Study On Process Control Method For Ferrochrome Refining With Argon-oxygen Decarburization

Argon Oxygen Decarburization(AOD)is the major refining method for stainless steel and a variety of high quality alloys at present,and also one of the main manufacturing methods for high quality alloy steel products.In recent years,with the development of the online-monitoring technology,the smelting furnace has satisfied the condition of real-time monitoring and process adjustment towards the refining process.However,the refining process involves plenty of physicochemical reactions with complex mechanisms,so currently the mainstream control methods still rely on experience,which have severely hindered the process research and performance improvement of AOD furnace refining process.This paper studies on the refining process control of AOD furnace.Main contents and results of this paper are as follows:(1)The dynamic models of decarburization rate,dechroming and temperature variation in the refining process of ferrochrome alloy were studied.The redox reaction law of carbon and chromium and the law of temperature variation in the top-blowing high-carbon,top-blowing low-carbon,and top-bottom double-blowing stages were further analyzed based on the existing refining model.And a dynamic model of the whole refining process was established to provide a method for process simulation and a basis for the research of process control methods.(2)The flow control method of the refining process is studied and the top-bottom lance flow dynamic process is analyzed.It is proposed that the flow control in the refining process is a control problem disturbed by many factors.The linear active disturbance rejection based on known parameter models is applied to the flow control of the refining process,in order to improve the control accuracy and anti-disturbance ability.The transition process arrangement is introduced,and the flow control model of top blowing and bottom blowing is established.The experiments have proved that the control performance and the ability of disturbance resistance of the established controller are far better than those of the traditional PID controller.The controller is insensitive to modeling error and exhibits relatively high robustness.(3)The carbon content of the AOD furnace refining process and temperature control theory are investigated.And a three-loop control structure of flow loop,decarburization loop and temperature loop is proposed.The control strategies of decarburization loop and temperature loop are studied.The temperature control is the outer part in the three-loop structure,and the decarburization rate is determined by the temperature profile.The decarburization loop determines the given value of the flow loop.The flow loop controls the flow to the given value.Oxygen flow distribution principle is proposed based on the volume of the top lance and the bottom lance in top-bottom blowing stage,along with the computation method for argon-oxygen ratio and control strategy for two temperature curves based on carbon content and decarburization rate.A complete refining process control strategy is proposed,in which an active disturbance rejection controller that contains given parameter models is applied.(4)Based on intelligent model prediction control(MPC),the control theory for AOD furnace refining process and its implementation method are proposed.The theories on MPC structure,evaluation function,rolling optimization and feedback emendation are also analyzed,which provide theoretical base for further investigation on process optimization method.(5)Based on the existing AOD furnace control system,the refining process control system is integrated with the original system while clarifying the boundary between them,providing an approach to integrate the refining process control system into the existing AOD furnace control system.On the integrated system,the three-loop control structure and the refining process control strategy technology based on the intelligent model control structure are tested.The feasibility of the two control strategies is verified in the controlled refining of chromite in AOD furnace.