Code of Practice to reduce emissions of PM2.5 from aluminium sector: glossary

Official title: Code of practice to reduce emissions of fine particulate matter (PM_2.5) from the aluminium sector

Glossary

Aluminate

A compound containing aluminium, sodium and oxygen that is found in Bayer liquor in a precipitated or dissolved state,  following bauxite digestion.

Anode butt

Residue of prebaked anode (comprising the rod, cast iron, carbon residue and cryolite bath crust) following consumption in the electrolytic cell.

Anode cover material

Solid mix of alumina and crushed cryolite bath used to cover prebaked anodes after installation in the electrolytic cell. Also used to plug holes in the crust.

Anode effect

Phenomenon causing a sudden increase in voltage and decrease in amperage in electrolytic cells due to the presence of a gas film on the surface of the anode.

AQMS

Canadian policy on air quality management.

Baghouse

Type of dust collector that uses filtering bags to capture particles contained in gas.

Bath/electrolytic bath

Molten liquid at a temperature of around 960°C composed primarily of aluminium fluoride (AlF ₃) and cryolite (Na ₃AlF ₆).

Bauxite

Ore varying in structure which is composed predominantly of aluminium oxides, iron and silicon.

Bayer process/liquor

Process for the alkaline extraction of alumina contained in bauxite which uses Bayer liquor (concentrated sodium hydroxide solution). It involves preparing and digesting bauxite, red mud settling, crystallization and precipitation of aluminate, and calcining of hydrated alumina.

Boehmite/gibbsite

Polymorphic aluminium oxides (AlO(OH), Al(OH) ₃) that make up bauxite.

Busbar

Low impedance conductor bars to which the electrical circuits of the electrolytic cells are attached.

Calcined coke

A form of petroleum coke that has undergone calcining. Primary raw material of green/prebaked anode.

Casting centre

Facility in an aluminium production plant where liquid aluminium from electrolytic cells is transformed into a semi-finished solid product.

Casting machine

System used to transform molten aluminium into ingots, according to the required specifications.

Carbon dust

Dust that accumulates in the cryolite bath and is generated primarily by prebaked anodes.

Coal tar

By-product of coal coking or gasification.

Crushed frozen bath

Crushed cooled cryolite bath, or a crushed mixture of cryolite, alumina and carbon recovered from anode butts.

Crust

Solidified bath and alumina mix covering the cryolite bath in electrolytic cells.

Cryolite

Main chemical compound (Na ₃AlF ₆) of the cryolite bath in electrolytic reduction cells that reduces the melting temperature of aluminium.

Dry scrubber

Gas cleaning system consisting of several vertical reactors into which an adsorbent (calcined coke or alumina) is injected.

Dust collector

Processing unit designed to capture most particles contained in gas.

Enriched alumina

Alumina that has been used in the GTC or FTC to capture fluorinated gas. It is enriched with fluorides.

Feeder/breaker

Automated system that feeds metallurgical grade alumina into electrolytic cells using a breaker that breaks the crust before injecting the alumina into the liquid bath.

FTC

Treatment system for combustion gases from the baking furnace. Composed of a dry scrubber with alumina injection followed by a dust collector.

Green (petroleum) coke

Product derived from the delayed coking of refined crude oil.

Green anode

Compact block formed from green paste, which is a mixture  of calcined coke and tar pitch.

Green paste (facility)

Section of the prebaked anode production plant that produces green anode paste, a mix of calcined coke and tar pitch.

Grit blasting

Technique for cleaning a surface that involves blasting abrasives against anode butts to break off cryolite bath residue.

GTC

Treatment system for gases from aluminium production (electrolytic reduction) cells. It consists of a dry scrubber with alumina injection followed by a dust collector.

Hard gray scale

Amorphous solid product consisting of alumina, cryolite and water which accumulates on the inner walls of some ducts in a GTC or FTC using an alumina injection system.

Hydrated alumina

A form of alumina chemically bound to water molecules (Al ₂O ₃∙xH ₂O).

Induction furnace

Furnace in which the heat required to melt metal is supplied through induction between two electric coils.

LMRC

Light Metals Reserach Centre: research and consultation centre in Auckland, New Zealand that studies the smelting of aluminium, magnesium and other light metals.

Metallurgical grade alumina

A form of alumina containing very few or no water molecules (Al ₂O ₃).

Packing coke

Calcined coke inserted into baking furnace pits with green anodes to protect them against oxidation by the combustion air, and to promote good heat exchange.

PFTC

Treatment system for pitch fumes from the green paste facility. It consists of a dry scrubber with calcined coke injection followed by a dust collector.

Potroom

Building in which electrolytic cells connected in series are operated.

Pyroscrubber

Cleaning system for gases from the calcining of green coke that incinerates volatile organic compounds.

Red mud

Solid by-product of the Bayer process containing mainly iron oxides as well as aluminium, silicon, titanium, sodium and calcium oxides.

Sealed prebaked anode

Final product of prebaked anode production consisting of one or two blocks of anodes attached by means of cast iron to a rod that conducts electric current. The anodes are used in electrolytic reduction pots.

Sealing facility

Area of the prebaked anode production plant where carbon blocks are attached to rods that conduct electric current.

Self-ignition

Occurs when the energy necessary for calcining comes from green coke alone, without an external fossil fuel.

Söderberg process

Electrolytic reduction process that uses carbon briquettes (or paste) and is characterized by in situ baking in the electrolytic cell.

Superstructure

Electrolytic cells, doors, hoods and the system that extracts gas to the GTC.

Tap hole

Opening in the crust through which molten aluminium or cryolite bath is extracted from the pot.

Tar pitch

By-product of the distillation of coal tar which is used as a binder in the production of green anode paste.

Under-calcined coke

By-product of coke recovered by dust collectors from calcining gas released from the green coke calciner.

Venturi wet scrubber

Gas cleaning system that atomizes wash water, thereby improving particle capture.