Experimental study of high-temperature chlorine-induced corrosion in dependence of gas velocity

High-temperature chlorine-induced corrosion is mainly responsible for the limitation of plant availabilities and electrical efficiencies of waste- and biomass-fired boilers. According to the current state of research, it is controversial if the flue gas velocity influences the corrosion on heat-transfer surfaces. References regarding the behavior of corrosion at different gas velocities are scarcely available, and the complexity in chemistry as well as the varying combustion conditions in conventional plants complicates the interpretation of observations. On the basis of this background, this paper aims to discuss the theoretical background of velocity-dependent corrosion and also investigates the influence of gas velocity on corrosion under ideal laboratory conditions. The work includes both experimental and numerical simulations to study the deposition and corrosion behavior at velocities of 0.6, 1.7, 2.8, and 3.9 m/s. The experimental corrosion tests were carried out in an electrically heated laboratory test rig, where a defined mass of KCl was vaporized and transported by different air flows. An air-cooled corrosion probe was inserted into the reaction tube, and after a set exposure time, the oxide layer thicknesses of the corrosion rings were analyzed metallographically. Accompanied by ANSYS simulations, the condensing rates of KCl on the probe surface were calculated for the different velocity cases. The experiments show tendencies that the mean corrosion rates rise with increasing flue gas velocities. From the experiments and simulations, it can be concluded that the gas velocity influences the condensation and deposition mechanisms, which also directly affects corrosion.