Cooling and washing papermaking pulp from horizontal screw digester, using counter current flow technique and pushing pulp upwards with perforated screen plate

摘要

The pulp is washed using a counter-current technique where the pulp moves upwards and the wash liquor trickles downwards in a vertical tower containing screen elements. The pulp is pushed upwards by a perforated screen plate (2) towards the downward trickle of wash liquor so that the upward movement of pulp and wash liquor displaces black liquor from the pulp by a combination of displacement and diffusion. A method for simultaneously cooling and washing pulp for papermaking which has been produced from a raw material such as straw (from e.g. rice, wheat or oat) or bagasse is carried out immediately after a horizontal screw-type digester and comprises the following steps: (1) washing the cooked material in order to remove black liquor using a counter-current technique where the pulp moves upwards and the wash liquor trickles downwards in a vertical tower containing louver-shaped screen elements; (2) introducing the cooked pulp at a temperature of 130-170[deg]C and consistency of 5-10% to the bottom part of the tower, which contains a conical shape stationary screen (8); and (3) moving a reciprocating circular screen plate with conical holes (3) upwards at a low speed of 50-300 mm/minute, so that the drained pulp is pushed upwards and meets the downward trickle of wash liquor with a lower temperature and progressively cleaner composition, so that this upwa! rd movement of pulp and wash liquor displaces the hot concentrated black liquor from the pulp by a combination of displacement and diffusion.