Experimental and numerical study of the influence of syngas composition on the performance and stability of a laboratory-scale MILD combustor

This work presents the thermal performance, emissions and stability limits for steady-operations of a laboratory-scale combustor operating in the Moderate or Intense Low oxygen Dilution (MILD) combustion regime and fed with syngas fuels. The device was operated at 12-kWth using syngas with different H2/CO composition (H2/CO by v/v = 1–3). The global performance of the device, namely thermal efficiency, pollutant emissions, heat flux distribution and stability limits, were measured as a function of the heat extracted. It was found that the MILD combustion regime can be achieved over a broad range of fuel composition and operating parameters, with nearly-zero NOx and CO emissions. An increase in the H2/CO ratio of the syngas stream was found to increase both the stability limits for steady MILD processes and the NOx emissions. Irrespective of the fuel type, similar thermal efficiencies were measured for all cases investigated, providing evidence that the device can efficiently (i) operate with low-calorific fuels and (ii) accommodate for variability in the composition of the syngas fuel stream. In addition, the numerical analysis highlighted that the syngas composition strongly influences the rate of radiative heat transfer and reactions as well as the characteristics of the reaction zone.