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The carbon content in fine slag during entrained-flow gasification is very high, at present, most of the fine slag was disposed by landfill. It is expected to provide a favorable technology by adding the fine slag to the circulating fluidized bed boilers to participate in combustion reaction. In this study, the gasification fine slags generated from GE, OMB and GSP gasifier, which are typical gasification processes in Ningdong energy and chemical base, was selected for investigation. The structural features and combustion reactivity of the residual carbon in the gasification fine slag were systematically studied by physical adsorption apparatus, laser Raman spectrum and thermogravimetric analyzer. The results showed that the materials in the original gasification fine slag could be divided into cohesive spherical particles, porous irregular particles and isolated large spherical particles, while the acid-washed gasification fine slag was mostly composed of loose fine particles and porous irregular massive particles. Additionally, the particle size of the residual carbon was clustered to 4–8 nm, and the specific surface area and active sites of that decreased orderly as follows: GE>OMB>GSP. The order degree of the residual carbon structure in GE slag was the lowest, and the amorphous carbon structure in it was the highest, while the case in GSP was the opposite. The combustion rate of the residual carbon in GE slag was the fastest, mainly due to its large specific surface area, more amorphous carbon structure and active site, and the comprehensive combustion index of residual carbon in GE slag was 5.26×10−7 %2/(min2·°C3).

A thermogravimetric analyzer and in-situ heating microscope were used to study gasification reaction of coal char particles on the interface of ash layer and slag at 1100, 1200 and 1300°C, using typical Ningdong coal-Yangchangwan coal as gasification raw material. The results show that the shape change of ash layer interface and slag interface under different gasification temperature is the main factor that affects the gasification reactivity of coal char particles. When the gasification temperature is 1100°C, the ash layer shrinks and wraps on the surface of coal char particles at high temperature, preventing the contact between gasifying agent and coal char particles and reducing the gasification reaction of char particle. However, the interface of slag does not change significantly, and the gasification reaction rate of coal char on the slag interface remains unchanged. When the gasification temperature is 1300°C, the interface of both ash layer and slag turns into a liquid phase. Under the surface tension, the char particles are broken, the effective reaction area became larger, and the heat transfer rate increases, thereby increasing gasification reaction rate of the coal char.

Meihuajing coal and Yangchangwan coal from Ningdong, China are chosen as raw materials to study char gasification reactivity using thermogravimetric analyzer and in-situ heating stage microscope, and typical gasification coal-Shenfu bituminous coal char is used as reference char sample. The char physicochemical properties are systematically characterized. The results show that the order for gasification reactivity of 3 chars at the same gasification temperature is Yangchangwan char > Meihuajing char > Shenfu char. In-situ study of heating stage microscope shows that with the progress of char-CO2 gasification, most of char particles react with CO2 as shrinking particle mode, and the particle reaction form changes from shrinking particle mode to shrinking core mode at high carbon conversion level. Additionally, it can be found from the results of shrinkage ratio variation of the particle projected area during gasification that Yangchangwan char shows the largest shrinkage area when undergoes the same reaction time, followed by Meihuajing char and Shenfu char. The difference in gasification reactivity is mainly attributed to the difference of physicochemical properties of chars. i.e.,Yangchangwan char shows the largest specific surface area and the total contents of K, Na and Ca and the lowest order degree of carbon structure, followed by Meihuajing char and Shenfu char.

Based on the bench-scale opposed multi-burner (OMB) coal-water slurry gasification experimental platform, the transformation and release characteristics of sodium during the reaction of coal in the gasifier were studied. Particles sampled at different axial distances from burner plane to top and bottom along the gasifier chamber were analyzed. After the microwave digestion and chemical fractionation analysis, the content of sodium was tested by flame atomic absorption spectrometer (FASS). The morpholo gy and elements of particles were analyzed by scanning electron microscopy and energy spectrum application system (SEM-EDS). The FASS results showed that the release rate of sodium increased first then decreased with increasing distance to the burner plane. The area near the burner plane was the major release area of sodium. With the reaction in progress in the gasifier the occurrence form of sodium was transformed from water-soluble sodium and ion-exchangeable sodium into the acid-soluble sodium and residual sodium. Combining the SEM-EDS and FASS results, the spherical particles which were formed through melt minerals reacted with sodium in the gas phase to form silicate and sialic acid salt in gasifier. The increasing number of spherical particles led to an increase in the sodium content in the particles.