JP2021041365A - Biogas power generation system - Google Patents

Abstract

To provide an improved biogas power generation system capable of reliably preventing moisture from becoming condensate and interfering with the supply of biogas in piping, or causing problems in a generator due to moisture being supplied into the biogas power generator, by removing moisture from the biogas while minimizing cost increase for water removal and deterioration of power generation efficiency.SOLUTION: In a system which generates electricity by supplying biogas extracted from fermented organic waste to a gas engine generator, the biogas is cooled and dehumidified by using diluted water which is mixed with the organic waste to make a slurry in a pre-fermentation stage.SELECTED DRAWING: Figure 1

Description

The present invention relates to an improvement of a power generation system that uses organic waste such as livestock manure and food residue as a biomass resource and uses biogas obtained by anaerobic fermentation as a raw material to generate electricity.

In Japan, where resources such as fossil fuels are scarce, the benefits of introducing renewable energies such as solar power, wind power, geothermal power, and biomass are great, and it will be possible to reduce the dependence of resources on overseas and reduce fossil fuel procurement costs.

In addition, these renewable energies emit less carbon dioxide than thermal power generation and are effective against global warming. Geothermal and biomass are lagging behind compared to solar and wind power, but it is expected that they will be effectively used for power generation as biomass resources in order to improve the recycling rate of organic waste such as livestock manure and food residues. Has been done.

There are two types of power generation using biomass: biomass power generation and biogas power generation. Biomass power generation is a mechanism that directly burns organic waste such as livestock manure and food waste, and uses the generated heat to turn a turbine with steam to generate electricity. Biogas power generation is a mechanism in which organic waste such as livestock manure and food waste is fermented to extract flammable biogas, and the biogas is used to generate electricity. In either case, power generation using biomass is carbon-neutral and does not affect the increase or decrease of carbon dioxide in the atmosphere, so it is effective for environmental measures.

As biogas power generation, as described in Patent Document 1 below, the extracted biogas is reformed into hydrogen to generate electricity by a fuel cell, or as described in Patent Document 2 below, the extracted biogas is generated. It is known that a micro-turbine generator (gas engine generator) is rotated by gas to generate electricity.

JP-A-2010-198920 Patent No. 36068554

Since the biogas obtained by anaerobic fermentation of organic waste has high humidity (containing a large amount of water), it is necessary to sufficiently separate and dehumidify the water, as described in Patent Documents 1 and 2 above. Has been done.

In the case of Patent Document 1 in which power is generated by a fuel cell, the temperature of the biogas is lowered by heat radiation in the gas tank for temporarily storing the biogas and then in the piping for use in the desulfurization device and the fuel reformer, and the biogas is contained in the biogas. A part of the steam is condensed water.

Since the generated condensed water obstructs the flow of biogas in the piping, the supply of gas to the fuel cell becomes unstable, and the supply corresponding to the power generation output of the fuel cell may not be performed. It also causes failures of various devices and devices on the biogas supply path.

Therefore, in Patent Document 1, a method is adopted in which a biogas cooler is provided and cold water is circulated in the cooler to cool the biogas and reduce the water vapor content in the gas. Further, a heater is provided to heat the biogas to further remove the remaining water vapor. The heat of the exhaust gas is used as the heat source of the heater.

As described above, in the case of Patent Document 1, cold water is circulated in the cooler to cool the biogas and the water vapor in the gas is removed. Therefore, a device (hot water type chiller / heater) for circulating the cold water is required. And the cost increases. In addition, the power efficiency of the power generation system is poor because power is required to cool the water by the device.

On the other hand, when the micro-turbine generator of Patent Document 2 generates electricity, the water contained in the gas may be liquefied or frozen, which may hinder the operation of the turbine. Therefore, after the gas is compressed by a compressor, it is cooled by a radiator to condense water, and the condensed water is separated and removed by a water removing means. As the water removing means, a mechanical gas-liquid separator, an adsorbent, or the like is used.

After the water is removed, most of the water is removed by heating the gas with the exhaust heat of the compressor.

As described above, in the case of Patent Document 2, since the electric power for removing the water in the gas is not required, the electric power efficiency of the power generation system is good, but it is necessary to separately prepare a gas-liquid separator, an adsorbent and the like. , Cost up.

Therefore, the present invention removes the water in the biogas while suppressing the cost increase for removing the water and the deterioration of the power generation efficiency as much as possible, so that the water becomes condensed water and the biogas is supplied in the pipe. It provides an improved biogas power generation system that can surely prevent a malfunction of the generator by inhibiting or supplying water into the biogas generator.

The invention according to claim 1 is a system in which biogas extracted by fermenting organic waste is supplied to a gas engine generator to generate electricity. In a pretreatment stage of fermentation, the biogas is mixed with organic waste to form a slurry. It is characterized by cooling and dehumidifying biogas using water.

The invention according to claim 2 is the biogas power generation system according to claim 1, wherein the fermenter recovers heat from the cooling water for cooling the gas engine generator and uses the heat to ferment organic waste. It is characterized in that it is configured to be heated or to heat the biogas with a heater.

According to the third aspect of the present invention, in the biogas power generation system according to the first aspect, heat is recovered from the exhaust gas after power generation by the gas engine generator, and the heat is used to heat a fermenter for fermenting organic waste. It is characterized in that it is configured to heat the biogas with a heater.

In the invention according to claim 4, in the biogas power generation system according to any one of claims 2 or 3, the fermenter and the heater are heated to an optimum temperature by the heat recovered from the cooling water and the exhaust gas. If so, it is characterized by stopping the supply of heat to the fermenter or heater.

According to the invention of claim 1, the biogas can be cooled without using electric power, and the power generation efficiency is improved.

According to the invention of claim 2, in addition to the effect of claim 1, the fermenter and the heater can be heated by utilizing the exhaust heat of the cooling water of the gas engine, and the power generation efficiency is improved.

According to the invention of claim 3, in addition to the effects of claims 1 and 2, the heat of the exhaust gas after power generation can be used to heat the fermenter and the heater, and the power generation efficiency is improved.

According to the invention of claim 4, in addition to the effects of claims 2 and 3, it is possible to prevent the fermenter and the heater from being excessively heated, thereby inhibiting methane fermentation in the fermenter and in the heater. It is possible to prevent the biogas from being overheated.

It is a conceptual diagram of the biogas power generation system of this invention. It is a block diagram which concerns on other embodiment of the biogas power generation system of this invention.

Hereinafter, embodiments of the present invention will be described with reference to FIG. FIG. 1 is a conceptual diagram showing the overall configuration of the biogas power generation system A according to the present invention. In FIG. 1, 1 is a raw material containing organic waste such as livestock manure and food waste (hereinafter referred to as raw material). A raw material tank that is mixed with diluted water and subdivided (slurried) is shown.

Reference numeral 2 denotes a water storage tank for storing the diluted water to be supplied to the raw material tank 1, and reference numeral 3 denotes a fermenter in which the slurryed raw material is charged and methane-fermented to take out biogas.

Reference numeral 4 denotes a gas holder for storing the biogas taken out from the fermenter 3, and 5 indicates a cooler for cooling the biogas taken out from the gas holder 4.

Reference numeral 6 denotes a heater for heating the cooled biogas, and 7 indicates a desulfurization tank for removing harmful sulfur from the heated biogas.

Reference numeral 8 denotes a gas engine generator that uses biogas as fuel to generate electricity after removing sulfur, and the electricity generated by the gas engine generator is supplied to, for example, the power system via the grid interconnection facility B. ..

As an operation in the case of power generation by the biogas power generation system A configured as described above, first, a raw material for generating biogas and diluted water for diluting the raw material are put into the raw material tank 1.

This diluted water is supplied from the water storage tank 2. The water in the water storage tank 2 is stored in advance via the cooler 5. In addition, a pipe for discharging the water passed through the cooler 5 to the outside may be provided in case the water is sufficiently stored in the water storage tank 2.

In the raw material tank 1, the raw material diluted with diluted water is subdivided (slurried) as a pretreatment for fermentation. The slurried raw material is transferred into the fermenter 3.

The fermenter 3 is controlled to a predetermined temperature, and the raw material is methane-fermented in the fermenter 3 to generate biogas.

The biogas generated in the fermenter 3 (for example, 38 to 42 ° C.) is recovered in the gas holder 4 and then cooled in the cooler 5. Cooling is performed for the purpose of removing the water contained in the biogas.

Biogas obtained by methane fermentation (anaerobic fermentation) of raw materials that are organic waste has high humidity, so if water is not sufficiently separated and dehumidified, water will condense in the piping and cause blockage. It may cause a failure of the gas engine generator that supplies biogas.

In the present invention, the method for cooling biogas by the cooler 5 is different from the prior art. In the present invention, the biogas cools the biogas passing through the cooler 5 by passing the diluted water (for example, 0 to 30 ° C.) supplied to the raw material tank 1 through the water storage tank 2 through the cooler 5. It is characterized by points.

That is, unlike the technique described in Patent Document 1 described above, it is not necessary to prepare a device (hot water type chiller / heater) for circulating cold water in order to cool the biogas, and the cost can be suppressed.

Further, since the electric power for driving the hot water type chiller / heater is not required, the electric power efficiency of the power generation system A can be improved.

Further, unlike the technique described in Patent Document 2, it is not necessary to separately prepare a gas-liquid separator, an adsorbent, or the like.

The water supplied to the cooler 5 is connected to, for example, a faucet, and the faucet is opened at the timing of cooling the biogas. The water that has passed through the cooler 5 is then stored in the water storage tank 2, and the required amount of water is sent from the water storage tank 2 to the raw material tank 1 at the timing when the supply to the raw material tank 1 is required.

Moisture that has been cooled by the cooler 5 and condensed is recovered from the drain of the cooler 5.

The biogas from which the water has been removed is then heated by the heater 6 to prevent dew condensation again. The heater 6 reheats the biogas by using the heat of the cooling water (hereinafter referred to as generator cooling water) of the biogas generator 8 heated to, for example, 70 to 90 ° C. by the biogas generator 8. To do. That is, the generator cooling water is circulated between the heater 6 and the biogas generator 8 by a pump (not shown).

Further, the generator cooling water is circulated between the fermenter 3 and the gas engine generator 8 by a pump (not shown), and the heat of the generator cooling water heated to, for example, 70 to 90 ° C. in the biogas generator 8 is used. Then, the raw material in the fermenter 3 is warmed.

That is, in the present invention, since the exhaust heat of the biogas generator 8 is used for reheating the biogas in the heater 6 and heating the raw material in the fermenter 3, the power generation efficiency is improved.

When the fermenter 3 and the heater 6 are heated to the optimum temperature by the circulation of the generator cooling water, the pump is stopped to prevent the fermenter 3 and the heater 6 from being excessively heated. It may be configured.

The biogas reheated by the heater 8 is sent to the gas engine generator 8 after the sulfur content is removed by the desulfurizer (dry desulfurizer or the like) 7. The gas engine generator 8 uses the supplied biogas as fuel to generate electricity, and supplies electricity to the power system via the grid interconnection facility B.

FIG. 2 is a configuration diagram showing by extracting only a portion different from the power generation system A of FIG. 1 from the biogas power generation system A ′ according to another embodiment of the present invention. In the power generation system A'shown in FIG. 2, the heat source of the fermenter 3 and the heater 6 uses the exhaust heat of the exhaust gas of the gas engine generator 8.

Specifically, the exhaust gas discharged from the gas engine generator 8 is discharged to the outside via the heat exchanger 9, and the exhaust heat recovered by the heat exchanger 9 is used to heat the fermenter 3 and the fermenter. Heat the vessel 6.

In the case of FIG. 2, as in the power generation system A of FIG. 1, the fermenter 3 and the heater 6 are heated by using unnecessary heat, so that the power generation efficiency can be improved.

When the fermenter 3 and the heater 6 are heated to the optimum temperature by the exhaust gas, the pump may be stopped to prevent the fermenter 3 and the heater 6 from being excessively heated.

As described above, according to the biogas power generation systems A and A'of the present invention, since electric power for cooling the biogas is not required, the power generation efficiency can be improved.

It is applicable to gas appliances that require water supply.

1 Raw material tank 2 Water storage tank 3 Fermentation tank 4 Gas holder 5 Cooler 6 Heater 7 Desulfurizer 9 Heat exchanger 10 Fan A, A'Biogas power generation system B System interconnection equipment

Claims (4)

In a system that generates electricity by supplying biogas extracted by fermenting organic waste to a gas engine generator, biogas is generated using diluted water that is mixed with organic waste and slurried in the pretreatment stage of fermentation. A biogas power generation system characterized by cooling and dehumidifying. The heat is recovered from the cooling water for cooling the gas engine generator, and the heat is used to heat the fermenter for fermenting the organic waste, or the biogas is heated by a heater. The biogas power generation system according to claim 1, wherein the biogas power generation system is characterized in that. Heat is recovered from the exhaust gas after power generation by the gas engine generator, and the heat is used to heat the fermenter for fermenting the organic waste, or the biogas is heated by a heater. The biogas power generation system according to claim 1, wherein the biogas power generation system is characterized. 2. When the fermenter or heater is heated to an optimum temperature by the heat recovered from the cooling water and the exhaust gas, the heat supply to the fermenter or heater is stopped. The biogas power generation system according to any one of claims 3.

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