Improved annealing furnace control for fuel efficiency and cycle time reduction

Annealing heat treatment cycle times are often based on operator visual assessments of when the furnace load is up to operating temperature. Operator load-to-furnace color matching for annealing furnace control introduces process variation, long heat treatment cycle times, and excessive energy consumption. Improved control strategies for determining furnace load temperature can potentially yield more consistent products, increase productivity, and conserve energy. A project is currently underway to develop such a robust strategy appropriate for large natural gas fired annealing furnaces. Enhanced monitoring with advanced load and furnace sensors, such as infrared thermometers and gas flow meters has been evaluated. Using these sensor outputs, an annealing cycle control strategy has been developed that automatically adjusts for furnace dynamics and furnace loading. The developed control strategy proceeds by numerically evaluating analytical equations of transient one -dimensional heat diffusion and is capable of accurately determining center temperatures based on measured surface temperatures via an infrared thermometer. By directly measuring load surface temperature, the rate of change in temperature at the center of the cylindrical load can be quantified without prior knowledge of specific furnace characteristics.