Impingement Drying of Printing Papers at Elevated Temperatures, 2000 Engineering Conference Proceedings

Kari Juppi, Juha Kaihovirta--The first impingement drying unit was installed in a production machine in spring 1999, where it has operated since. Before the commercialization of the OptiDry impingement dryer, an extensive research program was carried out. All the main printing paper grades as well as heavier board grades have been studied on pilot machines during the past years.

Initially, impingement drying was planned to be restricted to air temperatures not exceeding 300°C, because this was considered to be the maximum temperature which the fabrics could withstand. Paper quality in high temperature impingement drying has also been thought to be a limiting factor. Higher temperatures are desirable since they facilitate higher drying rates and more efficient use of energy which results in more effective drying and a shorter dryer section.

The studies described in this paper were carried out on pilot machines located in Jyväskylä. The first machine consists of a cylinder dryer group followed by an impingement dryer unit, which operates at speeds up to 2400 m/min. The other impingement dryer unit is installed on Rautpohja’s pilot machine #2 dryer section, which runs up to 2500 m/min.

The results of the high temperature impingement drying studies performed are presented in this paper. Evaporation rates at temperatures up to 450 °C are given together with the effects of high temperatures on paper quality (rheological and optical). The method for preventing fabric damage is also discussed, as well as the improved energy efficiency at higher temperatures.