steam pressure drop through a control valve (evaporator case)
steam pressure drop through a control valve (evaporator case)
(OP)
Hi Everyone,
This is a situation about the steam pressure drop at the steam feeding of a 3 effect evaporator.
The steam for various process of the plant is produced on another 1 effect evaporator, and the pressure of this steam is 2.6 bara (measured). Part of this steam is used to evaporate juice in a 3-effect evaporator.
The steam is supplied by a 6” pipe, like is shown in the next picture:
http://files.engineering.com/getfile.aspx?folder=d...
The control valve datasheet is shown in the next link:
http://files.engineering.com/getfile.aspx?folder=d...
I want to estimate the heating supplied to the 1st effect of the evaporator. When the control valve is at its 100% of lift the steam pressure upstream of this valve is 0,8 bara. So the question is. Why this pressure is less than the 2.1 bara (showed at maximum flowrate of the control valve; 98,7 lift). What am I missing?.
Thank you for you time.





RE: steam pressure drop through a control valve (evaporator case)
RE: steam pressure drop through a control valve (evaporator case)
I have done the pressure loss calculation and is negligible at 4000 kg/h of steam
http://www.tlv.com/global/TI/calculator/steam-pres...
RE: steam pressure drop through a control valve (evaporator case)
RE: steam pressure drop through a control valve (evaporator case)
RE: steam pressure drop through a control valve (evaporator case)
RE: steam pressure drop through a control valve (evaporator case)
yet, it doesn't make sense to me.
-The pressure at the valve inlet should not be a bit less than 2.6 bara, considering the friction losses are negligible.
-Based on the valve Data Sheet the maximum pressure drop across the valve is 0.5 bar. So the minimum pressure at the valve outlet should be 2.6 bara - 0.5 bar = 2.1 bar?
-Why the reading is 0.8 bara?
RE: steam pressure drop through a control valve (evaporator case)
RE: steam pressure drop through a control valve (evaporator case)
Sorry I made a mistake in the first post
"When the control valve is at its 100% of lift the steam pressure
upstreamof this valve is 0,8 bara.". It's really downstream the control valve where the pressure is measured.a draft of a P&ID of the steam line is in the next link:
http://files.engineering.com/getfile.aspx?folder=2...
So, the only measurements are the inlet valve pressure (pressure indicator) and the valve outlet pressure (pressure transmitter). There's no temperature measurement.
RE: steam pressure drop through a control valve (evaporator case)
RE: steam pressure drop through a control valve (evaporator case)
RE: steam pressure drop through a control valve (evaporator case)
RE: steam pressure drop through a control valve (evaporator case)
From a theoretical point of view it could be possible to have what you've described, but in real world applications, where steam is never ideally saturated (its quality is below 100%) the result of the steam passage through the control valve is very hardly that of having a superheated steam downstream the valve, but rather it’s that of having an increase of steam quality (indeed very small in this specific case, taking into account the quite low pressure reduction).