Rapid start fuel reforming systems and techniques
An on-board fuel processor includes a microchannel steam reforming reactor ( 30 ) and a water vaporizer ( 40 ) heated in series with a combustion gas. The reformer ( 30 ) and the vaporizer ( 40 ) are both of a cross-flow panel configuration that allows for low combustion side pressure drop. Fuel is directly injected into the steam, and during a rapid cold start, both the combustion gas flow rate and the steam to carbon ratio are substantially increased relative to their steady state operating values. A rapid cold start can be achieved in under 30 seconds with a manageable amount of electric power consumption, removing impediments to use in automotive fuel cell applications.
1. A method comprising:
providing a fuel cell system including a fuel reforming reactor and at least one blower for selectively conveying combustion gas through a heating side of the reforming reactor at different mass flow rates;
starting-up the reforming reactor by heating a reforming side of the reactor with a combustion gas flowing through the heating side of the reactor, wherein the combustion gas flows through the heating side of the reactor from a first face of the reactor to a second face of the reactor, and wherein the first and second faces each have a length and width substantially greater than the distance between the faces; and then
operating the reactor to produce a reformate stream by driving an endothermic reforming reaction on the reforming side with heat from a combustion gas flowing though the heating side;
wherein a mass flow rate of combustion gas through the heating side during the starting-up is at least about five times a mass flow rate of combustion gas through the heating side during the operating.
2. The method of claim 1 wherein the pressure drop across the heating side of the reforming reactor during the starting up is less than about 10 inches of water.
3. The method of claim 2 wherein the system includes a vaporizer having a heating side downstream from the heating side of the reforming reactor, and the combined pressure drop across the heating side of the vaporizer and the heating side of the reforming reactor during the starting-up is less than about 10 inches of water.
4. The method of claim 2 wherein a Reynolds number of the combustion gas flowing through the heating side during the starting up is less than about 2000.
5. The method of claim 1 wherein the system includes a vaporizer having a heating side downstream from the heating side of the reforming reactor, the vaporizer including a first face and a second face each having a length and width substantially greater than the distance between the faces, the method further comprising flowing the combustion gas through the heating side of the vaporizer from the first face of the vaporizer to the second face of the vaporizer.
6. The method of claim 5 wherein there is no intervening heat exchanger between the heating sides of the reforming reactor and the vaporizer.
7. The method of claim 1 wherein there are at least two blowers.
8. The method of claim 1 wherein the starting up includes raising an internal temperature of the reforming side from below about 50° C. to above about 400° C. while the at least one blower consumes an amount of power less than about 4% of the steady state electrical output of the fuel cell system.
9. The method of claim 1 wherein the S:C ratio during the starting-up is at least about 4 times greater than during the operating.
10. The method of claim 9 wherein the S:C ratio during the starting-up is at least 8 times greater than during the operating.
11. The method of claim 1 , wherein the temperature of the combustion gas at the first face of the reactor is at least 200° C. greater than the temperature of the first face of the reactor during the operating.
12. The method of claim 1 further comprising conducting heat through the reactor away from an inlet to the heating side of the reactor to prevent the metal temperature at the inlet from exceeding a maximum operating temperature when the combustion gas at the inlet is at least about 200° C. above the maximum operating temperature.