NOx reduction using advanced techniques in a 175MWth multi-fuel corner-fired boiler

A site assessment and a baseline testing programme were performed to obtain detailed process data. The 2.2 fuel ratio coal proved to be difficult to burn, and resulted in baseline carbon-in-ash levels over 20%, with NOx emissions above 470mg/Nm3. The experimental results were replicated in computational fluid dynamics and used to calibrate the full-furnace combustion CFD model used to confirm the design of the final solution. Bespoke burners were designed and installed for each fuel and an advanced over fire air system was installed to allow heavy staging of the combustion air. Low NOx performance was achieved through a combination of the ultra-low NOx burner design and the use of vapour injection, which, in conjunction with an efficient overfire air system, allowed the plant to achieve a NOx reduction of up to 39%, while carbon-in-ash was reduced by up to 88%.