Pinchanalys av det integrerade massa- och pappersbruket i Obbola

Sammanfattning: The aim of this thesis is to investigate possibilities to reduce primary steam consumption of the integrated pulp and paper mill in Obbola. For this purpose, a pinch analysis has been performed. The thesis has been carried out on site and necessary data for the analysis was produced mainly using the sensors installed for controlling the process. Based on the data, a representation of the heat exchanges at the mill was obtained and from this emerges an understanding of how optimized the heat exchange is. From the analysis, it was found that the energy savings potential amounts to 7 MW, which corresponds to 6% of present steam consumption of approximately 112 MW. One of the identified pinch violations was the flue gases in the recovery boiler used to preheat combustion air and process ventilation when it can be used to meet a thermal demand at higher temperatures or potentially to generate steam, the latter has not been investigated. Steam preheating of air to the paper dryer, steam preheating of water that is used to thaw logs and steam that is used in some of the process ventilations were also among the identified violations. Possible measures to optimize heat exchange and eliminate pinch violations have been investigated. These include flashing of paper mill condensate to replace the live steam in the air preheaters to the paper dryer and replace this thermal energy with secondary heat in the feed water treatment plant. As well as using part of the heat from the flue gas cooling system to preheat feed water. Increasing the operational temperature in the water treatment plant turned out to be possible regardless of whether a flash is introduced or not. The savings with contra without the flash would amount to 1.13 MW and 0.85 MW, respectively, and the net heat savings of a reconstruction is only 0.28 MW. The heat that can be released from the flue gas cooling system corresponds to 0.46 MW and is expected to be higher in the summer when heat necessity in other ends of the system decreases. To suggest optimization of heat exchanges at the mill, it was also investigated how much excess of warm and hot water was that present in the secondary heating system. The investigation showed that if the temperature in the warm water tank would be regulated, an excess of hot water would be sufficiently large to provide secondary heat to the optimization measures discussed and to provide for all ventilations currently using live steam. In all cases profitability should be investigated and for the case of any ventilation consideration should be given to distance from a secondary heating source and if there is a glycol circuit present or not.