Dryer section and method for drying a web of fibrous material, and machine having such a dryer section

#The invention relates to a dryer section for drying a web of fibrous material having the features of the preamble of claim 1. A dryer section of this type is, for example, known from DE 199 44 266 A1. The invention also relates to a method for drying a web of fibrous material and to a machine having a dryer section.

#The dryer section of a paper machine is arranged between the press section, which dewaters the material web in a mechanical manner, and a rolling apparatus, which rolls up the dried web. The dryer section has the object of thermally removing the moisture remaining in the web after the mechanical dewatering down to the desired final moisture content. Steam-heated cylinders are traditionally used for this purpose, the material web being guided over said cylinders. In the case of these dryer sections based on the principle of contact drying, the heat required to remove the moisture is introduced by the drying cylinder into the material web. DE 199 44 266 furthermore describes the use of drying or nozzle hoods, which are arranged along the running direction of the material web in the dryer section. Hoods of this type are used to apply a hot fluid to the material web and work according to the principle of convection drying.

#The energy that has to be used to dry the paper web is an important cost factor in paper production. The dry content is generally in a range from 45% to 98%. This cost factor will be all the more important in the foreseeable future if one considers that energy saving will form a central requirement for the paper industry because of generally increasing energy prices. There is also the fact that the dryer section of a paper machine has the greatest space requirement of the entire paper machine. To this extent, the dryer section is a limiting factor not only with regard to the energy requirement but also with regard to the space requirement.

#The invention will be described in more detail below with reference to the accompanying schematic drawings, in which:

#FIG. 1 shows a side view of a dryer section according to an embodiment according to the invention;

#FIG. 2 shows a side view of a drying cylinder, which is combined with ultrasound-assisted drying units;

#FIG. 1 shows a dryer section 20 according to an example according to the invention, which is part of a paper machine. The dryer section 20 may also be part of a machine for producing tissue or sanitary paper or part of a machine for producing cardboard webs.

#The dryer section 20 is arranged between a press section and a rolling apparatus. The paper machine may be equipped with or without smoothing unit(s) and/or with/without a size or film press and/or an on-line coating unit. The aforementioned assemblies may be arranged downstream of the dryer section in the running direction of the web. The dryer section 20 is distinguished by ultrasound-assisted drying units 11, with the aid of which the moisture content of the web together with the further drying units of the dryer section is brought to the desired final moisture content.

#The object of the dryer section 20 is to bring the paper web taken over by the press section to the desired final moisture content. The final moisture content may be in a range from about 2 to 15%, especially in a range from about 2 to 10%, especially about 2 to 8%, especially about 2 to 6%, especially about 2 to 4%. In general, contact drying, convection drying and infrared drying are possible for drying, the convection drying being intensified in the dryer section 20 according to FIG. 1 by the excitation of the drying fluid at an ultrasound frequency. In other words, the drying fluid, for example hot air or hot steam, is sprayed at ultrasound frequency onto the wet paper web leaving the press section.