CFD study of pulverized coal-fired boiler evaporator and radiant superheaters at varying loads

Highlights: • Computational Fluid Dynamics capture trend of boiler heat uptake at reduced loads. • Imperative to capture flame position and radiation shielding in superheater volumes. • Requires explicit modelling of superheater elements with variable surface temperatures. • Reveals high temperature spots on the final superheater tubes at reduced loads. -- Abstract: This paper describes a CFD modelling methodology used to evaluate the thermal performance of the water wall evaporator, platen and final stage superheaters of a subcritical pulverized coal-fired boiler at full and reduced boiler loads. The heat exchanger elements are modelled as explicit walls with an effective thermal resistance boundary condition rather than fixed wall temperatures. This enables the direct radiation component to be properly accounted for together with variations in the wall temperatures. The modelling approach was applied to the boiler of a 620 MWe power plant. The results for 99%, 81% and 60% boiler loads compare well with experimental data. The proposed methodology forms the bases for a co-simulation framework which combines the CFD with a systems-level process modelling tool that can capture the internal steam maldistribution at low loads and the resultant effect on the metal temperatures.