The DD-Washer was introduced in the early 1980s when the first commercial-scale unit went into production in a kraft pulp mill in Finland. Today, five generations later, every kraft pulp mill in Finland has ordered at least one DD-Washer (the latest order is for Stora Enso’s Kemi mill) – and the washer has achieved global acceptance. With more than 340 installations in 24 countries, the multi-stage washing efficiency and extremely high production throughput of the DD-Washer is clearly preferred for all fiberline washing applications – brownstock, post-oxygen, and bleaching. The largest DD-Washer today has almost 150 times the capacity of the first washer sold.
In the early days, almost all mills had vacuum drum filter washers. The main disadvantage was the amount of serial equipment to reach a certain wash result and a limited process temperature. Following this, wash presses were introduced. The main disadvantage was the requirement to dilute and then mechanically press the pulp several times to reach a desired high consistency. The DD-Washer performs all washing stages in a single rotating drum and roughly at the same consistency without dilution. Since there is no mechanical pressing during washing, the DD-Washer is extremely gentle, retaining all the bulk, stiffness, and strength of the original fibers.
PASI IMMONEN
Manager Washers and Filters
ANDRITZ Fiber Technologies
