Ash deposition and NO x emission behaviors of high-alkali coal under air-staged dynamic parameter conditions

The flexibility regulation processes in power plants possibly yield significant impacts on ash deposition behaviors and fuel nitrogen migration, thereby affecting boiler safety and impeding efforts to reduce nitrogen oxide emissions. However, existing studies have primarily focused on steady conditions, with limited mechanistic understanding under dynamic parameter operations. Hence, this study employs a vertical two-stage furnace experimental system to investigate the ash deposition behavior and NO x emission characteristics of high-alkali coal combustion under air-staged, dynamic parameter conditions, with particular emphasis on the previously overlooked influence mechanisms of dynamic variations in temperature and coal feeding rate. Experimental results indicate that dynamically increasing the feeding rate reduces the ash deposition propensity ( DP ), but slightly increases the nitrogen conversion rate ( X NO ). The ramp-down condition enhances calcium sulfation at normal load and also promotes Fe 2 O 3 generation at low load compared to the ramp-up condition, leading to the easier formation of adhesive ash. The variable temperature conditions show increases in both X NO and DP compared to the stable temperature condition, while the combustion efficiency significantly decreases. The combustion efficiency declines even further when the excess air ratio is further increased to 1.4. In comparison to stable conditions, the temperature ramp-down condition promotes calcium sulfation, and the temperature ramp-up condition further facilitates the generation of sodium-containing crystalline minerals, exacerbating the ash deposition issue. This research can provide instructive significance for the low-carbon development and the safe variable load operation of power plants.