Research On Related Basic Problems Of Production Planning And Scheduling In Steelmaking Process

Production planning and scheduling is a base for production operation control of steelmaking process, which is the critical process in the iron and steel manufacture process. A reasonable plan and schedule can reduce production cost on materials and energy, increase revenues, guarantee quality stability, and promote the core competence of the company directly. Hence, an important topic which attracts a wide spread attention from steel enterprises and needs to be solved eagerly has sprung up, so as to improve and utilize the production planning and scheduling functions of Manufacturing Execution System(MES) by means of the intensive studies on the casting start time decision, improving production stability and efficiency and other problems related to the production planning and scheduling in steelmaking process. Finally, the traditional control pattern based on artificial experience will be displaced by the optimized production operation control based on informatization.Steelmaking process is a complex system with multi objectives, multi constraints and dynamic characteristics, which consists of multi-stage high-temperature production cells and multi procedures both with continuity and discreteness. It is difficult to build a uniform and effective model for production planning and scheduling due to the various characteristics of production process in different steel plants, and there is a huge gap between the existing simplified models or algorithms and the realistic requirements of steel plants. According to a investigation on the researches for production planning and scheduling in steelmaking process and the application situation of MES in steel plants, existing researches on the casting start time decision problem, the continuous cast decision problem and the integrated decision problem of charge batching and casting start time are lacking in simulation methods which can reflect the production stability dynamically, and the production planning and scheduling functions of MES in steel plants can adapt to the production management requirements hardly, which hinders the realization of the well-organized, stable and efficient productionobjectives. Therefore, the Ph D thesis “Research on basic problems of production planning and scheduling in steelmaking process” is proposed, which mainly foucus on the modeling, solving and optimized analysis for the casting start time and continuous cast decision problems, the multi-objective optimization of the charge batching and casting start time decision problems, and the optimization method based on simulation for production operation. These works create a suitable environment for the application of existing research achievements, and they also provide a new analysis method based on simulation for the planners in steel plants.The main innovations and conclusions are summarized as follows:1) A mixed integer linear programming model is established and solved by YALMIP optimizer based on MATLAB. In order to reduce production cost by stable production control, a mixed integer linear programming model of casting decision is built for the continuous cast and casting start time decision problem with the goal of minimizing the cost of metal iron overstocked and maximizingthe continuous degree of continuous casting. The factors including the steel material balance, such as the hot metal amount from blast furnace, the safe amount of hot metal on production line(the safe amount of metal on production line), the loss of hot metal and the weight of casting steel, as well as the constraints of time and the amount of hot metal on production line(the amount of metal on production line), are considered in the model. Besides, the corresponding algorithm is developed to solve the model.2) A multi-objective optimization model is built for the integrated decision of charge batching and casting start time decision on continuous caster, and a solving algorithm based on the non-dominated sorting genetic algorithm-II(NSGA-II) is designed. The multi-objective optimization model is developed for the integrated decision making of charge selection and sequencing in the batch plan as well as the casting start time for continuous caster. The objectives are set to minimize(1) the penalty of implementation of the production batch plan in steel plans,(2) the amount of metal stocked in the production line, and(3) the non-effective usage amount of high quality hot metal. An improved solving multi-objective evolutionary algorithm is derived based on the non-dominated sorting genetic algorithm-II(NSGA-II). The chromosome is represented with the serial number of all the charges in the charge batching pool to decrease the invalid searching space of solution. In addition, to reduce the computational complexity, the computation order of elitist solution in classical NSGA-II is modified and the crowding distance calculation times for individuals are restricted. Finally, a fuzzy selection method is employed to choose the final solution among the Pareto solutions.3) A system dynamic model for the control of metal stocked in the production line is built, and a simulated analysis based on actual production data is carried out to reflect the stability of actual production dynamically. According to the systematic engineering method, by setting the metal stocked in the production line as the level variable, the model is established based on the consideration of the requirements of production plan, the target inventory level of metal stocked in the production line, the actual inventory level, the stock deviation and other aspects.4) The application results of the optimization model tested on a steel plant show that:(1)the optimization model for casting start time decision of continuous caster can be used for the scientific calculation of the casting start times, which is beneficial to stabilize the production conditions between the successional working groups, reduce the amount of hot metal/ molten steel stored in the production process and make a feasible schedule;(2) A model for multi-objective decision integrated charge batching and casting start time on continuous casters benefits to the stable control for the charge’s casting cycle on continuous casters and practical implementation plan management of steel manufacturing process, the modified non-dominated sorting genetic algorithm-II is better than the classical NSGAII and the strength pareto evolutionary algorithm-II(SPEA-II). Research on system dynamic model simulation show that:(1)operating condition of steelmaking--continuous casting undering production plan is more stable than hot metal pretreatment station undering non- production plan. Therefore, steel plant shoud implement production plan operation controling in the whole production process;(2)whenthe casting speed of continuous caster is improved because of quickening production rhythm, the amount of metal in the production line should be improved at the same time. Otherwise, the less amount of metal in the production line will result in a unstable production.5) For further testing the practicability of the established model for multi-objective decision casting start time on continuous casters and the system dynamic model, a union simulation research was conducted. By using the former decision result as the latter input parameter, a series of simulation experiments are conducted for analyzing the influence relation between the factors, including the casting start times of continuous casters, high grade steel ratio, the number of continuous casters, etc, and the stock amount of hot metal in the production line. The results of simulation research show that: when the rhythm of hot metal supply is constant,(1) puting off casting start times of continuous casters or increasing high grade steel ratio will improve stock amount of hot metal in the production line;(2) increasing amount of continuous casters will reduce stock amount of hot metal in the each production area of steel plants;(3) when the rhythm of hot metal supply is nonconstant, stable hot metal supply will be more favorable to stability control of stock amount of hot metal in the production line than random hot metal supply.In conclusion, in this paper, the established models, inculding a model for casting start time decision of continuous caster in steel plant and a model for multi-objective decision integrated charge batching and casting start time on continuous casters, provide a new technical means for scientifically determining the casting start times of continuous casters and charge batching, and a new scientific decision method for the assumption problem of production planning and scheduling; the system dynamic model for the control of hot metal’s amount in the production and the union simulation research of a model for multi-objective decision casting start time on continuous casters and system dynamic model provide a new method for deeply recognizing the dynamic evolution of hot metal amount in the production, and also provide a effective simulation analysis method for stability production control in steel plants.