Research On Rescheduling Software System Of Steel-making And Continuous Casting Production

Modern steel-making and continuous casting production is usually composed of multiple converters,refining furnaces,tundishes,continuous casting machines and steel ladles.The molten steel is firstly poured into a transfer ladle after being processed on the converter.The molten steel in the same converter is called a charge.After that,the charge of molten steel is transported by a crane to a refining furnace.The molten steel undergoes various refining processes at the refining stage.Finally,the molten steel is transported by a crane to a caster.A set of charges incessantly drained into a tundish of a continuous caster and solidifies in a crystallizer is called a cast.The static scheduling of steel-making and continuous casting production takes the production process routes and the processing time of charges as fixed constants.The production objectives are three aspects:i)each cast should start on time on the caster;ii)a set of charges within the same cast should be casted consecutively on the same caster;and iii)the processing of adjacent charges should not conflict on the same machine.It decides the processing machines for charges at the steel-making stage and the refining stage.The starting time and the completion time of charges should also be obtained for converters,refining furnaces,and continuous casters.In steel-making and continuous casting production processes,the starting time delay happens frequently,which may lead to casting break or processing conflict so that the static scheduling plan becomes unrealizable.The rescheduling of steel-making and continuous casting production aims at continuously casting many charges with the same cast and avoiding conflicts of adjacent charges on the same machine.It decides the slelected processing machines,the starting time and the completion time for not started charges at the steel-making stage and the refining stage.The completion time also should be decided for being processed charges.The rescheduling optimization of steel-making and continuous casting production aims at minimizing the waiting time of all charges.Constraints include continuously casting many charges within the same cast and not processing conflict of adjacent charges on the same machine.So it leads to hundreds of conflicting constraint equations.It is difficult to satisfy above hundreds of conflicting constraint equations simultaneously by the optimization algorithms that adopt mathematical programming or evolutionary computation.Therefore,it can only rely on experienced scheduling practitioners to make rescheduling plan.However,the manual rescheduling scheme not only has less decision charges and long preparation time,but also has a long waiting time and low rescheduling efficiency.This dissertation is motivated by the steel-making and continuous casting line of a large iron and steel group in Shanghai.The rescheduling software system of steel-making and continuous casting production is studied to address the starting time delay problem of multiple converters,refining furnaces,continuous casting machines and refining modes.The major contributions of the work are summarized as follows:1.Rescheduling optimization model of the steel-making and continuous casting production is built,which aims at minimizing the waiting time of all charges.Its constraint conditions are that continuously casting many charges within the same cast and not processing conflict of adjacent charges on the same machine,etc.The decision variables include the completion time of processing charges,the processing machines,the starting time and the completion time of not started charges.The rescheduling strategy of steel-making and continuous casting production is proposed by interval processing time of charges and scheduling experts' experience.The rescheduling strategy consists of five parts:processing conflict and casting break identification,rescheduling charges decision,charges processing machines decision,the starting time and the completion time decision of charges on machines,and the human-computer interaction adjustment algorithm of the processing machines,the starting time and the completion time based on Gantt chart and linear programming.2.The rescheduling algorithm of steel-making and continuous casting production is designed based on the combination of the heuristic method,linear programming,directed graph and Gantt chart.The algorithm consists of five sub-algorithms listed as follows:(1)Directed graph-based conflict and casting break identification algorithm.It consists of the adjacency matrix based on directed graph representing processing machines,processing order and their relationship,the starting time and completion time calculation under starting time delay,the processing conflict and casting break identification formula.(2)Rescheduling charges decision algorithm.It consists of processing state judgement and rescheduling charges selection.The principle of rescheduling charges selection is to select processing charges and not started charges.(3)Heuristic algorithm of charges processing machines decision.The heuristic factor gives priority to the machine with minimum collision value,the machine with minimum transportation time and the machine with minimum charges.The algorithm consists of four parts,i.e.,batch partitioning and sorting,the starting time and the completion time calculation,charges collision value calculation and processing machines decision.(4)The starting time and the completion time decision algorithm of charges on machines based on the heuristic method and linear programming.It includes a heuristic algorithm of optimizing starting time and the completion time pre-decision and linear programming for adjusting starting time and completion time.The pre-decision algorithm consists of charges collision value calculation,conflict elimination,casting break time calculation and casting break elimination.The adjustment algorithm aims at minimizing the waiting time of all charges.The constraint conditions are interval processing time of charges,etc.Simplex algorithm is used to solve the starting adjustment time and the completion adjustment time.(5)The human-computer interaction adjustment algorithm of the processing machines,the starting time and the completion time based on Gantt chart and linear programming.It consists of Gantt chart-based rescheduling visualization and the human-computer interaction adjustment of the processing machines,the starting time and the completion time.A heuristic algorithm is adopted to adjust the processing machines and the linear programming algorithm is adopted to adjust the interval processing time.3.The simulation experiment of the steel-making and continuous casting production rescheduling algorithm is carried out by using practical data.Various charges number,refining number,different refining modes,disturbance and the delay time value are selected to study the rescheduling algorithm performance.A number of different rescheduling sequences and different machines assignment rules in the rescheduling algorithm are simulated.The proposed rescheduling algorithm is compared with the complete rescheduling algorithm.The simulation results demonstrate the effectiveness of the proposed rescheduling algorithm.4.The rescheduling software system of steel-making and continuous casting production is designed and developed based on the rescheduling algorithm proposed in this dissertation.It uses Client/Server(C/S)system architecture,Oracle 10g database,Microsoft Visual C++6.0,Borland Delphi 6.0 and other development tools.The object oriented idea and modular reuse technology are adopted.It consists of realtime data acquisition,charges tracking,charges query,machines assign,the starting time and the completion time adjustment based on the heuristic method,the starting time and the completion time adjustment based on the linear programming,the human-computer interaction adjustment,performance evaluation of rescheduling algorithm,process data management,equipment environment configuration and user management.5.The rescheduling software system of steel-making and continuous casting production is successfully applied to a practical steel-making and continuous casting line of Baosteel company.There are three parallel converters of 250t at the steel-making stage,three kinds of refining machines,three continuous casters and multiple refining modes.The running results show that the rescheduling operation is flexible and convenient,and the rescheduling effect is significantly improved.(1)The average daily waiting time is reduced from 234 minutes to 166 minutes and the average daily load ratio is increased from 50.44%to 55.16%.The charges number increases from average 1980 to average 2040 within 30 days,which greatly improves the production efficiency.(2)The rescheduling time is shortened from 1 minute to less than 10 seconds,which improves the rescheduling efficiency.