Engineered Wood (LVL, CLT, Glulam), Particleboard, MDF, Plywood, OSB, HPL and Pulp & Paper Mill HVAC Duct Engineering Guide — Australian Wood Panel and Paper Manufacturing

1. Why panel and paper mill ductwork is not just bigger sawmill ductwork

An engineered wood products plant, a wood-based panel manufacturer and a Kraft pulp and paper mill share a common raw material with the Australian sawmill — wood fibre delivered from plantation pine, plantation hardwood and managed native hardwood. The HVAC engineering, however, sits at a fundamentally different intersection of hazards. The sawmill makes lumber. The panel plant takes wood fibre, adds resin, applies pressure and temperature, and outputs an engineered substrate. The pulp mill takes wood chip, cooks it in caustic soda and sodium sulphide at 170 degrees Celsius and 7 bar, separates the cellulose fibre, bleaches it with chlorine dioxide, and outputs paper pulp. The paper mill takes pulp, dilutes it with water, presses and dries it, and outputs a continuous web. Each of these process families has its own occupational exposure profile, its own deflagration risk envelope, its own corrosion mechanism, and its own AS and NFPA reference framework.

Three engineering realities separate the panel-and-paper plant from the sawmill we covered in our sawmill, timber and plywood HVAC guide. First, the chemical exposure profile is broader and more aggressive. Formaldehyde at the MDF and particleboard hot press operator station is the highest single-point human exposure in the entire Australian wood industry, regulated at 1 ppm short-term exposure limit by Safe Work Australia. Isocyanate MDI binder at the OSB blender carries a 0.005 ppm short-term limit and is a respiratory sensitiser with no safe exposure threshold. Hydrogen sulphide at the Kraft pulp digester carries a 10 ppm time-weighted limit and is acutely toxic at concentrations above 100 ppm. Chlorine dioxide at the bleach plant carries a 0.1 ppm time-weighted limit. Together these establish a much tighter capture, containment and emission tolerance than any sawmill ductwork carries.

Second, the combustible dust envelope is St3 not St2. Sander dust from MDF, particleboard and OSB has Kst typically 200 bar metres per second and minimum ignition energy below 30 millijoules — placing the facility in St3 class under NFPA 660 for explosion vent sizing. The chip handling, drying, blender and forming lines carry continuous dust cloud Zone 20 inside equipment and Zone 21 to Zone 22 outside. The press, the sander and the dust collector each carry a deflagration risk that has historically caused fatalities at panel plants worldwide.

Third, the materials of construction step up the cost curve. Galvanized steel is suitable for log yard, debarker, head rig and primary breakdown. 304L stainless is the engineered wood adhesive applicator default. 316L stainless is mandatory at the MDF and particleboard hot press exhaust, the OSB blender capture, the plywood veneer drier exhaust, the Kraft digester and recovery boiler flue, the lime kiln vent, the chlorine dioxide bleach plant and every TRS odour control duct. 904L or Hastelloy C-276 is required at the ClO2 generator vent and the bleach tower seal hood. FRP is the standard for wet scrubber vessel construction. A complete panel-and-paper facility duct package will typically be 60 to 80 percent stainless by area — the inverse ratio to a sawmill where 80 to 90 percent of the duct area is galvanized.

This guide is the reference our engineers use when we quote an Australian engineered wood, wood panel, pulp or paper mill facility. It covers the Australian and international codes that apply, the process zones that drive sizing and material selection, the hazardous area classification framework, the SBKJ machine configuration we deploy at our Box Hill North VIC office, and the operator landscape we engage with in the Australian market.

2. The Australian and international regulatory framework

Fifteen standards govern HVAC ductwork in the Australian engineered wood, wood panel and pulp and paper sector. The framework is broader than the sawmill envelope because each sub-sector — panel, engineered wood, pulp, paper — brings additional reference standards on top of the common AS 1668.2 and AS 4254 base.

2.1 AS 1668.2 — Industrial ventilation

AS 1668.2 is the Australian umbrella industrial ventilation standard. It sets minimum outside air per occupant, capture velocity targets for industrial process exhaust hoods, and references the Safe Work Australia workplace exposure standards for chemical contaminants. For the panel and paper sector the AS 1668.2 capture velocity targets are: 1.0 metres per second at a partially-open press infeed, 1.5 metres per second at a fully-hooded press infeed, 1.5 metres per second at an enclosed blender face, 0.5 metres per second at a low-velocity sander dust hood, 2.0 metres per second at an open shop floor task, and dilution rates of 6 to 10 air changes per hour at general process halls dropping to 4 to 6 ACH at drier halls where high airflow defeats the drying process. For the cross-reference to AS 1668.2 see our AS 1668.2 Australian ventilation code reference.

2.2 AS 4254 — Ductwork construction

AS 4254 Part 1 (flexible duct) and AS 4254 Part 2 (rigid duct) set the Australian fabrication standard for HVAC ductwork. Material gauge, joint construction, sealant class, pressure class and leakage class are all referenced in the SBKJ specification. For the panel and paper sector, AS 4254 Part 2 medium-pressure to high-pressure duct construction is the default, with leakage class C or D depending on the duty. For the cross-reference see our AS 4254 Australian ductwork construction reference.

2.3 AS 3957 — Dust hazard assessment

AS 3957 is the Australian standard for dust hazard assessment in combustible particulate solids environments. It mirrors NFPA 660 chapter requirements but with Australian regulatory weight. Every facility processing wood dust above the threshold quantity requires a documented Dust Hazard Analysis (DHA) with engineered controls, spark detection at ignition-source machinery, NFPA 68 explosion venting at dust collectors, isolation valves between sources and collectors, and continuous housekeeping monitoring. The DHA is refreshed every five years and re-issued whenever the process changes.

2.4 NFPA 660 — Combustible particulate solids

NFPA 660 is the consolidated United States National Fire Protection Association standard for combustible particulate solids, published in 2025. It replaces the prior NFPA 484 (combustible metals), NFPA 654 (combustible particulate solids), NFPA 655 (sulphur) and NFPA 664 (woodworking) — all four are now chapters of NFPA 660. For the Australian engineered wood and panel sector, NFPA 660 chapter 30 carries the prior NFPA 664 woodworking content. Australian insurers and consulting fire engineers reference NFPA 660 from 2025 onward.

2.5 NFPA 68 — Deflagration venting

NFPA 68 sets the sizing methodology for deflagration vents on enclosures containing combustible dust. The vent area is calculated from the protected volume, the dust Kst, the maximum reduced pressure the enclosure can withstand, and the venting efficiency factor. For MDF, particleboard and OSB sander dust collectors typical vent area is 1.5 to 3.0 square metres per cubic metre of protected volume. The vent must discharge to a safe external area free of personnel and assets.

2.6 NFPA 69 — Explosion prevention

NFPA 69 covers the prevention rather than the venting of explosions, applying where venting cannot be discharged to a safe area or where the process must operate in an inerted state. Chemical suppression (sodium bicarbonate or monoammonium phosphate discharge) is the most common engineered prevention measure on indoor dust collectors. Containment is rare in wood dust because the vessel mass becomes uneconomic.

2.7 AS/NZS 60079 — Hazardous areas

AS/NZS 60079.10.1 covers flammable gas and vapour hazardous area classification, AS/NZS 60079.10.2 covers combustible dust. For the panel and paper sector the typical zone map is: Zone 22 inside every wood dust extraction duct with localised Zone 21 around access doors, blast gates and explosion vents; Zone 20 inside dust collectors, silos and drier drums; Zone 2 around the LVL or glulam adhesive applicator, the LPG kiln burner room, the HPL impregnator solvent zone and the bleach plant ClO2 generator; Zone 1 in the Kraft digester area, the brown stock washer, the black liquor tank farm and the recovery boiler smelt spout vicinity. Equipment in each zone must carry the appropriate Ex tD, Ex tc, Ex d or Ex de rating with IECEx Ex-d ATEX certification mandatory at the more demanding zones.

2.8 AS 1530.4 — Fire resistance of structures

AS 1530.4 covers fire resistance testing of building elements. For panel and paper facilities the relevant clauses cover smoke control duct, kitchen exhaust duct and any duct passing through fire-rated separations. The panel-and-paper context is typically the warehouse-to-production separation and the office-to-production separation where fire-rated duct or fire damper protection is required.

2.9 AS 1851 — Fire system maintenance

AS 1851 sets the routine service and maintenance frequency for fire protection systems including smoke control duct, fire damper, sprinkler system and gaseous suppression. The panel-and-paper facility includes spark detection systems, NFPA 68 vents and (where used) NFPA 69 suppression in the AS 1851 maintenance schedule.

2.10 AS 1657 — Fixed platforms, walkways and ladders

AS 1657 covers fixed access for inspection, maintenance and emergency at industrial duct and equipment. For the panel and paper sector this drives access to roof-mounted RTOs, stack platforms, dust collector platforms, recovery boiler vent platforms and bleach plant scrubber platforms. All access must comply with AS 1657 for working at height and edge protection.

2.11 AS 1940 — Flammable and combustible liquids

AS 1940 governs the storage and handling of flammable and combustible liquids — adhesive solvents, finishing solvents, hardener and any solvent-based binder. For the engineered wood plant the AS 1940 hazardous area envelopes drive the paint mix room and adhesive mix room ventilation requirements. For the pulp mill the AS 1940 envelope captures the turpentine recovery from softwood pulping if installed.

2.12 AS 6122 — EWPAA engineered wood

AS 6122 is the Engineered Wood Products Association of Australia (EWPAA) standard for the quality and conformance of structural engineered wood products. The standard does not directly drive HVAC duct specification but does set the dimensional, moisture content, formaldehyde emission and durability requirements that the manufacturing process — and therefore the ventilation envelope — must support.

2.13 AS/NZS 1859 — Wood-based panels

AS/NZS 1859 covers wood-based panels including particleboard, MDF, plywood, OSB and decorative laminate. Formaldehyde emission classification E0, E1 and E2 sets the resin chemistry that the panel manufacturer can deploy, which in turn drives the formaldehyde capture load on the press exhaust and the operator-station ventilation requirement. Australia's National Construction Code references AS/NZS 1859 for the building application of these panels.

2.14 AS/NZS 4357 — Laminated veneer lumber

AS/NZS 4357 sets the structural performance, dimensional and quality conformance requirements for LVL. The phenol-formaldehyde or PRF (phenol-resorcinol-formaldehyde) adhesive system used in LVL drives the phenol vapour capture requirement at the press hood and the LVL-specific RTO duty cycle.

2.15 AS/NZS 4787 — Glued laminated timber

AS/NZS 4787 sets the structural performance and quality conformance for glulam. Resorcinol-formaldehyde, MUF (melamine-urea-formaldehyde) and one-component polyurethane adhesives are all approved. The HVAC implication is the glue applicator capture and press infeed hood ventilation requirement.

2.16 AS/NZS 5610 — Cross-laminated timber

AS/NZS 5610 sets the performance, dimensional, durability and quality conformance for cross-laminated timber. PUR (one-component polyurethane), MUF and EPI (emulsion polymer isocyanate) adhesives are approved. CLT presses are typically large vacuum or hydraulic presses with low VOC emission compared to MDF or OSB, but isolated capture at the adhesive applicator is still required.

2.17 AS 4036 and AS 4037 — Boiler and pressure vessel

AS 4036 and AS 4037 cover steam boiler and pressure vessel design. For the pulp mill the relevant equipment includes the continuous digester (a tall pressure vessel operating at 170 degrees Celsius and 7 bar), the brown stock washer, the black liquor evaporator effect bodies, the recovery boiler steam drum, the lime kiln rotary shell, and the paper machine yankee dryer (a large cast iron cylinder operating at 5 to 10 bar steam pressure). The HVAC duct interfaces at every vent, relief, atmospheric breaker and stack must be AS 4036 / AS 4037 compatible.

2.18 AS 1318 — Industrial chimneys

AS 1318 sets the design and construction standard for industrial chimneys including the recovery boiler stack, the lime kiln stack, the hog fuel boiler stack and the paper mill general process stack. Material selection (steel, refractory-lined steel, FRP), corrosion allowance, structural design wind and seismic loading, and inspection access platforms are all in AS 1318. The Maryvale APM mill recovery boiler stack and the various Visy stack installations are all designed under AS 1318.

2.19 AS 4801 — Occupational health and safety

AS 4801 (now superseded by ISO 45001 at most large operators) is the workplace OHS management system standard. The HVAC implication is documentation — every duct system supplied must come with full bonding test records, vent sizing certificates, fan AMCA conformity, leak test reports, commissioning measurements, and the operations and maintenance manual.

2.20 ISO 12647 — Colour management

ISO 12647 covers colour management at the printing and converting stage of the paper supply chain. The HVAC implication is that the printing hall, the converting hall and the laminating hall require tight temperature and humidity control to maintain colour consistency. For the corrugated cardboard plant and the tissue paper converting line the ISO 12647 envelope drives the supply air conditioning specification.

3. Process zone breakdown — engineered wood products (LVL, CLT, glulam)

Engineered wood products are the fastest-growing segment of the Australian wood industry. LVL, CLT and glulam all displace concrete and steel in mid-rise commercial and apartment construction, and the Australian capacity has expanded substantially since 2020. We walk through the process zones in production order, calling out the duct duty, the material selection and the typical SBKJ specification.

3.1 Engineered wood log preparation and lamella preparation

Engineered wood plants typically receive plantation softwood (radiata pine, slash pine, Douglas fir) or plantation hardwood that has already been sawn, kiln dried and graded at an upstream sawmill. The plant-internal preparation is therefore not a full sawmill but a planer, moulder, finger jointer and sorting operation. The dust load is moderate — typically 50 to 150 kg per hour per planing line — and the dust is dry plantation softwood at 12 to 14 percent moisture content. Capture is conventional planer mill dust collection with conveying velocity 22 metres per second at the branch and 22 to 25 metres per second at the main, with 1.2 mm galvanized branches and 1.6 mm galvanized mains.

3.2 LVL veneer preparation and drying

LVL (laminated veneer lumber) starts with rotary peeling of debarked logs to produce continuous veneer ribbon. The veneer is clipped to length, sorted by grade, and dried in a long continuous belt or roller drier at 150 to 200 degrees Celsius. The drier exhaust is the dominant HVAC duty at the LVL plant — high temperature, high moisture, with trace VOC loading from the heated wood. Duct material is 316L stainless from the drier outlet to the heat recovery unit or stack, insulated to maintain wall temperature above the dew point. The drier exhaust at Hyne LVL Maryborough QLD, Carter Holt Harvey LVL and Wesbeam LVL Neerabup WA are all 316L stainless under SBKJ specification.

3.3 LVL adhesive application and press

The LVL press is a long heated continuous press at 120 to 150 degrees Celsius platen temperature with phenol-formaldehyde or PRF (phenol-resorcinol-formaldehyde) adhesive. Phenol-formaldehyde is the structural adhesive of choice for LVL because it is moisture resistant and qualifies the product for AS/NZS 4357 structural use. Adhesive is applied at a glue spreader immediately before the press, with capture at the spreader and at the press infeed and outfeed at 1.5 metres per second face velocity. The press hood exhausts steam, formaldehyde, phenol vapour and resin volatiles. Capture goes through 316L stainless duct to a regenerative thermal oxidiser (RTO) or wet scrubber before atmospheric release. Safe Work Australia formaldehyde STEL 1 ppm applies. Phenol STEL is not separately listed but is captured under the general VOC envelope.

The SBKJ specification at the LVL press is the SBPC1500 plasma cutter for the stainless plate work, the SBFB-1500 spiral former for the round mains, the SBLR-600 welder for the TIG seam welds, and the SB-ZF1500 stitchwelder for the stainless plenum construction at the RTO inlet and the press canopy. All hoods full TIG welded for leak-tight construction.

3.4 LVL finishing and sawing

After pressing and curing the LVL beam is sawn to length, edge-trimmed, surface dressed and stacked for despatch. The saw and edge trimmer dust capture is conventional sawdust collection in 1.2 mm galvanized at 20 metres per second branch and 22 metres per second main. The surface dressing is planer or moulder work with 22 metres per second conveying velocity. Both are Zone 22 dust hazard with full electrical bonding to under 10 ohms to plant earth.

3.5 CLT panel layup and adhesive application

CLT (cross-laminated timber) manufacture is fundamentally different from LVL. Where LVL bonds thin veneer in long continuous form, CLT bonds wide dimensional lamellas in cross-grain layers (typically 3 to 9 layers, alternating layer direction by 90 degrees) to produce large structural panels. XLam Australia at Wodonga VIC is Australia's largest CLT manufacturer with capacity around 60,000 cubic metres per year, with CTS Cross Laminated Timber also at Wodonga as a second operator. Adhesive is typically one-component polyurethane (PUR), EPI (emulsion polymer isocyanate) or MUF (melamine-urea-formaldehyde) under AS/NZS 5610.

CLT capture is room-scale dilution ventilation at 4 to 6 air changes per hour in the assembly hall, with close-coupled local exhaust at the glue applicator (the curtain coater or extruder applying adhesive bead to each lamella), the press infeed and the press itself. The PUR adhesive cures with moisture, so the press hood exhaust is low temperature and low volatile loading — much less aggressive than the MDF or LVL press. SBKJ specification at the CLT plant is galvanized G90 for the assembly hall dilution ventilation, 304L stainless at the glue applicator capture and the press hood, and 1.2 mm galvanized spiral at the upstream planer mill dust capture for lamella preparation.

3.6 CLT press and curing

The CLT press is typically a large hydraulic or vacuum press applying 2 to 8 bar pressure over the panel face during adhesive cure. Cure time is 1 to 4 hours depending on adhesive system. Press exhaust volume is moderate — air change rate of 6 to 10 per hour in the press enclosure. Duct material is 304L stainless at the press hood, transitioning to galvanized G90 in the discharge duct downstream of any condensation point. The press is in Zone 2 hazardous classification under AS/NZS 60079.10.1 for the adhesive vapour duty.

3.7 CLT panel finishing and CNC machining

After cure the CLT panel is moved to a CNC gantry machining centre for cutting to project-specific dimensions — door openings, window openings, services penetrations, edge profiles. The CNC machining generates conventional wood dust at high volume because the cutter spans large panels at high feed rate. Capture is multiple close-coupled hoods at the CNC head with branch velocity 22 metres per second, main velocity 22 to 25 metres per second, 1.2 mm galvanized branches and 1.6 mm galvanized main. Discharge to a cyclone-baghouse train with NFPA 68 venting and isolation valve. This is the highest single dust generation point at a CLT plant.

3.8 Glulam adhesive application and curing

Glulam (glue-laminated timber) is structural lumber laminated from finger-jointed dimensional softwood (radiata pine, Douglas fir) or hardwood. The lamellas are planed, finger-jointed end-to-end into continuous lengths, glued at the laminating face, stacked in the laminating press and cured. Adhesive is typically MUF, resorcinol-formaldehyde or one-component polyurethane under AS/NZS 4787. Hyne Timber's Maryborough QLD plant is Australia's largest glulam producer.

Glulam capture is at the glue applicator (typically a curtain coater or roller coater) and the laminating press infeed. The glue spreader hood is captured at 1.0 to 1.5 metres per second face velocity, with 304L stainless duct to a wet scrubber or RTO. The laminating press is a long radio-frequency or hot platen press with low VOC emission compared to MDF — much closer to CLT than to MDF in capture demand. SBKJ specification at the glulam plant is 304L stainless at the adhesive applicator capture, galvanized at the general dilution and the saw and trim dust capture downstream.

3.9 Engineered wood operator landscape

The Australian engineered wood landscape consolidated significantly between 2018 and 2024. Current operators we engage with at SBKJ:

• XLam Australia at Wodonga VIC — the dominant CLT manufacturer, integrated with Hyne Timber upstream and the Australian construction supply chain downstream. The Wodonga plant is the SBKJ benchmark for the CLT envelope.
• CTS Cross Laminated Timber at Wodonga VIC — the second CLT manufacturer, supplying mid-rise commercial and apartment projects nationally.
• Hyne LVL at Tumut NSW and Caboolture QLD — Australia's largest LVL manufacturer, integrated with the Hyne softwood sawmill upstream. Hyne LVL Tumut is the SBKJ benchmark for the LVL envelope.
• Carter Holt Harvey LVL — multi-site LVL production supplying the building and construction industry.
• Wesbeam LVL at Neerabup WA — the Western Australian LVL manufacturer supplying the WA and SA construction market.
• Hyne Glulam at Maryborough QLD — Australia's largest glulam producer, supplying structural glulam beams to the building industry nationally.
• Tilling Engineered Timber — long-established engineered timber supplier with LVL, glulam and I-beam product range across multiple Australian sites.
• Australian Hardwood Network (AHN) — hardwood engineered timber producer supplying speciality structural and appearance grade engineered hardwood.

Industry body coordination is through the Engineered Wood Products Association of Australia (EWPAA), the Forest and Wood Products Australia (FWPA) and the Timber Development Association (TDA). The EWPAA AS 6122 conformance scheme is the benchmark for product quality, and indirectly drives the HVAC envelope by setting the formaldehyde emission, dimensional and durability requirements that the manufacturing process must support.

4. Process zone breakdown — particleboard and MDF

Particleboard and MDF are the two dominant wood-based panel products produced in Australia. Both follow the same broad process — chip preparation, drying, resin blending, mat forming, hot pressing, cooling, sawing, sanding, despatch — but with different raw material (coarse chip and shaving for particleboard, refined fibre for MDF) and different end-use (structural and substrate for particleboard, decorative substrate and panel for MDF). The HVAC envelope is similar between the two but with MDF carrying slightly more demanding formaldehyde capture because the finer fibre and the higher resin loading generate more free formaldehyde at every process step.

4.1 Particleboard and MDF chip preparation

The chip yard receives wood waste from upstream sawmills (sawdust, shavings, edgings, trim ends) and plantation thinnings. The material is screened, crushed to uniform size, washed if necessary, and stored in chip silos. The HVAC duty at the chip yard is dust suppression at the unloading and crushing stations, with capture at the crusher and the screen discharge. Conveying velocity 25 metres per second at the pneumatic main, branch 22 metres per second. Duct material is 1.6 mm galvanized at the main and 1.2 mm galvanized at the branches with abrasion-resistant elbows. Zone 22 dust hazard with full electrical bonding.

4.2 Particleboard chip drying

Particleboard chip is dried in a rotary drum drier or flash drier from typical 50 percent moisture content at the silo discharge to 3 to 5 percent moisture content at the drier outlet. Drier inlet temperature is typically 400 to 500 degrees Celsius (direct-fired) or 200 to 300 degrees Celsius (indirect heated), with outlet temperature around 80 to 120 degrees Celsius. The drier exhaust is the dominant HVAC duty in the chip preparation zone — high volume, hot, moisture-laden, with trace VOC and particulate loading. Duct material is 316L stainless from the drier outlet to the cyclone, the wet electrostatic precipitator or the regenerative thermal oxidiser, insulated to maintain wall temperature above the dew point. Galvanized fails within 24 to 36 months because the moisture and trace acetic acid attack the zinc coating.

4.3 MDF refiner and fibre drying

MDF uses refined fibre rather than coarse chip. The chip is preheated in a pre-steamer at 8 to 10 bar saturated steam, then refined between rotating discs at high temperature to break down the wood matrix into individual fibres. The refiner discharge is at high temperature (around 170 degrees Celsius) and saturated with steam. The fibre is dried in a flash drier with hot air or hot gas, with the drier exhaust carrying steam, trace VOC and fine fibre. Duct material at the refiner discharge and the flash drier exhaust is 316L stainless throughout because the combination of high temperature, high humidity and acidic condensate is too aggressive for any other material. The Borg Manufacturing Oberon NSW MDF plant and the Laminex Australia MDF plants at Dardanup WA and Gympie QLD are all 316L stainless at the refiner discharge under SBKJ specification.

4.4 Particleboard and MDF resin blender

The resin blender mixes dried chip or fibre with the binder resin — urea-formaldehyde (UF), melamine-urea-formaldehyde (MUF), phenol-formaldehyde (PF) or polymeric methylene diphenyl diisocyanate (PMDI) — and hardener and wax. The blender is the highest single formaldehyde release point in the particleboard or MDF plant. Capture is full enclosure of the blender with face velocity 1.5 metres per second at any opening, 316L stainless duct from the enclosure to the RTO or wet scrubber inlet, and TIG-welded seam construction throughout for leak-tight performance. Safe Work Australia formaldehyde STEL 1 ppm applies — operator station monitoring at the blender is mandatory.

4.5 Particleboard and MDF mat forming

The resin-blended chip or fibre is formed into a continuous mat on a long forming belt. The forming station is enclosed and exhausted at the full mat width with capture velocity 1.0 metres per second face. Duct material is 316L stainless because formaldehyde condensate is acidic. Modern forming lines include scalping (removing oversized particles), pre-pressing (light compaction before the main press) and trimming. Each step has its own local capture with branch duct to the main forming line exhaust header.

4.6 Particleboard and MDF hot press — the critical zone

The hot press is the heart of the particleboard or MDF plant. The press is a continuous belt-press or a multi-daylight platen press operating at 180 to 220 degrees Celsius platen temperature, 30 to 50 bar press pressure, and a cycle time of 90 to 300 seconds depending on panel thickness. Every press cycle releases steam, free formaldehyde and resin volatiles through the press infeed, the press outfeed and the platen edge seals. The press operator station is the highest single human formaldehyde exposure point in the entire wood panel industry.

SBKJ engineers the press exhaust capture as a fully hooded press infeed at 1.5 metres per second face velocity, a fully hooded press outfeed at 1.5 metres per second, a full press canopy hood over the press body at 1.0 metres per second, and edge seal capture along the full press length. Total exhaust volume at a continuous press is typically 60,000 to 120,000 cubic metres per hour at temperatures around 80 degrees Celsius and saturated with steam. Duct material is 316L stainless throughout — TIG-welded longitudinal seams, conductive gaskets at every flange, full external insulation maintaining wall temperature above the dew point. Discharge goes through a regenerative thermal oxidiser (RTO) for VOC destruction or a wet scrubber for formaldehyde absorption before atmospheric release.

The Borg Manufacturing Oberon press, the Laminex Australia Dardanup WA press, the Laminex Australia Ipswich QLD press and the Laminex Australia Gympie QLD press are all 316L stainless full-canopy SBKJ specification. The Polytec Penrith NSW HPL press is similar but with melamine-formaldehyde rather than UF as the dominant resin.

4.7 Particleboard and MDF cooling, sawing and sanding

After pressing, the panel cools on a star cooler or fan-assisted cooler, is cross-cut to length, edge-trimmed, sanded to thickness and stacked for despatch. The cooling section needs general dilution ventilation only at 4 to 6 air changes per hour. The saw and edge trimmer dust capture is conventional Zone 22 sawdust collection in 1.2 mm galvanized at 20 metres per second branch and 22 metres per second main. The sanding line is the most hazardous combustible dust station in the plant — fine MDF or particleboard dust below 80 microns with Kst typically 200 bar metres per second placing the facility in St3. Sander capture velocity 18 metres per second branch, hood face 0.5 to 1.0 metres per second, with the sander baghouse carrying NFPA 68 deflagration venting (typical vent area 2.0 square metres per cubic metre of protected volume) and isolation valves on every inlet branch. Full electrical bonding to under 10 ohms to plant earth, conductive gaskets, AMCA 99 Type B spark-resistant fan minimum, spark detection at the cyclone inlet with infrared sensor and water injection response.

4.8 Particleboard and MDF operator landscape

The Australian particleboard and MDF landscape is dominated by two large groups operating multiple plants:

• Borg Manufacturing at Oberon NSW and Mt Druitt NSW — Australia's largest particleboard and MDF producer. Oberon is integrated chip preparation, refining, drying, blending, forming, pressing and finishing. Borg supplies the AS/NZS 1859 substrate and decorative panel market nationally. SBKJ has supplied 316L stainless duct packages at multiple Borg plants over the past decade.
• Laminex Australia (Fletcher Building) at Dardanup WA, Ipswich QLD and Gympie QLD — Australia's second largest particleboard and MDF producer plus decorative laminate line. Laminex supplies the Australian kitchen, joinery and interior building market. Laminex Ipswich QLD is one of the larger MDF plants in the Southern Hemisphere.
• Polytec at Penrith NSW — Australia's largest decorative laminate (HPL) and edge-band producer. Polytec uses kraft paper substrate impregnated with melamine-formaldehyde resin, pressed at high temperature to produce HPL sheet and decorative edging. The HPL impregnator solvent zone is the unique HVAC duty at Polytec compared to Borg or Laminex.
• CSR Cemintel in Sydney — fibre cement panel manufacturer. Cemintel uses Portland cement plus cellulose fibre plus sand in an autoclaved process rather than wood-resin pressing, so the HVAC envelope is closer to a precast concrete plant than to a particleboard plant. Refer to our concrete precast guide for the Cemintel envelope.

5. Process zone breakdown — plywood

Plywood manufacturing predates particleboard and MDF by decades but the HVAC envelope is in many ways more demanding because the veneer drier is one of the larger continuous-process exhaust duties in the Australian wood industry. Plywood is multi-ply veneer pressed with phenol-formaldehyde (structural plywood for outdoor and structural use) or urea-formaldehyde (interior plywood) under AS/NZS 1859.

5.1 Plywood log preparation and rotary peeling

Plywood logs are typically debarked, conditioned (warmed or steamed to soften the wood for peeling), then rotary peeled on a peeler lathe. The lathe rotates the log at constant feed rate against a long knife, peeling continuous veneer ribbon. The veneer is clipped into sheets at the discharge and graded. HVAC duty at the lathe is conventional log handling dust and chip extract — galvanized G90 with abrasion-resistant elbows.

5.2 Plywood veneer drying — the dominant duty

Green veneer is dried in a long continuous belt drier or roller drier at 150 to 200 degrees Celsius from green moisture content (around 60 to 100 percent for plantation pine) to 4 to 8 percent for plywood production. The drier exhaust is the dominant HVAC duty at the plywood plant — high volume, hot, moisture-laden, with trace VOC. Duct material is 316L stainless from the drier outlet to the heat recovery unit or the stack, insulated externally to maintain wall temperature above the dew point. The Hyne Plywood Tumut NSW drier, the Boral Plywood drier and the Carter Holt Harvey Plywood Eden NSW drier are all 316L stainless under SBKJ specification.

5.3 Plywood glue spreader and lay-up

Dried veneer is spread with phenol-formaldehyde or urea-formaldehyde glue, with alternating sheets oriented at 90 degrees to produce cross-grain ply construction. The glue spreader is enclosed and captured at the spreader head with face velocity 1.5 metres per second. Duct material is 316L stainless because the resin condensate is acidic and would attack zinc within 24 months. Discharge to a wet scrubber or RTO before atmospheric release.

5.4 Plywood hot press

The plywood hot press is a multi-daylight platen press at 130 to 160 degrees Celsius platen temperature for urea-formaldehyde or 130 to 150 degrees Celsius for phenol-formaldehyde. Press cycle is 3 to 8 minutes depending on panel thickness. Capture at the press is a full canopy hood at 1.0 metres per second face velocity plus close-coupled press infeed and outfeed hoods at 1.5 metres per second. Duct material is 316L stainless throughout to the RTO or wet scrubber inlet. The Hyne Plywood Tumut press and the Carter Holt Harvey Plywood Eden press are both 316L stainless canopy-and-edge SBKJ specification.

5.5 Plywood sawing, sanding and finishing

After pressing, the plywood panel is sawn to size, sanded to thickness and stacked. Saw dust capture is conventional in 1.2 mm galvanized at 20 metres per second branch. Sander dust capture is the worst-case combustible dust hazard — same envelope as MDF and particleboard sander capture, with NFPA 68 venting, isolation valves, full bonding and St3 classification.

5.6 Plywood operator landscape

Australian plywood operators we engage with:

• Hyne Plywood at Tumut NSW — integrated with the Hyne softwood sawmill upstream. Hyne is Australia's largest structural plywood producer.
• Carter Holt Harvey Plywood at Eden NSW — the long-established Eden plywood plant supplying structural and appearance grade plywood.
• Boral Plywood — multi-site plywood production supplying the structural and substrate market.
• Federation of Australian Plywood and Veneer Manufacturers (FAPVM) — industry body coordinating Australian plywood production standards and conformance.

6. Process zone breakdown — oriented strand board (OSB) and high-pressure laminate (HPL)

OSB and HPL are smaller-volume but distinct product families. OSB uses wood strand rather than chip or fibre, and PMDI isocyanate binder rather than formaldehyde resin. HPL uses kraft paper substrate impregnated with melamine-formaldehyde resin and pressed at high temperature.

6.1 OSB strand preparation and drying

OSB uses long wood strands (typically 75 to 150 millimetres in length, 25 to 35 millimetres in width, 0.6 to 0.8 millimetres in thickness) cut from debarked round wood on a strander. The strand is dried in a triple-pass rotary drier at 200 to 250 degrees Celsius inlet, 80 to 120 degrees Celsius outlet. The drier exhaust is similar in duty to the particleboard drier — high volume, hot, moisture-laden, with strand-size combustible particulate carryover. Duct material is 316L stainless from the drier outlet to the cyclone train. The strand carryover is St2 combustible dust with Kst typically 150 to 180 bar metres per second.

6.2 OSB blender — the MDI capture critical zone

The OSB blender is the highest single isocyanate release point in the entire Australian wood panel industry. Polymeric methylene diphenyl diisocyanate (PMDI) is sprayed onto the strand in a horizontal drum blender or a high-speed inline blender. The Safe Work Australia workplace exposure standard for isocyanate expressed as MDI is 0.005 ppm short-term exposure limit and 0.005 ppm time-weighted average — two hundred times tighter than the formaldehyde STEL. Isocyanate is a respiratory sensitiser with no safe exposure threshold. A single uncontrolled exposure can sensitise a worker for life.

SBKJ engineers the OSB blender capture as a fully enclosed blender with face velocity 1.5 metres per second at any opening, 316L stainless duct from the enclosure to the dedicated isocyanate scrubber or RTO inlet, TIG-welded seam construction throughout, leak-test at 1500 pascals positive pressure before commissioning, and continuous MDI monitoring at the operator station with alarm and auto-shutdown above 0.003 ppm. The blender area is Zone 2 hazardous under AS/NZS 60079.10.1 for the isocyanate vapour duty.

6.3 OSB forming line

The MDI-blended strand is formed into a continuous mat with alternating layer orientation (long dimension at 0 degrees in face layers, 90 degrees in core layer) to produce the oriented strand characteristic of OSB. Capture is full enclosure of the forming line with face velocity 1.0 metres per second at any opening, 316L stainless duct to the RTO.

6.4 OSB hot press

The OSB hot press operates at 200 to 220 degrees Celsius platen temperature, 40 to 60 bar press pressure, with a press cycle of 200 to 400 seconds. Press exhaust capture is full canopy hood at 1.0 metres per second face velocity plus close-coupled infeed and outfeed hoods at 1.5 metres per second, with full edge seal capture along the press length. Duct material is 316L stainless throughout to the dedicated isocyanate destruction RTO. The press operator station carries the same MDI monitoring and auto-shutdown as the blender. Continuous MDI exposure monitoring is mandatory under any Australian OHS jurisdiction for OSB production.

6.5 OSB operator landscape

Australia has limited OSB production capacity compared to North America. The Australian construction market continues to import OSB panel from New Zealand, North America and Asia. Where OSB is locally produced the plant follows the international PMDI binder envelope above.

6.6 HPL kraft paper preparation and resin impregnation

High-pressure laminate (HPL) starts with kraft paper substrate (the "core" layers) and decorative paper (the "decor" surface layer) and overlay paper (the "wear" surface layer). Each paper layer is impregnated with phenol-formaldehyde resin (core layers) or melamine-formaldehyde resin (decor and overlay) in a continuous impregnator. The impregnator runs paper through a resin bath and a metering roller, then through a drying and B-staging oven at 130 to 180 degrees Celsius to partially cure the resin to a tack-free state. Capture at the impregnator is full hood over the resin bath and the drying oven outlet, with face velocity 1.0 metres per second. Duct material is 316L stainless because both phenol-formaldehyde and melamine-formaldehyde condensate are acidic and aggressive to zinc. The HPL impregnator solvent zone (if solvent-borne resin is used) is Zone 2 hazardous under AS/NZS 60079.10.1 with AS 1940 governing solvent storage.

6.7 HPL hot press

The HPL hot press stacks the impregnated paper layers with the decor and overlay on each face of a stack of core layers, presses at 140 to 160 degrees Celsius platen temperature and 80 to 100 bar press pressure (much higher than particleboard or MDF), and cures the resin to fully bonded HPL sheet. Press exhaust capture is full canopy hood at 1.0 metres per second face velocity. Duct material is 316L stainless to the RTO inlet. The Polytec Penrith NSW HPL plant and the Formica and Laminex HPL lines are all 316L stainless SBKJ specification.

7. Process zone breakdown — pulp and paper mill

Pulp and paper manufacturing is fundamentally different from wood panel manufacturing. The pulp mill converts wood chip into cellulose fibre suitable for paper manufacture. The paper mill takes the pulp, dilutes it with water, presses and dries it, and outputs a continuous paper web. Australia's only operating Kraft pulp and paper mill is Australian Paper Manufacturers (APM) Maryvale in the Latrobe Valley Victoria, integrated pulp through paper production. Visy Industries operates multiple paper mills including the Tumut NSW integrated pulp and paper mill, Coolaroo VIC, Smithfield NSW, Yatala QLD and the recycling-fed paper machine at Wollongong NSW. The HVAC envelope at the Kraft pulp mill is one of the most demanding in any Australian industrial sector.

7.1 Pulp mill wood preparation

The pulp mill chip yard receives wood chip from upstream sawmills and dedicated chipping operations, or whole logs that are debarked and chipped on site. Chip is screened to remove oversize and fines, washed, and stored in chip silos. HVAC duty is conventional chip yard dust capture in 1.6 mm galvanized spiral at 25 metres per second pneumatic main, with cyclone discharge and bag filter. Zone 22 dust hazard with full electrical bonding.

7.2 Kraft pulp digester

The Kraft digester is the heart of the pulp mill — a tall pressure vessel where wood chip is cooked with white liquor (sodium hydroxide plus sodium sulphide) at 170 degrees Celsius and 7 bar absolute pressure for typically 2 to 4 hours. The cooking process dissolves lignin (the wood polymer that bonds individual cellulose fibres) and separates the cellulose fibre. The digester relief gas is the highest single Total Reduced Sulphur (TRS) release point in the mill — hydrogen sulphide (H2S), methyl mercaptan (CH3SH), dimethyl sulphide and dimethyl disulphide are all generated during the cook and vent through the digester relief.

Capture at the digester relief is a closed-loop collection system feeding the dedicated non-condensable gas (NCG) incinerator or the recovery boiler combustion chamber, where TRS compounds are destroyed at 1100 degrees Celsius. Duct material is 316L stainless throughout because H2S aggressively attacks both galvanized steel and 304 stainless in the presence of moisture. The Maryvale APM digester relief, the Visy Tumut pulp mill digester relief, and any other Australian Kraft pulp digester are all 316L stainless SBKJ specification.

Safe Work Australia workplace exposure standards: H2S 10 ppm time-weighted average, 15 ppm short-term exposure limit; methyl mercaptan 0.5 ppm time-weighted average; dimethyl sulphide 10 ppm time-weighted; sodium hydroxide caustic mist 2 mg/m3 ceiling. The digester area is Zone 1 hazardous under AS/NZS 60079.10.1 for the H2S vapour duty. IECEx Ex-d ATEX motors mandatory at every fan, every actuator and every instrument in the digester vicinity.

7.3 Brown stock washing

After the cook the pulp is discharged from the digester into the blow tank and then washed in a counter-current series of vacuum washers to remove the spent cooking liquor (now called "weak black liquor"). The brown stock washer hoods and the seal tanks are continuous TRS sources at lower concentration than the digester relief but at much larger volume. Capture at every washer hood and seal tank vent is to the NCG incinerator or the recovery boiler. Duct material is 316L stainless throughout.

7.4 Black liquor evaporators

The weak black liquor from brown stock washing is concentrated in a multiple-effect evaporator train from typical 15 percent solids at washer discharge to 70 to 75 percent solids at the concentrator outlet. The evaporator train operates under vacuum at the first effect (around 50 degrees Celsius and 100 millibar absolute) up to atmospheric or slightly above at the concentrator (around 130 degrees Celsius). Vents from each effect carry TRS, water vapour and trace organics. Capture is to the NCG incinerator. Duct material is 316L stainless throughout. The concentrator carries the highest temperature and the heaviest TRS load.

7.5 Recovery boiler — the chemical recovery furnace

The concentrated black liquor (70 to 75 percent solids) is sprayed into the recovery boiler furnace at temperatures around 1100 degrees Celsius. Combustion of the organic fraction generates process steam (typically 80 bar, 480 degrees Celsius for modern boilers), and the inorganic fraction collects in the smelt bed at the furnace floor — sodium carbonate plus sodium sulphide that is dissolved out as "green liquor" for reuse in the cooking cycle. The recovery boiler is therefore both a power boiler and a chemical recovery furnace simultaneously, with no equivalent in any other Australian industrial sector.

The recovery boiler flue gas carries sulphur dioxide, sulphur trioxide, trace H2S that escapes the smelt spout area, sodium sulphate and sodium carbonate carryover particulate, and lime mud particulate. The flue cools through the economiser to around 200 degrees Celsius at the electrostatic precipitator inlet, then to around 150 degrees Celsius at the induced draft fan and stack base. The cooling profile crosses the SO3 acid dew point at around 130 to 150 degrees Celsius depending on moisture content, and the uninsulated duct surface temperature will spend time below the dew point during start-up, shutdown and upset conditions.

SBKJ specifies 316L stainless throughout the flue from the boiler outlet to the stack base, with external insulation (minimum 75 mm rockwool with aluminium cladding) to maintain wall temperature above the dew point during normal operation. Galvanized steel fails within 12 months because sulphuric acid condensate strips the zinc. 304L stainless fails within 36 months because the chloride content of carryover salt drives chloride pitting at the heat-affected zone. The stack itself is unlined carbon steel per AS 1318 with refractory at the base for the highest temperature exposure, transitioning to 316L liner at the upper exposed section.

The Maryvale APM recovery boiler and the Visy Tumut recovery boiler are both 316L stainless flue SBKJ specification. The smelt spout area at every recovery boiler is Zone 1 hazardous under AS/NZS 60079.10.1 for the trace H2S duty. IECEx Ex-d ATEX motors mandatory at every fan, actuator and instrument in the smelt spout vicinity.

7.6 Lime kiln

The Kraft recovery cycle includes a causticising stage where green liquor (sodium carbonate plus sodium sulphide in water) is reacted with calcium hydroxide to convert sodium carbonate back to sodium hydroxide, generating calcium carbonate "lime mud" as the byproduct. The lime mud is filtered, washed and calcined in a rotary lime kiln at 1000 degrees Celsius to regenerate calcium oxide ("lime") for reuse in the causticising stage.

The lime kiln flue gas carries carbon monoxide, sulphur dioxide, lime dust particulate, and trace TRS compounds depending on the kiln fuel and operating conditions. Capture at the lime kiln hood and the cooler is via wet scrubber and electrostatic precipitator, with 316L stainless duct throughout. The kiln is fired with natural gas or fuel oil at modern Australian mills. The kiln area carries CO 30 ppm STEL and 30 ppm TWA workplace exposure limit.

7.7 Bleach plant — chlorine dioxide ECF

The bleach plant takes brown pulp from washing and bleaches it through a sequence of stages — typically chlorine dioxide (ClO2) extraction, alkaline extraction with sodium hydroxide, hydrogen peroxide brightening — to produce fully bleached pulp suitable for white paper, tissue and printing grade. Modern Australian Kraft mills use the ECF (elemental chlorine free) process with chlorine dioxide as the primary bleaching agent rather than elemental chlorine.

Chlorine dioxide is generated on site from sodium chlorate, sulphuric acid and a reducing agent (typically methanol). The generator is a separate plant adjacent to the bleach plant. The ClO2 vapour is dissolved in chilled water for application to the pulp. Safe Work Australia workplace exposure standards: chlorine dioxide 0.1 ppm short-term and 0.1 ppm time-weighted average — twenty times tighter than the chlorine STEL. Chlorine 0.5 ppm short-term and 1 ppm time-weighted is the equivalent for residual chlorine.

SBKJ specifies 316L stainless duct from the bleach tower hood to the scrubber inlet as the standard, stepping up to 904L super-austenitic stainless or Hastelloy C-276 at the highest concentration points — the ClO2 generator vent and the bleach tower seal hood. FRP (fibre-reinforced plastic) is the standard material for the scrubber vessel itself because of the chloride resistance requirement. The bleach plant ClO2 generator is Zone 2 hazardous under AS/NZS 60079.10.1.

7.8 Paper machine wet end and press section

The paper machine takes bleached pulp (or recycled pulp at recycled-fibre mills) at very low consistency (typically 1 to 2 percent fibre, 98 to 99 percent water), distributes it across the full machine width on a continuous wire mesh ("the wire"), and progressively removes water through a sequence of foils, vacuum boxes, press rolls and drying cylinders to produce a continuous paper web at 5 to 8 percent moisture content at the dry end.

The wet end and press section HVAC duty is essentially water mist removal and ventilation of the open-section equipment. Galvanized G90 spiral is suitable for the wet end ventilation because there are no acidic condensate or aggressive chemicals — the wet end is essentially water and cellulose fibre. Conveying velocity 15 to 20 metres per second for the mist-laden extract, branch 12 to 15 metres per second.

7.9 Paper machine dryer section and yankee dryer

The paper machine dryer section is a series of large steam-heated cast iron cylinders (typically 1.5 to 2.5 metres in diameter) that the paper web passes over alternately to remove the bulk of the water by evaporation. For tissue paper a single very large "yankee dryer" (typically 4.5 to 5.5 metres in diameter) replaces the multiple-cylinder dryer section. The yankee dryer surface is heated by internal steam at 5 to 10 bar and externally fired by impingement air at 400 to 500 degrees Celsius.

The dryer section is enclosed by a "dryer hood" — a sheet metal hood structure that contains the evaporated water vapour and recovers the heat for return to the supply air. The hood exhaust is the dominant single HVAC duty in the paper mill — typical volumes of 50,000 to 200,000 cubic metres per hour at temperatures around 80 to 90 degrees Celsius and dewpoint around 70 degrees Celsius.

Duct material at the dryer hood and the hood exhaust is 316L stainless because the moisture is continuous and the wall temperature would otherwise spend significant time at the dew point. The tissue paper yankee dryer hood at Sorbent Solaris Millicent SA, the Kimberly-Clark Australia Millicent SA tissue line, and the Visy Tissue lines at Coolaroo VIC and Smithfield NSW are all 316L stainless SBKJ specification.

7.10 Paper coating and calendering

Coated paper grades (gloss magazine, label, photographic base) receive a coating of clay or calcium carbonate plus latex binder on the surface after the dryer section but before the calender. The coating is applied at the coater station and dried in a continuous infrared or hot air drying oven. Capture at the coating station is a low-volume extract for binder vapour, with 316L stainless duct because the latex binder condensate is mildly aggressive.

The calender stack is a series of polished steel rolls that flatten the dried paper surface to produce the gloss or matte finish. HVAC duty at the calender is general dilution ventilation with galvanized G90 ductwork. The calender hall is acoustic-sensitive (typical NC-50) because the rolls operate at high speed.

7.11 Tissue paper, paper towel and disposable hygiene

Tissue paper production at Sorbent Solaris (Millicent SA), Kimberly-Clark Australia (Millicent SA), Visy Tissue (Coolaroo VIC and Smithfield NSW), Tork (Essity Australia) and Detmold Group (Adelaide SA) follows the yankee dryer envelope above. The converting line downstream of the tissue machine (cutting, embossing, folding, packaging) is conventional paper conversion HVAC with galvanized G90 ductwork and ISO 12647 temperature and humidity control for product consistency.

7.12 Corrugated cardboard — Visy Industries and Orora

Corrugated cardboard manufacture combines a roll of "fluting medium" (a lighter paper grade typically around 100 to 150 grams per square metre) sandwiched between two rolls of "liner board" (a stronger paper grade typically 150 to 200 grams per square metre) to produce double-faced corrugated sheet. The fluting medium is corrugated by heated rollers at 170 to 190 degrees Celsius to develop the flute profile, then glued to the liner with starch-based adhesive applied at the glue station.

HVAC duty at the corrugator is the heated roller area extract (steam and trace adhesive vapour) and the glue station local exhaust. Galvanized G90 ductwork is the SBKJ standard at the corrugator because there is no significantly aggressive chemical exposure. Conveying velocity 15 to 20 metres per second.

Visy Industries (Pratt family) operates corrugated cardboard plants across Australia including the integrated Tumut NSW operation, plus dedicated converting plants at multiple sites. Orora (ASX:ORA, headquartered at Box Hill VIC — SBKJ's local neighbour) is Australia's second corrugated and packaging producer with multiple converting plants nationally. Amcor (ASX:AMC) operates flexible packaging with multiple paper-based plants. All three are SBKJ engagement targets for the corrugated cardboard duty.

8. Material selection summary

The SBKJ material specification framework for the Australian engineered wood, wood panel and pulp and paper sector reduces to a single decision tree. This is the framework we apply on every quotation.

• Galvanized G90, 1.0 to 1.6 mm — log yard, debarker (with abrasion-resistant elbows), head rig, edger, trimmer, planer mill, sander branches, particleboard and MDF saw and edge trim, OSB strand handling and downstream conversion, CLT and glulam assembly hall dilution ventilation, plywood log handling and saw and trim, paper machine wet end and press section ventilation, corrugated cardboard heated roller extract, calender hall and dryer hood downstream where condensate is no longer a concern, office and amenities supply and return, general dilution ventilation.
• 304L stainless, 1.2 to 2.0 mm — engineered wood (LVL, CLT, glulam) adhesive applicator capture, engineered wood press hood, chemical recovery boiler economiser to electrostatic precipitator inlet where temperature is well above the dew point, regenerative thermal oxidiser inlet from formaldehyde sources where chloride exposure is low, hog fuel boiler flue economiser to ESP.
• 316L stainless, 1.5 to 2.5 mm — MDF and particleboard hot press exhaust, MDF and particleboard glue line, MDF refiner and drier exhaust, OSB blender capture, OSB hot press exhaust, plywood veneer drier exhaust, plywood glue spreader, plywood hot press, HPL impregnator and hot press, Kraft digester relief, brown stock washer hood, black liquor evaporator vent, recovery boiler flue from boiler outlet to stack base, lime kiln vent and cooler, chlorine dioxide bleach plant ductwork, all TRS odour control duct runs, tissue paper yankee dryer hood, paper machine dryer hood, paint mix room and finishing line exhaust.
• 904L super-austenitic stainless or Hastelloy C-276, 1.5 to 2.5 mm — ClO2 generator vent, bleach tower seal hood, the highest concentration chloride-bearing duty in the bleach plant.
• FRP (fibre-reinforced plastic) or PP-lined steel — wet scrubber vessels for ClO2, formaldehyde and TRS, chlorine dioxide scrubber, alkaline scrubber for caustic mist control.
• Carbon steel with refractory lining, 5 to 6 mm — hog fuel boiler flue between economiser and stack where gas temperature exceeds 200 degrees Celsius, recovery boiler furnace zone, lime kiln rotary shell, ID fan inlet and outlet on the recovery boiler.
• Carbon steel unlined, 4 to 6 mm — cyclone bodies, large baghouse plenums, silo connecting duct where mechanical strength dominates over corrosion, recovery boiler stack outer shell per AS 1318.
• Aluminium — prohibited in Zone 22 hazardous areas, prohibited in NFPA 33 finishing booth exhaust, prohibited in any duct conveying combustible wood dust. Permitted only at office HVAC supply and return where life-safety dust hazards do not apply.

9. Hazardous area classification and bonding

Every engineered wood, wood panel, pulp and paper facility we have surveyed in Australia has a more complex hazardous area profile than the sawmill envelope. Three zone families coexist on the same site and the duct package must handle all three.

9.1 Combustible dust zones (AS/NZS 60079.10.2)

Zone 22 inside every duct conveying combustible wood dust — sander dust, MDF and particleboard dust, OSB strand dust, plywood saw dust. Zone 22 around every duct flange, branch and access door. Zone 21 around every transfer point, blast gate, baghouse explosion vent and silo loading point. Zone 20 inside every dust collector internal volume, every chip and fibre silo, every drier drum. MDF, particleboard and OSB sander dust is St3 with Kst 200 bar metres per second placing the facility at the higher end of NFPA 660 vent sizing.

9.2 Flammable gas and vapour zones (AS/NZS 60079.10.1)

Zone 2 around the LVL or glulam adhesive applicator for the phenol-formaldehyde and PRF resin vapour duty. Zone 2 in the LPG kiln burner room or the natural gas burner room for any direct-fired drier or hot press. Zone 2 in the HPL impregnator solvent zone if solvent-borne resin is used. Zone 2 around the OSB blender for the MDI vapour duty. Zone 1 in the Kraft pulp digester area, the brown stock washer area, the black liquor tank farm, the recovery boiler smelt spout vicinity and the bleach plant ClO2 generator area for the highest concentration TRS and ClO2 duty.

9.3 Bonding, earthing and Ex equipment

The implications for duct fabrication and installation:

• Electrical bonding. Every flange joint bridged with 6 mm² copper bonding strap, terminated to a brass M8 bonding lug welded to each spiral section at SBKJ. Resistance across every joint under 1 ohm, system to plant earth under 10 ohms. Measured at commissioning, re-tested every two years and after any modification.
• Conductive gaskets. All access doors, hatches and inspection ports fitted with conductive EPDM or conductive silicone gaskets. Non-conductive gaskets prohibited in dust-conveying duct.
• Flexible connectors. Conductive construction with internal bonding strap. Non-metallic flexible connectors prohibited in dust service and prohibited in Zone 1 vapour service.
• Ex-rated equipment. Ex tD or Ex tc in Zone 22 dust areas. Ex tc in Zone 21 dust areas. Ex db or Ex de in Zone 1 vapour areas including the Kraft digester and recovery boiler smelt spout vicinity. Ex db or Ex de in Zone 2 vapour areas including the engineered wood adhesive applicator. IECEx Ex-d ATEX certification mandatory in Zone 1. SBKJ-supplied duct accessories include certified actuators, instruments and motors as standard on Zone 22 and Zone 1 projects.
• Spark-resistant fans. AMCA 99 Type B (Class 2) construction minimum on every fan handling combustible wood dust per NFPA 660. Type A (Class 3) on the bleach plant duty where chloride and chlorine dioxide are present.

10. Deflagration protection and explosion prevention

NFPA 660, NFPA 68 and NFPA 69 set the engineered controls for combustible wood dust deflagration in the engineered wood and panel sector. Every dust collector serving any wood panel, engineered wood or pulp mill chip handling process must have:

• NFPA 68 deflagration venting sized per the protected volume and the dust Kst — typically 1.5 to 3.0 square metres of vent area per cubic metre of protected volume for MDF, particleboard and OSB sander dust at Kst 200 bar metres per second. Vents must discharge to a safe area outside the building, free of personnel and assets.
• NFPA 69 chemical suppression using a fast-acting suppression system (sodium bicarbonate or monoammonium phosphate discharge) where venting cannot be discharged to a safe area or where the protected enclosure is indoors.
• NFPA 69 inerting using nitrogen or carbon dioxide blanket to maintain oxygen concentration below the limiting oxygen concentration (LOC) for the dust — uncommon in the wood industry but used at some highly hazardous duties.
• Isolation valves on the duct between the source machinery and the dust collector — detect a pressure rise from a developing deflagration and slam shut within milliseconds, preventing flame propagation back into the building. Mandatory on every combustible wood dust collector under NFPA 660.
• Spark detection at the cyclone or bag filter inlet with infrared sensor and water injection or fast-acting damper response. Mandatory on every continuous-operation dust collection system in the engineered wood and panel sector under NFPA 660.

11. Kraft pulp mill TRS odour control

Total Reduced Sulphur (TRS) is the defining HVAC duty at any Kraft pulp mill. Hydrogen sulphide (H2S), methyl mercaptan (CH3SH), dimethyl sulphide and dimethyl disulphide together create the characteristic Kraft mill odour signature detectable at the lower part-per-billion range. Victorian EPA licence conditions for the Maryvale APM mill, NSW EPA conditions for the Visy Tumut mill, and the equivalent conditions at any other Australian Kraft operation typically require:

• Boundary TRS limit — typically less than 5 ppm continuous at the boundary with sensitive receptors, and less than 1 ppm 99th percentile annual.
• Source-by-source capture and destruction — every TRS source (digester relief, brown stock washer hood, black liquor evaporator vent, recovery boiler smelt spout area, lime kiln vent, dissolving tank vent) captured into a closed-loop collection system feeding a dedicated non-condensable gas (NCG) incinerator, the recovery boiler combustion chamber, or a regenerative thermal oxidiser.
• Backup destruction — secondary destruction route available during NCG incinerator or recovery boiler outage, typically a flare or auxiliary RTO.
• Continuous monitoring — real-time H2S, methyl mercaptan and total TRS monitors at the stack and at the boundary, with telemetry to the EPA continuous emission monitoring database.

SBKJ duct package at the TRS sources is 316L stainless throughout, leak-tested at 1500 pascals positive pressure, with TIG-welded longitudinal seams and TIG-welded circumferential joints at every flange. Conductive gaskets at every access door and conductive flexible connectors at every fan inlet. The Maryvale APM mill TRS collection network and the Visy Tumut TRS network are both SBKJ engineering targets and benchmarks.

12. Chlorine dioxide bleach plant material selection

The bleach plant is the second critical chemical exposure HVAC duty at the Kraft pulp mill. Chlorine dioxide (ClO2) is the modern ECF (elemental chlorine free) bleaching agent of choice, replacing elemental chlorine at all Australian Kraft operations from the late 1990s onward. ClO2 is a powerful oxidiser that attacks both galvanized steel and 304L stainless at the chloride-bearing heat-affected zone of welded joints.

• 316L stainless is the standard at the bleach tower hoods, the bleach plant scrubber inlet duct and the bleach plant exhaust ducting up to the scrubber stack. 316L molybdenum content (2 to 3 percent) provides the chloride pitting resistance required for continuous ClO2 exposure at concentrations below 5 ppm.
• 904L super-austenitic stainless or Hastelloy C-276 is required at the ClO2 generator vent where concentration is the highest in the plant, at the bleach tower seal hood directly above the chemical addition point, and at any duct run where ClO2 concentration may exceed 10 ppm during normal operation.
• FRP (fibre-reinforced plastic) is the standard material for the scrubber vessel itself because of the extreme chloride resistance requirement. The FRP vessel typically incorporates a chemical-grade vinyl ester or epoxy resin matrix with a corrosion-barrier inner layer.

The SBKJ specification at the bleach plant uses the SBPC1500 plasma cutter for the 316L and 904L plate work, the SBLR-600 welder for the TIG seam welds, the SB-ZF1500 stitchwelder for the stainless plenum and scrubber inlet construction, and the SBAL-V auto duct line for any rectangular plenum. FRP scrubber vessel is sourced from a specialist supplier and integrated into the SBKJ duct package at the inlet flange interface.

13. Recovery boiler flue and lime kiln stack

The recovery boiler and the lime kiln are the two major combustion equipment items at the Kraft pulp mill and both have demanding flue gas HVAC duties under AS 1318 and AS 4036.

13.1 Recovery boiler flue

The recovery boiler flue gas at the furnace outlet is around 1100 degrees Celsius, cooling through the boiler superheater, economiser and air heater to around 200 degrees Celsius at the electrostatic precipitator inlet, then to around 150 degrees Celsius at the induced draft fan and stack base. The flue gas carries sulphur dioxide, sulphur trioxide, trace H2S that escapes the smelt spout, sodium sulphate and sodium carbonate carryover particulate, and lime mud particulate. The SO3 acid dew point is around 130 to 150 degrees Celsius depending on moisture content. Uninsulated duct surface temperature spends significant time below the dew point during start-up, shutdown and upset conditions.

SBKJ specifies 316L stainless throughout the flue from the boiler outlet to the stack base, with external insulation (75 mm rockwool minimum, aluminium cladding) to maintain wall temperature above the dew point. The stack itself is unlined carbon steel per AS 1318 with refractory at the base for the highest temperature exposure, transitioning to a 316L liner at the upper exposed section.

13.2 Lime kiln stack

The lime kiln flue gas at the kiln outlet is around 200 to 300 degrees Celsius depending on operating mode, cooling through the wet scrubber and electrostatic precipitator to atmospheric discharge at around 70 to 90 degrees Celsius. The flue gas carries carbon monoxide, sulphur dioxide, lime dust particulate, and trace TRS compounds. SBKJ specifies 316L stainless duct from the kiln hood to the scrubber inlet, transitioning to FRP at the wet scrubber vessel, then 316L stainless again from the scrubber outlet to the stack. The stack itself is unlined carbon steel per AS 1318.

14. Pulp and paper mill operator landscape

The Australian pulp and paper landscape is concentrated. Three integrated pulp and paper operations plus multiple recycled-fibre paper machines, tissue lines and corrugated converters dominate the sector.

14.1 Australian Paper Manufacturers (APM) — Maryvale Latrobe Valley VIC

The Maryvale APM mill is Australia's only integrated Kraft pulp and paper mill. The operation includes wood preparation, Kraft pulp digester, brown stock washing, black liquor evaporators, recovery boiler, lime kiln, ECF bleach plant with chlorine dioxide generation, multiple paper machines for fine paper and packaging grades, and the integrated heat and power generation. Maryvale is the Australian benchmark for every aspect of the Kraft pulp envelope — TRS odour control, recovery boiler flue, lime kiln, bleach plant, paper machine. SBKJ engineering targets Maryvale as the highest-value engagement opportunity in the Australian pulp and paper sector.

14.2 Visy Industries — Tumut NSW, Coolaroo VIC and multi-site

Visy Industries (Pratt family) is Australia's largest paper company by revenue. The Tumut NSW operation is integrated pulp and paper at smaller scale than Maryvale, with neutral sulphite semi-chemical (NSSC) pulp for liner board production rather than Kraft pulp for fine paper. Visy also operates the Coolaroo VIC paper machine (recycled fibre), the Smithfield NSW paper machine, the Yatala QLD paper machine, the Wollongong NSW recycled paper machine, the multiple tissue paper lines, and the integrated corrugated cardboard converting network including the Box Hill VIC neighbour to SBKJ's headquarters. SBKJ engineering supports Visy across every paper mill HVAC duty.

14.3 Amcor (ASX:AMC) — flexible packaging

Amcor is the Australian-listed flexible packaging multinational with multiple paper-based plants across Australia and globally. The Amcor paper-based plants follow the converting envelope rather than the integrated pulp envelope — paper roll receiving, printing, laminating, slitting, packaging — with conventional galvanized HVAC. The flexible packaging extruder lines are a separate HVAC duty closer to the plastics extrusion envelope.

14.4 Orora (ASX:ORA) — Box Hill VIC HQ, corrugated and packaging

Orora is the Australian-listed corrugated cardboard and packaging producer headquartered at Box Hill VIC — SBKJ's local neighbour. Orora operates corrugated converting plants at multiple sites and the integrated glass and can plants in the Australian beverage supply chain. Orora corrugated converting follows the corrugated envelope above — galvanized G90 ductwork at the heated roller and glue station, with no significantly aggressive chemical exposure.

14.5 Sorbent Solaris and Kimberly-Clark Australia — Millicent SA tissue

Sorbent (now owned by Solaris Paper through the Asaleo Care transition) and Kimberly-Clark Australia (Sorbent legacy brand plus Kleenex and Huggies) both operate tissue paper mills at Millicent SA. The Millicent operations include yankee dryer tissue machines, tissue converting lines, and packaging operations. SBKJ engineering supports the Millicent tissue lines with 316L stainless yankee dryer hood and exhaust ductwork.

14.6 Tork (Essity Australia) and Detmold Group

Tork is the Swedish-owned Essity tissue brand with Australian distribution and converting. Detmold Group is the Adelaide-based paper cup, plate and takeaway specialist. Both follow the tissue and converting envelopes above.

14.7 Norske Skog Boyer — closed 2024

The Norske Skog Boyer Tasmania newsprint mill closed permanently in 2024 after sixty-plus years of operation. The closure removed the last Australian newsprint capacity and consolidated the paper supply chain around Maryvale and Visy. Norske Skog Boyer is included here for historical context — SBKJ engineered duct packages were supplied to the operation over multiple decades and the legacy infrastructure remains a reference for any future Tasmanian paper operation.

14.8 Industry body coordination

The Pulp and Paper Manufacturers Federation Australasia, the Australian Council of Recycling (ACOR — paper recycling), the Australian Forest Products Association (AFPA), Forest and Wood Products Australia (FWPA) and the Timber Development Association (TDA) coordinate Australian paper and engineered wood industry activity. The Engineered Wood Products Association of Australia (EWPAA) coordinates the engineered wood sub-sector and the AS 6122 conformance scheme. The Federation of Australian Plywood and Veneer Manufacturers (FAPVM) coordinates the plywood sub-sector. Forest Stewardship Council Australia (FSC) and PEFC Australia coordinate the chain-of-custody certification that drives the upstream forest input to all of these operations. The Australian Forestry Standard (AFS) is the Australian-domestic certification scheme operating in parallel with FSC and PEFC.

15. Conveying velocity targets

Conveying velocity in the engineered wood, wood panel and pulp mill chip handling pneumatic conveying is set by the heaviest particle that must remain entrained at the lowest design flow rate. The SBKJ targets used in our duct sizing calculations:

• MDF and particleboard sander fine dust — 18 metres per second minimum at the worst-case branch flow.
• OSB strand and chip dust — 22 metres per second minimum.
• Plywood saw dust and edge trim — 20 metres per second minimum.
• LVL and glulam saw and planer dust — 22 metres per second minimum.
• CLT CNC machining dust mix — 22 metres per second minimum.
• Raw chip pneumatic conveying main — 25 metres per second minimum.
• Hog fuel and bark conveying main — 28 metres per second minimum.
• Debarker discharge pneumatic — 25 metres per second minimum.
• Head rig pneumatic conveying (upstream sawmill) — 25 metres per second minimum.
• Paper machine wet end mist extract — 15 to 20 metres per second.
• Paper machine dryer hood exhaust — 12 to 15 metres per second (lower because of the high temperature and moisture, with the duct sized for heat recovery rather than particulate conveying).

These are minimum velocities at the worst-case branch flow, not average velocity at design flow. SBKJ engineering specs the spiral main to these velocities at the peak operating condition including the case where 70 to 80 percent of branches are open and the rest are blanked off — the load case where main flow drops without changing main diameter. Designing for average flow guarantees blockages within 12 months and progressive accumulation of combustible dust deposits that violate NFPA 660 housekeeping limits.

16. Acoustic targets

Australian engineered wood, wood panel and pulp and paper mill HVAC noise targets follow AS 1668.2 and AS 2107 guidance, with state EPA boundary limits.

• Industrial process area (chip yard, refiner hall, press hall, paper machine hall, recovery boiler hall) — NC-50 to NC-55 acceptable. Process noise dominates and HVAC duct noise is a secondary contribution.
• Operator pulpit and control room — NC-40 typical. Operators spend full shifts in these rooms; HVAC duct noise must not interfere with intercom communication or fatigue the operator.
• Office and amenities — NC-35 typical. General commercial HVAC acoustic standard.
• Boundary noise to neighbours — Victorian EPA Publication 1826 sets 50 dB(A) at sensitive receptors at night for industrial premises, dropping to 35 dB(A) in residential-adjacent zones. NSW EPA Industrial Noise Policy and Queensland Environmental Protection (Noise) Policy set similar limits. Acoustic louvres, silencers and stack noise reduction at the intake and discharge stacks are typically required to meet boundary limits.

17. Worker amenity and change room — wood dust and chemical contamination

Engineered wood, wood panel and pulp mill operations all carry workplace contamination from wood dust, formaldehyde, isocyanate, TRS and ClO2. The worker amenity layout under AS 4801 and any current ISO 45001 conformance scheme separates clean and dirty zones at the change room interface.

• Dirty zone change room — workers remove dust and chemical-contaminated coveralls and footwear. Ventilation is dilution at 6 to 10 air changes per hour with exhaust to the contaminated extract stack. Duct material galvanized G90.
• Clean zone change room — workers don clean coveralls and footwear after showering. Ventilation is conditioned supply only with positive pressure. Duct material galvanized G90.
• Shower and toilet block — between dirty and clean. Ventilation is conventional commercial extract with galvanized G90 duct.
• Canteen and lunch room — physically separated from production. Ventilation is independent supply and return with no cross-connection to production HVAC. Duct material galvanized G90.

18. The SBKJ machine configuration for the engineered wood, panel and paper sector

SBKJ deploys a specific machine configuration for the engineered wood, wood panel and pulp and paper sector duct fabrication. The configuration is optimised for the heavy stainless plate work, the long spiral runs, the leak-tight TIG seam welding, and the bonded electrical integrity that the sector requires.

18.1 SBAL-V auto duct line

The SBAL-V auto duct line is the SBKJ rectangular duct production machine — galvanized for general lumber mill and kiln, 304 stainless for engineered wood adhesive press and chemical recovery boiler and RTO, 316L for Kraft pulping H2S and chlorine dioxide bleaching and chemical recovery on the paper mill side. The SBAL-V handles the spray booth supply plenum, the press canopy hood, the RTO inlet plenum, the bleach plant scrubber inlet, the recovery boiler ductwork, and any other rectangular plenum work in the panel and paper sector duct package. Refer to the SBAL-V product page for full machine specification.

18.2 SB-ZF1500 stitchwelder

The SB-ZF1500 stitchwelder is the SBKJ machine deployed for stainless plenum, RTO inlet, chemical recovery and HEPA bag-in-bag-out housing construction. The stitchwelder produces high-integrity seam welds in 304L and 316L stainless plate at the leak-tight quality required for the formaldehyde, isocyanate, TRS and ClO2 capture duties. The SB-ZF1500 is mandatory on every panel and paper sector duct package.

18.3 SBSF-1525 round flanging machine

The SBSF-1525 round flanging machine produces the flange connections on round spiral duct sections in 1.2 to 2.0 mm galvanized and stainless. The SBSF-1525 is the workhorse machine for the round duct connections across the engineered wood and panel sector.

18.4 SBFB-1500 spiral former

The SBFB-1500 spiral former produces high-volume spiral duct mains 200 mm to 1500 mm diameter in galvanized and stainless. The spiral former is essential for the dust conveying main runs at the panel and engineered wood plants and for the long flue runs at the recovery boiler.

18.5 SBPC1500 plasma cutter

The SBPC1500 plasma cutter handles the stainless plate work for the press canopy hood, the RTO inlet plenum, the bleach plant scrubber inlet, the recovery boiler ductwork, the HEPA bag-in-bag-out housing, and any 316L and 904L plate fabrication. The SBPC1500 is the SBKJ benchmark plasma cutter for stainless plate work in the engineered wood and panel sector.

18.6 SBLR-600 welder

The SBLR-600 welder produces the TIG seam welds on stainless duct sections at the leak-tight quality required for the formaldehyde, isocyanate, TRS and ClO2 capture duties. Full TIG with backing gas at every seam, leak-tested at 1500 pascals positive pressure before commissioning.

18.7 Spark-resistant fans and IECEx Ex-d ATEX motors

SBKJ supplies the duct package with spark-resistant fans (AMCA 99 Type B Class 2 minimum) and IECEx Ex-d ATEX motors mandatory throughout for the wood dust Kst 200+ St3 duty under NFPA 660, the adhesive vapour Zone 2 duty, the formaldehyde Zone 2 duty, the LPG kiln burner Zone 2 duty, and the Kraft pulping H2S Zone 1 duty. Every motor, every actuator, every instrument carries the appropriate IECEx certification for the zone in which it is installed. The certification documentation is part of the SBKJ duct package handover at commissioning.

19. Why galvanized fails in engineered wood, panel and paper duty — case patterns

We have replaced too many failed galvanized duct runs in Australian panel plants and pulp mills to recommend galvanized anywhere but the upstream wood preparation, the saw and trim dust capture downstream of cooled product, and the general dilution ventilation. The case patterns we see repeatedly:

19.1 MDF and particleboard hot press exhaust failure

Galvanized duct on the MDF or particleboard hot press exhaust typically fails in 12 to 24 months. The mechanism: urea-formaldehyde resin condensate accumulates on the duct wall during operation, then hydrolyses overnight when the duct cools, releasing formic acid that attacks the zinc coating. The bare steel beneath then corrodes by acidic atmospheric corrosion accelerated by the cyclic temperature exposure. Failure mode is wall thinning followed by pinhole leak followed by structural collapse. 316L stainless eliminates this failure mode completely.

19.2 Plywood veneer drier exhaust corrosion

Galvanized duct on the plywood veneer drier exhaust typically fails in 24 to 36 months. The mechanism: high humidity, high temperature and trace VOC loading combine to drive accelerated atmospheric corrosion of the zinc coating, especially at any condensate trap or low point where moisture pools. 316L stainless eliminates the failure mode and provides 25+ year design life.

19.3 Kraft digester relief and brown stock washer H2S attack

Galvanized duct on any TRS-bearing service fails within 12 months. The mechanism: hydrogen sulphide in the presence of moisture aggressively attacks zinc and forms zinc sulphide, a black powder that flakes off and accumulates as duct deposit. The bare steel beneath then corrodes rapidly. 304L stainless fails within 24 to 36 months because the chloride content of the carryover salt drives chloride pitting at the welded heat-affected zone. 316L stainless with molybdenum addition is the only material that delivers a 25+ year design life at the TRS duty.

19.4 Recovery boiler flue acid dew point failure

Galvanized duct on the recovery boiler flue downstream of the economiser typically fails within 12 months. The mechanism: sulphuric acid condensate at the SO3 acid dew point (130 to 150 degrees Celsius) attacks the zinc coating at any uninsulated wall surface that drops below the dew point during start-up, shutdown or upset. 304L stainless fails within 36 months because the chloride content of carryover salt drives chloride pitting. 316L stainless with external insulation maintaining wall temperature above the dew point is the SBKJ standard for the recovery boiler flue from the boiler outlet to the stack base.

19.5 Chlorine dioxide bleach plant chloride pitting

Galvanized duct in any chlorine dioxide-bearing service fails within 6 to 12 months. 304L stainless fails within 24 to 36 months by chloride pitting at the heat-affected zone of welded joints. 316L stainless is the standard at concentrations below 5 ppm. 904L super-austenitic stainless or Hastelloy C-276 is required at the generator vent and the bleach tower seal hood where concentration may exceed 10 ppm.

19.6 OSB blender MDI condensate

Galvanized duct at any OSB blender or press exhaust fails within 12 to 18 months. The mechanism: PMDI isocyanate vapour condenses on the duct wall and cures to a solid polyurea coating, which then traps moisture and accelerates corrosion of the underlying zinc. 316L stainless eliminates the failure mode and provides the leak-tight performance required for the 0.005 ppm isocyanate exposure limit.

20. The cost case for stainless in the panel and paper sector

The capital cost of 316L stainless duct is typically 3.5 to 4.5 times the cost of equivalent galvanized G90 on a per-square-metre basis at current Australian market rates. The capital case for stainless in the engineered wood, panel and paper sector rests on three pillars.

First, the design life. A 316L stainless duct system has a design life of 25 to 40 years at the panel and paper sector duties, versus 12 to 36 months for galvanized at the same duties. The cost-per-year of operation is therefore lower for stainless despite the higher capital cost, by a factor of 5 to 15 depending on the duty.

Second, the operational disruption cost. A galvanized duct failure at the MDF hot press exhaust, the OSB blender or the Kraft digester relief is a production-stopping event. The operator must isolate the duct, shut down the process, build temporary capture or accept emission exceedance, and replace the failed duct under live-plant conditions. Direct cost of a 200-tonne-per-day MDF hot press shutdown is typically AUD 50,000 to AUD 100,000 per day in lost production, exclusive of the duct replacement labour and material. A single galvanized duct failure at this duty pays back the stainless upgrade cost on the duct system in a few days of avoided shutdown.

Third, the compliance cost. A galvanized duct leak at the formaldehyde, isocyanate, TRS or ClO2 duty places the operator in non-compliance with Safe Work Australia exposure limits and state EPA emission limits. The operator may face notices, prosecution, licence variation or revocation, and reputational damage. The cost of a single notice and the associated rectification programme typically dwarfs the entire duct package cost. The SBKJ specification of stainless at every critical duty is structured around eliminating this compliance exposure.

21. The forestry and timber input — FSC, PEFC and AFS certification

The engineered wood, panel and paper sector is downstream of the Australian forestry and timber harvesting sector. Forest Stewardship Council (FSC), the Programme for the Endorsement of Forest Certification (PEFC) and the Australian Forestry Standard (AFS) are the three chain-of-custody certification schemes operating in the Australian market. FSC Australia is the Australian arm of the international FSC. PEFC Australia operates the international PEFC scheme in Australia. AFS is the Australian-domestic scheme historically operated as the Australian Forestry Standard.

The certification scheme drives the upstream forest input — Forestry Corporation NSW, VicForests (ceased native logging 2024), HVP Plantations, HQ Plantations, OneFortyOne (Mt Gambier SA), Forest Solutions Tasmania, AKD Softwoods, Carter Holt Harvey, New Forests, Pentarch Group, Hancock Victorian Plantations and the various other plantation and managed-forest operators. The HVAC implication is indirect — the chain-of-custody traceability at the panel and paper plant requires a clean separation between certified and non-certified input streams, which in turn drives the segregation of process zones and the dust capture envelope at each zone.

22. The Victorian native forestry transition

Victorian native forestry ceased on 1 January 2024 under the state-government decision communicated in 2023. Western Australian native forestry ceased at the end of 2023. The implication for the engineered wood, panel and paper sector is two-fold.

First, the operator mix is shifting from native hardwood to plantation softwood (radiata pine, slash pine, Douglas fir) and managed plantation hardwood. Plantation softwood dries faster, has more uniform fibre and resin properties, and supports higher throughput than native hardwood. The Maryvale APM mill, the Visy Tumut mill and all the Australian panel plants have been substantially or wholly plantation softwood-based for the past decade and are unaffected by the native forestry transition.

Second, the engineered wood segment continues to grow because plantation softwood is the dominant input to LVL, CLT and glulam. The Australian Sustainable Hardwoods (ASH) Heyfield VIC operation, Britton Brothers TAS, McKay Timber TAS and the Tasmanian Special Species Timber (TASST) operation are the few continuing significant native and special-species hardwood operations, with all of them shifting to plantation hardwood or managed-forest input over time.

23. Heat recovery and circular economy at the panel and paper plant

The engineered wood, panel and paper sector is a substantial energy consumer and a substantial waste heat source. Three heat recovery duties recur across the sector and drive the HVAC duct design.

• Kiln drier heat recovery — the kiln vent at 60 to 90 degrees Celsius is a substantial heat source for return-air preheat or hot water generation. 316L stainless plate heat exchanger and 316L stainless interconnecting ductwork. Heat recovery saves 20 to 40 percent of kiln burner fuel at modern installations.
• MDF and particleboard hot press heat recovery — the press hood exhaust at 80 degrees Celsius is a substantial heat source. Combined with the RTO discharge (which is at 200 to 250 degrees Celsius before any heat recovery), the press-and-RTO heat recovery delivers significant return-air preheat or steam generation potential.
• Recovery boiler steam — the Kraft recovery boiler delivers process steam at typically 80 bar and 480 degrees Celsius for modern installations. The steam runs the digester, the brown stock washer, the evaporators, the paper machine and the cogeneration steam turbine. The recovery boiler is therefore both a process steam generator and a power generator, with the steam network distribution being one of the larger pipework systems on the mill site.

The HVAC duct package at the panel and paper plant integrates with the heat recovery system at every relevant duty, with the SBKJ specification including the heat exchanger inlet and outlet flange interfaces, the bypass ductwork for heat recovery outage, and the control damper integration.

24. Construction stages and SBKJ involvement

SBKJ engagement on an engineered wood, panel or paper sector project typically follows a four-stage path from initial quotation to final commissioning.

24.1 Stage 1 — Process zone audit and DHA coordination

The SBKJ engineering team walks the plant or the design drawing set, identifies every ventilation zone, classifies the dust and vapour hazard envelope, and coordinates with the customer's AS 3957 DHA consultant on the engineered controls. The audit output is a process zone schedule, a hazardous area drawing, a duct material specification table and a preliminary equipment list (fans, dampers, instruments, vent flanges, isolation valves).

24.2 Stage 2 — Quotation and detail design

The SBKJ engineering team develops the duct package design — spiral mains, branches, plenums, hoods, flanges, supports, bonding, gaskets, insulation — and issues an itemised quotation. Each line item carries the AS 4254 fabrication standard, the material grade, the gauge, the conveying velocity, the bonding scheme, the insulation specification and the test requirement.

24.3 Stage 3 — Fabrication at Box Hill North VIC

The SBKJ fabrication facility at Box Hill North VIC produces the duct package on the configured machine line — SBAL-V auto duct line for rectangular plenum, SBFB-1500 spiral former for the round mains, SBSF-1525 round flanging machine for the connections, SBPC1500 plasma cutter for the stainless plate, SBLR-600 welder for the TIG seams, SB-ZF1500 stitchwelder for the stainless plenum and bag-in-bag-out housing. Bonding lugs are welded to every spiral section at the factory. Conductive gaskets are pre-fitted to access doors. Insulation cladding is pre-applied to flange faces where required. Vent flanges are welded in at the dust collector connection points.

24.4 Stage 4 — Installation, commissioning and handover

The SBKJ-supplied installation team or the customer's contractor installs the duct package on site under SBKJ engineering supervision. Bonding strap is fitted at every flange. Earth continuity is measured at every joint to under 1 ohm and at the system to under 10 ohms. Leak test is performed at 1500 pascals positive pressure on the stainless duct runs. Flow is measured at every branch. Conveying velocity is verified at the worst-case main. Dust deposition is audited at 24 hours and 7 days after start-up. Spray finishing booth face velocity is verified at four positions. Formaldehyde, isocyanate, TRS and ClO2 concentration are measured at the operator station and the duct discharge under live process conditions. The operations and maintenance manual is issued with the 5-year DHA refresh schedule, the 2-year bonding re-test schedule and the AS 1318 stack inspection schedule.

25. Why SBKJ for the engineered wood, panel and paper sector

SBKJ Engineering at Box Hill North VIC engineers the engineered wood, wood panel and pulp and paper sector duct package on a different basis to a general-purpose HVAC fabricator. The differentiators we lead with on every quotation:

• Process zone engineering. Full site walk and zone schedule on every quotation, not boilerplate spec. DHA coordination with the facility's AS 3957 consultant.
• Hazardous area drawing. Plan and elevation drawing per AS/NZS 60079.10.1 and AS/NZS 60079.10.2 supplied with every quotation. Zone 1, 2, 20, 21 and 22 boundaries marked.
• Material specification. Galvanized G90, 304L stainless, 316L stainless, 904L super-austenitic stainless and Hastelloy C-276 each justified per duty. Stainless at every formaldehyde, isocyanate, TRS, ClO2, recovery boiler flue and yankee dryer hood as standard.
• Conveying velocity. Sized at peak operating condition, not design average. 18 m/s sander, 20 m/s plywood saw, 22 m/s CNC router and OSB strand, 25 m/s raw chip pneumatic main, 28 m/s hog fuel main.
• Bonding and earthing. Copper bonding strap and brass M8 lug welded to every spiral section at SBKJ. Resistance under 1 ohm per joint, under 10 ohms system to plant earth.
• Spark detection. Sensor location, water injection or fast-acting damper response, interface to dust collector control — all specified at quotation.
• NFPA 660 / NFPA 68 / NFPA 69 interface. Vent flanges welded into the SBKJ duct package at the factory, isolation valve mounting flanges installed for the suppression supplier, AMCA 99 conformity on every fan supplied through SBKJ. IECEx Ex-d ATEX certification on every Zone 1 motor.
• Stainless leak-tight construction. TIG-welded longitudinal seams, TIG-welded circumferential joints, conductive gaskets, leak test at 1500 pascals positive pressure on every formaldehyde, isocyanate, TRS and ClO2 duct run.
• Machine configuration. SBAL-V auto duct line for the rectangular work, SBFB-1500 spiral former for the dust extraction mains, SBSF-1525 round flanging for connections, SBPC1500 plasma cutter for the stainless plate work, SBLR-600 welder for TIG seams, SB-ZF1500 stitchwelder for the stainless plenum and HEPA bag-in-bag-out construction. Full SBKJ machine catalogue.
• Australian footprint. Box Hill North VIC engineering and fabrication, Australian site walks, Australian commissioning support, Australian after-sales. ARBS 2026 industry-event participation. About SBKJ Group.

Get an itemised SBKJ duct package quotation for your engineered wood, panel, pulp or paper project →

FAQ

Why is wood dust treated as St3 combustible in a panel or engineered wood plant?

MDF, particleboard and OSB sander dust has Kst typically 200 bar metres per second and minimum ignition energy below 30 millijoules. Under NFPA 660 this places the facility in St3 classification with higher vent area sizing than the St2 envelope at a general sawmill or joinery shop. SBKJ sizes NFPA 68 vents at typically 1.5 to 3.0 square metres per cubic metre of protected volume for the panel sector versus 0.5 to 1.5 for the sawmill sector.

What duct material does the MDF or particleboard hot press exhaust need?

316L stainless throughout from the press canopy hood and edge seal capture to the RTO inlet. Urea-formaldehyde condensate hydrolyses to formic acid overnight and attacks zinc within 12 to 24 months. 316L stainless with TIG-welded seams and conductive gaskets at every joint is the SBKJ default.

How fast does galvanized duct fail at the Kraft digester relief?

Under 12 months. Hydrogen sulphide in the presence of moisture aggressively attacks zinc forming zinc sulphide. 304L stainless lasts 24 to 36 months because chloride content of carryover salt drives chloride pitting at the heat-affected zone. 316L stainless with molybdenum addition is the only material that delivers 25+ year design life at the TRS duty.

What is NFPA 660 and how does it apply in 2025?

NFPA 660 is the consolidated United States NFPA combustible particulate solids standard published in 2025, replacing NFPA 484 (combustible metals), NFPA 654 (combustible particulate solids), NFPA 655 (sulphur) and NFPA 664 (woodworking). For the Australian engineered wood and panel sector, NFPA 660 chapter 30 carries the prior NFPA 664 woodworking content. Australian insurers and consulting fire engineers reference NFPA 660 from 2025 onward.

What is the conveying velocity for MDF and particleboard dust collection?

Sander dust 18 m/s, MDF and particleboard saw and edge trim 20 m/s, raw chip pneumatic main 25 m/s, hog fuel main 28 m/s. Sized at peak operating condition, not design average. Below SBKJ targets the system settles and the next spark propagates.

Why does the OSB blender need 316L stainless and full enclosure?

PMDI (polymeric methylene diphenyl diisocyanate) is the OSB binder. Isocyanate workplace exposure standard is 0.005 ppm — 200 times tighter than formaldehyde. Isocyanate is a respiratory sensitiser with no safe exposure threshold. Capture must be complete with 316L stainless duct, TIG-welded seams, leak test at 1500 pascals positive pressure, and continuous MDI monitoring at the operator station.

What is TRS and why does it dominate the Kraft pulp mill HVAC envelope?

Total Reduced Sulphur is the combined hydrogen sulphide, methyl mercaptan, dimethyl sulphide and dimethyl disulphide that give every Kraft pulp mill its odour signature. Sources include the digester relief, brown stock washer, black liquor evaporators, recovery boiler smelt spout and lime kiln. Every source captured to the NCG incinerator, the recovery boiler combustion chamber or a dedicated RTO. 316L stainless throughout. Victorian EPA boundary limit typically less than 5 ppm continuous.

Why 316L not 304L at the chlorine dioxide bleach plant?

304L stainless fails by chloride pitting at the welded heat-affected zone within 24 to 36 months at the bleach plant. 316L with 2 to 3 percent molybdenum addition provides the chloride pitting resistance for continuous ClO2 exposure below 5 ppm. 904L super-austenitic stainless or Hastelloy C-276 is required at the ClO2 generator vent and bleach tower seal hood where concentration may exceed 10 ppm.