Geoff White
Member
Hello All,
I have been PLC programming for a long time but I am doing my first process control project and it's a doozy. I have been reading up on the PID control thing for some time and I thought I would start trying to get some advice on control strategy and implementation.
I am working on a distillation water treatment plant. It heats up brine using steam and then uses a compressor to recover the latent heat and a heat exchanger to recover the sensible heat from the distillate back into the feed water.
The condensate collects in a tank. The tank level is controlled using a level controller which should produce a flow equal to the amount of condensate being produced.
The first problem I have is to control the level of brine in the "kettle". The kettle has a large volume compared to the flow in and out of it. Because of the heat exchanger, the flow into the kettle needs to be closely matched to the flow exiting in order to maximise the heat recovery.
Because of this I was proposing to control the flow of brine into the system using the measured flow of condensate leaving the system and try an modulate this based on level.
I have flow meters on the inlets and outlets as well a pressure transducers for level measurement. Fine control of the level is not needed but should help with balancing the flows as there is a need to remove some of the concentrated brine to stop the concentration from climbing too high with time.
So I now have a measured flow of distillate leaving the system. (Based on Level control of condensate tank)
A calculated flow for brine entering the system based on distillate flow.
A PID loop for controlling the flow into the system using the calculated value above as its setpoint.
How do I implement level control of the kettle (PID?) on top of the mass balance system in such a way that they don't fight each other?
Do I need to under drive calculated feed flow so that error in the level controller is able to lower the level?
I am using compactlogix PLC if that helps.
TIA
I have been PLC programming for a long time but I am doing my first process control project and it's a doozy. I have been reading up on the PID control thing for some time and I thought I would start trying to get some advice on control strategy and implementation.
I am working on a distillation water treatment plant. It heats up brine using steam and then uses a compressor to recover the latent heat and a heat exchanger to recover the sensible heat from the distillate back into the feed water.
The condensate collects in a tank. The tank level is controlled using a level controller which should produce a flow equal to the amount of condensate being produced.
The first problem I have is to control the level of brine in the "kettle". The kettle has a large volume compared to the flow in and out of it. Because of the heat exchanger, the flow into the kettle needs to be closely matched to the flow exiting in order to maximise the heat recovery.
Because of this I was proposing to control the flow of brine into the system using the measured flow of condensate leaving the system and try an modulate this based on level.
I have flow meters on the inlets and outlets as well a pressure transducers for level measurement. Fine control of the level is not needed but should help with balancing the flows as there is a need to remove some of the concentrated brine to stop the concentration from climbing too high with time.
So I now have a measured flow of distillate leaving the system. (Based on Level control of condensate tank)
A calculated flow for brine entering the system based on distillate flow.
A PID loop for controlling the flow into the system using the calculated value above as its setpoint.
How do I implement level control of the kettle (PID?) on top of the mass balance system in such a way that they don't fight each other?
Do I need to under drive calculated feed flow so that error in the level controller is able to lower the level?
I am using compactlogix PLC if that helps.
TIA