WO2016191842A1

WO2016191842A1 - Double refrigerated panel for electric arc furnaces

Info

Publication number: WO2016191842A1
Application number: PCT/BR2016/050122
Authority: WO
Inventors: LIMA DE SOUZA Marcelo GUERRA; SILVEIRA Fabrício GARAJAU; SILVA Marcelo DUARTE
Original assignee: Lumar Metals Ltda
Priority date: 2015-06-05
Filing date: 2016-06-02
Publication date: 2016-12-08
Also published as: BR102015013157A2

Abstract

A double-face panel is disclosed, with one operation face and one safety face, for use in an electric arc furnace, more specifically, a double panel in which the two faces comprise independent water circuits and fulfil independent functions, wherein the operation face is designed to provide correct heat extraction and the safety face to ensure the implementation of the process in safe conditions for the operators and the process operation, the double refrigerated panel having low weight and combinations of materials of low aggregated value and therefore constituting a low-cost panel with ergonomic advantages for servicing operations and operational features designed to optimise oven energy consumption and operators' safety during the operation of the electric arc furnace.

Description

COOLED DOUBLE PANEL FOR ARC ELECTRIC OVEN.

[001] The present invention relates to a refrigerated double panel for use in an electric arc furnace, more specifically to a double-sided panel, one of which is operational and one of safety, having both sides of water circuits. Independent and also independent functions, with the operating face designed to provide correct heat extraction and the safety face ensuring the process is carried out by observing the operator and operational safety aspects of the process. The dual refrigerated panel features low weight and low value-added material combinations and is therefore a low cost panel with ergonomic advantages for maintenance operations, notably assembly and disassembly, and operational characteristics aimed at optimizing the furnace energy balance combined with operator safety during electric furnace operation.

State of the Art

[002] Electric steel mills and their electric arc furnaces - FEA are recycling units that use ferrous scrap as the main raw material for steelmaking, characterizing the scrap-based route. Originally created in France in 1899 by Paul Héroult, the Electric Arc Furnace - FEA had its first commercial-scale plant installed in the United States of America in 1907. Initially electric arc ovens emerged as small production ovens ranging from 3 and 10 tons its capacity. With the development of technology, the capacity of these ovens quickly reached 100 tons. In the period of World War II Electric Arc Furnaces - FEA were widely used in steel production, but it was not until the sixties that this type of technology began to gain prominence in world steel production.

[003] The low cost of setting up steel mills compared to the cost of setting up an integrated mill enabled post-war Europe to rapidly resume its steel production, even in a position to compete with the major US long steel producers. From this time on, steel production in electric steel mills started to grow, gaining even more strength in the eighties, because in addition to the cost factor of production, the acquired technological developments further increased the productivity and competitiveness of electric arc furnaces. FEA. One of the technological developments that allowed major advances in the production of steel in Electric Arc Furnaces - FEA was the use of refrigerated panels on the metal housing of Electric Arc Furnaces - FEA. Initially, the refrigerated panels were installed on the side walls of the Arc Electric Furnaces - FEA replacing the refractory linings that remain today in the lower parts of Arc Electric Furnaces - FEA, in the region of contact with the liquid metal, in order to reduce downtime for repair ovens. The excellent results achieved led to the expansion of refractory lining replacement throughout the wall and even in the vaulted region, outer region around the crumb. [004] The first refrigerated panels were made of special steel plate with an internal baffle system for directing water flow. These refrigerated panels are also known as "box type" panels. The modern refrigerated panels can be made of steel or copper pipes, allowing the use of tubular panels and a reduction in the volume of circulating cooling water, which cooling water has a temperature rise between 10 and 35 ° C. and its flow rate is regulated to maintain control of the outlet temperature.

Although the use of refrigerated panels causes an increase in thermal losses, their use is highly offset by the possibility of greater furnace utilization and savings in the amount of refractory used. Panels have had particularly important use in furnaces using pre-reduced load. In this case, not only the electric arc heat, but also the heat from the overheated slag and liquid metal, is easily absorbed.

[006] The use of refrigerated panels has a number of advantages, such as: a) increased productivity; b) eliminating the need to reduce power during the flat bath period; c) 50% reduction in the repair time spent with refractory material; d) reduction of the time for the assembly of a new furnace, due to the reduction of the area of use of refractories; e) refractory economy, being an important economic advantage; and (f) the possibility of increasing the specific power level depending on the oven by using forced cooling of the be able to withstand higher arc thermal impacts when compared to ovens without refrigerated panels.

Typically, the refrigerated panels are installed at a distance of 300 to 400 mm above the level of the metallic bath, but variations may occur depending on the type of panel material, oven power etc. In modern furnaces refrigerated panels are also used to allow the assembly of process auxiliary equipment such as: refrigerated copper blocks, injectors and / or oxygen burners, carbon and lime fin injectors; sample makers etc.

[008] The use of refrigerated panels has also been extended to the FEA vaults to reduce their repair time. In this new vault design, the central part or core, region around the electrodes, is interchangeable and continues to be manufactured with refractories, while the remaining part of the vault or peripheral region has also become interchangeable, but made up of fabricated refrigerated panels. with metal pipes. The refrigerated area corresponds to approximately 90% of the vault area and can be made up of more than one panel to facilitate maintenance as well as increase the speed of any corrections.

The use of vaulted refrigerated panels has a number of advantages, such as: a) weight 30% less than that of refracted vaults; b) possibility of saving between 60 and 90% of refractory use; c) extended crumb life which can be easily changed; d) operation with lower temperatures around 60 ° C; and e) considerable increase in the service life of the vault.

[010] Due to their diameter, transformer power and input power, electric ovens have a particular characteristic of heat distribution inside. The three regions of the electric ovens that are closest to the electrodes are called hot spots. Refrigerated panels mounted in the hot spot regions of the electric oven are generally more thermally demanded and therefore more susceptible to problems such as thermal cracking, water leakage and short circuit due to the electric arc formed. through the oven electrodes. Therefore, FEA hot spot refrigerated panels require special attention both in the development and design phase (such as circuit optimization, use of copper and / or cladding etc.) as well as during FEA operation (such as preventive replacement being done in shorter periods than other panels).

[01 1] These are called cold spots or "cold spots", the regions of electric furnaces whose performance of the electrodes for melting the metal charge is inefficient. In order to avoid the accumulation of scraps and the formation of cascades in the furnace cold points, as well as time losses in the load melting process, it is necessary to install systems capable of providing auxiliary energy to the process, such as oxy-fuel burners. and oxygen injectors. The installation of burners, injectors and other process auxiliary equipment in the oven's cold spots causes a heating of these regions and a more homogeneous melting of the furnace metal charge. Depending on the type of equipment installed, burner power, injector flow rate, mounting angle etc., refrigerated panels installed in these cold spots will also require special care and follow-up.

[012] It is an object of the present invention to develop a refrigerated panel consisting of two independent refrigeration circuits using lower cost than light state of the art materials, which allow the reduction of the total weight, reducing the price. facilitating maintenance activities, reducing maintenance time for panel changes, and reducing the number of panel changes.

It is another object of the present invention to develop a geometry panel which associated with the use and application of certain materials in its constitution allows to increase the heat extraction through the possibility of determining optimal heat exchange conditions for each specific region of use in electric oven. For this purpose, cooling circuits made with half rods are used, which promote a larger contact area and a higher water velocity, thus increasing the heat extraction. In addition, the flat geometry reduces the number of bends in the circuit, reducing the final weight. The possibility of applying refractory or ceramic coatings allows the panel a lower heat extraction, which can represent energy gains for the oven and a longer life to the panel. [014] Another object of the present invention is related to the development of a panel whose geometry and the materials used can promote the increased operational safety of the electric furnace and especially of the operators when compared with the state of the art. Dual chamber geometry increases operational safety because if the first circuit is damaged, the second circuit works independently, acting as a protective shield for operators. On the other hand, the second circuit allows a programmed shutdown of the electric ovens avoiding emergency stops that increase the risk of accidents. In this way, it is possible to increase the resistance to failures caused by electric arc and flame rebounds, guaranteeing the operators safety due to the double chamber with independent cooling circuits.

Description of the Invention

[015] The working face consists of half rods (or half tubes) comprising bent flange profiles of varying dimensions according to panel measurements forming an independent cooling circuit which is welded to the intermediate plate and may cover the entire surface of the intermediate plate or only part of this surface, always forming a well-defined circuit with separation between the cooling water inlet and outlet, internal baffles and intermediate plate. On the surface of the work face, depending on the positioning of the panel inside the electric oven, a layer of thermal insulating coating can be applied, as well as having the option of profiles in steel or copper. [016] The intermediate plate has the primary function of separating circuits to ensure effective protection for operators as well as the basis for structural support of the equipment.

[017] The safety face consists of bent profiles of varying dimensions according to the panel dimensions, made of steel, which are fixed by welding to the intermediate plate, which must cover the entire length of it, forming a circuit of independent cooling, promoting safety and survival of the equipment in case of sacrifice of the work circuit, having intermediate plate, internal baffles and external plate.

[018] The dual refrigerated panel object of the present invention (107) consists of bent profiles of copper or steel plate and plate and / or inner coated steel (108), intermediate position steel plates (109) and plate external (110). The intermediate position steel plate (109) separates the cooling circuit from the inside or working face (204) from the cooling circuit from the outside or safety face (205). The dual refrigerated panel (107) with the functions split between work face (204) and safety face (205) allows the use of thin plates on the intermediate plate (109) and the outer plate (110), reducing weight when compared to traditional refrigerated panel, reducing the final cost of production. The cooling circuit (206) is easily mounted on the intermediate plate (109) on the working face (204) and safety face (205), consisting of half rods (207). [019] The working face (204) is coated with a non-conductive thermal insulating layer (1 1 1) and can be applied to hot spots (202) of the electric arc furnace. The working face (204) with copper half rods (108) may be applied in hot spots or with steel half rods (108) may be applied in regions with lower thermal stress. The ability of the work face combinations (204) allows the optimization of the energy balance of the electric arc furnace with significant impacts on the consumption of electric energy, combustible gases and oxidizing gases, as well as auxiliary equipment, notably water recirculation pumps. cooling systems and cooling circuit cooling systems.

[020] Arranged between the work face (204) and the safety face (205), the intermediate plate (109) functions as the first operator protection barrier, allowing operation to be halted without risk of damage to life.

[021] The occurrence of a hole in the refrigerated panel on the work face (204) is highly dangerous as water (306) circulates as a refrigerant inside the panels. When panels fail and the volume of water leaking into the electric furnace is greater than the ability to evaporate before contact, entrapment of slag and liquid metal may occur. This trapping of water at high temperatures causes the hydrogen constituents to decouple from oxygen, the constituents of water, causing catastrophic explosions, potentially potentially life-threatening operators and huge unplanned shutdowns of the FEA. The purpose of the panel of the present invention is to increase safety by the situation described above preserving the integrity of people and equipment.

Figure 1 shows a side cross-sectional view and Figures 2 and 3 show a three-dimensional view of the refrigerated double panel (107) object of the present invention, introducing the concept of faces, the working face (204) being shown. , the side of the panel that is in contact with the inner surface of the FEA. The working face 204 is a cooling circuit formed of steel or copper half rods 108. The circuit made on the work face 108 is fixed to the intermediate plate 109 by welding, forming channels for passage of the coolant, which in this case is water.

[023] It can be observed that the intermediate plate (109) has the function of dividing the circuits, but also has the important function of being the first protective barrier of the safety face (205). The intermediate plate (109) may consist of two thin plates for effective isolation of the work face (204) and safety face (205) circuits. Also, on the working face (204) on the half rods (108), depending on the positioning of the double refrigerated panel (107) inside the FEA, thermal insulating coatings (1 1 1) may be applied to cold spot regions. (203) which have a high incidence of short circuits and flame rebounds. For other regions, steel or copper may be used in the half rods to increase heat extraction and prevent premature damage to the panel. The thermal insulating coating (1 1 1) is a thin layer of the order of millimeter to centimeters. A vast composition of materials for thermal insulating coating (1 1 1), being dependent on the functions to be performed during the activity of the FEA and its positioning. Thermal insulating coating (1 1 1) may have impact resistance properties, electrical insulators, combinations of these and other properties. The intermediate plate (109) is made of high resilience material and reduced thickness contributing to the weight reduction of the double refrigerated panel (107). The intermediate plate (109) also has the function of separating the cooling circuits between the working face (204) and the safety face (205).

[024] The safety face (205) consists of lightweight and lightweight steel plates. Inside is also the assembly of a circuit made in half rods, properly positioned and welded on the intermediate plate (109) leading the passage of cooling water (306). The low material thickness as well as the low resilience give the system, in the event of an explosion inside the FEA, the ability of the double refrigerated panel (107) to deform without, however, rupturing the safety face (205). , acting as a shield for operators, thus contributing to operational safety. The lower weight of the dual refrigerated panel (107) as compared to the state-of-the-art panels allows maintenance activities to be performed with reduced ergonomic stresses for both removal and repositioning. [025] The constructive shape of the dual refrigerated panel (107) coupled with the choice of low thickness materials and insulating coatings (1 1 1) allows the panel of the present invention to be marketed at a very competitive and low cost price. maintenance and safety and operational guarantees superior to current refrigerated panels. The dual refrigerated panel (107) can be applied to other FEA refrigerated segments such as dome and exhaust ducts.

Claims

1. Refrigerated double panel for electric arc furnaces comprising a working face (204) and safety face (205), consisting of half rods (207), an inner part (108), steel plates in intermediate position ( 109) and outer plate (110), separating the steel plate in intermediate position (109), the internal or working face cooling circuit (204) of the external or safety face cooling circuit (205) .

Panel according to Claim 1, characterized in that the inner part (108) is composed of folded sheet metal profiles.

Panel according to Claim 1, characterized in that it is the inner part (108) composed of copper plate.

Panel according to Claim 1, characterized in that it is the inner part (108) composed of coated steel.

Panel according to Claim 1, characterized in that it uses low-thickness plates in the intermediate plate (109) and in the outer plate (110).

Panel according to Claim 1, characterized in that the working face (204) is coated with a non-conductive thermal insulating layer (11).

Panel according to Claims 1 and 6, characterized in that the working face (204) is applied to hot spots (202) of the electric arc furnace. 2/3

Panel according to Claims 1 and 6, characterized in that the working face (204) consists of a cooling circuit formed by steel half rods (108).

Panel according to Claims 1 and 6, characterized in that the working face (204) consists of a cooling circuit formed by half-copper rods (108).

Panel according to Claims 1 and 8, characterized in that the steel working face (204) is applied in regions with lower thermal stress.

1 1. Panel according to Claims 1 and 9, characterized in that the copper working face (204) is applied to hot spots in the electric arc furnace.

Panel according to Claim 1, characterized in that it is the circuit made on the work face (108) fixed to the intermediate plate (109) by welding, forming channels for passage of the coolant, which in this case is water.

Panel according to Claim 1, characterized in that the intermediate plate (109) consists of two thin plates for effective isolation of the work face (204) and safety face (205) circuits. 3/3

Panel according to Claim 1, characterized in that the thermal insulating coating (11) has impact resistance properties.

Panel according to Claim 1, characterized in that the intermediate plate (109) is made of highly resilient material of reduced thickness.

Panel according to Claim 1, characterized in that the intermediate plate (109) has the function of separating the cooling circuits between the working face (204) and the safety face (205).

Panel according to Claim 1, characterized in that the safety face (205) is made of thin and lightweight steel plates.

Panel according to Claim 1, characterized in that the safety face (205) has a half-tube circuit mounted and welded to the intermediate plate (109) for cooling water passage (306).