• Sugar production control

• A case study for large scale industrial control

• outline

• 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

• 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

• Exercise

• Design a control system for the evaporation process.

• You can use the described hierachic structure and elements from the fist mm

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