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Gas Flow Measurement

Gas Flow Measurement

Gas Flow Measurement

Is it always necessary to have temperature and pressure compensation when measuring fuel gas flow? I can understand it for custody transfer and for any down hole injection or gas extraction from a well. But if it is for something basic like instrument fuel gas supply I am not sure.

Any thoughts or knowledge on this?

Thank you.

RE: Gas Flow Measurement

What are you using it for? What measurement technology are you using? What algorithms?

If it is reported to a state or federal agency, sooner or later you will be audited and get hit with a fairly arbitrary fine. If you have to pay royalties on lease use, check your contract, some allow you to estimate (and most of those do not specify an estimation method) and you can get by without knowing current temperature (but you do always have to know pressure).

If you are using a differential producer then you can't do measurement without a pressure input. If you are using another technology, you'd be better off just making the numbers up. Really. The density and momentum of 15-30 psig natural gas is just too low for any other technology to provide meaningful numbers.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Gas Flow Measurement

Makeup at an instrument fuel gas system essentially replaces what is lost to the atmosphere through instruments, tubing fittings, relays, control valves etc., so this would fall under the category of greenhouse (methane) gas emissions. Check with the local authorities and/or your company guidelines on the accuracy required for this category and configure to suit.

RE: Gas Flow Measurement

Thanks for the input. This is fuel gas through a bubbler panel to measure down hole pressure. My process engineer stated we need pressure and temperature compensation since we are jamming this gas down hole. I procured a vortex meter with integral pressure and temperature elements that will do the trick. I didn't want to have to purchase an external pressure and temperature transmitter for this application as it is only a temporary set up and that is why I was curious if it was needed. Good thing I found this vortex unit with everything included.

RE: Gas Flow Measurement

Make sure you confirm your Reynolds Number before you rely on the vortex meter (these meters have the smallest acceptable range of Reynolds Numbers of any gas measurement technology). Also make sure that you know what the numbers mean. If you aren't compensating for pressure and temperature then you are getting actual volume flow rate and you can't add or subtract those numbers from anything else.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Gas Flow Measurement

Bubbler gas flows are usually small, so check the operating vs measurable flow range. Agree, you wont need P/T compensation if operating pressure / temperature swings at this vortex meter will only result in flow inaccuracy which is tolerable. If I'm not mistaken, these devices dont work well when gas dewpoint is higher than minimum ambient at the corresponding range of operating pressures, since you will have 2 phase flows and liquid slugs through low points in the piping /tubing, so the gas should be suitably dewpoint conditioned. Else this meter should be immediately downstream of a small liquids knock out drum.

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