Gas scrubbers: operation & legislation
A scrubber is a purification system for harmful gases. Products such as hydrochloric acid (HCl), acetic acid and ammonia (NH3) fume strongly at ambient temperature and are harmful to humans and the environment. A scrubber neutralises these vapours after they come out of the tank vent.
When do I need a scrubber?
- The harmful effect of the medium on humans or the environment determines whether a scrubber is needed or not.
- The volatility (vapour pressure) of the medium at the conditions used (temperature, humidity, etc.) is also a determining factor. The use of a scrubber is required by law (5.17.4.1.9 VLAREM II) at a vapour pressure from 13.3 kPa and at a temperature from 35°C. Products with a high vapour pressure evaporate faster and therefore require a scrubber.
- The relative density at 20°C of the saturated vapour or air mixture is a third important factor. If the density is between 0.9 and 1.1, the vapours can easily mix (dissolve) with air and a scrubber is recommended.
Operation of gas scrubbers
The technique of gas scrubbing can be applied for many emissions (gaseous). The scrubber brings a gas stream into intensive contact with a certain substance: water, activated carbon, bases, biofilters ... Consequently, this substance can absorb certain components (vapours) from the gas. However, depending on its flow rate, the substance becomes saturated, requiring replacement or regeneration.
Gas scrubbing is also called absorption and is thus basically the transition of components from the gas phase to the liquid phase.
There are different types of gas scrubbers. When choosing the right scrubber, you need to consider a number of crucial factors so that the air can be completely cleared of harmful vapours. On the basis of an in-depth analysis, we install the most suitable gas scrubbing system for you. a passive scrubber, an active scrubber (with circulation) or a filter.
Passive scrubber
A passive scrubber can be used under certain conditions at low tank flow rates for e.g. hydrochloric acid (HCL) or acetic acid.
The passive scrubber consists of a tank usually filled with water. Chemically laden air is passed through the water to neutralise the air. The neutral air then leaves the scrubber through the connection in the roof.
A major advantage of a passive scrubber is its simplicity: only on a regular basis, the liquid needs to be changed. So no pump or control is needed. The liquid can freeze, but you can easily avoid this by discharging it in winter, insulation and tracing or adding glycol to the water.
The contaminated water has to be processed by a wastewater treatment plant or can be used in a particular process. Water consumption depends mainly on the solubility of the medium to be washed, the odour threshold and the flow rates to be processed.
Active scrubber
Active gas excel especially at higher flow rates or very strong-smelling products such as ammonia 24%. Active scrubbers can handle any substance (HCl, acetic acid, NH3, HNO3, HF or SO2). Ditto for the cleaning fluid, from water to bases and acids.
In an active scrubber, air enters the column at the bottom, while nozzles atomise cleaning fluid at the top. Air and liquid flow against each other, washing the dirty air. The supply of water for the cleaning fluid occurs at two 2 levels: approximately in the middle of the scrubber and quasi at the top. Atomising the cleaning fluid is done on top of the gasket in each case.
Active scrubbers also remain fully atmospheric, with less risk of overpressure due to frozen liquid. The liquids go through water treatment after the process or are still used in another process. The consumption of water and cleaning product is higher than for a passive scrubber, though.
Active scrubber with circulation
the active scrubber with circulation works just like our standard active scrubber. The big difference is that the rinse water is reused for a certain time. The scrubber therefore includes a circulation pump, pH measurement, etc.
This type requires a thorough study of your situation.
Vapour filter
As a simple alternative, a filter is sufficient for smaller tanks. We place the filters on the vents of the tanks.
Our filters are a plastic or stainless steel housing filled with binders such as calcium hydrate or activated carbon that neutralise harmful vapours. Here, there are also options for air drying or sterilisation.
Gas scrubber(s) needed in your business?
Get more information or request a no-obligation quotation.
Tips & regulations
Heb ik een gaswasser nodig?
De noodzaak tot een gaswasser hangt af van de productvluchtigheid, de omgevingstemperatuur, de luchtvochtigheid ... Maar ook de dampspanning speelt een rol: hoe hoger de spanning, hoe sneller het product verdampt. Om de lucht 100% te zuiveren houdt het wasserontwerp rekening met allerlei factoren:
- Zit de wasser op de tankontluchting? Dan voorzie je best een onder- of overdrukbeveiliging op de tank.
- Een dampspanning van 13,3 kPA bij 35 °C? Dan is een gaswasser verplicht, zie ook 5.17.4.1.9 in Vlarem II.
- Tot slot is er de relatieve dichtheid van het verzadigd damp- of luchtmengsel bij 20 °C. Ligt ze tussen 0,9 en 1,1? Dan mengen de dampen zich makkelijk met lucht, ze lossen dus op.