Fouling Intensity of Three Indian Coals

Abstract

Ash particles can arrive at heat-transfer surfaces either in solid (solidified) state or in molten state, depending on the factors such as location inside the boiler, temperature, and residence time. In this study, arrival of ash particles in solid state, which can occur in the convective section of the boiler, was considered. Apart from the inertial force that drives particles \>10 µm to the surface, the low-melting inorganic alkali vapors play a vital role in deposit formation by promoting sticking. Chemical equilibrium calculations were performed to calculate the equilibrium composition of flue gas, as well as the amount of condensable inorganic alkali vapors at any particular temperature. Condensed alkali liquids act as \glue in holding together impacting fly ash particles. Eutectic formation between alkali salts was considered to accurately predict the condensation onset temperature. Using the glue volume fraction obtained as a function of temperature, we adopted a self-regulated deposit growth model to predict deposit growth rate. The uniqueness of the model is that it simultaneously incorporates sticking and particle-particle erosion, where both are dependent on available liquid fraction, to predict fouling intensity. The deposit growth rate of three Indian coals was simulated and compared with coal having lower ash content.