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With rising energy prices and stricter requirements for carbon dioxide emissions, it is becoming increasingly important for industries to be energy efficient. In the pulp and paper industry, an important aspect is to increase the use of secondary heat, i.e., waste heat from the manufacturing process in the form of hot water, to reduce the use of primary heat, steam.

The aim of the project is to investigate the factory's excess hot and warm water in the secondary heat system and different ways to utilize these to reduce the use of primary heat. Hot and warm water refer to water at 75 and 50 degrees Celsius, respectively. Reducing the plant's steam consumption would mean significant savings in the form of bark and oil for combustion.

In order to predict the surpluses based on different outdoor temperatures and production levels, regression models of the hot and warm water surpluses are developed using mass balances over the secondary heat system's accumulator tanks. The measurement period is from March 2023 to March 2024. Furthermore, existing proposals for energy saving measures are investigated; connecting secondary heat to the heating system in the old paper machine building and to the new paper machine's hot water system. Based on the mapping of the secondary heat system that has been carried out, our own proposals for energy saving measures are developed.

The results show a large surplus of hot and warm water. Higher temperature and production give a larger surplus, while lower temperature and production give a smaller one.

The heat demand in the old paper mill building can be met with warm water while still maintaining a large surplus, especially during higher production levels and during the warmer months of the year. The measure means that the steam currently used for heating can be completely replaced with warm water. There will be significant steam savings if the surplus hot water is added to the new paper machine's warm water system.

Mixing hot and warm water to supply the new paper machine's warm water system and redirecting the hot water flow from the hot water tank to the warm water bin are our own proposals for energy saving measures. Mixing hot and warm water means further steam savings, and if the hot water flow is redirected, the entire steam demand for the new paper machine's hot water system can be covered.

The conclusion is that the energy saving measures investigated would result in large steam savings and thus reduce the combustion of bark and oil.