Chemical looping reforming in packed-bed reactors: Modelling, experimental validation and large-scale reactor design

This paper addresses the experimental demonstration and model validation of chemical looping reforming in dynamically operated packed-bed reactors for the production of H₂ or CH₃OH with integrated CO₂ capture. This process is a combination of auto-thermal and steam methane reforming and is carried out at high pressure, as typical for reforming processes, and at relatively low to intermediate temperatures (ranging from 600 to 900 °C). The oxidation of the oxygen carrier is performed with air and the hot depleted air stream is fed to a gas turbine, which contributes to reduce the electricity demand. After oxidation, a low-grade fuel is used for the reduction of the oxygen carrier, e.g. off-gas from a PSA unit or non-condensable species from methanol synthesis and, when the bed is completely reduced, natural gas diluted with H₂O and CO₂ is reformed while the reactor is cooled down. An experimental campaign has been carried out in a 2 kW_th packed-bed reactor using 500 g of NiO supported on CaAl₂O₄ as reforming catalyst and oxygen carrier. This material has demonstrated very high stability over > 400 h of consecutive redox and reforming cycles. Due to the flexibility of the process, dry, wet and steam reforming compositions have been tested during the reforming phase. A 1D reactor model has been validated with the obtained experimental results, including also a detailed thermal model to account for the inevitable heat losses of the system. The experimental and model results are in good agreement in terms of breakthrough curves and temperature profiles. The experimental campaign during reforming also confirmed the possibility to carry out the heat removal phase by means of endothermic methane reforming. The validated reactor model has subsequently been used for the simulation of different configurations in terms of heat management in which the different phases (oxidation, reduction and reforming) are simulated in series. In these analyses, the reactor design and performance have been compared for two plant configurations based on H₂ and CH₃OH production integrated with CO₂ capture. For the case of H₂ production, the CH₄ conversion is 92% and all the CO₂ is captured from the plant, while for CH₃OH production the CH₄ conversion reaches 90% and all carbon species, except CH₃OH, are converted into CO₂, which is separated with high purity.