DESC:FIELD OF THE INVENTION
The present invention relates to fuel cells and more particularly to the solid oxide fuel cell with internal steam reformation on the stack. The present invention provides an integrated steam injection-mixing-solid oxide fuel cell stack. Also, the present invention provides a novel method and system for direct injection and mixing of steam into solid oxide fuel cell stack.
BACKGROUND
Solid Oxide Fuel Cell (SOFC) is a type of fuel cell that uses a solid oxide material as the electrolyte. SOFCs use a solid oxide electrolyte to conduct negative oxygen ions from the cathode to the anode. Single solid oxide fuel cells are typically only a few millimeters thick. Hundreds of these cells are then connected in series to form a stack, referred as “SOFC stack”.
Gaseous or liquid fuels are often reformed outside the solid oxide fuel cell stack by supplying air, steam or both. The fuel and oxidant streams are mixed before reformer for higher conversion. In case of internal steam reformation, fuel and oxidant stream is mixed before stack in a separate chamber. The conversion of hydrocarbon, yield of hydrogen and life of catalyst (reformer or anode) depends upon extent of mixing.
Out of partial oxidation (POX), Autothermal reforming (ATR) and Steam methane reformation (SMR); SMR type of reformation offers high efficiency. Hence, the overall efficiency of the fuel cell system can be increased. This reformation can happen outside the solid oxide fuel cell SOFC stack (external reformation) or within the SOFC stack (internal reformation).
For steam methane reformation (SMR), steam is often generated using the waste heat produced by the exhaust gas burner. In some system concepts, excess fuel is burnt in exhaust gas burner to have sufficient heat for steam generation and pre-heating of gaseous streams. Gaseous fuel and steam are mixed in a mixing chamber before sending the combined stream to reformer for external reformation or to stack for internal reformation. Figure 1 shows prior art method which shows scheme for pre-mixing of fuel and steam. Often a complex heat exchange loop is designed to exchange the heat between hot and cold streams. There are many drawbacks of the conventional methods.

To remove drawbacks of prior art, the present invention provides a new method and system for direct injection and mixing of steam into solid oxide fuel cell stack.

BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like characters represent like parts throughout the drawings wherein:

Figure 1 illustrates prior art (scheme for pre-mixing of fuel and steam).
Figure 2 illustrates a block diagram depicting direct injection of steam and steam injection-mixing-stack in accordance with an embodiment of the present invention.
Figure 3 illustrates steam generation and mixing inside SOFC stack in accordance with an embodiment of the present invention.
Figures 4 illustrates a steam injection tube/ pipe with different diameter of holes to ensure the steam uniformly distributed in overall volume in accordance with an embodiment of the present invention.
Figures 5 illustrates an experiment and provides experimental results with steam and CH4 (50 % CH4 and 50 % H2O) in accordance with an embodiment of the present invention. Figure 5a shows gas composition in percentage at anode and at cathode. Figure 5 b experimental results in graph. X-axis represents fuel utilization and Y-axis (on left side) shows Power in Watts/ 30 cell while Y -axis scale (on right side) shows Power in Watts/ cell. Figure 5 c shows thirty cell stack.
Further, skilled artisans will appreciate that elements in the figures are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the figures by conventional symbols, and the figures may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the figures with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

OBJECTIVES OF THE INVENTION
The main objective of the present disclosure is to design a system and method for steam generation and mixing of fuel.

Another objective of the present invention is to provide an integrated steam-injection-mixing-stack system.

Yet another objective of the present invention is to provide a method for direct injection and mixing of steam into solid oxide fuel cell stack.

Another objective of the present invention is to provide a solid oxide fuel cell (SOFC) with internal steam reformation on the stack.

SUMMARY OF THE INVENTION:
The present invention relates to fuel cells and more particularly to the solid oxide fuel cell with internal steam reformation on the stack. The present invention provides an integrated steam injection-mixing-stack. Also, the present invention provides a novel method and system for direct injection and mixing of steam into solid oxide fuel cell stack.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the figures and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.
The terminology and structure employed herein is for describing, teaching and illuminating some embodiments and their specific features and elements and does not limit, restrict or reduce the spirit and scope of the invention.
Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

Figure 2 illustrates a block diagram depicting direct injection of steam in accordance with an embodiment of the present invention. In an embodiment, method is provided for direct injection and mixing of steam into solid oxide fuel cell stack. Hence, there is no requirement for pre-mixing of fuel with steam. In another embodiment, steam is injected in opposite direction from the entry of “fuel in”. For example, if entry of steam is from “top” side of the system, then, entry of “fuel in” is from bottom side of the system. In one of the embodiments, steam is injected in the opposite direction to the “fuel-in” direction in order to ensure better mixing at each layer of the SOFC stack. In another embodiment, steam injection-mixing-stack is provided in accordance with our invention. Further referring to Figure 2, uniform mixing of fuel and steam occurs in the steam-injection-mixing stack. In contrast to the prior art, there is no requirement for separate unit of reformer. In one of the embodiments of our invention, reformation happens in the steam-injection-mixing stack. Hence, electrochemical reactions occur in the steam-injection-mixing stack. In yet another embodiment, superheat steam is present in the steam-injection-mixing stack as referred in Figure 2. Figure 2 only depicts embodiments of the present invention without showing directions of the entry of “steam” and “fuel-in”. Figures 3 and 4 shows the directions of the “steam” entry and “fuel-in” in accordance with a preferred embodiment of the present invention.

In an illustrated embodiment, the system for direct injection and mixing of steam into solid oxide fuel cell stack may include a fuel unit, a steam unit and a steam injection-mixing solid oxide fuel cell (SOFC) stack and other required sub-units.

Examples
Example 1:
Example 1 provides a method of injecting steam directly into the fuel inlet path at the cell plenum area that reduces the heat demand and eliminates separate system for steam generation and injection. Figure 3 illustrates steam generation and mixing inside solid oxide fuel cell (SOFC) stack in accordance with an embodiment of the present invention. In yet another embodiment, the present invention provides a system for injecting steam directly into the fuel inlet path at the cell plenum area that reduces the heat demand and eliminates separate system for steam generation and injection. Further referring to Figure 3, each fuel channels may receive uniform composition of the hydrocarbon to steam mixture. In another embodiment, the temperature effects along the height of the stack (one cell to another cell) may be nullified. In yet another embodiment, uniform fuel distribution along the cell length avoids fuel starvation towards end of the cell in accordance with our invention. As a result, hot spots and anode damage in such regions are prevented by the present disclosure.

In an embodiment of the invention, the present invention provides a method to use exhaust heat of the stack for steam in the close vicinity of the stack (heat source). Therefore, for cooling stack,
air requirement to the stack will be reduced. The present invention provides reduction in balance of plant (BoP) load. In another embodiment, fuel utilization at stack is increased. Again referring to Figure 3, fuel distribution at stack is improved which in turn improves fuel & steam mixing. Therefore, presently disclosed method and system maintains high efficiency.

Example 2:

In example 2, an injection tube/pipe is provided with different diameter of holes for entry of steam. Entry of “steam” and “fuel-in” are from opposite directions. As shown in Figure 4, entry for “steam” is from top of the system. Entry of “fuel-in” is from bottom of the system as shown in Figure 4. It ensures that the steam is uniformly distributed in overall volume in accordance with an embodiment of the present invention. Figure 4 illustrates a steam injection tube/ pipe with different diameter of holes to ensure the steam uniformly distributed in overall volume in accordance with an embodiment of the present invention. This makes proper mixing of the “steam” and “fuel-in” with many technical advantages. In one of the embodiments of the present invention, steam injection tube/ pipe is having different diameter of holes, wherein entry of “steam” and entry of “fuel-in” is from opposite directions.

In another embodiment, entry of steam is from right side of the system while entry of “fuel-in” are present from left side of the system. In yet another embodiment of the present invention, entry of steam is from left side of the system while entry of “fuel-in” is from right side of the system. In yet another embodiment of the system, steam comes from the top side while “fuel-in” comes from a position lower than the entry position of the steam. In yet another embodiment, entry of steam is in opposite angular position from the entry of “fuel-in”. Therefore, there may be various modifications or alternatives for providing a steam injection tube/ pipe with different diameter of holes to ensure that the steam is uniformly distributed in overall volume in accordance with an embodiment of the present invention.

Example 3:

In example 3, an experimental result with steam and CH4 (50 % CH4 and 50 % H2O) is provided.
Figures 5 illustrates a experimental set up with steam and CH4 (50 % CH4 and 50 % H2O). Increase in Steam % will provide more hydrogen atoms on stack, hence providing better performance (increased efficiency). If steam injection is about 10 % by volume, the performance will be close to optimum and will maintain uniform temperature in stack space. Present invention provide method to inject steam directly at fuel side near stack entry. For better clarity, figure 5 is further shown in expanded form as Figures 5a, 5b, 5c and 5d.

As shown in figure 5 a, there is 50.00% CH4 in H2O in the experiment. Experimental result with steam and CH4 (50 % CH4 and 50 % H2O.) The experiment shows that there is 2.5 sl/min N2 because of voltage fluctuation. The gas composition in percentage at anode and at cathode is provided below in tables 1 and 2: -

Table 1
Gas Composition in percentage at cathode
N2 0.00%
H2O 50.00%
CO2 0.00%
H2 0.00%
CO 0.00%
CH4 50.00%

Table 2
Gas Composition in percentage at anode
O2 0.00%
Air 100.00%

Figure 5 b shows operational conditions and results of the experiment in graph.
Reference operational conditions are given below:
Stationary ?P ? 1% /1000 h (degradation rate)
Temperature cathode space in stack ~ approximately 835 °C
Current: 35 Ampere
80 sl/min Air (for heat management – for maintaining stable temperature within range)
Fuel Utilization approximately 74 %.

In the graph, X-axis represents fuel utilization and the scale of fuel utilization ranges from 55 to 85 %. Y-axis (on left side) shows Power in Watts/ 30 cell and it shows range from 700 to 1200 Watts/ 30 cell. Y-axis (on right side) shows Power in Watts/ cell and it shows range from 23.3 to 40.0 Watts/cell. The results show three slopes which represents current at different values. In the graph, first slope represents 35 Ampere current, second slope shows 40 Ampere current and third ampere shows 50 Ampere current. Power reference point is selected as 808 Watt. Form the graph, it is evident that fuel utilization is approximately 80% in slopes of current 40 Ampere and 50 Ampere. The fuel utilization reaches approximately 85% in slopes of current 35 Ampere.
Increase in Steam % will provide more hydrogen atoms on stack, hence providing better performance (increased efficiency). If steam injection is about 10 % by volume, the performance will be close to optimum and will maintain uniform temperature in stack space. Present invention provide method to inject steam directly at fuel side near stack entry.

Results from figure 5b shows that there is increase in fuel utilization at stack. In comparison, there is about 7 to 10 percent steam addition. There is improvement in fuel distribution at stack because fuel comes from lower side while steam comes from top side. Improvement in fuel & steam mixing is shown in the experiment. There is improved high efficiency as every cell has fuel availability. Better thermal balance of SOFC system is observed. Exothermic reaction adds heat in it. Hence, present invention provides a stable operation of SOFC system.

Figure 5c shows thirty cell stacks. The number of cells in the fuel stack can be varied as per the requirements. The number of cells in the fuel stack can be lower or grater. In an embodiment of the invention, the present invention provides a solid oxide fuel cell (SOFC) with internal steam reformation on the stack. Also, stable operation of solid oxide fuel cell (SOFC) is maintained. In an embodiment, the present invention provides better thermal balance of solid oxide fuel cell system. In another embodiment, there is increase in fuel utilization at stack. In yet another embodiment, fuel distribution at stack is improved. In the present system, each fuel channels may receive uniform composition of the hydrocarbon to steam mixture. Hence, the temperature effects along the height of the stack (one cell to another cell) is nullified by the presently disclosed system. The system size is reduced because of direct injection and mixing of steam into solid oxide fuel cell stack. In one of the embodiments, the number of cells in the stack is greater than 30. In another embodiment, number of cells in the stack is lower than 30. In yet another embodiment, number of fuel cells in the stack varies from 1 to 100 or more than 100.

In an illustrated embodiment, the method for direct injection and mixing of steam into solid oxide fuel cell stack may include providing fuel to steam injection-mixing solid oxide fuel cell stack, injecting steam directly into the steam injection-mixing solid oxide fuel cell stack in same direction or opposite direction to the fuel flow direction, performing internal steam reformation and other required steps.

In an embodiment, the present invention provides a method for providing direct injection and mixing of steam in a solid oxide fuel cell stack, said method comprising the steps of:
a) injecting steam directly into the solid oxide fuel cell stack;
b) entering fuel-in into the solid oxide fuel cell stack in opposite direction to the injection of the steam;
b) uniform mixing of the steam and fuel-in at each layer of the solid oxide fuel cell stack and receiving uniform composition of the fuel-in to steam mixture by each fuel channels in the solid oxide fuel cell (SOFC) stack; and
(c) having internal steam reformation and electrochemical reactions in the solid oxide fuel cell stack.

In another embodiment, the present invention provides a method wherein the steam is injected directly into the solid oxide fuel cell stack by steam injection tube or pipe having same or different diameter of holes.

In another embodiment, the present invention provides a method, wherein steam is directly injected from top side of the solid oxide fuel cell stack and “fuel-in” is entered from bottom side of the solid oxide fuel cell stack.

In another embodiment, the present method provides uniform fuel distribution along the solid oxide fuel cell length, avoids fuel starvation towards end of the cell in the solid oxide fuel cell stack, prevents hot spots and anode damage in such regions and nullifying the temperature effects along the height of the stack (one cell to another cell).

In another embodiment, the present invention provides a method, wherein the steam is directly injected into the fuel inlet path at the cell plenum area in the solid oxide fuel cell (SOFC) stack for reducing heat demand, reducing balance of plant (BoP) load and increasing fuel utilization at solid oxide fuel cell stack.

In another embodiment, the present invention provides a method, further comprising using exhaust heat of the stack for steam in the close vicinity of the solid oxide fuel cell stack (heat source) and reducing air requirement for cooling the solid oxide fuel cell stack.

In another embodiment, the present invention provides an integrated system for providing direct injection and mixing of steam in a solid oxide fuel cell stack, said system comprising:
i) steam injection tube or pipe having same or different diameter of holes for directly injecting steam into the solid oxide fuel cell stack;
ii) fuel-in unit for entering fuel into the solid oxide fuel cell stack in opposite direction to the injection of the steam; and
iii) solid oxide fuel cell (SOFC) stack for uniform mixing of the steam and fuel-in at each layer of the solid oxide fuel cell stack, providing uniform composition of the fuel-in to steam mixture to each fuel channel in the solid oxide fuel cell (SOFC) stack and performing internal steam reformation and electrochemical reactions in the solid oxide fuel cell stack.

In another embodiment, the present invention provides a system, wherein steam is directly injected from top side of the solid oxide fuel cell stack and “fuel-in” is entered from bottom side of the solid oxide fuel cell stack.

In another embodiment, the present invention provides a system, wherein the steam is directly injected into the fuel inlet path at the cell plenum area in the solid oxide fuel cell (SOFC) stack and reduces the heat demand and eliminates separate systems for steam generation, injection and reformation.

In another embodiment, the present invention provides a solid oxide fuel cell (SOFC) with internal steam reformation on the stack, having:
direct injection of steam into the solid oxide fuel cell stack and entry of fuel-in into the solid oxide fuel cell stack which is in opposite direction to the injection of the steam;
uniform mixing of the steam and fuel-in at each layer of the solid oxide fuel cell stack and providing uniform composition of the fuel-in to steam mixture by each fuel channels in the solid oxide fuel cell (SOFC) stack; and
internal steam reformation and electrochemical reactions in the solid oxide fuel cell stack.

In yet another embodiment, a system for direct injection and mixing of steam into solid oxide fuel cell stack is provided. Without departing from the scope of the invention, all the elements of the method as described above, are implemented by the system. In an embodiment, the system provides injection of steam directly into the fuel inlet path at the cell plenum area. In yet another embodiment, the system reduces the heat demand and eliminates separate system for steam generation and injection. In the steam-injection-mixing stack, steam may be injected in the same direction to the fuel flow direction in order to ensure better mixing at each layer of the solid oxide fuel cell stack. Without departing from the scope of the invention, in another embodiment, steam may be injected in the opposite direction to the fuel flow direction in order to ensure better mixing. In the present system, each fuel channels may receive uniform composition of the hydrocarbon to steam mixture. Hence, the temperature effects along the height of the stack (one cell to another cell) is nullified by the presently disclosed system. The system size is reduced because of direct injection and mixing of steam into solid oxide fuel cell stack.

In an embodiment of the invention, the present invention provides a solid oxide fuel cell (SOFC) with internal steam reformation on the stack. Also, stable operation of solid oxide fuel cell (SOFC) is maintained. In an embodiment, the present invention provides better thermal balance of solid oxide fuel cell system. In another embodiment, there is increase in fuel utilization at stack. In yet another embodiment, fuel distribution at stack is improved.

In an illustrated embodiment, a solid oxide fuel cell (SOFC) with internal steam reformation on the stack may include direct injection of steam into the steam injection-mixing solid oxide fuel cell stack in same direction or opposite direction to the fuel flow direction and performing internal steam reformation.

ADVANTAGES:
• Increase in fuel utilization at stack: In comparison, there is about 7 to 10 percent steam addition.
• Elimination of a separate steam generator.
• Improve fuel distribution at stack: fuel comes from lower side, steam comes from top side.
• Improve fuel & steam mixing.
• Improved high efficiency.
• Better thermal balance of SOFC system.
• Stable operation of SOFC system.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The invention has been described with reference to preferred and alternate embodiments. Modifications and alterations will become apparent to those skilled in the art upon reading and understanding the detailed discussion of the invention provided herein. This invention is intended to include all such modifications and alterations insofar as they come within the scope of the present invention. These and other modifications of the preferred embodiments as well as other embodiments of the invention will be obvious from the disclosure herein, whereby the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.
,CLAIMS:Method for providing direct injection and mixing of steam in a solid oxide fuel cell stack, said method comprising the steps of:
a) injecting steam directly into the solid oxide fuel cell stack;
b) entering fuel-in into the solid oxide fuel cell stack in opposite direction to the injection of the steam;
b) uniform mixing of the steam and fuel-in at each layer of the solid oxide fuel cell stack and receiving uniform composition of the fuel-in to steam mixture by each fuel channels in the solid oxide fuel cell (SOFC) stack; and
(c) having internal steam reformation and electrochemical reactions in the solid oxide fuel cell stack.

2. The method as claimed in claim 1, wherein the steam is injected directly into the solid oxide fuel cell stack by steam injection tube or pipe having same or different diameter of holes.

3. The method as claimed in claims 1 and 2, wherein steam is directly injected from top side of the solid oxide fuel cell stack and “fuel-in” is entered from bottom side of the solid oxide fuel cell stack.

4. The method as claimed in preceding claims, comprising providing uniform fuel distribution along the solid oxide fuel cell length, avoiding fuel starvation towards end of the cell in the solid oxide fuel cell stack, preventing hot spots and anode damage in such regions and nullifying the temperature effects along the height of the stack (one cell to another cell).

5. The method as claimed in preceding claims, wherein the steam is directly injected into the fuel inlet path at the cell plenum area in the solid oxide fuel cell (SOFC) stack for reducing heat demand, reducing balance of plant (BoP) load and increasing fuel utilization at solid oxide fuel cell stack.

6. The method as claimed in preceding claims, further comprising using exhaust heat of the stack for steam in the close vicinity of the solid oxide fuel cell stack (heat source) and reducing air requirement for cooling the solid oxide fuel cell stack.

7. An integrated system for providing direct injection and mixing of steam in a solid oxide fuel cell stack, said system comprising:
i) steam injection tube or pipe having same or different diameter of holes for directly injecting steam into the solid oxide fuel cell stack;
ii) fuel-in unit for entering fuel into the solid oxide fuel cell stack in opposite direction to the injection of the steam; and
iii) solid oxide fuel cell (SOFC) stack for uniform mixing of the steam and fuel-in at each layer of the solid oxide fuel cell stack, providing uniform composition of the fuel-in to steam mixture to each fuel channel in the solid oxide fuel cell (SOFC) stack and performing internal steam reformation and electrochemical reactions in the solid oxide fuel cell stack.

8. The system as claimed in claim 7, wherein wherein steam is directly injected from top side of the solid oxide fuel cell stack and “fuel-in” is entered from bottom side of the solid oxide fuel cell stack.

9. The system as claimed in claim 8, wherein the steam is directly injected into the fuel inlet path at the cell plenum area in the solid oxide fuel cell (SOFC) stack and reduces the heat demand and eliminates separate systems for steam generation, injection and reformation.

10. Solid oxide fuel cell (SOFC) with internal steam reformation on the stack, having:
direct injection of steam into the solid oxide fuel cell stack and entry of fuel-in into the solid oxide fuel cell stack which is in opposite direction to the injection of the steam;
uniform mixing of the steam and fuel-in at each layer of the solid oxide fuel cell stack and providing uniform composition of the fuel-in to steam mixture by each fuel channels in the solid oxide fuel cell (SOFC) stack; and
internal steam reformation and electrochemical reactions in the solid oxide fuel cell stack.