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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.

The entrained-flow coal gasification is an important and attractive technology in large scale coal-based synthetic natural gas (SNG) process. In this study, an integrated entrained-flow coal gasification and pyrolysis system is proposed and investigated. The gasifier is divided into two stages in this system: one is mainly for the gasification of char and the other is mainly for the coal pyrolysis. The integrated system is studied by using a process simulation model and compared with a coal gasification system with the radiant and convective coolers. The effects of the operating conditions on the gasification performance are studied and the optimized operating conditions are obtained. It is found that the optimized steam coal ratio of the integrated system is about 250–300 kg(steam)/t (dry coal) while the gasification temperature is 1400°C. The cold gas efficiency of 88.18% of the integrated system is higher than that of 84.14% of the gasification and radiant+conductive cooler system. The coal and O 2 consumptions are relative low in the integrated system. The performance of the integrated system is highly related to the yield of tar and CH 4 in the pyrolysis stage. The overall energy conversion efficiency of the integrated system (92.26%) is slightly lower than that of the gasification and radiant+conductive cooler system (93.39%). However, the exergy efficiency is enhanced by more than 2.2% in the integrated system. The integration of the gasification and pyrolysis can effectively recover and promote energy grade of the sensitive heat in the hot syngas.