Steaming
The compressed and squeezed chips are heated with saturated steam at 6
to 10 bar, which creates an internal temperature of 175 – 195 °C for 3 to 7
minutes depending of the digester size (5-18 m³), wood species, chip size
and required fibre quality. The retention time of the chips in the
preheater influences fibre colour and quality and is determined by the
flow rate (screw feeder speed). The digester level is controlled by a
radio-active measuring device. The discharge is accomplished by ribbon
screw unit