No abstract

No abstract

The overall energy efficiency of the production of pure hydrogen using the pyrolysis oil driven steam-iron process is evaluated for different process conditions. The process consists of a two-step process (reduction with pyrolysis oil, oxidation with steam) from which pure hydrogen can be obtained, without purification steps. An optimum energy efficiency of 53% is achieved when the equilibrium conversion is obtained in the redox cycle at 800°C. When assuming chemical equilibrium, increasing the process temperature results in a low process efficiency due to a large amount of unreacted steam that needs to be condensed to separate the hydrogen product. Using experimental data in the process simulation, a high-energy efficiency is obtained at 920°C (39%) compared with the efficiency at 800°C (29%). This is caused by the low conversion in the reduction at 800°C. Improving the iron oxide material to enhance the reduction with pyrolysis oil at 800°C, is therefore suggested.

In the steam−iron process, relatively pure hydrogen can be produced from pyrolysis oil in a redox cycle with iron oxides. Experiments in a fluidized bed showed that the hydrogen production from pyrolysis oil increases with increasing temperature during reduction. The experimental hydrogen production at nearly 1000 °C with noncatalytic (blast furnace) and catalytic (ammonia synthesis) iron oxide was found to be 1.39 and 1.82 Nm3 of H2/kg of dry oil, respectively. However, this high hydrogen production could be achieved only when a low relative conversion (α) of the iron oxide in the reduction was maintained (about 7%). It was found in all experiments that the reduction rate decreased strongly with increasing relative conversion of the iron oxide [at 800 °C, the relative conversion rate (dα/dt) decreased from 3.0 × 10−4 s−1 at α = 0.6% to 8.8 × 10−6 s−1 at α = 10.0%]. The gasification of pyrolysis oil over an iron oxide bed results in an increased carbon-to-gas conversion compared to gasification over a sand bed. Near-complete gasification of oil is achieved when temperatures above 900 °C are applied in a fluidized-bed setup containing iron oxide. A lumped reaction path scheme is proposed for char formation in pyrolysis oil gasification.

No abstract