JP6080322B2 - Fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system that generates electricity by chemically reacting a hydrogen-rich fuel gas and air as an oxidizing gas through a solid electrolyte layer, and more particularly, a hydrocarbon system such as natural gas or LPG. The present invention relates to a water self-operating fuel cell system that self-supplies water necessary for reforming a raw material gas into a hydrogen-rich raw material gas.

  One typical fuel cell is a solid oxide fuel cell (SOFC). In this fuel cell, a fuel electrode is usually arranged on one surface side of a thin and brittle solid electrolyte layer made of a sintered body such as yttria stabilized zirconia (YSZ), and an air electrode is arranged on the other surface side. A laminated body having a layer structure is used as a single battery cell. Ni and YSZ cermets are used as the fuel electrode, and lanthanum strontium manganite (LSM) is used as the air electrode. Both are porous sintered bodies.

  In the operation of a fuel cell, a hydrogen-rich fuel gas obtained by preheating and reforming a hydrocarbon-based raw material gas such as natural gas or LPG on the fuel electrode side of a unit cell under a high temperature condition of 800 to 1000 ° C. And air preheated as an oxidizing gas is supplied to the air electrode side. Thus, an electromotive force is generated between the fuel electrode side and the air electrode side of the single battery cell. Since the voltage here is as low as 1 V or less, a flat battery cell is used as a cell stack by stacking a plurality of cells in the thickness direction and connecting them in series. More specifically, by stacking flat interconnectors in the thickness direction while sandwiching the single battery cells so that reaction spaces are formed on both sides of the flat single battery cell, the cell A stack is constructed. The cell stack is housed in a furnace and operated at a high temperature of 800-1000 ° C.

  By the way, the reforming of the hydrocarbon-based source gas here is performed by reacting the source gas and water at a high temperature. Specifically, hydrogen-rich fuel gas is generated by separating hydrogen atoms from carbon atoms in hydrocarbon molecules in the raw material gas to generate hydrogen molecules. In general, the fuel cell is required to be a self-sustaining operation type in which a raw material other than the raw material gas is self-supplied from the installation environment and installation conditions, and water used for reforming is no exception. From this point of view, Patent Documents 1 and 2 propose a water self-sustained fuel cell system that uses condensed water obtained by cooling exhaust gas generated from a cell stack for reforming.

  In the conventional water self-sustained fuel cell system described in Patent Literatures 1 and 2, condensed water is generated by cooling high-temperature combustion exhaust gas discharged from the cell stack through a heat exchanger, This is temporarily stored in a tank, and a necessary amount is extracted by a discharge pump, and is supplied to a reformer through a purifier filled with an ion exchange resin. The tank is used because the amount of condensed water produced exceeds the amount of water required in the reformer. For this reason, the tank is an overflow tank for overflowing excess water. The reason why the purifier is installed on the downstream side of the tank is to remove harmful substances for cells such as chromium contained in the condensed water.

  One of the problems in such a conventional water self-sustained fuel cell system is that a purifier is installed on the downstream side of the tank, so that the condensed water overflowing from the tank contains harmful substances such as chromium. In other words, this may cause environmental pollution. In order to solve this problem, it is conceivable to install a purifier upstream of the tank, but there is no evidence that such a measure has been taken. The reason for this is that if a purifier is arranged on the downstream side of the tank, the water pressure of the condensed water accumulated in the tank is added to the purifier, reducing the load on the discharge pump provided on the downstream side of the tank, in other words If a clarifier is placed upstream of the tank, the internal pressure of the tank cannot be expected, so a large capacity is required for the discharge pump installed downstream of the clarifier, resulting in poor economic efficiency and excessive condensation that overflows. For example, it is considered that high-level filtration treatment to water also leads to an increase in the size of the equipment, which causes the economy to deteriorate.

JP 2008-234869 A JP 2011-154975 A

  The object of the present invention is that there is no risk of environmental pollution due to out-of-condensed water containing harmful substances such as chromium, and water self-supporting that is excellent in safety and economy that can be downsized and simplified. An object is to provide an operation type fuel cell system.

  In order to achieve the above object, the present inventors paid attention to the structure of a purifier equipped with an ion exchange resin, which has been provided on the downstream side of the overflow tank. This purifier is a cylindrical vertical container with the top and bottom surfaces sealed and filled with ion exchange resin inside. Condensate is sent to the bottom of the container in accordance with the operation of the discharge pump placed between the tank and the purifier. From the top and discharged from the top of the container.

  The cylindrical vertical container used in this purifier contains condensed water inside, and it can be said that it can be used as a tank from the top. However, if it is a water flow mode in which condensed water is introduced from the lower part of the container and discharged from the upper part of the container as in the prior art, it does not function as a tank. Contrary to the conventional case, if the condensed water is introduced from the upper part of the container and changed to a water-flowing form in which the condensed water is discharged from the lower part of the container, both the name and reality can be used as a tank, and the overflow tank can be omitted. The present inventors have found from various research studies that the vessel is an alternative to the overflow tank.

The fuel cell system of the present invention has been completed based on such knowledge,
A reformer that reforms the hydrocarbon-based source gas into a hydrogen-rich fuel gas;
A fuel cell body that generates electricity by chemically reacting the hydrogen-rich fuel gas obtained in the reformer and air as an oxidizing gas through a solid electrolyte layer;
The exhaust gas discharged from the fuel cell main body is cooled to generate condensed water, and a self-supporting water supply system that guides the generated condensed water to the reformer is provided.
The free-standing water system accommodates the ion exchange resin into a vertical cylindrical vessel, the condensed water generated by cooling the exhaust gas discharged from the fuel cell body, introduced from the cylindrical container upper tubular A purifier discharged from the bottom of the container;
A discharge pump disposed downstream of the purifier in the supply line in order to distribute the condensed water to the purifier and supply the reformer;
An overflow pipe comprising a vertical pipe disposed in parallel to the purifier and provided upstream of the discharge pump in the supply line between the purifier and the discharge pump;
The purifier is configured such that a first purifier and a second purifier arranged in parallel are selectively used by a flow path switching valve, and are installed at a higher level than the discharge pump,
The overflow pipe formed of the vertical pipe also serves as a water level gauge of the purifier by including a water level sensor.

  In the fuel cell system of the present invention, the container for storing the ion exchange resin is a vertical cylindrical container, and the condensed water is introduced from the upper part of the container and the condensed water is discharged from the lower part of the container. Condensed water can be temporarily retained in the container, and water pressure can be applied to the discharge pump on the downstream side. As a result, an increase in the load on the discharge pump due to the omission of the overflow tank can be minimized.

  However, since the vertical cylindrical container in the purifier is originally an ion exchange resin container, it is sealed, and excess condensed water cannot be overflowed. Therefore, an overflow pipe composed of a vertical pipe is disposed between the purifier and the downstream discharge pump to overflow excess condensate water. The overflow pipe has a simple structure and does not increase the cost. Condensate overflowing from the overflow pipe is treated with ion exchange resin on the upstream side, so it does not contain harmful substances such as chromium. . For this reason, overflow water does not cause environmental pollution.

  In addition, in the overflow pipe consisting of vertical pipes, the water level matches the water level in the purifier placed upstream, and the water level of the purifier can be monitored by installing a water level sensor, and used as a water level gauge It becomes possible. The cylindrical container in the purifier is a sealed container and it is difficult to attach a water level gauge, but it is easy to divert an overflow pipe made of a simple vertical pipe to a water level gauge.

  Thus, in the fuel cell system of the present invention, a tank that also serves as a large overflow tank can be omitted from the self-supporting water supply system that guides the condensed water obtained by the heat exchanger for condensation to the reformer. Since the increase in capacity can be suppressed to a minimum, the structure of the self-sustained water supply system can be greatly simplified and the economy is high. Moreover, since the overflow of the condensed water is performed downstream of the purifier, the condensed water containing harmful substances such as chromium is not discharged out of the system, and there is no danger of environmental pollution due to this. Is also expensive.

  In the fuel cell of the present invention, the shape of the vertical cylindrical container in the purifier is important. In order to effectively apply water pressure to the discharge pump on the downstream side, it is desirable to have a vertically long shape with a large vertical dimension relative to the horizontal dimension, and it is desirable that the height is at least 200 mm. The extremely vertically long shape increases the height of the apparatus due to the structure in which the purifier is installed under the condensation heat exchanger. It is also advantageous from the viewpoint of securing the water pressure to make the installation level of the purifier higher than the installation level of the discharge pump.

  In the fuel cell system of the present invention, condensed water generated by cooling the exhaust gas discharged from the heat exchanger main body is used for reforming the raw material gas, so that it is substantially unnecessary to supply water from the outside. Since the purifier containing the ion exchange resin can be used as a condensate storage tank and the tank serving as an overflow tank can be eliminated, the structure is simple. Since overflow occurs downstream of the purifier, the overflow water does not contain harmful substances such as chromium. For this reason, there is no risk of environmental pollution caused by condensed water containing harmful substances being discharged out of the system.

1 is a schematic configuration diagram of a fuel cell system showing an embodiment of the present invention.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. The fuel cell system according to the present embodiment includes a combination of a fuel cell unit A that is a main part of the fuel cell system and a fluid circulation system B that transmits and receives various fluids to the fuel cell unit A.

The fuel cell unit A preheats the fuel cell main body 10 composed of the cell stack and various fluids supplied to the fuel cell main body 10 by exchanging heat with the high-temperature exhaust gas discharged from the fuel cell main body 10, and the process The heat exchange reforming unit 20 for reforming the hydrocarbon-based source gas into a hydrogen-rich fuel gas , and the burner 30 for preheating the fuel cell body 10 and the heat exchange reforming unit 20 at the start of operation are provided.

  The cell stack constituting the fuel cell main body 10 has a plate-shaped interconnector (separator) in the thickness direction while sandwiching a flat unit cell, which is the minimum structural unit of a solid oxide fuel cell, with a current collector. It is configured by stacking and pressing and holding the stacked body in the stacking direction. Here, each single battery cell includes a disc-shaped solid electrolyte layer made of yttria-stabilized zirconia, and a cermet of Ni and YSZ having the same outer diameter as the solid electrolyte layer laminated on one surface side of the solid electrolyte layer. And a very thin disk-shaped air electrode composed of lanthanum strontium manganite (LSM) disposed in a layered portion excluding the outer peripheral edge on the other surface side of the solid electrolyte layer. It is a thin disk with a three-layer structure. The current collector is a disc made of nickel foam having the same outer diameter as the fuel electrode arranged on the fuel electrode side of the single battery cell.

  The heat exchange reforming unit 20 heats the air supplied as the oxidizing gas to the fuel cell main body 10 by exchanging heat with the high-temperature offgas generated in the fuel cell main body 10 and combusts the offgas. A combustor to be heated, and a hydrocarbon-based source gas such as natural gas or LPG is heated by exchanging heat with the off-gas, and water is added to the heated source gas to reform it into a hydrogen-rich fuel gas. And a reformer with a built-in heat exchanger for heating. Also, the burner 30 burns the burner gas supplied from the outside with the burner air supplied from the outside until the heat exchanger shifts to a normal operation state at the start of operation of the fuel cell part A, and The battery body 10 and the heat exchange reforming unit 20 are forcibly heated to the operating temperature.

  As the fluid circulation system B, an oxidizing gas supply system 40 that supplies air as an oxidizing gas to the heat exchange reforming unit 20 in the fuel cell unit A, and a hydrocarbon to the heat exchange reforming unit 20 in the fuel cell unit A as well. In addition to the source gas supply system 50 for supplying the system source gas, and the burner gas supply system 70 and the burner air supply system 60 for supplying combustion burner gas and burner air to the burner 30 in the fuel cell section A, respectively, A self-supporting water supply system 80 that supplies water for reforming to the reformer in the exchange reforming unit 20 is provided.

  The self-sustained water supply system 80 cools high-temperature exhaust gas generated in the fuel cell main body 10 and discharged from the fuel cell unit A via the heat exchange reforming unit 20 with cooling water, and generates condensed water from the exhaust gas. Condensation heat exchanger 81, two purifiers 82 and 82 charged with ion exchange resin in a vertical cylindrical container, and condensed water generated by condensing heat exchanger 81 to purifiers 82 and 82 In order to circulate and supply to the heat exchange reformer 20 in the fuel cell part A, a discharge pump 83 disposed on the downstream side of the purifiers 82 in the supply pipeline is provided.

  The vertical cylindrical purifiers 82 and 82 are provided below the condensing heat exchanger 81 in order to introduce the condensed water generated by the condensing heat exchanger 81. These purifiers 82 and 82 are arranged in parallel in the supply pipe line, and supply the condensed water generated by the heat exchanger 81 for condensing to either one of the purifiers 82 or 82, that is, purification. For selective use of the units 82, 82, the upstream condenser heat exchanger 81 is connected via a flow path switching valve 84. The purifiers 82 and 82 also have a vertically long shape having a longitudinal inner dimension larger than the inner diameter so as to serve as a condensate storage tank, and are installed vertically at a level higher than the discharge pump 83 on the downstream side. Condensed water is introduced from the upper part of the container and discharged from the lower part of the container.

  Replenishment with an open / close valve 85 for supplying water from outside the system to the supply line between the flow path switching valve 84 and the purifiers 82 and 82 (the branch line corresponding to each of the purifiers 82 and 82) when necessary. The pipeline is connected. On the downstream side of the purifiers 82 and 82, on-off valves 86 and 86 are provided in relation to the selective use of the purifiers 82 and 82, respectively. The branch pipe is combined downstream of the on-off valves 86 and 86 and returned to one supply pipe. An overflow pipe 87 formed of a vertical vertical pipe is provided upstream of the discharge pump 83 in the supply pipe. Is located.

  The overflow pipe 87 is provided alongside the purifiers 82 and 82 (more specifically, disposed in parallel with the water purifiers 82 and 82) in order to serve as a water level meter for the purifiers 82 and 82 arranged in parallel. A water level detector 88 as a water level sensor is provided at a level corresponding to the lower limit of the water level in the purifiers 82 and 82. The upper end of the overflow pipe 87 is connected to a drain pipe indicated by a broken line in FIG. 1, and the downstream side of the on-off valves 86 and 86 is also connected to the drain pipe via another on-off valve 89.

  Next, the operation of the fuel cell system of the present embodiment will be described mainly with respect to the fluid circulation system B, particularly the self-supporting water supply system 80 that supplies the reforming water to the reformer in the heat exchange reforming unit 20.

  While power generation is performed in the fuel cell main body 10 in the fuel cell part A, high-temperature exhaust gas in which off-gas is burned is discharged from the heat exchanger reforming part 20. This exhaust gas is a combustion exhaust gas generated by the reaction between hydrogen and oxygen, and contains a large amount of water vapor.

  The high-temperature exhaust gas discharged from the fuel cell unit A is cooled by the cooling water in the heat exchanger 81 for condensation provided in the self-sustained water supply system 80 in the fluid circulation system B, thereby generating condensed water. While power generation is being performed in the fuel cell main body 10 in the fuel cell part A, the discharge pump 83 in the self-supporting water supply system 80 continues to operate. Further, the on-off valve 85 is closed, one of the on-off valves 86, 86 is closed, and the on-off valve 89 is closed. As a result, the required amount of the condensed water generated in the heat exchanger 81 for condensation passes through either one of the purifiers 82 and 82 arranged in parallel via the flow path switching valve 84. 20 is supplied. The other purifier 82 is kept in a state filled with water for backup. Thus, the condensed water from which harmful substances such as chromium have been removed is sent to the heat exchange reforming unit 20.

  Here, the purifiers 82 and 82 have a structure in which an ion exchange resin is loaded into a vertically long cylindrical container, and the condensed water is introduced into the container from the upper part of the container into the purifier 82 in use. It is discharged outside. Further, the amount of condensed water generated in the heat exchanger 81 for condensation is usually larger than the amount of condensed water consumed in the heat exchange reforming unit 20. For this reason, the condensed water temporarily stays in the container of the purifier 82 in use and is filled, and the purifier 82 functions like a storage tank of condensed water. Thereby, water pressure is added to the discharge pump 83 and the load of the discharge pump 83 is reduced. The amount of condensed water produced is greater than the amount consumed, and is discharged from an overflow pipe 87 provided in the purifiers 82 and 82, and is discharged outside the system through a drain pipe. Since the overflow pipe 87 is located downstream of the purifiers 82 and 82, the condensed water discharged outside the system does not contain harmful substances such as chromium.

  When high-temperature exhaust gas cannot be obtained at the start of operation and the amount of condensed water produced is insufficient, the on-off valve 85 is opened as necessary, and one or both of the purifiers 82 and 82 from outside the system. Water is supplied.

  In order to confirm the effectiveness of the present invention, the fuel cell system was changed from the conventional one to the present invention.

  Specifically, in a self-sustained water supply system that generates condensed water and supplies it to the heat exchange reforming unit, the tank that also serves as an overflow tank that temporarily stores the generated condensed water is eliminated, and ion exchange is performed on a vertical cylindrical container. The clarifier loaded with resin was also used as a tank. Along with this, condensed water was introduced into the container from the upper part of the container of the purifier, and discharged from the lower part of the container to the outside of the container. In addition, the discharge pump arranged between the tank and the purifier was moved downstream of the purifier. An overflow pipe was installed between the discharge pump and the purifier. Furthermore, the installation level of the purifier was made higher than the installation level of the discharge pump.

  When the capacity of the fuel cell main body is DC 5 V, the amount of condensed water required for the heat exchange reforming part is 38 mL / min under the conditions of 75% fuel utilization and S / C = 3 (S: water vapor, C: carbon). Condensed water exceeding this amount was discharged out of the system from the overflow pipe. The capacity of the omitted tank is 1L. The capacity of the cylindrical container in the purifier is 2.5 L, the effective height is 350 mm, and the effective inner diameter is 100 mm. The initial loading rate of the ion exchange resin is 60% by volume. The installation level difference between the purifier and the discharge pump is 300 mm.

  Although the capacity of the discharge pump was unchanged before and after the tank was omitted, the required amount of condensed water could be stably supplied to the heat exchange reforming unit even after the tank was omitted.

  When the chromium concentration in the condensed water discharged from the overflow pipe was measured, it was less than 0.5 mg / L, which is the standard value for hexavalent chromium and its compounds defined in the “Water Pollution Control Law”.

DESCRIPTION OF SYMBOLS 10 Heat exchanger main body 20 Heat exchange reforming part 30 Burner 40 Oxidizing gas supply system 50 Raw material gas supply system 60 Burner gas supply system 70 Burner air supply system 80 Self-supporting water supply system 81 Heat exchanger for condensation 82 Purifier 83 Discharge pump 84 Flow path switching valve 85, 86, 89 On-off valve 87 Overflow pipe 88 Water level detector (water level sensor)

Claims (1)

A reformer that reforms the hydrocarbon-based source gas into a hydrogen-rich fuel gas;
A fuel cell body that generates electricity by chemically reacting the hydrogen-rich fuel gas obtained in the reformer and air as an oxidizing gas through a solid electrolyte layer;
The exhaust gas discharged from the fuel cell main body is cooled to generate condensed water, and a self-supporting water supply system that guides the generated condensed water to the reformer is provided.
The self-supporting water supply system accommodates ion exchange resin in a vertical cylindrical container, and introduces condensed water generated by cooling the exhaust gas discharged from the fuel cell main body from the upper part of the cylindrical container. A purifier discharged from the bottom of the container;
A discharge pump disposed downstream of the purifier in the supply line in order to distribute the condensed water to the purifier and supply the reformer;
An overflow pipe comprising a vertical pipe disposed in parallel to the purifier and provided upstream of the discharge pump in the supply line between the purifier and the discharge pump;
The purifier is configured such that a first purifier and a second purifier arranged in parallel are selectively used by a flow path switching valve, and are installed at a higher level than the discharge pump,
The overflow pipe which consists of the said vertical pipe is a fuel cell system which also serves as the water level gauge of the said purifier by providing a water level sensor.

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