METHANOL PRODUCTION BY A CHEMICAL LOOPING CYCLE USING BLAST FURNACE GASES

Steel mills are responsible for high direct CO2 emissions. To mitigate climate changes, carbon capture and utilization strategies (CCU) aiming at neutralizing such emissions should be employed. Currently, the most widespread technologies for carbon capture (CC) are represented by chemical/physical absorption, adsorption, membrane separation, calcium looping cycles (CaL). One promising pathway for carbon capture and utilization (CCU) is represented by the coupling of chemical looping cycles with liquid fuel synthesis processes, such as methanol synthesis. Methanol is an interesting low-cost fuel for gas turbines engines, due to its potential reduction of NOX and particulate emissions along with the absence of SO2 emissions. Furthermore, being one promising solution to store excess power production from renewables, its availability is expected to increase significantly with the years. In this work, methanol production from the syngas generated by a three-reactors chemical looping process (TRCL) is investigated by mass and energy balances. The TRCL cycle is composed by a reducer reactor, where Fe2O3 is reduced to FeO by an endothermic reaction occurring at high temperatures and promoted by biogenic carbon; an oxidizer reactor, where FeO reacts exothermically with a gas stream composed of CO2 and H2O in order to produce a syngas (CO + H2); a fuel reactor, where the non-reacted FeO is oxidized to Fe3O4 and subsequently the whole amount of Fe3O4 is regenerated to Fe2O3 by the interaction with ambient air. The produced syngas is then sent to a methanol synthesis plant modelled with the Aspen Plus software. Several syngas compositions, deriving from different oxidizer’s inlet CO2/H2O molar fractions, are investigated and the resulting methanol production rates are compared. A WGS unit is located at the plant inlet in order to increase the H2 molar fraction in the feed stream. Results indicate that methanol production is almost equal in all investigated configuration and amounts to about 0.35 ton/h. From an energy standpoint, global heating/cooling duty is almost equal in all cases, while the electric power required is greater for higher hydrogen contents in the syngas. However, the case with high H2 content (0.75 in molar fraction) is characterized by the greatest methanol yield (12.6%), carbon efficiency (23%) and a limited feed over recirculation ratio, thus representing the most indicated configuration among the investigated ones