This can be expressed as: total chlorine/fluorine, water soluble chlorine/fluorine and water insol­uble chlorine/fluorine. Dealing with total chlorine/fluorine the sample is burned in an oxygen atmosphere transforming chlorine into chlorides and fluorine into fluorides and with the succes­sive absorption in an alkaline solution. Chlorine and fluorine in solution are determined through potentiometric titration. Soluble chlorides/fluorides are measured by extracting a portion of the sample with water and then through potentiometric titration. Insoluble chorine/fluorine is cal­culated subtracting the soluble components from the total. The eventual content of chlorine and fluorine in biomass is responsible for the emission of acid gases (HCl and HF) and also dioxins and furans.

5.1.3.4 Chemical analysis (EN 15297, 2011 andEN 15290, 2011)

Other trace elements in the fuel have to be analyzed: As, Cd, Co, Cr, Cu, Hg, Mo, Mn, Ni, Pb, Sb, Se, Sn, V Zn, Al, Si, K, Na, Ca, Mg, Fe, P and Ti, using methodologies and instrumentations adequate for the specific element. The presence of these elements in the fuel influences the choice of the conversion process to be adopted. As an example Miles et al. (1996) showed that Ca and Mg increase the melting temperature of ashes, while K and Na decrease it; Si if combined with K and Na can form low-melting silicates.

The behavior of ashes and the technical standard used for the determination of ash melting behavior will be analyzed in a specific section.