JPH0997622A - Fuel cell facilities - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make facilities compact and reduce running cost by concentrating methane gas contained in digestive gas obtained in sludge treatment and supplying to a fuel cell as fuel. SOLUTION: Sludge heated with digestive sludge through a sludge/sludge heat exchanger 11 is put into a digestive bath 10, an organic sludge 10a in the digestive bath 10 is bubbled by using a circulation digestive gas with a bubbling means to agitate digestive juice to accelerate methane fermentation. Sludge in a sludge circulation loop 62 is heat exchanged with a sludge/warm water heat exchanger 61 through the circulation water in warm water circulation loop 67 heated by heat of a fuel cell 50 and heat of a warm water boiler and the circulation water in a connecting warm water circulation loop 68, and warmed sludge is returned to the digestive bath 10. The exhaust gas of the fuel cell 50 is utilized for sludge heating, and extremely high heat efficiency can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system, and more particularly to a fuel cell system using methane gas contained in digestion gas obtained by sludge treatment as a fuel.

[0002]

2. Description of the Related Art Digestion gas obtained by sludge treatment contains a large amount of methane and is expected as a useful energy source in place of petroleum and coal. As a method of using digestive gas, power generation by a gas engine is widely used. by the way,
A recently developed fuel cell that electrochemically directly converts the chemical energy of a continuously supplied fuel into electric energy has higher power generation efficiency and heat recovery efficiency than those of the gas engine, and further reduces noise, vibration, NOx, etc. It is an environmentally friendly power generator with few occurrences. Therefore, if the fuel cell can be operated by digestion gas, it is considered to be very effective from the viewpoint of energy saving or environmental protection. For example, the 32nd Sewer Research Presentation Lecture Collection (July 2, 1995)
(Issued on the 5th), the organic sludge is biologically treated with anaerobic microorganisms in the digestion tank, and the digestion gas generated there is sequentially supplied to the first and second absorption towers, and the absorption solution of the alkaline aqueous solution is used in each absorption tower. It has been reported that carbon dioxide gas is removed by wet absorption and the obtained methane gas is used as a fuel for a fuel cell.

[0003]

However, in the conventional means for using methane gas contained in the digestion gas as the fuel for the fuel cell, the digestion gas generated in the digestion tank is wet-absorbed by the alkaline aqueous solution to generate carbon dioxide gas. Therefore, there is a problem that the apparatus as a whole becomes large in size, running costs increase, and a processing apparatus for absorbing the carbon dioxide is required after absorbing the carbon dioxide, resulting in increase in equipment cost. The present invention has been made in view of such a conventional technical problem, and an object of the present invention is to provide a fuel cell facility capable of downsizing the facility and reducing the running cost and the facility cost.

[0004]

The fuel cell facility according to claim 1 of the present invention comprises a digestion tank for biologically treating organic sludge with anaerobic microorganisms, and a digestion gas generated in the digestion tank.
It is intended to provide a fuel cell facility comprising a digestion gas separation membrane device for separating carbon dioxide concentrated gas and methane concentrated gas, and a fuel cell using the obtained methane concentrated gas as a fuel.

The fuel cell facility according to a second aspect is the fuel cell facility according to the first aspect, wherein the methane concentrated gas is separated into a lean methane gas and a high-concentration methane gas between the digestion gas separation membrane device and the fuel cell. A methane gas separation membrane device is provided, and a carbon dioxide gas circulation channel is provided to circulate a part of the carbon dioxide concentrated gas obtained from the permeation side of the digestion gas separation membrane device back to the digestion tank.

Further, the fuel cell equipment according to claim 3 is
The fuel cell facility according to claim 1, wherein a methane gas separation membrane device that separates the methane concentrated gas into a lean methane gas and a high-concentration methane gas is provided between the digestion gas separation membrane device and the fuel cell, and the permeate side of the methane gas separation membrane device. A dilute methane gas circulation channel is provided for returning a part of the dilute methane gas obtained as described above to the digestion tank for circulation.

[0007]

In the fuel cell equipment according to claims 1 to 3,
In the digestion tank, organic sludge is biologically treated using anaerobic microorganisms, and the digested gas generated here is passed through a digested gas separation membrane device to separate into carbon dioxide concentrated gas and methane concentrated gas. In this way, the digested gas separation membrane device supplies the concentrated methane-enriched gas as fuel to the fuel cell, so that the methane gas obtained by subjecting the organic sludge to methane fermentation can be used as fuel for the fuel cell. It can be concentrated and supplied to the fuel cell, and the equipment can be made compact, and the running cost and the equipment cost can be reduced as compared with the conventional method in which the digestive gas is wet-absorbed by the alkaline aqueous solution to remove the carbon dioxide gas.

In the fuel cell equipment according to claim 2,
Part of the carbon dioxide-enriched gas on the permeate side, which was separated by the digestion gas separation membrane device of the first stage, is returned to the digestion tank through the carbon dioxide gas circulation channel, so it was collected by the digestion gas separation membrane device. A high concentration of carbon dioxide-enriched gas can be used in an appropriate amount to adjust the carbon dioxide concentration in the digestion tank. This makes it possible to easily adjust the carbon dioxide concentration in the digestion tank with a small gas circulation amount, and The recovery rate can be improved. It should be noted that it is possible to return all of the carbon dioxide-enriched gas separated by the digestion gas separation membrane device to the digestion tank via the carbon dioxide gas circulation flow path. The amount of gas becomes too large, the entire equipment such as the digestion gas separation membrane device becomes large, and not only this, but the carbon dioxide concentration is too high,
The concentration of the obtained methane-enriched gas is reduced, which is not preferable as a fuel for fuel cells.

In the fuel cell equipment according to claim 3,
Part of the lean methane gas obtained from the permeate side of the second stage methane gas separation membrane device is returned to the digestion tank through the lean methane gas circulation channel, so the methane contained in this lean methane gas is passed through the digestion tank. Since it can be recovered by the separation membrane device, the recovery rate of methane gas is improved. At the same time, by using an appropriate amount of carbon dioxide gas contained in the dilute methane gas for adjusting the carbon dioxide concentration in the digestion tank, the carbon dioxide gas can be easily obtained with a relatively small gas circulation amount. It is possible to adjust the concentration.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to embodiments. Needless to say, the present invention is not limited to the embodiments described below. First, a first embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, the fuel cell equipment according to the first embodiment of the present invention has a digestion tank 10 for biologically treating organic sludge 10a with anaerobic microorganisms, and a digestion gas a generated in the digestion tank 10. A desulfurizer 20 for removing hydrogen sulfide and the like in the inside, a digestion gas separation membrane device 30 for separating the desulfurized digested gas a into a carbon dioxide enriched gas b and a methane enriched gas c, and the obtained methane enriched gas c as a fuel. And a fuel cell 50.

The digestion tank 10 is a cylindrical tank of RC structure or a PC.
It is an oval tank having a structure or a steel structure, and an upper and lower conical tank. The atmosphere in the tank is anaerobic, and the temperature and pH are maintained at a good temperature for the growth of methanogens. The organic sludge 10a put into the digestion tank 10 is decomposed by the action of various anaerobic bacteria. First, high molecular weight organic substances are decomposed by facultative anaerobic bacteria (substrate degrading bacteria) into low molecular intermediate products such as alcohols, organic acids, and organic salts. At this time, a large amount of hydrogen and a small amount of methane gas are released, which is also called hydrogen fermentation. Then, the low-molecular intermediate product is decomposed into water-soluble inorganic substances and gas by absolutely anaerobic bacteria (methane bacteria). That is, carbon dioxide gas, methane gas, ammonia, etc. are generated. At this time, particularly a large amount of methane gas is generated, so it is also called methane fermentation.

The sludge reaction is carried out according to the following equation. Carbohydrate (glucose); C ₆ H ₁₂ O ₆ + 2H ₂ O → 2
_{CH 3 COOH + 4H 2 + 2CO} 2 lipid _{(tributyrin); C 3 H 5 (C} 3 H 7 COO)
₃ + 10H ₂ O → 7CH ₃ COOH + HCOOH + 8H
₂ protein (threonic acid); 3CH ₃ CH (OH) CH
(NH ₂ ) COOH + 7H ₂ O → 4CH ₃ COOH + 8
The usable substrates of H ₂ + 4CO ₂ + 3NH ₃ methane bacteria are HCOOH, CH ₃ CO
OH, CH ₃ OH, and H ₂ and CO ₂ ,
Other fatty acids are produced by acetogenic bacteria that produce hydrogen.
After being converted into CH ₃ COOH, methane is produced by the methane bacteria. The proportion of methane produced by these methane production mechanisms is determined by means of CH ₃ COOH (CH ₃ C
OOH → CH ₄ + CO ₂₎ is about 70%, the rest is said to be due to the reduction of _{CO 2 (CO 2 + 4H 2} → CH 4 + 2H 2 O).

Ammonia remains in the digestive liquid in the form of ammonium nitrite, so that a gas containing methane gas and carbon dioxide gas as main components and a small amount of hydrogen and hydrogen sulfide is generated in the digestion tank 10 in the end. a. The composition of the digestion gas a thus generated is generally 65
It is a mixed gas of 70 wt% and 30-35 wt% carbon dioxide. Usually, the upper space of the digestion tank 10 is under the atmosphere of the digestion gas a having such a composition. Digestion gas a of this composition
Has a lower heating value of 23 to 25 MJ / Nm ³ , which can be used as fuel for gas engine power generation,
As the fuel for the fuel cell 50 targeted by the present invention, the carbon dioxide concentration is high and the hydrogen concentration after reforming is low, so the power generation efficiency is too low.

A sludge / sludge heat exchanger 11 for heating the input sludge by the discharged digested sludge is provided between the sludge input pipe and the digested sludge discharge pipe of the digester tank 10, and the digester tank is also provided. At the upper part of 10, bubbling means 1 for introducing a part of the digestion gas a below the water surface in the tank to improve the contact between gas and liquid.
2 are provided. A mechanical stirring type may be used. The digestion gas separation membrane device 30 is composed of two chambers separated by a polymer gas separation membrane having a high permeability coefficient ratio of carbon dioxide and methane. When the derived digestion gas a is guided to one chamber 30a (hereinafter referred to as "non-permeation side") and the pressure of the other chamber 30b (hereinafter referred to as "permeation side") is made lower than that of the non-permeation side 30a, the digestion gas a The carbon dioxide-enriched gas b containing the dilute methane gas therein permeates the polymer gas separation membrane to the permeation side 30b, and the methane-enriched gas c that does not permeate is separated. The carbon dioxide-enriched gas b is stored in the lean gas tank 31 connected to the surplus gas combustor 40 that burns the lean methane gas, while the methane-enriched gas c is between the digestion gas separation membrane device 30 and the fuel cell 50. It is stored in the methane-rich gas tank 32.

The polymer gas separation membrane used here is a cellulose triacetate membrane, a polysulfone membrane, a polyethersulfone membrane, a styrene-grafted and sulfonated polytetrafluoroethylene membrane, a polyimide membrane, a carbon membrane, a fine membrane. In addition to porous glass composite membranes, polymer membranes used for separating oxygen and nitrogen can be cited. Further, the digestion tank 10 and the fuel cell 50 (in the first embodiment,
35 to 5 that easily treats the organic sludge 10a in the digestion tank 10 with microorganisms.
A heat exchange system 60 for maintaining at 5 ° C is provided.

By the way, the fuel cell electrochemically directly converts the chemical energy of the continuously supplied fuel into electrical energy, and various types have been developed. The types of fuel cells are classified according to the type of electrolyte solution (electrolyte) used. An alkaline aqueous electrolyte fuel cell using an alkaline electrolyte solution, a phosphoric acid electrolyte fuel cell using an acidic electrolyte solution, and a molten carbonate electrolyte using a molten salt electrolyte. Fuel cell, solid electrolyte fuel cell using solid electrolyte,
There is an ion exchange membrane fuel cell using a polymer solid electrolyte.

Of these, the phosphoric acid electrolyte fuel cell can be used not only with pure hydrogen as a fuel but also with hydrogen gas obtained by reforming from natural gas, methanol, etc., and phosphoric acid is used as an electrolytic solution. It is a fuel cell that operates at low temperatures. In addition, the basic configuration of the battery is such that a fuel electrode and an air electrode are opposed to each other with a matrix (porous body) impregnated with phosphoric acid sandwiched therebetween, and a fuel gas or air passage is provided to surround the fuel electrode and the air electrode. Further, in the molten carbonate electrolyte fuel cell, various carbonates, for example, a mixture of lithium carbonate, potassium carbonate, sodium carbonate, etc. are melted at a relatively low temperature and show conductivity by carbonate ions. This is impregnated into a porous ceramic plate (matrix), or mixed with powder of magnesia and alumina to form an electrolyte as a paste. The cell operates at elevated temperatures such as 600-650 ° C. The basic configuration is such that a fuel electrode and an air electrode are provided with a molten salt electrolyte in a matrix or paste form sandwiched therebetween.

By the way, of the above fuel cells, the phosphoric acid electrolyte fuel cell is applicable to city gas in recent years, and its spread is particularly remarkable. This phosphoric acid electrolyte fuel cell uses a desulfurizer to protect the catalyst of the reformer and the electrodes of the cell body from sulfides such as hydrogen sulfide, a steam reformer that produces hydrogen from methane, and carbon monoxide to carbon dioxide. The CO converter for converting into water and the battery body are integrated with a water treatment device for treating the condensed water after the reaction.

The heat exchange system 60 comprises a sludge circulation loop 6 having a sludge / hot water heat exchanger 61 on the digestion tank 10 side.
2, a hot water circulation loop 67 having a hot water boiler 63, an exhaust heat recovery device 64, a high temperature water tank 65, and a low temperature water tank 66 on the fuel cell 50 side, and a connection hot water circulation loop connecting the sludge circulation loop 62 and the hot water circulation loop 67. And 68. The hot water boiler 63 has a hot water circulation loop 67.
In order to raise the temperature of the circulating water inside, the lean gas tank 31
The dilute methane gas is supplied as a fuel for heating while being guided from the exhaust gas combustion device 40 to the excess gas combustion device 40.

The heat exchange system 60 includes a hot water circulation loop 6
The circulating water in the fuel cell 5 in the exhaust heat recovery device 64
0 is generated by the reaction heat at the time of power generation and the combustion heat of the hot water boiler 63, and the raised circulating water is supplied to the high temperature water tank 65, which is used as the circulating water of the connection hot water circulation loop 68 for sludge / hot water heat. The sludge in the digestion tank 10 is maintained at the above temperature by sending it to the exchanger 61 and raising the temperature of the sludge in the sludge circulation loop 62. In FIG. 1, symbol 70 is various pressure pumps and symbol 71 is various vacuum devices.

Next, the operation of the fuel cell equipment 10 according to the first embodiment of the present invention will be described. The input sludge heated by the digested sludge is introduced into the digestion tank 10 via the sludge / sludge heat exchanger 11. Here, the bubbling means 12 bubbling the organic sludge 10a in the digestion tank 10 with the circulating digestion gas to stir the digestion liquid,
Good methane fermentation. At this time, the circulating water of the hot water circulation loop 67 heated by the heat of the fuel cell 50 and the heat of the hot water boiler 63, and then the connected hot water circulation loop 68.
The sludge in the sludge circulation loop 62 becomes sludge /
The sludge heated by the hot water heat exchanger 61 and warmed is returned to the digestion tank 10. In this way, since the exhaust gas from the fuel cell 50 can be used to heat the sludge in the digestion tank 10,
Extremely high thermal efficiency is obtained.

The digestion gas a generated in the digestion tank 10 is desulfurized with sulfides such as hydrogen sulfide in the desulfurizer 20, and then sent to the digestion gas separation membrane device 30. Here, the separated carbon dioxide-enriched gas b containing one diluted methane gas is sent to the lean gas tank 31, and the other methane-enriched gas c is temporarily stored in the methane-rich gas tank 32, and then supplied as fuel for the fuel cell 50. To be done. The carbon dioxide-enriched gas b containing the lean methane gas temporarily stored in the lean gas tank 31 is sent to the surplus gas combustor 40 and burned.
3 is introduced into the fuel cell 3 as heating fuel, and the combustion gas is discharged from the surplus gas combustion device 40.

By the way, in a digestion tank with a capacity of 3,000 m ³ ,
When sludge was added at 200 m ³ / D and methane fermentation was carried out at a sludge temperature of 50 ° C, digestive gas a with a methane gas concentration of about 63%
2,800 Nm ³ / D is generated, and when the digested gas is separated into carbon dioxide by the digestion gas separation membrane device 30, methane-enriched gas having a methane gas concentration of about 90% is 1,570 m ³ / D.
D obtained. It is used for city gas 20
It corresponds to a fuel of a 0 kw phosphoric acid fuel cell.

The methane-enriched gas c thus concentrated by the digestion gas separation membrane device 30 is reformed into hydrogen gas through a fuel reformer (not shown) and supplied to the fuel cell 50 as fuel. I did it. Therefore, the organic sludge 10
The methane gas obtained by methane-fermenting a is concentrated to a level that can be used as a fuel for the fuel cell 50, and the fuel cell 5
In addition, the equipment can be made compact, and the running cost and the equipment cost can be reduced as compared with the case where the digestive gas is wet-absorbed by the alkaline aqueous solution to remove the carbon dioxide gas as described in the section of the prior art.

Next, based on FIG. 2, the fuel cell equipment of the second embodiment of the present invention will be explained. As shown in FIG. 2, in the fuel cell equipment of the second embodiment of the present invention, the carbon dioxide concentration obtained from the digestion gas separation membrane device 30 is provided between the digestion gas separation membrane device 30 and the digestion tank 10. By providing a carbon dioxide gas circulation flow path 81 for returning a part of the gas b to the digestion tank 10 through the bubbling means 12 and circulating it, the high concentration carbon dioxide concentrated in the digestion gas separation membrane device 30 is concentrated. The gas b is used in an appropriate amount to adjust the carbon dioxide concentration in the digester tank 10, whereby in the digester tank 10,
The carbon dioxide concentration can be easily adjusted with a small gas circulation amount, and the methane contained in the carbon dioxide concentrated gas b is recovered.

Next, based on FIG. 3, the fuel cell equipment of the third embodiment of the present invention will be explained. As shown in FIG. 3, in the fuel cell equipment according to the third embodiment of the present invention, a dilute mental gas circulation channel 82 for returning a part of the methane gas obtained from the methane gas separation membrane device 80 to the digestion tank 10 and circulating it. By providing the methane, the methane contained in the dilute methane gas d is effectively recovered, and the carbon dioxide gas is used in an appropriate amount for adjusting the carbon dioxide concentration in the digestion tank 10 as in the second embodiment. This is an example in which the carbon dioxide concentration can be easily adjusted with a relatively small gas circulation amount.

Next, the fuel cell equipment of the fourth embodiment of the present invention will be explained based on FIG. As shown in FIG. 4, the fuel cell facility according to the fourth embodiment of the present invention is a carbon dioxide-enriched gas b obtained from the digestion gas separation membrane device 30.
Part of the methane gas separation membrane device 80 is returned to the digestion tank 10.
The diluted methane gas obtained from the digestive gas separation membrane device 30
It is possible to adjust the carbon dioxide concentration in the digestion tank 10 and improve the methane recovery rate at the same time by returning to the inlet side of.

The embodiment of the present invention has been described above.
The present invention is not limited to this embodiment, and any modification of the design without departing from the scope of the present invention is included in the present invention. For example, in the embodiment, the desulfurizer is provided between the digestion tank and the digestive gas separation membrane device, but the present invention is not limited to this and may be provided, for example, on the fuel supply side of the fuel cell. Further, since hydrogen sulfide is mixed in the carbon dioxide concentrated gas side of the digestion gas separation membrane, the desulfurizer is not always necessary.

[0029]

In the fuel cell equipment according to claims 1 to 3, the digested gas separation membrane device is used to supply the concentrated methane-enriched gas as fuel to the fuel cell. The equipment can be made compact, and the running cost and the equipment cost can be reduced as compared with the case where the carbon dioxide gas is removed by wet-absorbing the gas with an alkaline aqueous solution.

In the fuel cell equipment according to claims 2 to 3, a part of the carbon dioxide-enriched gas separated by the digestion gas separation membrane device is separated through the carbon dioxide gas circulation channel and from the methane gas separation membrane device. Since a part of the generated methane gas is returned to the digestion tank via the dilute methane gas circulation channel, the methane recovery rate can be improved and the carbon dioxide concentration in the digestion tank can be adjusted with a small gas circulation amount. Can be done easily.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a fuel cell facility according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a main part of fuel cell equipment according to a second embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a main part of fuel cell equipment according to a third embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of main parts of a fuel cell facility according to a fourth embodiment of the present invention.

[Explanation of symbols]

 10 Digestion Tank 10a Organic Sludge 20 Desulfurizer 30 Digestion Gas Separation Membrane Device 50 Fuel Cell 80 Methane Gas Separation Membrane Device 81 Carbon Dioxide Circulation Flow Path 82 Dilute Menthane Gas Circulation Flow Path a Digestion Gas b Carbon Dioxide Concentration Gas c Methane Concentration Gas d Dilute methane gas e High-concentration methane gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Taniguchi 2-1, Okawacho, Kawasaki-ku, Kawasaki-shi, Kanagawa Sanryo Kakoki Co., Ltd.

Claims (3)

[Claims] 1. A digestion tank for biologically treating organic sludge using anaerobic microorganisms, and a digestion gas separation membrane device for separating digestion gas generated in the digestion tank into carbon dioxide-enriched gas and methane-enriched gas. And a fuel cell using the methane-enriched gas as a fuel. 2. A methane gas separation membrane device for separating a methane-enriched gas into a dilute methane gas and a high-concentration methane gas is provided between the digestion gas separation membrane device and the fuel cell, and the methane gas separation membrane device is obtained from the permeation side of the digestion gas separation membrane device. The fuel cell facility according to claim 1, further comprising a carbon dioxide gas circulation flow path for returning a part of the carbon dioxide concentrated gas to the digestion tank for circulation. 3. A methane gas separation membrane device for separating the methane-enriched gas into a lean methane gas and a high-concentration methane gas is provided between the digestion gas separation membrane device and the fuel cell, and the lean gas obtained from the permeation side of the methane gas separation membrane device is provided. The fuel cell facility according to claim 1, wherein a dilute methane gas circulation channel is provided for returning a part of the methane gas to the digestion tank for circulation.