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• Desciption of the sugar plant• Description of the evaporation process• Control problems in the evaporation
process
Exercise
Make a contol concept for the evaporation process
Sugar production
• Extraction of sugar from sugar beets• Filtration of sugar juice• Concentration of the sugar juice through a
multiple-effect evaporator’• Crystallization through boiling and graining• Separation of sugar crystals and molasses
by centrifugation
Cleaning and slicing
diffusion
filtering
evaporation
crystallisation
separation
Heating steam from power plant
Steam flow
sugar
molasse
Sugar production
extraction filtration evaporation
In-house power plant
3 * crystallization
Curved lines condensate flow
Straith lines heating steam flow
Block arrows sugar flow
The evaporation process
• Energy consumption• Juice flow in 133 kg/sec• Juice flow out 28 kg/sec• Juice brix in 15.5• Juice brix out 72
Control problems in the evaporation process
• The output brix of the syrup must be high as the cheapest evaporation is carried out in the evaporation process
• To avoid spontanous crystallization in the pipes the output brix must be stable
• A adequate steam pressure for the crystallization process must be secured
• There must be a minimization of the energy consumption
• The plant must be robust to flow variations
Control characteristics in sugar production
• Sugar production is a combination of continous and batch process
• The sub-systems are strongly coupled by the flow of sugar juice and the flow of heating energy.
• In each sub-system there are several inputs, outputs and disturbances
Control characteristics in sugar production
• A large number of parameters and variables correlates to some extent determining the dynamics of the plant
• The correlation of parametersand variables makes it difficult to survey the important links in the process
• It can be difficult to distinguish inputs, outputs and disturbances according to the control strategy
Demands for the control system development concept
• it must be able to handle MIMO systems• It may rely on a hierarchic decomposition ot the
control goals• The modelling method must be able to describe
the functionality of the plant• It must be possibel to identify relevant control
loops without deveolpment of an entire matematical model
• It must be possibel to connect the goal description and the functional description
Modelling for control system design
• Modelling by a mathematical description of the static and dynamic relations according to system apparatus
• Modelling by a functional description of the plant
Hierarchic goal oriented functional description
• The goals due to plant functionallity, production rate, safety aspects and economy must be identified
• The goals must be arranged hierarchic due to the internal supporting relations
• the plant functionality must be described due to the flow of material, energy and information
• The low level goals in the hierarchy must be related to plant functionallity
Idiomatic control
• The basic idea is to setarate the system into a number of independent subsystems each controllable using well suited method
• Basic idioms are:• Feedback, feedforward, ratio control,
cascades, decoupling etc
Production flowsecurity
Cheap and high quality
High juiceflow
Minimization ofenergy
consumption
Adequate steamPressure for
crystallizationHigh, stable brix
Turbo compressorcontrol
Heating steamcontro
Stage 1 – 3control
Stage 4- 5control
Roboustness toflow variations
Goal hierarchy for the evaporation process