Gas supply system improvement method and gas supply system improvement device

Abstract

To utilize an existing facility at a demand destination while reducing carbon emissions of city gas when supplying the gas to a demand destination.SOLUTION: In an existing gas supply system 10, a hydrogen pipe 23 connected to a hydrogen gas supply source is connected to a portion of a gas pipe 15b upstream of a tank 16, and the tank 16 is used as a buffer tank 22 to adjust an opening of a flow control valve 24 provided on the hydrogen pipe 23 and a flow control valve 34 provided on the gas pipe 15b so that a volume ratio of hydrogen gas in mixed gas of hydrogen gas and city gas flowing into the buffer tank 22 falls within a range of combustion characteristics specified for the city gas originally supplied to a demand destination D1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for improving a gas supply system. [Background technology]

[0002] It has been known to supply gas obtained by vaporizing liquefied natural gas (LNG) as fuel gas to facilities such as boilers and power plants, as disclosed in the following Patent Documents 1 and 2. However, in recent years, in consideration of the environment, the use of hydrogen as a fuel for power generation and automobiles has been considered, and the demand for hydrogen has been increasing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-148211 [Patent Document 2] Patent No. 7007886 Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable to replace the fossil fuels used in gas (city gas) obtained from LNG with hydrogen, which reduces carbon dioxide emissions and is carbon-neutral, and which has a fast combustion rate and is relatively easy to combust with city gas. However, when replacing fossil fuels with hydrogen, it may be difficult to use existing equipment such as boilers and power plants as is, and new equipment may need to be designed. In other words, city gas is specified by standards to ensure that its calorific value, combustion characteristics, etc. fall within specified ranges, taking into account the stability of the combustion equipment that consumes the gas. Therefore, when replacing city gas with hydrogen gas, it becomes necessary to replace the equipment that consumes the gas. While replacing city gas with hydrogen gas can achieve low carbon emissions, it may also result in the waste of existing equipment.

[0005] Therefore, the present invention has been made in consideration of the above-mentioned conventional technology, and its purpose is to reduce the carbon footprint of the gas supplied to city gas consumers while making it possible to utilize existing facilities at the consumer's end. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the gas supply system improvement method of the present invention is a method for improving a gas supply system that supplies city gas to a consumer through a gas pipe, so that the gas supplied to the consumer has lower carbon dioxide than the city gas. The method involves connecting a hydrogen pipe connected to a hydrogen gas supply source to a tank provided in the gas pipe or to a location in the gas pipe upstream of the tank, using the tank as a buffer tank, and adjusting the opening of at least one of a flow control valve provided in the hydrogen pipe and a flow control valve provided in the gas pipe so that the volumetric ratio of hydrogen gas in the mixed gas of hydrogen gas and city gas flowing into the buffer tank falls within the range of combustion characteristics specified for the city gas originally supplied to the consumer.

[0007] In the method according to the present invention, a mixed gas obtained by mixing city gas with a predetermined ratio of hydrogen gas is stored in a buffer tank. That is, a tank originally installed in the gas piping of a gas supply system is used as a buffer tank for temporarily storing the mixed gas. The amount of storage in the buffer tank may vary depending on the demand for the mixed gas from the consumer and the flow rates of city gas and hydrogen gas into the buffer tank. Even in such cases, fluctuations in the volumetric ratio of hydrogen gas in the mixed gas in the buffer tank can be mitigated. Even if the ratio of city gas and hydrogen gas supplied to the buffer tank fluctuates over time, the buffer tank can mitigate fluctuations in the volumetric ratio of hydrogen gas in the mixed gas. This volumetric ratio of hydrogen gas falls within the range of combustion characteristics specified for the city gas originally supplied to the consumer, so that the combustion characteristics of the mixed gas acceptable to the consumer can be equivalent to those of city gas. In this case, the calorific value per unit volume of the mixed gas will be lower to a certain extent than the calorific value per unit volume of the city gas before hydrogen is mixed, but by increasing the flow rate of the mixed gas within the range of the consumer's specifications, the total calorific value required by the consumer can be secured. Moreover, because the increase in the flow rate of the mixed gas is smaller than the blending ratio of hydrogen gas, overall carbon dioxide emissions can be reduced.

[0008] For example, if the gas type is 13A city gas, the calorific value standard is approximately 45MJ / Nm 3 In this case, if hydrogen is mixed to a volume concentration of 20%, the calorific value is approximately 38 MJ / Nm 3 This means that the volumetric flow rate of the mixed gas will increase by approximately 15%, but carbon dioxide emissions can be reduced. At this time, due to factors such as the difference in density between city gas and the mixed gas, the loss of gas pressure at the demand facility is lower than the rate of increase in flow rate, and since the volumetric flow rate of the exhaust gas after combustion is roughly the same for city gas and the mixed gas, the impact on the demand facility is small, and the gas demand facility can be used as is. Moreover, because hydrogen gas is mixed into the city gas, it is possible to reduce the carbon dioxide emissions of the gas supplied to the demand facility.

[0009] Furthermore, the gas supply system improvement method of the present invention is a method for improving a gas supply system that supplies city gas to a consumer through a gas pipe, so that the gas supplied to the consumer has lower carbon dioxide than the city gas, by attaching a buffer tank to the gas pipe, and connecting a hydrogen pipe leading to a hydrogen gas supply source to the buffer tank or to a portion of the gas pipe upstream of the attachment portion of the buffer tank, and adjusting the opening of at least one of a flow control valve provided in the hydrogen pipe and a flow control valve provided in the gas pipe so that the volumetric ratio of hydrogen gas in the mixed gas of hydrogen gas and city gas flowing into the buffer tank falls within the range of combustion characteristics specified for the city gas originally supplied to the consumer.

[0010] In the method of the present invention, a mixed gas obtained by mixing city gas with a predetermined ratio of hydrogen gas is stored in a buffer tank newly attached to the gas pipe. Therefore, although the amount of storage in the buffer tank may fluctuate depending on the demand for the mixed gas from the consumer and the flow rates of city gas and hydrogen gas into the buffer tank, even in such cases, fluctuations in the volumetric ratio of hydrogen gas in the mixed gas in the buffer tank can be mitigated. Even if the ratio of city gas and hydrogen gas supplied to the buffer tank fluctuates over time, the buffer tank mitigates fluctuations in the volumetric ratio of hydrogen gas in the mixed gas. This volumetric ratio of hydrogen gas falls within the range of combustion characteristics specified for the city gas originally supplied to the consumer, so the combustion characteristics of the mixed gas accepted by the consumer can be equivalent to those of city gas. This allows the gas consumer's facilities to be used as is. Moreover, because hydrogen gas is mixed with city gas, the gas supplied to the consumer can be made low-carbon.

[0011] The supply source of the hydrogen gas may include a water electrolysis apparatus. In this case, the water electrolysis apparatus may be connected to the equipment of the demand destination or the gas piping by an oxygen gas pipe so that oxygen gas generated in the water electrolysis apparatus is supplied as a combustion improver to the boiler or heating furnace as the demand destination.

[0012] In this embodiment, oxygen gas is produced in addition to hydrogen gas in the water electrolysis device, and this produced oxygen gas can also be supplied to the consumer, so that the oxygen gas produced in the water electrolysis device can be effectively used at the consumer.

[0013] In the method, a setting unit may set the volumetric ratio of the hydrogen gas in the mixed gas, and in this case, the opening degree of at least one of the flow rate control valve of the hydrogen pipe and the flow rate control valve of the gas pipe may be adjusted so that the volumetric ratio becomes the volumetric ratio set by the setting unit.

[0014] In this embodiment, the setting unit can set the volume ratio of hydrogen gas according to the calorific value of the city gas originally supplied by the gas supply system. This makes it possible to set an appropriate volume ratio according to the gas supply system to be improved. This widens the range of applicable gas supply systems, thereby improving the versatility of the improvement method.

[0015] The setting unit may be configured to receive an input value from an input unit for inputting a volumetric ratio of the hydrogen gas in the mixed gas. In this case, when a volumetric ratio that falls within a range of combustion characteristics defined for the city gas originally supplied to the demand destination is input to the input unit, the setting unit may prompt the user to input a volumetric ratio within the range, or may issue a warning without setting the volumetric ratio.

[0016] In this embodiment, it is possible to prevent a situation in which a mixed gas having combustion characteristics exceeding those of the city gas originally supplied to the consumer is stored in the buffer tank, and therefore it is possible to prevent a situation in which a mixed gas having combustion characteristics exceeding those of the city gas originally supplied is supplied to the consumer.

[0017] In the above method, the hydrogen pipe may be connected to a portion of the gas pipe that is upstream of the buffer tank, and a calorimeter may be attached to a portion of the gas pipe between the connection portion of the hydrogen pipe and the buffer tank.

[0018] In this embodiment, the calorific value of the mixed gas flowing into the buffer tank can be monitored.

[0019] In the above method, the hydrogen pipe may be connected to a portion of the gas pipe that is upstream of the buffer tank, and a NOx meter may be provided in a portion of the gas pipe between the connection portion of the hydrogen pipe and the buffer tank.

[0020] In this embodiment, it is possible to monitor whether the concentration of NOx produced from the mixed gas is excessive.

[0021] In the above method, the hydrogen pipe may be connected to a portion of the gas piping that is upstream of the buffer tank, and a mixing means for promoting mixing of the city gas and the hydrogen gas may be attached to a portion of the gas piping between the connection portion of the hydrogen pipe and the buffer tank.

[0022] In this embodiment, the city gas and hydrogen gas flow into the buffer tank in a more mixed state, which prevents the volume ratio of city gas to hydrogen gas from varying from place to place within the buffer tank.

[0023] The gas supply system improvement device of the present invention is a device for carrying out the gas supply system improvement method, and comprises a hydrogen pipe that is connected to a hydrogen gas supply source and is configured to be attachable to a portion of the gas piping upstream of the buffer tank or to the buffer tank, and a flow control valve that is provided in the hydrogen pipe and adjusts the volumetric ratio of hydrogen gas in the mixed gas of hydrogen gas and city gas flowing into the buffer tank to a volumetric ratio that falls within a range that provides combustion characteristics equivalent to those of the city gas originally supplied to the demand destination.

[0024] The gas supply system improvement device may include a setting unit for setting the volume ratio of the hydrogen gas to be mixed with the city gas, and a valve control unit for adjusting the opening degree of the flow control valve so that the volume ratio set by the setting unit is achieved.

[0025] The setting unit may be configured to receive an input value from an input unit for inputting a volumetric ratio of the hydrogen gas to be mixed with the city gas. In this case, when a volumetric ratio outside a range in which combustion characteristics equivalent to those of the city gas supplied to the demand destination are obtained is input to the input unit, the setting unit may be configured to prompt the user to input a volumetric ratio within the range, or to issue a warning without setting the volumetric ratio.

[0026] The gas supply system improvement device may further include a calorimeter attached to a portion of the gas piping between the connection portion of the hydrogen pipe and the buffer tank. [Effects of the Invention]

[0027] As described above, according to the present invention, it is possible to reduce the carbon footprint of the gas supplied to city gas consumers, while utilizing existing facilities at the consumer's end. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a diagram schematically illustrating the configuration of an existing gas supply system to be improved. [Figure 2] FIG. 1 is a diagram showing a schematic configuration of a low-carbon gas supply system that has been completed by installing a gas supply system improvement device. [Figure 3] FIG. 10 is a diagram showing a case where a hydrogen pipe is directly connected to a buffer tank. [Figure 4] FIG. 2 is a diagram for explaining the operation of the low-carbon gas supply system. [Figure 5] FIG. 1 is a diagram schematically illustrating a configuration of a low-carbon gas supply system when a NOx meter is provided. [Figure 6]FIG. 10 is a diagram schematically illustrating a configuration of a low-carbon gas supply system when a mixing means is provided. [Figure 7] 10(a) and 10(b) are diagrams for explaining the configuration of a mixing means. [Figure 8] FIG. 1 is a diagram showing the schematic configuration of a low-carbon gas supply system that is created by attaching a gas supply system improvement device to an existing gas supply system that does not have a tank. DETAILED DESCRIPTION OF THE INVENTION

[0029] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] (First embodiment) The first embodiment is a method for improving an existing gas supply system that supplies city gas to consumers through gas piping in which tanks are installed, thereby reducing the carbon dioxide content of the gas supplied to consumers. For example, as shown in Fig. 1, an existing city gas supply system 10 includes a vaporizer 12 that vaporizes liquefied natural gas (LNG) stored in an LNG tank 11, and a gas piping group 15 that connects multiple city gas consumers D1 and D2.

[0031] Gas pipe group 15 includes upstream pipe 15a, which is connected to vaporizer 12 and sends city gas adjusted to a predetermined calorific value using gas obtained by vaporizer 12, and multiple gas pipes 15b and 15c branching off from upstream pipe 15a. Multiple gas pipes 15b and 15c are connected to city gas demand destinations D1 and D2, respectively.

[0032] One of the multiple gas pipes 15b, 15c is gas pipe 15b equipped with tank 16. City gas adjusted to predetermined combustion characteristics is temporarily stored in this tank 16. The city gas in tank 16 is supplied to demand destination D1 connected to gas pipe 15b. For this reason, demand destination D1 has equipment (boiler, heating furnace, power plant, etc.) designed to be suitable for burning city gas with predetermined combustion characteristics.

[0033] The gas supply system improvement method of the first embodiment is a method for making the gas supplied to the demand destination D1 through the gas pipe 15b equipped with this tank 16 into a gas with lower carbon dioxide than city gas. By attaching a gas supply system improvement device (hereinafter referred to as the improvement device) 20 to the gas pipe 15b, a low-carbon gas supply system 50 is created for supplying a mixed gas of city gas and hydrogen gas to the demand destination D1, as shown in Figure 2. In this case, the tank 16 of the gas pipe 15b is used as a buffer tank 22 for temporarily storing the mixed gas.

[0034] The improved device 20 has a hydrogen pipe 23 and a flow rate adjustment valve 24. The hydrogen pipe 23 is connected to a hydrogen gas supply source 26 and is a pipe through which hydrogen gas sent from the supply source 26 flows. Fig. 2 shows an example in which the hydrogen pipe 23 is connected to a portion of the gas pipe 15b that is upstream of the buffer tank 22. Note that the hydrogen pipe 23 may also be connected directly to the buffer tank 22 instead of being connected to the gas pipe 15b, as shown in Fig. 3.

[0035] The hydrogen gas supply source 26 has a water electrolysis device 26a that electrolyzes water to generate hydrogen gas. The water electrolysis device 26a is connected to a power generation mechanism 27 that uses renewable energy and a system power supply 28. The power generation mechanism 27 may be, but is not limited to, a solar panel, and may be a power generation mechanism that uses wind power, hydropower, wave power, tidal power, geothermal power, solar heat, atmospheric heat or other heat present in nature, or biomass. The water electrolysis device 26a may be connected to a storage battery (not shown) and receive power from the storage battery when the power supply from the power generation mechanism 27 is low. The storage battery may store surplus power generated by the power generation mechanism 27.

[0036] Therefore, the hydrogen gas supplied from the hydrogen gas supply source 26 is low-carbon hydrogen (clean hydrogen) in that the amount of carbon dioxide emitted to produce a predetermined mass of hydrogen is equal to or less than a predetermined mass. For example, 3.4 kg-CO2 / kg-H2 may be used as a criterion for determining low-carbon hydrogen.

[0037] The hydrogen gas supply source 26 may have a reservoir 26b that temporarily stores the hydrogen gas produced in the water electrolysis device 26a. In this case, at least a portion of the hydrogen gas produced in the water electrolysis device 26a is supplied directly to the buffer tank 22. Alternatively, the hydrogen gas stored in the reservoir 26b may be supplied to the buffer tank 22. The reservoir 26b may be omitted.

[0038] In the water electrolysis device 26a, oxygen gas is also generated while hydrogen gas is generated. Therefore, in the example shown in Fig. 2, the water electrolysis device 26a and the gas piping 15b are connected by an oxygen gas pipe 30 so that the oxygen gas generated in the water electrolysis device 26a is supplied to the demand destination D1. The oxygen gas pipe 30 may be connected to the buffer tank 22 or directly to the equipment of the demand destination D1. In Fig. 2, the oxygen gas pipe 30 is connected to a portion of the gas piping 15b downstream of the buffer tank 22, but it may also be connected to a portion of the gas piping 15b upstream of the buffer tank 22 as long as it is downstream of a calorimeter 38 described below. The oxygen gas pipe 30 may also be omitted.

[0039] Flow rate adjustment valve 24 is a valve for adjusting the flow rate of hydrogen gas flowing into buffer tank 22 (or gas pipe 15b), and is provided in hydrogen pipe 23. In addition, hydrogen pipe 23 is provided with a flow meter 31 that measures the flow rate of hydrogen gas flowing toward buffer tank 22 (or gas pipes 15b, 15c). In addition, hydrogen pipe 23 is also provided with a check valve 32 to prevent backflow from gas pipe 15b to supply source 26. Note that instead of measuring the flow rate of hydrogen gas with flow meter 31, the current value obtained by power generation mechanism 27 may be referenced.

[0040] If the gas pipe 15b is not provided with a flow control valve for adjusting the flow rate of the city gas flowing into the buffer tank 22, the flow control valve 34 is attached to the gas pipe 15b at a location upstream of the connection point of the hydrogen pipe 23. If an existing flow control valve exists, this flow control valve can be used as the flow control valve 34.

[0041] Furthermore, if a flow meter is not provided in the gas pipe 15b at a position upstream of the connection point of the hydrogen pipe 23, a flow meter 35 is attached to the gas pipe 15b at a position upstream of the connection point of the hydrogen pipe 23. If an existing flow meter exists, this flow meter can be used as the flow meter 35.

[0042] Furthermore, if the gas pipe 15b is not provided with a check valve to prevent the backflow of city gas, a check valve 36 is attached to the gas pipe 15b at a location upstream of the connection point to the hydrogen pipe 23. By attaching the check valve 36, it is possible to prevent hydrogen gas from flowing from the connection point to the hydrogen pipe 23 toward the upstream side of the gas pipe 15b.

[0043] In addition, a calorimeter 38 is attached to the gas piping 15b at a location between the connection part of the hydrogen pipe 23 and the buffer tank 22. The calorimeter 38 can measure the calorific value of the mixed gas, and by referring to this measured value, it can be confirmed whether the volumetric ratio of hydrogen gas contained in the mixed gas flowing into the buffer tank 22 is within an appropriate predetermined range. An example of the calorimeter 38 is one that has a substance whose heat capacity changes depending on the temperature difference with the temperature of the mixed gas, and is configured to be able to measure the calorific value of the mixed gas from the amount of change in temperature of this substance.

[0044] The improved device 20 has an input unit 40 for inputting the volumetric ratio of hydrogen gas in the mixed gas, and a controller 41 for adjusting the mixed ratio of hydrogen gas based on the input from the input unit 40.

[0045] The input unit 40 is configured with, for example, a keyboard, a touch panel, etc., so that the operator can input the volumetric ratio (mixing ratio) of hydrogen gas. The operator inputs through the input unit 40 the volumetric ratio of hydrogen gas that falls within a range that provides combustion characteristics equivalent to those of the city gas that was supplied to the demand destination D1 by the existing gas supply system 10. For example, when the type of city gas is 13A, a typical city gas with a calorific value of 45 MJ / Nm 3 In this case, if the volume ratio of the mixed hydrogen gas is kept to 22.2% or less, a mixed gas with combustion characteristics equivalent to that of city gas can be obtained.

[0046] The controller 41 is configured by a computer that performs predetermined functions by executing a stored program. The functions of the controller 41 include a setting unit 41a that stores the volumetric ratio of hydrogen gas input through the input unit 40 as a set value under predetermined conditions, and a valve control unit 41b that controls the flow rate adjustment valve 24 and the flow rate adjustment valve 34 so as to obtain the volumetric ratio set by the setting unit 41a. That is, when installing the improved device 20 in the existing gas supply system 10, the valve control unit 41b (or the controller 41) is connected to the flow rate adjustment valve 34 of the gas pipe 15b so as to be able to send and receive signals.

[0047] The setting unit 41a receives from the input unit 40 information (input value) indicating the volumetric percentage of hydrogen gas input to the input unit 40. The setting unit 41a stores the input value from the input unit 40 as a set value under predetermined conditions. That is, the setting unit 41a stores a range of volumetric percentages of hydrogen gas that will provide combustion characteristics equivalent to those of the city gas originally supplied to the demand destination D1, and if the input value is within this stored range, the setting unit 41a stores the input value as the set value. On the other hand, if the input value is outside this stored range, the setting unit 41a prompts the user to input a volumetric percentage within the range, or does not set an input value and issues a warning indicating that the input value is outside the range.

[0048] The valve control unit 41b controls the flow rate control valve 24 of the hydrogen pipe 23 and the flow rate control valve 34 of the gas pipe 15b so as to obtain the set value (mixing ratio of hydrogen gas) set in the setting unit 41a. Specifically, the valve control unit 41b receives information indicating the measurement value from the flow meter 31 of the hydrogen pipe 23 and information indicating the measurement value from the flow meter 35 of the gas pipe 15b, and adjusts the aperture of both the flow rate control valves 24, 34 based on these measurement values ​​and the set value. Note that if an ammeter (not shown) that measures the current value obtained by the power generation mechanism 27 is provided instead of the flow meter 31, the valve control unit 41b adjusts the aperture of both the flow rate control valves 24, 34 by also referring to this current value.

[0049] The hydrogen gas flowing through the hydrogen pipe 23 is generated in the water electrolysis device 26a, and therefore the flow rate fluctuates. For this reason, the valve control unit 41b adjusts the opening of both flow rate control valves 24 while repeatedly referring to the measurement value of the flow meter 31 (or ammeter) of the hydrogen pipe 23 at predetermined time intervals. This makes it possible to suppress fluctuations in the volumetric ratio of hydrogen gas in the mixed gas flowing into the buffer tank 22.

[0050] Here, the operation of the low-carbon gas supply system 50 completed by installing the improved device 20 will be described with reference to FIG.

[0051] First, the operator inputs the volumetric ratio (mixing ratio) of hydrogen gas through the input unit 40 (step ST11). At this time, the operator inputs a volumetric ratio according to the type of city gas supplied to the demand destination D1 by the existing gas supply system 10. For example, if the type of city gas is 13A, the operator inputs a predetermined ratio (e.g., 5%, 10%) of 22.2% or less as the volumetric ratio of hydrogen gas.

[0052] At this time, if the volume ratio value input to the input unit 40 exceeds the range of volume ratios stored in the setting unit 41a, the setting unit 41a issues a warning and prompts the user to input a value within the range of the stored volume ratios (step ST12). If the input value is within the range stored in advance, the value is stored as the set value (step ST13).

[0053] Next, the water electrolysis device 26a is started up, and hydrogen gas and oxygen gas are produced in the water electrolysis device 26a. The oxygen gas is sent to the gas pipe 15b through the oxygen gas pipe 30. Therefore, the oxygen gas produced in the water electrolysis device 26a can be supplied as a combustion improver to a boiler or a heating furnace, which is a demand destination D1.

[0054] Meanwhile, hydrogen gas generated in the water electrolysis device 26a flows through the hydrogen pipe 23. At this time, the flow meter 31 of the hydrogen pipe 23 measures the flow rate of the hydrogen gas (step ST14). Meanwhile, the flow meter 35 of the gas pipe 15b measures the flow rate of the city gas flowing through the gas pipe 15b (step ST15). Information indicating these measurement values ​​is received by the controller 41 of the improved device 20, and the valve control unit 41b (controller 41) adjusts the aperture of both flow rate control valves 24, 34 based on the measurement value indicated by the received information and the set value set by the setting unit 41a (the set value for the volume fraction of hydrogen gas in the mixed gas) (step ST16).

[0055] This adjusts the flow rate of hydrogen gas flowing toward the gas pipe 15b and the flow rate of city gas flowing toward the connection portion of the hydrogen pipe 23. This adjusts the volumetric ratio of hydrogen gas contained in the mixed gas to a predetermined ratio. The flow rate adjustment of hydrogen gas and the flow rate adjustment of city gas are repeated at predetermined time intervals.

[0056] If the flow rate of hydrogen gas output from the water electrolysis device 26a is excessively high as a result of adjustment of the flow rate of hydrogen gas by the flow rate adjustment valve 24, the excess hydrogen gas is stored in the storage section 26b. Note that if the flow rate of hydrogen gas is excessively high, the water electrolysis device 26a may be controlled so as to reduce the amount of hydrogen gas produced.

[0057] On the other hand, if the flow rate of hydrogen gas delivered from the water electrolysis device 26a is insufficient, the hydrogen gas stored in the storage unit 26b may be delivered to the hydrogen pipe 23. If the flow rate of hydrogen gas is insufficient, operation may be continued at that flow rate.

[0058] By adjusting the flow rate of hydrogen gas and the flow rate of city gas, the volumetric ratio of hydrogen gas in the mixed gas obtained by merging hydrogen gas with city gas is adjusted to a predetermined ratio. This mixed gas with the adjusted volumetric ratio of hydrogen gas flows into buffer tank 22 and is temporarily stored in buffer tank 22. Therefore, because the mixed gas with the adjusted volumetric ratio of hydrogen gas is stored in buffer tank 22, the volumetric ratio of hydrogen gas in the mixed gas sent from buffer tank 22 and supplied to demand destination D1 is also stabilized at a predetermined ratio.

[0059] As described above, in this embodiment, a mixed gas obtained by mixing city gas with a predetermined ratio of hydrogen gas is stored in the buffer tank 22. The amount of the stored volume in the buffer tank 22 may vary depending on the demand for the mixed gas from the demand destination D1 and the flow rates of city gas and hydrogen gas into the buffer tank 22. Even in this case, fluctuations in the volumetric ratio of hydrogen gas in the mixed gas in the buffer tank 22 can be mitigated. Even if the ratio of city gas and hydrogen gas supplied to the buffer tank 22 fluctuates over time, the buffer tank 22 can mitigate fluctuations in the volumetric ratio of hydrogen gas in the mixed gas. This volumetric ratio of hydrogen gas falls within a range that provides combustion characteristics equivalent to those of the city gas originally supplied to the demand destination. Therefore, the combustion characteristics of the mixed gas accepted by the demand destination D1 can be equivalent to those of city gas. This allows the equipment of the gas demand destination D1 to be utilized as is. Moreover, because hydrogen gas is mixed with city gas, the gas supplied to the demand destination D1 can be made low-carbon.

[0060] In this embodiment, the hydrogen gas supply source 26 includes a water electrolysis device 26a, which generates hydrogen gas using electricity derived from renewable energy. Furthermore, oxygen gas generated together with hydrogen gas in the water electrolysis device 26a can also be supplied to the demand destination D1. Therefore, the oxygen gas can be effectively utilized at the demand destination D1.

[0061] Furthermore, in this embodiment, the operator can input, via the input unit 40, the mixing ratio of hydrogen gas that corresponds to the combustion characteristics of the city gas originally supplied by the gas supply system 10. This makes it possible to set an appropriate volume ratio depending on the gas supply system 10 that is the target of improvement. This therefore broadens the range of applicable gas supply systems 10, improving the versatility of the improvement method.

[0062] Furthermore, in this embodiment, when a volume ratio that exceeds the range in which combustion characteristics equivalent to those of the city gas originally supplied to the demand destination are input to the input unit 40, the setting unit 41a prompts the user to input a volume ratio within the range, or issues a warning without setting a volume ratio. This prevents a situation in which a mixed gas having combustion characteristics exceeding those of the city gas originally supplied to the demand destination D1 is stored in the buffer tank 22. This prevents a situation in which a mixed gas having combustion characteristics exceeding those of the city gas originally supplied to the demand destination D1 is supplied to the demand destination D1.

[0063] In this embodiment, a calorimeter 38 is attached to the gas pipe 15b at a location between the connection portion of the hydrogen pipe 23 and the buffer tank 22. This makes it possible to monitor the calorific value of the mixed gas flowing into the buffer tank 22.

[0064] In this embodiment, the calorimeter 38 is attached to a portion of the gas pipe 15b through which the mixed gas flows, but this is not limiting. The calorimeter 38 may be omitted. In this embodiment, the calorimeter 38 is provided simply for monitoring purposes, but the improved device 20 may be configured to use the measurement value of the calorimeter 38 for feedback control.

[0065] That is, the range of allowable calorific value is stored in controller 41, and the measured value of calorimeter 38 is compared with this stored range, and if the measured value of calorimeter 38 exceeds the range stored in controller 41, flow control valve 24 of hydrogen pipe 23 may be controlled to reduce its opening. In this case, flow meters 31 and 35 may be omitted.

[0066] In this embodiment, the hydrogen gas supply source 26 includes a water electrolysis device 26a, but is not limited to this. For example, the hydrogen gas supply source 26 may be a tank (not shown) that stores hydrogen gas, or may be a combination of a tank that stores liquid hydrogen and a liquid hydrogen vaporizer (not shown). In these cases, the oxygen gas pipe 30 is omitted.

[0067] In this embodiment, the valve control unit 41b of the controller 41 controls both the flow rate adjustment valve 24 of the hydrogen pipe 23 and the flow rate adjustment valve 34 of the gas pipe 15b, but this is not limited to this. For example, if the flow rate of city gas supplied through the gas pipe 15b is adjusted to a constant value, only the flow rate adjustment valve 24 of the hydrogen pipe 23 may be controlled. Also, if the flow rate of hydrogen gas supplied from the hydrogen gas supply source 26 is adjusted to a constant value, only the flow rate adjustment valve 34 of the gas pipe 15b may be controlled.

[0068] In this embodiment, the demand destination D1 is a facility that requires strict temperature control of the heat output of a boiler or the like. Therefore, the valve control unit 41b controls the flow rate control valves 24, 34 so that the volumetric ratio (mixing ratio) of hydrogen gas becomes the set value set by the setting unit 41a. However, if such strict control of the heat output is not required at the demand destination D1, the volumetric ratio (mixing ratio) of hydrogen gas (e.g., the flow rate of city gas) may be adjusted according to the flow rate of the hydrogen gas generated by the water electrolysis device 26a within a range equal to or less than the combustion characteristics of the city gas supplied to the demand destination D1 by the existing gas supply system 10. In this case, the operation of storing hydrogen gas can be simplified. Note that when adjusting the hydrogen gas mixing ratio, sudden fluctuations in concentration can cause sudden fluctuations in flow rate, ultimately leading to unstable operation of the demand destination facility. For this reason, it is preferable to adjust the mixing ratio so that the hydrogen mixing concentration does not suddenly fluctuate. Furthermore, because the amount of hydrogen gas mixed determines the amount of carbon dioxide reduction, it is preferable to accurately measure the hydrogen flow rate.

[0069] In this embodiment, as shown in Fig. 5, a NOx meter 43 may be provided. The NOx meter 43 is placed in a portion of the gas pipe 15b between the connection portion of the hydrogen pipe 23 and the buffer tank 22. In this case, it is possible to monitor whether the concentration of NOx (nitrogen oxides) generated from the mixed gas is excessive. For example, since the concentration of NOx generated from the mixed gas may increase when the temperature of the hydrogen gas increases, the NOx meter 43 may be provided.

[0070] In this embodiment, as shown in FIG. 6, a mixer 44 may be installed to promote mixing of city gas and hydrogen gas. The mixer 44 is installed in the gas pipe 15b between the connection portion of the hydrogen pipe 23 and the buffer tank 22. The mixer 44 is configured to generate turbulence in the flow of the mixed gas by creating a pressure loss in the gas pipe 15b. For example, as shown in FIG. 7(a), the mixer 44 has multiple elbows 44a so that the gas pipe 15b is bent at multiple locations. It is preferable that each elbow 44a bends the gas pipe 15b in a different direction. This can further enhance the gas mixing effect. When the mixer 44 is installed, the calorimeter 38 may be located downstream of the mixer 44 to measure the calorific value of the mixed and stirred mixed gas.

[0071] The mixing means 44 is not limited to a configuration having a plurality of elbows 44a, and may be configured to cause turbulence in the flow of the mixed gas by changing the flow path cross-sectional area of ​​the gas pipe 15b, as shown in Fig. 7(b). The mixing means 44 may be configured as a mixer that uses power to perform mixing, but is preferably configured to promote mixing without using power.

[0072] The improved device 20 may be equipped with a pressure regulating valve (not shown) that adjusts the pressure of the hydrogen gas flowing through the hydrogen pipe 23 according to the pressure of the city gas flowing into the buffer tank 22. In this case, the pressure difference between the hydrogen gas and the city gas can be kept below a predetermined value so that the hydrogen gas can easily flow from the hydrogen pipe 23 into the gas piping 15b.

[0073] (Second embodiment) In the first embodiment, when the low-carbon gas supply system 50 is operating, the valve control unit 41b controls the aperture of the flow control valve 24 of the hydrogen pipe 23 and the flow control valve 34 of the gas pipe 15b at predetermined time intervals. In contrast, in the second embodiment, the aperture of the flow control valves 24, 34 is adjusted when the improved device 20 is installed, but the aperture of the flow control valves 24, 34 is not controlled during subsequent operation. Note that the same components as in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0074] Specifically, in the first embodiment, the aperture control of the flow rate control valves 24, 34 is performed during operation of the system 50, assuming that the flow rates of hydrogen gas and city gas fluctuate. In contrast, the second embodiment assumes that the flow rate of city gas flowing through the gas pipe 15b is stable, and that the flow rate of hydrogen gas supplied from the hydrogen gas supply source 26 is also stable. In this case, if the aperture control of the flow rate control valves 24 of the hydrogen pipe 23 and the flow rate control valve 34 of the gas pipe 15b is adjusted when the improving device 20 is installed in the existing gas supply system 10, the aperture control of the flow rate control valves 24, 34 can be omitted during subsequent operation. However, even in this case, the aperture control of the flow rate control valves 24, 34 is performed during installation of the improving device 20 so that the volumetric ratio of hydrogen gas in the mixed gas falls within the range of combustion characteristics specified for the city gas originally supplied to the demand destination D1.

[0075] In this case, the input unit 40 and the controller 41 may be omitted, and an operator may adjust the flow rate control valves 24, 34 when installing the improvement device 20. Alternatively, the input unit 40 and the controller 41 may be provided, while the valve control unit 41b may control the flow rate control valves 24, 34 only when installing the improvement device 20.

[0076] 2, 3, and 5 to 7 can also be adopted in the second embodiment. Although a description of other configurations, actions, and effects will be omitted, the description of the first embodiment can be applied to the second embodiment.

[0077] (Third embodiment) The first embodiment is an example in which the improvement device 20 is attached to a gas pipe 15b that is provided with a tank 16. In contrast, the third embodiment is an improvement method in which the improvement device 20 is attached to a gas pipe 15c that does not have a tank 16. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0078] In the third embodiment, as shown in FIG. 8, in order to attach the improved device 20 to the gas pipe 15c that does not have a tank, a step of attaching a buffer tank 22 to the gas pipe 15c that does not have a tank is added.

[0079] Then, the hydrogen pipe 23 is connected to a portion of the gas pipe 15c that is upstream of the buffer tank 22. In addition, a calorimeter 38 is attached to the gas pipe 15c between the connection between the buffer tank 22 and the hydrogen pipe 23. Note that the calorimeter 38 can be omitted.

[0080] If the gas pipe 15c is not provided with a flow control valve for adjusting the flow rate of the city gas flowing into the buffer tank 22, a flow control valve 34 is attached to the gas pipe 15c at a position upstream of the connection point of the hydrogen pipe 23.

[0081] Furthermore, if a flow meter is not provided in the gas pipe 15c at a position upstream of the connection point of the hydrogen pipe 23, a flow meter 35 is attached to the gas pipe 15c at a position upstream of the connection point of the hydrogen pipe 23. If an existing flow meter exists, this flow meter can be used as the flow meter 35.

[0082] Furthermore, if the gas pipe 15c is not provided with a check valve to prevent the backflow of city gas, a check valve 36 is attached to the gas pipe 15c at a location upstream of the connection point to the hydrogen pipe 23. By attaching the check valve 36, it is possible to prevent hydrogen gas from flowing from the connection point to the hydrogen pipe 23 toward the upstream side of the gas pipe 15c.

[0083] The operation of the low-carbon gas supply system 50 completed by installing the improved device 20 is the same as the operation of the system 50 in the first embodiment described with reference to FIG.

[0084] In the method according to this embodiment, a mixed gas obtained by mixing city gas with a predetermined ratio of hydrogen gas is stored in a buffer tank 22 newly attached to the gas pipe 15c. Therefore, although the amount of storage in the buffer tank 22 may fluctuate depending on the demand for the mixed gas from the demand destination D2 and the inflow rates of city gas and hydrogen gas into the buffer tank 22, even in such cases, fluctuations in the volumetric ratio of hydrogen gas in the mixed gas in the buffer tank 22 can be mitigated. Even if the ratio of city gas and hydrogen gas supplied to the buffer tank 22 fluctuates over time, the buffer tank 22 can mitigate fluctuations in the volumetric ratio of hydrogen gas in the mixed gas. Because this volumetric ratio of hydrogen gas falls within the range of combustion characteristics specified for the city gas originally supplied to the demand destination D2, the combustion characteristics of the mixed gas accepted by the demand destination D2 can be equivalent to those of city gas. This allows the equipment of the gas demand destination D2 to be utilized as is. Moreover, because hydrogen gas is mixed with city gas, the gas supplied to the demand destination D2 can be made low-carbon.

[0085] In this embodiment, as in the second embodiment, the openings of the flow rate control valves 24, 34 may be adjusted when the improved device 20 is installed, but the openings of the flow rate control valves 24, 34 may not be controlled during subsequent operation. Although a description of other configurations, actions, and effects will be omitted, the descriptions of the first and second embodiments can be applied to the third embodiment.

[0086] (Other embodiments) It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The present invention is not limited to the above-described embodiments, and various modifications and improvements are possible without departing from the spirit and scope of the present invention. Furthermore, in any of the above-described embodiments, when there is a shortage of power on the grid power supply 28 side, hydrogen production by the water electrolysis device 26a may be stopped, and electricity derived from renewable energy or electricity stored in a storage battery may be supplied to the grid power supply 28 side. In this case, hydrogen gas is no longer supplied to the city gas and hydrogen gas buffer tank 22 that produces the mixed gas, and the mixed gas will contain only city gas components. However, because the mixed gas of hydrogen and city gas is supplied by an existing city gas heating furnace, boiler, etc., the amount of NOx generated will be within the allowable limit, and there will be no operational problems. [Explanation of symbols]

[0087] 10: Gas supply system 15b: Gas piping 15c: Gas piping 20: Gas supply system improvement device 22: Buffer tank 23: Hydrogen pipe 24: Flow control valve 26: Source 26a: Water electrolysis device 30: Oxygen gas pipe 34: Flow control valve 38:Calorimeter 40: Input section 41a: Setting section 41b: Valve control section 43: NOX meter 44 :Mixing means D1: Demand destination D2: Demand destination

Claims

1. A method for improving a gas supply system that supplies city gas to a consumer through gas piping, to make the gas supplied to the consumer a lower carbon gas than the city gas, comprising: a hydrogen pipe connected to a hydrogen gas supply source is connected to a tank provided in the gas piping or to a portion of the gas piping upstream of the tank; A method for improving a gas supply system, in which the tank is used as a buffer tank, and the opening of at least one of a flow control valve provided on the hydrogen pipe and a flow control valve provided on the gas piping is adjusted so that the volumetric ratio of hydrogen gas in the mixed gas of hydrogen gas and city gas flowing into the buffer tank falls within the range of combustion characteristics specified for the city gas originally supplied to the consumer.

2. A method for improving a gas supply system that supplies city gas to a consumer through gas piping, to make the gas supplied to the consumer a lower carbon gas than the city gas, comprising: A buffer tank is attached to the gas pipe, a hydrogen pipe connected to a hydrogen gas supply source is connected to the buffer tank or to a portion of the gas piping upstream of the attachment portion of the buffer tank; A method for improving a gas supply system, comprising adjusting the opening of at least one of a flow control valve provided on the hydrogen pipe and a flow control valve provided on the gas piping so that the volumetric ratio of hydrogen gas in the mixed gas of hydrogen gas and city gas flowing into the buffer tank falls within a range that provides combustion characteristics equivalent to those of the city gas originally supplied to the consumer.

3. the source of hydrogen gas includes a water electrolysis device; 3. The method for improving a gas supply system according to claim 1, wherein the water electrolysis device is connected to the equipment at the demand destination or the gas piping via an oxygen gas pipe so that the oxygen gas produced in the water electrolysis device is supplied as a combustion improver to the boiler or heating furnace at the demand destination.

4. a setting unit sets a volume ratio of the hydrogen gas in the mixed gas; 3. The method for improving a gas supply system according to claim 1, further comprising adjusting the opening degree of at least one of the flow rate control valve of the hydrogen pipe and the flow rate control valve of the gas pipe so as to achieve the volume ratio set by the setting unit.

5. the setting unit is configured to receive an input value from an input unit for inputting a volume ratio of the hydrogen gas in the mixed gas; 5. The gas supply system improvement method according to claim 4, wherein, when a volume ratio exceeding a range that provides combustion characteristics equivalent to those of the city gas originally supplied to the demand destination is input into the input unit, the setting unit prompts the user to input a volume ratio within the range, or issues a warning without setting the volume ratio.

6. the hydrogen pipe is connected to a portion of the gas pipe that is upstream of the buffer tank; 3. The method for improving a gas supply system according to claim 1, further comprising the step of attaching a calorimeter to the gas piping at a location between the connection portion of the hydrogen pipe and the buffer tank.

7. the hydrogen pipe is connected to a portion of the gas pipe that is upstream of the buffer tank; 3. The method for improving a gas supply system according to claim 1, further comprising providing a NOx meter in the gas piping at a location between the connection of the hydrogen pipe and the buffer tank.

8. the hydrogen pipe is connected to a portion of the gas pipe that is upstream of the buffer tank; 3. The method for improving a gas supply system according to claim 1, further comprising the step of attaching a mixing means for promoting mixing of the city gas and the hydrogen gas to a portion of the gas piping between the connection portion of the hydrogen pipe and the buffer tank.

9. 3. An apparatus for carrying out the gas supply system improvement method according to claim 1 or 2, comprising: a hydrogen pipe connected to a hydrogen gas supply source and configured to be attachable to a portion of the gas pipe upstream of the buffer tank or to the buffer tank; a flow control valve provided in the hydrogen pipe for adjusting the volumetric ratio of hydrogen gas in the mixed gas of hydrogen gas and city gas flowing into the buffer tank to a volumetric ratio that falls within the range of combustion characteristics specified for the city gas originally supplied to the consumer.

10. a setting unit for setting a volume ratio of the hydrogen gas to be mixed with the city gas; 10. The gas supply system improving device according to claim 9, further comprising: a valve control unit that adjusts the opening of the flow rate adjustment valve so as to achieve the volume ratio set by the setting unit.

11. the setting unit is configured to receive an input value from an input unit for inputting a volume ratio of the hydrogen gas to be mixed with the city gas, The gas supply system improvement device of claim 10, wherein when a volume ratio exceeding a range that provides combustion characteristics equivalent to those of the city gas supplied to the demand destination is input into the input unit, the setting unit is configured to prompt the input of a volume ratio within the range, or to issue a warning without setting the volume ratio.

12. 10. The gas supply system improvement device according to claim 9, further comprising a calorimeter attached to a portion of the gas piping between the connection portion of the hydrogen pipe and the buffer tank.

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