1. Why aluminium HVAC is its own engineering discipline
The Australian aluminium industry is unique in this country's heavy-industrial portfolio. Four operating smelters — Tomago Aluminium at Tomago NSW (around 600,000 t/yr, Rio Tinto and Hydro Aluminium and CSR joint venture, the largest single aluminium smelter in Australia), Boyne Smelter at Gladstone QLD (around 600,000 t/yr, Rio Tinto-led joint venture, Australia's largest in Queensland), Bell Bay Aluminium at Bell Bay TAS (around 184,000 t/yr, Rio Tinto, the smallest of the four but the oldest, in operation since 1955) and Portland Aluminium at Portland VIC (around 360,000 t/yr, Alcoa) — collectively produce around 1.7 Mt/yr of primary aluminium, consume roughly 14 percent of Australia's total grid electricity, and run more than 1,200 Hall-Héroult electrolysis cells distributed across roughly fifteen kilometres of potline buildings. Upstream, six operating alumina refineries (Wagerup, Pinjarra and Kwinana in WA under Alcoa, Worsley Alumina in WA under BHP-led joint venture with Mitsubishi, Idemitsu and Yankuang, Yarwun in QLD under Rio Tinto and Queensland Alumina QAL in QLD under Rio Tinto and Rusal) produce around 19–21 Mt/yr of smelter-grade alumina, making Australia the world's largest exporter of alumina. Further upstream, Weipa bauxite (Cape York QLD, Rio Tinto, the world's largest single bauxite operation), Gove bauxite (Nhulunbuy NT, Rio Tinto), Worsley Alumina bauxite (Boddington WA, BHP joint venture), Bauxite Hills (NT, Metro Mining) and the Pinjarra-Wagerup-Huntly bauxite mines (WA, Alcoa) feed the refineries with around 100 Mt/yr of bauxite ore.
The combined HVAC load across this value chain is enormous, and it is fundamentally different from the steel mill and smelter scope we have covered in our companion Steel Mill and Smelter HVAC Duct Guide. Where a steel mill's HVAC challenge is dominated by sheer flue volume and primary off-gas temperature, an aluminium plant's challenge is dominated by a single chemistry: fluorine. Hydrogen fluoride from the Hall-Héroult bath, hydrogen fluoride from spent potlining, fluoride dust in the cryolite preparation room, fluoride condensate at every cold spot in the gas-collection main — fluorine is the corrosion driver that pushes the entire downstream duct system into 316L stainless and that drives the engineering specifications for hooding, scrubbing and stack discharge. Underneath that sits the second chemistry: sodium hydroxide in the Bayer process, where 4 M caustic at 240°C and 4 MPa dissolves alumina from bauxite, and where every flange, every fan, every condensate sump and every operator pulpit must be engineered against caustic-mist attack on carbon steel and galvanised steel.
Six characteristics make aluminium HVAC its own discipline. First, the corrosion environment is dominated by hydrogen fluoride on the smelter side and sodium hydroxide caustic mist on the refinery side, both of which destroy carbon steel and galvanised steel inside months, and both of which push duct construction into 316L stainless as the workhorse material. Second, the dust environment combines non-combustible alumina at the smelter charging end with combustible carbon anode coke and pitch dust at the anode plant — and the alumina, while inherently inert, is fine enough (D50 around 80–100 µm with up to 10 percent below 45 µm in modern sandy SGA) to flow freely through duct systems and create housekeeping headaches at every horizontal run. Third, the temperature gradient at the Hall-Héroult cell is staggering — molten cryolite bath at 950–980°C, off-gas at 100–140°C after the hood, alumina feed at ambient — and the duct system must accommodate the thermal swing from cold start-up through steady operation through hot anode-change events. Fourth, the perfluorocarbon emissions during anode effects (CF4 and C2F6) are extremely potent greenhouse gases (CF4 has a global warming potential of 6,500 and C2F6 of 9,200, against CO2 baseline of 1), and modern Australian smelters operate with anode-effect frequency below 0.1 per pot per day to keep PFC emission inside their state EPA licence — but when an anode effect does occur, the off-gas chemistry shifts abruptly and the duct system carries highly reactive species for minutes at a time. Fifth, the operator working environment is severe — pot tappers, anode setters and cast-house operators work within metres of 950°C molten cryolite and 700°C molten aluminium, in summer ambient temperatures that exceed 40°C at Gladstone and 35°C at Portland — and operator pulpit cooling, crane cabin air-conditioning and refrigerated spot-cooling are not optional comforts but mandatory engineering controls under Safe Work Australia heat-stress guidance. Sixth, the electrical infrastructure is enormous — a single potline draws 350–400 kA DC at around 1,000–1,200 V, delivered by rectifier substations that themselves have transformer-cooling and switchgear-room HVAC loads of 20–50 MW thermal — and the rectifier-room HVAC is its own significant scope with mineral-oil-mist capture and SF6 leak detection requirements.
This guide walks the complete value chain from bauxite mine to cast house, explains what changes at each station from an HVAC ductwork perspective, and identifies where SBKJ standard machinery covers the scope and where heavy welded fabrication takes over. We have shipped SBKJ duct fabrication machinery to fabricators serving aluminium projects in Australia, the Gulf, Southern Africa and South America since the mid-1990s, and the recurring theme is the same: the project economics live or die on whether the fabricator can run 316L stainless reliably at production tempo, with seam integrity good enough to pass leakage testing under AS 4254 high-pressure construction the first time.
2. The Australian regulatory stack — AS 1668.2, AS 4254, AS/NZS 60079, NFPA 660, NFPA 86 and the Aluminium Council
Aluminium HVAC in Australia sits at the intersection of more regulatory documents than almost any other industrial sector. The compliance question on every project is not whether one standard applies — they all apply — but how the layered requirements interact across the gas-collection main, the dry scrubber, the pulpit HVAC and the stack discharge.
2.1 AS 1668.2 — mechanical ventilation for buildings
AS 1668.2:2012 (Mechanical ventilation in buildings — Mechanical ventilation for acceptable indoor-air quality) sets the building-services baseline for occupied spaces. In an aluminium smelter or refinery this drives the outdoor-air rate at every pulpit, crane cabin, control room, electrical room, laboratory, amenity block and administration building. The standard requires 10 L/s per occupant minimum outdoor air for typical office and control-room occupancy, with higher rates for kitchens, change rooms, toilets and showers. Where AS 1668.2 matters most on a smelter project is the pulpit pressurisation requirement: it sets the engineering basis for the 25–50 Pa positive pressure that prevents pot-room fluoride and dust ingress into the operator cabin. The make-up air requirement layered on top of LEV — every cubic metre extracted from a pot room must be balanced by tempered outdoor make-up air — drives total smelter HVAC ductwork volume up by a factor of two compared with a building of equivalent floor area but no process exhaust.
2.2 AS 4254 — ductwork construction
AS 4254.1 (Flexible ductwork) and AS 4254.2 (Rigid ductwork) are the Australian duct construction standards that govern gauge, joint type, pressure class and reinforcement spacing. For aluminium smelter HVAC the typical pressure class is medium-pressure on supply and return runs (up to 750 Pa static), high-pressure on dry scrubber bypass and main collection duct (up to 2,500 Pa static), and ultra-high-pressure on the negative side of the ID fan upstream of the stack. The standard sets out the leakage class requirements (Class A, B, C) that drive the fabrication tolerance — SMACNA Class B equivalent for general HVAC, Class C for fluoride and Bayer scrubber-side ducting where leakage of corrosive gas to the surrounding building is unacceptable. AS 4254.2 also drives the duct joint specification: TDF (T-Drive Flange) or AS angle flange for galvanised and 304L medium-pressure; continuous seam-welded flange or full-perimeter gasket compression for 316L scrubber-side high-pressure.
2.3 AS 1530.4 — fire-resistant ductwork
AS 1530.4 (Methods for fire tests on building materials, components and structures) classifies fire-resistant duct construction for smoke-spill and stair-pressurisation duty. Aluminium plants have significant fire-load zones — anode butt storage with petroleum coke and pitch residues, cast house holding furnace area with molten metal, cable trench beneath rectifier substations, LPG fuel-supply rooms for bake furnaces — and the duct passing through these zones must be rated for the specified fire-resistance level (typically 60/60/60 to 120/120/120 minutes of structural integrity, insulation and integrity). AS 1851 (Routine service of fire-protection systems and equipment) overlays the maintenance requirements for fire dampers, smoke-spill dampers and motorised dampers along the route.
2.4 AS/NZS 60079 and IEC 60079 — explosive atmospheres
AS/NZS 60079 (Explosive atmospheres) and the underlying IEC 60079 series classify hazardous areas where flammable gas, vapour or combustible dust can reach explosible concentration. Aluminium plants have multiple Zone classifications: Zone 1 (gas, present in normal operation) around chlorine degassing rooms in the cast house, Zone 2 (gas, present only abnormally) around LPG-fired bake furnace and calciner fuel-supply trenches, Zone 21 (dust, present in normal operation) around anode paste plant mixers and butt cleaning stations, Zone 22 (dust, present only abnormally) around alumina charging conveyors and red mud filter cake transfer. The classification drives Ex-rated electrical equipment requirements for fans, motors, instrumentation, lighting and switchgear, and it drives bonding and grounding of every duct segment to prevent static-discharge ignition of combustible dust.
2.5 AS 4332 and AS 1604 — gases and timber treatment chemistry
AS 4332 (Storage and handling of gases in cylinders) and AS 1604 (Specification for preservative treatment) overlap the chlorine handling at the cast house degassing unit and the cryolite handling at the smelter — both standards reference the Australian Standard Dangerous Goods Code and drive the segregation, labelling and ventilation requirements for the relevant storage rooms. Chlorine bulk storage at the cast house typically requires its own dedicated extract system with caustic scrubber discharge, sized to evacuate a worst-case cylinder rupture within fifteen minutes.
2.6 AS 1940 — flammable and combustible liquids
AS 1940 (The storage and handling of flammable and combustible liquids) drives the LPG, mineral oil and process diesel storage requirements. Aluminium smelters use significant volumes of mineral oil for rectifier transformer cooling, hydraulic fluid for cell anode lifting and DC casting pit hydraulics, and process diesel for backup generators. Each storage area is a hazardous-area zone under AS/NZS 60079 and requires AS 1940-compliant ventilation, bunding and spill containment.
2.7 AS 3580 — boundary air quality
AS 3580 (Methods for sampling and analysis of ambient air) is the methods standard for compliance monitoring against state EPA Environmental Protection Licence (EPL) limits. NSW EPA, Queensland Department of Environment, Science and Innovation, EPA Tasmania, EPA Victoria and Western Australia DWER all set boundary fluoride, SO2, PM10, PM2.5 and total VOC limits at the smelter property line; the stack discharge from the dry scrubber must be sized so that the resulting ground-level concentration meets the EPL limits under worst-case meteorological dispersion. AS 1318 (Industrial chimneys) provides the structural design basis for the stack itself.
2.8 AS 3957 — dust hazard
AS 3957 (Methods of test for the resistance of materials to abrasion) and the related AS 1141 aggregate testing series underpin the dust-hazard classification at the bauxite mine and the anode coke handling. Bauxite is a hard, abrasive ore with Mohs hardness around 1–3 for the gibbsite and boehmite fractions but with significant silica and titania contamination — and at Weipa, Gove and Boddington the run-of-mine material moves through crushing, screening and drying stages where dust loading and abrasion both drive duct selection.
2.9 NFPA 660 (formerly NFPA 484) — combustible dust
NFPA 660 (Standard for Combustible Dusts), which consolidated NFPA 484, NFPA 652, NFPA 654, NFPA 655, NFPA 664 and NFPA 61 into a single combined standard from 2025, is the de-facto engineering reference for combustible-dust handling globally and is referenced extensively by Australian aluminium-industry insurance underwriters. The standard mandates a written Dust Hazard Analysis (DHA) at every dust-handling step, deflagration venting or chemical suppression on bag filters and cyclones, isolation dampers between the baghouse and the upstream duct trunk to prevent flame propagation, bonded and grounded duct construction with electrical continuity verified by bonding test, spark-resistant fan construction per AMCA 99-0401, and Ex-rated electrical equipment in the dust zone. On Australian aluminium plants NFPA 660 applies to the green anode mix building, the paste plant, the butt cleaning area, the cryolite preparation room, the spent potlining (SPL) handling area and the cast house aluminium dust capture (Class D combustible metal). Aluminium dust itself, when fine and dry, is a Class D combustible metal under NFPA 660 — water reacts violently with hot aluminium dust and wet collection requires careful engineering with inert gas blanketing.
2.10 NFPA 86 — industrial ovens and furnaces
NFPA 86 (Industrial Ovens and Furnaces) governs the gas-fired bake furnace, calciner, holding furnace and any LPG-fired oven inside the aluminium plant. It dictates the exhaust topology — lower explosive limit (LEL) monitoring on combustion air, purge cycles before lighting, explosion venting on the oven shell, dedicated stack risers separate from general extract, and fuel-piping segregation from the building service main.
2.11 ASHRAE Applications Chapters 16 and 35
ASHRAE Handbook Applications Chapter 16 (Industrial Power Generation) and Chapter 35 (Industrial Drying) provide the international engineering reference for the rectifier substation cooling loads and the calciner exhaust design respectively. The Australian Aluminium Council and International Aluminium Institute publish good-practice notes that overlay the ASHRAE reference with Australian-specific guidance.
2.12 The Aluminium Council and International Aluminium Institute
The Australian Aluminium Council (AAC) is the industry body representing the four Australian smelters and six alumina refineries. The International Aluminium Institute (IAI) publishes Best Available Techniques references for fluoride control, perfluorocarbon mitigation, energy efficiency and worker health that inform Australian smelter operations. The Aluminium Stewardship Initiative (ASI) provides the third-party sustainability certification that downstream automotive and packaging customers increasingly require, and the EU IPPC Best Available Techniques Reference Document for Non-Ferrous Metals Industries provides the European good-practice benchmark that Australian smelters voluntarily approach as part of their continuous-improvement programmes.
3. Bauxite mining, crushing, screening and drying
The aluminium value chain starts at the bauxite mine — an open-pit operation with dragline, hydraulic shovel or front-end loader fleets, run-of-mine bauxite haulage to a primary crusher, secondary crushing and screening to a target size distribution, and either direct shipment to an alumina refinery (Weipa, Gove, Bauxite Hills) or in-pit processing including washing and beneficiation before refinery feed (Boddington). Weipa is the world's largest single bauxite operation, producing around 35 Mt/yr from the Andoom, East Weipa and Amrun mines on the western Cape York peninsula, with shipping out of Weipa port via Mitchell Avenue or via the new Amrun export terminal. Gove produces around 13 Mt/yr from the Nhulunbuy operation under Rio Tinto, with shipping out of the Gove port to alumina refineries in Asia and historically into the (now decommissioned) Gove refinery itself. Worsley Alumina's Boddington bauxite mine produces around 18 Mt/yr feeding the Worsley refinery via the world's longest single-flight overland conveyor (51 km). Alcoa's Huntly and Willowdale bauxite mines feed Pinjarra and Wagerup respectively via shorter conveyor systems.
HVAC scope on a bauxite mine is dominated by dust extract. Primary crushing produces airborne dust at the rod-mill or hammer-mill discharge, secondary crushing produces fines, screening generates dust at every transfer point, and rotary drying (where bauxite is dried from 8–15 percent free moisture to 2–4 percent before refinery feed at WA operations) generates significant heat plus dust. The Safe Work Australia workplace exposure standard for respirable inhalable dust is 10 mg/m³ TWA with respirable fraction at 3 mg/m³ TWA, and the respirable crystalline silica limit at 0.05 mg/m³ TWA applies to the silica-bearing fraction in the bauxite. Dust capture at every transfer point is mandatory under AS 1668.2 and the state-level mining occupational health regulator (NSW Resources Regulator, DMIRS WA, NT Worksafe, Queensland Resources Safety and Health).
Duct material at the bauxite mine is typically galvanised carbon steel for the cold-side dust mains, with abrasion-resistant linings (chromium-carbide overlay or ceramic-bead lining) at elbows and tee-junctions where bauxite particle impact angle exceeds 30 degrees. Transport velocity in dust mains is 18–22 m/s; capture velocity at the hood is 0.5–1.0 m/s. The dryer exhaust runs at 120–180°C with 10–15 percent moisture, and material selection on the dryer stream is mild steel with paint corrosion allowance for the cold side and refractory-lined steel for the hot side near the dryer outlet. Bag filters or cyclone-plus-bag-filter combinations handle the particulate; discharge is to a stack designed under AS 1318 with continuous PM10 monitoring per AS 3580 and state EPA EPL conditions.
SBKJ SBAL-V and SBTF cover the cold-side galvanised dust mains and the building-services HVAC at the crusher building, screening tower, dryer building, control room, electrical room, workshop and amenity blocks. Abrasion-resistant ducting is procured separately from specialist wear-plate fabricators. SBKJ spark-resistant fan supply covers the bauxite handling extract per NFPA 660 — bauxite itself is non-combustible but iron-oxide tramp metal and organic contamination drive the spark-resistant fan specification on every bauxite-handling baghouse.
4. The Bayer process — alumina refining
The Bayer process is the chemical heart of an alumina refinery and the most chemically demanding HVAC environment in the Australian aluminium value chain. Karl Josef Bayer's 1888 patent describes the route: bauxite is digested with sodium hydroxide at elevated temperature and pressure, producing sodium aluminate solution which is filtered, cooled, seeded with aluminium hydroxide crystals, and precipitated. The precipitated aluminium hydroxide is washed, dewatered and calcined at 1,000–1,100°C to produce smelter-grade alumina (SGA, Al2O3). The bauxite residue — red mud — is the major waste stream and is disposed of in engineered residue storage areas (RSAs).
4.1 Bauxite grinding, predesilication and digestion
Run-of-mine bauxite at WA refineries (Wagerup, Pinjarra, Kwinana, Worsley) is wet-ground in rod or ball mills to a slurry, which is mixed with spent caustic liquor and pumped through preheaters into the digestion train. Australian Bayer plants operate primarily on the high-temperature route (240–280°C, 4–5 MPa) for high-temperature digestion of boehmite-rich bauxite, or the low-temperature route (140–160°C, 0.5–0.8 MPa) for gibbsite-rich bauxite. Wagerup, Pinjarra and Kwinana operate at the low-temperature end (Alcoa's WA bauxite is gibbsite-dominated), while Worsley operates closer to the high-temperature end. Yarwun in QLD operates at the high-temperature end on Weipa boehmite-rich bauxite.
The digestion vessels themselves are pressurised — the HVAC scope here is the local exhaust at flash tanks, slurry pump glands, vent valves, sample points and any flash steam release. Caustic-mist loading at these points is significant — 20–100 mg/Nm³ NaOH mist before mist eliminators — and the duct service is 316L stainless, sloped to condensate drain, with mist eliminators (mesh pad or chevron) sized to drop concentration below the Safe Work Australia WES of 2 mg/m³ NaOH at the building extract point. The flash steam recovered from the digester let-down is recovered into the live-steam ring main and is not a direct HVAC scope, but the building ventilation around the flash tank platform must extract residual caustic mist and ammonia at the slurry-pump glands and clarifier overflow.
4.2 Mud separation and washing
The digested slurry is separated in primary settlers (high-rate decanters or settling thickeners) where the alumina-bearing liquor decants and the bauxite residue (red mud) settles to the underflow. The mud underflow is then washed in counter-current washer trains to recover entrained caustic before disposal to the red mud residue storage area. The mud washer hall is the largest building in many Bayer refineries — Worsley has a multi-storey washer house with 4–6 washer stages.
HVAC scope in the mud separation and washing area is caustic-mist extract at every washer overflow launder, every flash-steam vent and every slurry-pump gland. The chemistry is alkaline (pH 12–13) with NaOH mist, ammonia from organic decomposition (bauxite contains 0.1–0.5 percent organic carbon which forms humates and oxalates in caustic solution), sulphide carry-over (from the sulphate-reducing organics) and water vapour. Material selection is 316L stainless for gas-contact duct, with sloping floors and condensate-drain sumps at every low point. Building-services HVAC at the mud washer hall control room and amenity block is conventional galvanised steel with 25–50 Pa positive pressure to keep caustic mist outside the operator cabin.
4.3 Liquor security filtration and seed precipitation
The clarified pregnant liquor is filtered to remove residual mud fines (security filtration) and then cooled and seeded with aluminium hydroxide crystals in precipitation tanks. Precipitation is the rate-controlling step in the Bayer process — large agitated tanks operate at 60–80°C with seed crystals that grow over 60–80 hours into product-size hydrate (D50 50–100 µm).
The precipitation tank farm is open or hooded, with caustic-mist evolution at the agitator boil. The mist loading is lower than at digestion (mist mostly water vapour with dissolved NaOH and aluminium hydroxide carry-over) but the volume of air to be extracted is enormous — a typical 2 Mt/yr refinery has 40–80 precipitation tanks each 4,000–8,000 m³ working volume, with hood extract velocities of 0.5–1.0 m/s at the hood face. Material is 316L stainless for the gas-contact duct, sized to AS 4254 medium-pressure construction. The precipitation tank hooding is one of the largest single HVAC scope items on a Bayer refinery project, and the duct length runs into the kilometres.
4.4 Hydrate classification, washing and filtration
The precipitated aluminium hydroxide is classified to separate product-size hydrate (which goes to calcination) from seed-size hydrate (which is recycled to the precipitator). Classification is typically by gravity in tray classifiers, hydrocyclones or settling thickeners; washing is by counter-current decantation; filtration to remove residual liquor before calcination is on rotary vacuum filters or pan filters. HVAC scope follows the precipitation tank pattern — caustic-mist extract at every classifier overflow, hood extract at every washer launder, vacuum-receiver vent capture at the rotary filter — with 316L stainless gas-contact duct and condensate drain points at every low spot.
4.5 Calcination — hydrate to alumina
The washed hydrate is calcined at 1,000–1,100°C to drive off the chemically bound water (2 Al(OH)3 → Al2O3 + 3 H2O) and produce smelter-grade alumina. Modern Australian refineries use circulating-fluid-bed calciners (Outotec or Hatch-licensed) or gas-suspension calciners (FLSmidth GSC) which are significantly more energy-efficient than the older rotary kilns. The calciner is the single largest gas-flow point in a Bayer refinery — flue gas at the calciner outlet runs at 200–300°C after the cyclone heat-recovery train, with residual particulate (alumina carry-over) at 100–500 mg/Nm³ before the dry electrostatic precipitator or fabric filter, plus combustion products (CO2, H2O, NOx, residual SO2 from sulphur-bearing organic carbon) and water vapour driven off from the hydrate. Volumetric flow at the calciner exhaust on a 1 Mt/yr calciner train is 200,000–400,000 Nm³/h.
Duct material on the calciner side is refractory-lined carbon steel from the calciner discharge to the heat-recovery cyclone exit, 309S/310S austenitic stainless from the cyclone exit to the ESP/fabric filter (250–350°C service), and 316L stainless from the dust collector outlet through the ID fan to the stack (140–180°C condensing service). The calciner duct is heavy welded fabrication procured separately from specialist boiler-and-pressure-vessel contractors; SBKJ scope on calcination is the building-services HVAC (calciner operator pulpit, ESP control room, electrical room, instrumentation room).
4.6 Boiler house, evaporators and live-steam ring main
A Bayer refinery is one of the most steam-intensive industrial plants in operation — every digester pass requires 2–4 tonnes of steam per tonne of alumina product, and the total steam demand on a 2 Mt/yr refinery exceeds 1,500 t/h. The boiler house is sized accordingly: typically natural gas-fired (Wagerup, Pinjarra, Kwinana, Worsley) or coal-fired (Yarwun has its own captive coal-fired boilers) with multiple 200–400 t/h steam generators feeding a live-steam ring main. The boiler house HVAC scope is conventional industrial — boiler combustion air supply (galvanised steel duct, sized for the burner combustion-air fan curve), flue-gas duct from the boiler economiser outlet through the ID fan to the stack (carbon steel with refractory-lined hot section, transitioning to 316L stainless on the cold side at 140–180°C condensing-acid service from residual SO2), boiler-house building ventilation (galvanised steel return air and supply, 8–12 air changes per hour to handle heat-soak from boiler walls), turbine-hall ventilation (where the refinery cogenerates electricity from let-down steam), and instrumentation-and-control-room air-conditioning. The boiler house operates under AS 4036 and AS 4037 (Boilers and pressure equipment) for the pressure parts and NFPA 86 for the combustion side.
Evaporators between the digester and precipitator handle the water balance — recovering water from the spent liquor and concentrating the caustic for return to the digesters. The evaporator hall is a major caustic-mist source with 316L stainless local extract at every vapour body vent, condenser hot-well, and demister bypass. Volumetric flow at evaporator extract is 30,000–80,000 Nm³/h per evaporator train.
4.7 Red mud disposal
Red mud (bauxite residue) is the major Bayer waste stream — typically 1.0–2.0 tonnes per tonne of alumina product, with composition dominated by iron oxide (30–60 percent), aluminium oxide (10–20 percent), silica (3–15 percent), titanium dioxide (2–10 percent), residual caustic (0.5–5 percent as Na2O) and various trace elements. Australian refineries dispose of red mud in engineered residue storage areas (RSAs) — typically dry-stacked mud or filter-cake stacked behind containment bunds. Pinjarra and Wagerup use a dry-stacking approach with rotary vacuum filters and conveyor transfer to the RSA; Worsley uses thickened tailings disposal; Yarwun uses a combination.
HVAC scope in red mud disposal is the residue filter building extract (caustic mist at filter cake transfer, sized to keep building NaOH below WES of 2 mg/m³), residue conveyor cover ventilation, and RSA approach road dust suppression (which is process-side, not HVAC). Material selection is 304L stainless for filter-cake transfer hood extract, with 316L for any liquor-contact surfaces.
4.8 Bayer HVAC summary
The Bayer process HVAC scope on a typical 2 Mt/yr Australian alumina refinery (Wagerup, Pinjarra, Worsley, Yarwun, QAL scale) is in the order of 20–40 km of 316L stainless ductwork plus 15–25 km of galvanised carbon steel building-services ductwork. SBKJ SBAL-V auto duct line in 316L mode, SBSF-1525 round-duct flanging in 316L, and SB-ZF1500 stitchwelder for continuous-seam scrubber housings cover the 316L scope. SBTF spiral tubeformer covers round galvanised return-air and supply runs. The SBPC1500 plasma cutter handles 316L cut-to-length parts; the SBLR-600 welder handles site repairs on stainless seam welds. The heavy welded calciner duct and evaporator vapour-body extract are heavy fabrication procured separately.
5. Carbon anode plant — green mix, paste, bake furnace and butt cleaning
Every prebake aluminium smelter (Tomago, Boyne Island, Bell Bay, Portland — all four Australian smelters operate prebake technology rather than the older Söderberg self-baking anode route) needs a carbon anode plant to manufacture the consumable carbon anodes used in the Hall-Héroult electrolysis cells. The anode plant is the single most complex HVAC environment in the smelter, combining combustible coke dust, polycyclic aromatic hydrocarbon (PAH) fume from coal tar pitch, high-temperature bake furnace flue gas, and fluoride contamination from the butt cleaning area where used anode butts are recycled.
5.1 Green anode mix and paste plant
Green anodes are formed by mixing calcined petroleum coke with coal-tar pitch binder at 150–180°C, plus recycled crushed anode butts as filler material. The paste plant is a hot operation — Eirich-type intensive mixers or continuous Buss kneaders at 170–200°C deliver the homogenised paste to vibratory compactors or hydraulic presses that form green anodes typically 1,000–1,800 mm long, 700–1,300 mm wide and 500–700 mm tall (mass 800–1,500 kg per anode depending on smelter generation).
HVAC scope in the green mix building is dominated by petroleum coke dust capture at the coke silo discharge, dust extract at the conveyor transfer points, paste plant mixer extract (PAH and pitch volatiles), and forming press hood extract (residual PAH plus volatile aromatics from the hot paste). The Safe Work Australia approach to benzo[a]pyrene as the PAH marker is conservative (the German MAK guidance of 0.002 mg/m³ is widely adopted in Australian smelter compliance programmes), and the paste plant extract is the largest single PAH source at the smelter. A dedicated regenerative thermal oxidiser (RTO) or thermal oxidiser destroys the PAH at the extract terminal point before discharge to atmosphere, with capture efficiency above 95 percent.
Duct material from the mixer extract through to the RTO inlet is 316L stainless — pitch-fume condensation on the cold side of any galvanised or carbon-steel duct creates a tarry deposit that contaminates the HVAC system within weeks and is extremely difficult to remove. The 316L surface keeps cleaner because pitch fume condenses but doesn't bond as tightly as it does to porous galvanised zinc. Capture velocity at the mixer hood is 1.0–1.5 m/s; transport velocity in the duct main is 18–22 m/s with steam tracing or electric trace heating to keep the duct above the pitch dew point (typically 80–110°C) and avoid condensation buildup.
5.2 Anode bake furnace
The green anodes are loaded into the open-top bake furnace and baked at 1,100–1,200°C for around 14 days in a closed-loop combustion-air recirculation system. The Riedhammer ring furnace and the KHD ring furnace are the two dominant designs globally; modern Australian smelters operate ring furnaces with 30–80 fire sections (pits) arranged in a closed loop, with the fire travelling around the loop in a 2–3 week cycle. Heating is by LPG or natural gas burners; the bake furnace exhaust runs through a regenerative thermal oxidiser to destroy the residual volatiles, then through an alumina-injection dry scrubber to capture residual fluorides (from any fluoride contamination in the recycled butts), and finally through a wet scrubber for SO2 and residual particulate before discharge to atmosphere.
Duct material on the hot side from the furnace exit to the RTO inlet is refractory-lined carbon steel (650–800°C service). From the RTO outlet to the dry scrubber inlet is 309S/310S austenitic stainless (250–350°C). From the scrubber outlet to the stack is 316L stainless (140–180°C condensing service — water vapour from combustion plus residual HF make this an aggressive condensing acid environment). The hot-side bake furnace duct is heavy welded fabrication procured separately; SBKJ scope is the cold-side 316L duct after the wet scrubber.
5.3 Anode butt cleaning and recycling
Spent anodes (anode butts) are returned from the potline with residual cryolite bath (Na3AlF6 + AlF3 + CaF2) frozen onto the carbon surface and with a fluoride content that is recycled back into the bath. The butt cleaning area uses mechanical shot blast, chiselling or thermal cleaning to remove the bath layer for recycling; the cleaned carbon butt is then crushed and recycled into the green mix as filler.
HVAC scope at butt cleaning is fluoride dust extract (the bath layer dust is 30–60 percent fluoride content, with the Safe Work Australia WES at 2.5 mg/m³ as F TWA being the driver), with a small but significant SO2 component from the carbon. The duct material is 316L stainless to handle the fluoride dust corrosivity; capture velocity at the cleaning station is 1.0–1.5 m/s with hooded enclosure. The cleaning area is typically Zone 22 under AS/NZS 60079 (combustible carbon dust, present only abnormally), and the fans are spark-resistant per NFPA 660.
5.4 Anode rodding bay
Baked anodes are rodded — the steel anode stem (called a "yoke" or "rod") is cast or thiotropically welded onto the carbon block using either thimble casting (molten cast iron poured around the rod-to-anode joint) or stub-to-carbon thermoset bonding. The rodding bay is a cast-iron foundry within the anode plant: induction-melted cast iron is poured at 1,400°C around the four to six stubs of the anode rod, producing significant fume from the cast iron melt (iron oxide, silicon dioxide, carbon monoxide) and from the carbon-iron interface burn-off.
HVAC scope at the rodding bay is foundry-grade fume capture — refer our companion Foundry HVAC Duct Guide for the engineering treatment. Duct material is refractory-lined carbon steel for the hot-side primary capture, 309S/310S stainless after the spark arrestor, and 316L stainless after the wet scrubber. Spark-resistant fans per NFPA 660 are mandatory.
5.5 Anode storage and yard handling
Finished baked anodes are stored in a covered yard awaiting transfer to the potline. Storage area HVAC is light-duty galvanised dust extract at the anode handling crane track, with low capture velocity (0.5–1.0 m/s). Anode transfer to the potline runs along covered conveyors with dust extract sized for the residual coke fines.
5.6 Anode plant HVAC summary
The carbon anode plant HVAC scope on a typical 600,000 t/yr Australian smelter (Tomago, Boyne Island scale) is 12–20 km of 316L stainless cold-side duct, 4–8 km of refractory-lined carbon steel hot-side bake furnace flue duct (heavy fabrication, separate), and 8–15 km of galvanised carbon steel building-services HVAC. SBKJ SBAL-V auto duct line in 316L mode, SBSF-1525 round-duct flanging, SB-ZF1500 stitchwelder and SBPC1500 plasma cutter cover the 316L scope. Spark-resistant fans per NFPA 660 are mandatory across the entire anode plant.
6. The Hall-Héroult potline — the heart of every aluminium smelter
The Hall-Héroult electrolysis process is the heart of every aluminium smelter and the most demanding single HVAC environment in the entire Australian industrial sector. Charles Martin Hall (USA) and Paul Héroult (France) independently invented the process in 1886, and the basic chemistry has been essentially unchanged for 140 years: alumina (Al2O3) is dissolved in molten cryolite bath (Na3AlF6) with aluminium fluoride (AlF3) and calcium fluoride (CaF2) additions, and direct current at 350–400 kA passes from a consumable carbon anode through the bath to a carbon-lined cathode at the cell bottom. The anode reaction (2 O²⁻ + C → CO2 + 4 e⁻) consumes the anode and produces CO2; the cathode reaction (Al³⁺ + 3 e⁻ → Al) deposits molten aluminium that pools at the cell bottom and is tapped every 32–36 hours.
Modern prebake cells operate at 950–980°C bath temperature, draw 350–400 kA at around 4.0–4.3 V cell voltage, and produce 2,500–3,500 kg of aluminium per cell per day. A 600,000 t/yr smelter (Tomago, Boyne Island) runs around 700 cells distributed across three to four potlines each 800–1,200 m long; a 360,000 t/yr smelter (Portland) runs around 400 cells across two potlines; the 184,000 t/yr Bell Bay smelter runs the smallest cell count.
6.1 Cell hooding and gas collection
Each cell is hooded — typically a fold-down side hood, an end hood at the anode bus end and a top hood that lifts for crust-breaking and alumina feeding. The hood capture efficiency is the single most important HVAC engineering parameter on the entire smelter: modern Australian smelters operate at 95+ percent hood collection efficiency, with the residual 5 percent escaping as fugitive emission into the pot-room above and exiting via roof ventilation. The hooded gas is drawn through a large central duct main running along the potline at roof level, feeding the dry scrubber and the ID fan.
Hooded gas leaves the hood at 100–140°C carrying hydrogen fluoride (HF) at 200–1,000 mg/Nm³ before the dry scrubber, sub-micron alumina from charging, sulphur dioxide from the petroleum coke and pitch in the anode, carbon particles (anode dusting), and perfluorocarbons (CF4 and C2F6) from anode effects. The volumetric flow per cell is typically 10,000–15,000 Nm³/h depending on cell amperage and hood design; total flow on a 240-cell potline is 2,400,000–3,600,000 Nm³/h. The main duct cross-section is enormous — 2,400–4,000 mm diameter on the largest mains, with branch ducts of 800–1,500 mm diameter feeding each cell or pair of cells.
Duct material is 316L stainless, 1.5–3.0 mm wall, fabricated to AS 4254 high-pressure construction with continuous-seam welded flanges or compressed-gasket flange joints. The main duct is heavy welded fabrication procured separately from specialist plate-roll-and-weld contractors — the section sizes exceed the SBKJ SBAL-V envelope. The branch ducts and the dry scrubber bypass duct sit within the SBAL-V 1,500 mm × 1,500 mm rectangular envelope and the SBSF-1525 1,525 mm round flanging envelope, and SBKJ machinery covers this scope.
6.2 Dry sorbent injection scrubber
The dry sorbent injection (DSI) scrubber is the workhorse of modern Hall-Héroult fluoride control. The potline gas is mixed with fresh smelter-grade alumina (SGA) at 200–600 kg per tonne of aluminium produced; the alumina chemisorbs HF onto the particle surface as aluminium oxyfluoride. The fluoride-loaded alumina is then collected in a fabric-filter baghouse with 99.5+ percent particulate removal efficiency, and the reacted alumina is recycled back to the potline as cell feed, returning the captured fluorine to the bath as a closed-loop fluoride balance. Total fluoride emission to atmosphere is reduced from 30 kg F per tonne of aluminium (uncontrolled) to under 0.5 kg F per tonne (modern DSI). The DSI is supplied by specialist licensors (Solios, Procédair, FLSmidth Airtech) and integrated by EPC contractors (Worley, Bechtel, Hatch).
The DSI duct between the cell hood and the baghouse is 316L stainless; the duct from the baghouse to the ID fan is 316L stainless; the duct from the ID fan to the stack is 316L stainless. Total DSI duct length on a 600,000 t/yr smelter is in the order of 25–40 km of 316L. The wet scrubber stage that some smelters operate downstream of the DSI for additional SO2 removal (using seawater or caustic scrubber liquor) introduces a wet condensing duct service from the wet scrubber outlet to the stack — also 316L with full condensate drainage.
6.3 Pot-room roof ventilation
Approximately 5 percent of the cell off-gas escapes hood capture as fugitive emission, mixing with the air in the pot-room above the cell line. This fugitive load combined with the heat radiation from the cells (each cell radiates 50–100 kW of waste heat through the hood and side walls into the pot-room) drives the pot-room roof ventilation requirement: a stack-effect-driven exit stream at the roof ridge, with optional axial-flow boosters for low-wind conditions. The pot-room is one of the largest single industrial buildings on any Australian site — Tomago's Potline 1+2+3 buildings are around 1,000 m long each. The roof ventilator design is structural-engineering-led with HVAC support; SBKJ scope is the operator pulpit air supply, the crane cabin air-conditioning and the pot-room makeup air at floor level.
6.4 Operator pulpits, crane cabins and pot tending machines
Pot tappers, anode setters and beam crane operators work inside positive-pressure cabins that are the single most engineering-critical operator-protection elements in the entire smelter. Pulpit pressurisation specification: 25–50 Pa positive pressure relative to the pot-room ambient, 100 percent outdoor air through a G4 pre-filter + F7 bag filter + H13 HEPA + activated-carbon train (carbon stage targeting HF and SO2 adsorption, alumina-impregnated carbon increasingly used for fluoride-specific service), redundant N+1 chilled-water or DX cooling rated for the local Australian ambient design (35°C at Gladstone, 32°C at Tomago, 28°C at Bell Bay, 32°C at Portland), and emergency back-up ventilation on UPS power for at least 30 minutes of fan operation during loss of grid supply.
Crane cabin HVAC sits inside the same envelope — pressurised, HEPA-filtered, air-conditioned, with the added challenge that the cabin moves with the crane (so flexible duct supplies hot/cold air to the cabin from a fixed plant on the crane structure). Pot tending machine cabs (PTM, the machines that crust-break and feed alumina along the cell line) likewise.
Duct material for pulpit supply is galvanised steel for the outdoor air intake and supply duct (clean air side), with 304L stainless at the intake plenum where outdoor air entrains nearby smelter discharge plume in worst-case wind reversal conditions. This is squarely SBKJ scope — SBAL-V auto duct line for rectangular pulpit supply duct, SBTF spiral tubeformer for round return-air runs, SBSF-1525 round-duct flanging for connection to the AHU.
6.5 Cell charging, anode change and tapping
The cell is fed alumina periodically through point-feeders that punch through the bath crust and inject 1–2 kg of alumina per shot, typically 60–80 shots per cell per day. The anodes are changed on a rotation cycle — each cell has 16–24 anodes depending on cell generation, with each anode replaced every 25–30 days (cell life) on a daily change cycle. Tapping draws molten aluminium from the cell bottom into a crucible truck every 32–36 hours.
HVAC scope on the cell deck (the elevated operating floor where the anode setter and tapping crane operate) is dominated by the hooded gas extract and the pot-room roof ventilation already discussed. Spot cooling of operator working positions during anode change and tapping is provided by refrigerated supply-air showers at the elevated cell-deck operating positions, with flexible duct from a fixed pulpit AHU.
6.6 Crucible truck and molten metal transfer
Tapped molten aluminium at 850–900°C is transferred from the cell to the cast house in crucible trucks (typically 10–20 tonne capacity ladles on dedicated rail or wheeled chassis). The crucible truck route is enclosed in a tunnel or covered way for fume capture and pedestrian safety. HVAC scope is heat extract along the route and at the cast house ladle receiving station — galvanised steel duct sized for 60–80°C extract air, with refractory-lined transition at the ladle exposure points. Material is galvanised for the cold side, 304L for the hot transition.
7. The cast house — DC casting, rod mill, holding furnace and degassing
The cast house is the smelter's downstream finishing operation: molten aluminium from the potline is transferred to holding furnaces, treated (degassing, fluxing, grain refining), and cast into the product form required by the customer — slab for hot rolling mills, billet for extrusion presses, sow ingot for export, or wire rod for cable manufacturers. Each Australian smelter operates an integrated cast house: Tomago cast house produces extrusion billet and rolling slab, Boyne Smelter cast house produces sow and ingot for export, Bell Bay cast house produces small rolling slab and ingot, Portland cast house produces extrusion billet and rolling slab.
7.1 Holding furnace
The holding furnace is an intermediate buffer between the potline tapping cycle and the casting cycle. Reverberatory or stack-melter design, gas-fired, 200–500 tonne capacity, operating at 720–760°C with continuous skimming of dross. Fume chemistry is dominated by aluminium oxide (Al2O3) from the molten surface oxidation, with secondary alkaline halide fume from any flux additions (typically NaCl-KCl-CaF2 fluxes for slag cleaning), and combustion products from the burner. The Safe Work Australia WES for aluminium oxide fume is 5 mg/m³.
Capture velocity at the furnace door (during skimming and tapping operations) is 1.5–2.5 m/s; transport velocity in the main is 18–22 m/s. Duct material is refractory-lined carbon steel for the first 3–5 m above the hood (1,000°C service during the open-door skim), 309S/310S stainless from 800°C down to 500°C, 304L from 500°C to 250°C, and galvanised carbon steel below 250°C. SBKJ scope is the cold-side galvanised mains; the hot side is heavy welded fabrication.
7.2 Degassing unit
Molten aluminium contains dissolved hydrogen at 0.1–0.4 cm³ per 100 g of metal, which produces gas porosity in the final casting if not removed. Degassing is by rotary or in-line gas-purging units (Foseco SNIF, Foundry Service degassers, FCS units), where chlorine gas (Cl2) and inert nitrogen are sparged through the metal in a sealed reaction vessel. The chlorine reacts preferentially with magnesium, sodium, calcium and lithium impurities to form chloride salts that float to the top as a removable dross; nitrogen carries the dissolved hydrogen out of the bath.
HVAC scope at the degasser is exhaust capture of the chlorine off-gas — the unreacted Cl2, hydrogen chloride (HCl) from any reaction with moisture, and the metal chloride salt vapour. This is a Zone 1 hazardous area under AS/NZS 60079 (chlorine present in normal operation), with a caustic scrubber (NaOH solution) downstream to neutralise the chlorine before stack discharge. Duct material is 316L stainless or Hastelloy C-22 (the chlorine + hydrogen chloride mix is more aggressive than fluoride alone) from the degasser exhaust to the scrubber inlet, with 316L stainless from the scrubber outlet to the stack.
SBKJ SBAL-V in 316L mode covers the cold-side degasser duct after the scrubber; the hot-side chlorine duct is heavy welded specialist fabrication.
7.3 DC casting (slab and billet)
Direct-chill (DC) casting is the dominant cast house technology: molten aluminium is poured into a water-cooled copper or graphite mould, where it solidifies on contact with the chilled surface, and is continuously withdrawn downward into a casting pit as a long slab (for rolling) or billet (for extrusion) below 4–8 m. The casting speed is typically 50–100 mm/min depending on alloy and section size.
HVAC scope at the DC casting pit is mould lubrication fume capture (the mould is lubricated with castor oil or proprietary release agents; the burn-off at the mould-metal interface generates aerosol mist), pit ventilation (significant heat release at the solidifying metal surface), and water-vapour management from the cooling water spray. Material is galvanised carbon steel for the general pit ventilation; 304L stainless at the mould lubrication fume capture hood.
The DC casting pit itself is a Zone 22 hazardous area for combustible aluminium dust (fine swarf from saw cutting of the cast slabs and billets after withdrawal). NFPA 660 applies — spark-resistant fans, bonded ductwork, and inert-gas suppression on the dust collection bag filter. Aluminium dust + water is a violent reaction (formation of hydrogen gas), so wet collection requires careful engineering.
7.4 Rod mill (continuous casting for wire rod)
Some Australian smelters (Tomago has historically operated a rod mill) produce aluminium wire rod for the cable industry via continuous casting and rolling: the molten aluminium is cast through a Properzi or SCR wheel-and-belt caster into a continuous bar that is hot-rolled inline to wire rod of 9.5–25 mm diameter, then coiled.
HVAC scope at the rod mill is heat extract at the caster, rolling mill stand cooling and oil mist capture, and coiler heat extract. Material is galvanised carbon steel for the general ventilation; 304L for the oil-mist coalescer extract. Spark-resistant fans on any aluminium dust capture.
7.5 Cast house HVAC summary
The cast house HVAC scope on a 600,000 t/yr Australian smelter (Tomago, Boyne Island scale) is 8–15 km of mixed galvanised steel and 304L stainless ductwork, plus 2–4 km of 316L for the chlorine degasser side. Operator pulpit and control room HVAC is conventional galvanised steel. SBKJ SBAL-V auto duct line and SBTF spiral tubeformer cover the bulk of the cast house scope. Refer also our companion Foundry HVAC Duct Guide for the casting-pit fume engineering treatment, which carries directly across from iron and steel foundries.
8. Rectifier substation and DC supply
The single largest industrial DC electrical load in Australia is the aluminium smelter rectifier substation. Each potline draws 350–400 kA DC at around 1,000–1,200 V cell-line voltage, which is supplied from a rectifier transformer-rectifier set sized at 280–400 MW per potline. A 600,000 t/yr smelter with three potlines therefore has 800–1,200 MW of installed DC supply — Tomago is around 1,000 MW grid demand, Boyne Smelter is around 900 MW, Portland is around 600 MW, Bell Bay is around 300 MW. These are individually larger electricity consumers than many Australian cities.
8.1 Rectifier transformer cooling
The rectifier transformer is the largest single piece of electrical plant in the smelter — typically 200–400 MVA with mineral-oil immersed core and windings. Cooling is forced-oil air-cooled (OFAF) with external fin-tube oil coolers, or oil-water cooling with a cooling tower for water rejection. The transformer hall HVAC scope is general ventilation for heat-soak (the oil cooler radiators reject several MW into the substation building), mineral-oil mist capture at the transformer breather and conservator (a small but persistent oil-mist generation at the breather seal), and SF6 leak detection per IEC 62271-4 on any SF6-insulated switchgear.
8.2 Rectifier hall
The rectifier hall houses the silicon-controlled rectifier (SCR) thyristor cabinets that convert the transformer secondary AC to the DC supply to the potline. Modern rectifiers are typically water-cooled at the thyristor stack — closed-loop deionised water — with a secondary heat-rejection cooling tower outside the building. Hall HVAC is heat extract for the residual radiated load (typically 1–3 percent of throughput) plus light positive-pressure ventilation to keep dust out of the thyristor cabinets.
8.3 DC cooling tower
The rectifier secondary cooling tower rejects 20–50 MW of waste heat to atmosphere. Water mist drift from the cooling tower is itself an HVAC capture point — operator buildings downwind of the tower need positive-pressure intake with filtered makeup air to prevent water mist ingress.
8.4 Rectifier substation HVAC summary
Total rectifier substation HVAC scope is 4–8 km of galvanised carbon steel duct on a 600,000 t/yr smelter. SBKJ SBAL-V auto duct line and SBTF spiral tubeformer cover the entire scope.
9. Cryolite preparation, spent potlining and waste handling
The cryolite preparation room maintains the bath chemistry on the potline: cryolite (Na3AlF6), aluminium fluoride (AlF3) and calcium fluoride (CaF2) are added as needed to maintain the bath ratio (the molar ratio of NaF to AlF3, typically 1.0–1.2 in modern cells), and used cryolite recovered from spent potlining (SPL) is processed and recycled. The room is a Zone 22 hazardous area under AS/NZS 60079 for combustible carbon dust (recycled bath layer contains residual carbon), with fluoride dust exposure as the dominant occupational hygiene driver.
HVAC scope is dust extract at every silo, conveyor and dosing station, sized to keep working zone fluoride below the Safe Work Australia WES of 2.5 mg/m³ as F. Material is 316L stainless throughout; spark-resistant fans per NFPA 660; bonded and grounded ductwork.
Spent potlining (SPL) is the carbon and refractory waste from cell relining — when a cell reaches end of life (typically 5–7 years), the cell is taken offline, the carbon cathode and refractory side-wall are demolished and removed for processing, and the cell is relined with fresh carbon and refractory. SPL contains residual cyanide (from carbon-bath reactions over the cell life), fluorides (around 10–15 percent), sodium and aluminium oxide. SPL is classified as a hazardous waste under Australian state regulations and is processed by specialist contractors (Regain Materials in WA, Befesa internationally) for cyanide destruction and fluoride recovery. The SPL processing area HVAC scope is hooded dust extract with caustic scrubber discharge — 316L throughout.
10. Worker amenity, change rooms and showering
Aluminium smelter operators work in a contaminated environment — fluoride dust, alumina, sometimes pitch and coke residues, and trace metal exposure from the cast house. Worker amenity blocks must include contamination-management facilities: dirty-side change rooms, mandatory showering before clean-side change, and laundering of contaminated workwear on-site.
HVAC scope is conventional comfort cooling for the clean-side amenity (offices, canteen, control rooms, training centre, medical centre) with full filtered outdoor air, and an extract-only dirty-side amenity (shoe-stripping bench, primary change room, shower) that maintains negative pressure relative to the clean side. The flow direction is one-way — clean air enters at the clean-side, passes through the worker boundary, and is extracted through the dirty-side to the smelter discharge. This prevents fluoride and alumina contamination from migrating into office and administration zones.
Total amenity scope on a typical 600,000 t/yr smelter is 4–6 km of galvanised steel ductwork. SBKJ SBAL-V and SBTF cover the entire scope.
11. SBKJ machine recommendation for the aluminium HVAC market
The SBKJ machinery configuration for an Australian aluminium plant project — whether new build, expansion or planned shutdown duct replacement — is built around 316L stainless steel as the workhorse material, with secondary capability for galvanised and 304L. The recommended machine list:
11.1 SBAL-V auto duct line — 316L mode
The SBAL-V auto duct line is SBKJ's flagship rectangular duct production line. The machine handles galvanised steel, stainless steel and aluminium up to 1,500 mm width and 3.0 mm wall thickness, with TDF, AS angle flange and drive cleat joint configurations. For Australian aluminium plant service the machine is supplied in 316L mode: dual-roll forming station configured for 316L work-hardening characteristics, hardened forming tooling, dedicated 316L coil reel, and PLC programme for AS 4254 high-pressure construction tolerance. This is the machine that fabricates the bulk of the rectangular HVAC duct across the pulpit, control room, electrical room, rectifier hall, amenity and general workshop scope on Tomago, Boyne Island, Bell Bay and Portland projects.
11.2 SB-ZF1500 automatic stitchwelder
The SB-ZF1500 automatic stitchwelder is the critical machine for stainless scrubber housing fabrication. The Bayer process digester local extract housings, the precipitator hood housings, the calciner ESP housings, the dry scrubber bypass plenums, the chlorine degasser scrubber sections — all require continuous-seam stainless steel welds to AS 4254 Class C leakage tolerance, and the SB-ZF1500 is the production machine that fabricates these housings at tempo. The machine handles up to 1,500 mm seam length per pass, 316L or 304L stainless, 1.0–3.0 mm wall thickness, with TIG or plasma welding heads.
11.3 SBSF-1525 round-duct flanging
The SBSF-1525 round-duct flanging machine (and the closely related SB-FS1535L variant) covers the round-duct termination, flange forming and connection scope on round 316L scrubber bypass, return-air runs and Bayer process round mains. The machine handles up to 1,525 mm diameter round duct and is the natural complement to the SBTF spiral tubeformer for round duct production.
11.4 SBTF spiral tubeformer
The SBTF series spiral tubeformer handles round duct production from 80 mm to 2,020 mm diameter (SBTF-1500, SBTF-1500C, SBTF-1602 and SBTF-2020 covering the size range), in galvanised steel, 304L, 316L and aluminium. Round duct dominates the return-air and supply-air scope across the smelter — pulpit supply, crane cabin flexible duct connection, amenity ventilation, control room supply — and the SBTF series produces this scope at high tempo with locked-seam construction to SMACNA and AS 4254 standards.
11.5 SBPC1500 plasma cutter
The SBPC1500 plasma cutter handles 316L stainless steel sheet cutting up to 1,500 mm width and up to 6.0 mm thickness for fittings, transition pieces, branch take-offs and custom cut-to-length parts. Plasma cutting of stainless requires the correct plasma gas (typically air or nitrogen, with H35 argon-hydrogen for thicker sections) and the SBPC1500 is configured for the 316L workload at Australian aluminium plant tempo.
11.6 SBLR-600 welder
The SBLR-600 welder is a manual or semi-automatic TIG/MIG welder for site repairs, custom fittings and seam-weld touch-up on stainless scrubber housings. Smelter site repair work (a flange seam failure, a damaged fitting after a shutdown, a custom duct branch added during commissioning) is bread and butter for this machine.
11.7 Spark-resistant fan supply per NFPA 660
Every fan in the anode plant, the cryolite preparation room, the spent potlining processing area, the green mix building, the paste plant, the butt cleaning area and the cast house aluminium dust extract must be spark-resistant under NFPA 660. SBKJ supplies fans built to AMCA 99-0401 Type B (non-ferrous impeller in steel housing) or Type C (non-sparking bronze rubbing rings) construction, with ATEX/IECEx certification for Zone 21/22 dust service.
11.8 ATEX/IECEx motors for Zone 1 and Zone 2 gas areas
The cryolite preparation room (Zone 22 dust + occasional combustible carbon vapour), the chlorine degasser cabin (Zone 1 chlorine), the LPG bake furnace fuel-supply trench (Zone 2), and the perfluorocarbon-affected anode-effect zone (occasional Zone 2 PFC for short minutes) all require Ex-rated motors. SBKJ supplies Ex de IIB T4 or Ex eb IIC T4 motors as the standard configuration for these zones, with ATEX certification matched to the buyer's specified zone classification.
12. Project economics — cost, schedule and risk
An Australian aluminium plant HVAC project — whether new smelter (unlikely in the current decade given electricity cost pressure on Australian smelters), refinery expansion, anode plant replacement, cast house upgrade or potline relining shutdown duct refurbishment — runs to AUD 30–150 million in HVAC duct fabrication and installation, depending on scope. The bulk of the cost is labour and material (316L coil is the largest single material cost driver, currently around AUD 6,000–9,000 per tonne for the gauge ranges typical in HVAC service), with machinery capital amortised over the project and successor work.
Schedule typically runs 18–36 months from initial scoping through detailed design, procurement, fabrication, installation and commissioning. SBKJ machinery lead time of 16–28 weeks from PO to commissioning sits inside this overall schedule and is rarely on the critical path provided procurement is initiated at the right phase.
The principal risk on Australian aluminium projects is electricity supply: every smelter project's commercial viability is sensitive to wholesale electricity price, and the Tomago renegotiation of its supply contract (concluded 2024 with a multi-year supply agreement) and the Portland Aluminium long-term arrangement set the precedent for the industry. From an HVAC perspective the implications are: a smelter shutdown for electricity-cost reasons creates a brownfield maintenance scope (potline duct refurbishment, scrubber overhaul, baghouse replacement) that is a steady source of HVAC project work. A smelter restart creates a major HVAC project. The Australian Aluminium Council and the operators publish capacity-curtailment and restart announcements periodically and these are the leading indicator for the HVAC work pipeline.
13. Worked example — a 240-cell potline expansion at a hypothetical 200,000 t/yr increment
To make the SBKJ machinery selection concrete, consider a hypothetical 240-cell potline expansion adding 200,000 t/yr of primary aluminium to an existing Australian smelter (a Tomago Potline 4 thought-experiment, or a Boyne Smelter potline upgrade). The HVAC scope:
- Hooded gas collection main — 240 cells × 12,000 Nm³/h = 2,880,000 Nm³/h. Main duct 3,000 mm diameter × 1,200 m length, 316L stainless, 3.0 mm wall — heavy welded fabrication, procured from specialist plate-roll-and-weld contractors. Out of SBAL-V envelope.
- Branch ducts from cell hood to main — 240 branches × 800 mm diameter × 8 m length, 316L stainless, 1.5 mm wall — total around 1,920 m. Within SBSF-1525 envelope. SBKJ scope.
- Dry scrubber bypass duct — 1,800 mm × 1,200 mm rectangular, 316L stainless, 2.0 mm wall, 400 m length. Within SBAL-V envelope (1,500 mm side). Some sections exceed envelope and split with longitudinal flanged joint. SBKJ scope.
- Pulpit HVAC supply and return — 24 pulpits across the potline, each with 4,000 m³/h supply at 100 percent outdoor air. Total 96,000 m³/h supply. Galvanised steel rectangular and round, 1.0 mm wall, 8 km total length. SBAL-V and SBTF scope.
- Crane cabin HVAC — 12 cranes (3 per potline × 4 potlines, plus the new potline 4) with flexible duct connection to fixed AHU on each crane. 304L flexible duct 250 mm diameter × 400 m total.
- Control room HVAC — central potline control room plus 3 sub-stations, total 25,000 m³/h supply. Galvanised steel rectangular, 1.5 km length. SBAL-V scope.
- Rectifier substation HVAC — new rectifier hall 280 MW capacity, 60,000 m³/h supply for transformer hall heat extract. Galvanised steel rectangular and round, 2.5 km length. SBAL-V and SBTF scope.
- Cast house HVAC (incremental) — additional holding furnace fume extract, DC casting pit ventilation, degasser scrubber duct. Mix of galvanised, 304L and 316L, 3 km total. SBAL-V scope.
- Anode plant HVAC (incremental) — additional green mix capacity, butt cleaning station, anode storage. 316L stainless, 4 km. SBAL-V (316L mode) scope.
- Amenity and admin (incremental) — new pot-room locker rooms, shower blocks, training centre. Galvanised steel, 1.5 km. SBAL-V scope.
Total SBKJ scope: around 22 km of mixed material rectangular and round HVAC duct. Total non-SBKJ scope (heavy welded main collection duct, refractory-lined bake furnace flue, ESP and baghouse housings procured packaged): around 18 km. The SBKJ machinery package for this project would be: one SBAL-V auto duct line (316L mode, with galvanised secondary capability), one SBTF-1602 spiral tubeformer, one SBSF-1525 round-duct flanging machine, one SB-ZF1500 stitchwelder, one SBPC1500 plasma cutter, and one SBLR-600 welder. The buyer's fabrication shop running this configuration with a single shift can complete the 22 km scope in 18–24 months — production rate around 1.0–1.4 km per month at a sustained tempo.
14. Related Australian aluminium downstream and integrated industries
Beyond the primary aluminium value chain itself, the downstream and adjacent industries that frequently overlap with the smelter project HVAC scope:
- Aluminium extrusion — Capral Aluminium ASX:CAA at Bremer Park QLD, plus a network of smaller extruders. Refer our Window, Door and Aluminium Joinery Manufacturing HVAC Duct Guide for the extrusion press HVAC engineering treatment.
- Aluminium rolling — historically Capral's Erskine Park NSW operations and the export sheet from the Australian smelters' cast houses. Hot rolling and cold rolling mill HVAC sits inside the Steel Mill and Smelter HVAC Duct Guide envelope.
- Aluminium re-melt and recycling — secondary aluminium production from scrap. Refer the Foundry HVAC Duct Guide for the re-melt furnace HVAC treatment.
- Power supply — every Australian smelter has dedicated power supply arrangements (Tomago from the NSW grid via Liddell historically, Boyne Smelter from Gladstone Power Station and Stanwell, Bell Bay from Hydro Tasmania, Portland from the Victorian grid via Mortlake). The on-site rectifier substation HVAC is in this guide; the supply-side coal-fired or gas-fired generation is in our Coal and Gas Power Plant HVAC Duct Guide.
- Cement and lime supply — alumina refineries are major lime consumers (for liquor causticisation). Refer the Cement Plant HVAC Duct Guide for the lime kiln HVAC treatment.
15. Industry bodies, EPC contractors and equipment suppliers
The Australian aluminium project ecosystem revolves around a manageable list of EPC contractors and specialist equipment suppliers:
- EPC and engineering — Worley ASX:WOR (Brisbane-headquartered, the largest single EPC for Australian smelters and refineries), Bechtel Australia (Perth, oil and gas plus selected smelter work), Hatch Australia (Brisbane, mining and metals specialist), KBR Australia, Mott MacDonald.
- Smelter operators — Rio Tinto Aluminium (Aluminium Pacific HQ Brisbane, operates Tomago JV interest, Boyne Smelter, Bell Bay, Weipa, Gove, QAL JV interest, Yarwun), Alcoa World Alumina (Alcoa Inc and Alumina Limited JV, operates Portland, Pinjarra, Wagerup, Kwinana, Huntly and Willowdale mines), Hydro Aluminium (Tomago JV partner), BHP (Worsley Alumina JV).
- Fluoride control and dry scrubber licensors — Solios (Fives Group), Procédair (Group Lhoist), FLSmidth Airtech, Andritz.
- Anode plant licensors — Riedhammer ring furnaces (now part of Sacmi), KHD ring furnaces, Outotec paste plants.
- Calciner licensors — Outotec (Metso Outotec) circulating fluid-bed calciners, FLSmidth gas-suspension calciners, Hatch licensed designs.
- Industry bodies — Australian Aluminium Council (AAC), International Aluminium Institute (IAI), Aluminium Stewardship Initiative (ASI), Bauxite Alumina Industry Coordinating Committee.
16. SBKJ commitment to the Australian aluminium industry
SBKJ Group is headquartered at Box Hill North VIC with engineering, sales and after-sales support staffed locally and reachable by Australian business hours (sales@sbkjduct.com, +61 435 074 994). Our engineering team has experience commissioning duct fabrication lines on aluminium projects across multiple jurisdictions, and we hold critical spares (316L flange dies, plasma consumables, welder electrodes, TDF rollers) in Victorian stock for same-week despatch to Tomago, Boyne Island, Bell Bay, Portland, Wagerup, Pinjarra, Kwinana, Worsley, Yarwun and QAL.
Our Australia presence is closely aligned with the Australian Aluminium Council operating members and with the major EPC contractors. We exhibit at ARBS 2026 in May at the Melbourne Convention and Exhibition Centre (stand 236 — operated by our Australian entity Australia Ducting Pty Ltd), and our engineers attend the annual Australian Aluminium Council technical conference and the AAC's Aluminium Stewardship Initiative working groups.
Every aluminium project we quote is reviewed by our senior engineering team before pricing is released — the difference between a 304L and a 316L specification is the difference between a fluoride scrubber duct that fails in 18 months and one that lasts 15 years, and we have seen the consequences of getting that decision wrong on competitor-supplied work that we have later been called in to replace.
Frequently asked questions
Why is 316L stainless steel mandatory for aluminium smelter fluoride scrubber and Bayer process ductwork?
Two of the most aggressive corrosion environments in Australian heavy industry sit inside the aluminium value chain. On a Hall-Héroult potline the off-gas leaves the hood at 100–140°C carrying hydrogen fluoride (HF) at 200–1,000 mg/Nm³ before the dry scrubber, sub-micron alumina dust, sulphur dioxide and perfluorocarbons (CF4 and C2F6) from anode effects — and after the dry sorbent injection the gas still contains residual HF, water vapour and reactive alumina. Carbon steel pits within months in this service, and even 304L stainless can develop pitting around chloride contamination from sea-air ingress at Tomago, Boyne Island, Bell Bay and Portland. On an alumina refinery the Bayer process operates 4 M NaOH caustic liquor at 240°C and 4 MPa inside the digesters, with caustic mist and ammonia carried into the local exhaust at the precipitation tanks, evaporators and red mud washers — exactly the conditions where 316L molybdenum-stabilised austenitic stainless outperforms 304L by a factor of 5–10 in service life. The SBKJ recommendation for both services is 316L (UNS S31603) duct fabricated on the SBAL-V auto duct line in 316L mode, joined by continuous TIG seam welding on the SB-ZF1500 stitchwelder for scrubber housings, and flanged to AS 4254 high-pressure construction.
What is the HVAC scope on a typical Australian aluminium smelter project?
A 600,000 t/yr Australian aluminium smelter such as Tomago Aluminium NSW or Boyne Smelter Gladstone QLD will run 250–400 Hall-Héroult cells distributed across three to four potline buildings each 800–1,200 m long. Total HVAC ductwork scope is typically 80–150 km, distributed across the potline hooded gas collection main and dry scrubber bypass ducts, carbon anode plant green mix dust extract and bake furnace flue duct, cast house heat extract and degassing fume capture, rectifier substation cooling, pulpit and operator control room positive-pressure HVAC, electrical room and cable trench ventilation, maintenance workshop welding fume capture, administration and amenity block conditioning, and boiler house combustion air and flue gas duct. SBKJ standard machinery covers the pulpit, control room, cast house comfort, amenity, electrical room and general workshop scope, plus the 316L scrubber bypass and Bayer-side ducts that fall within the SBAL-V 1,500 mm and SBSF-1525 1,525 mm rolling envelopes.
What does NFPA 660 require for aluminium smelter combustible dust?
NFPA 660 (Standard for Combustible Dusts), which consolidated the former NFPA 484, NFPA 652, NFPA 654, NFPA 655, NFPA 664 and NFPA 61 into a single combined standard in 2025, governs the design of dust-collection systems handling combustible particulates including fine aluminium dust, carbon anode coke dust, alumina (Al2O3 powder is non-combustible itself but acts as inert with coke contamination), and red mud carry-over. The mandatory engineering controls are: hazard analysis (Dust Hazard Analysis or DHA) for every dust-handling process, deflagration venting or chemical suppression on baghouses and cyclones, isolation dampers and chemical isolation valves between baghouse and upstream duct, bonded and grounded duct construction, spark-resistant fan construction per AMCA 99-0401, explosion-rated electrical equipment in the dust zone per AS/NZS 60079.10.2, conductive ducting and a written ignition-source control programme. SBKJ supplies spark-resistant fans and conductive 316L duct construction that complies with both the dust-explosion zoning and the corrosive-atmosphere service in a single machine package.
How is the Bayer process digester and red mud area ventilated?
The Bayer process is the chemical heart of an alumina refinery: bauxite is digested with 4 M sodium hydroxide at 240°C and 4 MPa, producing sodium aluminate liquor which is filtered, precipitated as aluminium hydroxide, and calcined to smelter-grade alumina (SGA). The HVAC challenge centres on caustic mist and ammonia vapour at the digester slurry pumps, flash tanks, precipitation thickeners, classifier seal pots, red mud washers and rotary vacuum filters. The exhaust at these sources is 60–95°C, 80–100 percent relative humidity, contains NaOH mist at 2–20 mg/Nm³, plus ammonia from organic decomposition, and condenses freely back to liquid alkaline solution if duct surfaces fall below saturation temperature. Material selection is 316L stainless for the gas-contact duct, with sloping floors and condensate drain points at every low spot, sized to AS 4254 medium-pressure construction. The pulpit and control-room HVAC serving the operator zones around digesters runs 100 percent outdoor air through HEPA + activated-alumina filtration at 25–50 Pa positive pressure to keep caustic mist outside the cabin.
What HVAC standards apply to carbon anode prebake plants?
Carbon anode prebake plants operate at the intersection of NFPA 86 (industrial ovens and furnaces), AS/NZS 60079 (hazardous atmospheres for coke dust and coal tar pitch volatiles), the Safe Work Australia workplace exposure standard for benzo[a]pyrene as a marker for total polycyclic aromatic hydrocarbons (PAH), and AS 4254 for the building-services HVAC. A modern Riedhammer or KHD-type ring furnace bakes green carbon anodes at 1,100–1,200°C in a closed-loop combustion-air recirculation system, producing flue gas at 200–300°C after the regenerative thermal oxidiser (RTO) and dry scrubber. The flue gas contains residual PAH, sulphur dioxide from petroleum coke and pitch, fluorides from green anode butts, dust and water vapour. Material selection for the bake furnace flue is refractory-lined carbon steel from the furnace exit to the RTO inlet, 309S/310S austenitic stainless from the RTO outlet to the scrubber inlet, and 316L stainless from the scrubber outlet to the stack.
How does the dry scrubber alumina-injection system work on a Hall-Héroult potline?
The dry sorbent injection (DSI) scrubber is the workhorse of modern Hall-Héroult fluoride control. The potline gas collected from the hooded cells leaves the hood at 100–140°C carrying hydrogen fluoride (HF) at 200–1,000 mg/Nm³, sub-micron alumina from charging, carbon particles, sulphur dioxide and perfluorocarbons. This stream is mixed with fresh smelter-grade alumina (SGA) injected at 200–600 kg per tonne of aluminium produced; the alumina has an enormous specific surface area (60–80 m²/g for sandy SGA) and chemisorbs HF onto the particle surface as aluminium oxyfluoride. The fluoride-loaded alumina is then collected in a fabric-filter baghouse with 99.5+ percent particulate removal efficiency, and the reacted alumina is recycled back to the potline as cell feed, returning the captured fluorine to the bath as a closed-loop fluoride balance. Total fluoride emission to atmosphere is reduced from 30 kg F per tonne of aluminium (uncontrolled) to under 0.5 kg F per tonne (modern DSI).
What does Safe Work Australia require for fluoride exposure in pot rooms?
Safe Work Australia's Workplace Exposure Standards for Airborne Contaminants set the legal upper limit for operator exposure to fluoride compounds in aluminium pot rooms: hydrogen fluoride (HF) at 1.8 mg/m³ TWA and 4.1 mg/m³ short-term exposure limit (STEL), total fluorides as F at 2.5 mg/m³ TWA. Aluminium oxide (as Al2O3 alumina dust) is set at 10 mg/m³ inhalable and 3 mg/m³ respirable, with aluminium oxide fume from molten metal at 5 mg/m³. Sulphur dioxide at 2 ppm TWA, carbon monoxide at 30 ppm TWA, and respirable crystalline silica at 0.05 mg/m³. These limits are met through hooded gas collection at the cell, pot-room roof ventilation by combined stack effect and mechanical extract, operator pulpit pressurisation at 25–50 Pa positive pressure with HEPA + activated carbon filtration, and crane cabin air-conditioning with the same filter train. SBKJ SBAL-V auto duct line + SBSF-1525 round-duct flanging covers the pulpit and crane cabin HVAC scope on every Australian smelter.
What is the typical lead time for HVAC ductwork on an Australian aluminium project?
For Australian aluminium smelter, alumina refinery, bauxite mine or anode plant projects, plan 16–28 weeks from purchase order to commissioning of the SBKJ duct fabrication line. The sequence is 8–12 weeks SBKJ machine manufacture (SBAL-V auto duct line, SBTF spiral tubeformer, SB-ZF1500 stitchwelder, SBSF-1525 round-duct flanging, SBPC1500 plasma cutter, SBLR-600 welder), 4–6 weeks ocean freight to Port Botany (Tomago supply), Port of Brisbane (Gladstone, Yarwun, QAL, Boyne Island), Port of Devonport or Bell Bay (Tasmania), Port of Portland (Portland Aluminium), Fremantle (WA refineries Wagerup, Pinjarra, Kwinana, Worsley) or Darwin (Gove bauxite), 2–3 weeks Australian Border Force and Department of Agriculture customs clearance and inland trucking, then 2–3 weeks installation, commissioning and operator training at the buyer's Australian workshop.
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