Modelling and control of a co-current sugar dryer.
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Date
2001
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Abstract
The drying of sugar is the last step in the recovery of solid sugar from sugar-cane. To ensure
that the sugar can be transported and stored, the final moisture content leaving the sugar mill
must be carefully controlled.
Data spanning periods of normal plant operation were collected at the Tongaat-Hulett Ltd
Darnall sugar mill. These measurements were reconciled to achieve instantaneous mass and
energy balances across the sugar dryer.
Using these measurements, a general model has been developed to simulate the sugar drying. It
includes ten compartments through which the sugar and drying air flow, with a mass and energy
balance in each compartment. It was assumed that a "film" around the sugar crystal is
supersaturated, and that crystallisation is still occurring. A sorption isotherm determining the
equilibrium moisture content of the sugar, at which point mass transfer ceases, was included.
The model has been matched to process measurements by adjusting the heat and mass transfer
coefficients.
A Dynamic Matrix Controller was developed and tested off-line on the model, using the
reconciled measurement sequences. The controller manipulated the inlet air temperature in order
to control the exit sugar moisture content. The model predictive control format successfully
dealt with the large process dead-time (5 minutes).
Description
Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.
Keywords
Sugar--Analysis., Sugar--Manufacture and refining--Mathematical models., Drying., Sugar--Manufacture and refining--Equipment and supplies., Process control., Theses--Chemical engineering.