Viscose ash deposition and dewpoint corrosion in an industrial coal-fired boiler were investigated by field study of temperature-controlled mild steel 20# test probes under different wall temperatures of 90℃

80℃

70℃

60℃

50℃ and 40℃. Ash deposits and metal samples were analyzed by X-ray fluorescence (XRF)

X-ray diffraction (XRD) and scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS). The results showed that when wall temperature fell to 70℃

viscose deposits and dewpoint corrosion began to form on probes due to condensation of H2SO4 on wall surface. The deposit accumulation and corrosion depth increased with the decrease of wall temperature

when wall temperature was lower than 80℃. At wall temperature of 40℃

HCl started condesing on wall surface which further enhanced ash deposition and corrosion. The coupling mechanism of viscose ash depostion and dewpoint corrosion was discussed and it was proposed that fly ash in flue gas could absorb and react with acid condensation to reduce viscose ash deposit and corrossion. Therefore

in order to avoid or reduce deposition and corrosion

it is recommended that low-temperature heating surface in industrial coal-fired boilers should be maintained above 70℃.