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

摘要

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, headerts for a natural circulation high pressure drum boiler power station in 206-COB, Russia (158 kG_f cm~(-2), capacity steam generatio 670 ton h~(-1), 210 MW unit) of a thermal power station in Bangladesh. The deposit and loose impurities consist of Fe_2O_3, CaO, MgO and SiO_2. On area basis the amximum quantity (98g~(-2)) of deposit was measured at boiler WWTs. During cleaning operation the loose imprities were withdrawn at first by flashing of the water. TSAC operation was carried out at two stages by re-circulation of hot 105 (+_5 deg C) cleaning solution H_2SO_4 + N_2H_4.H_2O (250 +_ 25 mg L~(-1)) at pH 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) N_2H_4 and 0.4% NH_4OH with pH 10.8 (+_2) at 60 deg C were found to be satisfactory.