Patent Application
20080057361
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Now, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
As shown in
The internal reforming molten carbonate fuel cell power generation system includes a stack 1 for generating power by the fuel cell reaction, a mixer 3 for mixing fuel to be supplied to the stack 1, a pre-former 2 disposed between the mixer 3 and the stack 1 for reforming a portion of fuel to be supplied to the stack 1 from the mixer 3, and a burner 4 for burning exhaust gas exhausted from a fuel electrode of the stack 1 to supply heat and carbon dioxide required for the air electrode of the stack 1.
Here, a line connecting the mixer 3, the pre-former 2, and the stack 1 is a fuel supply line 10, and a line connecting the stack 1 and the burner 4 is an exhaust gas line 11.
The fuel cell power generation system according to the present invention is constructed in a structure in which an exhaust gas recycling line 12 diverges from the exhaust gas line 11 between the stack 1 and the burner 4, and the exhaust gas recycling line 12 is connected to the fuel supply line 10 between the mixer 3 and the stack 1. Consequently, a portion of exhaust gas, exhausted from the fuel electrode of the stack 1 after the reaction is completed, is mixed with the fuel flowing along the fuel supply line 10 between the mixer 3 and the stack 1, and then the mixture is reintroduced into the fuel electrode of the stack 1.
Preferably, the exhaust gas recycling line 12 is connected to the fuel supply line 10 before the pre-former 2, as shown in
At the junction between the exhaust gas recycling line 12 and the fuel supply line 10 is mounted an exhaust gas discharger 7 for discharging the exhaust gas flowing along the exhaust gas recycling line 12 to the fuel supply line 10.
As the exhaust gas discharger 7, there may be used a venturi-type ejector for generating pressure difference between the fuel supply line 10 and the exhaust gas recycling line 12. In this case, negative pressure is formed in the exhaust gas recycling line 12 due to the flow speed of the fuel gas passing through the venturi-type ejector with the result that the exhaust gas is automatically suctioned into the fuel supply line 10. Since the fuel in the fuel supply line 10 is normally maintained at a pressure of 3 bar, the venturi-type ejector utilizes the kinetic energy of the introduced fuel to obtain cycling power without using an additional power source.
As the exhaust gas discharger 7, on the other hand, there may be used a high-temperature circulation fan instead of the venturi-type ejector. In this case, the exhaust gas flowing along the exhaust gas recycling line 12 is forcibly supplied to the fuel supply line 10 by the high-temperature circulation fan.
In the internal reforming molten carbonate fuel cell power generation system using the fuel electrode exhaust gas recycling process with the above-described description according to the present invention, natural gas and steam are sufficiently mixed by the mixer 3, and then the mixed fuel is supplied to the pre-former 2. The steam is supplied by an amount equivalent to 2 to 5 times that of the supplied carbon. In the pre-former 2, a portion of the hydrocarbon compound is reformed such that hydrogen concentration is maintained at 3 to 20%. As the fuel passes through the stack 1, more than 99% of the fuel is converted into hydrogen, which is used in the fuel cell reaction. Since the fuel is excessively supplied, hydrogen is naturally contained in the fuel electrode exhaust gas. Also, steam and carbon dioxide generated by the fuel cell reaction are also contained in the fuel electrode exhaust gas. Less than 40% of the exhaust gas is recycled into the exhaust gas discharger 7 along the exhaust gas recycling line 12, and the introduced exhaust gas is mixed with newly introduced natural gas and steam in the exhaust gas discharger 7. After that, the mixture is introduced into the pre-former 2. When the amount of the recycled exhaust gas exceeds 40% of the total amount of the exhaust gas, peak voltage is greatly reduced, and load of the stack 1 is increased. Consequently, it is preferable that the amount of the recycled exhaust gas is maintained at less than 40% of the total amount of the exhaust gas.
Table 1 below shows the results of process simulation based on a fuel electrode cycling rate to measure the improvement of system efficiency obtained through the present invention.
As can be seen from Table 1 above, when the hydrogen and the steam contained in the exhaust gas exhausted from the stack 1 are reused according to the present invention, (a) it is possible to reduce the amount of fuel consumed by the fuel cell power generation system through the reuse of the exhausted hydrogen, (b) it is possible to reduce the waste of the steam through the reuse of the steam generated from the stack and to reduce the size of the steam generator, (c) it is possible to reduce the amount of energy used to generate the steam, and (d) it is possible to increase the initial operation temperature of newly supplied fuel without the further introduction of energy by virtue of the temperature of the exhaust gas.
As can also be seen from Table 1 above, on the other hand, the peak voltage was slightly decreased due to the composition change of the fuel. However, the above-described improvement is tremendous as compared to the decrease of the peak voltage. Consequently, the decrease of the power generation rate is ignored, and it is possible to set the most economical cycling rate depending upon the properties of the fuel.
As apparent from the above description, the exhaust gas exhausted from the fuel electrode is used only to supply heat and carbon dioxide required for the air electrode in the conventional power generation system.
In the fuel cell power generation system using the fuel electrode exhaust gas recycling process according to the present invention, however, a portion of the exhaust gas exhausted from the fuel electrode is reintroduced into the fuel electrode of the stack, and therefore, the amount of used fuel is reduced by the amount of the recycled hydrogen. Furthermore, the high-temperature steam generated through the fuel cell reaction is utilized in the pre-former, and therefore, the amount of used steam is reduced. Consequently, the power generation efficiency of the fuel cell power generation system is improved, and the economic efficiency of the fuel cell power generation system is also improved.
Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0084043 | Sep 2006 | KR | national |
