5 replies to this topic

[CHEMSTRONG]

Dear All,

 

I have Natural gas compression simulation project. There is a blowdown valve on inlet separator vapor line which directs depressurization to HP flare header when emergency ... I am using API 520 method for getting the flow through the orifice.. Equation i am using is

 

If the
pressure ratio is greater than the critical, the flow is NOT choked:But my case is choked flow case, as pressure downstream is lower as flare header around 7 barg and upstream is at 13 barg...

 

here, I have a doubt, like flowrate through the BDV i m getting is around 50,000 kg/hr wherein process line which goes to next equipment flow is 10,000,00 kg./hr , upstream pressure is 13 barg, MW is 22.057, sp gravity is 0.013, K= 1.270( ratio of specific heat, PSV inlet line siz is 6 inch, outlet is 10"

 

Is this flowatte ok?

 

Request help here..

 

 

I am using API 520 equation for choked flow for modelling restriction orifiece and PSV also .. only thing is that BDV RO Op is 100% always and PSV opening changes from 0 to 100% based on inelt presure,,

 

Regards,

Chetan Chavan
 

 

 

[fallah]

Chetan Chavan,

 

Appears there is a confusion between BDV and PSV in the system you described. Please upload a simple sketch of the system...

 

Indeed, you should consider build up back pressure in chocked flow evaluation.

[ahmadikh]

 Chetan,

 

As Fallah said, downstream pressure of both PSV and BDV would be higher than 7 Barg due to the built-up back pressure. Also, assuming k=1.27 it does not seem that you may have choked condition across the valve considering the back pressure.

By the way, are you sure about the specific gravity of the gas? 0.013 is too low, maybe that's why you are getting such a low flowrate compared to the operating flowrate. Please clarify the density of the gas.

 

Best,

Milad

[Bobby Strain]

equipment flow is 10,000,00 kg./hr???

 

Bobby

[CHEMSTRONG]

Dear Sir,

 

thanks for prompt reply here..

 

Firstly, i want to tell u that i did a mistake in typing specific gravity here..I have cheked my inputs.. I have taken it as 10.931 as density of gas is 13.391 and density of air assumed is 1.225 kg/m3.

 

Secondly,

 

I have attached a sketch of the system in which please refer to stream inlet separator : inlet separator and also i have attched P & ID for this section....BDV0002 and PSV 0006A .. I am calculating flow through both these valves by API 520 method.. Only diff is for BDV , valve opening is always 100 % and for PSV, it depends upon set pressure and inlet pressure here..

Flow going to compressor suction header is around 10,00,000 kg/hr as it goes to four compressor trains with two stages so flow is very high.. It comes from 54 wells..

 

Request your help please...Composition of the gas is mainly methane aroound 76 %..

 

Request to revert as soon as possible.

 

Regards,

Chetan Chavan

 

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 inlet separator1.jpg   170.79KB   1 downloads

[latexman]

10,000,00 and 10,00,000 kg/hr?  Maybe you should spell it out?  Like ten thousand or 10 million kg/hr.