Morphological Evolution of a Single Char Particle with a Low Ash Fusion Temperature during the Whole Gasification Process

Abstract

The morphological evolution of a single char particle with a low ash fusion temperature (T f) was investigated during the whole gasification process using a high-temperature stage microscope. The experimental results showed that the final shrinkage ratio of char particles at the temperature above T f (1300 °C) was higher than that below the deformation temperature (1000 °C). The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analysis results showed that the ash distribution in coal char was uniformly dispersed. Dispersed molten slag gradually aggregated to the molten slag layer during the gasification process at the temperature above T f, and the slag layer evidently hindered the diffusion of the gasifying agent. Therefore, there was a critical shrinkage ratio during the gasification process when the temperature was above T f and the critical shrinkage ratio of Xiaolongtan lignite (XLT) char particles was 0.7–0.8. The SEM–energy-dispersive X-ray spectroscopy (EDS) analysis results indicated that the critical points in the curve of the shrinkage ratio with time were related to the molten slag on the char surface. In addition, the reaction mechanism in this experiment was analyzed. The calculating results indicated that the critical thickness of the molten slag layer of XLT and Shenfu bituminous (SF) coal chars with different ash contents showed good agreement and the critical thickness of the slag layer was 6–18 μm. Finally, the sensitive analysis was performed to analyze the factors affecting the calculating results.

New Slag–Char Interaction Mode in the Later Stage of High Ash Content Coal Char Gasification

“…A small number ofwhat carbon-containing material with high gray was observed on the surface of molten slag. New slag–char interaction characteristics were observed compared with the previous study …”

“…Besides, the critical conversion decreased with the increase of ash content. The critical slag layer thickness was about 6–18 μm for coal chars with different ash contents …”

“…Molten slag on a char particle surface decided the diffusion conditions of the gasifying agent. On the basis of the previous study, it was found that the characteristics of the slag layer on a particle surface was important for the gasification process. However, the effects of reaction temperature on characteristics of the slag layer on a particle surface was seldom referenced in the literature.…”

Mechanism of the evolution of pore structure during the preparation of activated carbon from Zhundong high-alkali coal based on gas–solid diffusion and activation reactions

“…Moreover, the surface of the char is covered with an ash layer due to the strong CO 2 activation reaction, and the ash layer further hinders the diffusion of CO 2 inside the char. 34 Thus, these factors lead to the formation of an AC sample with a dense surface and poor pore structure.…”

Study on Char-Ash-Slag-Liquid Transition and Its Effect on Char Reactivity

“…Ding et al in situ analyzed the char-ash/slag transition during char gasification and found that coal rank, ash properties and reaction conditions had great influences on the whole conversion process and the shrinking particle and shrinking core mode were two main reaction modes. Liu et al , proposed a new model of slag-char interaction during gasification and found that the ash was uniformly distributed on char surface when the reaction temperature exceeded the ash deformation temperature. There are many reports on the correlation between the ash change and reactivity.…”