Two Phase Flow in a meter run

[skuntz]

We are measuring Natural Gas Flow using a meter run where where we are expecting 99.84% vapor mass fraction and the remainder is NG liquids (P = 1100 psig). Yes the vapor fraction is very high, but it is still two phase flow. Will the flow calculations for pure vapor still apply? Any other considerations?

 

[zdas04]

Condensation can cause liquid accumulation that would require the gas to do work on the liquid. Violating several of the assumptions underlying the development of the AGA-3 equations. I have seen lines on orifice plates where the water was damned up on the upstream side on systems where the system balance was better than 1%. When I see evidence of liquid accumulation I take steps to eliminate it, but they are not crises steps--a meter can go from "great" to "good enough" to "OK" without having a material effect on your material balance.

In your case I would specify plate inspections more frequently than normal (maybe monthly instead of quarterly) to look for standing liquid. If it is there, then I'd put some sort of liquid knockout upstream of the tube.

David Simpson, PE
MuleShoe Engineering

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