Yin R. Metallurgical Process Engineering
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178 Metallurgical Process Engineering
process in entirety
of
steel plants. Sometimes, the model can be obtained based on
the understanding the micro and mesoscopic kinetics analysis-optimization
of
the
set
of
procedure's functions and further integration-optimization
of
the set
of
pro-
cedures in steel manufacturing process.
On studying dynamic processes at different scales and levels, it should be
noticed that the significance
of
the magnitude and the spatio-temporal scale
of
the matter or energy.
It
couldn't
be neglected. Space factors are rather steady
because the layout was fixed . Time-characteristic factor should be considered
much more. Time-coordinate axis is mostly to be as the backbone. Many fac-
tors such as production efficiency, product quality, product specification,
process emission,and process recycle, should match the time scheduling
of
manufacturing process. In other words, these factors should harmonize on the
time-coordinate axis
of
production. Meanwhile, details in the kinetics
of
mi-
cro or mesoscopic processes may be ignored, emphasis should be laid upon
the continuity, compactness and synergism
of
the production flow in entirety
of
the whole steel mill, as well as the coupling and efficiency on the func-
tion
-structure
of
procedures and devices. Otherwise, many problems as dis-
orientation, conceptual chaos and unmerited method would happen. The pro-
duction process
of
the steel manufacture from the storage
of
raw materials and
energy sources, coking, sintering, ironmaking, hot metal pretreatment, steel-
making, secondary refining, continuous casting, reheating to hot rolling could
be regarded as a typical multi-scale and long-route complex process system.
The research topics on the operating dynamics in the manufacture process
of
steel plant are as follows:
1. Manifestation and essence
of
operation;
2. Operating dynamic characteristics
of
production process;
3. Operating mode and rhythm
of
different procedures / devices in production
process;
4. Relationship between the pushing and pulling force
of
different procedures
/devices and the ability
of
matching, buffering and coordinating in manufacture
process;
5. Evolution and optimization
of
interface techniques in production process
such as ironmaking-steelmaking interface, steelmaking-continuous casting inter-
face, continuous casting-hot rolling interface;
6. Engineering synergistic effect
of
operations in the production process
of
steel
plant.
7.1 Evolution
of
Production Operation in Steel Enterprises
since 1990s
Guiding idea and its trendency for production operation in steel enterprises will
Chapter 7 Operating Dynamics in the Production Process
of
Steel Plant 179
be discussed in these sections.
7.1.1 Guiding idea
for
production operation in steel enterprises
in the first
half
of
the
2rJ"
century
In the first half
of
the
zo"
century, the production operation in steel plants took
the steadiness
of
the system as its target; the dominant trend
of
operation was sta-
bility. At that time, the main bottleneck was the long operation time with great
undulations about the open hearth steelmaking, ingot teeming and blooming. The
equipment durableness couldn't be desired and the production failures often ap-
peared. Therefore, the structure
of
the process system pursued the stationary im-
provement. Those were reflected in the technical measures taken by the iron and
steel enterprises:
I. Direct repetition. Many
of
the major technological equipment sometimes set
up spare devices, the results were more and more blast furnaces and open hearth
furnaces, ingot teeming and rolling lines.So it became more complicated.
2. Increasing the intermediate buffer devices, or the storage quantity. For ex-
ample, the rhythm
of
time between blast furnace and open hearth furnace was
not coordinated. The flow
of
liquid metals between the ironmaking and the
steelmaking could not be matched because the long time
of
the open hearth
heat. Therefore, bulky mixer for hot metal was introduced between blast fur-
nace and steelmaking.
It
seems to make coordination
of
liquid metal flow, but
a long intermittence
of
the ferruginous mass flow existed and the energy con-
sumption and the environment load were also increased. Similarly, ingot bay
and numerous soaking pits had been installed between ingot teeming and
blooming. Between blooming plant (including breakdown mill) and the finish-
ing mill section there were large stock
of
semi-finished products....Certainly,
these measures kept steady production
of
iron and steel enterprises, but there
were a series
of
issues in terms
of
per capita output efficiency, products deliv-
ery, logistic transport, energy depletion, material consumption, emissions and
environmental load.
3. Universal product mix. As the system ingot casting-breakdown rolling was
easy to get blooms with various sizes and various shapes, so the iron and steel
enterprises always made many diverse products
of
plates, tubes, pipes, sectional
bars, bars and wire rods. Even more than 8 hot rolling production lines were lo-
cated in one factory. This further led to the frequently reciprocating transportation
and the piecemeal workshop distribution. The final result was the total confusion
in the layout and the frequently reciprocating traffic.
In the first half
of
the 20
th
century, the production process structure was fea-
tured as simple repetition and overlap because
of
the lower technology and simple
facilities in ironmaking and steelmaking. The operation was characterized by fre-
180 Metallurgical Process Engineering
quent intermittence. The goal was stability under conditions
of
heavy ingot and
thick bloom with multiple reheating and rolling. This is actually a negative feed-
back strategy.
7.1.2 Guiding idea
for
production operation in steel enterprises
in the second
half
of
the
2r1"
century
Down to the later
half
of
the
zo"
century as the end
of
world war the global
reconstruction led to the increasing market demand for steel products. Moreover,
due to the implementation and the improvement
of
basic oxygen converter,
large volume blast furnace, tandem rolling mill and particularly continuous
casting technology, the manufacturing process became itself to the quest for
development. This is the development based on the steadiness
of
the process
system. Since development
of
the fully continuous casting technology the "bot-
tleneck"
of
the ingot
teeming-breakdown
rolling route had been eliminated.
It
coupled with the replacement
of
OHF by efficient BOF, the continuous/ quasi-
continuous and ordered operation
of
the steelmaking section was founded.
The high productive steel works with fully continuous casting appeared in the
1970s. Fully continuous casting in the iron and steel enterprises made the
steelmaking section not only to be continuous/quasi-continuous operation but
also to increase a substantial productivity. This, in turn, promoted develop-
ment
of
the facilities and functions in the up-stream and the down-stream
processes. Large blast furnace with the volume over 4000m
3
, hot rolling strip
mill with the productivity over 3.5 million t/a had developed well. These three
items had formed the back-bone
of
continuous/quasi-continuous operation
of
the steel manufacturing production process
of
whole steel works . The iron and
steel enterprises' structure were undergone an important revolution. Due to
the simplication and coordination
of
production process and also equipment, a
substantial increase in production capacity, production efficiency and energy
efficiency has been improved, the process emission reduced, and the product
quality improved.
After middle age
of
zo"
century, the mode
of
steel mill has changed basically
through three stages:
1. Since basic oxygen converter process appeared in 1952, the capacity
of
the
iron and steel production has been expanded step by step. Appearance and matur-
ity
of
mammoth converter's promoted the large blast furnace and the various roIl-
ing mills to be enlarged, continuous, automatic and high-speed. The hot rolling
strip mill was representative
of
which. Until the oil crisis, all the steel works kept
the core procedure
of
ingot teeming-breakdown mill, and usually being a univer-
sal steel factory which could produce all types
of
products, such as coils sheets,
plates, pipes, sections, bars, rods and wires. Even one plant for ultra-large-scale
of
Chapter 7 Operating Dynamics in the Production Process
of
Steel Plant 181
10 million t/a
of
products was targeted.
2. From 1973 to 1989, as the oil crisis and energy insufficiency the system
of
ingot teeming-blooming as well as the OH steelmaking were eliminated because
of
the rapid development
of
continuous casting, particularly the fully continuous
casting system. The process system had been changed thoroughly accompanied
with development
of
UHP-EAF, slab hot conveying and charging into reheating
furnace etc. Mode
of
the steel mills developed to energy saving, specialized prod-
uct competitory and with rational capacity.
3. Since 1989, the thin slab casting-rolling technology has been put into pro-
duction in Nucor. Steel production processes became "compactness and continu-
ous", the new "compact" steel plant mode has been applied in industrial produc-
tion. Meantime clean steelmaking, semi-endless rolling, ferrite rolling, substitut-
ing cold strip with hot strip etc. began practising to a certain extent.
Generally speaking, the guiding idea
of
the steel plants was development on the
base
of
the steady operation in the second half
of
the
zo"
century.
It
is a positive
feedback strategy.
7.1.3 Tendency
of
guiding idea
for
production operation
of
mod-
ern steelplants beyond the
2(/" century
Since the end
of
the 20
th
century, steel plants tend to sustainable development and
products' competitiveness with reasonable capacity for the following factors:
oversupply
of
steel products in the global market, problems
of
the resource limita-
tion and the earth environment pollution. Due to restriction from market space,
price, cost and offering radius, the process operation in iron and steel production
is designed considering not only the rationality
of
the operation inside the plant
but also the friendliness between mankind and nature. The unity of development
and environment, the adaptability for industrial ecology and the circular economic
society must be pursued. The premise
of
development depends on how to position
the iron and steel enterprises' social/economic functions. And the functions which
adapt and coordinate to neighbor urban, surrounding industrial zone and social
consumption are needed.
In the view
of
technological progress, the production process
of
steel plant de-
velops from simplicity to complexity and then returns to
simplifying, In the proc-
ess, matching, coordination, compactness, energy-saving, resources utilization,
cleaner production and eco-industrial chain should be attracted much attention.
Steel plant with the capabilities to consume a large amount
of
municipal wastes
by the way
of
resource recycling is interested.
Since the end
of
20
th
century, the developm ent strategy
of
steel plant
would not only limit to the inner issues but also extend to the society. So it
becomes an open, cooperative and comprehensive engineering system.
182
Metallurgical
Process
Engineering
Through the reasonable process system, rational sale region and production
capacity, then by means
of
organization, the steel group corporation even an
enterprise strategic alliance would realize the competition, cooperation and
win-win. Furthermore, the steel enterprise should be harmonized into the
circular economy based on the ideas
of
LeA
and inter-process linkage, be-
coming an important sector in the eco-industrial zone. This is a more inten-
sive development strategy.
7.2 Dynamic Features
of
Production Process Running
of
Steel
Plants-Operation
Form and Essence
From the history
of
the production process development
of
the iron and steel
manufacture, it can be seen that the production process went on the way from
batch running to continuous/ quasi-continuous. The compactness, quasi-
continuation /continuation and product specialization
of
manufacturing process
are still the main adjustment direction
of
the process structure. The variation
of
the production process resulted in not only the evolution
of
steel modes genera-
tion by generation, but also the product mix composition, the capacity rationality,
the gross domestic investment and the market competitiveness.
In the view
of
the
operation dynamics the character
of
the steel production process running feature
is developed from a series
of
batch operations structure to the integral continu-
ous/quasi-continuous operation.
The production process in steel plants which mainly use iron ore and coal as
raw materials is a complicated system consisting
of
the chemical metallurgy (re-
duction, oxidation, refining etc.), the solidification and the physical metallurgy
(rolling, forging, phase control, surface treatment etc.).
In the engineering essence,
the steel production process is a combination
of
the matter state transformation,
the matter property control and the mass flow control. The matter state transfor-
mation means course from oxides to metal; from liquid metal to solid; from cast-
ing structure to rolling/forging structure; from high temperature structure to room
temperature structure etc. The matter property control means the control
of
metal/slag behaviors, the control
of
steel cleanliness, the control
of
the shape and
size
of
rolled steels, the control
of
metal structure, the control
of
product proper-
ties
& surface feature etc. The mass flow control means the procedure's arrange-
ment and route
of
manufacturing process, transportation
of
materials and energy,
logistic transportation etc. (Fig.7.1, Yin, 1997a).
Taking a view
of
structure
of
plants, the steel production only considered the
combination
of
the matter state transformation and the matter property control
until the 1970s. The mass flow control was separated before the fully continu-
ous casting plant arising. This was manifested as the fact that there are many
ingot pits
& yards, bloom or billet storing bay and bulky mixers. As the fully
Chapter
7 Operating Dynamics in the Production Process
of
Steel Plant 183
Chemical metallurgy
··
--
A
·- c
I B
- ..- .•- .•- A : Matterslate transforming
-----
B: Matter property conlrolling
--_·_·-·-C
: Mass flow controlling
Fig. 7.1 Combination
of
the matter state transforming, the matter property controlling
and the mass flow controlling in the production process
continuous casting steel plant setting up, the ingot
teeming-blooming
disap-
peared, finish rolled metal was made with only one reheating operation. The hot
connection
of
steelmaking-refining-casting-reheating-hot
rolling began
realizing. Since that the matter state transformation, the matter property control
and the mass flow control are tightly combined in the production process. With
the near-net-shape casting as the core technology, a new generation
of
compact
steel plants is appeared. In such steel plants, the combination
of
the matter state
transformation, the matter property control and the mass flow control is much
more tighter. Moreover, the features
of
coordination and rhythmic became more
obvious. Differences about the tight degree
of
the combination
of
matter state
transformation, matter property control and mass flow control will lead the proc-
ess to various temperature undulations and unlike operation cycles as shown in
Fig.7.2(Yin, 1998).
Ingot teeming-cold (a)
chargingprocess 12
13
11
__ __ __ 11' 14
3500 4500 5500 6500 7500
3000 4000 5000 6000 7000
Time/min
9
1800.-----,,....----------------,
1600
u 1400 2
<, 1200
<>'e 1000
800
~
600
400
200
I 3 8
500 1500
1000
Ingot teeming-hot (b)
chargingprocess
12
13
II
LI'
14
2500 3500 4500 5500 6500 7500
2000 3000 4000 5000 6000 7000
Time/min
1800,-----------;'C-------=::-;:-::==-=-=--::-l
1600
1400 2
~
1200
0. 1000
E 800
~ 600
400
200
0.......,m:-........,'*":-'-~~~~"'_"7~=~P'-"""7:h",.......-:::-:!
184 Metallurgical Process Engineering
CC-cold
(c)
charging process
10
CC-hot
charging (d)
and rolling process
9 9'
800
1
00
(boJ
4
O<j
606
8
~006
2~400
28<J~2od400
Time/min
1800
.--
--
1600 2
2 1400
. 1200
Q.
E
1000
800
~
600
400
200
O-'-='±.----'--c'*----'---~.__'_~c.---''--=h____'___=±A~dv.__'__d____'~
.
1800r----
1600 2
u 1400
'0, 1200
~
1000
0> 800
~
600
400
200
O~
b:-
......."
b:-
y~~
'$:'
''=;;
~
'O'':~......,,
~
'_'__::_
~
~
.
1800
r--
--
- - - - - - - - - - - - - -
-----,
1600 2
1400
2 1200
ci. 1000
E 800
~
600
400
200
O...".*"....I-rh---'--:,.-,b.,.--'----.--};=-''---;-,.'=---'---..,.k,--L-,d,..--L.....,b=-'---..-.'.
Fig.7.2 Schemeofcompactness,
continu
ationand int
ermitt
ence inthesteelproductionprocess
Ingot teeming process(a,b):
I- Raw materials; 2- Sintering; 3---Orc chute; 4
-Bl
ast furnace tapping; 5- Hot metal charging;
6- Converter tapping; 7
-Tee
ming; 8(8' ) - Ingots; 9
-Soa
king pit; 10
-Br
eakdown mill;
II(I I')- Slab yard; 12
-R
eheating furnace; I3- Finishing-coiling; 14
-P
roducts warehouse;
Continuoas casting process(c,d):
I
-R
aw materials; 2
-Sint
ering; 3- 0 re chute; 4- Blast furnace tapping; 5- Hot metal charging;
6- Converter tapping; 7- Refining; 8
-Cas
ting; 9(
9')
- Slab yard; I
D-R
eheating furnace;
II
-H
ot rolling-coiling; 12
-Produ
cts warehouse;
Thin slab casting-rolling process(e):
I
-R
aw materials; 2
-Sint
ering; 3- 0 re chute; 4
-Bl
ast furnace tapping; 5- Hot metal charging;
6- Converter tapping 7- Retining 8- Casting 9- Slab transport I
D-R
eheating furnace:
II
-Rollin
g-coiling: 12
-Produ
cts warehouse
The variation in the structure
of
three generations
of
steel plants characterizes
sustained continuation
of
the manufacturing process. The gradual process con-
tinuation led to the minimum attenuation
of
mass flow
of
metals (high yield, low
cost
of
manufacture); the minimum undulations
of
metal temperature during the
process (energy saving, environmental protection, low cost, etc.); the minimum
processing time and inventory (productivity, cost, delivery time, etc.) as well as
the satisfaction on quality
of
products optimized (qualified metals and exact per-
formance).
Above all, the operating dynamics
of
the production running in steel plants in
Chapter 7 Operating Dynamics in the Production Process
of
Steel Plant 185
form
of
a series
of
batch operations
of
procedures or devices is cooperative to
continuous/quasi-continuous process by means
of
synergy and integration.
The continuation/quasi-continuation
of
the production process in the steel
plants takes the following features :
• The continuous / quasi-continuous mass flow;
• The continuous energy flow;
• The compact link
of
the material flow and energy flow in the space scale
(layout, transport route etc.);
• The exact coupling
of
the mass flow, energy flow and information flow on
the time axis.
7.3 Operating Mode
of
Different Procedures and Devices in
Steel Production Process
Through a great deal of long term practice in R&D and production, it is noted that the
steel manufacture process is very complex and is made up of many procedures. On
purpose to pursue continuation
ofthe
steel production process, we can notjust change
the batch operation
of
each device into continuous, nor also the whole process direct
into straight-way continuation at one go. Instead, the continuity
of
steel production
process should be obtained by the technical ways
of
the optimization
of
the procedure
functions, the joint among the short or long procedures with rhythmic, compact and
coordinative relationships via interface technique. Moreover, the continuation and
quasi-continuation of the steel production process had begun with some key proce-
dures, such as blast furnace, continuous casting and continuous rolling and then ex-
tended to the whole production process by effectivecombination.
In other words, the character
of
the steel production process should be de-
scribed with the physical model at first by the process engineering research. Then,
the Management Information System (MIS) in every section will be established
on the support
of
the management science and the information technology, ulti-
mately the Computer Integrated Manufacturing System (CIMS) for the whole
process.
It
is obvious that the continuation can be realized depending on the inte-
gration
of
process engineering, information technology and management science.
From the process engineering point
of
view, the running features
of
main pro-
duction procedures in the steel plant are as follows(Yin, 1997):
1. Blast Furnace. The running essence is the continuous reduction-
carbonization with heat transfer in a counter current moving bed
of
the shaft
furnace. But the iron tapping is with intermittence. So the blast furnace has a con-
tinuous operation process with batch iron tapping.
2. Converter. The running essence is the rapid reaction and heating-up
of
the
bath with high rate but not continuous. The steel tapping is batch operation also.
So the converter steelmaking belongs to the speedy, high frequent, periodic batch
186 Metallurgical Process Engineering
processes.
3. Secondary metallurgy. The running essence is the bath reaction- temperature-
control and time-control process with flexible and frequent intermittence. The
way
of
tapping is also flexible and intermittent with a coordinating function. Its
flexibility is expressed in parameters as mass flowrate, temperature, time, and just
metal quality etc.
4. Continuous Casting The running essence is the continuous/quasi-continuous
heat exchange-solidifying-cooling process. But the output way
of
slabs, blooms or
billets is quasi-continuous operation.
5. Reheating furnace. The running essence is heating-up temperature control
and time control process with continuous heat transfer. The output
of
slabs or bil-
lets is batch operating.
6. Hot Rolling Mill. Continuous operation is the essence
of
its plastic deforma-
tion and phase transformationat high temperature, but the way
of
input-output
of
rolled pieces is with intermittence. The endless/semi-endless rolling promotes the
continuation
of
input-output
of
metals.
According to the above-mentioned analysis about the running essence and the
output operation
of
the major procedures, as well as the structure evolution
of
the
three generations
of
steel plant, we can see that the progress
of
steel production
processes is based on the coordination
of
the batch or continuous operations in
various procedures and the output with intermittence. By the way
of
"generalized
loop engineering" for short and long processes, i.e. developing the interface
techniques among procedures or devices, the quasi-continuous / continuous
production process in entirety
of
steel plant can be gradually realized.
7.4 Running Strategy for Steel Production Process
From the analysis about the operation features
of
different procedures / devices in
the steel production process, it is obvious that different procedures and devices
have different running essences and operation modes. With a generalized observa-
tion on the coordinative running
of
the steel production process, different proce-
dures and devices play different roles in the operation dynamics
of
the entire co-
ordinative running
of
steel manufacture. From the view
of
the running time
of
material flow, different procedures and devices play different roles such as
of
pushing, buffering or pulling in the material flow
of
production in order to ad-
vance the time scheduling fluently, coordinatively and continuously.
7.4.1 Section division
of
running strategy
for
production process
of
steel plant
The steel production process can be divided into two sections: the upstream section
Chapter 7 Operating Dynamics in the Production Process
of
Steel Plant 187
from Blast Furnace to Continuous Casting and the downstream section from Con-
tinuous Casting output to Hot Rolling finish-up. The upstream section is mainly
of
chemical metallurgical process and solidification. The downstream section is the
physical change control
of
the slab/billet transportation, reheating and rolling, plastic
working, deformation and transformation. The process flow in steelworks could be
resolved into two stage: upsteam which is from ironmaking to continuous casting,and
downstream which is from runout
of
continuous casting to the end
of
hot rolling.
So the analysis-integration about the operation dynamics
of
steel production
process can begin with the three key procedures:
Blast Furnace, Continuous Cast-
ing
and Hot Rolling. The characteristics
of
upstream and downstream sections in
running strategy for steel production process are shown in Fig. 7.3.
Coking
__
Ore and
Coal
Hot metal
pretreatment
Pull Push
Fig.7.3 The scheme of the running dynamics of steel production process
7.4.2 Pushing force
and
pulling force in up-stream
of
steel
manufacturingprocess
1. Blast furnace. The running essence
of
blast furnace is a continuous moving bed
operation, which requires a fluent continuous and steady operation without inter-
mission even some undulations. As the hearth
of
blast furnace has a limited vol-
ume (the general design
of
the hearth volume is about 14%
of
the volume
of
the
blast furnace), hot metal should be tapped in time. So a pushing force for the mass
flow was originated with the tapping necessity for uninterrupted SF running. The
pushing force can be expressed as
F,pu
sh = r" V'7 dt
BF J,o
1440t
::
where
FJ
~I
Sh
is the pushing force from blast furnace production on the mass
flow,
t/min;
Vis
the volume
of
blast furnace, m';
17
is the utilization coefficient
of
blast
furnace,
t/(d-rrr
');
t:
: is the time-interval
of
blast furnace operation,
t:
: =(11-
to
),
min;
to
is the time-point
of
last iron tapping, min;
t1
is the time-point
of
current
iron tapping, min.
This pushing force has the significance
of
not only the mass flow rate but also
the energy flow and the time-rhythm.