## 3 Results
### Thermochemical Transformation of Briquette cyanobacteria in Single Fluidized Bed  
#### 3.3.1 Thermochemical Transformation with Quartz Sand as Bed Materials  
In order to study the thermochemical transformation of cyanobacteria, a series of tests about briquette samples were conducted in a single fluidized bed. At first, the tests with quartz sand were considered blank experiments to analyze the effect of the presence of hematite OC in the CLC of briquette cyanobacteria. The particle size of quartz sand and hematite are in the same size range of 0.3-0.45 mm. The briquette cyanobacteria sample was densified at the compressive load of 1 ton and the moisture content of 10%. The fluidizing agent of N\({}_{2}\) was fixed at 1.5 L/min, and steam flow was at 0.8 g/min. The steam was preheated at 180 \({}^{\circ}\)C and then introduced to the bottom of the fluidized bed as a gasification agent. The mass of quartz sand added into the reactor was 30 g, and the mass of briquette cyanobacteria was 0.5 g.  
Based on the previous conclusion, 10% is the optimal densification moisture content for the mechanical strength of briquette cyanobacteria, no matter its drying or devolatilization process. For the thermochemical transformation in a single fluidized bed, the gasification agent, i.e., steam, would possibly change the inner water content of the briquette cyanobacteria. Therefore, the mechanical strength change was not studied in this part, and the focus of the research was on the carbon conversion rate, gas yield and hematite oxygen carrier stability. Figure 15: Devolatilization process from the TGA reactor: the effects of compressive load, moisture content and heating rate on the forming rate and relax density (target temperature: 500 \({}^{\circ}\)C; compressive load: 1, 3 and 5 tons; moisture content: 5, 10 and 15%; heating rate: 10, 15 and 25 \({}^{\circ}\)C/min). Figure 16a-d shows the variations in gas concentrations of CO, CO\({}_{2}\), CH\({}_{4}\) and H\({}_{2}\) over time at different temperatures (750, 800, 850 and 900 \({}^{\circ}\)C). The biquette cyanobacteria in a single fluidized bed experience the whole transformation process, including drying, devolatilization and char burnout process. Meanwhile, char burnout is the longest duration process of biomass combustion following the drying and devolatilization process. In Figure 16, all of the gas concentrations show a similar changing trend, which increases during initial minutes and then decreases. The initial concentration increases in CO, CO\({}_{2}\), CH\({}_{4}\) and H\({}_{2}\) were mainly caused by the release of volatiles and the gasification reaction by steam. The peaks of CO, CH\({}_{4}\) and H\({}_{2}\) appeared at the first minute, and the peak of CO\({}_{2}\) was at the second minute. Additionally, the peak values increased with the temperature. It is inferred that the gasification process of biquette cyanobacteria in a single fluidized bed is enhanced by increasing temperature. The degree of gasification promotion needs to be further studied. Figure 17 shows the variations in the carbon conversion of biquette cyanobacteria in a single fluidized bed at different temperatures. The carbon conversion could reflect the biquette cyanobacteria combustion efficiency or transformation content. All carbon conversions dramatically increase during the initial 2 min and then increase slightly. The carbon conversion curve almost displayed a linear relationship with time during the initial 2 min. The duration time of carbon conversion increasing is longer with the temperature increasing. It is found that the carbon conversions at 750 and 800 \({}^{\circ}\)C remain almost unchanged from the 6 th minute, while the carbon conversions at 850 and 900 \({}^{\circ}\)C keep increasing. The final carbon conversions reach to about 35, 42, 55 and 65% at 750, 800, 850 and 900 \({}^{\circ}\)C, respectively.