Steel Mill and Smelter HVAC Duct Guide — BlueScope, Tomago Aluminium, Liberty Whyalla Green Steel, Heavy Industrial

Why steel mill and smelter HVAC is unique

HVAC ductwork on a steel mill or smelter is not the same engineering problem as a commercial office tower or even a typical heavy industrial workshop. The temperature gradients, particulate loadings, corrosive gas chemistry and worker heat-stress regulations turn what looks like a duct-sizing exercise into a multi-discipline integration job that crosses HVAC, process engineering, materials selection, occupational hygiene and emission control. We have shipped SBKJ duct fabrication machinery into more than 100+ countries since 1995, and the heavy industrial scope — steel mills, alumina refineries, copper smelters, nickel laterite plants and gold pressure-oxidation facilities — is consistently the most demanding HVAC environment we encounter.

Five characteristics make steel mill and smelter HVAC fundamentally different from conventional commercial or light industrial work. First, peak process temperatures reach 1500°C and beyond at the tap point of a blast furnace or electric arc furnace, with primary off-gas leaving the hood at 800–1200°C and secondary exhaust still arriving at duct entry around 300–600°C even after waste-heat recovery. Second, particulate loadings in process exhaust streams are measured in grams per cubic metre rather than milligrams — a basic oxygen furnace primary off-gas can carry 80–150 g/Nm³ of iron oxide fume before the wet venturi, and even after a baghouse the residual loading at duct entry is 5–20 mg/Nm³ versus the 0.1–1 mg/Nm³ typical of comfort HVAC return air. Third, corrosive species — sulphur dioxide from copper, nickel and zinc smelters, hydrogen fluoride from aluminium pot lines, hydrogen chloride from pickle lines, sulphuric acid mist from acid plants — drive material selection from galvanised steel into 316L stainless, 2205 duplex, FRP or rubber-lined carbon steel. Fourth, process exhaust volumetric flows of 500,000 to 2,000,000 Nm³/h on an integrated mill make the duct cross-sections enormous — five-metre-diameter risers and four-metre-by-three-metre rectangular trunks are routine. Fifth, Australian heat-stress regulations under Safe Work Australia guidance and state-level WHS legislation mean operator zones near the cast house, tap floor, charging floor and pot lines need refrigerated supply air with WBGT (wet bulb globe temperature) compliance, not just nominal outdoor-air rates.

This guide is the same one our engineers walk through with HVAC consultants, EPC contractors and end-user maintenance teams on heavy industrial projects in Australia and across our export markets. It separates the HVAC scope — pulpit pressurisation, control room cooling, electrical room ventilation, general workshop air, comfort cooling — which SBKJ standard machinery covers, from the process exhaust scope — primary off-gas, blast furnace top gas, smelter gas — which is heavy welded fabrication procured from specialist contractors. Knowing where that line falls is the first decision on every steel mill and smelter project.

Process types — integrated mills, mini-mills, DRI and the green steel pipeline

Steelmaking routes split cleanly into three families and HVAC scope follows the chosen route. The integrated steel mill uses blast furnace ironmaking with metallurgical coke, basic oxygen furnace (BOF) steelmaking, then continuous casting and rolling. BlueScope Port Kembla NSW operates Australia's only integrated mill at around 3.0 Mt/y of crude steel capacity, with a single operating blast furnace (No. 5 BF) of 3,000 m³ working volume after the No. 6 BF reline cycle. The HVAC scope on an integrated mill is typically 50–80 km of ductwork distributed across the coke ovens, by-product plant, sinter plant, blast furnace cast house and stockhouse, BOF shop, hot strip mill, cold rolling mill, pickle line, galvanising line and finishing operations. High-temperature CO-rich process exhaust dominates the engineering challenge on the BF, BOF and coke oven sections — top gas leaving the BF at around 200°C carries 20–30 g/Nm³ of dust before the gas-cleaning train, and BOF off-gas at the hood arrives at 1,200°C with 80–150 g/Nm³ of iron oxide fume.

The EAF mini-mill bypasses the entire ironmaking stage and starts with scrap, hot briquetted iron (HBI) or direct-reduced iron (DRI) charged into an electric arc furnace. Liberty Steel Whyalla SA is converting from integrated BF-BOF to EAF + DRI under the GFG Alliance restart programme announced in 2024 — once the BF is shut down and the EAF and DRI shaft furnace come online, total mill HVAC scope drops from typical integrated-mill 50–80 km to roughly 15–25 km because the coke ovens, sinter plant and BF stockhouse are eliminated. EAF off-gas leaves the fourth-hole exhaust at 1,400–1,600°C peak during charging and tap, settling to 600–900°C during steady-state melting, with 5–15 g/Nm³ of iron oxide and zinc oxide fume (zinc from galvanised scrap). The post-combustion chamber cools to 200–400°C before the baghouse, and downstream HVAC ducting after the baghouse is conventional 304L stainless or galvanised steel.

The direct-reduced iron (DRI) and hot briquetted iron (HBI) route uses a vertical shaft furnace fed with iron-ore pellets and reducing gas (currently natural gas reformed to syngas, transitioning to green hydrogen). The MIDREX and Energiron HYL processes both produce sponge iron at 700–900°C which is either used directly as EAF feed (DRI) or compacted into briquettes for transport (HBI). Roy Hill Iron Ore in WA has scoped a HBI study on its Pilbara reserves, and Fortescue's green-iron Pilbara concept proposes electrolytic and hydrogen-based ironmaking on-site. The HVAC scope on a DRI/HBI plant is dominated by the shaft-furnace top-gas system (CO, H2, H2O, CO2 mix) and the briquetting line dust collection — process exhaust is the dominant duct scope, with HVAC supporting roles in the operator pulpits, control room, electrical room and reagent-handling areas.

Green hydrogen DRI is the next-generation route. HYBRIT in Sweden (SSAB + LKAB + Vattenfall) commissioned the world's first fossil-free hydrogen DRI demonstration plant in Luleå and is targeting commercial scale at Gällivare. H2 Green Steel (now Stegra) is constructing a 5 Mt/y commercial green steel plant at Boden in northern Sweden using hydrogen DRI and EAF. ArcelorMittal Hamburg and ThyssenKrupp Duisburg are running parallel hydrogen DRI conversion projects in Germany. BlueScope Port Kembla announced a hydrogen DRI conceptual study in 2023 examining what it would take to convert Australia's only integrated mill to a green steel route, with the study examining hydrogen supply, electricity demand, capital cost and grid integration. Hydrogen DRI fundamentally changes the gas chemistry — primary exhaust shifts from CO-rich high-particulate to water vapour and unreacted hydrogen — which means smaller, cleaner ducts but stricter explosion zoning under ATEX/IECEx Zone 2 around the shaft furnace and reformer.

Smelter types — copper, aluminium, nickel, zinc and gold

Non-ferrous smelter HVAC has its own taxonomy. Copper smelters feed concentrate (typically 25–35 percent Cu after froth flotation) into a flash furnace (Outotec/Outokumpu Flash Smelting Furnace) or a top-submerged-lance furnace (Glencore-Britannia ISASMELT, Ausmelt TSL). Glencore Mt Isa Mines operates an ISASMELT in Queensland producing copper anode for export to refineries. Olympic Dam in SA (BHP) operates an integrated copper-uranium-gold smelter alongside the SX-EW (solvent extraction-electrowinning) tankhouse for copper. Smelter gas leaving a flash furnace at 1,250–1,300°C with 25–35 percent SO2 is fed to a sulphuric acid plant which converts the SO2 to commercial-grade H2SO4. The acid plant feed gas duct is heavy refractory-lined carbon steel at the smelter outlet, transitioning to FRP or rubber-lined steel after the gas cooling and cleaning train. Pulpit, crane cabin and operator HVAC inside the smelter building must handle residual SO2 carryover with positive-pressure operator cabins and HEPA + activated-carbon intake filtration.

Aluminium smelters use the Hall-Heroult process — alumina (Al2O3) dissolved in molten cryolite (Na3AlF6) electrolysed at 950–970°C in carbon-cathode pots drawing 200,000–600,000 amperes per cell. Australia operates four primary aluminium smelters: Tomago Aluminium NSW (Rio Tinto + CSR + AMP, around 580 kt/y), Boyne Smelter Gladstone QLD (Rio Tinto, around 550 kt/y), Bell Bay Aluminium Tasmania (Rio Tinto, around 190 kt/y) and Portland Aluminium Victoria (Alcoa + CITIC + Marubeni, around 300 kt/y). Pot-line gas — fluorine-rich (HF and particulate fluorides), with alumina dust, polycyclic aromatic hydrocarbons from the carbon anodes, and CO2 from the electrochemical reaction — is collected by hooded gas collection systems at 95+ percent capture efficiency, then scrubbed in dry alumina scrubbers (the alumina absorbs HF and is recycled into the cells, recovering both fluoride and process material). Pot room roof ventilation handles residual heat and gases by stack effect. The pot-line gas-collection ducting is heavy welded carbon-steel fabrication; the pulpit, crane cabin, anode bake operator cabin and control room HVAC is conventional rectangular and spiral ducting — squarely in SBKJ scope.

Nickel smelters follow either matte smelting (BHP Kalgoorlie Nickel Smelter, formerly the WMC operation, processing concentrate to nickel matte for refining) or laterite-pyrometallurgical processing. Matte smelter gas is SO2-rich and feeds an acid plant; the HVAC scope is similar to copper. Zinc smelters use the Imperial Smelting Process (ISP) for combined Zn-Pb production, the Ausmelt TSL for primary zinc, or roast-leach-electrowin (RLE) processing. Nyrstar Hobart in Tasmania and Sun Metals Townsville QLD operate primary zinc operations on the RLE route. Zinc roaster gas at 900–1000°C carries SO2 and zinc oxide fume, with similar acid plant integration to copper. Gold smelters are smaller volume but include high-pressure autoclaves for refractory ore pre-oxidation — Newmont Boddington WA operates one of the largest gold-copper autoclave operations globally, and Newcrest Lihir (now Newmont Lihir) PNG operates pressure oxidation on geothermal-heated autoclaves. Autoclave off-gas is mostly oxygen-depleted air with SO2 and elemental sulphur — handled by FRP or rubber-lined carbon-steel duct.

Australian context — the operating fleet and the green metal pipeline

Australia operates a concentrated but strategically critical heavy metal smelting and steelmaking fleet, with most facilities now in some stage of green-transition planning. The integrated steelmaking footprint is BlueScope Port Kembla NSW (3.0 Mt/y, integrated BF-BOF, with the BlueScope Steel Manufacturing Reset announced in 2025 examining the BF reline timing and hydrogen DRI conversion options). EAF mini-mill capacity is concentrated at Liberty Steel Whyalla SA (1.2 Mt/y, transitioning from integrated BF-BOF to EAF + DRI under the GFG Alliance restart programme), Liberty Steel Newcastle NSW (rolling mill only after the EAF closure), and BlueScope Glenbrook in New Zealand (EAF mini-mill exporting hot rolled coil to Australia). InfraBuild operates EAF rolling mills at Sydney Rooty Hill, Melbourne Laverton and Newcastle Mayfield.

Aluminium smelting is the largest non-ferrous footprint by power consumption — Tomago Aluminium NSW, Boyne Smelter Gladstone QLD, Bell Bay Aluminium Tasmania and Portland Aluminium Victoria collectively consume around 12 percent of the National Electricity Market (NEM) at full production. Each smelter has a separate green-electricity transition pathway: Tomago is in extended discussion with EnergyAustralia over Eraring closure timing and Liddell replacement; Boyne is examining Stanwell solar PPAs; Bell Bay benefits from Tasmania's hydroelectric resource; Portland is co-located with the Victorian renewable energy transition. Aluminium pot-line technology change is constrained by the 30+ year asset life of the cells themselves — the practical decarbonisation pathway is grid greening and inert-anode adoption rather than wholesale smelter rebuild.

Copper smelting is concentrated at Glencore Mt Isa QLD (ISASMELT) and BHP Olympic Dam SA (integrated Cu-U-Au smelter). Nickel smelting is BHP Nickel West Kalgoorlie WA (Kalgoorlie Nickel Smelter, KNS), supported by the Kambalda concentrator and Kwinana refinery — the entire BHP Nickel West operation entered care and maintenance in 2024 driven by Indonesian nickel oversupply. Zinc primary smelting is Nyrstar Hobart TAS (RLE) and Sun Metals Townsville QLD (RLE). Gold autoclave processing is Newmont Boddington WA. Iron ore HBI/DRI scoping is Roy Hill Iron Ore (Hancock Prospecting) in the Pilbara WA and Fortescue's green-iron concept at Pilbara Christmas Creek and Solomon hubs.

The forward green-metal pipeline includes Liberty Whyalla EAF + DRI restart (target 2027), BlueScope Port Kembla H2-DRI conceptual study (decision gate around 2027–2028), Roy Hill HBI study (feasibility stage), Fortescue green hydrogen + green iron Pilbara cluster (multiple stage gates), Hancock Prospecting Iron Bridge magnetite project (mining stage but with downstream HBI optionality), and the Calix-BlueScope Zero-Steel demonstration project in Wollongong. Each project at the scoping stage is generating HVAC consultant tenders for the operator pulpit, control room, electrical room and general HVAC scope — all of which fall squarely inside SBKJ standard machinery capability.

Standards stack — AS, NFPA, OSHA, ACGIH

Steel mill and smelter HVAC sits under a layered standards stack that combines Australian building services codes, international combustion-equipment standards and occupational hygiene exposure limits. Knowing which code applies to which duct run is the difference between a clean handover and a re-work cycle.

• AS 1668.2:2012 — Mechanical ventilation in buildings. Sets minimum outdoor air rates for occupied spaces in Australian industrial buildings — typically 10 L/s per occupant baseline, with specific allowances for contaminant control. AS 1668.1 covers fire and smoke control. AS 1668.4 covers natural ventilation. Heavy industrial pulpits, control rooms, amenities and crib rooms all fall under AS 1668.2.
• AS 4254.1 and AS 4254.2 — Ductwork for air-handling systems. Part 1 covers flexible duct, Part 2 covers rigid sheet-metal duct. AS 4254.2 specifies gauge thickness vs duct dimension, joint construction (drive slip, S-cleat, TDF flange), reinforcement, support and pressure classification (low, medium, high). SBKJ SBAL-V auto duct lines and SBTF spiral tubeformers fabricate to AS 4254.2 with Australian-spec tooling.
• AS 4655 — Fire-resistant ductwork. Applies to smoke spill, kitchen exhaust and pressurisation ducts. Heavy industrial smoke-spill ducting in process buildings often follows AS 4655 + NCC Volume One D-series provisions.
• NFPA 86 — Standard for Ovens and Furnaces. US-origin standard adopted internationally for direct-fired industrial process equipment. Reheat furnaces, ladle dryers, tundish dryers, annealing furnaces and heat-treatment lines fall under NFPA 86 — driving flue gas duct sizing, explosion relief venting, post-purge cycles, fuel piping segregation and combustion safeguards.
• NFPA 91 — Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Particulate Solids. Applies to process exhaust ductwork carrying combustible dust (iron oxide fume can be combustible at high concentration), VOC, mist or solvent vapour. Specifies duct construction, explosion isolation, deflagration venting and clean-out access.
• API RP 14C — Recommended Practice for Analysis, Design, Installation, and Testing of Safety Systems for Offshore Production Platforms. Originally an offshore standard, but its HVAC sections (pressurisation, smoke control, gas detection) are widely adapted as a reference for Australian heavy industrial control rooms and switch rooms because they are more prescriptive than AS 1668.2 alone.
• OSHA 29 CFR 1910.1000 — Air Contaminants. US permissible exposure limits — referenced by Australian operators as a comparison benchmark. Typical limits relevant to steel mills and smelters: iron oxide fume 10 mg/m³ TWA, manganese 5 mg/m³ TWA, hexavalent chromium 5 µg/m³ TWA, sulphur dioxide 5 ppm TWA, hydrogen fluoride 3 ppm ceiling.
• ACGIH TLV — Threshold Limit Values. The American Conference of Governmental Industrial Hygienists publishes annually-updated occupational exposure limits which Safe Work Australia and most Australian operators reference as the de-facto industrial hygiene standard alongside Workplace Exposure Standards (WES). ACGIH TLV-TWA for fluorides (as F) is 2.5 mg/m³, hexavalent chromium 0.0002 mg/m³, manganese 0.02 mg/m³ (respirable), iron oxide fume 5 mg/m³ (respirable). The ACGIH industrial ventilation manual (28th edition) is the standard reference for capture velocity and hood design.
• Safe Work Australia heat stress guidance. No prescriptive WBGT limit but employer obligation to manage heat stress through engineering controls, work-rest cycles, hydration and fitness-for-work assessment. WBGT-based work-rest tables from ACGIH TLV are widely adopted.

Process exhaust — what HVAC engineers need to know about gas chemistry

Even though SBKJ standard machinery is not the primary fabricator of high-temperature process exhaust ductwork, the HVAC engineer scoping a steel mill or smelter project needs to understand the process gas streams because they drive plant layout, segregation distances, building pressurisation, emergency back-up ventilation and the interface points where HVAC duct connects to process duct.

Blast furnace top gas exits the BF top at 100–250°C carrying 15–35 g/Nm³ of dust (mostly iron oxide and unburned coke fines) and 20–28 percent CO by volume. The CO content makes BF top gas a fuel — it is cleaned in a dust catcher, gas scrubber and ESP train, then distributed to the power plant, hot blast stoves and coke oven battery as a low-calorific-value fuel gas (around 3.0–3.5 MJ/Nm³). HVAC implications are gas-tight building envelope around the gas plant, CO detection at low ppm thresholds, emergency ventilation and exclusion zoning around the gas-cleaning train and any distribution piping.

BOF off-gas exits the converter mouth at 1,200–1,700°C peak during the oxygen blow, carrying 80–150 g/Nm³ of iron oxide fume and 50–75 percent CO. Two off-gas treatment philosophies exist: open-combustion (full combustion in the hood with air admission) which destroys the CO and produces a CO2-rich exhaust at lower temperature, and suppressed-combustion (sub-stoichiometric, OG/LT or similar systems) which preserves the CO as a fuel gas similar to BF top gas. Both approaches need refractory-lined hood and primary duct, water-cooled hood sections in the lower throat, then transition to either ESP + ID fan + stack (open combustion) or wet venturi scrubber + gas holder + clean BOF gas distribution (suppressed combustion). HVAC scope is on the BOF shop building ventilation, the operator pulpit, the secondary fume-extraction dog-house ventilation and the converter aisle air conditioning.

EAF off-gas exits the fourth-hole at 1,400–1,600°C peak during charging and tap, settling to 600–900°C during steady-state melting, carrying 5–15 g/Nm³ of iron oxide and zinc oxide fume. The standard EAF off-gas train is fourth-hole exhaust → water-cooled duct → drop-out box → post-combustion chamber → quench tower → baghouse → ID fan → stack. Modern EAF design also captures secondary emissions through canopy hoods over the charging area and tap stream, with the secondary stream merging into the primary baghouse upstream of the ID fan. HVAC scope is the operator pulpit, control pulpit at the EAF furnace transformer building, hot-metal aisle ventilation and the secondary canopy hood air make-up.

Coke oven gas exits the battery at around 800°C carrying tar vapour, ammonia, hydrogen sulphide, hydrogen cyanide, light hydrocarbons (BTX — benzene, toluene, xylene) and a heating value around 18–20 MJ/Nm³. Treatment is steam tracing of the collecting main, primary cooler (gas-to-water heat exchanger), tar precipitator (electrostatic), ammonia scrubber, hydrogen sulphide removal (Stretford or Sulfiban), benzol recovery and dehumidification. The clean coke oven gas is a high-value fuel for the coke oven battery underfiring and the integrated mill power plant. HVAC implications are extreme — the by-product plant has VOC, sulphur compound and PAH emissions requiring local exhaust at every flange and pump seal, with positive-pressure operator pulpits.

Smelter SO2-rich gas from copper, nickel, zinc or lead pyrometallurgy exits the smelting furnace at 1,000–1,300°C with 8–35 percent SO2 by volume. The gas is cleaned (cyclone, gas cooler, ESP, scrubber) and fed to a sulphuric acid plant on the contact process — converting SO2 to SO3 with vanadium pentoxide catalyst, then absorbing SO3 in concentrated H2SO4 to produce 98–99 percent commercial acid. HVAC implications are residual SO2 in the smelter building requiring positive-pressure operator pulpits and low-level emergency ventilation (SO2 is denser than air), corrosion-resistant duct in the gas-handling building, and acid plant cold-end corrosion management.

Aluminium pot-line gas from Hall-Heroult cells contains hydrogen fluoride (HF, around 100–500 mg/Nm³ before scrubbing), particulate fluorides (cryolite dust), alumina dust, polycyclic aromatic hydrocarbons (from the carbon anodes), and CO2. Hooded collection at 95+ percent capture efficiency, dry alumina scrubbing (HF + Al2O3 → AlF3 + H2O surface adsorption, then the alumina is fed back into the cells with the absorbed fluoride recycled), then bag filter and ID fan to stack. HVAC implications are pot room roof ventilation by stack effect (3–10 air changes per hour), positive-pressure operator pulpit and crane cabin, and HF-resistant duct material at any acid-mist scrubber drainage point.

Material selection for high-temperature exhaust

Material selection for steel mill and smelter ductwork is one of the most consequential design decisions on the project — getting it wrong drives early-life duct failure, unplanned outages, and in the worst case explosive depressurisation. The selection logic is dominated by service temperature, then layered with corrosivity, pressure, structural span and cost.

• Galvanised carbon steel (Z275 coating) — service to 200°C continuous, 250°C short-term. Standard for general HVAC return air, comfort cooling supply, electrical room ventilation, low-corrosion ambient air duct. SBKJ SBAL-V auto duct line and SBTF spiral tubeformer fabricate this in production volume.
• Aluzinc / Zincalume (AZ150) — service to 315°C continuous. Better high-temperature performance than Z275 galvanised because the aluminium-rich coating retains adhesion at higher temperatures. Common on Australian projects for hot-zone HVAC supply.
• 304L stainless steel — service to 600°C continuous, 800°C short-term. Standard for clean process exhaust, pickle line vent, mild-corrosion service. SBAL-V is offered with stainless-steel tooling on order; SBTF fabricates 304L spirally up to 1.5 mm wall in standard configuration.
• 316L stainless steel — service to 600°C continuous with better chloride resistance than 304L. Standard for coastal Australian smelters (Tomago, Boyne, Portland), pickle line acid mist, and any application near salt-laden marine air.
• 309S / 310S austenitic stainless — service to 800°C continuous, 1,100°C short-term. Used for EAF secondary off-gas duct after the post-combustion chamber, BOF off-gas after the gas cooler, and ladle metallurgy fume extraction. Welded fabrication scope, not roll-formed — SBKJ welded duct cells (SBWD) handle this on Australian heavy industrial projects.
• Inconel 625 / 718 — service to 1,000°C continuous. Used for high-temperature process exhaust where 310S is at its limit — uncooled BOF hood throat sections, BF tuyere coolers, copper smelter primary off-gas duct before the gas cooler. Heavy welded fabrication, specialist scope.
• Refractory-lined carbon steel — service above 1,000°C with the carbon-steel shell limited to 350°C maximum. Standard for primary BF off-gas duct, primary BOF hood, copper flash smelter primary off-gas, aluminium smelter pot-line ducting. Refractory selection (castable, fibre, brick) and anchorage design is a separate engineering discipline; the carbon-steel shell is conventional welded fabrication.
• FRP / GRP (fibreglass-reinforced polyester) — service to 90°C continuous, excellent acid corrosion resistance. Standard for sulphuric acid plant cold-end ducting, pickle line acid mist exhaust, copper SX-EW mist eliminator outlet, gold autoclave off-gas after the gas cooler.
• Rubber-lined carbon steel — service to 80°C continuous, used for slurry-handling and acid-handling duct where flexibility is needed (vibration, settlement). Common on smelter slurry-feed prep and ESP ash sluice systems.
• 2205 duplex stainless steel — service to 300°C with very high chloride and acid resistance. Used on coastal smelter pickle lines and SO2 cold-end ducting where 316L is marginal.

Heat recovery — economisers, regenerators and recuperators in the duct path

Heat recovery is now standard on every new and most retrofitted steel mill and smelter project because process gas at 600–1,200°C represents 25–40 percent of total mill energy input. Three approaches dominate, each with distinct duct integration requirements.

Economisers are gas-to-water heat exchangers placed in the duct path to recover 200–400°C exhaust into boiler feedwater preheating. Typical applications include reheat furnace flue gas, EAF secondary off-gas, and BOF gas cooler outlet. The economiser is procured from a heat-recovery vendor (Sumitomo SHI FW, Andritz, Doosan Lentjes, John Cockerill, Babcock & Wilcox) with the duct interface specified by inside diameter, gas mass flow, expected dust loading and pressure drop. Downstream HVAC duct after the economiser handles 100–150°C cleaned gas — squarely in conventional carbon-steel or 304L stainless territory.

Regenerators are refractory checker chambers that absorb heat from above-1,000°C process gas during a heating cycle, then release the heat to incoming combustion air during a reverse cycle. Hot blast stoves on a blast furnace (typical four-stove setup at Port Kembla No. 5 BF) work on the regenerator principle, recovering BF top gas combustion heat into hot blast at 1,200°C delivered to the tuyeres. Refractory-lined duct, valves rated for 1,300°C, and refractory-anchorage design dominate the engineering — none of this is HVAC scope, but the integration with the building ventilation and the operator pulpit on the cast house follows the regenerator timing cycle.

Recuperators are gas-to-gas heat exchangers preheating combustion air for reheat furnaces, ladle dryers and tundish dryers using the furnace's own flue gas as the heat source. Plate-type and tube-type recuperators are standard, with materials from carbon steel (low-temperature sections) through 310S stainless to Inconel 600/625 (high-temperature sections). The HVAC implications are the building ventilation handling the recuperator radiant heat losses and the operator pulpit cooling load increase from the high-temperature combustion air piping in the same building.

Emission control train — cyclone, ESP, baghouse, scrubber

The emission control train downstream of the process furnace is where most of the duct kilometres on a steel mill or smelter project actually live. Each emission control unit operation drives a specific duct geometry, velocity and material requirement, and the train sequence depends on the gas chemistry and target stack emission.

Cyclones are the first-stage coarse-particulate removal — knocking out particles above 10 microns by centrifugal force. Inlet velocity is typically 18–25 m/s, with the cyclone body sized for a target pressure drop around 1.0–1.5 kPa. Refractory-lined carbon steel for high-temperature service (BF top gas, EAF off-gas before quench), 310S or 304L for medium-temperature, and FRP or rubber-lined steel for cold acid service. Cyclones are usually procured as a packaged unit; the upstream duct geometry must give straight-run inlet of at least 5 diameters to avoid swirl distortion.

Electrostatic precipitators (ESPs) handle fine particulate (1–10 microns) by inducing charge on the particle and collecting it on grounded plates. Inlet face velocity is 1.0–1.5 m/s — much lower than cyclone — driving large plenum and duct cross-sections to slow the gas before the ESP entry. Gas distribution screens at the ESP inlet require a perpendicular flow profile within 15 percent uniformity, which means upstream duct geometry needs straight runs, vanes or perforated plate to achieve the profile. ESPs are common on BF top gas, sinter plant exhaust, and aluminium smelter pot-line dry alumina scrubber outlet.

Bag filters (baghouses) are dominant for sub-micron particulate capture, with PTFE membrane bags for high-temperature service (up to 260°C continuous), woven glass fibre for medium temperature (up to 260°C), and polyester/aramid for low temperature. Plenum velocity below 1.0 m/s is the design rule — pushing duct cross-sections wide. Air-to-cloth ratio (m³/h per m² of bag area) typically 60–120 m/h for high-temperature service. EAF baghouses, steel mill desulphurisation baghouses, smelter dust collection baghouses, and DRI/HBI dust collection baghouses are routine; pulse-jet cleaning is the standard cleaning method.

Wet scrubbers handle acid gas (SO2, HF, HCl) and submicron particulate via gas-liquid contact. Venturi scrubbers for high-energy dust capture (BOF off-gas suppressed-combustion route), packed-tower scrubbers for acid-gas absorption (pickle line acid mist, copper smelter cold-end SO2 polish), and spray-tower scrubbers for low-energy gas-liquid contact. Materials are FRP, rubber-lined carbon steel, 316L stainless or 2205 duplex depending on chloride content. Mist eliminators downstream of every scrubber prevent carry-over.

ID (induced draft) fans are the mechanical heart of the emission control train — drawing the gas from the process furnace through the entire treatment train at the operating pressure required to overcome combined system pressure drop. Fan static pressure on a steel mill ID fan is 5–15 kPa typical. Fan blade material is 304L stainless, 309S or duplex depending on temperature and corrosion, with abrasion-resistant overlay welding on dust-loaded streams.

Worker comfort cooling and heat stress mitigation

Australian heavy industrial sites face the most demanding heat stress environment of any HVAC scope SBKJ encounters globally. Pilbara summer ambient regularly exceeds 45°C dry-bulb with WBGT above 30°C; Mt Isa, Kalgoorlie, Whyalla and Gladstone all run summer extremes that combine with process radiant heat to push WBGT in operator zones above the ACGIH continuous-work threshold. Engineering controls are the first line of defence under Safe Work Australia heat stress guidance, and HVAC duct design is the single largest engineering control available.

Operator zones near hot processes require refrigerated supply air at 14–16°C delivery temperature, sized for the calculated heat gain from radiant load + convective load + metabolic load + process heat. The supply duct sizing follows AS 4254.2 medium-pressure classification, with insulated rigid spiral or rectangular construction. Diffuser layout puts the cool supply at chest height to the operator with a return at low level to capture the warmer convective layer.

For roving operators (cast house cleaning, EAF tap floor inspection, BOF charging floor patrols, smelter pot-line tending), spot-cooling air showers are deployed — local high-velocity supply at the work position from an overhead or side-mounted nozzle, with supply air at 12–14°C and 2.5–4.0 m/s velocity at the operator's chest. SBKJ SBTF spiral tubeformer fabricates the spot-cooling supply duct, with the diffuser nozzles procured separately.

For prolonged-occupation operator zones (control rooms, pulpits, crane cabins), fully air-conditioned hermetically sealed cabins are the standard — covered in the next section.

WBGT monitoring is increasingly automated — wet bulb globe temperature sensors at operator positions feeding data to the control system, with work-rest cycles automatically signalled when WBGT exceeds the ACGIH thresholds. Modern Australian mills (Liberty Whyalla EAF, BlueScope hot strip mill control room) integrate WBGT data with operator scheduling and automated rotation systems. The HVAC supply temperature control loop adjusts cooling capacity in real time to maintain operator zone WBGT below threshold.

Pulpit and control room HVAC — hermetically sealed positive pressure

Operator pulpits and control rooms in steel mills and smelters are the most demanding HVAC sub-system on the project — they protect personnel from process gas, fume, dust, heat, noise and (in the worst case) catastrophic process upsets. The standard specification has converged across the industry on hermetically sealed, positive-pressure, redundant-cooling cabin design.

• Pressurisation: 25–50 Pa positive pressure relative to the surrounding mill, maintained continuously when the cabin is occupied. Door interlocks (airlock entry) maintain pressure during ingress and egress. Pressure differential transmitter alarms on low-pressure event with operator escalation.
• Outdoor air: 100 percent outdoor air through a multi-stage filtration train. Stage 1 G4 panel pre-filter (catches lint and coarse fibre). Stage 2 F7 bag filter (catches fume and fine dust). Stage 3 H13 HEPA (catches submicron particulate including iron oxide fume). Stage 4 activated carbon (adsorbs sulphur, fluoride and VOC). Each filter stage instrumented with differential pressure transmitter for filter life management.
• Cooling: Redundant N+1 chilled water or DX cooling rated for 35–40°C ambient design (Australian summer extreme), with automatic transfer to standby unit on primary failure. Cooling coil sized for peak heat gain including solar load on roof, radiant load from adjacent process equipment, lighting load, occupancy load and process heat through walls and windows.
• Emergency back-up: UPS power on the supply fan and damper actuators. Emergency back-up ventilation cylinder (compressed air or N2) for short-term pressurisation during power loss. Process-trip interlock to seal the cabin in a confirmed gas release event.
• Construction: Low-leakage building envelope at less than 0.5 air changes per hour at 50 Pa. Continuous welded sheet construction at the floor joint, gasketted door seals, smoke detection on the supply air, gas-tight dampers for emergency isolation.
• Duct material: Galvanised steel for general supply and return air. 304L stainless steel for pulpits inside aggressive smelter environments (copper, nickel, zinc smelter buildings with residual SO2 carry-over). Insulated rigid spiral for the supply trunk, rectangular for the return air.

SBKJ SBAL-V auto duct line and SBTF spiral tubeformer cover the full pulpit and control room HVAC scope on Australian heavy industrial projects. Typical pulpit and control room duct fabrication on a single integrated mill project is 8–15 km of rectangular and spiral duct in galvanised, 304L and 316L stainless across an 18–24 month construction window.

Substation and electrical room HVAC — VRF, DX and SF6 ventilation

Substation and electrical room HVAC on a steel mill or smelter is dominated by transformer and switchgear heat dissipation, redundancy requirements driven by mill criticality, and SF6 gas management on modern medium-voltage switchgear. The HVAC scope is segregated from the main mill HVAC because the failure modes are different — an electrical room cooling failure trips the entire mill if the transformer thermal limit is exceeded, while the main mill HVAC failure is operator comfort, not process trip.

Variable refrigerant flow (VRF) systems are the dominant choice for distributed electrical rooms across the mill — multiple indoor units served from a single outdoor condenser bank, with simultaneous cooling and (rarely) heating. Capacity 5–50 kW per outdoor unit, with N+1 redundancy on critical control rooms. Mitsubishi City Multi, Daikin VRV and Toshiba SHRMi are the dominant brands on Australian heavy industrial projects.

Direct expansion (DX) packaged units are used for larger main electrical rooms and motor control centres — typically 50–500 kW packaged rooftop units with N+1 redundancy and remote condenser arrangement when the rooftop is unsuitable for the condenser load.

SF6 ventilation is mandatory under IEC 62271-4 for switchgear rooms containing SF6-filled equipment. SF6 is heavier than air (5x air density) and accumulates at floor level on a leak event, displacing oxygen. Standard requirement is low-level extraction sized to clear the room volume in 30 minutes on a worst-case leak, oxygen depletion sensors with alarm at 19.5 percent O2 and trip at 18 percent, and high-level supply air for sweep ventilation.

Battery room ventilation for UPS battery banks (lead-acid or lithium-ion) requires low-level extraction sized to keep hydrogen below 1 percent LEL — typically 6 air changes per hour on continuous extraction, with hydrogen detection and shutdown of charging if LEL is exceeded.

Coke oven and by-product plant HVAC

The coke oven and by-product plant is the most chemically aggressive HVAC environment on an integrated steel mill. Coke oven gas raw composition includes hydrogen, carbon monoxide, methane, ethylene, benzene, toluene, xylene, ammonia, hydrogen sulphide, hydrogen cyanide, naphthalene and tar vapour — each requiring dedicated extraction, treatment and emission control.

The by-product plant unit operations and their HVAC implications:

• Primary cooler. Coke oven gas at 800°C is cooled to 30–35°C by direct or indirect water spray. Tar and ammonia condense. HVAC scope is the building ventilation and the operator pulpit, with PAH (polycyclic aromatic hydrocarbon) sampling at the cooler outlet because PAH is a confirmed carcinogen with very low TLV (0.2 mg/m³ as benzene-soluble fraction).
• Tar precipitator. Electrostatic precipitator collecting tar mist from the cooled coke oven gas. Building ventilation must keep PAH below TLV at all sampling locations; positive-pressure operator pulpit; H13 HEPA + activated carbon at the pulpit air intake.
• Ammonia scrubber and recovery. Coke oven gas ammonia is absorbed in sulphuric acid producing ammonium sulphate fertiliser, or scrubbed in water and stripped to recover anhydrous ammonia for sale. NH3 ceiling exposure 35 ppm (ACGIH); HVAC scope includes positive-pressure operator pulpit and continuous gas detection.
• Hydrogen sulphide removal. Stretford or Sulfiban process removing H2S to elemental sulphur or to a dilute Claus plant. H2S TLV-TWA 1 ppm, ceiling 5 ppm. Continuous H2S detection at all flange and pump locations; high-velocity local exhaust at maintenance access points.
• Benzol recovery. Light oil (BTX) recovery from coke oven gas by absorption in straw oil and steam stripping. Benzene TLV-TWA 0.5 ppm — extremely low because of leukaemia risk. Hermetic seal containment; positive-pressure operator pulpit; continuous benzene detection.

The HVAC duct scope on a by-product plant is 304L stainless steel for general ventilation and operator pulpit air, 316L stainless for areas with chloride or sulphate carry-over, and FRP or PP-lined steel for specific acid-mist scrubber drainage. SBKJ SBAL-V and SBTF cover the rectangular and spiral HVAC duct; specialty stainless welded duct for the more aggressive zones is fabricated on SBKJ SBWD welded-duct cells with TIG and plasma processes.

Hot strip mill, cold rolling mill and pickle line HVAC

The downstream finishing operations of a steel mill — hot strip mill, cold rolling mill, pickle line, galvanising line, painting line — present a different HVAC challenge than the upstream BF/BOF/EAF: lower temperature but more diverse contaminant streams including acid mist, oil mist, scarfing fume and solvent vapour.

Hot strip mill heat sources are reheat furnaces (700–1,250°C slab reheat), roughing mill stand stands (slab at 1,100°C entry), finishing mill stands, downcoiler. Reheat furnace flue gas at 200–400°C is recovered through recuperators or economisers. The mill aisle building ventilation handles radiant and convective heat from the slab and from the rolls — typical aisle ventilation rate 10–20 air changes per hour with high-level extraction. Operator pulpit at the roughing stand and finishing stand entry/exit is hermetic positive-pressure cabin.

Cold rolling mill heat sources are the rolls (mechanical work at 200–400°C strip temperature), rolling oil (vapour and mist generation), and electrical drives. Oil mist generation is the dominant HVAC scope — local hood at each stand drawing oil mist to a centralised oil mist coalescer (mesh + electrostatic + media filter train) recovering 95+ percent of the oil for re-use. Material is 304L stainless steel duct, with oil-resistant gaskets and drainage at low points.

Pickle line uses hydrochloric acid (HCl) at 18–22 percent concentration and 80–90°C to remove mill scale from hot rolled strip. Acid mist generation is intense — local exhaust hooding at the entry, pickle tanks and exit zones drawing 5,000–25,000 m³/h per tank to an FRP scrubber train absorbing HCl in caustic solution. Duct material is FRP, PP-lined steel or rubber-lined steel for the acid mist exhaust; stainless steel will fail in months on chloride mist service. The acid mist scrubber outlet is bag filter and ID fan to stack.

Galvanising line heat sources are the zinc pot at 460°C, flame heating at the entry preheater, and induction heating on some lines. HCl flux mist (used to clean the strip surface before zinc immersion) is collected at the entry hood. Zinc oxide fume is collected at the pot exit and the after-pot wipe nozzles. Duct is 316L stainless or FRP for the flux mist, 304L stainless for the zinc oxide fume.

Scarfing fume from slab surface conditioning is iron oxide-rich fume at the scarfing machine producing 1–5 g/Nm³ at the hood. Local exhaust to a wet venturi scrubber or baghouse. Refractory-lined hood, 309S stainless duct close-coupled, 304L stainless downstream.

Smelter pot room ventilation — the aluminium case

Aluminium smelter pot rooms are the largest single HVAC volume on any heavy industrial project — Tomago Aluminium operates around 700 cells across multiple pot lines, Boyne Smelter operates around 700 cells, and Bell Bay Aluminium operates around 350 cells. Each cell is roughly 4 metres by 16 metres in plan, drawing 200,000–400,000 amperes at 4–4.5 volts, dissipating 13–14 MWh of electrical energy per tonne of aluminium produced (around half as electrochemical work and half as heat).

Pot-line gas collection uses hooded gas collection over each cell at 95+ percent capture efficiency, drawing 1,500–4,000 m³/h per cell of cell off-gas. The collected gas — HF, particulate fluorides, alumina dust, CO2, PAH — is treated in a dry alumina scrubber (HF + Al2O3 absorption) then bag filter, then ID fan to stack. Fluoride captured in the scrubber alumina is recycled into the cells, recovering both the fluoride and process material.

Pot-line roof ventilation handles residual heat (cells radiate around 10 percent of total energy as radiant heat to the building) and any uncaptured gas through stack-effect ventilation — large open monitor vents along the pot-line roof ridge with low-level air admission at the cell aisles. Typical roof ventilation rate is 3–10 air changes per hour, sized to keep building ambient below 40°C dry bulb.

Operator zones inside the pot room — pot-line operators tending cells, anode change crews, metal tapping crews, crane operators in cabin — are exposed to elevated ambient temperature, residual fluoride, alumina dust and PAH. The HVAC engineering response is:

• Hermetic positive-pressure crane cabin with H13 HEPA + activated carbon air intake; supply temperature 18–20°C; ergonomic seat with cooled airflow.
• Refrigerated drinking water stations and air-conditioned crib rooms at 5-minute walking distance from the work face.
• Spot-cooling air showers at fixed work positions (anode change platforms, metal-tap pits) — supply air at 14–16°C, 3–4 m/s velocity.
• Personal cooling vests with phase-change inserts for high-WBGT shifts.
• Continuous WBGT monitoring at five fixed positions per pot line; work-rest cycle automation.

The pot-line gas-collection ducting itself is heavy welded carbon-steel fabrication procured from specialist contractors (Fives Solios, Bechtel, MIM, Hatch design, local construction). The pulpit, crane cabin, control room, electrical room, anode bake operator cabin and general HVAC ducting is conventional rectangular and spiral fabrication — squarely in SBKJ standard machinery scope. Typical aluminium smelter HVAC scope is 12–25 km of rectangular and spiral duct in galvanised and 304L stainless across the pot-room building, anode bake plant, metal-cast house and ancillary buildings.

Green steel — H2-DRI, electrolysis and the HVAC implications

The green steel transition is moving from concept into commercial commissioning across Europe, with Australian projects in scoping and feasibility. The HVAC implications are significant enough that any consultant tendering on a green steel project needs to understand the gas chemistry shift before sizing duct.

HYBRIT (Sweden) — SSAB + LKAB + Vattenfall partnership, demonstration plant operational at Luleå since 2020, commercial-scale plant under construction at Gällivare for ironmaking and Oxelösund for steelmaking. Hydrogen DRI shaft furnace fed with green hydrogen from electrolysis. Sponge iron at 700–900°C; primary off-gas is unreacted H2 and H2O at 700°C. Off-gas is cooled, water condensed and removed, and the residual H2 recycled to the shaft furnace inlet (hydrogen recycle ratio 60–70 percent).

H2 Green Steel / Stegra (Sweden) — 5 Mt/y commercial green steel plant under construction at Boden, target first commercial coil 2026. Hydrogen DRI + EAF + downstream rolling. The hydrogen production is on-site with Siemens Energy electrolysers; the DRI is integrated; the EAF is a high-power 250+ MVA furnace.

ArcelorMittal Hamburg (Germany) — existing midrex DRI plant being converted from natural-gas reformed syngas to green hydrogen feed in stages; first 100 percent hydrogen demonstration completed 2024.

ThyssenKrupp Duisburg (Germany) — full integrated mill conversion programme replacing two existing blast furnaces with a 2.5 Mt/y hydrogen DRI plant + new EAF, with the first stage hydrogen DRI in commissioning 2026.

BlueScope Port Kembla H2-DRI conceptual study (Australia) — announced 2023, examining the hydrogen supply, electricity demand, capital cost and grid integration of converting Australia's only integrated mill from BF-BOF to H2-DRI + EAF. Decision gate around 2027–2028 on whether the BF reline cycle proceeds (sustaining BF-BOF for another 20–25 years) or the H2-DRI conversion is selected.

Liberty Whyalla green steel announcement (Australia) — GFG Alliance 2024 restart programme converting the existing integrated BF-BOF to EAF + DRI, with the DRI shaft furnace initially natural-gas-fuelled and convertible to hydrogen in a future stage.

The HVAC implications of hydrogen-based ironmaking are five-fold:

• Smaller, cleaner exhaust ducts. Hydrogen DRI primary off-gas is H2O + unreacted H2 at 700°C — far lower particulate loading than BF top gas (no coke fines, no iron oxide fume from the shaft furnace because the iron is not yet liquid). Duct cross-sections are 30–50 percent smaller than equivalent capacity BF top gas duct.
• Hydrogen explosion zoning. ATEX/IECEx Zone 2 around the shaft furnace, hydrogen storage, hydrogen distribution piping and electrolyser hall. HVAC ductwork in zoned areas requires explosion-proof fans, intrinsically safe instrumentation and continuous hydrogen detection. SBKJ SBAL-V and SBTF fabricate to AS 4254.2 with stainless and galvanised steel; the explosion-zone equipment selection (fans, motors, dampers) is procured from ATEX-certified vendors.
• EAF concentration of operators. Mini-mill ironmaking-to-finished-coil distance is far shorter than integrated mill, concentrating operators in a smaller air-conditioned footprint. Pulpit and control room HVAC scope per tonne of steel is higher.
• HBI handling. If the green-steel supply chain uses imported HBI (briquetted DRI shipped from a remote hydrogen site), HBI handling at the receiving port and the storage yard generates iron oxide dust that requires dust collection — typical 2–8 g/Nm³ at the hood with 80,000–200,000 m³/h per handling station.
• Hydrogen leak management. Continuous hydrogen detection, automatic shutdown of charging on confirmed leak, low-level extraction at electrolyser hall (hydrogen is lighter than air but accumulates in roof voids and inverted volumes). Specific to the electrolyser hall and hydrogen distribution rather than the broader mill HVAC.

Net zero ironmaking — direct electrolysis and molten oxide electrolysis

Beyond hydrogen DRI, the next generation of ironmaking technology bypasses hydrogen entirely with direct electrochemical reduction of iron ore to liquid iron. Two technology paths are in pilot stage:

Boston Metal molten oxide electrolysis (MOE) dissolves iron-ore concentrate in a molten oxide bath at 1,600°C and applies direct current to electrochemically reduce the iron ore to liquid iron at the cathode, with oxygen evolved at the anode. Similar in concept to aluminium Hall-Heroult but iron rather than aluminium. Pilot operation in Massachusetts, with commercial scale-up partnerships announced for Brazil and Saudi Arabia. The HVAC implications are oxygen-rich exhaust (handling required for non-combustible duct materials), electrolysis cell heat dissipation (similar to aluminium pot-line), and operator pulpit cooling on the cell line.

ArcelorMittal Siderwin (alkaline electrolysis at low temperature) uses an alkaline electrolyte at 110°C to electrochemically reduce iron-ore powder to iron metal powder at the cathode, with oxygen evolved at the anode. Pilot operation in Asturias, Spain. Lower temperature than MOE but produces solid iron powder rather than liquid iron — the iron powder is briquetted and fed to a downstream EAF for melting.

The HVAC scope on electrolytic ironmaking is fundamentally different from BF or hydrogen DRI:

• Oxygen exhaust. Both MOE and Siderwin produce oxygen-rich exhaust at the anode. Duct material must be non-combustible (no aluminium, no flammable polymer). Stainless steel or carbon steel with oxygen-clean fabrication standards — degreased, no organic residues, no hydrocarbon-based gasket materials.
• Cell heat dissipation. MOE cells operate at 1,600°C similar to Hall-Heroult cells, with similar pot-room building ventilation requirements. Siderwin at 110°C is far less demanding — typical chemical plant ventilation rates apply.
• Electrolyte management. MOE molten oxide spillage and alkaline Siderwin spillage require leak collection, with HVAC ducting routed to avoid exposure to spilled electrolyte.
• Operator pulpit and control room. Conventional positive-pressure cabin design — electrolytic ironmaking does not change this requirement.

None of the electrolytic ironmaking projects are at commercial scale yet, but the HVAC scoping is being done now in the engineering studies. SBKJ engineering team is engaged on multiple feasibility studies as the HVAC ductwork machinery vendor of choice for the pulpit, control room and general HVAC scope on prospective electrolytic ironmaking projects globally.

SBKJ machinery for heavy industrial HVAC scope

SBKJ standard machinery is sized and tooled for the HVAC scope on a steel mill or smelter project — pulpit, control room, electrical room, general workshop ventilation, comfort cooling, and worker spot-cooling supply. The high-temperature process exhaust scope (BF top gas, BOF off-gas, EAF off-gas, smelter primary off-gas, refractory-lined sections) is welded fabrication procured from specialist heavy contractors and is not standard SBKJ machinery scope. Three SBKJ product lines cover the heavy industrial HVAC duct fabrication need on Australian projects:

• SBAL-V auto duct line — fully automatic rectangular duct fabrication line covering coil decoiling, levelling, cutting, notching, beading, TDF flanging, lock-forming and folding. Standard configuration handles 0.5–1.5 mm galvanised steel coil to 1,250 mm width; heavy-gauge configuration handles to 2.0 mm galvanised or 1.5 mm 304L stainless to 1,500 mm width. Output is 25–40 m of duct per shift on standard configuration. Pulpit and control room rectangular duct, electrical room ventilation duct, and general HVAC supply and return — all fabricated on SBAL-V.
• SBTF spiral tubeformer — spiral-lock-seam circular duct from 80 mm to 1,500 mm diameter, 0.5–1.5 mm galvanised, AluZinc or 304L stainless. Output is 30–60 m of pipe per minute on standard configuration. Spiral round duct is the dominant geometry for return air, supply trunk, smoke spill and worker spot-cooling supply on heavy industrial projects because of its higher pressure rating and lower air-friction loss versus equivalent rectangular.
• SBWD welded-duct cells — TIG, plasma and longitudinal-seam welded duct fabrication for stainless-steel high-integrity duct in corrosive zones. Standard configuration handles 1.5–6.0 mm 304L, 316L, 309S and 310S stainless to 2,000 mm diameter. Used for by-product plant, pickle line acid mist, smelter cold-end SO2 and any zone where the integrity requirement exceeds lock-seam capability. Welded-duct fabrication is slower than roll-formed (3–8 m per shift versus 25–40 m) but produces a hermetic seam suitable for sub-Pa leakage requirements.

Heavy-gauge welded duct fabrication for high-temperature process exhaust above 800°C — Inconel 625, 310S thick-wall, refractory-lined carbon steel — is outside the standard SBKJ machinery envelope. Australian customers procuring this scope work with specialist heavy-fabrication shops in NSW, QLD or WA who handle the EAF off-gas duct, BOF off-gas duct, and smelter primary off-gas duct. SBKJ engineering team can introduce qualified heavy-fabrication partners on request.

SX-EW facility HVAC — solvent extraction and electrowinning

Solvent extraction-electrowinning (SX-EW) is the dominant hydrometallurgical route for copper from oxide ores and from heap leach operations, with major Australian operations at BHP Olympic Dam SA (copper SX-EW alongside the integrated Cu-U-Au smelter), Newmont Boddington WA (copper SX-EW alongside gold autoclave), and several smaller copper oxide operations across NSW, QLD and WA. The HVAC scope on SX-EW is dominated by acid mist control and organic phase ventilation.

The SX-EW process flow is:

1. Heap leach or tank leach — sulphuric acid extracts copper from oxide ore, producing a pregnant leach solution (PLS) with copper at 1–8 g/L.
2. Solvent extraction (SX) — PLS contacted with an organic phase (kerosene + extractant such as LIX 984) in mixer-settlers; copper transferred from PLS to organic phase. Stripped aqueous (raffinate) returned to leach.
3. Strip stage — loaded organic phase contacted with strong sulphuric acid (electrolyte from the EW tankhouse); copper transferred from organic phase to electrolyte at 35–55 g/L copper.
4. Electrowinning (EW) — DC current applied to the electrolyte; copper deposited on stainless-steel cathode plates as 99.99 percent copper cathode.

HVAC implications:

• Acid mist control at the EW tankhouse. Sulphuric acid mist is generated at the cathode-anode interface during electrowinning — mist eliminator on the cell hood collecting 99+ percent of the mist, with downstream wet scrubber, mist eliminator and ID fan to stack. Duct material is FRP, PP-lined steel or rubber-lined steel; mist eliminator design is mesh + chevron vane. The tankhouse roof ventilation handles residual acid mist by stack effect, with acid-resistant cladding on the roof.
• Organic phase ventilation at the SX mixer-settler building. Kerosene and LIX organic phase volatilises generating VOC at 5–50 ppm in the building ambient. Building ventilation rate 6–10 air changes per hour; explosion zoning (Zone 2) around the mixer-settler boxes; spark-resistant electrical equipment in the building.
• Operator pulpit at the EW tankhouse and SX building. Hermetic positive-pressure cabin with H13 HEPA + activated carbon air intake; supply temperature 18–20°C; continuous H2SO4 mist and VOC monitoring.
• Electrical room HVAC. EW tankhouse rectifier rooms dissipate large heat loads (10–30 MW DC rectifier banks) requiring N+1 redundant cooling. Standard VRF or DX with redundant outdoor units.

SBKJ SBAL-V and SBTF cover the rectangular and spiral HVAC duct in the SX-EW operator pulpit, electrical room and general ventilation. The acid mist exhaust to scrubber is FRP — procured separately from FRP fabrication specialists. The organic phase ventilation supply duct is 304L stainless or galvanised — squarely SBKJ scope.

Frequently asked questions

What materials are used for steel mill process exhaust ductwork?

Steel mill process exhaust ductwork material selection is driven by gas temperature and corrosivity. For exhaust below 600°C, 304L or 316L stainless steel is standard. For 600–800°C such as EAF secondary off-gas after the post-combustion chamber, 309S/310S austenitic stainless is used. For 800–1,000°C such as BOF off-gas before quench, Inconel 625 or 718 nickel-based alloys are specified. For temperatures above 1,000°C such as blast furnace tuyere coolers and uncooled BOF hood sections, refractory-lined carbon steel is the only viable approach. SBKJ standard rectangular and spiral machinery handles the secondary HVAC scope (pulpit cooling, control room return air, general ventilation) where galvanised steel and 304L are appropriate.

What is the typical lead time for HVAC ductwork on a steel mill or smelter project?

For Australian steel mill and smelter projects, plan 16–24 weeks from purchase order to commissioning of the SBKJ duct fabrication line. The sequence is 8–12 weeks SBKJ machine manufacture, 4–6 weeks ocean freight to Port Botany, Port Kembla, Newcastle, Port Adelaide or Fremantle, 2–3 weeks customs clearance and inland trucking, 2–3 weeks installation and commissioning. Process-exhaust welded duct fabrication (high-temperature stainless or Inconel) is typically procured separately from specialist heavy fabrication shops because SBKJ standard machinery is optimised for galvanised and stainless-steel HVAC ducting up to 3.0 mm wall thickness.

How is heat recovery integrated with steel mill ductwork?

Heat recovery is now standard on integrated steel mills and EAF mini-mills because process gas at 600–1,200°C represents 25–40 percent of total mill energy input. Three approaches dominate: economisers (gas-to-water heat exchangers in the duct path) recovering 200–400°C exhaust to preheat boiler feedwater, regenerators (refractory checker chambers) recovering above-1,000°C BF or BOF gas, and recuperators (gas-to-gas heat exchangers) preheating combustion air for reheat furnaces and ladle dryers. Duct geometry, thermal expansion joints and refractory lining design must be specified by a heat-recovery vendor — the SBKJ scope is typically the downstream low-temperature ducting after the heat exchanger has cooled the gas to below 200°C.

What does AS 1668.2 require for steel mill and smelter ventilation?

AS 1668.2:2012 sets minimum outdoor air rates for occupied spaces in Australian industrial buildings. For steel mill and smelter pulpits and control rooms it typically requires 10 L/s per occupant of outdoor air, mechanical exhaust of contaminants at the source, and pressure differentials between clean and dirty zones. Steel mill specific requirements layer over the top: WBGT compliance under Safe Work Australia heat stress guidance, ACGIH TLV compliance for iron oxide fume, manganese, hexavalent chromium, fluorides (aluminium smelters) and sulphur dioxide (copper, nickel, zinc smelters). The duct fabrication itself must comply with AS 4254.1 (flexible duct) or AS 4254.2 (rigid duct) for the HVAC scope.

What HVAC implications does the green steel transition have for Australian projects?

The Australian green steel transition has three direct HVAC implications. First, hydrogen-direct-reduced iron (H2-DRI) replaces blast furnace ironmaking with a shaft furnace producing iron at 700–900°C using hydrogen instead of metallurgical coke — exhaust streams shift from CO-rich high-particulate gas to water vapour and unreacted hydrogen, with smaller exhaust ductwork but stricter hydrogen-explosion-zoning (ATEX/IECEx Zone 2). Second, electric arc furnace ironmaking using HBI feedstock means more pulpit and control room HVAC because EAF mini-mills concentrate operators in a smaller air-conditioned footprint. Third, electrolytic ironmaking (Boston Metal MOE, ArcelorMittal Siderwin) produces oxygen exhaust that requires non-combustible duct materials and oxygen-clean fabrication standards. SBKJ standard machinery covers the pulpit, control room, electrical room and general HVAC ducting on all three transitions.

How are pulpits and control rooms ventilated in steel mills and smelters?

Operator pulpits and control rooms in steel mills and smelters are ventilated as hermetically sealed, positive-pressure cabins with redundant cooling. The standard specification is 25–50 Pa positive pressure relative to the surrounding mill, 100 percent outdoor air through a multi-stage filtration train (G4 pre-filter, F7 bag filter, H13 HEPA and activated carbon for sulphur and fluoride compounds), redundant N+1 chilled-water or DX cooling rated for 35–40°C ambient, and emergency back-up ventilation on UPS power. Duct material is typically galvanised steel for supply and return air, with 304L stainless steel for pulpits inside particularly aggressive smelter environments. SBKJ SBAL-V auto duct line and SBTF spiral tubeformer cover the full pulpit and control room HVAC scope on Australian heavy industrial projects.

What is the difference between an integrated steel mill and an EAF mini-mill from an HVAC perspective?

An integrated steel mill (BlueScope Port Kembla, ArcelorMittal Dofasco) uses blast furnace ironmaking with metallurgical coke and basic oxygen furnace steelmaking — total HVAC scope is typically 50–80 km of ductwork across coke ovens, sinter plant, blast furnace, BOF, hot strip mill, cold rolling mill and finishing operations, with high-temperature CO-rich process exhaust dominating the engineering challenge. An EAF mini-mill (Liberty Whyalla, BlueScope Glenbrook NZ, Nucor) uses scrap-melting electric arc furnace ironmaking and bypasses the coke ovens, sinter plant and blast furnace entirely — total HVAC scope is typically 15–25 km of ductwork concentrated around the EAF off-gas system, ladle metallurgy, continuous casting and rolling mill. EAF mini-mills are growing faster in Australia because the green steel transition favours scrap-based electric routes; the SBKJ scope (pulpit, control room, general HVAC) is similar on both but the high-temperature process duct scope is significantly smaller on a mini-mill.

What HVAC standards apply to aluminium smelter pot rooms?

Aluminium smelter pot rooms operate under three layered HVAC standards. AS 1668.2:2012 sets the building-services baseline for outdoor air rates. ACGIH TLV-TWA limits for fluorides (2.5 mg/m³ as F), aluminium oxide (1 mg/m³ respirable) and polycyclic aromatic hydrocarbons (PAH) drive the local exhaust velocity at the pot hooding. Safe Work Australia WBGT heat stress limits drive the supply-air cooling capacity for operator pulpits adjacent to 950–970°C cells. Tomago Aluminium NSW, Boyne Smelter Gladstone QLD and Bell Bay Aluminium Tas operate Hall-Heroult cells with hooded gas collection at 95+ percent capture efficiency, scrubbed for fluoride recovery, and pot-room roof ventilation by stack effect. The pulpit, control room and crane cabin HVAC is conventional rectangular and spiral ductwork — SBKJ scope; the pot-line gas collection ducting is heavy welded carbon-steel fabrication procured from specialist contractors.

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