Off-gas combustor, fuel cell system

Abstract

To provide an off-gas combustor and a fuel cell system, capable of increasing a temperature of a reformer while suppressing a heat loss.SOLUTION: An off-gas combustor 60 makes an off-air and an off-fuel as an off gas exhausted from a fuel cell 10. An off-gas combustor 60 comprises: a fuel part 63 that mixes and fuels the off-air and the off-fuel; a temperature rising part 64 that rises a temperature of a reformer 34 by using heat generated in the fuel part 63; and an off-air flow channel 61 in which the off-air exhausted from the fuel cell 10 flows. The off-air flow channel 61 contains: a primary air flow channel 611 in which one part of the off-air flows as a primary air to the fuel part 63; and a secondary air flow channel 612 in which the other air excluding the primary air in the off-air flows as a secondary air so as to bypass the fuel part 63.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an off-gas combustor that burns off-gas of a fuel cell and a fuel cell system including the off-gas combustor.

Background Art

[0002] Conventionally, a fuel cell module is known in which an off-gas combustor that burns off-air and off-fuel discharged as off-gas from a fuel cell is disposed directly below a reformer, and the reformer is directly heated by a flame generated when the off-gas is burned (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in order to appropriately raise the temperature of the reformer, it is a prerequisite that the combustion of the off-gas is stable. However, in Patent Document 1, the stability of the combustion of the off-gas is not particularly considered, and there is room for improvement.

[0005] For example, in the case of the fuel cell module described in Patent Document 1, if the entire amount of off-air is introduced into the off-gas combustor, the air ratio (= actual air amount / theoretical air amount) in the off-gas combustor becomes too large. In this case, the amount of off-air that does not contribute to combustion increases, and the heat loss (that is, the temperature decrease) becomes excessive, so that the combustion of the off-gas in the combustor becomes unstable.

[0006] An object of the present disclosure is to provide an off-gas combustor and a fuel cell system capable of raising the temperature of a reformer while suppressing the instability of the combustion of the off-gas.

Means for Solving the Problem

[0007] The invention according to claim 1 is an off-gas combustor that burns off-air and off-fuel, which are off-gases discharged from a fuel cell (10), a combustion part (63) that mixes and burns off-air and off-fuel, a temperature-raising part (64) that raises the temperature of a reformer (34) that generates reformed gas to be used as fuel for the fuel cell by using the heat generated in the combustion part, and an off-air flow path (61) through which off-air discharged from the fuel cell flows, wherein the off-air flow path includes a primary air flow path (611) that flows at least a part of the off-air into the combustion part as primary air, the combustion part has a combustion chamber (631) that mixes and ignites off-air and off-fuel, and a combustion flow path (632) through which off-combustion gas generated in the combustion chamber flows, and the primary air flow path is arranged adjacent to at least one of the combustion chamber and the combustion flow path so that the heat of the off-combustion gas is transmitted to the primary air.

[0008] Claim 7 The invention according to is a fuel cell system including a fuel cell (10), an off-gas combustor (60) that burns off-gas discharged from the fuel cell, and a reformer (34) that generates reformed gas to be used as fuel for the fuel cell, wherein the off-gas combustor includes a combustion part (63) that mixes and burns off-air and off-fuel, which are off-gases, a temperature-raising part (64) that raises the temperature of the reformer by using the heat generated in the combustion part, and an off-air flow path (61) through which off-air discharged from the fuel cell flows, the off-air flow path includes a primary air flow path (611) that flows at least a part of the off-air into the combustion part as primary air, the combustion part has a combustion chamber (631) that mixes and ignites off-air and off-fuel, and a combustion flow path (632) through which off-combustion gas generated in the combustion chamber flows, The primary air flow path is arranged adjacent to at least one of the combustion chamber and the combustion flow path so that the heat of the off-combustion gas is transferred to the primary air.

[0009] According to the invention described in claim 1 and claim 7 The off-air heated by the off-combustion gas is introduced into the off-gas combustor. According to this, since the introduction of the low-temperature off-gas into the off-gas combustor is suppressed, it is possible to suppress the combustion of the off-gas from becoming unstable and appropriately heat up the reformer.

[0013] Note that the reference numerals in parentheses attached to each component etc. indicate an example of the correspondence relationship between the component etc. and the specific components etc. described in the embodiments described later.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0015] An embodiment of the present disclosure will be described with reference to FIGS. 1 to 11. In this embodiment, as shown in FIG. 1, an example in which the off-gas combustor 60 of the present disclosure is applied to a fuel cell system 1 including a solid oxide fuel cell 10 will be described.

[0016] The fuel cell system 1 includes a hot module HM that is maintained at a high temperature by covering a fuel processing system and a battery system with a heat insulating element. The hot module HM includes a heat insulating container IC, a solid oxide fuel cell 10, an air preheater 22, a stack thermostat 23, a reformer 34, a vaporizer 42, and an off-gas combustor 60.

[0017] The solid oxide fuel cell 10 is generally also called an SOFC (abbreviation for Solid Oxide Fuel Cell), and has an operating temperature of a high temperature (for example, 500°C to 1000°C). The fuel cell 10 includes a plurality of cells C that output electrical energy by an electrochemical reaction of a fuel gas and an oxidant gas (air in this example). The cell C outputs electrical energy to an external circuit EC by an electrochemical reaction of hydrogen and oxygen shown in the following reaction formulas F1 and F2.

[0018] (Fuel electrode) 2H2 + 2O 2- → 2H2O + 4e - …(F1)

[0019] (Air electrode) O2 + 4e - → 2O 2- …(F2) Also, the cell C outputs electrical energy to the external circuit EC by an electrochemical reaction of carbon monoxide and oxygen shown in the following reaction formulas F3 and F4.

[0020] (Fuel electrode) 2CO + 2O 2- → 2CO2 + 4e -…(F3)

[0021] (Air electrode) O2 + 4e - →2O 2- …(F4) The electric power output by the fuel cell 10 is supplied to load equipment and a battery via a power converter such as an inverter INV. The fuel cell 10 of the present embodiment includes a plurality of cell stacks CS each formed by stacking a predetermined number of cells C. The cell stack CS has flat cells C stacked in a predetermined stacking direction. The predetermined number of cells C constituting the cell stack CS are electrically connected in series. The cell stack CS is a stacked body in which a predetermined number of cells C are stacked in a row. In the cell stack CS, a fuel gas inlet, an air inlet, an off-fuel outlet, and an off-air outlet are formed at the ends in the stacking direction of the cells C.

[0022] The fuel cell 10 configured as described above is disposed inside the heat-insulating container IC together with an air preheater 22, a stack temperature controller 23, a reformer 34, a water evaporator 42, an off-gas combustor 60, and the like. The arrangement mode of the fuel cell 10 inside the heat-insulating container IC will be described later.

[0023] An air path 20, which is an air flow path, is connected to the fuel cell 10. The air path 20 is constituted by piping or the like. The air path 20 is provided with a pressure blower 21 that pumps air to the fuel cell 10, an air preheater 22 that heats the air supplied to the fuel cell 10, and a stack temperature controller 23.

[0024] The pressure blower 21 is an oxidant pump that sucks air in the atmosphere and supplies it to the fuel cell 10. The pressure blower 21 is constituted by an electric blower whose operation is controlled by a control signal from a control device 100 described later.

[0025] The air preheater 22 is a heat exchanger that heats the air pumped from the pressure blower 21 by exchanging heat with the off-gas combustion gas generated by the off-gas combustor 60 during the power generation of the fuel cell 10. The air preheater 22 is provided to reduce the temperature difference between the air supplied to the fuel cell 10 and the fuel gas, thereby improving the power generation efficiency of the fuel cell 10.

[0026] The stack thermostat 23 is connected between the air preheater 22 and the fuel cell 10 so that the air passing through the air preheater 22 flows. As a result, the air before being supplied to the cell stack CS flows through the stack thermostat 23.

[0027] The stack thermostat 23 is arranged to face the cell stack CS of the fuel cell 10 with a predetermined interval so as to be heat-exchangeable with the cell stack CS of the fuel cell 10. When the fuel cell 10 is started up, the heat of the stack thermostat 23 is transmitted to the cell stack CS side. Also, when the fuel cell 10 is generating power, the heat of the cell stack CS is transmitted to the stack thermostat 23 side.

[0028] The stack thermostat 23 is provided adjacent to the warm-up gas flow path 51 through which the combustion gas generated by the warm-up burner 50 flows so that the air flowing through the stack thermostat 23 can exchange heat with the combustion gas generated by the warm-up burner 50 described later when the fuel cell 10 is started up. At least a part of the stack thermostat 23 is arranged between the warm-up gas flow path 51 and the cell stack CS of the fuel cell 10. The stack thermostat 23 is heated by receiving heat from the combustion gas flowing through the warm-up gas flow path 51 when the fuel cell 10 is started up. Also, when the fuel cell 10 is started up, the heat of the stack thermostat 23 is radiated to the cell stack CS. Note that the stack thermostat 23 absorbs heat from the cell stack CS whose temperature has risen due to self-heating accompanying power generation to adjust the temperature of the cell stack CS when the fuel cell 10 is generating power.

[0029] The above warm-up burner 50 generates combustion gas for warming up the cell stack CS when the fuel cell 10 is started up. The warm-up burner 50 burns a mixed gas of air blown from a start-up blower 52 provided separately from the pressure blower 21 and fuel supplied from a start-up pump 53 provided separately from the fuel pump 31 as combustible gas. The high-temperature combustion gas generated by the combustion of the combustible gas flows into the warm-up gas flow path 51.

[0030] Further, a fuel path 30, which is a flow path for a reforming raw material and fuel gas, is connected to the fuel cell 10. The fuel path 30 is constituted by piping or the like. In the fuel path 30, a fuel pump 31, a desulfurizer 32, an ejector 33, and a reformer 34 are provided in order from the upstream side.

[0031] The fuel pump 31 is a pump for supplying a reforming raw material toward the fuel cell 10 side. The fuel pump 31 is constituted by an electric pump whose operation is controlled by a control signal from a control device 100 described later.

[0032] The desulfurizer 32 is a device for removing sulfur components contained in the reforming raw material supplied from the fuel pump 31. Note that city gas contains an odorant (specifically, a sulfur component). Since the sulfur component is a catalyst poison, it is necessary to remove it upstream of the reformer 34.

[0033] The ejector 33 is disposed between the desulfurizer 32 and the reformer 34 in the fuel path 30. The ejector 33 has a nozzle portion 331, a suction portion 332, and a discharge portion 333. The nozzle portion 331 injects the reforming raw material supplied from the fuel pump 31 as a driving flow. The suction portion 332 sucks a gas flowing through a flow path connected to the suction portion 332 as a suction flow by the driving flow injected from the nozzle portion 331. The discharge portion 333 discharges a mixed flow of the driving flow and the suction flow. The nozzle portion 331 is connected downstream of the desulfurizer 32 in the fuel path 30. The discharge portion 333 is connected upstream of the reformer 34 in the fuel path 30. The suction portion 332 is connected to a branch flow path 66 branched from an off-fuel flow path 62 through which off-fuel flows.

[0034] The reformer 34 is connected downstream of the discharge part 333 of the ejector 33. The reformer 34 reforms the reforming raw material discharged from the ejector 33 using steam to generate reformed gas that becomes fuel gas. The reformer 34 is configured to include, for example, a steam reforming catalyst containing a noble metal such as rhodium or ruthenium.

[0035] Specifically, the reformer 34 heats the mixed gas of the reforming raw material and steam by heat-exchanging it with the combustion gas, and generates fuel gas (hydrogen, carbon monoxide) by the reforming reaction shown in the following reaction formula F5 and the shift reaction shown in reaction formula F6.

[0036] CH4 + H2O → CO + 3H2…(F5) CO + H2O → CO2 + H2…(F6) Here, the steam reforming in the reformer 34 is an endothermic reaction and has the characteristic that the reforming rate improves under high-temperature conditions. For this reason, the reformer 34 is disposed near the off-gas combustor 60 so that it can absorb the heat generated by the off-gas combustor 60 during the power generation of the fuel cell 10.

[0037] A water supply path 40 is connected between the fuel pump 31 and the ejector 33 in the fuel path 30. The water supply path 40 is provided with a water pump 41 and a water evaporator 42. The water pump 41 is a pump that supplies water to the water evaporator 42. The water pump 41 is composed of an electric pump whose operation is controlled by a control signal from a control device 100 described later. The water evaporator 42 has an evaporation function of turning the water from the water pump 41 into steam (that is, gas).

[0038] In addition, an off-gas combustor 60 is connected to the fuel cell 10. The off-gas combustor 60 burns off-air and off-fuel, which are off-gases discharged from the fuel cell 10 during power generation of the fuel cell 10.

[0039] The off-gas combustor 60 includes an off-air flow path 61, an off-fuel flow path 62, a combustion section 63, and a temperature-raising section 64 that uses the heat generated in the combustion section 63 to raise the temperature of the reformer 34.

[0040] The off-air flow path 61 is an off-gas flow path through which the off-air discharged from the fuel cell 10 flows. The off-air flow path 61 includes a flow path for communicating the off-air outlet of the fuel cell 10 with the combustion section 63. Details of the off-air flow path 61 will be described later.

[0041] The off-fuel flow path 62 is an off-gas flow path through which the off-fuel discharged from the fuel cell 10 flows. The off-fuel flow path 62 includes a flow path for communicating the off-fuel outlet of the fuel cell 10 with the combustion section 63.

[0042] A branch flow path 66 is connected to the off-fuel flow path 62. The branch flow path 66 is connected to the suction section 332 of the ejector 33. A part of the off-fuel flowing through the off-fuel flow path 62 is returned upstream of the fuel cell 10 via the branch flow path 66 and the ejector 33. According to this, the unreacted fuel gas contained in the off-fuel can be consumed by the fuel cell 10, and the efficiency of the fuel cell 10 can be improved.

[0043] The combustion section 63 burns the off-air and off-fuel to generate off-combustion gas. The combustion section 63 is not provided with a spark plug and is composed of a progress gas burner that burns the off-air and off-fuel by self-ignition. Details of the combustion section 63 will be described later.

[0044] The temperature-raising section 64 is a gas flow path through which the off-combustion gas generated in the combustion section 63 flows. The temperature-raising section 64 uses the off-combustion gas generated in the combustion section 63, rather than the flame generated in the combustion section 63, to raise the temperature of the reformer 34. Specifically, the temperature-raising section 64 is configured as a heat exchange section that heats the reformer 34 by heat-exchanging the off-combustion gas after passing through the internal flow path of the combustion section 63 with the reformer 34.

[0045] The off-gas combustor 60 is connected to an exhaust path 70 through which high-temperature off-combustion gas flows. The exhaust path 70 is thermally connected to an air preheater 22 or the like in order to effectively utilize the heat of the off-combustion gas.

[0046] Here, when the off-gas combustor 60 is configured as a self-igniting combustor, there is a concern that unreacted fuel containing hydrogen may flow out to the outside through the exhaust path 70 during the period until the mixed gas of off-fuel and off-air self-ignites.

[0047] In consideration of this, a combustion catalyst 71 for burning unreacted fuel contained in the off-combustion gas is disposed in the exhaust path 70 of the present embodiment. The combustion catalyst 71 includes, for example, an oxidation catalyst that oxidizes unreacted fuel.

[0048] Subsequently, the arrangement modes of various devices including the fuel cell 10 inside the heat-insulating container IC will be described with reference to FIGS. 2 to 10. The arrows indicating up and down in FIG. 2 and the like indicate the vertical direction DRg when the hot module HM is installed. Note that the installation mode of the hot module HM is not limited to that shown in FIG. 2 and the like, and may be different from that shown in FIG. 2 and the like.

[0049] As shown in FIG. 2, inside the heat-insulating container IC, a fuel cell 10, an air preheater 22, a stack thermostat 23, a reformer 34, a warm-up burner 50, an off-gas combustor 60, a combustion catalyst 71, etc. are arranged.

[0050] The heat-insulating container IC constitutes the outer shell of the hot module HM. The heat-insulating container IC has an outer shape that is substantially cylindrical.

[0051] The heat-insulating container IC has a triple cylindrical structure, and a cylindrical space and a donut-shaped space are formed inside thereof. Specifically, the heat-insulating container IC has a substantially circular upper wall Wu, a substantially circular lower wall Wd, a cylindrical inner cylinder wall Wi, a cylindrical intermediate cylinder wall Wm, and a cylindrical outer cylinder wall Wo. The upper wall Wu constitutes the top plate of the heat-insulating container IC. The lower wall Wd constitutes the bottom plate of the heat-insulating container IC. The inner cylinder wall Wi, the intermediate cylinder wall Wm, and the outer cylinder wall Wo constitute the side wall of the heat-insulating container IC. The inner cylinder wall Wi, the intermediate cylinder wall Wm, and the outer cylinder wall Wo increase in cylinder diameter (i.e., outer diameter) in this order. The inner cylinder wall Wi, the intermediate cylinder wall Wm, and the outer cylinder wall Wo are arranged such that their axial centers CL coincide. Note that the inner cylinder wall Wi has a cylinder diameter capable of accommodating the warm-up burner 50. The intermediate cylinder wall Wm has a cylinder diameter slightly larger than that of the inner cylinder wall Wi so that a gap for allowing air to flow between the inner cylinder wall Wi and the intermediate cylinder wall Wm can be formed. The outer cylinder wall Wo has a cylinder diameter capable of accommodating the cell stack CS between the intermediate cylinder wall Wm and the outer cylinder wall Wo.

[0052] Inside the inner cylinder wall Wi, the warm-up burner 50 is arranged. And the inner space of the inner cylinder wall Wi is configured as the warm-up gas flow path 51. Note that the warm-up burner 50 is fixed to the substantially central portion of the upper wall Wu.

[0053] The gap space formed between the inner cylinder wall Wi and the intermediate cylinder wall Wm serves as an air flow path into which air from the pressure blower 21 flows. A pipe constituting the air path 20 is connected to the upper wall Wu at a position corresponding to the gap space formed between the inner cylinder wall Wi and the intermediate cylinder wall Wm. Note that between the inner cylinder wall Wi and the intermediate cylinder wall Wm, a spacing defining portion such as a spacer or a dowel is provided, and a substantially constant gap is formed by the spacing defining portion.

[0054] The gap space formed between the inner cylinder wall Wi and the intermediate cylinder wall Wm has an upper portion on the upstream side of the air flow constituting the air preheater 22, and a lower portion on the downstream side of the air flow constituting the stack thermostat 23. Note that on the inner cylinder wall Wi and the intermediate cylinder wall Wm, a communication path PG is formed for guiding the combustion gas generated by the warm-up burner 50 to the battery accommodation space BS formed between the intermediate cylinder wall Wm and the outer cylinder wall Wo.

[0055] The space formed between the intermediate cylinder wall Wm and the outer cylinder wall Wo constitutes a battery accommodation space BS that houses the cell stack CS in its lower part, and a device accommodation space DS that houses the reformer 34, the off-gas combustor 60, etc. in its upper part. In addition, in order to suppress the heat of the off-gas combustor 60 from directly being transmitted to the cell stack CS, a partition plate SP and a heat insulating material HI are arranged between the battery accommodation space BS and DS.

[0056] Pipes constituting the air path 20, pipes constituting the fuel path 30, and pipes constituting the off-fuel flow path 62 are respectively connected to the plurality of cell stacks CS. In addition, the plurality of cell stacks CS are configured to discharge off-air into the battery accommodation space BS. For this reason, the battery accommodation space BS constitutes a part of the off-air flow path 61.

[0057] As shown in FIG. 3, in the battery accommodation space BS, a plurality of cell stacks CS are arranged radially around the axis CL of the heat insulating container IC. The plurality of cell stacks CS are arranged at equal intervals in the circumferential direction of the axis CL in the battery accommodation space BS. Note that the intervals between the plurality of cell stacks CS do not have to be the same, and some of them may be different.

[0058] As shown in FIG. 4, in the device accommodation space DS, a reformer 34, an off-gas combustor 60, a combustion catalyst 71, etc. are arranged. In the device accommodation space DS, the reformer 34 is arranged closer to the axis CL of the heat insulating container IC, and the off-gas combustor 60 is arranged at a position farther from the axis CL than the reformer 34.

[0059] Off-air and off-fuel are supplied to the combustion part 63 of the off-gas combustor 60 via the off-air flow path 61 and the off-fuel flow path 62. The off-fuel flow path 62 is constituted by a pipe that penetrates the partition plate SP and the heat insulating material HI.

[0060] Here, in the configuration where the total amount of off-air is introduced into the off-gas combustor 60, the air ratio (= actual air amount / theoretical air amount) in the off-gas combustor 60 becomes too large, resulting in an increase in off-air that does not contribute to combustion and an excessive heat loss (i.e., temperature drop).

[0061] Taking this into account, the off-air flow path 61 includes a primary air flow path 611 that flows a part of the off-air as primary air to the combustion section 63, and a secondary air flow path 612 that bypasses the combustion section 63 with the other air excluding the primary air in the off-air as secondary air. The primary air flow path 611 and the secondary air flow path 612 include through-holes that penetrate the partition plate SP and the heat insulating material HI. The cross-sectional areas of the primary air flow path 611 and the secondary air flow path 612 are set so that the air ratio in the off-gas combustor 60 becomes the target value (a value where the actual air amount is slightly more than the theoretical air amount). Note that the through-hole that constitutes a part of the primary air flow path 611 constitutes the introduction section 611a of the primary air flow path 611.

[0062] As shown in FIG. 5, a plurality of combustion sections 63 are provided in the off-gas combustor 60. The off-gas combustor 60 of the present embodiment is provided with the same number of combustion sections 63 as the cell stack CS. The plurality of combustion sections 63 are radially arranged around the axis CL of the heat insulating container IC in the same manner as the cell stack CS.

[0063] As shown in FIG. 6, the plurality of combustion sections 63 have a combustion chamber 631 that mixes off-air and off-fuel and ignites them, and a combustion flow path 632 through which the off-combustion gas generated in the combustion chamber 631 flows.

[0064] The plurality of combustion chambers 631 are arranged at equal intervals in the circumferential direction of the axis CL in the equipment accommodation space DS. Note that the intervals between the plurality of combustion chambers 631 do not have to be the same, and some of them may be different.

[0065] Specifically, as shown in FIG. 7, in the combustion chamber 631, a lead-out pipe 621 that constitutes a lead-out portion of the off-fuel in the off-fuel flow path 62 is disposed. In the lead-out pipe 621, two gas injection ports 621a and 621b are formed in the side wall. Note that the number of the gas injection ports 621a and 621b is not limited to two and can be arbitrarily set.

[0066] Around the lead-out pipe 621, a guide 633 for defining the ejection direction of the off-fuel is provided. This guide 633 is composed of a C-shaped pipe having a slit hole formed longitudinally. The off-fuel flowing through the off-fuel flow path 62 is ejected from the gas injection ports 621a and 621b of the lead-out pipe 621 and then flows in one direction in the circumferential direction of the axis CL by the guide 633.

[0067] Further, in the combustion chamber 631, a lead-out portion 611b of the primary air flow path 611 is open. Thereby, in the combustion chamber 631, the off-air and the off-fuel are mixed. Then, when the temperature of the combustion chamber 631 reaches an auto-ignition region where the mixed gas of the off-air and the off-fuel auto-ignites, the mixed gas is burned in the combustion chamber 631.

[0068] The off-combustion gas generated in the combustion chamber 631 flows through a combustion flow path 632 continuous with the combustion chamber 631. In the combustion flow path 632, communication holes 632a communicating with a temperature raising portion 64 are formed in the vicinity of the combustion chambers 631 adjacent to each other in the circumferential direction. The off-combustion gas flowing through the combustion flow path 632 flows into the temperature raising portion 64 through the communication holes 632a.

[0069] Here, the region where the off-fuel auto-ignites in the combustion chamber 631 is the auto-ignition region indicated by the dotted pattern in FIG. 8. The off-fuel auto-ignites when the temperature of the off-air (primary air in this example) is high even if the hydrogen concentration in the off-fuel is low, but does not auto-ignite when the temperature of the off-air is low and the hydrogen concentration in the off-fuel is low. Therefore, in order to expand the auto-ignition region in the combustion section 63, it is desirable to supply off-air at a higher temperature to the combustion section 63. Note that there is a certain variation in the auto-ignition region among the plurality of combustion chambers 631.

[0070] Taking these factors into consideration, the off-gas combustor 60 is configured to be able to preheat the off-air before flowing it into the combustion chamber 631 by utilizing the heat generated in the combustion section 63. As shown in FIG. 9, the primary air flow path 611 of the off-gas combustor 60 is arranged adjacent to the combustion flow path 632 of the combustion section 63 so that the heat of the off-combustion gas is transferred to the primary air. Note that the primary air flow path 611 may be arranged adjacent to the combustion chamber 631 so that the heat of the combustion chamber 631 is transferred to the primary air.

[0071] Specifically, as shown in FIG. 10, the primary air flow path 611 is set below the combustion flow path 632 of the combustion section 63. The primary air flow path 611 and the combustion flow path 632 are partitioned by a preheating plate 65 that transfers the heat of the off-combustion gas to the primary air. This preheating plate 65 has a convex portion protruding upward formed at the bottom of a base material having a U-shaped cross section. The preheating plate 65 of the present embodiment is composed of a formed material 651 obtained by forming a single long metal plate into a substantially M-shaped cross section in the short direction by press forming such as sheet metal bending. The preheating plate 65 is fixed to surrounding members such as a partition plate SP by spot welding SW. According to this, compared with the case where the primary air flow path 611 and the combustion flow path 632 are provided separately, a structure capable of efficiently heat-exchanging the primary air flowing through the primary air flow path 611 and the off-combustion gas flowing through the combustion flow path 632 can be easily realized.

[0072] Here, the same number of combustion sections 63 as the cell stack CS are provided. For this reason, it is conceivable that the off-gas combustor 60 is configured to supply off-fuel and primary air from the closest one among the plurality of cell stacks CS to the combustion section 63. For example, assuming that among the plurality of combustion sections 63, the one closest to the introduction section 611a of a predetermined primary air flow path 611 is the adjacent combustion section. At this time, it is conceivable to derive primary air from a derivation section 611b corresponding to the introduction section 611a of the predetermined primary air flow path 611 to the adjacent combustion section.

[0073] However, in the case of such a configuration, since the cell stack CS and the proximity combustion section approach each other, it becomes difficult to secure a section for heat-exchanging the off-gas and the primary air. Further, for example, if the primary air flow path 611 is extended by a U-turn or the like to secure a section for heat-exchanging the off-gas and the primary air, the flow path structure of the primary air flow path 611 becomes complicated.

[0074] Therefore, in the primary air flow path 611 of the present embodiment, the position of the outlet section 611b is set so that the primary air introduced from the introduction section 611a is led out to another combustion section other than the proximity combustion section.

[0075] As shown in FIG. 9, at least a part of the primary air flow path 611 is arranged adjacent to the combustion flow path 632 in the proximity combustion section so that the primary air flowing through the primary air flow path 611 exchanges heat with the off-gas flowing through the combustion flow path 632 in the proximity combustion section. Specifically, the primary air flow path 611 is arranged adjacent to the combustion flow path 632 in the proximity combustion section so that the primary air heated by the combustion flow path 632 in the proximity combustion section is led out to one of the combustion sections 63 adjacent to the proximity combustion section.

[0076] Here, the primary air flow path 611 and the combustion flow path 632 are provided so as to extend in the same direction so that the primary air and the off-gas become parallel flows. According to this, the directions of the gas flows in the primary air flow path 611, the combustion chamber 631, and the combustion flow path 632 are likely to be aligned, so that the pressure loss due to the backflow of the off-fuel gas or the like in the combustion section 63 can be suppressed.

[0077] The off-gas that has passed through the combustion flow path 632 flows into the temperature raising section 64 through the communication hole 632a. The temperature raising section 64 is configured as a heat exchange section that heat-exchanges the off-gas after passing through the combustion flow path 632 with the reformer 34 to raise the temperature of the reformer 34. Specifically, this temperature raising section 64 is constituted by a gap flow path 641 provided between the partition plate SP or the heat insulating material HI and the reformer 34. When the off-gas flows through the gap flow path 641, the heat of the off-gas is transmitted to the reformer 34, thereby raising the temperature of the reformer 34.

[0078] The secondary air flow path 612 of the off-air flow path 61 is connected to the temperature-raising section 64. In other words, the secondary air flow path 612 is connected to the temperature-raising section 64 so that the heat of the secondary air is transmitted to the reformer 34. Specifically, as shown in FIGS. 6 and 11, the downstream end of the secondary air flow path 612 is open at a portion that constitutes the temperature-raising section 64 and faces the reformer 34 among the partition plate SP and the heat insulating material HI.

[0079] The downstream end opening of the secondary air flow path 612 is set, for example, at a portion where it is assumed that the temperature difference between the off-combustion gas and the secondary air in the temperature-raising section 64 is within a predetermined temperature (for example, 10 to 20 °C). According to this, temperature fluctuations associated with the mixing of the secondary air and the off-combustion gas can be suppressed, and the occurrence of temperature unevenness in the reformer 34 can be suppressed.

[0080] The off-combustion gas that has passed through the temperature-raising section 64 is exhausted to the outside of the heat-insulating container IC via the exhaust path 70. The exhaust path 70 includes a first path 701 formed between the intermediate cylinder wall Wm and the heat insulating material HI, and a second path 702 formed between the upper wall Wu and the heat insulating material HI.

[0081] The first path 701 is provided adjacent to the air flow path formed between the inner cylinder wall Wi and the intermediate cylinder wall Wm, and heat-exchanges the off-combustion gas with the air flowing between the inner cylinder wall Wi and the intermediate cylinder wall Wm to raise the temperature of the air. The first path 701 constitutes a part of the air preheater 22.

[0082] A combustion catalyst 71 is disposed in the second path 702. The catalytic reaction in the combustion catalyst 71 is an endothermic reaction. For this reason, the combustion catalyst 71 is disposed in the second path 702 through which the off-combustion gas flows so as to be able to absorb heat from the off-combustion gas. Note that the combustion catalyst 71 promotes catalyst deterioration when the temperature becomes excessively high. For this reason, a heat insulating material HI is disposed between the combustion catalyst 71 and the combustion section 63 so that the heat of the high-temperature combustion section 63 does not directly act.

[0083] Next, the control device 100 that constitutes the electronic control unit of the fuel cell system 1 will be described with reference to FIG. 1. The control device 100 is composed of a microcomputer including a processor and a memory, and its peripheral circuits. The control device 100 performs various calculations and processes based on the control program stored in the memory and controls the operations of various control devices connected to the output side.

[0084] A group of sensors including a battery temperature sensor 100a, a reforming temperature sensor 100b, and a misfire sensor 100c is connected to the input side of the control device 100, and the detection results of the sensor group are input to the control device 100. The misfire sensor 100c is composed of a temperature sensor and a flame detector.

[0085] In addition, an inverter INV and an operation panel (not shown) are connected to the control device 100. The operation panel is provided with a start switch for turning on and off the power generation of the fuel cell 10, a display for displaying the operating state of the fuel cell 10, and the like.

[0086] On the other hand, on the output side of the control device 100, as control devices, a pressure feed blower 21, a fuel pump 31, a water pump 41, a starting blower 52, a starting pump 53, etc. are connected. The operations of these control devices are controlled according to the control signals output from the control device 100.

[0087] Next, the overall operation of the fuel cell system 1 will be described. When the start switch of the fuel cell 10 is turned on, the control device 100 executes a startup process of the cell C including an initial warm-up process, a CS reduction process, and a warm-up promotion process.

[0088] The initial warm-up process is a process of raising the temperature of various devices including the cell stack CS to an appropriate temperature. During the initial warm-up process, the control device 100 operates the starting blower 52 and the starting pump 53 to supply fuel and air to the warm-up gas flow path 51. In this state, the warm-up burner 50 is ignited to generate high-temperature combustion gas.

[0089] The stack temperature controller 23 is provided adjacent to the warm-up gas flow path 51. Therefore, the air flowing through the stack temperature controller 23 is heated by the combustion gas flowing through the warm-up gas flow path 51. The air heated by the stack temperature controller 23 is supplied to the cell stack CS. Thereby, the cell stack CS is heated.

[0090] After the start of the initial warm-up process, when a predetermined reformable condition is satisfied, the control device 100 executes a CS reduction process for suppressing the oxidation of the cell stack CS as the temperature of the cell stack CS rises. The reformable condition is, for example, a condition that is satisfied when the evaporator 42 reaches a temperature (e.g., 100°C) at which it can generate water vapor and the reformer 34 reaches a temperature (e.g., 300°C) at which it can generate fuel gas.

[0091] During the CS reduction process, the control device 100 controls the water pump 41 so that water is supplied to the evaporator 42 and controls the fuel pump 31 so that fuel is supplied to the reformer 34. Thereby, fuel and water vapor are supplied to the reformer 34. In the reformer 34, when a mixed gas of fuel and water vapor is supplied, fuel gas (hydrogen, carbon monoxide) is generated by the reactions shown in the above reaction formulas F5 and F6. The fuel gas generated by the reformer 34 is supplied to the cell stack CS. Thereby, the oxidation of the cell stack CS is suppressed. Specifically, by supplying fuel gas to the fuel electrode of the cell C, the oxidative degradation of the fuel electrode is suppressed.

[0092] After starting the CS reduction process, when a predetermined warm-up promotion condition is satisfied, the control device 100 executes a warm-up promotion process for promoting the warm-up of various devices including the cell stack CS. The warm-up promotion condition is, for example, a condition that is satisfied when the temperature of the cell stack CS reaches a temperature (e.g., 450°C) at which the internal resistance of the cell stack CS decreases.

[0093] After starting the warm-up promotion process, when predetermined power generation conditions are satisfied, the control device 100 executes a power generation process that causes the fuel cell 10 to perform a power generation operation. The power generation conditions are, for example, conditions that are satisfied when the cell C reaches a temperature suitable for power generation of the fuel cell 10 (e.g., 500°C or higher).

[0094] During the power generation process, the control device 100 controls the pressure blower 21, the fuel pump 31, and the water pump 41 so that an appropriate amount of air and fuel gas for power generation are supplied to the fuel cell 10. Further, the control device 100 turns off the warm-up burner 50, the start-up blower 52, and the start-up pump 53.

[0095] As a result, the fuel gas generated in the reformer 34 is supplied to each cell stack CS. Also, the air blown out from the pressure blower 21 flows into the air preheater 22 and is heated, and then flows into the stack thermostat 23. The air that has flowed into the stack thermostat 23 absorbs heat from the fuel cell 10 and is heated to near the temperature of the fuel cell 10, and then is supplied to each cell stack CS.

[0096] When an oxidant gas and a fuel gas are supplied to each cell stack CS, the cell C outputs electrical energy by the reactions shown in the above reaction formulas F1 to F4. Then, the off-gas discharged from the cell stack CS is burned in the off-gas combustor 60.

[0097] Specifically, in the off-gas combustor 60, as shown by the arrow F in FIG. 11, the off-fuel is supplied to the combustion section 63 through the off-fuel flow path 62. Since the off-fuel is discharged from the cell stack CS, it has a temperature similar to that of the cell stack CS (e.g., about 630°C).

[0098] The off-air is such that the primary air is supplied to the combustion section 63 through the primary air flow path 611 as shown by the arrow A1 in FIG. 11, and the secondary air is supplied to the heating section 64 through the secondary air flow path 612 as shown by the arrow A2 in FIG. 11. The primary air and the secondary air flowing into the off-air flow path 61 have a temperature similar to that of the cell stack CS (e.g., about 630°C).

[0099] Since the primary air flow path 611 is adjacent to the combustion flow path 632 of the combustion section 63, the primary air is preheated by the off-gas flowing through the combustion flow path 632. As a result, in the primary air flow path 611, the temperature of the primary air on the outlet section 611b side (for example, about 700°C) is higher than the temperature of the primary air on the inlet section 611a side (for example, about 630°C). Thus, for example, as shown in FIG. 8, when the temperature of the off-air supplied to the combustion section 63 increases, it becomes a situation where self-ignition of the off-fuel easily occurs in the combustion section 63.

[0100] In the combustion chamber 631 of the combustion section 63, the mixed gas of the off-fuel and the primary air burns, and high-temperature (for example, about 900°C) off-gas is generated. This off-gas flows to the temperature-raising section 64 after passing through the combustion flow path 632 of the combustion section 63 as shown by the arrow H1 in FIG. 11. The reformer 34 is heated by the off-gas flowing through the temperature-raising section 64 and is raised to a predetermined temperature (for example, about 620°C). On the other hand, the off-gas is reduced to a predetermined temperature by radiating heat to the reformer 34.

[0101] The off-gas after passing through the temperature-raising section 64 flows into the exhaust path 70 as shown by the arrow H2 in FIG. 11. The off-gas flowing through the exhaust path 70 radiates heat to the air supplied to the cell stack CS, the combustion catalyst 71, etc., and is then exhausted to the outside of the heat-insulating container IC.

[0102] The off-gas combustor 60 and the fuel cell system 1 described above include a primary air flow path 611 through which a part of the off-air flows as primary air to the combustion section 63, and a secondary air flow path 612 through which the remainder of the off-air flows around the combustion section 63 as secondary air. According to these, since a configuration is adopted in which not the entire amount of the off-air but a part thereof is introduced into the off-gas combustor 60, it is possible to suppress the air ratio (= actual air amount / theoretical air amount) in the off-gas combustor 60 from becoming too large. As a result, heat loss (that is, temperature drop) due to excessive air in the off-gas combustor 60 is suppressed, and combustion in the off-gas combustor 60 is stabilized, so that the reformer 34 can be appropriately heated.

[0103] Also, the off-gas combustor 60 of the present embodiment can achieve the following effects.

[0104] (1) The combustion part 63 has a combustion chamber 631 that mixes and ignites off-air and off-fuel, and a combustion flow path 632 through which the off-combustion gas generated in the combustion chamber 631 flows. And the primary air flow path 611 is arranged adjacent to at least one of the combustion chamber 631 and the combustion flow path 632 so that the heat of the off-combustion gas is transmitted to the primary air. In this way, if the configuration is such that the primary air is heated by the heat of the off-combustion gas, the self-ignition region where the off-fuel can be combusted expands, so that even if the off-fuel in the combustion chamber 631 is lean, it can be combusted. Also, since the heat received by the primary air only circulates in the combustion part 63, the combustibility of the off-gas in the combustion chamber 631 can be improved without causing heat loss. Furthermore, even if the gas consumption of the cell stack CS is increased, it can be combusted by the off-gas combustor 60, so that the power generation efficiency of the fuel cell 10 can be improved.

[0105] (2) A plurality of combustion parts 63 are provided. The primary air flow path 611 includes a primary air introduction part 611a and a primary air outlet part 611b. Assume that the one closest to the primary air introduction part 611a among the primary air introduction parts 611a in the plurality of combustion parts 63 is the adjacent combustion part. At this time, the position of the primary air outlet part 611b is set so that the primary air introduced from the primary air introduction part 611a is led out to other combustion parts other than the adjacent combustion part. According to this, a part of the section from the adjacent combustion part side in the primary air flow path 611 to other combustion parts can be used as a section for heat exchange between the off-combustion gas flowing through the combustion flow path 632 of the adjacent combustion part and the primary air flowing through the primary air flow path 611. Therefore, the simplification of the flow path structure of the primary air flow path 611 can be achieved.

[0106] (3) The primary air flow path 611 is arranged such that at least a part of the primary air flowing through the primary air flow path 611 is adjacent to the combustion flow path 632 in the proximity combustion part so that the primary air flowing through the primary air flow path 611 exchanges heat with the off-gas flowing through the combustion flow path 632 in the proximity combustion part. According to this, the primary air flowing through the primary air flow path 611 can be heat-exchanged with the off-gas flowing through the combustion flow path 632 in the proximity combustion part to increase its temperature. Also, for example, when another combustion part misfires, the primary air heated by the heat of the proximity combustion part is supplied to the other combustion part, making it possible to promote re-ignition in the other combustion part. Further, for example, when the proximity combustion part permanently misfires, the primary air is supplied to the other combustion part without being heated, making the other combustion part more likely to misfire. Therefore, if a misfire sensor 100c is installed at one location, it is possible to determine the misfire of all the combustion parts 63.

[0107] (4) In Patent Document 1 cited in the background art, the reformer 34 is directly heated by the flame when the off-gas is burned. In such a configuration, temperature unevenness occurs due to the temperature difference between the part of the reformer 34 exposed to the flame and the part not exposed to the flame. In particular, the part of the reformer 34 exposed to the flame becomes locally high temperature, making the reforming catalyst liable to deteriorate.

[0108] On the other hand, in the off-gas combustor 60 of the present disclosure, since the off-gas and the reformer 34 are heat-exchanged in the temperature raising part 64 to raise the temperature of the reformer 34, temperature unevenness of the reformer 34 can be suppressed as compared with the configuration in which the reformer 34 is directly heated by the flame. As a result, local catalyst deterioration in the reformer 34 can be suppressed.

[0109] (5) The off-air flow path 61 of the off-gas combustor 60 includes a secondary air flow path 612 that bypasses the combustion part 63 with the other air in the off-air except for the primary air as secondary air. According to this, it is possible to suppress the air ratio in the off-gas combustor 60 from becoming too large.

[0110] (6) The secondary air flow path 612 is connected to the temperature-raising section 64 so that the heat of the secondary air is transferred to the reformer 34. In this way, if the configuration is such that the heat of the secondary air flowing through the secondary air flow path 612 is transferred to the reformer 34, the flow rate of the fluid that dissipates heat to the reformer 34 can be ensured, so that the reformer 34 can be appropriately heated. Further, since the secondary air is merged into the off-gas combustion gas after the combustion reaction in the combustion section 63 is completed, the combustibility of the combustion section 63 is not deteriorated by the merging of the secondary air.

[0111] (Modification of the embodiment) (1) The preheating plate 65 shown in the above-described embodiment has a flat portion that partitions the primary air flow path 611 and the combustion flow path 632, but it is desirable that the portion be uneven. When the portion that partitions the primary air flow path 611 and the combustion flow path 632 is uneven, not only the heat transfer area is increased, but also the gas flow is disturbed, so that the temperature boundary layer on the surface of the gas flow becomes small, and thus the heat transfer performance can be improved.

[0112] (2) It is desirable that the off-gas combustor 60 of the above-described embodiment be provided with a buffer tank that temporarily stores the off-fuel gas from each combustion section 63, and the off-fuel gas flows from the buffer tank to the temperature-raising section 64. This is because the temperature of the off-gas combustion gas supplied to the temperature-raising section 64 becomes uniform, so that the reformer 34 can be heated evenly.

[0113] (Other embodiments) As described above, the representative embodiments of the present disclosure have been described. However, the present disclosure is not limited to the above-described embodiments, and can be variously modified, for example, as follows.

[0114] As in the above-described embodiment, it is desirable that the primary air flow path 611 be disposed adjacent to at least one of the combustion chamber 631 and the combustion flow path 632 so that the heat of the off-gas combustion gas is transferred to the primary air, but it is not limited thereto. The primary air flow path 611 may not be configured such that the heat of the off-gas combustion gas is transferred to the primary air.

[0115] Further, the primary air flow path 611 may be configured such that, for example, if the heat of the off-gas combustion gas is configured to be transferred to the primary air, the entire amount of the off-air rather than a part of the off-air may flow. The primary air flow path 611 may be configured such that not a part of the off-air always flows, but rather a part of the off-air temporarily flows.

[0116] In the above-described embodiment, an example is shown in which a plurality of combustion units 63 are provided in the same manner as the cell stack CS, but the present invention is not limited thereto. The combustion unit 63 may be one, or may be a number different from that of the cell stack CS.

[0117] As in the above-described embodiment, it is desirable that the off-gas combustor 60 is configured to heat-exchange the off-gas combustion gas and the reformer 34 in the temperature-raising unit 64 to raise the temperature of the reformer 34, but the present invention is not limited thereto. The off-gas combustor 60 may be configured such that, for example, the heat of the combustion unit 63 directly acts on the reformer 34.

[0118] As in the above-described embodiment, it is desirable that the secondary air flow path 612 is connected to the temperature-raising unit 64 such that the heat of the secondary air is transferred to the reformer 34, but the present invention is not limited thereto. The secondary air flow path 612 may be connected to, for example, the exhaust path 70. Note that the secondary air flow path 612 is not essential.

[0119] In the above-described embodiment, the fuel cell system 1 may have a configuration different from that described above. In particular, in the above-described embodiment, the detailed configuration and the arrangement mode of various configurations of the hot module HM have been described, but the present invention is not limited thereto. For example, the plurality of cell stacks CS may be arranged in a row in a predetermined direction inside the heat-insulating container IC. The primary air flow path 611 and the combustion flow path 632 may be partitioned by members different from the preheating plate 65.

[0120] In the above-described embodiment, an example in which the off-gas combustor 60 of the present disclosure is applied to the fuel cell system 1 including the solid oxide fuel cell 10 has been described. However, the application target of the off-gas combustor 60 is not limited thereto. The off-gas combustor 60 can be widely applied to systems including other fuel cells such as fuel cells having a solid electrolyte membrane (i.e., PEFC).

[0121] In the above-described embodiment, it goes without saying that the elements constituting the embodiment are not necessarily essential except when explicitly stated as being essential or when considered to be clearly essential in principle.

[0122] In the above-described embodiment, when numerical values such as the number, numerical value, quantity, range, etc. of the components of the embodiment are mentioned, they are not limited to the specific number except when explicitly stated as being essential or when clearly limited to a specific number in principle.

[0123] In the above-described embodiment, when referring to the shape, positional relationship, etc. of the components, etc., they are not limited to the shape, positional relationship, etc. except when explicitly stated or when clearly limited to a specific shape, positional relationship, etc. in principle.

Explanation of Reference Numerals

[0124] 1 Fuel cell system 10 Fuel cell 34 Reformer 60 Off-gas combustor 61 Off-air flow path 611 Primary air flow path 612 Secondary air flow path 63 Combustion section 64 Temperature-raising section

Claims

1. An off-gas combustor that burns off-air and off-fuel, which are off-gases discharged from a fuel cell (10), comprising: A combustion section (63) that mixes and burns the off-air and the off-fuel; A temperature-raising section (64) that raises the temperature of a reformer (34) that generates reformed gas serving as fuel for the fuel cell by utilizing the heat generated in the combustion section; An off-air flow path (61) through which the off-air discharged from the fuel cell flows; and The off-air flow path includes a primary air flow path (611) that flows at least a part of the off-air as primary air into the combustion section, The combustion section has a combustion chamber (631) that mixes and ignites the off-air and the off-fuel, and a combustion flow path (632) through which the off-combustion gas generated in the combustion chamber flows, The off-gas combustor, wherein the primary air flow path is arranged adjacent to at least one of the combustion chamber and the combustion flow path so that the heat of the off-combustion gas is transmitted to the primary air.

2. A plurality of the combustion sections are provided, The primary air flow path includes an introduction section (611a) and a derivation section (611b) of the primary air. When the one closest to the introduction section among the introduction sections in the plurality of combustion sections is defined as the adjacent combustion section, the position of the derivation section is set so that the primary air introduced from the introduction section is derived to other combustion sections other than the adjacent combustion section. The off-gas combustor according to Claim 1.

3. At least a part of the primary air flow path is arranged adjacent to the combustion flow path in the adjacent combustion section so that the primary air flowing through the primary air flow path exchanges heat with the off-combustion gas flowing through the combustion flow path in the adjacent combustion section. The off-gas combustor according to Claim 2.

4. The temperature-raising section is configured as a heat exchange section that exchanges heat between the off-combustion gas after passing through the combustion section and the reformer to raise the temperature of the reformer. The off-gas combustor according to any one of Claims 1 to 3.

5. The off-air flow path includes a secondary air flow path (612) that bypasses the combustion section with other air in the off-air excluding the primary air in the off-air as secondary air, and the off-gas combustor according to any one of claims 1 to 4.

6. The secondary air flow path is connected to the temperature-raising section so that the heat of the secondary air is transmitted to the reformer, and the off-gas combustor according to claim 5.

7. A fuel cell system, a fuel cell (10), an off-gas combustor (60) that burns off-gas discharged from the fuel cell, and a reformer (34) that generates reformed gas serving as fuel for the fuel cell, and the off-gas combustor includes a combustion section (63) that mixes and burns off-air and off-fuel that are off-gas, a temperature-raising section (64) that raises the temperature of the reformer using heat generated in the combustion section, and an off-air flow path (61) through which the off-air discharged from the fuel cell flows, the off-air flow path includes a primary air flow path (611) that flows at least a part of the off-air as primary air into the combustion section, the combustion section has a combustion chamber (631) that mixes and ignites the off-air and the off-fuel, and a combustion flow path (632) through which off-combustion gas generated in the combustion chamber flows, the primary air flow path is disposed adjacent to at least one of the combustion chamber and the combustion flow path so that the heat of the off-combustion gas is transmitted to the primary air, and the fuel cell system.

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