Occurrence modes of water in gasification fine slag filter cake and drying behavior analysis——A case study

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• Hydrophilic components and macropores are essential factors for water occurrence. • About 86 wt. % of total water is free water type which could be removed first. • The water existed in macropores is less affected by capillary force during drying. • Water occurrence study is an basis for developing efficient dewatering theory. • Two-dimensional growth model is suitable for drying kinetics study. Coal gasification fine slag is one of the major industrial wastes produced from coal gasification technology and its landfill disposal of the high-moisture product has brought harmful environmental impacts. The characteristic of water occurrence modes in gasification slag filter cake has positive effects on guiding high-efficiency dewatering processes which benefits to the environment. Gasification fine slag particles and water exist simultaneously in the gasification fine slag filter cake, and the physicochemical properties of the gasification fine slag have significant influences on the water occurrence mode and the effective dewatering process. The hydrophilic components and abundant macropores in the gasification slag are favorable for water occurrence. The water in the gasification fine slag filter cake was classified according to the freezing types and size distribution by low-temperature DSC and LF-NMR, respectively. ∼86 wt% of total water corresponding to the free water form which would be removed first during drying process. The visualization of water was determined by three-dimensional reconstruction technology, there are distinct water channels in the gasification fine slag filter cake from the direction in which the filter cake is formed, and the volume of water was estimated at ∼56 %. The drying behaviors were tested by TGA with the heating rates of 2, 7, and 15 K/min, and the maximum drying rate and critical water content increased as the increasing heating rates. The two-dimensional growth kinetic model was applied for describing the drying kinetic process, and the activation energy decreased as the increasing heating rate, and the drying rate reduction stage has higher activation energy compare to the increasing and constant drying stage.