Design Project Group 3 Rev A FINAL.1

Department of
Chemical Engineering
CHEE 457: Design Project II
Production of Stainless Steel
Presented to:
Prof. Dimitrios Berk
Mrs. Nadia Romani
Dr. Roger Urquhart
Submitted by:
Mohammed Abu Shark - 260376614
Spencer John Brennan - 260315605
Saikat Chanda - 260372492
Michael Garibaldi - 260353823

Design II Production of Stainless Steel
2
Friday April 11th, 2014

Design II
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Acknowledgements
As a group we would like to sincerely thank Mrs. Romani and Dr.
Urquhart for all their guidance and supportthroughout the year. Their
engineering experience and knowledge were instrumental in our
learningprocess. Wearegratefulto havelearnedfromsuch professional
instructors.

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1. INTRODUCTION .......................................................................................................................................................1
1.1PROJECT MANDATE.................................................................................................................................................1
1.2PROJECT SCOPE .......................................................................................................................................................1
1.3DELIVERABLES........................................................................................................................................................3
2. PROCESS DESIGN .....................................................................................................................................................4
2.1PROCESSDESCRIPTION...........................................................................................................................................4
2.1.1 Midrex Direct Iron Reduction ..................................................................................................................4
Midrex Shaft Furnace.............................................................................................................................................................................................................4
Steam Reformer..........................................................................................................................................................................................................................6
Venturi Scrubber........................................................................................................................................................................................................................8
Boiler ....................................................................................................................................................................................................................................................9
2.1.2 Electric Arc Furnace...................................................................................................................................9
EAF Function .................................................................................................................................................................................................................................9
Process Overview......................................................................................................................................................................................................................9
Block Flow Diagram............................................................................................................................................................................................................10
Process Description.............................................................................................................................................................................................................10
Summary of EAF Reactions...........................................................................................................................................................................................12
2.1.4 Continuous Casting ..................................................................................................................................13
2.2DESIGNCRITERIA..................................................................................................................................................14
2.3MATERIAL AND ENERGY BALANCE.......................................................................................................................15
2.3.1Midrex Direct Iron Reduction .................................................................................................................15
Midrex Shaft Furnace.........................................................................................................................................................................................................15
Steam Reformer......................................................................................................................................................................................................................18
Boiler ................................................................................................................................................................................................................................................22
Energy Balance for Remaining Equipment.....................................................................................................................................................23
2.3.2 Electric Arc Furnace.................................................................................................................................24
2.3.4 Continuous Casting ..................................................................................................................................27
Water-Cooled Mould Methodology........................................................................................................................................................................28

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Water Spray Chamber.......................................................................................................................................................................................................32
Blower Section.........................................................................................................................................................................................................................35
3. OPERATING PHILOSOPHY ................................................................................................................................36
3.1CONTROL THEORY................................................................................................................................................36
3.2PROCESSAND INSTRUMENTATION DIAGRAM DEVELOPMENT.............................................................................37
3.2.1 Overall P&ID Development .....................................................................................................................37
3.2.2 Common Unit Control Philosophy .........................................................................................................38
Pumps and Compressors................................................................................................................................................................................................38
Control Valves ..........................................................................................................................................................................................................................38
3.2.3 Midrex Direct Iron Reduction ................................................................................................................40
Midrex Shaft Furnace and Conveyor Belts......................................................................................................................................................40
Steam Reformer......................................................................................................................................................................................................................41
Boiler ................................................................................................................................................................................................................................................43
Venturi Scrubber....................................................................................................................................................................................................................43
Heat Exchanger.......................................................................................................................................................................................................................44
3.2.4 Control Philosophy Electric Arc Furnace.............................................................................................45
Cooling water flow rate....................................................................................................................................................................................................45
Hydraulic mechanisms.....................................................................................................................................................................................................48
Bin weighing control ..........................................................................................................................................................................................................53
Fan speed control..................................................................................................................................................................................................................54
3.2.6 Continuous Casting Section ....................................................................................................................55
Flux Transport Control.....................................................................................................................................................................................................55
Molten Stainless Steel Flow Control .....................................................................................................................................................................56
Cooling Water Flow Control.........................................................................................................................................................................................57
Mist Flow Control ..................................................................................................................................................................................................................58
4. PLANT DESIGN.......................................................................................................................................................59
4.1 EQUIPMENT SIZING...............................................................................................................................................59
4.1.1 Midrex Direct Iron Reduction ................................................................................................................59

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Shaft Furnace............................................................................................................................................................................................................................59
Air blower ....................................................................................................................................................................................................................................59
Air compressors......................................................................................................................................................................................................................60
Venturi Scrubber....................................................................................................................................................................................................................61
Boiler ................................................................................................................................................................................................................................................63
Conveyor belts.........................................................................................................................................................................................................................63
Heat Exchanger.......................................................................................................................................................................................................................64
4.1.2 Electric Arc Furnace.................................................................................................................................65
Transformers............................................................................................................................................................................................................................67
Axial Vane Fans.......................................................................................................................................................................................................................68
Ladles...............................................................................................................................................................................................................................................68
Bins ....................................................................................................................................................................................................................................................69
Lime Pebble Silos...................................................................................................................................................................................................................70
Cranes..............................................................................................................................................................................................................................................70
Conveyors.....................................................................................................................................................................................................................................71
Suspended Magnet...............................................................................................................................................................................................................72
Cooling Bed and Excavator...........................................................................................................................................................................................72
4.1.4 Continuous Casting Section ....................................................................................................................73
Tundish...........................................................................................................................................................................................................................................73
Flux Silo and Hopper (SI-03-401 and HP-03-401 and HP-03-402)..........................................................................................74
Oscillating Water-Cooled Mould (MD-03-401 and MD-03-402).................................................................................................75
Spray Chamber (SC-03-401 and SC-03-402)................................................................................................................................................77
Pneumatic Conveying........................................................................................................................................................................................................78
Rotary Screw Air Compressor (CP-03-401 A/B).......................................................................................................................................80
Membrane Air dryer (DR-03-401).........................................................................................................................................................................80
Bottom Discharge Blow Tanks (TA-03-401 to 404)...............................................................................................................................80
Axial-Flow Compressor and CentrifugalPump for Spray Chamber Mix (CP-03-402 A/Bto403 A/B and
PP-03-403 A/B to 404 A/B).........................................................................................................................................................................................81
Water-Cooled Mould Pump..........................................................................................................................................................................................82
Power-Driven Roller Conveyors (RL-03-401 to 458)...........................................................................................................................83

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Roller Conveyor Slab Collection Rack (RA-03-401)...............................................................................................................................84
Blowers (BL-03-401 to 420).......................................................................................................................................................................................85
4.2PLANT LAYOUT .....................................................................................................................................................86
5. ENVIRONMENTAL EVALUATION ....................................................................................................................87
5.1MIDREX PROCESS..................................................................................................................................................87
5.2 ELECTRIC ARC FURNACE.......................................................................................................................................87
5.4CONTINUOUS CASTING..........................................................................................................................................88
6. COST ANALYSIS ....................................................................................................................................................89
6.1CAPITAL EXPENDITURE (CAPEX) .......................................................................................................................89
Indirect Costs.......................................................................................................................................................93
6.2OPERATING EXPENDITURES (OPEX) ...................................................................................................................94
6.2.1 Net Present Value of Investment ...........................................................................................................96
6.3INTERNAL RATE OF RETURN................................................................................................................................96
7. REFERENCES...........................................................................................................................................................97
APPENDIX A - MASS & ENERGY BALANCE............................................................................................................I
A.2ELECTRIC ARC FURNACE .........................................................................................................................................I
A.4CONTINUOUS CASTING........................................................................................................................................VIII
APPENDIX B – EQUIPMENT SIZING ....................................................................................................................XV
B.4CONTINUOUS CASTING..........................................................................................................................................XV
APPENDIX C – CAPEX & OPEX.........................................................................................................................XXVII
C.1CAPEX ............................................................................................................................................................... XXVII
C.2- OPEX...............................................................................................................................................................XXXI
APPENDIX D – PROCESS FLOW DIAGRAMS .....................................................................................................38
APPENDIX E – PROCESS & INSTRUMENTATION DIAGRAMS ....................................................................45

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APPENDIX F – PLANT LAYOUT.............................................................................................................................52
APPENDIX F – EQUIPMENT LIST .........................................................................................................................57
List of Figures
Figure 1 ............................................................................................................................... 5
Figure 2 ............................................................................................................................... 7
Figure 3 ............................................................................................................................... 8
Figure 5 ............................................................................................................................... 9
Figure 6 ............................................................................................................................. 10
Figure 7 ............................................................................................................................. 20
Figure 8 ............................................................................................................................. 33
Figure 9 ............................................................................................................................. 38
Figure 10 ........................................................................................................................... 39
Figure 11 ........................................................................................................................... 39
Figure 12 ........................................................................................................................... 41
Figure 13 ........................................................................................................................... 42
Figure 14 ........................................................................................................................... 42
Figure 15 ........................................................................................................................... 43
Figure 16 ........................................................................................................................... 44
Figure 17 ........................................................................................................................... 45
Figure 18 ........................................................................................................................... 46
Figure #9 ........................................................................................................................... 47
Figure 20 ........................................................................................................................... 47

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Figure #21 ......................................................................................................................... 48
Figure 22 ........................................................................................................................... 49
Figure 23 ........................................................................................................................... 50
Figure 24 ........................................................................................................................... 51
Figure 25 ........................................................................................................................... 52
Figure 26 ........................................................................................................................... 53
Figure 27 ........................................................................................................................... 53
Figure 28 ........................................................................................................................... 54
Figure 29 ........................................................................................................................... 55
Figure 30 ........................................................................................................................... 56
Figure 31 ........................................................................................................................... 57
Figure 32 ........................................................................................................................... 58
Figure #33 ......................................................................................................................... 61
Figure #34 ......................................................................................................................... 61
Figure #35 ......................................................................................................................... 62
List of Tables
Table 1............................................................................................................................... 16
Table 2............................................................................................................................... 19
Table 3............................................................................................................................... 28
Table #4............................................................................................................................. 63
Table 5............................................................................................................................... 90
Table 6............................................................................................................................... 94
Table 7............................................................................................................................... 96

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Table 8...................................................................................................................................i
Table 9...................................................................................................................................i
Table 10................................................................................................................................ii
Table 11...............................................................................................................................iii
Table 12............................................................................................................................. viii
Table 13............................................................................................................................. viii
Table 14...............................................................................................................................ix
Table 15..............................................................................................................................xii
Table 16............................................................................................................................. xiii
Table 17............................................................................................................................. xiii
Table 18.............................................................................................................................xiv
Table 19..............................................................................................................................xv
Table #20...........................................................................................................................xvi
Table 21............................................................................................................................ xvii
Table 22........................................................................................................................... xviii
Table 23.............................................................................................................................xix
Table #24............................................................................................................................xx
Table #25...........................................................................................................................xxi
Table #26...........................................................................................................................xxi
Table #27.......................................................................................................................... xxii
Table #28......................................................................................................................... xxiii
Table #29......................................................................................................................... xxiii
Table #29......................................................................................................................... xxiv

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Table #30......................................................................................................................... xxiv
Table #31..........................................................................................................................xxv
Table #32......................................................................................................................... xxvi
Table #33......................................................................................................................... xxvi
Table 34......................................................................................................................... xxviii
Table #35......................................................................................................................... xxix
Table #36......................................................................................................................... xxix
Table #37......................................................................................................................... xxix
Table 39............................................................................................................................. 35
Table 40............................................................................................................................. 37

Design II
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1. Introduction
1.1 Project Mandate
Inox has selected three McGill consulting teams to design a complex in Quebec for
the production of stainless steel slabs by exploiting the chromite deposit from the “Ring of
Fire”. The project mandate of Group 3 is to produce 2 million tonnes of stainless steel per
annum. In order to satisfy the mandated tonnage, 1,400,550 tonnes per annum of iron ore
pellets, 150,000 tonnes per annum of steel scrap and 400,000 tonnes per annum of
ferronickel are procured, while, 600,000 tonnes of high carbon ferrochromium (HCFeCr)
is received from Groups 1 and 2.
1.2 Project Scope
Group 3 will design processes to produce the solidified stainless steel slabs with
dimensions 10 m x 0.25 m x 1 m at a composition of 18 % chromium, 0.08 % carbon and
8 % nickel. To produce such slabs, there are four main process steps required:
(1) Iron ore reduction in the Midrex Direct Iron Reduction Process
(2) Heating and further reduction of carbon in the Electric Arc Furnace (EAF)
(3) Oxidation and addition of chromium in the Argon Oxygen Decarburizer (AOD)
(4) Cooling of molten stainless steel for slab production by continuous casting
The aforementioned processes will be designed in full, from mass and energy
balance considerations and engineering drawings such as block flow diagrams (BFD),
process flow diagrams (PFD) and process and instrument diagrams (P&ID). Equipment
will be sized based on process flow calculations and the most suitable will be chosen and
recommended for implementation. A layout of the stainless steel production plant will be
provided – both top view and side view – indicating the preferred location of the process
equipment. A complete capital and operating economic evaluation (CAPEX and OPEX)
will be performed and the return on investment (ROI) based on the produced tonnage per
annum will be determined. To ensure the plant has the ability to meet future imposed

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environmental regulations, sustainable design aspects will be considered and a full
environmental evaluation completed.
Battery limits of the project define a process perimeter, limiting the scope of group
3’s design responsibilities. Engineering design, sizing and costing of the processes used to
produce stainless steel are all within the battery limits of the outlined Inox project. The
specific aspects not within the battery limits of this project are:
 The source and transportation of high carbon ferrochromium received in either
granulated or molten form Groups 1 and 2
 The source and all aspects of pumping (including costing) of coolingwater, which is
received from Group 2
 All aspects of the process watertreatment and return to the environment (although
pumping to the wastewater treatment plant is accounted for)
 The distribution of slabs to their final market destination
The cost of all other raw materials (iron ore pellets, ferronickel (FeNi40) and steep scrap)
and utilities are accounted for during operation and procurement. Transportation costs
upon procurement are included in the price per unit quantity purchased.

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1.3 Deliverables
The following deliverables were included on the final report:
 Executive Summary
 Overall Block Flow Diagram (BFD)
 Overall Process Flow Diagram (PFD)
 Process description
 Equipment description
 Overall Control strategy
 Engineering Drawings :
 Individual Block Flow Diagram (BFD)
 Individual Process Flow Diagram (PFD)
 Individual Piping & Instrumentation Diagram (P&ID)
 Plot Plan
 Economic evaluation (CAPEX, OPEX, ROI)
 Environmental Evaluation
 Mass and Energy balances
 Equipment Sizing
 Breakdown of Responsibilities

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2. Process Design
2.1 Process Description
2.1.1 Midrex Direct Iron Reduction
Midrex Shaft Furnace
The Midrex direct reduction system is a gas-based reduction process from which
the production of sponge iron can be achieved. The main difference between the sponge
iron, commonly referred to as direct reduced iron (DRI), and iron ore pellets feed is their
oxygen content. The iron ore contains approximately 30wt% oxygen while the direct
reduced iron has 3wt%. In order to reduce the oxygen content, the iron oxide (fe2O3;
96.8wt%) present in iron ore will undergo a series of consecutive oxidation-reduction
reactions, shown below, with a gas stream high in CO and H2 content, to form metallic
iron, carbon dioxide and steam:
(1) 3Fe2O3 + CO → 2Fe3O4 + CO2
(2) 3Fe2O3 + H2 → 2Fe3O4 + H2O
(3) Fe3O4 + CO → 3FeO + CO2
(4) Fe3O4 + H2 → 3FeO + H2O
(5) FeO + CO → Fe + CO2
(6) FeO + H2 → Fe + H2O
To a small extent, the metallic iron product is further reduced by carbon monoxide
and hydrogen by the following carburization reactions:
(7) 3Fe + 2CO → Fe3C + CO2
(8) 3Fe + CO + H2 → Fe3C + H2O
Traditionally, this process has been completed using blast furnaces, however since
they require high quality coke, auxiliary plants for raw material handling, higher operating
temperature and three times the CO2 emissions of direct iron reduction methods, they are
not favoured for iron ore reduction processes (Chatterjee, 1994). The oxidation-reduction
reactions are carried out in a shaft furnace where the iron ore pellets are fed from the top
through a charge hopper while the syngas stream flowing from the bottom through tuyere.

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Feeding the reactants to the Midrex furnace in this counter-current fashion allows for
efficient heat transfer to occur between the solids and gases (Anameric et al., 2007).
Figure 1
The Midrex unit is operated in a counter-current fashion to increase heat transfer between the gases and
solids (Anameric et al., 2007).
The incoming syngas enters the furnace at 894oC, heating the iron ores and leaves
as off-gas at 450 oC. The overall reduction process is endothermic (105 kJ/mol; 25 oC),
thus requiring an additional source of heating.
The sponge iron can be discharged in three different manners from the Midrex
furnace: cold DRI, hot DRI and hot briquetted DRI. Cold and briquetted DRI are effective
for storage and shipping, however since the reduced iron will be further processed in the
electric arc furnace (EAF), hot DRI is preferred since it is discharged at a temperature of
650 oC, thus cutting down on the EAF’s energy consumption.
The chemical composition of the DRI is dependent on the quality of the iron ore
feed. A higher iron oxide percent in the pellets will give higher iron content in the product
and lower gangue amount (Anameric et al., 2007). Referring to the list of design criteria in
section X, the DRI composition has four criteria that need to be met: 3wt%FeO, 1.6wt%C,
90% of FeS retained in the DRI and 100% of the remaining gangue material retained in the

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DRI. The iron metallization percent is used to determine the extent of iron reduction. For
the given iron ore pellet composition and the DRI criteria needed, the sponge iron has a
degree of metallization of 93.3%. This is within the common metallization range of 90-
94% for Midrex processes (Midrex Technologies, 2013).
Steam Reformer
The steam reformer is a catalytic process that converts natural gas and steam into
hydrogen and carbon monoxide gas. The reformer has two sets of reactions taking place:
the reforming reactions, which produced the syngas mixture (CO and H2) and the
combustion reactions which provides the heat input required for the endothermic reforming
reactions. The reforming reactions taking place depends on the composition of the natural
gas feed. For this case, methane, ethane, propane, butane and pentane react to form syngas
as follows:
(9) CH4 + H2O → CO + 3H2
(10) C2H6 + 2H2O → 2CO + 5H2
(11) C3H8 + 3H2O → 3CO + 7H2
(12) C4H10 + 4H2O → 4CO + 9H2
(13) C5H12 + 5H2O → 5CO + 11H2
The reforming reactions take place inside nickel catalyst-filled tubes that are vertically
mounted inside the combustion chamber. The burners and tubes can be arranged according
to either a top-fired or side-fired design. A top-fired design was used in this process because
of higher heat transfer efficiency compared to side-fired designs, using twice as less
burners (GBH Enterprises, 2013). The Midrex steam reformer recycles the off-gas from
the shaft furnace to generate more syngas, according to the following reaction, thus
lowering the natural gas demand:
(14) CH4 + CO2 → 2CO + 2H2

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Figure 2
Top-fired steam reformer set-up (ThyssenKrupp, 2014).
The feed natural gas and steam are pre-heated to approximately 500oC using a heat
exchanger, thus cutting the reforming reactant heating requirement by more than half. The
off-gas from the electric arc furnace and argon oxygen decarburization processes are sent
to a gas scrubber and then recycled to the reformer, thus lowering the natural gas amount
needed for reforming reactions. The following combustion reactions take place inside the
combustion chamber:
(15) CH4 + 2O2 → CO2 + 2H2O
(16) C2H6 + 7/2O2 → 2CO2 + 3H2O
(17) C3H8 + 5O2 → 3CO2 + 4H2O
(18) C4H10 + 13/2O2 → 4CO2 + 5H2O
(19) C5H12 + 8O2 → 5CO2 + 6H2O
Air is used as the source of oxygen and is blown into the system using an air blower.
It is assumed that the syngas leaves the reformer furnace at approximately 900oC and is
heated entirely by the combustion of natural gas by reaction 15-19. The combustion flue
gas leaves the system through tunnels located at the bottom and is used to pre-heat
incoming reactants in the heat exchanger.

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Venturi Scrubber
A venturi scrubber is used to remove dust particles contained in the off-gasses of
the EAF and AOD process before recycling them into the Midrex reformer. Venturi’s are
classified as a wet scrubber method since water is used to remove the particles of interest.
The incoming gas stream’s speed is accelerated due to inertia when moving down the throat
section of the scrubber. This will cause, upon contact with water, the formation of many
small water droplets at the throat section of the scrubber. When the dust particles enter the
throat section of the venturi scrubber, they collide with the tiny water droplets by
impaction, illustrated below. The removal efficiency by impaction is proportional to the
dust particle diameter, but decreases exponentially for particle size less than 0.2𝜇m (EPA,
1991).
Figure 3
Left: Impaction mechanism is used to trap the dust particles into the water droplets.
Right: venturi scrubber where the water is fed at the converging section (EPA, 2014).
The scrubber consists of three main parts: converging, throat and divergent
sections. The gas stream enters from the top of the venturi while the water stream is fed
from either the throat or converging section. Since the stream to be treated consists of hot
dry gas, the preferred region to feed the water is from the convergent section, because this
will prevent abrasion of the throat wall (EPA, 2014).

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Due to high gas velocity at the throat section of the venturi scrubber, some of the
water droplets are carried by the gas stream, creating entrainment droplets, thus venturi
scrubbers are commonly followed by a cyclone for mist elimination.
Boiler
The reforming reactions require steam in order to produce the syngas stream. This
will be provided by boiling process water and heating to 400oC by using a water boiler to
form super-heated steam. The boiler consists of a three-pass steam fire-tube. The boiler
transfers heat similar to a shell-and-tube heat exchanger, where the hot gases from
combustion flow through the tubes, while the water is contained in the shell. A large
capacity boiler was chosen (1300-2300 BHP) to meet the required power of 1800 boiler
horsepower (BHP). The heating will be provided by the combustion of natural gas instead
of oil, since natural gas is already used in other equipment of the Midrex process.
2.1.2 Electric Arc Furnace
EAF Function
An electric arc furnace (EAF) has three primary functions:
1. To contain the steel scrap and direct reduced iron;
2. To heat and melt the steel scrap and direct reduced iron;
3. To transfer the molten steel to the next processing stage.
Process Overview
Figure 4
Furnacecharging Melting De-slagging Metal pouring
Furnaceturn-around
• Routine inspection of all
furnace components
• Lubrication

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Block Flow Diagram
DRI: 1016174 t/a
Steel Scrap: 150000 t/a
Lime: 60000 t/a
Steel: 1094550 t/a
Slag: 112125 t/a
Off-gas: 64604 t/a
EAF
Atmospheric Air: 51141 t/a
Figure 5
Block flow diagram of EAF unit.
Process Description
Receive DRI
Direct reduced iron pellets arrive from the Midrex unit from the DRI conveyor (CV-
03-103). These pellets are directed into a chute which feeds into a bin (BN-03-201/202).
The bin is suspended from an overhead crane (CN-03-201) which measures the change in
weight of the bin. One-hundred and twenty-four tonnes of DRI are loaded into this bin.
Once the desired weight is reached, the DRI conveyor is stopped and the lime pebble
conveyor is activated.
Receive Lime
The lime pebbles are stored in three separate silos (SI-03-201). Only one of these
silos feeds the conveyor at a time. The silo hatch is opened and feeds lime onto the
conveyor (CV-03-201) as the conveyor moves below. Seven tonnes of lime are loaded into
the bin and then the silo hatch is closed and the conveyor is stopped. The bin is then
elevated and carried by the crane to the steel scrap transfer station.
Transfer of Steel Scrap
Steel scrap is purchased from an external vendor. CN Railways is under contract
with the company to deliver the steel scrap via rail car. A rail branches from the main CN

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line and enters the plant in the EAF section. The rail cars are detached from the locomotive
and rest inside the plant. The overhead crane (CN-03-201) binds the suspended magnet
(CN-03-204) and takes scrap from the rail car (BN-03-203), placing it in the bin filled with
DRI and lime. The crane measures 18 tonnes of scrap and then detaches from the magnet,
lifts the bin and carries it to the crane transfer station. Here the bin is placed below another
overhead crane (CN-03-202/203).
Charging EAF
The second crane in the process lifts the bin and positions it above the electric arc
furnace. With the roof of the EAF (RF-03-201/202) raised and to the side, the crane charges
the furnace by emptying the materials of the bin into the hearth (EAF-03-201/202).
Moving of Roof, Turning on Fan, Switching on Current, Lowering Electrodes
The roof (RF-03-201) then moves into position above the furnace shell. Once the
roof is in place, the axial vane fan (FA-03-201) is turned on to begin venting. The control
valve for the cooling water (FCV-03-205) is opened to begin the flow of water to the roof,
bus bar (BB-03-201) and electrodes (EE-03-201). Pressure of the furnace is measured to
regulate the fan speed. The switch is then turned on to initiate the current transfer from the
transformer station, through the power cables and the bus bar and into the three graphite
electrodes. The height of the bus bar is then lowered, bringing the hot electrodes into
contact with the contents of the hearth.
Melting Charge
The initial melt takes fifteen minutes to achieve. To avoid fracturing the electrodes,
the height of the electrodes is initially above the mass of DRI, scrap and lime. After fifteen
minutes, the top layer of scrap and DRI is melted and the electrodes are lowered further to
bore into the material and expedite melting. The height of the electrodes gradually
decreases over the remaining forty-five minutes. After an hour, the current is switched off
and the bus bar is raised to remove the electrodes from the bath of slag and hot metal.
During the melting period, temperatures inside the bath reach 1600°C.

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Slag Removal
The slag forms a fluid layer on top of the molten metal. The slag door is located
above the top of the slag. It is opened using the hydraulic mechanism, creating a path for
slag to flow down the slag launder (LA-03-202) and into the slag pot (LC-03-201). The
furnace is tilted using the hydraulic mechanism and the slag pours out of the furnace. The
slag door is closed and the furnace is tilted upright once the slag ceases to flow.
The slag pot is positioned on a slag pot car, which moves automatically along a rail
to the outdoor cooling bed (CB-03-201). Upon reaching the cooling bed, the slag pot is
tipped on its side to pour out the molten slag. It is left to cool and solidify into grains. An
excavator (EX-03-201) removes the slag from the concrete bed and piles it on the slag
deposit (DP-03-201). It remains in the deposit until a disposal contractor moves it to
another remote location.
Hot Metal Tapping
The hot metal door is located above the hot metal launder (LA-03-201). It is opened
with the hydraulic mechanism and the furnace is tilted to allow the hot metal to flow along
the launder and into the hot metal ladle (LD-03-201).
Transfer of Hot Metal Ladle
The hot metal ladle is located beneath the overhead crane (CN-03-202). The crane
lifts the ladle and carries it to the Argon Oxygen Decarburization unit, where it undergoes
further processing.
Summary of EAF Reactions
Reaction 1: Fe3C → 3Fe + C
Reaction 2: FeS + CaO → FeO + CaS
Reaction 3: FeO + C → Fe + CO

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2.1.4 Continuous Casting
Continuous strand casting is the process by which molten metal is solidified to a
strand of solid. Through the storage of molten stainless steel in the tundishes the stainless
steel production process is converted from batch to continuous. The restricting element of
the casting process is the heat removal rate. At the specified design capacity of 2 million
t/a stainless steel production, there are two full gravity arc casting systems employed.
Cooling of the stainless steel from 1800 °C to room temperature occurs in three main stages
in continuous casting:
1. Primary coolingvia the water-cooledcopper mould
2. Secondary cooling via the spray chamber
3. tertiary cooling via numerous air blowers
Molten stainless steel tapped from the AOD in batches, is delivered to the tundishes
in crane-transported ladles. The stopper-controlled rod and nozzle allows for the casting
rate to be kept constant while the tundishes’ volumes vary. A CaF2 flux is added to the
tundish to minimise oxidation of the stainless steel, as well as provide vital lubrication
between the solidified stainless steel wall and oscillating water-cooled mould.
Molten steel is partially solidified in primary cooling, whereby the cooling water
runs counter-current to the stainless steel being cast. The mould removes approximately
20 % of the total required sensible and latent heat load, however, it provides integral outer
wall strength to the strand (solidifying 18 % of the steel) prior to reaching the spray
chamber.
Secondary cooling in the spray chamber, removes heat via evaporation of a water
mist created by mixing compressed air and water at an equal volumetric ratio. The spray
chamber introduces the water mist via nozzle spray directly onto the cast (and rollers),
while the rollers provide directional guidance to the strand, ensure it is properly supported
as well as imposing its shape via compression. The spray chamber guides the strand down
the 12.2 m radius arc from upper plant floor to the ground floor. It also extends for four

Design II
14
meters beyond the arc in a straight section. This cooling process solidifies the remainder
of the strand and reduces the temperature at the outlet to 400 °C.
The strand is transported by individually power-driven stainless steel rollers upon
exit from the spray chamber. The strand is cut into individual slabs 10 m in length by an
oxyacetylene torch and eventually rolled to the slab collection rack. The slabs remain on
the collection rack for 4.21 hours, where tertiary heat removal occurs via forced air
convection with industrial scale blowers to 90 °C. From here slabs are lifted by a large
hoisting crane to inventory and subsequently to a flatbed truck or to a railcar for transport
to industry.
2.2 DesignCriteria
Parameter Value
Plant Operation
Pre-Production Span 3 years
Production Span 17 years
Operation per Annum 351 days
Required Tonnage of Stainless Steel
per Annum
2,000,000 tonnes
Feed Specifications
Iron Ore Composition (Weight %)
Fe2O3 96.79
SiO2 1.66
CaO 0.57
AlO3 0.41
MgO 0.31
TiO2 0.16
MnO2 0.049
Na2O 0.036
P2O5 0.013
FeS 0.006
Steel Scrap (Weight %)
Fe 96.85
C 1.35
Mn 1.65
Si 0.06
P 0.04
S 0.05
High Carbon Ferrochromium from Group 1
(Weight %)
Cr 60.00
Fe 29.50
Si 3.00

Design II
15
2.3
Material and Energy Balance
2.3.1Midrex Direct Iron Reduction
Midrex Shaft Furnace
Mass balance
The mass balance on the shaft furnace was started by first specifying the amount of
reactants and products needed for each reaction taking place in the system. The reactions
in the shaft furnace happen consecutively in group of two reactions, meaning a group of
two reactions can be written as one reaction for the purpose of calculating the
stoichiometric amount of reactants and products. Thus, the first two reactions take place
simultaneously and are followed by reaction 3-4 and so forth. The amount of reactants and
products are calculated based on stoichiometric amount of mol of the limiting reactant in
each group of reaction, while taking into consideration the conversion % for each reaction.
Table #1 below shows the limiting reactant and conversion % for each group of reaction
taking place together. Based on the design criteria provided by Inox Inc, the 3wt% FeO in
the DRI output is achieved by setting the conversion % to 97.5 in reaction 5-6. This number
was found using the excel solver function, where the conversion rate of reaction 5-6 is
iterated such that the FeO amount needed is achieved. The same method was used to meet
C 7.50
High Carbon Ferrochromium from Group 2
(Weight %)
Cr 60.00
Fe 30.20
Si 1.20
C 8.60
Ferronickel (Weight %)
S 0.05
P 0.025
Fe 59.32
Si 0.6
Cu 0.5
C 0.1
Ni 40
Product Specifications
Maximum Stainless Steel Compositions
(Weight %)
C 0.08
Cr 18.00
Ni 8.00
Utilities
Cooling Water Supply 30 °C
Cooling Water Return 38.5 °C
Process Water Supply 30 °C
Ambient Air Supply 25 °C

Design II
16
the design criteria of 1.6wt%C in the DRI output, by setting the conversion% of reaction
7-8 to 24.5.
Table 1
The limiting reactant and conversion % for each group of reactions taking place in the shaft furnace.
Reaction
Limiting
Reactant
Conversion %
1 3Fe2O3 + CO → 2Fe3O4 + CO2 Fe2O3 100
2 3Fe2O3 + H2 → 2Fe3O4 + H2O
3 Fe3O4 + CO → 3FeO + CO2 Fe3O4 100
4 Fe3O4 + H2 → 3FeO + H2O
5 FeO + CO → Fe + CO2 FeO 97.50
6 FeO + H2 → Fe + H2O
7 3Fe + 2CO → Fe3C + CO2 Fe 24.50
8 3Fe + CO + H2 → Fe3C + H2O
Due to strict CO emission requirements, the amount of CO and H2 provided for reactions
5 to 8 are not based on stoichiometric amount of the limiting reactant, but are calculated
based on how much is needed for the conversion % stated.
The DRI output needed is specified by the downstream EAF process and is used to
specify the first limiting reactant of the eight reactions (Fe2O3). This is done by taking the
ratio of the iron ore input to the DRI output, by taking a basis of calculation of Fe2O3 mass.
Once the amount of first limiting reactant is computed, all stream flowrate except the
syngas can be known.
Once the amount of reactant and products are calculated by taking a basis of
calculation, the next step is to determine the stream composition and mass flowrate of each
stream of the system. The iron ore pellet composition is given by Inox Inc, which contains
the Fe2O3 reactant. It is assumed that it is the only species that react from the iron ores.
Thus, knowing the Fe2O3 needed allows us to specify the mass flowrate of the iron ore
stream. Similarly, the DRI flowrate is determined by adding the ferrous products and
reactant left from each of the eight reactions and adding them to the unreacted species

Design II
17
contained in the iron ore. The other two reactants (CO and H2) are coming from the syngas
produced from the steam reformer.
The syngas mass flowrate and composition is determined from the reformer’s mass
balance. The off-gas stream of the Midrex shaft furnace consists of the CO2 and H2O
generated from all eight reactions and any gas and solid that does not react from the syngas
stream.
The mass balance on the shaft furnace is:
ṁ syngas + ṁ iron ore = ṁ DRI + ṁ flue gas
Where ṁ represents the mass flowrate of a stream.
Energy Balance
The eight reactions taking place in the furnace are either exothermic or
endothermic, but overall requiring a heat input. It was assumed that: the reactions start at
650oC, the system operates at steady state and the heating is provided by the hot syngas
stream and electric heating.
First, the temperature of the iron ore heated by the syngas is calculated according to the
following energy balance:
∑.
j
a
ṅ #112 ,aCp,a(Tf − 25) = ∑.
j
a
ṅ #110 ,aCp,a(900 − Tf)
Where,
a to j= species in the stream specified
𝑛̇#122 ,𝑎= molar flowrate of species a in iron ore stream (mol/hr)
𝑛̇#110 ,𝑎= molar flowrate of species a in syngas stream (mol/hr)
Cp,a= average Cp value of species a within temperature range (j/mol.k)
The final temperature, Tf, was found to be 575oC, however the off-gas temperature
of the Midrex shaft furnace, from various source, indicate that it is between 400-450oC. It

Design II
18
was assumed that the final temperature of the off-gas and heated iron ore temperature is
450oC. Thus, the iron ore pellet will need to be heated from 450oC to 650oC by electrical
heating. The heat transfer efficiency for heating the iron ore is:
𝜀 =
450
575
∗ 100 = 78%
The ferrous product’s molar flowrate was used to compute the heat of reaction
released. For example, for the reaction 3Fe2O3 + CO → 2Fe3O4 + CO2, the molar flowrate
of Fe3O4 is used to compute the heat of reaction. Thus, the final energy balance used to
compute the energy requirement of the system is:
∑.
j
a
ṅ #112,a ∫ CpdT
650
450
+ ṅ Fe3O4,#1HRxn,#1
650
+ ṅ Fe3O4,#2HRxn,#2
650
+ ṅ FeO,#3HRxn,#3
650
+ ṅ FeO,#4HRxn,#4
650
+ ṅ Fe,#5HRxn,#5
650
+ ṅ Fe,#6 HRxn,#6
650
+ ṅ Fe3C,#7HRxn,#7
650
+ ṅ Fe3C,#8HRxn,#8
650
= Q̇ f
Where,
ṅ #112 ,a= molar flowrate of species a in iron ore stream (mol/hr)
ṅ Fe3O4,#1= molar flowrate of Fe3O4 for reaction #1 (mol/hr)
HRxn,#1
650
= Heat of reaction at 650oC for reaction #1 listed in the process description
(j/mol)
Steam Reformer
Mass Balance
The mass balance on the reformer is split into two parts: mass balance for reforming
reactions and mass balance for combustion reactions. Both mass balances follow the same
methodology of the Midrex’s mass balance for computing the reactants and products mass
based on stoichiometric amount, by taking a basis of reactant for each reaction. However,
unlike the shaft furnace’s mass balance, the reactions take place at the same time instead
of consecutively. For both the reforming and combustion reactions, all reactions conversion
is assumed to be 100% and the hydrocarbon reactants are provided by a natural gas stream
with a range for each species composition.

Design II
19
For the reforming reactions, both products (CO and H2) are the same for all
reactions. CO was taken as the basis of calculation for all reactants and products, since its
amount is calculated from the Midrex shaft furnace’s mass balance, but also because the
reforming reactions produce an excess amount of H2 than is needed for the shaft furnace.
In order to split how much CO is produced from each reforming reaction, the
composition of natural gas is used, since all the hydrocarbon reactants are provided only
from the natural gas feed. The natural gas composition was compared between Enbridge
and Union gas from their respective websites. Enbridge provides fixed natural gas
composition while union gas provides a range of composition. The Enbridge compositions
were first taken to provide a basis of calculation for the reforming reactions.
The CO amount produced from the reforming reactions was first split based on the
Enbridge composition, however the presence of unreactive species in the stream requires
the percentage of CO generated from each reactions to be changed. For example, the
reactive species from the natural gas stream makes up 97.8mol% of the total stream,
therefore, when splitting how much CO is produced from each reaction, the remaining
2.2mol% were divided between each reaction. This method however would always produce
less CO than is needed by nearly 1-2%. To meet the CO flue gas emission requirements,
excess amount of CO was not added. This was fixed using the excel solver function where
the amount of CO produced from each reaction is iterated to meet the required demand of
the shaft furnace. This process alters the composition of the reactive species from the
natural gas stream but is within the range given from Union gas’s website, as shown in
table #2 below.
Table 2
Natural gas composition from Enbridge and Union gas supplier, compared to the iterated values from the
reformer process.

Design II
20
The
amount of steam required for the reforming reactions was not based on stoichiometric
amount of CO needed, but is instead based on steam to carbon ratio (S/C), in order to
reduce the risk of carbon deposition on the catalyst surface (Subramani et al, 2009), as
illustrated in figure #7 below:
Figure 6
Steam to carbon ratio with respect to operating temperature, pressure and conversion % (Subramani et al,
2009).
The operating temperature of 900oC was picked from the literature on the Midrex process,
thus in order to achieve a 100% conversion as is assumed for the reforming reactions, a
minimum S/C ratio of 1.4 would be needed.
Species Enbridge (mol%) Union gas (mol%) Final (mol%)
methane 95 87-97 95.40
ethane 2.50 1.5-7 1.47
propane 0.20 0.1-1.5 0.43
butane 0.06 0.01-0.3 0.25
pentane plus 0.02 trace-0.4 0.19
nitrogen 1.60 0.2-5.5 1.60
carbon dioxide 0.62 0.1-1 0.62

Design II
21
The recycle stream from the Midrex shaft furnace is specified based on how much
CO2 reactant is needed from the reforming reactions. Thus, 39% of the shaft furnace’s off-
gasses are recycled back to the reformer, which includes any unreacted species coming
from the syngas stream of the reformer.
The following mass balance shows the final incoming and outgoing streams of the system,
for the reforming reactions:
ṁ natual gas + ṁ steam + 39% ∗ ṁ Midrex off gas = ṁ syngas
For the combustions reaction of it was assumed that the air stream is the source of
oxygen and that the natural gas composition is the same from table #2 above. The natural
gas flowrate is specified from the energy balance of the system. The mass balance for the
combustion reaction is:
ṁ natual gas + ṁ air = ṁ flue gas
Energy Balance
Incoming reforming feed enter the reformer at 494oC and will be heated to 900oC.
It is assumed that the reforming reactions start at 900oC and that all flue gas leave the
system at 900oC, thus heating was accounted for the air stream. This specified value is
lower than typical furnace outlet temperature of 1200oC (Song et al, 2004), however it is
enough to be used to pre-heat the reforming feed to near the target value of 500oC. With
the system at steady state, the heating requirement is:
∑.
j
a
∫ ṅ #122 ,aCp #122,a
900
494
dT + ∑.
j
a
∫ ṅ #103 ,aCp #103,a
900
25
dT = Q̇ heating
ṅ #122 ,a= molar flowrate of species a in reforming feed (mol/hr)
ṅ #103 ,a= molar flow rate of species a in air stream (mol/hr)
When calculating the heat needed for each reforming reaction, the molar flowrate
of the hydrocarbon reactant was used. For example, for reaction 10, C2H6 + 2H2O → 2CO

Design II
22
+ 5H2, the molar flowrate of C2H6 was used to compute the heat required for the reaction.
For reaction 9 (CH4 + H2O → CO + 3H2) and 14 (CH4 + CO2 → 2CO + 2H2), the molar
flowrate of CH4 is shared between both reactions.
Thus the final energy requirement of the steam reformer is the sum of the heating
requirement Q̇ heating and the heat needed for the reforming reactions:
Q̇ heating + ṅ CH4,#9HRxn,#9 + ṅ CH4,#14 HRxn,#14 + ṅ C2H6 HRxn,#10
900
+ ṅ C3H8 HRxn,#11
900
+ ṅ C4H10 HRxn,#12
900
+ ṅ C5H12 HRxn,#13
900
= Q̇ f
Boiler
Energy Balance
The water boiler is responsible to heat incoming process water to its boiling point
and further heat the steam produced to 400oC. It was assumed that the system operated at
steady state and that the heating requirement is met by the combustion of natural gas. The
heating required is calculated from the following energy balance:
ṅ #102 ∫ Cp,H2O (L)
100
25
dT + ṅ #102 ∗ Hvap,H2O + ṅ #102 ∫ Cp,H2O (g)
400
100
dT = Q̇
Where,
ṅ #102 = molar flowrate of the process water stream (mol/hr)
Since the equipment has a percent efficiency, the final heat required is:
Q̇
ε
= Q̇ f

Design II
23
Energy Balance for Remaining Equipment
The energy balance equation for the venturi scrubber, heat exchanger and when
calculating the outlet stream temperature of two streams that are combined, have the same
methodology. For the venturi scrubber and heat exchanger, the energy balance is used to
find an unknown outlet temperature by specifying the other outlet temperature to a desired
value. For example, for the heat exchanger used to heat the reforming feed, the outlet
reforming feed was specified, thus the energy balance is set up to calculate the outlet
temperature of the other outlet stream. It is assumed that the system is at steady and no
generation of heat occurs, thus for example, the heat exchanger energy balance can be
written as:
∑.
j
a
ṅ cold,aCp cold,a(Tdesired,cold − Tin,cold) = ∑.
j
a
ṅ hot,aCp hot,a(Tout − Tf)
Where,
ṅ cold,a= molar flowrate of species a in the cold stream
Tdesired = Specified temperature outlet
Tf = temperature outlet to be calculated
The Tdesired and Tf can be switched in the equation above depending on known and desired
values of the system.
The energy balance for calculating the outlet temperature of two streams that are
combined is similar, with the only difference is that the Tdesired is switch with Tf, as follows:
∑.
j
a
ṅ cold,aCp cold,a(Tf − Tin,cold) = ∑.
j
a
ṅ hot,aCp hot,a(Tout − Tf)

Design II
24
2.3.2 Electric Arc Furnace
An element balance is performed on a per annum basis to calculate the mass of
materials being processed by the EAF unit. The first important step in the balance is to
know the EAF output. This is determined from the AOD output, which is known to be two
megatons per year. From the reactions taking place in the AOD, the necessary input is
calculated and is used as the output for the EAF. This sets a basis for input calculations.
Next of importance is the composition of steel leaving the EAF and the composition of
steel scrap and direct reduced iron entering the EAF. The final composition of the steel is
given by the information provided by the client. The weight percentages of the different
components in direct reduced iron are known from the Midrex stage calculations. Steel
scrap is assumed to be comprised solely of plain steel, the conformation of which can be
found from various resources on the internet. With all of the steel and DRI compositions
known, only the slag make-up is unknown, but can be calculated from the mass balance.
User defined values for steel scrap input and lime input are defined as a first approximation.
With all of this information it is possible to construct the element balance matrix in a
spreadsheet.
In this system it is assumed that the mass entering the furnace is the same as the
mass leaving. There are five streams in total: the DRI feed, the steel scrap feed, the lime
input, the atmospheric air input, the steel outlet, the slag outlet and carbon-rich off-gas.
To begin calculations, an initial mass flow rate for steel scrap is assumed. Then, an
initial guess is made for the mass of DRI. This is followed by an element balance on the
iron component. In order to complete this balance without the actual conversion known, it
is assumed that 100% of the iron is extracted from the DRI and steel scrap. Because the
inflow is equal to the outflow, the sum of the moles of iron entering must equal the sum of
the moles leaving, or,
∑ Ṁ in − ∑ Ṁ out = 0
Where Ṁ = molar flow rate of Fe.

Design II
25
This is where the Solver Add-in is used in Microsoft Excel to optimize the mass
flow rate of DRI entering the EAF. Solver is commanded to satisfy the above equation by
changing the inflow of DRI. Now, with the mass flow rate of DRI entering the EAF known,
the slag mass flow rate is also known by the same property above, or,
∑ 𝑚̇ 𝑖0
− ∑ 𝑚̇ 𝑖 = 0
Where m = mass flow rate.
Once this has been completed, the element balance is performed for the remainder
of the species entering and leaving the reactor and the composition of the slag is found.
Note that the mass flow rates can be altered for all parameters in the case of
changing specifications. To account for changes, only the Solver Add-in must be used
again to find the new DRI input. For example, if the input changes from 30% DRI and 70%
steel scrap to 100% DRI, Solver will find the new mass flow rate based on the same
elemental iron balance as mentioned above. The amount of lime needed is approximated
according to the final slag composition, which should contain in the range of 50 to 60 wt%
CaO.
Other assumptions made in the mass balance calculation is that only Fe3C, FeO,
FeS and CaO react inside the heated bath. FeS reacts with CaO to form FeO and CaS. Fe3C
breaks down into three Fe atoms and C combines with 0.5O2 to form CO. It is assumed
that no CO2 is formed in the reaction. The oxygen is received from either FeO, which
breaks down to form one Fe atom and one O atom or from atmospheric oxygen. Nitrogen
does not participate in any reactions and leaves as the largest fraction of the off-gas. No
oxygen besides that bound in CO or other particles is assumed to leave in the off-gas: all
oxygen molecules that enter from the atmosphere are used to bind carbon to decrease the
steel’s C composition.
A very large assumption that has been made is that conversion of reactants, or inputs, is
100%. All Fe3C and FeO is broken down into iron and carbon monoxide. This is typically

Design II
26
not the case in reality and process conditions must be tuned according to measurements of
actual outputs.
Other important assumptions are that 99% of the input Fe leaves in the hot metal
and 0.5% in the slag as FeO and 0.5% in the off-gas as entrained FeO dust. Also included
is that 0.99% of the C input remains in the hot metal, while the rest leaves in the off-gas as
CO. For SiO2, 7.5% leaves with the hot metal, 91.5% leaves in the slag and the remaining
1% is assumed to leave in the off-gas as entrained particles. Ninety-nine percent of the
Al2O3 leaves in the slag while 1% becomes entrained and leaves with the off-gas. Lastly,
it is assumed that 10% and 1% of P2O5 and elemental sulfur leave in the steel, while the
remainder of the P2O5 and sulfur leaches into the slag and is removed as waste product.
All other components which enter the furnace, which are not Fe, C, SiO2, P2O5 or
S are assumed to leave in the slag and off-gas. The amount of DRI input needed to satisfy
the conditions for the reactions taking place in the EAF is calculated from a mass input-
output balance. The overall mass balance is presented in the Appendix.
The energy balance for the EAF also requires a number of assumptions. The first is
that the temperature inside the hot bath is uniform, which realistically is not true until after
the entire charge has been melted, though a gradient between the electrode center and the
walls is always noticed. There is also a gradient between the top of the hearth and the
bottom of the hearth, where the bottom is typically cooler. It has also been extrapolated
from graphs of off-gas temperature versus bath temperature that the off-gas temperature is
1200 degrees Celcius when the bath is 1600 degrees Celcius. One-thousand six-hundred
Celcius is also the assumed maximum temperature of the bath.
Last of the energy balance assumptions is that DRI enters the furnace at 650 degrees
Celcius and that all other materials start at room temperature, 25 degrees Celcius. Do to
mixing of materials and variable temperatures within the plant, it may be found that this is
not the case in practice.

Design II
27
2.3.4 Continuous Casting
The mass of stainless steel lost in the caster itself is nil. Flux introduced into the
tundish via the pneumatic conveyor plays a significant role in decreasing oxidation and
therefore losses of stainless steel to slag. The amount of molten stainless steel, which cools
and solidifies in the tundish prior to casting is negligible. The flux also ensures lubrication
between the solidifying strand and the water-cooled mould, eliminated no mass build-up.
Therefore, without any accumulation of mass in the casting process, the mass of molten
stainless steel supplied to the mould is equivalent to that solidified and cut into slabs. The
mass balance, i.e. the water requirement, is directly governed by the heat removal rate of
the different cooling processes. Thus, the mass and energy balance has been solved
simultaneously. Although continuous cast cooling typically follows a transient, two-
dimensional differential equation, the following description and list of assumptions
indicates an original, reliable engineering approach to the calculation of industry standard
cooling rates.
The three major cooling processes are as follows:
(1) Cooling through a water-cooled mould
(2) Cooling of the strand in the water spray chamber and
(3) Forced-air convective cooling with multiple blowers
The overall underlying heat removal methodology is simple: there is a specified
amount of heat removed in the water-cooled mould (and a specified percentage of that goes
to solidification) and there is a specified strand temperature out of the spray chamber. With
these three specifications (including the parameter specifying the amount of heat removed
to solidification), the overall water duty may be calculated and yields results in table #3.
These values include overcapacity, which will be elaborated on below. Only cooling water
may be used in the mould (and recycled), where the water never actually comes in contact
with the stainless steel. In the spray chamber the water sprayed directly on the strand and
therefore must be sent to wastewater treatment before being discarded back to the
environment. A significant amount of compressed air is also required to cool the steel and

Design II
28
is utilised in both the spray chamber (to atomise the water creating a spray mist) and in the
blowers for forced convection. The air duty is also outlined in table #3.
Table 3
Cooling
Stage
Cooling Process Fluid
Volumetric
Requirement
(m3/hr)
Percentage of
Required Heat
Removed (%)
Primary Water-Cooled
Mould
Cooling Water 1173 17.24
Secondary Spray Chamber
Process Water 3126
69
Compressed Air 3126
Tertiary
Forced
Convection on
Slab Collection
Rack
Compressed Air 108000 13.78
The overall casting rate is specified similar to industry standards (Sengupta et al., 2004) at
a rate of 59.35 m/hr. Continuous casting may occur at rates much, however heat removal
limits final production rate. It is also unwise to solidify stainless steel too quickly, causing
significant strained zones within the slabs, which prove to be very brittle and liable to fast
fracture. In the calculations performed, casting at rates higher than 59.35 yielded
insufficient heat removal in the mould, and therefore this speed was specified as the
operation rate.
Each caster solidifies 1 million tonnes of stainless steel (allowing for 14 days of
shutdown time) per annum. Therefore, to supply the required 2 million tonnes of stainless
steel as per the design criteria, there must be two continuous casting processes running
simultaneously, each for 351 days / annum. Industry standard also prompts a water
overcapacity of 81 %, and this number is used as well to ensure there is sufficient water
flow in both the spray chamber and the water-cooled mould.
Water-Cooled Mould Methodology
Primary cooling of the stainless steel is carried out in the oscillating water-cooled
mould. Through specification of the percentage of total heat removed in the water-cooled
mould (typically approximately 20% in an average steel casting process (Sengupta et

Design II
29
al.,2004) and the percentage of total molten stainless steel solidified (18%), a flowrate of
cooling water can be calculated, which extracts this amount of energy. With knowledge of
the average casting rate, limiting the outlet water temperature to 38.5 °C and assuming
there is no vaporisation of water in the mould at the surface (with water under pressure at
3.86 bar), the energy removed is simply by that sensible heat transfer:
𝑄𝑟𝑒𝑚𝑜𝑣𝑒𝑑 = 𝑡𝑚̇ 𝐶𝑝∆𝑇
Where 𝑡 is the time spent in the mould, 𝑚̇ is the mass flowrate of the water, 𝐶𝑝 is the heat
capacity at constant pressure and ∆𝑇 is the temperature change from the inlet to the outlet
of the mould.
This, however, is a very crude approximation and one much more accurate would be
through the modelling of the system as a heat exchanger with the following resistances.
Rtotal = RWater + RCopper Mold + RAir Gap + RSolidification of SS
The energy must pass through each successive resistance to heat transfer adequately be
removed by the cooling water on the other side of the mould. The air gap resistance is
particularly large and arises from the gap formed between the mould wall and the strand
during thermal contraction upon stainless steel solidification. The flux layer decreases this
gap. Therefore the total resistance can be written as the inverse of the overall heat transfer
coefficient 𝑈 in the following manner:
1
𝑈𝐴
=
1
ℎ 𝑤𝑎𝑡𝑒𝑟 𝐴 𝑚𝑜𝑙𝑑
+
𝐿 𝑐𝑜𝑝𝑝𝑒𝑟 𝑤𝑎𝑙𝑙
𝑘 𝑐𝑜𝑝𝑝𝑒𝑟 𝐴 𝑚𝑜𝑙𝑑
+
1
ℎ 𝑎𝑖𝑟 𝐴 𝑚𝑜𝑙𝑑
+
𝐿 𝑠𝑜𝑙𝑖𝑑𝑖𝑓𝑖𝑒𝑑 𝑆𝑆 𝑎𝑣𝑔
𝑘 𝑠𝑡𝑎𝑖𝑛𝑙𝑒𝑠𝑠 𝑠𝑡𝑒𝑒𝑙 𝐴 𝑚𝑜𝑙𝑑
Where ℎ is an individual heat transfer coefficient, 𝐿 is the length, 𝑘 is the thermal
conductivity and 𝐴 is the area.

Design II
30
As seen previous equation, the average distance inward of solidified stainless steel
from the mould wall along the entire length of the mould is needed and therefore the final
width and height into the steel solidified on mould exit is required. These values are also
pertinent to the calculation of the mould outlet solidified temperature, which is significant
for the heat transfer calculations in the spray chamber to follow.
Through knowledge of the latent heat of fusion, the mass of solidified stainless steel
is calculated and the subsequent volume of solidification. Cooling is occurring from all
sides of the mould, and therefore solidification is proceeding from the mould wall inwards
(as heat flux moves in the opposite direction). The solidification process is approximated
as linear throughout the mould in two dimensions. Some molten stainless steel is still
present at the outlet of the mould though and it is required to know the cross-sectional area
of molten stainless steel at this point. For this, calculus was used and the volume of molten
stainless steel was calculated as a pyramid with the top cut off (initially all molten at the
base of the pyramid and moving to a smaller rectangle at the mould outlet). The amount
solidified is thus the total volume of the mould minus the amount still remaining molten.
See Appendix A.4, for a description and Table 14 for the full calculation.
Using the average width and height solidified, the average distance of solidified
stainless steel from the mould wall can be calculated for both the width and height. The
resistance due to conduction of heat through the stainless steel then takes on two different
equations: one for heat transfer through the width and one through the height. The
following equation outlines this:
𝐿 𝑠𝑜𝑙𝑖𝑑𝑖𝑓𝑖𝑒𝑑 𝑆𝑆 𝑎𝑣𝑔
𝑘 𝑠𝑡𝑎𝑖𝑛𝑙𝑒𝑠𝑠 𝑠𝑡𝑒𝑒𝑙 𝐴 𝑚𝑜𝑙𝑑
= (
𝑤 − 𝑤 𝑚𝑜𝑙𝑡𝑒𝑛
4
)(
1
𝑘 𝑆𝑆 𝑙ℎ
) + (
ℎ − ℎ 𝑚𝑜𝑙𝑡𝑒𝑛
4
)(
1
𝑘 𝑆𝑆 𝑙𝑤
)
Therefore, overall heat transfer multiplied by the area is given in the following equation:
𝑈𝐴 =
1
ℎ 𝑤𝑎𝑡𝑒𝑟 𝐴 𝑚𝑜𝑙𝑑
+
𝐿 𝑐𝑜𝑝𝑝𝑒𝑟 𝑤𝑎𝑙𝑙
𝑘 𝑐𝑜𝑝𝑝𝑒𝑟 𝐴 𝑚𝑜𝑙𝑑
+
1
ℎ 𝑎𝑖𝑟 𝐴 𝑚𝑜𝑙𝑑
(
𝑤 − 𝑤 𝑚𝑜𝑙𝑡𝑒𝑛
4
)(
1
𝑘 𝑆𝑆 𝑙ℎ
) + (
ℎ − ℎ 𝑚𝑜𝑙𝑡𝑒𝑛
4
) (
1
𝑘 𝑆𝑆 𝑙𝑤
)

Design II
31
Finally, to model the system as a heat exchanger, the following standard equation for heat
rate is utilized:
𝑄̇ = 𝐹𝑈𝐴∆𝑇𝐿𝑀
In the water-cooled mould, however, there are four different ∆𝑇𝐿𝑀 temperature gradients
due to both the sensible heat transfer in the molten stainless steel and the solidified stainless
steel as well as the latent heat transfer during solidification. The ∆𝑇𝐿𝑀 temperature
gradients effectively create four heat transfer equations and can be seen as follows:
𝑄̇ = 𝐹𝑈𝐴(∆𝑇𝐿𝑀,𝑚𝑜𝑙𝑡𝑒𝑛 𝑡𝑜 𝑓𝑢𝑠𝑖𝑜𝑛 + ∆𝑇𝐿𝑀,𝑓𝑢𝑠𝑖𝑜𝑛 + ∆𝑇𝐿𝑀,𝑓𝑢𝑠𝑖𝑜𝑛 𝑡𝑜 𝑐𝑜𝑜𝑙𝑒 𝑑 𝑠𝑜𝑙𝑖𝑑 + ∆𝑇𝐿𝑀,𝑓𝑢𝑠𝑖𝑜𝑛 𝑡𝑜 𝑐𝑜𝑜𝑙𝑒𝑑 𝑚𝑜𝑙𝑡𝑒𝑛 )
Where,
∆𝑇𝐿𝑀 =
∆𝑇𝐴 − ∆𝑇𝐵
ln (
∆𝑇 𝐴
∆𝑇𝐵
)
Here ∆𝑇𝐴 is the temperature gradient at the inlet between the hot steel and cold
water, while ∆𝑇𝐵 is the temperature gradient at the outlet. In fact this could be switched to
yield the same result.
The temperature of molten out of the mould is better approximated by a geometric
mean as opposed to a linear average due to diffusion of heat in the molten steel. The
general geometric mean formula follows:
𝐺𝑒𝑜𝑚𝑒𝑡𝑟𝑖𝑐 𝑀𝑒𝑎𝑛 = (∏ 𝑎𝑖
𝑛
𝑖−1
)
1
𝑛⁄
Imagining a cross sectional picture of the mould at the outlet, the temperature at the
middle of the molten portion is still 𝑇 𝑚𝑜𝑙𝑡𝑒𝑛,𝑖𝑛 and the temperature at the interface of the
solidified stainless steel is effectively 𝑇𝑠𝑡𝑎𝑖𝑛𝑙𝑒𝑠𝑠 𝑠𝑡𝑒𝑒𝑙 𝑓𝑢𝑠𝑖𝑜𝑛 . Therefore the temperature of
molten at the outlet is the following:
𝑇 𝑚𝑜𝑙𝑡𝑒𝑛 𝑜𝑢𝑡 = √𝑇 𝑚𝑜𝑙𝑡𝑒𝑛 𝑖𝑛 𝑇𝑓𝑢𝑠𝑖𝑜𝑛

Design II
32
Knowledge of the final molten temperature at the mould outlet allows for all final ∆𝑇𝐿𝑀 to
be solved and the overall model may now be employed. The heat exchanger model
specifies that 99% can be removed as an approximation, amounting to nearly all of the
specified 20% required removal. See Appendix A.4, Table 16 for full calculations.
The strand is particularly vulnerable to buldging at the exit of the water-cooled
mould when it hits the first curvature of the arc. To ensure buldging is not an issue,
significant calculation has gone into determining the ferrostatic pressure and to ensuring
that this value is far less than the reduced yield strength of the solidified stainless steel
strand wall. See Appendix A.4 for the description and Table 15 for full calculations.
Water Spray Chamber
Secondary cooling of the stainless steel occurs as the strand passes through the
spray chamber. The strand is cooled to a uniform temperature of 400 °C and is completely
solidified upon exit of the arced spray chamber. Heat is removed by spraying a mixture of
compressed air and water, which atomises the water creating a mist. The mist is imparted
onto the slab through specialized nozzles. The use of compressed air to atomise the water
is much more efficient than reducing the nozzle diameter as small outlet nozzle diameters
tend to block easily.
Assuming the nozzles are placed all around the slab - except only 25 % of the slab faces
are directly sprayed by the mist, while the entire strand side remains open to water flux -
the chamber’s heat transfer can be evaluated. The spray chamber’s length is the first
calculation and is evaluated through knowledge of the radius of casting (or the radius due
to the arc formed in the casting process). Industry standard radii are 12.2 m (Making,
Shaping and Treating of Steel, 1998) and therefore the length of the ¼ circle and the
subsequent straight portion can be calculated as follows:
lspray chamber =
πrarc
2
+ lstraight portion
The chamber removes heat in four ways:

Design II
33
1. Through evaporation of the mist falling ontothe strand
2. Through sensible heat removal from the mist within the film boiling regime
3. Through conduction of heat through water cooled rollers (whichare also being
sprayed by the mist)
4. Through water running downthe arc on the top surface of the strand
Since the water running down the strand both increases the effective water flux for
sensible heat transfer as it passes to the lower stages of the arc, but also decreases the
impinging mist, this will be neglected. In order to neglect this, it has to be ensured that
most of the water removed should be vaporized and discharging through the top of the
spray chamber instead of running down the strand. A sensible model has been developed
relating the water flux evaporated and the water flux sprayed.
Figure 7
The model of water evaporation, with water evaporated flux on the y-axis and total mist flux on the x-axis.
The maximum water flux evaporated is 0.0025 m3/m2s, which amounts to a 0.25 cm thick
film of water sprayed per second over a unitary area. This intuition is modeled by the
following equation:
Ẇ ′
evaporated =
Ẇ ′
400Ẇ ′ + 1
Where 𝑊̇ ′
is the mist flux reaching the strand surface.
Heat removal by evaporation therefore is given by the following equation:
Qevaporation = Ẇ ′
evaporated
Amist spray tin mold ρwater∆Hwater,vaporisation

Design II
34
A majority of the heat removed is from the latent heat of vaporization of the water
(Sengupta et al., 2004) and therefore evaporation is much more significant than sensible
heat transfer from the strand to the mist. The calculated sensible heat removal is only 0.11
%. From Figure #8, therefore, it is ideal to keep the water flux in the vicinity of 0.01
m3/m2s as this is where there is significantly more evaporation per unit impinging water
flux. The calculated water flux is 0.0101 m3/m2s.
The heat removed by sensible heat transfer is modeled with an imperial formula for the
heat transfer coefficient ℎ:
ℎ = 𝛼𝑊̇ 𝑛
Where the constants 𝛼 and 𝑛 are empirically determined constants from industry, typically
between 0.45 – 0.75 and 0.5 – 1 respectively. For the calculation, the average value has
been taken (i.e. 𝛼 = 0.6 and 𝑛 = 0.75).
Separate from the strand surface mist requirement is the mist required to cool the
rollers of the spray chamber since the atmoising nozzles are located around the entire
system of strand-compressed rollers. The conduction of heat through the water-cooled
rollers does remove a significant amount of the heat from the strand and can be
approximated through the following conductive heat transfer equation:
Q = −kA
dT
dr
= −kAroller touching strand
(Tstrand − Troller )LM
rroller
Where 𝑘 is the thermal conductivity of the copper roller, the area of the strand is estimated
as 5 % of the area of the top and bottom of the strand and a log mean temperature difference
is employed due to the fact that the strand is being cooled from the inlet of the spray
chamber to the outlet. The temperature of the roller has been estimated as one half of the
strand temperature at the inlet of the spray chamber. See Appendix A.4, Table 17 for full
calculations.

Design II
35
Blower Section
The rack section collects the cut slabs on a roller system where they are cooled by
large blower fans situated in staggered fashion on both sides of the rack. By specifying the
number of blowers employed to be 20 (10 per side of rack) and maximum allowable outlet
temperature of the strand (90 °C), only one parameter is needed to fully specify the entire
system. By solving for the spacing between blowers, all variables are calculated including
the length of the blower section (25 m), the time on slab spends on the rack (calculated
from the roll speed to be 4.21 hours)
Through estimation of the heat transfer coefficient for forced-convective mass
transfer of air over a flat plate, the overall transfer of heat from the strands to the cooling
air supplied by the blowers can be calculated. Through specification of one single industry
stand blower flowrate (1.5 m3/s) and the assumption 70 % of the air is effectively cooling
the entire surface of the slabs the entire way down the length of the roller section, the
velocity of air can be simply calculated:
𝑣 =
𝑉̇
𝐴 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛
𝜂
Where 𝑉̇ is the volumetric flowrate, the cross sectional area is assumed to be the
spacing between blowers times 1 m height above the strand and 𝜂 is the efficiency of air
reaching the strand on average (i.e. 70% as previously stated due to staggering the blower
placement).
With the velocity the Reynolds number can be simply calculated:
𝑅𝑒 =
𝜌𝑣𝐿
𝜇
Where 𝜌 is the density of air, 𝐿 is the characteristic length, which is the length of
the strand specified by the client (as the blower is blowing parallel to the direction of the
length) and 𝜇 is the dynamic viscosity of air.

Design II
36
The Prandlt number can also be calculated using properties of air at 40 °C:
Pr =
𝐶 𝑝 𝜇
𝑘
Where 𝐶 𝑝is the heat capacity of air at 40 °C and 𝑘 is the thermal conductivity of air at 40
°C.
Knowing these two values we can use a standard equation for calculating the
Nusselt number of the convective air flow over a flat plate under turbulent conditions.
Since Nusselt number is directly proportional to the average heat transfer coefficient, this
equation can be rearranged to find the coefficient:
ℎ 𝑥
̅̅̅ =
0.0308 𝑘
𝐿
𝑅𝑒
4
5 𝑃𝑟
1
3
Now the heat rate of removed energy from the slabs can be estimated using the
convection equation with a log mean temperature difference expressing the difference
between the temperatures of the slab at the start of the blowing section to the final
temperature:
Q̅ = ABlower sectionhx
̅̅̅(Tslab − Tair)LM
Therefore by knowing the average heat transfer rate across the blowing section, an
estimated time requirement can be calculated for the strand to remain within the influence
of the forced air currents. See Appendix A.4, Table 18 for full calculations.
3. Operating Philosophy
3.1 Control Theory
The following section outlines the control philosophy of the stainless steel plant,
including detailed control methodology of main operating units. An overall control

Design II
37
philosophy is first documented, followed by plant-wide control similarities such as pump
control and control valve control and finally the detailed control methodology of the main
operating units. All control functioning can be visualised in the P&IDs in Appendix D.
3.2 Process and Instrumentation Diagram Development
3.2.1 Overall P&ID Development
The Midrex, the EAF and the AOD units all operate in on a batch-to-batch basis.
The entire semi-batch process operates via tapping, until the ladle from the molten stainless
steel is discharged into the tundish, where the process becomes continuous. Fe… from
Groups 1 and 2 are assumed to have fixed composition outside of the responsibilities of
Group 3. Control of the processes ensures production of 2 million tonnes of stainless steel
per annum safely from the batch to continuous process.
All vital, supporting operating units, which are required to ensure operation have
been designed with redundancies, where the operator may simply switch from one to
another at an instance of breakdown or if one requires maintenance. Controllers, for the
most part, are all wired to the central control room and indicate the measured value to the
main operating engineers. Alarms are installed at sensitive measurement sites to alarm
operators and the control room of operation at process range limits.

Design II
38
3.2.2 Common Unit Control Philosophy
Pumps and Compressors
The following is a typical illustration of a pump (where the control is identical to a
compressor although it is regulated by pressure control rather than flow control).
Figure 8
Figure #9 illustrates the enclosure of the pump by drain valves (with blind flanges) directly
on the lines surrounding the pump. The pump itself is drained to wastewater treatment
(WT) and is powered electrically, represented by the dashed line, by the motor (M). A
swing check valve is employed with the arrow to ensure no backflow in case of downstream
pipe blockage. The two outmost valves are for isolation purposes. The suction side control
valve is an on/off gate valve, which can be operated to restrict flow to the pump. This
valve is not used for control purposes, but is especially usefully when switching between
the main pump and its redundant counterpart when maintenance is being performed.
Control Valves
The following is a typical illustration of a control valve. A flow control valve is
shown, however the same control operation is used for a pressure control valve.

Design II
39
Figure 9
Figure #10 illustrates the isolation of the control by gate valves on both the
upstream and downstream of the valve in case maintenance or replacement is required.
Drain valves with blind flanges provide the ability to drain the pipe prior to removal. A
control valve may either be fail opened (FO) or fail closed (FC), whereby on a loss of
actuated air pressure, the valve defaults to the specified position. The control conditions
downstream determine the fail selection.
A bypass line with a ball valve is connected in parallel to the control valve to ensure
processes are not halted while the valve is repaired or replaced. This valve is closed during
normal operation.
The following is a typical illustration of a level measurement and control system.
Figure 10

Design II
40
Figure #11 illustrates a typical level control system. Unlike other transmitters, a level
transmitter is typically isolated from the equipment with gate valves. It can be drained via
the drain valves with blind flanges upon replacement or if maintenance is required. Notice
the alarms indicating high and low levels of the measured vessel for any vital system
component.
3.2.3 Midrex Direct Iron Reduction
Midrex Shaft Furnace and Conveyor Belts
The conveyor belts make use of cascade control in order to reduce time lag. This
control mechanism is used since the amount of iron ores received from shipment will
fluctuated during the week, thus the need for a more fine-tuned control strategy. The
primary controller is a level controller located at the Midrex furnace. The level indicator
controller (LIC) will send a signal to the LIC of the charge hopper (HP) and will change
its set point value, such that immediate response take place to bring the level of iron ores
in the furnace to the desired level. The LIC of the charge hopper acts as a primary controller
to the speed signal converter (SY) set up for each conveyor belts. For each conveyor belt,
a speed transmitter (ST) sends an electrical signal to a speed indicator controller (SIC)
when the measured speed at one end the conveyor belt does not match the set point value.
The conveyor belts (including pan conveyor) contain at least four hand stop switch (HSS)
for manual control of the belt speed in the case of emergency shutdown. The Midrex shaft
furnace’s incoming syngas stream is regulated by the cascade control mechanism described
for the steam reformer section, however a simple feedback loop system is set up to regulate
its flowrate before entering the furnace. The furnace’s level indicator also includes a high
and low level alarm for iron ore level. The flue gas leaving the system is regulated using a
feedback loop system to regulate its flowrate.

Design II
41
Figure 11
Conveyor belt and shaft furnace control are interconnected by cascade control mechanism.
Steam Reformer
It is desired to maintain the syngas temperature produced from the steam reformer
at 900oC when the Midrex process is operating. The two outlet streams of the reformer
can be used to control the upstream processes to maintain this desired temperature,
however it would be more difficult to find the appropriate set point value using the flue gas
stream. Thus, the syngas stream temperature is used to control upstream processes. The
feedback loop control mechanism was not chosen, since a temperature controller will not
respond to sudden change in flowrate due to pressure change of the inlet gas streams. This
is remedied by using a cascade control mechanism, where there is a primary (temperature)
and secondary (pressure) controller. The cascade control mechanism works as follows:
A temperature transmitter (top right box in figure #13) sends an electrical signal to
a temperature indicator controller (TIC), where the measured value is compared to the set
point value of 900oC. When there is a difference, the TIC sends an electrical signal to all
three inlet stream’s pressure indicator controller (PIC) so that the set point value of the PIC
is changed, thus changing their flowrate according to the primary controller. Each PIC is
operated independently from the primary controller when their set point value is not
changed, by adjusting the inlet flowrate to the reformer to the desired value.

Design II
42
Figure 12
Cascade control mechanism is used to control syngas temperature.
A feedback loop system is used to control selected streams (2 more not shown in
figure #14) upstream of the reformer, since they do not feed directly into it. This would
suffice due the more thorough control mechanism set up for streams directly upstream of
the reformer. In this case, the TIC (top right box) sends a electrical signal to the pressure
signal converter to act on the control valve, when the measured syngas temperature is
different than the set point value. Since most gas streams contain flammable compounds,
drainvalves are installed to send the streams to flare, in case of emergency shutdown.
Figure 13
Feedback loop mechanism is used for selected streams

Design Project Group 3 Rev A FINAL.1

Design Project Group 3 Rev A FINAL.1

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