Evaluation of abnormal burner operation in an entrained flow coal gasifier using numerical modeling

The Shell coal gasifier adopts four horizontally biased coal burners to create an axisymmetric swirling flow in the middle of the reactor for intensive mixing and reactions. However, during startup, shutdown, or operational troubles, the axisymmetric can break and result in damages to the refractory lining or burners. Using two numerical modeling approaches, this study investigated various scenarios of abnormal burner operation by uneven load and O₂/coal ratio between burners. Computational fluid dynamics provided detailed flow and reaction characteristics together with the molten slag deposition. Subsequently, the slag layer model analyzed the resultant heat flux and slag thickness around the hotspots on the wall. A smaller load or oxidant feed in a single burner by 30% or larger created hotspots above or below the burner level with a peak heat flux as large as 36% and loss of the existing slag layer by more than 24% compared to the axisymmetric case. Maintaining the axisymmetry of opposing jets by equally adjusting the operating conditions in two opposed burners was effective in minimizing hotspots. However, severe consequences were expected when two opposed burners were turned off, creating hotspots with a 75% larger heat flux close to the burners, which increased the risk of damage to the refractory lining and overflow of liquid slag that blocks the burner tips. In contrast, the three-burner operation decreased the slag thickness below the burners by 60–77% but was not expected to cause significant damages because the slag layer was thick around the hotspot.