Patent ID: 8048392

Claim:
A method for cleaning off-gas comprising the following steps: 1. sulphur dioxide is partly separated from the off-gas in a first scrubber stage (c) by means of ammonia or ammonium compounds, 2. the off-gas is then transferred into a second scrubber stage (d), 3. the sulphur dioxide not separated in the first scrubber stage (c) is oxidised to sulphuric acid by means of the addition of hydrogen peroxide into the second scrubber stage (d) and separated whereby the ammonia released from the first scrubber stage (c) is simultaneously separated with the formed sulphuric acid in the second scrubber stage (d), wherein the oxidation in the second scrubber stage (d) is carried out by way of the addition of hydrogen peroxide, wherein in the first scrubber stage (c) a variable desired pH-value is adjusted in the range between 4 to 6 by controlled addition of ammonia, and the desired pH-value is adjusted by means of a cascade control based on the pH-value in the second scrubber stage (d), which ranges from 1 to 5.