Wet Scrubbers

A wet scrubber is industrial air pollution control equipment that removes particulate, soluble gases, or both from an exhaust stream by contacting the gas with a scrubbing liquid (usually water with reagent dosing). The three primary types — venturi, packed bed, and spray tower — each use a different contact mechanism. Venturi shatters the liquid into fine droplets to impact mist, condensable fume and coarser particulate by inertial impaction. Packed bed creates wetted surface area for mass-transfer absorption of soluble gases. Spray tower atomises liquid into the gas for lower-efficiency, lower-cost duty.

A venturi scrubber captures condensable fume, mist and coarser particulate by inertial impaction at high gas velocity through an accelerating throat (1.5 to 10 kPa pressure drop typical). A packed bed scrubber absorbs water-soluble gases by mass transfer at low gas velocity through plastic or ceramic packing (0.5 to 2 kPa pressure drop). Venturi handles sticky, condensable and hot abrasive duties that would foul a filter. Packed bed handles soluble gases like HCl, SO₂, and NH₃. They are often paired in series for combined particulate-plus-gas duty.

HCl, HF, SO₂, ammonia (NH₃), amines, hydrogen sulphide (H₂S), mercaptans, chlorine (Cl₂), hydrogen cyanide (HCN), mercury vapour (with sulphur-impregnated carbon polishing downstream), VOCs after carbon adsorption, sulphur compounds, condensable fume and oily aerosol, and hot abrasive metallurgical dust. NO_x requires oxidising chemistry (NaOCl), not just caustic.

Venturi: 1.5 to 10 kPa across the throat, tunable with variable-throat designs. Packed bed: 0.5 to 2 kPa across the bed plus a small allowance for the mist eliminator. Spray tower: 0.2 to 1 kPa. Pressure drop drives fan power and operating cost.

Removal efficiency depends on technology and duty. Venturi captures condensable fume, mist and coarser particulate well by inertial impaction — sub-µm dry-dust capture is generally lower and is usually handled by Wet ESP polishing downstream rather than by the venturi alone. Packed bed: 95 to 99.9% on soluble gases like HCl, SO₂, NH₃. Spray tower: 70 to 90% on absorbable species. Wet ESP polishing achieves outlet PM under 10 mg/Nm³. Process guarantees are written against measured inlet conditions, not catalogue numbers.

Sizing is project-specific and driven by gas flow rate, gas chemistry, temperature, target outlet emission limit and material constraints. We run ChemCAD process simulation and in-house design tools against your measured inlet conditions to size the throat, packing depth, recirculation rate and material spec. Our delivered envelope ranges from sub-metre pilot units to 3 m+ diameter production scrubbers.

The shell material is matched to the gas chemistry, not chosen from catalogue. 3Cr12 for hot abrasive metallurgical duty. 304 or 316 stainless for general SS service. Duplex 2205 or 2507 for chloride-bearing acid and demanding-alloy duty. FRP for cold acid, HCl, HF, and mixed halides. CPVC or PP for chlor-alkali. Hastelloy C-276 for severe acid and mixed-halide environments. Refractory-lined steel for high-temperature duty.

Baghouses filter dry particulate through fabric media — best for dry dust where the gas is below the bag temperature limit. Wet scrubbers absorb soluble gases or capture condensable and sticky particulate in a liquid stream. Choose baghouse for dry-only duty. Choose wet scrubber for gas chemistry or sticky particulate. They are often paired: a baghouse on the bulk particulate followed by a packed-bed scrubber on the acid-gas tail.

Depends on scope. Design phase 6 to 12 weeks. Fabrication 8 to 16 weeks. Installation 2 to 6 weeks. Large turnkey wet scrubber packages run 9 to 18 months from enquiry to commissioning.

Gas composition (concentrations of acid gases, particulate, volatiles), mass or volume flow rate, gas temperature and pressure, target outlet emission limit, available utilities (compressed air, electrical, water, dosing chemicals), site footprint and access restrictions, and regulatory or licence drivers. The more specific the inlet conditions, the tighter the outlet guarantee.

Yes, most duties require reagent dosing. Caustic (NaOH) for acid gases like HCl and SO₂. Sulphuric acid (H₂SO₄) for ammonia absorption. Hypochlorite (NaOCl) for NO_x oxidation or chlorine duty. Hydrogen peroxide or other oxidants for specific reductive duties. Dosing is automated with pH, ORP and conductivity control loops.

Fan power (a function of pressure drop times gas flow), pump power for recirculation, reagent cost, and water plus blowdown cost. Venturi scrubbers have the highest fan power due to high pressure drop; packed bed is typically the lowest of the three.

Venturi yes — that is actually its specialty. Oily fume from fibreglass production, pyrolysis tars, condensable styrene aerosol, plasticiser vapours. Packed bed no — the packing fouls if loaded with sticky particulate. The canonical configuration for sticky sub-µm duty is venturi pre-conditioning followed by Wet ESP polishing.

Blowdown from the recirculation loop contains absorbed contaminants. Typical disposal paths: pH neutralisation, settling and discharge to sewer under trade-waste licence; evaporation to dry cake; or reuse back into process as a closed loop. Treatment design depends on the duty and the disposal pathway at site.

AS/NZS 5131 (structural steelwork), AS/NZS 1554.6 (welding of stainless), ASME Section IX (welding procedure and welder qualification), AS 1210 (pressure vessels where duty applies), NFPA 68/69 (combustible-dust explosion protection), ISO 9001/14001/45001-aligned QHSE. Region-specific licence drivers — NSW EPA, EU IED, US EPA NESHAP — addressed project-by-project.