Measuring the flow of hydrogen Measuring with ultrasonic waves

We are conducting research on hydrogen gas meters in preparation for the coming hydrogen society.


Hydrogen is attracting attention as a clean energy resource that does not emit carbon dioxide in order to realize a decarbonized society (carbon neutral), which is the goal of the SDGs. In recent years, its use has been steadily expanding, including in cars equipped with hydrogen engines that directly burn hydrogen, and as a power source for the Olympic Village and as fuel for the cauldron at the Tokyo Olympics.

Hydrogen fueled vehicles (FCVs) and hydrogen stations are gradually increasing in cities, and pure hydrogen fuel cells for home use that use hydrogen supplied through pipelines are now in practical use. Come. For the hydrogen supplied at this time, it is necessary to accurately determine the amount used for fair price transactions, and a hydrogen gas meter plays this role.

Noise removal

Hydrogen gas meters have a characteristic that the intensity of the ultrasonic waves is weak and the signal is difficult to transmit, so the measurement performance is affected by noise at a level that would not be a problem with a normal gas meter. We addressed this issue by raising the transmission voltage higher than that of a normal gas meter and increasing the amplification factor. However, simply increasing the amplification factor will also amplify the noise component and will not improve the S/N ratio. Therefore, we used the following techniques to remove these noise components and improve the S/N ratio.

Noise removal

■ Removal of housing noise (patent registered)

In flow measurement using ultrasonic waves, in addition to the ultrasonic signals that propagate through the fluid to be measured, there are also ultrasonic waves that propagate through the casing, and the ultrasonic sensor also receives such disturbing ultrasonic waves (this is called chassis noise.)
In fuel gas and air, the casing noise is sufficiently small compared to the magnitude of the ultrasonic signal, and the propagation speed of the casing noise is much faster, so the ultrasonic signal and the casing noise can be separated on the time axis. Since it is easy to separate, it does not pose a major problem for measurement.
However, with hydrogen, the ultrasonic signal is small, so the housing noise is relatively large, and the high speed of sound makes it difficult to separate the ultrasonic signal from the housing noise on the time axis. It will have an impact.
Therefore, as shown in the figure, we made the housing shape more complex and lengthened the propagation path to promote the attenuation of housing noise, making it possible to perform measurements that minimize the effects of housing noise.

■ Removal of housing noise (patent registered)

■ Removal of noise during transmission

Since the ultrasonic signal in a hydrogen gas meter is small, it is affected by electrical noise, which is not a problem when measuring with fuel gas. In particular, it was found that the physical distance between the ultrasonic signal transmitting circuit and the receiving circuit affects the magnitude of electrical noise (noise during transmission). For this reason, we revised the circuit pattern and separated the transmitting and receiving circuits to reduce noise during transmission.

■ Removal of noise during transmission

High resolution measurement

To measure flow rate using ultrasonic waves, it is necessary to accurately measure the difference in time (arrival time) from when ultrasonic waves are transmitted from upstream to downstream and from downstream to upstream until the signal is received. A normal gas meter measures the difference in arrival time multiple times and uses the processed values to determine a more accurate arrival time. However, the sound speed of hydrogen is about four times faster than fuel gas or air, so if you measure the arrival time with the same number of measurements as with a regular gas meter, the measurement values will vary widely and the measurement accuracy will deteriorate. In order to ensure sufficient accuracy, we aggregated dozens of times more data than a regular gas meter and averaged it to ensure accuracy.

powered by batteries

A normal gas meter can be operated for 10 years using only the built-in battery. Similarly, we aimed to run the hydrogen gas meter for 10 years using only batteries. However, measures to measure hydrogen such as increasing the transmission voltage to increase the strength of the ultrasonic signal and increasing the number of measurements to ensure measurement accuracy use more electricity than usual. Masu. By further refining our technology to reduce current consumption, we have created a hydrogen gas meter that runs solely on internal batteries and does not require an external power source.

■ Transmission of ultrasonic signals with reduced current consumption (patent registered)

When transmitting ultrasonic waves, a voltage higher than the battery voltage of 3V is generated in a booster circuit and applied to the ultrasonic sensor. However, increasing the voltage increases power consumption. For this reason, we have improved the method of applying voltage to the ultrasonic sensor and reduced current consumption by increasing the efficiency of boosting the voltage so that sufficient pulses can be generated with half the boost of the conventional voltage.

■ Transmission of ultrasonic signals with reduced current consumption (patent registered)

■ Minimize circuit operating time (patent registered)

In order to reduce power consumption, ultrasonic gas meters turn on the power to the circuit only when operation is necessary, and turn it off when operation is not necessary to save power. In hydrogen gas meters, this power saving operation is managed more precisely than before to further reduce current consumption.

■ Minimize circuit operating time (patent registered)

Researcher's voice

■ What other issues and discoveries did you come up with during your research on hydrogen gas meters?

When we first started this project, there was an overwhelming lack of information about measuring hydrogen using ultrasound, and even when we conducted tests, we were met with a series of unexpected results. For example, we were predicting that we could measure air without any problems, but that we would get 1/4 of the signal strength for hydrogen, but the moment we measured hydrogen, the ultrasonic signal disappeared. . It turned out that the cause of this was a slight gap in a certain part of the flow path, but this gap was at a level that was not a problem at all according to textbooks and literature on acoustics. In this way, even if we apply theoretical values obtained from textbooks and literature, we have had many difficulties in finding that things do not actually work out as expected. Conversely, with a normal gas meter, the ultrasonic signal becomes smaller as the flow rate increases (flow rate dependence of the ultrasonic signal), but it was also found that when measuring with hydrogen, the signal strength hardly depends on the flow rate. In fact, there were some parts that were easier to design.

■ What kind of response or solution did you take from there?

It was discovered that the gap was the cause of the ultrasound not transmitting properly, as the signal strength recovered when the gap was filled in for another test. With such a lack of information, I was acutely aware that all kinds of data and their analysis results, while interrelated, can provide hints for solving various problems.

■ Please tell us about further improvements and future improvements.

We are currently installing a hydrogen gas meter and collecting data from actual operation in a demonstration test of a pure hydrogen fuel cell that is operated by supplying hydrogen through a pipeline. We also have plans to install other hydrogen gas meters, and by combining the data obtained from these with the gas meter technology that we have cultivated to date, we will continue to develop new "hydrogen gas meters" for the coming hydrogen society. I would like to make a proposal.

Our company's ultrasonic hydrogen technology is being used by Brother Industries, Ltd. in the "Pole-top pipeline transportation demonstration project to promote the use of hydrogen energy (adopted by the Ministry of Economy, Trade and Industry)" being carried out in Namie Town, Fukushima Prefecture. A gas meter was installed and a demonstration experiment was conducted from October 2021 to February 2022.
We collect measurement data under a hydrogen supply environment similar to actual operation, and use it to confirm the results of demonstration experiments and identify issues, as well as contributing to consideration of security functions and billing system construction toward the realization of a hydrogen society. .

|Related links|
>Brother Industries, Ltd.|Public, private, and academic teams are taking on the challenge of creating Japan's first hydrogen column Pipeline demonstration project
>Brother Industries, Ltd.|Pillars to promote the use of hydrogen energy Pipeline transportation demonstration experiment

With the cooperation of Iwatani Sangyo Co., Ltd. and Kitakyushu City, we have installed an "ultrasonic hydrogen meter" in Kitakyushu Hydrogen Town and are conducting demonstration experiments.
The "Ultrasonic Hydrogen Meter" has been renewed by taking advantage of the knowledge gained from the previous model, which achieved stable hydrogen flow measurement. With safety in mind for practical use, we packaged it with a mechanism to shut off hydrogen in case of a disaster or trouble, and a sensor to detect earthquakes.
We are continuing to take on the challenge of finding a form of hydrogen meter that can contribute to society beyond measuring the flow of hydrogen.

Since June 2016, with the cooperation of Iwatani Sangyo Co., Ltd., a participant in the demonstration project, the "Regional Collaboration Low Carbon Hydrogen Technology Demonstration Project" (a project commissioned by the Ministry of the Environment) is being carried out in Shunan City, Yamaguchi Prefecture. We have installed our hydrogen gas meters and are collecting data in actual operation.
In Shunan City, we are conducting a demonstration experiment by installing a hydrogen meter in an outdoor piping/outdoor installation environment for the first time for our company.
We have collected measurement data for about five years, and like conventional gas meters, we have been able to perform stable measurements even in harsh environments exposed to direct sunlight, and have achieved good results.
The "Ultrasonic Hydrogen Meter" is extremely compact* and allows for stable measurements.
*In comparison with membrane gas meters.

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