# Study of the Applicability of Thermochemical Processes for Solid Recovered Fuel
## 3 Results
### Gasification  
According to the procedure explained in Section 2.3.3 (Equation (10)), the heat generated or required in the gasification process has been calculated (\(Q\)) and displayed in Table 7. The values obtained indicate that, considering the gasification gas composition obtained experimentally (Table 5) and 15% heat losses in the gasifier, air gasification of dry SRF with an ER = 0.296 at 800 \({}^{\circ}\)C is an exothermic process (negative value for \(Q\)), but air/steam gasification with S/C = 1 and ER = 0.377 is endothermic (positive value for \(Q\)). These results suggest that air gasification of dry SRF at 800 \({}^{\circ}\)C could be performed with a lower ER than 0.296, which would improve the gas quality, but air/steam gasification would require higher ER to be autothermal, which would result in poorer gas quality. This important difference in the enthalpy balance of the gasification among both conditions arises from the important difference in the enthalpy of the feedstock, caused by the significant feed of liquid water to the system. Therefore, to improve the enthalpy balance and obtain an autothermal process, reducing moisture in the input SRF stream is another possible option for the gasification route. Combustion of the gasification gas and subsequent steam generation allows energy recovery from the gasification process. The enthalpy balance developed for this process is similar to the one carried out for the SRF combustion (Section 3.2). Tables 8 and 9 show, respectively, the mass and energy balance results for the combustion of the gasification gas obtained from air and air/steam gasification experiments. As commented before, 1 kg of dry SRF fed to the gasifier has been considered as the calculation basis for mass and energy balances. The temperature of the flue gas produced in the combustion of the syngas from air gasification is higher than the one from the combustion of the gas stream produced in air/steam gasification, because although the amount of gases generated during air gasification is lower, its LHV is much higher. The results obtained for the enthalpy balance in the gasification process and in a heat exchanger are presented in Table 9. The energy recovered to produce high-pressure steam in the heat exchanger is directly related to the amount of hot flue gas entering the exchanger and its temperature. The flue gas temperature was significantly higher when syngas from air gasification was burned (2112 \({}^{\circ}\)C) than when burning the syngas from air/steam gasification (1647 \({}^{\circ}\)C). Therefore, the high-pressure steam production rate was higher in the first case (4.12 vs. 3.53 kg/kg dry matter in SRF), and, in turn, more enthalpy was recovered as high-pressure steam when the fuel gas was produced by air gasification instead of air/steam gasification. Furthermore, air gasification was found to be an exothermic process (\(Q=-3.43\) MJ), while air/steam gasification was found to be endothermic (\(Q=+2.23\) MJ), so these energy terms should be considered to calculate the final energy that could be recovered from the entire process. In the first case, the total thermal energy recovered is the sum of the high-pressure enthalpy and the heat released during air gasification, while in the second case the energy required for air/steam gasification must be subtracted from high-pressure enthalpy. Finally, by subtracting the energy required for SRF drying, the final net energy benefit can be obtained. \begin{table}
\begin{tabular}{c c c} \hline
**Test Number** & **1** & **2** \\ \hline Experiment code & T800\_S/C0\_ER29.6 & T800\_S/C1\_ER37.7 \\ \hline Moisture of the input SRF stream to gasification (\%) & 0 & 33.7 \\ \hline Energetic assessment in gasification trials & & \\ \hline \(\Delta h_{input}\) (MJ/kg of dry matter in SRF) & \(-2.78\) & \(-10.87\) \\ \(\Delta h_{output}\) (MJ/kg of dry matter in SRF) & \(-6.21\) & \(-8.64\) \\ \(Q\) (MJ/kg of dry matter in SRF) & \(-3.43\) & \(2.23\) \\ \hline \end{tabular}
\end{table}