Cooling Water Flow Shortage to Trim Coolers less than design rate??

[rtaneja]

I would really appreciate all your responses to my questions. Part of the current project that I am working on entails two trim coolers that are designed for a cooling water flowrate of 1100gpm but are currently receiving 600gpm. The two exchangers are in parallel. What could possibly be causing this shortage in flow? The inlet is at 90F which is to be reduced as well as part of the project. The coolers are part of a fractionator off-gas system. One thing that I have been working on is a cw utility summary table where I have jotted down all the take-offs from the main cooling water header that serves the trim coolers (right from the cooling tower). The same header, ofcourse serves several other unit areas in the refinery. Like cw supply to sample coolers, seal oil coolers, other exchangers...etc.The table has the duties,mass flows and temperatures. Is this going to help me evaluate something?? Fouling in the tubes could be a reason too. But is there anything else that is a prominent cause for this?The main users of the cooling tower are already at about 89MMbtu/hr and the overall duty of the cooling tower is at 97.5MMbtu/hr.

Any suggestions and guidance really appreciated!!

Thanks!!

 

[tkdhwjd]

Either restriction in CW header/subheader or declining of cooling water pump performance.

 

[chemjock]

Trim coolers are usually elevated. Are the lower level coolers taking a majority of the flow? Is the ccoling water system flow balanced?

 

[djack77494]

Try checking historical data. See if this is a recent occurance or has been developing over a period of time. If the time scale is large, maybe small CW user additions over a period of time have "robbed" the existing users of their share. Tends to happen in our maxed out units.

 

[Jason5000]

Good posts above. Elevated exchangers tend to struggle on cooling water systems. Also other exchangers in the circuit being upsized can have a big impact. I've also seen booster pumps used to boost flow on problem exchangers, and this practice tends to "rob" from other heat exchangers that share that supply header.

A pressure survey on the cooling water supply and return and comparison of available DP to design DP may shed some light on the situation. Try to get it as close to your problem exchanger as you can, particularly if its elevated. Perhaps a booster pump to help your current situation; just watch out for the second order effects on the rest of your system.

 

[Artisi]

First step would be to check the pump performance, ie flow, head and power input against design, without this all other investigation could be a waste of time.

 

[cub3bead]

Did you check the coolers to see if all of the air was vented?