Numerical evaluation of a novel double-concentric swirl burner for sulfur combustion. (November 2020) - Zhang, Feichi
Abstract: A burner system for the efficient and clean combustion of sulfur is introduced, which serves as a key component in a novel solar power cycle using sulfur as chemical storage medium of solar energy. In order to validate the proposed design concept, highly-resolved numerical simulations have been performed. The current setup is operated with a thermal load of 20 kW or power density of 5 MW/m 3 . Two nozzle configurations with different swirl intensities (SI) of the airflow are studied. A large inner recirculation zone is observed for the nozzle with a high SI (HSI), which leads to a strong radial dispersion of the sulfur spray and a broad, short flame in the combustion chamber; although this HSI design is beneficial from the viewpoint of flame stabilization, it causes a large number of sulfur droplets hitting the chamber wall. In contrast, the nozzle design with a low SI (LSI) yields a narrow spray and a long jet flame, with much less droplets hitting the wall. The HSI nozzle shows an overall higher flame temperature compared with the LSI nozzle, which is confirmed to be caused by burning at a higher local fuel equivalence ratio. This is attributed to the strong inner recirculation flow generated by the high swirl intensity, which results in an enhanced evaporation and mixing of sulfur droplets with air. In terms of operability and NOx emission, the LSI burner is preferred due to less sulfur droplets hitting the chamber wall and the lower flame temperature. Highlights: Storage and utilization of solar power by sulfur as chemical carrier. Development of a novel burner system for the efficient/clean combustion of sulfur with high power density. Assessment of different nozzle design concepts with highly-resolved, transient numerical simulations. Detailed resolution of underlying turbulent flow, spray dispersion and flame stabilization behaviours. Burner design with small swirl intensity is preferred in terms of long-term operability and low NOx emissions.