Hydrogen for Fuell Cells by Sponge Iron Process

The application of fuel cells in our future energy system depends on a cost-efficient production and supply of hydrogen. Usually, hydrogen is gained by steam reforming of natural gas and subsequent conversion of the resulting synthesis gas in the catalysed water gas shift reaction. by which CO and H2 0 are transformed to CO 2 and H2 . The process cycle iron oxide/sponge iron/hydrogen offers a simple possibility to store the energy of synthesis gases in the reduced form of an iron oxide (wuestite or sponge iron) and at the same time to reform and condition a wide range of synthesis gases and gases arising from biomass gasification. As "product" of this energy storage systern one receives pure hydrogen, when steam is used for the re-oxidation. The SIR ("Sponge Iron Reactor") process offers some advantages against conventional gas cleaning and conversion processes: (i) Low-cost hydrogen by using cheap sponge iron materials, (ii) high-quality hydrogen from low-BTU gases. (iii) high efficiency compared to competitive technologies and (iv) system versatility and ease of siting. As hydrogen can be gained from regenerative or fossil sources in one facilitv, the SIR can be regarded as veritable transition technology. Commercially available iron ore pellets (hematite Fe2 O3 ) and self produced pellets are used as contact mass. While in preceding projects. the applicability of the SIR process with varying gas compositions and catalyst materials has been investigated on principle. the process shall henceforth be studied and optimised under realistic conditions in order to collect all data necessary for its technical realisation. The optimisation of all parameters influencing the redox process requires precise and reliable data, which can now be provided by a new lab scale reactor constructed and financed within the FWF 11908 project. This reactor allows the on-line monitoring of weight (corresponding to conversion rate), temperature and exhaust gas composition as well as the application of pelletised or granulated iron ore material in representative sample sizes up to 6 kg and provides defined gas flow conditions. Data obtained from redox cycles in this reactor shall serve as the basis for simulation of a larger scale process and for energetic and economic calculations. Comparison of various industrially and self-produced iron ore pellets in a tube furnace yielded the basic information for material improvement concerning cycle stability and reaction kinetics. For practical realisation a cheap and resistant iron ore catalyst is crucial for economic feasibility. So, further efforts shall concentrate on a systematic material optimisation. On the one hand, commercial iron ore pellets shall be improved by dotation with catalysts. On the other hand. pellets with optimal properties for individual applications (for example special gas mixtures) shall be developed. Beside pellet composition, the production procedure shall be studied with respect to its influence on porosity, lattice structure and mechanical strength. Material optimisation requires the determination of redox behaviour in the new reactor as well as a complex material characterisation which will always be accompanied by TGA measurements of pulverised samples to determine chemical reaction kinetics. Comparison of kinetics in the reactor with TGA findings represents the basis for quantification of diffusion processes. The applicability of reducing gases of variable composition and the intluence of minor components which will naturally occur in biomass gases (sulfur and nitrogen compounds and halogenides) shall be tested under realistic conditions after preceding thermodynamic calculations in order to define a range of usable gases. Finally, the entire process shall be investigated and optimised under variation of several crucial parameters. It is intended to use the data obtained from the laboratory reactor for the calculation of energy balances as well as for simulation of a complete energy system into which the SIR is integrated. An estimation of costs, emissions and required materials as well as an enviromnental compatibility study shall be added. The works carried out within the applied project shall provide the basis of the extensive EU project "Solid Biomass Gasification for Fuel Cells".