Chemistry variation of slag and the layered characteristics of deposits in an industrialized entrained-flow gasifier system with radiant syngas cooler

Slag particles experience a series continuous transformation during the industrial gasification system and slag behavior is critical for stable operation. A proper slag layer needs to be formed in the gasifier to protect the reactor wall and the fluidity of liquid should be maintained for smooth tapping. When slag particles enter the syngas cooler, deposition is one of the obstacles restricting stable operation. This study took slag samples from a stable operational gasifier, syngas cooler and slag pool respectively, which can reveal slag chemistry transformation from the input ash to the output slag. The deposits taken from gasifier and syngas cooler are in layers. The chemical comparison result shows that the deposition in syngas cooler is more sensitive to slag composition than that in gasifier and the elements Fe, Na and K are abundant in the first deposition layer. The in-situ observation by a confocal scanning laser microscope shows that crystallization of this slag can last as low as 1000 °C. Thus, the solid-liquid mixture leads to sticky particles due to low liquid viscosity, increasing the deposition tendency. •Chemistry variation of slag is investigated in a coal gasification system.•Slag composition influences deposition more in the cooler than in the gasifier.•Low temperature eutectics deposit in the syngas cooler.•Layered deposition results in the syngas cooler are illustrated.