JPS58136730A - Blowing gas control device for reflux type vacuum degassing device - Google Patents

Abstract

PURPOSE:To maintain the reflux velocity of molten steel constant and to prevent the decrease in the degassing and refining speed of the molten steel by detecting the flow rates of the gases in plural inert gas blow pipes provided to a suction pipe of the vacuum vessel in a reflux type vacuum degassing device and controlling the total flow rate of the gases constant at all times. CONSTITUTION:The flow rates of gases in plural inert gas blow pipes 22a-22e provided to a molten steel suction pipe 16 of the vacuum vessel in a reflux type vacuum degassing device for molten steel are detected with respective flow rate sensors 28a-28e. The detected signals SFa-SFe are outputted to flow rate controllers 32a-32e, which compare the same with the target set flow rate SC from a main controller 34, and output the driving signals SDa-SDe for regulating the openings of flow rate control valves 30a-30e to the valves 30a-30e to control the flow rates of the gases of the respective pipes 22a-22e so as to make the differences therebetween zero. The total flow rate of the gases is operated with an adder 36, and the signal ST thereof is outputted through a delay element 38 to the main controller 34, so that the total flow rate is controlled similarly to a target total flow rate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a blown gas control device for a recirculation type vacuum degassing device, and in particular, to make gas blown in from a plurality of inlets into an equal flow rate, and to prevent some of the inlets from becoming clogged due to clogging. This invention relates to a blowing gas control device that keeps the total flow rate of blowing gas constant even if the flow rate of the blowing gas decreases.

A vacuum tank, a suction pipe and a discharge pipe that communicate with the vacuum tank and are immersed in molten steel, and a plurality of blowing pipes connected to a plurality of blowing ports provided in the suction pipe, In a circulation type vacuum degassing device that circulates molten steel in a vacuum chamber by blowing inert gas into the suction pipe from a blowing pipe and degasses the molten steel, the circulation speed of the molten steel is determined by the degassing efficiency and In order to maintain product quality, the amount of gas blown into the suction pipe is kept constant to maintain a predetermined constant speed. In order to prevent a decrease in the service life of the gas, it is desired that the amount of gas blown in from each inlet be as equal as possible.

To deal with this, each of the above-mentioned blowing pipes is provided with a flow rate control valve and a flow rate detector, and the target flow rate of each blowing pipe is set in advance by equally dividing the gas flow rate necessary for blowing into the suction pipe. A blowing gas control device has been proposed that drives a flow rate control valve based on the actual gas flow rate detected by a flow rate detector, and controls the gas flow rate of each blowing pipe to match its target flow rate.

However, according to such a conventional blown gas control device,
If a blockage occurs in one of the blowing pipes and the operation amount (opening degree) of the flow rate control valve of that blowing pipe reaches 100% and exceeds the controllable range, the other blowing pipes are set in advance. Since the flowmeter is controlled by a target flow meter, there is a problem that the total gas flow rate blown into one suction pipe is insufficient. In other words, clogging is likely to occur near the injection port due to the adhesion of foreign substances such as solidified steel and iron oxide, and if the total gas flow rate is insufficient due to clogging, the velocity of one flow of molten steel decreases and the work time is reduced for a certain period of time. Since sufficient degassing cannot be obtained within the tank, product quality may deteriorate.

The present invention was made against the background of the following two circumstances, and its purpose is to maintain a constant total gas flow rate blown into the suction pipe even if a blockage occurs in the blowing pipe. It is an object of the present invention to provide a blowing gas control device for a recirculation type vacuum degassing device in which the amount of gas blown through other blowing pipes without clogging is evenly controlled.

In order to achieve such an object, the present invention provides a vacuum tank, a suction pipe connected to the vacuum tank and immersed in molten steel, and a discharge pipe, and a plurality of blowing pipes provided in the suction pipe. and a plurality of blowing pipes each connected to the suction pipe.
A blowing gas control device for a circulation type vacuum degassing device that circulates molten steel into the vacuum chamber by blowing an inert gas into two pipes, the flow rate of each gas flowing into the blowing pipes and a flow rate detection device that detects the total gas flow rate of the blowing pipes and outputs a pipe flow rate signal representing the pipe flow rate and a total flow rate signal representing the total gas flow rate; , a flow rate control valve that adjusts the flow rate of gas flowing into the blowing pipe, and a flow rate control valve that compares each pipe flow rate represented by the pipe flow rate signal with a common target value so that the difference between them becomes zero. a first control means for driving the flow rate control valve to make the gas flow rate of each of the blowing pipes match the target value; and a second control means for determining the target value so that the difference between them becomes zero, and for adjusting the amount of gas blown into the suction pipe to match the constant value. , characterized by including.

In this way, the target value is determined so that the difference between the total gas flow rate and a predetermined constant value is zero, and the gas flow meter of each blowing pipe line matches the common target value. Therefore, even if some of the plurality of blowing pipes become clogged, the target value of the other blowing pipes will be raised so that the total gas flow rate will match a predetermined constant value. As a result, the total gas flow rate is maintained constant, and the gas flow meters in the other blow lines are equally controlled.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below based on the drawings.

In FIG. 1, a vacuum tank 10 is formed with a pumping pipe 16 and a discharge pipe 18 that communicate with the vacuum tank IO and are immersed in the molten steel 14 in the ladle 12. The inside of the vacuum chamber 10 is evacuated by an exhaust device that does not require a vacuum pump.

In addition, 19 is a refractory material used as an inner lining.

A plurality of blowing pipes 20a to 200 are connected to the suction pipe 16, and when inert gas is blown into the suction pipe 16 through the blowing pipes 20a to 20e, the molten steel 14 is The gas rises in the suction pipe 16 and enters the vacuum chamber 10, and is returned to the ladle 12 through the discharge pipe 6-18 for circulation. In such a reflux process, the vacuum chamber 1
The molten steel 14 exposed to the atmosphere is degassed, and the reflux rate is set at a desired constant value in order to maintain degassing efficiency, product quality, etc. In other words, if the reflux rate is too high, it not only causes consumption of the refractories used for lining the vacuum chamber 10, etc., but also is unfavorable for degassing reactions, while if the reflux rate is too low, it takes time for the degassing process. This results in a decrease in degassing efficiency.

As shown in detail in FIG. 2, five inlets 22a to 22e are provided at equal angular intervals on the peripheral wall of the two suction pipes 16, and these inlets 22a to 22(! and inert gas A blowing pipe 20) is connected to the header 24 to which the
20C to 20C are connected. Flow rate sensors 28a to 28e that detect the flow rate of the inert gas and flow rate control valves 30a to 30e that adjust the flow rate are inserted into the blowing pipes 20a to 20e, respectively.

Flow rate sensors 28 In to 28 (l) detect the gas flow rate by an orifice or the like, and send pipe current signals SFa to SFe, which are analog electric signals representing the gas flow rate, to flow rate adjustment sensors 32a to 82Q, respectively. The flow rate controllers 828 to 3 which are the first control means
Reference numeral 2c is a so-called cascade type controller, which compares a target value represented by a target signal SC supplied from a main controller 34 to be described later with an actual gas flow meter represented by pipe flow rate signals SFa to SFt. , a drive signal S that changes the opening degree of the flow rate regulating valves 30a to 3oe so that the difference between them becomes zero.
, D a to SDe are connected to the flow rate control valves 3 oa to 3.
Output each to 0e. Flow control valve Boa to 80e
is equipped with an actuator such as a diaphragm or an electric motor, and changes the valve opening according to the supplied drive signals SDa to SDe.

Said line flow signals 8Fa to 8F O are also supplied to an adder 36, and their signals S , F a to 8 F 1
! (current signal or voltage signal) are added together to provide a total flow signal ST representing the total gas flow rate from adder 36 via delay element 38 to master controller 34 . Therefore, the flow rate sensors 28a to 28e and the adder "i86" constitute a flow rate detection device that detects the flow rate of gas flowing into the blowing lines 20& to 20e and the total gas flow rate.

In the main controller 34 which is the second control means, the suction pipe 6
A desired constant value M of gas flow rate to be blown into the gas chamber is set in advance, and the actual total gas flow rate X represented by the total flow rate signal 8T is compared with the constant value M, and the difference between them becomes zero. The target signal SC is determined as follows. For example, assuming that the total gas flow rate is X, the target value A, which is the content of the target signal SC, is controlled by the following equation.

Here, K is the gain, E is the deviation (M-X), and Ti is the integration time. In this way, the main controller 34 and the flow controller 8
2a to 82B constitute a control device that controls the total gas flow rate sucked into the suction pipe 16 to a constant value, and uniformly controls the gas flow rate of each of the blowing pipes 20a to 20e. It is.

Note that the delay element 38 has a transmission time @ G (s) of 1/
(1-1-T8), and its time constant T is appropriately determined based on the response characteristics of the control system in order to stabilize the control system.

The operation of this embodiment will be explained below.

When there is little foreign matter adhering to the suction ports 22) 1 to 22(), each of the current control valves 301L to 30e adjusts the driving values SDa to S from the flow rate controllers 8211 to 32e.
Adjust the gas flow rate according to the DO and each blowing line 2
The gas flow rate from 0a to 200 is made to match the target value A. This target value A is determined by the main controller 34 according to equation (1), and the flow rate of each blowing line 20 & to 20e is controlled to the target value without clogging -1
- In the case described above, the deviation E is usually almost zero. For example, if the predetermined constant value M to be blown into the suction pipe 16 is lo o o N g/min, then the target value A (
1) Therefore, 2 Q Q N l / +nin is obtained, and each flow rate adjustment word 32+1 to 32()10- performs constant value control according to the target signal SC representing the value, and the total amount blown into the suction pipe 16 is The gas flow rate is 100ONe/min.

Next, as the adhesion of foreign substances such as iron oxide progresses in the suction I'm 22a to 22e, for example, the blowing pipe 20
If +L is clogged and the gas flow rate falls below the target value A even if the flow rate control valve 80a is fully opened,
The total gas flow rate X will begin to decrease. However, since the target value A is automatically increased by the 1mm controller 34, the total gas flow rate blown into the suction pipe 16 is maintained constant regardless of the decrease in the flow rate of some of the blowing pipes 2Qa. It will be done.

That is, for example, if the total gas flow rate X represented by the total flow rate signal ST is 900 Nl/rnin, the target value A is set to 222 in the main adjustment 34 according to equation (1).
5 Nl/min. For this reason, the gas flow rate of the other blowing pipes 20j) to 20(u) is 225N/2, respectively.
! /min, so the total gas flow rate blown into the suction pipe 16 is 1000 Nl/min.

As described above, according to this embodiment, the total gas flow rate blown into the two suction pipes 16 is set to a predetermined value of 9 (preferably constant value M
The target value A is determined so that each blowing pipe 20 I
Since the flow rate of the pipes L to 20 is controlled to match the common 11 standard value A, even if a part of the blowing pipe 20 is clogged, the flow rate is low due to the blockage. The target value A is determined so that the flow rate [1 Since a constant flow rate of molten steel can be obtained in the suction pipe 16 regardless of clogging, a constant degassing effect can always be obtained and product quality can be maintained at a high level.
The maintenance cycle against blockage can be extended. Moreover, the blowing pipes 20+1 to 201! Since the pipes that have not yet been clogged are controlled to have a uniform current flow according to the common target value A, the height of the molten steel splashing into the vacuum chamber IO increases due to the concentration of the blown gas in the specific pipes, and the vacuum This prevents the part of the refractory 19 at the top of the tank 10 from being eroded and damaged.

Next, another embodiment of the present invention will be described. Incidentally, the same reference numerals are given to the parts common to those of the above-mentioned embodiment, and the explanation thereof will be omitted.

In the exemplary embodiments described above, the adjustment device enclosed by the dash-dot line in FIG. 2 is also constituted by a so-called digital computer. That is, in FIG. 3, the pipe flow signals SFa to S li'
It is supplied to boat 42.

The T10 boat 42 sends these signals 8Fa to SFe to the CPU 44. RAM46, R.O.
Supply to M48. The CPU 44 processes the signals 8Fa to SFe according to the control program stored in advance in the ROM 48 while utilizing the storage function of the ELAM 46, determines the total gas flow rate and the target value A, and also uses the drive signal 8Da.
8De is calculated and supplied to the flow rate control valves 30a to 30e via the T10 boat 42 and the A/D humbator 40, respectively.

That is, as shown in the flowchart of FIG.
When the control program is started by a start signal 13- (not shown), the pipe flow signals 8Fa to S Fe are read in step sl.

Next, in step S2, the signals SF1 to SFe are added to calculate the total gas flow rate, and
Based on the pre-stored constant value M and its total gas flow iX, for example, from the above equation (1), the total gas flow rate X is a constant value M
Calculate a target value A that matches. Steps sl and S2 below-H are the second control means.

Next, steps S3 to S6 are executed, and the new target value Af is updated after a certain time T in order to stabilize the control system, and the blowing pipe 2
Control is performed to keep the gas flow rates of B to 20e constant.

That is, in step S3, interrupts are permitted, and in step S4, the control program is made inactive for a certain period of time T. In step S5, after a certain period of time T, interrupts are not permitted, and then in step S6, the control program determined in step S2 is new 11 target price A
New target values will be set for the prefecture. Then, between step 14-S3 and 85, an interrupt routine, which is the first control means shown in FIG.
The gas flow rates of 0& to 2(l) are controlled. The interrupt routine is configured by a similar control subroutine for each of the blowing lines 20& to 20C being continued in steps 881 to 885. The control routine S81 of 20a is constructed as shown in FIG.

That is, first, step SB1 is executed to read the actual gas flow rate represented by the pipe flow wheel signal SFa, and step SB2 is executed to read the actual gas flow rate represented by the pipe flow wheel signal SFa.
The gas flow rate of 0+1 and the target value A are compared, and it is determined whether the actual gas flow rate exceeds the target value A. If the actual gas flow rate does not exceed the target value A, step sn3 is executed and a drive signal SDa that opens the flow rate control valve 30a by a certain opening degree is output, and the actual gas flow rate is increased so that it approaches the target value A. If it is rotating, a certain step SB4 is executed and a drive signal Sl'la is output that closes the flow rate regulating valve 30a by a certain opening degree, and the actual gas flow rate becomes the target value A.
It is decreased so that it approaches .

Then, such a control subroutine is repeatedly executed, and the gas flow rate of the blowing pipe 20a is controlled to match the target value A.

Therefore, according to this embodiment, the gas flow rate of each blowing pipe 20a to 20(-) is controlled to be constant according to the common 1-1 target value A, and the target value A is equal to the total gas flow rate
It has the advantage that it can be shared with a control computer for the purpose of determining M to be a constant value M.

Although the following description has been made based on the drawings showing one embodiment of the present invention in 1-1, the present invention is also applicable to other embodiments.

For example, suction 1 = the total gas flow rate blown into the tube 16 may be detected by a flow sensor installed in the tube supplying the inert gas to the header 24 .

In this case, there is an advantage that there is no need for means for adding and calculating the pipe flow rate signals SFa to S F (5).

In addition, the number of blowing pipes 20& to 20e, the flow rate sensor 2
The types of the flow control valves 8a to 28e and the flow control valves 30a to 30C3 can be selected from various types.

Furthermore, the operating amounts of the flow rate control valves 30a to 300 determined in steps SB3 and SR4 of the flow rate regulators 30a to 30e1 are determined based on the deviation between the target value A and the actual gas flow rate of each blowing pipe 20a to 20e. proportionally, if necessary;
Of course, integrated and differentiated quantities can be used.

It should be noted that the above is just one embodiment of the present invention,
The present invention can be modified in various ways without departing from its spirit.

As described in detail above, according to the blown gas control device of the present invention, the total gas flow rate blown into the two suction pipes is determined to be a predetermined desirable constant value, and the gas in each blown pipe is Since the flow rate is controlled to match its common target value, even if a part of the suction line becomes clogged, the amount of flow reduction caused by the blockage will be reduced by a proportionate amount in other normal blow line lines. Gas Flow 17 - The amount is increased so that the total gas flow meter remains constant. Therefore, even if some of the blowing pipes are clogged, a constant flow rate of molten steel in the suction pipe cannot be obtained, so a constant degassing effect can always be obtained and the product quality can be maintained at a high level. At the same time, regardless of the blockage of a part of the blowing line, other i
Since the gas flow rate in the regular pipes is uniformly controlled according to a common target value, the height of the splash of molten steel in the vacuum tank is prevented from increasing due to the concentration of the blown gas in a particular pipe.
l- to prevent melting and damage of the refractories especially in the openings in the vacuum chamber7.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of a circulation type σ air removal/j gas device to which the present invention is applied. FIG. 2 is an explanatory diagram showing the configuration of an embodiment of the present invention. FIG. 3 is a diagram corresponding to FIG. 2 showing another embodiment of the present invention. FIGS. 4 to 6 are flowcharts 1, respectively, showing programs that make the embodiment of FIG. 3 Hi-. 10-Vacuum tank 14; Molten steel 16: Suction pipe 18: Discharge pipe -18 = 20a~20 +! :Blowing pipes 22a to 22 (j:Blowing 1-1 Applicant: Daido Steel Co., Ltd. 19- Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] A vacuum tank, a suction pipe that communicates with the vacuum tank and is immersed in molten steel in a molten steel container, a discharge pipe, and a plurality of suction pipes each connected to a plurality of inlets provided in the suction pipe. Equipped with a blowing pipe line,
A blowing gas control device for a circulation type vacuum degassing device that circulates molten steel into the vacuum chamber by blowing an inert gas into the suction pipe from the blowing pipe, the gas flowing into the blowing pipe. a flow rate detection device that detects the flow rate of each of the pipes and the total gas flow rate of the blowing pipes, and outputs a pipe flow rate signal representing the pipe flow rate and a total flow rate signal representing the total gas flow rate; A flow rate control valve provided in each of the pipes to adjust the flow rate of gas flowing into the blowing pipe, compares each pipe flow rate represented by the pipe flow rate signal with a common target value, and calculates the difference. a first control means that drives the flow rate control valve so that the gas flow rate of each of the blowing pipes becomes zero, and makes the gas flow rate of each of the blowing pipes match the target value; a second control means that determines the common target value so that the difference between the two constant values becomes zero, and makes the total amount of gas sucked into the suction I-pipe match the constant value; A blowing gas control device for a recirculation type vacuum degassing device, characterized in that it includes a control device having the following.