Filter and Fly Ash Washing (FLUWA Process)

The acidic filter- and fly ash leaching system (FLUWA Process) is the core of BSH technology solutions. Today over 50% of the filter ash quantities generated in Switzerland are treated with FLUWA processes. True to the motto “recycling before disposal” the FLUWA process enables recycling of the heavy metals and minimises the quantity of residue to be landfilled.

For the most ecological and economical recycling benefits the FLUWA process uses the synergies inherent in the filter ash and scrubbing water residues, which accumulate during the wet flue gas cleaning process. The acidity levels in the scrubbing water cause the heavy metals present in the filter ash to be dissolved in the acidic leaching process. At the same time the excess acidity of the scrubbing water is neutralised by the alkalinity of the filter ash. Once the heavy metals have been reduced and the acid leached, the filter ash cake can be jointly recycled with the bottom ash.


In a waste water treatment (WWT) system, the dissolved heavy metals are precipitated with lime wash as hydroxide sludge. This hydroxide sludge with its high concentration of zinc is sent as secondary feedstock to the zinc smelting industry.