Lime kiln hybrid control system

This paper describes the successful application of a hybrid hierarchical control system to perform the real time control of lime kilns. Calcination of limestone occurring in the kilns is a process exhibiting long time delays, nonlinearities and interrelationships between variables, which challenges the most experienced operator and exposes the weakness and limitations of classical control systems. The new hybrid control system uses predictive-adaptive controllers to keep the main variables close to the set points and reject disturbances. Rule-based expert systems are used to improve production and optimize fuel efficiency. The different steps in the design are reviewed and explained with special emphasis on the expert system. Programmable logic controllers, man machine interfaces and computer networks complete the control system. The results after a year of operation are presented as well as the limitations, successes and projections to the future