Research On Simulation Models And Control Guidance Expert System Of Grate-Kiln Process For Iron Ore Oxide Pellet Production

In order to meet the burden structure requirement of large-scale blast furnace, iron ore oxide pellet with high grade, good reducibility, homogeneous particle size, stable composition and favorable metallurgical performance is becoming popular. The output of pellet has been keeping rising since the turn of this century. As the dominant process in China, the characteristics of large-scale equipments, continuous process, severe environment and close system make grate-kiln process hard for parameter detection and difficult to control. The accuracy and normalization of grate-kiln process control need to be improved. Therefore, research on simulation models and control guidance expert system of grate-kiln process was carried out and software was developed to make the production process transparent and realize real time control guidance.Mathematical models were developed based on heat transfer theory, fluid mechanics, reaction thermodynamics and kinetics. Models of temperature distribution were developed to obtain pellet temperature at any point of grate, along axial direction of kiln and running direction of cooler during pellet production. Model of moisture distribution in drying section was developed to detect pellet moisture and water evaporation rate at any point of pellet bed, and monitor emergence and migration of over-wet zone as well as the drying results. Model of oxidation degree distribution in preheating section was developed for online detection of oxidation degree of magnetite and FeO content of preheated pellet at any point of pellet bed. These models were validated with detected gas temperature. The accuracies of grate model and kiln model were90.25%and92.25%, respectively.Mass balance model, gas flow balance model and heat balance model of grate-kiln-cooler process were developed under the law of conservation of mass and energy. With the combination of instrumental detection and model calculation, on-line estimation of heat distribution and utilization level can be implemented. To solve the control difficulties caused by initiative change of raw material structure or daily output plan, a balance based method for production status prediction was put forward. And supplementary measures can be provided by expert system for production stabilization and optimization.Expert system for grate-kiln process control was developed for real time production control guidance, using the summary of decades of operational experience and fundamental principles of pelletizing. The "roasting temperature of pellet in kiln&gas temperature in gas hood of preheating section" dominated control strategy was put forward for grate-kiln process, while "pellet temperature at discharging end of cooler" was chosen to be control core for cooler process. More over, rules were established to detect the location of air leakage anomalies in grate. A multistage reasoning strategy was put forward based on the reasoning process of "estimation of parameter status-reason analysis-adjustment measure selection".Software was developed with Visual C++. It is stable, user-friendly, and easy operated. This system was put into practice in a domestic pellet plant. The application results show that the stability rate of production is increased from91.0%to94.2%. Quality indexes of pellet product are improved, for FeO content of finished pellet is0.05%lower, compressive strength is86N/P higher, tumbler strength is increased by0.09%, abrasion resistance index and screening index are0.1%and1.04%lower respectively, while first grade rate of pellet is increased by2.54%. The total economic benefit is about7.5million RMB per year.