multi effect evaporator control strategy
multi effect evaporator control strategy
(OP)
Dear all,
PS. Brix = sugar concentration
In our tomato paste plant we have a huge triple effect evaporator unit in order to concentrate tomato juice to thick tomato paste (=evaporate the water out of the juice).
The current control works through controlling input Brix changes to a fixed Brix at the outlet by changing the main product flow rate. Altough it works quite well, a disantage is that you change the main flow all the time. Changing the evaporator steam pressure in order to compensate for input Brix variations is to slow for fast fluctuations.
Does anybody have experience with this?
Better control strategies? Feedforward, etc. etc.?
Good evaporator control schematics examles?
Thanks for sharing knowledge!
PS. Brix = sugar concentration
In our tomato paste plant we have a huge triple effect evaporator unit in order to concentrate tomato juice to thick tomato paste (=evaporate the water out of the juice).
The current control works through controlling input Brix changes to a fixed Brix at the outlet by changing the main product flow rate. Altough it works quite well, a disantage is that you change the main flow all the time. Changing the evaporator steam pressure in order to compensate for input Brix variations is to slow for fast fluctuations.
Does anybody have experience with this?
Better control strategies? Feedforward, etc. etc.?
Good evaporator control schematics examles?
Thanks for sharing knowledge!





RE: multi effect evaporator control strategy
RE: multi effect evaporator control strategy
I think a have the idea. So you want to do rough adjustment through a sort of feedforward based on the incoming flow and composition of it. This feedforward should adjust the setpoint of the fine-tuning feedbackloop which controls the outgoing flow more precisely.
Did I understand you correctly?
Well thanks, good idea, any comments ?
RE: multi effect evaporator control strategy
Your steam controls sound fine, but your evaportator level controls need to be configured to allow for inlet flow surges instead of setpoint control.
RE: multi effect evaporator control strategy
Dynamic feedforward. With this ratio setpoint system, however the product is initially more concentrated when the product in-feed rate is increased. This happens because the ratio system increases steam before the increase in-feed works through the evaporator. A dynamic compensation times the increase in steam rate to nearly coincide with the response to the in-feed increase. With no dynamic compensation, the steam is changed as soon as the feed is changed, and could result in an upset that is actually worse than obtain form an ordinary feedback system.
At this moment I making a dynamic model in Simulink to investigate the proposed control strategy in more detail.
ThX,
MVD
RE: multi effect evaporator control strategy
At a minimum you would need:
steam flow controller,
steam pressure controller,
outlet consistency/solids controller
flow rate into evaps
consistency/solids into evaps
consistency/solids out of evaps
steam flow
steam pressure
The steam flow setpoint is determined by the calculated amount of water to evaporate from the product based on the inlet flow and consistency/solids. This setpoint can adjusted (fine tuned) by the output of the outlet consistency/solids controller. The output of the steam flow controller controls the setpoint to the steam pressure controller which currently exists.
This is only a suggested control strategy and I personally have never seen it work on tomato juice.