GB1564278A - Electric arc furnace roof cooling system - Google Patents

Description

(54) AN ELECTRIC ARC FURNACE ROOF COOLING SYSTEM (71) We, VSESOJUZNY NAUCHNO ISSLEDOVATELSKY I PROEKTNY INSTITUT PO OCHISTKE TEKHNO LOGICHESKIKH GAZOV STOCHNYKH VOD I ISPOLZOVANIJU VTORI CHNYKH ENERGORESURSOV PRED PRIYATY CHERNOI METALLURGII "VNIPICHERMETENERGOOCHISTKA", of prospekt Lenina 9, Kharkov, and ELEKTROMETALLURGICHESKY ZAVOD "DNEPROSPETSSTAL" IMENI A.N. KUZMINA, of Zaporozhie, both Union of Soviet Socialist Republics, both Corporations organised and existing under the laws of the Union of the Soviet Socialist Republics, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statment: The present invention relates to roof cooling systems for electric arc furnaces.

One of the major trends in present day electric steel-melting practice is continuous enhancement of both the capacity and specific power of arc steel-making furnaces.

Recent years mark the construction of large-capacity electric furnaces which, along with converters, are considered to be promising in terms of their future development as compared with other metallurgical units.

Intensification of electric steel-melting production by using gaseous oxygen and higher-rating transformers for melting steels of various chemical composition has to a considerable extent worsened the operating conditions of the refractory brickwork in electric-arc steel-making furnaces.

The roofs of such electric-arc furnaces ;are operating under especially severe conditions, being exposed to the combined effect of extremely high temperatures and variable thermal loads, on the one hand, and heat products and reducing furnace atmospheres, on the other. All these factors are responsible for reduced strength of the roof brickwork, more irregular wear of roof brick, brickwork deformation, and early stoppage of the furnaces, in spite of considerable remaining thickness of their lining, which results in a higher consumption of expensive refractory materials.

Moreover, with the present-art roofs of such electric steel-making furnaces there is always a danger of brickwork disruption even before the beginning of operation of the roof, since the bricks are wedged to such an extent as to preclude their falling out.

Thus, when the furnace roof is erected and then brought into operation, i.e. under heating to a temperature of 1700 to the refractory brick is able neither to elongate nor to expand, its absolute elongation and expansion characteristics in the above temperature range being quite substantial. This gives rise to thermomechanical stresses originating in the roof brickwork and causing cracking, which, in the case of recurrent heating and cooling cycles, is liable to develop, with the ensuing spalling of the refractory lining of the roof.

Therefore, attempts have been made to compensate for the stresses arising in the brickwork in the course of operation of a furnace roof by placing burning-out strips in the roof or using various mortars for laying roof brickwork. This has not, however, produced the desired effect, the life period of the furnace roofs being extended almost negligably.

The life of electric furnace roofs has been extended by constantly improving the quality of the refractories used and by developing new kinds of refractory materials and bricks. However, this trend is inefficient, the cost of refractories growing constantly and practically out of proportion to the extension of the life of the roor, a feature that should not be overlooked.

An alternative in this search for possibilities and means for extending the life of the roofs of electric furnaces lay in developing cooled structures.

What is desired is a cooled roof featuring a more extended period of life than the' prior-art roofs and minimum heat losses.

The roof should be simple in design, particularly from the standpoint of erecting the roof proper and its lining. It should be possible to replace a worn-out section of the lining of the roof without removing it from the furnace. The roof should be designed to ensure a minimum consumption of electric power per unit product owing to an optimized lining/cooled tube area ratio.

The present invention provides an electric arc furnace roof cooling system comprising a roof ring, headers and tubes supported by the roof ring, the tubes being suspended from the headers and extending transversely to them, the tubes and the headers being interconnected for coolant flow therethrough, and a refractory lining comprising bricks which rest on the tubes, the bricks being located by and between upstanding fins which run along the tubes and are spaced apart sufficiently to allow thermal expansion of the bricks.

The refractory bricks are thus placed freely on the cooled tubes without resorting to any mortar whatsoever, i.e., in service each refractory brick is capable of expanding freely in any direction, which prevents thermal stresses arising in the refractory brickwork, eliminating thereby a major kind of wear of the roof lining in electric furnaces, i.e., cracking and spalling of refractories.

No additional appliances are required for binding the refractory bricks to the cooled tubes, the bricks being placed freely thereon, which cuts down both the time and labour inputs in erecting a roof lining.

Moreover, it is possible to remove any worn-out brick to be replaced by a new one directly on the furnace, i.e., without removing the furnace roof.

By increasing the spacing between the cooled tubes, the number of tubes can be diminished materially as compared with prior-art tube-cooled roofs or, in other words, the area of cooled surface can be reduced substantially as compared with box-cooled roofs, with the resultant appreciable decrease in power requirements per unit product.

The invention will be described further, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a plan view, partly broken out, of an electric arc furnace roof cooling system; Fig. 2 is a cross-section on line II--II of Fig. 1; and Fig. 3 is an enlarged cross-section on line 111-111 of Fig. 1.

The electric arc furnace roof illustrated comprises parallel tubes 1 whose end portions rest on a hollow roof ring 2. In the central part of the roof, the tubes 1 are suspended from two beams each comprising a pair of headers 3 and 4 (as shown in Fig. 2), of which the bottom header 3 is for supplying and the top header 4 for draining a coolant. The tubes 1 are suspended from the headers by way of hangers such as that shown at 5 in Fig. 1. The tubes 1 of the cooled furnace roof are coupled with the header 3, such as that shown in Fig. 2, through pipe connections 6 and with the header 4 through pipe connections 7. The ends of the tubes are interconnected by tube bends. The headers 3 and 4 are welded in pairs to each other, a plate 8 being placed therebetween to provide better attachment of the headers.

The tubes 1 run transversely to the headers 3 and 4 forming therewith a roof framework with fixtures for supporting the refractory lining of the furnace roof.

A shell 9 is welded round the circumference of the roof ring 2. Each tube bend is attached to the roof ring 2 by a clip 10. A metal strip, such as that shown at 11 in Fig. 3, is welded along the top generatrix of each tube 1 and acts as an upstanding fin for locating the refractory lining. Adjacent metal strips 11 locate bricks 13 which are placed therebetween with a clearance 12 and have edges resting on the adjoining tubes 1. The refractory bricks 13, acting as a refractory lining, are placed on the tubes 1 to form at least one layer of bricks. The side wall of the roof ring 2 (Fig. 2) facing the furnace interior, is protected with a refractory material 14. For suspending the roof, lugs 15 (Fig. 1), are provided and for handling it there are hooks 16. To enable the passage of electrodes 17 through the roof, it is provided with appropriate holes (not shown).

As shown in Fig. 1, the roof is suspended by means of the hooks 16 and relevant hoisting means and placed on the furnace to be secured thereto by way of the lugs 15. A system of pipelines (hoses and pipings) is adapted for supplying the coolant into the headers 3, the coolant flowing through the pipe connections 6 onto the cooled tubes 1 and through the pipe connections 7 into the top headers 4, wherefrom it is drained into a discharge funnel. The refractory bricks 13 are arranged on the cooled tubes 1 so that even in case of their maximum expansion during furnace firing a clearance is retained between each strip 11 and each adjacent refractory brick 13.After a number of heats slag-metallic deposits, formed on the entire bottom surface of the tubes 1 and brick 13, preclude the outflow of heat products through the gaps in the refractory lining of the furnace roof and cut down heat losses by protecting the cooled tubes 1.

The roof is characterized by extremely slow wear of its refractories, since the major kind of wear in electric furnace roofs, cracking and spalling, is avoided. Moreover, it allows utilizing actually the entire thickness of the refractory roof arch; a worn brick can be easily replaced in any roof section without stripping the furnace roof.

The above-described design of the cooled roof has been tested on a 60 t electric-arc furnace and the experiments have fully demonstrated both its reliability and its technological effectiveness. Lining thickness was 150 mm, which was half as great as that in the prior-art roofs. As for the period of life of the cooled roof, it increased 2.5 times and amounted to 244 heats.

The consumption of electric energy was only from 1 to 1.5% more than the power requirement per unit product when using an uncooled roof. Moreover, the life period of wall brickwork was extended to 244 heats, whereas commonly the brickwork withstood only 160 heats. This close agreement between the periods of life of the roofs and walls of electric-arc furnaces offers a reduction in the number of repairs, since there is no need whatsoever to stop the furnace firstly for repairing its walls and then for replacing its roof.

The present invention thus offers a solution to the problem of extending service life of roofs for electric steel-making furnaces, with the additional advantage of minimum heat losses, the increased power requirement in comparison with furnace roofs not employing any cooling system being almost negligible; if compared with prior-art cooled roofs the roof of the present invention provides a considerable saving in power.

WHAT WE CLAIM IS: 1. An electric arc furnace roof cooling system comprising a roof ring, headers and tubes supported by the roof ring, the tubes being suspended from the headers and -extending transversely to them, the tubes and the headers being interconnected for coolant flow therethrough, and a refractory lining comprising bricks which rest on the tubes, the bricks being located by and between upstanding fins which run along the tubes and are spaced apart sufficiently to allow thermal expansion of the bricks.

2. An electric arc furnace roof cooling system substantially as described herein with reference to, and as shown in, the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. refractory brick 13. After a number of heats slag-metallic deposits, formed on the entire bottom surface of the tubes 1 and brick 13, preclude the outflow of heat products through the gaps in the refractory lining of the furnace roof and cut down heat losses by protecting the cooled tubes 1. The roof is characterized by extremely slow wear of its refractories, since the major kind of wear in electric furnace roofs, cracking and spalling, is avoided. Moreover, it allows utilizing actually the entire thickness of the refractory roof arch; a worn brick can be easily replaced in any roof section without stripping the furnace roof. The above-described design of the cooled roof has been tested on a 60 t electric-arc furnace and the experiments have fully demonstrated both its reliability and its technological effectiveness. Lining thickness was 150 mm, which was half as great as that in the prior-art roofs. As for the period of life of the cooled roof, it increased 2.5 times and amounted to 244 heats. The consumption of electric energy was only from 1 to 1.5% more than the power requirement per unit product when using an uncooled roof. Moreover, the life period of wall brickwork was extended to 244 heats, whereas commonly the brickwork withstood only 160 heats. This close agreement between the periods of life of the roofs and walls of electric-arc furnaces offers a reduction in the number of repairs, since there is no need whatsoever to stop the furnace firstly for repairing its walls and then for replacing its roof. The present invention thus offers a solution to the problem of extending service life of roofs for electric steel-making furnaces, with the additional advantage of minimum heat losses, the increased power requirement in comparison with furnace roofs not employing any cooling system being almost negligible; if compared with prior-art cooled roofs the roof of the present invention provides a considerable saving in power. WHAT WE CLAIM IS:

1. An electric arc furnace roof cooling system comprising a roof ring, headers and tubes supported by the roof ring, the tubes being suspended from the headers and -extending transversely to them, the tubes and the headers being interconnected for coolant flow therethrough, and a refractory lining comprising bricks which rest on the tubes, the bricks being located by and between upstanding fins which run along the tubes and are spaced apart sufficiently to allow thermal expansion of the bricks.

2. An electric arc furnace roof cooling system substantially as described herein with reference to, and as shown in, the accompanying drawings.