Synthesis of methanol from a chemical looping syngas for the decarbonization of the power sector

One promising pathway for carbon capture and utilization is represented by the coupling of chemical looping cycles with liquid fuel synthesis processes. Methanol is an interesting fuel for gas turbines engines, due to its potential reduction of NOX and particulate emissions along with the absence of SO2 emissions. In this work, methanol production from the syngas generated by a three-reactors chemical looping process is investigated by mass and energy balances. The cycle is composed by a reducer reactor, where Fe2O3 is reduced to FeO by the injection of a reducing agent; an oxidizer reactor, where FeO reacts with CO2 and H2O to produce a syngas; an air reactor, where Fe3O4 is regenerated to Fe2O3 by ambient air. The produced syngas is then sent to a methanol synthesis plant. Several syngas compositions deriving from different CO2/(H2O+ CO2) molar fractions (1–3) at the oxidizer inlet are taken into account. The resulting methanol flow rates are almost equal in all investigated configurations (about 0.35 t/h). From an energy standpoint, the required electric power is greater for higher hydrogen mole fractions in the syngas. However, the case with 75% H2 content is characterized by the greatest methanol yield (⁠12.6%⁠), carbon efficiency (⁠23%⁠) and a high feed/recirculation ratio (⁠0.80⁠), thus representing the most indicated configuration among the investigated ones. Finally, by burning methanol in a gas turbine, the total CO2 emissions are halved with respect to the case without the system (if the CO2 associated with biogenic carbon in the reducer reactor is considered as net-zero).