Hybrid modelling of a sugar boiling process

TL;DR

This paper develops and compares two models for the nonlinear crystal growth rate in a sugar boiling process, one empirical and one hybrid neural network-based, using industrial data to improve predictive control.

Contribution

It introduces a novel hybrid modeling approach combining neural networks with physical knowledge for better flexibility in sugar crystallization modeling.

Findings

Hybrid model offers greater flexibility than empirical models.

Both models successfully fitted industrial data.

Hybrid approach potentially improves process control accuracy.

Abstract

The first and maybe the most important step in designing a model-based predictive controller is to develop a model that is as accurate as possible and that is valid under a wide range of operating conditions. The sugar boiling process is a strongly nonlinear and nonstationary process. The main process nonlinearities are represented by the crystal growth rate. This paper addresses the development of the crystal growth rate model according to two approaches. The first approach is classical and consists of determining the parameters of the empirical expressions of the growth rate through the use of a nonlinear programming optimization technique. The second is a novel modeling strategy that combines an artificial neural network (ANN) as an approximator of the growth rate with prior knowledge represented by the mass balance of sucrose crystals. The first results show that the first type of model performs local fitting while the second offers a greater flexibility. The two models were developed with industrial data collected from a 60 m3 batch evaporative crystallizer.