An experimental study of the stability and performance characteristics of a Hybrid Solar Receiver Combustor operated in the MILD combustion regime

Abstract

This study describes the performance and stability characteristics of a Hybrid Solar Receiver Combustor operated in the Moderate or Intense Low oxygen Dilution (MILD) combustion regime, in which the functions of a solar receiver and a combustor are integrated into a single device. The device was built and tested at a nominal capacity of 20 kWth for both the combustion-only (MILD and conventional combustion) and mixed-mode (a combination of both solar and combustion). Here, a 5 kWel xenon-arc solar simulator and natural gas were used as the energy sources, while the combustion mode was operated in the MILD combustion regime. The thermal efficiency, wall cavity temperature, heat flux distribution within the cavity and pollutant emissions are reported for the two modes of operation for a range of energy input, equivalence ratio, heat extraction, air preheat and solar-to-fuel energy input ratio. The stability limits for stable operations are also identified for each mode of operation. It was found that MILD combustion can be successfully stabilised within the HSRC in a wide range of operating conditions with and without air preheating, and in the mixed-mode of operation, providing ultra-low NOx and CO emissions. Also, the stability limits were found to increase by adding concentrated solar radiation to the combustion process. The thermal performance was found to be similar in both combustion-only (conventional combustion and MILD) and mixed-mode (up to ≈ 88% assuming reasonable heat recovery from the exhaust gas), confirming that an overall benefit can be derived from the device.