14 replies to this topic

[motaleby]

Hi engineers

 

Would you please tell me the design criteria for the Process Fluid outlet temperature in air coolers?

 

Best regards

Edited by motaleby, 11 December 2014 - 11:30 PM.

[AlertO]

Hi

 

i don't think there is any criteria of outlet temperature for process fluid. This should come from your application requirement. There is only one disadvantage point of air coolers that is you cann't cool your process fluid to a temeperature near ambient temperature i.e. below 50 degC.

[ColinR33]

The outlet temperature is determined by your process requirements, but AlertO makes a good point. To elaborate a bit, the minimum economical temperature of approach (difference between design ambient air temperature and process outlet temperature) is about 15°F (some would say 20°F). Any lower than that and the air cooler size gets significantly larger and your economics go out the window.

Example:
Here in Alberta, design ambient air temperature is typically around 95°F/35°C (as low as 85°F in some areas), so with a 15°F approach, your minimum process outlet temperature is 110°F/43°C (of course in the winter when ambient is much lower the cooler can over-perform if not controlled correctly).

In the Middle East, I have worked with design ambient air temperatures of 120°F (49°C), so the design process outlet temperature is 135-140°F (57-60°C). If you want a lower process temperature you will need water cooled trim coolers, an evaporative cooler or some other type of circulating cooling medium.

Bear in mind that the achievable design process outlet temperature is driven by the DESIGN ambient air temperature.

HTH
Cheers,

[breizh]

motaleby ,

 

http://www.gearainey...Calculator.html

 

This simple calculator may help you to support your work on top of the explanation given above.

Hope this helps.

 

Breizh

[motaleby]

Hi

Thank you all

 

We’re working on a basic design of a compressor station beside Persian Gulf. Our consult insists on setting outlet gas temperature from the last air cooler at 60°C. The simulation shows the gas contains about 400 bbl of water at this temp. Due to the fact that gas should be transferred to the refinery by a 30 km pipeline, it is predicted some of water may condense in the pipeline. Moreover, if we increase the outlet temp by 7° C about 95% of water will be vanished. But the designer doesn’t accept this suggestion and refers us to some oil company practices to maintain it at 60°C. How can I convince him?

 

Thanks you again

motaleby

Edited by motaleby, 18 December 2014 - 05:59 AM.

[AlertO]

Hi Motaleby

 

Is 60-degC the minimum temperature for process outlet from air cooler? I don't think there is any criteria mentioning to fix the last discharge temperature at 60 degC.

[motaleby]

Hi AlertO
Yes I do agree.
What do you think about Material, safety or disboundment phenomenon?
By increasing the temperature of a fluid entering to an existing pipeline, its allowable working pressure will be decreased and this may be important in somewhere.

[shan]

What you need to do is to install a KO drum after the air cooler to eliminate the 400 bbl liquid.  Even if you specify a higher process temperature from air cooler, the compressed gas stream will be cooled down through the 30 km pipeline to the ambient temperature and liquid (water/condensate) will accumulated in the line.

[motaleby]

Dear Shan

Yes exactly! after about 10 km we will have the first droplets. Your suggestion is a reasonable alternative of increasing outlet temp but you should note that we're talking about 50 MMMSMD gas, so the proper vessel for water separation will be too huge.

[colt16]

If you increased the outlet temperature of the air fin cooler you are not solving the problem. You are merely converting it to a vapour as it enters the compressor but it will also condense at the compressor discharge due to long pipe line.

 

Why is there so much water at the inlet to the compressor? There should be a KO drum before a compressor anyway.

[motaleby]

Thank you tanykiat

You are right, we should eliminate water from the fluid. Meanwhile it is outlet gas not inlet.

[colt16]

It may be a good idea to make the temperature of the outlet of the air fin cooler as low as possible and place a KO drum between the air fin cooler and the compressor to remove the water before it enters the compressor. 

[motaleby]

Let me clarify again the problem comes from the last aircooler not the intermediate one and the gas PQT are about 90 bar,50 MMSCMD and 60°C. Therefore what size of a separator should be used to handle such a huge gas? There's a suggestion to use a set of 20m inclined pipes (you could name it mini-finger type slug catcher) so that the water is separated from gas in the pipes route before enters into the main transfer pipeline.

[breizh]

motaleby ,

 

Consider these papers to support your query .

Hope this helps.

 

Breizh

[motaleby]

Thank you Breizh