[Objective]To reveal the impact mechanism of biomass co -firing on the flue gas temperature distribution along the flow path in a 660 MW W-flame boiler, and to provide a theoretical basis for optimizing the co-firing operation of large -scale W -flame boilers. 

[Method]Taking a 660 MW supercritical W -flame once-through boiler as the research object, sugarcane leaves were selected as the biomass fuel under the 100% 2 THA (Turbine Heat Acceptance) condition. A thermal calculation model was constructed based on the boiler's heating surface structure. Using an equivalent fuel processing method, five co -firing ratios (2%, 5%, 10%, 20%, and 30%) were established based on the lower heating value. The variation characteristics of the flue gas temperature at the outlet of each heat exchanger along the flow path were systematically investigated. 

[Results] The results indicate that biomass co -firing does not alter the basic rule that the flue gas temperature at the heat exchanger outlets decreases progressively along the flow direction. The heat exchangers along the flow path can be divided into three combined zones based on the temperature variation characteristics, and the trends of outlet flue gas temperatures within the same zone are highly consistent. As the co-firing ratio increases from 2% to 30%, the flue gas temperatures at the outlets of the furnace and the platen superheater decrease simultaneously, with reductions of 33 ° C and 16 ° C, respectively, while the theoretical combustion temperature drops by 142 ° C. The outlet flue gas temperatures of the final superheater and final reheater exhibit a consistent trend of "initially decreasing, then increasing, and eventual ly stabilizing," with fluctuation ranges of 6 ° C and 9 ° C, respectively. Conversely, the outlet flue gas temperatures of the low -temperature reheater, low -temperature superheater, economizer, and air preheater all consistently increase. Notably, the outlet flue gas temperature of the air preheater rises from 140 ° C to 158 ° C, marking an increase of 18 ° C. 

[Conclusion] When biomass is co-fired in a 660 MW W-flame boiler, the variation in the outlet flue gas temperature of heat exchangers within the same char acteristic zone exhibits high consistency. Co -firing has the most significant impact on the flue gas temperatures in the furnace and the upper radiant zone. The flue gas temperatures of the heat exchangers in the horizontal flue are jointly regulated by upstream temperatures and heat redistribution. Furthermore, the consistent increase in flue gas temperatures across the heat exchangers in the rear pass leads to the accumulation of flue gas sensible heat at the tail, which may reduce the thermal efficiency of the boiler.