1000 MW Ultra-supercritical Unit Feed Water With Oxygen Treatment Experiment And Application Research

Developing high-parameter,large capacity unit has become an inevitable trend to improve the economic efficiency of thermal power units.In developed countries,large capacity,supercritical even ultra-supercritical thermal power units have already been widely used or are being developed because of the high energy and economic efficiency,With the rapid development of national economy,the ultra-supercritical thermal power unit has begun to be large-scale used in China.The design and manufacture of the ultra-supercritical thermal power unit is still in the initial stage in China.At present,a number of domestic 1000MW ultra-supercritical thermal power units have been put into operation or under construction.The ultra-supercritical thermal power unit with Characteristics of high efficiency,environmental friendly,energy saving will become China’s main coal-fired power units.Foreign ultra-supercritical thermal power units operating experience shows that the key to ensure the success of the ultra-supercritical thermal power unit design and operational is how to solve the two professional problems of materials and chemical.The failure of vertical water wall for the domestic 1000MW ultra-supercritical pressure boiler,it is analysised that is caused by partial overheating due to magnetic iron oxide seriously deposited and abnormal water wall flow distribution at the water wall inlet orifice plates.Fundamentally,the failure of vertical water wall is resulted from excessive corrosion products deposit at the orifice plate due to the corrosion is accelerated by boiler feed water flow(Flow Accelerated Corrosion,called FAC).The solubility of magnetic iron oxide is bigger under AVT(R))operating conditions(All-Volatile Treatment(Reduction).The minimum solubility calculated by Fe is about 5.6μg/kg within full pH range and 250 ℃ temperature.Iron content in feed water may be reduced to 2μg/kg or less when the All-Volatile Treatment(Oxidation)or AVT(O)is adopted.To slow down or inhibit the furnace feed water flow accelerated corrosion,fundamentally to reduce the deposition of corrosion products at economizer and water wall inlet throttle orifice,the iron content of the feed water must be controled under 1μg/kg or less.The feed water for ultra-supercritical boiler can be treated by Oxidizing water conditions(E.g Oxygenation treatment,Oxygenated Treatment,abbreviated OT).Taking two 1000MW units of Guodian Taizhou Power Plant as a study case,the mechanism of the frequent overheating or even failure for the vertical water wall is analyzed,The characteristics of ultra-supercritical units and the vapor quality requirements are discussed.The feed water oxygenation treatment program for 1000MW unit is formulated by analysis of oxygenated water theory,origin,development,The successfully implementation of the feed water oxygenation treatment program in domestic import-type 1000MW ultra-supercritical thermal power units inhibits accelerated water flow corrosion in water supply system and good results are achieved,such as:(1)inhibition of the feed water flow accelerated corrosion before furnace,significantly decreasing the iron content of economizer inlet feed water,avoiding by saving coal device and import flow water wall hole harden scale caused water wall tube overtemperature and even failure,due to non stop unit;(2)reducing operating costs of the generating unit startup;(3)extending the boiler chemical cleaning cycle;(4)extendeding operation cycle of condensate polishing treatment;(5)slowing down the raising rate of boiler differential pressure;(6)significantly reducing the rate of fouling,extending the life of the equipment;(7)reducing the outage corrosion;(8)reducing heat losses.The application of feed water oxygenation treatment sets an example and has a great practical significance to the prevention of vertical water wall tube screen failure caused by orifice plates fouling and ensures the safe operation of high parameter and large units.