Application of Control Theory to Production Process Stabilisation in Nigerian Cement Industry

Process instability in cement clinker production manifests as kiln temperature fluctuations, inconsistent feed rate delivery, and variable product quality, all of which increase energy consumption and reduce throughput efficiency. This study applies classical and modern control theory to design a stabilising control system for the rotary kiln process at a cement manufacturing plant in Obajana, Kogi State, North Central Nigeria. Transfer function models for the kiln thermal process are derived from step response data collected during controlled test experiments at the plant. A proportional-integral-derivative controller is designed using the Ziegler-Nichols tuning method and subsequently refined through frequency domain analysis to achieve desired gain and phase margin specifications. State-space representation of the multi-variable kiln process, incorporating temperature, feed rate, and fuel flow as state variables, is developed and a Linear Quadratic Regulator is designed to minimise a weighted cost function of state deviations and control effort. Simulation results demonstrate that the LQR achieves 47 percent faster disturbance rejection compared to the PID controller when subjected to feed composition disturbances. Practical implementation considerations including actuator saturation and sensor delay effects are discussed and accommodated in the controller design. Keywords: control theory, PID controller, LQR, cement manufacturing, kiln stabilisation.