One-step hydrogen through water splitting with intrinsic CO2 capture in chemical looping

Hydrogen is produced in a redox chemical loop in which the oxygen atom is 'stolen' from water by a circulating solid based on iron oxides. In addition to the transportation of oxygen, the circulating solid, having a high heat capacity, ensures heat transfer in the cycle. Water is split by the oxidation of FeO to Fe3O4, this producing H-2 and leaving the oxygen of the water in the solid. The back-reduction to FeO occurs in a separate reactor using natural gas, the structural oxygen producing a concentrated CO2 stream. The exothermicity of the water splitting does not balance the endothermicity of the flameless combustion of natural gas with Fe3O4. Hence, before this combustion is carried out, super-oxidation by air of some or all of the Fe3O4 to Fe2O3, carried out in a third reactor, supplies the heat required for the reaction enthalpy balance as well as the energy required by the plant energetic balance. In this "One-Step Hydrogen" process, intrinsically separated streams of hydrogen and storage-ready CO2, suitable for Enhanced Oil Recovery (EOR) applications, are produced. Thus, any upstream (N-2-O-2 separation) or downstream (transformations and CO2 capture) energy intensive steps are avoided. The use of fluidized bed technology allows also the management of the heat flows and of thermodynamic equilibria constraints and ensures the most efficient heat exchange in the loop. The chosen circulating solid consists of 30% Fe on an Mg-Al2O3 spinel; this is perfectly suitable with respect to its structural and mechanical properties for use in a commercial fluidized bed technology. Management of the amount of super-oxidation allows one to target the OSH technology to produce hydrogen (with or without steam export), co-produce hydrogen and electric power, or even to supply only energy by integrating this process into a hydrogen-powered combined cycle energy production plant (H2CC). In comparison with the current technologies with CO2 recovery, the one-step process described here shows better efficiencies and much better environmental performance because CO2 removal is virtually complete. (C) 2016 Elsevier B.V. All rights reserved.