# A Detailed One-Dimensional Hydrodynamic and Kinetic Model for Sorption Enhanced Gasification
## 1 Introduction  
Global greenhouse gas (GHG) emissions have been increasing exponentially for the past 60 years, mostly due to the use of oil, coal, and natural gas [1; 2]. Hereby, CO\({}_{2}\) is the major GHG, accounting for 65% of the total amount. Replacing the usage of fossil fuels in combustion or gasification processes with biomass enables the reduction of CO\({}_{2}\) emissions.  
Sorption enhanced gasification (SEG) has been considered a promising technology for tailored syngas production with in situ CO\({}_{2}\) capture. The plant configuration of a SEG process is based on the conventional steam gasification process carried out in indirect heated (or allothermal) dual fluidized bed systems. This conventional steam gasification process uses an inert bed material as a heat carrier to deliver the heat for the endothermic gasification, enabling N\({}_{2}\)-free syngas with typical hydrogen content of 20-40 vol% (on a dry basis). The syngas of this process can be used for power and heat generation, and the technology has already been applied in a number of industrial-scale facilities with thermal power ranging from 2-20 MW [3; 4; 5]. Accordingly, a number of different models describing the steam gasification of biomass have been developed and published [6; 7; 8].  
[PERSON] and [PERSON] [9] developed a two-phase model for steam gasification of biomass char which considers hydrodynamic phenomena; however, pyrolysis was not included, which is an importantstep in the biomass gasification process. [PERSON] et al. [10] proposed a detailed one-dimensional model for steam gasification in a bubbling fluidized bed, which considers a Lagrangian approach for solid fuel particles extending the often used assumption of a uniform distribution of fuel particles. In contrast to conventional steam gasification, the SEG uses a reactive bed material (e.g., limestone) as the heat carrier, which enables the in situ capture of CO\({}_{2}\) in the gasifier. This CO\({}_{2}\) capture affects gasification reactions and shifts hydrogen concentrations in the syngas up to 75 vol% (on a dry basis) [11]. Thus, SEG has been considered to be a suitable process for the synthesis of hydrogen, transport fuels, and chemicals [12; 13]. Hereby, models are important in finding the best operation strategies for the gasifier, especially if the gasifier is part of a complex production path, including mass and energy integration. However, few models exist which have considered the CO\({}_{2}\) sorption characteristics in fluidized bed reactors. [PERSON] et al. [14] and [PERSON] et al. [15] used a detailed approach based on reaction kinetics, but hydrodynamics were not in focus. In the work of [PERSON] et al. [16; 17], a model to describe sorption enhanced gasification in a bubbling fluidized bed was presented. This model considers hydrodynamics in the fluidized bed, but evaluations of process parameter over reactor height were not included due to the assumption of a uniform temperature throughout the dense bed. Another comprehensive SEG model has been published by [PERSON] et al. [18]. This model considers a transport disengaging height to describe the amount of reacting particles in the freeboard, which is important for the overall syngas composition. However, minor focus is placed on the bed activity, which depends (in a dual fluidized system) on the mean particle residence time, as well as the carbonation/calcination cycles. Considering the issues discussed above, we developed a detailed SEG model focusing on various key aspects, including (i) hydrodynamic features of the fluidized bed reactor and evaluation of the process parameters over reactor height; (ii) kinetic aspects of the steam gasification process; and (iii) reaction kinetics of CO\({}_{2}\) capture through carbonation in the fluidized bed, as well as by elutriated particles in the freeboard. As deactivation of the sorbent is an important issue in a SEG process, a deactivation model is included in this work.