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

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

Exercise

• Design a control system for the evaporation process.

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