PRV w/ Desuperheating Calculator

Calculates the properties of steam after a pressure drop with optional desuperheating.


Inlet

Pressure* psig
* °C btu/lbm kJ/kg/K
Mass Flow * klb/hr
Outlet Pressure * psig

Feedwater

Pressure* psig
* °C btu/lbm kJ/kg/K
Desuperheating Temperature * °C
* Required
Allowed Range / Limits
Minimum
Maximum
Examples: Mouse Over
Random - No Desuperheating Random - With Desuperheating

Calculation Details and Assumptions below


Calculation Details

Step 1: Determine Inlet Steam Properties

Using the Steam Property Calculator, properties are determined using Inlet Pressure and the selected second parameter (Temperature, Specific Enthalpy, Specific Entropy, or Quality):

Step 2 'If NO Desuperheating': Determine Outlet Steam Properties

A PRV is an isenthalpic process, meaning the inlet enthalpy is equal to the outlet enthalpy. The outlet properties are determined using the inlet enthalpy and outlet pressure:

Step 2 'If Desuperheating': Determine Cooling Water Properties

Using the Steam Property Calculator, properties are determined using Inlet Pressure and the selected second parameter (Temperature, Specific Enthalpy, Specific Entropy, or Quality):

Step 3: Determine Desuperheated Outlet Steam Properties

Using the Steam Property Calculator, properties are determined using Outlet Pressure and Desuperheating Temperature:

Step 4: Determine Feedwater and Outlet Mass Flows

If the Desuperheated Outlet specific enthalpy is less than the Feedwater specific enthalpy or greater than the Inlet Steam specific enthalpy, the PRV outlet cannot be desuperheated to the set temperature and desuperheating is canceled.
Flows are determined using mass and energy balance equations:
  1. Mass Flow = MF
  2. Specific Enthalpy = SE
  3. Energy Flow = MF * SE
  4. Outlet Steam MF = Inlet Steam MF + Feedwater MF
  5. [Outlet Steam MF * Outlet Steam SE] = [Inlet Steam MF * Inlet Steam SE] + [Feedwater MF * Feedwater SE]
  6. [(Inlet Steam MF + Feedwater MF) * Outlet Steam SE] = [Inlet Steam MF * Inlet Steam SE] + [Feedwater MF * Feedwater SE]
  7. [Inlet Steam MF * Outlet Steam SE] + [Feedwater MF * Outlet Steam SE] = [Inlet Steam MF * Inlet Steam SE] + [Feedwater MF * Feedwater SE]
  8. [Feedwater MF * Outlet Steam SE] - [Feedwater MF * Feedwater SE] = [Inlet Steam MF * Inlet Steam SE] - [Inlet Steam MF * Outlet Steam SE]
  9. [Feedwater MF * (Outlet Steam SE] - Feedwater SE)] = [Inlet Steam MF * (Inlet Steam SE - Outlet Steam SE)]
  10. Feedwater MF = Inlet Steam MF * (Inlet Steam SE - Outlet Steam SE) / (Outlet Steam SE - Feedwater SE)
  11. Outlet Steam MF = Inlet Steam MF + Feedwater MF

Assumptions

  • The PRV (without desuperheating) is an isenthalpic process where inlet and outlet specific enthalpy is the same.
  • Feedwater is pumped into PRV at outlet pressure without a change in energy.