EP1560937A1

EP1560937A1 - Method and device for cooling blowing lances

Info

Publication number: EP1560937A1
Application number: EP03779686A
Authority: EP
Inventors: Arno Luven; Andrzej Sakowicz; Werner Kircher; Revold Adamov
Original assignee: VAI Fuchs GmbH
Current assignee: Primetals Technologies Germany GmbH
Priority date: 2002-11-16
Filing date: 2003-11-12
Publication date: 2005-08-10
Anticipated expiration: 2023-11-12
Also published as: BR0316215B1; WO2004046391A1; BR0316215A; ZA200503850B; CN1320131C; RU2333254C2; RU2005118555A; CN1708591A; DE50302627D1; EP1560937B1; DE10253463A1; AU2003287860A1; ATE319862T1; KR20050059336A; KR101024824B1

Abstract

The invention relates to a method for cooling blowing lances that, in order to treat liquid metal melts contained in metallurgical vessels, particularly a steel contained in RH vessels and optionally being subjected to a vacuum, and/or in order to heat metal melts (optionally under a vacuum), can be introduced into and withdrawn from the inside of the vessel by means of a lifting device. A blowing lance comprises at least one inner guiding tube, which serves to guide gases, particularly oxygen, and which has a head-end lance mouth for blowing the gas onto the metal melt, and comprises a cooling jacket, which extends over the length of the lance and which serves to lead a cooling medium therethrough. The cooling jacket is provided in the form of a double-walled jacket tube, which has an inner and an outer cooling channel and which is provided with a redirecting tube in the area of the head end. The metallurgical vessel is connected to a vacuum pump in order to lower the pressure. According to the invention, the instantaneously available suction capacity of the pump limits the maximum flow rate of the gas serving as the cooling medium.

Description

Method and device for cooling blowing lances

The invention relates to a method for cooling blowing lances for treating liquid metal melts located in metallurgical vessels, in particular steel, possibly exposed to vacuum in RH vessels, and / or for heating metal melts (optionally under vacuum) by means of a lifting device in the inside of the vessel can be led in and out and has at least one inner guide tube for guiding gases, in particular oxygen, with a head-end lance mouth for inflating the gas onto the molten metal and has a cooling jacket extending over its length for carrying out a cooling medium, which as double-walled jacket tube having an inner and an outer cooling channel is formed with a deflection tube in the region of the head end, the metallurgical vessel being connected to a vacuum pump for lowering the pressure.

The invention further relates to a device for carrying out the aforementioned method, with a metallurgical vessel into which a blowing lance can be inserted and removed by means of a lifting device, which has at least one inner guide tube with a head-end lance mouth and a cooling jacket which consists of a inner cooling duct and an outer cooling duct, which are connected via a deflection tube, and with a pump, by means of which the metallurgical vessel can be evacuated via a vacuum connection.

Blow lances of the aforementioned type are known in principle according to the prior art. Water is regularly used as the cooling medium during the inflation of gases or solids onto the molten steel, which is flushed into the lance head in a large volume flow under pressure. Particularly in the focal spot on the bath surface radiating onto the end face of the lance head, extremely high temperatures occur which lead to gradual wear and / or Crack formation on the lance head, due to which the wall thickness of the cooling chambers in the lance head becomes thinner until the walls soften, with the result that breakthroughs can occur. Escaping water then evaporates, exceeds the suction power of the vacuum pump and leads to an explosive overpressure in the recipient.

In order on the one hand to avoid the risk of water breakthrough of a blowing lance in the operating position and, on the other hand, to intensively cool the lance, DE 3543 836 C2 has proposed alternating with two in another method in which the blowing lance is immersed in the melt to use blowing lances that can be cooled with both cooling and cooling water. Of the two blowing lances, only the blowing lance that is currently in the blowing position and immersed in the melt is cooled with cooling air, while the blowing lance that is just outside the melt is intensively cooled with cooling water. The alternate use of two blowing lances is relatively complex. For a water-cooled blowing lance it has therefore been proposed in DE 19948 187 C2 that the temperature detected by the temperature sensor arranged in heat-conducting contact with the wall of the lance head via the water cooling and / or the oxygen supply and / or the addition of additives and / or the Distance of the lance head from the weld pool is regulated.

The disadvantage associated with the water cooling of blowing lances is that in the event of a defect (break or tear) occurring in the area of the cooling jacket of the lance and an associated entry of water into the reaction space above the hot molten metal in the vessel, there is an abrupt and strong expansion of the released water comes as water vapor and a possible splitting off of hydrogen gas (H ₂ ), however, is not eliminated. Especially with RH vessels that only have a small free vessel volume, there are great dangers at internal vessel temperatures of up to 1800 ° C. That through the lance circulating cooling water with a flow rate of 30m ³ / h to 50m ³ / h can only be extracted to a small extent with the vacuum pumps available according to the state of the art, whereby based on the above-mentioned amounts of cooling water there is a ratio of the suction line to the breakthrough amount of steam present is between 1:20 to 1: 100. In RH vessels, the two cause immersion in the molten steel

Immersion tubes a siphon-like closure, which, because the introduction of pressure relief openings (expansion flaps) is not possible, may serve as the only pressure compensation openings. In the event of a chain of unfortunate circumstances, a water ingress due to a defective oxygen lance in a RH vessel with subsequent expansion can result in an expansion pressure of approx. 14x10 ⁵ Pa. At an explosion speed of 2 x 10 ⁷ Pa / s and a pressure relief through the existing dip tubes, large quantities of liquid steel would inevitably be thrown into the system environment.

It is an object of the present invention to further develop the method of the type mentioned above in such a way that, in the event of a cooling jacket leakage of the lance, the disadvantages described above are prevented and accordingly the safety of the operating personnel is increased and the entire system is protected. The same applies to the device to be further developed.

The above object is achieved by the method according to claim 1. The first measure is to use a gas as the cooling medium, which drastically reduces the amount of cooling medium released in the event of a lance defect. Calculations carried out show that in oxygen blowing processes under a pressure of 1 to 2x10 ⁴ Pa in a RH vessel, a cooling steam flow of 1000 kg / h and in VCD operation under a pressure of 70 Pa to 4x10 ³ Pa, a cooling steam flow of 360 kg / h h are sufficient. This small amount of steam compared to water cooling can be easily extracted from the vacuum pump in the event of a lance break or broken lance, without causing a dangerous one Expansion within the vessel occurs. The ratio of the suction power of the (vacuum) pump to the amount of steam available is approx. 2: 1 to 6: 1, which effectively prevents pressure development with expansion through the immersion tubes. Another measure according to the invention is that the suction power of the pump currently available regulates the flow rate of the gas used as the cooling medium. If the suction power of the pump drops or if it is low or low for other reasons, the cooling gas flow is minimized accordingly in order to create a sufficient ratio of the suction power of the pump to the amount of cooling gas to be extracted in the event of damage.

Further developments are described in claims 2 to 8.

According to a further development of this method, the pump suction power that is currently available additionally regulates the lance feed, the lance feed and the gas supply preferably being stopped immediately when there is a measured difference between the amount of gas supplied for lance cooling and the gas discharged. The first measure serves to prevent further damage to the lance by a sharp increase in temperature when approaching the surface of the bath level. The other measure means that only the amount of gas currently in the cooling jacket of the lance can flow out.

Superheated steam, in particular steam overheated by 20 ° C. to 50 ° C., is preferably used as the cooling medium. For cooling with steam, the same applies to the volume to be conveyed as for any other cooling gas known from the prior art, in particular nitrogen or argon. Due to the smaller volume that is required for cooling, the width of the cooling channels can also be minimized.

According to a further embodiment of the invention, the cooling medium is introduced into the inner cooling channel and discharged via the outer cooling channel during the inflation of oxygen. This ensures that immediately after the greatest heat absorption of the superheated water vapor introduced as the cooling medium in the area of the outer cooling channel, the water vapor is led directly out of the lance. Furthermore, there is the advantage that the oxygen fed in via the inner guide tube is heated due to the amount of water vapor flowing along the inner guide tube and, in this respect, is blown onto the molten steel in the vessel in the already heated state. This results in a lower temperature loss of the liquid steel, a more intensive carbon reaction in the case of decarburization to be carried out by the oxygen blowing, a more intensive aluminum reaction in chemical heating and an improved oxygen efficiency and finally a lower oxygen consumption.

In the event that the lance is in the upper park position between the treatment phases in VCD operation, it is furthermore provided that the water vapor is fed into the outer cooling duct of the cooling jacket and is discharged via the inner cooling duct after a head-end deflection. If the ambient temperature of the lance is lower compared to the oxygen blowing mode, this water vapor routing in the cooling jacket ensures that the water vapor first heats up the area of the outer cooling channel, so that the cooling of the water vapor and the associated condensate formation in the area of the cooling channels is avoided ,

To avoid overheating of the cooling jacket and to optimize the amount of cooling medium required in the different lance positions and operating conditions, according to a further embodiment of the invention it is provided that the amount of the cooling medium to be introduced into the cooling jacket, in particular water vapor, as a function of that measured on the outer jacket of the lance Temperature and / or the current lance position is regulated.

To prevent condensation from forming in the head area of the lance, the lance is initially preheated without cooling in start-up mode, preferably by moving the lance into the already heated metallurgical vessel and only then switching on the steam cooling. When using water vapor, it is preferably supplied as a coolant under a pressure of at least 7 × ^{10 5} Pa at a temperature of 160 ° C. to 210 ° C.

The object is further achieved by the device according to claim 9 which, according to the invention, the flow rate of the cooling medium by means of a control unit for adjusting the flow rate of the gas used as the cooling medium as a function of the current lance position, the available suction power of the vacuum pump and the lance outside wall temperatures regulates, is marked. The lance feed is preferably also set via the control unit.

In order to be able to better grasp the temperature load of the lance and thus the essential influences of wear, sensors are connected to the blow lance head and on the blow lance jacket at longitudinally different distances, which are connected to the control unit. The flow rate of the cooling medium can be increased or decreased via the control unit according to the measured temperatures. In order to avoid condensate formation in the cooling channels in the area of the lance head, a condensate separator is preferably provided, through which the cooling medium is guided before entering the cooling channel of the blowing lance.

Improved heat dissipation can be ensured if the inner surface of the outer cooling jacket tube facing the cooling channel has ribs projecting radially into the cooling channel.

The lance mouth is preferably designed as a Laval nozzle.

Further advantages of the invention and exemplary embodiments are shown in the drawings. Show it: 1 is a schematic cross-sectional view of a blowing lance,

1 in a section along line II-II in Fig. 1,

Fig. 3 is a cross-sectional view of an RH vessel with the retracted

Lance including control unit in a schematic representation,

4 to 7 each show cross sections of RH vessels with different lance positions or in different operating states and

8 to 11 each show time-temperature diagrams of the temperatures calculated under process conditions according to FIGS. 4-7.

The lance 10, which is known in principle according to the prior art, has an inner guide tube 11 which ends at the head end in a nozzle 20, preferably a Laval nozzle, as a lance mouth 12. A gas, in particular oxygen, can be supplied via this guide tube 11. The guide tube 11 is surrounded by a cooling jacket 13 with an outer tubular cooling jacket tube 13a, the interior of which is divided by an inserted deflection tube 14 into an inner cooling channel 15 surrounding the inner guide tube 11 and an outer cooling channel 16. The deflection tube 14 does not reach in the head region of the lance 10 as far as the nozzle 20, so that here a deflection region 17 results as a connection between the inner cooling duct 15 and the outer cooling duct 16. Each of the two cooling channels 15 and 16 is connected at the foot end of the lance to an associated opening 18, which is switched as an inlet or an outlet depending on the desired cooling medium flow direction.

As shown in FIG. 2, in order to improve the heat transfer to the cooling medium flowing through the cooling jacket, the inner surface of the outer cooling jacket tube 13a facing the cooling channel 16 is formed with ribs 19 projecting radially into the cooling channel 16. To cool the lance in its possible operating states, which will be discussed later, a cooling gas, preferably overheated by 20 ° C. to 50 ° C., is supplied via the cooling channels 15 and 16 of the cooling jacket 13.

In order to avoid the formation of condensate in the cooling channels of the cooling jacket of the lance, a cross connection can be provided with regard to the loading of the inner cooling channel 15 or the outer cooling channel 16 for the supply and removal of the water vapor. For example, with the highest lance heat load in the oxygen blowing mode, the cooling steam is supplied via the opening 18 connected to the inner cooling duct 15, so that the water vapor flows long past the inner guide tube 11 to the deflection region 17 of the cooling jacket 13 and from here via the outer cooling duct 16, which is in contact with the reaction chamber of the vessel surrounding the lance via the tubular cooling jacket 13. If, on the other hand, the lance is in the upper parking position between the treatment phases of individual batches, the outer cooling jacket 13 is exposed to a significantly lower amount of heat. In this case, the water vapor is first blown into the outer cooling channel 16. The water vapor is discharged via the inner cooling duct 15 and its outlet opening 18 on the head side. The same applies in the case of VCD operation.

The same applies in start-up mode, i. H. that in the case of a cold lance, the lance 10 is first moved into the vessel 200 without steam cooling in order to preheat the lance. Steam cooling is therefore only activated after the lance has been preheated.

As can be seen in detail in FIG. 3, the metallurgical vessel 200 with its dip tubes 21 is introduced into the metal melt 29 filled into a pan 23. The treatment vessel 200 can be evacuated via a connecting piece 22 by means of a pump 30. Like the pump 30, the lance drive 24 is also connected to a control unit 27. An encoder 25 is provided to determine the current lance position. Likewise, temperature sensors are provided on the lance jacket at different longitudinal axial distances and at the lance mouth, of which only the temperature sensor 26 is shown in FIG. 3. The temperatures measured by this sensor and the other temperature sensors are also transmitted to the control unit 27. The regulating unit 27 regulates the introduced amount of cooling gas via the regulator 28 as a function of the suction power of the pump 30 and the temperatures measured via the existing temperature sensors. Flow measuring devices are not shown in detail, which determine the quantity of cooling steam that has been introduced and the quantity that has been exported, and send a signal to the control unit 27 in the event of any deviations that are an indication of existing leaks. In the event of a leak, the further introduction of cooling gas and the lance feed are stopped or the lance is moved out of the vessel 200.

FIG. 4 shows a lance inserted into the vessel 200. In the state shown there is normal pressure inside the vessel, ie the pump 30 is not in operation. Neither the guide tube 11 nor the cooling channels 15 and 16 are initially supplied with gas. Under these conditions, the vessel interior temperature Tj is 1500 ° C in a specific application. The temperatures T * -, T ₂ , T ₃ and T measured here on the lance within the first two minutes are shown in FIG. 8. In the specific application, a temperature rise of up to 1060 ° C is measured on the top of the lance. If steam cooling is switched on after two minutes by letting in steam at a temperature of 160 ° C below 7x10 ⁵ PA, the temperatures Ti and T ₂ measured on the lance head drop to 260 and 215 ° C, respectively. The amount of steam conveyed through the cooling channels 15 and 16 is then approx. 179 kg / h.

Figure 5 shows the lance 10 in the oxygen blowing mode. Inside the vessel there is a pressure of 2x10 ⁴ Pa and a temperature Tj of 1800 ° C. Through the guide tube 11 oxygen in an amount of z. B. 1000 NπfVh inflated. For lance cooling, water vapor is introduced at a pressure of 7x10 ⁵ PA at a temperature of 160 ° C. The corresponding temperature profiles T * ι, T ₂ , T ₃ , T and the steam outlet temperature are shown in Fig. 9. FIG. 6 shows a lance introduced into the vessel 200 in a VCD process, ie without oxygen supply via the guide tube 11. The pressure set inside the vessel is between 70 Pa and 4x10 ³ Pa. The lance is cooled with water vapor (7x10 ⁵ Pa, 160 ° C). The internal vessel temperature Tj is 1200 ° C, the amount of steam conveyed through the cooling channels 15 and 16 is 360 kg / h. The course of the temperatures Ti to T ₄ and the steam outlet temperature T _Da can be seen in FIG. 10. The amount of steam delivered was 360 kg / h.

Figure 7 shows the lance in an upper parking position. The vessel 200 is immersed in the metal melt with its immersion nozzles. As can be seen in FIG. 11, the measured lance temperatures rise within a short time from 20 ° C. to 160 ° C. or 200 ° C., although the water vapor flow rate let in is 1464 kg / h.

The operating situations described above and investigated in each case show that at a oxygen blowing, which is operated under a pressure of 0.5 x10 ⁴ to 2 x 10 ⁴ Pa, h a cooling steam flow rate of 1000 kg / and at a VCD operating under a vacuum of 70 Pa to 4x10 ³ Pa, a cooling steam flow of 360 kg / h is to be used. Compared to water cooling, there are significantly smaller amounts of steam which can be easily sucked off safely by the vacuum pump in the event of a lance break or broken lance, ie without dangerous expansion occurring within the vessel 200.

A measurement of the difference between the amount of steam admitted and the amount of steam escaping, in particular with regard to the flow and pressure measurements in the supply and discharge lines, shows immediately occurring lance leakages. To prevent condensation from forming when the lance is in the upper position, the direction of steam flow is preferably reversed with a corresponding valve circuit.

Claims

claims

Process for cooling blowing lances which are used to treat liquid metal melts in metallurgical vessels, in particular steel which may be exposed to a vacuum in RH vessels and / or to heat metal melts, optionally under vacuum, by means of a lifting device into the interior of the vessel. and can be led out and which have at least one inner guide tube for guiding gases or solids, in particular oxygen, with a head-end lance mouth for inflating the gas onto the molten metal and have a cooling jacket extending over their length for carrying out a cooling medium which is designed as a double-walled, an inner and an outer cooling duct jacket tube is formed with a deflecting tube in the region of the head end, the metallurgical vessel for reducing the pressure being connected to a pump, characterized in that the suction power currently available d he pump limits the maximum flow of the gas used as the cooling medium

A method according to claim 1, characterized in that the currently available pump suction power limits the maximum permissible cooling gas flow rate by means of flow measurements and switches off when exceeded.

Method according to one of claims 1 or 2, characterized in that superheated steam, overheated by 20 ° C to 50 ° C, is used as the cooling medium.

Method according to one of claims 1 to 3, characterized in that the cooling medium is introduced into the inner cooling channel and discharged via the outer cooling channel during the oxygen blowing.

5. The method according to any one of claims 1 to 4, characterized in that in the upper parking position of the blowing lance set between the treatment phases and during VCD operation, the cooling medium is fed into the outer cooling duct and is discharged via the inner cooling duct.

6. The method according to any one of claims 1 to 5, characterized in that the flow rate of the cooling medium is controlled depending on the temperature measured on the outer jacket of the lance and / or the current lance position.

7. The method according to any one of claims 1 to 6, characterized in that the lance is initially preheated in the start-up mode without cooling, preferably by moving the lance into the already heated metallurgical vessel and only then switching on the steam cooling.

8. The method according to any one of claims 1 to 7, characterized in that the water vapor is supplied as a coolant under a pressure of at least 7x10 ⁵ Pa at a temperature of 160 ° C to 210 ° C.

9. Device for performing the method according to one of claims 1 to 8, with a metallurgical vessel (200) into which a blowing lance (10) can be inserted and removed by means of a lifting device (24) into the interior of the vessel, said at least one inner guide tube (11) with a head-end lance mouth (12) and a cooling jacket (13), which consists of an inner cooling channel (15) and an outer cooling channel (16), which are connected via a deflection tube (14), and with a pump (30) by means of which the metallurgical vessel (200) can be evacuated via a vacuum connection (22), characterized by a control unit (27) for setting the flow rate of the gas used as cooling medium, the control unit (27) depending on the current lance position , the suction power of the vacuum pump and the measured lance outer wall temperatures regulate the flow rate of the cooling medium.

10. The device according to claim 9, characterized in that temperature sensors are arranged on the blow lance head and on the blow lance jacket at a longitudinal axial distance and are connected to the control unit (27).

11. The device according to one of claims 9 or 10, characterized by a condensate separator through which the cooling medium passes before entering the cooling channel (15, 16).

12. Device according to one of claims 9 to 11, characterized in that the inner surface of the outer cooling jacket tube (13a) facing the cooling channel (16) has ribs (19) projecting radially into the cooling channel (16).

13. Device according to one of claims 9 to 12, characterized in that the lance mouth is designed as a Laval nozzle (20).