Analysis and optimisation of energy and environmental performance of an integrated steel plant by process integration

Abstract: The process industries stand for a substantial part of the energy used in Sweden. Industrial systems, such as an integrated steel plant, involve large interchange of energy between various processes and process streams. A major task for the steel industry is to minimize environmental impact, the consumption of energy and raw materials. A natural step is to improve the efficiency of the individual processes. However, since the processes within the steel plant system are connected to each other, energy savings in one individual unit does not necessarily lead to an energy saving for the total system. According to the Swedish National Energy Administration and Statistics, the steel industry used approximately 17.1 % of all industry related energy use the year 2001. Thus will small efficiency changes will result in large absolute energy savings. In order to make a successful energy saving one must understand the interactions between different processes. Methods are needed to optimize the consumption of energy and raw materials for the total system. The purpose of this thesis is to develop and implement such methods. The main method used in the analysis is based on mathematical optimisation. A steel mill in north of Sweden is used as case study, when actual processes and steel plant system are analysed. It is shown that the method used is appropriate for analysing the material and energy system in a steel plant.