Assessment of different paper drying processes to reduce the total energy costs from a mill perspective

Since the energy required in the paper drying process gives rise to substantial costs for the paper producing companies, it is of great interest to reduce the input of primary energy resources to the dryer. Either process changes or further heat recovery can be employed. A simulation tool was developed, using the programming tool Extend, with the aim to accurately describe the energy use and costs in different paper drying processes to make possible the evaluation of different process changes from an energy point of view. The tool was used to evaluate the total use of and costs for energy in a fictive conventional paper dryer at various dew points in the PM-hood air. Also the potentials for heat recovery were assessed. From the simulation results, the overall economics of the drying process at the various conditions were calculated. The overall energy efficiency was shown to increase with increasing dew points since the required energy for air heating was reduced and the potential for heat recovery was improved. The prices of energy resources were shown to have a large effect on the total economics of the drying process. For a dryer limited paper machine, the increased production at lower dew points was shown to increase the profitability of the paper machine