A CYCLE FOR IMPLEMENTING SUPERHEATED-STEAM DRYING OF PAPER

When paper is dried in superheated steam, the water in the wet sheet i s converted to pure steam. It should be possible to dry the web partia lly using conventional dryer cylinders and complete the process by imp ingement drying in superheated steam, with the dryer cylinders operati ng on the steam produced by impingement drying. Steam can be circulate d around the impingement-dryer circuit using either a fan or a thermoc ompressor with externally supplied motive steam. Overall performance i s favored by using the highest steam temperature and lowest jet Reynol ds number possible. Steam circulation by thermocompressor consumes mor e energy than with a fan, but its lower capital cost may be attractive in regions where electricity is expensive The proposed drying cycles indicate that paper machines can be retrofitted or redesigned to achie ve higher drying capacity and reduce energy consumption.