What Are Venturi Scrubbers?
A venturi scrubber is an industrial air pollution control device that uses a high-velocity gas stream and a scrubbing liquid, usually water, to capture fine dust, fumes and sub-micron particulate from process or flue gas. As the contaminated gas is forced through a narrowed “throat” section, it accelerates sharply and mixes intensely with liquid droplets, so particulate becomes entrained in the liquid and can be separated from the cleaned gas.
Venturi scrubbers are among the most effective wet scrubbing technologies for very fine particulate, capable of capturing particles down to around 0.2 microns — far smaller than many dry filtration methods can reliably handle.
How Do Venturi Scrubbers Work?
The defining feature of a venturi scrubber is its shape: a section of ductwork that narrows to a constriction (the “throat”) before widening out again — the same principle as a venturi tube used to measure flow.
1. Gas enters and scrubbing liquid is introduced. Contaminated gas enters the top of the venturi, where recirculated scrubbing liquid is sprayed into the gas stream.
2. The gas accelerates through the throat. As the duct narrows, the gas speeds up dramatically, creating intense turbulence and eddies within the throat.
3. Particulate is captured by the liquid. This turbulent mixing shatters the liquid into fine droplets and forces particulate in the gas to collide and combine with them — a process called inertial impaction.
4. Gas and liquid are separated. As the gas slows and expands beyond the throat, the now-heavier droplets recombine and pass into a cyclone separator, where they’re spun out and drained to a sump tank for recirculation. A final mist elimination stage removes any remaining fine droplets before the cleaned gas is discharged.
The pressure drop across the throat is the key design parameter: the smaller the target particle size, the higher the pressure drop needed to capture it.
Fixed-Throat vs. Variable-Throat Venturi Scrubbers
Venturi scrubbers are typically supplied in one of two configurations:
– Fixed-throat venturis have no moving parts in the throat, making them simple to operate and maintain. Because the throat size doesn’t change, pressure drop — and therefore removal efficiency — varies with gas flow rate.
– Variable-throat venturis use adjustable blades in the throat that open or close to maintain a constant pressure drop as gas flow varies, keeping removal efficiency high and consistent regardless of flow. The adjustment mechanism sits outside the gas path for reliability, and can be automated or manually set depending on the application.
What Do Venturi Scrubbers Remove?
Venturi scrubbers are primarily used for particulate control, effective against:
– Fine and sub-micron dust — down to around 0.2 microns
– Fumes and mists from combustion or chemical processes
– Both mechanically generated (coarser) and chemically generated (finer) particulate, typically in the 0.5–10 micron range
Venturis are used for soluble acid/alkaline contaminant scrubbing and are around 50-80% efficient. Where a gas stream contains both particulate and soluble contaminants — such as HCl, Cl₂, HF or NH₃ – a venturi scrubber is typically paired with a downstream absorption stage, such as a packed tower or tray tower, to remove the gas-phase pollutants.
Where Are Venturi Scrubbers Used?
Venturi scrubbers are widely used wherever hot flue gas or process vents carry fine particulate, including:
– Flue gas cleaning — removing particulate from combustion and incineration processes, often integrated with a quench stage to cool hot gas before the throat
– Chemical and process industries — capturing fine, chemically generated particulate from reactors and process vents
– Metals and materials processing — controlling fume and dust from thermal processes
– General industrial gas cleaning — as the particulate-removal stage within a larger, multi-technology air pollution control system
They are especially valuable when hot gas needs to be quenched and cleaned in a single, compact vessel — ERG can integrate a quench section directly above the venturi throat for this purpose.
Venturi Scrubbers vs. Other Air Pollution Control Technologies
– Packed towers, v-tex and tray towers are used for absorbing soluble gases rather than capturing fine particulate —two technologies are often combined, with a venturi scrubber handling particulate upstream and a packed tower handling gas absorption downstream.
– Chemical scrubbers neutralise acid or basic gases through a chemical reaction; a venturi scrubber’s job is almost entirely physical particulate capture, though some particulate can carry chemically reactive components.
– Carbon filters target VOCs and odour molecules rather than particulate, and would typically sit further downstream in a treatment train, after any particulate has already been removed.
Benefits and Limitations
Benefits:
– Captures very fine particulate, down to around 0.2 microns, that many dry technologies can’t reliably handle
– Simple, robust design with no moving parts in fixed-throat configurations
– Can be integrated with a quench stage for hot flue gas in a single vessel
– Variable-throat designs maintain consistent efficiency even with fluctuating gas flow
Limitations:
– Higher removal efficiency requires higher pressure drop, increasing fan power and running costs
– Doesn’t remove soluble gas-phase contaminants on its own — usually needs a downstream absorption stage for those
– Produces a liquid effluent (often a slurry) that needs settling, dewatering or disposal
– Variable-throat designs add mechanical complexity versus a fixed-throat unit
Frequently Asked Questions
What are venturi scrubbers used for?
Venturi scrubbers are used to remove fine dust, fumes and sub-micron particulate from industrial flue gas and process vents by accelerating the gas through a narrow throat and capturing particulate in liquid droplets.
How small a particle can a venturi scrubber capture?
A well-designed venturi scrubber can capture particulate down to around 0.2 microns, making it the most effective wet scrubbing technologies for very fine dust and fume.
What’s the difference between a fixed-throat and variable-throat venturi scrubber?
A fixed-throat venturi has no moving parts, so removal efficiency varies with gas flow rate. A variable-throat venturi uses adjustable blades to maintain a constant pressure drop, keeping removal efficiency consistently high even as flow varies.
Do venturi scrubbers remove gases as well as dust?
Not on their own — venturi scrubbers are primarily a particulate control technology. Where soluble acid or alkaline gases are also present, a venturi scrubber is usually paired with a downstream packed tower, tray tower or chemical scrubber to remove them.
Explore ERG’s Venturi Scrubber Technology
ERG designs and manufactures venturi scrubbers — as stand-alone particulate control units or integrated with quench and downstream absorption stages — for flue gas, process vent and industrial gas cleaning applications.
– See ERG’s full technical venturi scrubber range: Venturi Scrubbers – See how venturi scrubbers pair with soluble gas absorption: Packed Towers and Tray Towers
– Explore chemical abatement systems where particulate and gas removal are combined: Chemical – Read the companion guide on chemical (gas-phase) scrubbing: Chemical Scrubbers Guide
Talk to our team about a venturi scrubber solution for your site’s particulate emissions.
