Batch Alkoxylations reaction heat transfer delay question

[hswang2]

Alkoxylations are commonly performed in industry for the production of surfactants and polyglycols by means of a simple semi-batch liquid-stirred reactor
During the EO addition to reactor, pressure will increase due to the EO vapour partial pressure and the compression of the nitrogen present in the Reactor.
Temperature is allowed to increase (TIC-001) in a ramp mode up to the desired reaction set point value. The heat of reaction is then totally removed directly by means of Reactor heat exchanger, using water from the secondary loop. This water is circulated by Recirculation pump. Reaction heat is removed at Reactor heat exchanger.
The reaction between EO and starter occurs in the liquid phase. As soon as the reaction starts and produces heat, Reactor temperature controller automatically closes the steam flow to Water Circulation Heater, and starts the heat removal through the Water Circulation Cooler.
There are three heat exchangers are used. Is there any delay for switching when the heat demand swings fromheating through zero to cooling?

 

[StoneCold]

hswang2.
You have kind of an odd heat exchanger configuration, but I suppose academically it is fine. Obviously what will happen is that the steam heating will slowly taper off and cooling will begin slowly as the temperature continues to rise until you reach the set point. Then depending on tuning you will either be critically damped and not overshoot or there will be some acceptable overshoot for the system. But just like adjusting the water temperature at a faucet the best way to get what you want is a gradual transition from heating to cooling. Does that help at all?

Regards
StoneCold

 

[hswang2]

Dear all
I am not sure the control scheme in the attachment is match the following description I wrote.
TIC-001 and TIC-120 are temp to temp cascade control scheme.

if the reactor temp is increasing, the reactor temp controller increase theset poit of TIC-120 for the cooling water flow, which cause much more cooling water flow into reactor heat exchanger If the TT-120 is increasing, the controller TIC-120 must reduced TV-120B opening, that is,the controller must be reverse acting.

If the liquid inlet temp is below its set point,the controller will increse the opening of the TV-120B.If the TT-120 is increasing, the controller TIC-120 must increase TV-120C opening, that is,the controller must be direct acting. If the liquid intlet temp is above its set pint, this controllerwill increase the TV-120C.a

Please comment if I am wrong

Thank you very much.