Low carbon power generation system

Abstract

To provide a low carbon power generation system capable of easily reducing emissions of greenhouse effect gas caused by combustion of BOG while treating the BOG from a cryogenic liquefied gas storage tank with low energy.SOLUTION: A low carbon power generation system 1 includes: a power generator 10 that uses an internal combustion engine using boil-off gas in an LNG storage tank 70 as fuel; a water electrolytic device 20 that generates hydrogen and oxygen through electrolysis of water; an exhaust gas discharge line 81 for discharging combustion exhaust gas in the power generator 10 to outside; an oxygen supply line 82 for supplying oxygen generated in the water electrolytic device 20 to the power generator 10 as an oxidant; a fuel supply line for supplying boil-off gas to the power generator 10; an exhaust gas circulation line 84 branched from the exhaust gas discharge line 81 to circulate exhaust gas in the power generator 10; and an exhaust gas cooler 30 that cools the exhaust gas circulated in the power generator 10.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a low-carbon power generation system capable of easily reducing the emission of greenhouse gases due to the combustion of power generation fuel.

Background Art

[0002] From an LNG storage tank installed at a cryogenic liquefied gas base, such as a liquefied natural gas (hereinafter referred to as "LNG") base, LNG evaporates due to natural heat input from the atmosphere or work heat input from a pump, and boil-off gas (hereinafter referred to as "BOG") is generated. BOG (abbreviation for Boil Off Gas. Evaporation gas of LNG.) is generally processed by compressing it and merging it into a gas supply pipe. However, since the pressure of BOG is almost atmospheric pressure, a large amount of power is required to compress it to a high pressure, increasing the operating cost of the LNG base.

[0003] In this regard, Patent Document 1 discloses a technique for reducing the compression power of BOG by generating power using the low-pressure BOG extracted from the intermediate stage of a BOG compressor as fuel for a gas engine.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since Patent Document 1 does not describe the treatment of exhaust gas associated with the operation of a gas engine using BOG as fuel, it is considered that the exhaust gas is dissipated into the atmosphere. Since the exhaust gas contains a large amount of carbon dioxide, which is a greenhouse gas, the technology of Patent Document 1 promotes global warming even though it can reduce the compression power. Even if it is assumed that carbon dioxide is separated and recovered from the exhaust gas, since the carbon dioxide concentration is low, the energy required for recovery increases, making it difficult to recover efficiently.

[0006] The present invention has been made to solve such problems, and an object thereof is to provide a low-carbon power generation system that can easily reduce the emission of greenhouse gases due to the combustion of BOG while treating BOG from a cryogenic liquefied gas storage tank with low energy.

Means for Solving the Problems

[0007] (1) The low-carbon power generation system according to the present invention includes a power generation device using an internal combustion engine fueled by boil-off gas from a cryogenic liquefied gas storage tank, a water electrolysis device that generates hydrogen and oxygen by electrolyzing water, an exhaust gas discharge line that discharges the combustion exhaust gas of the power generation device to the outside, an oxygen supply line that supplies oxygen generated in the water electrolysis device to the power generation device as an oxidant, a fuel supply line that supplies the boil-off gas to the power generation device, an exhaust gas circulation line that branches from the exhaust gas discharge line and circulates the exhaust gas to the power generation device, and an exhaust gas cooler that cools the exhaust gas circulated to the power generation device.

[0008] (2) Further, in the one described in (1) above, the cryogenic liquefied gas is liquefied natural gas, and it is disposed downstream of the branch portion to the exhaust gas circulation line in the exhaust gas discharge line, and solidifies moisture contained in the exhaust gas by heat exchange between the exhaust gas and the liquefied natural gas and / or its boil-off gas. It is characterized by having a moisture solidification device.

[0009] (3) Further, in the one described in (2) above, it is disposed downstream of the moisture solidification device in the exhaust gas discharge line, and solidifies carbon dioxide contained in the exhaust gas by heat exchange between the exhaust gas and the LNG and / or its boil-off gas. It is characterized by having a carbon dioxide solidification device.

[0010] (4) Further, in the above (1), the cryogenic liquefied gas is liquefied natural gas, and a carbon dioxide liquefaction device is provided downstream of the branch portion to the exhaust gas circulation line in the exhaust gas discharge line for liquefying carbon dioxide contained in the exhaust gas. The carbon dioxide liquefaction device obtains the cooling heat required for liquefying carbon dioxide by heat exchange with the liquefied natural gas.

Effect of the Invention

[0011] According to the present invention, it is possible to easily reduce the emission of greenhouse gases due to the combustion of the internal combustion engine of the power generation device while treating BOG from the cryogenic liquefied gas storage tank with low energy.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0013] [Embodiment 1] First, with reference to FIG. 1, the configuration and function of Embodiment 1 of the present invention will be described. The low-carbon power generation system 1 according to the first embodiment of the present invention includes a power generation device 10, a water electrolysis device 20, an exhaust gas cooler 30, an exhaust gas discharge line 81, an oxygen supply line 82, a fuel supply line 83, and an exhaust gas circulation line 84.

[0014] The power generation device 10 is driven by a gas engine using natural gas as fuel, operates according to power demand, and generates electric power. The water electrolysis device 20 is a PEM (abbreviation for Polymer Electrolyte Membrane) type electrolysis device that uses a solid polymer as an electrolyte, and decomposes water into hydrogen and oxygen using electricity with water as a raw material. The electricity supplied to the water electrolysis device 20 is provided by the electricity generated by the power generation device 10, and the shortage is compensated by the electricity supplied from the power grid. In addition, if the electricity supplied from the power grid to the water electrolysis device 20 is electricity derived from renewable energy, it is more preferable because the hydrogen produced by the water electrolysis device 20 will be derived from renewable energy.

[0015] The exhaust gas discharge line 81 is connected to the power generation device 10 and discharges the exhaust gas of the power generation device 10 to the outside. The oxygen supply line 82 is connected to the water electrolysis device 20 and the power generation device 10, and introduces the oxygen generated in the water electrolysis device 20 into the power generation device 10 as an oxidant for driving the gas engine. By using oxygen as an oxidant instead of air, the nitrogen component, which accounts for about 80% of the air, is reduced, so that the exhaust gas components become carbon dioxide and water, and the exhaust gas with a high carbon dioxide concentration and easy carbon dioxide recovery can be obtained. Also, nitrogen oxides (NOx) are not generated in a situation where nitrogen is completely exhausted. The hydrogen generated in the water electrolysis device 20 is supplied to a user (not shown) through the hydrogen supply line 86.

[0016] The fuel supply line 83 is connected to the BOG header 85 of the LNG storage tank 70 and the power generation device 10, and introduces the BOG generated in the LNG storage tank 70 into the power generation device 10 as fuel. The surplus of the BOG that did not flow into the fuel supply line 83 is pressurized by a BOG compressor (not shown) from the BOG header 85 and sent to the user.

[0017] The exhaust gas cooler 30 is propane (C 3 H 8It is a heat exchanger using [[ID=]] as an intermediate refrigerant and is disposed in the exhaust gas discharge line 81. The exhaust gas cooler 30 cools the exhaust gas by heat-exchanging the cryogenic (e.g., -150°C) BOG and the high-temperature (e.g., 300°C) exhaust gas using propane as a heat transfer medium, and condenses moisture in the process. The condensed moisture is discharged to the outside from the water discharge line 87.

[0018] One end of the exhaust gas circulation line 84 is connected to the downstream of the exhaust gas cooler 30 in the exhaust gas discharge line 81, and the other end is connected to the power generation device 10, and returns the exhaust gas cooled in the exhaust gas cooler 30 and having its temperature reduced to the power generation device 10.

[0019] Next, the operation of the low-carbon power generation system 1 according to the present embodiment will be described. Since various heats such as heat input from the atmosphere and heat input from the pump enter the LNG storage tank 70, the stored LNG evaporates, and BOG, which is high-purity methane gas, is generated. If BOG continues to be generated, the internal pressure of the LNG storage tank 70 continues to rise and exceeds the design pressure. Therefore, the internal pressure of the LNG storage tank 70 is adjusted within a certain range by discharging the BOG to the outside of the LNG storage tank 70 through the BOG header 85.

[0020] As one of the internal pressure adjusting means of the LNG storage tank 70, the power generation device 10 is used. That is, the BOG is diverted from the BOG header 85 to the fuel supply line 83, and is heated in the exhaust gas cooler 30, so that its temperature rises from cryogenic (e.g., -150°C) to normal temperature (e.g., 10°C), and is supplied to the power generation device 10.

[0021] The BOG supplied to the power generation device 10 is burned using oxygen supplied from the water electrolysis device 20 as an oxidant, and exhaust gas with a high carbon dioxide concentration is discharged. The exhaust gas of the power generation device 10 flows through the exhaust gas discharge line 81 and is supplied to the exhaust gas cooler 30, and is cooled by the BOG flowing through the fuel supply line 83. The cooled exhaust gas further flows through the exhaust gas discharge line 81 and is discharged to the outside, but is diverted to the exhaust gas circulation line 84 on the way and supplied to the inlet of the power generation device 10.

[0022] The water electrolysis device 20 electrolyzes water using the power from the power generation device 10 and, for the shortage, the power derived from renewable energy from the power grid. The hydrogen generated at the cathode of the water electrolysis facility 20 by electrolysis is supplied to a user (not shown) through the hydrogen supply line 86. The oxygen generated at the anode of the water electrolysis facility 20 by electrolysis is supplied to the inlet of the power generation device 10 through the oxygen supply line 82.

[0023] The power generation device 10 takes in BOG (methane gas) supplied through the fuel supply line 83, the exhaust gas supplied through the exhaust gas circulation line 84, and the oxygen supplied through the oxygen supply line 82, and burns them in an internal combustion engine to generate power. The power generated by the power generation device 10 is mainly supplied to the water electrolysis device 20, but when it is not necessary to supply it to the water electrolysis device 20, it may be supplied to the power grid and used for selling electricity or the like.

[0024] As described above, in the power generation device 10, since BOG (methane gas) is burned using the oxygen supplied from the water electrolysis device 20 as an oxidant, exhaust gas with a high carbon dioxide concentration is discharged, and it is possible to facilitate the recovery of carbon dioxide from the exhaust gas. On the other hand, in the combustion of only methane and oxygen, when the temperature of the combustion chamber becomes too high, excessive temperature rise is prevented by mixing the exhaust gas, which is an inert gas. Although the control method will not be described in detail, for example, it is conceivable to adjust the flow rate of the exhaust gas flowing through the exhaust gas circulation line 84 so that the temperature of the combustion chamber becomes constant.

[0025] Due to the above actions, in the low-carbon power generation system 1, in the process of using the cryogenic BOG as fuel for the power generation device 10, the waste heat can be used to cool the exhaust gas of the power generation device 10, so that the energy for exhaust gas cooling can be minimized.

[0026] Also, by supplying a part of the cooled exhaust gas to the inlet of the power generation device 10, power generation using oxygen can be performed while preventing excessive temperature rise in the combustion chamber.

[0027] Furthermore, since the components of the exhaust gas of the power generation device 10 are carbon dioxide and water, carbon dioxide can be extremely easily separated and recovered from the exhaust gas.

[0028] Also, while the water electrolysis device 20 is generally used to produce hydrogen, oxygen, which is a by-product thereof, can also be effectively utilized in the power generation device 10.

[0029] Also, in the present embodiment, the power generation device 10 has been described as a gas engine, but it is not limited to a gas engine. The power generation device 10 may be any internal combustion engine, or may be a gas turbine.

[0030] Also, while the water electrolysis device 20 has been described as a PEM type water electrolysis device, an SOEC (abbreviation for Solid Oxide Electrolyzer Cell) type water electrolysis device or an alkaline water electrolysis device may also be used. Also, while the power supplied to the water electrolysis device 20 from the power grid has been described as power derived from renewable energy, it may also be power derived from fossil fuels.

[0031] Also, while the exhaust gas cooler 30 has been described as a heat exchanger using propane as an intermediate refrigerant, other intermediate refrigerants such as ethane, methane, ammonia, non-fluorocarbon refrigerants, etc. can also be adopted according to conditions, and a heat exchanger that does not use an intermediate refrigerant may also be used.

[0032] Also, while it has been described that the water condensed in the exhaust gas cooler 30 is discharged to the outside, it may be made into clean water by neutralization treatment or the like and then circulated to the water electrolysis facility 20. The amount of newly used water can be reduced.

[0033] Further, the exhaust gas cooler 30 has been described as cooling the exhaust gas flowing in the exhaust gas discharge line 81 and circulating the cooled exhaust gas to the power generation device 10 via the exhaust gas circulation line 84. In this case, the exhaust gas discharged to the outside is cooled to the same temperature as the exhaust gas circulated to the power generation device 10. However, there may be cases where the temperature of the exhaust gas discharged to the outside is desired to be higher than the temperature of the exhaust gas circulated and supplied to the power generation device 10. In such a case, the exhaust gas flowing through the exhaust gas circulation line 84 may be cooled by the exhaust gas cooler 30. In addition, when it is desired to cool the exhaust gas discharged to the outside to some extent, the cooled exhaust gas flowing through the exhaust gas circulation line 84 may be used to cool it to the target temperature.

[0034] Also, in this embodiment, LNG has been described as the low-temperature liquefied gas. However, not limited to LNG, liquefied ethane, liquefied propane, liquefied ammonia, etc. may also be applied.

[0035] [Embodiment 2] Next, with reference to FIG. 2, the configuration and functions of Embodiment 2 will be described. Those having the same configuration and functions as in Embodiment 1 are given the same numbers. The low-carbon power generation system 100 according to Embodiment 2 is provided with specific means for recovering carbon dioxide from exhaust gas with a high carbon dioxide concentration, and includes a moisture solidifier 40, a carbon dioxide solidifier 50, and a low-temperature liquefied gas supply line 88.

[0036] The moisture solidifier 40 is a scraping heat exchanger and is disposed downstream of the branch portion of the exhaust gas circulation line 84 in the exhaust gas discharge line 81. The moisture solidifier 40 gives the cold heat of LNG or its evaporation gas (NG) supplied from the LNG storage tank 70 to another natural gas user through the low-temperature liquefied gas supply line 88 to propane, which is an intermediate refrigerant, and cools the exhaust gas flowing through the exhaust gas discharge line 81 with the propane to solidify the moisture in the exhaust gas. The generated ice is discharged to the outside from the ice discharge line 89.

[0037] The carbon dioxide solidifier 50 is a scraping type heat exchanger, and is disposed downstream of the moisture solidifier 40 in the exhaust gas discharge line 81. The carbon dioxide solidifier 50 gives the cold heat of the LNG supplied from the LNG storage tank 70 to another natural gas user through the low-temperature liquefied gas supply line 88 to propane which is an intermediate refrigerant, and solidifies the exhaust gas (substantially carbon dioxide) after moisture separation flowing through the exhaust gas discharge line 81 by cooling it with the propane. The generated dry ice is discharged to the outside from the dry ice discharge line 90.

[0038] Next, the operation of the low-carbon power generation system 100 according to the present embodiment will be described. Descriptions of parts similar to those in Embodiment 1 will be omitted.

[0039] In the downstream where the exhaust gas circulation line 84 branches from the exhaust gas discharge line 81, in the moisture solidifier 40, the exhaust gas is cooled to a temperature higher than the solidification temperature of carbon dioxide and as low a temperature as possible (for example, -70°C), and moisture solidifies on the surface of the heat transfer tube. The solidified moisture is scraped off by a mechanical mechanism (not shown) and discharged from the ice discharge line 89.

[0040] The low-temperature exhaust gas dehumidified until the temperature reaches -70°C flows through the exhaust gas discharge line 81 and is introduced into the carbon dioxide solidifier 50. In the carbon dioxide solidifier 50, the exhaust gas which has become substantially only carbon dioxide is cooled to at least about -80°C by the cold heat of the LNG and solidifies on the surface of the heat transfer tube. The solidified carbon dioxide is scraped off by a mechanical mechanism (not shown) and discharged from the dry ice discharge line 90.

[0041] According to the low-carbon power generation system 100 according to the present embodiment, since the cold exhaust heat of the LNG is utilized, carbon dioxide can be separated and taken out as dry ice while minimizing external energy.

[0042] [Embodiment 3] Next, with reference to FIG. 3, the configuration and function of Embodiment 3 will be described. For those having the same configurations and functions as those in Embodiments 1 and 2, the same reference numerals are given and the description thereof is omitted. The low-carbon power generation system 400 according to Embodiment 3 includes a carbon dioxide liquefaction device 460 and a liquefied carbon dioxide discharge line 490.

[0043] The carbon dioxide liquefaction device 460 is a general carbon dioxide liquefaction device including, for example, a gas compressor, a dryer, a refrigerator, and a heat exchanger, and is disposed downstream of the branch portion to the exhaust gas circulation line 84 in the exhaust gas discharge line 81. The carbon dioxide liquefaction device 460 utilizes the cold heat of the cryogenic liquefied gas flowing through the cryogenic liquefied gas supply line 88 via propane as an intermediate refrigerant to liquefy carbon dioxide.

[0044] Next, the operation of the low-carbon power generation system 400 according to the present embodiment will be described. The exhaust gas flowing through the exhaust gas discharge line 81 and from which the circulating exhaust gas to the exhaust gas circulation line 84 has been subtracted is introduced into the carbon dioxide liquefaction device 460.

[0045] In the carbon dioxide liquefaction device 460, the exhaust gas is compressed by a compressor (not shown) and dehumidified by a dryer (not shown). The carbon dioxide having reached a medium pressure (about 0.6 MPaG) receives cold heat from the cryogenic liquefied gas in the cryogenic liquefied gas supply line 88 via propane and is liquefied by the cold heat.

[0046] By the above operation, in the low-carbon power generation system 400, exhaust gas containing high-concentration carbon dioxide can be supplied to a general carbon dioxide liquefaction device 460 and the carbon dioxide can be liquefied by the cold heat of LNG, so that carbon dioxide can be separated and recovered in a liquid form with minimized external energy.

Industrial Applicability

[0047] The present invention can be used as a low-carbon power generation system capable of easily reducing the emission of greenhouse gases due to the combustion of power generation fuel.

Explanation of Signs

[0048] 1, 100, 400 Low-carbon power generation system 10 Power generation device 20 Water electrolysis equipment 30 Exhaust gas cooler 40 Moisture solidifier 50 Carbon dioxide solidifier 70 LNG storage tank 81 Exhaust gas discharge line 82 Oxygen supply line 83 Fuel supply line 88 Cryogenic liquefied gas supply line 84 Exhaust gas circulation line 85 BOG header 86 Hydrogen supply line 87 Water discharge line 89 Ice discharge line 90 Dry ice discharge line 460 Carbon dioxide liquefaction device 490 Liquefied carbon dioxide discharge line

Claims

1. A power generation device using an internal combustion engine fueled by boil-off gas from a cryogenic liquefied gas storage tank, A water electrolysis device that generates hydrogen and oxygen by electrolyzing water, An exhaust gas discharge line for discharging the combustion exhaust gas of the power generation device to the outside, An oxygen supply line for supplying oxygen generated in the water electrolysis device as an oxidant to the power generation device, A fuel supply line for supplying the boil-off gas to the power generation device, An exhaust gas circulation line that branches from the exhaust gas discharge line and circulates the exhaust gas to the power generation device, A low-carbon power generation system, characterized by having an exhaust gas cooler for cooling the exhaust gas circulated to the power generation device.

2. The cryogenic liquefied gas is liquefied natural gas, A moisture solidification device disposed downstream of the branch portion to the exhaust gas circulation line in the exhaust gas discharge line, and solidifying moisture contained in the exhaust gas by heat exchange between the exhaust gas and the liquefied natural gas and / or its boil-off gas. The low-carbon power generation system according to claim 1, characterized by having the same.

3. A carbon dioxide solidification device disposed downstream of the moisture solidification device in the exhaust gas discharge line, and solidifying carbon dioxide contained in the exhaust gas by heat exchange between the exhaust gas and the LNG and / or its boil-off gas. The low-carbon power generation system according to claim 2, characterized by having the same.

4. The cryogenic liquefied gas is liquefied natural gas, A carbon dioxide liquefaction device disposed downstream of the branch portion to the exhaust gas circulation line in the exhaust gas discharge line, and liquefying carbon dioxide contained in the exhaust gas, The low-carbon power generation system according to claim 1, characterized in that the carbon dioxide liquefaction device obtains the cold heat required for liquefying carbon dioxide by heat exchange with the liquefied natural gas.

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