8 replies to this topic

[petroabbes]

I want to have a calculation basis for the estimation of the PSV relieving temperature for the case of a two phase scenario” 2 Phase Sat Non condensable or Highly Subcooled” is it the same a methodology same as used in gas thermal expansion with a correction factor?

[fallah]

Hi,

 

Please submit your query clearly...if it's a fire gas expansion why you refer to two phase or...?

[petroabbes]

it is a Blocked Liquid Outlets scenario: If the Tower liquid outlets are blocked the tower could overfill with liquid leading to a blocked flow case due to the liquids not being able to flow through tower bottom.( there is a reboiler).. This would lead to a 2-phase relief , the case specified is : Case Omega A: Blocked Liquid Outlets..I am stucked at the level of relief load flowrate calculation also the relief Temperature estimation.

 

Hope it is clear

[MTumack]

I am not sure what you are referring two with respect to the 2-phase system.

 

As for the relieving temperature of the fire gas expansion condition, at a minimum this should be the temperature required to move your gas inside the vessel, assuming completely full and shut off from upstream and downstream block valves, operating pressure temperature, to overpressure (as per ASME; Set pressure x 1.15). Think real gas law; P1v1/z1T1 = P2V2/z2T2. Obviously V1=V2. You will likely have to iterate this calculation, originally assuming Z1=Z2, get preliminary Z1 & Z2 based on gas properties, pressures, and temperatures, then calculate again to get a more accurate figure.

 

It is my experience in many applications that this temperature quickly becomes ludicrous and makes this scenario negligible. Unless you are using an exotic material, often times you`re temperature brings your pressure retaining material into creep range before over-pressure, and theoretically you`d have mechanical failure due to temperature before your PSV would go off.

[petroabbes]

Dear MTumack

This is true for a gas expansion, and not for a Scenario: Omega A / Two Phase (as per API) with Two Phase Sat Noncond or Highly Subcooled relief fluid

[fallah]

petroabbes,

 

Can you upload a simple sketch of the system you described?

[petroabbes]

Dear fallah

This is a common configuration: we have a column with a reboiler, there is a PSV in the top of the Tower set @ 30 barg.

 one of the scenarios of the PSV sazing is Two Phase  Sat Noncond or Highly Subcooled relief fluid in case of blocked outlet in the reboiler, then what happen the tower will be flooded, this is the scenario case, the relief pressue is set P*10%, what I want to calculate is the relief T.

[flarenuf]

Dear Petroabbes

 

Please find attached a PDF containing 4 papers which if you read will explain a  lot for you

 

Attached Files

•  Tower PSV calcs.pdf   1007.84KB   31 downloads

[petroabbes]

flarenuf many thanks

for the calculation of the LHV in case of fire, the procedure is based on 5% flash calculation ( we assume the column as a vessel and we complete the successive flashing of 5% of mass?)