Acid cleaning operation for a natural circulation high pressure drum boiler unit of a thermal power station

Abstract

Two-stage acid cleaning (TSAC) operation has been employed and investigated to clean up undesired impurities (deposit) in boiler water wall tubes (BWWT), boiler drum, super heater, economizer, feed water lines, live steam lines, hot reheat lines, cold reheat lines, dearator, collectors, headers for a natural circulation high pressure drum boiler unit. TGME -

206-COB, Russia (158 kG_f cm^-2, capacity steam generation 670 ton h^-1, 210 MW unit) of a thermal power station in Bangladesh. The deposit and loose impurities consist of Fe₂O₃, CaO, MgO and SiO₂. On area basis the maximum quantity(98g ^-2) of deposit was measured at boiler WWTs. During c leaning operation the loose impurities were withdrawn at first by

flashing of the water. TSAC operation was carried out at two stages by re-circulation of hot 105 (±5°C) cleaning solution H₂SO₄+N₂H₄.H₂O (250±25 mg L^-1) at <i>p</i>H 2.0 (±0.5) for 24 h. The TSAC operation revealed that not less than 95% of impurities were removed . The cleaning mechanism and passivation on clean surface of tubes by circulation of 500 mg L^-1

N₂H₄ and 0.4% NH₄OH with <i>p</i>H 10.8 (±2) at 60° C were found to be satisfactory.