Optimisation of a sorption-enhanced chemical looping steam methane reforming process

An intensified hydrogen production steam reforming process named 'Sorption-Enhanced Chemical Looping Steam Methane Reforming' (SE-CL-SMR) was studied. Aspen Plus was used to carry out a thermodynamic investigation into the influence of various operating conditions on hydrogen production and process thermal efficiency. The steam to carbon molar ratio (S/C), the CaO to carbon molar ratio (CaO/C), the metal oxide to carbon molar ratio (MeO/C), the metal oxide composition (NiO:CuO), and the oxidising agent species were all shown to influence the process performance. The main findings were that; (1) the introduction of CaO reduces the potential for coke formation with predicted zero coke formation for CaO/C ratios > 0.4; (2) increasing amounts of metal oxide (MeO/C) and steam (S/C) enhance the hydrogen production yield and purity; (3) due to its involvement in an exothermic reaction, the presence of CuO allows for the reforming reactor to operate as an adiabatic reactor with an operating temperature within the range of 600 degrees C-700 degrees C; (4) an increase in the NiO:CuO ratio leads to an increase in methane conversion. With the operating conditions of S/C = 3, CaO/C = 1, MeO/C = 1, NiO:CuO = 0.9 and air as the oxidising agent, a hydrogen purity as high as 98% was predicted for the SE-CL-SMR process, along with the lowest observed CO2 production rate. Under the same conditions and using pinch analysis, the thermodynamic model prediction of the thermal process efficiency is reported as ca. 86%. This is significantly higher than the reported efficiency of 79% for the 'Sorption-Enhanced Steam Methane Reforming' (SE-SMR) process, predicted using similar thermodynamic models. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

The study investigated the impact of operating conditions on hydrogen production and process thermal efficiency for the SE-CL-SMR process, finding that factors such as CaO/C ratio, MeO/C ratio, and oxidising agent species play a significant role. The introduction of CaO reduces coke formation, while increasing MeO/C and S/C enhances hydrogen yield and purity. The presence of CuO allows for adiabatic reactor operation and an increase in NiO:CuO ratio leads to higher methane conversion rates.