Biomass powder suspension furnaces have attracted increasing attention due to their potential for efficient biomass utilisation. The effective suppression of NO_x formation during biomass power combustion remains a critical issue to be addressed. A recent study at the Sheyang University of Chemical Technology in China provides both theoretical insight into and practical guidance for optimising combustion and achieving low-NOₓ operation in biomass powder suspension furnaces.

The study investigates a 3MW industrial-scale biomass powder suspension furnace. A CFD-based numerical simulation combined with industrial-scale experimental validation was conducted to investigate combustion characteristics, NOₓ formation, and the emission-reduction mechanism of flue gas recirculation (FGR).

A three-dimensional vertical suspension furnace model was developed using an Euler–Lagrange gas–solid two-phase framework, incorporating turbulence, radiative heat transfer, devolatilization, char combustion, and NOₓ formation sub-models. The simulation results show good agreement with the measured data from an industrial-scale furnace with identical configuration and dimensions.

Results indicate that a stable swirling recirculation structure and a continuous high-temperature combustion core form inside the furnace. NOₓ is mainly generated via fuel-NOₓ pathways, with negligible contributions from thermal-NOₓ and prompt-NOₓ. An excess air ratio of 1.2–1.4 balances combustion completeness and NOₓ reduction.

FGR shows the greatest NOₓ mitigation when injected through secondary air, which favors the conversion of fuel-bound nitrogen to N₂. As the FGR ratio increases from 10% to 30%, the NO_x concentration at the furnace outlet decreases significantly. At an FGR ratio of 30%, the measured NOₓ concentration decreased to 146mg/m³, representing a reduction of 43% compared with the non-FGR condition, while a thermal efficiency of 93.2% is maintained. The resulting emissions comply with the industrial emission limit of 150mg/m³.