To calculate the Relieving temperature & Latent Heat of Vaporization for Fire case PSV sizing by Shell DEP method.

OBJECTIVE: To calculate the Relieving temperature & Latent Heat of Vaporization for Fire case PSV sizing by Shell DEP method.

(This method is based on mass flow it gives somewhat higher relieving temperature)

PFD: PFD developed in Aspen HYSYS

1.     Methodology: Following are the steps to be followed for developing the model in HYSYS.

a.     Open HYSYS and define the stream component, Select fluid package then go to simulation environment and pick a material stream from HYSYS utility panel.

b.     Define the stream conditions Temperature as Operating temperature and Pressure as Relieving Pressure give some mass flow rate let say 100 kg/hr.

c.      Once stream (14) is conversed now put a heater (E-100) downstream of material stream (14).

d.     Now define the vapor fraction of stream (17) for 5% flashing by mole if the composition basis is mole % and after that go to heater parameter and define pressure drop across heater zero, now E-100 and stream 17 is conversed.

e.     Now put an Adjuster on stream 17 to adjust vapor fraction 5% by mole basis to convert into 5% weight basis.

f.       Now place a Flash drum (V-104) for flashing stream no 17.

g.     Define two outlet streams 15 & 16 for V-104, 15 for vapor outlet and 16 for liquid outlet from the flash drum.

h.     If the stream 16 vapor fraction is zero then automatically stream 16 is at its bubble point, therefore got into the properties of stream 16 and note down the mass enthalpy (-1969KJ/Kg).

i.       Now place a heater E-102 downstream of stream16 to bring the stream at its dew point.

j.       Define a heater E-102 outlet stream 18, now define the pressure drop across heater zero and stream vapor fraction 0.00001.

k.     Now stream heater E-102 and stream 18 is conversed and stream 18 is at Dew point.

l.       Note down the temperature of stream 18, which your relieving temperature (194.8 deg C) at relieving pressure.

m.  Now got to the stream 18 properties note the value of mass enthalpy (-1610 KJ/Kg).

n.     Subtract the liquid mass enthalpy (-1969 KJ/kg) from vapor mass enthalpy (-1610KJ/Kg), you will get the latent heat of vaporization 358.6 KJ/Kg.

Result:

1.     The Relieving Temperature at relieving Pressure is 194.6 deg C.

2.     Latent Heat of Vaporization is 358.6 KJ/Kg.