7 replies to this topic

[krishnamurthy]

in hysis while doing doing psv sizing for fire case am getting an error " the temperature in stream is not found at the requested conditons" how to solve this one, i want to do fire case psv sizing for the wetted wall separator. pls explain.

[ChemEng01]

What is the pressure of relief?

 

HYSYS does this sometimes when the fluid turns supercritical. 

 

Why not use API equations for sizing instead. 

[serra]

probably the software is attempting to calculate a VLE condition in order

to estimate some parameters as for example latent heat for fire case,

the error could indicate a problem in convergence or a condition where

VLE doen't exist,

with PRODE PROPERTIES the procedure to simulate a PSV with fire case works above

cricondenbar as it solves a H-P flash,

you can do something equivalent with your software

or use the predefined value suggested in API for minimun latent heat value.

[ChemEng01]

The problem is that is the fluid is supercritical the latent heat is non existent as there is no phase change. 

 

There are equations in API for supercritical fire case scenarios.

[oscarsender]

API 5.15.3.2 states that:

 

The recommended practice of finding a relief vapour flow rate from the heat input to the vessel and from the latent heat of liquid contained in the vessel becomes invalid near the critical point of the fluid, where the latent heat approaches zero and the sensible heat dominates.

 

If no accurate latent heat value is available for these hydrocarbons near critical point, a minimum value of 115 kJ/kg (50 BTU/lb) is sometimes acceptable as an approximation.

 

This can be done to save time but consult your superior if they will accept this approach. Otherwise a more detailed calculation will be required which unfortunately I haven't done yet.  

[sathesh034]

Hi,

 

i had a query related to PSV set pressure. In general we are considering PSV set pressure = 1.1 x pump operating pressure. My boss is saying that it should be "Op.pressure/0.9". Both these values are having difference in decimals.

 

Which one is right and is there reference in API related to this set pressure calculation.

[Bobby Strain]

Well, there isn't much difference. Usual references suggest that operating pressure should be no more than 90% of relief valve set pressure.

 

Bobby

[fallah]

sathesh,

 

The maximum operating pressure should normally be not more than 90% of the PSV set pressure, but contrary to your statement it's not a method of the PSV set pressure and it's to check having no problem in PSV reseating due to higher operating pressure than PSV blowdown....

Edited by fallah, 17 July 2014 - 12:21 PM.