## 3 Results and Discussion
### Influence of Gasification Temperature on the Release Rate of Alkali Metals  
The release rates of K and Na during gasification versus an increasing temperature are shown in Figure 3. The temperature on the release of Na is complicated. However, the release rate of Na is up to 50.2-70.8%, which means that the Na is easily released to its gas phase. [PERSON] has explained this phenomenon as Na reacting with Cl to form NaCl [35]. At 700-800 \({}^{\circ}\)C, with a temperature increase, the release rate of Na increases with non-linear growth. This may because of the following. First, during the gasification process, that part of the Na which is released to its gas phase in the fuel gas is transferred to solid char. With a temperature increase, the mass transfer coefficient of gaseous Na to solid char increases, and makes the alkali metal transfer faster to solid char. Second, with a temperature increase, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Alkali Metals** & **Water-Soluble** & \begin{tabular}{c} **Ammonium** \\ **Acetate-Soluble** \\ \end{tabular} & \
\begin{tabular}{c} **Hydrochloric** \\ **Acid-Soluble** \\ \end{tabular} &
\begin{tabular}{c} **Aluminosilicate** \\ **Combination-Soluble** \\ \end{tabular} & **Total** \\ \hline Na (mg/g low-temperature ash) & 6.34 & 3.33 & 1.14 & 0.53 & 11.34 \\ Proportion of total Na (\%) & 55.91 & 29.35 & 10.07 & 4.65 & 100 \\ K (mg/g low-temperature ash) & 49.96 & 25.06 & 7.38 & 1.47 & 83.86 \\ Proportion of total K (\%) & 69.64 & 20.73 & 7.87 & 1.76 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Occurrence modes and contents of alkali metals in rice straw. Figure 2: Effect of gasification temperature on combustible gas composition (air flow rate of 0.7 m\({}^{3}\)/h, biomass feed rate of 0.11 kg/h). _LHV_: low calorific value. the Na in the raw rice straw would be trapped and would interact with SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) in the bed material to form sodium aluminosilicates with low volatility according to the reactions (1) and (2) [34], which would result in the release rate of the Na in the gaseous phase being reduced. Third, the higher the temperature is, the more sufficient is the gasification conversion rate. Therefore, more Na adsorbed in the char can expose the surface to release it in its gaseous phase. Fourth, as shown in Table 1, the volatilization of rice straw is high (76.28%), so that with a temperature increase, a large amount of volatile material would be released quickly. So, a large number of free radicals would be released for thermal action. The free radicals released can react with the Na combined in the carbon substrate and improve the Na's evaporation to its gaseous phase. There is a competitive relationship between the factors 1, 2, 3 and 4. Therefore, the release rate of Na does not linearly increase with temperature. \[2\text{NaCl}+\text{SiO}_{2}+\text{H}_{2}\text{O}=\text{Na}_{2}\text{SiO}_{3}+ 2\text{HCl} \tag{1}\]  
\[2\text{NaCl}+\text{Al}_{2}\text{O}_{3}+6\text{SiO}_{2}+\text{H}_{2}\text{O}= \text{Na}_{2}\text{Si}_{3}\text{O}_{8}+2\text{HCl} \tag{2}\]  
The release rate reached the highest value of 70.8% at 750 \({}^{\circ}\)C. In this period, the evaporation of Na was faster than the conversion of non-volatile formation. However, when the temperature was higher than 750 \({}^{\circ}\)C, the release rate of Na decreased. It means that the conversion rate of non-volatile formation was much faster at 750 \({}^{\circ}\)C. Above all, the trend of the points appeared to be consistently increasing but nonlinear with gasification conversion. It can be deduced that temperature is not the only factor that impacts Na emission. The release rate of K had an obvious step with the gasification temperature that was different from the high Na evaporation [35]. The release rate of K can be divided into two stages. The first stage is considered invariable below 700 \({}^{\circ}\)C, where the release rates of K range from 23.3% to 26.0%.