What is an appropriate flow rate for the hydrogen gas?

Based on the information provided, if you wish to change the flow meter to a DN50 diameter, you need to consider the flow rate of hydrogen and safety issues. First, it is necessary to calculate the flow velocity of hydrogen in a DN50 pipe. Assume that for a DN80 diameter flow meter at a flow rate of 400 Nm3/h, the hydrogen gas velocity is V1 m/s. According to the gas flow rate calculation formula: Q = V * A, where Q is the flow rate, V is the velocity, and A is the cross-sectional area of the pipe. It can be obtained that V1 = Q / A1, where A1 is the cross-sectional area of the DN80 pipe. Then, calculate the upper flow velocity V2 in m/s based on the DN50 pipe diameter. Using the same formula, with Q set to 260 Nm3/h and A set to the cross-sectional area of a DN50 pipe, it is possible to calculate V2 = Q / A2, where A2 represents the cross-sectional area of the DN50 pipe. If V1 < V2, it indicates that a pipe with a DN50 diameter can meet the flow rate requirements; therefore, a DN50 flow meter can be used instead. It should be noted, however, that excessively high flow rates can lead to problems such as pressure loss, vibration, and noise. Therefore, it is recommended to communicate thoroughly with the manufacturer before making any modifications, to ensure that the DN50 flow meter functions properly and poses no safety risks. As for the issue of static electricity generation in hydrogen containing water, the water present in 99% hydrogen with water content may increase the risk of static electricity formation. If static electricity cannot be effectively discharged, it may pose a danger to equipment and personal safety. Before selecting a flow meter, it is advisable to consult professional engineers or suppliers to find out whether their products are suitable for use in hydrogen gas containing water, as well as to ensure that they have appropriate anti-static measures. .

The gas flow rate should not be too high, as considerations for pressure loss and safety are primary. When it is safe and under control, a lower overall flow rate in the pipeline results in less resistance. The local flow velocity at components such as valves and flow meters can be higher than that in the pipes; for example, the flow velocity at the small orifice of a pressure regulator can reach hundreds of meters per second. At the flow meter, a smaller size can be used to increase the local flow velocity in order to meet the measurement requirements

According to the standards, the flow rate of hydrogen gas in carbon steel pipes at 1–3 bar is generally kept below 15 m/s. The main reason for this is that over time, rust deposits form inside the carbon steel pipes and fall out; these deposits collide with the gas flowing through the pipes, generating static electricity or sparks. However, due to the explosion limit (4–71% for hydrogen), pipes containing 99% hydrogen are less likely to explode (the presence of water further hinders the formation of static electricity). Nevertheless, it is important to monitor the oxygen content in such pipes.

Flowmeters and valves are elements of local resistance, and the data on pipe resistance does not apply to them. When gas flows through these local resistance elements, the gas velocity can be very high

I did some calculations, and it seems that using Yokogawa’s reduced-bore vortex flowmeter would be an excellent solution to the original poster’s problem. There is no need to modify the pipelines, nor the flanges at the flowmeter’s installation location; it’s sufficient to specify that a reduced-bore model is required when placing the order. Yokogawa Electric’s this product is standard. I had this model specification when I was working at Yokogawa Electric, and the calculation sheets were also generated using Yokogawa Electric’s previous software. It is possible to reduce the inner diameter to either 50 mm or 40 mm.

I asked Yokogawa, and they said that with 0.1 Mpa of hydrogen gas, Yokogawa’s vortex flow meter cannot detect it

The person you’re asking probably doesn’t have a good understanding of technology; you should ask someone who truly knows technology, not a salesperson. Also, if you are simply looking to purchase one vortex flow meter and your company is trying to push for a lower price, then I won’t do business of this kind.

For example, in a DN100 pipeline, if a DN100 control valve is installed, it cannot be opened fully; even at a low opening degree, the flow velocity remains high