Method and apparatus for humidification control of an energy recovery device in a fuel cell power plant

1. A fuel cell power plant ( 10 ) for generating electrical energy from a process oxidant stream ( 53 , 42 , 28 ) and a reducing fluid stream ( 26 ), the plant comprising:

a) at least one fuel cell ( 12 ) for producing the electrical energy from the process oxidant stream ( 53 , 28 ) and the reducing fluid stream ( 26 ), and providing a fuel cell exhaust stream ( 48 ) containing moisture and sensible heat;

b) an energy recovery device ( 32 ) having first and second gas flow channels ( 44 , 42 ) separated by a respective enthalpy exchange barrier ( 46 ), the fuel cell exhaust stream ( 48 ) connected to pass through the first gas flow channel ( 44 ) and a source of process oxidant ( 30 ) for the process oxidant stream ( 53 ) connected to pass through the second gas flow channel ( 42 ), thereby to allow mass and heat transfer between the gases in the first and second gas flow channels via the enthalpy exchange barrier;

c) a supply of liquid medium ( 66 ); and

d) means ( 58 , 60 ) for injecting the liquid medium ( 66 , 64 ) substantially directly into the process oxidant stream ( 53 ) preparatory to the process oxidant passing through the energy recovery device second gas flow channel ( 42 ) for regulating the transfer of mass and heat between the fuel cell exhaust stream ( 48 ) and the process oxidant stream ( 53 , 42 ).

2. The fuel cell power plant ( 10 ) of claim 1 wherein the energy recovery device includes an inlet ( 54 ) for receiving the process oxidant stream ( 53 ) to pass through the second gas flow channel ( 42 ), the liquid medium for injection is water, and the injecting means ( 58 , 60 ) is positioned to inject the water into the process oxidant stream ( 53 ) immediately upstream of said inlet ( 54 ).

3. The fuel cell power plant ( 10 ) of claim 2 including a plenum ( 62 ) located immediately upstream of said inlet ( 54 ), said process oxidant stream ( 53 ) flows through said plenum ( 62 ), and wherein the injecting means ( 58 , 60 ) is operative to inject water ( 66 , 64 ) into the plenum ( 62 ) for intimate mixing with and humidification of the process oxidant stream.

4. The fuel cell power plant ( 10 ) of claim 3 wherein the injecting means comprises one or more spray nozzles ( 60 ) disposed to inject a spray of water ( 66 , 64 ) into the plenum ( 62 ).

5. The fuel cell power plant ( 10 ) of claim 1 including control means ( 70 , 74 , 78 , 80 , 84 ) operatively associated with the injecting means ( 58 , 60 ) for controlling at least the amount of the liquid medium ( 66 , 64 ) being injected.

6. The fuel cell power plant ( 10 ) of claim 5 wherein the control means ( 70 , 74 , 78 , 80 , 84 ) include at least one or the other of a temperature sensor ( 80 ) for sensing the temperature of ambient process oxidant and a humidity sensor ( 84 ) for sensing the moisture content of the ambient process oxidant.

7. The fuel cell power plant ( 10 ) of claim 6 wherein the control means ( 70 , 74 , 78 , 80 , 84 ) includes both the temperature sensor ( 80 ) and the humidity sensor ( 84 ).

8. The fuel cell power plant ( 10 ) of claim 1 wherein the enthalpy exchange barrier ( 46 ) of the energy recovery device ( 32 ) comprises a fine-pore support matrix.

9. The fuel cell power plant ( 10 ) of claim 8 wherein the fine-pore support matrix is one or a combination selected from the group consisting of porous graphite layers; porous graphite-polymer layers, inorganic-fiber thermoset polymer layers, glass fiber layers, synthetic-fiber filter papers treated to be wettable, porous metal layers, and perforated metal layers with particulate material in the pores.

10. In a fuel cell power plant ( 10 ) for generating electrical energy from a process oxidant stream ( 53 , 42 , 28 ) and a reducing fluid stream ( 26 ), the plant comprising a fuel cell ( 12 ) for producing the electrical energy from the process oxidant stream ( 53 , 28 ) and the reducing fluid stream ( 26 ), and providing a fuel cell exhaust stream ( 48 ) containing moisture and sensible heat; and an energy recovery device ( 32 ) having first and second gas flow channels ( 44 , 42 ) separated by a respective enthalpy exchange barrier ( 46 ), the fuel cell exhaust stream ( 48 ) connected to pass through the first gas flow channel ( 44 ) and a source of process oxidant ( 30 ) for the process oxidant stream ( 53 ) connected to pass through the second gas flow channel ( 42 ), thereby to allow mass and heat transfer between the gases in the first and second gas flow channels via the enthalpy exchange barrier, the method comprising: dispensing water ( 66 , 70 , 74 , 60 , 64 ) substantially directly into the process oxidant stream ( 53 ) preparatory to the process oxidant passing through the energy recovery device second gas flow channel ( 42 ) for regulating the transfer of mass and heat between the fuel cell exhaust stream ( 48 ) and the process oxidant stream ( 53 , 42 ).

11. The method of claim 10 wherein the step of dispensing water ( 66 , 70 , 74 , 60 , 64 ) into the process oxidant stream ( 53 ) comprises monitoring ( 80 , 84 , 90 ) one or more parameters of the fuel cell power plant ( 10 ), including the process oxidant stream ( 53 , 42 , 28 ), and controllably injecting water into the process oxidant stream ( 53 ) in response to the one or more of the monitored parameters.

12. The method of claim 11 comprising the steps of monitoring ( 80 ) the temperature of the process oxidant stream ( 53 ), and injecting water ( 66 , 70 , 74 , 60 , 64 ) into the process oxidant stream when the temperature exceeds a threshold, thereby to cool and humidify the process oxidant stream ( 53 , 42 ) to inhibit dry-out of the enthalpy exchange barrier 46 in the energy recovery device 32 .

13. The method of claim 12 wherein the temperature threshold is higher than about 95° F. and lower than about 90° F.

14. The method of claim 11 wherein the operating status of the power plant ( 10 ) is monitored ( 70 , 80 ) to identify a start-up condition, and injecting water ( 66 , 70 , 74 , 60 , 64 ) into the process oxidant stream upon start-up, at least after a shutdown exceeding a predetermined duration, for assuring sufficient wetting of the enthalpy exchange barrier ( 46 ) during start-up.

15. The method of claim 14 wherein a temperature of the power plant ( 10 ), including the inlet temperature of the process oxidant stream ( 53 , 42 , 28 ), is monitored ( 80 ) to detect a freezing condition, and controllably ( 70 , 78 ) injecting heated water ( 66 , 58 , 60 , 64 ) during start-up in response to detection of a freezing condition to defrost at least the energy recovery device 32 .

16. The method of claim 11 wherein the fuel cell power plant ( 10 ) includes a coolant system ( 38 , 88 ) having a coolant, the coolant having a level, and including the steps of monitoring ( 90 ) the level of coolant in the coolant system ( 38 , 88 ) and injecting water ( 66 , 58 , 70 , 74 , 78 , 60 , 64 ) into the process oxidant stream when the coolant level exceeds a threshold, thereby to raise the dew point of the process oxidant stream ( 53 , 42 ) to inhibit recovery of water from the fuel cell exhaust stream 48 via the enthalpy exchange barrier 46 to the process oxidant stream ( 42 ).