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Flexible aluminium smelting -the how and why of modulating energy consumption

Future Aluminium ForumNovember 2020

Dr. Mark Dorreen – CEODr. Nick Depree – Senior Design EngineerGeoff Matthews – Energy Sector Lead

Decarbonised aluminium smelting industry 2050:→ decarbonised energy generation

→ renewable energy generation

→ variable energy supply

→ smelters must deal with variability

HOW?

Heat Balance – some comments• Approximately 50% of the energy input to aluminium

reduction cells is lost to the atmosphere as heat.

• Of that 50% lost heat, 35% is lost through the sidewall. Sidewall heat loss is critical to ensure a protective side ledge is maintained.

• Cells are designed to operate at a pre-determined heat balance. Any deviation from the designed heat balance can lead to severe overheating or freezing.

• Due to this restriction the operating window (amperage and voltage range) of a modern cell is quite small and inflexible.

• Not being able to reduce amperage quickly with low risk has meant that some smelters quickly become non-profitable when metal price is low and power prices increase

• Some smelters are unable to respond quickly and adequately to changes in electricity supply.

Increasing air flow

Increases HTC

More heat removed

Enables Power Input to be increased above design

Decreasing air flow

Decreases HTC

Less heat removed (Insulates)

Enables Power Input to be reduced below design

EnPot allows hourly, daily, weekly or seasonal power modulation

• Smelters can vary their energy consumption both up and down for an indefinite period of time (and as a consequence the rate of aluminium production will vary correspondingly), while at all times maintaining the delicate heat balance required for stable, efficient pot operation.

Low Profitability Scenario

High Profitability Scenario

Short Term Variable Profitability Scenario

Unpredictably Variable Profitability Scenario

Challenges of Modulation:process, logistics, people• Smelters like to keep things constant

• Short term disruption = within operating “buffer”• Alumina feeding – pot control• Fume volume to gas treatment• Anode changing schedule• Tapping schedule – casthouse throughput – push to pull

– how to accommodate push again• Personnel

• Long term disruption = outside of operating “buffer”• Alumina supply• Coke supply• Anode production• Personnel

What do we need to solve?

• ? When to modulate• ?? How much to modulate• ??? How long to modulate

• Integration with the energy grid = optimisation opportunity

• Long term disruption – outside of operating “buffer”= optimisation opportunity

+ what is the benefit of the modulation- what is the downside of reoptimized operations= overall $ impact to plant performance

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Curtailment

Charging

Discharging

Wind

Solar

Dispatchable

Demand

Transforming the world of aluminium smelting• ENABLE POWER MODULATION

• Quickly change cell power input by as muchas ± 20-30% for periods ranging from hoursto months

• Integrating aluminium smelters intorenewables-friendly energy grids

• OPTIMISE OPERATING PERFORMANCE• superior heat balance control

• ENABLE CAPACITY CREEP• Remove excess heat

EnPot installation at EssenAir based, heat exchanger units are custom designed to fit any cell.

• Suction fans are used to draw air through the exchanger units. Control of the air flow through the exchangers, controls the heat transfer coefficient (HTC) at the shell wall.