Gas injection lance

Details Gas injection lance Gas injection lance

2002-07-09

2004-08-10

Kastler, Scott (Department: 1742)

Metallurgical apparatus

Means for melting or vaporizing metal or treating liquefied...

By means introducing treating material

C266S046000

Reexamination Certificate

active

06773659

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention provides a lance for injecting preheated gas into a vessel.
The invention has particular, but not exclusive, application to a lance for injecting a flow of preheated gas into a metallurgical vessel under high temperature conditions.
The metallurgical vessel may for example be a direct smelting vessel in which molten metal is produced by a direct smelting process.
The present invention also provides a direct smelting apparatus which includes a lance for injecting gas into a direct smelting vessel.
2. Description of Related Art
In general, molten bath-based processes for direct smelting ferrous material into molten iron that are described in the prior art require post-combustion of reaction products such as CO and H
2
released from a molten bath in order to generate sufficient heat to maintain the temperature of the molten bath.
The prior art generally proposes that post combustion be achieved by injecting oxygen-containing gas via lances that extend into a top space of a direct smelting vessel.
For economic reasons, it is desirable that direct smelting campaigns be relatively long, typically at least one year, and therefore it is important that gas injection lances be capable of withstanding the high temperature environment, typically of the order of 2000° C., within the top space of a direct smelting vessel for the prolonged periods of campaigns.
One option for providing oxygen-containing gas is to use air or oxygen-enriched air that is preheated to above 800° C.
Stoves or pebble heaters are the only currently viable options for pre-heating air or oxygen-enriched air. One consequence of the use of stoves and pebble heaters is that the air or oxygen-enriched air will pick up hard particulate material as it passes through the stoves and pebble heaters and this material can cause considerable wear to the internal surface of a lance.
The use of air or oxygen-enriched air also means that considerably larger volumes of gas are required to achieve a given level of post combustion than would be required if oxygen was used as the oxygen-containing gas. Consequently, a direct smelting vessel operating with air or oxygen-enriched air must be a considerably larger structure than a direct smelting vessel operating with oxygen.
Consequently, a lance for injecting air or oxygen-enriched air into a direct smelting vessel must be a relatively large structure that can extend a relatively substantial distance into a direct smelting vessel and be unsupported over at least a major part of the length of the lance. By way of context, 6 meter diameter HIsmelt vessels proposed by the applicant include lances having an outer diameter of 1.2 m that are of the order of 60 tonnes and extend approximately 10 m into the vessel.
In addition, such a lance must be capable of delivering relatively large volume flow rates of pre-heated air or oxygen-enriched air and withstanding wear of the interior of the lance due to erosive particulate material in the air or oxygen-enriched air over prolonged smelting campaigns.
For economic and structural reasons, carbon steel is the preferred material for constructing a lance for injecting pre-heated air or oxygen-enriched air.
However, carbon steel is not a preferred material in terms of resisting wear of the interior of the lance and particularly in light of the risk of rapid oxidation (ie ignition) of steel under hot injection conditions.
It is evident from the above that the use of pre-heated air or oxygen-enriched air presents significant issues in terms of the construction of lances for injecting the air or oxygen-enriched air into direct smelting vessels over prolonged smelting campaigns.
An object of the present invention is to provide a water cooled lance that may be constructed using carbon steel as a major structural component of the lance and is capable of injecting pre-heated air or oxygen-enriched air into a direct smelting vessel during a lengthy operating campaign.
SUMMARY OF THE INVENTION
According to the present invention there is provided a lance for injecting a pre-heated oxygen-containing gas into a vessel containing a bath of molten material, the lance including:
(a) an elongate gas flow duct extending from a rear to a forward end of the duct from which to discharge gas from the duct, the duct including; (i) inner and outer concentric carbon steel tubes which provide major structural support for the duct, (ii) cooling water supply and return passage means extending through the duct wall from the rear end to the forward end of the duct for supply and return of cooling water to the forward end of the duct, (iii) an exterior surface that includes a mechanical means adapted to hold a layer of frozen slag on the duct;
(b) a gas inlet for introducing hot gas into the rear end of the duct;
(c) tip means joined to the concentric tubes at the forward end of the duct,
(d) a protective lining formed from a refractory or other material that is capable of protecting the duct from exposure to gas flow at 800-1400° C. through the duct, the lining being a non-metallic material with heat insulating properties when compared to the steel tubes; and
(e) a means located in the duct for imparting swirl to gas flow through the forward end of the duct.
Preferably the duct includes three or more concentric steel tubes extending to the forward end of the duct.
Preferably the gas inlet includes a refractory body defining a first tubular gas passage aligned with and extending directly to the rear end of the duct and a second tubular gas passage transverse to the first passage to receive hot gas and direct it to the first passage so that the hot gas and any particles entrained therein impinge on the refractory wall of the first passage, with the gas flow undergoing a change of direction in passing from the second passage to the first passage.
Preferably the mechanical means on the exterior surface of the duct includes projections that are shaped to interlock with and hold frozen slag on the duct.
Preferably the projections are lands with each land having an undercut or dovetail cross-section so that the lands are of outwardly diverging formation and serve as keying formations for solidification of slag.
Preferably the tip means is of hollow annular construction and is formed from a copper-containing material.
Preferably the forward end of the duct is formed as a hollow annular tip formation and the duct includes duct tip cooling water supply and return passages for supply of cooling water forwardly along the duct into the tip means and return of that cooling water back along the duct.
Preferably the lance includes an elongate body disposed centrally within the forward end of the duct such that gas flowing through the forward end of the duct flows over and along the elongate central body.
Preferably a forward end of the elongate body and the tip means co-act together and form an annular nozzle for flow of gas from the duct with swirl imparted by the swirl means.
Preferably the swirl means includes a plurality of flow directing vanes connected to the elongate body to impart swirl to gas flow through the forward end of the duct.
In one embodiment of the present invention the elongate body is an elongate central tubular structure extending within the gas flow duct from its rear end to its forward end and the vanes are disposed about the central tubular structure adjacent the forward end of the duct to impart swirl to the gas flow to the forward end of the duct.
Preferably the central tubular structure includes a water cooling passage for flow of cooling water forwardly to its forward end.
More preferably the central tubular structure includes cooling water passages for flow of cooling water forwardly through the central structure from its rear end to its forward end and to internally cool the forward end and thence to return back through the central structure to its rear end.
Preferably the central tubular structure defines a central water flow passage for flow of water forwardly through that structure direc

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