The development, verification, and application of a steady-state thermal model for the pusher-type reheat furnace

Abstract

This article outlines the development of a steady-state thermal model for the pusher-type steel reheating furnace. Problems commonly encountered with this furnace type are skidmark generation, scale formation, and high energy consumption. The objective of the work is to provide a means by which furnace users might assess the effectiveness of changes to current operating practice, proposed furnace modifications, or new furnace designs in controlling these difficulties. Since a requirement imposed on the model is to operate on current PC hardware, the assumptions and modeling procedures necessary to achieve this goal are discussed. The operation of the model, which develops the thermal history of an individual slab or billet as it passes through the furnace, is presented, and each of the three modules that comprise the model is described. Initial verification of the model has been carried out using data obtained in a separate campaign of plant trials on several 32-m furnace reheating slabs, and model predictions for steel temperatures at six locations within the steel are shown to be in good agreement with the experimental results. The model is used to examine the influence of two skid designs and several placement strategies on skidmark severity and energy losses to the skid system. Although skidmark severity at the intermediate stages of heating is shown to be dependent on both the skid type and the location of any offsets, it is demonstrated that the skidmark present in the discharged steel is determined primarily by the skid type employed over the final section of the furnace. The inclusion of a hearth in the furnace soak zone was found to impose the least severe skidmark on the product, reducing the temperature variation over the bottom face from the level of 130 °C incurred by the best of the soak zone skid configurations examined, to the level of ~85 °C. The results suggest that, in the absence of a hearth section, the use of a well-insulated, cold-rider skid system over the majority of the furnace length, followed by a single offset of all skids occurring at the transition to a short section of hot-rider skids near the furnace discharge, is sufficient to suppress the final skidmark to a level very close to the minimum achievable with that particular skid design. When assessed on the basis of minimizing both the final skidmark and the energy loss to the skid system, this configuration was found to be the best of the skid layouts examined.