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Air Exhaust Temperature from Air Cooled Heat Exchanger

Air Exhaust Temperature from Air Cooled Heat Exchanger

Air Exhaust Temperature from Air Cooled Heat Exchanger

Hello all,

Looking for some direction for any codes, standards or best practice guidance when it comes to the maximum temperature limits that would be considered acceptable for the discharge air stream for an air cooled heat exchanger. Our ACHEs would be mounted on a pipe rack at high level and we have some high temperature process streams (temperatures up to 400 Deg. C range) to be cooled. I would like to understand if there are any legal requirements or best practice guidelines for maximum discharge temperature or is this project specific and subject to risk assessment? Location Europe.

Many thanks.

RE: Air Exhaust Temperature from Air Cooled Heat Exchanger

I don't know of any regulations limiting air cooler heat rejection but I do see some red flags here. In order to set an air cooler on top of a pipe rack you would need to use an induced-draft design. With an induced-draft cooler the fan blades, fan rings, and bearings are all be exposed to the hot air stream, so the discharge air temperature is typically limited to somewhere around 220F. I don't think it will be practical to get an airflow high enough to keep your effluent temperature below 220F.

For the tubes I think you would have to use embedded fins as extruded fins are typically limited to 550F and L-footed fins are usually limited to 300F.


RE: Air Exhaust Temperature from Air Cooled Heat Exchanger

There are also safety considerations; skin touch burn temperatures are in the range of 50 degC, so if people can get access to those surfaces, that would be a problem. Likewise, peoples' exposure to hot effluent would be a safety concern.

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RE: Air Exhaust Temperature from Air Cooled Heat Exchanger

If there are any elevated operator access platforms that may be in the path of the cross wind deflected hot plume from this cooler, then occupational safety considerations would apply - talk to your tech safety engineers on what the limits would be for your jurisdiction-see also OSHA / NIOSH requirements. If operators may be at these elevated platforms for extended periods of time, then 8hour exposure limits would apply. Get a specialist company to do a hot plume study to see the plume envelope for varying wind speeds.

The cooler the exit air stream from this air cooler, the smaller the hot plume envelope would be. What is the required exit process stream temp from this cooler?

@Christine, GPSA says a forced draft setup would be preferred when process fluid feed temp exceeds 350degF, since on fan failure, fan bearings and blades would be exposed to high temp for the alternate induced draft setup.

RE: Air Exhaust Temperature from Air Cooled Heat Exchanger

Thank you all for the advice and suggestions. We will speak to some vendors for further advice on air cooler type and design and look to appoint a specialist company to undertake a hot plume study. To answer the query from @georgevarghese, the required exit process stream temp is approx. 260 Deg. C.

RE: Air Exhaust Temperature from Air Cooled Heat Exchanger

Okay, with an exit air temp of say 60-65degC, you've got plenty of dT at the cold end of the cooler to make this work.

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