JP2005268180A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system with improved comprehensive fuel consumption efficiency by saving the energy for warming the fuel cell system. <P>SOLUTION: The fuel cell system 1 is provided with an antifreezing fluid container 19 that can be adhered/separated to/from the fuel cell stack 2 provided with a solid polymer electrolyte. A control unit 23 controls an oil pressure cylinder 20, and when starting the fuel cell system 1, it separates the antifreezing fluid container 19 from the fuel cell stack 2, and when the temperature of the fuel cell stack exceeds a prescribed temperature, the antifreezing fluid container 19 is adhered to the fuel cell stack 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system provided with a solid polymer electrolyte.

  A fuel cell is a power generator that directly converts chemical energy of a fuel into electric energy by electrochemically reacting a fuel such as hydrogen as a reaction gas with an oxidant such as air. This fuel cell is classified according to the type of electrolyte used and the fuel. As one of them, a solid polymer electrolyte fuel cell using a solid polymer electrolyte as an electrolyte is known.

  The electrode reaction that proceeds at both the fuel electrode and the oxidant electrode of the solid polymer electrolyte fuel cell is as follows.

(Chemical formula 1)
Fuel electrode: 2H ₂ → 4H ⁺ + 4e ⁻ (1)
Oxidant electrode: 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O (2)
When fuel is supplied to the fuel electrode, the reaction formula (1) proceeds and hydrogen ions are generated at the fuel electrode. The hydrogen ions permeate (diffuse) through the solid polymer electrolyte membrane in a hydrated state to reach the oxidant electrode, and the electrons reach the oxidant electrode through an external circuit. When an oxygen-containing gas such as air is supplied to the oxidant electrode, the reaction formula (2) proceeds at the oxidant electrode. When the electrode reactions (1) and (2) proceed at each electrode, the fuel cell generates an electromotive force.

  Since the hydrogen ion conductivity of the solid polymer electrolyte utilizes hydrogen ion diffusion in a hydrated state, the hydrogen ion mobility decreases at low temperatures, and when water freezes below freezing point, it does not function as an electrolyte.

In order to start such a solid polymer electrolyte fuel cell in a low-temperature environment, a fuel gas is burned by a combustor, and an antifreeze heated by the combustion heat is caused to flow through a coolant flow path in the fuel cell stack. Methods for heating the stack are known. Moreover, the fuel cell stack is also heated from the outside by circulating the exhaust gas from combustion around the fuel cell stack (Patent Document 1).
JP 2000-164233 A (page 7, FIG. 1)

  However, in the above prior art, since the fuel cell stack is heated by chemically burning the fuel gas for power generation, there is a problem that the fuel efficiency of the fuel cell system is deteriorated.

  In order to solve the above-mentioned problems, the present invention provides a polymer electrolyte membrane, a membrane electrode assembly comprising a fuel electrode and an oxidant electrode sandwiching the polymer electrolyte membrane, and supplies fuel and an oxidant to the membrane electrode assembly. In a fuel cell system including a fuel cell stack in which a plurality of fuel cells each having a separator having a flow path are stacked, an antifreeze liquid container containing an antifreeze liquid having a freezing point of less than 0 ° C. is disposed around the fuel cell stack. The gist of the invention is to bring the antifreeze container into close contact with the fuel cell stack.

  According to the present invention, an antifreeze liquid container containing an antifreeze liquid having a freezing point lower than 0 ° C. is arranged around the fuel cell stack, so that the temperature drop rate after the fuel cell operation is stopped is reduced, and the fuel cell is restarted at the time of restart. The energy for warming up the system can be saved, and the overall fuel efficiency of the fuel cell system can be improved.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, when the fuel cell system is started, raising the temperature of the fuel cell stack to a temperature suitable for operation (for example, 80 [° C.]) is called warming up.

  FIG. 7 is a schematic cross-sectional view showing a structural example of a fuel cell in a solid polymer electrolyte fuel cell to which the present invention is applied. In FIG. 7, a fuel cell 101 as a unit of a fuel cell includes a membrane electrode assembly 105, a fuel electrode gas diffusion layer 106 and an oxidant electrode gas diffusion layer 107 that sandwich the membrane electrode assembly 105 from both sides. , Separators 108 and 110 having fuel gas passages 109 and oxidant gas passages 111 for supplying fuel gas and oxidant gas from the outside are provided.

  The membrane electrode assembly 105 includes a polymer electrolyte membrane 102 made of a solid polymer membrane having hydrogen ion (proton) conductivity, such as a fluorine resin, and platinum (Pt) formed on both sides of the polymer electrolyte membrane 102. ) And the like, and a oxidant electrode 104 having a reaction catalyst.

  The separators 108 and 110 are made of a dense carbon material that is impermeable to gas, respectively, and a large number of ribs are arranged on one side or both sides thereof, so that the fuel gas passage 109 and the oxidant gas passage 111 are respectively formed. Forming. Oxidant gas and fuel gas are respectively supplied from a gas inlet (not shown) and discharged from a gas outlet.

  FIG. 1 is a system configuration diagram illustrating a schematic configuration of an embodiment of a fuel cell system according to the present invention. 1, a fuel cell system 1 includes a fuel cell stack 2 in which a plurality of polymer electrolyte fuel cells as shown in FIG. 7 are stacked, and a fuel gas (hydrogen-containing) supplied from a fuel supply source outside the figure. Gas) through the humidifier 7 or directly to the fuel supply line 9 and the humidifier with the oxidant gas (oxygen-containing gas, air) supplied from an oxidant supply source (not shown). 8 or directly to the oxidant supply line 10, the three-way valves 5 and 6, the fuel supply line 9 for supplying fuel and oxidant to the fuel cell stack 2, the oxidant supply line 10, and the fuel cell stack, respectively. 2, a fuel discharge line 11 for discharging fuel and an oxidant, an oxidant discharge line 12, a fuel pressure difference detecting means 13 for detecting a pressure difference between the fuel inlet and the fuel outlet of the fuel cell stack 2, The oxidant pressure difference detecting means 14 for detecting the pressure difference between the oxidant inlet and the oxidant outlet of the fuel cell 2, the ambient temperature sensor 15 for detecting the ambient temperature of the fuel cell stack 2, and the resistance value of the fuel cell stack 2 Resistance value measuring means 16 for measuring, resistance value measuring electrode 17 provided in the fuel cell stack 2 for measuring the resistance value by the resistance value measuring means, and fuel cell stack temperature sensor 18 for detecting the temperature of the fuel cell stack 2 An antifreeze liquid container 19 that can be brought into close contact / separation with the fuel cell stack 2, a hydraulic cylinder 20 that makes the antifreeze liquid container 19 and the fuel cell stack 2 come into close contact with each other, and an antifreeze liquid pump that circulates the antifreeze liquid into the coolant passage of the fuel cell stack. 21, an antifreeze liquid tank 22 for storing the antifreeze liquid, and a control unit 23 for controlling the entire fuel cell system.

  The antifreeze container 19 is a container containing a liquid having a freezing point of less than 0 [° C.], and this liquid is ethylene glycol or methyl alcohol (methanol) or an aqueous solution thereof. When the antifreeze solution is an aqueous solution of ethylene glycol or methyl alcohol, it is preferable to adjust the concentration so that the aqueous solution does not freeze in the environment where the fuel cell system 1 is used.

  When the antifreeze solution is an aqueous solution of ethylene glycol, it can be used in common with the fuel cell stack 2 or a cooling liquid of a power control system (not shown), and it is not necessary to provide a separate tank, thereby preventing an increase in the size of the fuel cell system. .

  When the antifreeze is an aqueous solution of ethyl alcohol, a fuel reforming fuel cell using alcohol as a fuel can be used in common with a fuel tank, eliminating the need for a separate tank and preventing an increase in the size of the fuel cell system. be able to.

  The resistance value measuring means 16 applies an alternating current from a resistance value measuring electrode 17 provided on each of the anode (negative electrode) and cathode (positive electrode) of a certain cell of the fuel cell stack 2 or a plurality of cells, and Information for determining the wetness of the solid polymer electrolyte membrane of the cell is obtained by measuring the AC resistance value. It can be determined that the wetness of the solid polymer electrolyte membrane is low if the resistance value is high, and the wetness of the solid polymer electrolyte membrane is high if the resistance value is low.

  The control unit 23 is connected with a fuel pressure difference detecting means 13, an oxidant pressure difference detecting means 14, an ambient temperature sensor 15, a resistance value measuring means 16, and a fuel cell stack temperature sensor 18 as input devices. ing.

  The control unit 23 is connected with three-way valves 3, 4, 5, 6 and a hydraulic cylinder 20 as output devices.

  Then, the control unit 23 is based on information input from the fuel pressure difference detection means 13, the oxidant pressure difference detection means 14, the ambient temperature sensor 15, the resistance value measurement means 16, and the fuel cell stack temperature sensor 18. The three-way valves 3, 4, 5, and 6 are controlled to control the supply of humidified fuel gas and oxidant gas or non-humidified dry fuel gas and oxidant gas to the fuel cell stack 2, and hydraulic pressure. By outputting the valve control signal of the cylinder 20 and controlling the expansion and contraction of the hydraulic cylinder 20, the antifreeze liquid container 19 is brought into close contact with the fuel cell stack 2 or separated.

  Although not particularly limited, in this embodiment, the control unit 23 is composed of a microprocessor having a CPU, a program ROM, a working RAM, and an input / output port. This is achieved by the CPU executing the control program.

  If the antifreeze container 19 is kept in close contact with the fuel cell stack 2 when the operation of the fuel cell system is stopped, the temperature drop rate of the fuel cell stack 2 decreases due to the heat capacity of the antifreeze container 19, and the fuel cell is restarted when the fuel cell system is restarted. The range of temperature rise due to warming up of the stack 2 is reduced, energy required for warming up can be saved, and the overall fuel efficiency of the fuel cell system can be improved.

  The fuel cell system 1 includes an electric hydraulic pump (not shown) that is driven by power of a secondary battery that is an auxiliary power source of the fuel cell, and hydraulic pressure from the electric hydraulic pump is supplied to the hydraulic cylinder 20. Shall.

  FIG. 2 is a conceptual diagram for explaining the state of (a) contact and (b) separation between the fuel cell stack and the antifreeze container. In the figure, the antifreeze liquid container 19 is divided into two antifreeze liquid containers 19a and 19b that are bent substantially at right angles so as to be in contact with two adjacent surfaces of the substantially rectangular parallelepiped fuel cell stack 2, for example. And between the both ends of the antifreeze liquid containers 19a and 19b, hydraulic cylinders 20a and 20b for expanding and contracting the distance between the two antifreeze liquid containers are provided, and at the center of each antifreeze liquid container 19a and 19b, the hydraulic cylinders are respectively provided. 20d and 20c are provided.

  As shown in FIG. 2 (a), when the fuel cell stack 2 and the antifreeze liquid containers 19a and 19b are brought into close contact with each other, the hydraulic cylinders 20a and 20b are contracted and the hydraulic cylinders 20c and 20d are extended to thereby increase the antifreeze liquid container 19a. , 19b is brought into close contact with the fuel cell stack 2.

  By bringing the antifreeze liquid containers 19a and 19b into close contact with the fuel cell stack 2, the temperature decrease rate of the fuel cell stack 2 after operation stop is reduced, and by separating the antifreeze liquid containers 19a and 19b from the fuel cell stack 2 at the time of restarting, It is possible to reduce the temperature rise of the fuel cell stack 2 during warm-up and save energy for warm-up.

  On the contrary, when the fuel cell stack 2 and the antifreeze containers 19a and 19b are separated, as shown in FIG. 2B, the hydraulic cylinders 20c and 20d are contracted and the hydraulic cylinders 20a and 20b are extended, The antifreeze containers 19 a and 19 b are separated from the fuel cell stack 2. By arranging a plurality of the hydraulic cylinders 20a to 20d in the stacking direction of the fuel cells, it is possible to more effectively adhere and separate.

  As described above, the antifreeze liquid containers 19a and 19b and the fuel cell stack 2 can be brought into close contact with each other. Therefore, when the fuel cell stack 2 is warmed up, the antifreeze liquid containers 19a and 19b are separated from the fuel cell stack 2 and Since only the fuel cell stack 2 can be warmed up without warming up 19a, 19b, the warm-up time is not extended.

  The portions of the antifreeze liquid containers 19a and 19b that contact the fuel cell stack 2 have sufficient rigidity, and the rigidity of the portion that does not contact the fuel cell stack 2 is lower than the rigidity of the contact portion. Thereby, even if the ambient temperature below the antifreeze liquid freezing temperature continues for a long time and the antifreeze liquid in the antifreeze liquid container 19 may freeze, the increase in volume due to the freezing expansion of the antifreeze liquid can push the rigidity-decreasing part, The highly rigid portion can maintain the shape. Therefore, stress due to freezing and expansion does not act on the fuel cell stack 2, and deterioration of the fuel cell stack can be prevented.

  Although not shown, if the gas discharged from the fuel cell stack 2 is made to circulate around the antifreeze liquid containers 19a and 19b, the antifreeze liquid containers 19a and 19b can be warmed by the exhaust of the fuel cell stack, and the next operation is performed. Can be prepared for a stop.

  FIG. 3 is a conceptual diagram showing a method of changing the amount of antifreeze liquid in the antifreeze liquid container. The antifreeze liquid containers 19a and 19b communicate with the antifreeze liquid tank 22 through a pipe (not shown). A plate 24 having a plurality of hydraulic cylinders 25 is provided outside the antifreeze liquid containers 19 a and 19 b arranged around the fuel cell stack 2. When reducing the amount of liquid in the antifreeze liquid containers 19a and 19b, each hydraulic cylinder 25 is extended and the plate 24 is pressed against the antifreeze liquid containers 19a and 19b, thereby transferring the antifreeze liquid in the antifreeze liquid containers 19a and 19b to the antifreeze liquid tank 22. The amount of liquid can be reduced. On the contrary, when increasing the amount of liquid in the antifreeze liquid containers 19a and 19b, the antifreeze liquid is sent from the antifreeze liquid pump 21 into the antifreeze liquid containers 19a and 19b.

  Next, with reference to the flowchart of FIG. 4, the control content implemented at the time of fuel cell system operation stop operation by the control unit 23 of a present Example is demonstrated. When the process of this flowchart starts, the antifreeze container 19 is in close contact with the fuel cell stack 2 and is capable of transferring heat to each other.

  First, in step (hereinafter, step is abbreviated as S) 10, whether the ambient temperature of the fuel cell stack detected by the ambient temperature sensor 15 in FIG. 1 is read and measured, and the dry purge and antifreeze liquid container volume operation are performed. Judge whether or not. If the ambient temperature of the fuel cell stack is 0 [° C.] or higher, the operation for stopping the operation is terminated without performing the dry purge and the liquid volume operation, and if it is 0 [° C.] or lower, the process proceeds to the next S12.

  In S12, for each of the fuel and the oxidant, the pressure difference between the inlet and outlet of the fuel cell stack in the fuel and oxidant supply / discharge lines detected by the fuel pressure difference detection means 13 and the oxidant pressure difference detection means 14 in FIG. ΔP (a fuel pressure difference ΔPf and an oxidizer pressure difference ΔPo are collectively referred to as ΔP) is detected. Next, in S14, it is determined whether any of detected ΔP exceeds the second predetermined value ΔPc.

  Here, the second predetermined value ΔPc is the pressure difference ΔPc between the inlet and outlet of the fuel cell stack 2 determined based on the result of the water clogging experiment in the fuel or oxidant gas flow path inside the fuel cell stack 2. , ΔPc or less, it is a value that does not cause deterioration of the fuel cell stack even if the residual moisture in the gas flow path is frozen.

  If any of ΔP exceeds ΔPc, the process proceeds to S16, and if neither exceeds, the process proceeds to S22.

  In S16, the three-way valves 3, 4, 5 and 6 are switched to bypass the humidifiers 7 and 8, and the fuel gas and oxidant gas dried from the fuel supply source and the oxidant supply source (these are collectively referred to as dry gas). ) To the fuel cell stack 2 and the process proceeds to S18. Thereby, dry purge is performed to discharge moisture remaining in the gas flow path in the fuel cell stack 2 to the outside of the fuel cell stack. Thereby, liquid water does not remain inside the fuel cell stack, stress due to freezing and expansion of liquid water inside the fuel cell stack 2 does not occur, and deterioration of the fuel cell stack 2 can be prevented.

  If it is determined in S14 that ΔP does not exceed ΔPc, the supply of fuel and oxidant gas is stopped in S22, and the process proceeds to the next S24.

  In S18, the detection values of the fuel pressure difference detection means 13 and the oxidant pressure difference detection means 14 are read, and the process waits until both ΔP becomes less than ΔPc. When both ΔP are less than ΔPc, the process proceeds to S20 and the supply of dry gas is stopped.

  Next, in S24, the resistance value of the fuel cell stack 2 is detected by the resistance value measuring means 16 of FIG. Next, in S26, the detected values of the ambient temperature sensor 15 and the fuel cell stack temperature sensor 18 are read, and the temperature difference between the fuel cell stack temperature and the ambient temperature is calculated.

  Next, in S28, the amount of antifreeze in the antifreeze container 19 is determined based on the resistance value of the fuel cell stack 2 and the temperature difference between the fuel cell stack temperature and the ambient temperature of the fuel cell stack. Here, the larger the resistance value of the fuel cell stack 2, the smaller the amount of antifreeze liquid, and the larger the temperature difference, the larger the amount of antifreeze liquid may be determined.

  For example, as shown in FIG. 6, there is a map of (a) the amount of antifreeze with respect to the stack resistance value, and (b) the amount of antifreeze with respect to the temperature difference, and the final amount of antifreeze is obtained by the sum of the values obtained from both maps. Can be determined.

  The map of the antifreeze amount with respect to the stack resistance value in FIG. 6A shows that the lower the resistance value of the fuel cell stack 2, the more the antifreeze amount. As a result, the greater the amount of water in the fuel cell stack 2 that is likely to freeze, the greater the amount of antifreeze liquid, and the lowering of the temperature of the fuel cell stack after operation stop can be reduced.

  In the map of the antifreeze amount with respect to the temperature difference in FIG. 6 (b), the larger the temperature difference between the fuel cell stack temperature and the ambient temperature, the greater the antifreeze amount and the amount of heat dissipated in proportion to the temperature difference. Thus, it is possible to increase the amount of antifreeze in the antifreeze container that is in close contact with the fuel cell stack.

  Alternatively, a stack resistance value and a temperature difference may be used as two variables, and a three-dimensional map for obtaining an antifreeze amount as a function of these two variables may be used. Thereby, the coagulation latent heat of antifreeze can be used effectively. Finally, in S30, the amount of antifreeze in the antifreeze container 19 is adjusted to the determined amount.

  Next, with reference to the flowchart of FIG. 5, the contents of control performed when the fuel cell system is started up by the control unit 23 of the present embodiment will be described with reference to the flowchart of FIG. 5. When the process of this flowchart starts, the antifreeze container 19 is in close contact with the fuel cell stack 2 and is capable of transferring heat to each other.

  First, in S40, supply of fuel gas and oxidant gas to the fuel cell stack 2 is started and the fuel cell system is started. Then, in S42, the hydraulic cylinder 20 is operated to remove the antifreeze container 19 from the fuel cell stack 2. To separate. Thereby, when the fuel cell stack 2 is warmed up, the antifreeze container 19 is separated, so that only the fuel cell stack 2 can be quickly heated to a temperature suitable for operation.

  Next, the temperature Ts of the fuel cell stack is read from the fuel cell stack temperature sensor 18 in S44. Next, in S46, it is determined whether or not the fuel cell stack temperature Ts has exceeded a first predetermined value Tc (for example, Tc is a warm-up completion determination temperature, 80 [° C.]). If it is determined in S46 that the fuel cell stack temperature Ts does not exceed the first predetermined value Tc, the process returns to S44.

  If it is determined in S46 that the fuel cell stack temperature Ts exceeds the first predetermined value Tc, the process proceeds to S48, the antifreeze liquid container 19 is brought into close contact with the fuel cell stack 2, and the temperature of the low-temperature antifreeze liquid in the antifreeze liquid container 19 is increased. Or thaw frozen antifreeze. Hereinafter, the operation shifts to normal operation.

1 is a system configuration diagram illustrating a configuration of a fuel cell system according to the present invention. (A) The conceptual diagram explaining the state which closely_contact | adhered the antifreeze liquid container to the fuel cell stack, (b) The conceptual diagram explaining the state which isolate | separated the antifreeze liquid container from the fuel cell stack. It is a figure explaining the method to reduce the amount of antifreeze liquid in an antifreeze liquid container. 4 is a control flowchart at the time of operation stop operation in the fuel cell system according to the present invention. 4 is a control flowchart at the time of start-up in the fuel cell system according to the present invention. (A) Example of map showing amount of antifreeze liquid with respect to resistance value of stack, (b) Example of map showing amount of antifreeze liquid with respect to temperature difference between fuel cell stack temperature and ambient temperature. It is a schematic cross section of the fuel cell which comprises a fuel cell stack.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 2 ... Fuel cell stack 3, 4, 5, 6 ... Three-way valve 7, 8 ... Humidifier 9 ... Fuel supply line 10 ... Oxidant supply line 11 ... Fuel discharge line 12 ... Oxidant discharge line 13 ... Fuel pressure difference detection means 14 ... Oxidant pressure difference detection means 15 ... Ambient temperature sensor 16 ... Resistance value measurement means 17 ... Resistance value measurement electrode 18 ... Fuel cell stack temperature sensor 19 ... Antifreeze liquid container 20 ... Hydraulic cylinder 21 ... Antifreeze liquid pump 22 ... Antifreeze tank 23 ... Control unit

Claims (9)

A fuel cell having a polymer electrolyte membrane, a membrane electrode assembly comprising a fuel electrode and an oxidant electrode sandwiching the polymer electrolyte membrane, and a separator formed with a flow path for supplying fuel and oxidant to the membrane electrode assembly In a fuel cell system provided with a plurality of stacked fuel cell stacks,
An antifreeze container containing an antifreeze liquid having a freezing point of less than 0 ° C. is disposed around the fuel cell stack, and the antifreeze container is brought into close contact with the fuel cell stack. The fuel cell system according to claim 1, wherein the antifreeze is ethylene glycol or methanol or an aqueous solution thereof. The portion of the antifreeze container that does not contact the fuel cell stack has elasticity,
2. The fuel cell system according to claim 1, wherein a portion of the antifreeze container that contacts the fuel cell stack has higher rigidity than the stretchable portion. The fuel cell system according to claim 1, wherein the antifreeze container is separable from the fuel cell stack. Comprising temperature detecting means for detecting the temperature of the fuel cell stack;
The antifreeze container is separated from the fuel cell stack when starting the fuel cell system, and when the temperature of the fuel cell stack reaches a first predetermined value, the antifreeze container is again connected to the fuel cell stack. The fuel cell system according to claim 4, wherein the fuel cell system is closely attached to the fuel cell system. The fuel cell system according to claim 1, further comprising a mechanism for circulating exhaust gas discharged from the fuel cell stack around the antifreeze liquid container. Ambient temperature detection means for detecting the ambient temperature of the fuel cell stack;
Pressure difference detection means for detecting a pressure difference between a fuel inlet and a fuel outlet of the fuel cell stack and a pressure difference between an oxidant inlet and an oxidant outlet of the fuel cell stack, and
If the ambient temperature detected by the ambient temperature detection means is 0 ° C. or less and any pressure difference detected by the pressure difference detection means exceeds a predetermined value when the fuel cell is stopped, the fuel 2. The moisture remaining in the fuel and oxidant flow paths is discharged by performing a dry purge that purges the fuel and oxidant flow paths of the battery stack with a gas that is not humidified. Fuel cell system. Resistance value detecting means for detecting a resistance value of the fuel cell stack;
A tank for storing the antifreeze,
A mechanism for changing the amount of antifreeze liquid in the antifreeze liquid container based on the resistance value detected by the resistance value detecting means;
The fuel cell system according to claim 1, further comprising: A temperature difference detecting means for detecting a temperature difference between the temperature of the fuel cell stack and its ambient temperature, a tank for storing the antifreeze liquid, and a mechanism for changing the amount of the antifreeze liquid in the antifreeze liquid container,
2. The fuel cell system according to claim 1, wherein the amount of the antifreeze liquid in the antifreeze liquid container is changed based on the temperature difference detected by the temperature difference detection means.

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