JPH11116202A - Pressurized reformer - Google Patents

Abstract

(57) [Problem] To provide a pressurized reforming apparatus capable of obtaining high reforming efficiency under pressure without increasing operating temperature. A heat transfer plate (14) is provided between a reforming chamber (12) filled with a reforming catalyst (3) and supplied with a source gas (2), and a reforming chamber.
a heating chamber 14 partitioned by a and supplied with a high-temperature gas;
A permeation chamber 16 which is separated from the reforming chamber by a hydrogen separation membrane 16a and to which a sweep gas 15 is supplied, whereby the raw material gas is reformed into a reformed gas containing hydrogen in the reforming chamber, The generated hydrogen is discharged together with the sweep gas from the permeation chamber through the hydrogen separation membrane. The sweep gas flow rate is set such that the hydrogen partial pressure in the reforming chamber is always higher than in the permeation chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure reformer for maintaining a high reforming rate under pressure.

[0002]

2. Description of the Related Art Molten carbonate fuel cells have features not found in conventional power generation equipment, such as high efficiency and little impact on the environment, and are attracting attention as power generation systems following hydro, thermal and nuclear power. Are being researched and developed in various countries around the world. In particular, in a power generation facility using a molten carbonate fuel cell using natural gas as a fuel, a reformer is used to reform a source gas such as natural gas schematically shown in FIG. 5 into a gas containing hydrogen. . The reformer includes a combustion chamber Co and a reforming chamber Re separated by a partition wall.
(For example, anode exhaust gas from a fuel cell),
The reforming chamber Re is heated by the heat, and the raw material gas 2 flowing through the reforming chamber is reformed into a gas 4 containing hydrogen (hereinafter, referred to as a reformed gas) by the reforming catalyst 3 filled therein. Has become.

[0003] As such a reformer, a tubular type developed for a conventional plant has been developed as disclosed in
No. 35778, JP-B-5-9362, JP-A-62-2
No. 7303 has already been proposed for use in fuel cells.

On the other hand, a plate reformer having a configuration completely different from the above-mentioned conventional tubular reformer has already been proposed by the applicant of the present invention and is partially used. As illustrated in the principle diagram of FIG. 6, the plate reformer is configured such that the reforming chamber Re and the combustion chamber Co are each configured in a plate shape and are alternately stacked. The combustion catalyst 5 is filled in a flat plate shape, and the fuel gas 1 and the combustion air 7 supplied from the external manifolds 6a and 6b flow as indicated by broken lines in FIG. ) And heat is generated, and the flue gas 8 is discharged to the external manifold 6 on the opposite side.
discharged from c. On the other hand, the reforming chamber Re is similarly filled with a particulate reforming catalyst 3 in a plate shape, and the raw material gas 2 supplied from the external manifold 6d flows as shown by a solid line in the drawing, and The raw material gas 2 is reformed by the action of
The reformed gas 4 is discharged from the external manifold 6e on the opposite side.

Further, the fuel chamber Co shown in FIG. 6 is replaced with a heating chamber H through which a high-temperature gas flows, and a separate combustion chamber (for example, a catalytic combustor) for supplying high-temperature combustion exhaust gas to the heating chamber H from another combustor. Other plate reformers have also been developed.
Compared with the tubular reformer, such a plate reformer has a large heat transfer area per volume and has a feature that it can be made very small and lightweight, and is not only used for fuel cells but also used in other fields (for example, hydrogen). Application).

[0006]

In the plate reformer described above, increasing the operating pressure is effective for improving plant efficiency and reducing the size. Therefore, it is desired to increase the operating pressure of the plate reformer to about several ata in accordance with the operating pressure of the fuel cell. However, the reforming reaction of methane is CH ₄ + H ₂ O → 3H ₂ + CO. . (formula)
And the number of moles (volume) increases by the reaction, the equilibrium constant decreases due to the increase in pressure, and the reforming rate decreases.

On the other hand, it is possible in principle to improve the reforming rate by increasing the reforming temperature. However, in a plate reformer, if the reforming temperature is increased due to the temperature limitation of the partition walls, it is expensive. It is necessary to use a heat-resistant material (for example, a ceramic material) having poor workability, which is not practical.

The present invention has been made to solve such a problem. That is, an object of the present invention is to provide a pressurized reforming apparatus capable of obtaining high reforming efficiency under pressure without increasing the operating temperature.

[0009]

According to the present invention, a thin plate having high thermal conductivity is provided between a reforming chamber filled with a reforming catalyst and supplied with a hydrocarbon gas containing steam. And a permeation chamber partitioned between the reforming chamber and a hydrogen separation membrane and supplied with a sweep gas, thereby providing a hydrocarbon gas in the reforming chamber. Is reformed into a reformed gas containing hydrogen, and the generated hydrogen is discharged through a hydrogen separation membrane together with a sweep gas from a permeation chamber.

[0010] With this configuration, since the partition walls of the reforming chamber and the permeation chamber are constituted by the hydrogen separation membrane, hydrogen in the reformed gas reformed in the reforming chamber is selectively passed through the hydrogen separation membrane in situ. Since the hydrogen is separated, the hydrogen concentration decreases, the methane reforming reaction (formula) in the reforming chamber is promoted, and even at a relatively low temperature,
A high reforming rate can be achieved without being limited by the equilibrium constant.

According to a preferred embodiment of the present invention, the pressure in the reforming chamber is maintained higher than that in the permeation chamber, and the flow rate of the sweep gas is such that the hydrogen partial pressure in the reforming chamber is always higher than that in the permeation chamber. Is set. With this configuration, it is possible to avoid reverse permeation that occurs when the hydrogen partial pressure of the reforming chamber is lower than that of the permeation chamber, increase the hydrogen permeability, and increase the reforming rate.

It is preferable that the hydrogen separation membrane is a palladium alloy membrane having a thickness of 20 μm or more maintained at a temperature of about 400 ° C. or more. With this configuration, the selective separation of hydrogen by the hydrogen separation membrane can be stably performed.

Further, it is preferable to provide a recycling line for returning the gas passing through the reforming chamber to the inlet side of the reforming chamber.
With this configuration, a part of the reformed gas is recycled to the inlet side of the reformer through the recycling line, so that the partial pressure of hydrogen in the reforming chamber can be increased, and the membrane permeation rate in the hydrogen separation membrane can be increased.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In the drawings, common parts are denoted by the same reference numerals. FIG. 1 is a configuration diagram of a pressure reformer according to the present invention. In FIG. 1, a pressurized reforming apparatus 10 of the present invention includes a reforming chamber 12 to which a hydrocarbon gas containing steam (source gas 2) is supplied, a heating chamber 14 to which a high-temperature gas 11 is supplied, and a sweep gas. Fifteen
Is supplied to the transmission chamber 16. A plurality of the reforming chambers 12, the heating chambers 14, and the permeation chambers 16 are stacked with the heating chambers 14 and the permeation chambers 16 positioned on both sides of the reforming chambers 12 to constitute the above-described plate reformer. It is supposed to.

The hydrocarbon gas used is, for example, city gas containing methane as a main component. The high-temperature gas 11 is
It may be combustion gas supplied from a combustor (not shown). Further, the sweep gas 15 is preferably steam or nitrogen gas.

In FIG. 1, a reforming catalyst 3 is provided in a reforming chamber 12.
Is filled. Further, the heating chamber 14 and the reforming chamber 12 are separated by a thin plate 14a (heat conductive plate) having high thermal conductivity. The heat conductive plate 14a is preferably an airtight metal plate, for example, a heat-resistant steel plate, a copper alloy, stainless steel, or the like. Further, the permeation chamber 16 and the reforming chamber 12 are partitioned by a hydrogen separation membrane 16a. This hydrogen separation membrane 16a
It is a palladium alloy film having a film thickness of several μm maintained at a temperature of about 400 ° C. or higher, which is preferably provided on a surface of a permeable ceramic or the like and has a pressure resistance.

Referring to FIG. 1, a pressure reforming apparatus 10 according to the present invention is shown.
Further includes a recycling line 18 for returning the gas (reformed gas) that has passed through the reforming chamber 12 to the inlet side of the reforming chamber. A recycle blower 18a is provided in the recycle line 18 so that a required flow rate of the reformed gas can be returned to the upstream side. Further, the pressure of the reforming chamber 12 is maintained higher than that of the permeation chamber 16, and the flow rate of the sweep gas 15 is set or controlled so that the hydrogen partial pressure of the reforming chamber 12 is always higher than that of the permeation chamber 16.

With the above-described structure, the hydrocarbon gas 2 is reformed into a reformed gas containing hydrogen in the reforming chamber 12, and the generated hydrogen is discharged together with the sweep gas 15 from the permeation chamber 16 through the hydrogen separation membrane 16a. Can be. Sweep gas 1
When water vapor is used as 5, high-purity hydrogen gas can be obtained by condensing and separating this.
Alternatively, nitrogen gas or the like may be used as a sweep gas, which may be pressurized by a pressure pump or the like and supplied as it is to the anode side of the fuel cell.

FIG. 2 shows the principle of the hydrogen separation membrane. It is known that palladium and palladium alloy films have a property of selectively transmitting hydrogen. This hydrogen permeation mechanism is considered as follows. Hydrogen molecules are adsorbed on the palladium film. The adsorbed hydrogen molecules dissociate into hydrogen atoms. Since the reaction is an endothermic reaction, atomic hydrogen can be easily formed on the surface of the film when the film is heated or the raw material gas is heated and used. Hydrogen atoms are ionized and split into protons and electrons. Atomic hydrogen is a proton (proton) and an electron (electron), and since palladium lacks two electrons in the outermost shell, it can easily take off hydrogen electrons. Protons diffuse from the front surface of the palladium to the back surface.
For this movement, the hydrogen concentration (hydrogen partial pressure) on the front surface / source gas side must be higher than the hydrogen concentration (hydrogen partial pressure) on the back surface / purified hydrogen side. The protons that have reached the back surface recombine with the electrons on the palladium film surface to become hydrogen atoms. Hydrogen atoms combine to form hydrogen molecules. It is molecularly associated with the catalytic ability of the palladium film surface. Hydrogen molecules are desorbed from the pallet membrane. Hydrogen permeates through the above process.

Since only hydrogen which can be in a proton state permeates the palladium film in this manner, other molecules which cannot be in such a state cannot permeate the palladium film. It is also called atomic sieves because hydrogen appears to be transmitted in atomic form. The hydrogen permeation rate of the palladium film changes depending on factors such as pressure, temperature, and film thickness. The permeation amount increases as the partial pressure difference increases, as the temperature increases, and as the film thickness decreases.

[0021]

FIG. 3 is an analysis result showing the hydrogen separation characteristics in the pressurized reformer of the present invention.
a, reforming chamber pressure is 3 ata, hydrogen separation membrane thickness is 20μ
In the case of m, (A) hydrogen partial pressure distribution and (B) hydrogen permeation flow rate distribution are shown. In FIG. 3A, the horizontal axis represents the distance from the inlet, the vertical axis represents the hydrogen partial pressure, the solid line represents the permeation chamber,
The broken line indicates the reforming chamber. In the paired solid line and broken line, the upper pair has no sweep gas, the middle pair has a sweep gas / methane flow ratio of 1, and the lower pair has a sweep gas / methane flow ratio of 3. It is.

In FIG. 3B, the vertical axis represents the total amount of hydrogen permeation, and the three curves in the figure indicate that the sweep gas / methane flow ratio is 1 when no sweep gas is present. , The case where the ratio is 3 is shown.

From the analysis results of FIGS. 3A and 3B, when there is no sweep gas (upper side), the hydrogen partial pressure in the reforming chamber is lower than the hydrogen partial pressure in the permeation chamber until X = about 0.2 m. It can be seen that reverse permeation occurs due to the low flow rate, and the hydrogen permeation flow rate becomes negative. In addition, it can be seen that by increasing the flow rate of the sweep gas, the partial pressure of hydrogen on the permeation side decreases, and the total amount of hydrogen permeation increases.

Therefore, the pressure of the reforming chamber is maintained higher than that of the permeation chamber, and the flow rate of the sweep gas is controlled by the hydrogen partial pressure of the reforming chamber.
By setting or controlling to be always higher than the permeation chamber, it is possible to avoid reverse permeation that occurs when the hydrogen partial pressure in the reforming chamber is lower than that in the permeation chamber, to increase the hydrogen permeability, and to increase the reforming rate. You can see that you can do it.

FIG. 4 is an analysis result showing the reforming rate and the hydrogen recovery rate of the pressurized reformer of the present invention. FIG. 4A shows the relationship between the sweep gas / methane flow ratio and the reforming rate, and FIG. ) Shows the relationship between the reforming outlet temperature and the reforming rate. FIG. 4A shows that the reforming rate and the recovery rate are improved by increasing the sweep gas flow rate. This is considered to be because the partial pressure of hydrogen on the permeation side is reduced by increasing the flow rate of the sweep gas. Further, from this figure, it can be seen that, contrary to the characteristics of the conventional reformer, the reforming rate is increased by increasing the pressure of the reforming chamber. This is considered to be because the equilibrium reforming rate is lowered by increasing the reforming chamber pressure, but the hydrogen partial pressure in the reforming chamber is increased.

Further, from FIG. 4 (B), it can be seen that increasing the reforming outlet temperature increases both the reforming rate and the hydrogen permeation flow rate. On the other hand, the hydrogen recovery rate can maintain a relatively high value of about 90 to 93% regardless of the reforming outlet temperature. Therefore, using a palladium membrane, about 550 ° C.
In the vicinity, a reforming rate of about 93% and a hydrogen recovery rate of about 92% can be achieved.

It should be noted that the present invention is not limited to the above-described embodiment, but can be variously modified without departing from the gist of the present invention.

[0028]

As described above, according to the structure of the present invention,
Since the hydrogen in the reformed gas reformed in the reforming chamber is selectively separated in situ through the hydrogen separation membrane, the hydrogen concentration is reduced, the reforming reaction in the reforming chamber is promoted, and relatively low. Even at temperature, a high reforming rate can be achieved without being limited by the equilibrium constant.

Further, by maintaining the pressure of the reforming chamber higher than that of the permeation chamber and setting the flow rate of the sweep gas such that the hydrogen partial pressure of the reforming chamber is always higher than that of the permeation chamber, Reverse permeation, which occurs when the hydrogen partial pressure is lower than that in the permeation chamber, can be avoided, and the hydrogen permeability and the reforming rate can be increased. Furthermore, by providing a recycle line for returning the gas that has passed through the reforming chamber to the inlet side of the reforming chamber, a part of the reformed gas is recycled to the inlet side of the reformer via the recycling line, so that the gas is reformed. The partial pressure of hydrogen in the chamber can be increased, and the membrane permeation rate in the hydrogen separation membrane can be increased.

Therefore, the pressurized reforming apparatus of the present invention has an excellent effect such that a high reforming efficiency can be obtained under pressure without increasing the operating temperature of the plate reformer.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a pressure reformer according to the present invention.

FIG. 2 is a principle view of a hydrogen separation membrane.

FIG. 3 is an analysis result showing hydrogen separation characteristics in the pressurized reformer of the present invention.

FIG. 4 is an analysis result showing a reforming rate and a hydrogen recovery rate of the pressure reforming apparatus of the present invention.

FIG. 5 is a schematic configuration diagram of a conventional reformer.

FIG. 6 is a principle diagram of a conventional plate reformer.

[Explanation of symbols]

 Reference Signs List 1 fuel gas 2 raw material gas (process gas) 3 reforming catalyst 4 reforming gas 5 combustion catalyst 6a to 6e external manifold 7 combustion air 8 combustion gas 9 hydrogen gas 10 pressurized reformer 11 high temperature gas 12 reforming chamber 14 Heating chamber 14a Heat conducting plate 15 Sweep gas 16 Permeation chamber 16a Hydrogen permeable membrane 18 Recycle line 18a Recycle blower

Claims (4)

[Claims] 1. A reforming chamber filled with a reforming catalyst and supplied with a hydrocarbon gas containing steam, and a reforming chamber is partitioned by a thin plate having high thermal conductivity and supplied with a high-temperature gas. The heating chamber is composed of a permeation chamber partitioned between the reforming chamber and the hydrogen separation membrane and supplied with a sweep gas.
A pressurized reforming apparatus characterized in that a hydrocarbon gas is reformed into a reformed gas containing hydrogen in a reforming chamber, and the generated hydrogen is discharged together with a sweep gas from a permeation chamber through a hydrogen separation membrane. 2. The pressure of the reforming chamber is maintained higher than that of the permeation chamber, and the flow rate of the sweep gas is such that the hydrogen partial pressure of the reforming chamber is:
The pressure reforming apparatus according to claim 1, wherein the pressure reforming apparatus is set to be always higher than the permeation chamber. 3. The pressure reforming apparatus according to claim 1, wherein the hydrogen separation membrane is a barium alloy film having a thickness of several μm and maintained at a temperature of about 400 ° C. or higher. 4. The pressurized reforming apparatus according to claim 1, further comprising a recycle line for returning gas passing through the reforming chamber to an inlet side of the reforming chamber.