Three-reactors chemical looping process for hydrogen production

This paper analyzes a novel process for producing hydrogen from natural gas, based on chemical looping (CL) techniques, allowing for intrinsic capture of carbon dioxide. The core of the process consists of a three-reactors CL system, where iron oxide particles are circulated to: (i) oxidize natural gas (thus providing, after cooling and water condensation, a CO2 stream ready for sequestration), (ii) reduce steam, to produce hydrogen as the final product of the process, (iii) consume oxygen from an air stream, to sustain the thermal balance of the system. The process is intrinsically very attractive, because it directly produces hydrogen and CO2 from natural gas, by means of a process simpler than the conventional technologies with CO2 capture capabilities. Hence, a significant potential for investment cost reduction can be anticipated. However, to fully exploit the system potential, an efficient energy recovery from the gaseous streams exiting the reactors must be arranged, taking into account power and steam production needed to support internal consumptions. Therefore, after an introduction clarifying the concept and the scope of the system, as well as its basic chemistry, this paper presents a discussion of two plant configurations, including different integration levels with power production (fired gas turbine (GT) vs. unfired turbocharger) and/or heat recovery steam production methods (also considering steam compression devices). A comparison with ‘‘proven technology’’ plants, based on steam reforming, is also carried out. Due to the lack of reliable estimates of the investment costs for components to be developed from scratch (CL reactors), the analysis is limited to the thermodynamic and technological aspects. Results show, however, that an impressive potential exists for CL systems for hydrogen production, thus deserving substantial R&D activities in the near future.