JPH02153017A - Method for controlling composition of atmosphere gas in furnace - Google Patents

Abstract

PURPOSE:To easily and surely control the compsn. of the atmosphere gas in a furnace by calculating the deviation value of a carbon potential factor in accordance with the analysis values of the gas in the furnace and correcting the value, the regulating the flow rate of the supply gas. CONSTITUTION:The gaseous RX to increase the carbon potential factor(PF) and the gaseous NX to lower this factor are supplied at supply flow rates mu1, mu2 respectively via gas flow rate regulating means 6, 13 to the treating furnace 1 using the atmosphere gas where steel products 8 are treated by the PF of the prescribed target value. The atmosphere gas of the above-mentioned furnace 1 is analyzed by an analyzer 2 by which the CO concn. x1 and the CO2 concn. x2 are detected. From the x1, to x2, PF=x /x2 is calculated in a computing element 3. The deviation PF between this measured value and the set value is determined by a PI integrating meter. Further, the relations between PF and mu1, mu2 are calculated in a computing element 11 and the gas flow rate command signals are outputted to the above-mentioned gas flow rate regulating means 6, 13 so as to satisfy the above-mentioned relations. The PF in the furnace 1 is surely controlled in this way by which the desired compsn. of the atmosphere gas is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for controlling the composition of atmospheric gas in a furnace for atmospheric heat treatment of steel materials to a desired carbon potential.

[Prior Art] In an atmospheric heat treatment furnace for heat treating steel materials, etc., the composition of the atmosphere gas in the furnace is determined by calculating the square of the CO concentration, which is generally referred to as the carbon potential factor (hereinafter referred to as PF).
This is done by controlling the amount of endothermic atmospheric gas or exothermic atmospheric gas supplied into the furnace so that the value divided by two concentrations matches a predetermined target value. That is, for example, as shown in FIG.
The CO concentration x1 and CO2O2 concentration x2 are detected, and from this the carbon potential factor PF (=χ
i/χ2) is calculated by the PF calculator 3, and a proportional term and an integral term are used as adjustment elements in order to eliminate the deviation ΔPF between this PF measurement value and the PF target value preset in the PF pattern setting device 4. An opening command signal is sent to the gas amount adjusting means (valve) 6 via the PI controller 5 to adjust the amount of endothermic atmosphere gas generated by the gas generator 7 into the Class 1 interior. There is. In the figure, 8 indicates a steel material within Class 1, 9 indicates an atmospheric gas stirring fan within Class 1, and 10 indicates an atmospheric gas discharge port.

[Problems with the Prior Art] However, in the conventional PF control system described above, when a certain amount of endothermic atmospheric gas is supplied into Class 1, the increase in carbon potential factor PF, that is, the gain, is the CO concentration within Class 1 at that time. And since it varies greatly depending on the CO2 concentration, no matter how you select the proportional band Kp and integral time T1 of the PI controller 5, it is impossible to command an appropriate gas supply amount at any given time.
For this reason, the carbon potential factor PF in the furnace remains significantly different from its target value even after a long period of time, or the control becomes oversensitive and the carbon potential factor PF in the furnace greatly hunts, resulting in the steel material in the furnace being damaged. There was a risk that the desired heat treatment could not be achieved due to unnecessary decarburization or carburization.

[Purpose of the Invention] Accordingly, the present invention provides a method for controlling the composition of a furnace atmosphere gas, which makes it easier and more reliable to control the carbon potential factor PF, and maintains the desired furnace atmosphere gas composition, thereby enabling high-quality heat treatment. That is.

[Means for achieving the object] In order to achieve the above object, the present invention provides an endothermic atmospheric gas (
A gas having a property of increasing the carbon potential factor) and an exothermic atmospheric gas (a gas having a property of decreasing the carbon potential factor) are each supplied into the furnace through a gas amount adjustment means, and the endothermic atmospheric gas is supplied. The atmosphere inside the furnace is controlled to a predetermined target value of carbon potential factor PF (the value obtained by dividing the square of the C0 concentration by the CO□ concentration) by adjusting the amount U and the supply amount U2 of exothermic atmosphere gas. In a gas heat treatment furnace, the CO concentration x1 and CO2 concentration χ2 in the furnace are detected at every predetermined sampling time Δ, and the CO concentration χ4. The measured value of the carbon potential factor PF in the furnace is calculated from the CO□ concentration χ2, and the deviation ΔPF between the target value and the measured value of the carbon potential factor PF is calculated by incorporating the CO concentration x1 and CO2'a degrees χ2 as calculation elements. The present invention is characterized in that a relational expression between and the supply amount Uk+u2 is calculated, and a gas amount command signal is output to the gas amount adjusting means so as to satisfy the relational expression.

[Operation] CO in the furnace atmosphere gas every predetermined sampling time Δ
A relational expression is calculated in which J degree χ1 and CO, and fA degree χ2 are incorporated as calculation elements, and the supply amount u4. By commanding the supply amount u2, it is possible to always command a suitable supply amount U and supply amount u2.

[Example] Next, an embodiment of the present invention will be described with reference to FIG.

In the figure, 1, 1 is a furnace, 2 is a gas analyzer, 3 is a PF calculator, 4 is a PF pattern setter, 5 is a PI controller, 6 is a gas amount adjustment means (valve), and 7 is an endothermic layer atmosphere gas ( 8 is a steel material, 9 is a fan for stirring the furnace atmosphere gas, and 10 is a furnace atmosphere gas discharge port, which has a carbon potential factor PF similar to the conventional example explained according to FIG. 3. The deviation ΔPF between the target value and the measured value is calculated. The RX gas generated by the gas generator 7 is supplied to the furnace 1 after its supply amount is adjusted by the gas amount adjusting means 6. Further, 12 is a gas generator for exothermic atmospheric gas (hereinafter referred to as NX gas), and 13 is a gas amount that adjusts the supply amount u2 of NX gas generated by the gas generator 12 to the furnace 1 by rA! l! ! It is a regulating means (valve).

An example of the components of the atmospheric gas generated by the gas generator 7 and the gas generator 12 is as follows.

RX gas component Co; 24.1 to 23.3% N2; 31.6 to 30.3% Co2; 0.2 to 0.5% N2; remaining NX gas component CO; 1 to 4% N2: 0.5 〜3% CO
The gas amount adjusting means 6. uses the relational expression calculator 11 to adjust the gas supply amount u2 according to the deviation ΔPF so that the following relational expression is satisfied. The gas amount adjustment means 13 is caused to issue a gas amount command signal, and the relational expression thereof is determined as follows.

First, define each character necessary to find the relational expression.

U; Rx gas supply amount [27 minutes]〉O u,; NX gas supply amount [I/min]〉0 χ; CO concentration of furnace atmosphere gas [VOL%] χ2; CO2 concentration of furnace atmosphere gas [VOL%] V; Furnace internal volume (
Note that the exhaust volume from this furnace with a constant volume is U + u2.

Furthermore, when we assume that after RX gas is supplied into the lrn' reactor and the chemical changes within the furnace are balanced, the amount of CO increases by volume by g/100. It will be called "rate".

Similarly, “contribution rate from RX gas to C02a degrees” is gzL
Let ``contribution rate from NX gas to CO concentration'' be g 2 and ``contribution rate from NX gas to CO□ concentration'' be iz2. Note that when no chemical change occurs, these are equal to the CO and CO□ concentrations of each gas. Here g ts + g
The unit of iz v g zz + g 22 is VOL%.

Now, the concentrations χ and χ2 in the furnace 1 are detected at every predetermined sampling time Δ, and the amount of CO in the furnace that increases due to the atmospheric gas supplied to the furnace in time Δ is expressed by the following equation. expressed.

1'-(ul・Δt) 100% (u,・Δt)
(1) In addition, the amount of CO lost from the furnace 1 due to the exhaust gas from the atmospheric gas outlet 10 is determined by Δ=(U+t+z)・Δt(2 ) The increase in the amount of CO in the furnace 1 is V...and 5 - V equivalent = V = Equation (3) = Equation (1) - (2)... (4) Similarly, regarding CO2H... ( 5) It is expressed as Differentiating the above equation (6) and approximately finding the deviation ΔPF, ...(7) ΔPF=2-"-"Δχ, -(-)"・Δχ2
(8) χ2 χ2 On the other hand, by rearranging equations (4) and (5) and combining them with U + u, the following equation is derived.

d Z x = L22・u, +−2, u, (9
)dt V VdZ2
=E≦LL,u, +LL2mu,u, (1
o) dt V VHere, to simplify the formula, make the following substitutionsC4=2-
, C2=(Work”)'χ1 χ2 χ2 c,=raL2LL, (4=g-7v
v c,=raL2ri1,CG=raL2Zi (11
)■ v When formulas (9) and (10) are written in differential form, Δχ, = C1・
ul・Δt+C4・u2・Δt (12)Δχ2
=Cs-u□・Δt+C6・u2・Δt (1,
3) Also, formula (8) is ΔPF=C・Δχ1−C2・ΔχZ (
t4), so by substituting equation (12) and (13) into equation (14), ΔPF=(C,,・C−,−C,・C,)
・ul・Δt+(CL'C4Cz'Cs)'u2'Δt
(15) From equation (15), air pressure = (Cz'C3-Cz''C5)uxΔt + (C, -C, -C, -Cs)u2 (16).U work v u in equation (16) , coefficients C1 to C
5 is the concentration χ4.5 as defined in equation (11). It is a function of concentration χ2. In this way, the deviation ΔPF is the concentration χ11a degrees χ2
is expressed as a function of the supply amount "11" and the supply amount u2 by the relational expression (16) in which "11" is inserted as a calculation element.For the concentration χ1, the concentration χ2 inputs the value Δ detected every time.In this way, ( 16) Equation has two variables U.

Since it has u2, the actual supply amount ux + supply amount u
To command 2, either the supply amount U or the supply amount u
A possible method is to set 2 as a constant value and control the other according to the deviation ΔPF. Alternatively, one supply amount tlL or ul may be changed in several stages, and the other supply amount may be adjusted steplessly so that equation (16) is always satisfied. For example, the supply amount u2 may be changed to 0.5. 10.15Nrn"/h and adjust the supply amount U according to the 8 PF. At that time, even if the supply amount U reaches the maximum, if the Bonn potential factor PF does not rise to the specified value, u2 = PF may be increased by setting it to 0.Also, even if U is set to 0 when decreasing the carbon potential factor PF, u2 may be increased if PF does not decrease yet.

Based on the above deviation ΔPF, RX gas supply 1u, NX
The gas supply amount u2 can be calculated.

In the embodiment shown in FIG. 1, the RX gas generator 7 and the N
Each is equipped with a gas generator 12 for X gas,
If two gases with different gas supply capacities are provided, for example, as shown in Fig. 2, the supply capacity is 25N rd/h.
(7) RX gas generator 14 tons, supply capacity cuff 5Nrrr
/h RX gas generator 15 and supply capacity 5Nrri'/
h NX gas generator 16 and supply capacity 1ONrn'/h
If two NX gas generators 17 are provided, one of them may be used preferentially.

[Effects of the Invention] A relational expression incorporating the concentration χ and the concentration χ2 as calculation elements is calculated, and a gas amount command signal is issued to the gas amount adjustment means in accordance with the deviation ΔPF so that this relational expression is always satisfied. Therefore, the gas supply amount uL commanded by this
lu2 is always an appropriate value to eliminate the deviation ΔPF between the target value and the measured value of the carbon potential factor PF, and the carbon potential of the furnace atmosphere gas can always be maintained at an appropriate value with high reliability. Therefore, the material to be treated such as steel in the furnace can always be heat-treated at an appropriate carbon potential, which has the beneficial effect of improving its quality.

[Brief explanation of the drawing]

Fig. 1 is a control system diagram showing one embodiment of the furnace atmosphere gas composition control method of the present invention, Fig. 2 is a diagram showing another embodiment of the atmospheric gas supply system, and Fig. 3 is a diagram showing a conventional furnace atmosphere gas composition control method. FIG. 3 is a control system diagram of an internal atmosphere gas composition control method. DESCRIPTION OF SYMBOLS 1...Furnace, 2...Gas analyzer, 3...PF calculator, 4...PF pattern setter, 5...PItJR moderator, 6...Gas amount adjustment means, 7... ... Endothermic layer atmosphere gas generator, 8... Steel material, 11... Relational expression calculator, 1
2... Exothermic atmosphere gas generator, 13... Gas amount adjustment means.

Claims (1)

[Claims] Carbon potential factor (the square of the CO concentration is C
A gas that has the property of increasing the carbon potential factor (value divided by the O_2 concentration) and a gas that has the property of reducing the carbon potential factor are each supplied into the furnace through the gas amount adjustment means, and the gas has the property of increasing the carbon potential factor. Gas supply amount u_1 and gas supply amount u_2 with the property of lowering
In a processing furnace using atmospheric gas, in which the inside of the furnace is controlled to a predetermined target value of carbon potential factor by adjusting the
Calculating the measured value of carbon potential factor PF in the furnace from O concentration x_1 and CO_2 concentration x_2,
By incorporating the CO concentration x_1 and CO_2 concentration x_2 as calculation elements, the deviation ΔPF between the target value and the measured value of the carbon potential factor PF and the supply amounts u_1, u_2 are calculated.
A method for controlling an atmosphere gas composition in a furnace, characterized in that a relational expression is calculated between the above and a gas amount command signal is outputted to the gas amount adjusting means so as to satisfy the relational expression.