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Mixing System Design for the Tati Activox® Autoclave
Marc Nicolle, Mark Bellino – Hatch Africa (Pty) Ltd.Gerhard Nel –Norilsk Nickel South Africa (Pty) Ltd.Tom Plikas, Umesh Shah, Lyle Zunti – Hatch - Ltd.Herman J. H. Pieterse – Pieterse Consulting, Inc.
Agenda
• Introduction– Location of Tati– TA®P Flowsheet– Demo Plant Autoclave
• Autoclave Design Review– Different Oxygen Mass Transfer Coefficients– Prudent Option Selected– Autoclave Design Modified (5 vs. 4 Comp)
• Design Modification• Evaluation
– Design Concerns• Demo Plant Test Work• CSTR modelling• CFD modelling
• Final Agitator Design• Conclusions
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Where is Tati?
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Basic Process FlowsheetTATI ACTIVOX® PROCESS FLOWSHEET
ULTRA-FINE GRINDING
COBALT SOLVENT EXTRACTION
COPPER SOLVENT EXTRACTION
ACTIVOX®
SOLID LIQUID SEPARATOR
COBALT PRECIPITATION
FIRST STAGE IRON REMOVAL
COPPER ELECTROWINNING
NICKEL SOLVENT EXTRACTION
AMMONIA RECOVERY
NICKEL ELECTROWINNING
AMMONIA STRIPPING
TAILINGS DAM
ORE
SOLID RESIDUE TO PLATINUM GROUP ELEMENTS RECOVERY
RELEACH
COBALT PRODUCT
COPPER RAFFINATE
WASH WATER
SECOND STAGE IRON REMOVAL
NICKEL PRODUCT
COPPER PRODUCT
STEAM
AMMONIA
SODIUM CARBONATE
QUICKLIME
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Demo Plant Autoclave
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Autoclave Design Review
• Autoclave design review in Canada• Over 75% of Ni is recovered in C1• Concern on the original O2 mass transfer
coefficient used to size the agitators in C1• This indicated a lower agitator power
requirement than the empirical correlation
• Two options:– Increase power to C1 agitators or,– Increase the number of C1 agitators
• Autoclave design modified from five compartments to four
76.0
397.381
V
PakL
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Autoclave Design Review
Why remove a compartment?• Increased power per agitator:
– P/V between 3.9 kW/m3 – 4.7 kW/m3
– Outside range of commercial autoclaves– Agitator mass and bending moment – shell
stress
• Increased number of agitators:– P/V between 2.3 kW/m3 – 2.9 kW/m3
– Within the range of existing autoclaves
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Design Modification
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Slurry FeedPipes
Quench WaterInlet
Flash RecyclePipes
Slurry OverflowWeir
8 Blade Rushton Turbine
Baffles Oxygen Sparger
Evaluation
Design Concerns to be Evaluated:1. Validity of Empirical Correlation2. Drop in Metal Recovery3. Hot Spots4. Brick Lining Wear (swirling under the impeller)5. Residence Time Comparison
Method of Evaluation– Point 1 – Testwork – Point 2 – Theory– Point 3, 4 & 5 – CFD analysis
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Validity of Empirical Correlation -Demo Plant Test Work
• Measured P/V > empirical correlation (2.6kW/m3 vs. 1.4kW/m3)
• Subsequent runs were carried out• Significant Ni recovery drop off
below 1.4kW/m3
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
86
87
88
89
90
91
92
0 0.5 1 1.5 2 2.5 3
P /V kW/m3
Validity of Empirical Correlation –
Test Results
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
%Recovery
Gassed power per unit volume [kW/m3]1.4kW/m3
Comparatively Consistent Recoveries
Drop in Metal Recovery – Theoretical CSTR Evaluation
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 100 200 300 400 500
Time [min]
Cu
mu
lati
ve M
ass
Fra
ctio
n E
xiti
ng
C
om
par
tmen
t
CFD Results Theoretical values for 2 CSTRs in series Theoretical values for 1 CSTR
105 min
Inflection point
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Hot Spots – CFD Analysis Velocity Profile
0.00
3.00
0.50
1.50
2.50
Velocity Magnitude, m/s
View
All Agitators – Same Rotation
Middle Agitator – Reverse Rotation
Feed and flash discharge pipe section
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Brick Lining Wear – CFD Analysis Velocity Profile
0.00
7.00
2.00
4.00
6.00
Velocity Magnitude, m/s
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Residence Time Comparison – Agitator Rotation Direction
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Residence Time Comparison – Agitator Rotation Direction
0%10%20%30%40%50%60%70%80%90%
100%110%
0 200 400 600 800
Residence Time (min)
Cu
mu
lati
ve F
resh
Feed
, w
t%
Reverse Rotation
Same Rotation
Rev Rot mean residence time = 105.95 minSame Rot mean residence time = 105.38 min
0%10%20%30%40%50%60%70%80%90%
100%110%
0 200 400 600 800
Residence Time (min)
Cu
mu
lati
ve F
resh
Feed
, w
t%
Reverse Rotation
Same Rotation
Rev Rot mean residence time = 105.95 minSame Rot mean residence time = 105.38 min
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Final Agitator Design
• Eight blade Rushton turbine• Increased blade height• 186kW VSD motor• 69% - 2.8kW/m3
• 85% - 3.4kW/m3
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions
Conclusions
1. Reducing the number of compartments (5 -4) should have negligible impact on metal recovery
2. Commercial design finalised with 3 agitators in the 1st compartment
3. Well mixed 1st compartment – 7.2 turnovers/min
4. Theoretical residence time of C1 same as modelled CFD residence time
5. Expect a uniform reaction extent and temperature through the compartment
6. Weir wall allowed for between agitators 2 and 3 to allow for a 5 compartment scenario to be run if required
Introduction
Autoclave Design Review
Design Modification
Evaluation
Final Agitator Design
Conclusions