CONTROL OF AN INDUSTRIAL LIME KILN OPERATING CLOSE TO MAXIMUM CAPACITY

Two control strategies have been compared for an industrial lime kiln operating close to maximum capacity. Transfer functions between process inputs (fuel flow rate, air flow rate, and lime mud flow rate) and process outputs (oxygen excess, cold-end gas temperature, and hot-end solids temperature) have been used to present the dynamics of the industrial kiln. Control Strategy 1 manipulates the fuel flow rate to control the cold-end gas temperature and the combustion airflow rate to control the hot-end bed temperature. Control Strategy 2 uses the combustion airflow rate to control the cold-end gas temperature and the fuel flow rate to control the hot-end bed temperature. Both strategies use feedback proportional integral (PI) controllers, decouplers, and feedforward loops. Simulations show that Strategy 1 would maintain better product quality than Strategy 2 in the event of periodic fuel actuator saturation resulting from increased production requirements.