How is a typical flue gas treatment system operated?
Passing a scrubbing system the heavy metals from the flue gas are transfered into the scrubbing water. Usually, the concentration of heavy metals in the scrubbing water exceeds the allowed discharge limit and as a consequence have to be eliminated. For the first step the acid scrubbing water is neutralised with lime [(Ca(OH)2] or caustic soda [NaOH]. During this step most of the heavy metals are precipitated as hydroxides. However, especially mercury [Hg] is only partially removed, as it forms a soluble and very stable mercury-tetrachloro-complex [(Hg(Cl4))2-] in the presence of chlorides in high concentrations. As a consequence other technologies for its removal are required. Neutralisation combined with TMT 15® is an effective process for separating mercury. Neutralisation followed by TMT 15® dosing yields a precipitate consisting of metal hydroxides and metal-TMT compounds. Most of the heavy metals are removed by the lime or caustic soda, whereas the remaining metal complexes – espe