• • Single-pipe 45° oblique purging achieves 57.6% effective clearing area, a 35.7% improvement over conventional horizontal purging, directly reducing the risk of ammonium salt deposition in stagnation zones.
• • Increasing pipe diameter from 200 mm to 280 mm yields ~40% improvement in flow uniformity, which is more effective than raising gas velocity alone, indicating that geometric optimization should precede operational adjustments.
• • The optimal configuration (single-pipe 45°, 280 mm diameter, 14 m·s−1) attains 88.2% purging efficiency without additional fan power, a 45.6% increase over the baseline, offering a cost-neutral solution to mitigate NH4Cl fouling.
• • Low-velocity zones (below minimum fluidization velocity) are identified as the primary cause of acidic combustion product residue and subsequent ammonium salt blockage, validating the need for active flow organization rather than passive countermeasures.