Model based optimisation of continuous annealing operation for bundle of packed rods

Abstract

A typical industrial thermal processing operation has multifold complexity, with varying charge dimensions, multiple grades and inconsistent loading patterns as well as the absence of in situ sensors. These operational characteristics and restrictions invariably lead to empirical design for the temperature time cycles, which often results in suboptimal operation in terms of higher energy consumption, inconsistent quality and lower productivity. In the present work, a process model is proposed for designing the heating cycles for bundles of packed rods with different rod diameters, bundle diameters and packing fractions in a continuous annealing furnace. The process model has the capability of predicting spatial and temporal evolution of temperature and hardness in the bundle as it traverses through the furnace. Interestingly, the model based process cycles are found to be counterintuitive as compared with the empirically designed cycles normally employed in the plant. It is shown that instead of designing the process cycles on the basis of rod diameters, which is the general practice in the plant, it should be based on bundle characteristics, such as bundle diameter and packing fraction. These concepts have been implemented in an industrial operation resulting in around 20% energy reduction and 15% productivity enhancement.