14 VOITH
machine compared with the stock preparation. Efficient water management allows the lowest fresh water consumption by controlling the mill’s internal process water distribution during all operating conditions. This also ensures stable conditions for biological water treatment, resulting in a constant and best- treated effluent water that can be re-used or send out. Additionally, a key issue is the quality of the process water. The levels of solids in the water loops should be kept as low as possible to prevent accumulation. The water quality also determines how much yield of fibres and fillers gets lost with the effluent. “A typical weak point in
conventional OCC systems are the filter systems used in thickening,” says Schuster. With plastic filter bags on disc filters, there is a risk of holes and cracks forming. This reduces the quality of the filtrate significantly. It leads to clogged cleaning nozzles, for example at the paper machine, and can reduce the lifetime of press felts. The efficiency of the entire
process decreases due to longer downtimes and more demanding maintenance requirements, resulting from the components’ shorter operating lives. This is why Voith relies on filter systems made of corrugated stainless steel. These rugged components have outstanding service lives and guarantee the best results in the long term.
Each unravelled fibre is a double gain A significant factor for the profitability of a paper mill is its yield, in other words the proportion of accepts that can be extracted from the OCC raw material. The process benefits in two
January/February 2020
Pulp Paper & Logistics
From wooden boards to metal parts to a whole car engine: Voith systems such as the IntensaDrum pulping drum remove many different contaminants
ways: First, the amount of fibre material recovered for paper production increases. And second, the improved yield reduces the amount of reject that has to be disposed of. For this reason, Voith systems are designed in such a way that the fibres are washed out of the reject as cleanly as possible wherever fibre loss can occur. The significance of this is demonstrated by the Voith IntensaScreenDrum, part of the TwinPulp System. In an OCC line with a production capacity of 1,000 tons per day, the particularly effective washing of the reject helps to avoid fibre losses worth up to €315,000 per year. 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.
High-performance components to meet the highest quality demands Another challenge in the OCC process is the clean removal of stickies. With its specialised systems, such as the multi-foil rotor for particularly gentle stickie
removal, Voith has been setting benchmarks for years. Slot widths and process variants can be precisely adapted to individual requirements. In high-speed paper machines with low basis weights, four-stage sorting has proven to deliver excellent results. It enables the best sticky separation with low fibre loss. For slower running paper machines and higher basis weights, three-stage sorting is usually sufficient.
Constant production conditions as a basis To ensure consistent production quality, Voith BlueLine OCC systems are designed to compensate for fluctuations in the quantity and quality of the raw material as efficiently as possible. The raw material input itself is a frequently underestimated factor. However, fluctuations that occur with regard to quality, fibre material and stock consistency can no longer be completely compensated by the system later on, but only minimised. To counteract this, Voith systems
regulate the raw material input by conveyor belt from the stock consistency in the pulper. At the end of the OCC process, systems that are thoroughly tested and
have been refined by years of experience ensure production conditions that are as constant as possible. To compensate for process fluctuations, the screw press is for example controlled by the torque. Unlike many other systems, the Voith InfibraDisp disperser has an adjustable gap that opens or closes depending on the specific power consumption, thus guaranteeing uniform quality. In the final process step, the
Voith TwinFlow refiner with energy-controlled gap adjustment ensures that the fibres are treated consistently even when process fluctuations occur. This guarantees a high and uniform strength development of the fibres, so that the paper machine can be operated safely at maximum speed.
Tailor-made systems from a full-line supplier Paper manufacturers benefit from Voith’s BlueLine OCC process expertise on many levels. One main advantage is that the manufacturer handles the entire conception, planning, manufacturing, startup and optimisation of the complete OCC plant. “It was important for us to partner with a single-source supplier who could provide us with everything from the conveyor system for waste paper to the winder,” says Armin Vetter, managing director at Schoellershammer and a Voith customer. Furthermore, Voith offers
to identify opportunities for production increases and optimisation in existing plants. In this way, significant improvements in robustness, quality, efficiency and yield can be achieved quickly and easily.
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