| JP2004335166 | SOLID OXIDE FUEL CELL |
| WO/2008/029862 | FUEL CELL SYSTEM AMD MOBILE BODY |
| JP3040896 | IMAGE PROCESSOR |
HONG, Byung-Sun (282-3, Yatap-dong Bundang-gu,Seongnam-city, Gyeonggi-do 463-816, KR)
SHINN, Mee-Nam (300-7, Pyeongchang-ri Yangji-myeon,Yongin-city, Gyeonggi-do 449-821, KR)
KIM, Ho-Suk (1Giheung Samjeong Seonbi MaeuL, 289-12 Bora-dong, Giheung-gu,Yongin-si, Gyeonggi-do 446-953, 01-1603, KR)
HONG, Byung-Sun (282-3, Yatap-dong Bundang-gu,Seongnam-city, Gyeonggi-do 463-816, KR)
SHINN, Mee-Nam (300-7, Pyeongchang-ri Yangji-myeon,Yongin-city, Gyeonggi-do 449-821, KR)
[CLAIMS] [Claim 1 ]
A fuel cell system comprising: a reformer for generating a reformed gas using a fuel; a fuel cell stack for generating electric power using the reformed gas and oxidizing agent; and a valve unit for purging the fuel cell stack by filling the fuel cell stack with carbon dioxide contained in the reformed gas, wherein the valve unit comprises a supplying valve installed on a supplying line interconnecting the reformer and an inlet of the fuel cell stack, a recovery valve installed on a recovery line interconnecting the reformer and an outlet of the fuel cell stack, and a bypass valve installed on a bypass line interconnecting the supplying line and a discharge line.
[Claim 2]
The fuel cell system of claim 1 , further comprising a voltage reducing unit connected to the fuel cell stack.
[Claim 3] The fuel cell system of claim 1 , wherein the valves are solenoid valves.
[Claim 4] The fuel cell system of claim 1 , further comprising a pressure sensor installed at the inlet of the fuel cell stack.
[Claim 5] The fuel cell system of claim 1 , wherein the fuel is a hydrocarbon-based fuel.
[Claim 6]
A purging method of a fuel cell system for discharging a reformed gas out of a fuel cell stack, the purging method comprising: disconnecting electrical connection between the fuel cell stack and a load; reducing an amount of the reformed gas that is being supplied to the fuel cell stack; opening a supplying valve for controlling supply of the reformed gas to the fuel cell stack and a bypass valve installed on a bypass line and closing a recovery valve for controlling discharge of the reformed gas recovered from the fuel cell stack; and filling the fuel cell stack with the carbon dioxide by consuming hydrogen in the fuel cell stack.
[Claim 7]
The purging method of claim 6, wherein, in the filling the fuel cell stack with the carbon dioxide, the consumption of the hydrogen is realized by a voltage reducing unit connected to the fuel cell stack.
[Claim 8] The purging method of one of claims 6 and 7, wherein, in the filling the fuel cell stack with the carbon dioxide, the hydrogen is consumed until a cell voltage of the fuel cell stack becomes 0.5V or less.
[Claim 9] The purging method of one of claims 6 and 7, wherein, in the reducing the amount of the reformed gas, the reformed gas is reduced to 1/3-1/5 of the amount of reformed gas present in normal operation.
[Claim 10] The purging method of one of claims 6 and 7, wherein, in the reducing the amount of the reformed gas, the reformed gas is reduced to 1/4 of an amount of reformed gas present in normal operation.
[Claim 1 1 ] A purging method of a fuel cell system for discharging a reformed gas out of a fuel cell stack, the purging method comprising: a) disconnecting electrical connection between the fuel cell stack and a load; b) reducing an amount of the reformed gas that is being supplied to the fuel cell stack; c) opening a supplying valve installed at an inlet of the fuel cell stack and closing a bypass valve installed on a bypass line and a recovery valve installed at an outlet of the fuel cell stack; d) opening the bypass valve and closing the supplying valve; e) reducing internal pressure of the fuel cell stack by consuming hydrogen contained in the reformed gas in the fuel cell stack; f) repeating steps c) to e) when a maximum cell voltage of the fuel cell stack is compared with a reference voltage and it is determined that the maximum cell voltage is greater than the reference voltage; and g) closing the supplying valve when the maximum cell voltage is equal to or less than the reference voltage.
[Claim 12]
The purging method of claim 11 , wherein, in step e), the consumption of the hydrogen is realized by a voltage reducing unit connected to the fuel cell stack.
[Claim 13]
The purging method of claim 11 , wherein, in step d), when the pressure of the reformed gas in the fuel cell stack is 8-15kPa, the bypass valve is opened and the supplying valve is closed.
[Claim 14]
The purging method of claim 11 , wherein in step e), the hydrogen is consumed until the pressure of the reformed gas in the fuel cell stack is reduced to 1-3kPa.
[Claim 15]
The purging method of claim 11 , wherein the reference voltage is 0.5V. |
[DESCRIPTION] [Invention Title]
FUEL CELL SYSTEM AND PURGING METHOD THEREOF
[Technical Field] The present invention relates to a fuel cell system. More particularly, the present invention relates to a fuel cell system that is designed to effectively discharge moisture generated in a fuel cell. [Background Art]
Fuel cells are designed to electrochemically generate electric power using a fuel (hydrogen or a reforming gas) and an oxidizing agent (oxygen or air). That is, the fuel cells generate electrical energy using an electrochemical reaction between the fuel (hydrogen or a reforming gas) and the oxidizing agent
(oxygen or air).
Pure oxygen or air containing a large amount of oxygen is used as the oxidizing agent. Pure hydrogen or a fuel containing a large amount of hydrogen generated by reforming a hydrocarbon-based fuel such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), and CH 3 OH is used as the fuel.
For better comprehension and ease of description, a polymer electrolyte membrane fuel cell among the fuel cells will be exemplarily described. The polymer electrolyte membrane fuel cell has relatively high density and relatively high energy conversion efficiency, and is operable at a relatively low
temperature of 80° C or less. In addition, the polymer electrolyte membrane fuel cell can be miniaturized and sealed and thus it has been widely used as a power source for a variety of applications such as for a pollution-free vehicle, home power equipment, mobile communication equipment, military equipment, medical equipment, and the like.
The polymer electrolyte membrane fuel cell system includes a reformer for generating a reformed gas from a fuel containing a large amount of hydrogen, and a fuel cell stack for generating electricity using the reformed gas.
That is, the reformed gas and oxygen are supplied to the fuel cell stack to generate electricity by a hydrogen-oxygen reaction. For a fuel cell system using the reformed gas as a reaction gas, when the system stops operating and the reformed gas remains in the fuel cell stack, a catalytic layer formed on a polymer electrolyte layer or hydrogen and air electrodes may be deteriorated.
In order to prevent this, the supply of the reformed gas is stopped and nitrogen (N 2 ) that is an inert gas is supplied to purge the reformed gas remaining in the fuel stack.
However, the purging using the nitrogen has limitations in that the nitrogen must be externally supplied and thus additional equipment is needed for supplying the nitrogen. This increases the manufacturing cost of the fuel cell system. Further, the additional equipment becomes a major stumbling block for commercializing the fuel cell system due to limited space for installing a nitrogen container.
The above information disclosed in this Background section is only for
enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.
[DETAILED DESCRIPTION] [Technical Problem]
Since the purging using the nitrogen requires the additional equipment, the manufacturing cost increases. In addition, the additional equipment becomes a major stumbling block for commercializing the fuel cell system due to the limited space for installing a nitrogen container. Therefore, there is a need for a purging system and method that can more easily and effectively purge the fuel cell system. [Technical Solution]
In order to meet the above need, a fuel cell system in accordance with an exemplary embodiment of the present invention includes a reformer for generating a reformed gas using a fuel, a fuel cell stack for generating electric power using the reformed gas and oxidizing agent, and a valve unit including a supplying valve installed on a supplying line interconnecting the reformer and an inlet of the fuel cell stack, a recovery valve installed on a recovery line interconnecting the reformer and an outlet of the fuel cell stack, and a bypass valve installed on a bypass line interconnecting the supplying line and a discharge line.
A voltage reducing unit may be connected to the fuel cell stack, and the valves may be solenoid valves.
A pressure sensor may be installed at the inlet of the fuel cell stack, and the fuel may be a hydrocarbon-based fuel.
A purging method of a fuel cell system in accordance with an exemplary embodiment of the present invention includes disconnecting electrical connection between the fuel cell stack and a load, reducing an amount of the reformed gas that is being supplied to the fuel cell stack, opening a supplying valve for controlling supply of the reformed gas to the fuel cell stack and a bypass valve installed on a bypass line and closing a recovery valve for controlling discharge of the reformed gas recovered from the fuel cell stack, and filling the fuel cell stack with carbon dioxide by consuming hydrogen in the fuel cell stack.
In the filling of the fuel cell stack with the carbon dioxide, the consumption of the hydrogen may be realized by a voltage reducing unit connected to the fuel cell stack. In the filling of the fuel cell stack with the carbon dioxide, the hydrogen may be consumed until a cell voltage of the fuel cell stack becomes 0.5V or less.
In the reducing of the amount of the reformed gas, the reformed gas may be reduced to 1/3-1/5, and preferably 1/4, of the amount of reformed gas present in normal operation. A purging method of a fuel cell system in accordance with another exemplary embodiment of the present invention includes a) disconnecting electrical connection between the fuel cell stack and a load, b) reducing the amount of reformed gas that is being supplied to the fuel cell stack, c) opening a
supplying valve installed at an inlet of the fuel cell stack and closing a bypass valve installed on a bypass line and a recovery valve installed at an outlet of the fuel cell stack, d) opening the bypass valve and closing the supplying valve, e) reducing internal pressure of the fuel cell stack by consuming hydrogen contained in the reformed gas in the fuel cell stack, f) repeating steps c) to e) when a maximum cell voltage of the fuel cell stack is compared with a reference voltage and determined to be greater than the reference voltage, and g) closing the supplying valve when the maximum cell voltage is equal to or less than the reference voltage. In step e), the consumption of the hydrogen may be realized by a voltage reducing unit connected to the fuel cell stack. In step d), when the pressure of the reformed gas in the fuel cell stack is 8-15kPa, the bypass valve may be opened and the supplying valve may be closed.
In step e), the hydrogen may be consumed until a pressure of the reformed gas in the fuel cell stack is reduced to 1-3kPa and the reference voltage may be 0.5V. [Advantageous Effects]
As described above, the fuel cell stack can be purged by carbon dioxide contained in the reformed gas without using nitrogen. Therefore, no nitrogen container for storing nitrogen is necessary and thus the manufacturing cost can be reduced. Particularly, since there is no need to provide separate purging equipment, the fuel cell system for an electronic device can be easily designed. [Brief Description of the Drawings]
FIG. 1 is a schematic diagram of a fuel cell system according to a first exemplary embodiment of the present invention.
FIG. 2 is a flowchart illustrating a purging method for a fuel cell system according to a first exemplary embodiment of the present invention. FIG. 3 is a flowchart illustrating a purging method for a fuel cell system according to a second exemplary embodiment of the present invention. [Mode for the Invention]
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.
FIG. 1 is a schematic diagram of a fuel cell system according to a first exemplary embodiment of the present invention. Referring to FIG. 1 , a fuel cell system in accordance with the present exemplary embodiment may employ a polymer electrolyte membrane fuel cell (PEMFC) that generates hydrogen by reforming a fuel, and generates electrical energy through an electrochemical reaction between oxygen and hydrogen.
A hydrocarbon-based fuel that is in a liquid-phase or gas-phase state such as methanol, ethanol, natural gas, LPG, and the like is generally used as the fuel in the fuel cell system.
The oxygen used in the fuel cell system and reacting with the hydrogen may be stored in a separate storing unit.
The fuel cell system in accordance with the present exemplary embodiment includes a reformer 110 generating a reformed gas using the fuel, a fuel cell stack 210 connected to the reformer 110 and generating electric power using the reformed gas and oxidizing agent, a valve unit 320 for controlling the connection of the reformer 110 to the fuel cell stack 210, and a load 230 and voltage reducing unit 220 that are connected to the fuel cell stack 210.
The reformer 110 is a fuel processing unit that generates the hydrogen gas by reforming the fuel and supplies the hydrogen gas to the fuel cell stack 210. A fuel tank 120 for supplying the fuel, an air pump 140 for supplying the air, and a water tank 130 for supplying water are connected to the reformer.
The reformer 110 generates heat using the supplied fuel, and further generates the reformed gas containing a large amount of hydrogen from the fuel through an oxidizing reaction using the generated heat. The reformed gas is directed to the fuel cell stack 210 through a supplying line 312 between the fuel cell stack 210 and the reformer 110. The fuel cell stack 210 in accordance with the present exemplary embodiment is typically structured to have a plurality of fuel cells (not shown) stacked on one other, and generates the electric power through an oxidation-reduction reaction. A variety of different structures of fuel cell stacks can be applied to the fuel cell system of the present invention. That is, the fuel cell stack 210 of the present invention is not limited to a specific structure.
The fuel cell stack 210 is supplied with the reformed gas and the air
containing the oxygen through the air pump 250 connected to the fuel cell stack 210. The fuel cell stack 210 generates the electrical energy by allowing the oxygen contained in the air to react with the hydrogen contained in the reformed gas. The fuel cell stack 210 includes fuel cells, each of which is a minimum unit for generating the electric energy. The fuel cells may be formed by disposing separators on opposite surfaces of a membrane electrode assembly (MEA). A pressure gage 270 for measuring pressure of the reformed gas in the fuel cell stack 210 is installed at an inlet 212 of the fuel cell stack 210 that is connected to the supplying line 312.
The load 230 consuming the electric energy generated by the fuel cell stack 210 is electrically connected to the fuel cell stack 210. The load 230 may include a variety of electric devices such as a motor for a vehicle, an inverter for converting a direct current into an alternating current, or a home electric heating device.
Further, the voltage reducing unit 220 is connected to the fuel cell stack 210. The voltage reducing unit 220 functions to consume electrical energy when the fuel cell stack 210 is purged.
The voltage reducing unit 220 in accordance with the present exemplary embodiment is a device that applies a minute load to each fuel cell. The voltage reducing unit operates by the operation of a voltage reducing circuit as circuits formed with a bundle of four unit cells are connected in series, and simultaneously operates when an operation command signal is input and a
current is applied to photodiodes of photocouplers connected in series to conduct internal transistors of the photocouplers.
Meanwhile, a recovery line 314 connecting an outlet 214 of the fuel cell stack 210 to the reformer 110 and a bypass line 316 connecting the recovery line 314 to the supplying line 312 are further installed between the reformer 110 and the fuel cell stack 210 to recover non-reacted reformed gas that is not consumed in the fuel cell stack 210.
The valve unit 320 for controlling opening/closing of the lines is installed on the lines. The valve unit 320 includes a supplying valve 321 installed on the supplying line 312, a recovery valve 323 installed on the recovery line 314, and a bypass valve 325 installed on the bypass line 316.
The bypass line 316 is closer to the reformer 110 than the supplying valve 321 and the recovery valve 323. Therefore, the reformed gas from the reformer 110 can be returned to the reformer 110 through the bypass line 316 even when the supplying valve 321 and the recovery valve 323 are closed.
The valves 321 , 323, and 325 may be solenoid valves.
FIG. 2 is a flowchart illustrating a purging method for a fuel cell system according to a first exemplary embodiment of the present invention.
Referring to FIG. 2, a hydrocarbon-based fuel such as LNG, LPG, and the like are used as a fuel of the present exemplary embodiment. The reformed gas attained by reforming the hydrocarbon includes hydrogen (H 2 ) at about 70-75%, carbon dioxide (CO 2 ) at about 20%, and other gases such as nitrogen.
According to the present exemplary embodiment, instead of supplying nitrogen gas that is an inert gas to the fuel cell stack 210 to purge the hydrogen gas in the fuel cell stack 210, the carbon dioxide gas contained in the reformed gas is filled in the fuel cell stack 210. To achieve the above, a purging method for the fuel cell system in accordance with the present exemplary embodiment includes the steps of disconnecting electrical connection between the fuel cell stack 210 and the load 230 (S201), reducing an amount of the reformed gas that is being supplied to the fuel cell stack 210 (S202), opening the supplying and bypass valves 321 and 325 and closing the recovery valve 323 (S203), filling the fuel cell stack 210 with carbon dioxide while consuming the hydrogen in the fuel cell stack (S204), closing the supplying valve (S205), and stopping the operation of the fuel cell system (S206).
In step S202 of reducing the amount of the reformed gas that is being supplied to the fuel cell stack 210, the amount of the reformed gas that is being supplied to the fuel cell stack 210 can be reduced to 1/3-1/5, and preferably 1/4, of the amount of reformed gas present in normal operation.
The reduction amount of the reformed gas is determined depending on capacity of the voltage reducing unit 220. That is, as the power consumption of the voltage reducing unit 220 increases, the supplying amount of the reformed gas increases. As the power consumption of the voltage reducing unit 220 is reduced, the supplying amount of the reformed gas is reduced.
In S203, when the supplying and bypass valves 321 and 325 are
opened and the recovery valve 323 is closed, a predetermined amount of the reformed gas is introduced into the fuel cell stack 210 and the rest of the reformed gas is directed to the reformer 110 along the bypass line 316. In this state, when the voltage reducing unit 220 is operated, the hydrogen contained in the reformed gas introduced into the fuel cell stack 210 is consumed by the voltage reducing unit 220. At this point, since the recovery valve 323 is closed, the carbon dioxide contained in the reformed gas is filled in the fuel cell stack 210.
Meanwhile, when a relatively large amount of the reformed gas is supplied to the fuel cell stack 210 in a state where the recovery valve 323 is closed, the internal pressure of the fuel cell stack 210 may be excessively increased. Therefore, the bypass line 316 and the bypass valve 325 are installed to allow the reformed gas to bypass through the bypass line 316 when the internal pressure of the fuel cell stack 210 increases above a predetermined level.
When the filling of the carbon dioxide is completed, the supplying valve 321 is closed to stop the reformed gas from being introduced into the fuel cell stack 210. As the amount of carbon dioxide in the fuel cell stack 210 increases, the amount of hydrogen gas is relatively reduced and thus the cell voltage is gradually reduced. Step S204 is continued until the cell voltage becomes 0.5V, after which the supplying valve is closed.
In accordance with the present exemplary embodiment, since the carbon dioxide contained in the reformed gas is used to purge the oxygen in the
fuel cell stack during the stopping of the operation of the fuel cell system, no separate nitrogen storing tank is required. Therefore, the manufacturing cost of the fuel cell system is reduced and the volume and weight of the fuel cell system can be reduced. FIG. 3 is a flowchart illustrating a purging method for a fuel cell system according to a second exemplary embodiment of the present invention.
Referring to FIG. 3, a purging method for a fuel cell system in accordance with the present exemplary embodiment includes the steps of disconnecting electrical connection between the fuel cell stack 210 and the load 230 (S301), reducing an amount of the reformed gas that is being supplied to the fuel cell stack 210 (S302), opening the supplying valve 321 and closing the recovery and bypass valves 323 and 325 (S303), closing the supplying valve 321 and opening the bypass valve 325 (S304), reducing internal pressure of the fuel cell stack 210 by consuming the hydrogen in the fuel cell stack (S305), repeating steps S303 to S305 when cell voltage is greater than a reference voltage (S306), closing the supplying valve 321 when the cell voltage is equal to or less than the reference voltage (S307), and stopping the operation of the fuel cell system (S308).
In step S302, the amount of the reformed gas that is being supplied to the fuel cell stack 210 can be reduced to 1/3-1/5, and preferably 1/4, of the amount of reformed gas present in normal operation.
In step S303, when the reformed gas is supplied to the fuel cell stack 210 in a state where the recovery valve 323 is closed, the internal pressure of
the fuel cell stack 210 increases. Therefore, the pressure of the reformed gas in the fuel cell stack 210 is measured, and when it is determined that the pressure of the reformed gas increases to the reference pressure, the supplying valve 321 is closed and the bypass valve 325 is opened. When the pressure of the reformed gas in the fuel cell stack 210 is 8-15kPa, the supplying valve 321 is closed and the bypass valve 325 is opened. The reference pressure of the reformed gas in the fuel cell stack 210 is determined within the above range in accordance with the size and structure of the fuel cell stack 210.
In step S304, when the supplying valve 321 is closed and the bypass valve 325 is opened, the supply of the reformed gas to the fuel cell stack 210 is stopped and the reformed gas is returned to the reformer 110 through the bypass line 316.
In step S305, the hydrogen in the fuel cell stack 210 is consumed until the internal pressure of the fuel cell stack 210 becomes 1-3kPa. Additionally, as the consumption of the hydrogen in the fuel cell stack
210 increases, the cell voltage is lowered. Therefore, the process for consuming the hydrogen may be performed with reference to the cell voltage. That is, the hydrogen in the fuel cell stack 210 may be continuously consumed until the cell voltage becomes 0.5-0.3V. Therefore, as alternatives, the consumption of the hydrogen may be maintained until the internal pressure of the fuel cell stack becomes 1-3kpa or the cell voltage becomes 0.5-0.3V.
When the cell voltage is greater than the reference voltage in the course of consuming the hydrogen, steps S303-S305 are repeated to fill the fuel cell
stack 210 with the carbon dioxide.
As the reference voltage is set to be 0.5V, when the maximum cell voltage becomes 0.5V or less during the repeating of steps S303-S305, the supplying valve is closed and the fuel cell system stops operation. According to the present exemplary embodiment, as the processes for supplying the reformed gas to the fuel cell stack 210 and consuming the hydrogen are repeated, the hydrogen in the fuel cell stack can be removed while the carbon dioxide is filled in the fuel cell stack.
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.