Numerical Simulation and Experimental Investigation of Wall-Attached Air Retrofit for a 1000 MW Ultra-Supercritical Reverse Double Tangentially Fired Coal-Fired Boiler
High-temperature corrosion of water-cooled walls is recognized as one of the major factors limiting the safe and stable operation of large coal-fired boilers. To address the high-temperature corrosion caused by the reducing atmosphere in the near-wall region of a 1000 MW ultra-supercritical reverse double tangentially fired coal-fired boiler, an optimized wall-attached air strategy is proposed. Numerical simulations and industrial tests are combined to investigate the effects of different wall-attached air fractions (2%, 3%, and 4%) on the temperature field and the distributions of O2, CO, and H2S in the near-wall region of the furnace. The results show that the combustion atmosphere adjacent to the water-cooled walls is improved after wall-attached air is introduced. The O2 concentration is increased, whereas the CO and H2S concentrations are reduced. However, the improvement is found to depend strongly on the wall-attached air fraction. At a wall-attached air fraction of 3%, the near-wall regions exhibit the highest O2 concentrations and the lowest CO and H2S concentrations among the investigated cases, and the lowest near-wall gas temperature are obtained, indicating the most favorable near-wall combustion environment. When the wall-attached air fraction is further increased to 4%, the improvement becomes less pronounced because of changes in the local combustion organization. The experimental results are found to be in good agreement with the numerical predictions. Under the 3% wall-attached air condition, the O2 concentration in the high-temperature corrosion regions is increased to 2.15% - 19.90%, while the CO and H2S concentrations are maintained within 0.01% - 3.51% and 0 - 518 ppm, respectively. The results demonstrate that an appropriate wall-attached air fraction improves the near-wall oxidizing atmosphere of a reverse double tangentially fired coal-fired boiler and suppresses the formation of reducing corrosive species, thereby mitigating the tendency for high-temperature corrosion of the water-cooled walls. The present study provides theoretical support and engineering guidance for the optimization of wall-attached air systems and the mitigation of water-cooled wall high-temperature corrosion in large tangentially fired coal-fired boilers.
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