## 3 Results and Discussion
### Effect of Steam-to-Biomass Ratio  
The steam-to-biomass ratio (SBR) represents a ratio of the mass flow rate of steam to biomass fed into the reactor [48]. Along with operating temperature, the steam-to-biomass ratio is a crucial operating parameter that affects significantly hydrogen production from biomass gasification [49]. The SBR was investigated in this study ranging from 0 to 1.6, and the temperature was at 850 \({}^{\circ}\)C.  
In the following Figures 7-12, the simulation results were compared with experimental data for gas composition at various steam-to-biomass ratios. Generally, the H\({}_{2}\) and CO\({}_{2}\) fractions increase (see Figures 7 and 8), while CO and CH\({}_{4}\) show a downward trend (Figures 9 and 10). In the range of 0 to 0.9, the H\({}_{2}\) concentration rises considerably. Afterward, its increase slows down in the higher SBRs. A steady rise in the content of CO \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{8}{c}{**Mean Error**} \\ \cline{2-7}  & **H\({}_{2}\)** & **CO** & **CO\({}_{2}\)** & **CH\({}_{4}\)** & **Gas Yield** & **CCE** \\ \hline T (\({}^{\circ}\)C) & 0.115 & 0.17 & 0.222 & 0.303 & 0.235 & 0.2 \\ SBR & 0.193 & 0.174 & 0.329 & 0.134 & 0.076 & 0.033 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Analysis of data. Figure 6: Effect of gasification temperature on carbon conversion efficiency. is found in the SBR range from 0.7 to 1.6, reaching a peak of 16.1% at the SBR of 1.6. Those trends of the model predictions are similar to those found from the experimental data. Compared with other species, the difference between simulation results and experimental data in CH\({}_{4}\) content is the lowest, while in the case of CO\({}_{2}\), the fraction is the highest with the mean error of 0.329. The simulation results for hydrogen and carbon monoxide also display a good qualitative prediction of experimental data in the whole range of SBR. The mean errors of the effect of SBR on gas composition, presented in Table 6, are in acceptable ranges. Figure 8: Effect of SBR on carbon dioxide content. Figure 7: Effect of SBR on the hydrogen content. Figure 10: Effect of SBR on methane content. Figure 9: Effect of SBR on carbon monoxide content. The dry gas yield of the product gas as a function of SBR is illustrated in Figure 11. As can be seen in the figure, the gas yield increases rapidly until an SBR of 0.9 before slowing down. It is noted that simulation results for gas yield are better in agreement with measured data from SBR of 1.2. Its mean error is about 0.17 that is acceptable for the investigation of steam-to-biomass ratios. Figure 12 shows the comparison of the simulation results with the measured data for carbon conversion efficiency versus the SBR in the range of 0-1.6. Increasing trends of CCE are observed in both simulation and experimental results. A high SBR improves the gasification process and increases efficiency. The efficiency rises considerably at low SBRs, then its rate decelerates at high SBRs. The high accuracy of model predictions in carbon conversion efficiency compared to experimental data is determined by the mean error of 0.033. Figure 11: Effect of SBR on dry gas yield. Figure 12: Effect of SBR on carbon conversion efficiency. The effect of SBR on the performance of biomass gasification is mainly due to the reactions with the presence of steam. The high amount of steam in the gasifier promotes char gasification and water-gas shift reactions, resulting in increasing hydrogen production and the amount of char consumed. The largest difference in CO\({}_{2}\) content is observed in this evaluation. This error is due to the combustion reactions of char and CO which are neglected. Additionally, this difference could be attributed to equilibrium assumptions. As discussed above, the main error of the simulation is likely attributed to simplified calculations and assumptions during the simulation.