Dec 11, 2018
Refining is the key process when producing both mechanical pulp and fiberboard. By optimizing the refining process and refiner segments, mills, operational costs and product quality can be greatly affected. In the field of refining, Valmet is continuously developing new refiner segment technology to improve customer competitiveness. As a result of this we present a new unidirectional segment concept called ServoNavitas.
Valmet’s concept combines a number of patented innovations and details. The use of features in ServoNavitas is made based on customer needs and refiner operation. ServoNavitas offers an effective patented, segment design toolbox to change the basics of refining. Energy consumption, fiber quality and segment lifetime can all be tuned to new levels.
Valmet has a long tradition of serving customers on all continents. We have gained detailed knowledge for most types of refiners, both ours and those made by our competitors. We are cooperating with our customers and commit ourselves to optimization of refiner processes with new technology.
We offer customers an extensive contact network, experienced refiner specialists, an effective refiner segment design toolbox with patented features and the most effective research and development support. Our philosophy is that every refiner is unique and needs tailor made designed refiner segments.
Shives and coarse fibers hinder the reduction of energy consumption when producing CTMP. Retaining strength is a problem when targeting reduced energy consumption in softwood fibers for the production of printing grade papers.
Reducing the amount of shives in CTMP production requires low freeness and this costs energy. Retaining long fiber strength requires operating with a wide disc gap. Valmet tested a number of new ideas at mill scale to simultaneously achieve low energy consumption and good fiber quality. ServoNavitas is the Valmet concept for optimizing rotor and stator technology to reach new levels of refiner operation. This technology, together with Attack bar and Shive clean segment innovations, opens a totally new window in mechanical pulping refining.
The use of low consistency refining in mechanical pulping significantly reduces energy requirements. To achieve the best performance, the LC-refiner must be equipped with suitable segments custom-designed for the fiber source and refining degree. LC-refining can be used in secondary, third stage or reject position.
Greater understanding of the interaction between rotors and stators and their influence on both energy consumption and fiber quality is the most innovative finding of recent years in the MDF industry. Earlier segments were typically designed to find the correct feeding forces needed for a certain rotational acceleration. The same design was also used on the stator side. Mill scale trials have clearly proven that the stator has at least as great impact on refining as the rotor and that the interaction between them sets the limitation as to the extent of cost optimization possible.
Stator design can be set to optimize fiber quality and refiner operation by tuning rotor segments to gain the lowest possible energy consumption. Precise tuning of rotors and stators, together with Attack bar and Turbine Segments innovations, widen the operating window for MDF defibration allowing cost savings never before possible.
The flow optimized refiner segment design principles, first applied in Turbine Segments technology, guarantee the shortest possible residence time for fibers and minimized flow turbulence inside the refiner.
Energy saving designs spread the wood flow evenly over the segment rings. The homogeneous flow allows fiber acceleration and energy savings at levels unreachable in the past.
In large scale high consistency CD refiners, effective feeding from the flat zone to the conical zone is essential. Patented unidirectional feeding solutions, together with steam handling capacity maximization, save energy and make it possible to reach the highest production rates.
Feeding to the conical zone is improved with Valmet's patented innovation Flat feed where flat zones outlet segment design is designed to perfectly fit and feed the new conical zones.
Shive clean is a patented innovation from Valmet which reassesses the basics of refiner segment geometry.
Traditionally, a high amount of flow restriction dams between the segment bars lowered the shive content of the pulp. However, the most effective Turbine Segments concept is to reduce energy consumption, enabling fast throughput and short residence time for fibers inside the refiners. Therefore adding more dams would be compromising. To correct this, Valmet changed the basic design of bars and dams. Shive clean ensures that shives and coarse fibers are well refined while the flow through the refiner can be adjusted to be even faster than before.
Together, the Turbine Segments concept and Shive clean result in low energy consumption and low shive content. Shive clean together with the Turbine Segments concept can save close to half of refining energy and substantially reduce shive content.
Rotor segments should be designed to enable an optimized flow-feeding pattern when maximizing energy saving is the main target. Usually, if the same design is also used on the stator side, the intersection angle of rotor and stator bars is large. This reduces the opening forces that the segment bars create and leads to operation with a small disc gap. A small gap causes fiber cutting when long softwood fibers are refined. These fibers are often used for producing paper grades where strength of the mechanical pulp is important. With the new patented Hold back stator design, the intersection angle of the segment bars can be controlled without losing the feeding or steam handling capacity of the segments. The combination of the feeding rotor and Hold back stator allow reduced energy consumption without losing long fiber strength.
Increasing the lifetime of refiner segments is not necessarily a main target when optimizing production, although changing refiner segments involves downtime and therefore production losses. Segment wear is typically a combination of bar-edge rounding and segment groove plugging. Valmet has patented technology to overcome these problems.
The Attack bar features inclined bars for sharper leading edges and cleaner grooves, which provide for energy savings and a long segment lifetime.
Often, process residues plug segment grooves requiring changing segments due to reduced flow volume. StayClean segments have modified material surface properties which reduce or even prevent groove plugging.
StaySharp segments have an extra hard edge on the bars, which reduces the impact of abrasive materials on segments. And this, of course, increases segment lifetime.
Low consistency refining is generally used to modify fibers to increase strength properties for paper making. LC refining is one of the major electricity consumption areas in stock preparation. Valmet has a new segments solution as well as the completely new OptiFiner Pro LC refiner for more energy efficient refining.
In mechanical pulping, LC refining is an energy efficient refining technology to reduce shives or freeness in second or third stage refining. LC refining is also widely used for reject refining in mechanical pulp mills as well as chemical pulp mills.
For stock preparation applications, Valmet has developed a low consistency refiner, the OptiFiner Pro. The completely unique flow-through refining principle gives efficient treatment to fibers. The new refiner is suitable for all low consistency refining applications and has proven to be especially good in hardwood and softwood/hardwood mixed pulp refining.
The Micro bar enables high cutting edge length and hydraulic capacity, which provides efficient refining on hardwood and mixed pulp. Energy saving of up to 10-30% compared to traditional patterns can be reached, depending on the application. The Micro bar pattern utilizes Vario groove to preserve efficient refining performance until the last millimeters of bar height.
Maxi flo provides increased hydraulic refiner capacity. The inlet bars are designed to increase the pumping effect. It is especially suitable for high-capacity and high-speed applications. The pumping inlet also improves feeding to both gaps in double disc Twinflo refiners.
Vario groove allows variable groove volume for forcing the pulp flow into the disc gap. This design is suitable for reducing shives and improving pulp strength in mechanical pulping applications. It also provides forced pulp transportation between the rotor and stator over the entire refining surface and is therefore a good alternative to segments using dams when high hydraulic capacity is required.
For assistance in improving your refiner operation, contact your Valmet representative.