Mapping and analysis of an internal heating network at Holmen Paper Braviken

Abstract: The pulp and paper industry is the most energy intensive industry in Sweden. Most of the energy usedaims to supply the large amount of heat to the production processes that is required to produce pulp andpaper . By increasing the energy efficiency of paper mills, there is great potential to reduce productioncosts and reduce its environmental impact. This project involves mapping, analyzing and investigation ofmeasures that can contribute to increased thermal efficiency of an internal heating network at Holmen’spaper mill, Braviken. The heating network, called VVG, utilises excess heat from the pulp and paperproduction and supplies heat to production processes and premises at the factory. When the heat demandof the VVG-system exceeds the available recovered heat, heat from live steam is transferred. This projectaim at identifying measures with potential to reduce demand of live steam supply. The project started bymapping the entire VVG-system to identify which consumers are included and how it is connected. Thenthe consumers were studied and data was collected to determine their power and energy demands. Basedon the mapping and collected data, proposals for measures that have the potential to increase thermalenergy efficiency were noted which in turn can reduce the need for live steam supply. The measures havebeen focused on reducing the return temperature of the VVG-system and reducing the heat demand of thesystem. Reduced return temperatures are achieved by more efficient use of the existing heat flow. Thisleads to increased heat recovery potential which means that more excess heat can be utilised.The proposed measures that were identified as having potential to contribute to reduction of the returntemperatures of the VVG-system are as follow: • Utilising return flows with high flow rates and high temperatures to provide other consumers inVVG with heat. This allows the hot flow to be used instead of going directly into the return line. • Eliminate short circuits in the system where the supply line goes directly into the return line. Thesewere detected in the forms of three-way valves and flows through consumers that were not running. The proposed measures that have been identified as having the potential to contribute to reduction of theheating demand of the VVG are as follows: • Turning off flows passing through consumers that are not in use to reduce unnecessary temperaturedrops which will result in decreased power losses. • Preheating via residual flows at consumers where raw water tempered circuits is heated. As theraw water is cold during large parts of the year, a lot of heat can be saved by preheating it with aflow of lower energy quality than VVG. • Shut down the VVG flow through heat exchangers in the heat recovery system when the heatrecovery process not are running to avoid negative heat transfer. By implementing these measures, large improvements regarding the thermal efficiency of the VVG-system can be achieved at Holmen Paper Braviken. How much the return temperatures decrease and howmuch the heat recovery potential increases with the proposed measures has not been quantified during thisproject. However, the measures aimed at lowering the heat demand in the VVG-system can be quantifiedto contribute to an predicted energy saving of at least 2.8 GWh annually, but the investigations of themeasures indicates that significantly larger energy savings can be achieved. To ensure the potential of theproposed measures to contribute to the reduction of the demand for live steam supply, Holmen needs tocarry out further studies of the VVG system where this work is intended to form the basis for their furtherwork.