Melting furnace for metallurgical plant and operating method therefor

Abstract

A melting furnace for metallurgical plant comprising a vessel provided with a bottom; a tapping duct passing through the bottom; rotation means to rotate the vessel so that the tapping duct passes from a first reference position to a second position inclined with respect to said first reference position, and vice versa; wherein said tapping duct has a first stretch arranged in the thickness of the bottom and completely passing through the bottom, and a second stretch, adjacent to the first stretch, protruding inside the vessel; wherein there is provided a cover of the second stretch shaped as a tube closed at an upper end thereof and open at a lower end thereof; said tube being coaxial and spaced from said second stretch, and being spaced from a zone of the bottom which includes the first stretch of the tapping duct, whereby the cover, in cooperation with the second stretch of the tapping duct, acts as a tapping hood.

Claims

1. An operating method of a melting furnace comprising a vessel provided with a bottom; a tapping duct passing through the bottom and having a first stretch arranged in a thickness of the bottom and completely passing through the bottom, and a second stretch, adjacent to the first stretch, protruding inside the vessel; a fixed cover of the second stretch shaped as a bell, closed at an upper end thereof and open at a lower end thereof; said bell being coaxial and spaced from said second stretch, and being spaced from a zone of the bottom which includes the first stretch of the tapping duct, whereby the fixed cover, in cooperation with the second stretch of the tapping duct, defines a volume inside the fixed cover and adapted to act as a tapping hood; rotation means adapted to rotate the vessel so that the tapping duct passes from a first reference position to a second position inclined with respect to said first reference position, and vice versa; the method comprising the following steps: a) providing the vessel with the tapping duct in the first reference position and providing a bath of molten metal material at an equal level both inside and outside the fixed cover and comprised between the lower end of the fixed cover and an upper edge of the second stretch, a slag being kept on a surface of said bath outside the fixed cover; b) rotating the vessel in a first direction so that the tapping duct passes from said first reference position to said second position inclined until the level of molten metal material reaches the upper edge of the second stretch so that the molten metal material begins to be tapped through the tapping duct creating a depression inside the volume; c) rotating the vessel in a second direction, opposite the first direction, so that the tapping duct returns to the first reference position, while, due to said depression, the molten metal material passes from the outside of the fixed cover to the inside of the volume and continues to be tapped through the tapping duct until said depression is canceled.

2. The method according to claim 1, wherein in step c) said depression is canceled when the level of molten metal material outside the fixed cover reaches a lower edge of the lower end of the fixed cover, whereby, at a passage of air from the outside of the fixed cover to the inside of the volume, the level of molten metal material inside the fixed cover is lowered, reaching the lower edge, and therefore reaching the level of the molten metal material outside the fixed cover; or wherein said depression is canceled by operating a relief valve provided on the fixed cover; or wherein said depression is canceled by further rotating the vessel in said second direction, so that the tapping duct passes from said first reference position to a third position inclined with respect to said first reference position until the level of molten metal material inside the volume reaches the lower edge of the fixed cover.

3. The method according to claim 1, wherein, following step c), with the tapping duct in the first reference position, there are provided the steps of: returning the bath of molten metal material to a level between the lower end of the fixed cover and the upper edge of the second stretch; repeating steps b) and c).

4. The method according to claim 1, wherein during at least steps b) and c) it is possible to load and/or melt scrap inside the vessel, also during the tapping.

5. The method according to claim 1, wherein the tapping duct is always kept open, also during the melting of scrap inside the vessel.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further features and advantages of the present invention will be more apparent in light of the detailed description of a preferred, but not exclusive, embodiment, of a melting furnace illustrated by way of non-limiting example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic section view of part of a melting furnace according to the invention;

(3) FIG. 2 is an enlargement of some components of the furnace in FIG. 1;

(4) Figures from 3a to 3h diagrammatically represent some working sequences of the melting furnace according to the invention.

(5) The same reference numbers in the figures identify the same elements or components.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(6) The figures show a melting furnace for metallurgical plant according to the invention.

(7) The melting furnace is only partially shown in the figures and is represented as a whole by reference numeral 1. The melting furnace 1 is described only partially with particular reference to the elements which distinguish it from known furnaces. The parts of the furnace which are not described in detail herein should be understood as being in themselves known and conventional.

(8) The melting furnace 1 of the invention comprises in all its embodiments:

(9) a vessel having a bottom 2 which is part of the floor of the furnace and which comprises an inner surface adapted to be in contact with the metal mass or metal bath contained in the furnace 1;

(10) a tapping duct 3 passing through the bottom 2;

(11) rotation means to rotate the vessel about a rotation axis X so that the tapping duct 3 passes from a first reference position to a second position inclined with respect to said first reference position, and vice versa.

(12) The rotation means comprise, for example, slides or rack mechanisms or shoes.

(13) The tapping duct 3, preferably eccentric with respect to the bottom 2, has a first stretch 6 arranged in the thickness of the bottom 2 and completely passing through the bottom itself, and a second stretch 5, adjacent to the first stretch 6, protruding inside the vessel. A third stretch 10 of the tapping duct 3 can be provided which protrudes outside the vessel, under the base floor of the furnace. The stretches 5, 6 and the possible stretch 10 have the same longitudinal axis.

(14) Advantageously, there is provided a cover 7 of the second stretch 5 shaped as a bell, preferably a tube closed at an upper end 8 thereof and open at a lower end 9 thereof. The cover 7 is a fixed cover, e.g. fixed to the walls of the vessel, coaxial and spaced from said second stretch 5 and also spaced from a zone of the bottom 2 which includes the first stretch 6 of the tapping duct 3, whereby the cover 7, in cooperation with the second stretch 5 of the tapping duct 3, defines a volume 4 inside the cover 7 and adapted to act as a siphon.

(15) Both the cover 7 and the tapping duct 3 are made of refractory material or simply coated with a refractory material.

(16) In the variant shown in FIGS. 1-2, having defined a maximum level 20 of the bath of molten metal material 16 inside the vessel, always comprised between the lower end 9 of the cover 7 and an upper edge 13 of the second stretch 5, said second stretch 5 of the tapping duct 3 has a length H, measured starting from the part of bottom 2 from which it protrudes, so that the upper edge 13 of the second stretch 5 is always over said maximum level 20.

(17) Advantageously, the length of the second stretch 5 is greater than or equal to the thickness of the zone of the bottom 2 which includes the first stretch 6, preferably greater than or equal to the length of the first stretch 6.

(18) Preferably, the length H of the second stretch 5 of the tapping duct 3, measured starting from the part of bottom 2 from which it protrudes, is comprised between 800 and 1100 mm.

(19) The length of the first stretch 6 is preferably comprised between 600 and 850 mm. The length of the possible third stretch 10, for example, is comprised between 0 and 300 mm.

(20) At least one burner can be provided at the outlet section of the stretch 6 or of the stretch 10, adapted to be actuated at the end of tapping to clean the lower end of the tapping duct.

(21) The tube defining the cover 7 is defined by a base 11, placed at the upper end 8 thereof and spaced from an upper edge 13 of the second stretch 5 of the tapping duct 3, and by a cylindrical lateral surface 12 arranged coaxially to the tapping duct 3 and spaced from the outer wall 14 of the second stretch 5.

(22) Preferably, the distance A between the base 11 and the upper edge 13 of the second stretch 5, the distance B between the cylindrical lateral surface 12 and the outer wall 14 of the second stretch 5, and the distance C between a lower edge 15 of the lower end 9 of the cover 7 and the zone of the bottom 2 which includes the first stretch 6, satisfy the following relationship: A=(B+C)*0.7.

(23) Preferably, the distance A is comprised between 100 and 400 mm.

(24) Preferably, the distance B is comprised between 80 and 300 mm.

(25) Preferably, the distance C is comprised between 50 and 250 mm.

(26) The angular distance between the second position and the first position of the tapping duct 3 is advantageously less than 10° so as to allow, even during the handling of the vessel and/or the tapping of the molten metal material, that further scrap can be charged into the vessel and that the melting can continue without interruption.

(27) Preferably, said angular distance is comprised in the range between 3° and 8°, possibly including the limit values, still more preferably equal to 5°-6°, i.e. comprised in the range between 5° and 6° including the limit values.

(28) Alternatively, the cover 7 can be a movable cover adapted to move along its own longitudinal axis.

(29) An operating method of a melting furnace according to the invention, diagrammatically shown in Figures from 3a to 3h, is described below.

(30) Initially, the vessel is provided with the tapping duct 3 in the first reference position, e.g. a vertical position, and there is provided a bath of molten metal material 16 at an equal level both inside and outside the cover 7 and comprised between the lower edge 15 of the cover 7 and an upper edge 13 of the second stretch 5, the slag 17 being kept on the surface of said bath 16 outside the cover 7 (FIG. 3a).

(31) Therefore, the method of the invention does not provide an initial level of the molten metal material bath higher than the upper edge 13 of the second stretch 5 of the tapping duct, and therefore does not provide an initial tapping obtained exclusively by gravity.

(32) The vessel is then rotated in a first direction of rotation (FIGS. 3b and 3c) so as to raise the molten metal material level in the vessel zone comprising the tapping duct 3, so that the tapping duct 3 passes from said first reference position to a second position inclined with respect to said first reference position, preferably by an angle lower than 10°, until the level of molten metal material reaches the upper edge 13 of the second stretch 5 so that the molten metal material begins to be tapped through the tapping duct 3 whereby creating a depression inside the volume 4.

(33) In particular, FIG. 3c shows a moment in which the level of the molten metal material inside the cover 7, i.e. inside the volume 4, exceeds the level of the upper edge 13 of the tapping duct 3, whereby the molten material starts flowing through the tapping duct 3.

(34) The depression produced inside the cover 7, because of the beginning of the tapping, determines the passage of the molten metallic material from the outside of the cover 7 into the volume 4 while the tapping continues, whereby causing a difference of level between the molten material inside the cover 7 and the molten material outside said cover 7, the level becoming increasingly lower on the outside of the cover with respect to the inside.

(35) The vessel is then rotated in a second direction of rotation (FIGS. 3d, 3e, 3f), opposite to the first direction of rotation, so that the tapping duct 3 returns in the first reference position (FIG. 3f) while the tapping of the molten metallic material continues.

(36) Advantageously, it is possible to load and/or melt the scrap in the vessel also while tapping. Indeed, FIGS. 3c to 3e, for example, show how the amount of molten metal material 16 increases inside the vessel.

(37) The molten metal material continues to pass from the outside of the cover 7 into the volume 4 and continues to be tapped through the tapping duct 3 until the level of molten metal material outside the cover 7 reaches the lower edge 15 of the lower end 9 of the cover 7 (FIG. 3g).

(38) At this point, with the passage of a minimum amount of air from the outside of the cover 7 into the volume 4, accompanied by a negligible amount of slag 17, the depression inside the volume 4 is canceled and the level of molten metal material 16 inside the cover 7 lowers quickly reaching the lower edge 15, and thus the same level of the molten metal material outside the cover 7 (FIG. 3h).

(39) When the tapping ends (FIG. 3h), and either scrap is loaded and/or melted in the vessel also during tapping or not, the method provides:

(40) returning the bath of molten metal material 16 to a level between the lower edge 15 of the cover 7 and the upper edge 13 of the second stretch 5 of the tapping duct (FIG. 3a);

(41) repeating the steps illustrated in FIGS. 3b to 3h.

(42) Advantageously, the tapping duct 3 is always kept open, even during the melting of the scrap inside the vessel, without needing to obstruct the tapping hole with sand and without needing to provide a closing valve.

(43) A first alternative to the one described above, in order to cancel the depression inside the volume 4 and interrupt the tapping, provides actuating the relief valve of the cover itself to equalize the pressure inside the cover 7 with that contained outside the cover, which generally corresponds to the atmospheric pressure present inside the vessel.

(44) A second alternative provides, instead, tilting the vessel with respect to the horizontal plane in direction opposite to the tilting direction activating the tapping, i.e. so as to raise the level of molten metal material in the vessel zone in which the tapping duct is not present. In this manner, the tapping duct 3 passes from said first reference position to a third position, inclined with respect to said first reference position, until the level of molten metal material inside the volume 4 at least partially reaches the lower edge 15 of the cover 7, whereby allowing the passage of air inside the cover.

(45) In these different manners, a perfect control on the amount of molten metal to be maintained inside the furnace (hot heel) is obtained for the successive melting.