Brown Coal Dewatering
“Materials Grand Challenges”
Melbourne Materials Institute, 20 August 2012
Anthony Stickland, Robin Batterham,
Antoinette Tordesillas and Peter Scales
Particulate Fluids Processing Centre
A Special Research Centre of the Australian Research Council
Background
• Victorian Brown Coal is very wet
• High moisture costs energy to remove
 Reduces net calorific value
 Increases CO2 / MW
 “Dirty” moniker (it does burn clean…)
• Holy Grail for any processing of brown
coal is Efficient Dewatering
– Make brown coal into black coal at minimum
cost and energy
– Vast resource with large potential impact
Particulate Fluids Processing Centre
A Special Research Centre of the Australian Research Council
Victorian Brown Coal
www.dpi.vic.gov.au
Structure of Coal
• 2-phase micro-porous sponge
• Solid network is continuous
– Particulate gel held together by
van der Waals, hydrogen bonding
and electrostatics
– Able to support a load and transmit
pressure
100 nm
TEM image of raw Loy Yang
brown coal
from McMahon, Snook and Treimer, ‘The Pore
Structure in Processed Victorian Brown Coal’, J
Colloid Interface Sci. 252, 177 – 183 (2002)
• Fluid has both continuous and
discrete parts
– Must break structure to get water
out
Particulate Fluids Processing Centre
A Special Research Centre of the Australian Research Council
Dewatering Options
• Solid-Liquid Separation
– Thermal dewatering
• Boiler flue gases
• Drying beds
– Mechanical dewatering
• E.g. filtration
• Structure Breaking
– Shear
• ‘Kneading’
– Hydrothermal reaction
• E.g. Exergen CHTD
• Structure Breaking with
SLS
– Mechanical/Thermal
Expression
• Compression + heat
• Batch process, low
throughput
– Compression + Shear
• Modified High
Pressure Grinding
Rolls
Particulate Fluids Processing Centre
A Special Research Centre of the Australian Research Council
Combined Shear + Compressive
Loadings
Raked thickeners
Belt press filters
Cross-flow filters
Compression
Shear
Compression
+ Shear
• Many SLS processes involve combined loadings
• Generally enhances operational performance
• Need to understand particulate network
behaviour under combined loads
Lamella settlers
Disc stack centrifuges
Decanting centrifuges
Suspension cracking
Wall slip in rheometry
Particulate Fluids Processing Centre
A Special Research Centre of the Australian Research Council
New Experimental Techniques
• Need to measure
behaviour under shear and
compression
• Requires novel
experimental methods
• Shear using “vane-ininfinite-medium” geometry
• Compression in a filter or
under a sediment bed
• E.g. ‘Vane-in-a-filter’
(H. Teo, The University of Melbourne)
Particulate Fluids Processing Centre
A Special Research Centre of the Australian Research Council
New Microstructural Understanding
Photoelastic birefringent patterns of
force chains
(R. Behringer, Duke University)
• Columns of particles
bear most of the load in
powders
• Breaking structure
necessitates shear to
buckle the column
• ‘Confined Force Chain
Buckling’ model
• Link microstructure and
macroscopic behaviour
Particulate Fluids Processing Centre
A Special Research Centre of the Australian Research Council
New Technology
• Modified High Pressure Grinding Rolls (HPGR)
• Compression at nip
• Shear through different
rotational rates
• Perforated rolls give
short Solid-Liquid
separation pathway
• Continuous, high
Throughput
(H. Teo, The University of Melbourne)
Particulate Fluids Processing Centre
A Special Research Centre of the Australian Research Council
Summary / Discussion Points
(A Innocenzi, International Power)
• Structure of Brown Coal
• Dewatering of Brown Coal
– Mechanical and thermal options
• Combined Compression and Shear
– Measuring constitutive behaviour
• Confined Force Chain Buckling
– A microstructural description of
suspension rheology
• Modified HPGR
– High throughput processing
Particulate Fluids Processing Centre
A Special Research Centre of the Australian Research Council
(courtesy A. Innocenzi, International Power)