PLASMA HEATED FURNACE FOR IRON ORE PELLET INDURATION

Abstract

In the present pelletizing apparatus, the induration of iron ore concentrate pellets is achieved in a tunnel furnace heated by plasma torches, wherein the generation of CO2 by the conventional iron ore pelletizing processes is reduced by using electricity powered plasma torches instead of burning natural gas, heavy oil or pulverized coal in burners, thereby reducing considerably industrial pollution of the atmosphere.

Claims

1. A pelletizing apparatus, comprising a firing chamber, a traveling grate for sequentially transporting ore pellets in drying, firing and cooling zones, and at least one plasma torch for providing a heat required for indurating the ore pellets in the firing chamber.

2. The pelletizing apparatus according to claim 1, wherein means are provided for conveying air heated by the plasma torch to the drying zone for drying green pellets located upstream of the firing zone.

3. The pelletizing apparatus according to claim 1, wherein means are provided for introducing air recuperated from the pellet cooling zone in at least one chamber, where it is mixed with the extremely hot air from the plasma torch, prior to entering the pellet firing chamber.

4. The pelletizing apparatus according to claim 1, wherein there are provided two plasma torches.

5. A pelletizing method, wherein ore pellets are fed sequentially through drying, firing and cooling zones, and wherein heat required for the process is provided by at least one plasma torch.

6. The pelletizing method according to claim 5, wherein the ore pellets are transported by a traveling grate through the drying, firing and cooling zones.

7. The pelletizing method according to claim 5, wherein recuperated air from the cooling zone is introduced in at least one chamber, where it is mixed with the extremely hot air from the plasma torch, prior to entering the pellet firing chamber.

8. The pelletizing method according to claim 5, wherein air heated by the plasma torch is used in the drying zone for drying green pellets located upstream of the firing zone.

9. A firing device in a pelletizing apparatus, comprising a firing chamber for ore pellets being transported through the pelletizing apparatus, and at least one plasma torch for providing a heat required for indurating the ore pellets in the firing chamber.

10. The firing device according to claim 9, wherein at least one conduit is provided to convey hot air from a cooling zone of the pelletizing apparatus to the plasma torch, where the hot air from a cooling zone is mixed with very hot air heated by the plasma torch, a resulting hot air mixture being directed to the firing chamber.

11. The firing device according to claim 9, wherein there are provided two plasma torches, each being fed via conduits with hot air from the cooling zone.

12. The firing device according to claim 11, wherein a common main conduit is provided for conveying hot air from the cooling zone to the at least one conduit associated with each plasma torch.

13. A plasma torch for use in a firing device of an iron ore pelletizing apparatus, comprising at least two electrodes, namely one cathode and one anode, an electric arc being sustained between the two electrodes, a vortex ring for injecting compressed gas, such as air, between the two electrodes and for spinning the gas at high speed, an electrical insulator placed between the two electrodes, a jet of hot plasma gas exiting the torch for use in heating air before it reaches a firing chamber of the firing device.

14. The plasma torch according to claim 13, wherein multiple anodes and vortexes are used to increase arc length and volume of hot gas.

15. The plasma torch according to claim 13, wherein internal parts of the torch are mounted inside a water cooled shell for keeping the electrodes cool relative to the hot process environment.

16. The pelletizing apparatus according to claim 2, wherein means are provided for introducing air recuperated from the pellet cooling zone in at least one chamber, where it is mixed with the extremely hot air from the plasma torch, prior to entering the pellet firing chamber.

17. The pelletizing apparatus according to claim 2, wherein there are provided two plasma torches.

18. The pelletizing apparatus according to claim 3, wherein there are provided two plasma torches.

19. The pelletizing method according to claim 6, wherein recuperated air from the cooling zone is introduced in at least one chamber, where it is mixed with the extremely hot air from the plasma torch, prior to entering the pellet firing chamber.

20. The firing device according to claim 10, wherein there are provided two plasma torches, each being fed via conduits with hot air from the cooling zone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Reference will now be made to the accompanying drawings, showing by way of illustration an illustrative embodiment of the present invention, and in which:

[0025] FIG. 1 is a schematic transverse vertical cross-sectional view of a conventional firing chamber construction;

[0026] FIG. 2 is a graphic representation of the dependence of the energy transfer efficiency on the off-gas temperature for a fuel or gas burner and a plasma torch;

[0027] FIG. 3 is a schematic transverse vertical cross-sectional view of a firing chamber of an induration tunnel furnace showing the location of the plasma torch, in accordance with the present invention;

[0028] FIG. 4 is a schematic vertical cross-sectional view of the plasma torch; and

[0029] FIG. 5 is a schematic transverse vertical cross-sectional view of a firing chamber of an induration tunnel furnace, in accordance with another embodiment of the present invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0030] The present pelletizing apparatus uses a plasma heated furnace to reduce, or even eliminate, the generation of CO.sub.2 in an iron ore pelletizing process, to increase the energy transfer efficiency of the pellet heating process, and to provide a dry gas (air) in the green pellets drying section. Plasma torches are used to heat the induration furnace in place of the conventional natural gas, heavy oil or/and pulverized coal burners and, in doing so, to contribute to reducing considerable pollution of the atmosphere and saving energy.

[0031] For a conventional burner section of the firing zone equipped, for example a 3.75 MW Metal7 burner, the required combustion air consumption would be about 3500 Nm.sup.3/h. By contrast, given both the facts that no combustion air is required and the higher heat transfer efficiency of the substitute plasma torch, as illustrated in FIG. 2, the air flow required would be only about 430 Nm.sup.3/h with the present plasma heated furnace.

[0032] In the induration tunnel, the green pellets are charged onto a grate; with the grate moving, the pellets sequentially pass through drying, preheat, firing and cooling zones.

[0033] With reference to FIG. 1, a transverse vertical cross-section of a conventional firing zone is therein shown with two possible and different burner arrangements: on the left of FIG. 1, a burner 42 is horizontal while on the right of FIG. 1, a burner 52 is in a vertical position. Depending on the arrangement considered, hot recuperated air is conveyed from the pellet cooling zone of the tunnel furnace, via conduit 40 and downcomer pipe 41, or conduit 51, to be heated by the flame from the fuel burner 42, or burner 52, and the heated air being directed horizontally into a firing chamber 43 via a laterally extending tunnel 44, or a shaft 50.

[0034] Green pellets 45 distributed on pallets 46 and previously dried and preheated, are then heat-hardened in the firing chamber 43.

[0035] In a typical pelletizing plant such as that shown in FIG. 1, a plurality of downcomers 41 or conduits 51, burners 42 or 52 and laterally extending tunnels 44 or shaft 50, are employed at spaced intervals along the firing chamber 43.

[0036] Now referring to FIG. 3, a transverse vertical cross-section of the firing zone of the present pelletizing apparatus is shown with two possible locations for the installation of a plasma torch: on the left of FIG. 3, a plasma torch 12 is horizontal while on the right, a plasma torch 22 is mounted vertically. Depending on the arrangement considered, hot recuperated air is conveyed from the pellet cooling zone of the tunnel furnace, via conduit 10 and downcomer 11, or conduit 21, to be mixed with extremely hot air heated by plasma torch 12, or 22. The hot air mixture is then directed towards a firing chamber 13 via a conduit 14, or a shaft 24.

[0037] Green pellets 15, uniformly distributed onto a grate 16 and previously dried and preheated, are then heat-hardened in the firing chamber 13.

[0038] In a plasma fired iron ore induration furnace, from conduit 10 providing hot recuperated air from the pellet cooling zone, there would be a plurality of downcomers 11, or conduits 21, leading to the laterally extending tunnels 14, or shafts 24, where the hot recuperated air would be mixed with the extremely hot air heated by the plasma torches 12, or 22, before entering the firing chamber 13. Such a plurality of downcomers 11, conduits 21, plasma torches 12 and 22, laterally extending tunnels 14 and shafts 24 would, as required by the process, be employed at spaced intervals along the length of the firing chamber 13.

[0039] It is important to notice that, in both proposed arrangements for the installation of the torches 12 and 22, the pellets are shielded from exposure to the plasma flame intense radiant heat, thus preventing local pellet overheating.

[0040] The plasma torches 12 and 22 each use electricity to heat air to very high temperatures (5000-10000 Kelvin). No fossil fuels are used to generate the heat. Other gases can be heated by the plasma torch such as nitrogen or argon.

[0041] As seen in FIG. 4, the plasma torches 12 and 22 can each comprise at least two electrodes: one cathode 23 and one anode 26. An electric arc 18 is sustained between the two electrodes 23 and 26. Compressed air (or another gas) is injected between the two electrodes through a vortex ring 20 that spins the air at high speed, limiting point erosion on the anode. An electrical insulator 25 made of ceramic or other electrically insulating material is placed between the two electrodes. In order to attain high power, multiple anodes and vortexes are used to increase arc length and volume of hot gas. The internal parts of the torch are mounted inside a water cooled shell 27 that keeps the electrodes cool relative to the hot process environment. A jet of hot plasma gas 28 exits the torch and is used to heat the air in the downcomer pipe 11.

[0042] FIG. 5 shows another embodiment, similar to that of FIG. 3, but wherein there is only the plasma torch 12. Hot recuperated air is conveyed from the pellet cooling zone of the tunnel, via the conduit 10 and the downcomer pipe 11, such that it can be heated to a higher temperature by the mixing thereof with the extremely hot air heated by the plasma torch 12. The heated air is directed horizontally into the firing chamber 13 via the laterally extending tunnel 14. The pellets 15, distributed onto the grate 16 and previously dried and preheated, are then heat-hardened in the firing chamber 13.

[0043] Although the invention has herein been described in detail with reference to a preferred embodiment, many variations may be made by those skilled in the art without departing from the spirit and scope thereof. For example, the placement of the plasma torch may vary. In addition, although the invention has been illustrated with reference to a straight-line type of pelletizing apparatuses, it is equally applicable to a pelletizing apparatus having a circular configuration.

[0044] Finally, although the present invention has been described hereinabove by way of embodiments thereof, it may be modified, without departing from the nature and teachings of the subject invention as described herein.