Characterization and mitigation of NOx emissions across a wide load range in supercritical 350 MW circulating fluidized bed boiler

YANG Jingchi; WANG Jing; WANG Pengcheng; WANG fei; YANG Fengling

doi:10.13226/j.issn.1006-6772.23110303

Abstract：Under the background of"dual carbon",with the continuous increase of new energy installed capacity,thermal power units are gradually transforming from primary power sources to auxiliary service power sources.Due to the intermittent nature of new energy,thermal power units need to frequently change loads to maintain grid stability in the form of deep peak shaving.In order to solve the common problem of NOx emission control under low load during deep peak shaving,this paper takes a certain supercritical 350 MW circulating fluidized bed boiler as the research object,analyzes the operating data of the boiler unit under deep peak shaving conditions,and comprehensively investigates the influence of various factors such as bed temperature,coal type characteristics,and sulfur fixing agent addition on NOx mass concentration,and explores the NOx emission characteristics and influencing mechanisms under variable load and low load conditions.Research has found that changes in bed temperature are positively correlated with load,and the oxidation of volatile nitrogen is significantly weakened when the temperature decreases,reducing the generation of NOx;but as the boiler load continues to decrease,in order to maintain the fluidized state,the excess air coefficient in the dense phase zone increases,resulting in a relatively higher NOx concentration compared to medium to high loads;when using coal with higher sulfur content simultaneously,the amount of limestone required for desulfurization in the furnace increases,and the effect of promoting NOx becomes more significant.To control ultra-low NOx emissions,zone based low nitrogen combustion technology and upper secondary air SNCR denitrification technology are used for regulation.Refine and rationalize the control of coal feeding and air distribution in low nitrogen combustion zones,and match the fuel and air quantities reasonably to achieve precise control of NOx;the secondary air SNCR retrofit technology sprays reducing agents at more suitable locations to keep the denitrification reaction within a reasonable temperature range,thereby improving denitrification efficiency.The results indicate that these two technologies can effectively control NOx emissions under low load conditions,providing a feasible technical path for thermal power generation units to maintain stable operation in the context of frequent fluctuations in new energy.This is of great significance for achieving lower emission levels and ensuring stable operation of the power grid.The study confirms that employing zoned low-NOx combustion strategies or denitrification techniques such as secondary air SNCR can effectively reduce NOx emissions during low-load operations,thereby addressing this environmental challenge in the power generation industry.