Models for predictive thermal control in steel heat treatment using the continuous HD galvanizing units

The paper considers problems in developing models for the predictive thermal processes control in the multi-zone heating furnaces at a steel strip heat treatment using the continuous hot-dip (HD) galvanizing units. Complexity in developing such models is due to three reasons. First is the object significant inertia making it difficult to analyze the zone thermal balances under unknown disturbances caused by variability of the heat loss and interzone heat transfer parameters. The second reason is the lack of objective information on heat exchange between the metal and the furnace working space in separate zones, since metal temperature is usually controlled only at the inlet and outlet of the heat treatment sections. The third reason is that results of measuring the working space zone temperature only approximately characterize its actual temperature state. Taking into account these reasons, the paper proposes two types of models for the thermal processes predictive control. Models of the first type are introduced to estimate the working space zone temperature based on data obtained before the technological disturbance, as well as to predict the strip temperature. Models of the second type are designed to predict estimates of the working space zone temperature when changing assortment, line speed, fuel and air consumption. Models of the second type are operating with signals presented in the form of increments relative to the initial moment of the time period under consideration. The models are designed to solve problems such as robust control; timely account of technological limitations associated with the heating and cooling systems; transient processes planning and predictive control to save energy by reducing the metal overheating; heat loads optimization by the heat treatment section zones based on the heat loss observer. A system of robust temperature control in the working space zones is proposed. It is based on the system structure with multiple degrees of freedom, where the direct open-loop control using the model is combined with the deviation control. Methods for using the model to optimize the heat loads distribution across the furnace zones were considered. As an example, results are provided of setting up the model for the thermal holding section of the continuous hot-dip galvanizing unit No. 1 at the PJSC MMC. Based on the set-up results, variation limits in the control object dynamic parameters are demonstrated.

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