The effect of coal sulfur on the behavior of alkali metals during co-firing biomass and coal

Biomass contains high amounts of volatile alkali metals and chlorine, which can cause deposition, corrosion and agglomeration during combustion. Meanwhile coal contains a certain amount of sulfur that produces serious environmental pollution following combustion. To investigate the effects of sulfur on the migration of alkali metals during biomass and coal co-combustion, thermodynamic equilibrium calculations were applied and experiments were performed in a laboratory scale reactor combining with a scanning electron microscope (SEM), X-ray powder diffraction (XRD) and other analytical approaches. The results indicate that inorganic sulfur FeS2 addition significantly enhanced the formation of potassium sulfate when the S/K molar ratio was less than 2. Meanwhile increasing FeS2 dosage reduced the formation of KCl(g) and KOH(g) and increased the release of HCl(g). In addition potassium sulfate can react with silica and aluminum to form potassium aluminosilicates and release HCl at the S/K molar ratio above 4.

► The effects of other coal minerals can be avoided by using the sulfur additive FeS2.
► The study introduced a new potential sulfur additive FeS2 to avoid the formation of alkali chlorides.
► Thermodynamic equilibrium calculations were applied to predict the effects of sulfur on the chemical morphology and distribution of alkali metals and help in interpretation of the experimental results.