Depositional characteristics of Ningdong coal under a reducing atmosphere

As an important raw coal for gasification, the deposition characteristics of Ningdong coal have a great influence on the long-term stability of the gasifier. In this work, a one-dimensional drop-tube furnace was employed to examine the depositional behaviour of Ningdong coal under a reducing atmosphere at different temperatures and deposition times. The thickness and morphology of the minerals in the deposits were analyzed by Digimizer image analysis software, X-ray diffraction, and scanning electron microscopy-electron dispersion spectroscopy (SEM-EDS). With the temperature increases from 1050 to 1300 degrees C, the thickness of the deposit at each deposition time monotonously decreases, whereas the deposition rate initially decreases until reaching its minimum at 1100 degrees C before increasing again at higher temperatures. Furthermore, the deposit morphology changes from a grain-like form into a floccule-like form as the temperature increases to 1050 degrees C, and the deposition rate increases with deposition time. It was found that Fe-containing minerals are the dominant factors of deposit formation based on SEM-EDS analysis. The transformation of the mineral matters of the coal ash at each temperature was simulated using FactSage computational thermochemistry software. It was found that the Fe-containing minerals responsible for deposit formation are clinopyroxenes (FeO) and liquid slag (Fe2O3). This work could be used as a theoretical guide to reveal the mechanism of deposit formation with Ningdong coal gasification.