Effects of boron compounds on decomposition of chlorides to control clinkers under solid refuse fuel combustion conditions

Abstract

The chlorides of sodium and potassium and other mineral salts are often present in solid refuse fuel (SRF) in concentrations of at least 1–2%. These salts can generate clinker during combustion and cause serious operational problems, such as blocking of the gas passage, reduction in boiler operational efficiency, and corrosion of the heat exchanger tubes in the boiler. Although many solutions have been proposed to control clinker formation in boilers, herein we investigated the effects of boron compounds (boric acid and borax) on the decomposition of the mineral salts present in SRF to control the formation of fly ash. Using a laboratory-scale reactor, isothermal reactions between the boron compounds and the chlorides were performed at 900 °C for 10 h. HCl gas was released during the decomposition reactions, indicating that a chemical reaction had occurred on the surfaces of the boron compounds. Peaks related to sodium and potassium borates were observed in X-ray diffraction patterns, suggesting that these compounds had been formed during the reactions. Scanning electron microscopy images of the reaction products showed clusters of the mineral salts on the matrix of the borax particles, indicating that changes in the morphology owing to physical adsorption had also occurred during the reactions.