Inhibition of K2SO4 on evaporation of KCl in combustion of herbaceous biomass

Abstract Several types of salts coexist in biomass and eutectic melting often occurs during combustion. The effect of eutectic melting on evaporation of salts is not well understood. The objective of this study is to investigate the interaction of two typical salts–potassium chloride (KCl) and potassium sulphate (K2SO4)–and the effect of eutectic melting on evaporation of KCl. Firstly, different potassium and their respective amounts in agro-stalks and their ashes were analyzed using X-ray fluorescence (XRF), X-Ray diffraction (XRD), and simultaneous thermogravimetric analyzer (STA). Then, the melting and evaporation behaviors of potassium salts were investigated using STA and evaporation rates of KCl in mixtures of KCl + K2SO4 as well as in agro-stalks ashes were calculated. Results show that KCl and K2SO4 (K3Na(SO4)2) are the main species of potassium, accountings for about 13% of agro-stalks ashes formed at low temperature. The evaporation rate of KCl is significantly inhibited by K2SO4 via decreasing vapor pressure of KCl due to eutectic melting. Its evaporation rate is approximately proportional to partial pressure of KCl in mixture of KCl + K2SO4, and the calculation using this partial pressure agrees well with experiment.