Method and a device for drying or heat treatment of a web-formed material

A method for drying or heat treating a web-formed material having a width, the method comprising:

• transporting the web-formed material, in contact with a gas-permeable dryer screen, through a drying plant in a direction of transport;
• establishing high and low-pressure sides of the web-formed material by blowing a hot process air against the web-formed material and drawing the process air through the web-formed material, to dry said material;
• mixing water leaving the web-formed material with the process air;
• discharging a first portion of the mixed water and process air as exhaust air and replacing the exhaust air with a corresponding portion of supply air with a low water content;
• recirculating a second portion of the mixed water and process air;
• generating a pressure drop in a zone disposed proximate to the high-pressure side of the web-formed material, the zone extending substantially the width of the web-formed material;
• and
• distributing the process air in a region upstream of the pressure-drop zone with a distribution member, the distribution member
• forming a first flow of process air having a width extending substantially across the width of the web-formed material and a length in the direction of transport of the web-formed material, the length of the first flow of process air being smaller than the width of the first flow of process air, the first flow of process air having a direction of flow substantially perpendicular to the surface of the web-formed material,
• dividing the first flow of process air into a plurality of jets directed substantially in a plane defined by the direction of transport and the normal direction of the web-formed material, said jets being distributed over substantially an angular region facing the web-formed material, and
• mixing the jets with one another again into a second flow of process air, the second flow of process air being conducted through the pressure-drop zone and then against and through the web-formed material lying on the gas-permeable dryer screen.