Air Fan Coolers

[ag92]

API RP 521 Section3.15.7.2 This section refers air cooled exchangers in condensing service. An alternate heat flux value of 12,000 is given to use in place of the standard value of 21,000. Is this value only good for condensing service exchangers? Or can it also be used in a liquid sub-cooling service.

Section 6.3.4 refers to fan power failure on an air fan exchanger. If I have temperature switches on an air fan, which shut down the motors on high ambient air temperature, can I take credit for cooling due to natural convection, during a fire relief scenario? This paragraph indicates that 20% - 30% cooling can be maintained when the fan is off. Does this refer to condensing only, or could I take credit for this in liquid sub-cooling service as well?

 

[samuelliu]

API RECOMMENDED PRACTICE 521 - Guide for Pressure-Relieving AND Depressuring Systems.

API Standard 661 - Air Cooled Heat Exchangers???

 

[22082002]

Air cooler can also subcool...

In case of power failure, air cooler can do it's job by 20-30 % duty.
Now this has to be done in a new calculation, better if you have simulation package, do a new simulation with duty 25% and get outlet condition for the power fail case.

Hope your query is answered...

PS:
Samuelliu : ag92 is not wrong and you are also not wrong....

 

[ag92]

I understand that the code gives you some credit for natural draft cooling on a fan failure. However, I have a hard time seeing how this is applicable in a fire case, since your ambient air temperature will be much higher than normal.

 

[22082002]

In fire case: You can consider fire upto the height og 25 ft only. So in case of fire, you will not have any cooling... and if you can let me know which case you are considering.

You cannot have two unrelated cases. So fire is one case and loss of cooling is another case.

Further to this, you need to do fire ball analysis. You cannot have all vessels under fire simultaneously. I am sorry I won't be able to help you on this issue.

Best Regards,
Satish