Systems and processes for operating fuel cell systems

Abstract

Processes and systems for operating molten carbonate fuel cell systems are described herein. A process for operating a molten carbonate fuel cell system includes providing a hydrogen-containing stream comprising molecular hydrogen to an anode portion of a molten carbonate fuel cell; controlling a flow rate of the hydrogen-containing stream to the anode such that molecular hydrogen utilization in the anode is less than 50%; mixing anode exhaust comprising molecular hydrogen from the molten carbonate fuel cell with a hydrocarbon stream comprising hydrocarbons, contacting at least a portion of the mixture of anode exhaust and the hydrocarbon stream with a catalyst to produce a steam reforming feed; separating at least a portion of molecular hydrogen from the steam reforming feed; and providing at least a portion of the separated molecular hydrogen to the molten carbonate fuel cell anode.

We claim: 
     
         1 . A molten carbonate system, comprising:
 a molten carbonate fuel cell comprising an anode portion and a cathode portion, said molten carbonate fuel cell configured to receive a hydrogen-containing stream comprising molecular hydrogen at a flow rate such that hydrogen utilization in an anode of the molten carbonate fuel cell is less than 50%;   one or more reformers operatively coupled to the molten carbonate fuel cell, at least one reformer being configured to receive anode exhaust from the molten carbonate fuel cell and hydrocarbons, and being configured to allow the anode exhaust to sufficiently mix with a stream comprising hydrocarbons to at least partially reform some of the hydrocarbons to produce a reformed product stream, wherein the reformed product stream comprises molecular hydrogen and at least one carbon oxide; and   a high temperature hydrogen-separation device that is part of, or coupled to, at least one of the reformers and operatively coupled to the molten carbonate fuel cell, wherein the high temperature hydrogen-separation device is configured to receive a reformed product stream and to provide a stream comprising at least a portion of the molecular hydrogen to the anode portion of the molten carbonate fuel cell.   
     
     
         2 . The molten carbonate system of  claim 1 , comprising at least two reformers including, a first reformer configured to receive anode exhaust, and a second reformer configured to receive product from the first reformer and a stream comprising hydrocarbons. 
     
     
         3 . The molten carbonate system of  claim 2 , wherein the high temperature hydrogen-separation device is operatively coupled to the second reformer. 
     
     
         4 . The molten carbonate system of  claim 3 , further comprising an oxidizing unit. 
     
     
         5 . The molten carbonate system of  claim 3 , wherein the high temperature hydrogen-separation device comprises one or more high temperature hydrogen-separating membranes. 
     
     
         6 . The molten carbonate system of  claim 4 , wherein the oxidizing unit is a catalytic partial oxidation reformer. 
     
     
         7 . The molten carbonate system of  claim 6 , wherein the second reformer includes a reforming zone, a high temperature hydrogen-separation device and a catalytic partial oxidation reformer. 
     
     
         8 . The molten carbonate system of  claim 1 , wherein at least a portion of the carbon dioxide provided to the cathode portion of the molten carbonate fuel cell is provided by the high temperature hydrogen-separation device. 
     
     
         9 . The molten carbonate system of  claim 1 , wherein the molten carbonate fuel cell is operated at a pressure of 0.1 MPa or less. 
     
     
         10 . The molten carbonate system of  claim 2 , where at least some of the hydrocarbons of the hydrocarbon stream comprise one or more vaporizable hydrocarbons having a carbon number of at least 4. 
     
     
         11 . The molten carbonate system of  claim 1 , wherein the hydrogen-containing stream comprises at least 0.6 mol fraction molecular hydrogen. 
     
     
         12 . The molten carbonate system of  claim 1 , further comprising providing air and carbon dioxide to the cathode portion of the molten carbonate fuel cell, wherein air comprises molecular oxygen, and the flow rate of air and carbon dioxide are controlled such that the molar ratio of carbon dioxide to molecular oxygen is at least 2. 
     
     
         13 . The molten carbonate system of  claim 1 , wherein electricity is generated from the molten carbonate fuel cell at an electrical power density of at least 0.1 W/cm 2  at 1 bara. 
     
     
         14 . The molten carbonate system of  claim 13 , wherein the flow rate of air and carbon dioxide are controlled such that the molar ratio of carbon dioxide to molecular oxygen is at least 2.5. 
     
     
         15 . The molten carbonate system of  claim 1 , wherein the anode exhaust that is mixed with the stream comprising hydrocarbons has a temperature from 500° C. to 700° C.; 
     
     
         16 . The molten carbonate system of  claim 14 , wherein electricity is generated from the molten carbonate fuel cell at an electrical power density of at least 0.3 W/cm 2  at 1 bara.