Knowledge-base simulation systems are useful for imitating real-world situations and they provide mechanisms for understanding and organising them in a manageable way. A knowledge-based simulation is described for the monitoring and regulatory control of a juice purification process in cane sugar production. In the paper, the problem description is analysed and a set of requirements are identified. To meet these requirements, a scheme is presented that organises the domain knowledge into suitable structured modules, such as object classes, libraries, rule sets, rules, instance objects etc. A number of user interface facilities are developed to monitor and exercise the application, such as tuning the PID regulators, diagnosis of faults, restoring the normal status etc. Two scenarios are described to explain the remedial operations carried out when a regulator is out of tune or faulty, or when a valve is stuck. The system can be used with the actual process in a sugar factory or with other similar process control applications.