Hello All,
Preamble: I am in the middle of Commissioning a R717 Screw Refrigeration System with a Thermosiphon Oil Cooler. I currently have a problem of high discharge pressure in the Evaporative Condenser which is higher by 3 barg than it should have been for which I seek help from this forum. (Current 14 barg, expected 11 - 11.5 barg).
The Thermosiphon Cooling I have used is slightly different from the standard P&ID used. In that, I have drawn a pipeline directly from the Evaporative Condenser (6 meters above the Oil Cooler) to the Oil Cooler rather than through a Priority Vessel with a tapping to the HP Receiver which is placed at a height of 1.5 meters from the Oil Cooler. The refrigerent is vented out into the reciever which is at a height of 1.5 meter from the Oil Cooler. The receiver is equilized with the Inlet of the Condenser.
The idea behind doing this was to use the entire 5-6 meter height between the Oil Cooler and the Condenser to generate more gravity pressure to cool the oil which I thought would improve the cooling in the Oil Cooler due to higher velocity. With this arrangement, I don't have a problem with the temperature of the oil, however the Condenser Pressure is higher by 2-3 barg.
An increase in the Discharge Pressure was anticipated, so a tapping was taken to the bottom of the receiver to collect the excess refrigerant into it directly thinking it would free the condenser coils of the liquid due to the pressure drop in the Oil Cooler, but this doesn't seem to be working. The Discharge Pressure remains the same even when I open the valve to the receiver.
Attached is the P&ID for your understanding. I wish to have an opinion on where I have gone wrong and what could be a possible solution to this issue I am facing.
Regards,
Pratap
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From here is my post i.e. answer to you....
So: I do not like to criticise people becuse they do not know something (I was young too and I did not know a lot of things), but usually people first did the things wrong and then revert for help ... what is not a right way and sometimes can be expensive too ...
first we go to school to learn something and then we start to make things or maybe I am wrong ;) ... anyhow ....
So according to your scheme liquid line is OK ( liquid is draining into oil cooler and surplus is going into receiver .... but return line from oil cooler must go directly into condenser inlet pipe from above side and not into receiver because receiver is not designed for that kind of return line connection ...
went line from receiver must be connectet also in that way ... so you will have two
went pipes connected into condenser inlet pipe from above ... I have to find a scheme how to execute that connection ... but for sure that must be within my RE forums posts ...
another big problem can be ... according to your scheme you have double coil condenser and your outlet from condenser is not good ...
each outlet must be with its own siphone to balance coils ... and then both outlet after siphone connect into pipe going down to oil cooler ... the elbow on that pipe (right side on your scheme at bottom) must be the lowest part of that pipe and from that elbow pipe must climb up into oil cooler ..
also on horizontal outlet pipes from each condenser coil but before elbow going down you must instal purging valves 3/8" on the top of both pipes ... there is only place where you can purge air from your coils ....
further ... kind of siphon ahead of condenser inlet must be upside down ... i.e. inlet pipe to condenser must be with slope to condenser ...
condenser inlet must be the lowest part of inlet pipe ...
This is all for the moment ... hope to be of some help ....
if you have any question please ask
Best regards, Josip