The inherent structural complexity of H/J-class heavy-duty gas turbine-based novel heat recovery steam generator (HRSG) will reduce flow field uniformity upstream of the selective catalytic reduction (SCR) system. To achieve efficient denitrification under full-load operations

this study aims to optimize the flue gas flow characteristics within the HRSG under varying load conditions. Through computational fluid dynamics (CFD) modeling

this study investigates flue gas flow field characteristics in an HRSG under four load levels (100%

75%

50%

and 30% of the rated load). The research reveals the vortex generation mechanism induced by recessed structures and proposes a composite optimization strategy combining "flow straightening grid and zoned ammonia injection". The findings reveal that higher operating loads lead to enhanced vortex intensity and aggravated deterioration of flue gas flow homogeneity. At 50% load

the HRSG exhibits ±25 K localized temperature variations in heat exchange tube bundles due to high flue gas inlet temperatures and entry geometric factors. After optimization

the flow straightening grid effectively eliminated vortex

reducing the velocity coefficient of variation (CV) to 3.36%. The zoned ammonia injection strategy decreases the CV of NH3 concentration by 3.31% while reducing ammonia consumption and ammonia slip. The proposed method creates favorable conditions for denitrification reactions without structural modifications to the HRSG itself

effectively resolving the inherent conflict between load variations and flow uniformity. This approach provides theoretical foundations for next-generation HRSG design.