摘要
现代钢铁联合企业是复杂的铁—煤化工系统,钢铁生产过程实质上是物质流在能量流的驱动和作用下,在流程网络中,按照一定的“程序”动态—有序地运行。对典型钢铁企业—宝钢、鞍钢、首秦公司能耗影响因素的分析表明,研究钢铁企业物质流、能量流及其相互作用对节能降耗,建设资源节约型、环境友好型企业具有重要意义。本文应用冶金流程工程学的理论和系统节能的方法,重新审视钢铁企业生产过程的物理本质,把钢铁企业的生产系统抽象为物质流转变过程和能量流转变过程,剖析物质流、能量流在钢铁生产过程中的运行行为、效果及二者的相互作用机制,为钢铁企业的进一步节能减排寻求新的突破口。主要研究内容如下：
1.钢铁企业的各种物料沿着产品生命周期的轨迹流动形成物质流(以铁素流为主体)。将某个生产单元或工序的物质流分为来自上道工序物质流、循环利用物质流等5股,构造了钢铁生产单元、生产工序及钢铁生产流程的物质流图,建立了物质流输入输出模型；剖析了各股物质流大小及物质流参数对工序金属收得率、流程资源效率和工序材比系数的影响,结果表明：降低废品率是提高生产工序金属收得率的主要途径；降低流程废品率,提高流程废弃物循环率及吨材外加物质流,是提高生产流程资源效率的主要措施；增加下游工序外加物质流,减少下游工序排放物质流,减少上游、下游循环物质流,均可降低工序的材比系数。将钢铁生产流程网络总结为串联型和串—并联型,引入时间增量系数及通路堵塞系数,剖析了流股交叉干扰及通路堵塞等因素对流程网络中物质流的运行时间周期及连续化度的影响,提出了流程网络优化的基本原则：减少工序间物质流流股,尽可能实现单元之间一一对应的匹配关系以降低通路堵塞程度,缩短物质流运行的运输时间和等待时间。应用上述方法对典型企业生产流程的物质流进行了分析。
2.各种能源沿着转换、使用、回收、排放的路径在钢铁企业内流动形成能量流(以碳素流为主体)。将某个能源转换单元或工序的能量流分为被转换的能源、转换后的能源产品等6股，构造了能源转换单元、转换工序及转换网络的能量流图,建立了能量流输入—输出模型；研究了各股能量流大小及设备大型化、余热余能回收利用对工序能源产品能值的影响；剖析了各种转换方式权重、转换装置数量、装置能量转换效率及能量输送效率对能源转换网络产品能值的影响。分析表明：降低工序能源产品能值,一方面依靠各转换工序设备的大型化或采用先进的转换方式来降低能源投入量；另一方面依靠余热余能的合理有序回收；提高效率较高的能量转换方式的权重,减少各种转换方式中装置的数量,优化能量输送方式,缩短能量输送距离,是提高某种能源介质能量转换效率或降低某种能源产品能值的主要措施。应用上述方法分析了典型钢铁企业能量流网络的特征,并重点阐述了各企业煤气网络和发电网络对煤气转换效率和电力能值的影响。
3.物质流与能量流在钢铁生产工序上协同作用：能量流推动物质流的转变,过剩的能量流或依附于物质流进入下一道生产工序,或分离运行形成独立的能源回收—转换网络。生产工序的余热余能回收水平越高,工序产品带入下道工序的能量越多,则物质流—能量流的协同度越高,二者的协同作用越大,相关工序的工序能耗越低。从优化物质流、能量流运行模式的角度指出了降低企业能耗的措施：①提高各工序设备大型化程度,降低工序间物质流流股密集程度,减少通路堵塞,进而优化工序间界面模式,加强工序间的热衔接,最大程度地利用依附于物质流的各种能量；②优化能源转换网络,降低能源产品能值；③合理有序地回收利用各种余热余能,从而最大程度地利用从钢铁生产流程输出的过剩能量。
4.应用以上物质流、能量流研究方法,研究了工序间界面模式、富余煤气发电及余热回收利用等重要问题。建立了高炉—转炉区段铁水和连铸机—热轧机区段连铸坯的温度预测模型,给出了各区段不同界面模式下铁水、连铸坯温降与物质流运行时间的定量关系,提出了各区段的最佳界面模式；论述了钢铁企业煤气富余的原因,提出了以小时为时间尺度的煤气富余量预测方法,在剖析各种煤气发电方式优缺点的基础上,以实现煤气的近零放散和高效发电为目标,给出了富余煤气发电方式的选择原则：同时,分析了热电联产的节能效果,质疑了“有多少(富余)煤气发多少电”的错误观点,论证了不同企业实现“只买煤不买电”的可行性和科学性。总结了我国钢铁工业余热余能回收利用的现状及存在的问题,论述了热平衡法、(?)分析法、能级分析法及其相关效率指标分析余热回收利用过程的局限性；用火用效率和产品能耗改变量等评价指标比较了若干典型余热回收技术的优劣,给出了各种余热的合理回收利用模式及其节能效果。
5.针对流程网络复杂、产品多样化的大型联合企业—鞍钢和流程网络简单、产品专业化的中小型企业—首秦,应用物质流、能量流研究方法,分析了物质流、能量流运行模式对两类企业吨钢能耗的影响,结果表明：鞍钢复杂的流程网络使得物质流运行时间周期长、连续化度低,能量流运行效率低,最终导致其吨钢能耗明显偏高；而落后的能量流运行模式是导致首秦吨钢能耗高的主要原因。研究表明,采取物质流、能量流优化措施后,鞍钢吨钢综合能耗(不含冷轧)降低到670kgce/t左右,首秦降低到640kgce/t左右是可以实现的。
The modern iron & steel joint enterprise is a complicated iron-coal chemical system, and the steel production process is, in essence, the dynamic operation of the material flow under the drive and effect from energy flow following the definite rules. Analysis on the influencing factors of the energy intensity of Bao Steel, An Steel and Shouqin metal material company indicates that the research on material flow, energy flow and the relationship between them will benefit the construction of a resource saving and environment-friendly enterprise. Based on the theory of Metallurgical process Engineering and methodology of Systems Energy Conversion, the physical essence of the steel production process is reobserved, and the steel production system is decomposed into two parts:materials transformation process and energy transformation process. The operating behavior and effectiveness of material flow and energy flow and the interacting mechanism between them are analyzed in order to find out the new direction of energy conservation in an iron and steel enterprise. The main contents of this paper are as follows:
1. The material flow is formed when the material runs along its life cycle trace in an enterprise. Based on the 5 material flows including those from the anterior producing unit or process and those recycled through a unit or process, the material-flow diagrams for a production unit, a process and a production flow are constructed, the material input-output model is established; the influence that the material flow of a process has on the metal yield ratio is described, and so is the influence of the parameters on the resource efficiency of a production flow and the product ratios of each process. It is indicated that the main approach to increase the metal yield ratio is to reduce the defective index; the measure to improve the resource efficiency is to reduce the defective index of the flow sheet, increase the recycle rate and the material flow from out of the flow sheet per product; the path to reduce the product ratios of each process is to increase the material flow from out of the upstream processes, reduce the discharged material flow from the downstream processes, and reduce the recycled material flow.The network of flow sheet in a steel mill is classified into two sorts:connection in series & series and parallel, and the parameter of time increasing and that of channel blocking are introduced in to discuss the influence of the disturbance of cross flow and the block of channel on the time cycle and the extent of serialization of material running. Thus, the optimizing principle of the network of flow sheet is put forward:reducing the material stream, realizing the one-one corresponding relationship between the units of the processes, so as to shorten the time for transportation and waiting. Furthermore, this method is used to analyze the material flow in the typical enterprises.
2. The energy flow is formed when the energy runs along the route of conversion, usage, recovery and emission. The energy flow through an energy conversion unit or a process, such as the converted energy and the energy of the product, is discomposed into 6 parts, and the energy-flow diagrams for a conversion unit, a process, and a network are designed and energy input-output model established. The influence that the flux of each energy flow, the largening extent of equipments and the recovery of residual heat (or energy) have on the energy value of the product is analyzed. The influence that the weight factor of each conversion mode, the amount of the units, the efficiency of each unit and that of energy transportation have on the energy value of final product is discussed. It is indicated that there are two methods to reduce the energy value of an energy product:largening the related equipments, adopting the advanced energy conversion modes, and recovering the residual heat and energy rationally and in the certain order. For an energy conversion network, some measure must be taken to improve the conversion efficiency and reduce the energy value of an energy product. They are: increasing the weight factors of the energy conversion modes whose efficiency is higher; reducing the amount of the conversion units, optimizing the transportation mode of energy, and shortening the distance of transportation. This method is used to analyze the energy flow in the typical enterprises, especially the influence that the conversion network has on the conversion efficiency of off-gases and the energy value of electricity.
3. Material flow and energy flow cooperate with each other on a steel production process: the energy flow drive the material flow to transform, and surplus energy moves to the next steel production process or departs from the material flow to form an independent conversion network. Some measure can be used to enhance the synergetic effect between material flow and energy flow, so as to reduce the energy intensity of the processes concerned:recovering much more residual heat and energy, bringing much more energy carried by the process to the next process. Measures to reduce energy consumption per ton steel of an enterprise based on the optimization of running mode of the two sorts of flows are indicated:①increasing the large extent of equipment in a process, reducing the density of the flow between the processes, reducing the channel block, therefore optimizing the interface between the processes, strengthening the hot linkup between the processes and utilizing the energy carried by the material flow farthest;②optimizing the energy conversion network, and decreasing the energy value of the main energy product;③recovering the residual heat and energy rationally and in the definite order, so as to reuse the surplus energy out of the steel production process farthest.
4. Several important issues concerned with material flow and energy flow in an iron and steel enterprise, including the interface between the processes, generating electricity with residual off gases, and recovery of residual heat are discussed by the analyzing method concerned with material flow and energy flow. The temperature predicting models of hot iron between BF and BOF and billet steel between Conticaster and Mill are constructed, and the models are used to analyze the influence of interface mode and running time of material flow on the temperature fall of hot iron and billet steel, so that the optimal interface is put forward. Why the off gases are surplus is discussed, and the method of calculating the quantity of residual off gases based on the flux per hour is put forward; the electricity generating modes with residual gases are analyzed. Based on this, the optimizing principle of generating electricity with residual gases is indicated. Furthermore, the energy saving effectiveness of co-generation of heat and electricity is discussed, the viewpoint "using all the residual gases to generating electricity" is disproved, and the viewpoint "Buying only coal and no electricity" is proved. The recovery of residual heat and energy in China steel industry is summed up, base on which, the limitations of heat balance analysis, exergy analysis, energy level analysis and related efficiency indicators are discussed; exergy efficiency and variation of energy consumption per ton product have been used as the evaluating indicators to analyze the current technologies for recovery of typical residual-heat in steel industry, and the reasonable mode of residual-heat recovery and its energy saving effect are indicated.
5. For a large-sized joint enterprise, An Steel, which produces all sorts of products with complicated network of flow sheet and a medium and small-sized enterprise, Shouqin, which produces special product with simple network of flow sheet, the analyzing method of material flow and energy flow is applied to discuss the influence of the running mode of material flow and energy flow on the energy intensity of the two enterprise. It is indicated that the time cycle of material flow running in the network of flow sheets in An Steel is longer, the serialization extent is lower, and the efficiency of energy flow running is lower, too. This results in the much higher energy intensity of An Steel. At the same time, the lower efficiency of energy flow running is the main reason that results in the higher energy intensity of Shouqin. It is also indicated that energy intensity of the joint enterprise, An Steel, can be reduced to 670kgce/t, and that of the medium and small-sized enterprise, Shouqin,640kgce/t if taking some optimization measure concerned with material flow and energy flow.
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