JPH10130716A - Method for estimating decarburizing quantity in vacuum decarburizing furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately predict decarburizing quantity by using a value deducting booster gas vol. calculated from a booster capacity and the change of pressure as an exhaust gas flow rate in the increasing rate of the exhaust gas flow rate after starting an ejector pump. SOLUTION: The shifting vol. of the gas in a vacuum evacuating system just after starting of an ejector pump is deducted from the exhaust gas integrating flowing vol. in the carburizing quantity calculation to further accurately grasp the flow rate. That is, in the curve 31 on the change with time of the exhaust gas flow rate in the figure, the gas vol. to be exhausted, is shown in the range 32. Further, the gas vol. 33 to be calculated in the decarburizing quantity calculation is the range in the shaded lines. The gas vol. to be exhausted is calculated with (the vacuum evacuating system capacity)×(the change of pressure before and after driving the booster)/(gas constant × gas temp.).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for estimating the amount of decarburization by exhaust gas analysis in a vacuum decarburization furnace.

[0002]

2. Description of the Related Art In general, there are the following methods for analyzing exhaust gas from a vacuum decarburization furnace. (A) A method of sampling gas near a furnace. JP-A-4-143210, JP-A-6-81027
There is a gas sampling technique in a place where the degree of vacuum is high (= low pressure) as provided in Japanese Patent Application Laid-Open Publication No. H10-260,086. (B) A method of sampling a gas at a position (middle) after passing through a vacuum exhaust system.

[0003] As a method for the method (a), for example, as disclosed in Japanese Patent Application Laid-Open No. 4-72121, the gas sampling position in the exhaust gas analysis method is not limited, so that the gas after passing through the vacuum exhaust equipment (middle). Methods for sampling gas at locations are also included.

[0004]

The problems of the conventional method are summarized as follows. In the above method (a),
Since the gas generated from the furnace is not sufficiently mixed and a large amount of dust is generated, stable analysis for a long time is difficult. The method (b) is suitable for long-term stable analysis because the gas mixture is sufficient and dust is greatly reduced by the bag filter, but the gas at the start of the operation of the booster (ejector pump) is used. As a result, it was difficult to obtain an accurate numerical value because the movement of the gas became a noise and the analysis value and the flow rate of the exhaust gas were measured.

An object of the present invention is to provide a method which solves the problem of the method (b).

[0006]

According to the present invention, when estimating a decarburization amount based on an exhaust gas analysis value and an exhaust gas flow rate in a vacuum decarburization furnace, the booster volume and the booster exhaust gas increase amount immediately after the operation of an ejector pump are used. An object of the present invention is to provide a method for estimating a decarburization amount in a vacuum decarburization furnace, wherein a value obtained by subtracting a booster gas volume calculated from a pressure change is used as an exhaust gas flow rate.

After the start of the booster (ejector pump), the rapid increase in the exhaust gas flow rate is not due to the actual process reaction, but the increase in the exhaust gas flow rate is calculated back from the booster (ejector pump) volume and pressure change to obtain the exhaust gas flow rate. After deducting from the integrated value, calculate the decarburization.

[0008]

FIG. 1 shows an exhaust system of a vacuum decarburization furnace to which the present invention is applied. The exhaust gas from the vacuum decarburization furnace 1 passes through an exhaust gas pipe 2, passes through a gas cooler 3, passes through a bag filter 4,
It is sucked by the booster 5. The exhaust gas passing through the booster 5 passes through the condenser 6 and the mist separator 7,
It is supplied to an afterburner 9 and is discharged as a combustion gas 10. Part of the gas supplied to the afterburner 9 is sampled from the sampling hole 8 and analyzed for gas. FIG. 2 shows a VOD degassing apparatus 1 as a vacuum decarburization furnace 1.
In this example, acid is fed from the lance 11 and the molten steel is deoxidized in a decarburizing furnace by the reaction formula of C + (1/2) O ₂ = CO CO + (1/2) O ₂ = CO ₂ . Try to decarburize. In the exhaust gas pipe 2,
The generated CO and CO ₂ are discharged, analyzed by the mass spectrometer 13 through the gas analysis pipe 8, and calculated by the high-speed computer 14 and the arithmetic unit 15. FIG. 3 shows a vacuum decarburization furnace 1 with R
In the apparatus using the H apparatus, CO and CO _{2 which} are sent from the lance 21 and produced by the reaction in the apparatus are discharged, and analyzed by the mass spectrometer 13 through the gas analysis pipe 8 as in FIG. The calculation is performed by the high-speed computer 14 and the calculation device 15.

The flow rate of the gas in the vacuum exhaust system immediately after the operation of the booster 5 (ejector pump) is subtracted from the integrated flow rate of the exhaust gas in the calculation of the decarburization amount, so that the flow rate can be grasped more accurately. The booster (ejector pump) moving gas elimination processing is shown below. Q _total = V × _Δt -Q _bst Q _total : integrated exhaust gas flow V: exhaust gas flow Δ _t : integrated cycle Q _bst : booster moving gas Q _bst = {V _vac × (P _st -P _end )} / RT V _vac : Vacuum exhaust system volume P _st -P _end : Pressure change before and after the booster movement R: Gas constant T: Gas temperature The results above are schematically shown in FIG. FIG. 4 shows the change over time of the exhaust gas flow rate with a flow rate curve 31. The amount of gas to be deleted is indicated by a region 32 and corresponds to the above Q _bst , and the gas amount 33 included in the decarburization amount calculation is a hatched region, which is the above Q _total .

[0010]

According to the present invention, the amount of decarburization in steel is accurately predicted by filtering a sudden increase in the flow rate of exhaust gas when the booster (ejector pump) of the vacuum exhaust system operates so as not to be included in the decarburization calculation. And the prediction of the amount of [C] in the steel became accurate.

[Brief description of the drawings]

FIG. 1 is a diagram of an evacuation system.

FIG. 2 is a flow sheet of a system for performing decarburization calculation according to the embodiment.

FIG. 3 is a flow sheet of a system for performing decarburization calculation according to the embodiment.

FIG. 4 is a schematic chart showing a flow rate calculation example of a decarburization calculation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum decarburization furnace 2 Exhaust gas pipe 3 Gas cooler 4 Bag filter 5 Booster 6 Capacitor 7 Mist separator 8 Sampling hole (Gas analysis pipe) 9 Afterburner 10 Combustion gas 11 Lance 12 VOD degassing device 13 Mass spectrometer 14 High-speed calculator 15 Calculation Device 21 Lance 22 RH device 31 Flow rate curve 32 Gas volume region to be deleted 33 Gas volume included in decarburization calculation

Claims (1)

[Claims] When estimating a decarburization amount based on an exhaust gas analysis value and an exhaust gas flow rate in a vacuum decarburization furnace, a booster gas calculated from a booster volume and a pressure change in an increase in the exhaust gas flow rate immediately after the operation of an ejector pump. A method for estimating a decarburization amount in a vacuum decarburization furnace, wherein a value obtained by subtracting a volume is used as an exhaust gas flow rate.