Irreversible adsorption, or heel buildup, negatively impacts activated carbon performance and shortens its lifetime. This study elucidates the interconnections between flow rate and the oxygen impurity of desorption purge gas with heel buildup on beaded activated carbon (BAC). Nine thermal desorption scenarios were explored, varying nitrogen purge gas oxygen impurity levels (<5 ppmv, 10,000 ppmv, 210,000 ppm (21%)) and flow rates (0.1, 1, 10 SLPM or 1%, 10%, 100% of adsorption flow rate) during thermal desorption. Results reveal that increasing purge gas flow rate improves adsorption capacity recovery and mitigates adverse effects of purge gas oxygen impurity. Cumulative heel increased with higher purge gas oxygen impurity and lower flow rates. In the least effective regeneration scenario (0.1 SLPM N2, 21% O2), a 32.8wt% cumulative heel formed on BAC after five cycles, while the best-case scenario (10 SLPM N2, <5 ppmv O2) resulted in only 0.3wt%. Comparing the pore size distributions of virgin and used BAC shows that heel initially forms in narrow micropores (<8.5Å) and later engages mesopores. Thermogravimetric analysis (TGA) showed that oxygen impurity creates high boiling point and/or strongly bound heel species. TGA confirmed that higher purge gas flow rates reduce heel amounts but encourage chemisorbed heel formation in oxygen's presence. These findings can guide optimization of regeneration conditions, enhancing activated carbon's long-term performance in cyclic adsorption processes. Environmental ImplicationHeel buildup is a complex process influenced by various factors and mechanisms, yet information on how thermal regeneration parameters affect heel buildup remains limited. This study explores the simultaneous effects of thermal regeneration parameters on heel buildup and proposes increasing the purge gas flow rate to mitigate the effect of impurity in the purge gas. Such intervention reduces the energy consumption associated with purification of purge gas, extends the lifespan of the adsorbent, and decreases waste generation from spent adsorbent replacement.