WO1993001461A1

WO1993001461A1 - Process and equipment for reducing electrode consumption and improvement of other operational parameters in electric arc furnace

Info

Publication number: WO1993001461A1
Application number: PCT/BR1992/000010
Authority: WO
Inventors: Alexandre Ferraz Naumoff; Muhamed Jahic; Carlos Luis Pissaldo; Simão Pedro de OLIVEIRA; Adonis Marcelo Saliba; Wagner GONÇALVES
Original assignee: De Acos Especiais Itabira - Acesita Cia; Instituto de Pesquisa Tecnologicas do Estado Sao Paulo S/A (IPT)
Current assignee: De Acos Especiais Itabira - Acesita Cia; Instituto de Pesquisa Tecnologicas do Estado Sao Paulo S/A (IPT)
Priority date: 1991-07-05
Filing date: 1992-06-26
Publication date: 1993-01-21
Anticipated expiration: 1994-01-05
Also published as: BR9102906A

Abstract

The present invention presents a process and equipment to improve the operational and productive conditions for an electric arc furnace with a plasma thermal arc with longer and more stable arc using the controlled injection of inert gases, especially argon and/or its mixtures (or another convenient) through the hollowed electrodes. The present invention comprises an exact measurement of voltage between the electrode and the material charge by an electronically corrected system of data acquisition for a microcomputer processing. The formation of such long and stable electrical arc is based on a central beam of ionized gas with high conductivity that elongates and stabilizes the main arc avoiding the extinction of it, and in other promoting it to be more stable and effective. The creation of such pilot flame of ionized gas is a result of gas pressure/flow and velocity combination with the hole diameter, electrode diameter and electrical parameters. With positive results of this long and stabilized arc, especially during melting phase in electric arc furnace, it has emphasized the following points: significant economy of electrodes; reduction of flickering of electrical network, by stabilization of arc; reduction of process time; improving of productivity; economy on refractory lining; reduction of global energy consumption for melting; less risk of electrode cracking and fallings.

Description

PROCESS AND EQUIPMENT FOR REDUCING ELECTRODE CONSUMPTION AND IMPROVEMENT OF OTHER OPERATIONAL PARAMETERS IN ELECTRIC ARC

FURNACE The production of steel in electric arc furnaces achieved high technological improvement in the last years. This growing owes to several changes and improvements related to the furnaces constructions to electrical installations and to the auxiliary equipment, as well by bringing into practice new operating process. All this complex ensemble resulted in productivity growth, reduction of energy consumption, savings in electrodes, alloys and additives. All this resulted in an important production costs¹ reduction. During the sixties, in Canada and Germany, some studies and laboratory experiments tried to inject gases, especially inert gases, through hollowed electrodes at electric arc furnaces. The purposes of these studies were to get eventually improvement of some parameters and operating phenomena. Nevertheless, the results were not very convincing and did not suit to industry.

The study carried out by us, in spite of having the same purposes, comprehended a greater number of operating parameters and showed successfully for industrial purposes. In our present work, we made some tests of injecting argon gas through hollowed electrodes in a Detroit type monophase electric arc furnace. Figure 1 shows an arrangement for the tests.'

The tests showed some good results as reduction of flickering in the electrical feeder, a more stabilized arc, reduction of noise, resing of an extended arc (from 10mm to 120mm) and a significant reduction of electrode consumption (about of 30%) .

Afterwards, a project was made and an equipment in industrial scale have been assembled with controlled argon injection through hollowed electrodes into a three phase arc furnace of nominal capacity of 10 metric ton in molten stell. This furnace had a 3000kVA of power transformer and 250mm diameter electrodes. To assure a stabilized and controllable injection, the electrodes were bored to have central holes with reduced diameter. The process and the industrial equipment to make the boring through the electrodes is object of Pending Patent PI 9.003.824 (Brazilian-INPI) of 31 Jul 90. Several heats were performed and the changes of operating parameters were confirmed such as observed in Detroit furnace trials, especially the oscillations noise at feeding in electrical net, a more stabilized arc and a clear reduction of electrode consumption, around 30 to 35%.

Figure 2 shows a schematic view of the installation: main body of electric arc furnace (1) ; transformer (2) ; electrodes' holders (3) ; bar conductors (4) connecting the transformer (2) with the furnace (1) ; graphite electrodes (5) ; couplings (7) of gas piping (6) with electrode (5) ; control panel (8) and bars (4) ; main argon gas piping (10) ; microcomputer for data processing (11) .

The control panel (8) is equipped and assembled with necessary instruments and devices for system operation and controlling, such as: amperimeters, voltmeters, quilowattmeters, pressure meters, flow meters, meters of gas temperature, solenoide valves for gases, pressure regulator valve, thick hollowed plate (IPT type) , electronic data acquisition system, Rogowski coils, current transformers, voltage transformers and several ball type valves for opening and blocking the gases. According to the results of these operations, the present inventions show also one step more in terms of improving the operational and productive conditions of electric arc furnace. The process is characterized by forming a thermal plasma of higher intensity due to the formation of an elongated and stabilized arc with the controlled injection of inert gases through the hollowed electrodes. The make up of this stabilized extended arc is able for the action of the central jet of ionized argon (mixed or another convenient gas) of high conductivity in the shape of a long pilot flame. This one extends the main arc and avoids interruption of the arcing, which becomes than more stable and more effective. The ionized argon pilot flame is the result of an arrangement of pressure and flow combination, the electrode hole diameter, electrode size and the internal counter pressure of the furnace at melting phase. Good results have been achieved using this extended and stabilized arc, such as follows:

- reduced electrode consumption due to the lack of wearing action of the high power short circuits;

- reduced flicker in the electrical net; - reduced noise;

- reduced melting time and consequently getting higher productivity by around 5 to 10%;

- reduced refractory wearing;

- reduced electrode breakage for the extended arc during the initial period of melting;

- reduced energy consumption.

Claims

CLAIMS We Claim:

1. "Process and Equipment for Reducing Electrode Consumption and Improvement of other Operational Parameters in Electric Arc Furnace" characterized to be a process and equipment of controlled injection of inert gases, especially of argon and/or its mixtures (with another convenient gas) through the hole of hollowed electrodes, with the aim of improving several operational parameters and, mainly, the reducing of electrode consumption during melting and refining in electric arc furnace.

2. "Process and Equipment for Reducing Electrode Consumption and Improvement of other Operational Parameters in Electric Arc Furnace", according to claim 1, is characterized by the use of electrode employing reduced dimensions of bore diameter through its whole length. This is in function of required electrical parameters to be developed.

3. "Process and Equipment for Reducing Electrode Consumption and Improvement of other Operational Parameters in Electric Arc Furnace", according to claim 1, is characterized by the formation of longer and more stable arc than in common use of other electric arc furnaces, without necessity of increasing the nominal power of furnace.

4. "Process and Equipment for Reducing Electrode Consumption and Improvement of other Operational Parameters in Electric Arc Furnace", according to claim 1, is characterized by the formation of a pilot inject in length, speed and controllable intensity, stabilizer of electric power and current of main arc by the controllable injection of inert gases and its mixtures through hollowed electrodes in electric arc furnaces.

5. "Process and Equipment for Reducing Electrode Consumption and Improvement of other Operational Parameters in Electric Arc Furnace", according to claim 1, is characterized for being constituted by the following main parts (as shown in figure 2) of system for controllable injection of inert gases and/or its mixtures through hollowed electrodes in electric arc furnaces: hollowed electrodes (5) , feeding tubes of gases between control panel and the electrode itself (6) , joining between the tube and the electrode (7) , commands panel, control keys with respective instruments, electronic corrected tension between each electrode and material and its panel indication (8) , electric cables between panel and power bars (9) , microcomputer for process data control (11) .