3 replies to this topic

[gimenz]

Dear Sirs,

 

Good day.

Hope everyone is doing well.

Please excuse my ignorance but i would like to seek your opinion regarding backflushing of heat exchangers. Currently I am having a consistency check in our P&ID and I came across this subject.

 

I understand that backflushing is washing the silts and solid deposits in the tube side of heat exchanger by redirecting the cooling water to pass through the outlet nozzle of the tubeside and exit in the inlet nozzle and out in the "backwash valve" as shown in attached drawing.

 

I have come across three (3) configurations in our PID

   -->  there is a  3/4"-drain valve downstream of isolation valve in backflush line

   -->  there is a  3/4"-drain valve upstream of isolation valve in backflush line

   -->  there is no drain valve in backflush line

 

My queries are as follows,

  1) how does this 3/4-drain valve works? is it to monitor if there's a flow?

  2) there is a vent valve that has a note "top connection". Does this monitor if there's a flow during backflushing? (like overflowing?)

  3) I have observe that in small piping like 3" and below, the PID shows a globe valve in the cooling water return line (does this means that during back flushing, cooling water return to header is gradually close and not instantaneously?)

 4) There are three (3) exchangers having the third configuration, i.e. having no TI on the outlet piping (the PID is from a different licensor). I believe TI is necessary, please enlighten me.

 

Thank you so much for taking your time.

 

Sincerely,

gimenz

Attached Files

•  backwash.jpg   30.07KB   61 downloads

[thorium90]

I think the presence of that top connection is to remove trapped air or to allow one to connect compressed air.

 

The 3rd one without the TI, probably they left it out or its not too important or maybe it goes into a return header downstream and the header has the TI instead? Some of my exchangers dont have TI on their CW out, we just assume the temperature is enough by feeling the pipe and looking at the inlet pressure gauge. haha... not a very good practice, but if the pressure is ok, and the shell side temperatures are ok, then the outlet temperatures must be ok!

 

The 3/4" drain valve, im not sure, but it might help to understand if there was an isometric diagram.

 

The globe valve, im not too sure why, probably to throttle the flow if the heat duty is not too much?

Edited by thorium90, 11 February 2013 - 10:28 AM.

[gimenz]

Dear Sir,

 

I have appreciate for sharing your thoughts. I can't get my hands on isometric drawing at the moment.

I was thinking the drain will only be use during shutdown or turnaround for complete drain in the backflushing line during maintenance. And has little purpose during periodic backwashing of the exchanger during normal operation. But I am not sure if this will be the sole purpose or the "backwashing valve" will just do the trick for complete drain during maintenance.

And so I am wondering if it is a part in backflushing procedure like checking if there is flow (i.e. overflowing the cooling water though this valve and then closing it) and perhaps the location for drain valve may matter. These are only my thoughts.

 

Sincerely,

gimenz

[kabtik]

The TI in the cooling water outlet is useful as far as I know. It has helped us to suspect leakage of  hot product into the cooling water line when it indicated abnormally high temperatures. As for the globe valve in the outlet line, it is used to indirectly control the temperature of the cooled fluid  .