Fiber treatment with Durabond refiner plates
TechTalk-Durabond-Figure5-Laser-cut-bars

Tech Talk:

Energy-efficient fiber treatment with Durabond refiner plates

The cost of fiber and energy represent about 60% of a paper mill’s manufacturing cost. Optimizing refiner plates can have a significant impact on the bottom line. This TechTalk discusses the development of low-cost, energy-efficient fiber treatment in the refining process.

Energy accounts for about 16% of the total production cost in a paper mill.  When added to the cost of fiber (approx. 44%), these two factors constitute about 60% of a paper mill’s manufacturing costs. The ability to save energy at a very low investment cost is an important factor in a mill’s profitability.

 

No-load savings 

Treating fiber in a refiner requires the expenditure of Net Refining Energy (gross refining energy minus “no-load” energy). No-load is the power consumed when the refiner is in idle (i.e., stock flowing, motor at normal RPM, and plates moved apart so that there is no impact on fiber morphology).  Once fiber treatment is optimized, gross refining energy consumption is fixed. However, the no-load energy can still be optimized.

This can be accomplished by reducing rotational speed (RPM), reducing the active plate diameter, or both based on calculations in Figure 2.  One approach (reducing rotational speed by installing a frequency converter) can be capital-intensive.  Another approach which requires no capital investment is to reduce the active diameter of the refiner plate (Figure 3).

The amount of energy saved through reduction of the active plate diameter is limited by the accompanying drop in available edge length and hydraulic capacity of the refiner plates. Using the ANDRITZ Magnus Refining Simulator, the edge length and hydraulic capacity can be “dialed in” to a mill’s specific requirements through a proprietary Fiber Floc Analysis (Figure 4).    

 

Figure 1: Best practice energy values (final and primary) for standalone paper mills in the world


Product

          Paper machine 
      energy use (kWh/ADt)

          Final     Primary*

                 Refiner 
      energy use (kWh/ADt)

          Final     Primary*

Glassine            900           2.727            400           1.212
Uncoated fine            640           1.939            144              436
Packaging            535           1.626            112              339
Newsprint            570           1.727             68               206
Tissue         1.000           1.030             44               133

ADt = Air-dried metric tonne
*Primary energy assumes electricity generation, transmission, and distribution losses of 67%

Figure 2

No-load power = k x Diameter4.25 x RPM3

Figure 3: Energy reduction potential (final and primary)

Active
plate
diameter    

Reduced
plate
diameter

     Estimated power 
       savings (kWh)

      Annual power 
       savings (kWh)

Inch

Inch

   Final       Primary*

   Final              Primary*

4643    43             130    339.012          1.027.206
4239    50             152    394.200          1.194.426
3835    35             106    275.940             836.098
3431    42             127    331.128          1.003.318
3027    27               82    212.868             644.990
2623    33             100    260.172             788.321
2017    32               97    252.288             764.433

Power savings calculations are based on 90% availability

* Primary energy assumes electricity generation, transmission, and distribution losses of 67%

Durabond development   

ANDRITZ began in intensive development program to minimize the Total Cost of Ownership (TCO) for refiner plate customers which resulted in the creation of the Durabond plate family (Durabond and Durabond Light).

 

The bars on Durabond plates have no draught (zero side angles) and smooth groove surfaces to achieve the best hydraulic performance. A high ratio of bar height to width (thin tall bars) increases productive life, while the bar and groove widths allow maximum available edge length. This is what makes it possible to reduce the active plate diameter. 

 

An innovative manufacturing concept is to disassociate the materials for the refining bars from the materials for the base plate. This allows the use of new materials and new methods to create a refiner plate with minimal weight, maximum toughness, and the highest repeatable precision. Precision lasers are used to cut the bars, which are bonded into laser-cut slots in the base plate (Figure 5).     

 

Figure 4: Fiber floc analysis

Durabond manufacturing

The innovative concept behind Durabond manufacturing is to disassociate the materials for the refining bars from the materials for the segment base plate. This allows the use of new materials (i.e., work-hardened steel) and new manufacturing methods to create a refiner plate with minimal weight, maximum toughness, and the highest repeatable precision. Precision lasers are used to cut bars from work-hardened stainless steel. These bars are then inserted into the laser-cut slots in the base plate (Figure 5).

Laser technology represents the highest standard in accuracy and repeatability. This is combined with low-temperature bonding techniques to ensure that distortions from warp and twist are eliminated. Proprietary bonding agents are used, which are safe and durable in elevated temperature applications such as TMP post refining. The modular construction method ensures the highest strength and sturdiness.

Figure 5: Durabond laser-cut bars

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Regular and light versions

Durabond plates can be installed on every single- or double-disc refiner in the market.  For refiners with 12-26ʺ rotor sizes, Durabond refiner plate segments are produced in their regular shape (Figure 6) since these segments are comparatively small and lightweight. For larger sizes, ANDRITZ developed a multi-segment design concept – Durabond Light (Figure 7).  Durabond Light segments are mounted on a reusable base plate, which is delivered with the first installation (Figure 8).

 

Figure 6: Regular Durabond segment

Figure 7: Durabond Light segment

Best applications for Durabond    

Durabond plates have tailored bar geometries for maximum fiber quality development at and work best in applications where fiber quality development is critical (e.g., tissue, printing/writing grades, TMP post refining, high-test packaging grades, etc.). The energy-saving characteristics of the plate design, however, are noticeable in virtually all refining applications.

Figure 8: Durabond Light mounting method

Conclusion

Focusing solely on energy efficiency in refiner plate applications limits the likelihood of sustainable success. Pursuing the best fiber treatment and energy efficiency combined should, therefore, be the goal. This involves detailed refining system audits by qualified product specialist, analyses, and Magnus simulations. The result will be a customer-specific optimum bar and groove configuration at minimum plate diameters. In this way, Durabond will sustainably improve the bottom line of paper mills.

 

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