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We need to have pressure reduction from 47 Bar to 40 bar by pressure control valve. Will the steam be still saturated after pressure reduction and what will be the temp after pressure reduction?? How can I calculate this?? Can any one provide me this information??

[Art Montemayor]

ashokan:

I’m going to assume that you’re really a student posting in this industrial professionals’ Forum. A professional engineer should always know better than to fail to state the quality of the steam (saturated or superheated?) and his pressure units (absolute – bara, or gauge – barg?). I’m going to assume you mean saturated steam at 47 bara.

One quick and efficient way to solve this problem is to go to: http://webbook.nist....hemistry/fluid/

There, you will find all the thermodynamic properties of water (steam). Select your units for the water fluid and also select Saturated properties between the pressures of 35 and 50 bara. You will get a down-loadable table that identifies the 47 bara saturated steam as having 260.1 oC and 2,796.5 kJ/kg of Enthalpy. If you now repeat the process of data retrieval for an isobaric (constant pressure) process instead of a saturated process, then you’ll find that at 40 bara you are in the zone of a phase change:

Temperature = 250.35 oC
Physical state = Liquid, with enthalpy of 1,087.5 kJ/kg
Physical state = Vapor (steam), with enthalpy of 2,800.8 kJ/kg

The thermodynamic process that occurs when steam is regulated by a control valve is isenthalpic (Enthalpy = constant); as you can see, if the original enthalpy is to remain constant at 2,796.5 kJ/kg, then at the reduced pressure of 40 bara the steam will fall below the saturated vapor enthalpy of 2,800.8 kJ/kg – slightly inside the “dome” on the Mollier Diagram or the T-S chart for steam. You can easily calculate the “wetness” - or quality - of your steam product by making a heat balance around your control valve.

I believe this answers your four questions:

1. Will the steam be still saturated after pressure reduction?
2. What will be the temp after pressure reduction?
3. How can I calculate this?
4. Can any one provide me this information?

Art Montemayor