Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1998-05-15
2000-03-21
Willis, Jr., Prince
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75500, 75501, C21C 530, C21C 532, C21C 534
Patent
active
06039787&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for working up combustion residues and slags from waste incineration plants or steel works slags in a converter, wherein the molten slag is reacted with a metal bath while blowing oxygen through the metal bath.
2. Prior Art
Working-up processes in which slags are reacted with a metal bath, thereby enabling the successful reduction of metallic portions from the slags, have already been suggested. In the processes suggested so far, the reduction potential of the metal bath was controlled by suitable measures, to which end the blowing in of carbon while simultaneously blowing in oxygen through submerged tuyeres has been proposed in the first place.
Yet, a relatively high dust emission rate and hence relatively high iron losses have been observed in pertinent tests. When operating the proposed processes in a conventional manner, converter emissions were found to constitute 10 to 15% of the total converter contents, thus involving considerable expenditures in the subsequent purification of offgases.
SUMMARY OF THE INVENTION
The invention aims at further developing a process of the initially defined kind with a view to increasing the recovery of iron and substantially reducing the dust emission rate and hence the loss of iron. To solve this object, the process according to the invention essentially consists in that the slag is introduced at a slag layer height of above 1.2 m and the oxygen is introduced into the bath for cooling the submerged tuyeres in the form of air or along with CO.sub.2 or water vapor. The process control according to the invention is based on the consideration that, due to extremely high temperatures prevailing in the iron bath, iron particles evaporate around the submerged tuyere mushrooms at temperatures of up to 2400.degree. C. At such high temperatures, iron has already a quite considerable vapor pressure, the super-heated iron vapor passing through the iron and slag bath layers and partially condensing to colloidal iron droplets in the micrometer range within the converter gas space. Such iron droplets in the micrometer range are readily discharged from the converter, wherein offgas measurements revealed that the fine dust particles in the offgases contained relatively high portions of metallic iron. Additional iron droplets and slag particles are thrown out of the converter through the submerged tuyere system.
By cooling the tuyeres through the use of air and, in particular, through the simultaneous blowing-in of CO.sub.2 and water vapor for cooling the tuyeres, it is feasible to lower the temperature level around the submerged tuyeres to justifiable values at which the iron vapor pressure gets already negligible. As a result, it will do to adjust the tuyere pressure such that no iron droplets can penetrate the slag melt. Due to the favorable heat transfer between slag and iron bath, a respective minimum height of the slag layer thickness has, however, been observed for this purpose, wherein, in addition to an iron bath height of approximately 1 m, a minimum height of the slag layer of more than 1.2 m has been shown to suffice in order to drastically minimize iron emissions and hence iron losses.
Advantageously, the process according to the invention is carried out in a manner that hydrocarbons are additionally introduced through the submerged tuyeres for cooling the tuyeres. Bearing in mind the blowing pressures that are partially higher as compared to conventional bottom-blowing converters, the admixture of CO.sub.2 or water vapor for cooling and rendering inert is of particular importance in any event. Advantageously, the process is controlled in a manner that CO.sub.2 and H.sub.2 O vapor as well as optionally CH.sub.4 are injected in amounts capable of adjusting a bath temperature of less than 1700.degree. C. in the vicinity of the tuyeres, the bath temperature in the vicinity of the tuyeres advantageously being maintained between 1450.degree. C. and 1650.degree. C. At such temperatures,
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"Holderbahk" Financiere Glarus AG
McGuthry-Banks Tima
Willis Jr. Prince
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