Liutyi Oleg

Summary of research and developments

Introduction (Motivation)

Recently in the world spreading receives the electrothermal equipment which works on a direct current. Steel furnaces which work on a direct current, have current-carrying bottom, or bottom anode, and one roof electrode (in rare cases two roof electrode), located in the center of the furnace. These furnaces enable to improve operating techniques and to create new, to ensure excellence of metal at use of ordinary cheap mix material, including that, what hard gives in to processing. New furnaces and electrotechnological process in them have high indexes on technical, economic and ecological parameters. In electric arc furnaces of direct current (DC-EAF) advantages of electroarc heat are realized, its opportunities are develop and augmented, the basic deficiencies are liquidated. Thus, electric arc furnaces of a direct current have following advantages: lowering specific expenditures of the electric power on ton of production on 10-12 %; lowering expenditures of graphitic electrodes in 2 - 5 times at depending of preparation of mix material; increase in a recovery ratio at 4 % - of 6 % (in ore heat-treating furnace); improvement of ecological indexes, lowering dust and gas purification in 3 - 5 time, noise on 25 - 30 %; reduction of an intoxication of technological components on 30 - 70 %; an opportunity of use of electrochemical reactions on a direct current for removal of harmful admixtures and improvement of quality of production; increase in life expectancies of lining; heightening a resource of high-voltage transformers and cutout switches, lowering of "flicker-effect" in 2 - 5 times; According to the foreign information and operating experience at the factory’s re-equipment of furnaces of an alternating current on power supply by a direct current pays off for one year. Direct current electric arc furnaces (DC EAF) attract the attention in machine-building industry and a “big” metallurgy . Bottom electrode (anode) is necessary part of these furnaces. Among four types of anodes, using in DC EAF: conductive refractory, pin-type, fin-type and billet-type, the last seems most convenient from the positions of steelmaking technology and maintenance]. Conventionally billet-type anode comprises conjoined upper steel rod, contacting with the bath, and down copper water cooled part. According to practice in such solution liquid meniscus of molten steel rod drops down to furnace shell level forming so-called anode pit of molten metal into bottom refractory. These pits (EAF usually includes 2-4 anodes) render a very negative influence on durability of anode and adjoining refractory especially in ultra-high power EAF. In a mechanism of anode and adjoining refractory wear prevail role of electromagnetic effect which creates intensive motion of liquid bath under action of electromagnetic forces (Lorentz forces). At that in iron part of bottom electrode a liquid-solid phase boundary is establishing. Position of it defines behavior of the anode, its durability and safety of exploitation. most important operating factors influenced on bottom electrode behavior, are liquid bath temperature and current force. Is suggested an idea of bottom electrode protection by “mushroom” of solid metal crust (Fig.1), under formation due to local intensive cooling of the bath in process of endothermic reaction of blowing hydrocarbons decay . But there is no information about real embodiment of mentioned solution and obtained results.

Рисунок 1 - Ожидаемый «гриб» при локальном охлаждении ванны

The present work target is experimental campaign to test the active anode sleeve wear resistance in conditions closer to industrial scale DC-EAF by using experimental DC-EAF facilities using gas-dynamic method of protection .
For operation with mentioned bottom electrode (anode) 80-kg crucible-type DC EAF was elaborated and manufactured. EAF adapted for operation together with standard ESR device У-360, equipped by welding single-phase transformer A-622M and rectifier. Furnace uses 200mm graphite electrode as cathode, which introduces into crucible through refractory roof. Crucible provides channel for tapping of excessive liquid metal (see Chapter 3). Feeding of addition scrap fulfilled through funnel into the roof. Transformer parameters are given below:Primary voltage 380V,Secondary voltage 40-72V,Maximal current force 10kA.
Gas mixture in order to create “mushroom” due to local cooling, we used methane (CH4) с СО2. Cracking of methane (CH4 = C+ 2H2), which becomes essential at temperatures more than 773-873 K, results endothermic effect 4,97 MJ/kg CH4 and promotes local cooling.at temperatures over 1273 K takes place practically irreversible Bell’s reaction CO2+C=2CO, which gives endothermic effect 3,69 MJ/kg CO2 . That is useful from the position of more intensive cooling of the sleeve. The venting intensity was about 1,3-1,4 l / min., and metal velocity – 0,2 m/s.

Рисунок 2 - Схема опытной установки и измерения износа футеровки

Wear of refractory is defined in a fixed area, positioned at distance 1,2 bottom electrode radius (RBE) as a sum of differences (relatively reference plan- upper section of the crucible) between dimension A in the start and tapping of each heat of the session. Values of A measured with the aid of 20mm diameter steel rod, inserted firmly into liquid bath.
Using of “active sleeve” concept in order to protect of anode zone DC EAF refractory gives moderate positive results. Lorentz force action on refractory wear, apparently, decreases by cooling action of gas and gas-powder mixtures, blowing into the bath through “active sleeve”, due to formation of protective crust of semi-solid material. Using of “active sleeve” concept allows decreasing refractory wear velocity on 19 % in comparison with the case of traditional sleeve(0,80 mm/hour against 0,98 mm/hour).

Currency

As a result of the several factors in the region of electrode the increased wear of the brick lining is observed. As a result this is strengthened heat emission from the bath to the electrode. This leads to the increased wear of refractory and the premature failure of electrode. Therefore the study of this problem is extremely urgent.

Purpose

Enhancing the resistance of bottom electrode using a gas-dynamic method of protection.

Survey of research and developments

Conclusion

Engineering process intends theoretical calculation for the purpose configuration and operating conditions optimization of bottom electrode as well as physical simulation for the purpose study function of DC EAF bottom electrode. At the moment on basis of computer mathematical simulation did research of bottom electrode intensive cooling influence.

References

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