Yin R. Metallurgical Process Engineering
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168 Metallurgical Process Engineering
Continued Table 6.4
Proc
edur
e
Actual time Cumulative time
Ternperature/X'
consumption
Imin consumption Imin
Hot metal transportation 15 627
Hot metal pretreatment 40 667
Deslagging and hot metal transpor-
30 697 1300
tation
Converter blowin g
36 733 1650
Ladle delivering and waiting 8 741
Secondary metallurgy 25 766 1580
Ladle delivering and waiting 10 776 1570
Continuous casting 60 836 1550
Slab transportation 10 846 500
Slab stocking 1440 2286 60
Slab transportation and reheating 100 2386
11
80
Hot rollin g and coiling 10 2396 700
Products transportation to
stor
e-
60 2456 100
house
Table 6.5 Processing time, temperature in blast furnace
-hot
metal pretreatment-
converter-r-secondary metallurg
y-continuous
casting
-hot
charging
-hot
rolling process
Procedu re
Actual time Cumulative time
Temperature
consumption
Imin consumption Imin rc
Taking out
of
raw material 10
Raw material transportation 30 40
Sintering 32 72 1400
Sinter tran sportation and stocking 120 192 350
Charging and smelting in blast furnace 390 582
Blast furnace tapping 30 612 1450
\-lot metal transportation 15 627
Hot metal pretreatment 40 667
Deslagging and hot metal transportation 30 697 1300
Converter blow ing 36 733 1650
Ladle delivering and waiting
8 741
Secondary metallurgy 25 766 1580
Ladle delivering and waiting
10 776 1570
Continuous casting 60 836 1550
Slab transportation and waiting
540 1376 650
Reheatin g 60 1436 1180
Hot rollin g and coilin g 10 1446 700
Products transportatio n to storehouse 60 1506 100
Chapter 6 Time Factor in Manufacturing Process 169
Table 6.6 Processing time, temperature in blast furnac
e-p
retreatment
of
hot metal-
convert
er-
secondary metallurgy
-t
hin slab casting - rolling process
Procedure
Actual time con- Cumulative time
Temperature
sumption /min consumption /min
rc
Taking out
of
raw material 10
Raw material transportation 30 40
Sintering 32 72 1400
Sinter transportation and stocking 120 192 350
Charging and smelting in blast furnace 390 582
Blast furnace tapping 30 612 1450
Hot metal transportatio n 15 627
Hot metal pretreatment 40 667
Deslagging and hot metal transportation 30 697 1300
Converter blowing 36 733 1650
Ladle delivering and waiting 8 741
Secondary metallurgy 25 766 1580
Ladle delivering and waiting
10 776 1570
Continuous casting 50 826 1550
Thin slab transportation and waiting I 827 950
Reheating 20 847 1100
Hot rolling and coiling 10 857 700
Products transportation to storehouse 60 917 100
6.5 The Analysis for Time Factor
of
Thin Slab Casting-Rolling
Process
The thin slab casting as an advanced technology is also called near-net-shape
casting which developed at the end years
of
the 20
th
century. The compact steel
plant was formed from it. Here, the meaning
of
compactness is the compact of
space and shorten of time.
The characteristics
of
the compact steel manufacturing process are as follows:
• By selecting critical slab thickness for reasonable rolling mill, the slab can be
filled into hot strip mill directly without roughing mill.
• By rapidly regulating temperature
of
slabs with ultra cut-length in tunnel re-
heating or holding furnace to get further spatio-temporal compactness and much
lower consumption of material and energy.
• By the se
lf
-organization function among steelmaking furnace-refining fur-
nace-thin slab caste
r-
tunnel furnace-hot strip mill-coiler, including control meas-
ure of information integration, the online operation coordination with time among
procedures and devices in manufacturing process would be realized, then the con-
tinuation degree would be improved.
Obviously, thin slab casting-rolling process is a sort of compact-coordinating-
170 Metallurgical Process Engineering
continuous production process. From the view point of continuous-coordination run-
ning, the manufacturing process can be regarded as an elastic syntony chain consti-
tuted
of
rigid components and flexible. components. The rigid components contain
steelmaking furnace, caster, hot rolling mill. The flexible components contain secon-
dary metallurgy, reheating furnace, ladle and tundish. For the sake of continuation-
coordinationrunning among these components, the principles should be considered as
following:
• Optimization
of
operation time
of
procedures and devices as well as optimi-
zation
of
time scheduling
of
the whole manufacturing process;
• Coordination optimization and minimization
of
transporting time, waiting
time and buffering time among procedures and devices;
• Optimization
of
overheat degree
of
molten steel in tundish and estimation
of
tapping temperatures
of
secondary metallurgy and steelmaking ;
• Determination
of
casting speed and surface temperature
of
slab according to
overheat degree
of
molten steel in tundish, and calculation
of
minimum time
through reheating furnace or holding furnace correspondingly;
• Rational temperature range
of
molten steel in procedures/devices, and the
corresponding successive convergence
of
temperature range in each proce-
dure/device(Fig.6.9);
• Time scheduling
of
mass flowrate - temperature - time among procedures;
• Combination
of
static optimization at designed condition (convergence) and
dynamic control under practical operating condition (divergence-convergence).
1750
I
1700
I
f::l
~
:::l
e
"
I
0-
E
1600
I
"
E-
I
• Mean limit
o
Lower
limit
- Upper limit
After At turret Tundish
refining
Ladle Before
refining
Tappmg
1500
L-
-
---
-----
-----'
Fig.6.9
Convergence analysis
of
temperature in steelmaking process
(Yin,
1998)
In regulation and control
of
the thin slab casting-rolling, the mass flowrate and
process temperature should be coupled on time axis for continuationand coordination
of whole process. So, the processing time in steel manufacturing process can be ana-
lyzed and integrated briefly by using concepts such as time-point, time-order, time-
position, time-intervaland time-cycleunder designed layout (Fig.6.10).
1..•·• •..·• •• · ·• •
••
..
••
•·..•..· ·
••
• • ·•..·• •..
•·
••
•..
··
··
· ·
c
~
;
;
~
..··..
·
..
······
..
··
..
··
~
Ladle : :
circulating
1 1
systern i i
L.................................... . .
1st heat
Fig. 6.10
...,
~r
(l)
"Tl
"
r:
0-
...,
5·
$:
"
:l
e
;-
r:
2
...,
5·
(JQ
-0
d
o
(l)
V>
V>
n
:r
"
-s.
(l)
...,
0\
2ndheat
OTime-point
Rigid unit
c=:>
Flexible unit
3
- I I
I
-II
I
CJlCllCJl CIlCJl
Q. CIl
00
CJlCJl
00
:;
CIl
CJlCJl CJl
00
c:c:
c:
C:C:
:::l c:
c:
c:c:
c:
.§
c: c: c: c:
·c·;:;::
';;=
Cl)
':;;
o
~
o
~
§
.;:
0
~:s
.
~
.
~
<.>
.0
is
c~
·
-
°E'= ;§ 3
E
'"'
'"'
~~...J
U
U
;.)
iii
c:u
o-
.c:
<t:
,=...J
t:
.",
"
:::::
8
v
.",
g
...
'"'
c:
.0
c:
til
Vi
t.:.l .!l
..
t.:.l
Time analysis and integration in thin slab casting-rolling process ( Yin, 1998)
l::
CIl CJlCJlCJl
~a
'
5:~~
~
Q.
c.
L";S
'-
, ,", '"'..:l...J
~
~;
c:c:
~
I
w
.
~
g
~
.
~
g
e.o~
~
e.o
~
~:::
~
~
~
...c O
.....
.c
0
~
c...
g'i
u
c..
....
.. '"I
Entity
Time-interval
I
...
-l
Time-position
l- EAF; 2- Refining furnace;3- Tundish; 4- Caster;5
-R
eheating furnace;
6
-R
olling mill; 7- Molten steel; 8- Slab ; 9- Products
f-'
-....J
f-'
172 Metallurgical Process Engineering
It can be seen from Fig. 6.10 that time-order in process is decided by function or-
der in process firstly. Taking the electric arc furnace
-thin
slab casting-rolling proc-
ess as an example, the functions
of
melting-temperature control-time scheduling are
realized by electric arc furnace, the functions
of
refining-temperature control-time
scheduling by refining furnace, the functions
of
casting-shaping-temperature con-
trol-time scheduling by caster, the functions
of
heating or holding-time scheduling
by reheating furnace and the functions
of
deforming-phase transforming-
temperature control-time scheduling by hot rolling mill. Similarly, the time-
charocteristic order
of
a series of unit operations is also arranged by corresponding
function order for a certain procedure.
The time-interval
of
a procedure/device consists
of
main operation, supplemen-
tary operation, transportation, loading/unloading, buffering and waiting time for
realizing the specific functions such as steelmaking, refining, casting and rolling
in the corresponding procedure/device. Because
of
the difference
of
the time-
interval values in every procedure/device, one or more key procedures, their time-
intervals and running rhythms should be found, and then the time-intervals and
time-positions
of
other procedures/devices would be determined for continuation!
quasi-continuation and compactness. So the thin slab caster is the key procedure
in electric arc furnace workshop. For continuous and compact running, the rule
of
key parameters
of
time-interval control among procedures should be
tE F
~t
c c
t
L
F
«t
E
F
~t
c c
where tEF is tap-to-tap time
of
EAF, min; tee is casting time
of
one heat steel in
caster, min;
tLF is refining operation cycle
of
ladle furnace, min.
In normal conditions, the reasonable range
of
operation time fluctuations
should be
i1t
~ c
~
i1t
~F
<
i1t~F
where,
i1t
~ c
is the rea sonable range
of
operation time fluctuations
of
caster, min;
M
~
F
is the reasonable range
of
operation time fluctuations
of
electric arc furnace,
min;
i1t
~F
is the reasonable range
of
operation time fluctuations
of
ladle furnace,
min.That means the operation time
of
thin slab caster should be stabilized and
optimized.
The range
of
waiting time fluctuations
of
each procedures should be
i1t
~vc
~
i1t
~~
< i1t
~
~
where,
i1t
~
V
c
is allowed range
of
time fluctuations
of
caster, min;
M~
~
is al-
lowed range
of
time fluctuations
of
electric arc furnace, min;
M
~
is allowed
range
of
time fluctuations ofladle furnace, min.
That means the waiting time
of
thin slab caster should be minimized as much
as possible. At the same time, the total waiting time
of
all procedures should be
Chapter
6
Time
Factor
in
Manufacturing
Process
173
stabilized and minimized.
The overheat degree
of
molten steel in tundish should be controlled within
lO
~20
'e
above liquidus.The objective temperature fluctuations ranges
of
molten
steel leaving EAF and LF should be restricted within
±20'e and ±lO'C
respectively.
The objective temperature fluctuations ranges
of
molten steel in EAF, LF and
ee
should be
/';.T
cc
<
/';.T
~
::
<
/';.T
~
;
f
where
/';.T
~
;
r
is the objective temperature ranges leaving LF, 'C,
/';.T
~
;
r
is the
objective temperature ranges leaving EAF,
'C, /';.T
cc
is the objective temperature
ranges
of
tundish metal for ee, 'e.
That means by coordination
of
procedures, the overheat degree
of
molten steel
in tundish could be controlled within
IO
~20
'e
above liquidus.
The coordinative rule
of
mass flowrate
of
procedures is
QEF=QLF=QCC
where Q
EF
is the average output per minute from EAF, t/min; QLF is the average
output per minute from LF (ladle furnace), t/min; Qcc is the average slab output
per minute from caster, t/min.
It
means that stable sequence casting had been realized and slab output opti-
mized by coordination
of
mass flowrate from EAF(electric arc furnace) and
LF(ladle furnace).
The relationship between temperature drop and waiting time in thin slab cast-
ing-rolling process can be expressed as
/';.T=f(/';.
/", G, R)
M
=f
(/';.T
, R)
where
/';.T is the temperature drop
of
molten steel between procedures,'C;
/';./"
is the
waiting time between procedures, min;
M is the transporting and loading time, min;
G is molten steel capacity ofladle or tundish, t;
R is other correlation factors.
That means the molten steel temperature drop is related with capacity
of
ladle
or tundish, and also with waiting time, transporting time, etc.
To maintain continuation and compactness
of
manufacturing process, the rules
of
operation time minimization, mass flowrate coordination and energy consump-
tion minimization must be abided by from thin slab caster to hot rolling mill.
The mass flowrate coordination takes
nQcC=nQ
rh
=Q
ro
where Qcc is the average output per minute from thin slab caster, t/min; n=2 or I;
Q
rh
is the average output per minute from reheating furnace or holding furnace,
t/min; n=2orI; Q
ro
is the average output per minute from hot rolling mill, t/min.
Actually, the mass flowrate
of
reheating/holding furnace and rolling mill are
decided according to the mass flowrate of thin slab caster.
If
there is accident
of
rolling mill and intermittent time is too long, the mass flowrate
of
thin slab caster
174 Metallurgical Process Engineering
would be influenced. For example,
if
intermittent time
of
rolling mill exceeds
20min, casing speed should be reduced;
if
exceeds 40min, the thin slab casting
would be interrupted. For compact steel plant, the accident feed back
of
rolling
mill to thin slab caster should be paid attention to. The total time
of
t~~
, t
rh
,
t;~
and troshould be minimized. Here
t~
~
is the transportation time from
cutting machine to reheating/holding furnace, min;
t
rh
is the operation time
of
slab
in reheating/holding furnace, min;
t;~
is the transportation time from reheat-
ing/holding furnace to rolling mill, min;
tro is the operation time
of
rolling mill,
mm.
Reduction
of
slab processing time from thin slab caster to rolling mill would
benefit the energy consumption, production efficiency and cost saving.
The total temperature loss
I1Tc~h,
l1T;h
and
11T;~
o
should be minimized to
save energy. Here
I1Tc~'
is the slab temperature drop from cutting machine to re-
heating/holding furnace, 'C ;
l1T,h
is the slab temperature increase in reheat-
ing/holding furnace,'C;
11T,~
o
is the slab temperature drop from reheating/holding
furnace to rolling mill, 'C.
The waiting time between rolling mill and reheating furnace should be
where
11t;
~
is the range
of
waiting time
of
rolling mill, min;
I1t~
is the range
of
waiting time
of
reheating/holding furnace, min.
In order to coordinate the time-intervals
of
every procedures, the flexible
components, such as secondary metallurgy, reheating furnace or holding furnace,
are necessary not only for controlling the time-interval lengths but also for co-
ordinating the time-positions. For example,
if
the time-intervals t
EF,
tee, and t
LF
are 60 min,60 min and 40 min respectively, there are some time-interval lengths
used for transporting, buffering as well as waiting before and after
tLF. time-
position designing
of
ladle furnace is how to set start and end time-points
of
tLF.
The selection
of
time-position has a critical influence on parameters time and
temperature
of
the corresponding procedure and device operation.
It
also influ-
ences whole process continuity and stability as well as the techneconomic in-
dexes such as energy consumption etc.
The time-point in process running is often take as a target value to be con-
trolled.
It
means the clock measured start and end time
of
a procedure or an
operation in the procedure and characterizes the clock measured time-cycle or
rhythm running.
It
is also the objective function for arranging, regulating and
controlling
of
time scheduling.
Generally speaking, the dissipation value, consisting
of
decay
of
mass flowrate,
temperature undulation, and time-space interval
of
mass flow in manufacturing
process, will be minimum because
of
the high continuation degree and spatio-
Chapter 6 Time Factor in Manufacturing Process 175
temporal
compactness
of
thin
slab
casting-rolling
process.
References
Prigogine I, Stengers I (I984) Order Out
of
Chaos. Zeng Qinghong and Shen Xiaofeng
transIated.(1987), shanghai Trauslation Pub.Shanghai: 29, (In Chinese)
Lin J F (2002)What does the time be. Studies in Dialectics
of
Nature. I8(2): 75-76 (in
Chinese)
Xu G Z (2000) System Science. Shanghai Scientific
& Technological Education Publishing
House, Shanghai:30 (in Chinese)
Yin R Y (I 998) The Engineering analysis
of
thin slab casting and rolling process, Iron and
Steel, 33 ( I ) : 2-6 (in Chinese)
Chapter 7
Operating Dynamics in the
Production Process of Steel Plant
From the viewpoint of the time operations
of
massflow in steel plant manufactur-
ing processes, the diverse procedures and devices in the steel manufa cturing
process should function as pushing forces, buffers, and pulling forces respec-
tively in order to ensure continuous and smooth implementation of production
operations and schedules. Analysis of the operating dynamics of the upstream and
downstream sections of steel plant manufacturing processes shows that blastfur-
nace acts as a pushing force in the entire operation; continuous caster plays a
dual role, i.e. as a pullingforce in the upstream section and as a pushingforce in
the downstream section; whereas downstream hot rolling mill acts as a pulling
force.
To
ensure continuous and coordinated operations between the pulling
forces and pulling forces, it
is necessary to set up a number of procedures and
devices that serve as buffers or flexible loops between the two forces,
so as to
coordinate these two forces and bring about a continuous or quasi-continuous
operation of massflow in the
manuf
acturing process.
In general, process dynamics is a science
of
the mechanism and the regularity
about the state of matters or objects with time. Dynamic process characteristics at
different scales and levels may be general or different. The difference shows in
dimension, scale and space-time.
Process dynamics at the micro and meso scopic levels in the iron and steel
manufacture is easy to be observed, estimated and simulated. This type
of
dy-
namic process can easily be modeled for its short cycle and on small scale.
It
is difficult to estimate the dynamics
of
evolutionary process at the macro-
scopic level for its large space scale, long time cycle and the complexity. This
large scale complex process system is often considered as to be disordered and is
hard to study for many influencing factors and instable inte
rf
erence sources.
It
is
difficult to model the macro process operation dynamics such as the production
R. Yin, Metallurgical Process Engineering
© Metallurgical Industry Press, Beijing and Springer-Verlag Berlin Heidelberg 2011