Wire (forming), press and the drying sections are the three successive steps where water is removed in a paper machine. As a rule of thumb it can be said that removing one unit of water in the press and dryer sections takes 5 and 25 times more energy, respectively, compared to what is needed in the forming section. There are significant energy gains to be made by removing as much water already in the forming section.
Many paper machines perform with sub-optimal water removal in the forming sectio –due to equipment limitations, inadequate and/or poorly maintained instrumentation and controls in the low and high vacuum dewatering elements. On older paper machines, there is often an excessive quantity of high vacuum elements which add to the vacuum system operating power as well as increasing the forming fabric drag load and associated drive power.
Rewetting of the paper after the wire and the press sections can potentially take place and can increase energy consumption in the drying section. Rewetting can be eliminated by using the right felt for the produced paper grade. As grades on a machine often change, it is essential to optimize the choice of felt. It is also important to optimize the geometry of the web path and the felt paths such that the two are separated as early as possible to minimize rewetting. The “double doctor” approach may be an effective option for couch rolls and suction rolls to reduce rewetting when leaving the Fourdrinier and press nips (Kramer et al., 2009. p.101).