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• Effects of pyrolysis temperature, residence time and atmosphere were investigated. • Release of AAEMs was associated with char structure evolution in rapid pyrolysis. • CO 2 promoted Na release in early stage and Ca and Mg release in late stage. The release law of alkali and alkaline earth metals (AAEMs) during coal pyrolysis is crucial for controlling scaling, corrosion and slagging in the utilization of high AAEMs coal. To approximate entrained-flow bed gasification process, a free-falling reactor was used for coal pyrolysis to study the release characteristics of AAEMs in nascent char. Effects of pyrolysis temperature, residence time and atmosphere were investigated. The cumulative release of Na, Ca and Mg at 1100 °C was 68.0%, 47.5% and 69.8%, respectively. As pyrolysis temperature increased from 900 °C to 1100 °C, the release of Na, Ca and Mg increased by 7.0 %, 3.5% and 5.3%, respectively. The cumulative release of AAEMs increased with the pyrolysis residence time, but the release rate decreased significantly in middle and late stages. The promoted thermal decomposition of functional groups by CO 2 resulted in a lower char yield. CO 2 promoted Na release in early stage and Ca and Mg release in late stage. Furthermore, release of AAEMs was associated with char structure evolution in rapid pyrolysis. The presence of CO 2 , high temperature and prolonged residence time led to enhanced particle fragmentation, increased surface cracks, and intensified thermal decomposition of functional groups, resulting in the migration of AAEMs in carbon matrix to char surface and the release of AAEMs organically bound to carbon matrix. [ABSTRACT FROM AUTHOR]

Pyrolysis and catalytic pyrolysis behaviors of two kinds of coals with different ranks were determined by thermogravimetric analyzer–mass spectrometry (TG–MS) and a high-frequency furnace. A quantitative method of on-line gas analysis was proposed using quadrupole mass spectrometry. The effects of pyrolysis temperature (650–800 °C) and Na 2 CO 3 loading amount (0–15 wt.%) on the gaseous compounds evolution were investigated. The results show that loading Na 2 CO 3 on coal was favorable for gas production in pyrolysis process. The yields of light gas species in the high-frequency furnace were lower than those in TG–MS. By comparing the pyrolysis yields of gas and solid in the high-frequency furnace and TG–MS, it was concluded that heating methods had great effects on the reaction mechanism and product distribution of pyrolysis and catalytic pyrolysis of coals. Moreover, the evolution processes of gaseous compounds were related to the presence of different functional groups in the solid samples. [ABSTRACT FROM AUTHOR]

Catalytic pyrolysis and gasification characteristics of coal using Na 2 CO 3 as a catalyst were studied in a high-frequency furnace and thermogravimetric analyzers (TGA), respectively. Interactions of Na 2 CO 3 with carbon at both pyrolysis and gasification phases were observed by in-situ heating stage microscope. The effects of pyrolysis temperature (650–800 °C) and catalyst loading amount (0–15 wt.%) on the associated pyrolysis and gasification processes were investigated. The results show that, H 2 and CO are the main pyrolysis gas products and the yields of these two gas increase with the increasing of Na 2 CO 3 in the range of 0–15 wt.%. The in-situ heating stage experiments indicated that one main gasification reaction form was observed for Shenfu char samples. Most of SF char particles reacted with CO 2 in the form of shrinking core mode without cracking, and certain particles presented fragmentation phenomenon in the reaction process. There is an optimal loading amount of Na 2 CO 3 for the best catalytic gasification effect of Shenfu bituminous char, while Na 2 CO 3 does not reach the saturation amount for the catalytic gasification of Zunyi anthracite coal. The activation energy of catalytic Shenfu coal gasification with 10 wt.% Na 2 CO 3 is 31.5 kJ mol − 1 less than that of non-catalytic coal gasification, which indicates that Na 2 CO 3 can improve the kinetics of coal gasification with CO 2 . [ABSTRACT FROM AUTHOR]

• In-situ Raman spectroscopy was innovatively used to characterize carbon structure. • AAEM promoted continuous breaking/reforming of bonds in polycondensation. • Inherent AAEM promoted the miniaturization of carbon crystal structure. Inherent minerals, especially alkali and alkaline earth metals (AAEM), are reactive constituents that interact with organic matter during pyrolysis and have significant effects on thermal characteristics and carbon structure evolution of char. The pyrolysis of raw and leached coal samples was conducted by using thermogravimetric analyzer and in-situ Raman system to explore the effects of content and chemical form of AAEM on pyrolysis characteristics and carbon structure evolution of single char particle. The water-soluble and ion-exchangeable AAEM promoted continuous breaking/reforming of bonds between alkyl substitutional groups and aromatic ring systems, resulting in the delay of volatiles release and orderly evolution of carbon structure during pyrolysis. The effects of water-soluble AAEM was more severe, because the divalent alkaline earth metal bonds to carbon was much more stable than the monovalent alkali metal for the inherent AAEM participated in the polycondensation reaction. Besides, the ion-exchangeable AAEM inhibited the generation of cross-linked structures more effectively than water-soluble AAEM, because ion-exchangeable AAEM existed in the form of AAEM-carboxylates and delayed the thermal decomposition. Moreover, the inherent AAEM promoted the miniaturization of carbon crystal structure in the carbon matrix, forming char with disordered carbon structure. [ABSTRACT FROM AUTHOR]

This study focuses on characteristics of structure evolution during pyrolysis and subsequent char gasification of lignite and bituminous coal. Coal pyrolysis was conducted on induction-heating reactor. As pyrolysis temperature increased, the graphitization degree of char increased, and the amount of C-O and -CH in char decreased, resulting in poorer gasification reactivity of char. Char gasification was conducted by thermogravimetric analyzer (TGA), high-temperature stage microscope (HTSM) and in-situ Raman system to investigate gasification reactivity, in-situ evolution of morphology structure and in-situ evolution of carbon structure, respectively. As gasification proceeded, the projected area of char particle decreased rapidly first and then kept consistent, and degree of graphitization of char gradually increased. In-situ Raman parameters indicated difference in increasing rate of graphitization between lignite char and bituminous char decreased with increasing temperature. Higher temperature deactivated the alkali metals, leading to attenuation of their inhibitory effect on graphitization. Gasification reactivity index R 0.9 was in positively correlated with in-situ I D1 /I G value, and corresponding correlation coefficient (R2) for TGA and HTSM were 0.8108 and 0.9829, respectively. The higher R2 for HTSM was due to the weaker diffusion effect. In-situ Raman parameter was more suitable for predicting gasification reactivity of single particle char. [ABSTRACT FROM AUTHOR]