Numerical study on combustion characteristics and heat flux distributions of 660-MW ultra-supercritical double-reheat tower-type boiler

Ultra-supercritical double-reheat technology, as one of the most advanced coal-fired power generation technology, is an important direction for emission reduction and energy saving in the world. In this study, the numerical calculation was executed in a 660-MW ultra-supercritical double-reheat tower-type boiler under deep-air-staging conditions. The refined HCN oxidation model was adopted to substitute the default model implemented by the user-defined functions to calculate the NOx emission. The influences of the boiler load, over-fire air (OFA) ratio, and excess air coefficient on temperature, species, and heat flux distributions were investigated. Results show that the decrement of the boiler load from boiler maximum continuous rating to 50% turbine heat acceptance gives rise to an increase of NOx emission. The heat flux distributions along with the furnace width direction present bell shaped. When the OFA ratio rises from 17% to 43%, NOx emission descends from 357.7 to 179.3 mg m(-3) at the furnace outlet, and the heat flux distributions become more uniform along with the furnace width direction with lower peaks. Temperatures, species, and heat flux distributions are similar under the three different excess air coefficients. The NOx emission is the lowest when the excess air coefficient is 1.15. The results could provide a reference for combustion characteristics optimization and hydrodynamic calculation of ultra-supercritical double-reheat tower-type boiler.