**5. Conclusions**

The one-dimensional sorption enhanced gasification model developed in this study was verified with experimental data obtained from a 200 kW facility at IFK, University of Stuttgart. The results showed that the model is able to successfully predict the performance of the pilot plant at di fferent operation conditions. With this model, the influence of important process parameters, such as gasification temperature, steam-to-carbon ratio, solid inventory, and fuel mass flow, can be simulated. On the basis of gas composition (H2, CO, CO2, CH4, and C2H4), *LHV*, and the *M* module, the model was validated over the whole SEG temperature range. As the activity of the limestone sorbent decreases after several carbonation/calcination cycles, an additional model was integrated, which adapts the carbonation reaction kinetics depending on the circulation rate and molar flow of fresh limestone. With this possibility, three di fferent fresh limestone make-up flow rates (0.2 kg/h, 6.6 kg/h, and 15 kg/h) were simulated. A parametric study revealed a larger dependence on the limestone make-up, especially for gasification temperatures below 650 ◦C. This e ffect probably has to do with the lower circulation rate between gasifier and regenerator and the reduced transfer of fresh CaO into the gasifier with di fferent CO2 capture activities. Increasing the make-up flow rate also increases the bed activity for the same quantity of mass transferred into the gasifier. At higher temperatures, it can be assumed that this e ffect is reduced by limitations of the carbonation reaction equilibrium. Considering the reaction rates in the temperature range between 600 and 750 ◦C, a strong dependency of the limestone make-up on the carbonation reaction can be identified. Furthermore, the water–gas shift reaction is influenced due to the CO2 capture. For the other reactions considered, only a minor influence from the limestone make-up was observed.

Variation of the fuel feeding rate (22 kg/h to 40 kg/h) with a constant *S*/*C* ratio (2.2 mol/mol) revealed an increase of the bed height by a factor of 2. From the gas velocity ratio (*u*/*umf*) along the reactor height, di fferent fluidization states can be recognized. While a low fuel input led to low mixing in certain areas of the fluidized bed (*u* was only higher than *umf* by a factor of 20), high fuel input increased mixing in the whole fluidized bed. However, the entrainment of particles was also higher. Based on these evaluations, the syngas power and the gas velocities of the bubbling fluidized gasifier were described in a performance diagram which is dependent on the gasification temperature and the fuel input. Therefore, the developed model can be used as a fast and reliable engineering tool for reactor design or scale-up purposes.

**Author Contributions:** M.B. is responsible for conceptualization, simulation studies, validation, and original draft preparation. M.B. and M.S. designed the methodology of the software. Writing—review and editing, A.M.P.; supervision, G.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Ministry of the Environment Baden-Württemberg, Germany, gran<sup>t</sup> number BWE13008.

**Acknowledgments:** The authors gratefully acknowledge financial supports from the project BioenergieFlex (BWE13008) funded by the Ministry of the Environment Baden-Württemberg, Germany.

**Conflicts of Interest:** The authors declare no conflict of interest.
