JP6265166B2 - Monitoring system for hydrogen leakage from conduit - Google Patents

Description

Detailed Description of the Invention

  In accordance with the transition from the present gasoline car era to the age of fuel cell cars fueled with hydrogen, the leakage of hydrogen from the conduit when transporting hydrogen from the hydrogen plant to the hydrogen station using the conduit. Regarding monitoring.

  Fuel cells that are expected to be the next generation clean energy source are already on the market with fuel cell vehicles equipped with these batteries. On the other hand, the absolute number of hydrogen stations that supply hydrogen to fuel cell vehicles is still insufficient, and the maintenance is urgently needed.

  Hydrogen stations are classified into on-site and off-site types depending on the location where hydrogen is produced. On-site type refers to hydrogen stations that produce hydrogen at the same time where hydrogen is charged, but both have advantages and disadvantages in production and transportation costs, and there is still no conclusion as to which method is superior at this time. Not.

  An off-site type hydrogen station has an advantage that hydrogen can be produced in a concentrated manner and can be produced at a low cost, but the hydrogen must be transported from the hydrogen production site to the hydrogen station. There are two methods for transporting hydrogen: a method in which high-pressure cylinders are filled with hydrogen gas and transported by a dedicated vehicle, and a method in which hydrogen is liquefied and transported by a liquefied hydrogen lorry vehicle. The former has already started operation tests for the hydrogen station.

In addition to this, there is a method of transporting hydrogen using a conduit, and the following documents have been published.
JP 2004-146212 A JP 2006-173068 A JP 2006-207785 A Document 1 describes a method of transporting hydrogen as a mixed gas of hydrogen and nitrogen in order to avoid the danger of hydrogen explosion. Document 2 describes a method of laying the ground on the ground using the frame and side surfaces of the expressway without using the burial system. Document 3 describes a method of separating hydrogen and nitrogen from a mixed gas of hydrogen and nitrogen by a simple method at a hydrogen station.

In 2011, a method for supplying hydrogen from a hydrogen plant to a hydrogen station using a conduit was tried in Kitakyushu City as part of a hydrogen / fuel cell demonstration project. At this hydrogen station, pure hydrogen produced from hydrogen produced as a by-product at an adjacent steel works was received using conduits laid above and below the ground. The pipe used is a general-purpose steel pipe, and the length of the conduit is about 2 km in total length. The project introduced this method as “Japan's first next-generation hydrogen station using conduits”. This hydrogen station is still in operation.

  When transporting hydrogen through a conduit, the biggest challenge is how to quickly detect and stop the leak if hydrogen leaks from the conduit. When laying pipes over long distances using the sides of highways, etc., it is said that hydrogen transport using pipes is difficult unless the disaster prevention measures are established, especially on Japanese highways with many tunnels. ing.

  In general, as a method of detecting leakage of combustible gas from a conduit, there is a method of adding an odorant to combustible gas and calling attention when a human notices the smell. This method has a drawback that the range that can be detected is extremely limited, and cannot be monitored by an unattended person.

  In addition, there is a method that uses double pipes to detect gas leaks from the inner pipe with a detector and alerts them with an alarm, etc., and has already been proven as a method for monitoring toxic gas leaks in a small laboratory. There is. However, a method for monitoring hydrogen leakage across all conduits across a wide-scale hydrogen infrastructure has not yet been disclosed.

  The present invention has been made in view of the above problems. Under the hydrogen leakage monitoring system proposed by the inventor, hydrogen leakage is prevented over the entire section of the conduit from the hydrogen production plant to the hydrogen stations nationwide. It provides a means to monitor and transport hydrogen safely.

  First, the configuration of the entire system of the present invention will be described. The present invention comprises a hydrogen production plant, a hydrogen station, a conduit connecting the two, and a monitoring center for monitoring leakage of hydrogen from the conduit. In the present invention, hydrogen is supplied from a hydrogen plant through a conduit to a hydrogen station as a mixed gas of hydrogen and nitrogen, not hydrogen alone.

A dedicated double pipe is connected to the conduit. In the inner pipe of the double pipe , a mixed gas of hydrogen and nitrogen flows from the hydrogen production plant to the hydrogen station. Nitrogen is allowed to flow from the hydrogen station to the hydrogen production site in the space between the inner and outer tubes of the double tube (hereinafter referred to as the outer tube). This nitrogen is used after separating hydrogen from a mixed gas of hydrogen and nitrogen at a hydrogen station.

  The pressure for transporting the mixed gas and nitrogen is 10 atm or less. Below this pressure, both gases are outside the scope of the High Pressure Gas Safety Law. Furthermore, the nitrogen pressure flows through the outer pipe portion of the double pipe while maintaining a pressure lower than the pressure of the mixed gas of hydrogen and nitrogen in the inner pipe.

In the monitoring center at all times in each separate detected method described below inner tube and the outer tube or these leaks of the double pipe over the entire area of the conduit to monitor. If a leak is detected, the gas flow is shut off by a command from the monitoring center. An outline of the hydrogen / nitrogen mixed gas and nitrogen flow is shown in FIG. In the figure, there are two representative hydrogen stations. H2 represents hydrogen and N2 represents nitrogen.

  In the present invention, a safety measure against leakage of hydrogen in underground tunnels and long tunnels exceeding 1 km, which has been considered the most difficult problem in conventional pipe transportation, has been established to prevent fires and explosions caused by hydrogen. Provide a means to prevent.

  When constructing a hydrogen infrastructure that uses pipes to supply hydrogen from a hydrogen plant to a hydrogen station, the most important safety measure for transporting pipes is hydrogen leak detection. This measure was a difficult problem especially when laying hydrogen conduits in Japan, where there are many tunnels. According to the present invention, if this solution is found, it is highly possible that hydrogen transport by conduit will attract attention as a new means for building a hydrogen infrastructure.

  First, the means for detecting leakage of hydrogen from the inner pipe is described. A hydrogen gas detector is used to detect hydrogen leakage. In general, a catalytic combustion type or semiconductor type detector is put to practical use as a hydrogen gas detector. However, in the present invention, a detector using the thermal conductivity or electric conductivity of hydrogen is adopted.

  Thermal conductivity detectors have already been put into practical use as gas chromatography TCD detectors in the field of analytical chemistry, taking advantage of the fact that the thermal conductivity of hydrogen is an order of magnitude smaller than that of air and nitrogen. The invention has sufficient capability for hydrogen detection.

Recently, a new hydrogen gas sensor using a thin film of Pt / WO ₃ or SnO ₂ has been developed as a detector utilizing electric conductivity, and these also have sufficient capability for hydrogen detection of the present invention. doing. These detectors are installed in the outer tube portion of the double tube at a fixed interval, for example, 500 m to 1 km, but the installation interval can be increased or decreased depending on the risk of the surrounding environment.

Each detector through transmission cable of the flexible type installed in the same space, and transmits the presence or absence of leak detection and its location to the monitoring center. The monitoring center that has received the leak signal from the hydrogen detector knows the leak point from the signal, and the hydrogen / nitrogen mixed gas emergency shut-off valve installed in the flow path (hereinafter referred to as the hydrogen emergency shut-off valve) Is closed.

  All of the above detectors have a detection capability of several ppm as the sensitivity for detecting hydrogen, but the alarm setting value for notifying the danger of hydrogen concentration leaking from the inner pipe to the outer pipe is about 1% by volume. As long as the concentration of hydrogen in nitrogen does not exceed 7% by volume, there is no danger of ignition even if this gas leaks into the air, so this set value can ensure sufficient safety. Rather than setting the concentration setting value smaller than necessary and causing malfunction, it is important to set it to an appropriate value and accurately detect it.

  Since the pressure in the outer tube is kept lower than the pressure in the inner tube, hydrogen flows from the inner tube to the outer tube if there is a leak in the inner tube. In the outer pipe, nitrogen always flows from the hydrogen station side to the hydrogen production site side. When hydrogen leaks from the inner pipe, hydrogen is carried on this nitrogen, and when it reaches the detector, the leak is detected and a hydrogen leak signal is transmitted.

  The use of nitrogen as a hydrogen carrier gas enables the hydrogen leak detection speed to be increased because the hydrogen leaked from the inner tube can be transported to the detector more quickly than when natural diffusion occurs. Both thermal conductivity type and electric conductivity type hydrogen detectors have the ability to detect hydrogen even in an atmosphere of nitrogen gas.

  Furthermore, both thermal conductivity type and electrical conductivity type detectors have a heat generating part in the detection part, and if the heat generating part generates heat abnormally, there is a risk that the detector body will become an ignition source. Yes. Nitrogen also serves to prevent this ignition risk.

Next, means for detecting leakage of nitrogen flowing through the outer tube will be described. Conventionally, a method that is commonly implemented as a leakage detection unit in the pipe flowing the poisoning gas such as passing a toxic gas into the tube a double tube piping poison gas, toxicity from one million inner tube when gas is leaked, a method such as sounding an alarm upon detection of leaks by using a toxic gas detector installed in the outer tube portion thereto.

  However, in the case of hydrogen pipes using double pipes, the method described in the previous section is incomplete. This is because when hydrogen pipes are laid on public roads, hydrogen is lighter than air, so the leaked hydrogen can easily diffuse into the atmosphere and ignite hydrogen. This is because if the double pipe body is damaged, there will be a risk of fire and explosion due to the hydrogen gas filling the tunnel.

  As a safety measure, in the present invention, in addition to the method of monitoring the inner pipe of the conduit, a method of independently monitoring whether or not the outer pipe is broken is adopted. For this method, a nitrogen flow meter is installed at intervals of 2 km, for example, at every predetermined section of the conduit, and the flow rate is constantly monitored. A specific method was adopted.

  Nitrogen flows from the hydrogen station side toward the hydrogen plant side, and the hydrogen plant receives this nitrogen at a constant flow rate (= FRC method). FRC is a flow recording controller. The FRC flow rate setting value on the hydrogen production site side is set so that the amount of nitrogen released to the atmosphere and the amount of feedback from the storage tank are as small as possible when adjusting the pressure of nitrogen described later.

  On the hydrogen station side, nitrogen is sent out while keeping the pressure of a small nitrogen storage tank installed in the station constant (= PRC method), and the flow rate is recorded (= FR method). PRC is a pressure recording regulator, and FR is a flow recording meter. A combination of these instruments is shown in FIG.

  In FIG. 2, the number of hydrogen stations is representatively two. However, when an actual hydrogen infrastructure is built, one large-scale hydrogen production plant has several dozen or more hydrogen stations and the source of instrumentation in the previous section. Connected through a conduit.

  The nitrogen pressure in the outer pipe is always kept lower than the pressure in the inner pipe. Although not shown in FIG. 2, this pressure adjustment is performed by a pressure regulator added to the hydrogen plant side. Specifically, when the pressure of the receiving conduit rises above a set value at the hydrogen production site, a part of nitrogen is released into the atmosphere from the outer pipe portion of the conduit. Conversely, when the pressure in the conduit drops, nitrogen is fed back from the large nitrogen storage tank in the hydrogen plant to the outer tube.

  The amount of nitrogen generated at the hydrogen station varies with the frequency of hydrogen filling the vehicle. On the other hand, the hydrogen station generally has no space for installing a large nitrogen storage tank like a hydrogen factory, and it is difficult to smooth out the amount of nitrogen to be sent out. As a result, the flow rate of nitrogen delivered from each station constantly fluctuates. However, the fluctuation range of the nitrogen flow rate from each hydrogen station is extremely small compared to the sudden leakage from the conduit. In the case of monitoring nitrogen leakage, this sudden flow rate fluctuation may be set as a monitoring target.

  In a steady state, the amount of nitrogen entering and leaving the nitrogen channel is balanced, and the flow rate of nitrogen is almost constant. However, if a sudden nitrogen leak occurs in the nitrogen flow path, the flow rate changes. That is, the flow rate of the flow meter downstream of the location where the leakage has occurred decreases, and the flow of the flow meter upstream increases. Other flow meters in the flow path also exhibit the same increase / decrease phenomenon, but the section with the largest increase / decrease flow difference indicates the section where leakage occurred, so it is possible to identify the section leaked from the magnitude of this flow change. it can.

  The set value for detecting leakage from the conduit is set so that a leak signal is generated when an increase / decrease of ± 10% or more occurs compared to the normal flow rate. In the case of nitrogen leakage, the set value is sufficient because the leaked nitrogen may be at a level at which the oxygen concentration of the ambient air is reduced and oxygen deficiency does not occur. If the increase / decrease width of this flow rate is measured, it is sufficiently possible to measure with an orifice flow meter used in normal flow rate measurement.

  The nitrogen flow path is provided with a nitrogen shut-off valve for each predetermined section. Nitrogen shut-off valves are less urgent to operate safely than hydrogen emergency shut-off valves, so the number of installations may be limited. However, when a conduit is passed through a closed space such as a tunnel, the probability of oxygen deficiency occurring in the tunnel is higher than that on flat ground, so it is desirable to install a shut-off valve at the entrance. The means for detecting leakage of hydrogen and nitrogen has been described above.

  Next, the structure and arrangement of various related equipment will be described. First, the structure and connection of the double pipe will be described. In the double pipe, the inner pipe is made of steel, the outer pipe is made of resin, and the length of one pipe is about 5 to 10 m. These will be sequentially connected locally to form a conduit.

  The reason why the material of the outer pipe of the double pipe is made of resin is that the outer pipe may have a lower pressure resistance than the inner pipe, that it protects the inner pipe when subjected to external impacts, In addition to the advantages such as easy welding and no need for painting, above all, vinyl chloride and polyethylene resin pipes are already on the market, and these are combined with steel inner pipes to make steel pipes. This is because a double pipe can be manufactured at a lower cost.

An appropriate space area is provided between the inner pipe and the outer pipe of the double pipe through a resin spacer. For example, assuming a combination of a double pipe of a steel pipe of the inner pipe 6B and a resin pipe of the outer pipe 8B with a pipe diameter, the cross-sectional area of the inner pipe is 190 cm ₂ , and the spatial cross-sectional area of the outer pipe portion is 140 cm ₂ , The outer tube portion can be provided with a cross-sectional area for flowing nitrogen and a sufficient space portion for accommodating the hydrogen detector and the transmission cable.

  To connect the pipes, use a welding method or flange. First, the inner pipes are connected. Since the inner pipe is a gas containing hydrogen, it is made of steel with sufficient pressure resistance, and the inner pipes are connected using a welding method.

  The outer tube is then connected. In order to connect the outer pipes, a slidable outer pipe is attached to the outer pipe end of the pipe in advance to connect the outer pipes. After the inner tube is welded, the outer tube is slid to align the connecting portion with the other's outer tube, and then the outer tubes are connected using welding or a flange. Finally, the outer tube is welded to the outer tube body. This connection procedure is shown in FIG. The vertical arrows in the figure indicate the order of connection.

  Second, the arrangement of the hydrogen emergency shutoff valve is described. An emergency shutoff valve for hydrogen is attached to the inner pipe through which a mixed gas of hydrogen and nitrogen flows, at intervals determined by the degree of danger, for example, at intervals of 1 km. In order to connect the emergency shut-off valve and the pipe, a short pipe with a flange is attached in advance to the emergency shut-off valve side, and the inner pipe of the double pipe is welded to the inner pipe of the short pipe. On the other hand, when a hydrogen emergency shut-off valve is installed, the nitrogen flow path in the outer tube section is closed at that position, so a flow path that bypasses the hydrogen emergency shut-off valve is necessary to secure the nitrogen flow path. Become.

  Third, the arrangement of the nitrogen flow meter is described. In the present invention, the orifice method is adopted for measuring the flow rate of nitrogen. In order to use the orifice, a straight pipe portion to which the orifice is attached is required, and the length of the straight pipe portion must be about 15 times the inner diameter of the straight pipe where the orifice is installed. The bypass flow path in the previous section is used as a position for attaching the orifice.

  In order to secure a nitrogen flow path, a spare nozzle is attached in advance to the outer tube of the double tube. A bypass pipe is connected to the spare nozzle to form a new nitrogen flow path, and an orifice is attached to the straight pipe portion. Furthermore, the transmission cables of the detector inserted into the outer pipe portion of the conduit are connected to each other in the same manner as the nitrogen flow path using a dedicated connection terminal. The above connection method is shown in FIG.

  The bypass path in the previous section can be used as a position to install a nitrogen shutoff valve in addition to installing a nitrogen flow meter. Nitrogen shut-off valves are installed mainly for pipe leak inspections and to prevent oxygen deficiency when a large amount of nitrogen leaks in tunnels, but they are used less frequently than hydrogen emergency shut-off valves. The number of installations can be small. In the section where it is not necessary to install the nitrogen shut-off valve, the bypass flow path may simply be used as a nitrogen flow path. The arrangement of the nitrogen shut-off valve is shown in FIG.

The structure and arrangement of each device have been described above with respect to the present invention. Finally, the features of the present invention are described as a summary. The first feature is that many of the devices involved in the invention utilize those that are already widely used in the world. For example, resin pipes using polyethylene and vinyl chloride, hydrogen gas detectors utilizing thermal conductivity, orifice flowmeters, etc. are all in practical use and have high reliability.

  The next characteristic is the software ingenuity that activates the functions of the monitoring system. In the present invention, the conditions for detecting an abnormality are defined as “with a plurality of hydrogen detectors”, “with a plurality of nitrogen flow meters”, and “with any one of the flow paths”. This means that a strict guard is applied so that hydrogen leakage is not overlooked on the logic circuit (= software side) of the system.

In the leakage monitoring system of the present invention, each detection element for shutting off hydrogen is connected not by an “AND circuit” but by an “OR circuit” on the logic circuit. If the operation of each detector is connected by a logic circuit with an “OR circuit”, n detectors connected in series are assumed if the probability that each detector overlooks the leak is assumed once in N encounters. The probability of overlooking a leak is (1 / N) ⁿ , and if a leak occurs, the probability that the detector will miss it is very small.

  The last feature of the present invention is the easy maintenance of the monitoring system. For example, in maintenance management of nitrogen leakage, a spare nozzle is used in the middle of the conduit to provide a nitrogen discharge valve for maintenance, and temporarily discharge the nitrogen flow to the atmosphere by 10% or more to check whether the flow detection system operates correctly. can do. In the case of hydrogen detection, it is possible to easily check whether the hydrogen detection system operates correctly by temporarily mixing 1% or more of hydrogen into nitrogen from the hydrogen station side.

  Each of the above features is unique to the present invention. Assuming nationwide pipe laying, the conventional idea of adding an odorant to hydrogen gas to detect hydrogen leakage from the pipe is not a sufficient disaster prevention measure. The present invention provides a simple and reliable leakage monitoring means by combining existing techniques with respect to this problem.

  Compared to other supply systems, the hydrogen supply system using a conduit does not require labor costs or transportation equipment, and the construction of the hydrogen station is simplified and construction costs can be reduced. is there. The biggest challenge is the potential danger of catastrophic disasters when large leaks occur in conduits. In order to avoid this danger, early detection of leaks and prompt shut-off of leaks are essential. In the present invention, leakage detection, particularly the role of nitrogen flowing in the outer pipe portion of a conduit using a double pipe and monitoring of the leakage are regarded as the most important.

  The composition of the gas supplied as a premise of the invention is not hydrogen alone but a mixed gas of hydrogen and nitrogen. Although hydrogen is light and easily diffuses in the atmosphere, it has a large explosive range in the air and is easily ignited by a small ignition source. Mixing nitrogen with hydrogen serves to reduce the explosion range of hydrogen. In the early stages of introduction of fuel cell vehicles, hydrogen starts with a composition that is as safe as possible, and it is important in terms of safety to gradually increase the mixing ratio of hydrogen as people become accustomed to handling hydrogen.

  In the present invention, nitrogen was selected as the carrier gas that carries the leaked hydrogen to the detector. This nitrogen increases the detection rate of hydrogen leakage, and the nitrogen that has finished serving as a carrier gas is recycled to the hydrogen plant. The iron and steel industry, one of the promising candidates for the hydrogen production plant, has a large amount of by-product nitrogen associated with oxygen steelmaking, but other hydrogen production plants that do not have a nitrogen source, such as petroleum and gas-based hydrogen. In the factory, this nitrogen can be effectively used as a nitrogen source when adjusting the mixed gas of hydrogen and nitrogen.

  On the other hand, when the present invention is used in the industrial world, the remaining major problem is how to deal with existing laws and regulations. For example, the current road law prohibits the passage of vehicles with dangerous goods in long tunnels and underground tunnels. If hydrogen is regarded as a dangerous substance equivalent to this dangerous substance, it is legally difficult to install a hydrogen conduit in the tunnel.

However, when it is assumed that a conduit is laid in the tunnel, the amount of hydrogen gas present in the conduit is extremely small. For example, assuming a case where a pipe with an inner diameter of 6B is used and transported at a pressure of 1 MPa as a mixed gas with a hydrogen content of 50%, the amount of hydrogen held in the pipe in the tunnel is about 19 Nm ₃ per 1 km of the length of the pipe. Compared with the amount of hydrogen possessed by a fuel cell vehicle equipped with a high-pressure cylinder, it is only an amount corresponding to one fuel cell vehicle.

  Currently, regulations are gradually being eased for traffic of fuel cell vehicles inside tunnels. As detailed above, if it is possible to establish a system that doubles the pipe against an emergency hydrogen leak from the pipe and monitors the leak from the inner pipe and the outer pipe of the pipe by independent means, the law pertaining to the pipe transportation We believe that the environment for relaxing regulations is being prepared.

  If the above-mentioned problems related to transportation can be solved by hydrogen transportation using a conduit according to the present invention, it will be used in the industry as a new transportation means to replace the method of filling a high-pressure cylinder with hydrogen and transporting it to a hydrogen station by a dedicated vehicle. The potential is great.

  It is the schematic which shows the structure of the whole installation.   It is a figure which shows the instrumentation of the nitrogen which flows through the outer tube | pipe part of a double tube.   It is a figure which shows the connection of a double cage.   It is a figure which shows arrangement | positioning of the measurement orifice of a nitrogen flow rate.   It is a figure which shows arrangement | positioning of the shutoff valve of nitrogen.

1 Hydrogen Plant 2 Hydrogen Station 3 Monitoring Center 4 Double Pipe Inner Pipe 5 Double Pipe Outer Pipe 6 Double Pipe Outer Pipe 7 Hydrogen Leakage Detector 8 Nitrogen Leakage Detector 9 Transmission Cable 10 Hydrogen / Nitrogen Emergency gas shutoff valve (= hydrogen emergency shutoff valve)
11 Nitrogen shut-off valve 12 Double pipe spare nozzle 13 Nitrogen flow metering orifice

Claims (5)

  This is a hydrogen leak monitoring means used in the hydrogen supply infrastructure that transports hydrogen from the hydrogen plant to the hydrogen station using a double pipe. In the transport path for flowing nitrogen mixed gas and flowing nitrogen from the hydrogen station to the hydrogen plant in the space between the inner tube and the outer tube, a plurality of transmission cables with transmission cables installed in the space between the inner tube and the outer tube Detecting hydrogen leakage with a hydrogen gas detector and detecting nitrogen leakage using multiple nitrogen flow meters installed in the same system flow path, either the inner pipe or the inner pipe or outer pipe space On the other hand, when a leak is detected, the location or section where the leak is detected is transmitted to the monitoring center through the transmission cable, and the flow of the hydrogen / nitrogen mixed gas is blocked by a command from the monitoring center. Specially Hydrogen leakage monitoring system to.   2. The hydrogen leakage monitoring system according to claim 1, wherein the hydrogen leakage detector includes a hydrogen gas detector using the thermal conductivity or electrical conductivity of hydrogen.   The nitrogen leak detector installs multiple nitrogen flow meters for each defined section of the space between the inner and outer pipes of the double pipe, and nitrogen leaks from the magnitude of the flow fluctuation difference between adjacent flow meters. The hydrogen leakage monitoring system according to claim 1, further comprising a nitrogen gas leakage detection device that identifies the section. The pipe using the double pipe has an inner pipe made of steel, and the inner pipes can be connected by welding, and has an emergency shut-off valve of a mixed gas of hydrogen and nitrogen in each fixed section. Is made of resin, and has a structure in which a slide type outer tube having a flange or a welding surface is attached to the end, and the outer tubes can be connected to each other using the outer tube. Item 2. The hydrogen leakage monitoring system according to Item 1. A spare nozzle is attached in the vicinity of the end of the outer pipe of the pipe constituting the double pipe, and a nitrogen passage for bypassing the emergency shutoff valve of the mixed gas of hydrogen and nitrogen is provided using the spare nozzle. 2. The hydrogen leakage monitoring system according to claim 1, wherein the straight pipe part is provided with a nitrogen flow meter or a nitrogen shut-off valve.

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