Metallurgical apparatus – Process – Cooling
Patent
1993-04-19
1994-09-27
Andrews, Melvyn J.
Metallurgical apparatus
Process
Cooling
266225, 266270, C21C 546
Patent
active
053501586
DESCRIPTION:
BRIEF SUMMARY
This invention relates to metallurgical apparatus and processes, and is particularly concerned with lances for use in metallurgical processes, and with methods of cooling such lances.
In many metallurgical applications which utilise high temperature furnaces or reactors or molten salt baths, there is a requirement to introduce heat through combustion or the feed of reactants. The furnace environment is subject to very high heat flux.
Most conventional furnaces have combustion systems which are often refractory-lined combustion chambers, in which gaseous, liquid or solid fuels are combusted together with air or an oxidant such as oxygen or oxygen-enriched air. Normally, a combustion system is mounted in the freeboard or combustion space above the working bath or melt and the heat flux by radiation from the furnace environment back to the combustion chamber is accommodated by virtue of the flow of the combustion reactants through the burner together with the use of suitable refractory materials or by using water-cooled metals for the combustion parts.
In other metallurgical operations it is desirable to contact the melt more efficiently and use the combustion products or potential reactants within the metallurgical bath, both augmenting heat and mass transfer. In this instance, the combustion system has to accommodate the heat flux from the melt itself, plus potential corrosive effects due to the chemistry of the slag, matte or metal that is present. Further, there is a need to overcome any back pressure effects due to the hydrostatic head created by the melt.
In the steel industry it is common to use lances for the injection of gases or reagents into the melt. Such lances frequently involve the use of refractory-coated steel tubes down which a gas such as nitrogen, argon or oxygen passes at high velocity (with or without solid reagents). These lances eventually corrode, melt or fail and are considered consumable. In another type of furnace, common in the non-ferrous metal industry, it is desirable to contact reactants of a gaseous nature with the melt. Specially designed tuyeres, or tubes, are used which are mounted flush with the refractory of the vessel to minimise the impact of the corrosive melt and its temperature on the materials of construction of the infection tube itself. Alternatively, some metallurgical converters use water-cooled lances, but generally only in the free-combustion space, not in the submerged melt, or sometimes submerged but flush with the refractory wall. Traditionally, there has been a resistance to the use of water cooling for submerged lance devices, especially where they actually enter the melt, due to the potential hazard from fracture of a cooling jacket and the consequent vapour explosion. Yet, to accommodate the high heat fluxes within a melt, it is necessary to ensure that the lance materials are adequately cooled. One way of achieving this has been to use a cooling oil which passes through a metal annulus and both cools the metal of the lance and enters the melt. The latent heat of evaporation of the oil creates local cooling of the injector or nozzle. Another alternative for such an injector
ozzle or lance is to use methane gas as a coolant. This so-called shrouded-tuyere arrangement takes advantage of the cooling gas flow through a narrow annulus at high velocity directly into the melt. One obvious disadvantage of this is that the melt is contaminated with the oil or methane gas, which may not always be desirable. Another disadvantage, in the case of oil as a coolant, is that pyrolytic cracking or coking of the injector assembly may occur with subsequent blockage and ultimate failure of the assembly. Careful arrangements have to be made to ensure that there is no back flow of the melt into the gas or oil passageways and elaborate mechanical arrangements have to be made for their start-up.
Combinations of ceramic-coated cooling systems have been applied where water is used in either a jacket or a coil to ensure the integrity of the metal (steel) inner surfaces. This ar
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patent: 3310238 (1967-03-01), Bryant et al.
patent: 3828850 (1974-08-01), McMinn et al.
patent: 4235173 (1980-11-01), Sharp
patent: 4303230 (1981-12-01), Bleloch
patent: 4792126 (1988-12-01), Nagy et al.
Andrews Melvyn J.
Mincorp Limited
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