Development of a novel carbon capture and utilization approach for syngas production based on a chemical looping cycle

Abstract

The present work assesses the potential of reducing CO2 emissions associated with steel production through the introduction of a decarbonization process downstream of a steel mill eventually producing an alternative fuel/syngas. The analysed system is composed of a calcium looping process for CO2 separation followed by a chemical looping section for syngas production from CO2 and H2Os. The main units in the chemical looping cycle are: the oxidizer, where a flux of CO2 and H2Os reacts with an oxygen carrier to produce CO and H2; the air reactor, where the oxidation of the oxygen carrier is completed by the interaction with air; the reducer, where the reduced oxygen carrier is regenerated to the initial state (Fe2O3 or NiFe2O4 in the present case) through an endothermic reaction occurring at high temperatures. A MATLAB model was created to determine the molar flow rate of the components flowing through the thermochemical cycle and the thermal power associated with each unit at the operating conditions. The analysis is carried out focusing on the treatment of 1t/h of CO2, resulting in 7.1t/h of NiFe2O4 or 12.1t/h of Fe2O3. The syngas at the outlet from the oxidizer reactor is composed of equimolar H2 and CO with a mass flow rate of 0.05t/h and 0.64t/h, respectively. A separate MATLAB model was developed to identify the experimental conditions necessary to reach fluidization of FeO particles in a lab-scale oxidizer reactor (umf=0.162m/s). Companion CFD simulations were carried out to evaluate the hydrodynamics of the lab-scale oxidizer reactor and the associated reaction kinetics (Langmuir-Hishelwood) above minimum fluidization conditions with the aim of assessing the assumptions performed in the MATLAB in terms of conversion rates. For the imposed inlet velocity conditions of the gas mixture (2.6 times above the minimum fluidization velocity) large bubbles with low frequency are observed, while full consumption of the reactant gases is achieved during the first 15 s of simulation, due to the significant reaction rate (2.6kmol/sm3). The results of the CFD simulation and the comparison with existing literature allow to validate the assumptions on the oxidizer conversion and the overall accuracy of the model.