Upon closer inspection, however, the following becomes apparent: Sheet formation has a large influence on drying and up to 65% of the total energy demand can be attributed to this part of the drying process. Precisely here lies enormous potential for increasing the energy efficiency.
Thus, a great deal of energy can be saved, particularly in the drainage cycle: analysis of the wire section often shows serious deficiencies, especially in the arrangement of the drainage elements and the adjustment of the vacuum near the flat suction boxes. To achieve the maximum dryness at the end of the wire section, the drainage process should run as smoothly as possible – this saves the most energy. It is much more economical to mechanically remove water in the wire and press sections than to thermally evaporate it in the dryer section. Drainage analyses and expert interpretation of the results by experienced paper engineers aid in optimising the wire section.
Another component also which has high potential for energy savings: is the area of the suction boxes. Up to 75% of the driving power of a wire section is consumed here. This is because the vacuum causes the fibre mat together with fabric to be firmly pressed against the surface of the suction boxes and these normal forces cause friction and wear. Until now, this wear on the fabrics has been countered by alternatively weaving abrasion-resistant polyamide (PA) and polyester (PET) yarns on the bottom side of the fabric.
The polyamide does prevent abrasion, but its main disadvantage is that it absorbs water and therefore swells up, causing fabric edges to lift. Another disadvantage is that the tensile values of polyamide are too low. A fabric made from 100% polyamide yarns would be as elastic as a rubber band. Polyester, on the other hand, is the stronger material and absorbs no water but its abrasion resistance is poor.
The yarn diameters of PET and PA are initially identical. But after they have absorbed water, the diameter of the PA yarns increases. This leads to a step-like structure on the bottom side of the fabric and causes increased friction and wear as it passes over the drainage elements. It is even sometimes possible for the fabric to make a whistling sound due to the vibration effect caused by the step-like structure.
There is, however, a material which combines the advantages of polyester and polyamide: the new Villforth Vextreme yarn. This new development is dimensionally stable and, at the same time, resistant to abrasion. As a result, Vextreme can be used up to 100% on the machine side, whereby it forms a monoplane machine side.
The Villforth Vextreme yarn reduces frictional loss to a minimum, thereby lowering the driving power. In a nutshell: the adjustment of the drainage process offers the greatest potential for reducing energy demand in the wire section. The second main area is a tailor made fabric design – here, efficiency can be increased considerably and a great deal of energy saved during drainage. In this regard, the use of the new Villforth Vextreme yarn makes a convincing contribution.
But sustainable, full use of all potential savings of the paper machine can only be achieved through intense collaboration between customers and suppliers. This partnership is and remains the most important instrument for all efforts to optimise and is our strength. All Villforth forming fabrics are produced with the highest quality standards in the plant in Reutlingen in the German state of Baden-Württemberg.
