Mono-dimensional and two-dimensional models for chemical looping reforming with packed bed reactors and validation under real process conditions

Abstract

Chemical looping reforming (CLR) is an emerging hydrogen/syngas production technology, integrated with CO₂ capture. Packed bed reactors are widely used in the hydrogen production industry as they are preferred for high pressure operation and the mathematical modelling describing their operation is very important for their design. In this study, a one-dimensional (1-D) and a two-dimensional (2-D) model have been developed to describe the dynamic operation of chemical looping reforming processes in packed bed reactors (CLR-PB). The reactor under study (L: 400 mm ID: 35 mm) contains an axially placed thermowell (OD: 6.35 mm) to monitor the temperature across the reactor bed at 6 points and 440 g of NiO/CaAl₂O₄ oxygen carrier (OC). Both models have been validated presenting very good agreement with the experimental results. The comparison between modelling and experimental results has been carried out in terms of thermowell temperature and the gas composition breakthroughs, with the 2-D model capturing the thermowell temperature recordings with high accuracy, while the 1-D model delivered results that underestimated it by 2.5%. Nonetheless, the predicted average bed temperature presented a difference limited to 1% lower estimation of the 1-D to the 2-D model. The temperature difference between the bed and the thermowell has achieved a value of >180 °C thus resulting also problematic in terms of safe operation if not properly considered. with temperatures during oxidation being higher even by 181 °C inside the bed, emphasizing the importance of the model in the proper design and safe operation of the reactor. The 1-D model, due to the significantly lower computation time (∼21 times faster than 2-D), has been selected to be tested against a range of operating conditions for oxidation (500–600 °C, 1–5 bar, 10–40 NLPM, 10–20% O₂), reduction (600–900 °C, 1–5 bar) with H₂, syngas and CH₄-rich reducing agents and dry reforming (700–900 °C, 1–5 bar), delivering results with good agreement especially under high temperature conditions where solid conversion is high and under conditions which resemble the expected industrial ones.