When it comes to recycling recovered papers, the first principle we apply is to remove the contaminants as early as possible in the process, in as large a format as possible. For systems with low consistency continuous pulpers (which covers the vast majority of applications) the technology has evolved from early days where contaminants would accumulate in the tub until it got to be excessive and then sluiced or grappled out of the pulper and the process restarted. Most mills have adopted three standard technologies to deal with contaminants in the pulper: raggers, detrashers, and heavies removal (the later initially done with double valve junk traps but now typically with a grapple/hoist servicing a trashwell). These technologies make up the ‘three-legged stool’ of pulper contaminant management.  

As the contaminant level in the furnish increases the standard technology begins to show its weaknesses. Rag tails become soft as the percentage of baling wire compared to the ropes, plastics, and textiles is reduced. Soft ropes have to be allowed to grow to a larger diameter to hold together, but the nip on the ragger requires higher PLI loading and a tendency for nip ejection (the rope is harder to grip and harder to squeeze through the nip point). Grapple/hoist systems can service the trashwell at higher frequencies, but this requires increased operator attention and results in the trash bin filling up more quickly and with some increase in useable fiber loss as a consequence. Additional detrashing can be added, but by doing so the amount of variation in the process increases and the water balance for the pulper can be put at risk.  

At Kadant we’ve been working on solutions to the challenges that stem from dealing with higher contaminant loading. In some cases, we’ve installed drum pulpers which can handle very high trash loads, but for our customers processing North American OCC the fiber loss is too high to make that technology practical. We have new technology that addresses each of the problems cited above. For the ragger, we have recently deployed a design that incorporates a top roll helper drive. The dual drive design allows for a reduced nip loading and the speed-matched top roll helps to pull the heavy, bulking rag tail from the tub easily.  

For the grapple/hoist, we have begun installing intelligent, automated technology and paired it with a ‘Wash Tank’. The system grapples the trashwell, making note of the pick depth and pick weight, and then deposits the load into the wash tank. The wash tank, which is fed much of the needed pulper dilution water, pushes lights and fiber back into the pulper tub by over-flow. The grapple will service the trashwell a few more times before it pauses and then services the wash tank, making note of the pick depth and weight each time. Based on its measurements, it adjusts its delay time between trashwell picks, and also the number of trashwell picks before a wash tank pick, continually adjusting its settings to manage the trash load. The addition of the wash tank has been shown to reduce the wet weight discharged into the trash bin by as much as 90%, all without any operator interaction required. An added benefit is that the system provides reports on the amount of debris removed, providing additional insight into the process and allowing the mill to correlate trash load with raw material supply.

When it comes to detrashing, the name of the game is to keep the pulper ‘clean enough’ through enough volume exchanges (turns per hour). To manage the increased load, we are working on modeling the components of the stock using our PaperFront simulation tools. This effort has led to the design of buffer tanks that can help reduce the fluctuations in the tub and collect wash and drum screen filtrate water for reuse, allowing the mill to significantly increase pulper turns per hour while improving the pulper discharge consistency.

Taken together, these advancements help to keep the ‘three-legged stool’ of pulper contaminant removal stable and adaptable to the higher contaminant loads that plague the recovered paper streams used in all the markets where Kadant supplies these systems.  

By Pat McEnroe

Product Group Director

Kadant Black Clawson, LLC

In today's competitive industrial landscape, process managers are continually challenged to find solutions that reduce operating costs without impacting production, either through capacity or reliability. Kadant Black Clawson’s breakthrough Supra rotor is an innovation that is making significant waves as a low-speed, low-power option for use in Fine Screening and Fractionation applications. This innovative technology not only minimizes power consumption but also delivers substantial cost savings – early adopters have reported up to a 35% reduction in energy consumption. However, this advancement is much more than merely slowing down an existing rotor; it represents a comprehensive design aimed at optimizing performance in a shifting screening environment.

The Challenge of Modern Screening

Traditionally high-speed screen rotors have been employed to maximize production, but at a lower efficiency. Increasing the speed of a rotor can yield more production while also increasing not only the overall power consumed, but also the specific energy, or horsepower days per ton. Additionally, the accelerated wear on components and the reduction in separation efficiency seen in high-speed rotor applications contribute to increased operating costs in multiple departments and a higher environmental footprint. With the rising emphasis on energy efficiency and sustainability, process managers are increasingly seeking solutions that align operational efficiency with cost reduction.

A New Step in Rotor Design

The Supra screen rotor introduces a shift in screening technology. One of the most innovative aspects of the new rotor design is its comprehensive approach to the challenges posed by different screening environments. Attempts to reduce energy usage by simply dialing down the speed of conventional rotors have demonstrated some of the changes that occur within the screen. This design incorporates a suite of features engineered to excel in a lower-speed operation.

Key design innovations include:

• Optimized Foil Geometry: The rotor blades have been carefully designed to improve material flow and separation efficiency at lower speeds. Engineered around the reality that lower speed operation changes the relative velocity of the pulp slurry in the screening zone, foils are designed to efficiently provide the pressure pulses at the turbulence needed for full production screening. This design ensures that screening performance remains robust even as energy input is minimized.

Picking up on what I mentioned in the last issue of "Fiber Foundations", it is amazing the improvements that have been made in equipment such as screen baskets in the last couple of decades. Perhaps they are still housed in a cylindrical vessel and have ports and shafts sticking out of them in all the places an old timer like me is used to seeing them, but the internals are from the equivalent of Star Trek.

The driving force, in my opinion, has been the tremendous reduction in the cost of computing power coupled with the increased computer modeling capabilities. Now, design engineers can try out their designs in 3-D and dynamically before they ever put a torch or shear to a raw steel plate. It makes me think that the cost of buying a used piece of equipment in stock prep must be carefully weighed against the performance and efficiency of new.

It is like my other field of interest, agriculture. Most farm equipment from the 1980's is simply antiques compared to that of today.

Same is true in pulp and paper manufacturing. You may be able to recognize the old equipment, but the performance of today's is far ahead of the equipment just a couple of decades ago.

By Jim Thompson, CEO

Talo Analytic

International &

Paperitalo Publications

jthompson@taii.com

Brussels-based paper and board manufacturers’ organization releases 16-page update to its recyclability methodology parameters.

Western Michigan University's visiting scholar Dr. Sinan Sonmez has helped developed a method to achieve savings in terms of energy and cost by reducing the use of raw cellulose to recycled paper. As result of this work, Sonmez’s has had seven research papers accepted for publication.

Producing paper with recycled paper consumes about 30-70% less energy and emits less GHG than using virgin wood.

Researchers at McGill University have come up with an innovative approach to improve the energy efficiency of carbon conversion, using waste material from pulp and paper production.