4 replies to this topic

[Skyline]

Dear all,

I have an off gas line to flare from a vessel. I want to know how much the gas being flared. But instead of finding FI (flow meter), i only find PI (pressure indicator). Do you have any idea to convert/calculate the flow from the pressure? Literature will be fine.

Thank you before


Skyline

[ankur2061]

Skyline,

You need to have a differential pressure to calculate flow. It means, that you need to know the pressure at the start point of the off gas line to the flare and the pressure at the other end in the off gas line near to the flare. Additionally the following data will be required to calculate the flow:

1. Off gas Pipeline Size or Inside Diameter
2. Off gas composition and / or properties
3. Off gas temperature from the vessel

Regards,
Ankur.

[sheiko]

Skyline,

You can also estimate the missing flowrate by mass balance, if the vessel is level controlled (that is there is no change in level and as a result, no mass accumulation in the vessel).

Another way is to calculate the flow through a control valve on the off-gas line, if any. But in this case, the displayed % opening (on DCS) is reliable only if the valve has a positioner.

Edited by sheiko, 06 May 2012 - 12:32 PM.

[kkala]

You could estimate flow rate from vessel to flare header, in case that off gas flow is choked. Start from a simple sketch, indicating position of Pi as well as any valve (control valve, PSV) on the off gas line. Note pressure at vessel and header, gas MW and temperature, off gas line diameter (and approx length).
Someone could probably help, if above info were available.

[breizh]

If the flow is choked you may use this resource .

http://en.wikipedia....iki/Choked_flow

Breizh