Benny E. Raahauge, General Manager, FLSmidth A/S, Denmark

SGA Quality beyond Consistency:

– Wishful Thinking against Mother Nature and Economics?

Overview of Presentation

1) Major Technology Trends over Time up to 2010: Bayer Process, SGA, Calcination & Smelters? 2) Mother Natures Impact on Refiners and Calciners? Sodium & Excess Bath Generation Particle Size, Strength & Dust Generation? Alumina Feeding , Crusting Tendency & Dissolution Rate? HF Generation & Capture, Specific Surface Area, Gibbsite, MOI &

LOI?

3) Economics – Who Pick up the Bill?

1) Major Technology Trends over Time - Bayer Refinery: Process:

1.6 Mill TPY Alumina

1) Major Technology Trends over Time – Bayer Refinery Process:

Parameter ~ 1940 ~ 1970 ~ 2010

Refinery Capacity 50 – 100 ktpy 600 -800 ktpy 1.6 - 2.4 Mtpy

Energy Consumption incl. Calcination

- Bayer Process: 13 – 14 GJ/ton

Bayer Process: 8 – 9 GJ/ton

Digestion Batch/Continous 250 m3 Autoclaves Tube Digestion

Precipitation Batch/Continous 3000 m3 Continous Continous

Settlers , Footprint (Flocculants) Effluent

-

1.8 - 2.3 m2/tpd 100-200 ppm O/F

0.5 m2/tpd < 50 ppm O/F

Washers, Footprint (Flocculants) Effluent

- 0.9 - 1.1 m2/tpd 300-400 gpl U/F

0.25 m2/tpd > 500 gpl U/F

Red Mud Residue Lagoons & Wet Ponds

Dry Stacking Britsh Aluminium

Dry Stacking/Storage

Particulate Emissions - Electrostatic Precipitators

Fabric Filters 20 mg/Nm3(dry)

1) Major Technology Trends over Time: SGA Quality from Floury to Sandy Alumina.

Alumina Type & Typical Values Floury Sandy

Precipitation Yield, g Al2O3/L 70 50 - 80+

SSA (m2/g) 5 50-80

Alpha Alumina (%) 80-90 10-25

% Alumina < 45 Microns, Typical 45-60 10

Angle of Repose 45O 30-32O

Bulk Density, Loose (kg/L) 0.8 0.95

Change to Sandy Alumina from Floury Alumina around 1980 was Driven by the demand for Dry-Scrubbing of HF in the Smelters.

1) Major Technology Trends over Time–Calcination: Technology Shift to Stationary Calciners Driven by Energy Savings

Nine (9) Rotary Kilns at QAL. Replaced with Three (3) FLS GSC Units of 4500 tpd SGA. The world largest Stationary Calciners Producing Alumina.

QAL 2004

Fabric Filters Eliminate Power Failure Caused Dust Emission from ESP’s.

1) Technology Shift in Primary Aluminium Smelting – IAI, ICSOBA 2009

1) Major Technology Trends over Time – Smelters: Key Performance Metrics

Parameter 1945 1995 2009-10

Cell Amperage, kA 25 - 50 300 200 - 500

Cell Voltage, Volt 5.0 4.1 3.85 - 4.20

Current Efficiency, % 80 - 58 92 - 95 91 - 96

Power Consumption, kWh/kgAl

20 - 25

13

12.5 - 13.5

Anode Consumption Kg/t-Al

< 776

420-550

< 400

Anode Effects, #/p/d

- - < 0.08 - 0.1

Total Flouride Emission, Kg/t-Al

- - <0.35 – 1.0

Average PFC Gas (IAI), ton CO2-eqv/ton Al

- - ≤ 0.6 Welch, Alzarouni & Lindsay, ICSOBA 2010

Metson TMS 2009

Smelter Grade Alumina Quality Parameters – The Interface between Refinery & Smelter

Welch & Kuschel: JOM May 2007

Sodium & Excess Bath Generation increases with Pot Size & Time!

Lindsay, TMS 2012

1) Purity: Sodium & Excess Bath Generation

3Na2O + 4AlF3 -> 2Na3AlF6 + Al2O3

Lindsay, TMS 2012

Na2O in SGA – What can the Refiner Do?

1) Purity: Sodium & Excess Bath Generation

Produce a Hydrate Particle that, when calcined has less than about 0.30 wt% Na2O, which seems to be the equillibrium value in modern pots (P. Homsi, Aluminium Pechiney)?

Armstrong et all AQW 1996

Lower Soda content in the SGA, from lower Supersaturation in Precipitation will reduce Refinery Yield & Productivity - and Increase OpEx! Lower Soda may also produce a weaker SGA particle - Potentially increasing fines problems in the Smelter!

But, Soda becomes Leachable after Calcination and can be partly removed by a Leaching & Drying Process as shown -> Can/will the Smelter justify the higher alumina price to cover the additional Refinery cost?

1) Purity: Sodium & Excess Bath Generation - Who to Pay the Bill?

Lindsay, TMS 2012

0 5 10 15 20 18

20

22

24

26

28

30

% -38 MICRON ALUMINA

FLOW

RA

TE ( g/m

in)

Increased content of Fines Reduces the Flowability of the Alumina and Reduces the Point Feeding Rate. Alumina Particle Size, Strength and Breakdown, Determines the Ultimate Particle Size fed to the Pot - and thus Dust Generation.

2) Particle Size, Strength & Dust Generation?

Welch, Alzarouni & Lindsay, ICSOBA 2010

2) Particle Size, Strength & Dust Generation?

Alumina Fines (< 45 Microns) and Superfines (< 20 Micron) content impacts: Flowrate / Flowability or Funnel flow time.

Particle Segregation Emission of Dust

Angle of Repose and Anode Cover. Loose Bulk Density => Impacts on:

Thermal Conductivity of Crust and thus Thermal Balance of the Pot. Massflow in Volumetric Point Feeders and thus Un-controlled Feeding.

Dissolution Rate through Alumina Dispersion, Wetting with bath and Crust formation.

FLS R&D Work shows that Large Particles Breaks more than Smaller Particles!

2) Particle Size, Strength & Dust Generation?

Weak Alumina with high Attrition Index (AI) generates relatively more fines on its journey to the pots.

18

0 5 10 15 20 25 30

TIME INTERVAL (day)

5

10

15

20

25

% -

45

MIC

RO

N A

LUM

INA

AFTER SCRUBBER

AS RECEIVED

Increase in Alumina Attrition Index leads to Particle Breakdown in scrubber

An example of severe attrition or particle breakdown

Welch, Alzarouni & Lindsay, ICSOBA 2010

2) Particle Size, Strength & Dust Generation? FLS R&D Work: Particle Breakdown Increases with: (Alumina AI) * (Velocity)2

Alumina Particle Strength (AI) is partly correlated with Hydrate Particle Morphology.

Strong Alumina Particle

Weak Alumina Particle

How to Lower Attrition Index (AI) of Alumina Particles and Dust Generation?

Design and Operate the Precipitation Circuit to: Produce Alumina with, say AI < 15% on 45 micron? =>

Lower Supersaturation, Yield and total Na2O – This may be costly to the Refinery???

Produce a Hydrate Particle with Optimized Morphology, and: A Hydrate with Less Over Coarse Particles and Superfines? =>

Increased Yield and Productivity – That is easy to say, but difficult or costly to do!

2) Particle Size, Strength & Dust Generation?

Parameter GSC Plant A GSC Plant B GSC Plant C GSC Plant D

Alumina AI, % 24 8 26 14

Total Na2O, % 0.283 0.399 0.43 0.33

2) Particle Size, Strength & Dust Generation?

Dust is Generated in Calciners and Collected in ESP’s or Fabric Filters: Calciner Dust is the primary source of Fines and Superfines in SGA shipped to the Smelter. Degree of Calcination in Dust deviates from the SGA produced in the Calciners.

Dust Management Options: Recycle Dust to Digestion loosing Refinery Productivity and increasing OpEx? Mix Dust with alumina from the Fluid-Bed Cooler producing SGA with Gibbsite content? Recover coarse dust by Dynamic Separation and Recycle mainly Superfines to Digestion, whenever Precipitation experiences a Fines Generation Cycle? Back - Mixing Dust into the Hot Back-end of Calciner removing Gibbsite from the SGA.

Recover coarse dust by Dynamic Separation and Recycle Superfines to Digestion

Forces on Particle in Dynamic Classifier

100% Hot Dust Recycle in FLS Gas Suspension Calciner => SGA with ZERO Gibbsite.

GSC Alumina Gibbsite LOI(300-1000C) Alpha (%) SSA(m2/g) % < 45μm % < 20μm

Dust: 2–3 wt% 9 .6 – 19.4 wt% 0.94 - 1.41 wt% 47 - 56 19 - 35 92.8 - 93.8 60.8 - 74.2

SGA incl. Dust 0 wt% 0.62 – 0.77 wt% 2 - 3 75 - 81 7.6 - 8.2 1.5 – 2.3

3) Alumina Feeding , Crusting Tendency & Dissolution Rate?

Wang, TMS 2009

Dispersed Single Alumina Particles/Grains Dissolves in Seconds, but Crust in Minutes/Hours.

Thonstad et all, Metrallurgical Trans. Feb. 1972

Bath

Ledge

Anode

Aluminium

Sludge

Old Side Worked Pre Baked (SWPB) Pots:

100-200 kgs/shot may take hours to dissolve.

Welch, Alzarouni & Lindsay, ICSOBA 2010

Bath velocity

Metal velocity

Modern Pre Baked Pots with Point Feeders:

1 - 5 kgs/shot every 10 - 300 sec ~ 65 kg/hr must dissolve in minutes.

Welch, Alzarouni & Lindsay, ICSOBA 2010

Narrow Cell Operating Region and Temperture Effect of Alumina Dissolution

Welch, Alzarouni & Lindsay, ICSOBA 2010

Taylor et all, TMS 1996

1. Alumina Powder Heating Up

2. Good dispersion and mixing of the powder

can lead to fairly fast dissolution. Gamma to

Alpha conversion releases heat, BUT excessive powder agglomerate and forms a Solid Crust.

3. Solid Alpha Alumina Crust dissolves relatively slowly and become the limiting rate of dissolution.

Free Flowing Alumina, Low Alpha, 0.6 – 0.8% LOI (300-1000C) without Gibbsite is preferred:

Alumina Feed Rate, Cell Operation & Control is Essential

Welch, Alzarouni & Lindsay, ICSOBA 2010

Welch & Kuschel: JOM May 2007

4) HF Generation & Capture: Specific Surface Area, MOI, Gibbsite & LOI (300-1000C)

Welch, Alzarouni & Lindsay, ICSOBA 2010

Hyland et all. TMS 2004

Metson TMS 2009

4) HF Generation: MOI, Gibbsite & LOI (300-1000C)?

H2O Release to the Gas Phase during Alumina Heating Up

NOTE: x = 3 for Gibbsite!

4) Calcination: Specific Surface Area, MOI & LOI (300-1000C)

SSA & LOI Increases with Decreasing Calciner Furnace Temperature or By - Pass

SGA from Furnace

Inlet to GSC Furnace

GSC with Holding Vessel

High Temperature

Low Temperature

Calciner with By-Pass of CFB Furnace => SGA: A Mix of Under & Over Calcined Alumina

Perander, ICSOBA 2013

4) Calcination Gibbsite => Specific Surface Area, LOI (300-1000C) & MOI Adsorption

Lindsay, TMS 2009

4HF + Al2O3..H2O 2 AlF2(OH).2H2O

70 - 75 m2/g

4) HF Capture: Specific Surface Area?

Lindsay, TMS 2009

Pore Diffusion becomes Rate Limiting

Pore Size Increases with Decreasing SSA GSC Alumina => Uni - Modal Pore Size Distribution

In order to produce SGA that: 1) Minimize HF Generation

from Gibbsite and residual –OH Groups in the SGA - and:

2) Maximize sorption capacity of SSA in the SGA.

Avoid Gibbsite - and: Minimize Furnace By-Pass to: Avoid Bi–Modal Pore Size Distribution from Bi–Modal SGA Quality comprised of Under – and Over Calcined Alumina.

Refinery Calciner Option:

Metson, TMS 2009

Bi – Modal Pore Size Distribution

Wishful Thinking by Smelter Mother Natures Impact on Refinery

Purity: Sodium & Excess Bath Generation Not more than 0.28-0.32 wt-% Na2O

=> Lower Yield and Particle Strength, or Justify Investment in Leaching/Drying Plant?

Particle Size, Strength & Dust Generation: Free Flowing - No Segregation or Dusting

Produce Strong Alumina Particle, Narrow PSD. Dust Management Options & Cost => Mix Dust into Hot Alumina for Calcination.

Alumina Feeding , Crusting Tendency & Dissolution Rate: Fast without Volcanos and Muck Formation

SGA with Low Alpha => Relative High LOI => Gamma -> Alpha => Hard Crust Formation => Avoid Gibbsite & Optimized Alumina Feeding is very Critical.

Surface Area, LOI, MOI & HF Generation: Enough to Maintain Lincense to Operate

More Surface Area => Higher LOI => More HF? Avoid Gibbsite & Bi-Modal SGA Quality from: Bi–Modal LOI (300-1000C) and: Bi-Modal Pore Size Distribution. Minimize Calciner Furnace By-Pass!

SUMMARY: SGA Quality beyond Consistency

TGA – DTA of GSC Alumina

showing: Zero Gibbsite

MOI Evaporation

X-Ray Diffraction of GSC Alumina shows: 4% Alpha Phase, 6% Gamma Phase & 89% Amorphous or Disordered Phase assisting Dissolution.

GSC Alumina with ZERO Gibbsite

Thanks to Mother Nature and Thanks You – Any Questions?