Effect of water vapor on viscosity behavior of coal slags with high silicon-aluminum level under gasification condition

For the slagging gasifiers, the slag viscosity behavior is a critical parameter for the smooth slag tapping and long term operation. Water vapor is an important component of the syngas in the gasifier, especially for coal water slurry gasification. This paper presents the results of a study to investigate the effect of water vapor on viscosity behavior of coal slags with high silicon-aluminum level. The viscosities of three synthetic coal slags with different Si/Al ratios (mass ratio of SiO2 and Al2O3) was measured in argon with 10%, 20% and 30% water vapor as a function of temperature. As the water vapor proportion increased, the viscosity of the slag with high silicon-aluminum level at same temperature increased slightly. Besides, the slag with Si/Al of 2.0 transformed from a glassy slag to a crystalline one when the water vapor proportion was increase up to 30%. The oxidation state of iron of the slags was not affected by the increase in water vapor proportion under Ar with water vapor condition. Analysis of the slag structure demonstrated that water vapor entering the slag was benefit to the formation of Si-O-Si bridges and [AlO4](5-) structure. Meanwhile, activation energy for viscous flow (E-eta) increased with the increasing water vapor proportion. Water vapor also promotes crystallization and growth of crystals of the slag with high silicon-aluminum level during cooling, leading to the increase in the temperature of critical viscosity (T-cv).