Water distribution and adsorption behaviors of two typical coal gasification fine slags from Ningxia Region

Abstract

In this study, the water distribution and adsorption behaviors of two typical coal gasification fine slag (GFS) samples with different moisture contents were studied. Both of the samples were collected from entrained-flow coal gasifiers with the same coal as feedstock from Ningxia Region. The GFS sample collected from a GSP gasifier (2.5–4.0 MPa, 1400–1750 °C), with lower moisture content, was named as GFS-L, and the sample collected from a Texaco gasifier (4.0–6.5 MPa, 1300–1400 °C), with higher moisture content, was GFS-H. As the water distribution and adsorption behaviors in GFS samples, largely depending on the pore structure, had not been extensively analyzed, this study was investigated by the means of nitrogen adsorption analysis, mercury intrusion porosimetry (MIP), low field nuclear magnetic resonance (LF NMR) and dynamic water vapor sorption analysis (DVS). Experimental results revealed that the surface area, pore volume and average pore diameter of GFS-L were all lower than those of GFS-H. The fractal dimension analysis results illustrated that the GFS-L sample had smoother surface but more complicated internal pore structure than the GFS-H sample. Accordingly, the moisture content in GFS-L (45.42%) was slightly lower than that in GFS-H (48.78%). Water distributed in macropores decreased significantly during dehydration process, whereas decrease of water in mesopores was not apparent. And negligible water was found in micropores. Moreover, it was found that the water adsorption behaviors in both of the GFS samples could be characterized by the monolayer adsorption and multilayer adsorption over the relative humidity (RH) range of 0–0.7. Beyond the RH range of 0.7, it was found that water adsorption in the GFS-H sample transitioned to the capillary condensation, leading to higher moisture content. This study is envisaged to provide some new insights into developing GFS dehydration technology.