A Study Of Steam Heating Start-up Technology For Large SC/USC Once-Through Boiler

Large energy consumption, problems in the vapor-water side andwind-fume side may occur when supercritical or ultra supercriticalonce-through boiler is started up in the conventional mode. Such ashydrodynamic instability, superheater and reheater overheating, oxide scaleissues in the vapor-water side and pulverized coal low burnout rate, SCRdenitration catalyst short service life, air preheater corrosion and fouling,electrostatic precipitator running late, FGD system corrosion and slurry bepolluted in the wind-fume side, which are related with improper startup way.The new once-through boiler steam heating start-up technology uses steaminstead of fuel to preheat boiler by heating feed water. It can make up for thedefects of conventional start-up and ignition mode. This technology greatlyreduces the boiler startup energy consumption and improve the low loadcondition stable combustion performance. It is discussed the fundamentalmechanism of the steam heating start-up technology effectively solve the seriesof problems from the essential reasons.The prevention of tube blocked and burst by oxide scales exfoliation anderosion of turbine blades by solid particles are mainly studied. It is obtainedthat the mechanism of oxide scale is mainly generated in the overheating andoxygen-rich conditions, by comparing the oxidation characteristics of T91steelin the high temperature air and steam. Taking a600MW supercritical boiler as aexample, which the temperature of platen superheater tube and steam in thetube is600℃and100℃, respectively. And simplified model of tube heattransfer was established. Then using analytical solution and numerical solutionto calculate the tube temperature trend and the transient temperaturedistribution. It turned out that the tube temperature dropped quickly, the drop ofthe temperature is more than the critical oxide exfoliating temperature drop,and a large amount of oxide scales exfoliated. Using fluid dynamics theoryanalysis the mechanism of exfoliated oxide scales blocked the bottom of Uarrangement tube and resulted the tube burst. Through steam flow around oxidescales as a model to analysis the movement mechanism of oxide scales carriedby steam. Established physical and mathematical mode of solid particlesmovement in the governing stage nozzle, calculated steam and solid particles motion in four typical operation conditions, then compared and analyzed theblade erosion rate in different conditions. Steam heating start-up technologyeliminates the generation and exfoliation of the oxide scales, and throughShanghai Waigaoqiao NO.3Power Plant successfully solved the oxide scalesissues, which verified the correctness of the study.At last, based on the comprehensive effects analysis of steam heatingstart-up technology, it is obtained that this technology can significantly improvethe boiler startup security, economy and environmental performance. This studyhas certain theoretical and reference value on the application to other units.