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MINERALS DOWN UNDER NATIONAL RESEARCH FLAGSHIP
Current Status & Future Direction of CSIRO’s Dry Slag Granulation Process
with waste heat recovery
ICST 2012, Dresden, Germany: 1-3 October, 2012
Sharif Jahanshahi and Dongsheng Xie
ICST 2012, Dresden
Presentation by Sharif Jahanshahi PhD, FAusIMM
Sharif Jahanshahi has over 30 years experience in R&D across; high temperature processing of ferrous and base metals, thermodynamics and kinetics of high temperature systems, melt chemistry, process modelling, simulation and development
Currently consulting for leading global players in the metallurgical industry through Meta-Logical Solutions Pty Ltd.
Website: http://www.metalogical.solutionsEmail: [email protected]
Outline
• Drivers• Concept & Technical Challenges• Progress & Current Status • Fundamentals of Droplet Collision• Future Direction
3 ICST 2012, Dresden
ICST 2012, Dresden
Drivers
Each year > 400 million tonnes of slags is producedEach tonne of molten slag can liberate 1.6 - 1.8 GJ of thermal energy on cooling
Opportunities (globally): • 100s million tonnes of cement from blast furnace slag each year• ~ 720 PJ of energy (high grade waste heat)
• Reduction in GHG emission by 100s million tonnes of CO2 per year
• Reduction of up to 600 GL of fresh water usage per year• Avoiding sulphur emission and contamination of biosphere
Conceptual Two-step Process (2006/07)
Dry granulation Spinning discatomisation
Solid granules 800°C
Hot air 600°C
Granules 50-100°C
Hot air 600°C
air 25°C
air 25°C
Heat Exchanger(Counter-current moving bed )
Slag 1500°C
• Drying• Preheating• Steam• Power• Desalination• Others
Cement
ICST 2012, Dresden5
CSIRO’s Dry Slag Granulation Process
Technical Challenges– Optimum disc and reactor design– Handling of hot granules– Compact reactor for efficient
recovery of high grade waste heat and lower capital cost
Concept Development
2006/7
Motor
Air
Hot air >600 C
Discharge 500 C
100 C
Slag 1500 C
Air
ICST 2012, Dresden6
Video - Integrated DSG & Heat Recovery Process Proof-of-concept through 1.2 m diameter pilot plant (0.6 t/h)
Concept Development
Proof of Concept2007/92006/7
ICST 2012, Dresden7
Process Modelling Using 3D CFD SimulationVelocity
(m/s)
Predicted droplet generation and size distribution in broad agreement with measurement
0
10
20
30
40
50
60
70
80
90
100
6.683.3272.3621.180.8330.2950.1060.0530.001
Droplet diameter, mm
Cum
ulat
ive
wei
ght f
ract
ion
(CW
F), %
0
5
10
15
20
25
30
35
40
45
50
Wei
ght f
ract
ion
(WF)
, %
Predicted WF
Measured WF
Predicted CWF
Measured CWF
5 cm diameter disc, at 1780 RPM, 2 kg/min slag
ICST 2012, Dresden8
Fundamental Studies - Droplet collision with inclined plate
Experimental conditions:• Ground stainless steel plate, Plate angle: 30°• BF slag: 43% CaO-35% SiO2-15% Al2O3-6% MgO
• Temperature: 1450 °C, Droplet falling height: 1.7 m
Measurements from high speed video:• Droplet diameter = 6 mm• Impact velocity = 6.51 m/s• Time for reach maximum contact area = 4 ms• Total contact time = 20 ms• Maximum specific contact area (A/V) = 0.59 mm-1
Droplet Collision Process:Contacting Spreading Reforming Bouncing Rolling/Tumbling
ICST 2012, Dresden9
Effect of Plate Angle
15°
Slag droplet diameter: 5 – 6 mm
Experimental conditions: Plate type: Ground stainless steel, Droplet falling height: 1.7 m, Temperature: 1450 °C
30° 45°
ICST 2012, Dresden10
Effect of Surface Type – Angled PlateSlag droplet diameter: 5 – 6 mm
Experimental conditions: Droplet falling height: 1.7 m, Temperature: 1450 °C, Wall angle: 15°
Smooth stainless steel
Ground stainless steel
Sand-blasted stainless steel
Ground mild steel
Sand-blasted mild steel
ICST 2012, Dresden11
Effect of Droplet Size
0
5
10
15
20
25
30
0 2 4 6 8
Spr
eadi
ng le
ngth
, mm
Droplet diameter, mm
Stainless steelAngle: 30o
Droplet T: 1500 oCFalling height: 1.7 m
0
10
20
30
40
50
0 1 2 3 4 5 6 7 8
Spr
eadi
ng tim
e, m
s
Droplet diameter, mm
Stainless steelAngle: 30o
Droplet T: 1500 oCFalling height: 1.7 m
(a) (b)
• Spreading length and spreading time increase with droplet size
ICST 2012, Dresden12
Effects of Surface Finish and Plate Material
• Surface finish has a strong effect on the spreading time• Spreading length also seems to be affected by surface finish
0
10
20
30
40
50
60
Rough stainless steel
Smooth stainless steel
Smooth mild steel
Spr
eadi
ng le
ngth
or t
ime
(mm
or m
s)
Material and surface condition
Droplet diameter: 6 mmDroplet temperature: 1500 oCDroplet falling height: 1.7 mPlate surface angle: 30o
Spreading length
ICST 2012, Dresden13
ICST 2012, Dresden
• Slag droplet colliding with a plate at a small impact/inclined angle becomes more elongated and show stronger tendency to break up.
• Large slag droplets have longer contact times on collision with plate than small droplets.
• Slag droplets have shorter contact times on collision with smooth plate than with rough plates.
• Slag droplets stick significantly longer to the sand-blasted steel plates. − This could be due to the capillary effects of micro cavities at the plate
surface.
− Heat transfer could also have a complex influence on the contact time.
Summary – Collision with Inclined Plate
14
CFD Process Modelling
Developed and applied to; optimise design, aid process scale-up, reduce development cost and risks
Fundamental steps covered by the CFD model: Spreading of molten stream of slag on the rotating disc caused by the centrifugal force Breaking up of the molten slag film to form ligaments at the edge of the spinning disc Breaking up of the ligaments into droplets at a short distance away from the spinning disc,
by the surface tension of the slag Flight of the molten droplets and heat transfer to the
gas phase Collision and heat transfer between droplets/granules
with reactor walls/roof Heat transfer between granules and air in the cyclone
section of the reactor.
ICST 2012, Dresden15
Scale-up to Semi-industrial Scale DSG Plant (2009/12)
Circulation and cooling of droplets and granules in the cyclonic section
High speed video of spinning disc during dry granulation of blast
furnace slag at 75 kg/min
• Designed, constructed, commissioned and used to generate data for validating CFD model
• 3 m diameter reactor, processing batches of 500 kg slags at 6t/h
• Pilot plant is instrumented with various sensors and cameras for on-line measurements and observations
ICST 2012, Dresden16
Properties of Granulated Blast Furnace Slag
Dry granulated slags• > 90% of granules were smaller than 1.5 mm
• Appear darker in colour due to their higher density, but change in colour on grinding
• XRD and optical microscopy of BF slag showed glass content of > 99%
• Tests showed good cementitious properties and suitable for cement production.
Water granulatedGround dry granulated
Dry granulated
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ICST 2012, Dresden
Future Direction
1. Scale up To an industrial scale (~1 tonne/minute) through optimisation of design and
operating parameters2. Steady state plant trials
At a metallurgical plant - access to large volume of molten slag– the process can run continuously for extended periods and reach steady state– off-gas temperature approaches the targeted theoretical values based on heat
balance/transfer calculations The full integration of moving packed bed with the dry granulation unit also needs
to be considered and demonstrated. 3. Conversion into cement
Use granulated slag product as feedstock in a cement production plant and demonstrate the product quality and performance as a substitute for Portland cement.
Concept Development
Proof of Concept
Semi-industrial Scale Piloting
Industrial Scale Piloting
2007/9 2009/12 2013/172006/7
ICST 2012, Dresden
Acknowledgments
Project Team: Jason Donnelly, Sharif Jahanshahi, Benny Kuan, Dylan Manley, Terry Norgate, Yuhua Pan, Steve Sanetsis, Bernie Washington, Peter Witt, Dongsheng Xie.
Sponsorship: CSIRO, BlueScope Steel and OneSteel
Collaborators: Staff from BlueScope Steel, OneSteel, Hatch and Australian Steel Mill Services.
Thank you
CSIRO - Minerals Down Under Flagship
Sharif JahanshahiTheme Leader – Sustainable Metal Production
