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Ashby ENGINEERING MATERIALS 2
Brook IMPACT OF NON-DESTRUCTIVE TESTING
Koppel AUTOMATION IN MINING, MINERAL AND METAL PROCESSING 1989
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Bickert REDUCTION AND CASTING OF ALUMINUM
Bouchard PRODUCTION, REFINING, FABRICATION AND RECYCLING OF LIGHT
METALS
Chalkley TAILING AND EFFLUENT MANAGEMENT
Closset PRODUCTION AND ELECTROLYSIS OF LIGHT METALS
Dobby PROCESSING OF COMPLEX ORES
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Jaeck PRIMARY AND SECONDARY LEAD PROCESSING
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Lait F. WEINBERG INTERNATIONAL SYMPOSIUM ON SOLIDIFICATION
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Macmillan QUALITY AND PROCESS CONTROL IN REDUCTION AND CASTING
OF ALUMINUM AND OTHER LIGHT METALS
Mostaghaci PROCESSING OF CERAMIC AND METAL MATRIX COMPOSITES
Plumpton PRODUCTION AND PROCESSING OF FINE PARTICLES
Puidy FUNDAMENTALS AND APPLICATIONS OF TERNARY DIFFUSION
Rigaud ADVANCES IN REFRACTORIES FOR THE METALLURGICAL INDUSTRIES
Ruddle ACCELERATED COOLING OF ROLLED STEEL
Salter GOLD METALLURGY
Thompson COMPUTER SOFTWARE IN CHEMICAL AND EXTRACTIVE
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TWIgge-Molecey MATERIALS HANDLING IN PYROMETALLURGY
IWigge-Molecey PROCESS GAS HANDLING AND CLEANING
Tyson FRACTURE MECHANICS
Wilkinson ADVANCED STRUCTURAL MATERIALS
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ACTA METALLURGICA
CANADIAN METALLURGICAL QUARTERLY
MATERIALS RESEARCH BULLETIN
MINERALS ENGINEERING
SCRIPTA METALLURGICA
PROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM
ON FERROUS AND NON-FERROUS ALLOY PROCESSES
HAMILTON, ONTARIO, AUGUST 26-30, 1990
Ferrous and Non-Ferrous
Alloy Processes
Editor
R.A. Bergman
University of Toronto
Toronto, Ontario
Symposium organized by the Non-ferrous Pyrometallurgy Section of
The Metallurgical Society of CIM
29th ANNUAL CONFERENCE OF METALLURGISTS OF CIM
29e CONFERENCE ANNUELLE DES METALLURGISTES DE L'ICM
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Introduction
The Symposium on Ferrous and Non-Ferrous Alloy Processes focusses primarily on alloys
used in the iron and steel industry, because the 1990 Conference of Metallurgists is held in
Hamilton, Ontario, which is Canada's steel city.
Operating papers discuss the production of stainless steel from nickel ore by combining
the Krupp-Renn with the BOF process, the production of ferro-nickel by a novel electric fur-
nace process and chromium containing iron in the BOF, as well as furnace lining problems
in ferro alloy smelting. A number of papers deal with various aspects of ferro-manganese produc-
tion and ferro-molybdenum. The use of an engineered carbide desulphurizer and the applica-
tion of innovative cored wire in steel making is highlighted. Studies into the production of titanium
suicide and the process leading to the recovery of vanadium from Suncor flyash is presented.
Results of experimental work dealing with the preparation of nickel chromium alloys from Bird
River chromite and nickel sulphide are discussed.
The editor expresses his sincere appreciation to the authors, session chairmen, institutes,
universities and companies who have so willingly and ably participated in making this symposium
R.A. Bergman
University of Toronto
Editor
August 1990
1
An economical process for stainless steel production
from nickel ores
H. Arai, K. Uchiyama, T. Matsumori
Oheyama Plant, Miyazu-shi, Kyoto, Japan
T. Tohge
Technical Research Centre, Kawasaki-shi, Kanagawa, Japan
ABSTRACT
Nippon Yakin Kogyo Co., Ltd. is producing various austenitic stainless steels
through rotary kiln-electric arc furnace-AOD furnace from garnieritic ores. Since
inexpensive coals could be used as reductant as well as fuel for smelting Ni ores in
the rotary kiln, this smelting process ( Nippon Yakin Oheyama process ) could produce
Fe-Ni in very low energy cost. Utilizing AOD's high desulfurizing capability, the
ferro-nickel could be directly used for stainless steel production without any
independent refining in the smelting process, so that this RK-EF-AOD stainless steel
producing process enables us to reduce production costs greatly, followed by great
reduction of impurity levels ( such as sulfur, oxygen and carbon ) and mass-production
of high grade stainless steels as well.
KEYWORDS
Nickel, Smelting, Rotary Kiln Electric Furnace, AOD, Ferronickel,
Stainless Steel, Japan.
§ 1 INTRODUCTION
Nippon Yakin Kogyo Co., Ltd. is a special producer of stainless steels in Japan,
which makes ferro-nickel in the Oheyama plant located on the northern coast of Kyoto
prefecture and refines stainless steels in the Kawasaki plant near Tokyo, using the
ferro-nickel as the main raw material.
In the Oheyama plant, Ni oxide ores imported from New Caledonia, Indonesia and the
Philippines are smelted in a rotary kiln for ferro-nickel particles ( luppen ). The
Oheyama process is an unique Ni smelting method in the world and it has the following
characteristic points.
(1) Inexpensive non-coking coals could be directly used for the main energy source,
resulting in inexpenive smelting cost.
(2) The process is rather simple, requiring no special facilities such as electric
power plant and oxygen generator.
(3) The product is easy to handle in the shape of particles, although it is a crude
ferro-nickel.
2 FERROUS AND NON-FERROUS ALLOY PROCESSES
In the Kawasaki steel plant on the other hand, stainless steels are produced by the
combination of an electric furnace and an AOD furnace. Since this process has an
excellent refining capability, the crude ferro-nickel produced in the Oheyama plant is
well fitted to use for production of good quality stainless steels, in the shape of
particles suitable for continuous charging into the AOD furnace. Thus Nippon Yakin
Kogyo Co., Ltd. has established an integrated line for the stainless steel production
from the Ni oxide ores.
The Oheyama plant has an annual capacity of about 11,000 tonnes of nickel in ferro-
nickel, while the Kawasaki plant has that of about 300,000 tonnes of Ni group stainless
steels, and all the ferro-nickel luppen produced in the Oheyama plant are provided for
self-consumption.
This paper deals with the ferro-nickel production technique of the Oheyama process.
§2 AN INTEGRATED STAINLESS STEEL PRODUCING PROCESS CONSISTING OF ROTARY KILN,
ELECTRIC FURNACE AND AOD FURNACE
2-1) Outline of the process
Figure 1 shows an integrated line of our stainless steel production.
Nickel oxide ores are smelted in the rotary kiln for ferro-nickel particles of
0.3 to 20mm in diameter. These ferro-nickel luppen are used not only as the
melting material in the electric furnace with other materials such as Fe-Cr and
Fe scrap, but also used mainly as coolant for the AOD furnace.
The AOD process adopts top 0 blowing along with the usual tuyer blowing and
2
uses computer system0for control of gas ratio, cooling practice, etc. They have
improved productivity by 40% and increased the charging rate of coolant greatly
compared with the conventional way, resulting in direct charge of more than 80%
of luppen into the AOD furnace.
Although S content in the luppen is relatively high since sulfurization in the
kiln is positively allowed for Ni recovery in high yield as described later, it
is no problem to refine stainless steels below 0.005% S only in the AOD furnace.
Figure 1 An integrated stainless steel production line of Nippon Yakin
Kogyo Co., Ltd.
FERROUS AND NON-FERROUS ALLOY PROCESSES 3
2-2) Ferro-nickel production technique
(1) Ferro-nickel production processz>
The whole process consists of three processes; pretreatment process, smelting
process and separation process, as shown in Figure 2.
Figure 2 Flowsheet of the Oheyama process
( i ) Pretreatment process
In this process, about half the ore is ground wet and the other half is
ground dry, because the combination of the both types of grinding is
considered as the most economically effective way to attain the appropriate
moisture for making solid briquette which is indispensable for high heat
exchange efficiency at the grate-type preheater as well as a stable kiln
operation.
In the wet grinding, ores suitable for filtration are ground with water in a
tube mill to minus 3mm slurry and then stored in an air-agitated holding tank,
4 FERROUS AND NON-FERROUS ALLOY PROCESSES
while in the dry grinding, ores unsuitable for the filtration are ground with
hot gas of 700 to 800 eC in an aerofall mill to minus 3mm dry powders of 5 to
6% in moisture.
Damp cake of about 32% in moisture gained after filtration of the slurry and
the dry powders are then mixed with anthracite and limestone by using weighing
machines so as to have the fixed moisture and composition. The mix is fed to a
briquetting machine after well kneading in a rod mill. Typical compositions of
the ores are shown in Table 1.
Ore Moisture Igloss Si0 Fe A10 Ni Cr0 CaO MgO
2 2 3 2 3
For wet A 22.0 10.61 44.86 9.42 0.73 2.45 0.88 0.08 26.09
B 27.0 10.32 42.58 11.52 0.83 2.40 1.11 0.11 25.49
C 30.0 9.75 41.61 13.85 2.68 2.34 1.25 0.59 21.39
For dry D 30.8 10.03 41.12 16.31 1.09 2.33 1.29 0.04 19.72
E 34.0 11.73 36.48 16.81 0.70 2.41 1.50 0.02 21.95
Table 1 Typical chemical compositions of the ores
(ii) Smelting process
Briquettes of 17 to 18% in moisture are charged into a preheater directly
connected with each of four rotary kilns, and are dried to 2 to 3 % in
moisture and heated up to about 300 *C by the combustion gas from the kiln
during its passage through the preheater. The dried material is then charged
into the kiln which is 3.6m in diameter by 72m in length and 2% in slope. The
charge inside the kiln travels slowly towards an outlet end, taking about 12
hours with a rotation speed of 50 to 60rph and is heated gradually up to a
maximum temperature of about 1400 eC with a countercurrent flow of hot gas
produced by combustion of pulverized coal and mixed anthracite in the charge,
while all the steps such as dehydration, reduction of nickel-and iron-oxides,
slag formation and luppen formation occurring within the kiln.
The kiln operation is controlled by a process computer, which has realized a
stable operation.
(iii) Separation process of metal and slag
Partially fused material discharged from the kiln ( clinker ) contains
interspersed metal particles inside. It is quenched by a heavy stream of water
for embrittling and is also transported to the next separation shop. The
clinker is then ground in a mercy mill to minus 3mm for metal liberation from
slag and jigged for recovery of ferro nickel luppen as product.
Overflow from the jigger is next magnetically separated for recovery of
middling which contains 7 to 8% metal and is returned to kiln feed. Most of
slag tailing from the magnetic separater is used for construction materials
after removal of its fine portion. Its typical analysis is shown in Table 2.
FERROUS AND NON-FERROUS ALLOY PROCESSES 5
c SiO Fe A1 0 CaO MgO Crz0 Ni
z Z 3 3
0.40 53.4 6.3 2.5 5.2 28.6 1.2 0.2
Table 2 Typical chemical composition of slag
(2) Kiln operation technique
( i) Raw material control
(a) Formation of good quality briquette2)
As described above, briquettes are preheated in the grate-type preheater for
drying and formation of the solid briquettes in high yeild is indispensable
for the high heat exchange efficiency at the preheater as well as the stable
operation of the kiln, because the quality of the briquettes affects directly
permeability of the gas flow through briquette bed, or kiln draught.
Although the addition of supplemental materials such as anthracite and
limestone, and return feeds such as fluedust and middling from the separation
shop, all exert negative effects on briquette strength, the ores have sticky
nature good for forming solid briquettes and a few ores are blended from the
viewpoint of their clay portion which has a close relation with stickiness.
Figure 3 shows the relation between clay portion of the ores and briquette
strength.
Homogeneity of the moisture in the mixed material is also very influential
on formation of good quality briquettes and the mixed material is fed to the
briquetting machine after sufficient kneading in a rod mill.
χ Ore D Clay Portion
\
\ Ore B \ Ore D > Ore B > Ore A
2 O
\
Briquette size
v
40 x 40 x 20 ma
A \ \
\ ^V
Figure 3 Squeezing strength of the green briquettes
7 FERROUS AND NON-FERROUS ALLOY PROCESSES
(b) Adjustment of reduction-softening temperature of the raw material3)
The characteristic of the Oheyama process is in the very point that the
reduction reaction of Ni oxide ores as well as agglomeration of the reduced
metals are carried out without liquefaction in a fairly low temperature. The
control of the reduction-softening temperature of the mixed material,
therefore, becomes very important. One of factors which greatly affect the
reduction-softening behavior is unreduced FeO content in the slag and the
other one is basicity (Al0+Ca0)/Si02 of the mixed material as shown in Fig.4
2 3
and Fig.5. They clearly show that the both indexes have good correlations with
the reduction-softening temperature, regardless of ore brands. Well known
basicity MgO/Si0 doesn't exert any influence on the reduction-softening
2
temperature as far as the Oheyama process is concerned (Mg0/Si0=0.48 —0.60)·
2
O
O ORE A
1440
1400 \° Δ B
• C
^ a D
1420 - A E
a. *\?
1350 ε DA X
£
E—
1400
bO
e O
1300 e
1380 •
**—
Fe % ; const ant
(AI203+CaO)/Si02;constant Ow D
1250 isfin 1 1 L_ j
0 5 10 15 0.10 0.12 0.14 0.16
Fe*(%)in slag (Al0+Ca0)/Si0
2 3 2
Figure 4 Effect of the unreduced Figure 5 Effect of the basicity
Fe++ content on the (Al0+Ca0)/Si0 on the
2 3 2
softening temperature softening temperature
Although unreduced Fe ++ content in the slag ranges normally from 6 to 6.5%
under the usual reducing atmosphere around the outlet end of the kiln, it
often varies with Fe content in the mixed material, mixing amount of
anthracite and heating condition of the charge inside the kiln. For the aim of
its stabilization, therefore, a few ores are blended before grinding so as to
keep the ratio Fe/Si0 of the blended ore constant and the mixing ratio of the
2
anthracite is also kept constant in the pretreatment process, while the
heating condition of the charge inside the kiln is tried to be held constant
as well by a process computer as described later.
The ratio (Al0+Ca0)/Si0 of the blended ore depends on the blending ratio
2 3 2
of the ores, as A10 comes mainly from the ores. The ratio (Al0+Ca0)/Si0
2 3 2 3 2
is, therefore, adjusted by the addition of limestone so as to be kept constant
as well. The influence of adding amounts of the both anthracite and limestone
on the kiln operation is great and a strict contrl is carried out by another
process computer.
