Modelling and Control of a Water-Cooled Duct and Cooling System

Abstract: In this thesis a water cooled duct and the surrounding cooling system, used for cooling hot off-gas from an electric arch furnace, is modelled for simulation. The model is then used to devise control strategies to keep the cooling water temperature at a given temperature to then be able to supply power to the district heating. The model consists of the heat transfer between the off-gas, steel of the water cooled duct and the cooling water, the transport delays of the water and a heat-exchanger used for cooling the water. The control problem is non-trivial as there are long time-delays and non-linear behavior, combined with large load disturbances caused by variations in off-gas temperature. Different control strategies of increasing complexity and performance are presented. The results show that a simple PID-controller is not enough and different feed-forward signals, which account for how the system behaves, are also needed. Using these additions the simulated system is controlled to a satisfactory degree.