the adaptive arc control system. The calculation takes into account: the initial values of the furnace bath temperature, the temperature in the furnace wall, the temperature under the electrodes, the temperature of the metal (melt). After the controller evaluates the temperature parameters from all measurement points, a control signal is sent to the drive for controlling the change in the position of the electrodes. With an abrupt change in the thermophysical properties of the lining and electrodes during operation, a correction factor is introduced so that the calculated temperature values coincide with the measured current data.

Measurement of temperature values and determination of temperature conditions during melting in an experimental setup (Fig. 3).

Two crucibles are used to simulate the furnace bath: the inner one is made of chamotte - imitates the lining, the outer one is graphite. To simulate the electrode holder, a tripod is used, on which the electrode is fixed. The electrode holder has an automatic drive, a current lead and a device that determines the distance the electrode moves, which makes it possible to control the arc length. A welding transformer is used as an alternating current source. Thermocouples are fixed on the electrode, between two crucibles around the perimeter. Temperature measurement data are sent to an analog-to-digital converter, then they are processed according to a special algorithm on a personal computer. The program controller, taking into account the correction factor, provides an electrical signal to the electrode drive.

On the basis of the experimental data, graphs of temperature changes (Fig. 4) explaining the method of controlling the parameters of the furnace were constructed.

From the presented graphs it can be seen that when the metal is heated and melted, the lining temperature changes more slowly than the metal temperature; the temperature of the electrode also changes more slowly than the temperature of the metal, that is, there is a lag. The calculated value of temperature (Tp) has large jumps compared to the value of temperature (T _M ) obtained using the proposed method for controlling the parameters of the furnace. Based on the foregoing, it can be concluded that the temperature when using this method changes smoothly, which contributes to uniform heating of the furnace lining. This helps to increase its service life.

Claims (11)

A method for controlling the parameters of arc furnaces, including controlling the thermal state of the furnace bath and the temperature of the working surface of the electrode, characterized in that the initial values of the temperature of the metal bath of the furnace, the lining temperature, the temperature under the electrodes, the metal temperature and the current melting time are measured, then the temperature parameters are estimated of all measurement points, the average values of the temperature of the metal bath of the furnace (T _m ), lining (T _f ), electrodes (T _e ) are determined, the measured temperature values are compared with the calculated ones, while, depending on the current melting time, a correction factor is used that takes into account an abrupt change in the thermophysical properties of the lining and electrodes during operation, then a control signal is supplied to the drive for controlling the change in the position of the electrodes, while, if the current value of the melting time is less than 10 min, then the coefficient (K _e ) of temperature change on the electric de:

Where

Where P is the power used for heating, W; C _m - average specific heat capacity of metal,

M _m is the mass of the metal, kg; t - current melting time, s, and change the position of the electrodes depending on the value of the coefficient K _e , if the melting time is more than 10 minutes, but less than 45 minutes, then the coefficients are calculated: K _E; the coefficient of change in the temperature of the metal bath of the furnace (K _m ) and the coefficient of change in the temperature of the lining (K _f ) and the total coefficient (K) according to the formulas:

the position of the electrodes is changed depending on the value of the coefficient K, if the current value of the melting time is greater than or equal to 45 min, then the temperature of the metal (T _met1 ) is _measured when immersed in the bath of the sensor - thermocouple, while if T _{m is} greater than T _met1 , the value of the coefficient K is set _{m is} greater than 1, and if T _{m is} less than T _met1 - the value of the coefficient K _{m is} less than 1, while the position of the electrodes is changed depending on the set coefficient K _m .

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