Beräkning av energiprestanda : Framtagning av verktyg för beräkning av energiprestanda som kan användas inom energiledning för Hallsta pappersbruk

Sammanfattning

The pulp and paper industry is one of the largest energy consumers in the Swedish industry with a yearly electricity consumption of 16.6 TWh. Modern paper mills use mostly electricity as a source of energy and the cost of electricity is estimated to be the third biggest cost for a paper mill. Holmen Board and Paper is one of Sweden's biggest electricity users with two paper mills and one paperboard mill in Sweden. Hallsta Paper Mill is the unit in the company with the highest electricity consumption and because of this there is a constant interest to improve the energy efficiency of the mill. In order to improve the efficiency there needs to be a way to measure it and in a way that is comparable over time. The purpose of this thesis was to develop a dynamic calculation model to estimate the specific energy consumption (SEC) and that excludes disturbances such as start and stop of the machines. Due to a declining market the paper mill is no longer operating at full capacity. Because of this the model was developed to calculate the SEC for different production scenarios. The model was built in the software Wedge, where data could be extracted directly from the mills production control system. The model was constructed to calculate the SEC independent from normal process variations such as the storage of pulp. Calculation method for the different parts were decided based on what data was available and how they behaved over time. Due to lack of data points in some parts of the process and to ensure that a mass balance in the system was achieved, a few values has to be estimated using different factors. The SEC was calculated for four different scenarios: full production, stop on PM 11, stop on PM 12 and other. The results from the model showed a SEC at full production between 2.86 MWh/ton and 3.21 MWh/ton depending on the seasons. This was found to be reasonable based on the results that was expected and when compared to SEC from other paper mills. A source of error which was found was the factor of estimation which adjusted the mass flow of produced pulp. This factor showed a difference of 10-15% between produced pulp and pulp in the paper. A few reasons were found but further investigation is needed to confirm the cause of error. The conclusion of the project is that the dynamic model developed in this thesis gives reasonable results and can be used as a tool for efficiency improvements.