Pulp Paper & Logistics
VOITH 13
and efficiency. In conventional systems, the fibre suspension is sorted and if needed deflaked in a three-stage system in several steps. The reject is temporarily stored in a chest or a stand pipe before being passed on to the next stage. In order to avoid the formation of a floating layer in the chests, the reject must be kept in motion with an agitator. However, agitators tend to spin
the contaminants, which leads to blockages and wear in the pumps and machines used in subsequent process stages. For this reason, Voith’s coarse screening process works without intermediate stock chests. This reduces potential sources of error and makes the process more reliable. The system’s efficiency also increases due to a reduced number of components, which in turn leads to lower energy consumption. Another point for robustness is the new added flushing sequence in the screening system. Pulping cannot eliminate all rejects and thus smaller plastics, cords, etc, come to the coarse screening system. The rotation movement of the pumps can create smaller rope-like agglomerations that can block the screens or pumps. The creation of such
agglomerations can hardly be avoided but they can be kept at a harmless size by flushing the coarse screening system frequently. This is only possible due to the gentle FiberSorter and IntegraCombiSorter that can swallow the temporarily increased flow without problems or additional losses. In this way, small agglomerations
are eliminated before they can cause problems. Thanks to their design, FiberSorter and IntegraCombiSorter can cope well with these rejects without crushing them.
The Feed-Forward Principle as a central idea Conventional systems often rely on recirculation of rejects. During recirculation, not only flakes and fibres but also contaminants and stickies enter the system again. Due to repeated treatment in the systems, they are crushed and sent forward unnoticed along with the accepts. This leads to wear on pumps and other downstream units and can have a negative impact on the runnability and efficiency of the downstream paper machine due to increased stickie content of the fibre suspension.
In order to avoid breakage, we have designed the ragger in such a way that it changes its contact pressure depending on the pulling efficiency of the ragger wheel. This minimises the risk of the ragger breaking and adds to the robustness of the processfor OCC process at Voith
A multi-stage fractionation system separates the inlet into three fractions; long fibres and short fibres are transferred to the next process stage as accepted stock, and the reject is removed from the cycle after several washing processes
The TwinPulp system prevents unnecessary shredding of impurities by early and consistently removing coarse contaminants. This relieves the whole downstream process and contributes to cleanliness at this early stage. Assuring good turnover in the pulper consumes most of the pulping energy. An optimised flow pattern in the pulper is key to reducing total energy consumption and achieving reliable operation of the ragger. One of the guiding principles in the design and optimisation of Voith BlueLine OCC systems is the Feed-Forward Principle. The goal is to consistently move the accept forward wherever possible. This results in significantly lower
volume flows in the systems and higher stock consistencies throughout the process, which benefits the entire plant. Thanks to the high stock
consistencies, the pump energy required to transport the pulp further is reduced. In addition, the pipeline diameters can be vastly reduced. This saves space and minimizes costs, as it enables savings in valves, instrumentation, pumps, motors and energy consumption.
Focus on each component To improve the efficiency of the entire OCC process, Voith identifies the optimisation potential for each individual component. The Voith IntensaPulper IP-R is a good example of that. Thanks to its optimised flow geometry, the pulping and mixing process has been significantly improved, reducing energy consumption by up to 20 per cent. In this way, an OCC system with an annual production capacity of 350,000 tons achieves savings of more than €100,000 per year. A further example of Voith’s pioneering stock preparation systems is the cleaning process. Standard systems only accommodate low stock consistencies to achieve the required removal rates. However, this reduces the energetic efficiency of the process. For this reason, Voith has designed the EcoMizer to achieve excellent separation and outstanding results with significantly higher stock consistencies.
Water management A further important aspect for an efficient plant is water management. Water loop separation results in better water quality in the paper
4 January/February 2020
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