Comparing conventional evaporation plants with plants using excess heat: A simulation study

Preprint, 2009

Pulp and paper mills are large energy consumers which can often achieve economic savings by implementing energy-saving measures. The process unit with the greatest energy demand in a mill is usually the evaporation plant. If excess heat can be made available in the mill, and the heat can be used in the evaporation plant, significant energy-savings can be achieved. This kind of evaporation is called process-integrated (PI) evaporation. In the present study, theoretical plants with 6{8 evaporation eects are simulated using an in-house simulation tool called OptiVap. The consequences for the evaporation plant of using excess heat, of lowering the surface condenser temperature, and of separating lignin are investigated. The results show that the additional prot of PI plants is 0.3–1.5 €/ADt in comparison with conventional plants. By lowering the temperature of the surface condenser, the profit is raised by 0.6{0.9 e/ADt for both conventional and PI plants. With lignin separation, the PI plants are 0.7{1.7 e/ADt more protable than the conventional ones.