Hydrogen enrichment of methane and syngas for MILD combustion

Abstract

Moderate or Intense Low-oxygen Dilution (MILD) combustion is a technology with important characteristics such as significant low emission and high-efficiency combustion. The hydrogen enrichment of conventional fuels is also of interest due to its favorable characteristics, such as low carbon-containing pollutants, high reaction intensity, high flammability, and thus fuel usage flexibility. In this study, the effects of adding hydrogen to methane and syngas fuels have been investigated under conditions of MILD combustion through numerical simulation of a well-set-up MILD burner. The Reynolds-Averaged Navier-Stokes (RANS) approach is adopted along the Eddy Dissipation Concept (EDC) combustion model with two different chemical mechanisms. Molecular diffusion is modeled using the differential diffusion approach. The effects of oxidizer dilution and fuel jet Reynolds number on the reactive flow field have been studied. Results show that with an increase in hydrogen portion of the fuel mixtures, the volume of the high-temperature region of combustion field increases whereas a reduction of oxidizer oxygen content leads to more proximity to the MILD condition. Increasing the fuel jet Reynolds number will result in an expansion of the combustion zone and shifting of this region in the axial direction. Predictions revealed that the methane flame is more sensitive to the oxidizer dilution and fuel jet Reynolds number than syngas. Moreover, enrichment of fuel with hydrogen seems to be better for acquiring condition of the MILD combustion for syngas rather than methane. Indeed, syngas shows more sensitivity to hydrogen enrichment than methane, which makes hydrogen a good additive to syngas in terms of MILD condition benefits.