Water purification by stripping

Water that has been in contact with a gas, absorbs some of what the gas contains. If oxygen is in contact with water, a little oxygen will be absorbed into the water. If the gas is a mixture of different gases, all these elements will be absorbed to some extent. Examples of where this effect is utilized in the wet gas cleaning are when the impurities in the gas are transferred to the aqueous phase to meet the air emissions requirements. By varying the properties of the water, it is possible to adjust how much of a substance that the water can receive. A common example of when absorption is used, is in the purification of NH3.  By lowering the pH in the water, NH3 reacts to become NH4+ which increases the total amount that can be washed from the gas. Another common example is that the CO2 is absorbed in the water and is transferred to carbonate. This absorption is often involuntary since it affects pH adjustments later in the process. To get rid of these compounds, a stripper is used. This means that the water is adjusted so that the substance changes to the gas phase. To speed up the process, the temperature is usually raised and a gas is added to dilute the substance for faster water cleaning. Water purification works very well this way and the pollution is easy to dispose of in several ways. One example is to return the gas to the boiler where its impact is small and often in a positive sense since the air is humidified.

Stripper characteristics:

  • Good separation ability
  • Robust equipment
  • Small “foot print”