On The Production Planning And Scheduling Optimization For Integrated Steel Production

Iron & steel industry provides raw materials for other industries and plays an essential role in the industrial economy.Since 1980s,steelmaking-continuous casting-hot rolling integrated production and continuous casting slab hot charging technology have been studied and applied by overseas large iron and steel plant to save energy resources and reduce wastage.In steelmaking-continuous casting-hot rolling integrated production,production technology is complex and the logistics management between continuous casting and hot rolling is difficult.The integrated planning and scheduling problem between steelmaking, continuous casting and hot rolling is the key of the integrated steel production management.In this dissertation,the characters of the steel production are analyzed and the sate of art of integrated production planning and scheduling is also reviewed.Taking a national steel plate integrated steel production line as study background and aiming at increasing hot charging ratio,four special planning and scheduling problems about integrated steel production order planning,batch planning and scheduling are solved.The four problems are the production order planning problem of integrated steel production,the plate hot rolling scheduling problem,the slab hot charging scheduling problem and the continuous casting-hot rolling integrated optimization planning problem.For the production order planning problem of integrated steel production,a multi-objective optimization model is formulated,where steelmaking and hot rolling are regarded as the key steps.The objectives are to maximize the hot charging proportion of slabs and minimize the early/delayed delivery time and the slabs which are surplus to the requirements for hot/rolling.The main constraints including steelmaking and hot rolling capacities,steel grade and slab and product dimensions are all taken into consideration in the model.Single objective and multi-objective optimization method are used to solve the model. The multi-objective model is transformed into the single objective model by using a weighting method and is solved by a two-level chromosomes genetic algorithm.Computation results of different order planning problems show the rationality of the model and validity of the algorithm.An improved NSGA-â…¡(Non-dominated Sorting Genetic Algorithm) algorithm is designed to solve the multi-objective model.The NSGA-â…¡algorithm is improved by mutating the superposition individuals in the objective space and adding some new individuals on every generation so that the population diversity is improved significantly. Computation results of different standard multi-objective mathematic test problems, multi-objective knapsack problems and production order planning problems show the improved NSGA-â…¡algorithm is able to find solution set with higher coverage than NSGA-â…¡.For the plate hot rolling scheduling problem,with the objective to increase the mill utilization,two types of scheduling problems of different composite multi-plate rolling processes are researched.One is the same dimension composite multi-plate rolling process. The other is different dimension composite multi-plate rolling process.On the first simple problem,three modes of the process are classified,i.e.,equal-interval alternating, symmetric-interval alternating and grouped alternating.Thus the characteristics and feasible conditions for each of the three modes are described with the formulae of optimum time interval for starting rolling operation and mill utilization both given.Taking account of the restriction of mill table length,the parameters relevant to the formulae are adjusted properly to provide a heuristic method.The computation results showed that the proposed heuristic method is better than existing heuristic method with wider applications available.On the second complex problem,it is a typical single-machine scheduling problem subjecting to multiple constraints including precedence constraints and limited waiting time and finite buffer capacity.Describing the plate hot rolling scheduling problem with an AON (Activity-On-Node) network,an equilibrium principle is formulated for single-machine scheduling problems on the AON networks.Subsequently,a nonlinear constrained optimization model is built for plate hot rolling scheduling problems.A neighborhood search algorithm is proposed to convert the nonlinear model into a linear programming model that can be solved by standard software.Numerical computations indicate that the neighborhood search algorithm may find out better production schedules than the heuristic methods.For the slab hot charging scheduling problem,it is difficult to solve it based on mathematical programming methods.It is complex problem to compute every slab's charging/outcharging order/time and hot charging mode.A logistics simulation system to make slab heating furnace hot charging planning and slab-yard charging/out charging planning is developed.For the continuous casting-hot rolling integrated optimization planning problem,a multi-objective optimization model is formulated.Minimizing the casting-rolling order diversity is the main objective.The constraints include continuous casting constraints and hot rolling constraints.NSGA-â…¡algorithm based on neighborhood is proposed to solve the problem.Simulation results show that the proposed integrated optimization method is feasible and hot charging ratio is increased. Based on the upwards works,integrated production planning and scheduling system and slab hot charging logistics simulation system are developed which validated the models and algorithms proposed in the dissertation.