Weakened redistribution of thermal non-uniformity in a 660 MW tangentially fired tower boiler under deep load reduction: A case study

Thermal non-uniformity near upper heating surfaces is a major operational concern for tangentially fired tower boilers under deep load reduction. This study investigates the load-dependent downstream evolution of thermal non-uniformity in a 660 MW supercritical tangentially fired tower boiler. A full-scale three-dimensional CFD model was established for loads ranging from boiler maximum continuous rating (BMCR) to 40% turbine heat acceptance (THA). Three characteristic sections, denoted as P1, P2, and P3, were selected at the main combustion-zone outlet, the region affected by separated overfire air (SOFA), and the final superheater inlet. Area-weighted tangential velocity , tangential-to-axial velocity ratio R ta , temperature non-uniformity coefficients C T , velocity non-uniformity coefficient C U , and inter-sectional thermal evolution factors G T were used to quantify tangential-transport decay and redistribution of thermal non-uniformity. The results show that load reduction progressively weakens tangential transport. decreases substantially from 19.32, 8.03, and 1.46 m/s at P1, P2, and P3 under BMCR to 8.98, 2.48, and 0.69 m/s under 40% THA. At relatively high loads, thermal non-uniformity is amplified in the SOFA region but attenuated downstream. At 40% THA, C T increases from 0.076 at P1 to 0.094 at P2 and then decreases to 0.089 at P3, with G T ,1→3 = 1.171, indicating net amplification along the upper-furnace flow path. These results suggest that deep-load operation weakens downstream thermal redistribution, allowing elevated thermal non-uniformity to persist near the final-superheater inlet.