Optimization of MILD chamber design for combustion of producer gas from biomass gasification

Abstract

Producer gas (PG) from biomass gasification is a promising carbon-neutral alternative fuel that can be utilized for power generation in steam boilers. However, conventional swirler axial burners design suffers from its low efficiency and high pollutant emission when using PG due to its low energy density caused by the high dilution with $N_2$ and CO₂. This study aims to address the need for optimizing Moderate or Intense Low-oxygen Dilution (MILD) combustion, a promising technique known for its temperature homogeneity and emissions characteristics. This is achieved through a two-stage full factorial statistical optimization using Design of Experiments (DoE) tools and ANSYS-FLUENT simulations to optimize the chamber geometry and operating conditions. Circular and square cross-section geometries were compared. The optimum geometry for Circular design was 200 mm in diameter and 1000 mm in length, while square design was 548.8 mm in height and 1500 mm in length. The Circular design with lower emissions and smaller size was further optimized in second-stage DoE where the equivalence ratio ($\phi$) and fuel inlet jet velocity ($V_f$) were manipulated. $\phi$ showed significant effect on pollutant emissions while 100 m/s provided adequate internal gas circulation to achieve MILD condition, and further increase in velocity did not show significant enhancement of combustion.