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Cooling Water System Optimization

process heat transfer

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#1 canhhienfamily

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Posted 08 April 2020 - 08:53 PM

Dear everyone

I obseved cooling water system in some refineries and see that they do not optimize the cooling water by throttling the outlet valve of each user, means that they keep vaves in fully open always during normal operation.

 I understand that at the outlet of each user is provided a butterfly valve (most of cases) to control the CW flowrate depend on its process requirement (process temp). 

If we optimize CW by throttling valves, we can save energy from pumps and can increase CW to users that need more water and reduce CW to users that need less CW.

However, I heard that if we reduce CW to user, it may get fouling due to low velocity and high outlet CW temperature.

In my refinery case: the return temp of CW header is only 35-36oC (Design supply/return temperature: Min (25/25oC), Normal (32/47oC) and Max (34/60oC)) and I think it is still low and the fouling may not be the concern.

Another concern is low velocity, even there is no flow indicator at each user but base on the total actual flow rate of CW compared to design I think it must be higher than velocity as designed.

Please share your experience/application of CW optimization.

1. SHould we optimize the CW system by throttling the outlet valve of each user?

2. Tthe minimum velocity of water side that can be acceptable while fouling issue is minimized?

3.Tthe max water temp that can cause fouling?

Thanks and best regards



#2 breizh

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Posted 08 April 2020 - 09:40 PM

Hi,

To me you should talk to your chemical treatment supplier and get advices . During turn around you should open some exchangers to assess the quality of the treatment .

You really need to be cautious ! I won't throttle the valves , the risks to generate fouling and the consequences to your operation could be huge compared to the "savings".

My views

Breizh



#3 canhhienfamily

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Posted 08 April 2020 - 10:44 PM

Hi,

To me you should talk to your chemical treatment supplier and get advices . During turn around you should open some exchangers to assess the quality of the treatment .

You really need to be cautious ! I won't throttle the valves , the risks to generate fouling and the consequences to your operation could be huge compared to the "savings".

My views

Breizh

Thanks Mr Breizh

However, In case of the actual flow and velocity are still higher than the design values, it should be optimized.

Suppose that CW at each user is controlled by a control valve, the flow of CW will be adjusted by process temperature. For this configuration, velocity of CW or fouling may not be the concerns.



#4 breizh

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Posted 08 April 2020 - 11:33 PM

Hi ,

You have to make sure that the velocity inside the equipment is well managed i.e ensure a minimum flow rate ( threshold on valve opening  ) on each HX to prevent fouling . 

Other parameter to monitor  is the quality of the treatment to prevent deposit (scale formation) and blow down .

Look for Langelier or Riznar indexes  , it will tell you about the ability to precipitate calcium carbonate within the equipments ,

Instead of working on the water flow , you might consider to work on the cooling tower i.e Fans RPM  to reduce the power consumption based on temperature of the return water in the basins , to me safer .

 

Good luck 

Breizh 


Edited by breizh, 09 April 2020 - 12:54 AM.


#5 canhhienfamily

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Posted 09 April 2020 - 01:10 AM

Hi ,

You have to make sure that the velocity inside the equipment is well managed i.e ensure a minimum flow rate ( threshold on valve opening  ) on each HX to prevent fouling . 

Other parameter to monitor  is the quality of the treatment to prevent deposit (scale formation) and blow down .

Look for Langelier or Riznar indexes  , it will tell you about the ability to precipitate calcium carbonate within the equipments ,

Instead of working on the water flow , you might consider to work on the cooling tower i.e Fans RPM  to reduce the power consumption based on temperature of the return water in the basins , to me safer .

 

Good luck 

Breizh 

Thanks



#6 breizh

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Posted 10 April 2020 - 01:27 AM

Hi,

To add to my previous posts a few document about energy management and Inverter .

Hope this is helping you

Breizh

Attached Files



#7 Pham Hong Phuc

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Posted 11 April 2020 - 02:56 AM

Hi all,

 

For CW, We have no flow indicater for each user. we can measure by portable flow meter, do you have idea to calculate flow for each user.

From using throtle valve for CW, i think fouling is more consider.



#8 canhhienfamily

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Posted 13 April 2020 - 03:02 AM

Hi all,

 

For CW, We have no flow indicater for each user. we can measure by portable flow meter, do you have idea to calculate flow for each user.

From using throtle valve for CW, i think fouling is more consider.

Yes Mr Phuc.

There is no flow indicator for each user. One way is to calculate duties of streams on tube side and shell side. Adjust CW flow to get the same duties. It is not 100% accurate but acceptable.

Tks



#9 naresh1537

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Posted 19 July 2020 - 12:30 AM

document mentioned by breizh has better view of Cooling water system!



#10 Chemitofreak

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Posted 19 July 2020 - 02:09 AM

Please share your experience/application of CW optimization.

1. SHould we optimize the CW system by throttling the outlet valve of each user?

2. Tthe minimum velocity of water side that can be acceptable while fouling issue is minimized?

3.Tthe max water temp that can cause fouling?

Thanks and best regards

 

1. I guess you have enough information about this in the above posts.

   Just to mention that usage of butterfly valve in cooling water circuit depends on the pipe size. For lower pipe diameter gate valve is used and for higher size butterfly valve.

 

2. Generally cooling water is considered as fouling service and hence kept in the tube side. The minimum velocity on the tube side should be 1.5 m/sec.

 

3. The fouling depends on the chemicals you dose in the cooling water, that depends upon the water quality you have. I had seen fouling in an exchanger with outlet temperature of 45+ degC.      






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