Experiments in a pilot-scale impulse unit - heat transfer and water removal rates

This is the first paper out of two dealing with heat transfer, water remova l and energy efficiencies in an impulse unit in the pilot-scale research pa per machine EuroFEX, located at the Swedish Pulp and Paper Research Institu te (STFI) in Stockholm, Sweden. The paper produced was made of kraft pulp a nd with basis weights of 60-120 g/m(2). The roll surface temperature ranged from ambient temperature to 350 degreesC and the press loads were between 400-800 kN/m. The paper was produced at machines speeds of 300-800 m/min. An energy balance was conducted for the impulse unit to determine the diffe rent heat flows. It was determined that about 60% of the electrical power i nput was transferred to the paper web. The major heat loss was caused by wa fer cooling of the induction heater. It was concluded that the heat transfer to the paper web was dependent on t he roll surface temperature, the machine speed and the ingoing moisture rat io. The heat transfer to the paper web was not affected by the press load t he basis weight or the roll cover. The water removal rate depended mainly o n the roll surface temperature, the press load and the ingoing moisture rat io.