Pulp Paper & Logistics


ANDRITZ 25


Figure 2: VST cross section and enhancement of hydrostatic pressure


deflection is minimised and a uniform gap can be maintained over the length of the screw.


Applicable to all kinds of pulp In 2015, a pilot VST was installed at the Andritz plant in Austria. The pilot machine was actually the smallest industrial size of the VST available, so that scale-up could be


more readily evaluated. Various types of pulp have been


tested in the pilot plant. The conclusion is that there are no limitations on the kinds of pulp that can be dewatered with the VST under various operating conditions. Table 1 shows the range of pulp properties and operating conditions that can be successfully dewatered. In a trial on hardwood chemical


pulp, the VST was compared side- by-side with a traditional Andritz Screw Press. Figure 3 shows the comparative results. At low feed consistency the VST demonstrated a 25 per cent increase in throughput at the same outlet consistency over the whole range of operating speeds. Similar results have been achieved with other types of pulp, including recycled deinked and OCC. Pilot trials have also shown lower


Table 1: Types of pulp that can be dewatered with the VST


energy demand for the VST, which would enable a reduction in the size of the motor and gearbox. The VST design is completely closed. It is designed with unique telescoping bottom filtrate housing and split screen baskets for easy maintenance. The screw shaft also has replaceable wear shoes to enable high efficiency over a long lifetime. More information from Peter Ortner at peter.ortner@andritz. com


Main benefits of the VST:


● Higher production – or higher output dryness at the same production – when compared with a traditional SCP of the same size


● Highest dewatering efficiency (particularly for low feed consistencies)


● 100 per cent filling degree - screen baskets fully utilized to increase dryness and throughput


● Gravity-aided filling – uniform dewatering from top to bottom


● Uniform and consistent pulp discharge, which is beneficial to downstream processes


● Small space requirement/ footprint


● Closed machine design


● Telescoping filtrate housing for easy maintenance access to screw and screens in the high-pressure zone.


July/August 2018


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