Fuel cell integration within a heat recovery steam generator
Systems and methods are provided for incorporating molten carbonate fuel cells into a heat recovery steam generation system (HRSG) for production of electrical power while also reducing or minimizing the amount of CO 2 present in the flue gas exiting the HRSG. An optionally multi-layer screen or wall of molten carbonate fuel cells can be inserted into the HRSG so that the screen of molten carbonate fuel cells substantially fills the cross-sectional area. By using the walls of the HRSG and the screen of molten carbonate fuel cells to form a cathode input manifold, the overall amount of duct or flow passages associated with the MCFCs can be reduced.
1. A method of treating exhaust gas to reduce CO 2 using a molten carbonate fuel cell located inside a heat recovery steam generator (“HRSG”), the method comprising:
receiving CO 2 -containing exhaust gas through an inlet of the HRSG to form a received gas flow;
passing the received gas flow through a fuel cell screen comprising a plurality of molten carbonate fuel cells to generate a cathode exhaust gas comprising at least about 50 vol % less CO 2 than the received gas flow, the fuel cell screen being located within the HRSG, wherein substantially all of the received gas flow is passed into a cathode section of the molten carbonate fuel cells;
passing the cathode exhaust gas into a first heat exchanger; and
passing the cathode exhaust gas into an exhaust stack.
2. The method of claim 1 , wherein the method further comprises passing the received gas flow into a duct burner prior to passing the received gas flow into the fuel cell screen.
3. The method of claim 2 , wherein passing the received gas flow into the duct burner comprises passing the received gas flow into the duct burner with a superficial velocity of at least about 4 m/s.
4. The method of claim 1 , wherein the method further comprises passing the received gas flow into the fuel cell screen with a superficial velocity of about 1 m/s or less.
5. The method of claim 1 , wherein the method further comprises passing the cathode exhaust gas into the first heat exchanger with a superficial velocity of at least about 4 m/s.
6. The method of claim 1 , wherein the CO 2 -containing exhaust gas received through the inlet of the HRSG has a superficial velocity at the inlet of at least about 4 m/s.
7. The method of claim 1 , wherein the fuel cell screen comprises a first layer and a second layer, and the method further comprises dividing the received gas flow into at least a first gas flow portion that is passed to the first layer and a second gas flow portion that is passed to the second layer.
8. The method of claim 1 , further comprising passing the received gas flow into a second heat exchanger prior to passing the received gas flow into the fuel cell screen.
9. The method of claim 1 , wherein the plurality of molten carbonate fuel cells are operated with a current density of greater than about 1500 mA/m 2 .
10. The method of claim 1 , wherein the CO 2 -containing exhaust gas comprises an exhaust gas from a gas turbine.
11. The method of claim 1 , wherein the cathode exhaust comprises substantially all of the gas in the flow path providing heat to the first heat exchanger.
12. The method of claim 1 , wherein the fuel cell screen is sized to reduce a CO 2 concentration in the cathode exhaust by at least about 65% relative to the received gas flow.