A 1 MWth pilot plant circulating fluidized bed (CFB) carbonator reactor is simulated under stable operating conditions with the coarse grain discrete element method (DEM). The heterogeneous reaction between CaO and CO2 is modelled using a reaction rate equation according to Bathia and Perlmutter with partially from experiment derived sorbent parameters. For model validation, pressure transducer measurements along several reactor heights, gas concentrations from 1 MWth circulating fluidized bed carbonator were used. The DEM model is investigated in association with the parcel approach in which up to several thousands of particles can be modelled by a representative single particle, so-called parcel. The Sauter mean diameter was used in the numerical model to represent the bed material. Additionally, several particle size distributions from three different extraction points in the riser were applied in the Lagrangian simulation to determine its influence on the flow hydrodynamics as well the results were compared using the Sauter mean diameter. Generally, the Sauter diameter overpredicted considerably the pressure profile in comparison to experimental data than the PSD simulations. Furthermore, the DEM model is analyzed in terms of drag models by applying the Tang, Gidaspow, Wen and Yu, Syamlal O'Brien and Gibilaro models using custom-built User-Defined-Functions. All drag models yield a comparable pressure distribution along the reactor height. Taking into account the location of the gas analyser downstream the cyclone, the predicted CO2 concentration at the riser outlet is in good agreement with the experiment.