Real-time simulation model of a billet reheating furnace for rolling mill

Abstract

This paper presents the development of a mathematical computer model to simulate the heating process of billets in a rolling reheating furnace. The proposed method simulates the combustion process, calculating the energy input, output and losses inherent of the process. The computational algorithm of the furnace simulation allows the user to reproduce the combustion process from the reactants flow measurements at the entrance and their respective compositions and, thereafter, it calculates the products composition through a complete combustion model to lean mixing and incomplete combustion, at a chemical equilibrium equation for rich mixtures. The billets temperature is calculated by determining the heat transfer coefficient between the furnace
atmosphere and the billets used for this, the forced convection with turbulent flow over an isothermal plate principle. The air energy and the Blast Furnace Gas energy recovered after passing through the heat exchangers is calculated using regression models developed empirically and the yields of such stoves are determined by the NTU effectiveness method (Number of Transfer Units). The loss by cooling water and the outer furnace walls are determined by simplified models, the other losses are calculated using an empirical regression model in which measured data is used in the process. To determine the final objective function, we adopted the Newton- Raphson method for finding roots. The simulation allows to calculate: the instantaneous process thermal balance, the furnace and heat exchangers efficiency, the chemical composition of the mixture of reactants and combustion products, the air excess used in the reaction, the reactants and combustion products temperature after passing through the heat exchangers; the billet temperature after heating and other important variables for process management. The model proved to be an effective tool for a more refined management of the process in real time.