# Recent Advancements in Anaerobic Digestion and Gasification Technology
## 8 Recent Studies on Gasification Focusing on Syngas Production
From the study, it was revealed that high temperature had a positive effect on gas yield and gasification efficiency (GE) due to the Boudouard reaction. As the particle sizes increased, GE first increased and then decreased due to the different heating conditions of the particle, with the highest GE of 88% at 0.8-1 mm obtained. The yield of CO and GE improved with an increase in the flow rate of CO\({}_{2}\) and CO\({}_{2}\) concentration. However, the conversion rate of CO\({}_{2}\) decreased at a large CO\({}_{2}\) flow rate, and the growth rate of GE decreased for CO\({}_{2}\) concentrations greater than 50%. Therefore, the maximum gasification efficiency (GE) reached up to 125% at the recommended optimum temperature, particle size, and CO\({}_{2}\) concentration of 850-900 \({}^{\circ}\)C, 50-100%, and 1 mm, respectively. Gasification efficiency (GE) is defined as the ratio of the low heating value (LHV) of gases to that of biomass feedstock. Synthesis gas composition was obtained from the gasification of biomass involving a mixture of carbon black, resulting from waste tires and sewage sludge. [PERSON] et al. [66] modelled the process via the response surface method, while optimization involved the use of Box-Behnken design. For the syngas composition, the determination coefficient obtained for H\({}_{2}\), CO, CH\({}_{4}\), and heating values was 92.86%, 95.40%, 96.15%, and 96.80%, respectively. These were the indicators used for the modelling using a second-degree polynomial equation. The high determination coefficient reported was an indication that the polynomial equation conformed to a sufficient level with the experimental data. Based on the validation result, the percentages of the H\({}_{2}\), CH\({}_{4}\), and CO were 12.75%, 8.07%, and 7.87%, respectively, whereas the heating value was 1420.3 kcal/m\({}^{3}\). The findings from the study confirmed that the gasification process was suitable for the production of high-quality syngas from waste material and recommended the use of the Box-Behnkan design for the optimization of the process. To produce syngas, [PERSON] et al. [67] employed the use of a catalyst during the gasification of wood residue in a fluidized bed gasifier while using a combination of air and steam as an oxidizing agent. During the study, the following parameters were considered; catalyst loadings (20%, 30%, and 40%) at residence time (20, 40, and 60 min) and temperature (750, 825, and 900 \({}^{\circ}\)C). The authors revealed that a high temperature of 900 \({}^{\circ}\)C, catalyst loading of 40%, and residence time of 60 min was found most suitable to produce syngas of high quality. To facilitate the optimization of energy efficiency and economic viability of biomass gasification, [PERSON] et al. [68] developed a gasification model. The model aimed to predict the rate of production and quality of syngas. It was mentioned that the three regions of the velocity profiles (natural convection region, mixed convection region, and forced convection region) were used for the development and building of the model. From the study, it was observed that the developed model provided accurate predictions against experimental data; nonetheless, there was a deviation of approximately 10%. Moreover, an equivalence ratio of 0.25 was found suitable for maximizing the economic benefits of biomass gasification. Air steam gasification of pine sawdust with calcined cement as a catalyst was investigated for the production of syngas. The study was motivated by the operational problems relating to the formation of tar during gasification. As a result, tar was minimized in the producer gas due to catalyst cracking. According to [PERSON] et al. [69], the employment of cement as a catalyst enhanced the hydrogen concentration and lowered the tar yield.