Scrubbers and gas cleaning
Neutralising acid gases and harmful emissions down to the limits — before an enforcement order requires it.
Industries
From scrubber to dosing unit
Each unit has its own job: the cyclone takes out the coarse fraction, the scrubber or absorber takes up the gas, the mist eliminator stops carry-over and the dosing unit holds the pH.
Wet gas cleaning with an absorbent: removal of acid gases, ammonia, VOCs and odours. It cools the hot gas at the same time.
- Casing: PP, FRP, PVC, SS316L
- Packing: Pall Ring, Tellerette, Raschig
- An effluent treatment system is required
- In winter the loop needs heating
Column units that dissolve and then recover the target component. Sized from the process equilibrium curve; they often work in tandem with a scrubber.
- Column diameter 0.5 – 4.0 m · packing height 2 – 12 m · 2 – 20 stages
- FRP and SS316L shells
- Structured and random packing, liquid distributors
- Trays: valve or sieve type
- Need a steady flow and concentration
Dry and wet precipitators for large gas volumes at low resistance. A WESP captures aerosols and acid mist; rebuilding the fields is cheaper than replacement.
- 20,000 – 1,500,000 m³/h · up to 99.9% · 150 – 300 Pa · up to 450 °C
- Plates: carbon or stainless steel
- Wet build: FRP, lead, SS316L
- Heated insulators, 30–100 kV power sets
- The dust resistivity must be analysed
They take the coarse fraction out ahead of the scrubber — less reagent used, less packing wear and a lower load on the effluent system.
- 500 – 200,000 m³/h · 70 – 92% on >10 µm · 700 – 1,500 Pa
- Lined carbon steel, stainless steel
- Basalt lining
- Extend the packing service life
- Reduce the load on the effluent system
They catch liquid carry-over after the scrubber — otherwise droplets go up the stack and into the air. Periodic washing is needed: a blocked mist eliminator raises the ΔP of the whole line.
- Carry-over < 50 mg/m³ · 100 – 300 Pa · gas velocity 3 – 5 m/s
- Vane type, PP / FRP
- Mesh type in PP, PVDF, SS316L
- Cyclonic stages
- Need periodic washing
Reagent dosing and control: without a stable pH the scrubber efficiency halves. pH-based control saves reagent.
- NaOH, Ca(OH)₂, lime milk · accuracy ±2% · pH, ORP and flow monitoring · PLC with data logging
- Diaphragm metering pumps
- PE / PP tanks with agitation
- pH meters and controllers, PP / PVDF piping
- Lime milk needs protection against scaling
Adsorption stage for odours, VOCs and selected gas contaminants after sorbent-capacity verification.
Corrosion-resistant materials
- PP — the standard for acidic media
- FRP (glass-reinforced plastic) — large vessels
- PVC — moderately aggressive solutions
- SS316L — high temperatures and chlorides
- Packing: Pall Ring, Tellerette, Raschig
- Nozzles: PP, PVDF, ceramic
- Mist eliminator: vane or mesh type
- Piping PP, PVDF; tanks PE / PP
Key figures of a scrubber solution
| Parameter | Value |
|---|---|
| Efficiency | up to 99.5% |
| Substances removed | SO₂, HCl, HF, NH₃, VOCs, odours |
| Gas flow | 1,000 – 300,000 m³/h |
| Gas temperature | up to 200 °C |
| Irrigation rate | 2 – 8 l per m³ of gas |
| Reagents | NaOH, Ca(OH)₂, lime milk |
| Pressure drop | 800 – 2,000 Pa |
Duties suited to wet cleaning
- Acidic and alkaline gases
- Soluble pollutants
- Odours and light organic compounds
- Simultaneous cooling of hot gas
Cases that need another method
- Dry abrasive dust as the primary duty
- A site with no effluent treatment
- Sub-zero temperatures without loop heating
- Water-insoluble substances — another method is needed
Gas cleaning questions
Why is a cyclone placed before the scrubber?
The cyclone takes the coarse fraction out ahead of the scrubber: less reagent is used, packing wear drops and its service life grows, and the load on the effluent system falls. A typical arrangement for cement, lime, metallurgy and CHP fly ash.
What happens if the pH is unstable?
The scrubber efficiency halves. pH-based control saves reagent; monitoring covers pH, ORP and flow, with a PLC and data logging in control. Lime milk needs protection against scaling.
Does a scrubber work in winter?
Yes, but the loop needs heating. Without heating, wet cleaning does not fit sub-zero temperatures. The site must also have an effluent treatment system.
Why is a mist eliminator needed?
It catches liquid carry-over after the scrubber — otherwise droplets go up the stack and into the air. Carry-over after the stage is below 50 mg/m³. Periodic washing is needed: a blocked mist eliminator raises the ΔP of the whole line.
When is an electrostatic precipitator chosen instead of a scrubber?
For large gas volumes (20,000 – 1,500,000 m³/h) with a low allowable pressure drop (150 – 300 Pa), at temperatures up to 450 °C. A wet precipitator (WESP) captures aerosols and acid mist. Dust resistivity is analysed before selection; on an existing precipitator, rebuilding the fields is cheaper than replacement.
How does an absorber differ from a scrubber?
Absorbers and strippers are column units that dissolve and then recover the target component. They are sized from the process equilibrium curve, need a steady flow and concentration, and often work in tandem with a scrubber.
The scrubber in 3D
Dry dust and measuring the result
If the primary duty is dry dust, see the dust collection solution; for continuous measurement of the cleaning result, see environmental monitoring.
3DDry dust collection and process extraction — from a single machine to a whole workshop: baghouse and cartridge filters, cyclones, electrostatic precipitators, hoppers and fans.
Open →Environmental monitoring
3DCEMS and AQMS stations, sampling, gas analysers, dust monitors and online water and effluent monitoring — with data transmission to the regulator.
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