Influences of Seasonal Variations on Energy-Saving Opportunities in a Pulp Mill

Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2008

Significant energy savings can be made in the pulp and paper industry by process integration. The aim of this paper was to investigate how much seasonal variations in the process influence the opportunities for energy savings. The hot and warm water system in a market pulp mill has been evaluated in an energy perspective, using pinch analysis. A large potential for energy savings was found, 41.3 MW, of which 16.5 MW is steam savings. New heat exchanger networks were designed. The influences from seasonal variations were estimated from the calculated energy savings when monthly averages were used in the new heat exchanger networks. With the seasonal variations considered, the opportunities were decreased by 2.4-5.1 MW, depending on design. Consequently, 88-92% of the theoretical energy savings could be recovered. An economic evaluation resulted in positive earnings from the investments in new heat exchanger network, even with low prices on the extracted steam and excess heat and with an annuity factor of 0.2. The payback period exceeds two years only with a steam and excess heat price of 5 €/MWh. Extra heat transfer area will give a small contribution to the potential for energy savings in relation to the increase in investment costs.