The Reduction of Iron Ores: Scientific Basis and Technology

591 Pages·1971·28.276 MB·English

by  Prof. Dr.-Ing. Ludwig von Bogdandy, Prof. Dr. rer. nat. Hans-Jürgen Engell (auth.)

The Reduction of Iron Ores
L. von Bogdandy . H.-J. Engell
The Reduction of Iron Ores
Scientific Basis and Technology
Revised and Translated Edition of
"Die Reduktion der Eisenerze"
With 381 Figures and 54 Tables
1971
Springer-Verlag Berlin Heidelberg GmbH
Prof. Dr.-Ing. LUDWIG VON BOGDANDY
Member of Managing Committee,
Hiittenwerk Oberhausen AG, Oberhausen
Prof. Dr. rer. nat. HANS-JURGEN ENGELL
Director, Max-Planck-Institut fiir Eisenforschung,
Diisseldorf
The translation of Chapters 1 to 4 was procured by arrangement with thc Trade and
Industrial Translation Centre Ltd., London. These four chapters were translated by
Commander E. R. DAWSON of the University of Dundee, Scotland, and edited by
Mr. F. B. TRAICE ofthe Swinden Laboratories of British Steel Corporation. - Chapter 5
has been translated and edited jointly by Messrs. R. S~;WELL and A. J. H. LEADLEY
of the Swinden Laboratories of British Stecl Corporatioll.
DK 669.051
669.046.46: 669.162.12
669.162.263.23
ISBN 978-3-662-10402-6 ISBN 978-3-662-10400-2 (eBook)
DOI 10.1007/978-3-662-10400-2
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© by Springer-Verlag Berlin Heidelberg 1971
Originally published by Springer-Verlag, Berlin/Heidelberg and Verlag Stahleisen m.b.R., Diisseldorf in 1971
Softcover reprint ofthe hardcover lst edition 1971
The reproductioll in this book of registered trade-marks does not warrant tho assumption, eveu
without auy special marking, that such names are to be considered free under tlle trade-mark law
and may be used by anyone.
Preface to the English Edition
For the English edition the book was revised by the authors, taking into
account a number of suggestions of the readers of the German edition. Some
of the most important publications in the field of iron ore reduction, which
appeared since 1967, have been used to bring the manuscript as far as
possible up to date. The kind assistance of Dr. K. BOHNENKAMP of the
Max-Planck-Institut fUr Eisenforschung, Dusseldorf, was much appreciated
in this respect. Ohapters 2.9 and 2.10, dealing with the reduction of molten
oxide slags by solid carbon and with the contribution of the water-gas
reaction to iron ore reduction, have been added for the English edition.
Ohapter 2.9 has been completely revised with the kind assistance of
Dr. H. J. GRABKE, Stuttgart. Dipl.-Ing. J. LODDE contributed to this edition
by revising the bibliography. Owing to the rapid development of the blast
furnace it was necessary to revise Ohapter 5 considerably. In this field many
valuable suggestions have been made by Dipl.-Ing. G. LANGE and Dipl.-Ing.
P. HEINRICH.
Furthermore, Ohapters3 and 4 have been thoroughly revised by Dr.-Ing.
E. FORSTER and Dr.-Ing. U. SCHIERLOH.
Last, but not least, we have to thank our translators for their excellent
work.
Oberhausen and Dusseldorf,
November 1970
L. von Bogdandy H.-I. Engell
Preface to the German Edition
In 1838 ROBERT WILHELM VON BUNSEN climbed up the blast furnace
of the Veckerhagen "Herrschaftliche" Ironworks and lowered into the
burden a tube made from gun barrels welded together and covered with
fireproof material. With the aid of lead pipes and glass tubes, bits of
rubber tubing and an air pump, BUNSEN drew from the furnace shaft, via
this tube, gas samples which he analyzed, finding carbon dioxide and mon
oxide, hydrogen and methane. He proved that it would be well worthwhile
to collect the gas and use it to heat the Henschel steam-engine which drove
the air blower, and which had previously required 35 lb. of beechwood
per hour. BUNSEN himself said: "Even if the experiments mentioned
cannot be regarded in any sense as exhausting the subject, they may still
be not without value as a preliminary report, since they embody the most
important features which can serve as a basis for practical investigations
into this subject, which is of such importance for the whole of metal
lurgy".
N o·one who reflects on the then state of affairs in science and engineering
and on their subsequent evolution can dispute this opinion. The methods
and aims of metallurgical research are shown quite clearly by this example.
The aim is to improve the degree of utilization of the raw materials employed,
and to increase manufacturing efficiency: the method consists in developing
suitable methods of making measurements (here it was the method of gas
analysis), combined with a scientifically based appraisal of the experimental
results. These methods, these aims - coupled with theoretical penetration
into the mechanism of the process, and with the development of better
designs and more efficient auxiliary plant for the blast furnace - these are
the foundation of the developments of the ensuing century. Countless
engineers and research-workers have concerned themselves with the blast
furnace process, with the result that the blast furnace of today must be
regarded as one of the most effieient devices used in metallurgy.
In this monograph, the thermodynamic principles and the basis in
reaction kinetics for the reduetion of ores are recounted first, and then the
laws of gas flow and heat transfer in packed columns are reviewed. Using
this background material, we try to describe scientifically the technology
Preface to the German Edition VII
of the blast-furnace process and to compute limits for its performance.
In particular, we discuss in detail: the preparation of the burden from the
standpoint of process technology and reaction kinetics; the significance
of the chemical and physical properties of the materials used, and the
methods for determining these properties; and the behaviour of alternative
fuels. The conditions in the "dry" part of the blast furnace where the react
ions between gases and solids predominate are discussed in particular
detail.
By means of this theoretical "tool-kit" we can in many cases distinguish
the essential from the fortuitous; we can calculate in advance the effect
of particular properties of the materials used, and the influence of the
operational parameters, on the manufacturing costs and on the operational
results, i.e., on the manufacturing performance and the specific fuel con
sumption. Hence a basis can be constructed for the optimization and
automation of blast-furnace operation, and we can judge whether improve
ments will be possible in the future, and what these may be.
Apart from this statement of problems, which is mainly directed
towards improving the blast· furnace process itself (the process which
today is of primary importance), we also discuss the problem of "direct
reduction", i.e., reduction without using a blast furnace. For several
decades attempts have been made to reduce iron ores to the metal in some
apparatus other than the blast furnace, obtaining the product either in the
form of molten pig iron or in the solid phase, as sponge iron or metallized
pellets, for example. It is true that no method of this sort has yet achieved
the performance of the blast furnace. However, the increasing availability
of economically priced gaseous and liquid fuels, especially of natural gas,
in the Middle East and in Central and South America, for instance, makes
it increasingly important to find a method for the reduction of iron ores
using these fuels instead of coke. The reduction of iron ores without a
blast furnace could be the key to the problem of providing the national
economies of these countries with supplies of iron on extremely economic
terms by using their indigenous raw materials and fuels. And iron is, of
course, essential for building up national industries and increasing the gene
ral prosperity.
We hope that this monograph may be of assistance to both research
workers and practising engineers in solving these and other problems
and that it will stimulate them to improve and cheapen iron production
by making well-conceived modifications of the methods of operation. But
we also address ourselves to students, hoping to enable them to become
more closely acquainted with the fundamentals of iron-ore reduction and
their application to technology, and to acquire an insight into the often
quite complicated relationships.
VIII Preface to the German Edition
It was not intended to compile a handbook that would take all opinions,
views and researches into account. Rather have we selected from the
literature those articles which we regarded as indicating a way forward,
which seemed to us to illustrate the way of thinking and working which
we have presented, and which were related to our own observations,
calculations and evaluations. This means that our choice of references
was subjective, and it should also be added that on occasion some omissions
may have occured.
The second-named of the two authors is responsible for Chapters I and 2,
the first-named for Chapters 3 to 5.
\Ve must thank our co-workers who have helped in the compilation
of references, in the calculations, the textual presentation, and in the
proof-reading. In particular, we should like to record the energetic assist
ance rendered by Dr.-Ing. G. GROSS and Dr.-Ing. U. PUCKOFF of Dort
mund, Dr.-Ing. H. D. PANTKE, Dipl.-Ing. H. SINGER and Dr.-Ing. D. TER
LAAK of Oberhausen, and Dr.-Ing. W. PLUSCHKELL of Stuttgart. We have
also to thank a large number of professional colleagues in the iron-making
industry and at the Universities and Research Institutes for communi
cating unpublished results to us and for fruitful discussions. Dipl.-Ing.
H. KEGEL of Dusseldorf has contributed to the success of thc project by
many informative and clarificatory conversations. The instigation to
write this monograph came from Professor H. SCHENCK, Dr.·lng., Dr.-Ing.
E. h., and to him we should like to express our sincere thanks for his
encouragement.
Oberhausen and Stuttgart,
October 1966
L. von Bogdandy II.-I. Engell
Contents
Frequently Used Symbols XIV
Thermodynamic Tables 1
1. Fundamentals . . . 18
1.1. Equilibria. . . . . . . . . . 18
1.1.1. The Iron-Oxygen System 18
1.1.2. The Iron-Oxygen-Hydrogen System and the Iron-Oxygen-Carbon
System . . . . . . . . . . . . . . . . . . . . . . . . .. 36
1.1.3. Reduction Equilibria of Mixed Crystals with Iron Oxides and of
Compounds Containing Iron Oxides . . . . . . . . . . . . . 39
1.1.4. The System FeO-CaO-Si0 and Equilibria in Sinter Formation 41
2
1.2. Fundamentals of Reduction Kinetics . . . . . . . . 47
1.2.1. Ore Reduction as a Sequence of Reactions. . . 47
1.2.2. Gas Diffusion in the Boundary Layer and Pores 50
1.2.3. Adsorption . . . . . . . . . 61
1.2.4. Chemical Adsorption . . . . . 66
1.2.5. The Phase-Boundary Reaction. 73
1.2.6. Formation of Nuclei . . . . . 81
1.2.7. Transport Processes in the Solid Phase 85
1.2.7.1. The Fundamentals of Diffusion in Iron Oxides 85
1.2.7.2. The Stability of the Surface Structure of the Oxide during
Reduction . . . . . . . . . . . . . . . . . . . . . 92
1.2.7.3. Transport Processes in the Reduction of Mixed Oxides and
Oxide Compounds ................. 96
1.2.8. "Direct" Reduction: the Solid-State Reaction between Carbon and
Iron Oxides . . . . . . . . . . . . . . . . . . . . .. 100
2. Results of Experimental Investigations of the Kinetics of Reduction 105
2.1. Methods and Apparatus for Measurements of the Course of the Reaction 105
2.1.1. Gravimetric Methods . . . . . . . . 106
2.1.2. Gas Analysis and Volumetric Methods . . . . . . 109
2.1.3. Special Methods . . . . . . . . . . . . . . . . 1I2
2.1.4. Preparation and Investigation of Oxide Specimens 1I3
2.2. Heat and Mass Transfer across the Gas-Flow Boundary-Layer. 1I4
2.3. The Diffusion of Gas and Solids in the Layer of Reaction Products 125
2.4. Investigations of the Phase-Boundary Reaction. . . . . . . .. 136
x
Contents
2.5. The Interaction of Diffusion and the Phase-Boundary Heaction ... 147
2.5.1. The Phase-Boundary Reaction and Diffusion in the End-Products
of the Reaction ...................... 147
2.5.2. Interaction of the Phase-Boundary Reaction with Diffllsioll in the
Reacting Layers . . . . . . . . . . . . . . . . . . . . . . 153
2.5.3. Consideration of the Combined Effects of the Phase-Boundary
Reaction, Gas Flow, Diffusion in the Reacting Layers, and Dif-
fusion in the End-Products of the Reaction WI
2.6. Observations on the Formation and Growth of Nuclei. . . . . . . . 105
2.7. The Reduction Kinetics of Mixed Oxides, Oxide Compounds, and Ninters 17;3
2.8. Reduction of Slags Containing Iron Oxides. . . . . . 188
2.9. Reaction Kinetics of the Gasification of Coal and Coke 193
2.10. The Water-Gas Reaction 200
3. Gas Flow and Heat Transfer in Granular i\Iaterials :W3
3.1. The Static Bed . . . . . . . . . . . . . 203
3.1.1. Gas Flow in a Static Packed Column 203
3.1.1.1. Equi-Granular Charges. 20;")
3.1.1.2. Multi-Granular Charges 209
:~.1.2. Heat Transfer in Static Beds . 214
3.1.2.1. Effect on the Heat Transfer of Longitudinal and Trans·
verse Intermixing of the Gas Flow in Packpd Beds . . 21;"';
3.1.2.2. The Heating of a Ch'lrge of :-':pheres in a Countpn'urrent of
Gas, Taking into Account tIlt' H pat Condudion in tIl('
:-':pheres . . . . . . . . . . . . . . . . . . .. 2Ul
3.2. The Fluidized Bed and the Transition to Pn,rticulate Fluidization 221
3.2.1. The Domains for Existence of Fluidiwd Beds and of Particulate
Fluidization . . . . . . . . . . . . . . .. ....... 224
3.2.2. Special Features in the Industrial Application of Fluidized-Tkd
Reactors . . . . . . . . . . . . . . . . . . . . . . 227
4. 'L'echniques for the Reduction of Iron Ores, Apart from tIt., Blast }'lIl'llaer 230
4.1. Statement of the Problem . . 230
4.1.1. Available Raw Materials 232
4.1.1.1. Ores. . . . . . 232
4.1.1.2. Fuels . . . . . 232
4.1.2. Classification of Operational Reduction Processes 234
4.1.3. Limiting Values for the Required Amounts of Heductant and Heat 235
4.1.4. The Products and their Further Treatment . . . . . . . 239
4.2. Reduction in Dispersed-Cloud Apparatus and Shower Furnaces 247
4.2.1. Limits of the Region of Applicability . . 247
4.2.1.1. Maximum Rates of Reduction . . . . . . . . . 247
4.2.1.2. The Most Favourable Operating Conditions. . 2;")0
4.2.1.2.1. Consumption of Reducing Gas for the Chemical
Reaction. . . . . . . . . . . . . . . 250
4.2.1.2.2. Gas Requirement for Heat Transfer . . .. 251
4.2.1.2.3. Maximum Loading of the Heduction Vessel. 251
Contents XI
4.2.2. Techniques for Carrying out the Reduction of Ores in the Form
of Suspended Clouds and Falling Curtains of Fine Particles 253
4.3. Reduction in Fluidized Beds . . . . . . . . . . . . . 256
4.3.1. Possible Charge Material and Limits of Operation. 256
4.3.2. Review of Processes . . . . . . . . . . . . . . 263
4.3.3. Energy Requirement for Fluidized-Bed Processes and Comparison
with the Blast Furnace 270
4.4. Reduction in Retorts. . . . . . . . . . . . . . . . 271
4.4.1. Fundamentals . . . . . . . . . . . . . . . . 272
4.4.2. Numerical Calculation for Reduction in a Retort 277
4.4.3. Experimental Investigation . . . . . . . . 280
4.4.4. Retort Reduction on the Commercial Scale. 282
4.5. Reduction in Rotary Kilns . . . . 286
4.5.1. Possible Methods of Working 286
4.5.2. The Reaction Kinetics . . . 289
4.5.3. Comparison with Experiment 297
4.5.4. Heat Transfer . . . . . . . 300
4.5.5. Pre-Determination of the Output. 302
4.5.5.1. Determination of the Size of the Preheating Zone 302
4.5.5.2. Determination of the Size of the Reduction Zone and of the
Whole Plant . . . . . . . . . . . . . . . . . . . . 302
4.;">.6. Reduction in Rotary Furnaces Carried out on the Commercial
Scale ...... : ........ . 303
4.5.6.1. Production of Sponge Iron. . . 303
4.5.6.2. Production of Molten Pig Iron. 310
4.5.6.3. Production of Iron Nodules . . 311
4.5.6.4. Pre-Reduction 312
4J;. Reduction in Shaft Furnaces (Without Melting). 313
4.6.1. Theoretical Basis. . . . . . . . . . . . 313
4.6.1.1. Restrictions Imposed by Fluid Dynamics on the Throughput 313
4.6.1.2. Kinetics of Reduction in Counterflow. . . . . . . . . 315
4.6.1.3. First Approximation (a Purely Reaction-Kinetic Approxi-
mation) ................ . 316
4.6.1.3.1. Basis of the Method of Calculation 316
4.6.1.3.2. Properties of the Charge Materials. 317
4.6.1.3.3. Numerical Example ....... . 318
4.6.1.3.4. Limitation of the Results. . . . . 322
4.6.1.4. Second Approximation (Setting up a Mathematical Model
with the Heat-Transfer Process Taken into Account) .. 323
4.6.1.4.1. The Temperature Difference between the Core
and Outer Surface of the Pellets . . . . . . 323
4.6.1.4.2. Reduction of a Charge (of Uniform Grains or
Spheres) in a Countercurrent Process; 8etting
up the Differential Equations . . . . 325
4.6.1.4.3. Solution of the Differential Equations 328
4.6.1.4.4. Results from the Mathematical Model 330
4.6.2. Countercurrent Reduction in Shaft Furnaces on the Commercial
Scale . . . . . . . . . .................. 333