Effect of fine ash particles on formation mechanism of fouling covering heat exchangers in coal-fired power plants

Highlights: • Thermodynamic iterative calculation is proposed for acid condensation. • Impacts of fine ash radius and flue gas contents on acid condensation are studied. • XRF and SEM equipped with EDS are used to analyze the ash deposit samples. • Presence of fine ash particle is vital for fouling notably superfine ash particle. The 1-D model of thermodynamic iterative calculation is put forward for the prediction of acid condensation considering the complexity of flue gas. The radius of fine ash particles is dominant for condensation rate around fine ash particles at ADP; flue gas components for ADP, critical radius, and condensation rates, especially acid vapor content of flue gas. X-ray fluorescence (XRF) and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) are used to analyze the ash samples collected during the field experiment of a 300 MW sub-critical coal fired boiler unit, i.e. fly ash deposits (>130 °C), dry loose ash deposits (85 °C) and viscous ash deposits (65 °C). The results show that S distribution is connected with the distributions of superfine particles and fine particles, especially superfine particles, which are dissolved in viscous ash samples. According to the experimental results and acid condensation analyses, the presence of fine ash particles (d_ash d₀) is the primary factor for the acid condensation at ADP and the coupling mechanism of the sticky ash particles. In the waste heat utilization system, the on-line monitoring of the sub-micron ash particles can be added to reflect the low temperature corrosion.