Measuring the flow of hydrogen Measuring with ultrasonic waves

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.

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.

■ 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.

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.

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