Fuel cell unit

Abstract

Fuel cell unit (FC) for generating an electric current by means of a fuel gas and an oxidizing active gas, wherein the fuel cell unit comprises: a reformer (302) that reforms a raw material gas to produce the fuel gas; a heating channel (40, 40B, 40D, 40E, 40E2) that heats the oxidizing active ingredient gas by allowing the oxidizing active ingredient gas to flow through the heating channel; a cell stack (CS) that generates an electric current by receiving a supply of fuel gas and oxidizing agent gas that has been heated by the heating channel; a drain channel (41, 41B, 41D, 41E) which allows a combustion exhaust gas to be produced by burning the fuel gas that is drained from the cell stack and flows through the drain channel; an inlet opening (401a, 401Ba, 401Da and 40Ea) provided on one end side of the heating channel; an outflow orifice (403b, 403Bb, 403Db and 40Eb) provided at the opposite end of the heating channel, wherein the oxidizing drug gas flowing from the inflow orifice absorbs heat from the cell stack and the outlet channel and flows out of the outflow orifice; and a heat recovery section (50, 50B, 50D, 50E, 50E1, 50E2) that returns heat from the oxidizing active ingredient gas on the other end side to the oxidizing active ingredient gas on one end side where: the heat recovery section (50, 50B and 50D) is configured such that at least the heating channel is bent back so that one end side and the other end side are arranged close to each other; the heating channel comprises a first channel section (401, 401B, 401D) and a second channel section (403, 403B, 403D) which is connected to the first channel section and leads in a direction opposite to the direction in which the first channel section leads; the drain channel comprises a third channel section (411, 411B, 411D) and a fourth channel section (412, 412B, 412D) which is connected to the third channel section and leads in a direction opposite to the direction in which the third channel section leads; the second channel section is configured to absorb radiant heat from the cell stack by being arranged to surround the cell stack; and The third channel section, the fourth channel section and the first channel section are arranged in that order outside the second channel section such that the first channel section absorbs heat from the fourth channel section and the second channel section absorbs heat from the third channel section.

Description

Technical area

[0001] The present disclosure relates to a fuel cell unit for generating electricity by a fuel gas and an oxidizing agent gas. State of the art

[0002] A fuel cell unit is a power-generating device that directly converts the chemical energy of a fuel gas and an oxidizing agent gas into electrical energy. Because of its high power generation efficiency and relatively clean exhaust gas, this device has attracted attention as a next-generation power-generating device. In a fuel cell unit, the temperature of a cell stack is lowered by introducing a cooling gas during high-load operation.

[0003] Although such an excessive temperature rise of the cell stack is avoided by introducing the cooling gas, there is a possibility that a difference in temperature distribution within the cell stack becomes significant. Therefore, the fuel cell unit disclosed in Patent Literature 1 has fine irregularities on a partition wall that introduces the fuel gas or the oxidizing agent gas to increase the heat exchange efficiency of the fuel gas and the oxidizing agent gas.

[0004] In JP 2010-27215 A, attention is paid to making the temperature distribution as uniform as possible in the direction along the main surfaces of the unit cells in a cell stack formed by stacking plate-type unit cells. However, measurements of the temperature distribution in the stacking direction alone are insufficient, which becomes apparent when the number of stacked unit cells increases and the thickness of the cell stack increases in the stacking direction. Furthermore, since the channel condition in the cell stack is also determined depending on the channel of the partition wall portion, the channel configuration of the cell stack is limited. Further fuel cell units of this type are known from the publications DE 11 2015 003 352 T5, WO 2009 / 119 616 A1, US 2005 / 0 123 808 A1, JP 2014- 86 180 A, JP 2013- 114 853 A and JP 2007- 287 424 A. Summary of the invention

[0005] The object of the invention is to provide a fuel cell unit capable of suppressing the difference in temperature distribution in the stacking direction in a fuel cell unit having a cell stack formed by stacking plate-type unit cells.

[0006] The object of the invention is achieved by a fuel cell unit according to claim 1. Advantageous embodiments are the subject of the dependent claims.

[0007] The fuel cell unit according to the present invention is a fuel cell unit for generating an electric power by a fuel gas and an oxidizing agent gas, and includes a reformer that reforms a raw material gas to generate a fuel gas, a heating channel that heats an oxidizing agent gas by allowing the gas to flow through the channel, a cell stack that generates electricity by receiving a supply of the fuel gas and the oxidizing agent gas heated by the heating channel, and a discharge channel that allows a combustion exhaust gas generated by burning the fuel gas discharged from the cell stack to flow through the channel.The oxidizing agent gas flowing out from an inflow port provided on one end of the heating channel absorbs heat from the cell stack and the exhaust port and flows out from an outflow port provided on the other end of the heating channel. This fuel cell unit includes a heat recovery portion that returns the heat of the oxidizing agent gas on the other end to the oxidizing agent gas on the one end. The heat recovery portion is configured such that at least the heating channel is bent back so that the one end and the other end are close to each other. The heating channel has a first channel portion and a second channel portion connected to the first channel portion and leading in the direction opposite to that of the first channel portion.The vent channel includes a third channel portion and a fourth channel portion connected to the third channel portion and extending in the opposite direction to the direction of the third channel portion. The second channel portion is configured to receive radiant heat from the cell stack by being positioned to surround the cell stack, and the third channel portion, the fourth channel portion, and the first channel portion are positioned in this order outside the second channel portion such that the first channel portion receives heat from the fourth channel portion and the second channel portion receives heat from the third channel portion.

[0008] Since the fuel cell unit according to the present disclosure includes the heat recirculation section, the heat of the oxidizing agent gas on the other end side of the heating channel can be returned to the oxidizing agent gas on the one end side of the heating channel. Since the temperature of the oxidizing agent gas flowing into the heating channel from the inlet port increases as the gas flows through the heating channel, the temperature of the oxidizing agent gas in the heating channel is adjusted to be uniform when the heat recirculation is performed, as described above. In order to equalize the amount of radiant heat from the cell stack in the stacking direction, it is desirable to reduce the temperature difference between the temperatures of the cell stack and the wall of the heating channel of each section in the stacking direction.In the present disclosure, since the temperature of the oxidizing agent gas in the heating channel is adjusted to be uniform, the temperature difference between the temperature of the cell stack and the temperature of the wall of the heating channel can be reduced.

[0009] In the fuel cell unit according to the present disclosure, it is further preferable that the heat recovery portion is configured at least by bending the heating channel to arrange the one end side and the other end side close to each other.

[0010] In this way, since the heat recovery section is formed by bending the heating channel, the difference in temperature distribution in the stacking direction of the cell stack can be suppressed with a simple configuration in which the heating channel is bent without adding a separate element.

[0011] Furthermore, in the fuel cell unit according to the present disclosure, the heating channel includes a first channel portion extending from bottom to top, and a second channel portion connected to the first channel portion and extending from top to bottom. The vent channel may further include a third channel portion extending from bottom to top, and a fourth channel portion connected to the third channel portion and extending from top to bottom. The second channel portion is configured to receive radiant heat from the cell stack by being arranged to surround the cell stack.By arranging the third channel section, the fourth channel section, the first channel section in this order outside the second channel section, a configuration is established such that the first channel section absorbs heat from the fourth channel section and the second channel section absorbs heat from the third channel section.

[0012] In this way, the second channel portion, the third channel portion, the fourth channel portion, and the first channel portion are arranged in this order to surround the cell stack, and the first channel portion, which is configured to sufficiently increase the temperature of the oxidizing agent gas flowing through the interior, is arranged at the outermost position. Therefore, the first channel portion can serve as a heat insulating material, thus reducing the amount of heat insulating material separately provided while also suppressing a difference in temperature distribution in the stacking direction.

[0013] According to the present disclosure, in a fuel cell unit having a cell stack formed by stacking plate-type unit cells, regardless of the structure of channels in the cell stack, a fuel cell unit capable of suppressing the difference in temperature distribution in the stacking direction can be provided. Brief description of the drawings

[0014] The above-mentioned objects, other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. Fig. 1 is a schematic view showing an internal structure of a fuel cell unit according to a first embodiment of the present disclosure; Fig. 2 is a block diagram to show flows of gas and water in the Fig. 1; Fig. 3 is a partial cross-sectional view to show a Fig. 1; Fig. 4 is a partial cross-sectional view to show a modification of the Fig. 3; Fig. 5 is a diagram to illustrate a configuration of a heat recovery portion of the fuel cell unit according to the first embodiment of the present disclosure; Fig. 6 is a schematic view showing an internal structure of a fuel cell unit according to a second embodiment of the present disclosure; Fig. 7 is a diagram to illustrate the configuration of the heat recovery portion of the fuel cell unit according to the second embodiment of the present disclosure; Fig. 8 is a diagram to illustrate the configuration of a heat recovery section of a fuel cell unit according to a third embodiment of the present disclosure; Fig. 9 is a diagram to illustrate the configuration of a heat recovery section of a fuel cell unit according to a fourth embodiment of the present disclosure; Fig. 10 is a diagram to illustrate a specific example of the heat recovery portion of the fuel cell unit according to the fourth embodiment of the present disclosure; Fig. 11 is a diagram to illustrate a specific example of the heat recovery portion of the fuel cell unit according to the fourth embodiment of the present disclosure. Description of embodiments

[0015] Embodiments of the present disclosure will be described below with reference to the accompanying drawings. To facilitate understanding of the description, the same components in each drawing are largely assigned the same reference numerals without redundant description.

[0016] A fuel cell unit FC according to a first embodiment of the present disclosure will be described with reference to Fig. 1 and Fig. 2. As described in Fig. 1, the fuel cell unit FC comprises a cell stack CS, a housing 10, a combustion chamber 20 and a reforming unit 30.

[0017] The cell stack CS is composed of a plurality of unit cells. Each unit cell is a solid oxide fuel cell (SOFC) and has a structure in which a fuel electrode (anode) is formed on one side surface of the flat, plate-shaped solid electrolyte, and an air electrode (cathode) is formed on the surface of the other side. Each of the fuel electrode and the air electrode has a porous body made of an electrically conductive ceramic.

[0018] In the cell stack CS, all the unit cells are stacked vertically, and the unit cells are electrically connected in series. The cell stack CS is constructed on the upper surface of the base plate PB via a stack adapter AD.

[0019] The stack adapter AD is a plate-shaped member with a plurality of gas channels formed therein. The supply of fuel gas to the cell stack CS is performed through the stack adapter AD. Furthermore, the exhaust of gases (the exhaust of residual fuel gas and air not used to generate electricity) from the cell stack CS is also performed through the stack adapter AD. A base plate BP is a circular metal plate arranged horizontally within the casing 10. The base plate BP generally divides the interior of the casing 10 into an upper and a lower space.

[0020] The casing 10 is a casing having a substantially cylindrical shape for accommodating the cell stack CS, the combustion chamber 20, the reforming unit 30, or the like. The casing 10 is covered with a thermal insulation material on its entire side surface and its entire top surface. The casing 10 includes a first tubular body 110, a second tubular body 120, a third tubular body 130, a fourth tubular body 140, a fifth tubular body 150, and a sixth tubular body 160.Each of the first tubular body 110, the second tubular body 120, the third tubular body 130, the fourth tubular body 140, the fifth tubular body 150, and the sixth tubular body 160 is made of a metal and formed into a substantially cylindrical shape around a central axis and is arranged such that the respective central axes are coaxial. Fig. 1 is a schematic cross-sectional view of the fuel cell unit FC, wherein a plane extending along the central axis represents the cross section.

[0021] The first tubular body 110 is an innermost tubular body disposed inside the casing 10 and accommodating the cell stack CS and the stack adapter AD therein. The upper end of the first tubular body 110 is covered with a horizontal upper plate 181. The lower end of the first tubular body 110 is fixed in contact with the upper surface of the base plate BP. The height of the first tubular body 110 from its lower end to its upper end is greater than the height from the lower end of the stack adapter AD to the upper end of the cell stack CS. For this reason, the upper plate 181 and the upper end of the cell stack CS are spaced apart from each other. A plurality of air outlets 111 are formed as through holes on the underside of the first tubular body 110.The plurality of air outlets 111 are formed so as to be aligned at the same height and at equal intervals. The air outlets 111 are holes through which a current-generating air (an oxidizing agent gas) flows, which is supplied toward the cell stack CS.

[0022] The second tubular body 120 is a tubular body arranged to externally surround the first tubular body 110. A fixed gap is formed along the entire circumference between the inner surface of the second tubular body 120 and the outer surface of the first tubular body 110. A space formed between the second tubular body 120 and the first tubular body 110 forms an air passage 403 through which air flows to generate a current while being heated (corresponding to a second passage section).

[0023] The inner diameter of the second tubular body 120 is approximately equal to the outer diameter of the base plate BP. The inner surface of the second tubular body 120 near its lower end is in contact with the lateral surface of the base plate BP over its entire circumference. The second tubular body 120 is fixed to the base plate BP at the contact portion. With this configuration, gas cannot migrate between the space on the lower side of the base plate BP and the air duct 403.

[0024] The third tubular body 130 is a tubular body arranged to surround the second tubular body 120 from the outside. A fixed gap is formed along the entire circumference between the inner surface of the third tubular body 130 and the outer surface of the second tubular body 120. A space formed between the third tubular body 130 and the second tubular body 120 is formed as an exhaust passage 411 through which a high-temperature combustion exhaust gas generated by combustion in the combustion chamber 20 (corresponding to the third passage portion) flows. The upper end of the third tubular body 130 is arranged at a position lower than the upper end of the second tubular body 120.The third tubular body 130 extends to a position located below the lower end of the base plate BP.

[0025] The fourth tubular body 140 is a tubular body arranged to surround the third tubular body 130 from the outside. A fixed gap is formed along the entire circumference between the inner surface of the fourth tubular body 140 and the outer surface of the third tubular body 130. A space between the fourth tubular body 140 and the third tubular body 130 is formed as an exhaust passage 412 through which a high-temperature combustion exhaust gas generated by combustion in the combustion chamber 20 flows (corresponding to the fourth passage portion). The exhaust passage 412 is connected to an exhaust passage 413 arranged at a position located below the exhaust passage 412. The exhaust passage 413 is a passage that guides the combustion exhaust gas to the reforming unit 30 side.

[0026] The upper end of the second tubular body 120 and the upper end of the fourth tubular body 140 are positioned at the same position in the height direction. The upper end of the second tubular body 120 and the upper end of the fourth tubular body 140 are connected by a top plate 182, which is a circular plate arranged horizontally and has a doughnut shape (hereinafter, this state means that a substantially circular hole is formed substantially in the center). That is, the upper end of the second tubular body 120 is connected to the inner peripheral end of the top plate 182, and the upper end of the fourth tubular body 140 is connected to the outer peripheral end of the top plate 182. A gap is formed between the upper end of the third tubular body 130 and the top plate 182.Therefore, the exhaust duct 411 and the exhaust duct 412 are connected to each other at the respective upper ends.

[0027] The lower end of the third tubular body 130 and the inner surface of the fourth tubular body 140 are connected by a lower plate 183, which comprises a circular plate in the shape of a circular ring arranged horizontally. In other words, the lower end of the exhaust duct 412 is covered with the lower plate 183.

[0028] A gas discharge pipe 191 is connected to the underside of the fourth tubular body 140 (the side slightly higher than the lower plate 183). The internal space of the gas discharge pipe 191 communicates with the exhaust duct 413. The gas discharge pipe 191 is a pipe that discharges the combustion exhaust gas that has flowed through the exhaust duct 413 into the exterior of the casing 10 and supplies the gas to a waste heat recovery unit 62, which will be described later.

[0029] The fourth tubular body 140 extends to a position below the lower end of the third tubular body 130. A horizontal flange 141 is formed at the lower end of the fourth tubular body 140, extending from the lower end toward the exterior. The flange 141 is a flange used for securing the casing 10 at the time of assembling the fuel cell unit FC.

[0030] Near the lower end of the fourth tubular body 140, a lower plate 184 is arranged, which is a horizontal circular plate.

[0031] The outer diameter of the lower plate 184 is substantially equal to the inner diameter of the fourth tubular body 140. The lower plate 184 is fixed such that its entire outer surface is brought into contact with the inner surface of the fourth tubular body 140. A thermal insulation material TI is arranged in the lower lateral space of the lower plate 184.

[0032] The fifth tubular body 150 is a tubular body located at the outermost position in the casing 10 and arranged to externally surround the upper portion of the fourth tubular body 140. A fixed gap is formed along the entire circumference between the inner surface of the fifth tubular body 150 and the outer surface of the fourth tubular body 140. A space formed between the fifth tubular body 150 and the fourth tubular body 140 is formed as an air passage 401 in which air flows to generate a current while being heated (corresponding to the first passage portion).

[0033] The fifth tubular body 150 extends to a position higher than any of the upper ends of the first tubular body 110, the second tubular body 120, the third tubular body 130, and the fourth tubular body 140. The upper end of the fifth tubular body 150 is covered with a horizontal upper plate 185. A gap 402 is formed between the upper plate 185 and the upper plate 182. The upper ends of the air duct 401 and the air duct 403 are connected to each other via the gap 402.

[0034] A lower end of the fifth tubular body 150 and the outer surface of the fourth tubular body 140 are connected by a lower plate 186, which is a circular plate in the shape of a circular ring and arranged horizontally. In other words, the lower end of the air duct 401 is blocked by the lower plate 186.

[0035] An air introduction pipe 192 is connected to the bottom of the fifth tubular body 150 (a side slightly higher than the bottom plate 186). The interior of the air introduction pipe 192 communicates with the air duct 401. The air introduction pipe 192 is a pipe that introduces air into the interior of the housing 10 to generate a flow.

[0036] In the present embodiment, a configuration was established such that the temperature rise of the air while flowing through the air duct 401, which corresponds to the first duct section of the present disclosure, is greater than the temperature rise of the air while flowing through the air duct 403, which corresponds to the second duct section of the present disclosure. More specifically, a heat transfer surface extension section 420 is provided between the air duct 401 and the exhaust duct 412, which corresponds to the fourth duct section.

[0037] The heat transfer surface extension section 420 is described with reference to Fig. 3. As described in Fig. As shown in Figure 3, the heat transfer surface extension portion 420 is configured as corrugated fins provided on both sides of the fourth tubular body 140. The corrugated fins, which have protrusions 421 and recesses 422 arranged alternately, are arranged outside the fourth tubular body 140, that is, on the air duct 401 side. The corrugated fins, which have protrusions 423 and recesses 424 arranged alternately, are arranged inside the fourth tubular body 140, that is, on the exhaust duct 412 side.

[0038] Since the heat transfer area between the air duct 401 and the exhaust duct 412 is expanded, the heat of the combustion exhaust gas flowing in the exhaust duct 412 is efficiently transferred to the fourth tubular body 140, and the transferred heat is also efficiently transferred to the air flowing through the air duct 401. Therefore, the temperature rise of the air flowing through the air duct 401 is greater than the temperature rise of the air flowing through the air duct 403.

[0039] In particular, although the temperature of the upper portion of the cell stack CS tends to be lower than the temperatures of its middle and lower portions, heated air from the air duct 401 efficiently enters the air duct 403 from above through the gap 402, and thereby heat can be efficiently supplied to the upper surface of the cell stack CS. Furthermore, the fact that air at a high temperature flows into the air duct 403 means that the temperature distribution in the stacking direction (the direction in which the air duct 403 extends) of the cell stack CS can be reduced. In the present embodiment, since a gap is provided between the upper plate 181 and the upper plate 185, and the air that has been heated while flowing through the air duct 401 enters the gap, heat can be more efficiently supplied to the upper surface of the cell stack CS.

[0040] As in Fig. 4, the same effect as that of the above-described heat transfer surface extension portion 420 can be achieved even if projections 421A and recesses 422A are directly provided on the fourth tubular body 140 so as to form a heat transfer surface extension portion 420A. Furthermore, since the number of components in the heat transfer surface extension portion 420A is reduced compared to that shown in Fig. 3, a reduction in weight and a reduction in cost can be achieved.

[0041] The description is made with renewed reference to the Fig. 1 and Fig. 2. The sixth tubular body 160 is a tubular body disposed at a position inside the third tubular body 130 and on the lower side of the base plate BP. The sixth tubular body 160 has an upper cylindrical portion 161 as an upper side portion and a lower cylindrical portion 162 as a lower side portion. The diameter of the upper cylindrical portion 161 is smaller than that of the lower cylindrical portion 162. The lower end of the upper cylindrical portion 161 and the upper end of the lower cylindrical portion 162 are connected by an intermediate portion 163, which is a circular plate in the shape of an annulus arranged horizontally. The upper end of the upper cylindrical portion 161 is in contact with the lower surface of the base plate BP.The lower end of the lower cylindrical portion 162 is in contact with the upper surface of the lower plate 184.

[0042] The diameter of the lower cylindrical portion 162 is smaller than that of the third tubular body 130. Therefore, a space is formed over the entire circumference between the third tubular body 130 and the sixth tubular body 160. The reforming unit 30 is disposed in the space, and a space is also formed over the entire circumference between the reforming unit 30 and the sixth tubular body 160. In the following description, the space formed inside the sixth tubular body 160 is also referred to as an "inner space 601." Furthermore, a space formed between the lower cylindrical portion 162 of the sixth tubular body 160 and an inner cylinder 320 of the reforming unit 30 is also referred to as an "outer space 602."

[0043] On the lower cylindrical portion 162, a plurality of exhaust ports 165 are formed as through holes at a position located below the lower end of the reforming unit 30. The plurality of exhaust ports 165 are formed so as to be aligned at equal intervals and at the same height. The inner space 601 and the outer space 602 communicate with each other via these exhaust ports 165. The exhaust ports 165 are through holes through which the high-temperature combustion exhaust gas generated by combustion in the combustion chamber 20 flows.

[0044] The combustion chamber 20 is a burner for mixing and combusting a residual fuel gas that was not used for power generation (hereinafter also referred to as "residual fuel") and residual air that was not used for power generation (hereinafter also referred to as "residual air"). The combustion chamber 20 is made of stainless steel. The entire body of the combustion chamber 20 is formed in a substantially cylindrical shape and is arranged to protrude downward from the center of the lower surface of the base plate BP. Furthermore, the combustion chamber 20 is arranged in the center of the housing 10 (the position along the central axis of the upper cylindrical portion 161) in a plan view.

[0045] Both residual fuel and residual air discharged from the cell stack CS are supplied to the upper end of the combustion chamber 20 through a passage formed in the stack adapter AD and a passage formed in the base plate BP. Then, the residual fuel and residual air reach the lower end of the combustion chamber 20 through a passage formed in the combustion chamber 20 and are discharged downward while being mixed with each other at the lower end. At the lower end of the combustion chamber 20, the discharged residual fuel and residual air combust, generating high-temperature combustion exhaust gas. Furthermore, the combustion chamber 20 also reaches a high temperature due to the heat of combustion.

[0046] An ignition device IG is arranged on the lower side of the combustion chamber 20. The ignition device IG is a device that starts combustion by igniting the gas mixed from the residual fuel and residual air that is expelled from the combustion chamber 20. The ignition device IG is arranged such that the upper end, where a spark discharge occurs, is close to the lower end of the combustion chamber 20 while vertically penetrating the lower plate 184 and the thermal insulation material TI. Ignition by the ignition device IG is performed at the time of startup of the fuel cell unit FC.

[0047] A description will be given of a configuration of the reforming unit 30. The reforming unit 30 is constructed by integrating a reformer 302, which generates a fuel gas (a hydrogen-containing gas) from a city gas through a reforming reaction, and an evaporator 301, which generates water vapor to be supplied to the reformer 302. The entire body of the reforming unit 30 has a substantially cylindrical shape and is arranged in the space between the third tubular body 130 and the sixth tubular body 160 in the housing 10. The reforming unit 30 includes an outer cylinder 310, the inner cylinder 320, an upper plate 330, a first lower plate 340, a second lower plate 350, a first partition plate 360, and a second partition plate 370.Among these, the outer cylinder 310, the inner cylinder 320, the upper plate 330, the first lower plate 340, the second lower plate 350, and the portion of the lower side of the first partition plate 360 ​​located below the first lower plate 340 form the outline of the reforming unit 30.

[0048] The outer cylinder 310 is a tubular body that forms the outer surface of the reforming unit 30. The central axis of the outer cylinder 310 coincides with the central axis of the third tubular body 130. The outer diameter of the outer cylinder 310 is substantially equal to the inner diameter of the third tubular body 130. Substantially the entire outer surface of the outer cylinder 310 is in contact with the inner surface of the third tubular body 130. The outer cylinder 310 extends to a position located below the lower plate 183.

[0049] The inner cylinder 320 is a tubular body that forms the inner surface of the reforming unit 30. The central axis of the inner cylinder 320 coincides with the central axis of the third tubular body 130. The outer diameter of the inner cylinder 320 is smaller than the inner diameter of the outer cylinder 310. For this reason, a space is formed between the outer cylinder 310 and the inner cylinder 320. Part of the space is formed as a space in which steam is generated from water and flows. Another part of the space is a space in which the reforming reaction takes place to produce a fuel gas.

[0050] The inner diameter of the inner cylinder 320 is larger than the outer diameter of the lower cylindrical portion 162 of the third tubular body 130. Therefore, as described above, a clearance is formed between the reforming unit 30 and the sixth tubular body 160 along the entire circumference. The height of the upper end of the inner cylinder is the same as that of the upper end of the outer cylinder 310. On the other hand, the height of the lower end of the inner cylinder 320 is larger than the height of the lower end of the outer cylinder 310 and is the same as the height of the lower end of the lower plate 183.

[0051] The upper plate 330 is a circular plate in the shape of a circular ring, arranged horizontally. The outer surface of the upper plate 330 is connected to the upper end of the inner surface of the outer cylinder 310. Furthermore, the inner surface of the upper plate 330 is connected to the upper end of the outer surface of the inner cylinder 320. Thus, the upper end of the outer cylinder 310 and the upper end of the inner cylinder 320 are connected by the upper plate 330.

[0052] The first lower plate 340 is a circular plate in the shape of a circular ring and arranged horizontally. The first lower plate 340 is arranged at a position having the same height as the lower plate 183. The outer surface of the first lower plate 340 is connected to the inner surface of the first partition plate 360, which will be described later. The inner surface of the first lower plate 340 is connected to the lower end of the inner surface of the inner cylinder 320.

[0053] The second lower plate 350 is a circular plate in the shape of a circular ring and arranged horizontally. The outer surface of the second lower plate 350 is connected to the lower end of the inner surface of the outer cylinder 310. The inner surface of the second lower plate 350 is connected to the lower end of the outer surface of the first partition plate 360, which will be described later. Therefore, the second lower plate 350 is arranged at a position below the first lower plate 340.

[0054] Part of the first partition plate 360 ​​is a tubular body arranged inside the reforming unit 30. The center axis of the first partition plate 360 ​​coincides with the center axis of the outer cylinder 310 and the center axis of the inner cylinder 320. The outer diameter of the first partition plate 360 ​​is smaller than the inner diameter of the outer cylinder 310. Thus, a fixed gap is formed between the outer cylinder 310 and the first partition plate 360 ​​over the entire circumference.

[0055] The height of the upper end of the first partition plate 360 ​​is less than the height of the upper end of the outer cylinder 310. Therefore, a gap exists between the upper end of the first partition plate 360 ​​and the lower surface of the upper plate 330. The height of the lower end of the first partition plate 360 ​​is the same as that of the lower end of the outer cylinder 310. As mentioned above, the second lower plate 350 is connected to the lower end of the first partition plate 360 ​​from the outside. Furthermore, the first lower plate 340 is connected to the first partition plate 360 ​​from the inside.

[0056] The entire body of the second partition plate 370 is a tubular body arranged inside the reforming unit 30. The central axis of the second partition plate 370 coincides with the central axis of the outer cylinder 310 and the central axis of the inner cylinder 320. The outer diameter of the second partition plate 370 is smaller than the inner diameter of the first partition plate 360. Accordingly, a fixed gap is formed between the second partition plate 370 and the first partition plate 360 ​​along the entire circumference. The inner diameter of the second partition plate 370 is larger than the outer diameter of the inner cylinder 320. Therefore, a fixed gap is also formed between the second partition plate 370 and the inner cylinder 320 along the entire circumference.

[0057] The second partition plate 370 is fixed to the upper plate 330, while the upper end is in contact with the lower surface of the upper plate 330. The height of the lower end of the second partition plate 370 is greater than the height of the lower end of the inner cylinder 320. Therefore, a gap exists between the lower end of the second partition plate 370 and the upper surface of the first lower plate 340.

[0058] With the above configuration, a first space 381 as a space formed between the outer cylinder 310 and the first partition plate 360, a second space 382 as a space formed between the first partition plate 360 ​​and the second partition plate 370, and a third space 383 as a space formed between the second partition plate 370 and the inner cylinder 320 are formed in the interior of the reforming unit 30. The first space 381 is connected to the second space 382 above the first partition plate 360, and the second space 382 is connected to the third space 383 below the second partition plate 370.

[0059] One end of a water supply pipe 391 is connected from below to the second lower plate 350. The water supply pipe 391 is a pipe that supplies water to the first space 381. The other end of the water supply pipe 391 is connected to a water supply pump (not shown) arranged outside the housing 10.

[0060] Water supplied to the first space 381 from the water supply pipe 391 is heated to be converted into water vapor by high-temperature combustion exhaust gas flowing through the exhaust passage 412. The water vapor reaches the entrance of the third space 383 through the first space 381 and then the second space 382. Thus, in the reforming unit 30, the first space 381, the second space 382, ​​and the wall surfaces defining these spaces constitute a section for generating water vapor by supplying water from the outside, that is, a section corresponding to the evaporator 301.

[0061] A support plate 352 is arranged in the first space 381. The support plate 352 is a plate in the shape of a circular ring, which is arranged horizontally so as to vertically divide the first space 381. The support plate 352 is fixed to the outer cylinder 310 and the first partition plate 360 ​​at a position having the same height as the first lower plate 340. A plurality of through holes are formed on the support plate 352 so that water can flow through the support plate 352. The heat transfer enhancing element CB, which promotes heat transfer from the outer cylinder 310 into the water, is packed on the upper side of the support plate 352 in the first space 381. The heat transfer enhancing element CB is a plurality of alumina balls (a plurality of ceramic balls).

[0062] One end of a city gas supply pipe 392 is connected from below to the first lower plate 340. The city gas supply pipe 392 is a pipe that supplies a city gas to the inlet portion of the third space 383. The other end of the city gas supply pipe 392 is connected to a desulfurization device 61 (see Fig. 2).

[0063] The reforming catalyst RC fills the third space 383. The reforming catalyst RC is obtained by allowing a catalytic metal, such as nickel, to be entrained on the spherical surface of alumina. A metal mesh (not shown) arranged horizontally is fixed to a position slightly above the lower end of the second partition plate 370 in the third space 383, and the reforming catalyst RC is supported from below by the metal mesh.

[0064] The city gas supplied to the interior of the reforming unit 30 from the city gas supply pipe 392 flows upward in the third space 383 after being mixed with water vapor at the inlet portion of the third space 383. At this time, a steam reforming reaction occurs due to the city gas and the water vapor being exposed to the reforming catalyst RC, and a fuel gas (a hydrogen-containing gas) is generated. Thus, in the reforming unit 30, the third space 383 and the wall surfaces defining this space are a portion where the steam reforming reaction takes place after receiving the water vapor from the evaporator 301 and the city gas from the outside, that is, a portion corresponding to the reformer 302. The reforming catalyst RC is packed over the entire circumferential direction of the third space 383.Therefore, the water vapor supplied from the evaporator 301 does not flow through the third space 383 without being exposed to the reforming catalyst RC.

[0065] One end of a fuel gas supply pipe 393 is connected to the vicinity of the upper end of the inner cylinder 320. The fuel gas supply pipe 393 is a pipe that supplies the fuel gas generated in the reforming unit 30 (the reformer 302) to the cell stack CS. The other end of the fuel gas supply pipe 393 is connected to the lower surface of the base plate BP. The fuel gas reaches the base plate BP from the upper portion of the third space 383 through the fuel gas supply pipe 393. Thereafter, the fuel gas is supplied to the cell stack CS through a channel formed in the base plate BP and a channel formed in the stack adapter AD.

[0066] The reforming unit 30 is supported from below by a cylindrical sealing block SB made of a heat-resistant material. The upper end of the sealing block SB is in contact with the lower surface (the first lower plate 340) of the reforming unit 30, and the lower end of the sealing block SB is in contact with the upper surface of the lower plate 184. The inner diameter of the sealing block SB is equal to the inner diameter of the reforming unit 30. Furthermore, the radial dimension (the thickness) of the sealing block SB is smaller than the radial dimension (the thickness) of the reforming unit 30. Therefore, a space SP is formed outside the sealing block SB (lower side of the reforming unit 30), as shown in Fig. 1 shown.

[0067] A space outside the sixth tubular body 160 and the space SP are separated by the reforming unit 30 and a sealing block SB, and no gas can flow between the spaces. Since the high-temperature combustion exhaust gas does not flow into the space SP, the temperature in the space SP is kept relatively low.

[0068] Next, the flow of gases (air, town gas, fuel gas and combustion exhaust gas) during the operation of the fuel cell unit FC is described, mainly with reference to Fig. 2.

[0069] First, a description will be given of the air flow (the oxidizing agent gas) for generating a flow to be supplied to the cell stack CS. The air is supplied by a fan (not shown) located outside the housing 10 through the air introduction pipe 192 into the housing 10.

[0070] The air supplied through the air introduction pipe 192 flows upward in the air duct 401. Then, the air flows through the gap 402 into the air duct 403 and flows downward in the air duct 403.

[0071] The exhaust passage 411 and the exhaust passage 412 are formed between the air passage 401 and the air passage 403. High-temperature combustion exhaust gas flows inside this exhaust passage 411 and this exhaust passage 412. Accordingly, air introduced into the casing 10 is heated and its temperature is increased by the combustion exhaust gas as it flows through the air passage 401 and the air passage 403. In other words, heat is exchanged between the air and the combustion exhaust gas.

[0072] The cell stack CS has a high temperature during current generation, and the first tubular body 110 also has a high temperature due to the radiant heat from the cell stack CS. Therefore, the air is further heated by coming into contact with the first tubular body 110 while flowing through the air channel 403.

[0073] Thus, the air duct 401 and the air duct 403 are ducts in which air flows while being heated by the heat of the combustion exhaust gas and the radiant heat from the cell stack CS. Therefore, the air duct 401 and the air duct 403 are collectively referred to as the "air heating duct 40" in the following description. Similarly, the exhaust duct 411 and the exhaust duct 412 are collectively referred to as the "gas discharge duct 41." The air heating duct 40 is arranged to surround the cell stack CS from its sides. The air heating duct 40 can be referred to as a component corresponding to a preheater for performing heat exchange between the combustion exhaust gas generated by combustion in the combustion chamber 20 and flowing through the gas discharge duct 41 and the air to be supplied to the cell stack CS.

[0074] The air reaching the bottom of the air channel 403 is expelled from the air outlets 111 formed in the first tubular body 110 toward the cell stack CS. The air then reaches the air electrode of each unit cell and is used to generate a current.

[0075] The flow of fuel gas to be supplied to the cell stack CS and the flow of city gas as the raw material for the fuel gas are described. The city gas is supplied to the reforming unit 30 from the exterior of the casing 10 through the city gas supply pipe 392. The desulfurization device 61 is arranged between the city gas supply source and the city gas supply pipe 292. The desulfurization device 61 is a device for removing sulfur components contained in the city gas. The city gas is supplied to the reforming unit 30 after sulfur components that impair the performance of the unit cell have been removed by the desulfurization device 61.

[0076] The city gas supplied from the city gas supply pipe 392 into the interior of the reforming unit 30 is mixed with water vapor at the inlet portion of the third space 383. Then, the city gas flows upward into the third space 383, which is filled with the reforming catalyst RC.

[0077] A high-temperature combustion exhaust gas flows into the space formed between the lower cylindrical portion 162 of the sixth tubular body 160 and the inner cylinder 320 of the reforming unit 30. Thus, the city gas and water vapor are heated by the combustion exhaust gas as they flow through the third space 383, thereby increasing their temperature. In other words, heat is exchanged between the city gas and the water vapor and the combustion exhaust gas. Furthermore, the reforming catalyst RC filling the third space 383 is also at a high temperature due to heat transfer through the inner cylinder 320.

[0078] The sixth tubular body 160 surrounding the combustion chamber 20 became extremely hot because the sixth tubular body 160 was heated by radiant heat from the combustion chamber 20 in addition to being heated by the combustion exhaust gas. As a result, radiant heat from the sixth tubular body 160, whose temperature had become high, reached the inner cylinder 320 of the reforming unit 30 (it may be referred to as radiant heat originating from the combustion chamber 20 via the sixth tubular body 160). That is, the reformer 302 including the inner cylinder 320 was heated not only by the combustion exhaust gas but also by radiant heat from the combustion chamber 20.

[0079] When the mixed gas of the city gas and steam is exposed to the reforming catalyst RC, the steam reforming reaction takes place under this condition in the third space 383 (the reformer 302). As a result, fuel gas is generated from the mixed gas. Since the steam reforming reaction is an endothermic reaction, heat input is necessary to maintain the reaction stably. In the present embodiment, both the heat from the combustion exhaust gas applied by the inner cylinder 320 and the radiant heat from the combustion chamber 20 are used as heat to maintain the steam reforming reaction.

[0080] The fuel gas generated in the reformer 302 is supplied to the cell stack CS through the fuel gas supply pipe 393 and the channel in the stack adapter AD. The fuel gas reaches the fuel electrode of each unit cell and is used to generate electricity.

[0081] A description of the combustion exhaust gas flow is given. As described above, the residual fuel and residual air discharged from the cell stack CS are supplied to the combustion chamber 20 and are combusted at the lower end of the combustion chamber 20. As a result of combustion, a high-temperature combustion exhaust gas is generated in the interior space (the inner space 601) of the sixth tubular body 160. The combustion exhaust gas flows out through the exhaust ports 165 into the exterior space (the outer space 602) of the sixth tubular body 160.

[0082] Thereafter, the combustion exhaust gas flows upward in the outer space 602 along the inner cylinder 320. As described above, the heat of the combustion exhaust gas in this case is transferred through the inner cylinder 320 to the third space 383 and is used as part of the heat to maintain the steam reforming reaction.

[0083] The combustion exhaust gas that has passed through the outer space 602 flows upward in the exhaust duct 411 while exchanging heat with the air flowing through the air duct 403. Subsequently, the combustion exhaust gas flows downward in the exhaust duct 412 and flows into the exhaust duct 413 while exchanging heat with the air flowing through the air duct 401.

[0084] The outer cylinder 310 of the reforming unit 30 is located in a portion on the upper side of the support plate 353 in contact with the inner surface of the third tubular body 130. For this reason, the outer cylinder 310 has a high temperature due to the combustion exhaust gas flowing through the exhaust passage 413.

[0085] Water supplied from the water supply pipe 391 into the first space 381 becomes water vapor by being heated by heat transfer from the outer cylinder 310 (heat of the combustion exhaust gas). In other words, heat exchange occurs between the water and the combustion exhaust gas, thereby generating water vapor in the first space 381.

[0086] The combustion exhaust gas, which has reached the lower end of the exhaust duct 413 through the exhaust duct 412, is supplied to the waste heat recovery unit 62 through the gas discharge pipe 191. The waste heat recovery unit 62 generates hot water by exchanging heat between the combustion exhaust gas and the water. Thus, the fuel cell unit FC can generate hot water in addition to generating electricity, and is a cogeneration system that utilizes energy with high efficiency.

[0087] Next, a description will be given of the flow of water and water vapor. Water is supplied to the reforming unit 30 (the evaporator 301) through the water supply pipe 391 from the water supply pump (not shown) arranged outside the casing 10. The water supply pipe 391 is connected to the second lower plate 350 from below. Therefore, the supplied water is stored in a space formed in the lower portion of the first space 381. To be more specific, the water is stored in a water storage WS, which is a space on the lower side of the support plate 352 in the first space 381.

[0088] The water storage WS is a space formed by a portion of the outer cylinder 310 below the lower plate 183 (hereinafter, the portion is also referred to as “partition wall 311”), the second lower plate 350, and a portion of the first partition plate 360 ​​below the first lower plate 340 (hereinafter, the portion is also referred to as “partition wall 361”).

[0089] The partition wall 311, the second lower plate 350, and the partition wall 361 for forming the water reservoir WS have shapes such that the lower surface of the reforming unit 30 is partially extended downward. The partition wall 311, the second lower plate 350, and the partition wall 361 are all located in the space SP. In other words, the partition wall 311, the second lower plate 350, and the partition wall 361 are arranged in a space that is not reached by the high-temperature combustion exhaust gas and is at a relatively low temperature.

[0090] Although the outer cylinder 310 is heated by the combustion exhaust gas flowing through the exhaust passage 412, the partition wall 311 is located below the lower plate 183 and is not directly heated by the combustion exhaust gas. Thus, no water boils in the water storage WS, and the entire water storage WS is filled with water (liquid).

[0091] Since water is supplied from the water supply pump, the water level in the first space 381 is maintained at a slightly higher position than the upper surface of the support plate 352. Therefore, the heat transfer enhancing element CB (alumina balls) packed in the upper surface of the support plate 352 is partially submerged.

[0092] Due to the heat transfer from the outer cylinder 310, which has reached a high temperature due to the combustion exhaust gas, the heat transfer enhancement element CB in the first space 381 also has a high temperature. Water present above the support plate 352 boils and turns into water vapor upon contact with the heat transfer enhancement element CB, which is at the high temperature.

[0093] Thus, the water in the first chamber 381 becomes steam, which flows upwards. The steam then flows downwards in the second chamber 382 and is fed to the third chamber 383 (the reformer 302).

[0094] In the first embodiment described above, a heat return section is configured by bending the air heating duct 40. Referring to Fig. 5. The air heating duct 40 includes the air duct 401 and the air duct 403. An inlet port 401a is provided at the lower end of the air duct 401 (on one end side). The upper end of the air duct 401 is connected to the upper end of the air duct 403. An outlet port 403b is provided at the lower end of the air duct 403 (the other end side).

[0095] Air flowing out of the inlet port 401a absorbs heat from the gas discharge duct 41 and the cell stack CS as it flows from the air duct 401 to the air duct 403, and its temperature rises. Air flowing through the air ducts 401 and 403 has the highest temperature near the outlet port 403b. Since the outlet port 403b and the inlet port 401a are located close to each other, heat transfer HF occurs from the high-temperature air near the outlet port 403b to the low-temperature air near the inlet port 401a. Therefore, a heat recovery portion 50 is formed to return the heat of the air at the other end side of the air heating duct 40 to the air at the one end side.

[0096] In the first embodiment described above, a configuration is established such that the temperature rise of the air while the air flows through the air passage 401 is greater than the temperature rise of the air while the air flows through the air passage 403 by providing the heat transfer surface expanding portion 420. The configuration that enables the temperature rise of the air while the air flows through the air passage 401 to be greater than the temperature rise of the air while the air flows through the air passage 403 is not limited to this, and a method such as that in a second embodiment to be described below may also be used.

[0097] Fig. 7 is a diagram showing a fuel cell unit FCB according to the second embodiment of the present disclosure. In the fuel cell unit FCB, only the configurations of an air heating passage 40B, which includes an air passage 401B and an air passage 403B, and the gas exhaust passage 41B, which includes an exhaust passage 411B and an exhaust passage 412B, differ from those of the fuel cell unit FC.

[0098] The channel width of the air channel 401B is configured to be smaller than the channel width of the air channel 403B. Therefore, the air absorbs more heat from the gas discharge channel 41 while flowing through the air channel 401B than while flowing through the air channel 403B. Therefore, the temperature rise of the air flowing through the air channel 401B is greater than the temperature rise of the air flowing through the air channel 403B.

[0099] Furthermore, in the present embodiment, the channel width of the exhaust channel 412B is configured to be narrower than the channel width of the exhaust channel 411B. With this configuration, the heat exchange between the exhaust channel 412B and the air channel 401B is accelerated, and the temperature rise of the air flowing through the air channel 401B becomes greater than the temperature rise of the air flowing through the air channel 403B.

[0100] In particular, although the temperature of the upper portion of the cell stack CS tends to be lower than the temperatures of the middle and lower portions, the efficiently heated air from the air duct 401B flows from the top through the gap 402 into the air duct 403B and can thus efficiently provide heat to the top of the cell stack CS. In the present embodiment, heat can be efficiently provided to the top of the cell stack CS because a gap is provided between the top plate 181 and the top plate 185, and air heated while flowing through the air duct 401B also enters the gap.

[0101] In the second embodiment described above, the heat return section is formed by bending the air heating duct 40B. Referring to Fig. 7. The air heating duct 40B includes the air duct 401B and the air duct 403B. An inlet port 401Ba is provided at the lower end of the air duct 401B (on one end side). The upper end of the air duct 401B is connected to the upper end of the air duct 403B. An outlet port 403Bb is provided at the lower end of the air duct 403B (on the other end side).

[0102] Air flowing out of the inflow port 401Ba absorbs heat from the gas discharge channel 41B and the cell stack CS while flowing from the air channel 401B to the air channel 403B, and its temperature is raised. The air flowing through the air channels 401B and 403B has the highest temperature near the outflow port 403Bb. Since the outflow port 403Bb and the inflow port 401Ba are located close to each other, heat transfer HF occurs from the high-temperature air near the outflow port 403Bb to the low-temperature air near the inflow port 401Ba. Therefore, a heat return portion 50B is formed to return the heat of the air on the other end side of the air heating channel 40B to the air on the one end side.

[0103] When attention is paid to the heat transfer HF from the air having a high temperature near the other end side of the air heating channels 40 and 40B to the air having a low temperature near the one end side, the heat transfer surface extending portion 420 in the first embodiment or the design of the channel width in the second embodiment are not necessarily indispensable. Fig. 8 shows a channel configuration according to the third embodiment.

[0104] At the Fig. In the fuel cell unit FCD shown in Figure 8, an air heating channel 40D is configured by an air channel 401D and an air channel 403D. A gas discharge channel 41D is configured by an exhaust channel 411D and an exhaust channel 412D. The air channel 401D and the air channel 403D are channels with the same width. The exhaust channel 411D and the exhaust channel 412D are channels with the same width.

[0105] At the lower end of the air duct 401D (on one end side), an inflow opening 401Da is provided. The upper end of the air duct 401D is connected to the upper end of the air duct 403D. At the lower end of the air duct 403D (on the other end side), an outflow opening 403Db is provided.

[0106] The air flowing out of the inflow port 401Da absorbs heat from the gas discharge channel 41D and the cell stack CS, and its temperature is raised as it flows from the air channel 401D to the air channel 403D. The air flowing through the air channels 401D and 403D has the highest temperature near the outflow port 403Db. Since the outflow port 403Db and the inflow port 401Da are located close to each other, heat transfer HF occurs from the high-temperature air near the outflow port 403Db to the low-temperature air near the inflow port 401Da. Therefore, a heat return portion 50D is formed to return the heat of the air on the other end side of the air heating channel 40D to the air on the one end side.

[0107] When attention is paid to the heat transfer HF from the air having a high temperature near the other end side of the air heating channels 40, 40B and 40D to the air having a low temperature near the one end side, a method other than the method of bending the air heating channels 40, 40B and 40D of the first embodiment to the third embodiment can achieve the heat transfer HF. Fig. 9 shows a channel configuration according to the fourth embodiment.

[0108] At the Fig. In the fuel cell unit FCE shown in Figure 9, neither an air heating duct 40E nor a gas discharge duct 41E has a bent structure, and both are configured as straight pipes. An inflow port 40Ea is provided at the upper end (on one end side) of the air heating duct 40E. An outflow port 40Eb is provided at the lower end (on the other end side) of the air heating duct 40E. Air flowing in from the inflow port 40Ea absorbs heat from the gas discharge duct 41D and the cell stack CS, and its temperature is raised as it passes through the air heating duct 40E. The air flowing through the air heating duct 40E has the highest temperature near the outflow port 40Eb.In the fourth embodiment, a heat recovery portion 50E is provided to return the heat of the air on the other end side of the air heating duct 40E to the air on the one end side of the air heating duct 40E. Therefore, the heat transfer HF occurs from the high-temperature air near the outflow opening 40Eb to the low-temperature air near the inflow opening 40Ea.

[0109] Fig. 10 shows a specific example of the heat recovery section 50E. A Fig. The heat recovery section 50E1 shown in FIG. 10 includes a pump 50E1a and a heat recovery pipe 50E1b. The heat recovery pipe 50E1b connects the upper end side (one end side) and the lower end side (the other end side) of the air heating duct 40E. The pump 50E1a is incidentally provided in the heat recovery pipe 50E1b. By driving the pump 50E1a, the high-temperature air on the lower end side of the air heating duct 40E (on the other end side) can be supplied to the upper end side (one end side). Therefore, heat transfer HF is generated from the high-temperature air near the outflow port 40Eb to the low-temperature air near the inflow port 40Ea.

[0110] Fig. 11 shows a specific example of the heat recovery section 50E. A Fig.The heat recovery section 50E2 shown in FIG. 11 is composed of a heat pipe. A working fluid is enclosed in the heat recovery section 50E2. The heat recovery section 50E2 is provided from the upper end side (one end side) of the air heating duct 40E to the lower end side (the other end side). The temperature is raised by the hot air on the lower end side of the heat recovery section 50E2 (the other end side). When the temperature of the lower end side of the heat recovery section 50E2 (the other end side) rises, the temperature of the working fluid enclosed in the section also rises, and the working fluid undergoes convection toward the upper end side (one end side).When the heat recovery portion 50E2 is formed by a heat pipe, heat can travel from the lower end side of the air heating duct 40E (the other end side) to the upper end side (the one end side) without using a power source.

Claims

[1] Fuel cell unit (FC) for generating an electric current by means of a fuel gas and an oxidizing agent gas, the fuel cell unit comprising: a reformer (302) that reforms a raw material gas to produce the fuel gas; a heating channel (40, 40B, 40D, 40E, 40E2) that heats the oxidizing agent gas by allowing the oxidizing agent gas to flow through the heating channel; a cell stack (CS) that generates an electric current by receiving a supply of the fuel gas and the oxidizing agent gas heated by the heating channel; a discharge channel (41, 41B, 41D, 41E) that enables a combustion exhaust gas to be produced by burning the fuel gas discharged from the cell stack and flowing through the discharge channel; an inflow opening (401a, 401Ba, 401Da and 40Ea) provided on one end side of the heating channel; an outflow opening (403b, 403Bb, 403Db and 403Eb) provided on the other end side of the heating channel, wherein the oxidizing agent gas flowing from the inflow opening absorbs heat from the cell stack and the exhaust channel and flows out of the outflow opening; and a heat recovery section (50, 50B, 50D, 50E, 50E1, 50E2) that returns heat of the oxidizing agent gas on the other end side to the oxidizing agent gas on one end side where: the heat return section (50, 50B and 50D) is configured such that at least the heating channel is bent back such that one end side and the other end side are arranged close to each other; the heating channel comprises a first channel section (401, 401B, 401D) and a second channel section (403, 403B, 403D) which is connected to the first channel section and leads in a direction opposite to the direction in which the first channel section leads; the discharge channel comprises a third channel section (411, 411B, 411D) and a fourth channel section (412, 412B, 412D) connected to the third channel section and leading in a direction opposite to the direction in which the third channel section leads; the second channel portion is configured to receive radiant heat from the cell stack by being arranged to surround the cell stack; and the third channel section, the fourth channel section and the first channel section are arranged in this order outside the second channel section such that the first channel section absorbs heat from the fourth channel section and the second channel section absorbs heat from the third channel section. [2] The fuel cell unit according to claim 1, wherein the oxidizing agent gas flows from bottom to top in the first channel portion and flows from top to bottom in the second channel portion, and the combustion exhaust gas flows from bottom to top in the third channel portion and flows from top to bottom in the fourth channel portion. [3] The fuel cell unit according to claim 1, wherein the oxidizing agent gas flows from top to bottom in the first channel portion and flows from bottom to top in the second channel portion, and the combustion exhaust gas flows from top to bottom in the third channel portion and flows from bottom to top in the fourth channel portion. [4] The fuel cell unit according to any one of claims 1 to 3, wherein a temperature rise of the oxidizing agent gas while the oxidizing agent gas flows through the first channel portion is greater than a temperature rise of the oxidizing agent gas while the oxidizing agent gas flows through the second channel portion. [5] The fuel cell unit according to any one of claims 1 to 3, wherein at least one of the first channel portion and the fourth channel portion comprises a heat transfer surface extension portion (420, 420A). [6] The fuel cell unit according to any one of claims 1 to 3, wherein a channel width of the first channel portion (401B) is configured to be smaller than a channel width of the second channel portion (403B). [7] The fuel cell unit according to claim 6, wherein a channel width of the fourth channel portion (412B) is configured to be smaller than a channel width of the third channel portion (411B).

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