Kinetic modeling of autothermal reforming of heptane for a fuel cell - auxiliary power unit
Licentiate thesis, 2007
The transport sector contributes significantly to the increasing amounts of air pollution. The pollution from idling heavy duty vehicles can be reduced by using a fuel cell auxiliary power unit (FC-APU) that supplies the vehicle with electricity. This licentiate thesis deals with production of hydrogen, which feeds the fuel cell. Hydrogen is generated by reacting a hydrocarbon with steam according to the steam reforming reaction. This endothermic reaction proceeds by oxidizing a part of the fuel which makes the process almost autothermal. Heptane has been used as the fuel in the reforming experiments. Diesel, which is the common fuel in heavy duty vehicles and would be the natural choice, consists of several hundred components, which makes determination of the reaction kinetics essentially impossible.
Experiments were performed on a monolith reactor coated with palladium supported on cerium oxide. The influence of temperature, feed composition (by changing the water to carbon ratio of the feed), and space velocity were studied. The results showed that a feed temperature of 650 oC was sufficient for complete conversion of heptane. At this temperature, the maximum yield of hydrogen was also achieved. Changing the water to carbon ratio (H2O/C) of the feed seemed to have negligible effects on heptane conversion but a ratio of 3 was found to be favorable for the hydrogen concentration.
Keywords: Steam reforming