COLD SERVICE FLOWMETER TECHNOLOGY 2

[compo]

Appreciate any feedback on flow meter selection types, configuration and suppliers who have the capabilty to accurately measure hydrocarbon gas predomin. methane MW (18-20) over a wide temperature range and specifically at the cold end- gas temperatures range from -80 to upper end 100degC. The application is mandatory measurement of flared gases from our flare knock out drum. Flow range 50mmscfd to purge.

 

[JLSeagull]

I assume that the flare line is SSt with lots of straight run, correct? Some flow elements exist that require no straight run. However, most flow elements are workable if you have 40 piping diameters available.
What flow rate range or ranges? Do you need to measure stable conditions to indicate the normal venting - and cover major blowdown releases? Perhaps the requirements only apply to the large releases.
What approximate pipe size? Different flow measurement technologies are optimum for small lines than large lines. I would assume the flare line to be large.
How accurately? Are regulations applicable? Is an accuracy of 2% full scale sufficient? Is an accuracy of 0.5% of the flow rate required?
What ambient? Installations suitable on the Red Sea may not apply at Prudoe Bay.

 

[compo]

JL thanks for your feedback - answers to your questions embedded- I am thinking a strap on ultrasonic or two may work for us. Another constraint is allowable pressure drop for the meter and I will avoid orifices
thanks
compo

a:I assume that the flare line is SSt with lots of straight run, correct?

a1: Yes SS - S run may an issue however as in design can look at more critically

b:Some flow elements exist that require no straight run. b1; would apprecicate feedback on this

c: However, most flow elements are workable if you have 40 piping diameters available.

c1;may struggle to achieve this would be 14m

d: What flow rate range or ranges?
d1: low end purge 0.2 mmscfd to 50 mmscfd emergency b/d
- may have to be practical and review low end

e: Do you need to measure stable conditions to indicate the normal venting - and cover major blowdown releases?
e1; see prev
Perhaps the requirements only apply to the large releases. No

f:What approximate pipe size?
f1: 14" (350mm)
Different flow measurement technologies are optimum for small lines than large lines. I would assume the flare line to be large. 14"

g: How accurately?
g1: 2% would be sufficient - 5 max

h:Are regulations applicable?
h1:Yes in that all hydrocarbon releases from the facility
to be recorded (we have ack-up nitrogen for purge which id not prefered

i: Is an accuracy of 2% full scale sufficient? yes
Is an accuracy of 0.5% of the flow rate required? No

j: What ambient? Ambient min 15 C max ave 35C

Installations suitable on the Red Sea may not apply at Prudoe Bay.

 

[JLSeagull]

Discuss the sensors for the trans-time ultrasonic meters. A clamp-on may be suitable. I do not know the low temperature limit. Also consider thermal mass flow such as FCI. I am not sure about the accuracy.

A few flow elements exist that require no straight run, or little straight run. Where this is an issue I would consider a cone type element. The McCrometer V-Cone is the standard but clones exist.

http://www.mccrometer.com

Fluidic Techniques sell a combination ventiri/flow conditioner is called the HHR FlowPak. Also, an annubar can be installed two diameters downstream of a short-radius

The ambient of 15 C to 35 C is well suited to the cold service installation practices that I mentioned in another thread in this forum. You can use standard differential pressure transmitters on the V-Cone, Annubar or other head type meter if you install with about five-foot of impulse line between the flow element taps and the transmitter.

Assure that your needs are covered in the specification; and that the selected manufacturer recommends their proposal for the -100 C design condition. The temperature and turn-down are the issues. If using a head type meter, consider multiple transmitters with different ranges.

 

[Ashereng]

Yes, the E&H Prosonic Clamp On W/U may work. You can google it to find the site or use:

http://www.us.endress.com/

It gives accuracy of +/- 0.1% full scale

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