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Air Cooler With Warm Air Recirculation


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#1 shvet1

shvet1

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Posted 02 October 2017 - 06:36 AM

Good day, forum

We struggle with air cooler control loop design. We have a new air cooler:
- air cooler with warm air recirculation
- ambient air min/max -35/+35°C
- process fluid freezing temperature +43°C
- louvers control - automated with pneumoactuators from DCS
- fans control - first fan on/off from DCS, second fan VFD controlled from DCS
- process fluid control - thermocouple in air cooler outlet, signal to DCS
- cooler internal air temperature control - 2 internal thermocouples, signal to DCS

Vendor has provided us with manual where it described that there 6 cases exist for air cooler autocontrol:
- 3 for overheating protection (modes "cold summer", "moderate summer", "hot summer")
- 3 for antifreezing protection (mode "cold winter", "moderate winter", "warm winter")
And 1 more mode for manual start-up during winter using steam coils.

All seems OK but we can't realize how overall control loop works and finish process and instrument diagram. We can't imagine and explain to a programmer how algorithm works. We have 3 input signals and 5 output signals in DCS:
1. How to choose air cooler internal temperature that is controlled during each mode?
2. When do we have to switch one mode to another?

If anybody have detailed P&ID or algorithm how air cooler with warm air recirculation works please share it.

 

https://drive.google...QTc4clV6T2g5Tjg



#2 Bobby Strain

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Posted 02 October 2017 - 09:24 AM

Probably you should have a vendor rep to the site for assistance in developing DCS controls. Or provide an independent PLC for control. Your sketch doesn't show any air temperature monitors. After reviewing your sketch, I think your vendor lacks knowledge on how to instrument and control your cooler. You might seek the service of an independent specialist. I have designed similar systems for cold climate. Usually, I provided a heating coil that is necessary to prevent low temperature during shutdown. And to permit startup in cold weather. So, you might have more problems than you first realized.

 

Bobby


Edited by Bobby Strain, 02 October 2017 - 10:20 AM.


#3 breizh

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Posted 02 October 2017 - 03:26 PM

Hi ,

For this type of equipment you should buy the associated PLC , Logic is part of the knowledge of the vendor and should be included in the package together with the equipment .

 

My view

Breizh



#4 shvet1

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Posted 02 October 2017 - 10:21 PM

 Usually, I provided a heating coil that is necessary to prevent low temperature during shutdown. And to permit startup in cold weather. So, you might have more problems than you first realized.

Steam coil is provided for winter start-up. Winter start-up is manually operated and therefore is not concerned DCS logic.

 

 

Logic is part of the knowledge of the vendor and should be included in the package together with the equipment .

This is an existing facility revamp and we are just a detailed design Contractor and can not influence procurement and therefore scope of supply. Principal would be unpleased to see PLC for control loop that can be realized on existing DCS.

 

May be an extract from vendor's manual can help.

https://drive.google...ZU8yM3VELWtSSzg

 

Thank you, all. Vendor has already provided us with detailed description (more or less) how air cooler is controlled. We thought that could use another's experience as air coolers with warm air recirculation are widespread in cold regions. It seems all is up to us. (


Edited by shvet1, 02 October 2017 - 11:26 PM.





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