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A Model for Sequencing and
Optimizing Steel Melt Shop
Operations
Using Iterative Hierarchical Decomposition
based Discrete Event Simulation
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Steelmaking
The Production Process Flow at the Client’s
Plant
2
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Blast
Furnace
Basic
Oxygen
Furnace
Basic
Oxygen
Furnace
PIG Casting
Machine
Slag
Dumping
Yard
Ladle
Refining
Furnace
Vacuum
Degassing
Unit
Continuous
Caster
Ho
t m
eta
l la
dle
by lo
com
otive
s
Liq
uid
Ste
el L
ad
le b
y
Tra
nsfe
r C
ar
and
Cra
ne
Liq
uid
Ste
el Ladle
by
Tra
nsfe
r C
ar
and
Cra
ne
Liq
uid
Ste
el L
ad
le b
y
Cra
ne
Sla
g p
ot b
y
Tra
nsfe
r C
ar
Scrap
Yard
Scra
p B
ox
by C
rane
Liquid Steel Ladle by
Transfer Car
and Crane
Ladle
Preparation
Aisle
Empty Ladle
by Crane
Ironmaking
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Objective: Overall Throughput Improvement
3
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Minimize tap-to-tap time of
furnace
Maximize utilization while
maintaining heat sequence
Optimal resource utilization
• Cranes
• Ladle cars
Basic Oxygen Furnace
(BOF)
Ladle Refining Furnace (LRF)
&
Vacuum Degassing Unit (VD)
Caster
Unit Optimization
Operations Synchronization
Overall Throughput Improvement
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Bottleneck Analysis Using Operational Laws
4
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Melt Shop
Operations
Use a queuing
model
Maintain job flow
balance
Apply utilization
law
BOFService Time
LRFService Time
VDUService Time
CasterService Time
Pro
port
ional
The unit with the
highest total
service time can
be a limiting
factor in
achieving higher
throughput
Reduce the cycle time to the minimum level possible at the
bottleneck unit
BOFUtilization
LRFUtilization
VDUUtilization
CasterUtilization
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Iterative Cycle Time Optimization
5
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Reduce the cycle time to
the minimum level possible
at the bottleneck unit
Sim
ula
te th
e m
odel
Again
with
the re
duce
d
cycle
times Stack rank the new
service times of the units
in the production chain
Bottle
neck s
hifts
during
itera
tion
s o
f
impro
vem
ent
Continue iterating
till there is no
further
opportunities for
practical cycle time
improvement
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Iterative Capacity Utilization Improvement
6
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
• Further scope for improvement might exist across
production units, service units and buffer units
• Observe the behaviour of capacity utilization of the units
which could potentially create a bottleneck
• Capacity utilization of units might change and tend to
move in a way affecting its performance
• Adding unit capacity and/or buffer capacity can further
improve system performance
Addition of unit capacity needed to be guided by • Economics
• Cost Benefit
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Cycle Time
Approach Using Iterative and Hierarchical
Decomposition
7
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Unit 3
Unit 1
Unit 2
Capacity Utilization
Unit 1
Unit 2
Unit 3
Progressive hierarchical decomposition of the chain and iteration based on
the two heuristics drives the simulation towards an optimal solution
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Baseline Simulation
8
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
• One year operation data was collected for
the BOF, LRF, VD and Caster
• Fitted into distributions and best fit
distribution was selected with the help of
goodness of fit tests
• The model was run with the existing
operation parameters
Results
Average heats per day 21
Average BOF tap-to-tap time 65 mins
LRF utilization 79 %
Caster utilization (using 2
strands) 53 %
VD utilization 48 %
Caster heat sequence Maintained
Snapshot of 10 days with existing
parameters after attaining stabilization
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BOF Basic Cycle Time Distribution
9
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Activities Time*
Scrap charging 1 to 2
Hot metal pouring 4
Blowing 16 to 18
Deslagging 2 to 3
Temperature & Analysis 5
Tapping 4 to 6
Slagging off 2
Slag coating 5
Ba
sic
activitie
s in
BO
F
*Figures in minutes
Weibull
Mean:43 ; Standard Deviation: 0.7
Average delta of 22 mins between Tap-to-Tap and BOF basic
cycle time
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BOF Cycle Time Improvement Strategy
10
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Event Average
Time*
Mouth jam cleaning and dozing after
every 8 heats 90
Tap hole changing after about 15
heats 45
Other maintenance after 75 heats 180
Current Maintenance Downtime
Practices
Event Average
Time*
Mouth jam cleaning and dozing after
every 15 heats 45
Tap hole cleaning and other
maintenance after 75 heats 180
Proposed Maintenance Downtime
Practices
*Figures in minutes
Use T
ap h
ole
sle
eves
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Improved BOF Tap-To-Tap Time Distribution
11
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Lognormal
Mean: 59; Standard Deviation: 4.6
Skewness: 1.21585
Although average tap-to-tap time improved to 59 mins,
non trivial positive skew indicates potential BOF
blockage due to downstream
*Figures in minutes
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Capacity Utilization Analysis
12
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Results
Average heats per day 23
Average BOF tap-to-tap time 59 mins
LRF utilization 92 %
Caster utilization (using 2
strands) 60 %
VD utilization 54 %
Caster heat sequence Maintained
Snapshot of 10 days with proposed
parameters after attaining stabilization
• Probable downstream blockage in the
LRF
• Removing downstream blockage can
further reduce BOF tap-to-tap time
• Make use of the blocked BOF capacity
as well as the additional caster capacity
with three strands in operation
?
45 60 65 (time in minutes)
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13
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Lognormal
Mean: 51; Standard Deviation: 0.8
Skewness: 5.93932e-002
Resulting improvement in BOF Tap-To-Tap
Time Distribution
Reduced skewness and more symmetrical
pattern indicates lesser system wide congestion
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Additional Capacity along with Cycle Time
Improvements Increases Throughput Significantly
14
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
• Average BOF tap-to-tap could be brought down further to an
average of 51 minutes
• The caster could be operated with three strands while
maintaining the heat sequence
• The overall throughput increased by about 20%
The increased overall steel production decreased the diversion of hot
metal to the pig casting machine improving the profitability of the melt
shop
![Page 15: A Model for Sequencing and Optimizing Steel Melt Shop ... · PDF fileTransfer Car and Crane Ladle Preparation Aisle Empty Ladle by Crane Ironmaking . Objective: Overall Throughput](https://reader033.vdocuments.us/reader033/viewer/2022052608/5a8312d77f8b9ada388e4e63/html5/thumbnails/15.jpg)
Cost Benefit Analysis
15
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Unit Costs & Operational Parameters
Tap hole sleeves 200 mm, 10 sleeve pack $3000
Sleeve change interval 75 heats
Electrode consumption in LRF 12 gm/KWH
Electricity consumption in LRF 0.5 KwH/Degree Celcius/ton
Average heating in LRF 5 Degree Celcius
Cost of Electricity 10 C/ KWH
Investments
1X35 Ton LRF 8 MM$
Product Price
Average Billet Price $480 /ton
Average Pig Iron Price $ 400/ton
Marginal Revenue R 5.3 MM$/year
Marginal Cost C (Sleeve Cost + Electrode
Consumption + Power Consumption) ~$400,000
Additional profit , P 4.9 MM$
Payback Period for Investment 1 Year and 7 Months
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Future Work
16
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
Large scale plant wide throughput improvement through
Cycle time reduction
Capacity addition
Include operational elements like intra-plant logistics, facility layout re-engineering,
plant wide inventory & movement buffers, routing sequences and material
allocations
Use hybrid models of discrete event and system dynamic simulation for overall
performance improvement
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17
Atanu Mukherjee, Arnab Adak
M.N. Dastur & Company
16.06.2015
M.N. Dastur & Company (P) Ltd Consulting Engineers
www.dastur.com