Slagging characteristics caused by alkali and alkaline earth metals during municipal solid waste and sewage sludge co-incineration

Municipal solid waste (MSW) and sewage sludge co-incineration is developing into a new method for sludge treatment. However, waste and sludge containing high levels of alkali and alkaline earth metals (AAEMs) will likely cause slagging, corrosion and deterioration of materials during incineration. The occurrence of AAEMs is studied through extraction experiments. Additionally, the surface microstructure and composition of samples are analyzed by SEM-EDS. XRF and XRD are used to analyze the content and crystalline phases of AAEMs. The experimental results indicate that slagging samples are characterized by high amounts of Ca, Na, K, Cl, and S elements. The samples contain numerous irregular particles due to the condensation and nucleation of AAEMs. The extraction experiments and XRD analyses indicate that the insoluble AAEMs are primarily Ca-diopside and gehlenite and Na and K-aluminosilicates in the furnace. The ammonium acetate-soluble Ca consists mainly of sulfates, and the water-soluble Na and K consist of alkali chlorides in the superheaters. In the reaction tower, AAEMs mainly exist as carbonates and the slagging mechanisms are caused by soda manufacture process. The transformation and deposition of AAEMs enhance the slagging and reduce the heat transfer efficiency. The release of AAEMs can be effectively decreased through using sludge granulation technology during MSW and sludge co-incineration, and the furnace running time is extended. (C) 2020 Elsevier Ltd. All rights reserved.