Syngas from biomass gasification can be used in downstream process industries such as city gas, hydrogen production, etc. In this review, the effects of biomass feedstock properties, and gasification reaction conditions (temperature, gasifier type, etc.) on syngas properties are systematically reviewed. In summary, the cracking and reforming of volatile fractions in the gasification process and the catalytic effect of alkali and alkaline earth metals in the ash on the gasification have a direct impact on the syngas yield. And biomass pretreatment (i.e., terrifying/hydrothermal carbonization) can reduce the moisture content, which can effectively reduce the energy required for gasification and enhance the calorific value and syngas yield further. The fixed-bed gasifiers produce lower amounts of syngas. The concentration of H₂ is significantly increased by adding steam as a gasification agent. Additionally higher gasification temperatures produce more syngas, and an equivalence ratio of about 0.2-0.3 is considered suitable for gasification. For the influence of feedstock on syngas, this paper not only reviews the feedstock properties (volatile, ash, moisture) but also compares the influence of two pretreatments on syngas yield and proposes that the combination of torrefaction/hydrothermal carbonization and a multistage air bed gasifier is an important research direction to improve the combustible components of syngas. In addition to the summary of commonly used single gasification agents, two or more gasification agents on the concentration of syngas components are also discussed in the gasification parameters, and it is suggested that further research into the use of more than one gasification agent is also important for future syngas production.

The primary aim of this study is to understand the effect of metal oxide flux on the fusibility of high-calcium coal ash. Based on the decomposition rate, the evolution of mineral matters in high-calcium coal has been investigated. The ash fusion temperatures of samples are measured by adding different flux Al₂O₃, Na₂O, K₂O, MgO, and TiO₂. The results show that Na₂O is the most effective in lowering ash fusion temperatures and its flow temperature could be 110 °C lower than that of the original ash. FactSage is used to calculate the proportion of solid phase and the mineral compositions as a function of the ash compositions and temperature. With the increase of Na₂O, mineral matters with a low melting point form in the mixture. Furthermore, the decomposition rate of mineral matters increases in the first stage. The phase diagrams and relative mineral variation illustrate that the mineral and the decomposition rate variations are the main reasons for the change of ash fusion temperatures.