The coupling characteristics between ash deposit and dew point corrosion of deep-cooling flue gas on ND steel and 316 L stainless steel(control) was investigated in a 65 t·h-1 circulating fluidized bed biofuel boiler. The ash deposit and corrosion layer were studied by X-ray fluorescence spectroscopy(XRF)

X-ray diffraction(XRD)

scanning electron microscope(SEM) and energy dispersive spectrometer(EDS). Results indicated that the deposits on tube surface could be classified as layers of corrosion

coupling and ash deposit(NH4Cl、SiO2 and(NH4)2SO4). The coupling layer contained ash deposit and metal corrosion by-product

which was prone to spall off because of strong adhesion to the ash deposit layer. The corrosion layer

mainly composed of metal compounds of chlorides and oxides

reduced dramatically in thickness with the decrease of inlet water temperature. The degree of corrosion of ND steel increased sharply when wall temperature was below water dew point of flue gas. ND steel showed corrosion resistance inferior to 316 L stainless steel at experimental conditions.