A Detailed Modelling of Deposition on Superheater Tubes to Enhance Boiler Flexibility

Biomass cofiring in coal-fired power plants is a promising way to reduce CO2 emissions from existing coal plants. However, the changes in the fuel composition influence the ash deposition mechanisms on superheater tubes, therefore negatively impacting the boiler efficiency, as well as promoting corrosion which compromises the life of the boiler tubes. The continuous fluid flow combined with the ash particle trajectories has been simulated using a Eulerian-Lagrangian model. A novel alkali vapour condensation model has been added to the previous in-house powdery dry deposition model. This paper describes the modelling methodology applied and the in-house user-defined functions. This work analyses the deposition flux, and deposit profiles around the superheater tubes for the changes in four different boundary conditions namely 1) flue gas temperature, 2) tube metal surface temperature, 3) flue gas inlet velocity, and 4) alkali vapour concentration from the flue gas by performing a series of sensitivity studies., revealing that flue gas temperature variation primarily influences the mean ash deposition flux. The tube-tube interactions were analysed in detail by simulating three rows of tube banks containing a total of six tubes arranged in a staggered manner, and results show that row 2 encounters the highest ash deposition flux.