Variable Flow Thru a Steam to Glycol Heat Exchanger

[UtilityLouie]

I have a large heat exchanger with steam on the shell side and 30% glycol solution on the tube side. My big question is:

Can I pump a variable speed pump to this heat exchanger or is there some minimum flow I need to maintain?

I am planning on pumping in parallel (two 1800 GPM pumps, both variable speed). This is a somewhat critical system, so I wanted to have some redundancy without 100% back up. Would there be a problem with just having one pump running?

I know that with a variable speed pump there will be a minimum flow it can provide, but are there special precautions I need to follow to make this system work.

Any suggestions would be appreciated!

 

[fredb]

Hello,

I would say that the concern you should have with minimum flow is that you don't turn any of the glycol solution into steam. You should be able to determine the temp. rise by using the appropriate equations for the specific heat exchanger type you have and your piping configuration i.e. counterflow, parallel flow.

As far as using one pump, I see no problem.

 

[Joesteam]

Since you will be cutting down the flow in the heat exchanger, you will also be reducing the steam load. Therefor there is a chance that the steam control valve will be oversized and not be able to control the temperature well. If this is the case you may have to change to a 1/3 - 2/3 split range control.
Also, most heat exchangers are designed for turbulent flow in the tubes, if the flow rate is reduced you may get laminar flow which will reduce the heat transfer.

 

[Cooky]

Hello,

When the fluid rate is decreased, the flow pattern will change from turbulent to laminar (as mentioned by 'joesteam'. This will result in a significant reduction in the rate of heat transfer. You should check the saturated temperature of the entering steam supply (plus any superheat value). Then ensure this is lower than boiling point of your fluid mixture. Otherwise you could suffer from fluid flashing inside the tubes.

 

[ChasBean1]

Louie - I think all of the above comments are valid and you can get good conceptual issues here in this forum. For a more concrete solution I think the answer would lie more with HX manufacturer. What are their specs for flow range through the tube bundle? What is the tube diameter, how many tubes are there and what do you anticipate will be the minimum system flow? Also, I think I've seen in the past a person or two in the heat transfer forum that are well versed with HX requirements/criteria - did you post this there also? I'm interested in this too and will look for follow-up. Tx, -CB