MILD combustion of grape marc as a source of renewable energy

The present study focuses on the experimental investigation of Moderate or Intense Low oxygen Dilution (MILD) combustion of grape marc as a potential biomass source of renewable energy. A vertical furnace with a cross section of 260 x 260 mm2 and 1200 mm long was used in this study. The fine particles of grape marc, 150-250 μm in size, are fed through a central jet, using CO2 as the carrier gas, and burned in a hot and vitiated co-flow. The furnace walls, as well as co-flow temperature and local oxygen concentrations, are controlled by a secondary swirling burner using non-premixed natural gas combustion. The co-flow stream temperature was fixed at 1320K with an excess O2 mole fraction of 6%. The jet exit velocity was varied from 5.75 ms-1 (~Rejet = 13,040) to 7.63 ms-1 (~Rejet = 17,300) to investigate the impact of turbulent jet velocity, as well as the particle residence time, on the burning characteristics of grape marc under MILD combustion conditions. Detailed measurements of in-furnace temperatures and in-furnace CO and NOx concentrations are presented and discussed, together with visual observations at the bottom, middle and top region of the furnace. It is found that, for both cases, a stable MILD combustion is established with a semi-uniform temperature profile. The measured NOx emission of the higher jet velocity case is found to be 38% higher than that of lower jet velocity case. While the CO emission for the higher jet velocity case is considerably, around 51%, lower than the lower jet velocity case.