Field study on the corrosion and ash deposition of low-temperature heating surface in a large-scale coal-fired power plant

- Corrosion and ash deposition of low-temperature heating surface before the precipitator.
- Three materials were tested under different tube wall temperatures in real flue gas.
- Mechanisms of dewpoint corrosion and viscous deposition were discussed.
- Coupling model of acid condensation and fly ash behaviors was proposed.
- Effects of sulphuric acid, hydrochloric acid and fluoric acid were all investigated.

The corrosion and ash deposition of low-temperature heating surface were investigated in a 660 MW coal-fired power plant. The temperature-controlled test probes constructed of three materials were tested under different wall temperatures (90 °C, 80 °C, 70 °C, 60 °C, 50 °C and 40 °C). The metal specimens and deposit samples were analyzed by X-ray fluorescence, X-ray diffraction and scanning electron microscope with energy dispersive spectroscopy. The results revealed that when the wall temperature fell to 70 °C, viscous deposits began to form on the probes due to the condensation of sulphuric acid, hydrochloric acid and hydrofluoric acid. Meanwhile, the sulphuric acid condensate and hydrochloric acid condensate stimulated the corrosion of the metal surface. The corrosion and deposits increased with the decrease of the wall temperature. The corrosion resistances of the three tested materials were 316 L > ND > 20#. The corrosion mechanism and ash deposition mechanism of low-temperature heating surface were discussed. The coupling model of acid condensation and fly ash behaviors was proposed, and the main factors affecting the corrosion and ash deposition were summarized. Suggestions were made to alleviate the corrosion and fouling of waste heat recovery devices in coal-fired power plants.