Feasible Investigation On Flexible Operation Of Coal Fired Boiler

Under the current background of a large number of renewable energy access to the power grid,the peaking of the power grid faces greater challenge.As a main way of peak regulation,the flexible and environmental friendly operation of coal-fired generating units has become the focus of attention.Due to the differences of design coal,operating mode and heating surface system,different boilers need different transformation program to improve flexibility.The paper target at several aspects of the flexibility of coal-fired boilers,including how to keep enough flue gas temperature at the inlet of SCR device,adequate mass flow of water wall and steam temperature at the full load range.In order to reduce the minimum operating load of coal-fired power plant,several modification schemes are put forward including economizer bypass cycle,feedwater recirculation and flue gas recirculation.Ebsilon Professional is used to simulate the entire plant thermal system of the selected boiler 600MW subcritical,1000MW supercritical and 1000MW ultra-supercritical double reheat with simplified boiler heating surface model.Besides,the parameters of boiler flue gas temperature and boiler thermal efficiency are calculated by use of approximate thermal calculation method.The range of The promotion of boilers' flexibility are indexed by three parameters,which are the increase of SCR device inlet flue gas temperature of subcritical boiler,the drop of Benson point of critical boiler and the temperature rise of reheat steam of ultra supercritical double reheat boiler.The results show that after the implementation of the corresponding reform program of the three boilers,the flue gas temperature at the inlet of the SCR has significantly increased.The Benson point of 1000MW supercritical bolier decreased from 30%THA to 27%THA due to increased mass-flow rate of water wall at low load conditions.The steam temperature of 1000MW ultra-supercritical double reheat boiler has also been increased by flue gas recirculation,and the higher the temperature of recirculation flue gas,the more obvious effect of increasing.After transformation,the temperature of the boiler exhaust gas slightly increased and the boiler efficiency decreased slightly.