JP4302266B2 - Stopping method of methanol reformer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for stopping a methanol reformer that generates hydrogen-enriched gas from water and methanol.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, fuel cells have been developed as a driving source for automobiles and other power generation devices aimed at reducing pollution.
As hydrogen as the energy source, compressed hydrogen or liquid hydrogen is simple, but there is a problem in safety and handling, so a safer hydrogen supply device is desired.
Recently, technological development for producing hydrogen-enriched gas by reforming alcohol or hydrocarbon with a catalyst has been actively carried out, and various catalysts and reaction apparatuses have been devised.
[0003]
[Problems to be solved by the invention]
However, when reforming methanol with high flammability and ignitability with a methanol reformer, especially when using an autothermal system in which a partial oxidation reaction and a steam reforming reaction proceed simultaneously, methanol vapor and air In order to coexist on the high-temperature catalyst, the mixing ratio of water, methanol and air must not be within the range where the reaction proceeds at a high speed (hereinafter referred to as “high-speed reaction region”). It is necessary to strictly manage the amount introduced.
[0004]
Conversely, when the methanol reformer is stopped, the introduction of water, methanol and air is stopped and the catalyst layer is cooled. However, when the autothermal method is used, the amount of air is excessive. In the state, the partial oxidation reaction proceeds, and the catalyst layer may run out of heat.
[0005]
Therefore, it is important to strictly control the mixing ratio of water, methanol, and air so that the mixing ratio of water, methanol, and air does not enter the high-speed reaction region even when the methanol reformer is stopped. In particular, the amount of air should not be excessive. Since it is necessary to stop while suppressing, conventionally, it took a long time to stop.
[0006]
The present invention has been made in view of the above circumstances, and an object of the present invention is to quickly cool the catalyst layer without causing thermal runaway when the methanol reformer is stopped.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, in the present invention, first, the introduction of air is stopped and only the water and methanol are continuously introduced into the catalyst layer (the reforming catalyst layer 41 in FIG. 1). The catalyst layer temperature is lowered using the endothermic reaction.
The introduction and stop of air may be fast interruption by a shut-off valve, or the introduction amount may be gradually cut off by a control valve or the like.
[0008]
On the other hand, by switching the water / methanol molar ratio continuously introduced after the stop of air introduction to a second molar ratio higher than the first molar ratio (for example, 1.0 to 2.0) during steady operation, Since the methanol steam reforming reaction, which is an endothermic reaction, is promoted, the catalyst layer temperature can be rapidly lowered. When the catalyst layer is cooled to a predetermined temperature, the introduction of water and methanol is stopped. If the water / methanol molar ratio is removed from the high-speed reaction region prior to stopping the fuel introduction, a gentle stop can be achieved without causing thermal runaway.
[0009]
The inventor found that the water / methanol molar ratio (hereinafter referred to as “S / C ratio”) is 4.6 (= 82 mol% / 18 mol%) from the three-phase mixed phase diagram of water, methanol and air in FIG. ) As described above, it has been found that if the mixing ratio of water, methanol and air is controlled, a gentle stop can be achieved without causing a high-speed reaction. In this figure, the hatched portion indicates the fast reaction region.
Therefore, in order to realize a gentle stop, it is preferable to stop the introduction of water and methanol after switching the S / C ratio to 4.6 or more.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a fuel supply system diagram for a fuel cell in an electric vehicle. Reference numeral 10 denotes a fuel cell.
The fuel cell 10 generates power using hydrogen and oxygen in the air as fuel.
Hereinafter, a hydrogen supply system and an air supply system for the fuel cell 10 will be described.
[0011]
[Hydrogen supply system]
The hydrogen supply system includes a combustor 21, an evaporator 22, a reformer (methanol reformer) 23, a CO remover 24, a starter heater 25, heat exchangers 26 a and 26 b, and a water methanol mixture. The liquid tanks 27a and 27b and the methanol tank 28 are the main components.
[0012]
The combustor 21 includes an electric heater 31 as an ignition source, a combustion catalyst 32 for maintaining the combustion state, and a temperature sensor 33 for detecting the internal temperature. Methanol and air from the air supply system are combusted to generate combustion gas used for warming up the evaporator 22 and vaporizing the water-methanol mixture supplied to the evaporator 22.
[0013]
Further, the combustor 21 is used for burning off-gas containing hydrogen-enriched gas generated by the reformer 23 from start-up to steady operation and unreacted hydrogen discharged from the fuel cell 10 during steady operation. An off-gas pipe 34 for reuse as fuel is connected.
[0014]
The evaporator 22 is a mixture of aqueous methanol supplied from an aqueous methanol mixed liquid tank 27a whose S / C ratio is adjusted to 1.5 or an aqueous methanol mixed liquid tank 27b whose S / C ratio is adjusted to 4.6. The liquid is sprayed from the nozzle, and this is vaporized by the combustion gas supplied from the combustor 21 to produce a water-methanol mixed gas.
Further, the evaporator 22 is provided with a temperature sensor 36 for detecting the internal temperature.
[0015]
The reformer 23 is provided with a reforming catalyst layer 41 in which the surface of the honeycomb structure is coated with a catalyst such as Ni, Ru, Rh, or Cu—Zn, and is mixed with water / methanol from the evaporator 22. The gas is passed through the reforming catalyst layer 41 to generate a hydrogen-enriched gas.
An O 2 sensor 42 is provided at the inlet portion of the reforming catalyst layer 41, and a temperature sensor 43 is provided inside the reforming catalyst layer 41.
[0016]
In the reformer 23, the following autothermal reforming reaction is performed.
CH ₃ OH + H ₂ O → 3H ₂ + CO ₂ (1)
CH ₃ OH + 2O ₂ → 2H ₂ O + CO ₂ (2)
Reaction formula (1) is a steam reforming reaction with methanol and water, and this reaction generates hydrogen as a target product.
On the other hand, the reaction formula (2) is a partial oxidation reaction of methanol, and the amount of heat necessary for the reaction formula (1) which is an endothermic reaction is replenished by the oxidation heat at the time of this oxidation reaction.
[0017]
In the reformer 23, in addition to the reaction formulas (1) and (2), a small amount of carbon monoxide is generated by the following unavoidable methanol decomposition reaction.
CH ₃ OH → 2H ₂ + CO (3)
The carbon monoxide is removed by a CO remover 24 provided at a later stage in order to poison the Pt catalyst in the fuel cell 10 to lower the power generation efficiency and shorten the battery life.
[0018]
The CO remover 24 is provided with a selective oxidation catalyst layer formed by coating the surface of the honeycomb structure with a catalyst such as Pt or Ru, and supplied with the hydrogen-enriched gas generated by the reformer 23. Then, carbon monoxide in the hydrogen-enriched gas is removed by the following CO selective oxidation reaction.
2CO + O ₂ → 2CO ₂ (4)
[0019]
A heat exchanger is provided between the reformer 23 and the CO remover 24 for the purpose of cooling the hydrogen-enriched gas from the reformer 23 and protecting the selective oxidation catalyst in the CO remover 24 from thermal damage. 26a is provided. Similarly, a heat exchanger is provided between the CO remover 24 and the fuel cell 10 for the purpose of cooling the hydrogen-enriched gas discharged from the CO remover 24 and protecting the Pt catalyst in the fuel cell 10 from thermal damage. 26b is installed.
[0020]
The valves 51,..., The pumps 55,... Provided in the hydrogen supply system are controlled by an ECU (Electronic Control Unit) 45.
The ECU 45 sends control commands to the valves 51,..., Pumps 55,... Based on output signals from the O2 sensor 42 and the temperature sensor 43, a stop command, etc., and operates them. That is, the ECU 45 also has a function as switching means for the water / methanol mixed liquid tanks 27a and 27b used as the fuel supply source.
[0021]
[Air supply system]
The air supply system mainly includes a PCU 61, a drive motor 62, a supercharger 63, an intercooler 64, and filters 65a and 65b. The air introduced from the outside is the fuel cell 10, the combustor 21, and the starter. To the heater 25.
The PCU 61 mainly adjusts the output of the drive motor 62, adjusts the electric power sent from the fuel cell 10, and supplies this to the drive motor 62.
[0022]
The supercharger 63 compresses and compresses external air taken in from the filter 65 a via the resonator 66.
The intercooler 64 is provided in order to lower the temperature of the air that has risen due to the pressure compression by the supercharger 63, and the air cooled thereby passes through the filter 65b provided in the subsequent stage of the intercooler 64, It is sent to the fuel cell 10, the combustor 21, and the starting heater 25.
[0023]
Next, a method for stopping the reformer 23 according to the present embodiment will be described. Prior to the description, an example of operation during steady operation (during normal reforming) will be outlined.
During steady operation, the valve 50 is open, introduced from the air supply system, that is, through the resonator 66 and the filter 65a, pressurized by the supercharger 63, and then cooled by the intercooler 64. Further, the air that has passed through the filter 65b is supplied to the combustor 21 and the evaporator 22, the reformer 23,.
[0024]
Further, the valve 51 is closed while the valve 52 is opened, and the water / methanol mixed solution in which the S / C ratio is adjusted to 1.5 from the water / methanol mixed solution tank 27 a toward the evaporator 22. Is fed by a pump 56, which is sprayed into the evaporator 22 from a nozzle.
In the evaporator 22, the water methanol mixed liquid is vaporized by the combustion gas from the combustor 21 to generate a water methanol mixed gas, which is sent to the reformer 23.
[0025]
In the reformer 23, the hydrogen-enriched gas is generated by the reaction formulas (1) and (2) by passing the water-methanol mixed gas through the reforming catalyst layer 41.
The hydrogen-enriched gas produced in the reformer 23 is cooled from about 300 ° C. to about 100 ° C. while passing through the heat exchanger 26 a and sent to the CO remover 24.
In the CO remover 24, carbon monoxide is removed by the reaction formula (4) by passing the hydrogen-enriched gas through the selective oxidation catalyst layer.
[0026]
Then, the hydrogen-enriched gas from which CO has been removed is cooled from about 180 ° C. to about 80 ° C. while passing through the heat exchanger 26 b and is sent to the fuel cell 10.
The fuel cell 10 generates power using the hydrogen-enriched gas supplied from the hydrogen supply system and the air supplied from the air supply system.
Off-gas containing unreacted hydrogen is discharged from the fuel cell 10, and the off-gas is returned to the combustor 21 through the off-gas pipe 34 and reused as combustion fuel.
[0027]
Next, a method for stopping the reformer 23 during steady operation will be described.
This reformer stopping method includes a first step of stopping the introduction of air into the reformer 23, and a step of switching the S / C ratio of the water-methanol mixed gas sent to the reformer 23 to be higher than that in the steady operation. And a third step for stopping the introduction of the water-methanol mixed gas into the reformer 23.
[0028]
First, in the first step performed, the valve 50 that was open during the steady operation is closed.
Then, air introduction from the air supply system to the hydrogen supply system, that is, the combustor 21 and the evaporator 22, the reformer 23,.
At this time, in the reformer 23, since the mixing ratio of air is lower than that of water and methanol, the endothermic reaction of the reaction formula (1) proceeds while the exothermic reaction of the reaction formula (2) is suppressed. Therefore, the reforming catalyst layer 41 is effectively cooled.
[0029]
Next, in the second step to be performed, the valve 52 that was open during the steady operation is closed and the valve 51 that was closed is opened.
Then, an aqueous methanol mixed liquid having an S / C ratio = 4.6 is fed from the aqueous methanol mixed liquid tank 27 b to the evaporator 22 by the pump 55, and the aqueous methanol mixed gas vaporized and generated by the evaporator 22 is supplied. It is sent to the reformer 23.
At this time, since the S / C ratio of the water-methanol mixed gas is switched higher than that during steady operation (for example, S / C = 1.0 to 2.0), the reaction formula (1 ) Is promoted, and the reforming catalyst layer 41 is quickly cooled.
[0030]
In the third step that is performed last, when the reforming catalyst layer 41 can be cooled to a predetermined temperature, the valve 51 opened in the second step is closed.
Then, the supply of the aqueous methanol mixture from the aqueous methanol mixture tank 27b to the evaporator 22 is interrupted, and the introduction of the aqueous methanol mixture gas to the reformer 23 is stopped.
At this time, since the S / C ratio is set to a value excluding the high-speed reaction region (see FIG. 2), a gentle stop is achieved without causing thermal runaway.
[0031]
(Second embodiment)
Hereinafter, the second embodiment of the present invention will be described with reference to FIG. 3, but the same components as those in FIG.
In this embodiment, a part of the hydrogen supply system and a part of the air supply system are different from those of the first embodiment, and other configurations are the same as those of the first embodiment.
[0032]
The hydrogen supply system is provided with a condenser 71 and an S / C adjustment tank 72 in place of the water / methanol mixture tank 27b whose S / C ratio is adjusted to 4.6 in FIG.
The condenser 71 collects water generated by the reaction and combustion of the fuel cell 10 from the evaporator 22.
The S / C adjustment tank 72 is a water methanol for starting / stopping using a water methanol mixed liquid (S / C ratio = 1.5) from the water methanol mixed liquid tank 27a and recovered water from the condenser 71. A mixed solution (S / C ratio = 4.6 or more) is prepared.
[0033]
The S / C ratio in the S / C adjustment tank 72 is always detected by the methanol sensor 73 and sent to the ECU 45.
The ECU 45 adjusts the opening degree of the valves 75 and 76 based on the detection result.
It should be noted that surplus water collected in the condenser 71 after the preparation of the aqueous methanol mixed solution by the S / C adjustment tank 72 and at the time of stopping is discarded.
[0034]
An air supply line 81 to the evaporator 22 is provided in the air supply system.
Thereby, the evaporator 22 also serves as a heater for heating the air supplied via the air supply line 81.
Therefore, in this embodiment, since the reformer 23 can be warmed up by this heated air, the activation heater 25 shown in FIG. 1 is unnecessary.
[0035]
Even in the above configuration, when the reformer 23 is stopped, the second methanol water tank 27a for normal reforming and the S / C adjustment tank 72 for starting / stopping are switched to switch the second. Since the S / C ratio can be switched in this step, even when the reformer 23 is likely to be unstable, the water / methanol mixed gas having the composition excluding the high-speed reaction region can be instantaneously supplied. Thus, the reforming catalyst layer 41 can be cooled gently and quickly without causing thermal runaway.
[0036]
Example 1
Using a test apparatus in which 9.2 g of methanol reforming catalyst pellets having a Cu / Zn / Al ratio of 1.3 / 1 / 0.05 were charged in a quartz reaction tube having an inner diameter of 20 mm, heated air was supplied to the catalyst at 40 ml / The catalyst layer was heated to 230 ° C.
Separately, a water-methanol mixed solution having an S / C ratio adjusted to 1.5 is supplied to the evaporator.
[0037]
The water-methanol mixed gas produced by the evaporator was introduced into the catalyst at 1.8 ml / min, and the reforming reaction was started by the autothermal method.
The amount of introduced air was adjusted so that the catalyst layer was 230 ° C., and the reforming reaction was stabilized.
Next, as a stop operation, the supply of water, methanol and air was stopped simultaneously, and the temperature transition of the catalyst layer was recorded (plot ♦ in FIG. 4).
[0038]
(Example 2)
Using the same test apparatus as in Example 1, the reforming reaction was started and stabilized in the same procedure as in Example 1.
Next, as a stop operation, the supply of water and methanol was first stopped, then the supply of air was stopped, and the temperature transition of the catalyst layer was recorded (plot □ in FIG. 4).
[0039]
(Example 3)
Using the same test apparatus as in Example 1, the reforming reaction was started and stabilized in the same procedure as in Example 1.
Next, as a stop operation, the supply of air was first stopped, then the supply of water and methanol was stopped, and the temperature transition of the catalyst layer was recorded (plot Δ in FIG. 4).
[0040]
(Example 4; the present invention)
Using the same test apparatus as in Example 1, the reforming reaction was started and stabilized in the same procedure as in Example 1.
Next, as a stop operation, first, the supply of air was stopped, and then the S / C ratio of water methanol being continuously supplied was switched to 4.6, and the temperature transition of the catalyst layer was recorded (plot ○ in FIG. 4). ).
[0041]
Compared with the case where the supply of water, methanol and air is stopped simultaneously as in Example 1 and the catalyst layer is naturally cooled, as in Example 2, when the supply of water and methanol is first stopped, It was confirmed that the residual methanol caused abnormal heat generation and the catalyst layer temperature rapidly increased.
This is because the amount of air on the catalyst layer becomes excessive and the exothermic reaction of the reaction formula (2) proceeds at a high speed.
[0042]
On the other hand, as in Example 3, when the supply of air was first stopped, it was confirmed that the catalyst layer could be cooled faster than natural cooling by the endothermic reaction accompanying the steam reforming reaction of water methanol. .
This is because the endothermic reaction of the reaction formula (1) proceeds while the exothermic reaction of the reaction formula (2) is suppressed.
[0043]
Then, as in Example 4, after the supply of air is stopped (or at the same time as the supply is stopped), the S / C ratio of water methanol is switched to a value that is excluded from the high-speed reaction region, compared to the case of Example 3. It was confirmed that the catalyst layer can be cooled quickly.
This is because the endothermic reaction of the reaction formula (1) can be further promoted while the exothermic reaction of the reaction formula (2) is suppressed by supplying water-rich fuel.
[0044]
As is clear from comparison between Examples 1 to 4, when the reformer 23 is stopped, the air supply is first stopped, and then the S / C ratio of water methanol is removed from the high-speed reaction region. It was confirmed that the catalyst layer could be cooled gently and quickly without causing thermal runaway when the water methanol supply was stopped after switching.
[0045]
【The invention's effect】
As is clear from the above description, according to the present invention, the following effects can be obtained.
(A) When the methanol reformer is stopped, the introduction of air is first stopped, then the water / methanol molar ratio is switched to a higher molar ratio than during steady operation, and then the introduction of water and methanol is stopped. Therefore, by stopping the first air introduction, the partial oxidation reaction, which is an exothermic reaction, can be suppressed and the steam reforming reaction, which is an endothermic reaction, can proceed. Thus, this endothermic reaction can be further promoted.
Therefore, the catalyst temperature can be lowered quickly, and the stop time can be shortened.
[0046]
(B) When the methanol reformer is stopped, the water / methanol molar ratio is switched to 4.6 or more, which is excluded from the high-speed reaction region, and then water and methanol introduction is stopped, which causes thermal runaway. A calm stop can be realized.
[Brief description of the drawings]
1 is a fuel supply system diagram for a fuel cell in an electric vehicle according to a first embodiment of the present invention;
FIG. 2 is a mixed phase diagram of water / methanol / air.
FIG. 3 is a fuel supply system diagram to a fuel cell in an electric vehicle according to a second embodiment of the present invention.
FIG. 4 is a transition diagram of catalyst temperature rise by a test apparatus.
[Explanation of symbols]
23 Reformer (Methanol reformer)
41 reforming catalyst layer

Claims (1)

A method for stopping a methanol reformer that generates a hydrogen-enriched gas by reacting a mixed gas of water, methanol and air on a catalyst,
A method for stopping a methanol reformer characterized by first stopping air introduction, then switching the water / methanol molar ratio to 4.6 or more, and then stopping the introduction of water and methanol.

Images