Opportunities for Process Integrated Evaporation in a Eucalyptus Pulp Mill and Comparison with a Softwood Mill Study
Paper i proceeding, 2007
Significant energy savings can be made in the pulp and paper industry by implementing process-integrated evaporation (PIvap). The concept of PIvap has been evaluated for a Eucalyptus mill producing bleached kraft market pulp in Portugal and the results were compared to the ones from an earlier model mill study of a soft wood mill. In the eucalyptus mill there were, theoretically, 0.86 GJ/ADt of excess heat suitable for a PIvap besides the 2.6 GJ/ADt of pinch violations. The pinch violations could be transferred to excess heat, but some pinch violations were cost effective to solve. A suggestion where 1.1 GJ/ADt of pinch violations are solved and 1.6 GJ/ADt of excess heat are extracted is presented. If the excess heat is used in a 7 effect PIvap with integrated stripper and increased dry solids content, steam savings of 2.7 GJ/ADt could be made in the evaporation plant. Together with the pinch violations and opportunities for improved soot blowing, the total steam savings from the suggested measures were 4.5 GJ/ADt or 35%. The amount of steam savings and associated costs were similar to the ones in the soft-wood model-mill. Hence, no significant differences could be found for the opportunities to implement PIvap in the hardwood mill compared to in the soft wood mill. The existence of a pre-evaporation plant, however, showed to hinder introduction of PIvap, since a pre-evaporation plant uses excess heat, and uses it ineffectively compared to a PIvap. Hence, the pre-evaporation has been removed in the suggestion for integration presented here.