Method in contact-free air-drying of a material web as well as a nozzle-blow-box and a pulp dryer that make use of the method

摘要

The invention relates to a method for air-drying material webs, in particular material webs of relatively high grammage such as pulp webs. The invention also relates to a nozzle-blow-box and a pulp dryer that make use of the method. Air blowings in a direction substantially perpendicular to the web and air blowings in a direction substantially parallel to the plane of the web are applied to the web to be dried from underneath the web. By means of these blowings, both heat is transferred to the web and the web is supported by the air free of contact, and the run of the web through the dryer is stabilized. In order to improve the transfer of heat in comparison with a planar carrier face, the air flow velocity parallel to the plane of the web is initially kept substantially invariable. The air flow velocity is lowered in the lateral areas of the carrier face by employing lateral areas of the nozzle-carrier face that become rampwise and/or stepwise lower in the air-flow direction.