CFD-based optimization of Tar destruction in downdraft biomass gasifiers via advanced injection strategies

The gasification technology still restricted by the generation of tar compounds during the gasification process, which restricts the direct utilization of the resulting syngas. To tackle this challenge, the present study introduces a two-dimensional CFD model of rubberwood downdraft gasification to investigate the formation and destruction of key tar compounds – benzene, toluene, naphthalene, and phenol (representing primary, secondary, and tertiary tars) – and to evaluate the impact of side-nozzle injections attached to the reduction zone. Steam, oxygen, and CO₂ were each injected downstream to assess their combined effects on syngas composition and tar species yields.

Oxygen and CO₂ downstream injections effectively reduced tar, but caused a significant drop in syngas heating value, limiting their practical application. In contrast, steam injection (at reduction zone) achieved a notable reduction of total tar content by 15–35 wt %, boosted hydrogen production, lowered CO₂ emissions, and preserved high heating values without the need for additional tar separation.

These findings demonstrate that steam injection in the reduction zone offers a practical, scalable strategy for tar mitigation in biomass gasification. This approach enhances syngas quality and supports possible broader adoption of sustainable gasification technologies.