Investigations on interactions between sodium species and coal char by thermogravimetric analysis

Sodium species in sodium-rich coals could be enriched in char residue after devolatilization. At high temperatures, there must exist some interactions between char and sodium species. It should be noted that the interactions have significantly affected the transformation of sodium species and gasification reactivity of char. Thus, the interactions were investigated in detailed by comparing TG-DTG curves of pure sodium species, char and graphite mixing with sodium species. Meanwhile, the properties of char samples after sodium temperature-programmed treatments were characterized by SEM, XRD, N2 adsorption and CO2 chemisorption. The results indicated that the interactions between them were closely associated with the occurrence modes of sodium. In the case of the transformation of sodium species, the presence of coal char significantly inhibited NaCl release; however, for CH3COONa and Na2CO3, coal char exhibited the catalytic effect for Na2CO3 decomposition and reducibility for the following Na generation; for Na2SO4, only an intense reducibility was discovered. In the case of char gasification reactivity, sodium species, especially those oxygen-containing species, could remarkably increase char BET surface areas and amount of active sites after temperature-programmed treatment; furthermore, the increase of active sites significantly enhanced char gasification reactivity.