Someone has done automation in cooling towers for cooling exothermic reactions?

What kind of reaction?

Hi Jean, the process é an amination (isopropylamine) of glyphosate acid. During the reaction the temperature get 65°C in the reactor. The reactor is semi-batch but the cooling tower everytime. My idea is reduce the flow of water or the rotation of the fan during the intervals of reaction (load and unload). I don't know what parameters I need to control and how to control this parameters. Where to measure the temperature? At the return of the water to the cooling tower, at the basin. It is necessary to measure the flow of water?

Data:
Inlet temperature (tower): 30°C
Output temperature (tower): 26°C
N° reactors: 4
Volume reactors: 10.000L
Maximmun temperature desired(in the reactor): 63°C

King regards

Did you recive my comment?

hi jean, I'll return later. Thanks for attention.

Hi Alex an alternative is to install a variable speed drive managing cooling water flow rate on the water pump in a control loop governed by the reactor temperature.

Just a couple more questions: 1. How tightly do you need to control the reactor temperature? 2. Is there a minimum reactor temperature that you do not wish to go below? 3. Can the reaction run away and become dangerous?

A conventional cooling tower is controlled by a VFD on the fan(s) as the tower discharge temperature goes up and down. Another consideration for this temperature is the area (climate) in which it is installed. If the area is too hot or humid you may not be able to achieve the tower temperatures you wish.

Also, as Rongai indicates, it may be better to control the reactor temperature with a separate tempered water loop. This will most likely give you tighter temperature control and allow better compensation for reaction rate changes.

think also to recovery heat ! with intensification solution, many application you can found in Your plant! and save money:
- first office heating during winter so that water go into the cooling towers, after exchange with fancoils circuit;
- second recovery heat , and suppy other necessary energy with alternative source, and produce distilled water in vacuum system membrane, for internal use.

Alex, From my experience you have a couple of options: 1) a three way control valve to allow some of the cooling water to bypass the reactor cooling coils / jacket when less cooling needed. 2) adjustment of the cooling tower fan operation, and 3) changing the gross cooling water re-circulation rate.

The first option is a fast response control with little dead / lag time. The second and third techniques are slower responding because of the "thermal flywheel" effect of the volume of cooling water in the cooling tower basin, and pumping loop.

Without additional information, I think a combination of 1 and 2 above will be your best bet. You setup the flow through the cooling coils / bypass to provide for rapid adjustments, and use the fan to handle the atmospheric cooling tower influences, (i.e. rain squalls, significant dew point changes, night to day temp changes etc.) the objective is to feed the quick flow control through the reactor coils or bypassing with a relatively steady inlet temperature. As i am sure you understand, by allowing more bypass you will reduce the heat removal from the reactor because the lower flow will heat up faster (in a shorter length) in the coils / jacket, and then reduce the heat transfer because of lower difference in temperature driving force. If the reactor can run away thermally, it's advisable to provide a "second" independent cooling liquid supply and control to protect from controller error / malfunction and / or control valve failure. The valve fail position should deliver full flow to the cooling coils / jacket on either electrical (or communication system) and air / drive power failure.

I hope this helps,

Don Jeter

Don't forget to consider ambient conditions and the potential hazard of ice build up on your cooling tower. If you are in a climate with freezing conditions, Option 3, changing the gross cooling water re-circulation rate, is ill advised without having Option 2, adjustment of the cooling tower fan operation, as your primary control method. With sub zero ambient temperatures, the cooling tower fans should be shut off before you significantly reduce water flow rate to the cooling tower. Also, depending on the design of your cooling tower, you may have cooling tower sump level control issues with varying re-circulation rate. The liquid hold up in the cooling tower inlet distributor may vary with flow rate. This is only an issue when the variation is extreme enough to cause cooling tower overflow and loss of treatment chemicals.

These are the main reasons why Option 1 is the best choice. If you can't get good enough control with Option 1, then do a combination of Option 1 and Option 2 as suggested above.

Two way valves may be suitable in Option 1 depending on ambient conditions and cooling tower inlet distributor design as discussed above. When using two way valves, you are essentially doing Option 1 and 3 together.

Extreme cooling tower sump level variation can also lead to cooling tower pump cavitation.