Apparatus for pre-heating a metal charge for a melting plant and connected method

Abstract

Apparatus for pre-heating and conveying a metal charge to a container of a melting plant, comprising at least a conveyor channel along which said metal charge is able to advance so as to be delivered to the container, and in which above said conveyor channel at least a hood is disposed which defines a tunnel inside which at least part of the fumes exiting from said container are able to advance. At least a zone of the hood comprises an expansion chamber located above at least a portion of said metal charge, and able to expand and keep said fumes inside it for a minimum desired time of at least 1.5 seconds before they go into contact with the metal charge.

Claims

1. Apparatus for pre-heating and conveying a metal charge to a melting furnace of a melting plant, comprising: a conveyor channel capable of advancing a metal charge to a lateral loading aperture of the melting furnace, having lateral walls and a bottom wall that define a substantially U-shaped cross section, a hood at least partially disposed above the conveyor channel and having a tunnel wherein at least part of the fumes generated from the melting furnace advance into the hood, an expansion chamber within the hood and at least partially located above the metal charge and the conveyor channel, a connection pipe disposed between a fume exit of the melting furnace and the expansion chamber, and in a direct fluid communication from the melting furnace to the expansion chamber, to introduce a substantial amount of fumes generated inside the melting furnace directly into the expansion chamber, to reduce the passage of the fumes through the conveyor channel; at least one suction pipe disposed within the lateral walls of the conveyor channel; and a longitudinal portion of the conveyor channel having at least one passage apertures disposed within the lateral walls and in fluid communication with one the at least one suction pipe; wherein the fumes entered from the melting furnace through the connection pipe do not directly contact the metal charge before the fumes reduce their speed and temperature in the expansion chamber, in order to avoid localized melting in the metal charge, wherein an internal volume of the expansion chamber is a function of the flow rate of fumes generated from the melting furnace so that the fumes remain in the expansion chamber for a time period of at least 1.5 seconds before contacting to the metal charge on the conveyor channel.

2. The apparatus of claim 1 wherein said time period is between about 1.5 seconds and about 6 seconds.

3. The apparatus of claim 1 wherein the volume of said expansion chamber is between about 200 m.sup.3 and about 600 m.sup.3.

4. The apparatus of claim 1 wherein said expansion chamber has a cross section whose size decreases in the direction opposite to the direction of advance of the metal charge.

5. The apparatus of claim 1 further comprising a plurality of partitions inside said expansion chamber, wherein said partitions are capable of creating a cascade expansion against the longitudinal movement of the fumes.

6. The apparatus of claim 1 wherein said expansion chamber further comprises at least one internal surface that is insulated.

7. The apparatus of claim 6 further comprising a cooling means within the expansion chamber.

8. The apparatus of claim 6 further comprising a nebulizer.

9. The apparatus of claim 1 wherein said suction pipes are connected to and separate from the conveyor channel.

10. The apparatus of claim 1 further comprising a suction means in fluid communication with said suction pipes.

11. The apparatus of claim 1 further comprising a vibratory means in communication with said suction pipes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other characteristics of the present invention will become apparent from the following description, given as a non-restrictive example with reference to the attached drawings wherein:

(2) FIG. 1 is a schematic lateral view of a melting plant to which a conveying and pre-heating apparatus according to the present invention is applied;

(3) FIG. 2 is a section view from II to II of FIG. 1;

(4) FIG. 3 is a section view from III to III of FIG. 1;

(5) FIG. 4 is a schematic plane view of a detail of the apparatus in FIG. 1;

(6) FIG. 5 shows a detail of FIG. 1 according to a variant;

(7) FIG. 6 is a variant of the section in FIG. 3;

(8) FIG. 7 is a variant of FIG. 4;

(9) FIG. 8 is a variant of FIG. 6;

(10) FIG. 9 is a variant of FIG. 6.

(11) In the attached drawings, the same reference numbers have been used, where possible, to identify common elements that are substantially identical. It is understood that elements and characteristics of one form of embodiment can conveniently be incorporated into other forms of embodiment without further clarifications.

DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF EMBODIMENT

(12) With reference to the attached drawings, the reference number 10 denotes in its entirety a conveying and pre-heating apparatus according to the present invention.

(13) With reference to FIG. 1, the apparatus 10 is installed in a melting plant 11, of a substantially known type and provided with a melting furnace 12, for example of the electric arc type, fed laterally through a loading aperture 14, with a metal charge 13 such as for example iron scrap, hot or cold sponge iron, cold pig iron or other.

(14) The apparatus 10 according to the present invention allows to transport and pre-heat the metal charge 13 before it is introduced into the melting furnace 12.

(15) In this case, the plant 10 comprises a loading module 15, in which the metal charge 13 is able to be deposited. Downstream of the loading module 15 the conveying and pre-heating apparatus 10 is disposed, into which the metal charge 13 is pre-heated before it is introduced into the melting furnace 12.

(16) The apparatus 10 comprises a conveyor channel 21 conformed so as to cooperate with the loading aperture 14.

(17) The conveyor channel 21 comprises a bottom wall 22, substantially horizontal, and two lateral walls 23 and 24 which define in this case a substantially U-shaped cross section (FIGS. 2 and 3).

(18) The metal charge 13 advances in this case by means of a vibratory or oscillatory movement in a longitudinal direction of the conveyor channel 21 generated by a known vibration device.

(19) The apparatus 10 also comprises one or more hoods 17 disposed above the conveyor channel 21 so as to define a pre-heating tunnel 17a functioning as an expansion chamber 18.

(20) In particular, in correspondence with a final zone of the tunnel 17a, that is, a zone near the entry of the conveyor channel 21 into the melting furnace 12, the hoods 17 have in this case lateral walls 20 and a covering wall 19, so as to define the expansion chamber 18 above the conveyor channel 21.

(21) The expansion chamber 18 can have different cross sections depending on the production techniques and the spaces available; it can also have the cross section decreasing in size in a direction opposite that in which the metal charge 13 advances.

(22) The expansion chamber 18 has a volume such as to allow the fumes to expand, slowing their speed and lowering their temperature.

(23) Inside the expansion chamber 18 one or more dividing partitions 16 may be present, which create an expansion and acceleration of the fumes, followed by another expansion, to accentuate the depositing of powders.

(24) The effect of the expansion of the fumes inside the expansion chamber 18 is such that the speed is reduced from about 40 m/s to about 10 m/s-14 m/s, and the temperature of the fumes is reduced from about 1300 C.-1400 C. at exit from the melting furnace 12 to about 800 C.-1000 C. when they contact the metal charge 13.

(25) Furthermore, the low speed at which the fumes pass through the metal charge 13 promotes their homogeneous contact with the metal charge 13, preventing localized overheating.

(26) As shown for example in FIG. 6, cooling panels 35, consisting of a plurality of tubes in which cooling water is made to pass, are associated with the lateral walls 20 and the covering wall 19 of the expansion chamber 18.

(27) In other forms of embodiment, the lateral walls 20 and the covering wall 19 consist of tubular elements, adjacent to each other and seal welded along their length so as to constitute the expansion chamber 18. In this case the tubular elements not only have a cooling function but also a function of sealing and conveying the fumes.

(28) In other forms of embodiment, the lateral walls 20 and the covering wall 19 are cooled by means of intense fins provided on the respective external surfaces to increase the heat exchange surface.

(29) In the solution shown in FIG. 6, on one of the lateral walls 20 one or more safety doors 47 are provided, to allow an energy vent following possible explosions that might occur in the expansion chamber 18.

(30) In the same way (FIGS. 6, 8 and 9), inspection doors 49 are provided on the covering wall 19, which allow access to the expansion chamber 18.

(31) Inside the expansion chamber 18 (FIG. 1) a burner cooperates, only shown schematically, to provide for the combustion of non-combusted fumes exiting from the melting furnace 12.

(32) In the same way, delivery lances 34 are provided to deliver nebulized water, to effect an active regulation of the temperature of the fumes, controlling them by means of temperature sensors disposed along the expansion chamber 18.

(33) The apparatus 10 comprises a conveyor channel 28 disposed so as to connect the fourth hole of the melting furnace 12 with the expansion chamber 18.

(34) The conveyor channel 28, when the loading aperture 14 is closed, allows to convey substantially the whole of the fumes produced inside the melting furnace 12 directly inside the expansion chamber 18.

(35) The ratio between the usable passage surface of the conveyor channel 28 and the sizes of the cross section of the expansion chamber 18 is such that the expansion conditions of the fumes are obtained inside the expansion chamber 18 as described above.

(36) According to another form of embodiment (FIG. 5), instead of using the conveyor channel 28, the cover of the melting furnace 12 is provided with a lateral aperture 55 which is connected directly with a first portion 56 of the expansion chamber 18. In particular, the first portion 56 of the expansion chamber is substantially divergent in the direction opposite the direction of advance of the metal charge 13, so as to impose on the fumes exiting from the melting furnace 12 a desired expansion, and is also disposed directly above the terminal discharge part of the conveyor channel 21.

(37) The first portion 56, as described with reference to FIG. 6, has cooling panels 35 to cool its surfaces on its external surface.

(38) This form of embodiment is more advantageously than other types of connection between the melting furnace 12 and the conveyor channel 21, since the losses of load due to curved pipes, narrow sections or other are considerably reduced and heat dissipations are limited, given that the fumes pass directly into the expansion chamber 18, hitting the metal charge directly which is about to be unloaded into the melting furnace 12.

(39) Advantageously, along the whole length of the tunnel 17a, at the side of the lateral walls 23 and 24 of the conveyor channel 21 suction pipes 25 and 26 are provided (FIGS. 2, 3, 5 and 6), which define between them a central conveyor channel compartment of the metal charge 13.

(40) Furthermore, the suction pipes 25 and 26 comprise the lateral walls 23 and 24.

(41) In the form of embodiment shown in FIGS. 2 and 3 and 9, the suction pipes 25 and 26 are made in a single piece with the conveyor channel 21.

(42) In the form of embodiment shown in FIGS. 6 and 9, the suction pipes 25 and 26 are associated independently with the conveyor channel 21.

(43) In this case, relative hydraulic seals 50 of a known type are provided to connect the suction pipes 25 and 26 to each other.

(44) In one form of embodiment (FIG. 8), the suction pipes 25 and 26 are mounted solid with the base of the whole apparatus 10, while the conveyor channel 21, as we said, is subjected to oscillations or vibrations to transport the material. This solution allows to keep the two suction pipes 25 and 26 substantially stationary, to limit the mechanical stresses due to the movement of the conveyor channel 21.

(45) Advantageously, each of the suction pipes 25 and 26 is provided with relative inspection doors 36, conformed to allow the selective inspection of the suction pipes 25 and 26 and/or to effect internal maintenance and cleaning.

(46) The lateral walls 23 and 24 of the suction pipes 25 and 26 have passage apertures 30 or slits lateral at intervals (FIG. 4), which allow the fumes to be discharged lateral from the central conveyor channel compartment 38 toward the suction pipes 25 and 26.

(47) In the solutions shown in FIGS. 4 and 7, the passage apertures 30 are conformed as, or comprise, means which allow the fumes to exit but at the same time prevent the metal charge from getting jammed.

(48) The passage apertures 30 are made in the lateral walls 23, 24 (FIG. 6) and, in other forms of embodiment can be made at least for a part on the bottom wall 22 too.

(49) In this case, vibration members 32 and 33 are provided, cooperating with the suction pipes 25 and 26 (FIG. 3), so as to prevent, or at least limit, the sedimentation of powders or other impurities inside them.

(50) In another form of embodiment (FIG. 9), the connection between the conveyor channel 21 and the suction pipes 25 and 26 is obtained by means of a labyrinth type mechanical seal 51 which comprises two separator elements 53 that extend substantially parallel to the lateral walls 23 and 24 of the conveyor channel 21, are solidly associated with the bottom of each suction pipe 25 and 26, and are lower I height than the lateral compartment 27 and 29.

(51) In this form of embodiment, the lateral walls 23 and 24 can have the passage apertures 30, as already described, or provide a continuous aperture that extends for its entire length and only in the lower part of the lateral walls 23 and 24.

(52) The fumes sucked in and made to pass through the scrap are obliged to follow a labyrinth-type path which lowers the speed of the fumes so as to deposit the powders and smaller fragments of metal charge on the bottom wall 22 of the conveyor channel 21, and thus to exert a first filtering of the fumes before they are treated.

(53) Each of the suction pipes 25 and 26 is connected to a respective fume discharge pipe 37, 39.

(54) In this case shown here, the discharge pipes 37, 39 converge in an exit pipe 40, connected to a fume suction plant of a substantially known type.

(55) The exit pipe 40 also connects the expansion chamber 18 with the suction plant, so as to determine a desired depression to take in the fumes.

(56) Inside each of the discharge pipes 37 and 39 a valve element 43 is disposed, able to be selectively activated to regulate the quantity of fumes taken in through the discharge pipes 37 and 39.

(57) In this way, a desired suction of the fumes through the discharge pipes 37 and 39 can be guaranteed, thus allowing to regulate the pre-heating temperature of the metal charge 13, as a function of the type of metal charge 13 used.

(58) The exit pipe 40 is also provided with a relative valve element 45, able to be selectively activated to regulate the heat exchange between the fumes and the metal charge 13.

(59) The selective opening of the valve elements 43 and 45 allows to use the apparatus 10 with different scrap heating modes, possibly regulating the penetration into the metal charge 13, or only making the fumes pass inside the expansion chamber 18.

(60) The apparatus 10 also comprises, in correspondence with the zone where the metal charge 13 enters inside the tunnel 17a, a static sealing device 46, of a known type, and/or of the dynamic type.

(61) The apparatus 10 as described heretofore functions as follows.

(62) By activating the suction plant upstream of the exit pipe 40, the stream of fumes produced in the melting furnace 12 is generated, inside the connection pipe 28, until they arrive inside the expansion chamber 18.

(63) When the fumes reach the expansion chamber 18, they reduce speed and lower their temperature.

(64) The suction action induces the fumes to pass through the passage apertures 30 provided along the tunnel 17a in proximity with the bottom wall 22 of the conveyor channel 21, thus passing through the moving metal charge 13 from the top to the bottom.

(65) By regulating the opening of the valve elements 43 and 45, depending on the type of metal charge 13 used, it is possible to regulate the heating temperature of the metal charge 13 itself.

(66) By inducing the passage of the fumes through the cross section of the metal charge 13, a substantially uniform heating is determined of the metal charge 13, with optimum use of the heat energy of the fumes.

(67) It is clear that modifications and/or additions of parts may be made to the apparatus 10 as described heretofore, and that a person of skill in the art shall certainly be able to achieve many other equivalent forms of conveying and pre-heating apparatus for conveying iron scrap in a melting plant, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

(68) For example, according to another variant, the passage apertures 30 can have an adjustable amplitude depending on the type of metal charge 13 provided, or can comprise protective grids to prevent parts of the metal charge 13 from entering inside the suction pipes 25 and 26.