JP2002104808A - Method of reforming fuel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of reforming a fuel by which a gas containing gaseous hydrogen mainly is produced from gaseous oxygen or air, a hydrocarbon and a steam. SOLUTION: Hydrogen is manufactured without external heating in the fuel-reforming method by making a raw material gas which contains oxygen or air, a hydrocarbon and a steam come in contact with a catalyst which simultaneously promotes an oxidation reaction of the hydrocarbon and a steam- reforming reaction of the hydrocarbon. A porous carrier of the catalyst consists of a metal oxide which contains at least Al and is loaded with precious metals such as Pd, Pt, Ru, and Rh, or the above metals and one or more metals selected from Ni, Co, Fe, Ag, Cu, Zn, Cr and rare earth elements. Exotherm of the oxidation reaction is balanced with endotherm of the steam-reforming reaction by controlling the supported quantity of the active component which promotes the oxidation reaction of the hydrocarbon and the active component which promotes the steam-reforming reaction of the hydrocarbon, as a result the whole catalyst is maintained at a prescribed temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel reforming method for producing a gas containing hydrogen as a main component by using oxygen or air, a hydrocarbon, and steam.

[0002]

2. Description of the Related Art A fuel reformer is a device that generates a gas containing hydrogen and steam as raw materials and containing hydrogen as a main component.
It is known as a supply device of hydrogen which is a fuel of a fuel cell.

In recent years, fuel cell systems are expected to be used as power systems for automobiles and homes. Therefore, not only the fuel cell body but also a fuel reformer that generates hydrogen serving as a fuel of the fuel cell is required to be reduced in size and start-up time.

[0004] The steam reforming reaction which proceeds inside the fuel reformer will be described by taking as an example the case where methane is used as a raw material.

[0005] The steam reforming reaction is a reaction for producing hydrogen by reacting methane and steam, as shown in the equation (1). Usually, the reaction temperature is 750 to 850 ° C. A nickel-based catalyst or the like is used.

[0006]

Embedded image CH ₄ + H ₂ O⇔CO + 3H ₂ (1) The reaction of the above formula (1) is an endothermic reaction, and a heat source is required to promote and continue this reaction. Conventional tubular and plate-type fuel reformers use an indirect heating method, in which the reforming section filled with catalyst is heated from the outside. There was a problem that it was extremely bad.

On the other hand, in addition to external heating, air or oxygen is supplied to the fuel reformer, and a partial oxidation reaction is caused on the reforming catalyst to generate heat of reaction. 2. Description of the Related Art A fuel reformer that heats from the inside to improve load following performance is known (for example, Japanese Patent Application Laid-Open No.
186570, JP-A-2-160603).

[0008]

In the above-mentioned fuel reformer, the amount of supply of hydrocarbons and the amount of oxygen or air supplied for partial oxidation are independently controlled at the time of starting and stopping or at the time of load fluctuation. Thus, the internal temperature of the reformer was adjusted, and the control was very complicated.

Further, since the oxidation reaction rate is higher than the steam reforming reaction rate, the inlet side of the gas having a high oxygen concentration has
There has been a problem that the temperature is increased mainly due to the progress of the partial oxidation reaction, and a temperature distribution is generated inside the reformer.

[0010] In view of the above, an object of the present invention is to provide a fuel reforming method in which the calorific value of the oxidation reaction and the heat absorption amount of the steam reforming reaction are balanced.

[0011]

The gist of the present invention for solving the above problems is as follows.

By contacting a raw material gas containing oxygen or air with hydrocarbons and steam with a catalyst having an active component which simultaneously promotes the oxidation reaction of the hydrocarbons and the steam reforming reaction of the hydrocarbons, heat from the outside is obtained. Fuel reforming method characterized by producing hydrogen without applying hydrogen.

That is, by adjusting the amount of the active component that promotes the oxidation reaction of the hydrocarbon and the amount of the active component that promotes the steam reforming activity of the hydrocarbon, the calorific value of the oxidation reaction and the amount of the steam reforming reaction are adjusted. There is a fuel reforming method that balances the amount of heat absorbed and maintains the entire catalyst at a desired temperature.

[0014] As the catalyst, Pd, Pt, Ru, R
h and / or the noble metal and Ni, Co, F
A catalyst supporting at least one of e, Ag, Cu, Zn, Cr and rare earth is used.

The following reaction takes place by bringing oxygen or air into contact with a hydrocarbon or steam with the catalyst of the present invention.

[0016]

CH ₄ + H ₂ O⇔CO + 3H ₂ (1) CH ₄ + 2O ₂ → CO ₂ + 2H ₂ O (2) The reaction of the formula (2) is a large exothermic reaction, for example, 1%
Of CH ₄ reacts according to the formula (2), the gas temperature becomes about 350 ° C.
To rise. On the other hand, in the formula (1), since the reaction is a large endothermic reaction as described above, it is necessary to constantly supply heat from the outside to continue the reaction.

The present invention is characterized in that the formula (1) and the formula (2) occur simultaneously on the same catalyst, so that the reaction of the formula (1) is continued without supplying heat from the outside.

FIG. 1 schematically shows a reaction on a catalyst in which Pd is supported as an active point for promoting an oxidation reaction and Ni is supported as an active point for promoting a steam reforming reaction. FIG.

On Pd, the reaction of equation (2) mainly occurs to generate heat energy ΔE (), and the generated ΔE is transmitted to nearby Ni (). Using this ΔE, Ni
Above, the reaction of the formula (1) occurs mainly (), and hydrogen can be produced.

Thus, according to the present invention, external heating,
In other words, the entire catalyst layer is directly heated by the generated reaction heat without relying on the heat transfer through the outer wall of the reaction tube, so that the load following ability can be significantly improved.

Further, since the calorific value of the oxidation reaction and the endothermic amount of the steam reforming reaction are balanced in any part of the catalyst layer, the temperature distribution inside the catalyst layer is improved.

At the time of startup, the temperature can be easily raised by increasing the supply amount by the heat capacity of the apparatus without changing the composition of the source gas. Further, even at the time of load fluctuation, the hydrogen production amount can be increased or decreased substantially without a temperature change by merely changing the supply amount without changing the composition of the source gas.

In a fuel reformer which generates a gas containing hydrogen as a main component using oxygen or air, hydrocarbons and steam as raw materials, the oxidation reaction of hydrocarbons in the raw materials and the steam reforming reaction are performed at a constant rate. The catalyst having the function of promoting the reaction plays an important role. Therefore, it is also a key point of the present invention. This catalyst is described in detail below.

First, a catalyst for oxidizing hydrocarbons represented by the above formula (2) needs to have heat resistance of 700 ° C. or higher and low-temperature activity for igniting at as low a temperature as possible. For this purpose, noble metals such as Pd, Pt, Ru, Rh, Ag, Mn, and the like are added to a porous ceramics carrier containing alumina, silica, silica-alumina and the like.
A catalyst supporting a transition metal such as Co is preferable. In particular, Pd,
Mn and Ag are effective.

In the vicinity of these elements, noble metals, Ni, Co, Fe, A, which are active components for promoting the formula (1),
g, Cu, Zn, Cr, and at least one of rare earths. As a result, the reactions of the formulas (1) and (2) occur simultaneously on the same catalyst surface, and hydrogen can be produced.

Among these, in particular, rare earth / β-alumina, particularly La · β-alumina, is used as a carrier, and the formula (1)
It is effective to use Ni, Ru as a component for activating the reaction of Pd and Pd, Pt as a component for activating the reaction of the formula (2). Here, β-alumina means alumina having a β structure. In addition, as La · β-alumina, L
The alumina having a β-structure containing La at a molar ratio of a to alumina of 5:95 is preferable.

Next, the catalyst is usually used in a granular form for ease of production. However, a monolithic structure is desirable because of its advantages such as low pressure loss and small heat capacity.

As the material of the monolithic structure, ordinary cordierite, mullite, silicon carbide, alumina, and metals having high thermal conductivity are also effective. The surface of these structures is coated with the above-mentioned porous carrier, and the above-mentioned noble metals such as Pd, Pt, Ru, Rh and / or the above-mentioned noble metals and Ni, Co, Fe, Ag, Cu, Z
At least one of n, Cr and rare earth is supported. By making the catalyst have a monolithic structure, the gas flow resistance, which has a problem with the granular catalyst, can be reduced.

Further, since the heat capacity of the carrier itself of the monolithic structure is smaller than that of the granular carrier, the time required for the entire catalyst layer to reach a predetermined temperature can be shortened. Furthermore, by making the catalyst carrier having a monolithic structure made of a metal having a high thermal conductivity, the time required for eliminating the temperature distribution of the entire catalyst at the time of starting and stopping or a load change can be significantly reduced.

Further, the catalysts represented by the formulas (1) and (2)
The reaction of the formula (1) may not be performed on the same catalyst surface, and a catalyst that promotes the reaction of the formula (1) and a catalyst that promotes the reaction of the formula (2) may be uniformly mixed. However, in this case, since the heat conduction efficiency is lower than the reaction on the same catalyst, the hydrogen production efficiency slightly decreases, but this is one of effective means.

Using the above catalyst, hydrogen can be produced with high efficiency from oxygen or air, hydrocarbons and water vapor.

The CO generated by the above formula (1) is also:
By the shift reaction of the formula (3) shown below, it is converted into hydrogen and the hydrogen concentration increases.

[0033]

[Image Omitted] CO + H ₂ O → CO ₂ + H 2 (3) In this case, a commonly used shift catalyst containing Cu, Cr, Zn or the like is effective. In addition, in the production of hydrogen for a polymer electrolyte fuel cell, CO ₂ is produced by the shift reaction of the formula (3).
It is necessary to reduce the CO that could not be converted to 100 ppm or less in order to deteriorate the performance of the electrode of the fuel cell. To this end, a CO selective oxidation catalyst is provided downstream of the shift catalyst, and oxygen or air is added to selectively oxidize CO. The catalyst may be a conventional CO selective oxidation catalyst.

The hydrocarbons used as raw materials in the present invention are gaseous hydrocarbons such as CH ₄ , natural gas (LNG), propane and butane, and liquid hydrocarbons such as naphtha, kerosene, gasoline and light oil, and the like. Those requiring relatively high temperatures for the reaction are the main targets.

[0035]

Embodiments of the present invention will be described below.

Embodiment 1 FIG. 2 is a schematic cross-sectional view of a test apparatus for performing a hydrocarbon reforming test of this embodiment. In this example, CH ₄ was used as a raw material hydrocarbon.

The reaction tube 11 is heated from the surroundings by an electric furnace 12. The reaction tube 11 is filled with a catalyst 13, and a filler 14 is filled upstream of the catalyst 13 so that the raw material gas is sufficiently mixed. A temperature sensor 15 is provided at the gas outlet of the catalyst 13 so that the temperature of the product gas passing through the catalyst 13 can be measured.

First, while supplying air to the reaction tube 11 at a rate of 2.99 l / min, the electric furnace 1
Heated at 2. Catalyst 13 measured by temperature sensor 15
When the gas temperature at the outlet reached 100 ° C., water was supplied from the upper part of the reaction tube 11 at a rate of 1.58 g / min.

When the temperature of the gas at the outlet of the catalyst 13 measured by the temperature sensor 15 reaches 400 ° C., CH ₄ is reduced to 0.78 l / m 2.
At the same time, the electric furnace 12 was stopped to stop the external heating.

The composition of the raw materials is as follows: H ₂ O (mol) / CH ₄ (mol) = 2.5, O ₂ (mol) / CH ₄ (mol) = 0.8,
The space velocity on a dry gas basis at the inlet of the catalyst 13 was set to 10000h- ¹ .

As the catalyst 13, the number of cells was 400 cells / i.
La-β- is added to the cordierite honeycomb structure of nch ²
After coating with Al ₂ O ₃ , Pd was 1.5 g / l honeycomb and Ru was 1.5 g / l honeycomb.
g supported catalyst was used.

FIG. 3 is a graph showing the temperature characteristics of the produced gas at the outlet of the catalyst 13 when the test was conducted under the above conditions.

The temperature of the produced gas rose with the heating by the electric furnace 12, and was stabilized at a predetermined temperature of 700 ° C. after one minute.

Further, even after the electric furnace 12 is stopped, while the supply of the raw material gas is continued, the temperature of the catalyst 13 becomes approximately 70 ° C.
It was constant at 0 ° C., indicating that it was thermally independent. When the reaction became completely steady, the outlet gas was analyzed and the amount of hydrogen generated was measured. Table 1 shows the results.

[0045]

[Table 1]

In Table 1, the theoretical calculation values are CH ₄ , H ₂
This is an equilibrium value when O and air are reacted at the composition and temperature of Example 1. From these results, hydrogen shows a value close to the theoretical calculation value, which indicates that the present invention is effective. It is clear that CO, CO ₂ , and CH ₄ other than hydrogen are close to the theoretical values.

[Embodiment 2] FIG. 4 is a schematic sectional view of a test apparatus for performing a hydrocarbon reforming test of this embodiment. This test apparatus is different from the test apparatus shown in FIG. 2 in that a preheater 1 for preheating air, CH ₄ and water supplied to the reaction tube 11 is provided.
6 is provided.

First, the reaction tube 11 was moved from the outer periphery to the electric furnace 12.
When the temperature of the gas at the outlet of the catalyst 13 measured by the temperature sensor 15 reaches 450 ° C., the air, methane, and water which have been heated to 450 ° C. Liter / min, 0.78 liter / min, 1.58 g / min. At the same time, the electric furnace 12 was stopped to stop external heating.

The composition of the raw materials is as follows: H ₂ O (mol) / CH ₄ (mol) = 2.5, O ₂ (mol) / CH ₄ (mol) = 0.6,
The space velocity on a dry gas basis at the inlet of the catalyst 13 was set to 10000h- ¹ . The catalyst 13 uses a metal honeycomb as a monolithic structure, and as an active component, 2 g of Pt and 18 g of Ni per liter of honeycomb.
What was carried was used.

As a result of the test under the above conditions, the gas temperature at the outlet of the catalyst 13 was maintained at the desired 700 ° C. even when the heating by the electric furnace 12 was stopped.

The time required to stabilize at 700 ° C. is shorter than that in Example 1, and the responsiveness is improved by using a metal honeycomb having a small heat capacity and good thermal conductivity as a carrier. I understand.

Table 2 shows the results of analysis of the outlet gas when the catalyst temperature became steady. Also in this example, hydrogen shows a value close to the theoretical calculation value, which indicates that the present invention is effective.

[0053]

[Table 2]

Embodiment 3 FIG. 5 is a schematic flow chart showing an example of a polymer electrolyte fuel cell system including a fuel reformer according to the present invention.

In this embodiment, LN was used as a raw material for hydrogen production.
The case where G is used will be described. This system is mainly
It comprises a fuel reformer 1, a starter burner 2, a heat exchanger 3, a shift reactor 4, a CO remover 5, a polymer electrolyte fuel cell 6, and a boiler 7. The fuel reformer 1 is filled with the catalyst according to the present invention. Air and LNG are supplied to the fuel reformer 1 via the heat exchanger 3.
The water is converted into steam by the boiler 7 and then supplied to the fuel reformer 1.

An operation method of the present system will be described.
First, a predetermined flow of air is introduced into the fuel reformer 1,
Simultaneously with the supply from the upstream side of the catalyst, the fuel and the combustion air are supplied to the starting burner 2 to ignite and generate combustion gas, which is heated to heat the catalyst.

Next, a predetermined flow rate of water is supplied to the boiler 7 and converted into steam, and then supplied to the fuel reformer 1 from the upstream side of the catalyst. Further, the heating of the catalyst is continued by the starting burner 2, and when the temperature of the catalyst becomes equal to or higher than the ignition temperature of LNG, a predetermined flow rate of LNG is supplied from the fuel reformer 1 to the upstream side of the catalyst.
Supply inside.

Although the temperature of the catalyst slightly decreases immediately after the supply of LNG, it immediately starts to increase again due to the heat of reaction generated by the oxidation of LNG. When the temperature rise starts, the supply of fuel and combustion air to the starting burner 2 is stopped, and the heating of the catalyst by the starting burner 2 is stopped.

Thereafter, the temperature does not decrease because the catalyst filled in the fuel reformer 1 generates heat, and the temperature is stabilized at a constant temperature in balance with the heat radiation. Fuel reformer 1
When the temperature reaches a steady state, the gas at the outlet of the heat exchanger 3 is introduced into the shift reactor 4, the hydrogen concentration is increased by the shift reaction, and the gas is introduced into the CO remover 5 to selectively oxidize CO. The CO concentration is set to a predetermined concentration or less, and the CO concentration is introduced into the polymer electrolyte fuel cell 6.

Conventionally, the temperature of the fuel reformer 1 is controlled by LN
The operation control was very complicated because the supply amounts of G, air, and water were individually adjusted, but according to the present invention, LNG
It can be easily performed by changing the total amount without changing the composition of air and water.

For example, at the time of the cold start, the amount of the source gas is increased so as to reach the steady temperature in a short time, and is reduced to a predetermined amount as the temperature approaches the steady state. Fluctuations in the amount of heat radiated from the device due to aging and aging of the outside air temperature also affect the reforming temperature, but in such a case, the composition of the raw material gas does not change, and it is easier to increase or decrease the total amount. It can be adjusted to a predetermined steady temperature.

In the case where the hydrogen production amount is changed in accordance with the load fluctuation, conventionally, the supply amounts of LNG, air, and water were independently adjusted. A complicated control was needed to avoid this. However, according to the present invention, the hydrogen production amount can be changed only by changing the total amount of the raw material gas, and at this time, since the temperature does not change, the operation control becomes extremely easy.

[0063]

According to the present invention, in a fuel reforming method for a fuel cell for producing hydrogen from LNG or kerosene as a raw material, the load following ability is remarkably improved as compared with the conventional method, and the fuel cell system for home use and the automotive fuel cell are used. It is possible to expand applications to devices that require high-speed startup such as a fuel cell system.

Further, it is possible to reduce the number of control auxiliary machines, use low-cost materials, simplify the structure, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a reaction on a catalyst.

FIG. 2 is a schematic cross-sectional view of a test apparatus for performing a hydrocarbon reforming test of Example 1.

FIG. 3 is a graph showing the performance of the catalyst of Example 1.

FIG. 4 is a schematic cross-sectional view of a test device for performing a hydrocarbon reforming test of Example 2.

FIG. 5 is a schematic flow chart showing an example of a polymer electrolyte fuel cell system including a fuel reformer according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fuel reformer, 2 ... Burner for starting, 3 ... Heat exchanger, 4
... Shift reactor, 5 ... CO remover, 6 ... Polymer fuel cell, 7 ... Boiler, 11 ... Reaction tube, 12 ... Electric furnace, 1
3 ... catalyst, 14 ... filler, 15 ... temperature sensor, 16 ... preheater.

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) H01M 8/10 H01M 8/10 (72) Inventor Noriko Yoshida 7-2-1, Omikacho, Hitachi City, Hitachi City, Ibaraki Pref. Within the Hitachi, Ltd. Power and Electricity Development Laboratory (72) Inventor Toshio Yamashita 7-2-1, Omika-cho, Hitachi, Ibaraki Prefecture Within the Hitachi, Ltd. Power and Electricity Development Laboratory (72) Inventor Teruhumi Kawasaki Hitachi, Ibaraki 7-2-1, Omikacho F-term in Hitachi, Ltd. Electric Power and Electric Power Development Laboratory Co., Ltd. BC66A BC67A BC68A BC68B BC70A BC70B BC71A BC72A BC72B BC75A BC75B CC17 DA06 EA19 EC22X EC22Y FA02 FA03 FB23 FC08 4G140 EA03 EA06 EA07 EB31 EB32 EC02 EC03 EC04 EC07 5H026 AA06 5H027 AA01 BA01 BA01

Claims (6)

[Claims] 1. An external gas by contacting a raw material gas containing oxygen or air with hydrocarbons and steam with a catalyst having an active component which simultaneously promotes the oxidation reaction of the hydrocarbons and the steam reforming reaction of the hydrocarbons. A fuel reforming method for producing hydrogen without applying heat from a precious metal such as Pd, Pt, Ru, Rh and / or a porous carrier composed of an oxide containing at least Al as the catalyst. Precious metals and Ni, Co, Fe, Ag, C
A catalyst carrying at least one of u, Zn, Cr, and rare earths is used, and the amount of the active component that promotes the oxidation reaction of the hydrocarbon and the amount of the active component that promotes the steam reforming activity of the hydrocarbon are adjusted. Wherein the calorific value of the oxidation reaction and the endothermic amount of the steam reforming reaction are balanced to maintain the entire catalyst at a desired temperature. 2. The fuel reforming method according to claim 1, wherein a rare earth β-alumina or La β-alumina is used as the porous carrier for supporting the catalyst. 3. The fuel reforming method according to claim 1, wherein a monolithic structure made of cordierite or mullite ceramics and / or metal is used as a carrier for supporting the catalyst. 4. A hydrocarbon oxidation catalyst comprising a porous carrier carrying a noble metal and a ceramic carrier comprising N
The fuel reforming method according to claim 1, wherein a catalyst formed by uniformly mixing a steam reforming catalyst supporting at least one of i, Co, Fe, Ag, Cu, Zn, Cr, and rare earth is used. 5. The fuel reforming method according to claim 1, wherein a shift reaction catalyst for reacting CO with H ₂ O and a catalyst for selectively oxidizing CO to CO ₂ are provided downstream of the fuel reformer. 6. A monolithic structure made of ceramics and / or metal of cordierite or mullite is converted into a raw material gas containing oxygen or air, a hydrocarbon, and water vapor.
.Beta.-alumina porous carrier is coated and P
d. Pt, Ru, Rh noble metal and / or the noble metal is brought into contact with a catalyst supporting at least one of Ni, Co, Fe, Ag, Cu, Zn, Cr, and rare earths, thereby oxidizing the hydrocarbon. And a steam reforming reaction at the same time to produce hydrogen without externally applying heat.