Research On The Optimization For Integrated Scrap Steel Charge And Production Scheduling Under Time-of-use Electricity Tariff

China is a country of producing and consuming a large amount of steel.However,the extensive production mode and rapid development of national economy have resulted in excess production capacity of steel industry and overstock of steel products.Therefore,steel industry has put forward the structural adjustment plan to reduce crude steel production but increase the scrap steel production.Meanwhile,in recent years,the issue of global warming has aroused worldwide attention.Various countries have set emission reduction targets to undertake corresponding emission reduction obligations.The objective of emission reduction on the national level should be decomposed into enterprises' production operation layer so that it can be effectively implemented.As a high-energy-consuming and high-emission industry,the steel industry has unshakable duties to explore a green production development path to save energy and reduce emission.Compared with the “long-process” steel-making with iron ores as the main raw materials and the blast furnace and converter as major smelting equipment,the “short-process” steel-making with the scrap steels as the main raw materials and the electric arc furnace as major smelting equipment is a more energy-saving,emission-reducing and environmentally-friendly green production mode that can make good use of scrap steel.Nevertheless,China has been facing with a high electrical load,and the electricity cost has been hovering at a high level.For a long time,the electricity kkkpolicies and cost have been major factors restricting the development of the “short-process” steel-making with electricity as the main energy.Steel-making schedule is a core step for scrap steel to re-materialize its value,and scrap steel charge is a critical link before steel-making.These two processes are mutually influencing and closely connected with each other.In this paper,integrated optimization of scrap steel charge and production scheduling under the time of use electricity tariff is studied,which is of vital academic value and practical significance.Combining theories of production scheduling,operational research and robust linear programming,this paper studies integrated optimization of scrap steel charge and scrap steel production scheduling under the time of use electricity tariff.To start with,the optimization of scrap steel charge and scrap steel scheduling under the time of use electricity tariff are explored,respectively,to realize their partial optimization and lay a solid foundation for the follow-up research.Next,integrated optimization of scrap steel charge and production scheduling under the time of use electricity tariff is further explored from a comprehensive perspective.Below is the specific research contents:(1)This paper provides a comprehensive literature review of optimization of scrap steel charge,workshop production scheduling considering energy factors,steel/scrap steel production scheduling,and robust linear programming.Among them,the issue of workshop production scheduling considering energy factors is expounded mainly from two aspects,including workshop production scheduling with single external grid power supplying under the time of use electricity tariff,and workshop production scheduling considering renewable energy power supplying.As to the issue of steel/scrap steel production scheduling,it is analyzed from four aspects,including static steel/scrap steel production scheduling,dynamic steel/scrap steel production scheduling,steel/scrap steel production scheduling with single external grid power supplying under the time of use electricity tariff,and the steel/scrap steel production scheduling considering renewable energy power supplying.All these can provide theoretical basis for the follow-up research.(2)Uncertain factor in the process of scrap steel charge is analyzed.On that basis,scrap steel charge optimization considering metal element concentration uncertainty is studied.Aiming at minimization of scrap steel and iron alloy cost,a robust linear programming model to solve the problem is built.Assume that the random parameters are valued in “bounded uncertainty” and “bounded and symmetric uncertainty” two sets.Based on theories related to robust linear programming,the robust optimization model is converted into the certain equivalent models under two sets.Through numerical analysis,the feasibility and validity of the models are verified,and the influence of major parameters in the model on the objective function value is analyzed.(3)Characteristics of scrap steel production scheduling process are analyzed,which are summarized as the issue of hybrid flow shop scheduling under the restrictions of special production process.On that basis,the condition that the electricity of steel-making plants relies on the single external grid is taken into consideration to examine optimization of scrap steel production scheduling under the time of use electricity tariff.With minimization of time of use electricity tariff cost as the objective,a mixed integer linear programming aiming at solving the problem is built.Through numerical analysis,the feasibility and validity of the model are verified,and the influence of the time of use electricity tariff on production scheduling and the use of production electricity is analyzed.(4)Based on the research work of(3),the production electricity of the steel-making plant both from external grid and internal renewable energy is considered,and how to optimize the scrap steel production scheduling under time of use electricity tariff is then studied.Aiming at minimizing the renewable energy power generation cost,time of use electricity tariff cost,and battery energy storage system operation cost,a robust mixed integer linear optimization model to solve the problem is built.And then based on theories of robust linear programming,the model is converted into a certain equivalent one.Through numerical analysis,feasibility and validity of the model are verified,and the influence of renewable energy power generation and its uncertainty on scrap steel production scheduling electricity costs,production scheduling activities and the use of production electricity is discussed.Meanwhile,the relationship among the grid power supply,renewable energy power supply and battery energy storage system charging/discharging/storage is examined.(5)Based on the research work of(2)and(3),the situation that the production electricity of the steel-making plant from single external grid and the uncertainty of metal element concentration in scrap steel charge process is considered to study how to optimize scrap steel charge and production scheduling jointly under the time of use electricity tariff.With minimization of time of use electricity tariff cost,production scheduling setup cost,scrap steel cost,and iron alloy cost as the objective,the block modeling method is adopted to build a robust mixed integer linear optimization model,and convert it into two certain equivalent models.Through numerical analysis,the feasibility and validity of the model are verified,and the influence of the uncertainty of metal element concentration on the production cost,the influence of time of use electricity tariff on production scheduling,and the influence of electricity tariff fluctuations on the times of setup,and the amount of scrap steel and iron alloy used are studied.(6)On the basis of(4)and(5),the situation that the production electricity of steel-making plant are both from external grid and internal renewable energy as well as the uncertainty of the metal element concentration in scrap steel charge process and renewable energy power generation is taken into account to study the integrated optimization of scrap steel charge and production scheduling under the time of use electricity tariff.With minimization of the renewable energy power generation cost,time of use electricity tariff cost,battery energy storage system operation cost,production scheduling setup cost,scrap steel cost,and iron alloy cost as the objective,the block modeling method is adopt to build a robust integer linear optimization model,and convert it into two certain equivalent models.Through numerical analysis,the feasibility and validity of the models are verified,and the influence of the renewable energy power supply on scrap steel charge and production scheduling under the time of use electricity tariff is studied.Meanwhile,the relationship among the grid power supply,renewable energy power supply,and battery energy storage system charging/discharging/storage under the time of use electricity tariff is discussed.Innovations of this paper are mainly reflected in the following aspects:(1)How to optimize scrap steel charge considering the uncertainty of metal element concentration is studied.Assume that the uncertain parameters are valued in the bounded uncertainty and bounded and symmetric uncertainty sets,robust optimization method is used to process them.Compared with the research that assumes the metal element concentration of scrap steel obeys certain probability distribution or belongs to certain type of fuzzy number,the charge model obtained in this paper is more consistent with real-life production activities.(2)Concerning the issue of scrap steel production scheduling under time of use electricity tariff,this paper builds a scrap steel production scheduling mixed integer linear optimization model under the time of use electricity tariff considering different process restrictions based on the traditional mixed flow shop production schedule model building method.Compared with relevant models put forward by the current literatures,this model is more concise and restrictive,demonstrating better expandability.(3)At present,research about production scheduling considering renewable energy power supply either disregards the influence of time of use electricity tariff or ignores the uncertainty of renewable energy power generation or assumes that the renewable energy power generation quantity obeys certain probability distribution type.However,in the real life,information related to the probability distribution type is hard to obtain accurately.This paper assumes that the renewable energy generation quantity is valued in certain set,and robust optimization theories are adopted to further process it.On that basis,scrap steel production scheduling robust optimization considering combined internal renewable energy power supply under time of use electricity tariff is studied.The production scheduling model obtained is closer to real production activities.(4)Currently,the issues of scrap steel charge optimization and scrap steel production scheduling optimization are mostly studied separately,thus resulting in inconsistency between these two kinds of activities.Considering that production electricity of steel-making plant is from single external grid,this paper integrates these two aspects so as to explore the influence of time of use electricity tariff on these them.And achieve integrated optimization and coordination of scrap steel charge system and scrap steel production scheduling system.(5)On the basis of research work of(4),the situation that production electricity of steel-making plant are both from external grid and internal renewable energy is considered so as to study integrated optimization of scrap steel charge and production scheduling under the time of use electricity tariff.Meanwhile,how to achieve effective coordination among the power supply system(renewable energy power supply,grid power supply,and battery storage energy storage system charging/discharging/storage),charge system,and production scheduling system under the influence of the time of use electricity tariff is explored.