Thermodynamic study of the behaviour of minor coal elements and their affinities to sulphur during coal combustion

zeThe behaviours of ten minor coal elements (Al, Ca, Fe, K, Mg, Mn, Na, P, Si and Ti) during coal combustion in the temperature range 400-2000 K, unde r both oxidising and reducing conditions, have been studied in detail by a thermodynamic equilibrium analysis. The partitioning of these elements is calculated both in single minor eleme nt-coal-chlorine systems and in minor elements co-existing systems. Their v aporisation tendency is found in the order: (Si, Al) < (Fe, Ti) < (Ca, Mn) < (K, Na, P, Mg). Si, Ti, Al and P are present mostly as oxides and K and N a as chlorides, whatever the combustion conditions. Al, Ca, Fe, K, Mn and N a sulphates are dominant at low temperatures under oxidising conditions, wh ereas under reducing conditions most of them are sulphides and/or chlorides . Moreover, the interactions between these elements affect their major spec iation: some species containing two elements among those studied are domina nt in the minor elements co-existing systems. The affinities of minor coal elements to sulphur have been studied versus both temperature (400 or 800 K ) and sulphur content (0.0062-6.20 wt.% in the coal), in order to find out their influence on the flue gas desulfurization. Two coal samples with diff erent ash contents were considered, and it was found that the ash compositi on affects greatly the minor elements partitioning. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.