The computational fluid dynamics (CFD) technique together with a black-box bed model are used to simulate and optimise the performance of a 25-MW industrial travelling grate fired boiler for coal combustion. A new advanced secondary/over-fire air (SOFA) system using an Ecotube technique is studied and five different air configurations are comprehensively calculated to optimise the SOFA configuration in the boiler. The results of the numerical modelling show that the Ecotube system can generate a local strong mixing zone, which produces good mixing and enhances the residence time. Results show that the Ecotube technique is quite effective in distributing the secondary/over-fire air, in improving the grate combustion and in reducing CO and NOx emissions. Complete combustion can be achieved by using the low position Ecotube air configuration, whereas NOx can be reduced by about 35% by using the upper position Ecotube air configuration in the boiler. Therefore, for grate combustion, the Ecotube system is effective and has a potential for future application in industry.