6 replies to this topic

[guoyinyanliner]

​"In a cooling water system, I have four shell-and-tube heat exchangers in cooling water service. How can I prevent flow maldistribution across these four heat exchangers

[breizh]

Perform heat and mass balances around your system (HX+ CW). Make sure you have sufficient enough water (flow rate) from the cooling water tower at the right temperature and pressure. Water should be distributed to each HX using a TCV at the inlet of each unit. The temperature at the outlet (process stream) of each HX should control the opening of each TCV .

 

I've attached a simple model produced by Stephen Hall for clarity.

 

Breizh

Attached Files

•  Cooling Water Model.xls   104.5KB   2 downloads

[Pilesar]

Cooling water flow will depend on pressure drop and flow path. A well-designed system should be able to accommodate variations in distribution. Each exchanger should have sufficient water velocity to avoid excessive rate of fouling formation.

[Pilesar]

Note that any TCV (if used) should be on the exchanger outlet (not the inlet) as shown by the spreadsheet Breizh posted. Computer software is available to help model cooling water hydraulic networks. For only four exchangers in a network, it is probably not worth learning a new program.

[breizh]

To add to my previous reply, make sure you have way to vent air which could be trapped in the shell of the HX at the start-up of the unit.

To answer to Pilesar, I've seen both, inlet and outlet of HX. Probably outlet is less troublesome.

Breizh

[guoyinyanliner]

To add to my previous reply, make sure you have way to vent air which could be trapped in the shell of the HX at the start-up of the unit.
To answer to Pilesar, I've seen both, inlet and outlet of HX. Probably outlet is less troublesome.
Breizh

"If the flow distribution is not ideal, is it a viable approach to install a butterfly valve at the heat exchanger outlet to add resistance and balance the flow?"

[breizh]

Yes, you can!

Not easy on operation point of view.

Note: Don't forget that you need to install isolation valves in case of maintenance of HX.

Breizh