Hydrogen production through chemical looping and sorption-enhanced reforming of olive mill wastewater: Thermodynamic and energy efficiency analysis

Abstract

A thermodynamic study was performed aiming to compare the performance of different reactor configurations, namely traditional (TR), sorption-enhanced (SER), chemical looping (CLR) and chemical-looping sorption-enhanced reforming (SE-CLR) for the steam reforming of olive mill wastewater (OMW), a byproduct of olive oil production, to produce green hydrogen. This analysis was accompanied by an energy balance in order to maximize energy efficiency and achieve autothermal operating conditions. The parameters assessed in the thermodynamic study were temperature (250–900 °C) and steam-to-carbon molar ratio (0.15–3.0), but also, for the sorption-enhanced process, the ratio between the CO2 sorbent and the OMW (0–8.0), and for the chemical looping process the ratio between the oxygen carrier and the OMW (0–6.0). The SER showed higher hydrogen yield for the range of conditions tested than both the traditional and chemical looping reformers, with a hydrogen purity above 99%. By combining sorption-enhanced with chemical looping reforming, an H2 purity above 99% and a yield higher than that for chemical looping by itself were observed. For the CLR and SE-CLR configurations, a system in which the energy released is higher than the required was achieved by varying the amount of oxygen carrier, enabling operating under autothermal conditions. A pinch analysis was performed for the CLR and the SE-CLR to quantify the possible heat integration in a realistic system. It was found that CLR can be 71% self-sufficient, whilst SE-CLR can be 55% self-sufficient.