The dew point corrosion characteristics of the heating surface in a 65 t/h biomass-fired circulating fluidized
bed boiler were experimentally studied. The cross-sectional morphology and composition
of the ash deposition were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD) and
X-ray fluorescence spectrum (XRF), respectively. The results showed that the test tube surface was covered
by ash deposit layer, coupling layer and corrosion layer. The ash deposit layer and the coupling layer were
prone to spall off together. The coupling layer consists of partial ash and corrosion products. The corrosion
layer was mainly composed of chlorides (FeCl3, FeCl2, and FeOCl) and oxides (FeOOH, Fe2O3). With
the increase of the tube wall temperature, the corrosion depth decreased dramatically and the dew point
corrosion was alleviated efficiently. The metal matrix simultaneously suffered from chlorine corrosion
and oxygen corrosion. As the tube wall temperature was above water dew point, the main corrosion mode
was oxygen corrosion. As the tube wall temperature was below water dew point, the main corrosion mode
was chlorine corrosion.