Why cement plant HVAC is unique
A cement plant is the heaviest dust environment in industrial process engineering. Raw cement kiln dust loadings run 100–500 g/Nm³ at the kiln tail before any treatment — that is two to three orders of magnitude higher than even an aggressive coal-fired power station and roughly 10,000 times higher than a typical commercial HVAC return air stream. Process gas temperatures are simultaneously punishing: kiln tail gas exits at 350–450°C upstream of the conditioning tower, calciner gas peaks above 850°C at internal points before it is mixed and ducted, and clinker cooler vent gas runs 250–350°C depending on heat recovery configuration. Underneath all of that, the dust itself is alkaline (pH 11–13 because of calcium hydroxide content), highly abrasive (silica plus aluminosilicates plus calcium oxide hard particles), and respirable down to PM2.5 with crystalline silica content that triggers occupational health limits.
Stitch all of those together and the duct designer is fighting four enemies simultaneously: heat, abrasion, dust loading, and chemistry. None of them is solvable by sheet-metal HVAC techniques alone. A typical 5,000-tonne-per-day clinker line generates roughly 250,000–350,000 Nm³/h of kiln tail gas at 350–450°C carrying 100–500 g/Nm³ of dust — a heat duty of around 50 MW and a particulate loading of up to 175 kg/min in the raw stream. The duct that carries it is welded heavy fabrication built from 6–10 mm carbon-steel plate, sometimes refractory-lined where surface temperatures climb. None of that is sheet-metal HVAC scope. It is the welded-fabrication scope that EPC contractors hand to specialist process-equipment shops.
What sits on the HVAC contractor's side of the line is just as important: pulpit and control room comfort cooling, motor control centre and substation HVAC, laboratory and quality control room conditioning, administration buildings, lunch rooms, change rooms, and the fume and dust extraction circuits inside the bagging plant and dispatch areas. These are conventional galvanised sheet-metal duct systems fabricated to AS/NZS 4254-1 (or AS/NZS 4254-2 for high-pressure spiral systems), and they are exactly what SBKJ auto duct lines and spiral tubeformers are designed to make. The trick is knowing which side of the scope split each piece of duct sits on, because pricing it on the wrong side is a six-figure mistake.
Cement production process — the duct map
To know where the HVAC duct sits on a cement plant, you need to know where the process gas is. The cement production sequence on a modern dry-process Australian plant runs as follows. Limestone (calcium carbonate, CaCO₃) and clay (or shale) are quarried near the plant — Boral's Berrima quarry is right next to the cement works, Holcim's Railton quarry similarly. Limestone is primary-crushed to typically minus-100 mm and conveyed to a crushed-rock storage stockpile. Raw materials are reclaimed in proportion (typically 78–82% limestone, 13–17% clay, plus iron and silica correctives), fed to the raw mill (vertical roller mill or ball mill) and ground to a fine raw meal — typically 12–15% retained on a 90 micron sieve. Raw meal is conveyed pneumatically to the homogenising silo, then fed to the preheater tower.
The preheater tower is a stack of 4–6 cyclone stages where raw meal exchanges heat with kiln exhaust gas in counter-current flow. Gas enters the bottom of the tower at roughly 1,000°C from the calciner, ascends through the cyclones and exits the top at 350–450°C carrying entrained raw meal dust. Calcination — the conversion of CaCO₃ to CaO + CO₂ — happens in the calciner stage at the bottom of the tower, fired with primary fuel (coal, petcoke or alternative fuels). Below the calciner, raw meal enters the rotary kiln, a 60–90 m long inclined steel cylinder rotating at 2–4 rpm and lined with refractory brick. Kiln main burner fuel raises material temperature to a peak around 1,450°C in the burning zone, where calcium silicates form (alite and belite) — these are the primary cement clinker phases.
Hot clinker exits the kiln at roughly 1,300°C and falls onto the clinker cooler — typically a grate cooler with multiple compartments and forced cooling air supply. Cooler vent air discharges at 250–350°C with a small dust loading. The cooled clinker (around 100°C) is conveyed to clinker storage. From there, clinker plus 4–6% gypsum (and supplementary cementitious materials such as fly ash, slag or limestone filler) is ground in the cement mill — vertical roller mill, ball mill, or roller press — to produce finished cement at typical Blaine fineness 350–450 m²/kg. Finished cement is pneumatically conveyed to cement silos for dispatch in bulk tankers, bulk rail wagons, or bag-packed in 25 kg bags for retail.
Each of those process steps generates a dust-laden gas stream that needs ductwork: the raw mill exhaust, the kiln main exhaust (preheater tower top), the calciner gas circuit, the cooler vent, the cement mill exhaust, the coal mill exhaust, the clinker conveyor pickup points, the cement silo vent filters, and the bagging plant dust extraction. All of it is welded process duct. Around all of it, the buildings — preheater tower control building, kiln pulpit, central control room, mill MCC rooms, substation, packing plant office, laboratory — need conventional comfort HVAC duct. That is where SBKJ machinery comes in.
Australian cement plants — who is buying HVAC duct
Australia has four large integrated cement makers operating clinker production locally, plus a network of grinding-only stations and lime producers. The integrated plants are where heavy process exhaust duct demand sits. Comfort HVAC duct demand is spread across all of them and is also strong at grinding stations, blended-cement plants, premix concrete batching plants and lime kilns.
Cement Australia (now part of Holcim Australia) operates clinker production at Gladstone in Queensland and Railton in Tasmania. Gladstone is a 1.4 Mtpa clinker line built in the 1980s and progressively upgraded; Railton is a 1.1 Mtpa plant that was modernised in the 2000s and is fed from local limestone. Holcim ECOPlanet low-carbon cement programmes are now being rolled out across both sites, with alternative fuel substitution and cement composition changes — these expand the alternative fuel handling building scope and add comfort HVAC demand for new control rooms.
Boral Cement operates the Berrima clinker plant in NSW (about 1.3 Mtpa) plus Maldon NSW grinding station and Marulan NSW limestone quarry and lime production. Berrima is the only operating wet-process kiln in Australia historically, although progressive dry-conversion projects have changed parts of the line. Boral's CleanTech Cement programme is the company's decarbonisation pathway and includes alternative fuels at Berrima, calcined clay trials, and supplementary cementitious materials. Each new CleanTech building adds comfort HVAC duct demand.
Adbri (formerly Adelaide Brighton, now part of CRH/Cement Australia ownership groupings) operates clinker at Birkenhead SA (around 1.4 Mtpa) and grinding stations at Munster WA. Galong NSW is the lime production site. Adbri sustainability programmes around lower-clinker cement and waste-derived fuels run across all sites and are major sources of new comfort HVAC duct demand at the moment.
Sunstate Cement is the Brisbane grinding station joint venture (Boral and Adbri). Independent Cement & Lime is the largest independent supplier of blended cement in the south-east markets, drawing clinker imports and local supply for blending. Premix concrete batching plants operated by Boral, Holcim, Hanson, Adbri and independents number in the hundreds across Australia — each batching plant has its own modest comfort HVAC scope (control room, lab, amenities) plus dust extraction at silos and weigh hoppers.
For HVAC contractors and duct machinery owners, the demand pattern is clear: large integrated plants produce a small number of large duct fabrication packages every shutdown cycle, while the broader cement and concrete network across Australia generates a steady backlog of smaller comfort HVAC fabrication jobs. The contractor that can fabricate both rectangular and spiral duct on demand, in galvanised and stainless and coated steel grades, is the one HVAC contractor invited back to the shutdown bid list.
Emission control standards — what your stack has to meet
Cement kiln stack emissions are tightly regulated. In Australia, regulation is state-by-state under EPA licences. A typical cement plant licence specifies emission limit values (ELVs) for total dust (particulate matter), nitrogen oxides (NOx), sulphur dioxide (SO2), carbon monoxide (CO), volatile organic compounds (VOC), heavy metals (mercury, cadmium, thallium, lead) and dioxins/furans (PCDD/PCDF). Common Australian cement kiln ELVs at the main kiln stack reference 10% O2 dry basis and run as follows.
- Total dust (particulate matter): 50 mg/Nm³ typical limit, with continuous emission monitoring (CEMS) downstream of the bag filter or ESP.
- Nitrogen oxides (NOx as NO2): 800 mg/Nm³ typical limit, achieved by low-NOx burner design plus selective non-catalytic reduction (SNCR) ammonia or urea injection in the calciner.
- Sulphur dioxide (SO2): 400–600 mg/Nm³ typical limit, naturally absorbed in the alkaline raw meal in most cases without external scrubbing.
- Carbon monoxide (CO): variable depending on fuel mix and combustion control, typically below 1,000 mg/Nm³.
- Mercury: low single-digit mg/Nm³ typical, controlled by activated carbon injection where required.
- Dioxins/furans: 0.1 ng I-TEQ/Nm³ following EU IED BREF cement reference.
The international benchmarks every Australian cement plant cross-references are US EPA NSPS Subpart F (40 CFR 60.60–60.66), which sets New Source Performance Standards for Portland cement plants in the United States, and the EU IED BREF document for cement, lime and magnesium oxide manufacturing, which sets best available techniques (BAT) emission ranges for European cement makers. Both documents inform Australian EPA licence conditions even though they are not legally binding here. AS 4655 specifies bag filter house design as an alternative to electrostatic precipitator dust collection and is the design code most often referenced by Australian process engineers when they specify a baghouse on a cement project. AS 4323.1 specifies stack sampling and emission measurement methodology. EN 13384 specifies chimney and flue gas stack thermal and flow design.
The reason this matters for the duct designer is that emission compliance cascades back into duct design: the duct between the kiln and the bag filter sees raw 100–500 g/Nm³ dust loading, the duct between the bag filter and the stack sees less than 50 mg/Nm³, and they have completely different abrasion exposure, condensation risk and material specifications. Any HVAC contractor or process engineer who is not clear on which duct segment they are pricing is going to lose money or fail compliance.
Process exhaust HVAC — kiln gas conditioning, baghouse, ESP
The kiln main exhaust gas path on a modern dry-process plant runs in this order: kiln tail at 350–450°C, preheater tower top at 350–450°C, conditioning tower (gas conditioning chamber) at 150–200°C outlet, dust collector inlet (bag filter house or ESP), induced draft fan, stack. Total path length is typically 100–200 m of large-bore welded ductwork ranging from 2.5 m to 6 m internal diameter depending on plant capacity. Every metre of it is welded heavy fabrication.
The conditioning tower is the heat-rejection unit for the kiln main exhaust. Gas enters at 350–450°C and is contacted with atomised water spray from spray nozzles or rotary atomisers. Evaporative cooling drops gas temperature to 150–200°C — comfortably above the acid dewpoint (around 130–140°C for typical cement kiln gas) but well below the upper temperature limit of PTFE-membrane filter media (around 250°C continuous). Conditioning tower outlet temperature control is a critical operational variable. Too hot and the bag filter sees thermal damage. Too cold and acid condensation corrodes the duct internal surfaces and blinds the filter media.
Bag filter houses are the dominant dust collection technology on new Australian cement plants and on most retrofits over the last 20 years. Pulse-jet bag filter houses with PTFE-membrane filter media are the standard configuration. Filter design follows AS 4655. Air-to-cloth ratios are typically 1.0–1.5 m³/m²/min for cement applications. A 5,000 tpd clinker line baghouse runs 8,000–12,000 filter bags in 8–16 compartments, allowing one compartment to be isolated for offline cleaning while the others stay on duty. Bag filter inlet duct sees dust loading 100–500 g/Nm³; bag filter outlet duct sees less than 30 mg/Nm³ when the filter is operating correctly. The differential pressure across the filter (typically 1.5–2.5 kPa stable) drives the induced draft fan power consumption — every 100 Pa of additional pressure drop adds roughly 1–2% to fan power.
Some Australian plants retain electrostatic precipitators on kiln exhaust, particularly older installations from the 1970s and 1980s. ESP design uses high-voltage plate or wire collectors charging dust particles and capturing them on grounded plates that are rapped to dislodge collected dust. ESP outlet duct runs cleaner gas but is sensitive to gas velocity stratification — duct internal flow distribution upstream of the first ESP field must be uniform within ±15% RMS, which dictates inlet duct geometry, turning vanes, perforated distribution plates and gas flow modelling during design.
Induced draft (ID) fans on cement kiln main exhaust are large radial fans, typically 1.5–4 MW shaft power for a major clinker line. Fan inlet duct sees high suction and is designed to avoid resonance with the fan blade-pass frequency. Fan outlet duct transitions to the stack via an expansion section that controls the velocity step-down from fan discharge (typically 25–35 m/s) to stack inlet (typically 15–20 m/s).
Stacks are designed per EN 13384 chimney code and locally calculated for wind, seismic, thermal, and corrosion loading. Stack height is typically 60–80 m above grade for a modern clinker line, set by EPA dispersion modelling for ground-level concentration of regulated pollutants. Stack lining is selected for acid dewpoint margin — AISI 316L stainless steel is common for the upper third where condensation risk is highest, with carbon steel below.
Duct design for high-dust streams — velocity, geometry, abrasion
The primary duct design rule for cement-laden gas is minimum transport velocity. Below the minimum transport velocity, dust drops out of suspension and accumulates in the duct, building cement-rock concretions that gradually reduce flow area until the duct chokes. Cement kiln dust and clinker dust transport velocity is conventionally 18–22 m/s, with 20 m/s the typical design point. Pneumatic conveying lines for finished cement run similarly — dilute-phase conveying at 18–22 m/s, dense-phase conveying at 5–10 m/s with appropriate wall thickness and pulse design.
Plenum sections — the wide low-velocity volumes inside dust collector inlet hoods — are deliberately designed in the opposite direction. Plenum velocities of 8–12 m/s allow dust to drop out of suspension into the hopper instead of being carried into the filter. The transition from the high-velocity inlet duct to the low-velocity plenum is a critical geometry — too abrupt and you get jet impingement on the back wall and rapid abrasion, too gradual and you have wasted floor space. Engineers typically use 15–20° taper angles and impingement-protected back walls.
Bend geometry on dust-laden duct is the largest single source of abrasion failure. A 90° bend on a 20 m/s dust stream sees centripetal acceleration of around 270 g at the outer radius for a 1.5 m duct diameter. Particles strike the outer wall at angles between 15° and 90° depending on bend ratio. Engineers design with bend radius-to-diameter ratios of 1.5–2.5 (long-radius elbows preferred), supplemented with abrasion liners on the outer wall: chromium carbide overlay plate (Bisalloy 80, Hardox 450), basalt-lined removable inserts, ceramic tile inserts, or sacrificial wear plates that are bolted on and replaced every shutdown.
Tee connections are second-worst. The branch line tee always sees impingement on the opposite wall of the run — engineers either install sacrificial wear targets, change the tee to a 45° lateral, or add a deflector plate. Reducer geometry similarly — eccentric reducers (flat-on-top) are preferred over concentric reducers on horizontal cement-laden duct because they prevent particle accumulation on the lower wall.
Materials for cement plant ductwork
Cement plant duct material selection is dictated by temperature, abrasion, dust loading and chemistry. The materials list runs as follows.
- Heavy-gauge mild steel (3–10 mm). The default workhorse for cement plant process duct. Used at 4–6 mm wall thickness for kiln exhaust downstream of the conditioning tower, baghouse inlet duct, ESP inlet duct, and ID fan inlet/outlet duct. Used at 6–10 mm wall thickness for high-temperature kiln tail duct and refractory-lined applications. Welded by SAW (submerged arc welding) for longitudinal seams and SMAW or FCAW for circumferential field joints.
- Refractory-lined steel. Used where internal gas temperature continuously exceeds 700°C or peaks above 900°C. Refractory linings are typically 75–150 mm thick castable (alumina-silicate, calcium aluminate cement) or insulating brick with anchor studs. Refractory-lined duct on cement plant calciner connections and tertiary air ducts is the heaviest fabrication scope on the plant.
- Hard-faced chromium carbide overlay (Bisalloy 80, Hardox 450, Quard 500). Used at the highest-abrasion zones on dust-laden duct — bend outer walls, tee impingement targets, distribution duct internal baffles. Typical hardness 55–62 HRC, abrasion resistance 5–15× plain mild steel depending on particle size and impact angle. Sold as overlay plate (Bisalloy on a mild steel substrate) or solid hardened plate (Hardox).
- Basalt-lined steel. Used on pneumatic conveying lines and filter inlet duct in high-abrasion zones. Cast basalt or fused basalt is set into a steel tube on a thin mortar bed; very hard (around 8 Mohs), highly abrasion resistant. Limit is thermal cycling — basalt fractures if it sees rapid temperature changes above 300°C.
- Ceramic tile lining. Used on selective wear-target zones where basalt is not appropriate. High-alumina (90–95% Al2O3) ceramic tiles bonded to a steel substrate by epoxy or vulcanised rubber. High abrasion resistance, lower impact resistance.
- Stainless steel (304L, 316L, 309S, 310S). Used on stack lining, bag filter outlet stack duct, acid-condensation zones. 316L for general acid resistance. 309S/310S for high-temperature service in calciner gas circuits where mild steel oxidation is unacceptable.
- Galvanised steel (G275, G300). Used on comfort HVAC ductwork in the pulpit, control room, MCC, lab and amenities. Standard sheet metal HVAC duct fabricated to AS/NZS 4254-1. SBKJ auto duct lines and spiral tubeformers are the right tool here.
- Fluoropolymer-coated steel (PVDF, ETFE). Used on supply HVAC duct in fly-ash exposure zones where condensation could attack galvanised coating. Common on fly-ash silo top vent filters and on supply duct in dispatch tower control rooms.
Pulpit and control room HVAC — positive pressure done right
The kiln pulpit and central control room are the brain of the plant. Operators spend 12-hour shifts in front of distributed control system screens reading kiln burning zone temperature, raw mill product fineness, ID fan amperage and a hundred other variables. The room has to be cool, dust-free, slightly positively pressurised relative to the surrounding plant, and quiet enough to talk to a colleague without raising your voice. Get any of those wrong and the operator's attention drifts, and the cost of an attention lapse on a cement kiln is a four-day refractory failure that costs millions.
Pulpit and control room HVAC design starts with positive pressure. Target +25 to +50 Pa relative to the surrounding plant, which keeps cement dust and process gas leakage out of the room. Achieve this with a make-up air handling unit drawing outside air through a two-stage filter bank: G4 prefilter (ISO 16890 ePM10 ≥50%) for coarse dust, then F7 or F9 final filter (ISO 16890 ePM2.5 ≥85% or ePM1 ≥80%) for respirable dust. Filter pressure drop monitoring with differential pressure transducers and stepped alarm thresholds is mandatory — ignored filter alarms are how cement dust slowly takes over a control room ceiling void.
Hermetic sealing of the building envelope matters. Door gaskets, cable penetration seals, expansion joints in roofing — all need to be cement-dust-tight. Air locks at main entry doors are standard practice; revolving doors are used at large plants. Window glazing is double-glazed sealed units with EPDM gaskets; access panels have cam-lock sealed gaskets. The HVAC supply duct fabricated for these rooms is conventional rectangular galvanised duct at 0.7–1.0 mm wall thickness, fabricated on an SBAL-V auto duct line to AS/NZS 4254-1 low-pressure tolerances, with TDF/TDC flange joints sealed with neoprene gasket and silicone bead.
Substation, MCC and electrical room HVAC
Cement plant electrical rooms — substations, motor control centres (MCC), variable frequency drive (VFD) rooms, and switchgear rooms — have stringent HVAC requirements because cement dust ingress into switchgear is catastrophic. Cement dust accumulates on insulating surfaces, absorbs moisture in tropical and coastal Australian climates (Gladstone, Munster, Birkenhead are all coastal), and tracks across insulators causing flashovers, short circuits and equipment fires. A single MCC fire from cement dust ingress can take out an entire mill section for a week.
Design intent for electrical room HVAC is positive pressure (+25 to +50 Pa), redundant cooling (N+1 chillers, N+1 air handling units), continuous particulate intake filtration (G4 + F8 minimum, ISO 16890 ePM2.5 ≥85%), and robust dehumidification to keep relative humidity below 60% RH in coastal locations. VFD rooms have higher heat loads (5–15 kW per drive cabinet typical) and may require dedicated close-control air handling units rather than building-wide HVAC. Cooling redundancy is critical because an MCC room loss-of-cooling event escalates rapidly — VFD cabinet over-temperature trips at 45–55°C and the kiln stops within minutes of widespread MCC trips.
Duct fabrication for these rooms is standard galvanised rectangular duct on the SBAL-V plus spiral duct from the SBTF for the larger trunk runs. Some sites specify aluminium-clad fibreglass insulation on supply duct to reduce thermal sweating. Fire-rated duct (1- or 2-hour rating) is specified on duct passing through fire-separated electrical room walls, with rated fire dampers at every penetration.
Mill exhaust ductwork — raw, cement and coal mill
The cement plant has three large mill systems, each with its own dedusting circuit. The raw mill grinds limestone and clay raw meal at typical capacity 200–400 tonnes per hour for a 5,000 tpd line. Raw mill exhaust gas typically passes through the same bag filter house as the kiln main exhaust on integrated plants — the raw mill exhaust adds 100,000–150,000 Nm³/h of gas at 90–110°C and a dust loading of 50–150 g/Nm³ of raw meal. The raw mill exhaust duct between the mill and the baghouse is welded heavy fabrication with abrasion liners at bends.
The cement mill grinds clinker and gypsum at typical capacity 100–200 tonnes per hour. Cement mill exhaust gas runs at 70–100°C and 50–150 g/Nm³ dust loading. Most plants run a separate dedicated bag filter house on the cement mill exhaust because the gas chemistry differs from the kiln main exhaust (lower CO2 partial pressure, lower SO2). Mill exhaust duct construction is identical philosophy to the kiln stream — 4–6 mm carbon steel with abrasion protection.
The coal mill grinds primary fuel for the kiln burner, typically pulverised coal or petcoke, sometimes blended with biomass or alternative solid fuels. Coal mill exhaust is special — it is hot (65–85°C), oxygen-lean (typically 8–12% O2 maintained inert with kiln exhaust gas recycle), and explosion-prone because pulverised coal is a deflagrating dust. Coal mill exhaust duct design follows EN 14491 dust explosion venting code: pressure-resistant duct walls (typically 6 mm carbon steel), explosion vents on the duct top, isolation valves at duct connections. CO and O2 monitoring is continuous, and coal mill systems are isolated by automated quick-closing dampers if either parameter deviates.
None of the three mill exhaust systems is sheet-metal HVAC scope. They are all welded process duct delivered by specialist fabrication shops working from EPC mechanical drawings.
Cement transport pneumatic conveying
Finished cement and clinker are transported between mills, silos, packers and trucks by pneumatic conveying — air-driven transport through closed pipes. There are two regimes: dilute-phase pneumatic conveying (high air velocity, low solids loading, gas-suspended particles) at 18–22 m/s; and dense-phase pneumatic conveying (low velocity, high solids loading, plug or slug flow) at 5–10 m/s. Dilute-phase is standard for long-distance horizontal runs; dense-phase is used where particle attrition must be minimised.
Pneumatic conveying pipe is typically 6–12 mm wall thickness carbon steel (cement is abrasive even in dense phase). Bend and elbow internal walls are protected with basalt-lined wear elbows or high-alumina ceramic tile. Compressor air supply for dilute-phase pneumatic conveying is significant — 2–5 kg of air per kg of cement transported, which translates to 1,000–3,000 Nm³/h compressor capacity for typical conveying rates. Receiving silo top filter vents handle the displaced conveying air at 50–80 mg/Nm³ dust outlet loading after the silo top vent filter.
Cement silo top vent filters are small dedicated bag filters mounted on each cement storage silo top, sized to handle the displaced air from pneumatic conveying inflow plus thermal venting on day/night cycles. Each silo top filter has its own short connecting duct (typically 0.5–1.0 m diameter, welded carbon steel). Silo top filter discharge is typically into a small atmospheric vent or a building roof penetration.
Bagging plant HVAC
Cement bagging plants are the dustiest part of any cement plant from a worker exposure perspective. The bagging line takes finished cement from the bulk silo and packs it into 25 kg paper bags via rotary or in-line packers, then palletises and shrink-wraps the pallets, then loads them onto road trucks at the dispatch dock. Every transfer point — packer spout, bag drop conveyor, palletiser, pallet wrap station, truck loading tower — is a dust generation point.
Localised dust extraction at packer spouts is the primary control. Each spout has a small extraction hood feeding a dedicated central dust collector, typically a small pulse-jet bag filter with 1,000–5,000 m³/h capacity per packer spout. Trunk extraction duct connecting hoods to the central baghouse is welded carbon steel at 4 mm wall thickness, with abrasion liners at bends. The hood-side flexible connection is critical — flexible neoprene or rubber sleeves with stainless mesh reinforcement that handle the small spout movements during packer indexing.
Truck loading tower dust extraction handles the bulk cement free-fall into truck tanker hatches. Typical extraction rate 5,000–10,000 m³/h per loading bay. Loading tower extraction duct is large-bore (1.0–1.5 m diameter), welded carbon steel.
Building-wide comfort HVAC for the bagging plant — supply air to the operator stations, control room HVAC, lunch room, change rooms — is conventional galvanised sheet-metal duct on SBKJ duct lines. Bag filter discharge duct from each compartment to the silo or to the cleaning auger is welded fabrication.
Gypsum, fly ash and additive handling
Modern cement plants blend several supplementary cementitious materials (SCMs) into finished cement: gypsum (4–6% added at the cement mill for setting time control), fly ash (Type F or Type C, up to 25% replacement of clinker), ground granulated blast furnace slag (GGBFS, up to 65% replacement of clinker in slag cement), limestone filler (up to 5% inert filler), and natural pozzolans. Each material has its own receiving, storage, weighing and feeding circuit, and each circuit has its own dust extraction.
Gypsum is typically received as raw rock or as desulphogypsum from coal-fired power station flue gas desulphurisation, crushed and ground in a dedicated mill or fed directly to the cement mill. Dust extraction at gypsum receiving bins is standard. Fly ash is received in pneumatic delivery tankers, blown into a fly ash silo, then conveyed to the cement mill or finished cement silo by air slide or pneumatic conveying. Fly ash silo top vent filters and tanker connection points generate dust.
Each addition point at the cement mill or finished cement silo has a dedicated extraction hood and connecting duct. None of it is sheet-metal HVAC scope. Comfort HVAC for the additive handling control room and addition operator station is conventional duct.
Clinker cooler air system and heat recovery
Clinker exits the rotary kiln at around 1,300°C and falls onto the clinker cooler, typically a grate cooler with stationary or moving grate plates. Cooling air is supplied from below the grate by multiple compartmentalised forced-draft fans, each fan supplying a different temperature compartment. Approximate air-to-clinker ratio is 2 kg of cooling air per kg of clinker — for a 5,000 tpd plant that is 10,000 tonnes per day of cooling air, which is 7,500–8,500 Nm³/min.
Cooling air heats up dramatically as it passes through the clinker bed. The hottest compartment air is recovered as secondary combustion air for the kiln main burner (typically 1,000–1,200°C secondary air temperature) and as tertiary combustion air for the calciner (typically 800–1,000°C tertiary air temperature). Secondary air ducts from cooler hot compartment to kiln hood are short and refractory-lined heavy fabrication. Tertiary air ducts from cooler intermediate compartment to calciner can be 50–100 m long and are refractory-lined throughout.
Cooler vent air — the cooler air not recovered as combustion air — exits at 250–350°C and is routed via a dedicated bag filter house or mixed with the kiln main exhaust upstream of the conditioning tower. Cooler vent ductwork is welded carbon steel 4–6 mm wall thickness with insulation.
Heat recovery from cooler vent air is a growing decarbonisation focus. Waste heat recovery (WHR) systems use organic Rankine cycle (ORC) or steam Rankine cycle plant to convert cooler vent and preheater outlet heat into electrical power, typically 5–10 MW for a 5,000 tpd plant. WHR plant adds new ductwork between the cooler vent, the preheater outlet and the WHR boiler.
Alternative fuel handling — RDF, biomass, tyres
Australian cement plants have substituted alternative fuels for primary coal and petcoke at increasing rates over the last decade. Boral, Holcim and Adbri all run alternative fuel programmes. Common alternative fuels are refuse-derived fuel (RDF, made from sorted municipal solid waste), tyre-derived fuel (whole tyres or shredded tyre chips), biomass (forestry residues, bagasse, wood chips), processed engineered fuel (PEF), solvent-based industrial waste fuels, and meat and bone meal (MBM).
Alternative fuel handling buildings are new infrastructure on many existing plants — feed reception, storage, shredding, screening, blending, conveying to the kiln main burner or calciner. Each handling step generates dust, fume, odour and combustion air supply requirements. Shredding and screening generates the most dust. RDF buildings have explosion-rated dust extraction with continuous CO and CH4 monitoring. Biomass storage has fugitive dust extraction at conveyor transfer points. Tyre handling has localised odour extraction at the shredder feed.
Combustion air supply duct from the alternative fuel feed point to the kiln burner or calciner is welded fabrication. Comfort HVAC for the alternative fuel control room, weighbridge office and operator station is sheet-metal duct on SBKJ machinery. Decarbonisation expansion of alternative fuel substitution at Australian plants is driving comfort HVAC demand growth at all major sites.
SCR and SNCR NOx control HVAC
Cement kiln NOx emissions are controlled by selective non-catalytic reduction (SNCR) or, less commonly in Australia, selective catalytic reduction (SCR). SNCR injects ammonia or urea into the calciner at temperatures around 850–1,050°C; the reagent reacts with NOx to form nitrogen and water. SCR injects ammonia or urea over a vanadium-titanium catalyst at lower temperatures around 300–400°C; SCR is more efficient (80–90% NOx reduction versus 40–60% for SNCR) but adds catalyst and ductwork.
SNCR equipment is typically a urea storage tank, urea pumps, atomisation skids, and injection lances penetrating the calciner wall. The injection ductwork is small-bore stainless steel pipework. SCR equipment adds a catalyst housing in the duct between the preheater outlet and the conditioning tower, with ammonia injection grid upstream. SCR retrofit is significant ductwork — the catalyst housing is several metres long and the ammonia injection grid covers the full duct cross-section.
Ammonia leak detection ductwork is mandatory in any building with bulk ammonia storage. Continuous ammonia monitors with stepped alarm thresholds and emergency ventilation duct activation are designed per AS 4332 anhydrous ammonia handling. Ventilation duct in the ammonia building is welded carbon steel with corrosion-resistant inner coating.
Decarbonisation pathways and the duct scope shift
Cement is approximately 8% of global carbon dioxide emissions, with roughly 60% of those emissions coming from the chemistry of calcination (CaCO₃ → CaO + CO₂) and 40% from fuel combustion. Decarbonising cement therefore requires changes on both fronts — alternative fuels and process electrification on the combustion side, and clinker substitution and CO2 capture on the chemistry side. Australian cement makers are pursuing all of these pathways.
Alternative fuels. Boral CleanTech Cement, Holcim ECOPlanet and Adbri sustainability programmes all run aggressive alternative fuel substitution targets. Substitution rates of 30–50% on primary heat input are achievable with current technology and are being delivered now at multiple Australian plants. Alternative fuel preparation buildings expand the comfort HVAC scope and add specialised dust and fume extraction.
Clinker substitution. Lower-clinker cement (LC3, calcined clay limestone cement, slag cement, fly ash blends) reduces clinker demand for a given cement volume. Calcined clay activation is a new process step — clay is calcined in a flash calciner at 750–800°C, generating its own gas stream and dust extraction needs. New calcined clay plants (proposed at Berrima, trialled at Gladstone) add full process duct scope.
Oxy-fuel combustion. Oxy-fuel cement kilns burn fuel in pure oxygen instead of air, producing a flue gas that is mostly CO2 and H2O — easier to capture and store. Oxy-fuel changes the kiln gas chemistry significantly, raising CO2 partial pressure and acid dewpoint. Duct material specifications shift toward higher stainless grades and lined duct.
CO2 capture. Post-combustion amine capture, calcium looping, and direct air capture pilots are running globally, with several Australian feasibility studies at Boral and Holcim sites. CO2 capture plants add a complete new flue gas treatment train — flue gas cooler, blower, absorber column, regenerator, CO2 compression — each with significant ductwork. Most of it is welded fabrication.
Electric kiln. Plasma electric kilns and resistive electric kilns are at pilot stage globally, with no commercial-scale Australian projects yet announced. Electric kilns eliminate combustion gas entirely, drastically reducing flue gas volumes — but generate concentrated CO2 from calcination chemistry that needs capture. Duct scope on an electric kiln is dramatically smaller than on a fuel-fired kiln.
Geopolymer and alternative cementitious materials. Geopolymer cement (alkali-activated aluminosilicates) is produced without a high-temperature kiln and at very different chemistry. Australian geopolymer producers (Wagners EFC) operate fundamentally different process plants. The duct scope is smaller and less heat-intensive but introduces new chemistry — alkali activator handling, silicate solution storage, mixing and pumping.
What all of these decarbonisation pathways have in common from an HVAC contractor's perspective: comfort HVAC scope (control rooms, MCC, lab, amenities) continues across every pathway, and is often expanded because new buildings are added; process duct scope changes significantly in chemistry, materials and sizing, and is welded-fabrication scope handled by EPC specialists. SBKJ machinery scope sits inside the comfort HVAC envelope and is largely unchanged across decarbonisation transitions.
Major Australian cement decarbonisation projects
The headline Australian cement decarbonisation projects in 2026 include the following. Note that this section reflects publicly available information at time of writing; live project status changes frequently.
- Boral CleanTech Cement. Boral's umbrella decarbonisation programme covering alternative fuel substitution at Berrima NSW, calcined clay trials, supplementary cementitious materials expansion, and lower-clinker cement product development. Major investment in alternative fuel handling buildings expanding the comfort HVAC scope across the site.
- Holcim ECOPlanet. Holcim's global low-carbon cement product line, deployed in Australia at Gladstone QLD and Railton TAS. ECOPlanet drives cement composition changes (lower clinker factor, higher SCM content) and supports alternative fuel substitution. Plant changes are largely in cement mill feed and additive handling, expanding extraction and comfort HVAC duct demand.
- Adbri sustainability programme. Adbri (Adelaide Brighton/Cement Australia) sustainability roadmap covering alternative fuels at Birkenhead SA, lime plant decarbonisation at Galong NSW, and SCM blending at Munster WA. New alternative fuel feed buildings have been added at multiple sites.
- Cement Industry Federation roadmap. Australian Cement Industry Federation has published an industry decarbonisation roadmap targeting 50% emission reduction by 2030 and net zero by 2050. Capital investment driven by this roadmap is the largest single demand driver for HVAC contractors over the 2026–2030 period.
SBKJ machinery for cement plant HVAC contractors
For HVAC contractors working on cement plant comfort HVAC, the standard machine package SBKJ recommends is built around three machines.
SBAL-V Auto Duct Production Line. The SBAL-V auto duct line is the workhorse for rectangular galvanised duct fabrication on cement plant pulpit, control room, MCC, lab and amenities scope. Coil-to-finished-duct in a single integrated line: decoiler, levelling rolls, notching station, beading, TDF flange forming, longitudinal seam locking, and cut-off. Single-shift output 10,000–15,000 m² per month for a typical SBAL-V configuration. See the auto duct lines category for the full machine range and specifications.
SBTF Spiral Tubeformer. The SBTF spiral tubeformer fabricates round galvanised duct from coil. Output diameters 80–1,500 mm typical, wall thickness 0.5–1.5 mm. Single-shift output of finished spiral duct length is 600–1,200 m per shift depending on diameter. Spiral duct is preferred for trunk supply runs in cement plant control rooms because of its strength and lower pressure drop. See the spiral tubeformer category for machine selection guidance.
TDF flange former and Pittsburgh seam machine. Standard sheet-metal HVAC accessories. Most SBKJ customers buying an SBAL-V already get integrated TDF flange forming on the auto line, but stand-alone TDF flange formers are available for retrofit workshops.
What SBKJ standard machinery does not address is heavy-gauge welded duct fabrication. Cement plant kiln exhaust duct, baghouse inlet duct, mill exhaust duct, cooler vent duct and pneumatic conveying lines are welded heavy fabrication built on plate-rolling, submerged-arc-welding and pressure-vessel equipment. That fabrication scope sits with structural-steel and pressure-vessel shops, not with HVAC contractors. SBKJ does, however, supply duct welding machines for sheet-metal welded seam applications — see the duct welding machines category for the relevant range. For very heavy welded fabrication, SBKJ refers customers to specialist welded-fabrication suppliers in the Australian and Southeast Asian heavy-fabrication market.
For comparison and cross-industry context, see our related guides on HVAC ductwork for mining ventilation and HVAC ductwork for steel mills and smelters, plus our overview of welding methods for HVAC duct fabrication. SBKJ Australia operates from Box Hill North VIC; see SBKJ Australia regional support for Australian-language commissioning, training and after-sales.
Construction phasing — shutdown-driven HVAC installation
Cement plants run 24 hours a day, seven days a week, 50–51 weeks a year. Continuous operation is critical to economics — every day a kiln is offline is roughly $200,000–$400,000 in lost margin for a 1.4 Mtpa plant. Planned maintenance shutdowns happen every 12–24 months and last 6–12 weeks. Shutdowns are when refractory is replaced, kiln tyres and rollers are inspected, mill internals are repaired, electrical equipment is overhauled, and major process duct sections are replaced.
Comfort HVAC duct installation can mostly happen during normal operation — fabrication off-site, then installation by HVAC contractors during ordinary working hours without affecting production. Process duct change-outs are shutdown-only because the system has to be cold and isolated. HVAC contractors working around a shutdown coordinate closely with the EPC shutdown coordinator to avoid clashes with crane lifts, scaffold installation, refractory work and electrical isolation lockouts.
The HVAC fabrication programme for a typical mid-sized cement plant comfort HVAC package (2,000–6,000 m² of duct across multiple buildings) runs 3–6 weeks of fabrication time and 4–8 weeks of installation time. Total programme from PO to handover is 12–20 weeks excluding any permit or design lead time. Design lead time on a cement plant project is typically 4–8 weeks for HVAC drawing approval through the EPC process.
FAQ
What duct materials are used for cement plant kiln exhaust?
Heavy-gauge mild steel 6–10 mm for kiln tail duct upstream of the conditioning tower (350–450°C), refractory-lined steel where surface temperatures exceed 700°C, 4–6 mm carbon steel between conditioning tower and bag filter, 3–5 mm carbon steel from baghouse outlet to stack, with chromium carbide overlay or basalt liners at high-abrasion bends. None of this is sheet-metal HVAC scope — it is welded heavy fabrication.
What is SBKJ machinery scope for cement plant projects?
SBKJ standard duct lines (SBAL-V, SBTF, TDF flange formers) fabricate the comfort HVAC scope: pulpit, control room, MCC, lab, amenities, lunch rooms, change rooms, administration. Heavy-gauge process exhaust duct is welded fabrication beyond standard SBKJ machinery scope — it sits with submerged-arc-welding and pressure-vessel shops.
Which Australian cement plants are major HVAC duct buyers?
Cement Australia (Holcim) at Gladstone QLD and Railton TAS. Boral Cement at Berrima NSW, Maldon NSW and Marulan NSW. Adbri (Adelaide Brighton) at Birkenhead SA and Munster WA, plus Galong NSW lime. Sunstate Cement Brisbane (Boral/Adbri JV). Independent Cement & Lime nationwide blending. Plus hundreds of premix concrete batching plants across Australia.
How does cement plant decarbonisation change the duct scope?
Comfort HVAC scope is largely unchanged or expanded (new alternative fuel buildings, calcined clay plants, CO2 capture plants all add comfort HVAC). Process duct scope changes significantly: oxy-fuel raises CO2 partial pressure and acid dewpoint requiring upgraded materials, alternative fuel preparation adds new dust and fume extraction, CO2 capture adds a complete new flue gas treatment train.
What standards govern cement plant duct emissions in Australia?
State EPA licences referencing AS 4655 (alternative dust collector), AS 4323.1 (stack sampling), EN 13384 (chimney design), AS/NZS 4254 (sheet-metal HVAC duct). International benchmarks: US EPA NSPS Subpart F (40 CFR 60.60–60.66) and EU IED BREF for cement, lime and magnesium oxide manufacturing. Typical kiln stack ELVs: dust 50 mg/Nm³, NOx 800 mg/Nm³, SO2 400–600 mg/Nm³.
What is typical lead time for cement plant comfort HVAC duct fabrication?
Comfort HVAC duct on SBKJ auto duct lines runs 3–6 weeks fabrication time for 2,000–6,000 m² of duct. Heavy-gauge process duct from welded shops runs 12–26 weeks. Total cement plant HVAC programmes from PO to handover are 12–20 weeks excluding design lead time. Plan around the planned major shutdown window every 12–24 months.
What duct velocities apply to cement-laden gas streams?
Minimum transport velocity 18–22 m/s for dust-laden duct (kiln exhaust, mill exhaust, pneumatic conveying dilute phase) to keep particulate suspended. 8–12 m/s in plenum sections inside dust collectors to allow drop-out. 5–8 m/s for comfort HVAC supply duct per AS 1668.2. Dense-phase pneumatic conveying 5–10 m/s with appropriate wall thickness.
Can SBKJ supply duct fabrication machinery to cement plant HVAC contractors?
Yes. Standard package is SBAL-V auto duct line plus SBTF spiral tubeformer plus TDF flange former plus Pittsburgh seam machine. SBKJ Australia in Box Hill North VIC provides English-language pre-sales, commissioning and after-sales for HVAC contractors. Heavy welded fabrication is outside SBKJ standard machinery scope — that sits with welded-fabrication specialists.
Talk to an SBKJ engineer about your cement plant HVAC duct fabrication scope →
