ULTRA low intensity pATTERNS

FINEBAR® low intensity refiner plate patterns offer a unique opportunity to improve paper quality and reduce the cost to produce it. Hardwood pulps, mechanical pulps and recycled fibers can all be dramatically improved by refining at ultra-low intensity. With improved quality of individual furnish components, your furnish mix can be cost optimized.

 

Hardwood Pulp

It is well documented that hardwood kraft pulps should be refined at the lowest practical refining intensity. In the past, this lower limit of intensity had been established at 0.6-0.8 Ws/m due to the limitations of plate manufacturing technology. FINEBAR® offers plate patterns able to achieve intensities of 0.2-0.6 Ws/m while maintaining efficiency and hydraulic capacity.



One of the key benefits of low intensity refining is the reduction in energy required to achieve a given pulp quality or drainage level. The accompanying graph is a compilation of pilot plant and mill data illustrating the impact of refining intensity on freeness drop for various bleached hardwood kraft pulps. The data points clearly show a trend of increased freeness drop per net hpd/t applied as the refining intensity is reduced from 2.0 to 0.2 Ws/m. In other words, less energy is needed to achieve a target freeness. This can translate into energy savings, or into an increase in power available for additional refining or to accommodate a higher throughput.

Among the most significant quality benefits are:

• Increased bulk at a given smoothness or porosity
• Improved internal bond properties
• Improved pick resistance of vessel segments

Shown below are results from a side-by-side mill comparison of hardwood kraft refined with FINEBAR® plates and the finest available cast pattern. In this particular installation, the FINEBAR® plates offered 50% more bar edge length (133 vs. 88 km/rev) for the same diameter plate.



This graph illustrates the significant improvements in sheet porosity at a given bulk which can be achieved when hardwood is refined at low intensity. Gentle refining develops the outer surface of the fibers for improved bonding and reduced sheet porosity, while minimizing fiber collapse to maintain sheet bulk. Typical bulk improvements at target properties have ranged between 2-5%.



As mentioned previously, energy requirements to achieve a given pulp quality or drainage level are reduced when refining hardwood at low intensity. For this example, refining to 300 CSF with FINEBAR® plates resulted in energy savings of 1.3 net hpd/t. For a 900 t/d paper machine with 15% filler and 70% hardwood, this would be equivalent to approximately 700 hp savings. At an electrical cost of $0.045/kWh, the annualized energy savings would be in the order of $200,000.

Mechanical Pulp

Mechanical pulps are very prone to fiber cutting due to the stiff nature of their fibers. Very low intensity refining allows for effective energy to be applied to the fibers to increase pulp strength, improve surface properties and reduce shives, while minimizing drainage changes at a given energy input. FINEBAR® plates are successfully running in several mechanical pulp post-refining applications with patterns as fine as 0.8, 1.0 (bar and groove width in sixteenths of an inch), providing comparable intensities to MultiDisk refining.

Recycled Fiber

Recycled fibers benefit from low intensity refining because they have already been processed at least once and require a gentle treatment to minimize fines generation. Low intensity will improve fiber quality development and achieve target specifications at higher drainage levels. Plate pattern selection will depend on the nature of the recycled fiber mix (e.g. OCC vs. mixed office waste).