JPS6151606B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a series of blowing gas switching operations in the operational status of the production of metals, in particular steel, by bottom blowing in converters equipped with at least one gas blowing tuyere at the bottom. This invention relates to a blowing control method.

The refining gas injection process in the bottom-blowing or top-blowing converter steelmaking process is usually divided into charging, refining, sampling, and tucking stages, and the amount of gas to be injected through the tuyere is determined according to each stage. It is necessary to switch types. For example, during the refining period when the converter is upright, oxygen is injected into the molten steel inside the converter through the tuyere, but once the refining period is over, the oxygen is switched to nitrogen or argon and the converter is tilted for sampling. or tapping and switching to low pressure nitrogen or argon during this sampling or tapping.

By the way, in converter operation, it is necessary to always ensure a gas flow rate greater than a specified value in order to prevent molten steel from being inserted into the bottom blowing tuyere. Therefore, when switching gases, it is confirmed that the flow rate in the supply pipe of the gas to be newly switched (referred to as trailing gas) is equal to or higher than the specified value, and then the gas that is currently being blown in (referred to as leading gas) It is common to cut off the supply of

Although such a flow rate control method by checking the trailing gas flow rate is effective in preventing molten steel from being inserted into the tuyere, the tuyere tip may undergo exothermic or endothermic reactions depending on the type of blown gas and violent flow of molten steel. The flow rate of the trailing gas may not be confirmed due to phenomena such as rapid growth, shrinkage, or falling off of the deposited metal called pine room, and fluctuations in the gas source pressure. In such a case, it is necessary to control the gas supply by setting the opening degree of the flow rate control valve and checking the opening degree.

The present invention provides a method for controlling the supply of bottom-blown gas during converter operation by setting the opening degree of a flow rate control valve.

The concept of setting the opening degree of the flow control valve in the present invention will be explained with reference to FIG. In the figure, 1 is a converter, 2 is molten steel, 3 is a tuyere nozzle, 4 is an A gas source,
4' is a B gas source, 5 is an A gas system conduit, 5' is a B gas system conduit, 6, 6' are gas source pressure gauges, 7, 7' are flow meters, 8, 8' are flow rate control valves, 9, 9' is a shutoff valve.

Here, it is assumed that the gas blown into the molten steel 2 of the converter 1 from the tuyere nozzle 3 has been switched from A gas to B gas. The discharge pressure P ₀ of the tuyere nozzle 3 must be a pressure that supports the head of the molten steel 2 in order to prevent the molten steel from being inserted into the tuyere nozzle 3.
Therefore, ΔP ₂ is the tuyere brick pressure loss, ΔP ₃ is the pipe pressure loss,
If ΔP ₄ is the pressure loss of the flow control valve 8', the overall pressure balance with the original pressure P ₂ of B gas is as shown in the following equation.

P ₂ =P ₀ +ΔP ₂ +ΔP ₃ +ΔP _4The B gas flow rate in this case is defined as the flow rate to obtain the discharge pressure P ₀ from the theoretical formula for the tapered nozzle.

In the above equation, under constant operating conditions, the tuyere nozzle discharge pressure P ₀ and the piping pressure drop ΔP ₃ are constant. However, the pressure drop ΔP ₂ of the tuyere brick decreases with wear due to the increase in the number of operations, and the gas source pressure P ₂
varies depending on usage at other factories. Therefore, in order to keep the nozzle discharge pressure P ₀ constant, these fluctuations can be compensated for by the flow rate control valve pressure loss ΔP ₄ that can be adjusted by the valve opening degree.

Therefore, the flow rate control valve pressure drop ΔP ₄ is ΔP ₄ =P ₂ −P ₀ −ΔP ₂ −ΔP ₃ , that is, ΔP ₄ =P ₂
−ΔP ₂ −C, and it is possible to set the opening degree of the flow rate control valve that can obtain a stable discharge pressure P ₀ even if the gas source pressure P ₂ fluctuates or the tuyere nozzle brick wears out. can.

Therefore, in actual operation, the opening degree of the flow rate control valve is set as follows.

Tuyere pressure loss according to each operating status of the converter,
The number of furnace operations and other furnace operation information are maintained in a table as shown in Figure 2 A, and the tuyere pressure drop ΔPy ₀ , which is approximated by a five-fold line, includes the piping pressure drop ΔP ₃ and the discharge pressure P ₀ (Figure 2 I). Reference) Can be set arbitrarily.

To set the opening degree of the flow control valve, subtract the tuyere pressure drop ΔPy ₀ obtained from the table from the gas source pressure at each time to obtain the flow control valve pressure drop ΔP ₄ , and from this, calculate the Cv value of the flow control valve, that is, the valve flow coefficient. Calculate and set the specified opening of the relevant flow control valve.

In this case, the gas flow rate is set to each specified discharge pressure flow rate, and when the number n of tuyeres decreases by X due to tuyere tightening, the Cv value is calculated by multiplying the flow rate value by n-X/n. The number of furnaces is constant after a certain number (after N×5 in Fig. 2A).

The third control flow for implementing the method of the present invention
As shown in the figure. Amount of wear and tear on tuyere nozzles, number of tuyere used depending on operational status, type of tuyere, gas flow rate,
Based on the type of gas used, extract the corresponding tuyere pressure loss value ΔPy ₀ from a pre-calculated table, and calculate the Cv value of the flow rate control valve using the following formula from the gas source pressure and gas flow rate.

Here, Q: Gas flow rate (target gas discharge flow rate from the tuyere nozzle) G: Gas specific gravity P ₁ : Pressure before flow rate control valve (≒ original pressure) P ₂ : Post pressure ∆P: P ₁ − P ₂ t: Gas Temperature The specified opening degree of the flow rate control valve is calculated and set by functional calculation from the thus obtained flow rate control valve Cv value.

An embodiment of the present invention will be described based on FIG.

(A) When operating in a new furnace first, the gas source pressure is P _1-1
(lower limit of operation), and assuming that the tuyere pressure loss Py ₀ is P _2-1 , the flow rate control valve pressure loss ΔP ₄ is determined from a table prepared in advance. Since this ΔP ₄ is less than P _1-1 /2, the Cv value is calculated according to Equation 1, and the valve opening corresponding to the Cv value is the valve Cv value calculated in advance by a function calculation - the valve opening. It can be found from the graph of

(B) Next _, at the end of the furnace operation (after the _number of furnace operations N ΔP ₄ is similarly determined from the table. Δ at this time
Since P ₄ is greater than or equal to P _2-1 /2, the Cv value is calculated according to Equation 2, and the valve opening degree corresponding to this value is determined in the same manner as above.

As described above, according to the present invention, when it is difficult to confirm the blown gas flow rate when supplying gas such as when switching to bottom blowing gas during converter operation, an appropriate flow rate can be determined by setting the valve opening of the flow rate control valve. Since it can be carried out, it is possible to reduce the yield due to molten steel being inserted into the tuyere due to insufficient discharge pressure, tuyere nozzle blockage due to pine room generated by overcooling of the tuyere tip due to excessive discharge pressure, or scattering of molten steel. This has the remarkable effect of avoiding wasteful consumption of expensive gases such as Ar and the like.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the pressure balance in the gas supply system of the bottom blowing tuyere, and Figure 2 A is an example of a chart of tuyere pressure loss created for each furnace number and other operation information corresponding to each operation status. Figure 2B is an example of a chart of the flow rate equivalent to the specified discharge pressure for each type of tuyere and gas type, and Figure 3 is a diagram showing the control flow of the present invention.
FIG. 4 is an explanatory diagram of an embodiment of the present invention.

Claims (1)

[Claims] 1. When controlling the gas supply during converter operation, such as switching the blown gas to the bottom blowing tuyeres, by controlling the opening of the flow control valve, the tuyere pressure drop ΔPy ₀ corresponding to each operation status is determined in advance for each number of furnace operations. Calculate it in advance and subtract the tuyere pressure drop ΔPy ₀ from the gas source pressure P ₂ each time to obtain the flow rate control valve pressure drop ΔP _4. From this, calculate the Cv value (valve flow coefficient) of the flow rate control valve and adjust the flow rate. A method for controlling bottom-blown gas injection into a converter, characterized in that the opening degree of the valve is set to a specified opening degree based on the Cv value.