Keywords: exergy efficiency, energy costs, exergy analysis, industrial energy systems, cost optimisation, pulp and paper mill, Sweden, cost reduction
Coordination of exergy analysis and the MIND method - applied to a pulp and board mill
The MIND (Method for analysis of INDustrial energy systems) method has been developed for cost optimisation of industrial energy systems, mainly with regard to quantities of energy. Exergy analysis reveals losses, efficiencies and possible improvements. These methods can be combined in order to improve industrial energy systems. In this paper, a Swedish pulp and board mill is used as a case study. The efficiencies of the processes in the mill are evaluated using exergy analysis. The most exergy inefficient processes are indicated and some improvements are suggested. This case study shows that it is the boilers and the evaporation plant that are the most inefficient processes, with efficiencies down to 29%. Different investment alternatives for these processes are studied and cost optimisation is achieved using the MIND method. The study shows that the energy costs can be reduced by up to 15 million Euros per year while the exergy efficiency can be improved by up to 14%. The combined approach shows that the energy cost-efficient alternatives are also usually exergy efficient.