4 replies to this topic

[rabindra]

In one of the Cooling Water Exchangers, the cooling water return line has been provided with a 3" connection to vent. In between there is small vertical vessel with a level gauge. The vent system with LG to indicate gas leakage to cooling water. The valve at the downstream of the vessel towards the vent is NC (normally closed).

 

I have no idea how the system will work. Please explain.

 

A copy of P&ID is attached.

Attached Files

•  CW Return Line.jpg   143.11KB   20 downloads

[RoyenG]

Hi,

 

I see that pipe with LG is for collecting any vaporized liquid that produced during heat transfer process upstream side.

There is also 20mm needle valve on the upstream side of the vent valve that need to be checked if it is NO or NC, and also note 17 (?). 

 

Regards,

Royen

[PingPong]

I agree with Royen. It is to detect leakage from the exchanger shellside into the cw.

 

Shellside liquid is naphtha stabilizer ovhd liquid, in other words: LPG. At cooling water pressure and temperature that will become vapor and the idea is that some of that vapor will accumulate in that vertical piece of pipe so an operator could detect it on the level gauge.

 

However the water from a cooling tower is air saturated, and when that saturated cw is warmed up in the exchanger it can release some air bubbles that can also accumulate in device, so if you see a water level on the level gauge, due accumulated gas, you still cannot be sure what gas you see.

[fallah]

rabindra,

 

There are two vents there, one a simple vent before NC valve to release the separated dissolved noncondensible gases to the atmosphere during the start up and periodically in normal operation. Another vent is activated by opening the NC valve if the level of the liquid in the vessel (i think better to call it pot) would suddenly drops lower than a prespecified value probably due to the HC leak into cooling water return line. This vent should be conducted toward safe location as it is in PID...

Edited by fallah, 27 March 2014 - 06:56 AM.

[TS1979]

probably the note already tells you how the leak detecting system works