Hi!
We do not cover the economical aspects here.
We have a discussion going on about steam flow in a low pressure net supplied from a high pressure net, either via pressure reducing valves or a steam turbine. Let's say we have HP steam of 50 bars and 450 deg.C, and the LP steam is 2.3 bars and 150 deg.C.
The claim is that we get more low pressure steam by utilizing pressure reducing valves instead of the steam turbine.
The question is why this is true?
What I see as a partly explanation is the need for more cooling water (which eventually will evaporate and mix with the steam) to decrease the temp to 150 deg.C downstream the valve. Considering the JT effect will off course to some extent reduce the need for cooling water.
However, this is also true for the turbine part but to a smaller degree.
Anyone who can offer some expertise here on this matter?
the mass flow rate of the steam must be the same. but maybe the volume is different. when 50 bar and 450 degC enters a turbine or a expansion valve, the outlet can be the same (2.3 bar and 150 deg C). I think for the same pressure, temperature will be different. on works almost isnetropic and the other does not.
the mass flow rate of the steam must be the same. but maybe the volume is different. when 50 bar and 450 degC enters a turbine or a expansion valve, the outlet can be the same (2.3 bar and 150 deg C). I think for the same pressure, temperature will be different. on works almost isnetropic and the other does not.
I don't quite understand your reply. Yes, as you mention the mass is constant, while the volume obviously varies (upstream vs. downstream) for both cases. And also, yes, the valve pressure reduction is isenthalpic while the turbine case is ideally isentropic.
However, this doesn't answer my question - as I read it at least..
Apart from my recension about the different amounts of cooling water needed (and thus provided to the steam flow), what else is contributing to the fact that the same amount of HP steam becomes a larger mass of LP steam when reducing pressure over a valve versus a turbine?
Andreas Volden
so sorry. I checked the answer now and i realized that some part of the message in missing, maybe i have made a mistake while typing and deleted a part of the answer.
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