Method and arrangement for reforming fuel
A method and an arrangement for reforming a hydrocarbon fuel such as dimethyl ether (DME), methanol, ethanol, propanol, or any variants or other oxidized fuels is disclosed for generating hydrogen especially for supplying a fuel cell. Furthermore, a fuel cell system is disclosed which includes such an arrangement, especially for providing power to a stationary or mobile power consuming unit like especially an auxiliary power unit (APU) for application in aircraft, ships and vehicles, or as a part of a hybrid drive or as a sole driving unit for, e.g., a ship or a vehicle.
1. Method for reforming a hydrocarbon fuel for generating hydrocarbon, comprising:
a start-up phase comprising establishing an autothermal fuel reforming process in a fuel reformer comprising an oxidation catalyst, which start-up phase comprises, in sequence, the following processes:
an initial phase of feeding hydrocarbon fuel and air into the fuel reformer as a lean mixture of the air-to-fuel ratio such that the fuel reformer is catalytically started and heated by an exothermic reaction;
a first stage of feeding hydrocarbon fuel and air into the fuel reformer as a fat mixture for initiating an exothermic catalytic partial oxidation process for reforming the hydrocarbon fuel to hydrogen,
a second stage for catalytically converting the hydrogen generated in the first stage into water steam by a catalytic combustion reactor;
a third stage for initiating an endothermic catalytic steam reforming process in the fuel reformer by feeding back into the fuel reformer the water steam which is generated in the second stage, so that by the combination of the exothermic and the endothermic processes the autothermal fuel reforming process is created; and
a steady state operation phase in which the hydrogen which is generated by the ATR process is fed to a fuel cell for operating the same.
2. Method according to claim 1 , wherein in the steady state operation:
the fuel reformer is operated only with water steam which is generated by a heat exchanger from the water which is supplied from the fuel cell, and
the heat exchanger is operated by heat supplied from the combustion reactor in the form of water steam which is generated in the combustion reactor from hydrogen which is supplied from the fuel cell.
3. Method according to claim 1 , wherein after creating the autothermal fuel reforming process in the third stage, the hydrogen which is generated by the autothermal fuel reforming process is purified prior to supplying it to a fuel cell, by especially reducing the amount of carbon monoxide.
4. Method according to claim 1 , wherein a transition phase precedes the steady state operation phase in which transition phase the fuel reformer is operated with water steam which is generated by the combustion reactor from excess hydrogen from the fuel cell, and with water steam which is generated by a heat exchanger from water which is generated in the fuel cell, wherein the heat exchanger is operated by heat of the water steam which is generated by and fed from the combustion reactor to the fuel reformer.
5. Method according to claim 1 , comprising feeding oxygen during the exothermic catalytic partial oxidation process into the fuel reformer in the form of ambient air such that an air-to-fuel ratio of the air to fuel mixture is about 0.1 to 0.7.
6. Method according to claim 1 , comprising feeding oxygen during the initial step into the fuel reformer in a form of ambient air such that an air-to-fuel ratio of the air to fuel mixture is between about 4 and about 8.
7. Computer program comprising computer program code means adapted to perform a method according to claim 1 when the program is run on a programmable microcomputer.
8. Computer program product stored on a computer readable medium, comprising computer program code means according to claim 7 .
9. Method according to claim 1 , wherein when the initial step is stable, the catalytic partial oxidation process is initiated by reducing the air-to-fuel ratio to a fat mixture of about 0.25.
10. Method according to claim 1 , wherein the transition between the initial step and the autothermal fuel reforming process is performed at a temperature of between about 300° C. and about 500° C.