Method and apparatus for purifying exhaust gas

A method for purifying exhaust gas comprising the steps of: 1. Sulfur dioxide is removed from the exhaust gas in a first washing stage (c) by means of ammonia or ammonium compounds deposited part, 2. The exhaust gas is then transferred to a second washing stage (d), 3. The in the first washing stage (c) is not deposited sulfur dioxide is oxidized by the oxidizing agent added in the second washing stage (d) to sulfuric acid and separated the from the first washing stage (c) ammonia released (simultaneously with the formed sulfuric acid in the second washing stage d ) is deposited, wherein the oxidation in the second washing stage (d) is carried out by addition of hydrogen peroxide and characterized in that in the first washing stage (c) a variable desired pH-value of between 4 to 6 is adjusted by controlled addition of ammonia and the pH setpoint (d) which is connected via a cascade control based on the pH of the second washing stage in the range of 1 to 5, is set.