Scrubber Tanks: Design, Types & Applications for Industrial Gas Cleaning

Emissions from the vessel enter the air scrubber tank, where they are sprayed with a special chemical solution. In the packed column, a thin liquid film forms to maximize contact with the gas. Pollutants are physically/chemically absorbed, followed by demister capture of entrained droplets. The contaminated water is pumped back into the system for reuse.

Let us list the main design components of the unit:

• Vessel — the main vessel where gas–liquid contact takes place. It is manufactured from steel, fiberglass (FRP), or chemically resistant plastics such as PVC / PP. The column may be vertical or horizontal.
• Inlet nozzle through which the contaminated flow enters the scrubber. It is often designed to reduce flow velocity and ensure uniform distribution.
• Irrigation (spray) system, consisting of nozzles and distribution piping.
• Packing (for packed-type units) — the contact zone is filled with Raschig rings, Intalox saddles, etc. These are used to increase the interfacial contact area between phases.
• Mist eliminator removes liquid droplets from the cleaned air. It may be mesh-type or vane-type.
• Slurry (sump) collector, usually located at the bottom of the unit. It serves to collect contaminated liquid and solution. The scrubber water tank collects sediments from gas cleaning and enables liquid regeneration for reuse.
• Circulation pump transfers liquid from the collector to the spray nozzles. It is selected based on flow rate, pressure, and chemical resistance.
• Gas outlet — conveys the cleaned flow to the atmosphere or to a stack.
• Instrumentation and control devices — pH sensors, level, pressure and flow transmitters, and sight glasses.
• Manholes and service elements — flanges, support structures, and anticorrosion coatings.

Scrubber tank design is a complex and highly critical stage in the production of a system. It should be carried out by an experienced engineer who, based on practical experience, can perform the correct calculations. We will discuss some of the main design parameters.

The size of the scrubber water tank is determined by operational and hydraulic requirements. The volume must ensure continuous circulation and minimize frequent replacement of the solution. The recirculation sump is usually calculated as at least 1.5 times the hourly flow to allow for sediment retention and accumulation of solid particles.

Universal solution scrubber tank – most commonly used for acidic/alkaline gases; removes contaminants using a liquid.
Venturi unit – high mass transfer coefficient, high flow speed; suitable for solid dust emissions.
Bubbling or foam system – also used for removing solids from the stream.
Packed bed tower – capable of handling large air volumes.
Dry/semi-dry unit — uses solid reagents when water use is undesirable.

At this design stage, air flow velocity is determined for optimal phase contact, vessel cross-sectional area is calculated, and chamber height is set based on required phase contact time and efficiency.

The choice of working liquid can be water, alkali, or acid, depending on the type of gas contamination.
The liquid flow rate is determined based on mass transfer and the required purification efficiency.
Parameters related to solution distribution are also calculated, including nozzles, packing, and sprayers.

The type of packing also depends on several factors. The packing layer is typically 10–16 feet high for acidic vapors, depending on the mass transfer efficiency.
The air velocity through the packing should not be too high, so as not to dislodge the liquid.

Comparison of Packing Types

A scrubber creates resistance to air flow. In Venturi devices, pressure losses can be higher, but the efficiency is greater. High pressure drops require a more powerful fan to push the gas through the system. For water scrubber tanks with high gas velocities, powerful fans are usually used, and packing or nozzles are carefully selected to reduce turbulence and prevent liquid carryover.

For aggressive media, it is preferable to use corrosion-resistant materials such as stainless steel, PVC, FRP (fiberglass-reinforced plastic), or titanium lining.

Features:
The internal hydrodynamics are engineered to ensure good phase contact while maintaining minimal ΔP; otherwise, the vacuum machine loses efficiency.

Often, a vacuum scrubber tank is combined with several carbon adsorbers: the liquid first removes the bulk of contaminants, and then the carbon completes purification to nearly zero emissions, even when handling heavily contaminated vapors (oil, gasoline, sludge, etc.).

For safety when working with toxic or explosive vapors, flame arresters, water/nitrogen purge systems, temperature control in carbon filters, emergency spraying, sampling systems, and other safety measures are often installed. This is because vacuuming vessels often involves handling flammable liquids (FL), H₂S, toxic VOCs, and other hazardous substances.

Anodizing tank scrubbers are installed above anodizing vessels or connected to the exhaust ventilation of the anodizing line.
During anodizing, the following are released:

• Sulfuric acid vapors (H₂SO₄ mist)
• Acidic aerosols
• Electrolyte mist
• Occasionally, nitric acid or chromic acid vapors (depending on the process)

Without a scrubber gas tank, emissions pose a risk to personnel, lead to equipment corrosion, and fail to meet environmental regulations.

Vapor capture is achieved via exhaust hoods or covers over the anodizing vessels. Air containing acid mist is directed into the scrubber tower. The gas passes through the spraying zone, where a solution (usually water or an alkaline solution such as NaOH or Na₂CO₃) binds the acid vapors, resulting in chemical neutralization of the acids. A droplet separator retains moisture. The output is a purified air stream.

A dissolving tank scrubber is a filtration system installed on the vent/air outlet of a dissolving vessel, designed to capture characteristic emissions such as alkaline aerosols, sodium salts, product dust, and solvent vapors. It is usually engineered for a specific dissolving process, taking into account fixed temperatures, humidity, aerosol composition and particle size, and often strictly tied to emission standards for that process unit.

Key features:
- Process-specific design:
For example, a smelt dissolving tank scrubber targets fine alkaline aerosols and sodium salts, uses appropriate materials (FRP, specialized rubber, highly alkali-resistant plastics), and optimized spray modes.
- Optimized hydrodynamics and control systems:
Specific L/G ratios, multiple cleaning stages, demisters, and sometimes heat recovery from the dissolving tank vapor.
Often tightly integrated into the process flow of a pulp and paper mill or chemical plant.