Air coolers vs water coolers on offshore installations

[Trond]

What are the criteria for selecting the types of coolers for offshore oil & gas facilities? Am I correct in assuming that the advantages of air coolers are:

More reliable
Less maintenance intensive
Shorter lead times

What about overall weight/cost conpared to a sea water cooled system? The latter obviously requires more equipment in terms of pumps, filters, valves & piping, however air coolers require a larger footprint than say, shell&tube type exchangers, although by placing the air cooler unit above other equipment (e.g. gas compressors) the impact may be reduced.

It seems to me that air coolers are usually the preferred choice for offshore platforms, whereas from what I hae seen FPSOs appear to select cooling water system - is this simply a case of old habits die hard, or is there an actual rationale for the apparent difference in systems used?

 

[willard3]

I don't know the requirements of offshore platforms, but the film coefficient of water is approx 100 times that of air meaning that heat transport can be done in smaller pipes.equipment.

Heat transfer is much higher for the same volume of water as opposed to air.

 

[speco]

Trond,

I work with manufacturers of exchangers, and am not a user. Therefore, I can't claim any inside knowledge of the operational advantages of air coolers over shell and tubes in offshore platform applications. However, I've worked on a number of air-cooler projects on platforms.

I generally agree with your logic.

Here are a few more considerations:

Sea water is pretty corrosive, so the material of choice for exchangers in contact with is is usually titanium. It's pretty expensive, and lead times may be long.

Willard3 is basically right about air as a heat transfer medium. However, that's why coolers have fins. You get about 25 times the bare surface with fins, and this tends to balance the scale a bit.

The size of coolers on platforms is always a problem. It's got to be the most expensive real estate on the planet. Coolers are generally mounted above the other equipment for that reason. A word of caution here. Generally the smaller the cooler's plot area is for a given service, the higher the horsepower and fan noise. This translates into both operating cost and health and safety issues. Trying to squeeze a big air-cooler into a small space can bite you in the end.

Regards,

Speco (

http://www.stoneprocess.com)

 

[CH5OH]

cooler of choice:
1.plate cooler+SW pump
2.tube cooler+SW pump
3.air cooler+fan

watercooling has slight more maintenance than air cooler
(moist air with high salt content is as corrosive as SW)
alu fins on air cooler more sensitive for wear than titanium plates on plate cooler

 

[rmw]

CH50H,

Wear or corrosion?

rmw

 

[CH5OH]

wear caused by corrosion
moist salty air, leaving the salt on the alu fins to corrode