JP7563013B2 - solid oxide fuel cell - Google Patents

Description

The present invention relates to a solid oxide fuel cell.

A solid oxide fuel cell (SOFC) has an electrode cell with an electrolyte layer sandwiched between an anode layer and a cathode layer. In order to efficiently supply sufficient fuel gas and oxidant gas to the electrode cell, it is necessary to uniformly flow the gas through the flow path on the power generation surface of the electrode cell. In the SOFC disclosed in Patent Document 1, multiple power generation cells are arranged in parallel in a direction perpendicular to the direction from the inlet manifold to the outlet manifold. In this SOFC, in order to uniformly distribute the gas, the length of the diffuser that distributes the gas in the open space on the upstream and downstream sides of the flow path is ensured, and multiple inlet manifolds and multiple outlet manifolds are arranged. Furthermore, a mechanism for adjusting pressure loss is arranged to uniformize the flow velocity distribution in the power generation cell, and the flow of gas (side flow) flowing through the end of the power generation cell is suppressed.

International Publication No. 2019/030919

The technology described in Patent Document 1 can distribute gas evenly, but there is a risk that the SOFC will become larger as the number of manifold sections increases. In addition, the placement of a mechanism for adjusting the pressure loss to suppress side flows can also result in the SOFC becoming larger.

Therefore, the present invention aims to provide a solid oxide fuel cell that can be made compact while achieving uniform gas distribution.

In order to achieve the above object, the present invention provides a solid oxide fuel cell including a plurality of power generating cells each having at least an electrolyte layer and a pair of electrode layers, a cell frame for holding the plurality of power generating cells, and at least a pair of separators for forming a fuel flow path and an oxidant flow path opposite the plurality of power generating cells. The cell frame includes an inlet-side manifold section through which gas supplied to the power generating cells flows, and an outlet-side manifold section through which gas discharged from the power generating cells flows. The cell frame includes a plurality of holding sections for holding the outer peripheries of the plurality of power generating cells in a state in which the plurality of power generating cells are arranged in series along a direction from the inlet-side manifold section toward the outlet-side manifold section. The cell frame includes an inlet section formed in the inlet-side manifold section for introducing gas flowing through the inlet-side manifold section, and a supply passage for branching and directing the gas introduced from the inlet section toward each of the plurality of power generating cells arranged in series. The cell frame includes a supply section for supplying gas from the supply passage to each of the plurality of power generating cells, and a discharge section for discharging gas from each of the plurality of power generating cells. The cell frame has an exhaust passage that guides the gas exhausted from the exhaust portion toward the outlet-side manifold portion, and an outlet portion that is formed in the outlet-side manifold portion and that allows the gas flowing through the exhaust passage to flow out to the outlet-side manifold portion. In at least one of the fuel flow path and the oxidizer flow path, only the gas exhausted from the power generation cell that is closest to the outlet portion among the plurality of power generation cells arranged in series flows through the exhaust passage.

According to the present invention, by providing a supply passage and a supply section within the cell frame, the gas (fuel gas and oxidant gas) flowing in from the inlet manifold section can be branched and supplied to each of the multiple power generation cells arranged in series. This makes it possible to reduce the gas flow rate flowing to each of the multiple power generation cells, reduce the pressure loss of the entire cell unit, and make the gas distribution uniform. Furthermore, it is possible to save space between the inlet manifold section and the outlet manifold section and the power generation cells, and since there can be only one inlet manifold section and one outlet manifold section for each gas, it is possible to make the stack smaller. Thus, it is possible to provide a solid oxide fuel cell that can be made smaller while still achieving uniform gas distribution.

FIG. 2 is a perspective view showing a cell unit of a solid oxide fuel cell, exploded into a separator, a power generating cell, and a cell frame. FIG. 2 is a plan view showing a cell unit. FIG. 2B is a cross-sectional view taken along line 2B-2B in FIG. 2A. FIG. 2C is a cross-sectional view taken along line 2C-2C in FIG. 2A. FIG. 2C is an enlarged cross-sectional view of portion 2D of FIG. 2B. FIG. 2D is an enlarged cross-sectional view of portion 2E of FIG. 2C. FIG. 2 is a plan view showing a cell frame. FIG. 3B is a cross-sectional view taken along line 3B-3B in FIG. 3A. FIG. 3C is a cross-sectional view taken along line 3C-3C in FIG. 3A. 3D is a cross-sectional view taken along line 3D-3D in FIG. 3A. FIG. 3E is a cross-sectional view taken along line 3E-3E in FIG. 3A. 3F is a cross-sectional view taken along line 3F-3F in FIG. 3A. FIG. 2 is a plan view showing the flow directions of fuel gas and oxidant gas in a plurality of power generating cells. FIG. 2 is an explanatory diagram used to explain miniaturization of a stack of solid oxide fuel cells, and is an enlarged plan view showing an end portion of a cell frame where an inlet side manifold portion is formed. FIG. 4B is an enlarged cross-sectional view of part 4B of FIG. 4A. FIG. 1 is an explanatory diagram used to explain improvement of reforming efficiency of a stack of solid oxide fuel cells, and is an enlarged plan view showing an end portion of a cell frame where an inlet side manifold portion is formed. FIG. 4 is a diagram illustrating the relationship between the flow velocity of fuel gas and the reforming property. FIG. 13 is a plan view showing a cell frame of the first modified example. FIG. 6B is a cross-sectional view taken along line 6B-6B in FIG. 6A. FIG. 6C is an enlarged cross-sectional view of part 6C of FIG. 6B. FIG. 6C is an enlarged cross-sectional view of part 6D of FIG. 6B. FIG. 11 is a plan view showing a cell frame of a second modified example. This is an explanatory diagram used to explain the improvement in the temperature rise property of the supply temperature of the fuel gas supplied to the most upstream power generation cell, and is a plan view showing an enlarged view of the end portion where the inlet side manifold portion of the cell frame is formed. This is an explanatory diagram of a comparative example used to explain the improvement in the temperature rise property of the supply temperature of the fuel gas supplied to the most upstream power generation cell, and is a plan view showing an enlarged view of the end portion where the inlet side manifold portion of the cell frame is formed. FIG. 13 is a perspective view showing a cell frame of a modified example 3. 13 is a plan view showing the flow directions of fuel gas and oxidant gas in a plurality of power generating cells of Modification 3. FIG. FIG. 11 is an explanatory diagram used to explain the increase in average temperature within the reaction surface in variant example 3. FIG. 13 is a perspective view showing a cell unit of a solid oxide fuel cell according to Modification 4, disassembled into a separator, a power generating cell, and a cell frame. FIG. 13 is a plan view showing a cell frame of a fourth modified example.

Below, an embodiment of the present invention will be described with reference to the attached drawings. Note that the following description does not limit the technical scope or the meaning of the terms described in the claims. Also, the dimensional ratios in the drawings have been exaggerated for the convenience of explanation and may differ from the actual ratios.

A solid oxide fuel cell (SOFC) according to an embodiment will be described with reference to the figure. For ease of explanation, an XYZ Cartesian coordinate system is shown in the figure. The X-axis and Y-axis are parallel to the horizontal direction, and the Z-axis is parallel to the vertical direction.

Figure 1 is a perspective view showing a cell unit 10 of an SOFC according to an embodiment, disassembled into a separator 20, power generation cells 31 and 32, and a cell frame 40. Figure 2A is a plan view showing the cell unit 10. Figure 2B is a cross-sectional view taken along line 2B-2B in Figure 2A, and Figure 2C is a cross-sectional view taken along line 2C-2C in Figure 2A. Figure 2D is an enlarged cross-sectional view of part 2D in Figure 2B, and Figure 2E is an enlarged cross-sectional view of part 2E in Figure 2C. Figure 3A is a plan view showing a cell frame 40. Figures 3B, 3C, 3D, 3E, and 3F are cross-sectional views taken along lines 3B-3B, 3C-3C, 3D-3D, 3E-3E, and 3F-3F in Figure 3A, respectively.

The SOFC stack is constructed by stacking multiple cell units 10 shown in FIG. 1. Hereinafter, the vertical direction indicated by the Z axis in the figure will also be referred to as the "stacking direction." The surface direction of each layer constituting the cell unit 10 corresponds to the XY surface direction.

1, 2A, 2B, 2C, 2D, and 2E, the cell unit 10 has a plurality of (two in the illustrated example) power generation cells 31, 32, a cell frame 40 that holds the plurality of power generation cells 31, 32, and a separator 20 that is sealed and fixed to the cell frame 40. The power generation cells 31, 32 have at least an electrolyte layer and a pair of electrode layers. A hollow portion partitioned by a plurality of partition walls is formed between the cell frame 40 and the separator 20. In the SOFC, the cell units 10 are stacked, and at least a pair of separators 20 face the plurality of power generation cells 31, 32 to form a fuel flow path 61 and an oxidant flow path 62 (see FIG. 2D and FIG. 2E). For convenience of explanation, the two power generation cells 31, 32 are also referred to as the first power generation cell 31 and the second power generation cell 32, in order from the upstream side.

The power generation cells 31 and 32 each have an anode layer, a cathode layer, and an electrolyte layer. The electrolyte layer is sandwiched between the anode layer and the cathode layer. The cathode layer is an oxidizer electrode that reacts an oxidizer gas (e.g., oxygen contained in air) with electrons to convert oxygen molecules into oxide ions. Examples of materials that form the cathode layer include oxides made of lanthanum, strontium, manganese, cobalt, and the like. The electrolyte layer has a function of separating the fuel gas and the oxidizer gas. The electrolyte layer allows oxide ions to pass from the cathode layer to the anode layer, but does not allow gas and electrons to pass through. The material for forming the electrolyte layer is not particularly limited, and examples thereof _{include solid} oxide ceramics such as stabilized zirconia doped with rare earth oxides (e.g., one or more selected from _{Y2O3, Sc2O3 , Gd2O3 , Sm2O3 , Yb2O3} , _{Nd2O3 ,} etc.), ceria-based solid solutions, and perovskite oxides (e.g., _{SrCeO3 , BaCeO3} , CaZrO3, _{SrZrO3 ,} etc.). The anode layer is a fuel electrode that reacts a fuel gas (e.g., hydrogen) with oxide ions to generate an oxide of the fuel gas and extract electrons. Examples of the material for forming the anode layer include metals such as Ni and Fe, and thermets of the metals and the ceramics listed as the material for forming the electrolyte layer. The anode layer is a porous body in which a plurality of pores are formed. The pores in the anode layer are impregnated with a catalyst, which may be, for example, a metal catalyst such as Ni or Cu.

3A, 3B, 3C, 3D, 3E, and 3F, the cell frame 40 has inlet side manifold sections 110a and 110c through which gas supplied to the power generation cells 31 and 32 flows, and outlet side manifold sections 120a and 120c through which gas discharged from the power generation cells 31 and 32 flows. Fuel gas flows through the inlet side manifold section 110a, and oxidizer gas flows through the inlet side manifold section 110c. Fuel gas flows through the outlet side manifold section 120a, and oxidizer gas flows through the outlet side manifold section 120c. The inlet side manifold section 110a is disposed on the Y positive side at the end side of the cell frame 40 in the X negative direction. The inlet side manifold section 110c is disposed on the Y negative side of the inlet side manifold section 110a. The outlet side manifold section 120a is disposed on the Y positive side at the end of the cell frame 40 in the X positive direction. The outlet side manifold section 120c is disposed on the Y negative side of the outlet side manifold section 120a.

In the following description, the suffix "a" attached to the reference numerals of components indicates that the component is for fuel gas, and the suffix "c" indicates that the component is for oxidizer gas.

The cell frame 40 has a plurality of holding parts 130 that hold the outer circumference of each of the plurality of power generating cells 31, 32. The holding parts 130 hold the plurality of power generating cells 31, 32 in a state in which they are arranged in series along the direction from the inlet side manifold parts 110a, 110c toward the outlet side manifold parts 120a, 120c (X positive direction). The cell frame 40 has a plurality of openings 131 in which the plurality of power generating cells 31, 32 are arranged. The holding parts 130 are formed from step parts 132 formed on the inner periphery of the openings 131 (see Figures 2D and 2E). In the illustrated example, the cathode layers of the power generating cells 31, 32 are joined onto the step parts 132.

The cell frame 40 has inlet sections 140a, 140c formed in the inlet manifold sections 110a, 110c for introducing gas flowing through the inlet manifold sections 110a, 110c, and supply passages 150a, 150c for branching and directing the gas introduced from the inlet sections 140a, 140c toward each of the multiple power generation cells 31, 32 arranged in series. The cell frame 40 has supply sections 161a, 161c, 162a, 162c for supplying gas from the supply passages 150a, 150c to each of the multiple power generation cells 31, 32, and exhaust sections 171a, 171c, 172a, 172c for exhausting gas from each of the multiple power generation cells 31, 32. The cell frame 40 has exhaust passages 180a, 180c that guide the gas exhausted from the exhaust sections 171a, 171c, 172a, 172c toward the outlet side manifold sections 120a, 120c, and outlet sections 190a, 190c that are formed in the outlet side manifold sections 120a, 120c and allow the gas flowing through the exhaust passages 180a, 180c to flow out to the outlet side manifold sections 120a, 120c.

The inlet section 140a is composed of multiple grooves formed in the rectangular partition wall that forms the inlet manifold section 110a and extends along the X direction. The inlet section 140c is composed of multiple grooves formed in the rectangular partition wall that forms the inlet manifold section 110c and extends along the Y direction and is located on the positive X direction side.

The supply passage 150a has a first supply passage 201a, a second supply passage 202a, a third supply passage 203a, and a fourth supply passage 204a (see FIG. 3A). The first supply passage 201a extends along the Y direction adjacent to the inlet manifold portions 110a and 110c (see FIGS. 3B and 3C). The second supply passage 202a is located on the Y positive side of the power generation cells 31 and 32 and extends along the X direction (see FIGS. 3D and 3E). The third supply passage 203a is located on the Y negative side of the power generation cells 31 and 32 and extends along the X direction (see FIGS. 3D and 3E). The fourth supply passage 204a extends along the Y direction between the two power generation cells 31 and 32 (see FIGS. 3B, 3C, and 3E). Similarly, the supply passage 150c has a first supply passage 211c, a second supply passage 212c, a third supply passage 213c, and a fourth supply passage 214c.

The supply section 161a of the first power generating cell 31 is composed of a plurality of grooves formed in the partition wall facing the first supply passage 201a among the rectangular partition walls surrounding the upstream opening 131. The supply section 162a of the second power generating cell 32 is composed of a plurality of grooves formed in the partition wall facing the fourth supply passage 204a among the rectangular partition walls surrounding the downstream opening 131. The supply section 161c of the first power generating cell 31 is composed of a plurality of grooves formed in the partition wall facing the first supply passage 211c among the rectangular partition walls surrounding the upstream opening 131. The supply section 162c of the second power generating cell 32 is composed of a plurality of grooves formed in the partition wall facing the fourth supply passage 214c among the rectangular partition walls surrounding the downstream opening 131.

The discharge section 171a of the first power generating cell 31 is composed of a plurality of grooves formed in the partition wall facing the fourth supply passage 204a among the rectangular partition walls surrounding the upstream opening 131. The discharge section 172a of the second power generating cell 32 is composed of a plurality of grooves formed in the partition wall facing the discharge passage 180a among the rectangular partition walls surrounding the downstream opening 131. The discharge section 171c of the first power generating cell 31 is composed of a plurality of grooves formed in the partition wall facing the fourth supply passage 214c among the rectangular partition walls surrounding the upstream opening 131. The discharge section 172c of the second power generating cell 32 is composed of a plurality of grooves formed in the partition wall facing the discharge passage 180c among the rectangular partition walls surrounding the downstream opening 131.

The discharge passage 180a is separated from the supply passage 150a and extends in the Y direction adjacent to the outlet manifold portions 120a and 120c (see FIG. 3A). Similarly, the discharge passage 180c extends in the Y direction adjacent to the outlet manifold portions 120a and 120c.

Outlet section 190a is composed of multiple grooves formed in the rectangular partition wall that forms outlet side manifold section 120a and extends along the X direction. Outlet section 190c is composed of multiple grooves formed in the rectangular partition wall that forms outlet side manifold section 120c and extends along the Y direction and is located on the negative X direction side.

The cell frame 40 is made of a dense metal material that is impermeable to gas, such as stainless steel.

As shown in FIG. 1, the separator 20 has a first opening 21 communicating with the inlet manifold 110a of the cell frame 40, a second opening 22 communicating with the inlet manifold 110c, a third opening 23 communicating with the outlet manifold 120a, and a fourth opening 24 communicating with the outlet manifold 120c. The first opening 21 and the third opening 23 allow fuel gas to flow, and the second opening 22 and the fourth opening 24 allow oxidizer gas to flow. The separator 20 is made of a dense metal material that does not allow gas to pass through, such as stainless steel. The outer periphery of the separator 20 is joined to the cell frame 40 by welding or brazing. A sealant 50 is disposed between the separator 20 and the cell frame 40 to prevent the fuel gas and the oxidizer gas from mixing. The sealant 50 is made of, for example, thermoculite, which has heat resistance and sealing properties. As described above, the SOFC stack is constructed by stacking a plurality of cell units 10, and a fuel flow path 61 and an oxidant flow path 62 are formed between a pair of separators 20 and the power generation cells 31, 32 in the stacking direction. As shown in FIG. 2B, FIG. 2C, FIG. 2D, and FIG. 2E, the space between the separator 20 and the anode layer of the power generation cells 31, 32 is the fuel flow path 61, and the space between the separator 20 stacked on the opposite side and the cathode layer of the power generation cells 31, 32 is the oxidant flow path 62. As shown in FIG. 2D and FIG. 2E, a current collector 70 is arranged in the fuel flow path 61 between the power generation cells 31, 32 and the separator 20. The current collector 70 forms a space through which gas can pass, and further ensures electrical contact between the power generation cells 31, 32 and the separator 20. Although not shown, a current collector 70 is also arranged in the oxidant flow path 62.

Next, the operation of this embodiment will be explained.

In the SOFC of this embodiment, the inlet side manifold parts 110a, 110c are arranged at one end along one direction (X direction) of the cell frame 40, and the outlet side manifold parts 120a, 120c are arranged at the other end along the one direction (X direction) of the cell frame 40. The two power generation cells 31, 32 are arranged in series along the direction from the inlet side manifold part 110a to the outlet side manifold part 120a (X positive direction).

The fuel gas flows as follows. The fuel gas flowing through the inlet manifold 110a flows through the inlet section 140a into the hollow space between the cell frame 40 and the separator 20. The fuel gas branches into the supply passage 150a (the first supply passage 201a, the second supply passage 202a, the third supply passage 203a, and the fourth supply passage 204a) and is directed toward each of the two power generation cells 31 and 32. The fuel gas flowing through the first supply passage 201a passes through the supply section 161a of the first power generation cell 31 and is supplied to the first power generation cell 31. The fuel gas that has flowed through the first power generation cell 31 passes through the discharge section 171a and is discharged to the fourth supply passage 204a. The fuel gas that has bypassed the first power generation cell 31 through the second supply passage 202a and the third supply passage 203a also flows into the fourth supply passage 204a. The fuel gas flowing through the fourth supply passage 204a (the fuel gas that bypasses the first power generation cell 31 and the fuel gas discharged from the first power generation cell 31) is supplied to the second power generation cell 32 through the supply section 162a of the second power generation cell 32. The fuel gas that has flowed through the second power generation cell 32 is discharged through the discharge section 172a to the discharge passage 180a. The fuel gas flowing through the discharge passage 180a flows out through the outflow section 190a to the outlet side manifold section 120a.

The oxidant gas flows in the same manner as the fuel gas as follows. The oxidant gas flowing through the inlet manifold 110c flows through the inlet section 140c into the hollow space between the cell frame 40 and the separator 20. The oxidant gas flows through the supply passage 150c (the first supply passage 211c, the second supply passage 212c, the third supply passage 213c, and the fourth supply passage 214c) and is directed toward each of the two power generation cells 31 and 32. The oxidant gas flowing through the first supply passage 211c is supplied to the first power generation cell 31 through the supply section 161c of the first power generation cell 31. The oxidant gas that has flowed through the first power generation cell 31 is discharged through the discharge section 171c to the fourth supply passage 214c. The oxidant gas that has bypassed the first power generation cell 31 through the second supply passage 212c and the third supply passage 213c also flows into the fourth supply passage 214c. The oxidant gas flowing through the fourth supply passage 214c (the oxidant gas that has bypassed the first power generation cell 31 and the oxidant gas discharged from the first power generation cell 31) is supplied to the second power generation cell 32 through the supply section 162c of the second power generation cell 32. The oxidant gas that has flowed through the second power generation cell 32 is discharged through the discharge section 172c to the discharge passage 180c. The oxidant gas flowing through the discharge passage 180c flows out through the outflow section 190c to the outlet side manifold section 120c.

By branching the gas (fuel gas and oxidant gas) flowing in from the inlet manifolds 110a and 110c, the gas flow rate through the first power cell 31 of the two power generation cells 31 and 32 arranged in series is reduced compared to the gas flow rate through the second power generation cell 32. The pressure loss of the cell frame 40 can be easily controlled by appropriately selecting the width, height, formation position, and shape of the grooves that constitute the gas passages in the inlet sections 140a and 140c, the supply passages 150a and 150c, the supply sections 161a, 161c, 162a, and 162c, the exhaust sections 171a, 171c, 172a, and 172c, the exhaust passages 180a and 180c, and the outlet sections 190a and 190c.

Figure 3G is a plan view showing the flow directions of fuel gas and oxidant gas in two power generation cells 31 and 32. The solid arrows indicate the flow of fuel gas, and the dashed arrows indicate the flow of oxidant gas.

As shown in FIG. 3G, the gas supply method in this embodiment is coflow. In each of the two power generation cells 31, 32, the direction in which the fuel flows and the direction in which the oxidizer flows are the same (X-positive direction). Note that, with regard to the gas supply method, when the fuel gas flow direction and the oxidizer gas flow direction are parallel, a method in which they flow in the same direction is coflow, and a method in which they flow in opposite directions is counterflow.

Figure 4A is an explanatory diagram used to explain the miniaturization of an SOFC stack, and is an enlarged plan view of the end of the cell frame 40 where the inlet manifold sections 110a and 110c are formed. Figure 4B is an enlarged cross-sectional view of part 4B in Figure 4A.

As shown in FIG. 4A, the inflow of fuel gas from the supply passage 150a to the fuel flow passage 61 in the first power generation cell 31 is controlled by the gas passage of the supply section 161a. As shown in FIG. 4B, the inflow from the supply passage 150a to the first power generation cell 31 is distributed according to the relationship between the main pipe (first supply passage 201a) and the branch pipe (supply section 161a). Since the gas is distributed according to the relationship between the main pipe and the branch pipe, a diffuser that distributes the fuel gas in an open space is not required, and the distance (diffuser distance) for diffusing is not required. This allows the first power generation cell 31 to be closer to the fuel inlet side manifold section 110a, thereby saving space between the inlet side manifold sections 110a, 110c and the first power generation cell 31 (see the white arrow 221 in FIG. 4A). Similarly, space saving is achieved between the outlet side manifold section 120a and the second power generation cell 32.

In the SOFC disclosed in the above-mentioned Patent Document 1, in order to arrange the inlet and outlet manifolds and the power generation cells symmetrically, multiple inlet and outlet manifolds are arranged. In contrast, the SOFC of this embodiment does not require a diffuser, so there is no need to arrange the manifolds and the power generation cells 31 and 32 symmetrically, and the inlet manifolds 110a and 110c and the outlet manifolds 120a and 120c can be one each. The inlet manifold 110a for fuel can be arranged in an asymmetric position with respect to the center O in the width direction (Y direction) of the first power generation cell 31 (see the white arrow 222 in FIG. 4A). The opening area of the inlet manifold 110a can be set to a minimum size taking into account the flow rate and pressure loss. Similarly, the outlet manifold 120a can be arranged in an asymmetric position with respect to the center in the width direction (Y direction) of the second power generation cell 32, minimizing the opening area.

The SOFC disclosed in the above-mentioned Patent Document 1 is provided with a mechanism for adjusting pressure loss to suppress side flow. In contrast, the SOFC of this embodiment is provided with a flow path structure in the cell frame 40 that branches and flows the fuel gas, so that a part of the fuel gas flowing in from the inlet side manifold section 110a can be made to flow into the second power generation cell 32 arranged in series along the flow direction. This makes it possible to adjust the pressure loss without providing a mechanism for suppressing side flow (see the white arrow 223 in FIG. 4A). In this specification, the structure in which multiple power generation cells 31, 32 are arranged in series along the gas flow and the gas flowing in from the inlet side manifold sections 110a, 110c is branched and led to the second power generation cell 32 is also simply referred to as a "series branch structure."

The above explanation focuses on the configuration on the fuel side, but the configuration on the oxidizer side is similar.

In this way, the space between the manifold sections 110a, 110c, 120a, 120c and the power generation cells 31, 32 is saved, the manifold sections 110a, 110c, 120a, 120c can be positioned asymmetrically with respect to the power generation cells 31, 32 and the opening area can be minimized, and the mechanism for suppressing side flow due to the serial branch structure is eliminated, making it possible to miniaturize the SOFC stack.

Figure 5A is an explanatory diagram used to explain the improvement of the reforming efficiency of an SOFC stack, and is an enlarged plan view of the end of the cell frame 40 where the inlet side manifold parts 110a and 110c are formed. Figure 5B is a schematic diagram showing the relationship between the flow rate of the fuel gas and the reforming property.

The SOFC stack can carry out a steam reforming reaction by utilizing heat at the operating temperature (internal reforming). As shown in FIG. 5B, the reforming performance in the steam reforming reaction is better when the space velocity (SV) of the fuel gas is smaller. The space velocity (SV) is expressed by SV=Q [m ³ /sec]/V [m ³ ]. Here, Q is the flow rate of the fuel gas, and V is the volume of the channel through which the fuel gas flows. In order to improve the reforming performance without increasing the volume of the stack (with V kept constant), it is sufficient to reduce the flow rate of the fuel gas. However, simply reducing the amount of fuel gas supplied will result in a lack of output due to a lack of fuel.

As shown in FIG. 5A, Q0 represents the flow rate of fuel gas flowing in through the inlet 140a, Q1 represents the flow rate of fuel gas branching off into the second supply passage 202a, Q2 represents the flow rate of fuel gas branching off into the third supply passage 203a, and Q3 represents the flow rate of fuel gas supplied from the first supply passage 201a through the supply section 161a to the first power generation cell 31. Q1+Q2+Q3=Q0, and the flow rate Q3 of fuel gas supplied to the first power generation cell 31 is less than the flow rate Q0 of the inflowing fuel gas (Q3<Q0).

The cell unit 10 of the internal reforming SOFC stack has a serial branch structure. Therefore, in the upstream part where the flow velocity is high, the fuel gas is branched into flow rates Q1, Q2, and Q3, and at the stage where the fuel gas is reformed (the stage where the fuel gas is supplied to the first power generation cell 31), the fuel gas is reduced to a flow rate Q3 (Q3<Q0). Therefore, in the first power generation cell 31, the space velocity (SV) appears to decrease relative to the supply amount (Q0), and even under conditions where the water vapor amount (S/C) is low, the amount of hydrogen produced increases, improving the reforming efficiency. Since the flow rate (Q0) of the inflowing fuel gas is not decreased, the reforming efficiency can be improved without incurring a power shortage due to a fuel shortage.

In the second power generating cell 32, the water vapor partial pressure decreases as the distributed fuel gas mixes, and the amount of hydrogen produced by reforming increases. As a result, the amount of electricity generated by the second power generating cell 32 increases.

As described above, the SOFC of this embodiment has two power generating cells 31, 32, a cell frame 40, and a separator 20. The cell frame 40 has inlet side manifold parts 110a, 110c, outlet side manifold parts 120a, 120c, and a holding part 130 that holds the outer circumferences of the two power generating cells 31, 32 in a state in which they are arranged in series along the direction from the inlet side manifold parts 110a, 110c toward the outlet side manifold parts 120a, 120c. The cell frame 40 has inlet parts 140a, 140c, supply passages 150a, 150c, supply parts 161a, 161c, 162a, 162c, discharge parts 171a, 171c, 172a, 172c, discharge passages 180a, 180c, and outlet parts 190a, 190c.

The solid oxide fuel cell thus configured is provided with supply passages 150a, 150c and supply sections 161a, 161c, 162a, 162c within the cell frame 40, so that the gas (fuel gas and oxidant gas) flowing in from the inlet manifold sections 110a, 110c can be branched and supplied to each of the two power generation cells 31, 32 arranged in series. This allows the gas flow rate flowing through each of the two power generation cells 31, 32 to be reduced, the pressure loss of the entire cell unit 10 to be reduced, and gas distribution to be uniform. The pressure loss of the cell frame 40 can be controlled by the width, height, formation position, and shape of the gas passages in the inlet portions 140a, 140c, the supply passages 150a, 150c, the supply portions 161a, 161c, 162a, 162c, the exhaust portions 171a, 171c, 172a, 172c, the exhaust passages 180a, 180c, and the outlet portions 190a, 190c. Furthermore, the space between the inlet side manifolds 110a, 110c and the outlet side manifolds 120a, 120c and the power generating cells 31, 32 can be reduced, and the inlet side manifolds 110a, 110c and the outlet side manifolds 120a, 120c for each gas can be reduced to one each, so that the stack can be made smaller. Thus, it is possible to provide an SOFC that can be made smaller while maintaining uniform gas distribution. Furthermore, the gas flow rate through the first power generation cell 31 is reduced compared to the flow rate entering through the inlet manifolds 110a and 110c, so the space velocity (SV) in the first power generation cell 31 decreases, improving reforming efficiency.

In each of the two power generation cells 31, 32, the direction in which the fuel flows and the direction in which the oxidant flows are the same (X-positive direction). By configuring in this way, the gas supply method in each of the first power generation cell 31 and the second power generation cell 32 is made coflow, and the space velocity (SV) in the first power generation cell 31 is reduced, thereby improving the reforming efficiency.

(Variation 1)
Fig. 6A is a plan view showing a cell frame 41 of Modification 1. Fig. 6B is a cross-sectional view taken along line 6B-6B in Fig. 6A, Fig. 6C is an enlarged cross-sectional view of part 6C in Fig. 6B, and Fig. 6D is an enlarged cross-sectional view of part 6D in Fig. 6B. Members common to the embodiment are given the same reference numerals, and their description will be omitted.

The cell frame 41 of the first modification differs from the embodiment in which the cross-sectional area of the gas passage is constant in that the cross-sectional area of the gas passage in the fuel gas supply section 261a is changed.

In the cell frame 41 of the first modification, the cross-sectional area of the gas passage in the fuel gas supply section 261a is larger at a position farther from the inlet manifold section 110a for fuel gas than at a position closer to the inlet manifold section 110a for fuel gas. The supply section 261a is composed of a plurality of grooves 262 formed in the partition wall facing the first supply passage 201a among the rectangular partition walls surrounding the upstream opening 131. In the illustrated example, the depth of the grooves 262 is the same, but the width of the grooves is larger at a position farther from the inlet manifold section 110a than at a position closer to the inlet manifold section 110a (see Figures 6C and 6D). In the supply section 261a, the pressure loss of the gas passage is smaller at a position farther from the inlet manifold section 110a than at a position closer to the inlet manifold section 110a. As a result, the fuel gas is evenly distributed from the position close to the inlet manifold section 110a to the position far from it and supplied to the first power generation cell 31.

As described above, in the cell frame 41 of the first modified example, the cross-sectional area of the gas passage in the supply section 261a is larger at a position far from the inlet manifold section 110a than at a position close to the inlet manifold section 110a. This configuration improves the distribution of the fuel gas, and the fuel gas is uniformly distributed from a position close to the inlet manifold section 110a to a position far from the inlet manifold section 110a and supplied to the first power generation cell 31. Since the distribution is improved, the first power generation cell 31 can be brought even closer to the inlet manifold section 110a of the fuel, making it possible to further reduce the size of the SOFC stack. Furthermore, since the distribution is improved, the space velocity (SV) in the first power generation cell 31 can be further reduced, and the reforming efficiency is further improved.

The cross-sectional area of the gas passages of the exhaust section 171a of the first power generation cell 31, the supply section 162a of the second power generation cell 32, and the exhaust section 172a of the second power generation cell 32 are constant, but the cross-sectional area can be changed according to the distribution of the fuel gas flow. The cross-sectional area of the gas passages of the supply sections 161c, 162c and the exhaust sections 171c, 172c on the oxidizer side are constant, but the cross-sectional area can be changed according to the distribution of the oxidizer gas flow.

(Variation 2)
Fig. 7A is a plan view showing the cell frame 42 of the second modified example. Fig. 7B is an explanatory diagram used to explain the improvement in the temperature rise characteristic of the supply temperature of the fuel gas supplied to the most upstream first power generation cell 31, and is an enlarged plan view showing the end of the cell frame 42 where the inlet side manifold parts 110a, 110c are formed. Fig. 7C is an explanatory diagram for comparison used to explain the improvement in the temperature rise characteristic of the supply temperature of the fuel gas supplied to the most upstream first power generation cell 31, and is an enlarged plan view showing the end of the cell frame 42 where the inlet side manifold parts 110a, 110c are formed. Members common to the embodiment are given the same reference numerals, and their description will be omitted.

The cell frame 42 of the second modification differs from the embodiment in that the ratio at which the fuel gas is branched to each of the two power generation cells 31, 32 is different, in that the branching ratio is approximately equal.

As shown in FIG. 7A, in the cell frame 42 of the second modification example, the ratio of fuel gas branched to each of the two power generation cells 31, 32 is greater for the second power generation cell 32 than for the first power generation cell 31. In order to make the branching ratios different, the width (Xb) of the supply passage 150a (fourth supply passage 204a) facing the second power generation cell 32 is greater than the width (Xf) of the supply passage 150a (first supply passage 201a) facing the first power generation cell 31 closer to the inlet manifold portion 110a (Xf<Xb).

The fuel gas flowing in from the inlet manifold 110a branches off and flows into the first power generation cell 31 and the second power generation cell 32. By setting the width of the supply passage 150a as described above, the ratio of the flow rate branching to the second power generation cell 32 is greater than the ratio of the flow rate branching to the first power generation cell 31.

7B and 7C, the first power generating cell 31 contacts the inlet manifold portion 110c of the heated oxidizer across the first supply passage 201a. As shown in FIG. 7C, when the volume 263 occupied by the first supply passage 201a is large, the heat capacity of the fuel gas increases and the temperature rise property decreases. On the other hand, as shown in FIG. 7B, when the volume 264 occupied by the first supply passage 201a is small, the heat capacity of the fuel gas decreases and the temperature rise property improves. In this way, the second modification can reduce the heat capacity of the fuel gas supplied to the first power generating cell 31 to promote the temperature rise. Furthermore, the supply temperature of the fuel gas increases and the spatial velocity (SV) is also reduced, so that the reforming performance of the first power generating cell 31 is further improved. In addition, since the second power generating cell 32 is hotter than the first power generating cell 31, it is expected that the power generating performance will be improved by supplying more fuel gas to the second power generating cell 32.

As described above, in the cell frame 42 of variant 2, the ratio of fuel gas branched to each of the two power generating cells 31, 32 is greater for the second power generating cell 32 than for the first power generating cell 31. By configuring in this way, the supply temperature of the fuel gas supplied to the first power generating cell 31 can be increased. Furthermore, since the supply temperature of the fuel gas is increased and the spatial velocity (SV) is reduced, the reforming performance of the first power generating cell 31 is further improved.

(Variation 3)
Fig. 8A is a perspective view showing a cell frame 43 of Modification 3, and Fig. 8B is a plan view showing the flow directions of fuel gas and oxidant gas in a plurality of power generation cells 31, 32 of Modification 3. Fig. 8C is an explanatory diagram used to explain the rise in average temperature in the reaction surface in Modification 3. The solid arrows in Fig. 8B indicate the flow of fuel gas, and the dashed arrows indicate the flow of oxidant gas. Members common to the embodiment are given the same reference numerals, and their explanation will be omitted.

The cell frame 43 of the third modification differs from the embodiment in that the gas supply method in the first power generation cell 31 is counterflow, which is the coflow method.

As shown in FIG. 8B, in at least one of the two power generation cells 31, 32, the direction in which the fuel flows is different from the direction in which the oxidizer flows. In the first power generation cell 31, the direction in which the fuel flows (positive X direction) is different from the direction in which the oxidizer flows (negative X direction). In the second power generation cell 32, the direction in which the fuel flows is the same as the direction in which the oxidizer flows (positive X direction).

In order to achieve the above gas flow, the surface of the cell frame 43 through which the oxidant gas flows (the back side of the paper in FIG. 8B) is formed in the same manner as in the embodiment. The surface of the cell frame 43 through which the fuel gas flows (the front side of the paper in FIG. 8B) is formed as follows. The supply passage 150a has a first supply passage 351a and a second supply passage 352a. The first supply passage 351a is located on the Y positive side and extends along the X direction. The second supply passage 352a extends along the Y direction between the two power generation cells 31 and 32. The supply section 161a of the first power generation cell 31 and the supply section 162a of the second power generation cell 32 both face the second supply passage 352a. The discharge section 171a of the first power generation cell 31 is located in the X negative direction, and the discharge section 172a of the second power generation cell 32 is located in the X positive direction. The discharge passage 380a has a first discharge passage 381a, a second discharge passage 382a, and a third discharge passage 383a. The first discharge passage 381a extends along the Y direction and faces the discharge portion 171a of the first power generation cell 31. The second discharge passage 382a is located on the negative Y direction side and extends along the X direction. The third discharge passage 383a extends along the Y direction and faces the discharge portion 172a of the second power generation cell 32.

In Figure 8C, the characteristics of the counterflow alone and the coflow alone are shown in the main parts of the cell frame 43, and the characteristics of variant 3 are shown diagrammatically below them. As characteristics, the fuel temperature is shown by a two-dot chain line, the air temperature is shown by a solid line, and the current density is shown by a dashed line. The white arrows 224 on the top and bottom indicate steady-state heat transfer due to temperature difference. In the characteristics of variant 3, the part surrounded by the dashed line indicates the part where performance has been improved by increasing the fuel input temperature.

By using a structure with different flow directions within the reaction surface, as in variant 3, the high inlet fuel temperature due to the high heat exchange efficiency of the counterflow can be distributed to the low fuel inlet temperature of the coflow. This increases the average temperature within the surface. Furthermore, the spatial velocity (SV) due to the flow distribution is reduced, improving the reforming efficiency.

As described above, in the cell frame 43 of variant 3, the direction in which the fuel flows is different from the direction in which the oxidizer flows in at least one of the multiple power generation cells 31, 32. By configuring in this way, the temperature and fuel consumption characteristics of each of the multiple power generation cells 31, 32 change. As a result, the average in-plane temperature of the cell unit 10 increases, and power generation performance is improved by isolating (raising) the in-plane temperature distribution.

(Variation 4)
Fig. 9A is a perspective view showing a cell unit 11 of an SOFC of Modification 4, disassembled into a separator 25, power generating cells 31, 32, 33, and a cell frame 44. Fig. 9B is a plan view showing the cell frame 44 of Modification 4. The solid arrows in Fig. 9B indicate the flow of fuel gas, and the dashed arrows indicate the flow of oxidant gas. Members common to the embodiment are given the same reference numerals, and their description will be omitted.

The cell unit 11 of variant 4 differs from the embodiment in the number of power generation cells 31, 32, and 33, and in that the multiple power generation cells 31, 32, and 33 are divided into a main reforming surface that mainly performs reforming and a main power generation surface that mainly generates power.

As shown in FIG. 9A, the cell unit 11 of the fourth modified example has three power generating cells 31, 32, and 33. For ease of explanation, the three power generating cells 31, 32, and 33 are also referred to as the first power generating cell 31, the second power generating cell 32, and the third power generating cell 33, in that order from the upstream side.

In the cell unit 11 of variant 4, the three power generating cells 31, 32, and 33 are divided into a main reforming surface that mainly performs reforming and a main power generating surface that mainly performs power generation. The main reforming surface is composed of the first power generating cell 31 and the second power generating cell 32. The main power generating surface is composed of the third power generating cell 33. The third power generating cell 33 that constitutes the main power generating surface is supplied with a mixture of fuel off-gas from the first power generating cell 31 and the second power generating cell 32 that constitute the main reforming surface.

The number of main reforming surfaces is preferably equal to or greater than the number of main power generation surfaces. In variant 4, the number of main reforming surfaces is "2" and the number of main power generation surfaces is "1".

As shown in FIG. 9B, in at least one power generating cell 31 among the three power generating cells 31, 32, and 33, the direction in which the fuel flows is different from the direction in which the oxidizer flows. In the first power generating cell 31, the direction in which the fuel flows (positive X direction) is different from the direction in which the oxidizer flows (negative X direction). In the second power generating cell 32 and the third power generating cell 33, the direction in which the fuel flows is the same as the direction in which the oxidizer flows (positive X direction). In this way, the cell frame 44 of variant 4 is counter-flow in the first power generating cell 31 and co-flow in the second power generating cell 32 and the third power generating cell 33.

In order to achieve the above gas flow, the surface of the cell frame 44 through which the oxidizer gas flows (the back side of the paper in FIG. 9B) is formed in the same manner as in the embodiment. The surface of the cell frame 44 through which the fuel gas flows (the front side of the paper in FIG. 9B) is formed as follows. The supply passage 150a has a first supply passage 451a, a second supply passage 452a, a third supply passage 453a, a fourth supply passage 454a, and a fifth supply passage 455a. The first supply passage 451a is located on the Y positive side and extends along the X direction. The second supply passage 452a extends along the Y direction between the first power generation cell 31 and the second power generation cell 32. The third supply passage 453a is located on the Y negative side and extends along the X direction. The fourth supply passage 454a extends along the Y direction between the second power generation cell 32 and the third power generation cell 33. The fifth supply passage 455a extends along the Y direction and faces the discharge portion 171a of the first power generating cell 31. The supply portion 161a of the first power generating cell 31 and the supply portion 162a of the second power generating cell 32 both face the second supply passage 452a. The supply portion 163a of the third power generating cell 33 faces the fourth supply passage 454a. The discharge portion 171a of the first power generating cell 31 is located in the negative X direction, and the discharge portion 172a of the second power generating cell 32 is located in the positive X direction. The discharge portion 173a of the third power generating cell 33 faces the discharge passage 180a. The discharge passage 180a is partitioned from the supply passage 150a and extends along the Y direction adjacent to the outlet side manifold portions 120a, 120c. In addition, the reference symbol 173c in FIG. 9A indicates the exhaust portion on the oxidant gas side of the third power generation cell 33, and the exhaust portion 173c of the third power generation cell 33 faces the exhaust passage 180c as in the embodiment.

The fuel off-gas that has passed through the first power generation cell 31 is discharged to the fifth supply passage 455a. The fuel off-gas that has passed through the second power generation cell 32 is discharged to the fourth supply passage 454a. The fuel off-gas that passes through the fifth supply passage 455a flows from the third supply passage 453a to the fourth supply passage 454a. The fuel off-gas from the first power generation cell 31 and the second power generation cell 32 is mixed in the fourth supply passage 454a and supplied to the third power generation cell 33.

In FIG. 9B, Q0 represents the flow rate of fuel gas flowing in through the inlet 140a, and Q1 represents the flow rate of fuel gas flowing through each of the first power generation cell 31 and the second power generation cell 32. There is a relationship of 2×Q1=Q0. The fuel gas flowing in through the inlet 140a is equally divided and flows to each of the first power generation cell 31 and the second power generation cell 32, and the fuel off-gas of the first power generation cell 31 and the second power generation cell 32 is supplied to the third power generation cell 33.

By using a structure with different flow directions within the reaction surface as in variant 4, the high inlet fuel temperature due to the high heat exchange efficiency of the counterflow can be distributed to the low fuel inlet temperature of the coflow, as in variant 3. This increases the average temperature within the surface. Furthermore, the spatial velocity (SV) due to the flow distribution to the first power generation cell 31 and the second power generation cell 32, which form the main reforming surface, is reduced, improving the reforming efficiency.

Furthermore, since the number of main reforming surfaces is greater than or equal to the number of power generation surfaces, internal reforming is further promoted.

As described above, in the cell frame 44 of the fourth modified example, the multiple power generation cells 31, 32, and 33 are divided into a main reforming surface that mainly performs reforming and a main power generation surface that mainly performs power generation, and the main power generation surface is supplied with a mixture of fuel off-gas from the main reforming surface. By configuring it in this way, the spatial velocity (SV) due to the flow distribution to the power generation cells 31 and 32 that make up the main reforming surface is reduced, improving reforming efficiency and power generation performance.

Furthermore, the number of main reforming surfaces is equal to or greater than the number of main power generation surfaces. By configuring it in this way, internal reforming is further promoted, and power generation performance is further improved.

10, 11 cell unit,
20, 25 Separator,
31, 32, 33 power generation cell,
40, 41, 42, 43, 44 Cell frame,
61 fuel flow path,
62 oxidant flow path,
110a, 110c inlet side manifold portion,
120a, 120c outlet side manifold portion,
130 holding portion,
131 opening,
132 step portion,
140a, 140c inflow section,
150a, 150c supply passage,
161a, 161c supply section,
162a, 162c supply section,
163a supply unit,
171a, 171c discharge section,
172a, 172c discharge section,
173a, 173c discharge section,
180a, 180c discharge passage,
190a, 190c outflow part,
201a to 204a: first to fourth supply passages,
211c to 214c: first to fourth supply passages,
261a supply unit,
262 Groove portion,
351a, 352a first and second supply passages,
380a discharge passage,
381a to 383a: first to third discharge passages,
451a to 455a: first to fifth supply passages.

Claims (8)

a plurality of power generating cells each having at least an electrolyte layer and a pair of electrode layers;
a cell frame for holding a plurality of the power generating cells;
at least one pair of separators facing the plurality of power generating cells to form a fuel flow path and an oxidant flow path,
The cell frame includes :
an inlet manifold portion through which gas supplied to the power generation cell flows;
an outlet side manifold portion through which gas discharged from the power generation cell flows;
a plurality of holding sections that hold the outer peripheries of the plurality of power generating cells in a state in which the power generating cells are arranged in series along a direction from the inlet side manifold section toward the outlet side manifold section;
an inlet portion formed in the inlet manifold portion to allow gas flowing through the inlet manifold portion to flow in;
a supply passage for branching and directing the gas introduced from the inlet portion toward each of the plurality of power generation cells arranged in series;
a supply unit that supplies gas from the supply passage to each of the plurality of power generating cells;
an exhaust section that exhausts gas from each of the plurality of power generating cells;
a discharge passage for guiding the gas discharged from the discharge portion toward the outlet manifold portion;
an outlet portion formed in the outlet manifold portion and allowing the gas flowing through the exhaust passage to flow into the outlet manifold portion,
A solid oxide fuel cell, in at least one of the fuel flow path and the oxidant flow path, wherein the exhaust passage is only for flowing gas exhausted from the power generation cell that is located closest to the outlet portion among the plurality of power generation cells arranged in series . The solid oxide fuel cell according to claim 1, wherein the cross-sectional area of the gas passage in the fuel gas supply section is larger at a position farther from the inlet manifold section for fuel gas than at a position closer to the inlet manifold section for fuel gas. The solid oxide fuel cell according to claim 1 or 2, wherein the ratio of fuel gas branched to each of the plurality of power generation cells is greater for the downstream power generation cell than for the most upstream power generation cell. The solid oxide fuel cell according to any one of claims 1 to 3, wherein the direction in which the fuel flows and the direction in which the oxidant flows are the same in each of the plurality of power generation cells. The solid oxide fuel cell according to any one of claims 1 to 3, wherein in at least one of the power generation cells, the direction in which the fuel flows is different from the direction in which the oxidant flows. The plurality of power generating cells are divided into a main reforming surface that mainly performs reforming and a main power generating surface that mainly performs power generation,
6. The solid oxide fuel cell according to claim 1, wherein the main power generation surface is supplied with a mixture of fuel off-gas from the main reforming surface. The solid oxide fuel cell according to claim 6, wherein the number of the main reforming surfaces is equal to or greater than the number of the main power generation surfaces. a plurality of power generating cells each having at least an electrolyte layer and a pair of electrode layers;
a cell frame for holding a plurality of the power generating cells;
at least one pair of separators facing the plurality of power generating cells to form a fuel flow path and an oxidant flow path,
The cell frame includes:
an inlet manifold portion through which gas supplied to the power generation cell flows;
an outlet side manifold portion through which gas discharged from the power generation cell flows;
a plurality of holding sections that hold the outer peripheries of the plurality of power generating cells in a state in which the power generating cells are arranged in series along a direction from the inlet side manifold section toward the outlet side manifold section;
an inlet portion formed in the inlet manifold portion to allow gas flowing through the inlet manifold portion to flow in;
a supply passage for branching and directing the gas introduced from the inlet portion toward each of the plurality of power generation cells arranged in series;
a supply unit that supplies gas from the supply passage to each of the plurality of power generating cells;
an exhaust section that exhausts gas from each of the plurality of power generating cells;
a discharge passage for guiding the gas discharged from the discharge portion toward the outlet manifold portion;
an outlet portion formed in the outlet manifold portion and allowing the gas flowing through the exhaust passage to flow into the outlet manifold portion,
A solid oxide fuel cell, wherein a cross-sectional area of a gas passage in the fuel gas supply section is larger at a position farther from the inlet manifold section for fuel gas than at a position closer to the inlet manifold section for fuel gas.