RhoV2 2

[Mondolfi]

Hi,

Can anyone explain me what is the use or the importance of the term RhoV2 in the desing of a flare header collector?

Thanks in advance,

 

[MortenA]

it means (as far as i remember) the average velocity (of liqud and gas) squared and multiplied with the average density.

 

[TD2K]

I know one company that uses this as a criterion for their flare headers. Their limit was 100,000 kg/ms2 (if I remember right) as a simple limit. With additional engineering, they would allow up to 150,000 kg/ms2 but no more than that. It was explained to me that it was used as an vibration criteria and potential energy threshold but I couldn't get any more specifics than that and nothing on the background how they determined it (other than 'we have studied it').

 

[hacksaw]

generally, the term is an aerodynamic pressure and is related to liquid carry over. if it is too high then you won't be allowing liquids to dropout of the gas phase.

beyond that you need to get a specialist's response

 

[TD2K]

If I remember correctly, when I played around with the units, I got essentially the API 14E equation but with a much higher C value.

I'll have to see if I can recreate it where I am and post the details. I remember the company was NOT impressed by this.

 

[EGT01]

&[ignore]rho[/ignore];V ² is one of those terms I've seen often but probably never took the time to fully understand. I think everyone's post so far constitutes a part of the significance of the term so I'll try to add a little more.

&[ignore]rho[/ignore];V ² is the velocity term from the Bernoulli equation. This parameter is often used as guiding criteria for design in fluid flow. The higher the number then you can expect higher pressure loss, something else you would want to avoid in a flare header. The TEMA standards use this parameter as a guide to select nozzle sizes for heat exchangers and when to use impingement protection. I've also seen the parameter used in conjunction for flow through a pipeline to avoid erosion concerns and in tower design for nozzle selection for vapor inlet lines.

 

[TD2K]

Showing the API 14E erosional velocity equation and rhov2 limit are the same is easy.

Let's take rhov2 = K (K being the value for a flare system)

Rearranging it, we get v2 = K/rho

or

v = K^0.5/rho^0.5

API 14E for the erosional velocity is

v = C/rho^0.5

Therefore, the rhov2 constraint is simply the same as the API 14E erosional velocity limit but with a different value of C than the 100 or so commonly used.

 

[NMcC]

rhov2 is a measure of the fluids momentum and is used in calculating stressess and loadings on vessel nozzles. I think it is being used in this context in your case as you mention a 'flare header collector'.
Talk to piping designers or the designers of your 'collector' for the maximum acceptable nozzle loadings (both inlet and outlet). The company for whom you are designing the system may also have design guidelines/requirements in this area. Check in design documentation (both from client and vendor) to see what has been used as maximum or acceptable loading.