Patent Application
20120000315
The invention relates to a method and a device for controlling vibrations of a metallurgical vessel that occur while gas is being injected from nozzles into liquid molten metal located in the metallurgical vessel.
In particular in the case of AOD (argon oxygen decarburization) converters used for producing stainless steel, large amounts of gas are introduced into the liquid molten material of the crude steel via nozzles. As a result, on the one hand the partial pressure of gases in the molten material can be influenced, on the other hand a bath flow is produced in the molten material by the injected gas bubbles rising up. This flow leads to a desired intermixing of the molten material. However, the rising gas bubbles lead to a randomly fluctuating displacement of the centre of gravity of the converter filled with liquid molten material, causing the converter to vibrate. Parts of the plant that are connected directly or indirectly to the converter—particularly those that are rigidly connected to the converter—may also be made to vibrate by the vibrations of the converter. Vibrations put a severe load on the converter and the parts of the plant connected to it, such as for example the gear mechanism provided for tilting the converter and the suspension thereof, and may lead to premature wear or rupture. The foundation on which the converter and associated parts of the plant are located, such as the gear mechanism for example, also undergo oscillations. These may have a damaging effect on the foundation itself and the surroundings thereof.
It is known from US20080047396 to monitor and control the intermixing of a liquid molten metal by means of gas injection from under-bath nozzles in such a way that the vibrations of the metallurgical vessel are measured. The measurement result is an indication of the quality of the intermixing. On the basis of the measurement result, the total amount of gas injected per unit of time, the blowing rate, is changed to achieve optimum intermixing. However, reducing the blowing rate with respect to values fixed in a blowing plan is synonymous with extending the tap-to-tap time, and consequently with reducing the productivity of the metallurgical vessel. Moreover, a change of the blowing rate may also influence the metallurgical properties of the product.
According to various embodiments, a method and a device for controlling vibrations of a metallurgical vessel occurring during the injection of gas into the metallurgical vessel filled with a liquid molten metal can be provided that allow the vibrations of the metallurgical vessel to be controlled while largely retaining the blowing rate.
According to an embodiment, in a method for controlling vibrations of a metallurgical vessel occurring during the injection of gas into the metallurgical vessel filled with liquid molten metal, a certain total amount of gas per unit of time being injected into the liquid molten metal, and the total amount of gas being injected into the liquid molten metal through a number of individual nozzles in the metallurgical vessel, and measured values correlating with the vibrations of the metallurgical vessel occurring being measured during the injection, wherein, while keeping the total amount of gas injected per unit of time largely constant, the amount of gas injected from individual nozzles per unit of time is changed in dependence on the measured values that are measured and correlate with the vibrations of the metallurgical vessel occurring.
According to a further embodiment, at least for one of the individual nozzles, preferably two or more of them, the amount of gas injected from them per unit of time can be changed, at least for a time, in dependence on measured values correlating with the vibrations of the metallurgical vessel occurring. According to a further embodiment, the changing of the intensity of at least one measured value correlating with the vibrations of the metallurgical vessel occurring that can be brought about by changing the amount of gas injected from an individual nozzle per unit of time is traced, and the changing of the amount of gas injected from an individual nozzle per unit of time is carried out until the at least one measured value correlating with the vibrations of the metallurgical vessel occurring reaches a prescribed value or until the gas flow from the nozzle reaches a prescribed maximum or minimum. According to a further embodiment, the measured values correlating with the vibrations of the metallurgical vessel occurring can be filtered and digitally processed before they are used for changing the amount of gas injected from the individual nozzles per unit of time. According to a further embodiment, when measuring the measured values correlating with the vibrations of the metallurgical vessel occurring, frequencies and/or intensities of vibrations can be determined. According to a further embodiment, the measured values correlating with the vibrations of the metallurgical vessel occurring may correlate with vibrations of the metallurgical vessel that have frequencies between 0.1 Hertz and 100 Hertz, preferably between 0.2 Hertz and 20 Hertz. According to a further embodiment, the measured values, correlating with the vibrations of the metallurgical vessel occurring, in dependence on which the amount of gas introduced from individual nozzles per unit of time is changed may correlate with vibrations of the metallurgical vessel of frequencies that lie between 0.2 Hertz and 20 Hertz.
According to another embodiment, a device for controlling vibrations of a metallurgical vessel occurring during the injection of gas into the metallurgical vessel filled with liquid molten metal and provided with a number of individual nozzles for the injection of gas, the individual nozzles being respectively connected to a gas feed line of their own, may have at least one sensor for measured values correlating with the vibrations of the metallurgical vessel occurring, and a processing unit for processing the measured values measured by the sensor, wherein in at least two gas feed lines there is at least one device for changing the gas flow through the gas feed line, and each device for changing the gas flow is connected to the processing unit.
According to a further embodiment of the device, the device for changing the gas flow through the gas feed line may allow a continuous changing of the gas flow. According to a further embodiment of the device, the device for changing the gas flow through the gas feed line can be a device for changing the gas flow in stages. According to a further embodiment of the device, the sensor for measured values correlating with the vibrations of the metallurgical vessel occurring can be a vibration sensor. According to a further embodiment of the device, the vibration sensor can be a torque measurement, a strain gage, a position pickup, a velocity pickup or an acceleration pickup.
The invention is described below on the basis of schematic figures, which represent embodiments.
According to various embodiments, in a method for controlling vibrations of a metallurgical vessel occurring during the injection of gas into the metallurgical vessel filled with liquid molten metal,
a certain total amount of gas per unit of time is injected into the liquid molten metal,
and the total amount of gas is injected into the liquid molten metal through a number of individual nozzles in the metallurgical vessel,
and measured values correlating with the vibrations of the metallurgical vessel occurring are measured during the injection,
wherein,
while keeping the total amount of gas injected per unit of time largely constant, the amount of gas injected from individual nozzles per unit of time is changed in dependence on the measured values that are measured and correlate with the vibrations of the metallurgical vessel occurring.
The amount of gas injected from individual nozzles per unit of time is changed in dependence on the measured values that are measured and correlate with the vibrations of the metallurgical vessel occurring. As a result, the intermixing of the liquid molten metal, and correspondingly the centre of gravity of the metallurgical vessel filled with liquid molten metal, changes. It is correspondingly possible to achieve the effect that vibrations are increased or reduced. As a result, it is possible to keep parts of the plant that are connected directly or indirectly to the metallurgical vessel—in the case of a converter, for example, essentially the suspension, support, baling ring, tilting drive, gear mechanism and foundation—free from harmful vibration frequencies or to reduce the intensity of vibrations with harmful frequencies. As a result, the mechanical stressing of these parts of the plant is reduced. Lower mechanical stressing, and accompanying longer lifetimes, of the parts of the plant increase the productivity of the metallurgical vessel.
Measured values correlating with the vibrations of the metallurgical vessel occurring should be understood as meaning measured values that allow a quantifiable conclusion to be reached as to the vibrations of the metallurgical vessel occurring. Measured values for the vibrations of the metallurgical vessel are also included by the term “measured values correlating with the vibrations of the metallurgical vessel occurring”. The measured values correlating with the vibrations of the metallurgical vessel occurring are, for example,
If directly or indirectly connected parts of the plant are made to vibrate by vibrations of the metallurgical vessel occurring, these vibrations correlate with the vibrations of the metallurgical vessel in a way that allows the vibrations of the metallurgical vessel to be concluded from the measurement of these vibrations of the parts of the plant. Such conclusions may be made possible, for example, by measuring at the same time
Parts of the plant connected directly to the metallurgical vessel should be understood as meaning parts of the plant that are connected straight to the metallurgical vessel. Parts of the plant connected indirectly to the metallurgical vessel should be understood as meaning parts of the plant that are connected to the metallurgical vessel via a part of the plant or a number of parts of the plant—that is to say indirectly.
Keeping the total amount of gas injected per unit of time, that is the blowing rate, largely constant, makes it possible for the productivity and the metallurgical properties of the product to be kept largely constant.
It is known to a person skilled in the art that, in industrial application, the blowing rate cannot be kept constant entirely exactly, but that the actual value fluctuates about a prescribed value over time. For the purposes of the present invention, keeping largely constant should be understood as meaning that the actual value fluctuates about a prescribed value over time by +/−5%.
The metallurgical vessel may be any type of process vessel for liquid molten metals, preferably for molten crude steel or molten pig iron, that is to say for example converters, ladles, crucibles or electric arc furnaces. A tiltable converter is preferred.
The metallurgical vessel has nozzles for injecting gas into the space enclosed by the vessel. The arrangement of the nozzles is in this case chosen such that, during the operation of the metallurgical vessel, they lie below the level of the liquid molten metal in the metallurgical vessel; such nozzles are also known as under-bath nozzles. Correspondingly, during operation, gas is injected into the liquid molten metal through these nozzles. The nozzles may be arranged in the bottom or the side walls of the metallurgical vessel. The nozzles are preferably under-bath nozzles arranged in the side walls of the metallurgical vessel.
The measurement during injection of the measured values correlating with the vibrations of the metallurgical vessel occurring is performed either continuously or at certain time intervals. A continuous measurement has the advantage of providing information at all times as to the current status of the vibrations, but involves a considerable data processing effort. A measurement at certain time intervals has the advantage over continuous measurement that the data processing effort is reduced on account of the lower amount of measurement data generated. However, it only provides information about the status of the vibrations at selected points in time.
According to one embodiment of the method, at least for one of the individual nozzles, preferably two or more of them, the amount of gas injected from them per unit of time is changed, at least for a time, in dependence on measured values correlating with the vibrations of the metallurgical vessel occurring.
The aim here should be to maintain for such a nozzle a gas flow through the nozzle at all times, in order not to risk any infiltrations of liquid molten metal into the nozzle and consequently caused damage to the nozzle. Therefore, complete switching-off of the gas flow through the nozzle should be avoided. The greater the number of individual nozzles for which the amount of gas injected from them per unit of time is changed, the more finely balanced the control of the vibrations of the metallurgical vessel can be.
The changing of the amount of gas injected per unit of time may be performed in stages or continuously. In the case of changing in stages, changes are made between setting stages predetermined on the basis of the process engineering conditions. Continuous changing offers the advantage over changing in stages that a more finely balanced control of the vibrations of the metallurgical vessel is possible, and is therefore preferred.
It is at the same time preferred that the changing of at least one measured value correlating with the vibrations of the metallurgical vessel occurring that is brought about by changing the amount of gas injected from an individual nozzle per unit of time is traced, and the changing of the amount of gas injected from an individual nozzle per unit of time is carried out until the at least one measured value correlating with the vibrations of the metallurgical vessel occurring reaches a prescribed value or until the gas flow from the nozzle reaches a prescribed maximum or minimum. The maximum or minimum is prescribed on the basis of process engineering specifications for the liquid molten metal that is actually to be treated. The prescribed value for the at least one measured value correlating with the vibrations of the metallurgical vessel occurring is dependent on the extent to which the vibrations of the metallurgical vessel are to be controlled.
Since the two variants, changing by stages and continuous changing, should be used at least for a time, mixed forms of them are also possible. For example, the amount of gas injected per unit of time may first be changed in stages and then, to make better fine setting possible, changed continuously. Or it is first changed continuously and then in stages.
According to a preferred embodiment of the method, the measured values correlating with the vibrations of the metallurgical vessel occurring are filtered and digitally processed before they are used for changing the amount of gas injected from the individual nozzles per unit of time. This makes it possible to trace more accurately the variation of certain vibrations of the metallurgical vessel, for example those known to be particularly disruptive.
According to a preferred embodiment, when measuring the measured values correlating with the vibrations of the metallurgical vessel occurring, frequencies and/or intensities of vibrations are determined.
According to one embodiment, the measured values correlating with the vibrations of the metallurgical vessel occurring correlate with vibrations of the metallurgical vessel that have frequencies between 0.1 and 100 Hertz, preferably between 0.2 Hertz and 20 Hertz. The values 0.1 Hertz and 100 Hertz are included here. Frequencies above 100 Hertz scarcely have any potential to be disruptive.
According to a further embodiment, the measured values, correlating with the vibrations of the metallurgical vessel occurring, in dependence on which the amount of gas introduced from individual nozzles per unit of time is changed correlate with vibrations of the metallurgical vessel of frequencies that lie between 0.2 Hertz and 20 Hertz. These frequencies should be monitored particularly closely, since they have the greatest potential for causing damage.
The frequencies and intensities of the vibrations of the metallurgical vessel are measured by means of a vibration sensor or a number of vibration sensors, it being possible for the measuring principle to be based, for example, on torque measurement, acceleration measurement, strain gages, position pickups or velocity pickups.
Acceleration pickups, strain gages or position pickups are preferably used, since they are inexpensive and can be fitted with little effort.
According to further embodiments, a device for carrying out the method according to various embodiments can be provided.
It is a device for controlling vibrations of a metallurgical vessel occurring during the injection of gas into the metallurgical vessel filled with liquid molten metal and provided with a number of individual nozzles for the injection of gas, the individual nozzles being respectively connected to a gas feed line of their own,
with at least one sensor for measured values correlating with the vibrations of the metallurgical vessel occurring,
with a processing unit for processing the measured values measured by the sensor,
characterized in that
in at least two gas feed lines there is at least one device for changing the gas flow through the gas feed line, and each device for changing the gas flow is connected to the processing unit.
The sensor measures measured values correlating with the vibrations of the metallurgical vessel occurring, which are processed in the processing unit. In this case, quantitative information as to the vibrations of the metallurgical vessel occurring, that is to say for example as to the frequency and intensity of the vibrations, is obtained from the measured values. The sensor may be fitted on the metallurgical vessel, for example a converter. According to another embodiment, the sensor is fitted on a part of the plant connected directly or indirectly to the metallurgical vessel; for example, in the case of a converter, on the gear mechanism provided for tilting the converter, on the suspension, or on the foundation on which the converter and associated parts of the plant, such as the gear mechanism for example, are located. There is at least one sensor, but there may also be a number of sensors. If a number of sensors are present, they may be fitted at one or more of the aforementioned locations.
Via the connection to the devices for changing the gas flow, the processing unit gives these devices specifications for changing the gas flow. On the basis of the information obtained in the processing unit as to the vibrations of the metallurgical vessel occurring, these specifications are devised such that vibrations of the metallurgical vessel with certain frequencies should be reduced. The specifications are devised on the basis of expert knowledge stored in the processing unit. This expert knowledge may, for example, be determined and stored during the commissioning of the metallurgical vessel and consists, for example, of the natural frequencies of the metallurgical vessel, the natural frequencies of the parts of the plant connected directly or indirectly to said vessel, or the natural frequency of the overall system comprising the metallurgical vessel and parts of the plant connected directly or indirectly to it. In the case of a converter as the metallurgical vessel, the overall system essentially comprises the foundation, gear mechanism, tilting drive, baling ring, suspension and support.
The connection of the processing unit to the devices for changing the gas flow may be direct. It may also be indirect; in the case of valves as devices for changing the gas flow, for example, via a valve unit for controlling the valves. The terms connect and connection should be understood in this context as meaning that the transmission of specifications to the devices for changing the gas flow is possible. In the case of an indirect connection, that is to say a connection via a further device, such as for example a valve unit, this means that the transmission of specifications from the processing unit takes place via the further device.
The fact that there is at least one device for changing the gas flow in at least two gas feed lines means that the total amount of gas introduced per unit of time, the blowing rate, can be kept largely constant, since a change at one nozzle can be compensated by an opposite change at another nozzle.
More preferably, the device for changing the gas flow through the gas feed line allows changing of the gas flow in stages. It is therefore, for example, a control valve which controls the current through-flow to the setpoint value.
According to one embodiment, the device for changing the gas flow through the gas feed line is a device for continuously changing the gas flow. It is therefore, for example, a control valve which controls the current through-flow to the setpoint value.
The sensor for measured values correlating with the vibrations of the metallurgical vessel occurring is preferably a vibration sensor. A vibration sensor is a device which converts the mechanical vibrations into signals that can be used further, which are preferably electrical signals.
More preferably, the vibration sensor is a torque sensor, an acceleration pickup, a position pickup, a strain gage or a velocity pickup. On account of price and simplicity, acceleration pickups, position pickups and velocity pickups should be preferred.
In
In
| Number | Date | Country | Kind |
|---|---|---|---|
| A2013/2008 | Dec 2008 | AT | national |
This application is a U.S. National Stage Application of International Application No. PCT/EP2009/064720 filed Nov. 6, 2009, which designates the United States of America, and claims priority to Austrian Application No. A2013/2008 filed Dec. 23, 2008, the contents of which are hereby incorporated by reference in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/064720 | 11/6/2009 | WO | 00 | 9/12/2011 |
