WO2022075961A1

WO2022075961A1 - A method for treating a liquid metal with a gas medium in a metallurgic container and a device for performing the same

Info

Publication number: WO2022075961A1
Application number: PCT/UA2021/000082
Authority: WO
Inventors: Vitalii MELNYK; Sergiy GIDLERCHUK; Larysa KARDASH; Yevgeniia KOSYH; Oleksiy KRYVOSHCHOKOV
Original assignee: Limited Liability Company "Innotech-Splav"
Priority date: 2020-10-05
Filing date: 2021-09-23
Publication date: 2022-04-14
Also published as: UA126511C2

Abstract

The invention relates to metallurgy, namely to a method for blowing of melt using a blowing device. Said blowing device is a block of heat-resistance concrete comprises a case (1), a gas distribution collector (2) having an intake nozzle (3), a refractor module (4) provided with pass-through vertical longitudinal slit capillaries (5). Said capillaries (5) are parallel and located apart from each other at a distance of 20-70 mm, wherein the width of each capillary (5) 50-80 µm and total area of the longitudinal section of said capillaries (5) are 0.008-5 % of the aria of the longitudinal section of a working part of the blowing device.

Description

A METHOD FOR TREATING A LIQUID METAL WITH A GAS MEDIUM IN A METALLURGIC CONTAINER AND A DEVICE FOR PERFORMING THE SAME

The invention relates to metallurgy, namely, to a method for treating metallurgical melts and/or slags by supplying a gas medium to a metallurgical apparatus and to a device for implementing the same, and it may be used to refine a melt, to modify the same, to saturate or to finish a steel and alloys during manufacture.

The prior art teaches a use of ejection technologies for treating liquid metals with gases in order to increase a quality of melts using an underblast by means of purging devices such as tuyeres, porous or slit plugs, and purging monoblocks.

Methods for metal purging are known which comprise supplying a gas medium via pass-through channels in a working part of the purging device that is a constituent part of a bottom lining of a metallurgical container, and forming a plurality of bubble flows or jet flows or a combination thereof on a boundary between the lining and the liquid metal.

Most frequently, such purging is intended to refine the melt by supplying inert gases for flotation and catching non-metal inclusions by the gas bubbles followed by removal of the passed particles from a surface of the melt. A specific example of such technology is a method for purging a liquid metal in a ladle that is described in the patent EP 1101825B1 dated 16.07.2003, the method comprising supplying an inert gas via pass-through channels in a working part of a purging device that is a constituent part of a lining of the ladle, at the same time forming jet and bubble flows on a boundary between the lining and the liquid metal. This patent discloses a fire-proof ceramic gas purging device that is a conical plug having a working part that is made of a ceramic material with non-oriented pores formed therein, the pores extend from a gas supplying side to an end surface from a side of discharging the gas into the melt, and a gas-proof ceramic material that surrounds the ceramic porous material and forms a slit circular channel on a joining plane. This enables to form both bubbles that form the gas flow when passing through the pores and the jet that passes through a circular slit capillary vessel and facilitates flotation of the bubbles in the melt.

Also, a method for a near bottom purging by means of a slit plug that is mounted in a bottom of a metallurgical container in order to increase a nitrogen content when manufacturing nitrogen-containing steels and alloys, the method is disclosed in the pat. GB1282161A dated 7/19/1972. A drawback of the methods utilizing the plugs lies in a locality of the ejection of the gas flows, thereby reducing the efficiency of a mass exchange process and not allowing to treat a great volume of the melt, as well as a high speed of the purging assembly due to clogging of the pores or bum-off of the slit capillary vessels. Furthermore, use of the plugs is not effective for other purposes of purging the melt with the gas medium such as, e.g., a gas-oxygen treatment or addition of reaction compounds such as ferrous alloys and deoxidizers to the liquid metal melts.

Usually, technologies of said treatments of the melt using the underblast are carried out using near bottom tuyeres having slit channels which are arranged in a metal sleeve that is mounted into a metal shell as disclosed, e.g., in the pat. DE4234974C2 dated 12/22/1994.

A drawback of using the tuyeres for purging lies in an insufficient intensification of the melt with the gas flows due to their intersection and mutual absorption, when an increased reaction wear of the fire-proof lining in the gas medium, as well as a limited possibility of their practical use, are seen, since the tuyeres must be a structural element of the metallurgical equipment and cannot be mounted and use in certain ladles or furnaces. The closest method, in terms of a usage versatility, is a method for treating melts by means of a purging device that consists of at least one monoblock that is suitable to be mounted in a bottom portion of a lining of a metallurgical container. The main problem of using the monoblocks lies in an insufficient area of interaction between gas flows and the melt, since the arrangement of capillary vessels on a working area of the monoblock that is limited with a housing, while an increase of a number of the capillary vessels is directly related to a reduction of their cross-section and reduction of intensification of the melt, and the increase leads to a rapid wear due to washout by flows of the metal. It is resolved in such a way as mentioned, e.g., in the pat. RU2309183C2 dated 27.10.2007 by forming jet flows at an angle to a normal of the working part of the purging device and by forming bubble flows by means of dividing single jet flows into elemental ones. However, in order to carry out this method, the working part of the monoblock must be made using a specialized profiling of cross sections of the capillary vessels, thereby making complex both a technology for manufacturing the monoblocks and a selection of the technology modes for optimizing the purging.

Technical solutions which are the closest ones to the group of inventions in terms of a set of essential features and an effect being achieved are the ones from the pat. UA99909U dated 25.06.2015 that describes a combined monoblock for a bottom purging comprising a composite capillary fire-proof module with capillary vessels having a cross section of from 100 to 330 pm, the module is mounted into a cartridge with a gas-distributing collector system that comprises a gas intake nozzle. A method for using this block comprises introducing a gas medium under pressure through fire-proof channels of the working part of the purging device that is mounted in a bottom lining of a metallurgical container, and forming flows in a metal melt, thereby enabling to form parallel jets and to disperse a large number of bubbles in the metal melt. A drawback of this purging device and the method for using the same lies in that the capillary vessels are made of a fire-proof material that differs from a material of the module by means of, e.g., filling slits which are preliminary punctured in the module with a highly inflammable refractory product followed by its burning, or by manufacturing them from a fire-proof metal followed by an embedment into the module. It causes that inner channels for the gas passage are relatively wide, thereby causing high loses of the pressure and the gas medium and leading to occurrence of bubbles having various non-controlled sizes that reduces an effectiveness of the melt homogenization significantly.

A task of the claimed invention is to provide a method and a device for treating a liquid metal with a gas medium to enable a formation of parallel flows of bubbles having smaller diameter in a metal melt without their intersection and mutual absorption, and being suitable for usage in all types of metallurgical containers of both furnace and out-of-fumace treatment by creating conditions and parameters that set initial sizes of the bubbles and their uniform distribution in the entire volume of the melt.

The posed task is resolved by the fact that the method comprising introducing a gas medium under pressure through fire-proof channels of a working part of a purging device that is mounted in a bottom lining of a metallurgical container, according to the invention, comprises forming at least two parallel bubble jets having a diameter of the bubbles of from 1 to 5 mm at a distance of from 20 to 70 mm between each other at a boundary of a contact with the metal melt. The formed jets are directed from a transverse plane of the purging device to the metal melt at a right angle relative to the working part by means of the fireproof channels which are slit capillary vessels having a width of from 50 to 180 pm, made integrally with the working part of the purging device. Therewith, a contact area of the working part of the purging device with the metal melt is maximum from 2 to 50% of the area of the bottom of the metallurgical container, and an overall area of a longitudinal section of the slit capillary vessels is from 0.008 to 5% of the area of the longitudinal section of the working part of the purging device. The pressure of introduction of the gas medium is from 0.05 to 0.25 MPa.

Therewith, argon or nitrogen or oxygen may be used as the gas medium. Dispersing and structural ferroalloys and deoxidizers having a fraction size of up to 10 pm also may be added to the gas medium.

Such implementation of the method enables to increase a quality of the produced metal significantly due to enabling the distribution of the bubbles across the entire volume of the melt and to almost avoid a presence of dead zones of the purging.

Therewith, said method may be used for refining the melt in case of using inert gases, for nitrodizing, modifying with additives, saturating with oxygen etc. and it may be suitable for use in all types of metallurgical containers in combination with any lining, namely, in electric arc and induction furnaces, in a steel-pouring ladle, in a tundish, in a ladle-furnace, in a drum ladle etc.

In order to enable implementation of the method and to resolve the task which the invention is based on, a purging device has been developed which represents, according to the invention, at least one block made of a heat-resistant concrete, the device comprising a housing that is equipped, in a bottom portion thereof, with a gas distribution collector having an intake nozzle, with a working part that is monolithically mounted in the housing over the collector, the working part is made in a form of a fire-proof module having pass-through vertical longitudinal slit capillary vessels which are integrally made therein, as well as which are parallel and spaced apart from each other at a distance of from 20 mm to 70 mm, and located in a transverse direction relative to the housing. Therewith, a width of each capillary vessel is from 50 to 180 pm, and an overall area of the longitudinal section of the capillary vessels is from 0.008 to 5% of the area of the longitudinal section of the working part of the purging device.

Such arrangement enables to disperse the gas medium in the melt into a maximum possible number of fine bubbles, thereby increasing an intensification of the purging with a multi-rate increase of an active interaction area without a risk of an excessive swirling of the melt, formation of splashes, and spitting of the metal out from the container.

A heat-resistant concrete of a tabular alumina with an addition of electrocorundum and/or spinel and with a content of AI2O3 of not less than 90% may be used as the material of the fire-proof module, thereby facilitating a resistance against a chemical and a thermal impact by the metal and a slag and against a washout by the metal flows which occur during the purging.

A possibility of implementation of the invention that is characterized by the above-mentioned set of features, as well as a possibility of implementation of its purpose, are confirmed by the description and illustrated by drawings.

Fig. 1 is a graph of dependency of the bubble’s rise speed in the metal melt on its diameter.

Fig. 2 is a schematic diagram of the purging block in a cross section.

Fig. 1 depicts the graph of dependency of the bubble’s rise speed in the metal melt on its diameter which is built with consideration of experimental and calculated data when passing gas jets through slits having various cross sections. As it is known, the bubble that is submerged in a liquid will rise to a surface with a continuous speed relative to the liquid. This rate is called as a critical speed, and this speed is from 0.33 to 0.43 m/sec in a steel melt when a size of the bubbles is from 9 to 15 mm (see, e.g., Belov I.V. Stationary rise speed of bubbles in certain liquids. // I.V.Belov, G.N. Elovikov, B.E. Okulov. - Steel. - 1975. -No. 3. -P. 85 - 92. ). By modeling the size of the section of the slits of the working part of the purging device, it has been established that by reducing the section down to 50 pm and in case of supplying the gas under pressure of up to 2.5 MPa, a diameter of the bubble in the melt will be not more than from 1 to 2 mm, and its rise speed increases to 0.5 m/sec, while in case of increasing the section of the slit up to 180 pm and under pressure of from 0.05 MPa, the bubble having a size of up to 5 mm with the rise speed of 0.3 m/sec will be formed. In case of increasing the section to greater size, the bubbles, regardless of increase or decrease of the pressure, will be formed with significantly greater diameters, and their rise speed will be gradually reduced and equalized to the known values. Therewith, the arrangement of bubble tails at a distance of from 20 to 70 mm between each other enables to maintain the size of the bubbles along their entire path of rise.

In order to use said gas tails in the metal melt to provide their maximum rise speed and, thus, an effective flotation, an important conditions was also, firstly, to provide their maximum vertical rise and, secondly, to define a necessary and a sufficient number of the area of the slits relative to the melt volume. By means of experimental researches, it has been established that the lowest sufficient area must be not less than 2% of the area of the bottom of the metallurgical container for different purposes of flotation, while in case of reduction of the area, only an outer surface of the bubble flow will contact the melt. The area of 50% was determined as the optimal greatest contact area, and in case of increasing the same, the tails will become intersected and the bubbles will be mutually absorbed. Therewith, a horizontal arrangement of the working surface relative to the melt and directing the tails in a transverse direction to the working surface has allowed to provide a maximum vertical rise of the bubbles.

In order to manufacture the device for implementation of said technology, a purging device has been developed that is schematically depicted in Fig. 2, the device comprising a housing 1 that is made of a heat-resistant stainless steel, the housing is equipped, in a bottom portion thereof, with a gas distribution collector 2 having an intake nozzle 3, a fire-proof module 4 made of a heat-resistant concrete that is monolithically mounted in the housing 1 over the collector 2, the fire-proof module is provided with pass-through vertical longitudinal parallel slit capillary vessels 5 which are integrally made therein and located in a transverse direction relative to the housing 1. In order to provide an external protection, the purging block, including the housing 1 with the collector 2 and the module 4 of the capillary vessels 5, may be protected with a pouring layer 6 of the heat-resistant concrete that is made flush with an upper portion of the module 4 and drawing the intake nozzle 3 of the gas distribution collector 2 outwardly.

In order to enable implementation of the method, a width of each slit capillary vessel 5 must be from 50 to 180 pm, and an overall area of the longitudinal section of the capillary vessels must be from 0.008 to 5% of the area of the longitudinal section of the module 4.

In order to manufacture the slit capillary vessels integrally with the working part of the purging device, molded members are formed from a thermoplastic polymer, e.g., polypropylene, with a size that corresponds to the given size of the slits which are arranged in a mold at the required distance, the heat-resistant concrete is poured into the mold and burned after it is solidified. During the burning process, the polymer bums out under influence by high temperatures, thereby forming slits which are homogeneous in shape and arrangement that avoids their clogging or burning out and which are not exposed to quick wear during usage. Afterwards, the module is joint to the gas distribution collector and poured with the heat-resistant concrete as well that forms a monolithic housing around the working part. Therewith, linear parameters of the purging device may vary depending on need and depend on a type of the metallurgical container and a type of the lining. The described structure is simple in manufacturing and maintenance and may be easily replaced upon depletion. Therewith, linear parameters of the purging device depend on a type of the ladle and a type of the lining. The claimed structure is simple in maintenance and may be easily replaced upon depletion of the device.

Example 1.

Testing the proposed method by means of the claimed device was carried out in a steel-pouring ladle and in a “ladle-furnace” apparatus for argon purging for the purpose of refining, degassing, and homogenization of the melt when melting the steel.

The tests shown that a time of the argon purging with the use of said purging blocks under a condition of providing the area of contact between the working part of the purging device and the metal melt of from 2 to 50% will be 10-20% less as compared to a standard purging through slit purging plugs or monoblocks having wider capillary vessels. Use of the claimed technology and the device with no clogging of the capillary vessels also allowed to avoid costs for using an oxygen lance to clean the purging members after pouring the metal from the ladle.

Investigatory and industrial uses have shown that this technology enables to reduce a time of presence of the ladle on a vacuum vessel twice and to reduce energy costs significantly, to shorten the gas expenses, and, thus, a prime cost of the steel being melted.

Example 2.

Testing of the proposed method by means of the claimed device was carried out in an arc electric smelting furnace.

In order to provide high technological requirements, modem electric smelting furnaces are equipped with systems for discharging and cleaning gases being discharged, which have a power that constitutes up to 15-20% of the overall energy costs for melting the steel in the furnace. Mounting of the claimed blocks in the bottom portion of the furnace in the area of a waist of electrodes enabled to provide a blockage of the arc burning zone by the gas tails against incoming air, thereby avoiding burning of iron and formation of nitrogen oxides. Therewith, when using the purging method, a continuous supply of cold bottom volumes of the melt directly into the hot zone and a discharge of an overheated melt to a colder periphery were noted, thereby avoiding overheating and evaporation of the iron. Results of operation of the arc furnaces using the claimed invention shown a significant reduction of emissions of a red fume and a not less than 10-20% shortening of the melting duration with the corresponding reduction of the prime cost of the products.

Therefore, the claimed group of inventions enables to perform the treatment of the liquid metal with the gas medium in a small bubble mode with parallel jets, thereby allowing to achieve high homogenization processes across the entire volume of the melt and to increase the quality of the produced metal significantly, while reducing the use of the gas mixture.

Claims

1. A method for purging a liquid metal in a metallurgical container, the method comprising introducing a gas medium under pressure through fire-proof channels of a working part of a purging device that is mounted in a bottom lining of the metallurgical container, and forming bubble jets in a metal melt, characterized in that it comprises forming at least two parallel bubblejets having a diameter of the bubbles of from 1 to 5 mm at a distance of from 20 to 70 mm between each other at a boundary of a contact with the metal melt, the formed jets are directed from a transverse plane of the purging device to the metal melt at a right angle relative to the working part by means of the fire-proof channels which are slit capillary vessels having a width of from 50 to 180 pm, made integrally with the working part of the purging device, wherein a contact area of the working part of the purging device with the metal melt is maximum from 2 to 50% of the area of the bottom of the metallurgical container, and an overall area of a longitudinal section of the slit capillary vessels is from 0.008 to 5% of the area of the longitudinal section of the working part of the purging device.

2. The method for purging according to claim 1, characterized in that the pressure of introduction of the gas medium is from 0.05 to 0.25 MPa.

3. The method for purging according to claim 1, characterized in that argon is used as the gas medium.

4. The method for purging according to claim 1, characterized in that nitrogen is used as the gas medium.

5. The method for purging according to claim 1, characterized in that oxygen or an oxygen-containing gas mixture is used as the gas medium. The method for purging according to claim 1, characterized in that dispersing and structural ferroalloys and deoxidizers having a fraction size of up to 10 pm are added to the gas medium. A purging device for performing the method according to claims 1-6, the device is at least one block made of a heat-resistant concrete comprising a housing that is equipped, in a bottom portion thereof, with a gas distribution collector having an intake nozzle, with a working part that is monolithically mounted in the housing over the collector, the working part is made in a form of a fire-proof module having pass-through vertical longitudinal slit capillary vessels which are integrally made therein, as well as which are parallel and spaced apart from each other at a distance of from 20 mm to 70 mm, and located in a transverse direction relative to the housing, wherein a width of each capillary vessel is from 50 to 180 pm, and an overall area of the longitudinal section of the capillary vessels is from 0.008 to 5% of the area of the longitudinal section of the working part of the purging device. The device according to claim 7, characterized in that a heat-resistant concrete of a tabular alumina with an addition of electrocorundum and/or spinel and with a content of AI2O3 of not less than 90% is used as the material of the fire-proof module.