Sofc system with selective co2 removal

Abstract

A system and method in which a high temperature fuel cell stack exhaust stream is recycled back into the fuel inlet stream of the high temperature fuel cell stack. The recycled stream may be sent to a carbon dioxide separation device which separates carbon dioxide from the fuel exhaust stream. The carbon dioxide separation device may be a carbon dioxide trap, an electrochemical carbon dioxide separator, or a membrane separator. A water separator may be used in conjunction with the carbon dioxide separation device or used separately to continuously remove water from the recycled stream.

1 . A fuel cell system, comprising:
 a fuel cell stack;   a first recycling conduit operatively connecting the fuel cell stack to a carbon dioxide separation device, the first recycling conduit adapted to recycle a portion of a fuel exhaust stream from the fuel cell stack to the carbon dioxide separation device, the carbon separation device adapted to remove carbon dioxide from the recycled fuel exhaust stream creating a purified recycled fuel exhaust stream;   a second recycling conduit operatively connecting the carbon dioxide separation device to the fuel inlet conduit, the second recycling conduit adapted to provide the purified recycled fuel exhaust stream to the fuel inlet conduit; and   an exhaust conduit operatively connecting the fuel cell stack to a collection side of the carbon dioxide separation device, the exhaust conduit adapted to provide a second portion of the fuel exhaust stream from the fuel cell stack to sweep carbon dioxide from the collection side of the carbon dioxide separation device.   
     
     
         2 . The system of  claim 1 , further comprising:
 an air conduit operatively connected to the exhaust conduit, the air conduit adapted to provide air into the second portion of the fuel exhaust stream provided to the collection side of the carbon dioxide separation device.   
     
     
         3 . The system of  claim 1 , further comprising:
 a membrane humidifier operatively connected to the exhaust conduit, the membrane humidifier adapted to provide water into the second portion of the fuel exhaust stream provided to the collection side of the carbon dioxide separation device.   
     
     
         4 . The system of  claim 1 , further comprising:
 a water separator operatively connected to the second recycling conduit, the water separator adapted to remove water from the purified recycled fuel exhaust stream;   a membrane humidifier operatively connected to the exhaust conduit, the membrane humidifier adapted to provide water into the second portion of the fuel exhaust stream provided to the collection side of the carbon dioxide separation device; and   a water conduit operatively connected to the water separator and membrane humidifier, the water conduit adapted to provide water from the water separator to the membrane humidifier.   
     
     
         5 . The system of  claim 1 , wherein the carbon dioxide separation device is a combination carbon dioxide and water separation device further adapted to remove water from the recycled fuel exhaust stream, and the fuel cell system further comprising:
 a membrane humidifier operatively connected to the exhaust conduit, the membrane humidifier adapted to provide water into the second portion of the fuel exhaust stream provided to the collection side of the carbon dioxide separation device; and   a water conduit operatively connected to the carbon dioxide separation device, the water conduit adapted to provide water from the carbon dioxide separation device to the membrane humidifier.   
     
     
         6 . The system of  claim 1 , wherein the fuel cell stack is a solid oxide fuel cell (SOFC) stack, the fuel cell system further comprising:
 an anode tail gas oxidizer operatively connected to the exhaust conduit, the anode tail gas oxidizer adapted to oxidize SOFC anode and cathode exhaust prior to providing the second portion of the fuel exhaust stream from the fuel cell stack to the collection side of the carbon dioxide separation device.   
     
     
         7 . A fuel cell system, comprising:
 a fuel cell stack;   a first recycling conduit operatively connecting the fuel cell stack to a carbon dioxide separation device, the first recycling conduit adapted to recycle a portion of a fuel exhaust stream from the fuel cell stack to the carbon dioxide separation device, the carbon separation device adapted to remove carbon dioxide from the recycled fuel exhaust stream creating a purified recycled fuel exhaust stream;   a second recycling conduit operatively connecting the carbon dioxide separation device to the fuel inlet conduit, the second recycling conduit adapted to provide the purified recycled fuel exhaust stream to the fuel inlet conduit;   a humidifier, adapted to humidify air; and   an air conduit operatively coupled to the humidifier and the carbon dioxide separation device, the air conduit adapted to provide humid air to a collection side of the carbon dioxide separation device.   
     
     
         8 . The system of  claim 7 , further comprising:
 a water separator operatively connected to the second recycling conduit, the water separator adapted to remove water from the purified recycled fuel exhaust stream; and   a water conduit operatively connected to the water separator and the humidifier, the water conduit adapted to provide water from the water separator to the humidifier.   
     
     
         9 . The system of  claim 7 , wherein the carbon dioxide separation device is a combination carbon dioxide and water separation device further adapted to remove water from the recycled fuel exhaust stream, and the fuel cell system further comprising:
 a water conduit operatively connected to the carbon dioxide separation device, the water conduit adapted to provide water from the carbon dioxide separation device to the humidifier.   
     
     
         10 . The system of  claim 7 , wherein the humidifier is a spray humidifier. 
     
     
         11 . The system of  claim 7 , wherein the first recycling conduit is operatively connected to a product side of the carbon separation device and adapted to provide the fuel exhaust stream to the product side of the carbon separation device, wherein the second recycling conduit is operatively connected to the product side of the carbon separation and adapted to receive purified recycled fuel exhaust from the product side of the carbon separation device, wherein the carbon dioxide separation device is adapted to enable carbon dioxide to diffuse through a separator from the product side to the collection side of the carbon dioxide separation device, and wherein the fuel cell stack is a solid oxide fuel cell (SOFC) stack, the system further comprising:
 a reactor operatively connected to the fuel cell stack, the reactor adapted to oxidize a SOFC fuel exhaust stream using a SOFC air exhaust stream to generate a reactor exhaust stream; and   an exhaust conduit operatively connected to the reactor and the humidifier, the exhaust conduit adapted to provide the reactor exhaust stream to the humidifier.   
     
     
         12 . The system of  claim 10 , wherein the carbon dioxide separation device is an electrochemical separator or a membrane separator. 
     
     
         13 . A fuel cell system, comprising:
 a fuel cell stack;   a first recycling conduit operatively connecting the fuel cell stack to a carbon dioxide membrane separator, the first recycling conduit adapted to recycle a portion of a fuel exhaust stream from the fuel cell stack to the carbon dioxide membrane separator, the carbon dioxide membrane comprising a carbon separating membrane containing a tailored membrane adapted to selectively transport more carbon dioxide than water from the recycled fuel exhaust, the carbon dioxide membrane separator thereby adapted to remove carbon dioxide from the recycled fuel exhaust stream creating a purified recycled fuel exhaust stream; and   a second recycling conduit operatively connecting the carbon dioxide membrane separator to the fuel inlet conduit, the second recycling conduit adapted to provide the purified recycled fuel exhaust stream to the fuel inlet conduit.   
     
     
         14 . The system of  claim 13 , wherein the tailored membrane comprises a polytetrafluoroethylene membrane. 
     
     
         15 . The system of  claim 13 , further comprising a water separator operatively connected to the second recycling conduit, the water separator adapted to remove water from the purified recycled fuel exhaust stream. 
     
     
         16 . The system of  claim 13 , further comprising an air conduit operatively connected to a collection side of the carbon dioxide membrane separator, the air conduit adapted to provide purge air to the collection side of the carbon dioxide membrane separator. 
     
     
         17 . The system of  claim 13 , further comprising:
 an output conduit operatively connected to a collection side of the carbon dioxide membrane separator; and   a vacuum pump operatively connected to the output conduit, the vacuum pump adapted to pull carbon dioxide from the collection side of the carbon dioxide membrane separator via the output conduit.   
     
     
         18 . A fuel cell system, comprising:
 a fuel cell stack;   a first recycling conduit operatively connecting the fuel cell stack to a water separator, the first recycling conduit adapted to recycle a portion of a fuel exhaust stream from the fuel cell stack to the water separator, the water separator adapted to remove water from the recycled fuel exhaust stream creating a drier recycled fuel exhaust stream before any portion of the fuel exhaust stream is recycled into the fuel inlet stream;   a second recycling conduit operatively connecting the water separator to the fuel inlet conduit, the second recycling conduit adapted to provide the drier recycled fuel exhaust stream to the fuel inlet conduit; and   a discharge conduit operatively connected to the water separator and adapted to discharge the removed water out of the water separator and away from the fuel inlet conduit.   
     
     
         19 . The system of  claim 18 , wherein the water separator is a vertically positioned water membrane separator, wherein the first recycling conduit is operatively connected to a product side of the water membrane separator and adapted to provide the fuel exhaust stream to the product side of the water membrane separator, wherein the second recycling conduit is operatively connected to the product side of the water membrane separator and adapted to receive the drier recycled fuel exhaust from the product side of the water membrane separator, and wherein the water membrane separator is adapted to enable water to diffuse through a membrane from the product side to a collection side of the water membrane separator, the system further comprising:
 an air conduit operatively connected to the collection side of the water membrane separator, the air conduit adapted to provide air into the collection side of the water membrane separator; and   wherein the discharge conduit is operatively connected to the collection side of the water separator and adapted to discharge the removed water and air out of the water membrane separator and away from the fuel inlet conduit.