Model order reduction for CAE simulation of the windbox in a 500 MW tangentially fired coal boiler

A non-intrusive reduced-order model (ROM) is developed to reproduce the steady-state three-dimensional velocity field in the windbox of a 500 MW tangentially fired coal boiler. The model is constructed using proper orthogonal decomposition (POD) of simulation results obtained under sampled operating conditions. These conditions are defined by the six key operational parameters: boiler power, coal heating value, excess air ratio, and damper angles for burner, separated over-fire air (SOFA), and under-fire air (UFA) nozzles. The POD mode coefficients are predicted using Kriging regression. The ROM demonstrates high accuracy, achieving a normalized root mean square error (NRMSE) below 1 %, and a maximum normalized error (MNE) approximately an order of magnitude higher and an R² exceeding 0.99, indicating good agreement with the full order model. A sensitivity analysis reveals that the steady-state convergence criterion has the greatest impact on accuracy, with the NRMSE reduced by up to fourfold when tightening the criterion from 10⁻⁴ to 10⁻⁶. Increasing the sample size from 100 to 150 reduces the NRMSE by 30–50 %, while increasing the POD energy level from 99 % to 99.9 % has little effect. The ROM can generate accurate 3-D velocity field in seconds, compared to 28 h per full order CFD simulation, supporting its potential as a real-time digital twin for thermal-fluid systems in complex industrial environments.