A novel reactor type for autothermal reforming of diesel fuel 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 kWe. The main component of the system besides the HT-PEFC stack is the autothermal reformer (ATR).
At Juelich, several reactor generations for autothermal reforming have been developed and experimentally validated in the recent years. Their fundamental design is shown in Fig. 1. At steady state, liquid fuel is injected at room temperature into the evaporation chamber. There, fuel is completely evaporated using the enthalpy flow from a mixture of steam and air (as carrier gas), which enters the evaporation chamber at an elevated temperature in the range of 420 °C to 460 °C. Steam at these temperatures is provided by feeding a stream of cold water and air through the internal steam generator of the ATR and then by passing the mixture of steam and air through an external heating cartridge. An additional flow of air is injected behind the fuel evaporation chamber. The educt mixture consisting of steam, air and evaporated fuel enters the catalyst where the autothermal reforming reactions take place. The waste heat from these reactions is used in the internal steam generator as mentioned above. With respect to its integration into an HT-PEFC system this reactor type for ATR has two main disadvantages. At first, it has to make use of an external heating cartridge for steam superheating. This balance of plant component makes the system more complex and less robust and, of course, reduces its overall efficiency. Secondly, the heat exchange in the internal steam generator reduces the outlet temperature of the reformate to temperatures in the range 180 °C to 200 °C. These temperatures are by far too low for the downstream water-gas shift reactor, which requires inlet temperatures in the range of 400 °C.

Fig. 1 Fundamental design of Juelich´s established reactor type for autothermal reformer
For the design and construction of Juelich´s novel reactor type for autothermal reforming (ATR AH2) as shown in Fig. 2, these two main drawbacks were considered and overcome. The ATR AH2 makes use of an additional enthalpy flow coming from a flow of steam, which was generated in the catalytic burner of the fuel cell system. It is fed into the steam generation chamber in the top part of ATR AH2, in which simultaneously cold water is injected via a pressure-swirl nozzle. Thereby, cold water is partly evaporated and a stream of saturated steam is sprayed onto a deflecting surface (hemispherical head), which is heated
from underneath by the hot reformate flow. While hitting the deflecting surface an additional enthalpy flow is transferred to the flow of saturated steam. As a consequence, the steam mass fraction of this flow increases. Then, the flow of saturated steam enters the internal steam generator, in which steam with temperatures higher than 400 °C is produced by transferring the residual waste heat from the reformate. As in the case of Juelich´s former reactor generations for ATR (cf. Fig. 1), this flow of steam is then used to completely evaporate the fuel, which is mixed with air before entering the catalyst.
An additional advantage of ATR AH2 in comparison to most other former reformer generations at Juelich is that this reactor has been industrially manufactured by a medium- sized German company thus optimizing production costs and material input. This transfer of production technology from a research institute to a medium-sized company constitutes an important step towards commercialization of the reformer technology developed at Juelich.

Fig. 2 Fundamental design of Juelich´s novel reactor type for autothermal reforming
This contribution will describe the experimental evaluation of ATR AH2. It will show experimental data with respect to the temperatures at all relevant positions in ATR AH2 and the gas concentrations in the reformate.