340
Alternative Fuels for Transportation
storage material M with the heat of formation ΔH (M + H 2 → MH 2 + ΔH) of
about 25 MJ kg –1 H 2 , a thermal load of 150 MJ is desired during refueling.
This leads to an average heat exchange of 800 kW. Such a high-performance device is unimaginable onboard a vehicle due to cost, volume, and
weight considerations. A further constraint is that many solid-state absorbers have to be limited to 70°C to be practical, which could be reached by
using the waste heat of the FCS. Hydrogen absorbers often consist of powder
materials. The absorber accounts for 50% of the total weight, whereas 50% is
due to valves, pipes, pressure vessels, heat exchanger, and so on. A 70 MPa
compressed gaseous hydrogen storage system is currently the best-in-class
option available for hydrogen storage onboard a vehicle.
The most important factor for the success of FCVs lies in the success of the
hydrogen economy and related technologies. McNicol, Rand, and Williams
(2001) reported that a FCV system equipped with a direct conversion fuel
processor could compete successfully with conventional ICEVs. Buses and
recreation vehicles have more space to house the fuel processor than passenger cars. Onboard fuel reforming is another option to utilize the existing
liquid hydrocarbon fuel infrastructure and to produce hydrogen onboard.
The desired reformer-FC system is obviously more complex than an onboard
hydrogen storage FC system.
Reforming for automotive applications requires an air-assisted primary reforming called Catalytic Partial-Oxidation (CPO) or Auto-Thermal
Reforming (ATR). During CPO, air is applied together with a hydrocarbon
fuel while, during ATR, air is supplied together with steam and a hydrocarbon fuel. The gas treatment consists of shift conversion and CO removal.
The architecture of the reformate system is influenced by the type of
the fuel used. There are many candidate fuels such as methanol, ethanol,
naphtha, low sulfur gasoline, and dimethyl ether. It is advisable to use
the existing infrastructure for fueling FCVs. Performance is also affected
by the architecture of the reformate system. A gasoline FCV equipped
with an ATR is estimated to emit almost the same level of CO 2 as a diesel
HEV. Accordingly, performance should be improved to be competitive
with HEVs in terms of fuel economy. If the target for volumetric power
density is achieved, a reformate system with a volume of 60 l will be able
to provide a power output of 100 kW by 2010. A system of that size will
be easy to install under the cabin floor. A small volume reformate system
will reduce heat losses from each component, resulting in improved system efficiency. In order to reduce the volume of each component, it will be
necessary to enhance the performance of the catalyst used in ATR, shift
reactors, and preferential oxidation (PrO x ) reactors, especially for activity
under gas high space velocity (GHSV) conditions. It is noteworthy that
using ceramic foam as a catalyst substrate helps reduce the volume of the
ATR reactor.
Onboard reforming presents a number of technical and economical challenges that include volume targets, weight targets, and start-up requirements.
Alternative Fuels for Transportation
storage material M with the heat of formation ΔH (M + H 2 → MH 2 + ΔH) of
about 25 MJ kg –1 H 2 , a thermal load of 150 MJ is desired during refueling.
This leads to an average heat exchange of 800 kW. Such a high-performance device is unimaginable onboard a vehicle due to cost, volume, and
weight considerations. A further constraint is that many solid-state absorbers have to be limited to 70°C to be practical, which could be reached by
using the waste heat of the FCS. Hydrogen absorbers often consist of powder
materials. The absorber accounts for 50% of the total weight, whereas 50% is
due to valves, pipes, pressure vessels, heat exchanger, and so on. A 70 MPa
compressed gaseous hydrogen storage system is currently the best-in-class
option available for hydrogen storage onboard a vehicle.
The most important factor for the success of FCVs lies in the success of the
hydrogen economy and related technologies. McNicol, Rand, and Williams
(2001) reported that a FCV system equipped with a direct conversion fuel
processor could compete successfully with conventional ICEVs. Buses and
recreation vehicles have more space to house the fuel processor than passenger cars. Onboard fuel reforming is another option to utilize the existing
liquid hydrocarbon fuel infrastructure and to produce hydrogen onboard.
The desired reformer-FC system is obviously more complex than an onboard
hydrogen storage FC system.
Reforming for automotive applications requires an air-assisted primary reforming called Catalytic Partial-Oxidation (CPO) or Auto-Thermal
Reforming (ATR). During CPO, air is applied together with a hydrocarbon
fuel while, during ATR, air is supplied together with steam and a hydrocarbon fuel. The gas treatment consists of shift conversion and CO removal.
The architecture of the reformate system is influenced by the type of
the fuel used. There are many candidate fuels such as methanol, ethanol,
naphtha, low sulfur gasoline, and dimethyl ether. It is advisable to use
the existing infrastructure for fueling FCVs. Performance is also affected
by the architecture of the reformate system. A gasoline FCV equipped
with an ATR is estimated to emit almost the same level of CO 2 as a diesel
HEV. Accordingly, performance should be improved to be competitive
with HEVs in terms of fuel economy. If the target for volumetric power
density is achieved, a reformate system with a volume of 60 l will be able
to provide a power output of 100 kW by 2010. A system of that size will
be easy to install under the cabin floor. A small volume reformate system
will reduce heat losses from each component, resulting in improved system efficiency. In order to reduce the volume of each component, it will be
necessary to enhance the performance of the catalyst used in ATR, shift
reactors, and preferential oxidation (PrO x ) reactors, especially for activity
under gas high space velocity (GHSV) conditions. It is noteworthy that
using ceramic foam as a catalyst substrate helps reduce the volume of the
ATR reactor.
Onboard reforming presents a number of technical and economical challenges that include volume targets, weight targets, and start-up requirements.