Pulp Paper & Logistics


ANDRITZ 13


SelectaFlot generation, the improved design of the multi- injectors achieves highly effective aeration at best energy efficiency, allowing operation at significantly lower pressure than before. Dispersing – The dispersion


process is responsible for detaching very small ink particles so that they can be removed, and also for the fragmentation of any remaining specks to render them invisible – improving the optical properties of the final pulp.


Figure 2: Modern 3-loop de-inking plant with ANDRITZ SelectaFlot flotation in the foreground


Pulping – The optical cleanliness of the pulp is initialised during pulping when the printing ink is detached. The high percentage of stickies in many office waste collections clearly favours the use of a drum pulper instead of a conventional high-density pulper. For example, the proven ANDRITZ FibreFlow drum pulper (pictured in Figure 1) uses gentle dropping and rolling forces to slush and defibreize the pulp. This allows


contaminants to be rejected almost intact, taking stickies and trash from the pulp very early in the process. Screening – The screening


process removes flat contaminants and stickies. For coarse screening, pressure screens are used having screen baskets with very small hole diameters. The latest technology uses small-slotted baskets, such as the ANDRITZ Bar-Tec Rejector basket, which is


an improvement over perforated designs, thanks to its specially shaped profile bar and slot geometry. Flotation – The selective separation of the suspension into two fractions, accept and reject – increases the brightness of the pulp. Dirt specks and ink particles are discharged with the help of foam that is generated by injectors (aerating elements mixing the pulp with air). In the new ANDRITZ


Comparison of the two concepts Using these main process steps, a complete modern de-inking system can be configured. For production of first-class paper grades, such as writing and photocopy paper, three loops are recommended in order to achieve highest pulp quality. A simpler single-loop de-inking system, with its lower investment cost, will necessitate compromises in pulp cleanliness.


Comparing the two plant


concepts, the reduction in sub- systems and machinery in the simplified system as a result of doing away with the second and third loops becomes evident, as outlined in Table 2. Considering


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Table 1: Main process stages in a de-inking plant and their effect on final pulp quality July/August 2015


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