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 removal and energy efficiencies in an impulse unit in the pilot-scale research paper machine EuroFEX, located at the Swedish Pulp and Paper Research Institute (STFI) in Stockholm, Sweden. The paper produced was made of kraft pulp and 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 different heat flows. It was determined that about 60% of the electrical power input was transferred to the paper web. The major heat loss was caused by wafer cooling of the induction heater. It was concluded that the heat transfer to the paper web was dependent on the roll surface temperature, the machine speed and the ingoing moisture ratio. The heat transfer to the paper web was not affected by the press load the basis weight or the roll cover. The water removal rate depended mainly on the roll surface temperature, the press load and the ingoing moisture ratio