Fixation of Phosphorus in Ash during Cocombustion of SewageSludge and Coals: Influence of Coal and Steam

Sewage sludge (SS) incineration technology hasbecome a primary method to recover and reuse SS, and thecocombustion with coal is a more feasible process due to thelimited heating value of wet SS and the difficulty of drying SS.Being that phosphorus is a major element in SS, its migrationduring cocombustion with coal was unclear but vital. Phosphorusmigration during the cocombustion of wet SS and various coalswas investigated by drop tube furnace in this study. Morephosphorus wasfixed as apatite in ash by calcic and magnesianminerals at 1000 degrees C than at 800-900 degrees C. Calcium was taken up bysulfur in Tianchi coal (TC) and subsequently captured phosphorus ineffectively at 800 degrees C, while the competition of sulfur oncalcium was alleviated over 900 degrees C. Silicic and aluminic minerals in Xiheishan coal (XHS) exhibited a good capacity for phosphoruscapture at 800 degrees C. The outstanding calcic proportion in Xiaolongtan coal (XLT) created the highest rate of phosphorusfixation inash, and the relative enrichment (RE) of phosphorus achieved up to 93.29% at 1000 degrees C. Steam generally deteriorated phosphoruscapture at 1000 degrees C. For SS cocombustion with XHS, the effect of sulfur was alleviated by steam, and the impact of steam was mainlycaused by Ca5(PO4)3OH. For SS cocombustion with TC or XLT, 10% steam still hindered phosphorus capture, while 5% steampromoted phosphorus capture. The RE of phosphorus in ash was positively correlated with coal content and increased from 69.64%with 30% XLT to 93.29% with 70% XLT. TC and XHS hindered phosphorusfixation in ash, and their content hardly affected the REof phosphorus.

Automated summary

This study investigated the migration of phosphorus during the co-combustion of wet sewage sludge and various coals. The results showed that phosphorus was more easily fixed in ash as apatite at higher temperatures. Different coal compositions had varying abilities to capture phosphorus, and steam generally had a negative impact on phosphorus capture.