Stack Rain Removal

Some coal fired power plants experience problems with the so called “Gypsum Rain” phenomenon.

The main cause of the problem is the wet Flue Gas Desulphurisation process design, which means that the wet exhaust gas leaving the scrubber will be not reheated before entering the stack. The mist eliminator is working correctly, but the wet gas will condensate at the cold stack wall, which is behind the mist eliminator stage. So condensate droplets won’t be separated anymore and will be throw out with the gas stream and will contaminate the surroundings.

The Helix Mist Eliminator consists of a helical drainage gutter, a film trap and the drainage system. The flow is set into rotation smoothly by the helical drainage gutter, droplets are separated at the wall and drained by the Helix itself and the film trap. Droplets smaller than the 300 µm are not supposed to fall to the ground because they disappear with the waste gas plume or evaporate. Therefore the Helix Mist Eliminator can achieve the separation of large droplets bigger than 300 µm giving the benefit of a lower pressure drop.