In China

there is no case that the SCR system was transformed during operating uninterruptedly in the period of grid operation for ultra supercritical units. In this paper

a 1 000 MW ultra-supercritical tower type boiler was taken as the research object. Considering the layout characteristics of the economizer of the tower type boiler and utilizing the favorable conditions of the high and low pressure series bypass system with large capacity

a combined scheme of economizer water bypass and hot water recirculation was proposed

which meets the requirements of ultra-low emission of NOx in the full load section. Furthermore

the control strategy of the scheme under three typical conditions of deep peak shaving

unit start-up and sliding parameter shutdown was proposed

which provides a reference for the design transformation and control optimization of full-load denitrification of the same type units.