# Biomass-Based Chemical Looping Gasification: Overview and Recent Developments
## 4 Effect of Process Parameters on Biomass Chemical Looping Gasification
### Gasification Temperature  
Temperature is one of the most significant factors in gasification since the gasification process is a thermochemical conversion process that uses heat to convert the fuel into product gas. Generally, most of the biomass gasification reactions are endothermic reactions, an increase in temperature promotes them. Additionally, higher temperatures increase the heating rate among the particles resulting in effective destruction of the particles and proceeds for complete gasification reactions [22]. Consequently, more yield of gaseous products is generated, and the amount of unreacted char reduces.  
Many researchers have studied the relationship between gasification temperature and process performance, as well as hydrogen production. As shown in Figure 10, hydrogen content slightly decreases in most cases, whereas studies conducted by [PERSON] [27] and [PERSON] [34] show a small increase in hydrogen fraction in the product gas. The possible explanation supporting this trend can be referred to [PERSON]'s principle. Elevated temperatures favor the reactants in exothermic reactions and the products in endothermic reactions. As a result, the endothermic reactions in gasification would be strengthened with an increase in temperature which leads to an increase in the content of H\({}_{2}\) and CO, as well as more solid char is consumed to produce gaseous products. Furthermore, higher temperature also promotes cracking heavier hydrocarbon and tars.  
Additionally, elevated temperature improves gas yield and process efficiencies during the BCLG process. [PERSON] et al. [42] reported that the total gas yield increased significantly with the gasification temperature. Additionally, the concentration of CO and CH\({}_{4}\) increased, while there was a slight decrease in the yield of H\({}_{2}\) and CO\({}_{2}\). [PERSON] et al. [27] investigated that H\({}_{2}\) content increased to the maximum value of 49.47% at 820 \({}^{\circ}\)C, then slightly dropped to approximately 47% at 880 \({}^{\circ}\)C. They also found that CGE increased with increasing temperature and reached a peak at 820 \({}^{\circ}\)C. [PERSON] et al. [117] carried out a study on BCLG in a 25 kW\({}_{\text{th}}\) reactor using natural hematite as oxygen carrier. The temperature range in the study was between 800 and 900 \({}^{\circ}\)C. The results showed that hydrogen concentration reached the maximum value at 860 \({}^{\circ}\)C, then it decreased considerably to 30.77% at 900 \({}^{\circ}\)C. Gas yield showed a similar trend with hydrogen content, while carbon conversion efficiency increased with elevated temperatures. In a study of BCLG using NiFe\({}_{2}\)O\({}_{4}\)[34], carbon conversion efficiency and syngas yield increased from approximately 26% and  
Figure 10: Hydrogen concentration as a function of fuel reactor temperature.  
0.32 m\({}^{3}\)/kg\({}_{\text{biomass}}\) from 700 to 850 \({}^{\circ}\)C. These variations of gas concentrations and total gas yield are related to a series of competing reactions in the gasifier. Under high temperatures, biomass pyrolysis, heavier hydrocarbon, and tars are promoted increasing gas yield and gas concentrations. High temperatures also thermodynamically favor the reactants in exothermic reactions and the products in endothermic reactions. At high temperatures, the reactivity of oxygen carriers with combustible gases is promoted, resulting in a reduction in the content and yield of hydrogen. This is rarely stated in small-scale experimental studies, but larger FR temperatures also mean that a higher heat transport (i.e., solid circulation) is required in the CLG unit.