JP6851261B2 - Cogeneration system - Google Patents

Description

The present invention relates to a cogeneration system including a solid oxide fuel cell.

A solid oxide fuel cell (SOFC) generates electricity by electrochemically reacting hydrogen, carbon monoxide, and hydrocarbons in a fuel gas with oxygen in an oxidizing agent gas at a high temperature of about 700 ° C to about 1000 ° C. Therefore, it is possible to construct a cogeneration system that utilizes the power generated by power generation and the heat generated during power generation. In addition to the solid oxide fuel cell described above, the fuel cell also includes a solid polymer fuel cell. The polymer electrolyte fuel cell monitors the balance of heat supplied from the fuel cell to the heat demand of the household, and performs operations such as stopping the fuel cell and reducing the power generation output. On the other hand, solid oxide fuel cells have high power generation efficiency and a small ratio of heat to electricity output, so they are generally operated in accordance with electricity demand regardless of the amount of heat demand. Another reason for operating the solid oxide fuel cell without stopping it is that it is not suitable for frequent start-up and stop due to the high power generation temperature.

Patent Document 1 (Japanese Unexamined Patent Publication No. 2005-285340) describes a reforming section for steam reforming raw fuel to generate fuel gas, and an anode and oxygen gas to which the fuel gas generated by the reforming section is supplied. A solid oxide fuel cell unit (cell stack) having a cathode to which is supplied, and a combustion unit that burns the fuel components in the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell unit. A device is described in which the combustion heat generated in the combustion section is used for steam reforming in the reforming section. In the apparatus described in Patent Document 1, the discharged fuel gas exiting the cell outlet of the fuel cell unit (cell stack) is burned on the spot, but FIG. 9 of Patent Document 2 (Japanese Unexamined Patent Publication No. 2008-021596). As described in the above, the exhaust fuel gas may be collected once and then burned in the combustion section.

Further, in Patent Document 3 (Japanese Patent No. 5433277), the exhaust fuel gas discharged from the anode is burned in the combustion section, and the combustion exhaust gas and the heat medium stored in the heat storage tank (hot water storage tank 70) are heated. A heat recovery unit (heat exchanger 74) that recovers heat from the combustion exhaust gas by exchanging the heat, and a water recovery unit that recovers the condensed water contained in the combustion exhaust gas after the heat is recovered by the heat recovery unit. The system to be equipped is described. In this system, a relatively low temperature heat medium taken out from the lower part of the heat storage tank is supplied to the heat recovery unit, and the relatively high temperature heat medium heated by the heat recovery unit is returned to the upper part of the heat storage tank. It is configured.

Japanese Unexamined Patent Publication No. 2005-285340 Japanese Unexamined Patent Publication No. 2008-021596 Japanese Patent No. 5433277

FIG. 3 is a diagram showing a configuration of a cogeneration system of a comparative example assumed based on a conventional system. In this cogeneration system, a reforming unit 4 that steam reforms raw fuel to generate fuel gas, an anode (not shown) to which the fuel gas produced by the reforming unit 4 is supplied, and oxygen gas are supplied. A solid oxide fuel cell unit (cell stack) 1 having a cathode (not shown) and a fuel component in the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell unit 1. The combustion unit 5 is provided, and the combustion heat generated in the combustion unit 5 is used for steam reforming in the reforming unit 4.

More specifically, the reforming unit 4 is supplied with raw fuel such as city gas, which is supplied via the fuel flow rate sensor 26, the fuel pump 25, the desulfurization unit 11, and the vaporization unit 6. Further, the reforming water supplied from the reforming water pump 29 is supplied to the reforming section 4 in a vaporized state by the vaporizing section 6. As described above, in the example shown in FIG. 3, the raw material fuel is also supplied to the vaporization unit 6, and the mixed gas is supplied to the reforming unit 4 in a state where the raw material fuel and steam are mixed in the vaporization unit 6. Will be done.

The hydrogen-based fuel gas generated in the reforming section 4 is supplied to the fuel cell section (cell stack) 1 in which a plurality of fuel cell cells are stacked via the inlet side fuel manifold 2. Further, oxygen gas (air) is also supplied to the fuel cell unit 1 via the air filter 22, the cathode air blower 21, and the air / exhaust gas heat exchanger (air preheater) 10. Then, in the fuel cell unit 1, power is generated by electrochemically reacting fuel gas containing hydrogen as a main component with oxygen.

The discharged fuel gas discharged from the anode of the fuel cell unit 1 after being used in the power generation reaction in the fuel cell unit 1 is supplied to the combustion unit 5 via the outlet side fuel manifold 3. Further, the exhaust oxygen gas supplied from the cathode is also supplied to the combustion unit 5. Then, the combustion unit 5 burns the fuel component in the discharged fuel gas. Since air is supplied to the cathode of the fuel cell unit 1, not only oxygen but also nitrogen originally contained in the air remains in the discharged oxygen gas.

The heat possessed by the combustion exhaust gas generated in the combustion unit 5 is used in the reforming unit 4 as described above, and is used in the vaporization unit 6 to vaporize the reforming water, and is used in the air / exhaust gas heat exchanger (air preheating). (Vessel) 10 is used to heat the air supplied to the cathode.

In the example shown in FIG. 3, the fuel cell unit 1, the reforming unit 4, the combustion unit 5, the vaporization unit 6, the air / exhaust gas heat exchanger (air preheater) 10, and the like have internal heat generated by using a heat insulating material or the like. It is installed inside a container M configured so as not to escape to the outside.

The combustion exhaust gas emitted from the container M is supplied to the exhaust heat recovery heat exchanger 12. In the exhaust heat recovery heat exchanger 12, heat is recovered from the combustion exhaust gas by exchanging heat between the combustion exhaust gas and the heat medium stored in the heat storage tank 13. At this time, the exhaust heat recovery heat exchanger 12 cools the combustion exhaust gas (CO ₂ , N ₂ , O ₂ , H ₂ O), so that condensed water is generated.

The condensed water contained in the combustion exhaust gas after being cooled by the exhaust heat recovery heat exchanger 12 is recovered by the water recovery unit (gas-liquid separator) 14, passes through the water purifier 71 and the water tank 72, and is as described above. It is reused for steam reforming in the reforming section 4 in the route. Further, the combustion exhaust gas after the condensed water is removed by the water recovery unit 14 is exhausted from the exhaust passage 34.

In the example shown in FIG. 3, a temperature stratification is formed inside the heat storage tank 13 such that a relatively high temperature heat medium exists in the upper part and a relatively low temperature heat medium exists in the lower part. The exhaust heat recovery pump 28 supplies a relatively low temperature heat medium taken out from the lower part of the heat storage tank 13 to the exhaust heat recovery heat exchanger 12, and the temperature is raised by the heat recovery of the exhaust heat recovery heat exchanger 12. The structure is such that the relatively high temperature heat medium is returned to the upper part of the heat storage tank 13. Further, a heat medium supply path 36 that supplies a high-temperature heat medium from the upper part of the heat storage tank 13 toward the heat utilization device side, and a heat medium return for returning or replenishing the low-temperature heat medium to the lower part of the heat storage tank 13. Road 35 is also provided.

With reference to FIG. 4, the heat exchange performed between the combustion exhaust gas obtained after the combustion in the combustion unit 5 and the heat medium in the exhaust heat recovery heat exchanger 12 will be described. FIG. 4 is a graph showing the amount of recoverable heat at the time of power generation with an input of raw material and fuel of 1.25 kW (low calorific value standard) and an AC power generation output of 705 W. The vertical axis is the temperature of the combustion exhaust gas after heat exchange, and the horizontal axis is the amount of heat recovered by the heat medium. Natural gas-based city gas is used as the raw material and fuel supplied to the reforming unit 4, and the molar ratio (S / C) of water vapor (S) to carbon (C) in the raw material and fuel gas supplied to the reforming unit 4 is Is set to 2.5, and it is assumed that the fuel utilization rate in the fuel cell unit 1 is 79% and the air utilization rate is 40%. In this case, when the combustion exhaust gas is cooled so that the temperature drops to 60 ° C., about 0.11 kW moves to the heat medium side. If heat is exchanged in the exhaust heat recovery heat exchanger 12 in a state where the combustion exhaust gas and the heat medium are in a countercurrent flow, the inlet temperature of the heat medium to the exhaust heat recovery heat exchanger 12 is the limit at which the combustion exhaust gas is cooled. It becomes the temperature. In other words, what is shown by the solid line in FIG. 4 is the limit of the amount of heat that can be recovered when the inlet temperature of the heat medium to the exhaust heat recovery heat exchanger 12 is on the vertical axis.

As described above, since the amount of condensed water that can be recovered by the water recovery unit 14 depends on how much the combustion exhaust gas can be cooled in the exhaust heat recovery heat exchanger 12, it is taken out from the lower part of the heat storage tank 13. The lower the temperature of the heat medium supplied to the exhaust heat recovery heat exchanger 12, the more preferable it is that the combustion exhaust gas can be cooled in the exhaust heat recovery heat exchanger 12. However, when the amount of heat used on the heat utilization device side is small, the temperature of the heat medium existing in the lower part of the heat storage tank 13 also rises, and as a result, the heat is taken out from the lower part of the heat storage tank 13 and the exhaust heat recovery heat exchanger 12 The temperature of the heat medium supplied to the heat medium also rises. In that case, since the combustion exhaust gas cannot be sufficiently cooled in the exhaust heat recovery heat exchanger 12, the amount of heat recovered is reduced, and the amount of condensed water that can be recovered by the water recovery unit 14 is also reduced.

Since the condensed water recovered by the water recovery unit 14 is reused for steam reforming in the reforming unit 4 via the water purifier 71 and the water tank 72, the amount of condensed water that can be recovered by the water recovery unit 14 is reduced. You need to avoid doing it. Natural gas-based city gas is used as the raw material and fuel supplied to the reforming unit 4, and the molar ratio (S / C) of water vapor (S) to carbon (C) in the raw material and fuel gas supplied to the reforming unit 4 is 2. When set to .5 and the fuel utilization rate in the fuel cell unit 1 is 79% and the air utilization rate is 40%, the amount of water supplied to the reforming unit 4 and the amount of water collected by the water recovery unit 14 It is necessary to cool the flue gas to 44.5 ° C. in order to equalize, for example, 4.4 ml per unit time (that is, to achieve water independence). However, as described above, when the temperature of the heat medium existing in the lower part of the heat storage tank 13 reaches, for example, 60 ° C. in a situation where the heat used on the heat utilization device side is small, the heat medium at 60 ° C. is exhausted heat recovery heat. Even if it is supplied to the exchanger 12, the combustion exhaust gas cannot be sufficiently cooled, and the amount of condensed water that can be recovered by the water recovery unit 14 also decreases, so that water independence cannot be achieved.

Therefore, the system shown in FIG. 3 includes a radiator 15 for forcibly cooling the heat medium taken out from the lower part of the heat storage tank 13 and supplied to the exhaust heat recovery heat exchanger 12. However, in the summer when the temperature is high, the radiator 15 must cool the heat medium using the high temperature air, so if you want to secure sufficient cooling capacity, prepare a large radiator. Alternatively, it is necessary to operate the radiator at a high output (for example, to operate the fan at a high rotation speed).

Further, the increase in the temperature of the heat medium supplied to the exhaust heat recovery heat exchanger 12 also leads to a decrease in the amount of heat recovery. Specifically, in the figure shown in FIG. 4 in FIG. 3, when the combustion exhaust gas can be cooled to 40 ° C., a heat recovery amount of about 0.29 kW can be obtained, but the combustion exhaust gas is cooled only to 60 ° C. If it cannot be done, only about 0.11 kW of heat can be recovered.

As described above, in the system as shown in FIG. 3, in order to increase the amount of heat recovery and achieve water independence, the exhaust heat recovery heat exchanger 12 is provided with a high-performance heat exchanger. There is a problem that it is necessary to use it and a large-sized and high-power radiator is required. That is, in the system as shown in FIG. 3, there is a problem that a large cost is required in order to increase the heat recovery amount and achieve water independence.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a cogeneration system that does not require a large cost to increase heat recovery and achieve water independence.

The characteristic configuration of the cogeneration system according to the present invention for achieving the above object is a reforming section for steam reforming raw fuel to generate fuel gas, and a reforming section.
A solid oxide fuel cell unit having an anode to which the fuel gas generated in the reforming unit is supplied and a cathode to which oxygen gas is supplied, and
It has a heat storage tank that stores a heat medium, and exchanges heat between the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell unit and the heat medium stored in the heat storage tank. As a result, the heat recovery unit that recovers heat from the exhausted fuel gas
A water recovery unit that recovers condensed water contained in the discharged fuel gas after heat is recovered by the heat recovery unit, and a water recovery unit.
A combustion unit that burns fuel components in the discharged fuel gas after the condensed water is recovered by the water recovery unit, and a combustion unit.
A heat exchanger that exchanges heat between the discharged fuel gas before reaching the heat recovery unit and the discharged fuel gas after the condensed water is recovered by the water recovery unit and before being burned by the combustion unit.
It is provided with a heat medium supply path for supplying the heat medium stored in the heat storage tank toward the heat utilization device side.
The condensed water recovered in the water recovery section is used for steam reforming of the raw material fuel in the reforming section.
The point is that the combustion heat generated in the combustion section is configured to be used for steam reforming in the reforming section.

According to the above characteristic configuration, in the heat recovery unit, the exhausted fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell unit is heat-exchanged with the heat medium stored in the heat storage tank to discharge the gas. Heat recovery from the fuel gas is carried out by a heat medium. Then, the heat recovered heat medium is stored in the heat storage tank to accumulate heat, and the stored heat can be supplied to the heat utilization device side via the heat medium supply path. That is, heat can be recovered from the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell section, and the heat can be stored in the heat storage tank and supplied to the heat utilization device as needed.

As described above, in the conventional configuration, _{heat exchange is performed between the combustion exhaust gas (CO 2} , N ₂ , O ₂ , H ₂ O) after being burned in the combustion section and the heat medium stored in the heat storage tank. _{On the other hand, in this feature configuration, the discharged fuel gas (CO, CO 2} , H ₂ , H ₂ O) discharged from the anode after being used in the power generation reaction in the fuel cell section and before being burned in the combustion section. ) And the heat medium stored in the heat storage tank are exchanged for heat. As described above, the composition of the gas that exchanges heat with the heat medium is different between the present feature configuration and the conventional configuration, and the dew point of the gas (exhausted fuel gas) is higher in this feature configuration. Therefore, in this feature configuration, even if the temperature of the heat medium is significantly higher than that in the conventional configuration, almost the same amount of condensed water can be obtained and almost the same amount of heat recovery can be obtained. For example, natural gas-based city gas is used as the raw material to be supplied to the reforming part, and the molar ratio (S / C) of water vapor (S) to carbon (C) in the raw material and fuel gas supplied to the reforming part is 2. When set to 5.5 and the fuel utilization rate in the fuel cell section is 79% and the air utilization rate is 40%, the amount of water supplied to the reforming section and the amount of water recovered by the water recovery section are set to, for example. In order to equalize at 4.4 ml per unit time (that is, to achieve water independence), it is necessary to set the heat medium for heat exchange with the combustion exhaust gas to about 44.5 ° C. in the conventional configuration, but in this feature configuration. The heat medium for heat exchange with the discharged fuel gas may be about 75 ° C. Therefore, in this feature configuration, if the heat consumption on the heat utilization device side is reduced, the heat medium stored in the heat storage tank becomes high temperature, and the high temperature heat medium is used to generate heat from the discharged fuel gas. Even if recovery must be performed, sufficient heat recovery and generation of condensed water can be performed.

Further, in the conventional configuration, the combustion exhaust gas, that is, the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell section and the emission discharged from the cathode after being used in the power generation reaction in the fuel cell section. After burning the mixed gas with oxygen gas (O ₂ , N ₂ ), heat was exchanged between the gas and the heat medium. On the other hand, in this feature configuration, heat exchange is performed between the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell section and the heat medium. Therefore, in this feature configuration, the _{molar flow rate is smaller because the exhausted oxygen gas (O 2} , N ₂ ) is not contained in the gas, and therefore the restriction on the pipe diameter for flowing the gas is smaller (that is,). The requirements for the structure of the heat exchanger are small), and there is an advantage that the power for flowing the gas may be small. That is, this feature configuration has the advantages that the equipment cost is smaller and the energy required for operation is smaller.
Therefore, it is possible to provide a cogeneration system that does not require a large cost to increase heat recovery and achieve water independence.

In addition, since the heat capacity of the discharged fuel gas after the condensed water is recovered in the water recovery unit is reduced, the temperature of the discharged fuel gas from which the water has been removed reaches the heat recovery unit in the heat exchanger. It can be easily increased by heat exchange with the previous exhausted fuel gas. Further, by supplying the exhaust fuel gas after the water is removed by the water recovery unit and the temperature is raised by the heat exchanger to the combustion unit, there is an advantage that the combustibility of the exhaust fuel gas in the combustion unit is enhanced.

Another characteristic configuration of the cogeneration system according to the present invention is such that in the heat recovery unit, the pipe through which the exhaust fuel gas flows passes through the heat medium stored in the heat storage tank. There is a point.

According to the above-mentioned characteristic configuration, it is possible to exchange heat between the discharged fuel gas and the heat medium stored in the heat storage tank without using a heat exchanger having a complicated configuration. In particular, in this feature configuration, heat exchange is performed between the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell section and the heat medium, so that the exhaust fuel gas is as in the conventional configuration. Compared with the case where heat exchange is performed between the gas and the heat medium after burning the mixed gas of the exhausted oxygen gas (O ₂ , N _{2), this characteristic configuration emits into the gas.} The molar flow rate is small because it does not contain oxygen gas (O ₂ , N _2). Therefore, there is an advantage that there are few restrictions on the diameter of the pipe for flowing the exhaust fuel gas in the part where heat is exchanged with the heat medium stored in the heat storage tank (that is, the requirement for the structure of the heat exchanger is small). ..

It is a figure which shows the structure of the cogeneration system of this embodiment. It is a graph which shows the relationship between the amount of heat recoverable by a heat medium, and the temperature of the exhaust fuel gas after heat exchange. It is a figure which shows the structure of the cogeneration system of a comparative example. It is a graph which shows the relationship between the amount of heat recoverable by a heat medium, and the temperature of the combustion exhaust gas after heat exchange.

The cogeneration system according to the embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a cogeneration system. This cogeneration system is a system that utilizes the electric power generated by the fuel cell unit 1 and the heat generated by the power generation. In the cogeneration system of the present embodiment, the reforming unit 4 for steam reforming the raw material and fuel to generate fuel gas, the anode (not shown) and oxygen to which the fuel gas generated by the reforming unit 4 is supplied. After having a solid oxide type fuel cell unit 1 having a cathode (not shown) to which gas is supplied and a heat storage tank 63 storing a heat medium, and being used in a power generation reaction in the fuel cell unit 1. By exchanging heat between the discharged fuel gas discharged from the anode and the heat medium stored in the heat storage tank 63, the heat is recovered by the heat recovery unit H and the heat recovery unit H that recover the heat from the discharged fuel gas. A water recovery unit 14 that recovers the condensed water contained in the later discharged fuel gas, a combustion unit 5 that burns the fuel components in the discharged fuel gas after the condensed water is recovered by the water recovery unit 14, and a heat storage tank 63. It is configured to include a heat medium supply path 65 for supplying the heat medium stored in the heat medium to the heat utilization device side.

More specifically, the reforming unit 4 is supplied with raw fuel such as city gas, which is supplied via the fuel flow rate sensor 26, the fuel pump 25, the desulfurization unit 11, and the vaporization unit 6. Further, the reforming water supplied from the reforming water pump 29 is supplied to the reforming section 4 in a vaporized state by the vaporizing section 6. As described above, in the example shown in FIG. 1, the raw material fuel is also supplied to the vaporization unit 6, and the mixed gas is supplied to the reforming unit 4 in a state where the raw material fuel and steam are mixed in the vaporization unit 6. Will be done.

The hydrogen-based fuel gas generated in the reforming section 4 is supplied to the fuel cell section (cell stack) 1 in which a plurality of fuel cell cells are stacked via the inlet side fuel manifold 2. Further, oxygen (air) is also supplied to the fuel cell unit 1 via the air filter 22, the cathode air blower 21, and the air / exhaust gas heat exchanger (air preheater) 10. Then, in the fuel cell unit 1, power is generated by electrochemically reacting fuel gas containing hydrogen as a main component with oxygen.

The discharged fuel gas discharged from the anode of the fuel cell unit 1 after being used in the power generation reaction in the fuel cell unit 1 is supplied to the heat exchanger 52 via the outlet side fuel manifold 3, and then the heat recovery unit. It is supplied to H. The heat recovery unit H has a heat storage tank 63 that stores a heat medium, and the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell unit 1 and the heat medium stored in the heat storage tank 63. By exchanging heat with and, heat is recovered from the discharged fuel gas. In the present embodiment, in the heat recovery unit H, the heat radiating pipe (piping) 62 through which the discharged fuel gas flows passes through the heat medium stored in the heat storage tank 63. Since the heat radiating pipe 62 has a coil shape inside the heat storage tank 63, the contact area between the outer surface of the heat radiating pipe 62 and the heat medium is large. Further, since the heat radiating pipe 62 has a shape having a uniform gradient downward, the generated condensed water easily flows to the lower water recovery unit 14 due to gravity.

As described above, the heat recovery unit H of the present embodiment can exchange heat between the discharged fuel gas and the heat medium stored in the heat storage tank 63 without using a heat exchanger having a complicated structure. Specifically, the heat recovery unit H exchanges heat between the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell unit 1 and the heat medium, and thus has a conventional configuration. Compared with the case where heat exchange is performed between the gas and the heat medium after burning the mixed gas of the discharged fuel gas and the discharged oxygen gas (O ₂ , N _{2) as in the above embodiment, the present embodiment is used.} However, the molar flow rate is small because the exhausted oxygen gas (O ₂ , N _{2) is not included in the gas.} Therefore, there is an advantage that there are few restrictions on the diameter of the pipe for flowing the exhaust fuel gas in the portion where heat is exchanged with the heat medium stored in the heat storage tank 63 (that is, the requirement for the structure of the heat exchanger is small). is there.

In this way, the discharged fuel gas (CO, CO ₂ , H ₂ , H ₂ O) after being discharged from the anode of the fuel cell unit 1 is cooled by the heat exchanger 52 and the heat recovery unit H, so that it is condensed. Water is generated. The condensed water contained in the discharged fuel gas after being cooled by the heat recovery unit H is recovered by the water recovery unit (gas-liquid separator) 14. Then, the condensed water recovered by the water recovery unit 14 passes through the water purifier 71 and the water tank 72, and is used for steam reforming of the raw fuel in the reforming unit 4 as described above. Therefore, the amount of condensed water that can be recovered by the water recovery unit 14 differs mainly depending on the dew point of the discharged fuel gas supplied to the heat recovery unit H and the temperature at which the discharged fuel gas can be cooled.

For example, the temperature of the discharged fuel gas after exiting the anode of the fuel cell unit 1 and before entering the heat exchanger 52 (part P1 in FIG. 1) is 681 ° C., and after exiting the heat exchanger 52, heat is generated. The temperature of the discharged fuel gas before entering the recovery unit H (part P2) is 473 ° C., and the temperature of the discharged fuel gas after exiting the heat recovery unit H and before entering the radiator 61 (part P3) described later is The temperature is 70 ° C., and the temperature of the discharged fuel gas after being cooled by the radiator 61 and before entering the water recovery unit 14 (part P4) is 55 ° C.
Further, the gas composition of the discharged fuel gas before cooling in the heat recovery unit H, that is, after exiting the heat exchanger 52 and before entering the heat recovery unit H (site P2), is, for example, 2% CO and CO. ₂ is 17%, H ₂ is 13%, and H ₂ O is 68%.
On the other hand, the gas composition of the discharged fuel gas after cooling in the heat recovery unit H, that is, after exiting the heat recovery unit H and before entering the radiator 61 (part P3) is, for example, 5% CO. CO ₂ is 44%, H ₂ is 35%, and H ₂ O is 16%.

The discharged fuel gas after the condensed water is removed by the water recovery unit 14 is heat-exchanged with the exhaust fuel gas before reaching the heat recovery unit H described above by the heat exchanger 52, and then supplied to the combustion unit 5. .. That is, in the system of the present embodiment, the exhausted fuel gas before reaching the heat recovery unit H and the exhausted fuel gas after the condensed water is recovered by the water recovery unit 14 and before being burned by the combustion unit 5 are heated. A heat exchanger 52 to be replaced is provided. Since the heat capacity of the discharged fuel gas after the condensed water is recovered by the water recovery unit 14, the heat capacity of the discharged fuel gas is lowered, so that the heat exchanger 52 sets the temperature of the discharged fuel gas from which the water has been removed before reaching the heat recovery unit H. It can be easily increased by heat exchange with the exhaust fuel gas of. In particular, in the example shown in FIG. 1, in the heat exchanger 52, both gases flow in a countercurrent state to exchange heat. Further, by supplying the exhaust fuel gas after the water is removed by the water recovery unit 14 and the temperature is raised by the heat exchanger 52 to the combustion unit 5, the combustibility of the exhaust fuel gas in the combustion unit 5 is enhanced. There are advantages.

Exhaust oxygen gas supplied from the cathode of the fuel cell unit 1 is also supplied to the combustion unit 5, and the fuel component (H ₂ or the like) remaining in the exhaust fuel gas is burned in the combustion unit 5. Since air is supplied to the cathode of the fuel cell unit 1, not only oxygen but also nitrogen originally contained in the air remains in the discharged oxygen gas. The combustion heat generated in the combustion unit 5 is used for steam reforming in the reforming unit 4. In addition, the heat possessed by the combustion exhaust gas generated in the combustion unit 5 is used for vaporizing the reforming water in the vaporization unit 6, and is supplied to the cathode by the air / exhaust gas heat exchanger (air preheater) 10. It is used to heat the air. After that, the combustion exhaust gas is discharged to the outside of the system.

In the example shown in FIG. 1, the fuel cell unit 1, the reforming unit 4, the combustion unit 5, the vaporization unit 6, the air / exhaust gas heat exchanger (air preheater) 10, a part of the heat exchanger 52, and the like are heat insulating materials. It is installed inside the container M, which is configured to prevent the heat inside from escaping to the outside by using or the like.

Further, in the example shown in FIG. 1, the heat storage tank 63 has a heat medium supply path 65 for supplying a heat medium from the upper part of the heat storage tank 63 toward the heat utilization device side, and a heat medium in the lower part of the heat storage tank 63. A heat medium return path 64 for returning or replenishing is also provided. As the heat medium, water (hot water) or other medium (for example, polyethylene glycol) can be used. For example, when the heat utilization device is a floor heating device or an air conditioning device that uses only the heat possessed by the heat medium, a relatively high temperature heat medium from the heat storage tank 63 passes through the heat medium supply path 65 to heat. The relatively low temperature heat medium supplied to the utilization device and after the heat is utilized in the heat utilization device returns to the heat storage tank 63 through the heat medium return path 64. Alternatively, when the heat utilization device is a hot water supply device that uses water (hot water) itself as a heat medium, relatively high temperature hot water (heat medium) from the heat storage tank 63 uses heat through the heat medium supply path 65. Hot water (heat medium) is supplied to the device and does not return to the heat storage tank 63, but instead, the same amount of low-temperature water as supplied from the heat storage tank 63 to the heat utilization device through the heat medium supply path 65. (Clean water) flows into the heat storage tank 63 through the heat medium return path 64.

FIG. 2 shows the amount of heat that can be recovered by the heat medium in the heat recovery unit H when the raw material input is 1.25 kW (low calorific value standard) and the AC power generation output is 705 W, as in FIG. It is a graph which shows the relationship with the temperature of the exhaust fuel gas after heat exchange. In FIG. 2, the vertical axis represents the temperature of the discharged fuel gas after heat exchange, and the horizontal axis represents the amount of heat that can be recovered by the heat medium. As shown in the figure, when the exhaust fuel gas (CO, CO ₂ , H ₂ , H ₂ O) is cooled so as to drop to about 75 ° C., about 0.29 kW moves to the heat medium side. As described above, in the comparative examples shown in FIGS. 3 and 4, the temperature of the heat medium entering the exhaust heat recovery heat exchanger 12 had to be lowered to about 40 ° C., but in the configuration of FIG. 1, about 75 The same amount of heat recovery can be obtained with a heat medium at ° C.

In addition, natural gas-based city gas is used as the raw material and fuel supplied to the reforming unit 4, and the molar ratio (S / C) of water vapor (S) to carbon (C) in the raw material and fuel gas supplied to the reforming unit 4 is used. ) Is set to 2.5, and when the fuel utilization rate in the fuel cell unit 1 is 79% and the air utilization rate is 40%, the amount of water supplied to the reforming unit 4 and the water recovery unit 14 collect the fuel. In order to equalize the amount of water, for example, 4.4 ml per unit time (that is, to achieve water independence), it is only necessary to cool the discharged fuel gas having a higher dew point than the conventional configuration to 75 ° C. It is not necessary to cool to about 44.5 ° C as in the configuration.

To give a specific example, as described above, in the case of a heat utilization device such as a floor heating device or an air conditioning device that uses only the heat possessed by the heat medium, the heat medium at, for example, 80 ° C. is the heat medium from the heat storage tank 63. It flows out through the supply path 65, and for example, a heat medium at 60 ° C. flows into the heat storage tank 63 through the heat medium return path 64. That is, the minimum temperature of the heat medium stored in the heat storage tank 63 is about 60 ° C. In such a case, the temperature of the discharged fuel gas can be lowered only to about 60 ° C. However, in the present embodiment, if the discharged fuel gas can be cooled to 60 ° C., a sufficient amount of heat can be recovered and a sufficient amount can be recovered. Condensed water can be obtained. As described above, in the present embodiment, even if the temperature of the heat medium stored in the heat storage tank 63 reaches, for example, 60 ° C., the discharged fuel gas can be sufficiently cooled, so that the condensed water that can be recovered by the water recovery unit 14 can be obtained. Sufficiently secured and water independence can be achieved.

Further, the system shown in FIG. 1 includes a radiator 61 that promotes heat dissipation from the discharged fuel gas after the heat is recovered by the heat recovery unit H and before reaching the water recovery unit 14. The radiator 61 is an air-cooled device provided with a heat-dissipating structure such as a heat-dissipating fin formed on the surface of a pipe through which exhausted fuel gas flows, or an electric fan in addition to such a heat-dissipating structure (heat-dissipating fin). It can be realized by using an air-cooled device equipped with. After the heat is recovered by the heat recovery unit H by such a radiator 61, the discharged fuel gas before reaching the water recovery unit 14 can be further cooled to obtain condensed water. In particular, since there is a large temperature difference between the temperature of the atmosphere around the radiator 61 and the temperature required for sufficient cooling of the discharged fuel gas (75 ° C. described above), for example, the temperature of the atmosphere Even in a hot season when the temperature is very high, a sufficient amount of condensed water can be obtained and a sufficient amount of heat can be recovered without using a large-sized and high-power radiator 61. Therefore, if a sufficient cooling effect can be obtained only by a heat radiating structure such as a heat radiating fin, the fan may not be provided.

When the radiator 61 is a device provided with an electric fan, the fan may be operated at all times, or the discharged fuel after the heat is recovered by the heat recovery unit H and before reaching the water recovery unit 14. The operation and stop of the fan may be switched according to the temperature of the gas. For example, the radiator 61 operates a fan when the temperature of the discharged fuel gas after the heat is recovered by the heat recovery unit H and before reaching the water recovery unit 14 is 75 ° C. or higher, and when the temperature is lower than 75 ° C. Operation control such as stopping the fan may be performed. Even if the radiator 61 is a device equipped with an electric fan, the atmospheric temperature is significantly lower than the temperature required for sufficient cooling of the discharged fuel gas (75 ° C. described above). It is not necessary to increase the size of the heat radiating fins and the fan of the radiator 61 or to operate the fan at high output.

As described above, in the conventional configuration, the combustion exhaust gas, that is, the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell unit 1, and the cathode after being used in the power generation reaction in the fuel cell unit 1. the heat exchange between the gas and the heat medium after burning a mixed gas of exhaust oxygen gas discharged (O _{2, N 2)} it has been performed from. On the other hand, in the cogeneration system of the present embodiment, heat exchange is performed between the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell unit 1 and the heat medium. Then, by such heat exchange, sufficient heat recovery and generation of condensed water can be performed. Therefore, in the present embodiment, the _{molar flow rate is smaller because the exhausted oxygen gas (O 2} , N ₂ ) is not contained in the gas, and therefore the restriction on the pipe diameter for flowing the gas is smaller (that is,). The requirements for the structure of the heat exchanger are small), and there is an advantage that the power for flowing the gas may be small. That is, the present embodiment has an advantage that the device cost is small and the energy required for operation is small.

<Another Embodiment>
<1>
In the above embodiment, the configuration of the cogeneration system of the present invention has been described with reference to specific examples, but the configuration can be changed as appropriate.

For example, in the above embodiment, the heat radiating pipe (piping) 62 through which the discharged fuel gas flows is coiled inside the heat storage tank 63, but the heat radiating pipe 62 is linear. May be good. Further, although the case where the heat radiating pipe 62 is one pipe is shown in the figure, it may have a structure in which the heat radiating pipe 62 is branched and then merged. By adopting such a branched structure, there is an advantage that the contact area between the heat radiating pipe 62 and the heat medium inside the heat storage tank 63 becomes large.
Further, a heat radiating pipe (piping) 62 through which the discharged fuel gas flows may be provided so as to crawl on the outer wall surface of the heat storage tank 63.

In addition, in FIG. 1, the heat recovery unit H has the heat storage tank 63, and the heat radiation pipe (piping) 62 through which the discharged fuel gas flows passes through the heat medium stored in the heat storage tank 63. Although the example having such a configuration has been described, the configuration of the heat recovery unit H can be changed as appropriate. For example, the heat recovery unit H has a configuration as shown in FIG. 3, that is, a heat medium circulates between the exhaust heat recovery heat exchanger and the heat storage tank, and the exhaust heat recovery device circulates the exhaust fuel gas and the heat medium. It may be configured to exchange heat with and.

<2>
In the above embodiment, the values such as the temperature, the amount of heat, and the amount of condensed water have been described with specific numerical values, but these numerical values are described for the purpose of exemplification and can be changed as appropriate.

<3>
The configurations disclosed in the above embodiment (including other embodiments, the same shall apply hereinafter) can be applied in combination with the configurations disclosed in other embodiments as long as there is no contradiction, and are disclosed in the present specification. The embodiment is an example, and the embodiment of the present invention is not limited to this, and can be appropriately modified without departing from the object of the present invention.

The present invention can be used in a cogeneration system that does not require a large cost to increase heat recovery and achieve water independence.

1 Fuel cell unit 4 Remodeling unit 5 Combustion unit 14 Gas-liquid separator (water recovery unit)
52 Heat exchanger 61 Heat exchanger 63 Heat storage tank 65 Heat medium supply path H Heat recovery unit

Claims (2)

A reforming unit that steam reforms raw fuel to generate fuel gas,
A solid oxide fuel cell unit having an anode to which the fuel gas generated in the reforming unit is supplied and a cathode to which oxygen gas is supplied, and
It has a heat storage tank that stores a heat medium, and exchanges heat between the exhaust fuel gas discharged from the anode after being used in the power generation reaction in the fuel cell unit and the heat medium stored in the heat storage tank. As a result, the heat recovery unit that recovers heat from the exhausted fuel gas
A water recovery unit that recovers condensed water contained in the discharged fuel gas after heat is recovered by the heat recovery unit, and a water recovery unit.
A combustion unit that burns fuel components in the discharged fuel gas after the condensed water is recovered by the water recovery unit, and a combustion unit.
A heat exchanger that exchanges heat between the discharged fuel gas before reaching the heat recovery unit and the discharged fuel gas after the condensed water is recovered by the water recovery unit and before being burned by the combustion unit.
It is provided with a heat medium supply path for supplying the heat medium stored in the heat storage tank toward the heat utilization device side.
The condensed water recovered in the water recovery section is used for steam reforming of the raw material fuel in the reforming section.
A cogeneration system configured so that the heat of combustion generated in the combustion section is used for steam reforming in the reforming section. The cogeneration system according to claim 1, wherein in the heat recovery unit, a pipe through which the discharged fuel gas flows passes through the heat medium stored in the heat storage tank.

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