Looking for a safe way of measuring the Hydrogen flow through a vent line. This application is for a power plant turbine/generator.

 

Most of the hydrogen-cooled generators I have worked on have had "flow-rators" or some other such means for setting the scavenging flow-rates. While these may not be the most accurate indicators, compared with total usage (if being fed through bottles or six-packs, etc.) they should be a good comparison to see if there are other areas the hydrogen might be escaping.

Presuming there is no leakage through the shaft seals or through some other area of the generator and casing (such as around high-voltage bushings or heat exchanger flanges, etc.), all of the hydrogen "consumption" should be through the scavenging lines.

So, if you could determine the flow-rate through the scavenging lines using the flow-rators or whatever was provided, and compare that against the amount used over time to maintain a relatively constant pressure, you should be able to tell if there are leaks (which is what I presume you are trying to determine--if all of the hydrogen consumption is through scavenging or if there are leaks elsewhere contributing to high hydrogen consumption).

Because the discharge of the scavenging lines is pretty low pressure, I would think it would be very difficult to measure flow without increasing the back-pressure on the scavenging lines.

There are other methods for checking for leaks. I seem to recall some people use a "halide" detector (if I recall correctly), or there are other types of hydrogen leak detectors. Of, course to do this would require a shutdown and some removal of covers and access to high-voltage bushings, etc.).

One of the most common leaks I know of is between the generator "hook-up" and the hydrogen supply piping. I've also seen the casing purge valve leak, and sometimes the H2 regulator leaks (which in some cases can be quite dangerous!). I've also seen leaks at the valve that blocks the CO2 from entering the casing under normal conditions.

But I would think it would be difficult to measure what should be relatively small flows at relatively low pressure (mm Hg) without creating a back-pressure on the scavenging system and reducing the scavenging flow-rate at least somewhat.

Hope this helps!