(620e) Chemical Looping Hydrogen Production By the Steam Iron Process

Hydrogen in combination with low temperature fuel cells offers a promising option to boost emission-free power generation and mobility. Alternative hydrogen technologies are under development, due to the fact that hydrogen transportation and storage infrastructure is currently not existing or insufficient. By using decentralised on-site production of hydrogen based on hydrocarbon fuels, both of these issues can be avoided.

The combination of conventional steam reforming with the cyclic reduction and oxidation of iron-based oxygen carriers enables the production of pure hydrogen based on any carbon containing feedstock [1,2]. In the first step a syngas is generated by steam reforming according to equation (1):

 C_xH_y + xH₂O -> (x+y/2)H₂ + xCO                                                        (1)

The syngas is directly used for the reduction of the oxygen carrier (2) which is a mixture of haematite (Fe₂O₃) and additional oxides, prepared by mechanical mixing.

 Fe₂O₃ + 3H₂/CO -> 2Fe + 3H₂O/CO₂                                                  (2)

The consecutive oxidation of iron with steam leads to the formation of magnetite (Fe₃O₄) and pure hydrogen (3), an additional oxidation step with air regenerates the magnetite and forms haematite (4).

3Fe + 4H₂O -> Fe₃O₄ + 4H₂                                                                 (3)

 2Fe₃O₄ + 1/2O₂ -> 3Fe₂O₃                                                                 (4)

Reduction and oxidation are carried out in fixed bed reactors which allow a compact and simple process design compared to interconnected fluidised bed configurations which are commonly used for chemical looping applications today. The feasibility of the process strongly depends on the gas composition of the available syngas.

In this presentation, the influence of gas composition on the efficiency and options to optimise the process conditions for the syngas generation as well as for the reduction reaction are discussed. Special emphasis is given to the formation of solid carbon during the reduction since this would lead to the formation of carbon monoxide in the product gas.  

Acknowledgment: This work is funded by the Research Studios Austria program of the Austrian Federal Ministry of Economy, Family and Youth.

REFERENCE:

[1] Hacker, V., “A novel process for stationary hydrogen production: the reformer sponge iron cycle (RESC)”, Journal of Power Sources 118 (2003) 1-2, S. 311 – 314.

[2] Nestl, S.; Voitic, G.; Geymayer, M.; Hacker, V. “Component Development for the Reformer Steam Iron Process for Decentralised Sustainable Hydrogen Production”, AIChE 2013 Annual Meeting. San Francisco, 05.11.2013.