Integrated Power Generation Using Molten Carbonate Fuel Cells

Abstract

In various aspects, systems and methods are provided for integrated operation of molten carbonate fuel cells with turbines for power generation. Instead of selecting the operating conditions of a fuel cell to improve or maximize the electrical efficiency of the fuel cell, an excess of reformable fuel can be passed into the anode of the fuel cell to increase the chemical energy output of the fuel cell. The increased chemical energy output can be used for additional power generation, such as by providing fuel for a hydrogen turbine.

What is claimed is: 
     
         1 . A method for producing electricity, the method comprising:
 introducing a fuel stream comprising a reformable fuel into an anode of a molten carbonate fuel cell, an internal reforming element associated with the anode, or a combination thereof;   introducing a cathode inlet stream comprising CO 2  and O 2  into a cathode of the molten carbonate fuel cell;   generating electricity within the molten carbonate fuel cell, the molten carbonate fuel cell being operated such that a fuel utilization in the anode is about 50% or less at steady state conditions;   generating an anode exhaust comprising H 2 , CO, and CO 2 ;   separating, from at least a portion of the anode exhaust, a first H 2 -rich gas stream; and   combusting at least a portion of the first H 2 -rich gas stream to produce electricity.   
     
     
         2 . The method of  claim 1 , further comprising performing a water gas shift process on the anode exhaust, the at least a portion of the anode exhaust, or a combination thereof. 
     
     
         3 . The method of  claim 1 , further comprising separating CO 2  and/or H 2 O from the anode exhaust, the at least a portion of the anode exhaust, or a combination thereof. 
     
     
         4 . The method of  claim 1 , wherein the separating step comprises:
 performing a water gas shift process on the anode exhaust or at least a portion of the anode exhaust to form a shifted anode exhaust portion; and   separating H 2 O and CO 2  from the shifted anode exhaust portion to form the first H 2 -rich gas stream.   
     
     
         5 . The method of  claim 1 , wherein the first H 2 -rich gas stream comprises at least about 80 vol % H 2 . 
     
     
         6 . The method of  claim 1 , wherein combusting step comprises (a) generating steam from heat generated by the combustion, and producing electricity from at least a portion of the generated steam, and/or (b) combusting the at least a portion of the first H 2 -rich gas stream in a turbine. 
     
     
         7 . The method of  claim 1 , wherein the cathode inlet stream comprises exhaust from combustion of a carbon-containing fuel in a combustion turbine, the carbon-containing fuel comprising at least 5 vol % of inert gases. 
     
     
         8 . The method of  claim 7 , wherein the carbon-containing fuel comprises at least about 10 vol % CO 2  and/or at least about 10 vol % N 2 . 
     
     
         9 . The method of  claim 1 , wherein the anode exhaust has a ratio of H 2 :CO of at least about 3.0:1. 
     
     
         10 . The method of  claim 1 , wherein at least about 90 vol % of the reformable fuel is methane. 
     
     
         11 . The method of  claim 1 , wherein one or more of the following is satisfied: the molten carbonate fuel cell is operated at a thermal ratio of about 0.25 to about 1.0 at steady state conditions; a ratio of net moles of syngas in the anode exhaust to moles of CO 2  in a cathode exhaust is at least about 2.0:1 at steady state conditions; an electrical efficiency for the molten carbonate fuel cell is between about 10% and about 40% at steady state conditions; and a total fuel cell efficiency for the molten carbonate fuel cell is at least about 55% at steady state conditions. 
     
     
         12 . The method of  claim 1 , wherein a CO 2  utilization in the cathode is at least about 60% and the first H 2 -rich gas stream comprises at least about 90 vol % H 2 . 
     
     
         13 . A method for producing electricity, the method comprising:
 introducing a fuel stream comprising a reformable fuel into an anode of a molten carbonate fuel cell, an internal reforming element associated with the anode, or a combination thereof;   introducing a cathode inlet stream comprising CO 2  and O 2  into a cathode of the molten carbonate fuel cell;   generating electricity within the molten carbonate fuel cell, the molten carbonate fuel cell being operated such that a CO 2  utilization in the cathode is at least about 60%;   generating an anode exhaust comprising H 2 , CO, and CO 2 ;   separating, from at least a portion of the anode exhaust, a first H 2 -rich gas stream; and   combusting at least a portion of the first H 2 -rich gas stream to produce electricity.   
     
     
         14 . The method of  claim 13 , wherein the CO 2  utilization in the cathode occurs at steady state conditions. 
     
     
         15 . The method of  claim 13 , further comprising: (i) performing a water gas shift process on the anode exhaust, the at least a portion of the anode exhaust, or a combination thereof; (ii) separating CO 2  from the anode exhaust, the at least a portion of the anode exhaust, or a combination thereof; (iii) separating H 2 O from the anode exhaust, the at least a portion of the anode exhaust, or a combination thereof or (iv) any combination thereof. 
     
     
         16 . The method of  claim 13 , wherein the first H 2 -rich gas stream comprises at least about 80 vol % H 2 , and wherein the combusting step comprises combusting the at least a portion of the first H 2 -rich gas stream in a turbine. 
     
     
         17 . The method of  claim 13 , wherein the cathode inlet stream comprises exhaust from combustion of a carbon-containing fuel in a combustion turbine, the carbon-containing fuel comprising at least 5 vol % of inert gases, wherein the carbon-containing fuel optionally comprises at least about 10 vol % CO 2  and/or at least about 10 vol % N 2 . 
     
     
         18 . The method of  claim 13 , wherein the anode exhaust has a ratio of H 2 :CO of at least about 3.0:1. 
     
     
         19 . The method of  claim 13 , wherein at least about 90 vol % of the reformable fuel is methane. 
     
     
         20 . The method of  claim 13 , wherein one or more of the following is satisfied: the molten carbonate fuel cell is operated at a thermal ratio of about 0.25 to about 1.0 at steady state conditions; a ratio of net moles of syngas in the anode exhaust to moles of CO 2  in a cathode exhaust is at least about 2.0:1 at steady state conditions; an electrical efficiency for the molten carbonate fuel cell is between about 10% and about 40% at steady state conditions; and a total fuel cell efficiency for the molten carbonate fuel cell is at least about 55% at steady state conditions.