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© CADFEM 2016

The Application of CFD within the Alumina Industry

James Scully, R&D Engineer, Rusal Aughinish

3rd CADFEM ANSYS Simulation Conference, Ireland

23rd & 24th November 2015 - Engineers Ireland, Dublin

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Rusal Aughinish: What we do

Refine Bauxite to Alumina

• 4 ton Bauxite

Import from Guinea and Brazil

• Produces 2 ton Alumina (Al2O3)

Export to Aluminium smelters globally including

Scandinavia, France, Russia and Latvia

• Produces 1 ton of Aluminium

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Process Flow

DigestionImpurities Removal

Precipitation Calcination

Port

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Value of CFD to Rusal Aughinish

• Potential new equipment designs can be tested quickly

• Many different scenarios and conditions evaluated

• Can design for future process changes

• New bauxites / Production increases

• Reduces risk of testing new designs in the field

• Reduction in equipment downtime

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Design Modeller

ANSYS Meshing / Fluent Meshing

ANSYS Fluent

CFD Post / Fieldview

CFD Modelling in Rusal Aughinish

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Mixing Tanks

• Used CFD and rheology

experiments to understand

process in tank

• Compared number of

different bauxite

combinations

• Power draw

• Viscosity

• Shearing

• Developed operating

parameters based on results

of both CFD and

experiments

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Settling Tanks

• Redesign of central feedwells to optimise flocculation performance of tank

• Improving flocculation Improve solids settling

• Reduce amount of solids (impurities) being transported to downstream areas of plant

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Cyclones

• Modelled dependency of separation efficiency and cut size, d50, on length of vortex

finder

• Various vortex finder compared with optimum length

• Original length = Twice size of optimum length

• Reduced particle residence time in cyclone

• Reduced particle breakdown

• Particle separation

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Digestion - Wear

• Multiphase Flow Modelling

• Cavitation

• Flashing Flows

• High Sand Loads

• Experimental erosion work carried out in

University of Limerick

• Used to develop erosion parameters

used within CFD models

• Wear rates validated using on-site NDT

• Allows refinement of CFD models

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Digestion - Wear

• Flashing Flows

• Slurry (liquor + sand) pressure drops below saturation pressure as travels through

pipework

• Slurry starts to boil (flash)

• Increase in velocities through pipelines

• Increase in wear through system

• Reduction in life of pipework and increase in maintenance costs

• ANSYS Fluent used to model flashing process within system and allow redesign of pipe

network and optimisation of process conditions to reduce wear

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Cavitation Wear

• Low liquid levels in tanks combine with low local pressures

Vortex formed behind support plates

High localised wear

• Redesign of support plates to eliminate vortex

• Maintaining sufficient tank levels

• Overall reduction in wear along tank wall

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Any Questions