JP4610097B2 - Fuel reforming system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel reforming system suitable for a mobile fuel cell device.
[0002]
[Prior art and problems to be solved]
As a reforming system suitable for a mobile fuel cell device represented by a fuel cell vehicle, the following is known. That is, a mixed liquid of methanol and water as fuel is sent to an evaporator, and a mixed vapor of water and methanol vaporized by the evaporator is supplied to the mixer. In addition, air is pumped into the mixer by a compressor. The mixed vapor and air are mixed in a mixer and then sent to an ATR (autothermal reactor). ATR fuel reforms methanol, which is fuel, by catalytic reaction using water and oxygen in the air, thereby generating a hydrogen-rich reformed gas to be supplied to the fuel cell.
[0003]
By the way, in such a fuel reforming system, the liquid mixture supplied to the evaporator temporarily increases under transient operation conditions such as startup and acceleration, so that the temperature in the evaporator temporarily decreases. To do. For this reason, the proportion of methanol, which is a low-boiling component, increases due to the delay in evaporation of water, which is a high-boiling component, in the mixed solution, and the component of the mixed vapor at the evaporator outlet It becomes a fuel component with a large amount of methanol relative to the component. This change in the fuel component changes into various states depending on the change in the operating condition in the transient state. As a result, under transient operation conditions such as startup and acceleration, the fuel component supplied to the ATR is a mixture of water and methanol adjusted so as to be optimal for the reaction in the ATR in the steady operation state. There is a problem that the amount of unreacted methanol, CO component and soot increases, and the amount of hydrogen decreases due to fluctuation from the ratio. (For example, see Japanese Patent Laid-Open No. 2000-154002 as a related art document.)
The present invention has been made paying attention to such conventional problems, and even when the steam component supplied from the evaporator to the fuel reformer changes greatly, it is used in the fuel cell according to the generated steam component. It is an object of the present invention to provide a fuel reforming system for a moving body that can obtain a possible reformed gas composition.
[0004]
[Means for Solving the Problems]
A first aspect of the present invention is a fuel reformer that generates a reformed gas containing hydrogen using an evaporator that generates a raw fuel vapor composed of a liquid mixture of liquid fuel and water, and the raw fuel vapor and a gas containing oxygen. And a means for controlling the amount of gas containing oxygen to be supplied to the reformer, the means for detecting the amount of the raw fuel vapor, and the concentration of water vapor in the raw fuel vapor And detecting the amount of gas containing oxygen based on the concentration of water vapor and the amount of raw fuel vapor.
[0005]
In a second aspect based on the first aspect, the ratio of the amount of liquid fuel in the raw fuel and the amount of gas containing oxygen supplied to the reformer is corrected from a predetermined value based on the concentration of the water vapor. Then, the amount of the gas containing oxygen is calculated based on the corrected ratio.
[0006]
According to a third invention, in the first or second invention, there is provided means for evaporating water or liquid fuel by hot surface heating and supplying the water or liquid fuel to a reformer, wherein the detected water vapor concentration is a predetermined concentration Supply water or liquid fuel.
[0007]
According to a fourth invention, in the first to third inventions, a concentration sensor in which a Peltier element functions as a cooling, heating, and thermocouple is used as means for detecting the concentration of the water vapor.
[0008]
According to a fifth invention, in the first to third inventions, a helium neon laser is used as means for detecting the concentration of the water vapor.
[0009]
[Action / Effect]
According to the first or second aspect of the invention, since the flow rate of the gas containing oxygen is corrected according to the concentration of the gas supplied to the fuel reformer, the gas supplied to the fuel reformer Even if the concentration of CO2 changes, it is possible to obtain a reformed gas having a specification in which the CO concentration and the amount of unburned methanol are reduced to an allowable level that can be used in a fuel cell.
[0010]
According to the third aspect of the invention, by supplying water or fuel vapor by hot surface heating according to the concentration of the gas supplied to the fuel reformer and correcting it to a predetermined concentration, the fuel cell The reformed gas and the maximum amount of hydrogen generated can be obtained with the CO concentration unburned methanol that can be used in 1) reduced to an extremely low level.
[0011]
According to the fourth or fifth invention, it is possible to detect the vapor concentration data with high response, and thereby the control accuracy of the first and second inventions can be further improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. First, the basic configuration and operation of the fuel reforming system will be described. In the figure, a mixed liquid 101 of methanol and water, which is fuel in the fuel tank 100, is sent to the evaporator 102 and heated and evaporated to be supplied to the mixer 180 as a mixed vapor 181 of water and methanol. Air 182 is pumped from the compressor 104 to the mixer 180. The mixed vapor 181 and air 182 are mixed by the mixer 180 and then supplied to the ATR 103. The ATR 103 reforms the fuel, methanol, using water and oxygen in the air by the following catalytic reaction to generate a hydrogen-rich reformed gas.
CH ₃ OH + H ₂ O⇔CO ₂ + 3H ₂ (1)
_{CH 3 OH + O 2/2} ⇔ CO 2 + 2H 2 ... (2)
Formula (1) is a water vapor reaction (endothermic reaction) of methanol, and Formula (2) is a partial oxidation reaction (exothermic reaction) of methanol. The reaction of the formula (1) proceeds stepwise mainly as shown below.
CH ₃ OH⇔CO + 2H ₂ (3)
CO + H ₂ O⇔CO ₂ + H ₂ (4)
Equation (3) is a methanol decomposition reaction (endothermic reaction), and Equation (4) is a carbon monoxide shift reaction (exothermic reaction). The ATR 103 is operated under autothermal conditions that balance the heat generation and endotherm of these reaction formulas. Therefore, if the size and configuration of the reactor or the performance of the catalyst is determined, the flow rate ratio such as the flow rate of water vapor and the flow rate of air is almost determined. In this proposal, the ratio of the methanol flow rate consumed in the partial oxidation reaction (POX) to the total methanol flow rate supplied is defined as the POX rate, and almost all of the supplied oxygen is converted into the partial oxidation reaction of formula (2). Since it is used, the required air flow rate with respect to the total methanol flow rate is determined from the POX rate.
[0013]
Further, at the time of start-up where the temperature of the catalyst is low, the following side reactions further occur.
CH ₃ OH⇔HCHO + H ₂ (5)
HCHO ＣＯ CO + H ₂ (6)
The operating temperature of the ATR103 is 300 to 600 ° C., and a reformed gas containing carbon monoxide on the order of several percent is obtained by thermodynamic chemical equilibrium. Since carbon monoxide poisons the fuel electrode electrode catalyst made of platinum or the like of the solid polymer fuel cell 200 and significantly reduces its activity, the shift reactor 105 and the PROX reactor (selective oxidation reactor) It is necessary to reduce the carbon monoxide to several tens to several hundred ppm and supply it to the fuel cell 200 by the carbon monoxide cleaner system composed of 106.
[0014]
The reformed gas containing carbon monoxide on the order of several percent is sent to the shift reactor 105, and carbon monoxide is reduced by the catalyst having a fast shift reaction of the formula (4). The operating temperature of the shift reactor 105 is 200 to 300 ° C., and is 0. 0 due to thermodynamic chemical equilibrium. The reformed gas contains carbon monoxide on the order of several percent. In some cases, a shift reactor is integrated into the ATR 103. The reformed gas in which carbon monoxide is reduced by the shift reaction is sent to the PROX reactor 106, and further, the carbon monoxide is reduced to several tens to several hundred ppm by the catalytic oxidation reaction (exothermic reaction) of the following formula (7). Reduced. Necessary oxygen is supplied as air by the compressor 104.
_{CO + O 2/2 ⇔ CO} 2 ... (7)
Since the PROX reactor 106 performs an oxidation reaction in a hydrogen atmosphere, the following hydrogen combustion reaction (exothermic reaction) also occurs, and the selectivity of the formula (7) with respect to the following formula (8) improves the efficiency of the reforming system. It has a big effect.
H ₂ + O ₂ / 2⇔H ₂ O (8)
The PROX reactor 106 is cooled by air, LLC (cooling liquid), oil, or the like by a cooling means (not shown) in order to remove the heat generated by the equations (7) and (8) and maintain the operating temperature at several tens of degrees Celsius. The
[0015]
In this way, the reformed gas in which carbon monoxide is reduced to a very low concentration and the air from the compressor 104 are sent to the fuel electrode and the air electrode of the fuel cell 200, and power generation is performed.
[0016]
In the fuel cell 200, it is difficult to use all the hydrogen in the reformed gas. The reformed gas that has been used for power generation, leaving some hydrogen, and used for power generation, leaving some oxygen. Spent air is sent to the catalytic combustor 107 for combustion. The obtained high-temperature exhaust gas is sent to the evaporator 102 and reused as energy for evaporating methanol and water.
[0017]
500 is a flow rate control valve that controls the flow rate of air supplied to the PROX reactor 106, 501 is a flow rate control valve that controls the flow rate of air supplied to the ATR 103, and 502 is supplied to the air electrode of the fuel cell 200. It is a flow control valve which controls the flow rate of the air to be performed. Reference numeral 510 denotes a pressure control valve for adjusting the operating pressure of the fuel electrode of the fuel cell 200, and 511 denotes a pressure control valve for adjusting the operating pressure of the air electrode of the fuel cell 200. Reference numerals 520 and 521 denote pressure sensors that detect operating pressures on the fuel electrode side and the air electrode side of the fuel cell 200, and pressure adjustment is performed so that these pressures are the same.
[0018]
Reference numeral 400 denotes a controller that performs energy management of a moving body such as a fuel cell vehicle, and sends an operation load signal 402 of the reforming system to the controller 401. Based on the operation load signal 402, the controller 401 drives the pump 170 to control the flow rate of the liquid fuel supplied to the evaporator 102 and the flow rate control valve 501 so that the flow rate of the fuel vapor and air necessary for the ATR 103 is obtained. To control. Reference numerals 601 and 602 denote flow rate sensors.
[0019]
In the present invention, for example, in such a fuel reforming system, in addition to the flow rate sensor 601 that is a means for detecting the vapor flow rate from the evaporator 102, a concentration sensor 600 is provided as a means for detecting the component concentration of the vapor, By appropriately controlling the supply air flow rate and the like based on these detection results, the amount of unreacted methanol, CO components, and soot is suppressed, and a transfer that provides an appropriate reformed gas composition that can be used in a fuel cell is obtained. A body fuel reforming system is provided. Hereinafter, the specific contents of such a control operation will be described with reference to FIGS.
[0020]
FIG. 2 shows the processing contents of a control program periodically executed by the controller 401. Hereinafter, the processing contents in this control operation will be described in order. In the following description, the symbol “S” corresponds to the processing step (Step) in FIG.
S1: Read the operation load signal 402 of the reforming system sent from the controller 400.
S2: A liquid fuel having a required flow rate is supplied to the evaporator 102 based on the operation load signal 402.
S3: The signal value of the vapor concentration of the concentration sensor 600 is read.
S4: From the signal value of the vapor concentration of the concentration sensor 600, the correction coefficient K _pox (%) of the POX rate at which the unburned methanol and CO concentrations shown in FIGS. 3 and 4 fall within the allowable values is obtained from the map A (see FIG. 5).
S5: The fuel vapor flow rate signal value of the flow rate sensor 601 is read.
S6: The flow rate of air to be supplied is obtained from the signal value of the fuel vapor flow rate and the correction coefficient K _pox (%) of the POX rate obtained in S4 using the map B (see FIG. 6). The map B is the following conversion formula.
F _air = (1 + K _pox / 100) k ₁ (r _{pox, 0/100} ) F _{Fuel, vap} (9)
Where F _air : Air flow rate (g / sec)
F _{Fuel, vap} : Flow rate of fuel vapor (g / sec)
r _{pox, 0} : Design specification POX rate (approximately 30% under auto-thermal conditions)
k ₁ : Constant S7: The valve opening of the flow control valve 501 is adjusted so that the air flow rate determined in Step 6 is obtained.
[0021]
Through the above processing, the air flow rate is always controlled and supplied to the ATR 103 so that the POX rate corrected in the map A (FIG. 5) is obtained according to the vapor flow rate and the vapor temperature supplied from the evaporator 102.
[0022]
The effect | action by the said process is explained in full detail. FIG. 3 shows the dependence of the unburned methanol concentration in the reformed gas supplied from the ATR 103 to the shift reactor 105 on the vapor concentration supplied to the ATR 103. Similarly, FIG. 4 shows the dependence of the CO concentration in the reformed gas supplied from the shift reactor 105 to the PROX reactor 106 on the vapor concentration supplied to the ATR 103. Lines 320 and 321 in FIGS. 3 and 4 are specification concentrations that define the upper limits of the methanol and CO concentrations of the reformed gas to be supplied from the ATR 103 to the shift reactor 105 and from the shift reactor 105 to the PROX reactor 106.
[0023]
A line 300 in FIG. 3 corresponds to an autothermal condition, that is, a case where the POX rate is fixed, and a point is a design point. When the vapor concentration becomes high, the unburned methanol concentration rises to the point b and does not satisfy the specification of the methanol concentration of the reformed gas to be supplied to the shift reactor 105 (in this case, it needs to be reduced to the point c). Further, when correction is made so that the POX rate r _pox (%) is increased, the unburned methanol concentration is decreased.
[0024]
A line 301 in FIG. 4 corresponds to a case where the POX rate is fixed under autothermal conditions, and a point a is a design point. If the vapor concentration has increased, the CO concentration will increase (point b), and the CO concentration will also increase when correction is made to increase the POX rate r _pox (%) (allowing unburned methanol) As the value 320 is reached, the CO concentration increases to point c). That is, the higher the MeOH (low boiling point component) concentration is, the higher the concentration is in a stricter direction than the permissible values of unburned methanol and CO. The white arrow) becomes narrower.
[0025]
Next, the structure and measurement method of the density sensor 600 will be described with reference to FIGS. 7 to 9 show examples based on temperature detection. In FIG. 7, the end face of the heat transfer block 11 held via the heat insulating material 10 so as to face the steam passage slightly protrudes into the steam passage, and the surface temperature thereof is measured by the thermocouple 12 incorporated in the heat transfer block 11. Ask. The other end face of the heat transfer block 11 is cooled or heated according to the direction of the current flowing through the Peltier element 13, and the condensation temperature at the end face of the heat transfer block 11 facing the steam 181 at this time is detected. For example, the heat transfer block 11 is cooled by the Peltier element 13, and the inflection point temperature of the surface temperature change of the heat transfer block 11 is detected based on the change in the transfer state of the surface of the heat transfer block 11 due to condensation (see FIG. 8). From the temperature, the vapor concentration is specified with reference to a map (see FIG. 9) corresponding to the vapor-liquid phase equilibrium diagram. When the surface temperature of the heat transfer block 11 is lower than the condensation temperature, the Peltier element 13 is used as a heater to increase the search region temperature and detect the condensation point.
[0026]
FIG. 10 shows an example in which the Peltier element is used as a thermocouple in addition to the cooling / heating means. The use of the Peltier element as a cooling and heating means and the measuring method are the same as those in FIG. 7, but in this example, the power of the Peltier element circuit is turned off and the metal surface S part in contact with the vapor from the voltage (V) at that time Detect the temperature of In this case, the response can be improved and the cost can be reduced by downsizing the sensor.
[0027]
FIG. 11 shows an example in which the vapor concentration is detected using a He—Ne laser. 20 is a laser oscillator, 21 is a chopper, 22 is a filter, and 23 is a detector. In this case, the vapor concentration is detected by transmitting, for example, a laser having a wavelength of 3.392 μm into the vapor in the vapor path by utilizing a light absorption characteristic that the hydrocarbon vapor absorbs an electromagnetic wave having a wavelength of about 3.3 μm. The formula for calculating the vapor concentration (molar concentration) is as follows.
[0028]
c = −1 / (ε · d) Log (I / I _O )
Where c: molar concentration of absorbed gas (mol / cm ³ ),
ε: molar extinction coefficient (cm ² / mol),
I _O : Incident light intensity,
I: transmitted light intensity,
d: Absorption gas path length (cm)
Next, a second embodiment of the present invention is shown in FIG. This embodiment differs from the first embodiment in that a hot surface evaporator 603 is provided between the concentration sensor 600 and the flow rate sensor 601 on the downstream side of the evaporator 102. In the first embodiment, as the MeOH (low boiling point component) concentration increases, the allowable region of the correction coefficient α is narrowed, and when the concentration exceeds a certain concentration, the allowable region may disappear. On the other hand, in this embodiment, by providing the hot surface evaporator 603, it is possible to evaporate water or methanol according to the MeOH (low boiling point component) concentration and to keep the vapor concentration to the mixer 180 more appropriate. It becomes. Since the configuration other than the above is the same as that of the first embodiment, the same portions are denoted by the same reference numerals and the description thereof is omitted.
[0029]
FIG. 13 shows processing contents of a control program periodically executed by the controller 401 of the second embodiment. Hereinafter, the processing contents in this control operation will be described in order.
S1: Read the operation load signal 402 of the reforming system sent from the controller 401.
S2: A liquid fuel having a required flow rate is supplied to the evaporator 102 based on the operation load signal 402.
S3: The signal value of the vapor concentration of the concentration sensor 600 is read.
S4: The steam flow signal of the flow sensor 601 is read.
S5: The liquid level evaporation amount of water in the liquid level evaporator 603 is calculated from the vapor concentration and the vapor flow rate.
S6: The liquid level evaporation amount of methanol in the liquid level evaporator 603 is calculated from the vapor concentration and the vapor flow rate.
S7: Supply the amount corresponding to the calculated amount of evaporation of water and methanol.
[0030]
By the above processing, the vapor concentration supplied to the mixer 180 is further optimized.
[0031]
Note that the temperature of the gas supplied to the fuel reformer changes by detecting the temperature of the gas supplied to the fuel reformer and correcting the flow rate of the gas containing oxygen in the same manner as the above concentration. However, it is possible to reduce the CO concentration usable in the fuel cell. That is, the temperature of the gas fuel or liquid fuel vapor supplied to the fuel reformer, the temperature of the gas containing oxygen supplied to the fuel reformer, the gas fuel or liquid fuel vapor and the gas containing oxygen Means for detecting at least one temperature of the temperature of the mixed gas, and the gas containing oxygen with respect to the flow rate of the vapor of the gaseous fuel or liquid fuel according to the signal value of the means for detecting the temperature By correcting the flow rate ratio and supplying the gas containing oxygen in accordance with the corrected ratio, it is possible to supply the reformed gas with the CO concentration reduced to the required limit.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a first embodiment of a reforming system according to the present invention.
FIG. 2 is a flowchart showing the contents of a control operation of the first embodiment.
FIG. 3 is a characteristic diagram showing the relationship between the unburned methanol concentration at the ATR outlet and the vapor concentration.
FIG. 4 is a characteristic diagram showing the relationship between the CO concentration at the ATR outlet and the vapor concentration.
FIG. 5 is an explanatory diagram of a map that gives a POX rate correction coefficient according to the generated vapor concentration.
FIG. 6 is an explanatory diagram of a map that gives a supply air flow rate from a steam flow rate and a POX rate.
FIG. 7 is a schematic configuration diagram of a first embodiment relating to a vapor concentration detection means.
FIG. 8 is an explanatory diagram of temperature characteristics used in a concentration detection method by the concentration detection means.
FIG. 9 is an explanatory diagram of phase change characteristics used in a concentration detection method by the concentration detection means.
FIG. 10 is a schematic configuration diagram of a second embodiment relating to a vapor concentration detection means.
FIG. 11 is a schematic configuration diagram of a third embodiment relating to a vapor concentration detection means.
FIG. 12 is a schematic configuration diagram of a second embodiment of the reforming system according to the present invention.
FIG. 13 is a flowchart showing the contents of a control operation of the second embodiment.
[Explanation of symbols]
100 Fuel tank 102 Evaporator 103 ATR
104 Air compressor 105 Shift reactor 106 PROX reactor 107 Combustor 180 Mixer 200 Fuel cell 401 Controller 600 Concentration sensor 601 Flow rate sensor 603 Hot surface evaporator

Claims (5)

A fuel reformer that produces a reformed gas containing hydrogen using an evaporator that produces a raw fuel vapor comprising a mixture of liquid fuel and water, and a gas containing the raw fuel vapor and oxygen;
A fuel reforming system comprising: means for controlling the amount of gas containing oxygen supplied to the reformer;
Means for detecting the amount of the raw fuel vapor;
Means for detecting the concentration of water vapor in the raw fuel vapor,
A fuel reforming system that controls the amount of gas containing oxygen based on the concentration of water vapor and the amount of raw fuel vapor. The fuel reforming system according to claim 1, wherein
Based on the concentration of the water vapor, the ratio of the amount of liquid fuel in the raw fuel and the amount of gas containing oxygen supplied to the reformer is corrected from a predetermined value, and the oxygen is included based on the corrected ratio. A fuel reforming system that calculates the amount of gas. In the fuel reforming system according to claim 1 or 2,
Means for evaporating water or liquid fuel by hot surface heating and supplying it to the reformer;
A fuel reforming system that supplies water or liquid fuel in an amount such that the detected water vapor concentration becomes a predetermined concentration. In the fuel reforming system according to any one of claims 1 to 3,
A fuel reforming system using a concentration sensor in which a Peltier element functions as a cooling, heating, and thermocouple as means for detecting the concentration of water vapor. In the fuel reforming system according to any one of claims 1 to 3,
A fuel reforming system using a helium neon laser as means for detecting the concentration of the water vapor.

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