JPH02302303A - Power generation system of fuel cell - Google Patents

Abstract

PURPOSE:To prevent deterioration of catalyst in a water vapor-improving device and make possible to operate cell for a long period of time by highly desulfurizing sulfur in fuel gas supplied into a fuel electrode of a fuel cell in a desulfurizer filled with Cu-Zn based desulfurizing agent. CONSTITUTION:The objective power generation system of fuel cell is composed of a desulfurizer 2a desulfurizing raw fuel 1 and a improving device 4 with water vapor improving-desulfurized raw fuel to fuel gas mainly containing hydrogen, etc. Said desulfurizer 2a is filled with Cu-Zn based desulfurizing agent. Then sulfur content of raw fuel highly desulfurized by the desulfurizer 2a is made to be <=5ppb.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a fuel cell power generation system. More specifically, the present invention relates to a fuel cell power generation system that improves the fuel gas system supplied to the fuel electrode and is particularly suitable for gaseous fuels such as city gas containing odorants.

<Prior Art> Fuel cells have conventionally been known as a system that directly converts chemical energy contained in fuel into electrical energy.

In this fuel cell, a pair of porous electrodes consisting of a fuel electrode and an oxidizer electrode are placed opposite each other with an electrolyte layer holding an electrolyte sandwiched between them to form a fuel cell. By bringing an oxidizing agent such as air into contact with the back of the oxidizing agent electrode, electrical energy is extracted from between the two electrodes by utilizing the electrochemical reaction that occurs at this time. . As long as fuel gas and oxidizer are supplied, electrical energy can be extracted with high conversion efficiency, and research into practical application is being actively conducted because it is advantageous in terms of energy saving and environmental protection.

In this type of fuel cell, hydrogen is commonly used as a fuel, and this hydrogen is usually methane, ethane, propane, butane, natural gas, naphtha, kerosene, diesel oil, liquefied petroleum gas (
It is obtained by subjecting raw fuels such as LPG) and city gas to a steam reforming reaction to convert them into fuel gas whose main component is hydrogen.

The sulfur component in the raw fuel mentioned above poisons the steam reforming catalyst (for example, Ru-based catalyst, Ni-based catalyst, etc.), and for example, if the sulfur content in the raw fuel is 0. Even in a state of about 1 ppm, about 90% of the surface of the Ru catalyst or Ni catalyst is covered with sulfur in a short time, resulting in a significant deterioration of catalytic activity. Under such circumstances, the raw fuel is subjected to a desulfurization reaction before being subjected to a steam reforming reaction.

A typical desulfurization method conventionally carried out prior to steam reforming of raw fuel is to remove organic sulfur from raw fuel at 350 to 400°C in the presence of a Ni-Mo or C0-M0 catalyst. After hydrogenolyzing, the H2S produced is 350 to 40
This is a hydrodesulfurization method in which Z n OL is adsorbed and removed at 0°C.

FIG. 2 is a system diagram showing an overview of the basic configuration of a typical example of a fuel cell power generation system having a desulfurization device using a hydrodesulfurization method and a steam reformer. In the figure, the raw fuel 1 is mixed with a fuel gas containing hydrogen as a main component derived from a carbon oxide shift converter 5 (described later), and is mixed with a hydrogen desulfurization device 2b.
will be introduced in

The hydrodesulfurization equipment 2b sequentially processes Ni from the inlet side of the raw fuel 1.
It is composed of a hydrogenation layer filled with a -Mo-based catalyst, a Co-Mo-based catalyst, etc., and an adsorption layer filled with an adsorbent such as ZnO. The raw fuel 1 is heated to 350 to 400°C in a heater, and then hydrogenated in a hydrogenation layer to convert the sulfur component in the raw fuel to H2S, and then the generated H2S is adsorbed and removed in an adsorption layer. Raw fuel 1 is desulfurized. The desulfurized raw fuel 1 is mixed with steam in a mixer 3 and sent to a steam reformer 4.
The gas is introduced into the fuel gas and is converted into a fuel gas containing hydrogen as a main component through a steam reforming reaction, which is then discharged. The discharged fuel gas is introduced into the carbon monoxide shift converter 5 filled with a shift catalyst to prevent the contained carbon monoxide from poisoning the catalyst of the fuel electrode 7 and to increase the conversion efficiency into hydrogen. Carbon oxide is converted to hydrogen and carbon dioxide. - A portion of the fuel gas discharged from the carbon oxide shift converter 5 is
The remainder is sent to the fuel electrode 7 of the fuel cell main body 6 and used as fuel. Hydrogen in the fuel gas that has flowed into the fuel electrode 7 undergoes an electrochemical reaction with oxygen in the air 9 that has flowed into the oxidizer electrode 10 by the compressor 8, and as a result, a portion of the fuel gas is consumed and electricity is generated. Energy is obtained and water is produced as a by-product.

The fuel gas discharged from the fuel electrode 7 is transferred to the steam reformer 4
The air 9 is sent to the burner 11 of the steam reformer 11 and joins with the air 9 supplied from the compressor 8, is burned in the burner 11, and is used as a heating source for the steam reformer 4. The exhaust gas containing water vapor discharged from the burner 11 passes through the heat exchanger 12, and then is separated into steam and water by the condenser 13, and the separated gas is exhausted. In addition, the aggregated water is removed from the water supply line 14.
The water flows through the water supply pump 15 and the cooling water pump 16, and is sent to the fuel cell main body 6, where it is used for cooling. Cooling water discharged from the fuel cell main body 6 is sent to a steam-water separator 18 via a heat exchanger 17, and is separated into water and steam. The separated water passes through the cooling water pump 16 and is circulated for cooling the fuel cell main body 6, and the steam is sent to the mixer 3 where it is mixed with the desulfurized raw fuel 1 and then sent to the steam reformer. 4 and used in the steam reforming reaction.

In such a fuel cell power generation system, there are many problems in the desulfurization process of raw fuel. In other words, the hydrodesulfurization catalyst has no catalytic activity unless the temperature is about 350°C or higher, making it difficult to respond immediately to changes in the load of the fuel cell, and special heating equipment and flow are required to operate without warm-up time. A road control device is required, and miniaturization is difficult.

In addition, in the hydrodesulfurization process, in the case of raw fuel containing more than a certain amount of organic sulfur, especially city gas, which contains persistent and non-adsorbable organic sulfur such as dimethyl sulfide as an odorant. In the case of gaseous fuel, undecomposed substances slip and pass through without being adsorbed by ZnO. Furthermore, during adsorption desulfurization, the amount of H2S5COS does not fall below a certain value due to the equilibrium represented by, for example, ZnO+H2S::ZnS+H20 ZnO+COS':ZnS+H2z. This tendency is particularly pronounced when H20 and CO2 are present.

Furthermore, if the desulfurization system is unstable during startup or shutdown of the device, sulfur may scatter from the adsorption desulfurization catalyst, increasing the sulfur concentration in the raw fuel. Therefore, in the current desulfurization process, the sulfur concentration in the raw fuel after refining ranges from several ppm to 0.5 ppm. It is carried out at a level of 1ppm, which is sufficient to prevent poisoning of the steam reforming catalyst.
There is a problem in that it cannot be suppressed and the fuel cell cannot be operated stably for a long period of time.

The present invention was devised to solve the problems of the prior art described above, and by improving the fuel gas system supplied to the fuel electrode, it is possible to reduce the size of the fuel and provide a fuel that can be operated stably for a long time. The purpose is to provide a battery power generation system.

Means and operation for solving the above problems> The fuel cell power generation system of the present invention, which has been made to solve the above problems, has the following features:
In a fuel cell power generation system having at least a desulfurization device for desulfurizing raw fuel and a steam reforming device for reforming the desulfurized raw fuel into fuel gas containing hydrogen as a main component, the desulfurization device uses a copper-zinc desulfurization agent. This power generation system is particularly suitable for fuel cells that use gaseous fuel such as city gas as raw fuel. In the present invention, the copper-zinc desulfurization agent includes at least copper and a zinc component (e.g., zinc oxide, etc.), and further contains an aluminum component (e.g., aluminum oxide, etc.), a chromium component (e.g., chromium oxide, etc.). This refers to a desulfurizing agent that may contain other components such as (etc.).

In the fuel cell power generation system of the present invention, for desulfurization of raw fuel,
Desulfurization equipment filled with steel-zinc desulfurization agent (
A copper-zinc desulfurization device (hereinafter referred to as copper-zinc desulfurization equipment) is used, and the desulfurization agent reduces the sulfur content in the raw fuel to 5 ppb (as sulfur,
The same applies hereinafter) or less, which can usually be 0.1 ppb or less. Therefore, poisoning of the steam reforming catalyst in the subsequent steam reforming reaction is suppressed, the catalyst activity can be maintained for a long time, and stable operation of the fuel cell becomes possible.

In the present invention having the above configuration, examples of the copper-zinc desulfurization agent to be filled in the copper-zinc desulfurization equipment used for desulfurization of raw fuel include Japanese Patent Application No. 62-279867 and Japanese Patent Application No. 62-1989. The copper-zinc desulfurization agent disclosed in No. 279868 is mentioned, and the same publication describes a desulfurization agent containing copper and zinc oxide as main components (hereinafter referred to as copper-zinc desulfurization agent).
and a desulfurizing agent containing copper, zinc oxide, and aluminum oxide as main components (hereinafter referred to as a copper-zinc-aluminum desulfurizing agent). More specifically, these desulfurizing agents are prepared by the following method.

(1) Copper-zinc desulfurization agent: Uses an aqueous solution containing a copper compound (e.g., copper nitrate, copper acetate, etc.) and a zinc compound (e.g., zinc nitrate, zinc acetate, etc.) and an aqueous solution of an alkaline substance (e.g., sodium carbonate, etc.) Then, a precipitate is produced by a conventional coprecipitation method. The formed precipitate is dried and calcined (about 300°C) to form a copper oxide-zinc oxide mixture (in atomic ratio, usually copper:zinc-1=about 0.
3 to 10, preferably 1: about 0.5 to 3, more preferably 1: about 1 to 2.3), the hydrogen content is 6% by volume or less, more preferably 0.5 to 4% by volume. The above mixture is reduced at about 150 to 300° C. in the presence of hydrogen gas diluted with an inert gas (for example, nitrogen gas) so as to achieve the desired temperature. The copper-zinc desulfurization agent thus obtained may contain other components, such as chromium oxide.

■Copper-zinc-aluminum desulfurization agent Copper compounds (e.g. nitric steel, copper acetate, etc.), zinc compounds (
Co-precipitation by a conventional method using an aqueous solution containing an aluminum compound (e.g., aluminum nitrate, sodium aluminate, etc.) and an aqueous solution of an alkaline substance (e.g., sodium carbonate, etc.). A method is used to form a precipitate. The generated precipitate was dried and calcined (30
(approximately 0°C) and then prepare a copper oxide-zinc oxide-aluminum oxide mixture (in atomic ratio, usually copper:zinc nialium-1
: about 0.3 to 10: about 0.05 to 2, preferably 1: about 0.6 to 3: about 0.3 to 1), the hydrogen content is 6% by volume or less, more preferably 0. The above mixture is reduced at about 150 to 300° C. in the presence of hydrogen gas diluted with an inert gas (for example, nitrogen gas, etc.) to a concentration of about 5 to 4% by volume. Copper obtained in this way...
The zinc-aluminum desulfurization agent may contain other components, such as chromium oxide.

The copper-zinc desulfurization agent obtained by methods (1) and 0 above has fine particulate copper with a large surface area uniformly dispersed in zinc oxide (and aluminum oxide), and zinc oxide (and aluminum oxide). It is in a highly active state due to chemical interaction with aluminum oxide and aluminum oxide). Therefore, the use of these desulfurization agents ensures that the sulfur content in raw fuels is reduced by 5.
ppb or less, usually 0.1 ppb or less,
Further, it is also possible to reliably remove refractory sulfur compounds such as dimethyl sulfide.

In the present invention, various fuels conventionally used as raw fuels for fuel cells can be used, but gaseous fuels are particularly preferred, such as methane, ethane, propane, butane, natural fuels, etc. Examples include gas, LPG, city gas, and mixtures thereof. In addition, the types of fuel cells are not particularly limited, and include low-temperature fuel cells (for example, phosphoric acid electrolyte fuel cells, solid polymer electrolyte fuel cells, super acid electrolyte fuel cells, alkaline electrolyte fuel cells, etc.) and high-temperature fuel cells ( For example, it may be a molten carbonate fuel cell, a solid oxide electrolyte fuel cell, etc.).

<Examples> Hereinafter, the present invention will be described in detail with reference to the accompanying drawings showing examples.

FIG. 1 is a system diagram schematically showing an embodiment of the fuel cell power generation system of the present invention, and the same members as in FIG. 2 are denoted by the same reference numerals.

In FIG. 1, raw fuel 1 is preheated by a separately provided heater or heat exchanger as required, and then flows into a copper-zinc desulfurization device 2a. The copper-zinc desulfurization equipment 2a includes
The desulfurizer 2 is filled with the above-mentioned copper-zinc desulfurization agent.
For example, the desulfurization in step a is performed at a temperature of about 10 to 400°C,
Preferably about 150~250℃, pressure 0~10kg/
It is performed for approximately c-φG and GH3V of approximately 500 to 3000, but is not limited to these conditions. The raw fuel 1 discharged from the desulfurizer 2a has been desulfurized to a sulfur content of 5 ppb or less, usually 0.1 ppb or less.

The raw fuel 1 desulfurized in this way is mixed with steam at an appropriate mixing ratio in a mixer 3, and then introduced into a steam reformer 4 where it is subjected to a steam reforming reaction to produce a fuel containing hydrogen as a main component. converted to gas. As the steam reformer 4, a steam reformer filled with, for example, a Ru catalyst, a Ni catalyst, etc. is used, similar to the steam reformer of a conventional fuel cell. Fuel gas containing hydrogen as a main component discharged from the steam reformer 4 is sent to the carbon monoxide shift converter 5 in the same manner as in the past, and the carbon oxide content is reduced and the hydrogen content is increased. Next, the fuel gas discharged from the carbon oxide shift converter 5 is sent to the fuel electrode 7 of the fuel cell main body 6, and undergoes an electrochemical reaction with oxygen in the air 9 flowing into the oxidizer electrode 10 by the compressor 8. As a result, part of the fuel gas is consumed, electrical energy is obtained, and water is produced as a by-product.

In addition, processing of the fuel gas discharged from the fuel electrode 7 (for example, sending it to the burner 11, burning it, and using it as a heating source for the steam reformer 4, etc.), processing of the exhaust gas discharged from the oxidizer electrode 10, The cooling of the fuel cell main body 6, the cooling water circuit, etc. are the same as those of the conventional device.

The present invention is not limited to the above-described embodiments, but can be implemented with various modifications without changing the gist thereof, and various conventionally known mechanisms can be added. For example, a mechanism that controls the fuel gas supplied to the fuel electrode 7 and the air 9 supplied to the oxidizer electrode 10 according to the load, or a mechanism that detects the differential pressure between the fuel electrode 7 and the oxidizer electrode 10 and adjusts the differential pressure. Alternatively, a plurality of fuel cell main bodies 6 may be connected in parallel or in series. Furthermore, a fuel recirculation fan is provided between the fuel gas supply line of the fuel electrode 7 and the fuel gas discharge line to return a part of the discharged fuel gas to the fuel electrode 7, and an air supply line of the oxidizer electrode 10 is provided. An air recirculation fan may be provided between the line and the air exhaust line to return a portion of the exhausted air to the oxidizer electrode 10. By providing these recirculation mechanisms, it is possible to reuse the reactive gas after the electrode reaction, adjust the hydrogen concentration of the exhaust fuel gas and the oxygen concentration of the exhaust air, and adjust the load fluctuation of the fuel cell. can.

Hereinafter, the present invention will be explained in more detail based on test examples and comparative examples, but the present invention is not limited to these test examples.

Test Example 1 A test was conducted using the fuel cell power generation system shown in FIG. In addition, as a steam reformer, Ru catalyst (R
u2%, AI) z03 supported) 5g (bulk density 0.8
kg #) (catalyst layer length approximately 1 m)
) was used. In addition, as a desulfurization device, a sodium carbonate aqueous solution is added as an alkaline substance to a mixed aqueous solution containing copper nitrate and zinc nitrate, and the resulting precipitate is washed and filtered, and then the precipitate is 1/8 inch in height x 1/8 inch in diameter. The fired product [copper dizinc - about 1=1 (atomic ratio)] was heated to about 300°C using nitrogen gas containing 2% by volume of hydrogen. A desulfurization device (desulfurization layer length about 50 marks) filled with copper-zinc desulfurization agent 2 (l) obtained by reduction treatment at 200° C. was used.

As raw fuel, city gas 13A consisting of the components shown in Table 1 below was preheated to 200°C in a preheater, and then heated to 10 m
''/h to the desulfurization equipment for desulfurization. After mixing the desulfurized gas with steam, it was introduced to the steam reforming equipment,
S/C (number of moles of water vapor per mole of carbon in raw fuel hydrocarbon) -3,3, reaction temperature 450 ° C (inlet) and 66
A steam reforming reaction was carried out at 5°C (outlet) and a reaction pressure of 0.2) cg/c-G. The steam-reformed fuel gas is −
It was led to the fuel electrode of the fuel cell main body through a carbon oxide transformer, and reacted with the oxygen in the air introduced to the oxidizer electrode to extract electrical energy.

Table 1 Methane 86.9% by volume Ethane
8.1% by volume propane
3.7% by volume butane
1.3% by volume odorant dimethyl sulfide 3m
g-8/Nrn” t-butyl mercaptan 2s+g-
8/Nm'' In the above test, the sulfur content in the gas at the desulfurizer outlet was measured over time, and even after 2000 hours, the sulfur content was 0.1 ppb or less.

Furthermore, no deterioration of the catalytic activity of the steam reforming catalyst was observed even after 2000 hours had elapsed, and the same activity as that immediately after the start of the reaction was maintained, and the fuel cell operated normally.

Comparative Example 1 In the fuel cell power generation system shown in FIG. 2, 5 g of Ni-Mo hydrodesulfurization catalyst and zinc oxide IC were used as desulfurization agents.
II! We created a system using a desulfurization equipment filled with
The fuel cell was operated in the same manner as Test Example 1. However, when the desulfurization temperature is 380℃ and the recycled reformed gas is supplied to the desulfurizer (
i.e. - fuel gas recycled from the carbon oxide transformer)
The amount was 2% by volume based on the raw fuel.

As a result, the sulfur content of the gas at the desulfurizer outlet immediately after the start of the reaction was 0.2 ppm, and remained almost unchanged thereafter, but after 500 hours, the methane slip at the reformer outlet increased. The fuel cell's electrical output began to decline, and eventually the device had to be shut down. At this time, the reforming catalyst had almost completely deteriorated.

Test Example 2 In the fuel cell power generation system used in Test Example 1, a heater and a cooler were temporarily installed in front of the desulfurization equipment so that the raw fuel could be heated or cooled, but the same equipment as Test Example 1 was used. A fuel cell power generation system was similarly operated using the same method. However, during this period, every 8 hours, the temperature at the inlet of the desulfurization equipment is lowered to about 20°C over 15 minutes, and then lowered to about 20°C over 15 minutes.
An operation was performed to return the temperature to 0°C. This simulates the conditions that the desulfurization equipment undergoes during start-up and shutdown of a fuel cell power generation system.

As a result, as in Test Example 1, even after a total of 2000 hours of operation, the sulfur content in the desulfurization equipment outlet gas remained at 0. 1p
pb or less, no deterioration of the catalyst was observed, and the fuel cell operated normally.

Comparative Example 2 Using the same device as in Comparative Example 1, a fuel cell was operated in the same operating pattern as in Test Example 2. However, the range of the desulfurizer inlet temperature was 20°C to 380°C (commonly used).

As a result, the sulfur content in the gas at the desulfurizer outlet was 0.2 ppm at normal temperature, but 3 ppm when the temperature dropped.
It had reached m. In addition, after 200 hours of operation, the slip of the feedstock hydrocarbon at the exit of the reformer increases,
The fuel cell's electrical output began to decline, and eventually the device had to be shut down. At this time, the reforming catalyst had almost completely deteriorated.

Test Example 3 In Test Example 1, a sodium carbonate aqueous solution was added as an alkaline substance to a mixed aqueous solution in which copper nitrate, zinc nitrate, and aluminum nitrate were dissolved as a copper-zinc desulfurization agent to be filled in a desulfurization equipment, and the resulting precipitate was washed and washed. After filtration, the tablets are formed into a size of 1/8 inch in height x 1/8 inch in diameter, fired at about 400°C, and then the fired body (copper oxide 45%
, zinc oxide 45%, aluminum oxide 10%) to hydrogen 2
Using a copper-zinc-aluminum desulfurization agent obtained by reduction using nitrogen gas containing % by volume at a temperature of about 200°C,
A test similar to Test Example 1 was conducted.

As a result, as in Test Example 1, it was found that the sulfur content in the desulfurization device outlet gas could be desulfurized to 0.1 ppb or less, that deterioration of the steam reforming catalyst could be suppressed, and that the fuel cell could be operated normally. It worked.

<Effects of the Invention> According to the fuel cell power generation system of the present invention, the following effects can be achieved.

(1) A desulfurization device with excellent desulfurization performance is used to highly desulfurize the raw fuel and subject it to a steam reforming reaction, which prevents deterioration of the steam reforming catalyst and allows the fuel cell to operate stably for long periods of time. In addition, it is possible to reduce the cost of the steam reforming catalyst and to downsize the device.

(2) Since the steam reforming catalyst can maintain high activity for a long time, high V operation is possible, making it possible to downsize the device and reduce catalyst cost. In addition, low S/C operation is possible,
It can contribute to improving thermal efficiency, power generation efficiency, etc.

G) Desulfurization is possible in a low temperature range, and there is no need for high-temperature desulfurization like in conventional hydrodesulfurization, so there is no need for a special heating device, and it is resistant to fuel cell load fluctuations. Able to respond quickly.

(4) When conventional hydrodesulfurization is used in the desulfurization process, a hydrogen recycle line is required from a steam reformer, etc., but the system of the present invention does not require a hydrogen recycle line, so the system is simple. It is possible to reduce the size of the device.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an overview of an embodiment of the fuel cell power generation system of the present invention, and FIG. 2 is a system diagram showing an overview of a conventional fuel cell power generation system.

Claims (1)

[Scope of Claims] 1. In a fuel cell power generation system having at least a desulfurization device for desulfurizing raw fuel and a steam reforming device for reforming the desulfurized raw fuel into fuel gas mainly composed of hydrogen, the desulfurization device - A fuel cell power generation system comprising a desulfurization device filled with a zinc-based desulfurization agent. 2. The fuel cell power generation system according to claim 1, wherein the desulfurization device desulfurizes the sulfur content of the raw fuel to 5 ppb or less. 3. Desulfurization equipment reduces the sulfur content of raw fuel to 0.1pp
The fuel cell power generation system according to claim 2, wherein the fuel cell power generation system desulfurizes to below b. 4. The copper-zinc desulfurization agent in the desulfurization equipment is a desulfurization agent obtained by hydrogen reduction of a copper oxide-zinc oxide mixture prepared by a coprecipitation method using a copper compound and a zinc compound, or a copper compound;
4. The fuel cell power generation system according to claim 1, wherein the desulfurization agent is obtained by hydrogen reduction of a copper oxide-zinc oxide-aluminum oxide mixture prepared by a coprecipitation method using a zinc compound and an aluminum compound. 5. The fuel cell power generation system according to any one of claims 1 to 4, wherein the raw fuel is a gaseous fuel.