JP5181857B2 - Reforming system - Google Patents

Description

  The present invention relates to a reforming system.

  A fuel cell is a device that generally obtains electric energy using hydrogen and oxygen as fuel. Since this fuel cell is excellent in terms of environment and can realize high energy efficiency, it has been widely developed as a future energy supply system.

  In order to generate fuel gas to be supplied to the fuel cell, a reformer for reforming the hydrocarbon fuel may be provided. This reformer can obtain a reformed gas by, for example, a reforming reaction between steam and hydrocarbon fuel. When this reforming reaction is used, it is necessary to control the amount of reforming water supplied to the reformer. For example, Patent Document 1 discloses a technique for controlling the supply amount of reforming water according to the detection value of a water vapor sensor.

JP 2003-212508 A

  However, the technique of Patent Document 1 does not take countermeasures for poor accuracy of the water vapor sensor. As a result, the control accuracy of the reforming water supply amount is lowered.

  An object of the present invention is to provide a reforming system capable of improving the control accuracy of the reforming water supply amount.

A reforming system according to the present invention includes a reformer that generates a reformed gas from a hydrocarbon fuel, a fuel cell that generates power using hydrogen contained in the reformed gas, and an anode off-gas of the fuel cell. A combustor that burns using oxygen contained in the cathode offgas, and an oxygen / water concentration sensor that is disposed downstream of the combustor and includes an oxygen ion conductive solid electrolyte and detects the water vapor concentration and the oxygen concentration according to the applied voltage. Downstream of the oxygen / water concentration sensor , a condensate water tank that stores at least a part of the condensate in the gas downstream of the reformer, a water level sensor that detects the water level of the condensate water tank , Based on the deviation between the integrated value obtained by integrating the detected value of the moisture concentration sensor for a predetermined time and the change in the water level obtained based on the detected value of the water level sensor, the amount of reforming water supplied to the reformer is determined. Control It is characterized in that and a supply amount control means.

  In the reforming system according to the present invention, even if the water concentration sensor has a poor accuracy, it was obtained based on the integrated value obtained by integrating the detected value of the water concentration sensor for a predetermined time and the detected value of the water level sensor. The supply amount of the reforming water is controlled according to the deviation from the water level change amount. Therefore, the reforming water supply amount can be appropriately controlled with respect to the hydrocarbon fuel amount.

The combustor may be a heating unit that applies heat to the reformer .

  According to the present invention, it is possible to improve the control accuracy of the amount of water supplied to the reformer.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a schematic diagram showing an overall configuration of a reforming system 100 according to a first embodiment of the present invention. As shown in FIG. 1, the reforming system 100 includes a control unit 10, a reformed fuel supply unit 20, a water supply unit 30, an air pump 40, a reformer 50, a fuel cell 60, and an oxygen / water concentration detector 70. .

  The reformed fuel supply unit 20 includes a reformed fuel tank 21, a fuel pump 22 and a pressure regulating valve 23. The water supply unit 30 includes a condensed water drain valve 31, a condensed water tank 32, a water level sensor 33, an ion exchanger 34, an evaporator 35, and a water metering valve 36. The reformer 50 includes a reforming unit 51 and a heating unit 52. The fuel cell 60 includes a cathode 61 and an anode 62.

  The control unit 10 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like. The control unit 10 controls each unit of the reforming system 100 based on detection results given from the water level sensor 33 and the oxygen / water concentration detector 70. Details will be described later.

  The reformed fuel tank 21 is a tank that stores hydrocarbon fuel for use as a reformed fuel. The fuel pump 22 is a pump that supplies the reformed fuel stored in the reformed fuel tank 21 to the pressure regulating valve 23 in accordance with an instruction from the control unit 10. The pressure regulating valve 23 is a valve that adjusts the pressure of the reformed fuel in accordance with an instruction from the control unit 10 and supplies the reformed fuel in an amount necessary for the reforming reaction in the reforming unit 51.

  The condensed water drain valve 31 is a valve for draining condensed water contained in the exhaust gas from the heating unit 52 to the condensed water tank 32 in accordance with instructions from the control unit 10. The condensed water tank 32 is a tank that stores condensed water. The water level sensor 33 is a sensor that detects the water level of the condensed water stored in the condensed water tank 32. The ion exchanger 34 is a device for removing impurities of condensed water stored in the condensed water tank 32. The evaporator 35 is a device for evaporating condensed water. The water metering valve 36 is a valve for supplying a necessary amount of water vapor to the reforming unit 51 in accordance with an instruction from the control unit 10.

  In the reforming unit 51, a reformed gas containing hydrogen is generated from the reformed fuel from the pressure regulating valve 23 and the water vapor from the water metering valve 36. First, a steam reforming reaction occurs between the hydrocarbon and the steam in the reformed fuel, and hydrogen and carbon monoxide are generated. Next, a part of the produced carbon monoxide reacts with water vapor to produce hydrogen and carbon dioxide.

  The reformed gas generated in the reforming unit 51 is supplied to the anode 62. At the anode 62, hydrogen in the reformed gas is converted into protons. Hydrogen that has not been converted into protons at the anode 62 and hydrocarbons, carbon monoxide, and water vapor that have not reacted in the reforming unit 51 are supplied to the heating unit 52 as anode offgas.

  The air pump 40 supplies a necessary amount of oxygen to the cathode 61 in accordance with instructions from the control unit 10. In the cathode 61, water is generated and electric power is generated from the protons converted in the anode 62 and oxygen in the air supplied to the cathode 61. The generated electric power is used for a load such as a motor (not shown). The generated water becomes water vapor by the heat generated in the fuel cell 60. The air that does not react with water vapor and protons generated at the cathode 61 is supplied to the heating unit 52 as cathode off-gas.

  In the heating unit 52, combustible components contained in the anode off gas are combusted by oxygen contained in the cathode off gas. The combustion heat generated by the combustion reaction in the heating unit 52 is used for the steam reforming reaction in the reforming unit 51. Exhaust gas generated by the combustion reaction is discharged to the outside through the condensed water drain valve 31.

  The oxygen / water concentration detector 70 is a sensor for detecting the oxygen concentration and the water concentration in the exhaust gas discharged from the heating unit 52. Details of the oxygen / water concentration detector 70 will be described below.

  FIG. 2 is a schematic cross-sectional view of the oxygen / water concentration detector 70. As shown in FIG. 2, the oxygen / water concentration detector 70 includes an anode 72 provided on one surface of an electrolyte 71, a cathode 73 provided on the other surface of the electrolyte 71, and a porous substrate 74 in which pores are formed. It has a structure arranged so as to cover the cathode 73. The electrolyte 71 is made of an oxygen ion conductive electrolyte, for example, zirconia. The anode 72 and the cathode 73 are made of platinum, for example. The porous substrate 74 is made of, for example, porous alumina.

The anode 72 and the cathode 73 form an external circuit through wiring. This external circuit is provided with a power source 75 and an ammeter 76. The power source 75 applies a positive voltage to the anode 72. This applied voltage is variable. When a voltage is applied to the anode 72 by the power source 75, oxygen becomes oxygen ions at the cathode 73 and conducts through the electrolyte 71 according to the following formula (1). In the anode 72, oxygen ions become oxygen molecules according to the following formula (2).
O ₂ + 4e ⁻ = 2O ²⁻ (1)
2O ²⁻ = O ₂ + 4e ⁻ (2)

  Since the amount of oxygen transported to the cathode 73 is governed by the pores of the porous substrate 74, the current generated by the reaction of the formulas (1) and (2) is the oxygen gas diffusion amount in the pores of the porous substrate 74. Determined by. This oxygen gas diffusion amount is determined by the oxygen concentration outside the porous substrate 74. From the above, the oxygen / water concentration detector 70 can acquire the oxygen concentration in the exhaust gas based on the detection result of the ammeter 76.

  Here, consider the case where the exhaust gas contains water vapor. In this case, when the voltage of the power source 75 is increased, oxygen ions generated by dissociation of water vapor are conducted through the electrolyte 71. Thereby, the current flowing through the external circuit increases. This increase width depends on the water vapor concentration in the exhaust gas.

  FIG. 3 is a diagram showing the relationship between the voltage and current of the power source 75 and the water vapor concentration in the exhaust gas when the oxygen concentration in the exhaust gas is constant. In FIG. 3, the horizontal axis indicates the voltage of the power source 75, and the vertical axis indicates the current detected by the ammeter 76. As shown in FIG. 3, the current is almost constant up to a voltage of about 0.7V. This is presumably because the dissociation of water vapor is not promoted at a low voltage. On the other hand, when the voltage is higher than 0.7V, the current increases. In this case, the increase width increases as the water vapor concentration increases.

  From the above, if the voltage of the power source 75 is controlled to 0.7 V or less, the oxygen concentration in the exhaust gas can be detected regardless of the water vapor concentration. Moreover, the water vapor | steam density | concentration in exhaust gas is detectable by making the voltage of the power supply 75 larger than 0.7.

FIG. 4 is a schematic diagram showing the flow of water content in the reforming system 100. Assuming that an ideal reforming reaction occurs when methane is used as the hydrocarbon fuel, 2 mol of water reacts with 1 mol of methane, resulting in 4 mol of hydrogen, as shown in the following formula (3). Generated. The 2 mol of water is supplied from the condensed water tank 32 as reforming water.
_{CH 4 + 2H 2 O → 4H} 2 + CO 2 (3)

When this hydrogen is completely oxidized by the power generation reaction in the fuel cell 60 and the combustion reaction in the heating unit 52, 4 mol of water is generated as shown in the following formula (4).
4H ₂ + 2O ₂ → 4H ₂ O (4)

  Further, the air supplied from the air pump 40 to the cathode 61 also contains moisture. The total of these moisture will be contained in the cathode off gas. The remaining moisture after deducting the device loss and the moisture removal due to the exhaust gas returns to the condensed water tank 32. In this case, if 2 mol of water returns to the condensed water tank 32, the water level in the condensed water tank 32 does not change. That is, the reformed water supplied from the condensed water tank 32 to the reforming unit 51 returns to the condensed water tank 32 again after a certain time delay.

  However, unless the proper amount of reforming water is supplied to the hydrocarbon fuel, the balance of the moisture loop in the reforming system 100 will not match. For example, if the reforming water supply amount is small with respect to the hydrocarbon fuel, the reforming reaction efficiency decreases, the moisture concentration in the cathode offgas decreases, and the amount of water supplemented by the condensed water drain valve 31 decreases. Thereby, the balance of the moisture loop in the reforming system 100 is not matched. On the other hand, if the amount of reforming water supplied is large relative to the hydrocarbon fuel, the cathode offgas contains more water than the amount of water supplemented by the condensate drain valve 31, and the amount of water released into the atmosphere increases. Thereby, the balance of the moisture loop in the reforming system 100 is not matched.

  Therefore, the reforming system 100 according to the present embodiment uses the oxygen / water concentration detector 70 to detect the oxygen concentration and the water vapor concentration in the exhaust gas, and to appropriately control the water supply amount to the reforming unit 51. To do. Hereinafter, the details will be described with reference to FIGS.

  FIG. 5 is a diagram showing an example of a flowchart for obtaining the oxygen concentration in the cathode off gas. This flowchart is executed periodically, for example, every 256 ms. As shown in FIG. 5, first, the control unit 10 controls the power supply 75 so that the voltage applied to the electrolyte 71 becomes the voltage v1 (step S1). This voltage v1 is a voltage that can avoid interference of water vapor concentration in the exhaust gas. In this embodiment, the voltage v1 is set to 0.4 V as an example.

  Next, the control part 10 determines whether time t_d passed (step S2). If it is not determined in step S2 that the time t_d has elapsed, the control unit 10 executes step S2 again. This time t_d is preferably a time until the output current of the oxygen / water concentration detector 70 is stabilized after the voltage of the power source 75 is controlled. In this embodiment, the time t_d is set to 128 ms as an example.

When it is determined in step S2 that the time t_d has elapsed, the control unit 10 acquires and stores the oxygen concentration O ₂ _v1 in the exhaust gas (step S3). In this case, the control unit 10 acquires the oxygen concentration based on the detection result of the ammeter 76. Since the oxygen concentration O _{2 —} v1 is a value obtained by avoiding the interference of the water vapor concentration, the oxygen concentration O _{2 —} v1 is equal to or close to the oxygen concentration in the exhaust gas.

  Next, the control unit 10 controls the power source 75 so that the voltage applied to the electrolyte 71 becomes the voltage v2 (step S4). This voltage v2 is a voltage within a range where interference of water vapor concentration in the exhaust gas is received. In this embodiment, the voltage v2 is set to 1.3 V as an example.

Next, the control part 10 determines whether time t_d passed (step S5). If it is not determined in step S5 that the time t_d has elapsed, the control unit 10 executes step S5 again. If it is determined that the time t_d has elapsed at step S5, the control unit 10 obtains the oxygen concentration _O 2 _v2, stores (step S6). Thereafter, the control unit 10 ends the execution of the flowchart.

According to the flowchart of FIG. 5, it is possible to detect the oxygen concentration O _{2 —} v 1 when avoiding the interference of water vapor in the cathode off-gas and the oxygen concentration O _{2 —} v ₂ when receiving the interference of water vapor.

FIG. 6 is a diagram illustrating an example of a flowchart for controlling the excess air ratio in the reforming unit 51 using the oxygen concentration O _{2 —} v1 obtained according to the flowchart of FIG. 5. This flowchart is executed, for example, in the same cycle as the reforming water supply cycle (for example, 256 ms) to the reforming unit 51 and at a timing different from the reforming water supply to the reforming unit 51.

As shown in FIG. 6, first, the control unit 10 obtains and stores the excess air ratio λ in the reforming unit 51 based on the oxygen concentration O _{2 —} v1 (step S11). The excess air ratio λ is the ratio of the combustible component in the anode off-gas to the stoichiometric air-fuel ratio. The relationship between the oxygen concentration O _{2 —} v 1 and the excess air ratio λ may be created in advance as a map. FIG. 7 shows an example of the relationship between the oxygen concentration O _{2 —} v 1 and the excess air ratio λ. For example, the excess air ratio λ increases as the oxygen concentration O _{2 —} v1 increases.

  Next, the control unit 10 determines whether or not the excess air ratio λ is equal to or less than the minimum value λmin (step S12). Here, the minimum value λmin is set to a value that can suppress incomplete combustion and suppress the NOx concentration below a predetermined value. The NOx concentration has a strong correlation with the flame temperature in the heating unit 52. FIG. 8 shows the relationship between the excess air ratio λ and the flame temperature in the heating unit 52. As shown in FIG. 8, when the excess air ratio λ is slightly smaller than 1.0, the flame temperature becomes the highest (the NOx concentration becomes the highest). The minimum value λmin is set so that the NOx concentration is not more than a desired value within a range larger than 1.0.

When it is determined in step S12 that the excess air ratio λ is equal to or less than the minimum value λmin, the control unit 10 determines the cathode air flow rate Qa according to the following equation (3) and controls the air pump 40. In this case, the excess air ratio λ increases.
Qa = Qf · λ_trg + Qa_fb (3)

  Here, Qf represents the anode fuel flow rate, λ_trg represents the control target value of the excess air ratio λ, and Qa_fb represents the corrected cathode air flow rate. The anode fuel flow rate Qf can be obtained from the command value to the pressure regulating valve 23 and can also be obtained from the generated current of the fuel cell 60. The corrected cathode air flow rate can be preset as an increment of the cathode air flow rate.

Next, the control unit 10 determines whether or not the excess air ratio λ is equal to or greater than the maximum value λmax (step S14). The maximum value λmax is set in a range where no misfire occurs in the heating unit 52. When it is determined in step S14 that the excess air ratio λ is equal to or greater than the maximum value λmax, the control unit 10 determines the cathode air flow rate Qa according to the following equation (4) and controls the air pump 40. In this case, the excess air ratio λ decreases.
Qa = Qf · λ_trg−Qa_fb (4)

  Thereafter, the control unit 10 ends the execution of the flowchart. When it is not determined in step S12 that the excess air ratio λ is equal to or less than the minimum value λmin, the control unit 10 executes step S14. On the other hand, if it is not determined in step S14 that the excess air ratio λ is greater than or equal to the maximum value λmax, the control unit 10 ends the execution of the flowchart.

  According to the flowchart of FIG. 6, the excess air ratio λ can be set so that the NOx concentration can be controlled to a predetermined value or less and misfire in the heating unit 52 can be suppressed.

  Here, the relationship among the control target value λ_trg, the minimum value λmin, and the maximum value λmax is shown in FIG. In FIG. 9, the horizontal axis represents the power generation load of the fuel cell 60, and the vertical axis represents the excess air ratio λ. As shown in FIG. 9, the minimum value λmin is set to a value larger than 1.0 in order to allow a control error and further reduce the NOx concentration. The maximum value λmax is set to a value smaller than the combustion limit (for example, “5”) in order to provide a margin for control error.

FIG. 10 is a diagram illustrating an example of a flowchart for feedback control of the water level in the condensed water tank 32. This flowchart is executed periodically, for example, every 256 ms. As shown in FIG. 10, the control unit 10 reads the oxygen concentration O ₂ —v1 and the oxygen concentration O ₂ —v2 stored when the flowchart of FIG. 5 is executed (step S21). Next, the control unit 10 reads the anode fuel flow rate Qf and the excess air ratio λ used when the flowchart 6 is executed (step S22).

Next, the control unit 10 obtains the instantaneous moisture amount dQs_O ₂ detected by the oxygen / water concentration detector 70 using the following equation (5) (step S23).
dQs_O ₂ = (O ₂ —v ₂ —O ₂ —v 1) · (Qf + Qf · λ) (5)

Here, the reason why the instantaneous moisture amount dQs_O ₂ is obtained from the equation (5) will be described. As described with reference to FIG. 4, the water concentration can be obtained from the difference between the oxygen concentration when the water vapor interference is received and the oxygen concentration when the water vapor interference is avoided. Multiplying this moisture concentration by the amount of gas gives the amount of moisture. Therefore, the instantaneous moisture content can be obtained from the oxygen concentration difference at a certain time and the gas amount at the certain time. The gas amount is the sum of the cathode air flow rate and the anode fuel flow rate. The cathode air flow rate is obtained by multiplying the anode fuel flow rate by the excess air ratio λ.

  To be precise, the gas type changes before and after the reforming step. Further, since the reformed water is added and combustible gas is consumed by the power generation reaction, the gas amount at the position of the oxygen / water concentration detector 70 is strictly different from the sum of the cathode air flow rate and the anode fuel flow rate. obtain. Therefore, if necessary, the map data obtained from the actual machine, or the value considering the generation reaction based on the generated power on the assumption that the reforming reaction is always in an equilibrium state, the cathode air flow rate and the anode fuel The gas amount at the position of the oxygen / water concentration detector 70 may be estimated based on the flow rate.

Next, the control unit 10 obtains an integrated value Qs_O ₂ of the moisture amount detected by the oxygen / water concentration detector 70 according to the following equation (6) (step S24). Thereby, the integral value Qs_O ₂ at the time of execution of step S24 can be obtained.
Qs_O ₂ = Qs_O ₂ + dQs_O ₂ (6)

  Next, the control unit 10 adds the number of integrations once (step S25). Next, the control unit 10 determines whether or not the number of integrations N has reached the maximum value Nmax (step S26). In this embodiment, the maximum value Nmax is set to 120 as an example. If it is not determined in step S26 that the number of integrations N has reached the maximum value Nmax, the control unit 10 ends the execution of the flowchart. In this case, steps S21 to S24 are executed until the number of integrations N reaches the maximum value Nmax.

  When it determines with the frequency | count N of integration having reached the maximum value Nmax in step S26, the control part 10 acquires the water level POS of the condensed water tank 32 from the water level sensor 33 (step S27). Next, the control unit 10 subtracts the water level POS_old obtained during the previous flowchart execution from the water level POS to obtain the water level change amount dPOS of the condensed water tank 32 (step S28).

  Next, the control unit 10 determines whether or not the absolute value of the water level change amount dPOS is greater than or equal to the water level change error limit POS_lmt (step S29). The water level change error limit POS_lmt is set to a value greater than or equal to the error of the water level sensor 33. Therefore, in step S29, it can be determined whether or not the water level has fluctuated more than the error of the water level sensor 33. For example, the water level change error limit POS_lmt is set to the design reference water level × k% (for example, 100 mm × 10%).

  If it is not determined in step S29 that the absolute value of the water level change amount dPOS is greater than or equal to the water level change error limit POS_lmt, the control unit 10 sets the number of integrations N to zero (step S30). Next, the control unit 10 substitutes the water level POS for the water level POS_old (step S31), and ends the execution of the flowchart.

If the absolute value of the water level variation dPOS is determined to be level changes error limit POS_lmt more in step S29, the controller 10 determines the deviation Qs_O ₂ _err (step S32). The deviation Qs_O _{2 —} err is a value obtained by subtracting the water level change amount dPOS from the integral value Qs_O ₂ .

Next, the control unit 10 obtains a correction amount Qs_fb_pos of the supply amount of reforming water to the reforming unit 51 according to the map of FIG. 11 (step S33). In FIG. 11, the horizontal axis represents the deviation Qs_O ₂ _err, and the vertical axis represents the map value map (Qs_O ₂ _err) obtained from the deviation Qs_O ₂ err. As shown in FIG. 11, when the absolute value of the deviation Qs_O ₂ err is small, the map value map (Qs_O ₂ _err) is set to zero in consideration of the recovery time delay of the water recovery loop. When the deviation Qs_O ₂ _err becomes positive, map (Qs_O ₂ _err) is increased. On the other hand, when the deviation Qs_O ₂ err becomes negative, map (Qs_O ₂ _err) is increased negatively. For the purpose of preventing overcompensation, a lower limit value and an upper limit value are set for the map value map (Qs_O ₂ _err).

Next, the control unit 10 obtains the amount of reforming water supplied to the reforming unit 51 according to the following formula (7) (step S34). Qs represents the amount of reformed water supplied. Qs_base is the amount of reforming water proportional to the fuel amount Qf, and is a value obtained by S / C ratio = 2.5. The S / C ratio refers to the ratio of the number of moles of water vapor to the number of moles of carbon in the hydrocarbon fuel. Further, Qs_fb_O ₂ indicates a feedback correction moisture amount based on the oxygen / water concentration detector 70. This value is well known as a feedback correction amount when using the oxygen sensor.
Qs = Qs_base + Qs_fb_O ₂ + Qs_fb_pos (7)

  Next, the control part 10 performs step S30 and step S31 in order. Thereafter, the control unit 10 ends the execution of the flowchart.

  As described above, the deviation between the value obtained by integrating the detection value of the oxygen / water concentration detector 70 for a predetermined time and the amount of change in the water level of the condensed water tank 32 is reflected in the amount of reformed water supplied to the reforming unit 51. By doing so, the water level of the condensed water tank 32 can be feedback controlled within a predetermined range. Thereby, the reforming water supply amount can be appropriately controlled with respect to the hydrocarbon fuel amount.

  In this embodiment, the oxygen / water concentration detector 70 detects the oxygen concentration and water concentration of the anode off-gas, but is not limited thereto. For example, the oxygen / water concentration detector 70 may detect the oxygen concentration and the water concentration at any location downstream of the reforming unit 51. Also in this case, the deviation between the value obtained by integrating the detection value of the oxygen / water concentration detector 70 for a predetermined time and the amount of change in the water level of the condensed water tank 32 is used as the amount of reformed moisture supplied to the reforming unit 51. By reflecting, the water level of the condensed water tank 32 can be feedback controlled within a predetermined range.

  In this embodiment, the oxygen / water concentration detector 70 is used as the moisture concentration sensor. However, any sensor capable of detecting the water vapor concentration can be used as the moisture concentration sensor.

  In the correspondence relationship between the present embodiment and the claims, the oxygen / water concentration detector 70 corresponds to a water concentration sensor, the control unit 10 corresponds to a supply amount control means, and the heating unit 52 corresponds to a combustor.

It is a schematic diagram which shows the whole structure of the reforming system which concerns on 1st Example of this invention. It is a typical sectional view of an oxygen and moisture concentration detector. It is a figure which shows the relationship between the voltage and electric current of a power supply, and the water vapor | steam density | concentration in exhaust gas in case oxygen concentration in exhaust gas is constant. It is a schematic diagram which shows the flow of the moisture content in a reforming system. It is a figure which shows an example of the flowchart at the time of acquiring the oxygen concentration in cathode off gas. It is a figure which shows an example of the flowchart at the time of controlling the excess air ratio in a reforming part using the value obtained according to the flowchart of FIG. It is a figure which shows the relationship between oxygen concentration and an air excess rate. It is a figure which shows the relationship between an air excess rate and the flame temperature in a heating part. It is a figure which shows the relationship between the control target value, minimum value, and maximum value of an excess air ratio. It is a figure which shows an example of the flowchart for performing feedback control of the water level of a condensed water tank. It is a figure which shows the correction amount of the supply amount of the reforming water to a reforming part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Control part 20 Reformed fuel supply part 30 Water supply part 31 Condensed water drain valve 32 Condensed water tank 33 Water level sensor water 36 Metering valve 40 Air pump 50 Reformer 51 Reforming part 52 Heating part 60 Fuel cell 61 Cathode 62 Anode 70 Oxygen / water concentration detector 100 reforming system

Claims (2)

A reformer for generating reformed gas from hydrocarbon fuel ;
A fuel cell that generates power using hydrogen contained in the reformed gas as a fuel;
A combustor that burns the anode off-gas of the fuel cell using oxygen contained in the cathode off-gas of the fuel cell;
An oxygen / water concentration sensor that is disposed downstream of the combustor, includes an oxygen ion conductive solid electrolyte, and detects a water vapor concentration and an oxygen concentration according to an applied voltage;
Downstream of the oxygen / water concentration sensor , a condensed water tank that stores condensed water of at least a part of moisture in the gas downstream of the reformer;
A water level sensor for detecting the water level of the condensed water tank;
Based on the deviation between the integrated value obtained by integrating the detection value of the oxygen / water concentration sensor for a predetermined time and the water level change obtained based on the detection value of the water level sensor, the reformer is improved. And a supply amount control means for controlling the supply amount of quality water. The reforming system according to claim 1 , wherein the combustor is a heating unit that applies heat to the reformer.

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