Analysis of Syngas Inlet Position for Optimization of Flameless Combustion in a Biomass Pyrolyzer

A new biomass pyrolyzer, named Biochar Oven, has been developed using flameless combustion technology, which provides uniform high temperature in the pyrolysis reactor. A computational fluid dynamics (CFD) model of flameless combustion was developed to analyze how the fuel inlet depth controls the reaction and heat transfer to a vertical biomass pyrolysis reactor. The combustor was modeled using the k–ε turbulence model, the discrete ordinates radiation model, and species transport with the reaction. The fuel nozzle relative depth ratios (RDR) of chamber height and equivalence ratios (ER) were varied to obtain optimal combustion and heat transfer performance. The internal recirculation ratio (Z) was calculated to evaluate the flameless combustion condition, with maximum values generally found at RDR 0.73 for each ER. Increasing depth strengthens the mixing zone closer to the reactor wall. With an ER of 0.9 and RDR of 0.73, the wall heat flux is up to 16.36 kW m−2, the average wall reactor temperature is up to 900 °C, and the heat transfer efficiency is up to 59.79%. These flow patterns and chamber–reactor results indicate that deeper nozzle insertions (RDR 0.73) provide better overall performance by improving recirculation intensity, wall heat flux, and heat transfer efficiency with lower CO emissions.