Vapours that are released during industrial processes can often be purified through gas washing or scrubbing. The technology involved is very simple: the contaminated vapour flow is passed through a purification column in the opposite direction to the washing fluid. For washing either water can be used or an aliphatic washing agent. Oil can also be used as a washing fluid. Non-polar substances such as (chlorinated) hydrocarbons dissolve much more easily as a liquid in oil than in water. Polar vapours or vapours that dissolve well in water are best washed with water from the vapour flow.
Gas washing is also known as scrubbing. The vapours are absorbed in the washing liquid. The effectiveness of scrubbing strongly depends on the nature and concentration of the vapours in combination with the type of washing agent. At a certain point the washing agent will become saturated and at that point desorption will start to take place. The washing agent therefore needs to be changed through a process of discharge and replenishment.
We sometimes deploy aliphatic scrubbers as ‘peak shaver’. This is a unit where the peaks in the vapour flow are absorbed by the scrubber and passed on to a second purification phase, for example a catalytic oxidation unit.
Also depending on the type of vapour, washing can be carried out with acidic or alkaline washing water. Or chlorine bleach lye can be added to bring about oxidation. If there is a mix of vapours, it may be useful to install multi-phase washing units.