Advice on condensate injection please 2

[lastone]

I'm looking for some advice on injecting hot condensate into a cooling water return line.

Process conditions:
Condensate is at 300 deg F, 135 psig, flowrate = 300 gpm
Cooling Water is 90 deg F, 5 psig, flowrate = 15000 gpm

The condensate injection line would be a 2" line coming off of a 4" vertical line, run horizontally about 7 ft, and inject into the top of a 24" cooling water line that runs horizontally. I know from the heat balance that my cooling water would see a temperature increase of approximately 3.5 degrees. This is not a problem, but what I am not sure of is what will happen in the 24" cooling water line. I suspect that the hot condensate will flash upon mixing with the cooling water and then immediately collapse upon itself, similar to cavitation. What I do not know is how this will affect the pipe. The 24" line is supported in an elevated pipe rack. Would this create vibration or potentially rock the 24" header around? Obviously I cannot afford to damage the 24" header so any advice or experience with something like this would be greatly appreciated.

 

[abeltio]

the main problem is not thermodynamics... but mechanics...
this type of tie-in when done improperly can result in a ruptured pipe (note the difference in temperature between the condensate and the cooling water).

what i have done in the past is:

prepare a flanged connection with a blind cover on the 24in line (e.g. 10 or 12in)
on the blind flange, close to the upstream nozzle wall install a gland packing that will sustain the 5 psig of the cooling water.
The 2 in pipe with the condensate goes thru the packing into the 24in pipe to approximately the center of the 24 in pipe and has a very smooth bend (4 or 5 diam).

The 2 in pipe is connected to the 4 in condensate line via a flanged connection, and should have some bends to provide enough flexibility (i.e do not run a straight pipe).

The idea is that the 2 in line carrying the hot condensate is NOT welded to the 24in line, because the local stresses would be too high... with this arrangement:
maintenance is very easy.
it is almost guaranteed there will be no cracks on the pipes.
by flowing the condensate in the center of the pipe the shock and flashing is minimized (otherwise you can create a steam blanket against the 24in pipe wall).

do not forget to:
install block valves
a vent to eliminate air in high point(S) - usually there are more than one high point.

is there a problem with cooling water going into the condensate line??? (contamination?)
then, it would be a good idea to have a check valve (or two in series!!!) to avoid backflowing and some means to detect this condition...
e.g. a delta p switch across the check valves that will detect a higher pressure on the 24 in line than on the condensate line.

HTH



saludos.
a.

 

[lastone]

Thank you abeltio. This is the kind of thing I was looking for. I appreciate the advice very much.