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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]

[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]

• 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]

[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]

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]