Development and validation of a 1D process model with autothermal operation of a 1 MWth chemical looping pilot plant

Chemical Looping Combustion (CLC) has been extensively investigated up to pilot scale. Despite promising results, this CO2 capture technology has to be further developed towards a potential industrial application. In order to accelerate the scale up of the process, it is essential to simulate the CLC using a process simulation software. In this study, a process simulation model of the CLC pilot plant at Technische Universität Darmstadt is developed employing Aspen Plus®. The air reactor and the fuel reactor are integrated in the process model to calculate the conversion of the oxygen carrier and gases. The solids distribution and also the chemical conversion of gases and solids are implemented by user-defined functions programmed with FORTRAN. These codes are based on mathematical equations for fluidized beds and kinetic data of the chemical reactions taken into consideration. For this reason, dedicated thermal gravimetric analysis (TGA) experiments were carried out to determine both kinetics of redox reactions of oxygen carrier and gasification kinetics of the coal used in the 1 MWth CLC unit. The one-dimensional solids distributions and gas/solid mixing are calculated from empirical correlations according to Kunii and Levenspiel. The models are validated by means of experimental data obtained from the 1 MWth CLC pilot plant with ilmenite as oxygen carrier and Russian hard coal (“Taldinsky”) as fuel. Among others, pressure profiles and gas concentrations at reactor exits are calculated for various operational points with autothermal operation. The results show good agreement with the experimental data. The process model was applied to optimize the operational conditions of the pilot plant.