Heat integration opportunities in average Scandinavian kraft pulp mills: Pinch analyses of model mills

Within the FRAM programme, two models of average Scandinavian mills producing bleached market pulp have been analysed from an energy perspective. The aim was to explore the opportunities for heat integration in order to create a steam surplus. The steam surplus gives opportunities for increased power generation or lignin extraction. The technical and economic consequences of using the steam surplus in this way are explored in a continuation of this project. Two different approaches for creating a steam surplus have been investigated: 1) conventional measures and 2) process-integrated evaporation (PIvap). The former approach includes improved heat integration and new equipment. The latter approach means that excess heat from the mill is used for evaporation to partly replace live steam. The two model mills created within FRAM both produce 1000 ADt/d softwood pulp. The mills differ in the level of water usage, since it is expected that the amount of excess heat for PIvap will increase with decreasing water usage. By investing 11 M Euro in conventional measures it is possible to create a steam surplus of 53 MW (about 26% of the total consumption), independent of the level of water usage. For the PIvap approach, the level of water usage matters, since there is more excess heat for PIvap in the mill with lower water usage. As a result, the total steam surplus with the PIvap approach differs in the two mills: up to 52 and 56 MW, respectively. Hence, the steam savings for the PIvap approach are similar to those in the approach with conventional measures; and so are the investments needed (10-12 M Euro). Even though the two approaches give approximately the same savings with the same investment, the PIvap approach might be easier to implement in an existing mill.