# Biomass-Based Chemical Looping Gasification: Overview and Recent Developments
## 4 Effect of Process Parameters on Biomass Chemical Looping Gasification
### Biomass Characteristics  
Biomass is a complex mixture of organic and inorganic substances. [PERSON] et al. [48] categorized types of biomass based on their biology diversity, source, and origins, such as woody plant, herbaceous and agricultural plants/grasses, aquatic plants, human and animal waste, contaminated and industrial waste biomass, and biomass mixtures. [PERSON] and [PERSON] [104] characterized biomass as follows:  
1. The chemical constituents: cellulose, hemicellulose, and lignin. 2. Elemental composition. 3. Inherent mineral content. 4. Proximate analysis: moisture, volatile, fixed carbon, and ash contents. 5. Physical properties: particle size, shape, and density. All these parameters have been investigated their effects on the product gas composition, yield, and process performance. The properties of different types of biomass are shown in Tables 4 and 5. Many studies have been carried out on various types of biomass for gasification and BCLG. Generally, the higher content of cellulose and lignin produces more gaseous products resulting in the increasing potential of hydrogen recovery from biomass. The hydrogen production from biomass gasification is attributed to the intrinsic properties, moisture content, and alkali content [105]. Additionally, biomass with high contents of oxygen and hydrogen results in highly liquid and volatile yields, thereby reducing the overall energy conversion efficiency of the combustion process. Furthermore, higher H/C ratios in fuels generate a greater heat of combustion, whereas higher ratios of O/C produce more CO\({}_{2}\) emission per amount of energy release [47; 106]. A simplified summary of biomass pyrolysis is illustrated in Figure 9 [107]. Some studies [108; 109; 110; 111] found that biomass with the proportions of cellulose and hemicellulose are directly related to higher CO and CO\({}_{2}\) concentrations, while higher lignin content leads to a higher char yield and CH\({}_{4}\) concentration during the pyrolysis process. Consequently, those intermediate products can vary in the final composition of the product gas. [PERSON] et al. [112] carried out an experimental study on biomass gasification for hydrogen production in a fluidized bed reactor. They gasified three different types of biomass (\(\alpha\)-cellulose, bagasse, and mushroom waste) at different temperatures (600-1000 \({}^{\circ}\)C), steam-to-biomass ratios, and equivalent ratios. The results showed that the highest hydrogen production was obtained in the case of using \(\alpha\)-cellulose, which has higher contents of carbon and hydrogen than those of the other species. [PERSON] et al. [113] studied the effect of torrefaction pretreatment on biomass gasification performance at different reaction temperatures (700-850 \({}^{\circ}\)C) and the steam-to-biomass ratio (0.6). In the study, biomass feedstock was Poplar wood and its torrefaction products. The hydrogen content increased corresponding to the increment of torrefaction degrees. Biomass particle size influences significantly the performance of biomass gasification and hydrogen production. Biomass with smaller particles provides a larger surface area per unit mass resulting in improving heat and mass transfer which promotes the gasification reactions (Boudouard reaction, water gas reaction) to produce significantly H\({}_{2}\) and CO. Several studies have been conducted to analyze the effect of biomass particle size on gasification reactions. [PERSON] et al. [114] found that CH\({}_{4}\), CO, and C\({}_{2}\)H\({}_{4}\) were produced more in the case of the smaller particles while less CO\({}_{2}\) was formed, and larger particles showed greater heat transfer resistance which led to incomplete pyrolysis and a higher amount of unreacted char. [PERSON] et al. [115] reported that the smaller particle size of the fuel improves mass and heat transfer due to higher external surface area/volume resulting in