Two kinds of essential equipment are applied to achieve energy conservation and emission reduction in coal-fired power plants, which are selective catalytic reduction (SCR) system and flue gas cooler. However, quite few studies have been published on the influence of ammonia escape caused by SCR system on flue gas cooler. In this study, the deposits are found on the surface of the flue gas cooler at the downstream of SCR system in a coal-fired power plant and verified by XRD, XRF, SEM and EDS. The reaction mechanism and growth mode of the deposition layer was analyzed. According to the results, the deposition layer consisted in a corrosion layer of steel and a crystallizing layer. The white crystal substances are mainly NH_4BF_4 and intermediates, such as NH_4F, H_3BO_3 and (NH_4)_2SiF_6. The crystallizing layer is caused by the coupling reaction of the ammonia escaped from SCR with both of fluorine element and boron element enriched in the coal, while the hydrofluoric acid in flue gas condensing on the heat transfer surface of flue gas cooler. Although the deposition layer has three millimeters thick, its cover would expand over time.
