Unmixed Steam Reforming of Liquid Fuels From Biomass and Waste for Hydrogen Production

Unmixed steam reforming is a promising alternative process of hydrogen production. It relies on the cyclic oxidation of a bed of nickel-based material and on the simultaneous regeneration of a CO₂-sorbent under airflow to provide the heat necessary for the steam reforming reaction. The latter occurs subsequently under a fuel/steam flow while the airflow is interrupted. The effluent gas of the fuel/steam step is much higher in hydrogen than the single reactor equivalent conventional process, and the oxidised catalyst is regenerated by reduction from exposure to the fuel. Because the carbon produced during the steam reforming step is subsequently burned under the airflow, the process is not sensitive to the gradual loss of conversion efficiency exhibited by the conventional process. Furthermore, in the unmixed steam reforming process, sulphur in the fuel is claimed to also undergo oxidation under the airflow rather than irreversibly poisoning the reforming catalyst. This process most importantly claimed to be economical at small scale, unlike the conventional process, and could thus be used in distributed power generation. These advantages open up opportunities for this novel process to apply to a whole range of fuels with coking tendencies and/or sulphur content, such as the combustible liquid mixtures derived from biomass or specific industrial / transportation waste. When using a suitable CO₂-sorbent in the reformer, the dry hydrogen content in the reformate gas reaches above 80% (90+% when using on methane fuel). In this case, most of the produced CO₂ and the N₂ from the airflow effluent leave the reactor separately to the H₂-rich reformate gas, and can potentially be easily filtered and stored. In the now completed GR/R50677/01 project, we showed the sequence via which the various reactions involved in the cycle proceeded, and we found clear evidence of the insensitivity of the process to coking. We concluded that certain developments would improve on the original process. These are listed in the objectives.