Sugar production control

1. Sugar production control A case study for large scale industrial control

2. 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

3. 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

4. Sugar production Cleaning and slicing diffusion filtering Steam flow evaporation Heating steam from power plant crystallisation molasse separation sugar

5. extraction filtration evaporation 3 * crystallization In-house power plant Curved lines condensate flow Straith lines heating steam flow Block arrows sugar flow

6. 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

8. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. Goal hierarchy for the evaporation process Production flow security Cheap and high quality High, stable brix Adequate steam Pressure for crystallization Minimization of energy consumption High juice flow Roboustness to flow variations Stage 4- 5 control Stage 1 – 3 control Heating steam contro Turbo compressor control

17. Exercise • Design a control system for the evaporation process. • You can use the described hierachic structure and elements from the fist mm