Mathematical Modeling and Computer Control of Lime Kilns

Lime kilns are used as part of the chemical and energy recovery cycle in the pulp and paper industries. The control strategy is sensor based and uses in addition to the usual sensors, a single sided infrared mud moisture sensor and a CO and CO2 flue gas analyzer for optimizing the kiln temperature profile, maximizing throughput, regulating the product quality and conforming to environmental regulations. A steady-state mathematical process model is also used to estimate the peak refractory temperature and predict the residual carbonate in the product. Control action is taken to prevent the peak refractory temperature from exceeding a preset limit, and to maintain the desired residual carbonate. The paper also discusses the simulation results from the mathematical model.