PID control - long residence time 1

[Extasis]

Hi there,

I am trying to control a mass flowmeter to input Chemical A into a series of reactors, each with a residence time of 30 mins. I need to dope enough of Chemical A to remove environmentally harmful Chemical B from the reactors (need <1ppm). My analysis sampling point for Chemical B is after Reactor 2, so total residence time is 1 hr (after 2 reactors x 30 mins each).

I am using a PID controller to control the flow of Chemical A into Reactor 1 based on the ppm level of Chemical B out of Reactor 2. It takes approximately 10 mins. to get a ppm reading of Chemical B fed back to the control system.

The problem is that if I change the flow of Chemical A, I do not see the effect of this change for at least 1 hr.

My knowledge of controllers is very limited; I appreciate that this problem may be very basic and so I appreciate any help/ideas I can get!

Thanks in advance!

 

[cawse001]

Suggest you might get a better response by re-posting on the Measurement and Control Instrumentation Forum.

For mine, it looks like you should have a combination of feed forward control,based on analysis of component B fed into the reactor and the existing feed back arrangement.

Cheers,

Nigel