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Binary catalyst composed of alkali metal and alkaline earth metal was widely used to overcome the shortcoming of single-metal catalyst. However, the synergistic mechanism between components remains unclear. In present work, sodium and calcium were loaded into the coal char individually or together. TGA gasification was used to investigate catalytic effect. In order to evaluate catalytic mechanism, Raman spectra of gasification residue, Raman spectra of quenched slag and phase composition at thermodynamic equilibrium were obtained. Loading of sodium or calcium significantly increased gasification rate of coal char and catalytic effect of sodium was better than calcium. Above 900 °C, catalytic effect of sodium-calcium binary catalyst was better than that of single catalyst, and gasification residue of binary catalyst loaded char had more calcium silicate and less sodium silicate than gasification residue of single-metal catalyst loaded char. It was speculated that calcium reacted first with silica in coal to inhibit sodium inactivation. Raman spectra of quenched slag and theoretical calculation showed that silica preferentially reacted with calcium oxide to form calcium silicate in calcium oxide-sodium carbonate-silica system, which proved above speculation. Furthermore, the significant catalytic activity of binary catalysts inhibited the graphitization evolution of carbon structure during char gasification, which is conducive to the improvement of gasification rate. [ABSTRACT FROM AUTHOR]

In this paper, the gasification reactivities of four types of Chinese coal were studied, each with different ash content and coal rank. Of the 4 coal types, 2 were HCl-washed and demineralized to investigate the effects of ash removal (for both dealkalization and demineralization) on coal gasification. The effects of ash on the evolution of physical and chemical structure were further studied using scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDX), N 2 absorption and FT-Raman techniques. The results show that the initial gasification rate of raw chars is twice as high as the HCl-washed and ash-free chars. The gasification rate of ash-free char significantly increases with the increase in carbon conversion and surpasses the gasification rate of raw char when carbon conversion is higher than 50%. Moreover, the specific surface area of ash-free char significantly increases with carbon conversion, resulting in the significant increase in the gasification rate. Whereas the specific surface areas of raw char and HCl-washed char both decrease during high-conversion stages. The FT-Raman analysis shows that the ash-free char band area ratios A D3 /A G and A D4 /A G are lower than those of raw char at the initial gasification stage; this results in the initial gasification rate decrease of ash-free chars. In addition, the ash-free char band area ratio A G /A all is smaller than that of raw char in the high conversion stages. [ABSTRACT FROM AUTHOR]

In this work, effects of K 2 CO 3 and Na 2 CO 3 additives on catalytic gasification of Shenfu coal were studied by the combination of thermogravimetric analyzer (TGA) and an in-situ heating stage microscope. Effects of loading amounts of catalysts (2.2 wt.%, 4.4 wt.%, and 6.6 wt.%) and gasification temperatures (700–950 °C) on the interactions during the char–ash/slag transition were analyzed. The results show that the interactions of catalysts with coal at gasification phase varied with reaction temperature, and compared to K-form char, Na-form char showed a more significant melt and flow of catalysts when the temperature was higher than the melting point of catalyst. The different aggregation states of catalysts on the surface of char matrix and development degrees of pore structure of char matrix accounted for the differences in interaction forms of K catalyst and Na catalyst with coal char. The interaction mechanisms of catalysts with char matrix during char–ash/slag transition were proposed and were related to the variation of gasification reactivity of char with increasing reaction temperature. Moreover, the ratio of the initial reaction rate of char loading catalyst to that of raw coal char (the specific reactivity) and the optimal loading amount of catalysts were analyzed considering the optimal gasification efficiency. There is a threshold value of reaction temperature lower than the melting point of catalyst for the optimal gasification efficiency during the gasification processes of Na-form and K-form chars. [ABSTRACT FROM AUTHOR]

The effects of water on the pyrolysis and gasification characteristics of coal water slurry (CWS) and pulverized coals with different ranks have been studied in the present work. Rapid pyrolysis characteristics (i.e. char yield, char structure evolution) of raw carbonaceous materials with varied water contents were investigated by using a high frequency furnace at 800–1200 °C. Moreover, gasification characteristics of the pyrolysis char were studied by using a thermogravimetric analyzer (TGA). The results indicate that at the pyrolysis temperature of 800 °C, the char yield of Wu-ran-cha-bu (WRCB) lignite slightly decreased with increasing the water content from 2.1 wt.% to 13.98 wt.%, while that of Yun-nan (YN) lignite showed a more significant decrease with increasing water content from 2.2 wt.% to 11.54 wt.%. This could be attributed to a higher coal reactivity of YN lignite than that of WRCB lignite. When the pyrolysis temperature was at or above 1000 °C, due to more significant in-situ coal-steam interactions, a lower char yield of both the pulverized lignites were observed with increasing water content from 2 wt.% to above 10 wt.%. CWS char presented a higher graphitization degree than pulverized coal char. The carbon microcrystalline structure factors (i.e. L 002 /d 002 value) of pyrolysis char increased with coal rank, which might reflect the variation trend of the graphitization degree from low rank coal to high rank coal. During the rapid heat treatment processes, the water evaporation and the in-situ steam-char gasification were favorable for void formation for both pulverized coals with high water contents and CWS. Notably, during the gasification processes of three different rank coals at 1200 °C, a more significant inhibition effect of residual ash on CWS char was observed compared to the pulverized parent coal char with high carbon conversion (x > 0.9). [ABSTRACT FROM AUTHOR]

Coal gasification fine slag (CGFS) from the entrained-flow coal gasification process mainly contains ash and residual carbon. Currently, the CGFS is normally stacked and landfilled in slag yards, resulting in huge resources waste and potential environmental risks. This study aims to review the research advances of the characterizations, carbon-ash separation and resource utilization of CGFS, so as to reveal the guiding role of CGFS characterizations on the process of separation and resource utilization. In this paper, the characterizations of CGFS are summarized from compositions, structures and dehydration. Methods for separating carbon-ash from CGFS are compared and analyzed. The resource utilization methods of CGFS are reviewed from direct utilization and high-value utilization. Moreover, the future research directions of carbon-ash separation and resource utilization are briefly discussed. Accordingly, this review identifies that particle size is a key factor determining the structure and composition of CGFS. Based on the analysis of the CGFS characterizations, froth flotation shows great application potential for carbon-ash separation from CGFS under the premise of reagent recycling. Blending combustion as the main direction of CGFS resource utilization should be considered. Although the synthesis of porous materials from CGFS is conducive to improving the environmental benefits of coal gasification plants, the optimization research on the preparation methods of CGFS-based porous materials is urgently needed. [Display omitted] • CGFS is a complex mixture composed of inorganic minerals and unburned carbon. • The structure and composition of CGFS are closely related to particle size. • Froth flotation shows great application potential for carbon-ash separation of CGFS. • Blending combustion as the utilization main direction of CGFS should be considered. • Optimization of CGFS-based porous materials preparation methods is urgently needed. [ABSTRACT FROM AUTHOR]

Based on percolation theory, the discrete model of char particle gasification with structure evolution under various distinct regimes was developed. Initial structure of individual char particle was modeled as a simple cubic lattice consisting of a large number of small sites. Sites arranged in the char lattice were randomly classified as either carbon, ash, or macropore, depending upon the proximate analysis data and the porosity of coal char. Suggested model was used to study the effects of structure parameter and reaction condition on the gasification reactivity and the evolution of char structure. Simulation results showed that under external diffusion controlled regime, the gasification rate decreased as reaction advanced for char particles with lower porosity (porosity < 0.15), and the gasification rate vs. conversion curves exhibited maxima for large char particles with higher porosity (porosity > 0.15). Besides, the particle sizes of coal char decreased slowly in the early stage of gasification, and then they decreased slightly fast. The gasification reaction of fine coal chars under the external diffusion controlled region could inhibit the particle fragmentation and reduce the formation of fine ash particles to a certain degree. [ABSTRACT FROM AUTHOR]

• 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]

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 this work, the influences of the gasification temperatures (1000–1150 °C) and blended ratios (3:1, 1:1, 1:3) on the co-gasification reactivity and synergy of petroleum coke (PC) and municipal solid waste (MSW)-derived hydrochar (HTC) were studied using a thermogravimetric analyzer (TGA). Chemical fractionation analysis (CFA) coupled with an inductively coupled plasma optical emission spectrometer (ICP-OES) was adopted for quantitatively investigating the active alkali/alkaline earth metal (AAEM) transformation (i.e., active AAEM content variation) during co-gasification in order to correlate the synergy mechanism of co-gasification. The results indicated that the co-gasification reactivity of the blended chars was enhanced with increasing gasification temperatures and HTC char proportions. The variations of the synergy behaviour on co-gasification reactivity at different conversions showed continuously enhanced synergistic effect at early co-gasification stage and decreased synergistic effect with further co-gasification. Moreover, higher gasification temperatures and HTC char proportions were more favourable for the continuous enhancement of the synergistic effect as co-gasification conversions increased. The overall synergistic effect on co-gasification reactivity was more obvious at higher HTC char proportions and lower gasification temperatures. The relative transformation ratio ( P ) was proposed to characterize the active AAEM content variation during co-gasification. P was negative when more active AAEM remained in blended chars, meaning that there was inhibition effect on the active AAEM transformation. It was found that the inhibition effect on the active Ca/K transformation was first enhanced and then weakened whereas the promotion effect on the active Na transformation showed an opposite trend with increasing conversion of co-gasification, which well correlated the synergy behaviour variations during PC-HTC blended char co-gasification. This work not only revealed synergy mechanism of petroleum coke and MSW-based hydrochar co-gasification but also provided reference data for the design and operation of industrial gasification units consuming mixture of petroleum coke and waste biomasses. [ABSTRACT FROM AUTHOR]

A series of thermogravimetric experiments were conducted to study the gasification kinetics of raw and demineralized coal char. The gasification mechanism was reveled through the kinetic analysis and the structure evolution. The systematic analyses showed that the reactivity of demineralized coal char was more sensitive to the heating rate β. The random pore model was more suitable for both raw and demineralized coal chars, where the pre-exponential factor (A) played the essential role in fitting performance. Moreover, the parameters of kinetic compensation effect were found to have a good linear relationship with ln β , and the variations of kinetic triplet (A , E a and f (X)) with the conversion level could be further explored accordingly. The reactivity predictions employing the integral and differential approaches were compared under the isothermal and non-isothermal conditions. The reactivity of raw coal char was more easily affected by diffusion, and the conversion-effectiveness factors increased with the conversion level at high temperatures. Finally, the local gasification mechanism was analyzed by piecewise comparing different single-step global models. The raw coal char featured the closed-pore reopening according to the distribution pore structure. The ash can act as the nuclei for gasification and affect pore growth and coalescence. [Display omitted] • KCE parameters had a good linear relationship with ln β. • Predications for non-isothermal and isothermal gasification were performed. • The local reaction pathway was analyzed by the piecewise SGMs. • The distribution structure parameter based on TGA was proposed. • The ash content affected the pore growth and coalescence during gasification. [ABSTRACT FROM AUTHOR]

• Carbon structure in thermochemical conversion of coal is characterized in-situ. • Transition mechanism between amorphous carbon and aromatic carbon is clarified. • Oxygen-containing functional groups are active sites for low temperature oxidation reactions. Thermal conversion is pivotal for clean and efficient coal utilization. Evolution of solid structure profoundly affects the gasification mechanism. However, in-situ study on coal structure evolution during gasification is limited. In this study, in-situ Raman spectroscopy was used to investigate the carbon structure evolution during thermal conversion. Results revealed two stages in coal pyrolysis: polycondensation and aromatic ring fusion. During polycondensation, numerous side chain groups break, while aromatic compounds condensed and rings fused in the aromatic ring fusion stage, increasing molecular size. In char gasification, larger particles required more time to achieve stable shrinkage, thus delaying coal char graphitization process. Low temperature oxidation led to decreased order due to oxygen-containing structure formation, evolving into a graphite-like structure as disordered carbon diminished. In addition, oxygen-containing groups acted as active oxidation sites. The insights into real-time structure evolution enhance understanding of the particle behavior during thermal conversion of coal. [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]

Based on a bench-scale impinging entrained-flow gasifier and visualization system, the conversion of particle group and a single coal particle in the impinging-flow zone below the burner plane is investigated in-situ. The axial evolution of particle group including particle size, particle concentration, velocity field and spatial distribution is characterized with image processing algorithm and statistical method. The particle fragmentation, single particle conversion process and volatile oxidation behavior are discussed. The results indicate that the Sauter mean diameter (SMD) is distributed in 560–720 µm in all statistical regions, and the particle concentration is distributed in 20,000–360,000. With the axial downward movement of the particle group, the SMD, particle concentration and spatial distribution frequency show an overall decreasing trend. The proportion of particles ranging in the velocity interval of 0–4 m/s increases in the three impinging-flow zones, which are 85.76 %, 92.33 % and 97.88 %, respectively. The fragmentation mode of a single coal particle can be classified into central fragmentation and peripheral fragmentation. The occurrence probabilities of the two modes in the upper impinging-flow zone are more than one-third, indicating that the particles tend to be fragmented near the burner plane. The conversion of a single coal particle can be divided into heat up and pyrolysis, volatile oxidation, volatile/char oxidation and char oxidation. In the upper impinging-flow zone, less than 30 % of the particles are in volatile oxidation stage, while about 50 % of the particles are in char oxidation stage. With the axial downward movement of the particle group, the proportion of particles in char oxidation stage decreases, while the proportion of particles in volatile oxidation stage shows an opposite trend. A macroscopic description of ignition and propagation of particle volatile flame is proposed. The propagation of volatile flame between singles particles can be extended to the propagation of volatile flame within particle groups. [ABSTRACT FROM AUTHOR]

Abstract Co-gasification reactivity of rice straw and bituminous coal/anthracite blended chars under CO 2 atmosphere was evaluated using thermogravimetric analysis, and the influences of coal type and gasification temperature on synergy behaviour variations on co-gasification reactivity as carbon conversions increased were quantitatively studied. Furthermore, the chemical forms and concentrations of AAEM species at different co-gasification conversions were quantitatively analyzed for revealing co-gasification synergy mechanism. The results demonstrate that as conversions increased, synergy behaviour on co-gasification reactivity of rice straw-bituminous coal blends was shown as the weakened inhibition effect firstly and then the enhanced synergistic effect. Moreover, the inhibition effect on co-gasification reactivity of rice straw-bituminous coal blends was sustained up to higher conversion with the increment of gasification temperature. Differing from rice straw-bituminous coal blends, synergistic effect on co-gasification reactivity of rice straw-anthracite blends was obviously enhanced at early stage of co-gasification and started to slowly weaken after reaching the most significant synergistic effect at middle stage of co-gasification. Additionally, it was revealed that synergy behaviour variations on co-gasification reactivity of rice straw-bituminous coal blends were mainly attributed to the combination effects of active K and Ca transformation during co-gasification, while those of rice straw-anthracite blends indicated a good correlation with active K transformation during co-gasification. Highlights • Synergy behaviour variations at different co-gasification conversions were quantified. • Mineral matter transformation during co-gasification was quantitatively studied. • Coal type showed great impacts on synergy behaviour variations on co-gasification reactivity. • Mineral matter transformation could well correlate co-gasification synergy mechanism. [ABSTRACT FROM AUTHOR]

Physicochemical evolution (i.e. pore structure variation, carbon structure change and active AAEM transformation) during rice straw (RS) and Shenfu bituminous coal (SF) co-pyrolysis was quantitatively determined in this work. Moreover, the corresponding char gasification was conducted using a thermogravimetric analyzer (TGA) and relative reactivity was proposed to quantify the co-pyrolysis impact on co-gasification reactivity. The results showed that the development of pore structure in co-pyrolyzed chars was first inhibited and then enhanced with the decrease of SF proportion. The promotion effect of co-pyrolysis on order degree of co-pyrolyzed chars gradually weakened with increasing RS proportion. Co-pyrolysis mainly enhanced active K transformation in co-pyrolyzed chars and the promotion effect was alleviated with increasing RS proportion. The inhibition effect of co-pyrolysis on co-gasification reactivity weakened with increasing RS proportion and gasification temperature, which was mainly attributed to the combination of carbon structure evolution and active AAEM transformation in co-pyrolysis. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) of carbonaceous waste is an important way of energy recovery to obtain renewable fuels. Here, cow manure (CM) and industrial sludge (IS), two kinds of wastes with different properties, were pretreated by HTC at different temperatures. The elements migration and the physicochemical structural characteristics of hydrochar during HTC were evaluated. The pyrolysis and gasification performance of hydrochar was also studied. The results show that HTC treatment can significantly increase the carbon content and reduce the oxygen content of feedstocks, so as to obtain clean solid fuels with high energy densification and realize energy recovery from low value wastes. The distribution of pyrolysis products of co-hydrochar is close to that of IS due to the interaction between the components of CM and IS. The co-hydrochar has good gasification reactivity, showing obvious synergistic effect. There is multi-component interaction in the process of co-HTC due to the difference of feedstocks composition and properties between CM and IS. The abundant aliphatic and oxidized aliphatic hydrocarbons in IS may inhibit the polycondensation and aromatization of cellulose and hemicellulose hydrolysates in CM due to hydrogen supply or steric hindrance. Therefore, co-hydrochar has carbon structure and fuel properties close to that of IS hydrochar. [Display omitted] [ABSTRACT FROM AUTHOR]

• Volatile–char interactions inhibited the gasification reactivity of coal char. • Five volatile–char interaction modes were designed and studied in detail. • The aromatic C-O was particularly important in char reactivity. • Volatile-char interaction and secondary cracking reduced the amorphous carbon structure. • Volatile–char interaction inhibits the cracking of alkyl aryl ethers. Cow manure is a special biological waste with potential for energy utilization and heat recovery. Various aspects of biomass utilization process is affected by volatile – char interaction. In order to reveal the changes of chemical structure and reactivity of coal char induced by cow manure biomass volatile–coal char interactions, five types of volatile–char contact modes were designed to obtain coal chars through fixed bed reactor. Fourier infrared transform spectroscopy (FT – IR), X-ray photoelectron spectroscopy (XPS), temperature programmed oxidation (TPO), and laser Raman spectroscopy (Raman) were used to analyze the change of char chemical structure. The results indicate that the type and content of O-containing functional groups have important influence on char reactivity, and the aromatic C – O is particularly obvious. Volatile–char interactions lead to the decrease of the gasification reactivity which is attribute to the decreased aromatic C – O, C = O and increased graphite carbon structures in coal char. By the deconvolution of the TPO curves, it found that the volatile–char interaction inhibits the cracking of alkyl aryl ethers structures. This work is helpful to understand the mechanism of volatile–char interaction on the structure evolution of coal char. [ABSTRACT FROM AUTHOR]