Restriction Orifices
Restriction Orifices
(OP)
Good day.
A boiler feed water pump, has a minimum flow line back to a deaerator storage tank. In this min flow line there is a flow control valve and a orifice plate just before the Deaerator Storage tank. The pressure of the water upstream of the orifice is 41 Bar and the temperature is 210 degrees C. The problem is that downstream of the RO the line deteriorates.
I want to know how I can drop this pressure from 41 Bar to 5 bar, without flashing and with the temp of the water staying below the Saturation temperature of water at 5 bar.
I am a bit confused since the pressure drop that occurs over a RO happens adiabatic, and the temperature only changes over a RO if flashing occurs.
How do I then get the temperature of the water down so that it stays below the saturation temperature.
A boiler feed water pump, has a minimum flow line back to a deaerator storage tank. In this min flow line there is a flow control valve and a orifice plate just before the Deaerator Storage tank. The pressure of the water upstream of the orifice is 41 Bar and the temperature is 210 degrees C. The problem is that downstream of the RO the line deteriorates.
I want to know how I can drop this pressure from 41 Bar to 5 bar, without flashing and with the temp of the water staying below the Saturation temperature of water at 5 bar.
I am a bit confused since the pressure drop that occurs over a RO happens adiabatic, and the temperature only changes over a RO if flashing occurs.
How do I then get the temperature of the water down so that it stays below the saturation temperature.





RE: Restriction Orifices
you may need to consider a valve designed for high pressure letdown, they are not cheap and usually require major piping changes.
One alternative, is to consider using a series of a multiple port restriction plates to reduce the pressure in stages in a more or less controlled fashion. You feed water pump supplier is usally a good source of options on that.
Per your initial query, reducing the water temperature is only possble if you remove the heat, that generally is not an option.
RE: Restriction Orifices
Suggest to have a look to the thread below
h
RE: Restriction Orifices
Note that I'm an electrical guy, I only did the controls for the example cited. I betya there are folks in this forum who could do the thermo in their heads though...
Good on ya,
Goober Dave
RE: Restriction Orifices
With multiple orifice plates you will bring the pressure down in a controlled fashion, but you will still have flashing since you cannot bring the temperature of the superheated water down with a RO. The flowrate of the superheated water is 90kg/s, and the request is to bring the pressure down to 5 bar and that the temperature of the fluid stays below saturation temperature at all times. This however seems not to be possible, since you cannot remove heat with RO's. There must then be another solution to bring the pressure down, while also reducing the temperature, to prevent flashing. FOr example the turbine solution might not be that far fetched.
RE: Restriction Orifices
The solution is to use a heat exchanger to bring superheated water temperature below saturation temperature at 41 barg and then pressure reducer (orifice or valve) to reach 5 barg.
RE: Restriction Orifices
One way of reducing the temperature and pressure at the same time would be to replace the orifice with an eductor. Use it to draw cold water in from your soft water make up tank. If the soft water is at 30°C you would have to draw in about 0.4 kg for every kg of 210°C water. A company like Graham manufacturing would be able to tell you if this is feasible.
Katmar Software
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RE: Restriction Orifices
Put more orifice plates reduce the pressure drop
across each plate and it may help to prevent cavitation.
RE: Restriction Orifices
plates would cause cavitation to occur.
Put additional orifice plates reduce the pressure drop
across each plate to prevent cavitation.
RE: Restriction Orifices
I calculate 11% vapor fraction going into the deaerator storage tank. The easiest thing to do is resize your line to handle the velocity of that sort of flashing. Drop the pressure right before the tank to minimize the length of the line. Some care should be taken in design and location of the control valves and orifice(s) in order to avoid localized impingment of a jet onto the pipe wall (i.e. give yourself some straight length on the downstream), but there is nothing that can be done to actually stop the flashing except by cooling to 159C prior to taking the pressure drop.
best wishes,
sshep