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Bath stirring in basic oxygen steelmaking by gas injection through basal tuyeres

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Industrial research and development

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Nombre de lectures 28
Langue English
Poids de l'ouvrage 1 Mo

Commission of the European Communities
technical steel research
Steel making
BATH STIRRING IN BASIC OXYGEN
STEELMAKING BY GAS INJECTION THROUGH
BASAL TUYERES
Report
EUR 10307 EN
Blow-up from microfiche original Commission of the European Communities
technical steel research
Steelmaking
BATH STIRRING IN BASIC OXYGEN
STEELMAKING BY GAS INJECTION THROUGH
BASAL TUYERES
A.S. NORMANTON
BRITISH STEEL CORPORATION
9, Albert Embankment
GB-LONDON SE1 7SN
Contract No 7210-CB/801
(1.7.1980 - 31.12.1983)
FINAL REPORT
Directorate-General
Science, Research and Development
I
1986 EUR 10307 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate­General
Telecommunications, Information Industries and Innovation
L­2920 LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of the n is responsible for the use which might be made of
the following information
© ECSC-EEC-EAEC, Brussels ■ Luxembourg, 1986 Bath Stirring in Basic Oxygen Steelmaking
By Gas Injection Through Basal Tuyeres
Agreement 7210.CB/801
A.S. Normanton
British Steel Corporation
Teesside Laboratories
EUR IO307 EN SR 81 9 832 7210.CB/801
BATHSTIRRINGINBASIC OXYGEN STEELMAKING BY GAS INJECTION THROUGH
BASAL TUYERES
British Steel Corporation
ECSC Agreement No. 7210.CB/801
Summary
The British Steel Corporation began studies into the effects of deep bath stirring
in LD converters in 1974 with the objectives of reducing processing problems
associated with compositional and temperature stratification within the
steelmaking bath. Early production plant work was carried out at Consett Works in
1976 and since 1980 collaborative trials with Hoogovens have led to the gradual
installation of bath stirring at all BSC plants.
The ECSC project work began in July 1980 with the objectives of examining aspects
on the 3 tonne converter to optimise the operation of air/nitrogen and
oxygen/hydrocarbon tuyeres as well as to optimise the thermal efficiency of the
bath stirred process. Modelwork on tuyere operational aspects was also to be
carried out.
As the project developed the aims were modified a little in the light of rapid
developments in this area of steelmaking, not least in the area of the Hoogovens ­
BSC collaboration. The one area not covered extensively during the project was
that of materials injection via the tuyeres because of problems in using oxygen
with the available dispensing system. Also e of the rapid cooling of the
pilot vessel, bottom protection methods could not be developed. However, more
extensive development in the secondary combustion of CO ·»■ CO2 was undertaken and
an in­vessel gas sample lance was developed for use within the converter.
The operation of the 3 tonne pilot vessel at the Grangetown Laboratories of the
British Steel Corporation on Teesside is described in detail in the main report
but only briefly in this summary report. This facility is fully equipped to
measure all aspects of converter processes. The process types studied can be
subdivided into conventional BOS operation, BAP (stirred with air/N2/argon), and
Combined Blowing (stirred with oxygen/hydrocarbon), the latter two categories
themselves being subdivided into several process routes which include lime and
graphite injection and several oxygen flow rates.
Initially, control sets of BAP data were obtained for a range of carbon steels in
order to identify the required slag compositional path to give good refining. In
the event, these were distinctly different from the conventional BOS. All the
process variants were then examined with respect to the identified slag
trajectory, and it has been shown that with careful attention to the details of
processing, that good refining can be obtained with all process variants.
With bottom stirring and in fact with fully bottom blown systems, phosphorus
removal will take place later in a heat, unless care is taken. Thus, although low
carbon steels are readily manufactured, particularly with the assistance of
post­blow stirring, catch­carbon grades can be difficult to make. The project has
shown that it is possible to make these grades with BAP and that it is also
inherently possible with the other modes of refining.
It is also shown that the stirring efficiency of the combined blowing mode of
operation is not necessarily greater than for equivalent inert or semi­inert stir
gas flow rates. However, the use of <10% oxygen via the tuyere can give some
advantages in scrap melting potential. This thermal aspect of the process
variants has been evaluated with some difficulty because of the non­continuous
mode of pilot plant operation. The advantages of the double flow oxygen lance for
melting scrap were only clearly evident at the higher ratios of secondary:primary
oxygen flow rates, particularly for the lower slag volume heats carried out at
~0.5% hot metal Si. The value of the in­vessel gas sample lance in assisting the SR 81 9 832 7210.CB/801
evaluation has been shown, although there are problems in keeping this
operational.
Tuyere development aspects have been confined to water model type studies for
single and annular tuyeres, and run-back, or wetting, phenomena have been studied
carefully.
The process variants are briefly compared.
This document was prepared at the request of the Executive Committee in addition
to the final report and the brief summary report included in that report. Data
were discussed more fully in the final report which has already been circulated
andd at the November meeting of the Committee in Liege. SR 81 9 832 7210.CB/801
CONTENTS
Page
1. INTRODUCTION 1
1.1 Aims Of The Project
2. SCOPE OF THE PILOT PLANT WORK 2
3. DESCRIPTION OF THE PILOT PLANT
4. PILOT PLANT RESULTS 3
4.1 Slag Formation And Phosphorus Removal
4.2 The Rate Of Decarburisation 4
4.3 Comparison Of Turndown Performance 5
4.4 Slag-Metal Distributions 6
4.5 Effect Of Basicity On Sulphur And Phosphorus Removal 6
4.6 Post-Blow Stirring
4.7 Gases In Steel 7
4.8 Yield 8
5. TUYERE DESIGN STUDIES 9
6. EFFECT OF DIFFERENT BLOWING STRATEGIES ON BOS THERMAL
CHARACTERISTICS 11
6.1 Utilisation Of In-Vessel Gas Sample Lance 1
6.2 Calculation Of The Process Heat2
6.3 Summary Of The Heat Balance Data3
7. OVERALL CONCLUSIONS AND GENERAL COMPARISON OF THE
PROCESS ROUTES4
8. REFERENCES6
TABLES7
FIGURES 21
APPENDICES 75
m