Gas density measurement

[rotw]

Hello,

Is there a way to measure/infer gas density (say in kg/m3 unit) using an orifice type of instrument / flowmeter (that is, based on Delta P measurement) ?

Example: If I have a gas line that is equipped with pressure, temperature instruments and a flow element device (orifice), is there a way to obtain gas density from these only three physical devices and information ?

Thanks

 

[georgeverghese]

Not possible I think. You still need gas composition to derive z from a simulator / with manual calcs. Else use an inline gas densitometer, especially if gas composition is expected to vary. If gas composition is fixed, there are many equations that can be used (Redlich Kwong, Virial, BWRS, SRK etc). Gas densitometers are notorious for producing erroneous results, which is why many operators prefer to use a online Welker gas sampler, then send on to a lab based GC to get the composition.

 

[rotw]

Thanks for the info.

What about ultrasonic flow meter ?

 

[georgeverghese]

Ultrasonic and coriolis meters can output gas density also.

 

[rotw]

I have an additional question..

Is it possible to measure gas volumetric flowrate (Am3/h) using a flow element (orifice plate) instrument when the gas molecular weight / composition is unknow? Let us consider there are pressure and temperature transmitters installed on the gas line under consideration (with purpose of doing flow compensation).

 

[georgeverghese]

Flow derivation with dp measurement across an FE requires a density input, so gas mol wt and z must be known or assumed.