Effect of phosphorus on ash fusion characteristics and mineral transformation during co-combustion of sewage sludge and coal

The influence of inorganic phosphorus on ash fusion characteristics of sewage sludge and coal were investigated by ash fusion temperature (AFT) detector and X-ray fluorescence (XRF), and the transformation of containing phosphate minerals of blended ashes with different temperatures between crystal and amorphous were explored using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). For the ash sample with high contents of Al₂O₃, which has higher AFT, raising content of phosphorus significantly results in a reduced ash fusion point, in particular it is lowered by 126℃ at 0-4% P₂O₅ content. But it has little effect on ash with high alkaline content. Aluminum phosphate (AlPO₄) crystals is the major phosphor containing minerals in low temperature ashes, witch react with calcium minerals (CaSO₄) and hematite (Fe₂O₃) to form Ca₃(PO₄)₂ crystal and (Fe₂O₃)_0.252(P₂O₅)_0.748 glass phase along with increasing temperature. Meanwhile, (Fe₂O₃)_0.252(P₂O₅)_0.748 in glass phase increases with an increase in phosphorus content, which may be the primary cause of AFT decreasing.