Table 2.

Gasification progression essentials with their merits and demerits. Reprinted with permission from Ref. [130].

Procedure rudiments	Merits and demerits
Gasifier	Categories of reactor: •Fixed bed: Downdraft and updraft are fit for temporary employment and raw materials with low gaseous material and high ash, including excellent moisture contents. •Fluidized bed: Bubbling and circulating beds are fit for the wide-scale product, homogenous dispersion of biomass scrap, including heat, uniform mixing, and low tar generation. •Entrained flow: Beneficial to an extensive section, helpful to coal gasification owing to high heat and low residence period. Not fit for biomass owing to high moisture, including robust content into biomass.
Gasifying agent	The different gasification agents including oxygen, air, steam besides combinations of: •Air: Helpful and cost-effective to small and lab-scale, the difficulty of high N2 content including the lower heating value of fumes, not fit for CH4 generation. •Oxygen: It is efficient for an extensive range but expensive for a small range, with no N2 content obstacle, including eliminating side reaction. •Steam: Beneficial for H2 generation, no N2 dilution obstacle, expertise in the elimination of extra steam, cost-effective for both short and extensive range.
Catalyst	Three kinds of substances are applied: •Dolomite: Cost-effective, expertise in distribution, beneficial to tar conversion, including CO2 adsorption. The difficulty of thermal resistance in higher heat and fluidized state. •Alkali and Alkaline earth material: It is suitable for tar conversion, good variety of produce gas-based, excellent stability of coke removal. It has the limitation of huge price, accumulation at high heat, blockage, no improvement, and high ash generation. •Nickel: General and economic catalysts suitable for tar conversion, including higher H2 content. It has a limitation in short active time, no recovery, and removal of coke at the catalyst.