Characteristics and mechanism of slagging in a 500 t/d MSW incinerator

Abstract

With the promotion of classified collection of municipal solid waste (MSW), the heating value of waste sent to incinerators has significantly increased, which affects slagging and ash deposition. Thoroughly studying the slag characteristics in incinerators is important for determining its formation conditions and processes. In this study, slag samples from the furnace and superheaters of a 500 t/d incinerator were comprehensively studied. The slag characteristics were measured using X-ray diffraction (XRD), X-ray fluorescence (XRF), and field-emission high-resolution scanning electron microscopy (SEM); the chemical thermodynamic equilibrium calculations were carried out using FactSage; and the melting kinetics were analysed using differential scanning calorimetry (DSC). It was found that under the high-temperature environment of the furnace, CaO and Fe2O3/MgO/Al2O3 react with SiO2 to form low-melting-point eutectic crystals, which are in a molten or semi-molten state and easily adhere to the inner wall of the furnace to form slag that is difficult to remove. CaSO4 does not melt in the furnace but moves with the flue gas and is mainly deposited on the surfaces of the third- and second-stage superheaters. Na2SO4 and K3Na(SO4)2 are in a gaseous state under high-temperature conditions in the furnace, and then transform into a liquid or solid state and condense on the surface of the superheaters. The ash melting process in the furnace can be described using zero-order kinetics. These research results provide a theoretical foundation for the detailed prediction of slagging and ash deposition in waste incinerators.