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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, a heating stage microscope and a thermogravimetric analyzer were adopted to explore behaviors of char-slag/ash transition during CO 2 gasification of rice straw (RS) and Neimeng lignite (NM). Effects of demineralized treatment and various gasification temperatures on the char-slag/ash evolution process were studied. Both RS and NM particles exhibited shrinkage particle form at a moderate reaction temperature (1000 °C). The variation of the existential state of K with char-slag/ash transition could well explain the reactivity differences between RS raw char and demineralized char. Compared to RS raw char, NM raw char showed a more significant flow of molten slag at 1350 °C, which accounted for the high inhibitory effects at the late stage of NM raw char gasification. There is a threshold conversion (x = 0.9) during the evolution processes of NM char samples to NM slag/ash at 1200 °C and 1350 °C, while this threshold value is only existing at 1000 °C for RS char gasification. [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]

[Display omitted] • Isothermal prediction based on model-free method was established. • Kinetic parameters form model-free and model-fitting method were compared. • Gasification mechanism was revealed from carbon and pore structure evolution. • The fractal dimension D 1 was related with amorphous structure. • Mesopore SSA increased by hundred times whereas active sites changed insignificantly. Biomass gasification integrated with leaching pretreatment can be conducive to the sustainable energy system. In this work, the biochar gasification was studied from structure to reactivity with the consideration of leaching pretreatment. The biochar was prepared from raw and leached corn straw (CS) and corncob (CC) in a fixed bed reactor. The gasification was performed in thermogravimetric analyzer with the emphasis on kinetic parameters comparison and reactivity prediction. The carbon and pore structure were investigated to reveal gasification mechanism. The prediction procedure based on model-free method was proposed. From the results, compared with CS, leaching pretreatment reduced gasification reactivity of CC considerably according to reactivity index and reactivity prediction. The random pore model showed the best fitting performance. Furthermore, the leaching pretreatment reduced inorganics (mainly K) in CS and CC, and removed water-soluble organics (pectin) in CC. The active sites and surface roughness in leached biochar decreased accordingly. The CO 2 gasification can activate initial biochar after pyrolysis. Specifically, the specific surface area of mesopore increased by hundred times and more active sites were also generated. However, as the gasification proceeding, the active sites and the fractional dimensions changed insignificantly for both raw and leached biochar. The leaching pretreatment mainly promoted the micropore development during gasification. The pore structure evolution was consistent with the carbon structure, which appeared to be correlated with the kinetic analysis. The research gives new insight into structure-performance correlation of biomass gasification and provides the implication for sustainable energy system based on gasification technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combining wet torrefaction (WT) and pyrolysis for bioresource utilization. • Global reactivity was inhibited whereas local reactivity could be promoted by WT. • WT changed the structure and reactivity of softwood biochar significantly. • WT temperature had limited effect on AAEMs removal efficiency in biochar. • Relationship between X - T - t was determined by model-free method. This study investigated the effect of wet torrefaction (WT) on biochar property derived from softwood (PIW) and hardwood (POW) pyrolysis. The biochar gasification was performed in a thermogravimetric analyzer, followed by kinetic modelling. The biochar structure was analyzed, including inherent metals, pore structure and carbon structure. The results showed that WT affected reactivity and structure of PIW-derived biochar more than that of POW-derived biochar. The critical WT temperature determined the reactivity changes together with kinetic parameters. The WT affected the inorganic and organic component in biochar simultaneously. As results of WT, more than 70 and 50% ion-exchanged AAEMs in PIW-derived biochar and POW-derived biochar were removed. Nevertheless, the organic structure had essential effect on the gasification reactivity. More pronounced structure evolution of PIW-derived biochar was observed, including lower mesopore surface area, more graphite structure and small rings. This research provides new insights into the structure–reactivity correlation for biochar utilization. [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]

• 300 °C torrefaction reduced gasification reactivity mainly in midterm and late stage. • Low-temperature torrefaction had slight effect on char gasification reactivity. • Gasification kinetics were analyzed based on the gas-solid reaction methods. • Pathways of char structure evolution changed after 800 °C pyrolysis. • Gasification reactivity decreased significantly for chars pyrolyzed after 800 °C. In this study, the effect of torrefaction on the gasification reactivity of chars from raw and torrefied biomass was investigated. Three torrefaction temperatures and four pyrolysis temperatures were taken into consideration. It was found that the severe torrefaction (300 °C) would reduce the char gasification reactivity by at least 19% according to the normalized gasification rate. Moreover, the reduction of gasification reactivity appeared after the midterm stage. The gasification reaction were further analyzed by nucleation/growth model and model-free method. The activation energy increased by ~80 kJ/mol with conversion, indicating an enhancement of the reaction resistance. Furthermore, 800 °C pyrolysis was found to be a turning point, beyond which the gasification reactivity reduced significantly. These reactivity changes were implied by the bio-char structure evolution and active alkali and alkaline earth metals (AAEMs) contents variations. The research results provide insights into the effect of torrefaction on biomass gasification. [ABSTRACT FROM AUTHOR]

• Structure of pyrolytic coal–biomass blends were not additive function of composition. • Co-pyrolysis enhanced the transformation of ion-exchanged AAEMs in residue char. • Synergy of isothermal co-gasification changed from inhibition to promotion. • Maximum reaction rate of non-isothermal co-gasification was increased. This work investigated the structural evolution of rapid co-pyrolysis char and its influence on co-gasification characteristics. The chars were prepared in a high frequency furnace at 900 °C with the heating rate of 300 °C/min, using Xinjiang lignite and cotton straw as raw materials. Blends of coal and biomass were prepared in proportions of 25:75, 50:50 and 75:25 wt.%. Compared to the individual pyrolysis, co-pyrolysis enhanced the transformation of ion-exchanged alkali and alkaline-earth metals (AAEMs). Moreover, the surface area of co-pyrolysis chars were enhanced, and the carbon structure of biomass char in mixtures became more ordered. The gasification reactivity of co-pyrolysis char was evaluated by thermogravimetric analyzer (TGA), including isothermal (800, 850 and 900 °C) and non-isothermal (5 °C/min) gasification using CO 2 as agent. For isothermal gasification, the synergistic effect of reactivity changed from inhibition to promotion with the increasing conversion. The synergy index changed obviously at 800 °C. For non-isothermal gasification, the maximum reaction rate was increased. The blends with 75% biomass had the minimum activation energy. The co-gasification reactivity varied with the temperatures, biomass blending ratios and conversions, which were well related to the char structural evolution caused by rapid co-pyrolysis. [ABSTRACT FROM AUTHOR]

• Fractal dimension was performed to quantify the structure complexity of soot. • The gasification reactivity is highly dependent on the graphitization degree. • Natural gas-derived soot has a potential replacement of N330. • Coal/Biomass-derived soot has better gasification reactivity than natural gas-derived soot. Soot formation has been a hurdle to the development of entrained flow gasification (EFG) technology, as it damages the apparatus and remains a pollutant. Soot has a poor gasification reactivity in the multiphase flow in furnace. In this study, differences in physicochemical properties and their relationship with gasification reactivity were revealed for natural gas-derived soot (NGS), coal-derived soot (CS), and biomass-derived soot (BS) from EFG process. A comparative study was also conducted between the gasifier soot and a commercial carbon black (CB), N330. The thermogravimetric analyzer (TGA) results showed the descending order of the activation energy (E a) of gasifier soot was NGS > BS > CS, in both CO 2 and H 2 O gasification process. Transmission electron microscopes (TEM) and Raman spectrum further determined that the gasification reactivity was highly dependent on the carbon content, carbon type, and graphitization degree but less dependent on soot microstructure. This study also investigated the potential replacement of commercial N330 as a rubber reinforcement additive with soot as a pollutant. This replacement was based on the microstructure similarities between soot and CB, as determined using fractal dimension (D p) as an indicator on a statistical level from TEM. The D p of NGS was 1.35, 1.06 times larger than that of CS, and 1.22 times larger than of BS. It was highly feasible that NGS would have the close physical property of N330 and could potentially replace the expensive N330 as a rubber reinforcement material. [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]

[Display omitted] • An integration of pilot-scale HTC, gasification, and anaerobic digestion for EFB conversion was investigated. • Inherent AAEMs have significant effects on gasification products. • CO and H 2 were enhanced under CO 2 /O 2 gasification. • Liquid products from HTC can be utilized for methane production via anaerobic digestion. • The mass and energy balance revealed that the whole process could be feasible. In the context of evolving a circular economy for the palm-oil industry, this article presents a study of oil-palm empty fruit bunch (EFB) conversion and utilization within a palm-oil mill. Pilot-scale hydrothermal carbonization (HTC), washing and gasification processes, as well as anaerobic digestion of the HTC liquid product were investigated. Results showed that the fuel properties of hydrochars had improved. In terms of air gasification, char and tar products accounted for 22.7–33.8 % and 17.3–28.8 %, respectively while CO 2 /O 2 gasification resulted in 31.3–36.6 % for char and 8.5–30.8 % for tar. In general, hydrochar (HT-EFB) gave the lower tar content compared to washed hydrochar (HTW-EFB) due to the catalytic effects of alkali and alkaline earth metals. Major tar components from HT-EFB and HTW-EFB were aliphatic and monoaromatic hydrocarbons, respectively. Syngas products from air gasification of hydrochars were 39.9–56.5 %, 11.4–21.4 %, and 9.0–14.4 % for CO, H 2 and CH 4 , respectively while CO 2 /O 2 gasification products yielded 45.1–56.6 %, 11.6–24.3 %, and 9.4–14.0 % for CO, H 2 and CH 4 , respectively. The lower heating value of syngas was in the range of 4.7–6.6 MJ/Nm3 and cold gas efficiency was approximately 39.1–55.1 %. The cumulative methane from the liquid products amounted to 213.8 and 154.5 L/kg COD for food/microorganism ratios of 1:2 and 1:3, respectively. The mass and energy balance showed that the whole process is promising for future commercialization. [ABSTRACT FROM AUTHOR]

Despite a small proportion of mineral in coal, inherent alkali and alkaline earth metals (AAEM) catalytically affected thermal conversion of coal. The gasification of raw and leached coal char was investigated by using an operando microscopic Raman spectroscopy to explore the effect of content and chemical form of the inherent AAEM on morphology and carbon structure evolution of a single particle during in-situ char gasification. The removal of water-soluble and ion-exchangeable AAEM reduced the R 0.5 of SF, NM and YN char by 53.31%, 49.09% and 35.02%, respectively. As a result, the shrinkage of leached coal char progressed slower than that of the raw coal char. Besides, both water-soluble and ion-exchangeable AAEM accelerated char gasification because of an inhibition of the orderly evolution of carbon structure. Higher gasification temperature weakened the catalytic performance of ion-exchangeable AAEM. With the consumption of carbon, carbon microcrystalline structure of the residual char tended to be ordered, which led to a decrease in active free carbon sites for gasification reaction. Kinetic analysis indicated both water-soluble and ion-exchangeable AAEM reduced the activation energy of SF, NM and YN char by 20.97, 20.82 and 9.38 kJ∙mol−1, respectively, and the effect of ion-exchangeable AAEM was more significant. • Coupling in-situ analysis of particle shrinkage and carbon structure was conduct. • Water-soluble AAEM had more significant effects on carbon structure evolution. • Catalytic performance of ion-exchangeable AAEM was better. • Evolution of carbon structure affected catalytic mechanism of AAEM. [ABSTRACT FROM AUTHOR]

Biomass gasification is a promising technology in current and future low carbon energy systems. Soot formation is a great technical challenge for the industrialization of biomass gasification that is inevitable at high temperature and fuel rich conditions. In this review, a comprehensive summary of soot formation in biomass gasification is provided with special focus on entrained flow technologies. The topics covered the state of the art knowledge of soot formation in different gasifiers, the fundamental knowledge, experimental methods and recent control strategies. Soot generation and oxidation mechanism are discussed while the relationship between soot, tar and char in biomass gasification are analyzed in detail. Reaction models for soot formation coupled to the gasification process are introduced, including (semi-)empirical and detailed models. Effect of biomass components and ash forming elements on soot formation are highlighted. This is followed by a detailed description of in-situ and ex-situ experimental measurements, such as the optical diagnostics, aerosol particle mass analyzer and mass spectrometer. Soot formation characteristics and properties in different types of gasifiers are then addressed in detail with an emphasis of entrained flow gasifiers. Finally, the soot control strategies in biomass gasification are reviewed and evaluated. This review concludes by summarizing the available knowledge and challenges in soot formation during biomass gasification. • State-of-the-art knowledge of soot formation in different gasifiers is reviewed. • Mechanism and model of soot formation and oxidation are summarized. • Effect of biomass components and ash on soot formation are highlighted. • Flow manipulation technique and catalytic gasification could suppress soot formation. [ABSTRACT FROM AUTHOR]