Process Heating/Cooling Loop

[ChipFuller]

I've got a project where we are retrofitting an existing heating and cooling loop going to 500 gallon reactor. The chemical engineer that I'm working with designed it with three heat exchangers piped in series with a 3-way mixing valve between each heat exchanger. The system is designed so that when the temperature is in a certain range one leg of the three valve closes off and the liquid is bypassed. My question is when using three heating/cooling loops like I have described is the system better piped in series or piped in parallel?

Thanks

 

[pmureiko]

Here are my guesses on the heat exchangers.

1) Series is better because it may be hard to balance flow in parallel. You can end up with control loops fighting each other.
2) Two of the exchangers are for cooling and the third is for heating.
3) The controls are on the process side and there are no controls on the heating and cooling media.
4) The coolers are downstream of the heater for safety. To avoid losing reaction control, the cooler is there as a last step in case the heater bypass fails.

 

[ChipFuller]

Wow-you hit it right on the head! We have a pump at a constant flow then a steam heat exchanger (S&T), an approximately 40 degree Plate and Frame heat exchanger, and then an approximately 10 degree Plate and Frame heat exchanger.

We will have no controls on either the steam or the chilled loops. My guess is that we will have a manual valve to turn on the steam when the batch process starts so we won't be constant dump condensate.

When you say series is better how are the loops typical set up? Do I have 10 degree temperature difference between loops?

 

[pmureiko]

I forgot to mention previously not to make a design changes without a safety review. It was probably designed a certain way for a reason.

Also check the failure positions of your 3-way valves. For failure with an exothermic reaction you probably want cooling of 100% and heating on 100% bybass.

The temperature difference in the control loops (gap control?) needs to be balanced with process sensitivity. Check with your design or operations engineer on what is acceptable.