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The study aims to explore the kinetics of coal char during high temperature gasification by thermogravimetric analyzer and in situ heating stage microscope. Yangchangwan coal (YCW) and Shenfu coal (SF) were selected as the feedstock. The kinetics was fitted by using shrinking core, random pore, and homogeneous models, respectively. The in situ heating stage microscope was used to observe the ash morphology change of coal char. The results show that the random pore model was optimal for fitting the kinetics of coals. At 1273–1673 K, the range of apparent activation energy of YCW and SF chars were 82.27–90.74 kJ mol−1 and 89.78–91.42 kJ mol−1, respectively. Most of the YCW and SF chars were observed to participate in gasification by random pore mode and amorphous ash was formed. A few of YCW char particles were observed to undergo gasification by both homogeneous and shrinking core modes. The area shrinkage ratio of YCW char involved in the gasification by shrinking core mode was reduced by 58% after 20 min of reaction. At 1573–1673 K, the char gasification was controlled by ash layer diffusion. Compared with the reactivity at 1273–1473 K, SF char gasification reactivity at higher temperatures was reduced for that SF coal ash could agglomerate into sphere to wrap the residual carbon, while YCW char reactivity was increased since YCW ash was agglomerated into sphere, the sphere were melting and flowing with each other, so the residual carbon was exposed on YCW char surface. [ABSTRACT FROM AUTHOR]

Gasification converts coal into syngas (CO and H 2) for downstream utilization. The most important reaction in an autothermal gasifier is the char−H 2 O/CO 2 reaction. The evolution of C(O) complexes on the coal char surface directly determines the pathways and rates of CO and H 2 generation. This study mainly used a fixed bed reactor to prepare Zhundong coal char with different reaction levels in H 2 O and CO 2 , and its surface carboxyl, lactone, phenolic hydroxyl, and hydroxyl functional groups were systematically analyzed by using Boehm titration, FT-IR, and XPS. The results show that the contents of the four oxygen-containing groups in raw coal are in the order of carboxyl＞lactone＞phenol hydroxyl＞hydroxyl. In H 2 O gasification, the lactone groups were more susceptible to H 2 O resulting in a significant increase in carboxyl content at the early stage of the reaction. The hydroxyl, as a very active group in the reaction, and the amount of its generation and consumption was very obvious. The phenolic hydroxyl−the least thermally stable group among these four types of groups, was unable to participate in the inter-transformation between oxygen-containing functional groups during the gasification. During CO 2 gasification, the hydroxyl was rapidly consumed at the initial stage of the reaction and then shown a slow growth trend, and the newly generated hydroxyl would continue to undergo dehydrogenation to form new functional groups. At the end of the reaction, the transformation of other oxygen-containing functional groups into more stable carbonyl groups leads to a sudden increase in the content of carboxyl and lactone. In this work, Boehm titration was introduced into the determination of oxygen-containing functional groups on the surface of char during gasification in H 2 O/CO 2. • Evolution of oxygen-containing functional groups on coal char surface during gasification was revealed. • The evolution of oxygen-containing groups in H 2 O/CO 2 was significantly different. • H 2 O has more noticeable effect in increasing aromatic C=C of char than CO 2 during gasification. [ABSTRACT FROM AUTHOR]

Highlights • Combined effect of Ca and Na during catalytic gasification was revealed. • Na and Ca favor the formation of micropores and mesopores respectively during gasification. • Interactions between Ca/Na compounds with char make the carbon matrix more vulnerable to steam. • Redox experiments show that Ca/Na-char produce more active intermediates during gasification. Abstract The main aim is to investigate the effects of Ca/Na compounds on coal pyrolysis, gasification reactivity as well as char characteristics during gasification. The pyrolysis and gasification tests of different metal loaded coals were performed on thermogravimetric analyzer and fixed bed reactor. The raw and gasified chars were prepared and characterized by nitrogen adsorption, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results indicate that Ca coexist with Na has a better catalytic activity compared to Ca and Na alone. The addition of metals can promote the pyrolysis gas release in advance and increase the release amount of H 2 and CO 2. The present of Ca/Na compounds have no significant effect on pore structure evolution during pyrolysis, but it inhibits the aromatic structure condensation of the coal char. The addition of Na and Ca is beneficial to the formation of micropores and mesopores respectively during gasification, the simultaneous existence of Ca and Na results in a more abundant pore structure. Both Ca and Na can inhibit the condensation of aromatic structures during coal char gasification, Ca together with Na will make the char has a higher degree of disorder. The interaction between Ca and Na with coal char makes the carbon matrix easier to be attacked by H 2 O to form more active intermediates. Redox experiments further verified that more active intermediates were generated during the gasification of Ca/Na loaded char. [ABSTRACT FROM AUTHOR]

Summary: In this work, we studied the effects of char structural evolution and alkali and alkaline earth metallic species (AAEMs) catalysis on the reactivity during the char gasification with CO2, H2O, and their mixture. The gasified chars with different carbon conversion levels were prepared, and their physicochemical structures were characterized via nitrogen adsorption and FT‐Raman techniques. The concentrations of AAEMs in different modes were obtained by the sequential chemical extraction method. The reactivities of the raw and gasified chars were analyzed by the thermogravimetric analysis. The gasification atmospheres had varied effects on the physicochemical structure of coal char. The gasified char obtained in the CO2 atmosphere had a lower aromatic condensation degree compared with that obtained in the H2O atmosphere, irrespective of the temperature. The impact of the atmospheres on the specific surface area of the char varied with the temperature because H2O and CO2 have different routes of development of pore structure with coal char. A large specific surface area facilitates the exposure and dispersion of more AAEMs on the surface of the channel, which is conducive to their contact with the gasification agent to play the catalytic role. Thus, the reactivity of the gasified char is well correlated with its specific surface area at different gasification temperatures. In the absence of AAEMs, the chemical structure of coal char becomes the dominant factor affecting the reactivity. [ABSTRACT FROM AUTHOR]

Experiments were conducted to investigate the coal gasification performance and char characteristics affected by Ca/Na compounds. Firstly, the gasification reactivities of Ca-loaded coal, Na-loaded coal, and Ca/Na-loaded coal were compared by TGA in different gasifying agents including 100% H 2 O, 100% CO 2 , and 66.7% H 2 O + 33.3% CO 2 . Then, partially-gasified chars of Ca/Na-loaded coal with carbon conversion of 50% were prepared in different gasifying agents and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption measurement. It was found that Ca together with Na showed a combined effect towards the gasification reactivity which was the most obvious in H 2 O/CO 2 mixtures, and Na could promote the synergistic effect caused by Ca catalysis at higher temperature (900 °C). Na can inhibit the agglomeration of CaO due to its excellent mobility and the formation of a eutectic mixture Na 2 Ca(CO 3 ) 2 . The marked improvement of CaO dispersion on the partially-gasified char in H 2 O/CO 2 mixtures results in the significant combined effect between Ca and Na and improves the synergistic effect at higher temperature. Moreover, the combined effect between Ca and Na during catalytic gasification can not only facilitate the gasification reactivity but also promote the development of pore structures for the gasified char. [ABSTRACT FROM AUTHOR]

In this work, the interaction between waste cypress sawdust (WCS) and coal liquefaction residue (CLR), a type of industrial solid waste, during co-pyrolysis was studied by thermogravimetry-mass spectrometry (TG-MS) and pyrolysis-gas chromatography mass spectrometry (Py-GC/MS). The gasification reaction characteristics of co-pyrolysis char were also evaluated. The results showed that both promoting and inhibiting effects existed in the co-pyrolysis process of WCS and CLR. When the pyrolysis temperature was less than 420 °C, the catalysis of minerals was conducive to the pyrolysis reaction. At higher temperatures, the polycondensation and carbonization produced by the interaction between the components inhibited the release of volatiles. The gasification reactivity of co-pyrolysis char was better than that of individual WCS and CLR chars. The synergistic effect was most obvious when the blending ratio of WCS to CLR was 3:1. In the gasification process of co-pyrolysis char, the WCS component with better reactivity preferentially reacted to form an abundant pore structure, which exposed more reactive sites and promoted the diffusion and mass transfer of gasification agent. Moreover, alkali and alkaline earth metal species in WCS and iron bearing minerals in CLR can catalyze the gasification reaction, contributing to the synergistic effect. Therefore, the addition of a suitable solid waste to biomass waste can improve the energy efficiency and simultaneously achieve solid waste utilization. [Display omitted] • Co-thermochemical conversion of biomass and industrial solid waste were conducted. • The formation characteristics of tar and gas during co-pyrolysis were evaluated. • Release of volatiles during co-pyrolysis has both promoting and inhibiting effects. • Co-pyrolysis char has good gasification activity and shows obvious synergistic effect. [ABSTRACT FROM AUTHOR]

• A VFB-LIBS online system was applied for the in-situ detection of released AMs. • The concentration of released AMs in gaseous phase was quantitatively measured. • The temporal release of AMs can be limited in the whole pyrolysis. • The higher content of C = O in coal, the stronger limitation on the release of AMs. • The inhibition of OCFG was not selective for the release of K and Na. Co-pyrolysis of coal and biomass is a promising technology for clean and efficient utilization of these two carbon resources. In this study, a visual fixed bed (VFB) combined with laser-induced breakdown spectroscopy (LIBS) was applied to investigate the effect of O-containing functional groups (OCFG) in coal on the release of alkali metals (AMs) during the co-pyrolysis of coal and biomass. The results showed that low temperature pre-oxidation increased the content of OCFG in coal, especially C=O and O–C=O groups, and limited the release of AMs during the co-pyrolysis. The higher pre-oxidation degree, the stronger limitation on the release of AMs. The increase of OCFG declined the maximum release concentrations of AMs and the temporal release of AMs in the whole pyrolysis process rather than some period. The release ratio of AMs can be maximally reduced about 39% by the OCFG. The relationship between release of AMs and structure of chars during the pyrolysis was also investigated. It was obtained that the layering placement of biomass and coal showed the less volatilization of AMs than the mixing placement of them. This study provided the theoretical basis for mitigating equipment corrosion problems caused by AMs in industrial applications. [ABSTRACT FROM AUTHOR]

In this study, three typical biomass ash (BA) components, KCl, CaCO 3 and SiO 2 , are selected as model compounds to construct BA-based key ternary component system for petroleum coke (PC) gasification. Gas product analysis was conducted using gas chromatography to study the influence of different catalysts on the gas product distribution, gas yield and carbon conversion of PC gasification, and clarify the synergistic effects of binary and ternary components in K-Ca-Si catalytic system. In addition, electron scanning microscopy (SEM) and Raman techniques are used to characterize the physicochemical structure of gasification semi-char to reveal the synergistic mechanism of K-Ca-Si system. The results show that the yield of different gases is ordered as H 2 > CO > CO 2 and the increment of H 2 yield, CO yield, syngas yield and carbon conversion in K-Ca-Si catalytic system is 43.41 mmol/g, 26.67 mmol/g, 80.37 mmol/g and 0.49, compared with single PC gasification, respectively. By comparing the theoretical and actual value of gas yield and carbon conversion, it is found that there are synergistic catalytic effects for K-Ca-Si ternary catalyst, but Si will inhibit the activity of K and Ca. Coupled with SEM and Raman analysis, synergistic mechanism of ternary catalytic system can be revealed. KCl and CaCO 3 reduce the graphitization degree of semi-char by reacting with carbon matrix, and CaCO 3 can stimulate the pore structure development of semi-char, which accelerate reaction between KCl and carbon matrix to form intermediate active sites, thus favoring gasification reaction and exhibiting a synergistic effect. SiO 2 , on the other hand, will combine with KCl and CaCO 3 to form inert silicates, resulting in the deactivation of KCl and CaCO 3. It could be concluded that for high K-high Ca-low Si ternary catalytic system, KCl and CaCO 3 would still show a synergistic effect due to higher CaCO 3 content than SiO 2. [ABSTRACT FROM AUTHOR]

• The difference of Ca-Si-Al interactions on CO 2 and H 2 O gasification was analyzed systematically. • The well dispersed SiO 2 particles cannot adsorb gasifying agent molecule to transfer oxygen. • Newly generated minerals in H 2 O have no ability to prompt the generation of active site. • CaO in Ca+Dem-coal favors mesopore formation, especially in H 2 O. Catalytic steam gasification, as a promising technology for producing hydrogen-enriched syngas, has been a hotspot in recent studies. This study aims to analyze the role of calcium-silicon-aluminum (Ca-Si-Al) interactions in char gasification and distinguish the difference of the interaction in different gasifying agent. The gasification reactivity of coal char was closely linked with the physiochemical structure and the mineral interactions. It was found that whether in CO 2 or H 2 O, the calcium oxide (CaO) has function to promote the generation of mesopores, which is beneficial to the diffusion of reactant and product gases. The scanning electron microscopy (SEM) images showed that no SiO 2 particles agglomerated in coal char containing silicon-aluminum ((Si-Al)-coal), which was a good reason why Si-Al inhibited gasification severely; the well dispersed SiO 2 particles have no function to adsorb the gasifying agent molecular to transfer oxygen. New minerals including Ca 2 Al 2 SiO 7 , Ca 2 SiO 4 and CaSiO 3 were formed in CO 2 and H 2 O, while CaAl 2 Si 2 O 8 only was detected in H 2 O. These new minerals exert a positive effect on active site in CO 2 but negative effect in H 2 O. While in H 2 O, compared with active sites, the mesopores dominate the reaction more. Overall, the interactions catalyze gasification to a moderate degree whether in CO 2 or H 2 O. [ABSTRACT FROM AUTHOR]

• Structural features of residue char from maceral concentrate gasification were revealed. • The shrinkage ability of inertinite char residual is stronger than that of vitrinite. • The fresh vitrinite char has lower order degree and more active sites. • The amount of vitrinite residual char active sites decreases rapidly during gasification. Gasification fine slag contains a high content of carbon, which causes waste of resources and environmental hazards. In essence, fine slag is a comprehensive reflection of the separate gasification of various macerals in coal. In this study, different macerals concentrates were firstly prepared from Yangchangwan (YCW) and Meihuajing coal (MHJ). The structure and pyrolysis characteristics of different macerals as well as the morphology and molecular structure of gasification residue carbon at different conversion levels were then investigated by a series of characterization techniques. The results show that the aromatic degree of inertinite concentrates of both coals is greater than that of vitrinite. During the active pyrolysis stage of 200–600 °C, the weight loss rate of vitrinite is higher than that of inertinite, and the weight loss rate reaches maximum at about 445 °C. Maximum thermal weight loss rate of YCW and MHJ vitrinite is 1.39 and 1.43 times higher than that of inertinite. The shrinkage ability of inertinite char is stronger than that of vitrinite and the surface of inertinite residue carbon is rougher and rich in porous structures during gasification, resulting in a higher final gasification carbon conversion level. The fresh vitrinite char obtained from pyrolysis has lower order degree and more active sites. As the gasification proceeds, the content of active sites in vitrinite gasification residue carbon decreases rapidly, while inertinite remains relatively stable. This research innovatively links the properties of macerals with the structure of residue carbon, which is helpful to deepen the understanding of the correlation between coal microstructure and reactivity. [ABSTRACT FROM AUTHOR]

In this study, the volatile–char interaction in coal and cow manure co-pyrolysis process was decoupled by adding internals in a two-stage fixed bed reactor, and the effect of vapor-residence time on coal char reactivity at 850 °C was investigated. The results indicated that the volatile–char interaction inhibited coal char reactivity, but the inhibition showed an opposite rule with the vapor-residence time in different co-pyrolysis modes. The reformed gas-phase volatiles entered the macromolecular framework of coal and generated PAHs, increasing the aromatization degree and large aromatic rings numbers of char, resulting in the reduction of the O-containing functional groups and the behavioral effects of C–O and C O being particularly pronounced. The interaction promoted the release of Na/K, and the release behavior changed when only volatile−volatile interaction existed in the co-pyrolysis samples. The reduction of O-containing functional groups resulted in the loss of active sites number after the interaction, AAEM showed limited catalytic behavior. The O-containing functional groups and cross-linking structure act as active sites in the interaction process. This work is beneficial to enrich and develop the synergistic transformation theoretical system of carbon-containing energy materials, and provides theoretical support for promoting the industrial application of related technologies. • The interaction behaviour in the biomass and coal co-pyrolysis process was decoupled. • Multifaceted characterization of the in-situ interacting char carbon chemical structure. • The increase of vapor-residence time promoted the precipitation of Na and K. • The interaction process was not conducive to the cracking of alkyl aryl ether. • C–O, C O content and cross-linking structure act as active sites in the interaction. [ABSTRACT FROM AUTHOR]

• The torrefaction method using CO 2 as a medium was used to pretreat the sludge. • The functional groups of CO 2 torrefaction-pretreated sludge has changed. • The CO 2 torrefaction-pretreated sludge can be applied to coal gasification. Take CO 2 as a torrefaction medium is effective in improving fuel performance. This study discusses the possibility of industrial solid waste sludge (SL) pretreated by torrefaction under CO 2 for gasification with Yangchangwan coal (YC). The study was performed in a thermogravimetric analyzer and a high-frequency furnace. The results showed that the optimal torrefaction temperature of SL was 300°C under CO 2 , and its release intensity of gases higher than that of Ar. –OH and C–H were decreased relative to Ar. At 1100°C, the reactivity index R 0.9 of SL pretreated under CO 2 was 1.78 times higher than that of untreated chars. At 1200–1400°C, the R 0.9 of chars was lower than that of 1100°C. The activation energy of chars was showed an overall increasing trend with increasing carbon conversion levels. The torrefaction-pretreated SL under CO 2 can be better applied to high-temperature gasification of YC. [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]

It is necessary to remove the tars present in gasification systems of biomass or low-rank coal to prevent the blockage and corrosion of downstream equipment. In this study, catalysts were prepared using different Ni loading methods: impregnation, pressure impregnation, and ion exchange methods using coal char as a catalyst support for tar removal. The catalyst prepared by ion exchange method showed considerably better performance for the steam reforming of toluene (model tar) compared with the other two catalysts. The oxygen-containing groups of low-rank coal acted as cation-exchange sites, and the oxidation significantly increased the number of oxygen-containing groups. Therefore, the intrinsic correlation between oxidation degree of support and catalytic property was further explored. ICP analysis, XRD spectroscopy, and TEM images confirmed that Ni loading and Ni crystallite size (NCS) significantly depended on the oxidation degree of support. When coal was oxidized with 30% H 2 O 2 and 30% HNO 3 , the Ni loadings of catalysts were 9.9 wt% and 12.1 wt%, and the NCS were 3.5 nm and 4.5 nm, respectively. Compared to HNO 3 , the catalyst prepared using H 2 O 2 pretreatment exhibited a higher toluene removal efficiency. • Char-supported Ni catalysts were prepared by different Ni loading methods. • The catalyst prepared by ion exchange method showed considerable performance. • Oxidation of the support can change the Ni loading and Ni crystallite size. • The catalyst prepared by the H 2 O 2 pretreatment has higher tar removal efficiency. [ABSTRACT FROM AUTHOR]