Deposition and corrosion characteristics of liquid-solid droplets on tubular corrosion probes in desulfurized flue gas

In coal-fired boilers, low-temperature corrosion occurring in the back-end is always threatening. Particularly, the desulfurized flue gas from outlet of the flue gas desulfurization (FGD) unit is quite aggressive. The flue gas reheater placed after FGD is usually operating under a much more severe condition than the condensing heat exchangers before FGD. In this paper, field corrosion tests were conducted in a coal-fired heating plant and tubular corrosion probes made of different grades of steels were tested. The total testing period was 6 weeks. The corroded probes were then analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), and the deposition and corrosion mechanisms were studied. The droplets entrained by the flue gas resulted in deposition and corrosion on the probe, especially on the windward side. During the tests, 2507 and 2205 showed good corrosion resistance, while ND, 304L, 316L suffered considerable corrosion.