Flare System Metering

[maddocks]

Has anyone used flare system meters that really work? I've tried a couple of different kinds, but they just don't seem to be reliable. Ultrasonic, optical, - I need something with a massive turndown, amazing accuracy and it has to work in dirty sour service, big ambient swings, and usually about 20' off the ground.

 

[cloa]

http://www.photon-control.com/oil_and_gas/images/pdfs/top-5-challenges-to-flare-metering-080303.pdf

Have you looked at that? Just for information

You sure don't ask much.

 

[moltenmetal]

Oh, and you forgot to mention that it ALSO needs to have a very low pressure drop at enormous flows.

Face it, there's never going to be a good way to do this. It's going to be a series of compromises, whatever you choose.

 

[maddocks]

I know, this is brutal service, but regulatory authorities aren't leaving us a lot of choice. They dictate maximum meter velocity during ESD events which leaves a huge blind zone on the bottom end of the meter - this is actually where the most common emissions will exist.

 

[JLSeagull]

Consider an ultrasonic flare gas flowmeter with turndown exceeding 200:1 and suitablility for various molecular weight, composition etc. You can buy all flanged with pipeline block valves etc. and obtain third party certification. These passed the Texas requirements at that plant site. Long term suitability is outside my experience. Some mfg PO terms and conditions interfaces can be a major issue with procurement.

 

[dcasto]

JLS, and Texas' CEQ was not going to be recertified by the US EPA too. I agree that ultrasonic, even external should be enough.

 

[maddocks]

We've installed 3 ultrasonics in 2 different plants and they're working intermittently. In one plant, the lens/sending head is getting droplets of snot and condensate and then it stops working. The other units are faulting out and of course, phone calls to the vendor are way too frustrating when they say "well, it should be working".

 

[SNORGY]

maddocks

Perhaps tell your operators to stop blowing their noses into the flare header?

Regards,

SNORGY.

 

[zdas04]

I wrote a Paper for the Western Gas Initiative discussing the difficulties involved in metering these intermittent, high-turn-down, and often short duration flows that might help you. While it doesn't specifically address flare headers, many of the flow streams that are being considered for regulation (e.g., control gas, and tank heaters) have exactly the same range and magnitude of problems.

Flare headers also have the possibility that the makeup of the stream can change dramatically from event to event. That seems to make an impossible problem even more difficult.

David

 

[maddocks]

Has anyone used pitot tube measurement devices in a flare line? Has any regulatory authority approved their use?

 

[zdas04]

maddocks,
Pitot tube "flow measurement" is appropriate inside of labs with absolutely controlled parameters. A couple of percent change in density (for example) results in tens of percent change in reported flow. Nothing about using them in flare metering makes sense.

David

 

[hacksaw]

traversing pitot and pitot arrays have been used in such measurements, but they are not for permanent installations in emergency flares and do have not the turn-down you seek

in really rough services, a remote IR camera to monitor the plume or the pressure of the line going to the flare is all that can be used, the flows are estimated from the material and energy balances

 

[JLSeagull]

Like an orifice plate, the pitot tube has a square-root flow so that it is not very accurate at a low flow compared to the maximum range. With a modern transmitter some would advise that it has about 5:1 turndown.