Analysis of the transformation behaviors of a Chinese coal ash using in‐/ex‐situ XRD and SEM‐EXD

Abstract

Crystal and phase transitions of a Chinese Datong coal ash were evaluated using room temperature X-ray diffraction (RT-XRD), in-situ high temperature (HT)-XRD, and scanning electron microscope combining energy dispersive X-ray analysis (SEM-EDX) as temperature varied from 300°C to 1600°C. The transforming behaviors of ash were related to its melting properties. Results revealed that the transforming behavior of minerals from in-situ HT-XRD was different with that from routine RT-XRD. Low-temperature Datong ash contained quartz and clays (such as kaolinite); the changes in minerals at low-temperature region (300-1000°C) were mainly due to the minerals decomposition and partial phase transition. Significant transition of quartz to cristobalite occurred at ca. 1100°C; the continuous transition and reaction of silica and alumina at ca. 1200°C accelerated the softening of the ash (ST ≈ 1290°C). An X-ray amorphous liquid phase was formed mainly by the eutectic solution of silica and mullite at ca. 1400°C, which obviously affected the hemisphere temperature (HT ≈ 1490°C) of ash; meanwhile, ultra fine alumina solid particles, which were probably derived from kaolinite, were found in the melted ash. Virtually, the fusing (FT > 1500°C) of Datong ash was considered to be determined by the formation of solid particles and eutectic solution. Eventually, the semi-quantitative evaluation of transformations of ash was successfully obtained through the combined methods.

Investigation on the Occurrences and Interactions of Corrosive Species during Pyrolysis of Zhundong Coal Using SSNMR and HT-XRD

“…28 Moreover, solid−liquid phase transformation could also be monitored by HT-XRD, enabling the detection on the fouling propensity induced by low-temperature eutectic. 29 Overall, the present study innovatively elucidated the original occurrences, especially the in situ transformation behavior and mechanism on the interactions among the corrosive substances during pyrolysis of Zhundong coal by combining the SSNMR, in situ HT-XRD and Factsagesimulation. The sequential removal of corrosive substances in high-basic coals and the strategic guidance on minimizing the fouling and slagging propensity during their utilization were proposed.…”

“…To some extent, in situ high-temperature X-ray diffraction (HT-XRD), an advanced analytical technique for characterizing inorganic matter in coal, could achieve the in situ analysis of minerals without recrystallization and decomposition of coal samples . Moreover, solid–liquid phase transformation could also be monitored by HT-XRD, enabling the detection on the fouling propensity induced by low-temperature eutectic …”

Experiment and Mechanism Study on the Effect of Kaolin on Melting Characteristics of Zhundong Coal Ash

“…As a effective additive for removal of alkali metal, kaolin has been studied by many researchers on its removal mechanism. Partial kaolinite could be easily decomposed at a high temperature condition . And Linak’s research has proved that kaolin was excessive molten between 1373 and 1573 K during the burning processes, which lead to it inactivated and cannot continue to be used for further capture alkali metal.…”

“…Partial kaolinite could be easily decomposed at a high temperature condition. 8 And Linak's research 9 has proved that kaolin was excessive molten between 1373 and 1573 K during the burning processes, which lead to it inactivated and cannot continue to be used for further capture alkali metal. Gale also found that, when the temperature increased to 1573 K, the kaolin crystal structure would be collapsed 10 and the sintering phenomenon would also be occurred by the excessively melten of eutectics, both of which would sharply decrease the specific surface area and porosity of kaolin and lead to the deactivation of kaolin, so the adsorption capacity of kaolin for metal would be obviously reduced.…”

Study on the fluidity of ash slag of liquefaction solid product and lignite co‐gasification

“…19 Therefore, it is of great significance to understand the influence of chemical composition and crystallization behavior on coal ash fusion mechanism and flow characteristics for the optimization design, stable operation, determination of operating parameters, and evaluation of coal adaptability in industrial gasification units. 20,21 The fluidity of coal ash slag is mainly determined by the chemical composition, atmosphere, and operating temperature during gasification. Coal ash is an extremely complex inorganic mixture composed of SiO 2 , A1 2 O 3 , Fe 2 O 3 , CaO, MgO, Na 2 O, K 2 O, TiO 2 , and other oxides.…”