Why tannery ductwork is its own discipline
HVAC ductwork inside an operating tannery is the single most chemically hostile mechanical service most Australian sheet-metal fabricators will ever encounter outside of a primary smelter or a pulp mill. The plant runs hydrogen sulphide from sulphide depilatory chemistry, ammonia from deliming and from raw-hide urine breakdown, chromium III sulphate aerosol with a trace chromium VI fraction from the tanning drums, dilute sulphuric acid mist from the pickle bath, aniline-related vapour and azo-dye aerosol from the dyehouse, fat-liquoring oil mist from the softening drums, saturated humid air at 60 to 90 degrees Celsius from the drying tunnels, combustible leather dust from buffing and snuffing, isocyanate-cured polyurethane finish aerosol from the spray booths, formaldehyde from certain retanning agents and adhesives, formic acid from acidification baths, and a steady background of lanolin and protein degradation products from the wool pulling fellmongery if the plant runs an integrated sheepskin line. Every one of those streams is regulated under a Safe Work Australia workplace exposure standard, several are notifiable trade waste streams under state EPA licences, and the combined plant emission is monitored at the boundary fence under AS 3580 ambient air quality methods if the plant sits within community complaint range of a residential receptor.
The result is that an Australian tannery ductwork specification cannot be lifted out of a commercial office handbook, a hospital handbook or even a general industrial ventilation handbook. The ductwork has to be designed stream by stream, with the material, the gauge, the seam construction, the fan selection, the scrubber or biofilter pretreatment and the discharge stack matched to the specific chemistry of the source it serves. Galvanised steel ductwork that would last forty years in a commercial office return-air system fails within eighteen months of service on beam house extract. Stainless 304L that handles food and beverage process exhaust without incident develops inter-granular corrosion at the heat-affected zone of every weld inside the chrome tanning extract within five years if it is not specified as 316L. Polyvinyl chloride ductwork that performs reliably in a battery acid mist application disintegrates inside three years on a fat-liquoring oil-mist stream because the oil migrates through the polymer and embrittles the wall. These are the engineering failures the SBKJ engineering team is asked to investigate when an Australian tannery owner-operator gets a corrosion report from the insurance assessor and rings us looking for replacement ductwork at short notice.
This guide consolidates the chemistry, the regulation, the materials science, the fan and air-handler selection logic and the fabrication-floor production approach into a single reference for the Australian engineering, fabrication and operating community supporting tanneries, leather processing plants, hide and skin operations, wool pulling fellmongeries and integrated leather finishing houses. It is the same playbook the SBKJ engineering team uses when our customers in this sector — Howe Leather at Rosebery Tasmania, Packer Leather at Narrandera New South Wales, Mastrotto Australia at Geelong Victoria, the Australian Country Hides Sydney operation, the Brettenwood Leather operation at Wagga Wagga, the Wagga Wagga Leather Processing Hub backed by the New South Wales Government, ARS Leather, the Penang, Bonnybank, Coopers, Schaeffer, Lyndoch, Lemnos, Stockyards, Sandgate, DSE Geelong and DSE Albury tanning houses, the South Australian Hide Skin and Tallow operation and the related members of the Federation of Australian Tanners and the Leather Council of Australia — ask us what to specify, what to fabricate from and what to commission against.
The guide is organised into thirteen parts. Part 1 frames the regulatory landscape every Australian tannery operates inside. Part 2 walks the plant process stage by stage and identifies the dominant emission at each step. Part 3 covers the beam house — soaking, liming, fleshing, unhairing — in detail. Part 4 covers the tanning house — chrome, vegetable and synthetic. Part 5 covers post-tanning operations: retanning, dyeing, fat-liquoring and softening. Part 6 covers drying, conditioning, staking and toggling. Part 7 covers buffing, snuffing and ironing dust collection and the NFPA 660 combustible dust hazard analysis. Part 8 covers spray finishing and roller and curtain coating. Part 9 covers wool pulling fellmongery operations. Part 10 covers the effluent treatment plant and odour control. Part 11 covers boundary fence-line monitoring and community amenity. Part 12 covers material selection and seam construction in detail. Part 13 covers the SBKJ machine configurations Australian fabricators deploy to produce the ductwork.
Part 1 — Regulatory framework
Twelve documents govern almost every Australian tannery HVAC ductwork design decision. Knowing which clause sits in which document is the difference between a smooth EPA licence pathway and a six-month redesign loop after the regulator's first site inspection.
AS 1668.2 mechanical ventilation in buildings
AS 1668.2 is the Australian standard for the use of mechanical ventilation to control the indoor air quality of buildings. For tannery applications it provides the baseline calculation methodology for outside air rates, exhaust rates and process exhaust where local capture is impractical. AS 1668.2 by itself is not enough — it does not specify the local capture velocity needed at a sulphide depilatory drum or the chromium VI exposure limit at a tanning drum — but it provides the structural framework the project ventilation report sits inside. Every Australian tannery HVAC report references AS 1668.2 even where the controlling clause is in ASHRAE, AIHA or the Safe Work Australia workplace exposure standard register.
AS 4254 ductwork for air handling systems in buildings
AS 4254 in two parts — AS 4254.1 for flexible duct and AS 4254.2 for rigid duct — specifies the construction, the gauge tables, the seam types, the support spacing, the leakage class and the testing methodology for HVAC ductwork in Australian buildings. AS 4254.2 supplies the minimum sheet thickness for every duct size and pressure class. For tannery service the project specification typically calls AS 4254.2 by default and then upgrades the material from galvanised to 304L or 316L stainless or to FRP per the chemistry of the stream. The seam and joint construction follows AS 4254.2 unless a specific clause — for example, the fully welded longitudinal seam required for fellmongery sulphide service — overrides it.
AS 1530.4 fire-rated ductwork
AS 1530.4 is the Australian fire test procedure that certifies fire-rated ductwork. Inside a tannery, fire-rated duct applies where the duct passes through a fire-rated wall or floor, where it exits a hazardous area zone classified under AS/NZS 60079, where it serves a kitchen exhaust component on the same building as a process exhaust, or where the project fire engineer's report requires it for compartmentation. The fire resistance level — typically minus, minus, 60 or minus, minus, 120 — is specified by the fire engineer. The ductwork manufacturer supplies a tested-and-certified product matched to the FRL.
AS/NZS 60079 hazardous area classification
AS/NZS 60079.10.1 is the Australian and New Zealand adoption of IEC 60079.10.1 for hazardous area classification of explosive gas atmospheres. AS/NZS 60079.10.2 covers explosive dust atmospheres. For tannery service, AS/NZS 60079 applies wherever the plant uses solvent-based dyes, solvent-based finishes, solvent-based adhesives or solvent-based cleaning chemistries. Most modern Australian tanneries have converted finishing operations to water-based polyurethane and other water-based finishes, which removes the AS/NZS 60079.10.1 classification from the finishing house, but the dyehouse and any solvent-based retanning chemistry still attract the classification. AS/NZS 60079.10.2 applies to the leather dust collection plenum and the dust collector housing because the dust is potentially combustible.
AS 1940 storage and handling of flammable and combustible liquids
AS 1940 governs the storage, dispensing and handling of flammable and combustible liquids on site. For a tannery the relevant volumes are the dye solvent storage, the finishing solvent storage where solvent finishes are still used, the cleaning solvent storage and the fuel storage for boilers and process heaters. AS 1940 drives the bunding, the ventilation rates inside chemical store rooms, the fire compartmentation and the spill containment design. The ductwork serving the chemical store rooms is normally galvanised because the storeroom is held under negative pressure with continuous ventilation, so the duct sees only dilute solvent vapour and ambient humidity.
AS 4801 and AS/NZS 4801 OHS management
AS 4801 and its derivative AS/NZS 4801 are the Australian standards for occupational health and safety management systems that many tanneries certify against. The HVAC ductwork design feeds the AS 4801 risk register through workplace exposure assessment, hazardous area registration, fire risk and confined space management. The ventilation report supports the AS 4801 evidence base; if the ventilation fails to control a hazard to below the workplace exposure standard, the AS 4801 certification is at risk.
AS 3580 ambient air quality methods
The AS 3580 series specifies sampling and measurement methods for ambient air quality. AS 3580.1.1, AS 3580.2.1, AS 3580.9.4 and related parts cover hydrogen sulphide, ammonia, particulate matter and odour by various measurement techniques. For tannery service AS 3580 governs the boundary fence-line monitoring programme that EPA Victoria, EPA NSW and equivalent state regulators require for tanneries within community complaint range of sensitive receptors. The ventilation system specification has to deliver an emission profile that complies at the boundary fence under worst-case meteorology, which traces back to the duct material, the fan curve, the scrubber removal efficiency and the discharge stack design.
AS 4974 leather processing wastewater
AS 4974 is the Australian standard guide for the handling and treatment of leather processing wastewater. It is referenced in tannery EPA trade waste licences and influences the HVAC ductwork because the effluent treatment plant — equalisation tank, primary settler, sulphide oxidation reactor, chrome recovery precipitator, biological reactor, secondary clarifier, sludge dewatering — is a significant source of fugitive odour. The HVAC system captures the headspace vapour from each ETP unit operation, routes it through scrubbers and biofilters, and discharges via the monitored boundary stack.
ISO 17074 leather chromium VI determination
ISO 17074 is the international test method for the determination of chromium VI in leather. It is referenced in the EU REACH regulation, which sets a 3 milligrams per kilogram chromium VI limit on leather articles in direct skin contact, and in the equivalent Australian customer specifications for automotive, footwear and apparel leather. The HVAC system supports compliance with ISO 17074 indirectly: the drying tunnel temperature and humidity profile, the storage room temperature, and the avoidance of chromium oxidising agents in the air handling system all influence the chromium VI level in the finished leather. Drying tunnels held below 60 degrees Celsius produce less chromium VI than drying tunnels held above 80 degrees Celsius, which is one of the reasons modern Australian automotive leather operations have moved to vacuum drying and low-temperature tunnel drying.
ISO 14001 environmental management system
ISO 14001 certification is effectively mandatory for any Australian tannery exporting finished leather to the European Union, and is increasingly demanded by automotive and apparel buyers globally. The HVAC ductwork specification, the emission monitoring program, the boundary fence-line monitoring data and the trade waste compliance evidence are all elements of the ISO 14001 environmental aspect register. Designing the HVAC system for ISO 14001 compliance from concept stage is materially cheaper than retrofitting it later, which is one reason the SBKJ engineering team is regularly asked to support pre-certification audits.
ASHRAE Applications Handbook Chapter 28 — Industrial Ventilation
ASHRAE Applications Handbook Chapter 28 is the global engineering reference for industrial process ventilation including chemical, food, textile and tanning operations. Chapter 28 supplies the local exhaust hood design philosophy, the dilution ventilation calculation methodology, the makeup air integration, the heat recovery considerations and the chemistry-specific material recommendations. Australian tannery HVAC engineers typically start every project with a copy of Chapter 28 open on the desk alongside the AS 1668.2 reference.
Safe Work Australia workplace exposure standards
The Safe Work Australia workplace exposure standard register is the controlling reference for occupational exposure limits in Australian workplaces. For tannery service the relevant entries are hydrogen sulphide at 10 ppm 8-hour TWA and 15 ppm 15-minute STEL; chromium VI compounds at 0.005 mg per cubic metre TWA; ammonia at 25 ppm TWA and 35 ppm STEL; formaldehyde at 1 ppm TWA and 2 ppm STEL; formic acid at 5 ppm TWA; sulphuric acid mist at 1 mg per cubic metre TWA; carbon monoxide at 30 ppm TWA; isocyanates including HDI, MDI and TDI at 0.005 ppm TWA; and a sodium sulphide dermal contact limit administered as part of the broader skin-notation framework. The ventilation system has to control every regulated exposure to below the WES at every operator position under every routine and foreseeable upset operating condition.
EU REACH regulation
The EU REACH regulation restricts chromium VI in leather articles in direct skin contact to 3 milligrams per kilogram. Australian tanneries producing finished leather for the EU market are bound by this limit through the customer-facing supply contract. The HVAC design contributes to compliance through tunnel drying temperature control and through the avoidance of chromium oxidising agents in the air handling system.
AS 4684 leather garment fire safety
AS 4684 covers the flame-spread behaviour of leather garments. It is referenced in motorcycle apparel, fire-fighter glove and protective apparel specifications. The HVAC system contributes to compliance through control of finishing chemistry residue; flame-retardant finishes have to be applied uniformly under controlled humidity, which traces back to the finishing room HVAC supply set-point.
Part 2 — Process flow and emission mapping
A traditional Australian tannery process flow runs from raw-hide receival through to despatch in roughly thirteen stages. Every stage has a dominant emission profile that the HVAC design has to capture, treat and discharge in compliance. The following table summarises the emission profile by stage; subsequent parts of this guide work through each stage in operating detail.
- Raw-hide receival, salting and curing — ammonia from urine breakdown, dilute hydrogen sulphide from microbial degradation if the curing is delayed, salt dust during salt application. General macro-environmental ventilation, 4 to 6 ACH.
- Soaking — dilute ammonia, surfactant aerosol, hide-water vapour. Local exhaust over pits, macro-environmental ventilation 4 to 6 ACH.
- Liming and unhairing — hydrogen sulphide from sulphide depilatory chemistry, ammonia, lime calcium hydroxide dust, hide dust during fleshing. Local exhaust at the drum face and the fleshing machine, 0.5 to 1.0 metre per second capture velocity.
- Deliming and bating — ammonia from ammonium salt deliming agents, dilute hydrogen sulphide. Local exhaust over the drum face.
- Pickling — sulphuric acid mist, sodium chloride mist, formic acid mist. Local exhaust over the drum face, 316L stainless or FRP ductwork.
- Chrome tanning — basic chromium III sulphate aerosol with trace chromium VI fraction, sulphate mist. Local exhaust at the drum face, 316L stainless or chemical-resistant FRP, dedicated wet scrubber pretreatment.
- Wringing and sammying — water vapour, dilute trace tannin aerosol. Local exhaust over the machine.
- Splitting and shaving — wet leather dust, water vapour. Local exhaust at the cutting head.
- Retanning, neutralising, dyeing and fat-liquoring — aniline and azo dyestuff vapour, ammonia, oil mist, dilute formic acid mist. Local exhaust at every drum face, 316L stainless or FRP, scrubber pretreatment.
- Setting and toggling — water vapour, dilute trace dye aerosol, hide dust. Local exhaust at the machine.
- Drying, conditioning, staking — saturated humid air at 60 to 90 degrees Celsius from tunnel drying; vacuum drying water vapour at room temperature. 304L stainless ductwork on tunnel exhaust, mild steel acceptable on vacuum drying because the stream is dilute room-temperature water vapour.
- Buffing, snuffing and ironing — combustible leather dust. Dust collection ductwork at 18 to 20 metres per second transport velocity, spark-resistant fan, deflagration-protected baghouse or cartridge filter.
- Finishing — spray, roller, curtain, embossing, ironing — water-based polyurethane and acrylic finish aerosol; solvent-based finish vapour where still in use; trace formaldehyde from certain crosslinker chemistries. Spray booth ventilation under NFPA 33 and AS 4114 principles, water-based finishes generally galvanised duct, solvent-based finishes hazardous area classified zone 1 inside the booth.
Each emission stream then feeds either directly into a treatment device — wet scrubber, biofilter, regenerative thermal oxidiser, activated carbon polishing — or into a combined manifold that is treated as a single stream by a centralised treatment plant. The design decision between dedicated and centralised treatment is driven by stream compatibility (acid and alkaline streams cannot be combined upstream of treatment without precipitating insoluble salts that block the duct), by space constraints, by treatment device capital cost and by the operating cost of fan power.
Part 3 — Beam house ventilation
The beam house is where raw hide is transformed into pelt ready for tanning. The process steps — soaking, liming, fleshing, unhairing, deliming, bating — all run in alkaline aqueous chemistry at 25 to 35 degrees Celsius, with strong sulphide depilatory chemistry in the liming drum and ammonia chemistry in the deliming drum. The beam house atmosphere is humid, alkaline, sulphidic and ammoniacal, and the ventilation has to control four separate emission streams against tight workplace exposure standards.
Soaking pits
Soaking pits rehydrate cured raw hide in dilute surfactant and biocide solution at 25 degrees Celsius over 12 to 24 hours. The emission is dilute ammonia from urine breakdown on the hide, dilute hydrogen sulphide if any microbial activity has started, and surfactant aerosol. The capture device is normally a slotted side-draft canopy along the long axis of the pit or a low-velocity overhead hood, with face velocity at the pit surface targeting 0.5 metres per second under quiescent conditions. Ductwork is 304L stainless because the air is humid, dilute alkaline and dilute sulphidic; galvanised steel survives soaking pit service only on macro-environmental extract well downstream of the source.
Liming drums and pits
Liming drums and pits run hide in calcium hydroxide and sodium sulphide solution at 25 to 30 degrees Celsius over 12 to 18 hours. The emission is hydrogen sulphide from the sulphide depilatory chemistry at concentrations that can exceed 100 ppm in the drum headspace under normal operation, ammonia from urine breakdown, and lime aerosol. Local exhaust at the drum charge and discharge door is mandatory because of the H2S concentration. Ductwork is 316L stainless because of the combined sulphide and humidity load; 304L survives liming drum service for a few years but inter-granular corrosion at the weld heat-affected zone is a known failure mode within the design life of the duct. The extract from the liming drum is normally routed to a dedicated wet caustic scrubber before joining the combined beam house extract, both to control H2S below the WES at the operator position and to prevent sulphide accumulation in the downstream ductwork.
Fleshing machines
Fleshing machines mechanically remove subcutaneous tissue from the wet limed hide. The emission is hide-fat aerosol, water vapour and trace hydrogen sulphide. The capture device is a hood directly over the working area of the machine with the capture velocity at the hide surface targeting 0.7 to 1.0 metres per second to overcome the aerosol generation rate. Ductwork is 304L stainless because the stream is dilute and humid; the fleshing solids fall to a collection trough and are removed as solid trade waste rather than entering the duct.
Unhairing drums
Unhairing drums run a more aggressive depilatory chemistry — typically calcium hydrosulphide or sodium sulphide at higher concentration than the lime-sulphide unhairing — to remove hair and epidermis. The hydrogen sulphide concentration in the drum headspace is the highest in the plant, routinely exceeding 200 ppm under normal operation. The capture device is a fully-enclosed door hood over the drum charge and discharge with a face velocity of 1.0 to 1.5 metres per second across the open face during charging and discharging. Ductwork is 316L stainless throughout, with TIG-welded longitudinal seams and full penetration weld at every transverse joint. The extract is dedicated and routed to the wet caustic scrubber alongside the liming extract; mixing with non-sulphide streams upstream of the scrubber is avoided because the high sulphide load consumes scrubber caustic faster than a diluted stream, which complicates the scrubber chemistry control.
Deliming and bating drums
Deliming drums run ammonium salt chemistry — ammonium sulphate or ammonium chloride — to neutralise the residual lime and remove calcium from the pelt. The emission is ammonia at 100 to 500 ppm in the drum headspace, trace hydrogen sulphide if residual sulphide is present from liming, and dilute alkaline aerosol. The capture device is a hood at the drum face with 0.7 metres per second capture velocity. Ductwork is 304L or 316L stainless; the choice depends on whether the deliming extract is routed with the sulphide extract to the wet caustic scrubber or with a dedicated ammonia scrubber. Combined extract requires 316L.
Macro-environmental extract
Above and beyond the local exhaust at each source, the beam house space itself is held under negative pressure relative to the rest of the plant to prevent migration of the beam house atmosphere into other operational areas. The macro-environmental extract draws air at 4 to 6 ACH from the ceiling space, supplements the local capture from each source and supports a stable pressure cascade across the plant. The macro-environmental extract ductwork is 304L stainless because the ambient beam house air is sulphidic, humid and alkaline even if dilute by comparison with the source extract.
Make-up air strategy
Make-up air to the beam house is 100 percent outside air because the extract load is heavily contaminated. Australian beam houses generally heat the make-up air to 18 to 22 degrees Celsius in winter to maintain operator comfort and to keep the pelt chemistry consistent with the drum temperature control. Heat recovery between the make-up air and the extract is technically feasible through a heat pipe or run-around coil but is not commonly installed in Australian tanneries because the extract contamination shortens the heat exchanger life. The energy penalty is normally accepted as the cost of the operational chemistry.
Part 4 — Tanning house
The tanning house is where pelt is cross-linked into stable leather using chromium III, vegetable tannin, synthetic tannin or aldehyde tanning chemistry. The dominant Australian tannery chemistry is chromium III sulphate, with vegetable tanning used for upholstery and saddlery leathers and synthetic and aldehyde tanning used for specialised applications. The HVAC implications differ materially between the three chemistries.
Pickle bath
Pickle bath drums bring the pelt to low pH using sulphuric acid and sodium chloride in advance of chrome tanning. The emission is dilute sulphuric acid mist, sodium chloride mist and water vapour. The capture device is a hood at the drum face with capture velocity of 0.5 to 0.7 metres per second. Ductwork is 316L stainless or FRP with vinyl ester resin; 304L is inadequate because the chloride load at low pH causes pitting corrosion at the weld heat-affected zone within five years.
Chrome tanning drums
Chrome tanning drums run basic chromium III sulphate at low pH over 6 to 24 hours, depending on the chemistry, generating a fine aerosol of chromium III sulphate and a much smaller fraction of chromium VI as an oxidation by-product. The Safe Work Australia workplace exposure standard for chromium VI compounds at 0.005 milligrams per cubic metre as an 8-hour TWA is one of the most stringent occupational exposure limits in the Australian regulatory register. The capture device is a fully-enclosed door hood at the drum charge and discharge, with face velocity of 1.0 metres per second across the open face during charging and discharging. Ductwork is 316L stainless or FRP with chemical-resistant resin matched to the chromium and sulphate chemistry. The extract is dedicated and routed to a wet scrubber before atmospheric discharge; the scrubber liquid loop is closed and the spent scrubber liquid is treated as chrome-bearing trade waste under the EPA licence.
The chromium VI emission is the limiting design case for the chrome tanning extract. The HVAC system has to control the operator exposure at the drum face below 0.005 mg per cubic metre TWA, and the boundary fence-line emission has to remain within EPA limits. The scrubber removal efficiency for chromium VI aerosol is normally 99 percent or better at the design face velocity and liquid loading; the residual emission discharged to atmosphere is dispersed through the discharge stack and falls below the boundary EPA limit at the nearest sensitive receptor under worst-case meteorology.
Vegetable tanning pits and drums
Vegetable tanning runs hide in aqueous extract of wattle, mimosa, quebracho, chestnut or similar tannin chemistry over 1 to 6 weeks for traditional pit tanning or 24 to 72 hours for drum tanning. The emission is dilute tannin aerosol, water vapour and dilute organic odour. The capture device is a low-velocity overhead hood at 0.4 to 0.5 metres per second. Ductwork is 304L stainless or aluminium because the tannin chemistry is acidic but the concentration is low and the chloride load is negligible. Australian vegetable tanning is largely confined to specialised saddlery, equestrian and high-end footwear leather operations; most Australian industrial-scale tanneries chrome-tan.
Synthetic and aldehyde tanning
Synthetic and aldehyde tanning chemistry is used for specialised leather applications including chrome-free automotive leather and certain technical leathers. The dominant emission is dilute aldehyde vapour and dilute organic acid mist. Glutaraldehyde-tanned leather extract has a free aldehyde concentration of trace levels in the drum headspace; the workplace exposure standard for glutaraldehyde is administered as a ceiling limit and the ductwork is held above dew point to prevent aldehyde-rich condensate. Ductwork is 316L stainless throughout because of the combined aldehyde, acid mist and humidity load.
Wringing, sammying and side-out
Wringing and sammying machines remove water from the freshly-tanned wet blue stock by mechanical squeezing. The emission is water vapour with trace chromium and sulphate aerosol. The capture device is an overhead hood over the working face of the machine at 0.5 metres per second. Ductwork is 304L stainless; the dilute chromium load over the design life is well below the 316L threshold, but galvanised steel is inadequate because of the residual chromium reactivity with zinc.
Part 5 — Post-tanning operations
The post-tanning operations — splitting, shaving, retanning, neutralising, dyeing, fat-liquoring and softening — transform wet blue stock into dyed and softened crust leather ready for drying. Each operation has its own HVAC profile, and the dyehouse in particular is one of the more complex ventilation problems in the plant.
Splitting and shaving
Splitting machines mechanically split the wet blue stock to a uniform thickness using a band knife. Shaving machines further reduce the thickness of the grain split using a helical cutter. Both operations generate wet leather dust and water vapour. The capture device is a hood at the cutting head with 1.0 metres per second capture velocity. Ductwork is galvanised steel because the dust is wet and the chemistry is dilute; 304L is used where the operation is downstream of chrome tanning and the dust carries trace chromium. The wet dust is normally collected in a wet cyclone or wet scrubber rather than a baghouse to avoid the combustion risk associated with dry leather dust.
Retanning, neutralising and dyeing drums
Retanning drums run synthetic tannin, vegetable tannin or polymer retanning chemistry to adjust the leather properties before dyeing. Neutralising drums adjust the leather pH before dye penetration. Dyeing drums apply aniline-related, azo or pre-metallised dye chemistry at 50 to 60 degrees Celsius. The emission profile is dilute dye aerosol, dilute ammonia from certain retanning chemistries, formic acid vapour from the acidification step, and water vapour. The capture device at each drum face is a hood with 0.7 metres per second face velocity. Ductwork is 316L stainless because of the combined acid, dye and humidity load; the dyestuff chemistry is sufficiently aggressive that 304L develops staining and inter-granular corrosion at welds within ten years.
The dyehouse extract is normally routed to a wet scrubber before atmospheric discharge. The scrubber removes the dye aerosol and the soluble acid mist; the residual organic odour is polished by an activated carbon bed before the discharge stack. Australian tanneries that have converted from solvent-based dye carriers to water-based dye chemistry have substantially reduced the HVAC load on the dyehouse, but the ammonia and formic acid load remains.
Fat-liquoring and softening
Fat-liquoring drums apply natural and synthetic oil chemistry to the wet leather to soften the fibre structure. Softening drums then mechanically work the leather to develop the final hand. The emission is fat-liquor oil mist at moderate concentration, dilute ammonia from emulsion stabilisers, and water vapour. The capture device at the drum face is a hood with 0.7 to 1.0 metres per second face velocity. Ductwork is 304L or 316L stainless; the oil mist load is the dominant design driver. The extract is normally routed to a wet scrubber followed by an oil mist eliminator before atmospheric discharge, both to control the operator exposure and to prevent oil deposit in the duct downstream.
Polyvinyl chloride and chlorinated polyvinyl chloride ductwork are inappropriate for fat-liquoring service because the oil migrates through the polymer and embrittles the wall over time. FRP ductwork is acceptable but requires careful selection of the resin system to resist oil swelling. Stainless is the long-term reliable choice.
Part 6 — Drying, conditioning and mechanical operations
The drying house dries dyed and fat-liquored leather to a controlled moisture content suitable for finishing. The dominant Australian drying technologies are tunnel drying, toggle drying, paste drying and vacuum drying. Each has its own HVAC profile.
Tunnel drying
Tunnel drying conveys leather through a heated chamber at 60 to 90 degrees Celsius for 20 to 90 minutes. The emission is saturated humid air at the discharge of the tunnel; the inlet air is normally dehumidified makeup air heated to the tunnel set-point. Ductwork serving the tunnel inlet is galvanised because the air is dry and hot. Ductwork serving the tunnel exhaust is 304L stainless because the air is saturated and warm; the condensate that forms inside the duct is dilute and not corrosive in itself, but the prolonged exposure to saturated air at 60 to 90 degrees Celsius accelerates galvanised corrosion. The tunnel exhaust is normally routed through a heat recovery unit before atmospheric discharge, both to reduce the energy demand of the makeup air and to lower the discharge plume temperature.
Vacuum drying
Vacuum drying applies heated plates at 50 to 70 degrees Celsius to the leather under vacuum, allowing water to evaporate at lower temperature than tunnel drying. The advantage is improved leather property control, especially for automotive and apparel leather where the chromium VI level has to remain below the EU REACH 3 mg per kilogram limit. The HVAC implication is that the vacuum pump discharge is a relatively dilute water vapour stream at room temperature; ductwork is galvanised because the stream is dilute and the load on the duct is light.
Toggle drying and paste drying
Toggle drying stretches the leather on a perforated board under controlled humidity and temperature to control the area yield. Paste drying glues the leather to a glass or steel plate before tunnel drying. Both operations generate water vapour at moderate temperature with trace dye and finish aerosol. Ductwork is 304L stainless because the chemistry is mild but the humidity load is high.
Conditioning, setting and toggling
Conditioning rooms hold the leather at controlled humidity to achieve target moisture content before mechanical operations. Setting machines mechanically smooth the wet leather. Toggling stretches the leather on toggle frames. The emission is dilute water vapour and trace hide dust. Ductwork is galvanised because the load is light; 304L is used where the conditioning room handles chrome-tanned wet blue stock and trace chromium aerosol is anticipated.
Staking and milling
Staking machines mechanically work the dry leather to develop softness. Milling drums tumble the dry leather to develop a uniform grain. The emission is hide dust, dilute fat-liquor oil mist and trace finish aerosol. The capture device is a hood at the machine with 0.7 metres per second face velocity. Ductwork is galvanised because the load is light and the dust is dry; transition to dust collection ductwork at 18 to 20 metres per second transport velocity downstream of the capture hood prevents fallout on the way to the baghouse.
Part 7 — Buffing, snuffing and ironing — combustible dust
Buffing, snuffing and ironing are the mechanical operations that prepare the leather surface for finishing. Buffing uses abrasive rolls to develop the leather grain and remove minor surface imperfections. Snuffing removes the grain layer to expose the corium for nubuck or split-grain leather. Ironing applies pressure and heat to flatten and consolidate the leather. All three operations generate dry leather dust at high mass loading, and the dust is potentially combustible.
Dust hazard analysis under NFPA 660
The 2025 consolidation of NFPA dust standards into NFPA 660 represents the current global state of the art for combustible dust hazard analysis. Australian leather processors generally adopt NFPA 660 principles in the absence of an equivalent Australian standard, supplemented by AS/NZS 60079.10.2 for dust hazardous area classification. The dust hazard analysis determines the Kst, the Pmax and the minimum ignition energy of the specific dust by laboratory test. Leather dust Kst values from published research typically fall in the 50 to 150 bar metres per second range, classifying as ST1 dust with potential to escalate to ST2 depending on the specific leather, the finishing chemistry and the moisture content. The dust collector specification has to be matched to the calculated severity class.
Capture, transport and dust collection ductwork
The capture device at each machine is an enclosing hood with high face velocity, typically 1.0 to 1.5 metres per second across the working face. The branch duct from the capture hood to the main collection trunk is sized to maintain 18 to 20 metres per second transport velocity at the design air volume; this prevents fallout and ensures the dust reaches the collector. The main collection trunk maintains the same transport velocity to the collector inlet. Horizontal runs are limited to 6 metres without an inspection panel, and cleanouts are installed at every bend and at every 6 metres on horizontal runs. The ductwork material is galvanised steel at 1.2 mm minimum thickness to provide abrasion resistance against the dust load.
Spark-resistant fans
Fans handling combustible leather dust must be spark-resistant under AMCA 99-0401 Type A or Type B classification. Type A fans have non-ferrous impellers, casings and inlet cones; Type B fans have non-ferrous impellers with steel casings. Type C fans — non-ferrous rubbing surface only — are inadequate for leather dust service because the casing-impeller contact under upset conditions can generate sparks. The fan motor is mounted outside the airstream or, where in-airstream mounting is unavoidable, is rated for the dust hazardous area classification under AS/NZS 60079.10.2.
Explosion protection
The dust collector — baghouse or cartridge filter — is fitted with explosion vents sized per NFPA 68 calculation methodology against the dust Kst and the collector volume. The inlet ductwork to the collector has a chemical or mechanical isolation valve to prevent flame propagation back to the source machines. Spark detection at the collector inlet, with high-pressure water injection for spark suppression, is installed where the dust hazard analysis identifies a credible ignition source. Inerting with nitrogen is reserved for high-severity ST2 and ST3 dust applications and is uncommon in Australian leather processing operations.
Earthing and static dissipation
Every section of dust collection ductwork is bonded to a common earthing system to prevent static accumulation. The bonding strap continuity is tested at commissioning and at scheduled intervals during operation. Flexible duct connections, where used, are specified with internal earthing wire continuity. Insulating duct material — FRP, PVC, CPVC — is generally avoided in dust collection service because of the static charge accumulation risk.
Part 8 — Finishing — spray, roller and curtain coating
Finishing operations apply pigment, binder, top-coat and protective layers to the dyed and dried leather. The dominant Australian finishing technology is water-based polyurethane and acrylic chemistry applied by automated spray booth, roller coating or curtain coating, with embossing presses and ironing rollers as secondary mechanical operations.
Spray finishing booths
Spray finishing booths apply finish to the moving leather under a high-velocity air curtain that captures the overspray and conveys it to the exhaust. The face velocity at the open face of the booth must be at least 0.5 metres per second under the most adverse spray gun discharge condition, per NFPA 33 spray application principles adapted to AS 4114 booth construction. Australian booths typically design for 0.6 to 0.7 metres per second to provide a margin against gun cluster discharge and operator movement at the booth opening. The capture and transport velocity in the exhaust duct is normally 8 to 12 metres per second to keep the finish aerosol airborne to the abatement device.
Ductwork material depends on the finish chemistry. Water-based polyurethane and acrylic finishes — the dominant Australian chemistry — allow galvanised steel ductwork because the booth atmosphere is below 25 percent of the lower flammability limit and the finish is not corrosive to zinc. Solvent-based finishes — nitrocellulose, polyurethane, acrylic in solvent carrier — trigger AS/NZS 60079.10.1 hazardous area classification of the booth and the immediate surrounds, and require zone-rated fans, explosion-proof motors and bonded ductwork to manage the static charge accumulation.
Roller coating and curtain coating
Roller coating and curtain coating apply finish to the leather by direct mechanical contact rather than atomised spray. The HVAC implication is significantly less aerosol load than spray finishing, but more solvent vapour load per unit finish applied because the larger exposed liquid surface area drives evaporation. The capture device is a hood over the coating head with face velocity of 0.5 metres per second. Ductwork is galvanised for water-based finishes; solvent-based finishes again trigger hazardous area classification.
Embossing presses and ironing rollers
Embossing presses apply pattern to the finished leather under heat and pressure, typically 90 to 130 degrees Celsius. Ironing rollers similarly apply heat and pressure to consolidate the finish. The emission is dilute solvent vapour from any residual finish solvent, dilute water vapour from residual finish water, and dilute formaldehyde where the finish chemistry includes a formaldehyde-based crosslinker. The capture device is a low-velocity hood over the press or roller. Ductwork is galvanised; the load is too light to justify stainless.
Part 9 — Wool pulling and fellmongery
Wool pulling fellmongery operations recover wool from sheepskin pieces before tanning the remaining pelt. The depilatory chemistry is similar to the unhairing chemistry in the cattle hide beam house but at higher concentration because the wool fibre is more strongly anchored than cattle hair, and the wool is recovered as a saleable product rather than dumped.
Sulphide depilatory drums
Sulphide depilatory drums apply sodium sulphide or calcium hydrosulphide chemistry to the wool side of the sheepskin to loosen the wool from the pelt. The emission is hydrogen sulphide at headspace concentrations of 200 to 400 ppm under normal operation, ammonia, and lanolin aerosol from the wool grease. The capture device is a fully-enclosed door hood at the drum charge and discharge with face velocity of 1.0 to 1.5 metres per second across the open face. Ductwork is 316L stainless throughout with TIG-welded longitudinal seams and full-penetration weld at every transverse joint.
Wool pulling tables
Wool pulling tables provide the working surface where operators pull the loosened wool from the pelt by hand or by mechanical wool-pulling machine. The emission is dilute hydrogen sulphide from residual sulphide in the wool, ammonia, lanolin aerosol and short wool fibre. The capture device is a downdraft table with capture velocity of 0.5 metres per second at the table surface. Ductwork is 316L stainless because of the sulphide load.
Wool drying and conditioning
Recovered wool is normally dried and conditioned in a separate building before despatch to the wool buyer. The emission is dilute lanolin aerosol, short wool fibre and water vapour. The capture device is a low-velocity overhead hood. Ductwork is galvanised because the load is light and the chemistry is mild.
Pickle and tan of the pelt
The depilated sheep pelt enters the tanning circuit through the standard pickle, chrome tan or vegetable tan, retan, dye, fat-liquor sequence. The HVAC implications are identical to the cattle hide tanning circuit, with the additional consideration that the sheep pelt is thinner than cattle hide and the chrome tanning extract concentration per kilogram of pelt is correspondingly lower.
Part 10 — Effluent treatment plant
The effluent treatment plant treats the combined trade waste from the tannery before discharge to the sewer or to a watercourse under the EPA licence. The HVAC implication is that several unit operations in the ETP are open or vented and generate fugitive odour that has to be captured and treated before atmospheric release.
Equalisation tanks
Equalisation tanks buffer the combined trade waste flow to a uniform rate for downstream treatment. The headspace is humid, alkaline, sulphidic and ammoniacal depending on the upstream operational mix. The capture device is a covered tank with continuous low-volume extract from the headspace at 4 to 6 air changes per hour. Ductwork is 316L stainless because of the combined sulphide and humidity load.
Sulphide oxidation reactor
Sulphide oxidation reactors apply manganese-catalysed air oxidation or chemical oxidation to convert dissolved sulphide to thiosulphate or sulphate before the wastewater proceeds to the next treatment stage. The reactor headspace is the highest hydrogen sulphide concentration in the ETP, and the local exhaust has to control fugitive emission against the workplace exposure standard at the operator position. Ductwork is 316L stainless with TIG-welded longitudinal seams.
Chrome recovery precipitator
Chrome recovery precipitators recover chromium III sulphate from the chrome tanning waste stream for reuse or for stabilised disposal. The headspace is acidic, chromium-bearing, and at concentrations that exceed the chromium VI workplace exposure standard at the operator position without local exhaust. Ductwork is 316L stainless or FRP with chemical-resistant resin.
Biological reactors
Biological reactors apply activated sludge or alternative biological treatment to remove residual organic load, dissolved nitrogen and dissolved phosphorus from the wastewater. The headspace is humid and dilute. Capture and treatment of the headspace vapour is normally through a biofilter because the dilute organic load is well matched to biofilter capacity. Ductwork from the reactor to the biofilter is 316L stainless because of the dilute sulphide and ammonia load.
Sludge handling and dewatering
Sludge handling and dewatering operations — thickener, belt press, filter press, centrifuge — concentrate the biological and chemical sludge for disposal. The emission is humid air carrying biological and chemical aerosol. The capture device is local exhaust at the sludge equipment, with the extract routed to the biofilter or the wet scrubber depending on the chemistry. Ductwork is 316L stainless.
Part 11 — Boundary fence-line monitoring
Australian tanneries that have been progressively surrounded by residential development — which describes most of the remaining industrial-scale plants in Victoria, New South Wales, South Australia and Tasmania — face boundary fence-line ambient air quality monitoring under AS 3580 series methods and EPA Victoria, EPA NSW, EPA South Australia, EPA Tasmania or equivalent state regulator requirements. The community amenity expectation is that the tannery does not generate detectable odour or measurable elevated ambient concentration of hydrogen sulphide, ammonia, particulate or volatile organic compounds at the nearest sensitive receptor.
Sensitive receptors
Sensitive receptors are normally residential dwellings, schools, hospitals, child-care centres and aged-care facilities within the assessment distance of the plant. The EPA licence identifies the specific receptors. The boundary fence-line monitoring program measures ambient concentration at the receptor under representative meteorological conditions and reports against the licence emission limit.
Dispersion modelling
Atmospheric dispersion modelling under AUSPLUME, CALPUFF or equivalent EPA-approved model calculates the ground-level concentration at the sensitive receptor as a function of the stack emission rate, the stack height, the discharge velocity, the discharge temperature and the meteorological condition. The HVAC design adjusts these parameters to achieve compliance at the receptor under worst-case meteorology. Increasing the stack height, increasing the discharge velocity through a smaller stack diameter, increasing the discharge temperature through reheat, and reducing the source emission through better scrubber and biofilter performance are all available levers.
Monitoring methods
AS 3580.1.1 covers continuous ambient air quality monitoring methods. AS 3580.2.1 covers hydrogen sulphide measurement. AS 3580.9.4 covers particulate measurement. Specific tannery odour assessment uses dynamic olfactometry under AS/NZS 4323.3 to quantify the odour concentration in odour units per cubic metre. Continuous boundary monitoring with telemetry to the EPA is increasingly required for tanneries with a community complaint history.
Stack design
The discharge stack design is the final HVAC element that converts the treated emission into a dispersion plume that disperses to ground level concentration below the receptor limit. Stack height of 1.5 to 2 times the adjacent building height is normally adequate for low-emission streams; tall, narrow stacks with high discharge velocity provide the best dispersion for higher-emission streams. The stack material is 316L stainless because of the residual sulphide and acid mist load after scrubber and biofilter treatment.
Part 12 — Material selection in detail
Material selection across the plant is summarised in the following framework. The chemistry of each stream determines the material; the static pressure and the leakage class determine the gauge; the seam construction follows the material and the leakage class.
Galvanised steel
Galvanised steel ductwork is appropriate for general factory makeup air, water-based spray finishing booth exhaust, leather dust collection ductwork from buffing and snuffing, conditioning and staking room extract, and macro-environmental supply where the chemistry is dilute. Galvanised steel is inappropriate for any beam house extract, any tanning extract, any fellmongery sulphide service, any dyehouse extract, any fat-liquoring service or any effluent treatment plant headspace service. The cost premium of stainless over galvanised — typically 2.5 to 3 times raw material cost — is offset by 30 years of service life with zero coating maintenance against the 5 to 10 year galvanised service life under tannery process conditions.
304L stainless steel
304L stainless steel is appropriate for general beam house extract where the chloride load is negligible, for tannin and vegetable tanning extract, for dilute dyehouse extract, for soaking pit extract, for tunnel drying exhaust, for the conditioning circuit downstream of chrome tanning, for macro-environmental beam house extract, and for the discharge stack where the residual treated emission is dilute. The 0.03 percent maximum carbon content of the 304L grade controls the inter-granular corrosion at the weld heat-affected zone that is the dominant failure mode of standard 304 in this service.
316L stainless steel
316L stainless steel is appropriate for chrome tanning extract, fellmongery sulphide depilatory extract, unhairing drum extract, pickle bath chloride extract, combined acid-bearing exhaust, sulphide oxidation reactor headspace extract, chrome recovery precipitator extract, formaldehyde-bearing finishing extract, and any duct exposed to combined sulphide and chloride loading. The 2 to 3 percent molybdenum content of the 316 grade provides the pitting resistance against chloride and the sulphide tolerance that 304L lacks. 316L is the default choice for any tannery duct where the chemistry is in doubt.
FRP fibreglass reinforced plastic
FRP ductwork with vinyl ester or epoxy resin chemistry is appropriate for high-concentration acid mist applications, dilute high-chloride streams, certain chromium-bearing applications where stainless cost is prohibitive, and high-volume low-pressure ETP headspace extract. The resin chemistry has to be specifically selected against the duct service chemistry; vinyl ester for acid and chloride, epoxy for amine and ammonia, isophthalic polyester for general corrosion resistance. The ductwork construction follows ASTM D5421 or equivalent FRP duct construction standards. FRP is inappropriate for dust collection service because of static accumulation and combustion risk, and is inappropriate for high-temperature service above 80 degrees Celsius without specialist resin selection.
Aluminium
Aluminium ductwork is occasionally used for vegetable tanning extract and for certain fat-liquoring applications where stainless cost is prohibitive. Aluminium tolerates the dilute organic chemistry but is inadequate for any beam house extract, any chrome tanning extract or any sulphide service. The aluminium-zinc galvanic couple at any galvanised steel transition is a documented failure mode; aluminium-stainless transitions require isolation gaskets.
Polyvinyl chloride and CPVC
PVC and CPVC ductwork is inappropriate for most tannery service because the temperature is normally above the PVC service limit, the abrasion from dust is excessive, and the oil mist from fat-liquoring degrades the polymer. PVC is occasionally used for short connecting runs to wet scrubbers serving cold trade waste streams where the chemistry is mild.
Part 13 — SBKJ machine configurations for tannery ductwork supply
Australian sheet-metal fabricators supplying tannery ductwork projects deploy a specific configuration of SBKJ machinery to produce the mix of galvanised, 304L stainless and 316L stainless ductwork the project schedule demands. The right machine selection depends on the volume mix between rectangular and round duct, between galvanised and stainless, between small-diameter and large-diameter spiral, and between simple straight duct and complex fittings.
Stainless ductwork production — SBAL-V auto duct line
The SBKJ SBAL-V is the flagship stainless auto duct line and the most-specified machine for tannery ductwork projects involving 304L and 316L stainless rectangular duct. The SBAL-V runs at up to 16 metres per minute through coil decoiling, levelling, notching, beading, longitudinal seam closure and length cut-off, on coil from 0.5 mm to 1.5 mm thickness at up to 1,500 mm coil width. With 87 kW total installed power, the SBAL-V handles full-day production of 304L and 316L stainless ductwork for chrome tanning service, fellmongery sulphide service and beam house service. The machine is configured at order time with TIG welding stations for Pittsburgh seam closure on critical ductwork where fully welded seams are specified. The SBAL-V is the right choice for any Australian tannery project with sustained stainless production above 200 metres of duct per day.
Mid-volume rectangular production — SBAL-III auto duct line
The SBAL-III auto duct line is the right choice for Australian fabricators with mid-volume galvanised production and modest stainless capability requirement. The SBAL-III runs at 14 metres per minute on 0.5 mm to 1.2 mm coil, with 15.7 kW installed power. The SBAL-III handles galvanised production for general beam house extract, macro-environmental supply, dust collection ductwork mains and water-based finishing booth ductwork. With stainless tooling and reduced production rate, the SBAL-III also handles low-volume 304L stainless production where the SBAL-V capacity is not justified by the project volume.
Entry-volume rectangular production — SBAL-II auto duct line
The SBAL-II auto duct line is the entry-level rectangular duct line at 18 metres per minute on 0.5 mm to 1.2 mm coil, with 5.5 kW installed power. The SBAL-II is the right choice for smaller Australian fabricators or for fabricators using the SBAL-II as a complement to a higher-volume SBAL-V or SBAL-III when the project schedule requires parallel production lines.
Spiral round duct production — SBTF tubeformer series
Round spiral ductwork is preferred for many tannery applications because the continuous spiral seam is more easily decontaminated, the pressure drop is lower than rectangular, and the structural strength is higher at large diameter. The SBKJ SBTF-1500C, SBTF-1602 and SBTF-2020 spiral tubeformers cover round duct production from small diameter to 1,500 mm, 1,600 mm and 2,000 mm maximum diameter respectively. The choice between the three depends on the largest duct diameter the project requires. The SBTF-1500C is the most-specified model for typical Australian tannery projects; the SBTF-2020 is reserved for very large makeup air or general factory extract trunk lines.
Elbow and fitting production — SBEM-1250
The SBEM-1250 elbow making machine produces gored elbows, transitions and offsets from coil up to 1,250 mm wide. The elbow maker handles galvanised, aluminium and stainless input material, with stainless requiring slower forming speed and adjusted tooling clearance. The elbow maker is the right machine for any tannery project where the fitting volume is significant relative to the straight duct volume; the alternative is hand-formed fittings which carry significantly higher labour cost per fitting.
Stitchweld Pittsburgh seam closure — SBSF-1525
The SBSF-1525 stitchwelder closes Pittsburgh seams on rectangular ductwork at 2.5 kW installed power. The stitchwelder is paired with the SBAL-V or SBAL-III auto duct line for seam closure on stainless ductwork where the auto line does not include integrated welding stations. The stitchwelder is also used for site-fabricated stainless fittings where the SBEM-1250 elbow maker is not deployed.
Hydraulic folding — SBFB-1500 and SBHF series
The SBFB-1500 hydraulic folder at 7.5 kW installed power and 1.20 metres per minute folding speed handles thicker gauge folding for fittings, plenum boxes and custom transitions in galvanised and stainless material up to 1,500 mm folding width. The SBHF series hydraulic folders complement the SBFB for higher-volume site fitting production. Australian tannery projects with significant transition and plenum box volume justify a dedicated hydraulic folder; smaller-volume projects use the folding capability built into the auto duct line.
Plasma cutting — SBPC1500
The SBPC1500 plasma cutting table handles sheet cutting up to 1,500 mm width for fittings, blank-outs, access doors and custom components. Plasma cutting is preferred over laser cutting for galvanised material because the zinc fume from laser cutting requires more aggressive extraction; for stainless, both plasma and laser are acceptable. The SBPC1500 is the right machine for fabricators with significant custom fitting volume; high-volume custom production justifies upgrade to laser cutting.
Roll bending — SBLR-600 and SBLR-600A
The SBLR-600 and SBLR-600A roll benders form cylindrical sections, large-radius transitions and curved fittings from sheet at 7.6 metres per minute. The roll bender complements the spiral tubeformer for short-run cylindrical sections, large-radius elbows and custom curved fittings where the SBTF spiral tubeformer is not the right tool. Australian tannery projects with significant custom curved fitting volume include a roll bender in the equipment list.
Production planning
The full SBKJ machinery list for a comprehensive Australian tannery ductwork fabricator typically includes one SBAL-V stainless auto duct line as the primary stainless production unit, one SBAL-III auto duct line as the galvanised production unit, one SBTF-1500C or SBTF-1602 spiral tubeformer, one SBEM-1250 elbow maker, one SBSF-1525 stitchwelder, one SBFB-1500 hydraulic folder, one SBPC1500 plasma cutting table, one SBLR-600 roll bender, and the supporting handling equipment for coil decoiling, sheet handling and finished duct movement. The total floor footprint is approximately 600 square metres of production space plus 200 square metres of coil and finished goods storage. The total installed electrical load is approximately 150 kW, plus compressed air at 7 bar and dust extraction for the cutting operations.
Conclusion — the ductwork is the licence
An Australian tannery operates inside a regulatory envelope defined by the EPA licence, the Safe Work Australia workplace exposure standards, the boundary fence-line monitoring program, the ISO 14001 environmental management system, the AS 4801 OHS management system, the EU REACH chromium VI limit on exported leather and the customer-facing quality specification. The HVAC ductwork is the engineering substrate that ties all of those documents together. Every workplace exposure assessment, every boundary fence-line monitoring result, every EPA emission report, every ISO 14001 environmental aspect register and every customer-facing quality certificate is contingent on the ductwork doing what the specification requires it to do, day in and day out, for the design life of the plant.
Specifying it correctly at concept design — 304L stainless as the minimum default, 316L where chromium, sulphide or chloride load demands, galvanised reserved for dust collection and water-based finishing only, FRP for high-concentration acid where stainless cost is prohibitive, fully welded seams in chrome and fellmongery service, spark-resistant fans in dust collection service, wet caustic scrubber pretreatment for sulphide and biofilter pretreatment for ETP odour, stack height and discharge velocity matched to the dispersion model for boundary fence-line compliance — is the cheapest insurance the operator will buy in the entire plant lifecycle. Skipping it costs a corrosion-driven shutdown in year three, an EPA notice in year four, a workplace exposure exceedance in year five, a complete envelope rebuild in year ten and a community complaint campaign that eventually closes the plant. The historical attrition from 50-plus Australian tanneries to the remaining industrial-scale plants today is partly the story of trade, exchange rate and labour cost economics, but it is also partly the story of operators who did not invest in the engineering early enough to keep their boundary fence-line compliance and their workplace exposure assessment defensible at the same time.
SBKJ Group supplies the machinery, the engineering and the after-sales continuity that Australian tannery ductwork fabricators rely on to fabricate ductwork that lasts the design life of the plant. Our engineering team in Box Hill North, Victoria, is available to answer specification questions within 12 hours. If you are designing, fabricating or operating an Australian tannery, leather processing plant, fellmongery, hide and skin operation, or integrated finishing house — Howe Leather Rosebery, Packer Leather Narrandera, Mastrotto Australia Geelong, Australian Country Hides Sydney, Brettenwood Leather Wagga Wagga, the Wagga Wagga Leather Processing Hub, ARS Leather, Penang, Bonnybank, Coopers, Schaeffer, Lyndoch, Lemnos, Stockyards, Sandgate, DSE Geelong, DSE Albury, South Australian Hide Skin and Tallow and the broader Federation of Australian Tanners and Leather Council of Australia membership — the SBKJ engineering team is ready to support your project from concept design through commissioning.
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FAQ
What air change rates apply to the beam house of an Australian tannery?
4 to 6 ACH as the macro-environmental baseline supplemented by local exhaust ventilation at every wet bath, drum and machine. The controlling number is the local capture velocity at each source — 0.5 to 1.0 metre per second face velocity at the open face of the hood over wet baths, drums and pits. The headline ACH falls out as a consequence of the total exhaust volume rather than driving the design directly.
Why does galvanised ductwork fail in tannery beam house service?
Hydrogen sulphide and sulphide aerosol consume the zinc coating within 18 to 36 months through formation of zinc sulphide. Ammonia from urine and from deliming reacts with zinc to form water-soluble zinc-ammine complexes that wash away in condensate. Constant 80 to 95 percent relative humidity accelerates both reactions. Once the zinc is gone, the carbon steel rusts rapidly. 304L stainless is the minimum specification for beam house extract; 316L is required where the extract joins chrome or chloride streams.
What material is required for chrome tanning drum extract ductwork?
316L stainless steel as the minimum specification, or FRP with vinyl ester or epoxy resin matched to the chromium and sulphate chemistry. Galvanised is inappropriate. Ductwork seams must be welded or sealed with chemical-resistant gasketing; mechanical lock-formed seams without sealant leak chromium aerosol into the plenum space within 12 months. The chromium VI workplace exposure standard at 0.005 mg per cubic metre TWA is the limiting design case.
How is combustible leather dust from buffing and snuffing managed?
Dust hazard analysis under NFPA 660 principles to determine Kst and Pmax; transport velocity 18 to 20 metres per second to prevent fallout; spark-resistant Type A or Type B fans per AMCA 99-0401; deflagration-protected baghouse or cartridge filter with explosion vents sized per NFPA 68; chemical or mechanical isolation valve at the collector inlet; bonded earthing throughout the duct system. Galvanised steel ductwork at 1.2 mm minimum thickness for abrasion resistance.
What ventilation rates apply to leather spray finishing booths?
Minimum 0.5 metres per second face velocity at the open face under the most adverse spray gun discharge condition per NFPA 33 and AS 4114. Australian booths typically design for 0.6 to 0.7 metres per second to provide margin. Water-based polyurethane and acrylic finishes allow galvanised duct; solvent-based finishes trigger AS/NZS 60079.10.1 hazardous area classification and require zone-rated equipment.
What duct material is appropriate for fellmongery sulphide depilatory exhaust?
316L stainless steel throughout, with TIG-welded longitudinal seams and full-penetration welds at every transverse joint. Hydrogen sulphide concentrations in the drum headspace routinely exceed 200 ppm. The extract is normally routed to a wet caustic scrubber before atmospheric discharge to comply with AS 3580 boundary monitoring and Safe Work Australia H2S workplace exposure standards.
How is boundary fence-line odour managed for tanneries in residential areas?
Every odour-bearing process stream is routed to a treatment device — wet caustic scrubber for hydrogen sulphide, biofilter for low-concentration H2S and amine, regenerative thermal oxidiser for solvent VOC, activated carbon polishing — before atmospheric release. Stack height and discharge velocity are calculated from atmospheric dispersion modelling under AS 3580 and EPA state-regulator guidance to achieve compliance at the nearest sensitive receptor under worst-case meteorology.
What SBKJ machines are appropriate for tannery ductwork fabrication?
The SBAL-V stainless auto duct line for 304L and 316L rectangular ductwork at up to 16 metres per minute on 0.5 to 1.5 mm coil up to 1,500 mm wide. The SBAL-III auto duct line for general galvanised production. The SBTF-1500C, SBTF-1602 or SBTF-2020 spiral tubeformers for round duct supply. The SBEM-1250 elbow maker, SBSF-1525 stitchwelder, SBFB-1500 hydraulic folder, SBPC1500 plasma cutter and SBLR-600 or SBLR-600A roll bender complete the production-floor configuration. All machinery is manufactured by SBKJ Group in Box Hill North, Victoria, and shipped CE-compliant under Machinery Directive 2006/42/EC.
