توسعه یک روش برای تجزیه و تحلیل انرژی، محیط زیست و بهره وری اقتصادی برای یک کارخانه فولاد یکپارچه

The steel industry has faced several challenges during the years. There has always been an aspiration towards higher economic profitability for the system. During the mid 1970s and 1980s the energy crises caused a dramatic rise in energy costs, which led to an increased awareness in energy conservation. In recent years, climate change issues have become more important for the industry. The operating practises for an industrial system are often affected by external restrictions concerning the economical, energy and environmental efficiency of the system. There are a large number of ways to increase the system efficiency, e.g. installation of new process equipment, and practice changes. However, industrial systems such as an integrated steel plant consist of a system of several processes connected together with product and by-product interactions, where changes in one unit may result in changes throughout the total system. A process integration method focusing on the total integrated steel plant system by a simultaneous approach is adopted. An optimisation model is developed and used to study the effect of changes in the existing material and energy system. Applications of the model on the energy and material system have been made. The model can be used to analyse energy, environmental and economic aspects making it a powerful complement as a decision making tool. Conclusions about energy, environmental and economic effects are presented.

In recent years, increased attention has been given by the steel industry to use energy more efficiently. Steel industry is one of energy-intensive industries, with high CO2 emissions from the production. Improvement of the energy efficiency, to reduce the energy consumption, will increase the economic profitability as well as reducing the environmental impacts. With increasing concerns of climate change issues, more efforts are made by the steel industry to reduce its CO2 emission. Steel production today can be divided into two main process routes: the integrated plant with the blast furnace/basic oxygen furnace (BF/BOF route) and the electro steel plant with the electric arc furnace (EAF route). In 2002, the BF/BOF route accounted for nearly 60% of the world steel production. The EAF accounted for 34% and the rest, 6%, was produced in other processes [1]. Both energy use and the source of energy and raw materials in steel production vary between the two routes. According to the Swedish Energy Agency [2], the energy use in the iron and steel industry accounted for 15% of the total energy use in the Swedish industry. Obviously small efficiency changes in these industries could result in large absolute energy savings. Several studies are available on calculation of the specific energy use and CO2 emissions from steel production and improvement possibilities, e.g. Fruhan et al. [3], Worrell et al. [4] and [5], Petela et al. [6] and Olynyk et al. [7]. In these studies the steel industry processes and the steel industry branch are studied in general. As an integrated system, a change of practice in one unit influences the behaviour, e.g. energy and material consumption of other units. It is therefore of interest to optimize the use of energy and raw materials for the total system by using a systematic approach. Several kinds of methods (here named process integration techniques, PI) have emerged for creating general models for global optimization. When process integration emerged as a scientific field, it was almost exclusively concerned with heat integration. Since then, the scope of process integration has widened to include a larger number of aspects, a more thoroughly definition of process integration can be found by IEA [8]. The most commonly used methodologies for process integration are Pinch Analysis, Exergy Analysis and Mathematical Programming. In this paper, the PI technology used is the mathematical programming method based on the mixed integer linear programming (MILP) approach. In a review article by Grossmann et al. [9], an overview of the main concept and applications in mathematical programming can be found. The method, which allows for both economical and environmental analysis possibilities for an integrated steel plant, is presented. In this paper, actual applications of the method to the material and energy network of an integrated steel plant, which have been preformed and presented in various publications, are summarised. The possibilities of using this method are discussed and general conclusions from these studies are presented.

A process integration method for the steel industry has been developed. Global mathematical models for the steel making processes have been developed in which the PI model for the integrated steel plant system, SSAB Tunnplåt AB, has been based on. • The PI model has been used in several studies of the material and energy system for the integrated steel plant SSAB. From the modelling results, conclusions on economical, energy and environmental aspects have been drawn. • The PI model is a good tool providing new insights into the material- and energy system from economical, energy and environmental points of view. It can serve as a benchmark for different steel making operations and constitute a basis for the continuous work of improving the material and energy efficiency. • The PI-model developed is a powerful complement to the existing analysis- and decision making tools. • The development of a method taking into account the various aspects of economy, energy and environmental impact is an important step towards sustainable system analysis.