(360d) Long-Term Stability At Fuel Processing of Diesel and Kerosene

Long-term Stability at Fuel Processing of Diesel and Kerosene

The scientific work in the fuel processing and systems group at Forschungszentrum Juelich has the strategic aim of developing a high-temperature polymer electrolyte fuel cell (HT-PEFC) system based on the autothermal reforming of middle distillates such as diesel and kerosene in the power class of 5 to 10 kW_e. This class is particularly interesting for HT-PEFC systems working as auxiliary power units (APUs) for on-board power supply in aircraft and trucks. The main component of the system besides the HT-PEFC stack is the autothermal reformer (ATR). It converts liquid fuels such as diesel or kerosene together with air and steam into a hydrogen-rich gas in a catalytic process (cf. equations (1) and (2)). The exothermic partial oxidation and the endothermic steam reforming reaction of the hydrocarbons contained in diesel fuel and kerosene proceed consecutively on the same monolith. In parallel, the water-gas-shift reaction and the methanation (cf. equations (3) and (4)) reaction also take place in an ATR to the thermodynamic equilibrium of the reactor temperature. Hydrogen, carbon monoxide, carbon dioxide and methane can be regarded as the desired main products of autothermal reforming.

C_nH_m + n H₂O    <---------->   n CO + (m/2 + n) H₂       (1)

C_nH_m + n/2 O₂   <---------->   n CO + m H₂                   (2)                  

CO + H₂O          <---------->   CO₂ + H₂                        (3)

CO + 3 H₂         <---------->   CH₄ + H₂O                      (4)

Reaction equations for autothermal reforming

This presentation will focus on the experimental investigation of the long-term stability of Juelich´s reactor for autothermal reforming ATR 9.2. Experimental results from an experiment for 10,000 h of time on stream using two different synthetic fuels (GTL kerosene and BTL diesel) will be presented, explained and discussed. Special emphasis will be given to the exact determination of hydrocarbon conversion at different points of time during the long-term experiments. For that, the spectra of undesired byproducts and their respective concentrations in the gas and liquid phase were qualitatively determined and quantitatively measured. The spectrum of the byproducts in the gas phase contained short chain hydrocarbons such as ethane, ethane, propene, propane etc. as well as benzene, while that of the liquid phase showed substances such as acetic acid, acetone and butanone. Additionally, the amount of fuel slip if accumulated was gravimetrically measured. After 9,200 h of time on stream for instance, hydrocarbon conversion was still more than 98 %. Furthermore, reaction conditions and operational strategies will be presented and discussed, which allow for at least a partial regeneration of the catalyst.