For a long time the pulp and paper industry had the image of being a destroyer of the environment and nature. Especially rivers have been polluted and because of that many animals and humans have been harmed. Since then the overall situation has significally improved. Because the product is based on a renewable resource, the high protection standards for air and water environment and the fact that a pulp and paper mill can deliver energy to households nearby, the pulp and paper industrial sector can be considered as a model industry. But still pulp and paper production is a very water- and energy intensive industry. This is why most paper producers try their best to reduce their use of resources and to find potential for improvement. The drying section of a paper machine, where the wet paper gets dried, is one of the most energy intensive sections in a paper mill. Mathematical models and simulations are used to locate inefficiency or to find potential for improvement. This thesis introduces one simulation program (PapDrySim), explains the background and simulates the dryer section of a real paper machine. The simulation is based on on-site measurements at the drying section and in the end simulations show the impact of changing the settings in the drying section.